EP3459904B1 - Industrial truck, hydraulic system for an industrial truck and method of operating a hydraulic system - Google Patents

Industrial truck, hydraulic system for an industrial truck and method of operating a hydraulic system Download PDF

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Publication number
EP3459904B1
EP3459904B1 EP18194815.9A EP18194815A EP3459904B1 EP 3459904 B1 EP3459904 B1 EP 3459904B1 EP 18194815 A EP18194815 A EP 18194815A EP 3459904 B1 EP3459904 B1 EP 3459904B1
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EP
European Patent Office
Prior art keywords
mast
lift cylinder
hydraulic
free
lift
Prior art date
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Active
Application number
EP18194815.9A
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German (de)
French (fr)
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EP3459904A1 (en
Inventor
Michael Knieriem
Thomas Stolten
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Jungheinrich AG
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Jungheinrich AG
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Publication of EP3459904A1 publication Critical patent/EP3459904A1/en
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
    • B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
    • B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
    • B66F9/075—Constructional features or details
    • B66F9/20—Means for actuating or controlling masts, platforms, or forks
    • B66F9/22—Hydraulic devices or systems
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
    • B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
    • B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
    • B66F9/075—Constructional features or details
    • B66F9/07504—Accessories, e.g. for towing, charging, locking
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
    • B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
    • B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
    • B66F9/075—Constructional features or details
    • B66F9/08—Masts; Guides; Chains
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/08—Servomotor systems without provision for follow-up action; Circuits therefor with only one servomotor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/405—Flow control characterised by the type of flow control means or valve
    • F15B2211/40523—Flow control characterised by the type of flow control means or valve with flow dividers
    • F15B2211/4053—Flow control characterised by the type of flow control means or valve with flow dividers using valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/70—Output members, e.g. hydraulic motors or cylinders or control therefor
    • F15B2211/71—Multiple output members, e.g. multiple hydraulic motors or cylinders

Definitions

  • the invention relates to an industrial truck with a lift mast with at least one mast lift stage driven by at least one mast lift cylinder and with a free lift stage driven by at least one free lift cylinder, with which a load handling device can be moved along the lift mast. Furthermore, the invention relates to a hydraulic system for an industrial truck with a lifting mast with at least one mast lifting stage and with a free lifting stage, with which a load handling device can be moved along the lifting mast, the hydraulic system having at least one mast lifting cylinder for driving the at least one mast lifting step and at least one free lifting cylinder for Driving the at least one free lift stage comprises.
  • the invention also relates to a method for operating a hydraulic system of an industrial truck with a lifting mast with at least one mast lifting step and with a free lifting step, with which a load handling device can be moved along the lifting mast, the hydraulic system having at least one Mast lift cylinder for driving the at least one mast lift stage and at least one free lift cylinder for driving the free lift stage.
  • Known forklift trucks have a common hydraulic lowering branch for the mast lift and the free lift, in which a lowering valve is integrated. So that the mast lift steps and the free lift retract in the desired sequence when the load handling device is lowered, the individual mast lift steps and the free lift have hydraulic cylinders with different cross-sections. If several mast steps are extended, when the truck is in load lowering mode, the mast step whose total effective hydraulic cross-section is the smallest moves in first. The greatest hydraulic pressure is applied to this hydraulic cylinder, so that it retracts first when the hydraulic pressure drops. Usually it is the top mast lifting step. As the hydraulic pressure continues to fall, the mast steps become serial, that is one after the other, lowered. Finally, after the mast steps are fully retracted, the free lift step retracts and lowers the load handling device.
  • a hydraulic system which comprises a free lift cylinder and a mast lift cylinder.
  • a load handling device is coupled to the free lift cylinder, and a mast step is coupled to the mast lift cylinder.
  • the two lifting cylinders are connected to a hydraulic tank via separate hydraulic return lines.
  • a first return valve is provided in the first return line and a second return valve is provided in the second return line.
  • the hydraulic fluid is supplied via a hydraulic pump, a supply valve and a first and a second connecting line. The supply of hydraulic fluid to the two lifting cylinders can take place at the same time.
  • the supply valve is also a proportional valve
  • the free lift and the mast lift can be moved independently of one another or together, depending on the valve position, to lift the load. It is also provided that shortly before the free lift cylinder reaches its end position, the feed valve is closed successively, so that the volume flow to the free lift cylinder is reduced. This document discloses the preamble of claim 1.
  • an industrial truck with a lifting mast with at least one mast lifting stage driven by at least one mast lifting cylinder and with a free lifting stage driven by at least one free lifting cylinder, with which a load handling device can be moved along the lifting mast
  • the industrial truck being further developed by a hydraulic system for supply the at least one mast lifting cylinder and the at least one free lifting cylinder with a hydraulic fluid
  • the hydraulic system for at least temporarily actuating the at least one mast lifting cylinder and the at least one Free lift cylinder is set up in load lowering operation
  • the hydraulic system for relieving the at least one mast lift cylinder and the at least one free lift cylinder in load lowering operation comprising separate hydraulic return lines
  • the hydraulic system comprising a first hydraulic return line which runs between the at least one free lift cylinder and a reservoir for the hydraulic fluid
  • the hydraulic system further comprises a second hydraulic return line, which runs between the at least one mast lifting cylinder and the storage container, wherein a first lowering valve is integrated into the first return line and a second lowering valve is integrated into the second
  • the mast lifting steps and the load handling device are advantageously retracted and / or extended at the same time.
  • the synchronous, i.e. H. At least temporarily simultaneous actuation of the at least one mast lifting cylinder and the at least one free lifting cylinder, the lowering time of the industrial truck can be reduced. This increases the handling capacity of the industrial truck. This applies if the truck reaches heights that can only be reached when the lifting mast is at least partially extended. In lifting operation, a jerky transition between free lift and mast lift can be avoided.
  • An industrial truck or floor conveyor is a means of transport for the transport of goods, which is mostly used in-house and on the ground, for example a forklift.
  • the industrial truck according to aspects of the invention is in load lowering mode when the load handling device is being lowered from the maximum height during the synchronous lowering process by the time span that is usually required to retract the load handling device with the free lift stage.
  • the extension process ie the lifting of the load handling device to the maximum height, is more homogeneous and fluid than before. This improves the handling of the industrial truck.
  • the lowering of the load handling device can be accelerated by simultaneously retracting the mast step (s) and the free lift step.
  • the mast lift cylinder and the free lift cylinder can be relieved at the same time through the separate hydraulic return lines. This also applies if the mast lift cylinder and the free lift cylinder or the mast lift cylinder of the individual mast lift stages have different cross-sections, so that they extend in series, i.e. one after the other, in load lift operation. If only a single hydraulic line were also used to relieve the lifting cylinder, then the retraction of the mast lift stage and the free lift would necessarily take place in the reverse order to the extension. This is now advantageously no longer the case.
  • the industrial truck is designed such that the hydraulic system comprises a first hydraulic return line that runs between the at least one free lift cylinder and a reservoir for the hydraulic fluid and the hydraulic system further comprises a second hydraulic return line that runs between the at least one mast lift cylinder and the reservoir , wherein a first lowering valve is integrated into the first return line and a second lowering valve is integrated into the second return line.
  • the first lowering valve and the second lowering valve separately i. H. can be controlled independently of each other. It is thus possible to lower the mast lifting stage (s) and / or the load handling device separately and independently of one another in load lowering mode.
  • the industrial truck comprises a controller which is set up to open the lowering valves at the same time when lowering the load handling device in load lowering mode.
  • a controller which is set up to open the lowering valves at the same time when lowering the load handling device in load lowering mode.
  • a displacement transducer is provided on the mast lift and on the free lift so that the respective speed at which the mast lift or the free lift is extended or retracted can be determined.
  • a regulation is possible with which a uniform and homogeneous lowering process can be achieved, in particular so that the mast lifting stage and the load handling device reach their lower end position at least approximately simultaneously.
  • the industrial truck is further developed in particular in that the hydraulic system comprises a hydraulic pump which is integrated in a hydraulic supply line and, in load lifting operation, is set up to apply pressurized hydraulic fluid to the at least one mast lifting cylinder and the at least one free lifting cylinder, the hydraulic supply line being forks between the hydraulic pump and the lifting cylinders into a first and a second supply branch and the first supply branch runs to the free lift cylinder and the second supply branch to the mast lift cylinder, with a lift valve designed as a proportional valve being integrated into the hydraulic supply line, with which a ratio between the volume flows is changeable in the first and in the second supply branch.
  • the hydraulic system comprises a hydraulic pump which is integrated in a hydraulic supply line and, in load lifting operation, is set up to apply pressurized hydraulic fluid to the at least one mast lifting cylinder and the at least one free lifting cylinder, the hydraulic supply line being forks between the hydraulic pump and the lifting cylinders into a first and a second supply branch and the first supply branch runs to the free lift cylinder and the
  • the free lift cylinder have a first cross section and the lift cylinder have a second cross section, the first cross section being larger than the second cross section and the lift valve being integrated into the first supply branch.
  • the arrangement of the lift valve in the first supply branch is advantageous since the effective hydraulic flow cross-section of the first supply branch can be reduced by means of the lift valve. It is thus possible that the free lift cylinder and the lift cylinder can be extended at the same time by appropriate selection or adjustment of the effective hydraulic flow cross section of this supply branch.
  • the control or control unit is in particular part of the operational control or operational control unit of the industrial vehicle.
  • a hydraulic system for an industrial truck with a lifting mast with at least one mast lifting step and with a free lifting step with which a load handling device can be moved along the lifting mast the hydraulic system having at least one mast lifting cylinder for driving the at least one mast lifting step and at least one Comprises free lift cylinder for driving the at least one free lift stage
  • the hydraulic system is further developed in that it is set up for at least temporarily simultaneously supplying the at least one mast lift cylinder and the at least one free lift cylinder with hydraulic fluid in load lowering mode
  • the hydraulic system comprising a first hydraulic return line between the at least one free lift cylinder and a reservoir for the hydraulic fluid
  • the hydraulic system further comprises a second separate hydraulic return line, which runs between the at least one mast lifting cylinder and the reservoir, a first lowering valve being integrated into the first return line and a second lowering valve being integrated into the second return line.
  • the hydraulic system further comprises a hydraulic pump which is integrated in a hydraulic supply line and is set up in load lifting operation to pressurize the at least one mast lift cylinder and the at least one free lift cylinder with pressurized hydraulic fluid, the hydraulic supply line between the Hydraulic pump and the lifting cylinders forks into a first and a second supply branch and the first supply branch to the Free lift cylinder and the second supply branch runs to the mast lift cylinder, with a lift valve designed as a proportional valve being integrated into the hydraulic supply line, with which a ratio between the volume flows in the first and second supply branch can be changed.
  • a hydraulic pump which is integrated in a hydraulic supply line and is set up in load lifting operation to pressurize the at least one mast lift cylinder and the at least one free lift cylinder with pressurized hydraulic fluid
  • the hydraulic supply line between the Hydraulic pump and the lifting cylinders forks into a first and a second supply branch and the first supply branch to the Free lift cylinder and the second supply branch runs to the mast lift cylinder, with
  • the object is also achieved by a method for operating a hydraulic system of an industrial truck with a lifting mast with at least one mast lifting step and with a free lifting step, with which a load handling device can be moved along the lifting mast, the hydraulic system having at least one mast lifting cylinder for driving the at least one mast lifting step and comprises at least one free lift cylinder for driving the free lift stage, the hydraulic system being developed in that it is operated in such a way that the at least one mast lift cylinder and the at least one free lift cylinder are operated at least temporarily simultaneously in load lift operation and / or load lowering operation, with the hydraulic System comprises a first hydraulic return line which runs between the at least one free lift cylinder and a reservoir for the hydraulic fluid and the hydraulic system further comprises a separate second hydraulic return line which between The at least one mast lifting cylinder and the storage container run, a first lowering valve being integrated into the first return line and a second lowering valve being integrated into the second return line, and the first lowering valve and the second lowering valve being opened at the same time in load lowering mode when the
  • the hydraulic system comprises a hydraulic pump which is integrated in a hydraulic supply line and with which the at least one mast lift cylinder and the at least one free lift cylinder in load lift operation pressurized hydraulic fluid is applied, the hydraulic supply line forks between the hydraulic pump and the lifting cylinders in a first and a second supply branch and the first supply branch to the free lift cylinder and the second supply branch to the mast lift cylinder, with a lift valve designed as a proportional valve in the hydraulic supply line is integrated, with which a ratio between a volume flow in the first and in the second supply branch can be changed, wherein the free lift cylinder has a first cross section and the mast lift cylinder has a second cross section, the first cross section being larger than the second cross section and the lift valve in the first supply branch is integrated and wherein the lift valve is controlled in such a way that the free lift cylinder and the mast lift cylinder are extended at least temporarily at the same time.
  • the lifting valve in a first position for a sequential extension of the free lift cylinder and the mast lift cylinder or in a second position for an at least temporarily simultaneous extension is brought.
  • the corresponding operating mode can be selected manually, for example. However, it is also provided that a corresponding operating mode, in which the mast lift stage and the free lift stage are moved simultaneously, is selected if, for example, a lift height is entered manually which is outside the range that can only be reached by means of the free lift.
  • Embodiments according to the invention can fulfill individual features or a combination of several features.
  • Fig. 1 shows an industrial truck 2, for example a forklift, with a lifting mast 4, comprising, for example, a first mast lifting stage 41, the inner mast, and a second mast lifting stage 42, the central mast.
  • the lifting mast 4 is supported by an in Fig. 1 Mast lifting cylinder (not shown, several mast lifting cylinders can also be provided) driven.
  • the lifting mast 4 comprises, in addition to the inner mast and the central mast, a stationary mast firmly connected to the vehicle frame.
  • the central mast is driven, for example, by the mast lifting cylinder, the inner mast is also coupled with the central mast, for example via a chain, so that these two extending masts extend at the same time.
  • Fig. 2 shows a schematic circuit diagram of a hydraulic system 10 as it is integrated in the industrial truck 2 according to an exemplary embodiment.
  • the hydraulic system 10 is used to supply a mast lift cylinder 12 and the free lift cylinder 8, with which the load handling device 6 is moved, with a hydraulic fluid 14.
  • the hydraulic fluid is taken from a reservoir 16 and also returned to it.
  • the hydraulic system 10 is set up to simultaneously operate the mast lifting cylinder 12 and the free lifting cylinder 8 in the load lifting mode and / or in the lowering mode, at least at times.
  • the hydraulic system 10 is set up to the mast lift cylinder 12 and the free lift cylinder 8 both in the load lifting operation, ie when lifting the Load suspension means 6, as well as in load lowering operation, that is, when lowering the load suspension means 6, to be actuated at the same time.
  • the hydraulic system 10 comprises separate hydraulic return lines 18.
  • a first hydraulic return line 181 runs between the free lift cylinder 8 and the storage container 16.
  • a second hydraulic return line 182 is included, which runs between the mast lift cylinder 12 and the storage container 16.
  • a first lowering valve 21 is integrated into the first return line 181 and a second lowering valve 22 is integrated into the second return line 182.
  • the lowering valves 21, 22 are, for example, proportional valves. These can be switched between a first switching position 21a, 22a, in which the lowering valves 21, 22 work as check valves, and a second switching position 21b, 22b. In the second switching position 21b, 22b, the lowering valves 21, 22 are set up to control or regulate a first volume flow or a second volume flow.
  • the first lowering valve 21 controls or regulates a first volume flow through the first return line 181, while the second lowering valve 22 controls or regulates a second volume flow through the second return line 182.
  • the lowering valves 21, 22 can be controlled separately from one another.
  • a controller 24 is included in the hydraulic system 10, which controls the two lowering valves 21, 22 via connecting lines (not shown).
  • the controller 24 is set up or programmed in such a way that in a load lowering operation, ie when lowering the load handling device 6, the lowering valves 21, 22 open at the same time.
  • the free lift cylinder 8 of the free lift stage and the mast lift cylinder 12 of the lift mast 4 are retracted at the same time.
  • the load receiving means 6 actuated by the free lift stage sinks along the first mast lift stage 41, while at the same time the lift mast 4, ie the first and second mast lifting stage 41, 42, retract.
  • FIG. 3a shows the industrial truck 2 with the lifting mast 4 fully extended.
  • the load handling device 6 is located at the upper stop of the first mast lifting stage 41.
  • a conventional industrial truck 2 comprises a common return line with which both the free lifting cylinder 8 and the mast lifting cylinder 12 are relieved of pressure.
  • FIGS. 4a to 4c show a lowering process of a load handling device 6 of an industrial truck 2 according to an exemplary embodiment.
  • Figure 4a shows the industrial truck 2 with the lifting mast 4 fully extended, with the load handling device 6 also being located at the upper stop of the first mast lifting step 41.
  • This situation is identical to that in Fig. 3a shown.
  • the in Fig. 4 illustrated industrial truck 2 the free lift stage and the mast lift stages 41, 42 by simultaneously opening the first and second lowering valve 21, 22 (cf. Fig. 2 ) lowered synchronously.
  • Figure 4b shows the industrial truck 2 after a first time interval, after which the conventional industrial truck 2 in FIG Figure 3b is shown.
  • the load handling device 6 has already reached the lower stop of the first mast lifting stage 41.
  • the load handling device 6 is lowered significantly more quickly. Exactly that time interval is saved which the load suspension means 6 in a conventional industrial truck 2 needs in order to be lowered along a mast lifting step 41, 42.
  • the hydraulic system 10 of the industrial truck 2 comprises a hydraulic pump 26 which draws hydraulic fluid 14 from the storage container 16 via a hydraulic supply line 28.
  • the hydraulic pump 26 is integrated into the hydraulic supply line 28.
  • the hydraulic pump 26 is used to pressurize the mast lifting cylinder 12 and the free lifting cylinder 8 with pressurized hydraulic fluid 14.
  • the hydraulic supply line 28 forks between the hydraulic pump 26 and the lifting cylinders, ie the free lift cylinder 8 and the mast lift cylinder 12, into a first supply branch 31 and a second supply branch 32.
  • the first supply branch 31 leads to the free lift cylinder 8
  • the second supply branch 32 leads to the mast lifting cylinder 12.
  • the two supply branches 31, 32 are also perceived as part of the hydraulic feed line 28.
  • a lift valve 34 which can be designed as a proportional valve, is integrated into the first supply branch 31. Like the hydraulic pump 26, the lift valve 34 can be controlled or regulated via the controller 24.
  • a ratio between the volume flows in the first and second supply branches 31, 32 can be changed via the settings of the lift valve 34.
  • the free lift cylinder 8 has a first cross section and the mast lift cylinder 12 has a second cross section, the first cross section being larger than the second cross section. For this reason, the free lift cylinder 8 is activated at a first pressure p1, the pressure p1 being lower than the pressure p2 at which the mast lift cylinder 12 is activated.
  • the effective hydraulic flow cross-section of the lifting cylinders 8, 12 can be variably adjusted via the settings of the lifting valve 34, so that it is possible to extend both lifting cylinders 8, 12 at the same time. This takes place in the first switch position 34a of the lift valve 34.
  • the free lift can be blocked so that only the mast lift cylinder 12 is actuated.
  • the dynamic setting of the lift valve 34 also makes it possible to achieve a smooth transition between a lift of the load-bearing means 6 effected by the free lift cylinder 8 and a lift of the same effected by the mast lift cylinder 12.
  • a check valve 36 is integrated into the respective supply branch.

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  • Engineering & Computer Science (AREA)
  • Structural Engineering (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Civil Engineering (AREA)
  • Geology (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • General Engineering & Computer Science (AREA)
  • Forklifts And Lifting Vehicles (AREA)
  • Fluid-Pressure Circuits (AREA)

Description

Die Erfindung betrifft ein Flurförderzeug mit einem Hubmast mit zumindest einer von zumindest einem Masthubzylinder angetriebenen Masthubstufe und mit einer von zumindest einem Freihubzylinder angetriebenen Freihubstufe, mit der ein Lastaufnahmemittel entlang des Hubmastes verfahrbar ist. Ferner betrifft die Erfindung ein hydraulisches System für ein Flurförderzeug mit einem Hubmast mit zumindest einer Masthubstufe und mit einer Freihubstufe, mit der ein Lastaufnahmemittel entlang des Hubmastes verfahrbar ist, wobei das hydraulische System zumindest einen Masthubzylinder zum Antreiben der zumindest einen Masthubstufe und zumindest einen Freihubzylinder zum Antreiben der zumindest einen Freihubstufe umfasst. Die Erfindung betrifft ebenso ein Verfahren zum Betreiben eines hydraulischen Systems eines Flurförderzeugs mit einem Hubmast mit zumindest einer Masthubstufe und mit einer Freihubstufe, mit der ein Lastaufnahmemittel entlang des Hubmasts verfahrbar ist, wobei das hydraulische System zumindest einen Masthubzylinder zum Antreiben der zumindest einen Masthubstufe und zumindest einen Freihubzylinder zum Antreiben der Freihubstufe umfasst.The invention relates to an industrial truck with a lift mast with at least one mast lift stage driven by at least one mast lift cylinder and with a free lift stage driven by at least one free lift cylinder, with which a load handling device can be moved along the lift mast. Furthermore, the invention relates to a hydraulic system for an industrial truck with a lifting mast with at least one mast lifting stage and with a free lifting stage, with which a load handling device can be moved along the lifting mast, the hydraulic system having at least one mast lifting cylinder for driving the at least one mast lifting step and at least one free lifting cylinder for Driving the at least one free lift stage comprises. The invention also relates to a method for operating a hydraulic system of an industrial truck with a lifting mast with at least one mast lifting step and with a free lifting step, with which a load handling device can be moved along the lifting mast, the hydraulic system having at least one Mast lift cylinder for driving the at least one mast lift stage and at least one free lift cylinder for driving the free lift stage.

Flurförderzeuge, wie beispielsweise Gabelstapler, verfügen vielfach über einen Hubmast mit einer oder mehreren Masthubstufen, die von einem Masthubzylinder oder mehreren Masthubzylindern hydraulisch betätigt werden. Der Hubmast umfasst einen fest mit dem Fahrzeug verbundenen Standmast und in der Regel zwei Ausfahrmasten, einem Mittelmast und einem Innenmast, die von dem Masthubzylinder ausgefahren werden. Ein Freihubzylinder bewegt eine Freihubstufe, mit der ein Lastaufnahmemittel, beispielsweise eine Gabel, entlang des Innenmastes des Hubmastes verfahrbar ist. Die Freihubstufe bewegt das Lastaufnahmemittel entlang dieser Maststufe und erlaubt es dem Bediener des Flurförderzeugs, das Lastaufnahmemittel der Höhe nach zu verfahren, ohne dass der Hubmast ausgefahren wird und sich somit die Bauhöhe des Flurförderzeugs ändert.Industrial trucks, such as forklift trucks, often have a lifting mast with one or more mast lifting stages, which are hydraulically actuated by a mast lifting cylinder or several mast lifting cylinders. The lifting mast comprises a stationary mast that is permanently connected to the vehicle and, as a rule, two extending masts, a central mast and an inner mast, which are extended by the mast lifting cylinder. A free lift cylinder moves a free lift stage with which a load handling device, for example a fork, can be moved along the inner mast of the lift mast. The free lift stage moves the load handling device along this mast step and allows the operator of the industrial truck to move the load lifting device according to the height without the lifting mast being extended and thus changing the overall height of the industrial truck.

Bekannte Gabelstapler verfügen über einen gemeinsamen Hydraulik-Senkzweig für den Masthub und den Freihub, in den ein Senkventil integriert ist. Damit beim Absenken des Lastaufnahmemittels die Masthubstufen und der Freihub in der gewünschten Reihenfolge einfahren, verfügen die einzelnen Masthubstufen und der Freihub über Hydraulikzylinder mit unterschiedlichen Querschnitten. Sind mehrere Maststufen ausgefahren, so fährt im Lastsenkbetrieb des Flurförderzeugs zuerst diejenige Maststufe ein, deren wirksamer hydraulischer Querschnitt in Summe am geringsten ist. An diesem Hydraulikzylinder liegt nämlich der größte hydraulische Druck an, so dass er bei sinkendem hydraulischen Druck als erstes einfährt. Üblicherweise handelt es sich um die oberste Masthubstufe. Mit weiter sinkendem hydraulischem Druck werden die Maststufen seriell, also nacheinander, abgesenkt. Schließlich fährt, nachdem die Maststufen vollständig eingefahren sind, die Freihubstufe ein und senkt das Lastaufnahmemittel ab.Known forklift trucks have a common hydraulic lowering branch for the mast lift and the free lift, in which a lowering valve is integrated. So that the mast lift steps and the free lift retract in the desired sequence when the load handling device is lowered, the individual mast lift steps and the free lift have hydraulic cylinders with different cross-sections. If several mast steps are extended, when the truck is in load lowering mode, the mast step whose total effective hydraulic cross-section is the smallest moves in first. The greatest hydraulic pressure is applied to this hydraulic cylinder, so that it retracts first when the hydraulic pressure drops. Usually it is the top mast lifting step. As the hydraulic pressure continues to fall, the mast steps become serial, that is one after the other, lowered. Finally, after the mast steps are fully retracted, the free lift step retracts and lowers the load handling device.

Aus der nicht vorveröffentlichten EP 3 336 051 A1 ist ein hydraulisches System bekannt, welches einen Freihubzylinder und einen Masthubzylinder umfasst. Mit dem Freihubzylinder ist ein Lastaufnahmemittel gekoppelt, mit dem Masthubzylinder ist eine Maststufe gekoppelt. Die beiden Hubzylinder sind über separate hydraulische Rückleitungen mit einem Hydrauliktank verbunden. In der ersten Rückleitung ist ein erstes Rückführventil vorhanden, in der zweiten Rückleitung ist ein zweites Rückführventil vorhanden. Die Zufuhr der Hydraulikflüssigkeit erfolgt über eine Hydraulikpumpe, ein Zuführventil sowie eine erste und eine zweite Verbindungsleitung. Die Zufuhr von Hydraulikflüssigkeit zu den beiden Hubzylindern kann gleichzeitig erfolgen. Da es sich bei dem Zuführventil außerdem um ein Proportionalventil handelt, kann zum Heben der Last der Freihub und der Masthub je nach Ventilstellung unabhängig voneinander oder gemeinsam verfahren werden. Außerdem ist vorgesehen, dass kurz bevor der Freihubzylinder seine Endstellung erreicht, das Zuführventil sukzessive geschlossen wird, so dass sich der Volumenstrom zum Freihubzylinder reduziert. Dieses Dokument offenbart den Oberbegriff von Anspruch 1.From the not pre-published EP 3 336 051 A1 a hydraulic system is known which comprises a free lift cylinder and a mast lift cylinder. A load handling device is coupled to the free lift cylinder, and a mast step is coupled to the mast lift cylinder. The two lifting cylinders are connected to a hydraulic tank via separate hydraulic return lines. A first return valve is provided in the first return line and a second return valve is provided in the second return line. The hydraulic fluid is supplied via a hydraulic pump, a supply valve and a first and a second connecting line. The supply of hydraulic fluid to the two lifting cylinders can take place at the same time. Since the supply valve is also a proportional valve, the free lift and the mast lift can be moved independently of one another or together, depending on the valve position, to lift the load. It is also provided that shortly before the free lift cylinder reaches its end position, the feed valve is closed successively, so that the volume flow to the free lift cylinder is reduced. This document discloses the preamble of claim 1.

Aus der DE 10 2009 011 865 A1 ist ein hydraulisches System bekannt, bei dem ein sanfter Übergang zwischen Freihub und Masthub realisiert werden kann. Kurz vor Erreichen der jeweiligen Endanschläge wird der Freihub oder der Masthub verringert oder bereits angefahren, so dass diese kurzzeitig gleichzeitig betätig werden, um einen sanften Übergang zu ermöglichen.From the DE 10 2009 011 865 A1 a hydraulic system is known in which a smooth transition between free lift and mast lift can be realized. Shortly before reaching the respective end stops, the free lift or the mast lift is reduced or already approached so that they are briefly actuated at the same time in order to enable a smooth transition.

Aus der EP 1 600 420 A1 ist ein weiteres hydraulisches System bekannt, welches einen Freihubzylinder und zwei Masthubzylinder umfasst. Die Hubzylinder werden über Hydraulikpumpen versorgt. Die Querschnitte der Hydraulikzylinder sind so gewählt, dass diese sequentiell betätigt werden. Um einen sanften Übergang zwischen den einzelnen Hubstufen zu schaffen, ist ein Ventil vorhanden, welches in einer vorgesehenen Schaltstellung den Fluss zu dem Freihubzylinder begrenzt.From the EP 1 600 420 A1 Another hydraulic system is known which comprises a free lift cylinder and two mast lift cylinders. The lifting cylinders are supplied by hydraulic pumps. The cross-sections of the hydraulic cylinders are chosen so that they are operated sequentially. In order to create a smooth transition between the individual lift stages, there is a valve which, in an intended switching position, limits the flow to the free lift cylinder.

Ein weiteres hydraulisches System ist aus WO 2009/141242 A1 bekannt. Zwischen einer Hydraulikpumpe und den Hydraulikzylindern des Freihubs und des Masthubs sind Ventile vorhanden, so dass beide Hydraulikstufen mit der gewünschten Geschwindigkeit verfahren werden können und ein ruckfreier Übergang zwischen der Freihubstufe und der Hauptstufe hergestellt werden kann.Another hydraulic system is off WO 2009/141242 A1 famous. There are valves between a hydraulic pump and the hydraulic cylinders of the free lift and the mast lift, so that both hydraulic stages can be moved at the desired speed and a smooth transition between the free lift stage and the main stage can be established.

Es ist eine Aufgabe der Erfindung, ein Flurförderzeug mit einem Hubmast mit zumindest einer Masthubstufe und mit einer Freihubstufe, ein hydraulisches System für ein solches Flurförderzeug sowie ein Verfahren zum Betreiben eines hydraulischen Systems eines Flurförderzeugs anzugeben, wobei ein Einfahren der zumindest einen Masthubstufe und der Freihubstufe im Lastsenkbetrieb schneller als bisher möglich sein soll.It is an object of the invention to provide an industrial truck with a lifting mast with at least one mast lifting step and with a free lifting step, a hydraulic system for such an industrial truck and a method for operating a hydraulic system of an industrial truck, with the at least one mast lifting step and the free lifting step being retracted should be faster than before in load lowering mode.

Die Aufgabe wird gelöst durch ein Flurförderzeug mit einem Hubmast mit zumindest einer von zumindest einem Masthubzylinder angetriebenen Masthubstufe und mit einer von zumindest einem Freihubzylinder angetriebenen Freihubstufe, mit der ein Lastaufnahmemittel entlang des Hubmastes verfahrbar ist, wobei das Flurförderzeug fortgebildet ist durch ein hydraulisches System zum Versorgen des zumindest einen Masthubzylinders und des zumindest einen Freihubzylinders mit einer Hydraulikflüssigkeit, wobei das hydraulische System zum zumindest zeitweise gleichzeitigen Betätigen des zumindest einen Masthubzylinders und des zumindest einen Freihubzylinders im Lastsenkbetrieb eingerichtet ist, wobei das hydraulische System zum Entlasten des zumindest einen Masthubzylinders und des zumindest einen Freihubzylinders im Lastsenkbetrieb separate hydraulische Rückleitungen umfasst, das hydraulische System eine erste hydraulische Rückleitung umfasst, die zwischen dem zumindest einen Freihubzylinder und einem Vorratsbehälter für die Hydraulikflüssigkeit verläuft und das hydraulische System ferner eine zweite hydraulische Rückleitung umfasst, die zwischen dem zumindest einen Masthubzylinder und dem Vorratsbehälter verläuft, wobei in die erste Rückleitung ein erstes Senkventil und in die zweite Rückleitung ein zweites Senkventil integriert ist und wobei eine Steuerung umfasst ist, die dazu eingerichtet ist, im Lastsenkbetrieb beim Absenken des Lastaufnahmemittels die beiden Senkventile gleichzeitig zu öffnen.The object is achieved by an industrial truck with a lifting mast with at least one mast lifting stage driven by at least one mast lifting cylinder and with a free lifting stage driven by at least one free lifting cylinder, with which a load handling device can be moved along the lifting mast, the industrial truck being further developed by a hydraulic system for supply the at least one mast lifting cylinder and the at least one free lifting cylinder with a hydraulic fluid, the hydraulic system for at least temporarily actuating the at least one mast lifting cylinder and the at least one Free lift cylinder is set up in load lowering operation, the hydraulic system for relieving the at least one mast lift cylinder and the at least one free lift cylinder in load lowering operation comprising separate hydraulic return lines, the hydraulic system comprising a first hydraulic return line which runs between the at least one free lift cylinder and a reservoir for the hydraulic fluid and the hydraulic system further comprises a second hydraulic return line, which runs between the at least one mast lifting cylinder and the storage container, wherein a first lowering valve is integrated into the first return line and a second lowering valve is integrated into the second return line and wherein a controller is included which is configured for this is to open the two lowering valves at the same time when lowering the load handler in load lowering mode.

Vorteilhaft werden bei einem solchen Flurförderzeug die Masthubstufen und das Lastaufnahmemittel gleichzeitig eingefahren und/oder ausgefahren. Durch die synchrone, d. h. zumindest zeitweise gleichzeitige, Betätigung des zumindest einen Masthubzylinders und des zumindest einen Freihubzylinders kann die Senkzeit des Flurförderzeugs reduziert werden. Dies erhöht die Umschlagleistung des Flurförderzeugs. Dies gilt, sofern das Flurförderzeug auf Höhen zugreift, die nur bei zumindest teilweise ausgefahrenem Hubmast erreichbar sind. Im Hubbetrieb kann ein ruckartiger Übergang zwischen Freihub und Masthub vermieden werden.In such an industrial truck, the mast lifting steps and the load handling device are advantageously retracted and / or extended at the same time. The synchronous, i.e. H. At least temporarily simultaneous actuation of the at least one mast lifting cylinder and the at least one free lifting cylinder, the lowering time of the industrial truck can be reduced. This increases the handling capacity of the industrial truck. This applies if the truck reaches heights that can only be reached when the lifting mast is at least partially extended. In lifting operation, a jerky transition between free lift and mast lift can be avoided.

Ein Flurförderzeug oder auch Flurfördergerät ist ein Transportmittel für den Transport von Gütern, welches zumeist innerbetrieblich und zu ebener Erde eingesetzt wird, beispielsweise ein Stapler.An industrial truck or floor conveyor is a means of transport for the transport of goods, which is mostly used in-house and on the ground, for example a forklift.

Im Idealfall ist das Flurförderzeug gemäß Aspekten der Erfindung beim Herunterfahren des Lastaufnahmemittels im Lastsenkbetrieb aus maximaler Höhe beim synchronen Senkvorgang um diejenige Zeitspanne schneller, wie sie üblicherweise zum Einfahren des Lastaufnahmemittels mit der Freihubstufe erforderlich ist. Der Ausfahrvorgang, d. h. das Anheben des Lastaufnahmemittels bis zur maximalen Höhe, ist homogener und flüssiger als bisher. Dies verbessert die Handhabung des Flurförderzeugs.In the ideal case, the industrial truck according to aspects of the invention is in load lowering mode when the load handling device is being lowered from the maximum height during the synchronous lowering process by the time span that is usually required to retract the load handling device with the free lift stage. The extension process, ie the lifting of the load handling device to the maximum height, is more homogeneous and fluid than before. This improves the handling of the industrial truck.

Das Flurförderzeug ist so ausgebildet, dass das hydraulische System zum Entlasten des zumindest einen Masthubzylinders und des zumindest einen Freihubzylinders im Lastsenkbetrieb separate hydraulische Rückleitungen umfasst.The industrial truck is designed in such a way that the hydraulic system for relieving the load on the at least one mast lifting cylinder and the at least one free lifting cylinder in load lowering operation comprises separate hydraulic return lines.

Durch die separaten hydraulischen Rückleitungen kann das Absenken des Lastaufnahmemittels durch gleichzeitiges Einfahren der Maststufe(n) und der Freihubstufe beschleunigt werden. Durch die separaten hydraulischen Rückleitungen können der Masthubzylinder und der Freihubzylinder gleichzeitig entlastet werden. Dies gilt auch, wenn der Masthubzylinder und der Freihubzylinder bzw. die Masthubzylinder der einzelnen Masthubstufen unterschiedliche Querschnitte aufweisen, sodass diese im Lasthubbetrieb seriell, also nacheinander, ausfahren. Würde lediglich eine einzige Hydraulikleitung auch zum Entlasten der Hubzylinder eingesetzt, so würde notwendigerweise das Einfahren der Masthubstufe und des Freihubs gerade in umgekehrter Reihenfolge wie das Ausfahren stattfinden. Dies ist nun vorteilhaft nicht mehr der Fall.Thanks to the separate hydraulic return lines, the lowering of the load handling device can be accelerated by simultaneously retracting the mast step (s) and the free lift step. The mast lift cylinder and the free lift cylinder can be relieved at the same time through the separate hydraulic return lines. This also applies if the mast lift cylinder and the free lift cylinder or the mast lift cylinder of the individual mast lift stages have different cross-sections, so that they extend in series, i.e. one after the other, in load lift operation. If only a single hydraulic line were also used to relieve the lifting cylinder, then the retraction of the mast lift stage and the free lift would necessarily take place in the reverse order to the extension. This is now advantageously no longer the case.

Das Flurförderzeug ist so ausgebildet, dass das hydraulische System eine erste hydraulische Rückleitung umfasst, die zwischen dem zumindest einen Freihubzylinder und einem Vorratsbehälter für die Hydraulikflüssigkeit verläuft und das hydraulische System ferner eine zweite hydraulische Rückleitung umfasst, die zwischen dem zumindest einen Masthubzylinder und dem Vorratsbehälter verläuft, wobei in die erste Rückleitung ein erstes Senkventil und in die zweite Rückleitung ein zweites Senkventil integriert ist.The industrial truck is designed such that the hydraulic system comprises a first hydraulic return line that runs between the at least one free lift cylinder and a reservoir for the hydraulic fluid and the hydraulic system further comprises a second hydraulic return line that runs between the at least one mast lift cylinder and the reservoir , wherein a first lowering valve is integrated into the first return line and a second lowering valve is integrated into the second return line.

Insbesondere ist vorgesehen, dass das erste Senkventil und das zweite Senkventil separat, d. h. unabhängig voneinander, angesteuert werden können. So ist es möglich, die Masthubstufe(n) und/oder das Lastaufnahmemittel separat und unabhängig voneinander im Lastsenkbetrieb abzusenken.In particular, it is provided that the first lowering valve and the second lowering valve separately, i. H. can be controlled independently of each other. It is thus possible to lower the mast lifting stage (s) and / or the load handling device separately and independently of one another in load lowering mode.

Das Flurförderzeug umfasst eine Steuerung, die dazu eingerichtet ist, im Lastsenkbetrieb beim Absenken des Lastaufnahmemittels die Senkventile gleichzeitig zu öffnen. Durch ein gleichzeitiges Öffnen der beiden Senkventile werden die Masthubstufe(n) und das Lastaufnahmemittel zumindest zu Beginn des Vorgangs gleichzeitig abgesenkt. Das Lastaufnahmemittel wird besonders schnell abgesenkt.The industrial truck comprises a controller which is set up to open the lowering valves at the same time when lowering the load handling device in load lowering mode. By opening the two lowering valves at the same time, the mast lift stage (s) and the load handling device are lowered simultaneously, at least at the beginning of the process. The load handler is lowered particularly quickly.

Es ist ferner insbesondere vorgesehen, dass die Senkventile Proportionalventile sind und die Steuerung ferner dazu eingerichtet ist, einen ersten Volumenstrom durch das erste Senkventil und einen zweiten Volumenstrom durch das zweite Senkventil so zu steuern oder zu regeln, dass im Lastsenkbetrieb beim Absenken des Lastaufnahmemittels die zumindest eine Masthubstufe und das Lastaufnahmemittel eine untere Endposition zumindest näherungsweise gleichzeitig erreichen.It is also provided in particular that the lowering valves are proportional valves and the controller is also set up to control or regulate a first volume flow through the first lowering valve and a second volume flow through the second lowering valve in such a way that in load lowering operation the at least a mast lifting step and the load handling device reach a lower end position at least approximately at the same time.

Gemäß dieser Ausführungsform kann ein homogenes und vergleichbares Verhalten des Flurförderzeugs beim Absenken des Lasthebemittels aus unterschiedlichen Hubhöhen erreicht werden. Dies erleichtert die Bedienbarkeit des Flurförderzeugs. Außerdem kann eine gleichmäßige Absenkgeschwindigkeit des Lastaufnahmemittels über den gesamten Absenkvorgang hinweg erreicht werden.According to this embodiment, a homogeneous and comparable behavior of the industrial truck when lowering the load lifting device from different lifting heights can be achieved. This makes it easier to operate the industrial truck. In addition, a uniform lowering speed of the load handling device can be achieved over the entire lowering process.

Um eine entsprechende Regelung bereitzustellen, ist beispielsweise ein Wegaufnehmer am Masthub und am Freihub vorgesehen, so dass die jeweilige Geschwindigkeit, mit der der Masthub bzw. der Freihub aus- bzw. eingefahren werden, feststellbar ist. Ausgehend von diesem Messwert ist eine Regelung möglich, mit der ein gleichmäßiger und homogener Absenkvorgang erreicht werden kann, insbesondere so, dass die Masthubstufe und das Lastaufnahmemittel ihre untere Endposition zumindest näherungsweise gleichzeitig erreichen.In order to provide a corresponding regulation, for example a displacement transducer is provided on the mast lift and on the free lift so that the respective speed at which the mast lift or the free lift is extended or retracted can be determined. On the basis of this measured value, a regulation is possible with which a uniform and homogeneous lowering process can be achieved, in particular so that the mast lifting stage and the load handling device reach their lower end position at least approximately simultaneously.

Das Flurförderzeug ist ferner insbesondere dadurch fortgebildet, dass das hydraulische System eine Hydraulikpumpe umfasst, die in eine hydraulische Zuleitung integriert ist und im Lasthubbetrieb zum Beaufschlagen des zumindest einen Masthubzylinders und des zumindest einen Freihubzylinders mit unter Druck stehender Hydraulikflüssigkeit eingerichtet ist, wobei sich die hydraulische Zuleitung zwischen der Hydraulikpumpe und den Hubzylindern in einen ersten und einen zweiten Versorgungsast aufgabelt und der erste Versorgungsast zu dem Freihubzylinder und der zweite Versorgungsast zu dem Masthubzylinder verläuft, wobei ein als Proportionalventil ausgestaltetes Hubventil in die hydraulische Zuleitung integriert ist, mit dem ein Verhältnis zwischen den Volumenströmen im ersten und im zweiten Versorgungsast veränderbar ist.The industrial truck is further developed in particular in that the hydraulic system comprises a hydraulic pump which is integrated in a hydraulic supply line and, in load lifting operation, is set up to apply pressurized hydraulic fluid to the at least one mast lifting cylinder and the at least one free lifting cylinder, the hydraulic supply line being forks between the hydraulic pump and the lifting cylinders into a first and a second supply branch and the first supply branch runs to the free lift cylinder and the second supply branch to the mast lift cylinder, with a lift valve designed as a proportional valve being integrated into the hydraulic supply line, with which a ratio between the volume flows is changeable in the first and in the second supply branch.

Gemäß dieser Ausführungsform ist nicht nur ein zumindest zeitweise gleichzeitiges Einfahren des Hubmastes bzw. der Masthubstufen und der Freihubstufe im Lastsenkbetrieb sondern auch ein zumindest zeitweise gleichzeitiges Ausfahren des Hubmastes und der Freihubstufe während des Lasthubbetriebes möglich. Auf diese Weise kann neben der Umschlagleistung auch die Handhabung und Bedienbarkeit des Flurförderzeugs weiter verbessert werden.According to this embodiment, not only an at least temporarily simultaneous retraction of the lifting mast or the mast lift stages and the free lift stage in load lowering operation, but also an at least temporary simultaneous extension of the lift mast and the free lift stage during the load lift operation is possible. In this way, in addition to the handling performance, the handling and operability of the industrial truck can also be further improved.

Gemäß einer weiteren vorteilhaften Ausführungsform ist vorgesehen, dass der Freihubzylinder einen ersten Querschnitt und der Hubzylinder einen zweiten Querschnitt aufweisen, wobei der erste Querschnitt größer als der zweite Querschnitt ist und das Hubventil in den ersten Versorgungsast integriert ist. Die Anordnung des Hubventils im ersten Versorgungsast ist vorteilhaft, da mittels des Hubventils der effektive hydraulische Strömungsquerschnitt des ersten Versorgungsastes verringert werden kann. So ist es möglich, dass durch entsprechende Wahl oder Einstellung des effektiven hydraulischen Strömungsquerschnitts dieses Versorgungsastes der Freihubzylinder und der Hubzylinder gleichzeitig ausgefahren werden können.According to a further advantageous embodiment it is provided that the free lift cylinder have a first cross section and the lift cylinder have a second cross section, the first cross section being larger than the second cross section and the lift valve being integrated into the first supply branch. The arrangement of the lift valve in the first supply branch is advantageous since the effective hydraulic flow cross-section of the first supply branch can be reduced by means of the lift valve. It is thus possible that the free lift cylinder and the lift cylinder can be extended at the same time by appropriate selection or adjustment of the effective hydraulic flow cross section of this supply branch.

Das Flurförderzeug ist ferner durch eine Steuerung fortgebildet, die dazu eingerichtet ist, das Hubventil derart anzusteuern, dass im Lasthubbetrieb der Freihubzylinder und der Masthubzylinder zumindest zeitweise gleichzeitig ausgefahren werden. Insbesondere ist vorgesehen, dass die Steuerung dazu eingerichtet ist, das Hubventil derart anzusteuern, dass ein ruckfreier Übergang zwischen Freihub und Masthub erreicht wird.The industrial truck is further developed by a controller that is set up to control the lift valve in such a way that the free lift cylinder and the mast lift cylinder are extended at least temporarily at the same time in load lifting operation. In particular, it is provided that the controller is set up to control the lift valve in such a way that a jerk-free transition between free lift and mast lift is achieved.

Die Steuerung oder Steuerungseinheit ist insbesondere ein Teil der Betriebssteuerung oder Betriebssteuereinheit des Flurfahrzeugs.The control or control unit is in particular part of the operational control or operational control unit of the industrial vehicle.

Die Aufgabe wird außerdem gelöst durch ein hydraulisches System für ein Flurförderzeug mit einem Hubmast mit zumindest einer Masthubstufe und mit einer Freihubstufe, mit der ein Lastaufnahmemittel entlang des Hubmastes verfahrbar ist, wobei das hydraulische System zumindest einen Masthubzylinder zum Antreiben der zumindest einen Masthubstufe und zumindest einen Freihubzylinder zum Antreiben der zumindest einen Freihubstufe umfasst, wobei das hydraulische System dadurch fortgebildet ist, dass dieses zum zumindest zeitweise gleichzeitigen Versorgen des zumindest einen Masthubzylinders und des zumindest einen Freihubzylinders mit einer Hydraulikflüssigkeit im Lastsenkbetrieb eingerichtet ist, wobei das hydraulische System eine erste hydraulische Rückleitung umfasst, die zwischen dem zumindest einen Freihubzylinder und einem Vorratsbehälter für die Hydraulikflüssigkeit verläuft und das hydraulische System ferner eine zweite separate hydraulische Rückleitung umfasst, die zwischen dem zumindest einen Masthubzylinder und dem Vorratsbehälter verläuft, wobei in die erste Rückleitung ein erstes Senkventil und in die zweite Rückleitung ein zweites Senkventil integriert ist.The object is also achieved by a hydraulic system for an industrial truck with a lifting mast with at least one mast lifting step and with a free lifting step with which a load handling device can be moved along the lifting mast, the hydraulic system having at least one mast lifting cylinder for driving the at least one mast lifting step and at least one Comprises free lift cylinder for driving the at least one free lift stage, wherein the hydraulic system is further developed in that it is set up for at least temporarily simultaneously supplying the at least one mast lift cylinder and the at least one free lift cylinder with hydraulic fluid in load lowering mode, the hydraulic system comprising a first hydraulic return line between the at least one free lift cylinder and a reservoir for the hydraulic fluid and the hydraulic system further comprises a second separate hydraulic return line, which runs between the at least one mast lifting cylinder and the reservoir, a first lowering valve being integrated into the first return line and a second lowering valve being integrated into the second return line.

Auf das hydraulische System treffen gleiche oder ähnliche Vorteile zu, wie sie bereits im Hinblick auf das Flurförderzeug selbst erwähnt wurden. Das hydraulische System erlaubt es, ein Flurförderzeug bereitzustellen, bei welchem das Lastaufnahmemittel schneller als bisher abgesenkt werden kann. Somit ist es möglich, mithilfe des hydraulischen Systems gemäß Aspekten der Erfindung ein Flurförderzeug so auszurüsten, dass dieses eine höhere Umschlagsleistung erzielt. Das hydraulische System ist vor allem im Hinblick auf die mögliche Auf- oder Umrüstung bestehender Flurfahrzeuge interessant und vorteilhaft.The same or similar advantages apply to the hydraulic system as were already mentioned with regard to the industrial truck itself. The hydraulic system makes it possible to provide an industrial truck in which the load handling device can be lowered more quickly than before. It is thus possible, with the aid of the hydraulic system according to aspects of the invention, to equip an industrial truck in such a way that it achieves a higher handling capacity. The hydraulic system is particularly interesting and advantageous with regard to the possible upgrading or retrofitting of existing floor vehicles.

Ferner ist insbesondere vorgesehen, dass das hydraulische System ferner eine Hydraulikpumpe umfasst, die in eine hydraulische Zuleitung integriert ist und im Lasthubbetrieb zum Beaufschlagen des zumindest einen Masthubzylinders und des zumindest einen Freihubzylinders mit unter Druck stehender Hydraulikflüssigkeit eingerichtet ist, wobei sich die hydraulische Zuleitung zwischen der Hydraulikpumpe und den Hubzylindern in einen ersten und einen zweiten Versorgungsast aufgabelt und der erste Versorgungsast zu dem Freihubzylinder und der zweite Versorgungsast zu dem Masthubzylinder verläuft, wobei ein als Proportionalventil ausgestaltetes Hubventil in die hydraulische Zuleitung integriert ist, mit dem ein Verhältnis zwischen den Volumenströmen im ersten und im zweiten Versorgungsast veränderbar ist.Furthermore, it is provided in particular that the hydraulic system further comprises a hydraulic pump which is integrated in a hydraulic supply line and is set up in load lifting operation to pressurize the at least one mast lift cylinder and the at least one free lift cylinder with pressurized hydraulic fluid, the hydraulic supply line between the Hydraulic pump and the lifting cylinders forks into a first and a second supply branch and the first supply branch to the Free lift cylinder and the second supply branch runs to the mast lift cylinder, with a lift valve designed as a proportional valve being integrated into the hydraulic supply line, with which a ratio between the volume flows in the first and second supply branch can be changed.

Die Aufgabe wird außerdem gelöst durch ein Verfahren zum Betreiben eines hydraulischen Systems eines Flurförderzeugs mit einem Hubmast mit zumindest einer Masthubstufe und mit einer Freihubstufe, mit der ein Lastaufnahmemittel entlang des Hubmasts verfahrbar ist, wobei das hydraulische System zumindest einen Masthubzylinder zum Antreiben der zumindest einen Masthubstufe und zumindest einen Freihubzylinder zum Antreiben der Freihubstufe umfasst, wobei das hydraulische System dadurch fortgebildet ist, dass es derart betrieben wird, dass im Lasthubbetrieb und/oder im Lastsenkbetrieb der zumindest eine Masthubzylinder und der zumindest eine Freihubzylinder zumindest zeitweise gleichzeitig betätigt werden, wobei das hydraulische System eine erste hydraulische Rückleitung umfasst, die zwischen dem zumindest einen Freihubzylinder und einem Vorratsbehälter für die Hydraulikflüssigkeit verläuft und das hydraulische System ferner eine separate zweite hydraulische Rückleitung umfasst, die zwischen dem zumindest einen Masthubzylinder und dem Vorratsbehälter verläuft, wobei in die erste Rückleitung ein erstes Senkventil und in die zweite Rückleitung ein zweites Senkventil integriert ist, und wobei im Lastsenkbetrieb beim Ablassen des Lastaufnahmemittels das erste Senkventil und das zweite Senkventil gleichzeitig geöffnet werden.The object is also achieved by a method for operating a hydraulic system of an industrial truck with a lifting mast with at least one mast lifting step and with a free lifting step, with which a load handling device can be moved along the lifting mast, the hydraulic system having at least one mast lifting cylinder for driving the at least one mast lifting step and comprises at least one free lift cylinder for driving the free lift stage, the hydraulic system being developed in that it is operated in such a way that the at least one mast lift cylinder and the at least one free lift cylinder are operated at least temporarily simultaneously in load lift operation and / or load lowering operation, with the hydraulic System comprises a first hydraulic return line which runs between the at least one free lift cylinder and a reservoir for the hydraulic fluid and the hydraulic system further comprises a separate second hydraulic return line which between The at least one mast lifting cylinder and the storage container run, a first lowering valve being integrated into the first return line and a second lowering valve being integrated into the second return line, and the first lowering valve and the second lowering valve being opened at the same time in load lowering mode when the load handling device is discharged.

Auch auf das Verfahren zum Betreiben des hydraulischen Systems treffen gleiche oder ähnliche Vorteile zu wie sie bereits im Hinblick auf das Flurförderzeug oder auch im Hinblick auf das hydraulische System erwähnt wurden.The same or similar advantages also apply to the method for operating the hydraulic system as were already mentioned with regard to the industrial truck or also with regard to the hydraulic system.

In einer weiteren Ausführungsform ist vorgesehen, dass die Senkventile Proportionalventile sind und ein erster Volumenstrom durch das erste Senkventil und ein zweiter Volumenstrom durch das zweite Senkventil so gesteuert oder geregelt werden, dass beim Absenken des Lastaufnahmemittels die zumindest eine Masthubstufe und das Lastaufnahmemittel eine untere Endposition zumindest näherungsweise gleichzeitig erreichen.In a further embodiment it is provided that the lowering valves are proportional valves and a first volume flow through the first lowering valve and a second volume flow through the second lowering valve are controlled or regulated in such a way that when the load handling device is lowered, the at least one mast lifting stage and the load handling device have at least one lower end position approximately at the same time.

Ferner ist das Verfahren vorteilhaft dadurch fortgebildet, dass das hydraulische System eine Hydraulikpumpe umfasst, die in eine hydraulische Zuleitung integriert ist und mit der im Lasthubbetrieb der zumindest eine Masthubzylinder und der zumindest eine Freihubzylinder mit unter Druck stehender Hydraulikflüssigkeit beaufschlagt wird, wobei sich die hydraulische Zuleitung zwischen der Hydraulikpumpe und den Hubzylindern in einen ersten und einen zweiten Versorgungsast aufgabelt und der erste Versorgungsast zu dem Freihubzylinder und der zweite Versorgungsast zu dem Masthubzylinder verläuft, wobei ein als Proportionalventil ausgestaltetes Hubventil in die hydraulische Zuleitung integriert ist, mit dem ein Verhältnis zwischen einem Volumenstrom im ersten und im zweiten Versorgungsast veränderbar ist, wobei der Freihubzylinder einen ersten Querschnitt und der Masthubzylinder einen zweiten Querschnitt aufweisen, wobei der erste Querschnitt größer als der zweite Querschnitt ist und das Hubventil in den ersten Versorgungsast integriert ist und wobei das Hubventil derart angesteuert wird, dass der Freihubzylinder und der Masthubzylinder zumindest zeitweise gleichzeitig ausgefahren werden.Furthermore, the method is advantageously developed in that the hydraulic system comprises a hydraulic pump which is integrated in a hydraulic supply line and with which the at least one mast lift cylinder and the at least one free lift cylinder in load lift operation pressurized hydraulic fluid is applied, the hydraulic supply line forks between the hydraulic pump and the lifting cylinders in a first and a second supply branch and the first supply branch to the free lift cylinder and the second supply branch to the mast lift cylinder, with a lift valve designed as a proportional valve in the hydraulic supply line is integrated, with which a ratio between a volume flow in the first and in the second supply branch can be changed, wherein the free lift cylinder has a first cross section and the mast lift cylinder has a second cross section, the first cross section being larger than the second cross section and the lift valve in the first supply branch is integrated and wherein the lift valve is controlled in such a way that the free lift cylinder and the mast lift cylinder are extended at least temporarily at the same time.

Gemäß einer weiteren Ausführungsform ist vorgesehen, dass in Abhängigkeit von einem Betriebsmodus des Flurförderzeugs und/oder in Abhängigkeit von einer vorgewählten Hubhöhe des Lastaufnahmemittels das Hubventil in eine erste Stellung für ein sequentielles Ausfahren des Freihubzylinders und des Masthubzylinders oder in eine zweite Stellung für ein zumindest zeitweise gleichzeitiges Ausfahren gebracht wird.According to a further embodiment it is provided that, depending on an operating mode of the industrial truck and / or depending on a preselected lifting height of the load handling device, the lifting valve in a first position for a sequential extension of the free lift cylinder and the mast lift cylinder or in a second position for an at least temporarily simultaneous extension is brought.

Der entsprechende Betriebsmodus kann beispielsweise manuell angewählt werden. Es ist jedoch ebenso vorgesehen, dass ein entsprechender Betriebsmodus, bei dem die Masthubstufe und die Freihubstufe gleichzeitig verfahren werden, ausgewählt wird, wenn beispielsweise manuell eine Hubhöhe eingegeben wird, welche außerhalb des ausschließlich mittels des Freihubs erreichbaren Bereiches liegt.The corresponding operating mode can be selected manually, for example. However, it is also provided that a corresponding operating mode, in which the mast lift stage and the free lift stage are moved simultaneously, is selected if, for example, a lift height is entered manually which is outside the range that can only be reached by means of the free lift.

Weitere Merkmale der Erfindung werden aus der Beschreibung erfindungsgemäßer Ausführungsformen zusammen mit den Ansprüchen und den beigefügten Zeichnungen ersichtlich. Erfindungsgemäße Ausführungsformen können einzelne Merkmale oder eine Kombination mehrerer Merkmale erfüllen.Further features of the invention will become apparent from the description of embodiments according to the invention together with the claims and the accompanying drawings. Embodiments according to the invention can fulfill individual features or a combination of several features.

Die Erfindung wird nachstehend ohne Beschränkung des allgemeinen Erfindungsgedankens anhand von Ausführungsbeispielen unter Bezugnahme auf die Zeichnungen beschrieben, wobei bezüglich aller im Text nicht näher erläuterten erfindungsgemäßen Einzelheiten ausdrücklich auf die Zeichnungen verwiesen wird. Es zeigen:

Fig. 1
ein Flurförderzeug in einer schematisch vereinfachten perspektivischen Darstellung,
Fig. 2
ein schematisches Schaltbild eines hydraulischen Systems,
Fig. 3a bis 3d
einen Absenkvorgang eines Lastaufnahmemittels bei einem Flurförderzeug gemäß dem Stand der Technik aus einer maximal mit diesem Flurförderzeug erreichbaren Höhe und
Fig. 4a bis 4c
einen Absenkvorgang eines Lastaufnahmemittels aus einer maximalen mit dem Flurförderzeug erreichbaren Höhe bei einem Flurförderzeug gemäß einem Ausführungsbeispiel.
The invention is described below without restricting the general inventive concept on the basis of exemplary embodiments with reference to the drawings, with express reference being made to the drawings with regard to all inventive details not explained in more detail in the text. Show it:
Fig. 1
an industrial truck in a schematically simplified perspective illustration,
Fig. 2
a schematic circuit diagram of a hydraulic system,
Figures 3a to 3d
a lowering process of a load suspension device in an industrial truck according to the prior art from a maximum height that can be achieved with this industrial truck and
Figures 4a to 4c
a lowering process of a load handling device from a maximum height that can be reached with the industrial truck in an industrial truck according to an exemplary embodiment.

In den Zeichnungen sind jeweils gleiche oder gleichartige Elemente und/oder Teile mit denselben Bezugsziffern versehen, so dass von einer erneuten Vorstellung jeweils abgesehen wird.In the drawings, the same or similar elements and / or parts are provided with the same reference numerals, so that they are not introduced again in each case.

Fig. 1 zeigt ein Flurförderzeug 2, beispielhaft einen Gabelstapler, mit einem Hubmast 4, umfassend beispielhaft eine erste Masthubstufe 41, den Innenmast, und eine zweite Masthubstufe 42, den Mittelmast. Der Hubmast 4 wird von einem in Fig. 1 nicht dargestellten Masthubzylinder (ebenso können mehrere Masthubzylinder vorgesehen sein) angetrieben. Der Hubmast 4 umfasst neben dem Innenmast und dem Mittelmast einen fest mit dem Fahrzeuggestell verbundenen Standmast. Der Mittelmast wird beispielhaft von dem Masthubzylinder angetrieben, der Innenmast ist ebenfalls beispielhaft über eine Kette mit dem Mittelmast gekoppelt, so dass diese beiden Ausfahrmasten gleichzeitig ausfahren. Ferner umfasst das Flurförderzeug 2 eine Freihubstufe mit einem Lastaufnahmemittel 6, beispielhaft eine Gabel, das entlang des Innenmastes des Hubmastes 4 verfahrbar ist. Zu diesem Zweck umfasst die Freihubstufe einen Freihubzylinder 8. Der Freihubzylinder 8 kann das Lastaufnahmemittel 6 entlang der ersten Maststufe 41 des Hubmasts 4 verfahren. Fig. 1 shows an industrial truck 2, for example a forklift, with a lifting mast 4, comprising, for example, a first mast lifting stage 41, the inner mast, and a second mast lifting stage 42, the central mast. The lifting mast 4 is supported by an in Fig. 1 Mast lifting cylinder (not shown, several mast lifting cylinders can also be provided) driven. The lifting mast 4 comprises, in addition to the inner mast and the central mast, a stationary mast firmly connected to the vehicle frame. The central mast is driven, for example, by the mast lifting cylinder, the inner mast is also coupled with the central mast, for example via a chain, so that these two extending masts extend at the same time. Furthermore, the industrial truck 2 comprises a free lift stage with a load handling device 6, for example a fork, which can be moved along the inner mast of the lifting mast 4. For this purpose, the free lift stage includes a free lift cylinder 8. The free lift cylinder 8 can move the load handling device 6 along the first mast stage 41 of the lift mast 4.

Fig. 2 zeigt ein schematisches Schaltbild eines hydraulischen Systems 10, wie es gemäß einem Ausführungsbeispiel in das Flurförderzeug 2 integriert ist. Das hydraulische System 10 dient dazu, einen Masthubzylinder 12 und den Freihubzylinder 8, mit dem das Lastaufnahmemittel 6 verfahren wird, mit einer Hydraulikflüssigkeit 14, zu versorgen. Die Hydraulikflüssigkeit wird einem Vorratsbehälter 16 entnommen und in diesen auch wieder zurückgeführt. Das hydraulische System 10 ist dazu eingerichtet, zumindest zeitweise den Masthubzylinder 12 und den Freihubzylinder 8 im Lasthubbetrieb und/oder im Senkbetrieb gleichzeitig zu betreiben. Fig. 2 shows a schematic circuit diagram of a hydraulic system 10 as it is integrated in the industrial truck 2 according to an exemplary embodiment. The hydraulic system 10 is used to supply a mast lift cylinder 12 and the free lift cylinder 8, with which the load handling device 6 is moved, with a hydraulic fluid 14. The hydraulic fluid is taken from a reservoir 16 and also returned to it. The hydraulic system 10 is set up to simultaneously operate the mast lifting cylinder 12 and the free lifting cylinder 8 in the load lifting mode and / or in the lowering mode, at least at times.

Im dargestellten Ausführungsbeispiel ist das hydraulische System 10 dazu eingerichtet, den Masthubzylinder 12 und den Freihubzylinder 8 sowohl im Lasthubbetrieb, d.h. beim Anheben des Lastaufnahmemittels 6, als auch im Lastsenkbetrieb, also beim Absenken des Lastaufnahmemittels 6, gleichzeitig zu betätigen.In the illustrated embodiment, the hydraulic system 10 is set up to the mast lift cylinder 12 and the free lift cylinder 8 both in the load lifting operation, ie when lifting the Load suspension means 6, as well as in load lowering operation, that is, when lowering the load suspension means 6, to be actuated at the same time.

Das hydraulische System 10 umfasst separate hydraulische Rückleitungen 18. Eine erste hydraulische Rückleitung 181 verläuft zwischen dem Freihubzylinder 8 und dem Vorratsbehälter 16. Ferner ist eine zweite hydraulische Rückleitung 182 umfasst, die zwischen dem Masthubzylinder 12 und dem Vorratsbehälter 16 verläuft. In die erste Rückleitung 181 ist ein erstes Senkventil 21 und in die zweite Rückleitung 182 ein zweites Senkventil 22 integriert. Bei den Senkventilen 21, 22 handelt es sich beispielsweise um Proportionalventile. Diese sind zwischen einer ersten Schaltstellung 21a, 22a, in der die Senkventile 21, 22 als Rückschlagventile arbeiten, und einer zweiten Schaltstellung 21b, 22b schaltbar. In der zweiten Schaltstellung 21b, 22b sind die Senkventile 21, 22 dazu eingerichtet, einen ersten Volumenstrom bzw. einen zweiten Volumenstrom zu steuern oder zu regeln. So steuert oder regelt das erste Senkventil 21 einen ersten Volumenstrom durch die erste Rückleitung 181, während das zweite Senkventil 22 einen zweiten Volumenstrom durch die zweite Rückleitung 182 steuert oder regelt. Die Senkventile 21, 22 sind separat voneinander ansteuerbar. Zum Steuern und/oder Regeln ist eine Steuerung 24 von dem hydraulischen System 10 umfasst, welche die beiden Senkventile 21, 22 über nicht dargestellte Verbindungsleitungen ansteuert.The hydraulic system 10 comprises separate hydraulic return lines 18. A first hydraulic return line 181 runs between the free lift cylinder 8 and the storage container 16. Furthermore, a second hydraulic return line 182 is included, which runs between the mast lift cylinder 12 and the storage container 16. A first lowering valve 21 is integrated into the first return line 181 and a second lowering valve 22 is integrated into the second return line 182. The lowering valves 21, 22 are, for example, proportional valves. These can be switched between a first switching position 21a, 22a, in which the lowering valves 21, 22 work as check valves, and a second switching position 21b, 22b. In the second switching position 21b, 22b, the lowering valves 21, 22 are set up to control or regulate a first volume flow or a second volume flow. The first lowering valve 21 controls or regulates a first volume flow through the first return line 181, while the second lowering valve 22 controls or regulates a second volume flow through the second return line 182. The lowering valves 21, 22 can be controlled separately from one another. For controlling and / or regulating, a controller 24 is included in the hydraulic system 10, which controls the two lowering valves 21, 22 via connecting lines (not shown).

Die Steuerung 24 ist derart eingerichtet bzw. programmiert, dass in einem Lastsenkbetrieb, d.h. beim Absenken des Lastaufnahmemittels 6, die Senkventile 21, 22 gleichzeitig öffnen. So werden der Freihubzylinder 8 der Freihubstufe und der Masthubzylinder 12 des Hubmasts 4 gleichzeitig eingefahren. Folglich sinkt das von der Freihubstufe betätigte Lastaufnahmemittel 6 entlang der ersten Masthubstufe 41 ab, während gleichzeitig der Hubmast 4, d.h. die erste und die zweite Masthubstufe 41, 42, einfahren.The controller 24 is set up or programmed in such a way that in a load lowering operation, ie when lowering the load handling device 6, the lowering valves 21, 22 open at the same time. Thus, the free lift cylinder 8 of the free lift stage and the mast lift cylinder 12 of the lift mast 4 are retracted at the same time. As a result, the load receiving means 6 actuated by the free lift stage sinks along the first mast lift stage 41, while at the same time the lift mast 4, ie the first and second mast lifting stage 41, 42, retract.

Dieser neuartige Vorgang wird anhand eines Vergleichs der Fig. 3 und 4 erläutert. Die Fig. 3a bis 3d zeigen einen Absenkvorgang eines Lastaufnahmemittels 6, wie er bei einem Flurförderzeug gemäß dem Stand der Technik stattfindet. Fig. 3a zeigt das Flurförderzeug 2 mit vollständig ausgefahrenem Hubmast 4. Das Lastaufnahmemittel 6 befindet sich am oberen Anschlag der ersten Masthubstufe 41. Ein herkömmliches Flurförderzeug 2 umfasst eine gemeinsame Rücklaufleitung, mit der sowohl der Freihubzylinder 8 als auch der Masthubzylinder 12 druckentlastet werden.This novel process is based on a comparison of the Fig. 3 and 4th explained. the Figures 3a to 3d show a lowering process of a load handling device 6, as it takes place in an industrial truck according to the prior art. Fig. 3a shows the industrial truck 2 with the lifting mast 4 fully extended. The load handling device 6 is located at the upper stop of the first mast lifting stage 41. A conventional industrial truck 2 comprises a common return line with which both the free lifting cylinder 8 and the mast lifting cylinder 12 are relieved of pressure.

Der Freihubzylinder 8 und der Masthubzylinder 12 weisen unterschiedliche Querschnitte auf. Diese sind so gewählt, dass bei einem ersten Druck p1 (vgl. Fig. 2) der hydraulischen Flüssigkeit 14 zunächst der Freihubzylinder 8 ausfährt. Erreicht die Freihubstufe den oberen Anschlag des Hubmastes 4, genauer der ersten Masthubstufe 41 (diese Situation zeigt die Fig. 3c), so steigt der Druck der Hydraulikflüssigkeit 14 im hydraulischen System 10 weiter an, bis er den gegenüber p1 größeren Wert p2 erreicht. Bei Überschreiten des hydraulischen Druckes p2 beginnen die Masthubstufen 41, 42 auszufahren. Die einzelnen Masthubzylinder 12 der Masthubstufen 41, 42 können wiederum so ausgestaltet sein, dass ihre unterschiedlichen Querschnitte dafür sorgen, dass zunächst die erste Masthubstufe 41 und anschließend die zweite Masthubstufe 42 ausfährt.The free lift cylinder 8 and the mast lift cylinder 12 have different cross sections. These are chosen so that at a first pressure p1 (cf. Fig. 2 ) the hydraulic fluid 14 first the free lift cylinder 8 extends. If the free lift stage reaches the upper stop of the mast 4, more precisely the first mast lift stage 41 (this situation is shown in FIG Figure 3c ), the pressure of the hydraulic fluid 14 in the hydraulic system 10 continues to rise until it reaches the value p2, which is greater than that of p1. When the hydraulic pressure p2 is exceeded, the mast lift stages 41, 42 begin to extend. The individual mast lifting cylinders 12 of the mast lifting stages 41, 42 can in turn be designed in such a way that their different cross-sections ensure that the first mast lifting stage 41 and then the second mast lifting stage 42 extend first.

Im in Fig. 3 dargestellten Ausführungsbeispiel fahren die beiden Masthubstufen 41, 42 in etwa gleichzeitig ein. Beim Ablassen der Hydraulikflüssigkeit 14 fahren der Hubmast 4 und die Freihubstufe in umgekehrter Reihenfolge ein. Ausgehend von einer Situation bei maximal ausgefahrenem Hubmast 4 und einem Lasthubmittel 6 am oberen Anschlag der ersten Masthubstufe 41 (vgl. Fig. 3a) fährt zunächst der Hubmast 4 ein (vgl. Fig. 3b). Da der Druck nach wie vor oberhalb von p1 liegt, verbleibt die Freihubstufe und somit das Lastaufnahmemittel 6 am oberen Anschlag, bis der Hubmast 4 vollständig eingefahren ist (vgl. Fig. 3c). Erst wenn anschließend der hydraulische Druck im hydraulischen System 10 weiter sinkt, nämlich unterhalb des Wertes von p1, fährt auch die Freihubstufe ein und das Lastaufnahmemittel 6 sinkt an den unteren Anschlag.In the in Fig. 3 The illustrated embodiment, the two mast lifting stages 41, 42 move in approximately at the same time. When the hydraulic fluid 14 is drained, the lift mast 4 and the free lift stage move in in reverse order. Based on a situation with the lifting mast 4 extended to the maximum and a load lifting device 6 at the upper stop of the first mast lifting stage 41 (cf. Fig. 3a ) drives first the mast 4 (cf. Figure 3b ). Since the pressure is still above p1, the free lift stage and thus the load handling device 6 remain at the upper stop until the lifting mast 4 is fully retracted (cf. Figure 3c ). Only when the hydraulic pressure in the hydraulic system 10 subsequently falls further, namely below the value of p1, does the free lift stage also retract and the load-bearing device 6 sinks to the lower stop.

Die Fig. 4a bis 4c zeigen einen Absenkvorgang eines Lastaufnahmemittels 6 eines Flurförderzeugs 2 gemäß einem Ausführungsbeispiel.the Figures 4a to 4c show a lowering process of a load handling device 6 of an industrial truck 2 according to an exemplary embodiment.

Fig. 4a zeigt das Flurförderzeug 2 mit vollständig ausgefahrenem Hubmast 4, wobei sich außerdem das Lastaufnahmemittel 6 am oberen Anschlag der ersten Masthubstufe 41 befindet. Diese Situation ist identisch zu der in Fig. 3a gezeigten. Im Lastsenkbetrieb werden bei dem in Fig. 4 dargestellten Flurförderzeug 2 die Freihubstufe und die Masthubstufen 41, 42 durch gleichzeitiges Öffnen des ersten und zweiten Senkventils 21, 22 (vgl. Fig. 2) synchron abgesenkt. Fig. 4b zeigt das Flurförderzeug 2 nach einem ersten Zeitintervall, nach dem auch das herkömmliche Flurförderzeug 2 in Fig. 3b dargestellt ist. Im Gegensatz zu dem herkömmlichen Flurförderzeug 2 in Fig. 3b ist bei dem Flurförderzeug 2 gemäß einem Ausführungsbeispiel in Fig. 4b das Lastaufnahmemittel 6 bereits am unteren Anschlag der ersten Masthubstufe 41 angelangt. Es befindet sich somit bereits deutlich tiefer als das Lastaufnahmemittel 6 bei dem herkömmlichen Flurförderzeug 2. Während eines weiteren Zeitintervalls sinkt der Hubmast 4 vollständig ein und das Lastaufnahmemittel 6 erreicht den untersten Anschlag (Fig. 4c). Bei einem herkömmlichen Flurförderzeug 2 (vgl. Fig. 3c) befindet sich nach diesem Zeitintervall das Lastaufnahmemittel 6 noch am oberen Anschlag der ersten Masthubstufe 41. Figure 4a shows the industrial truck 2 with the lifting mast 4 fully extended, with the load handling device 6 also being located at the upper stop of the first mast lifting step 41. This situation is identical to that in Fig. 3a shown. In load lowering mode, the in Fig. 4 illustrated industrial truck 2 the free lift stage and the mast lift stages 41, 42 by simultaneously opening the first and second lowering valve 21, 22 (cf. Fig. 2 ) lowered synchronously. Figure 4b shows the industrial truck 2 after a first time interval, after which the conventional industrial truck 2 in FIG Figure 3b is shown. In contrast to the conventional industrial truck 2 in Figure 3b is in the industrial truck 2 according to an embodiment in Figure 4b the load handling device 6 has already reached the lower stop of the first mast lifting stage 41. It is therefore already significantly lower than the load handling device 6 in the conventional industrial truck 2. During a further time interval, the lifting mast 4 sinks completely and the load handling device 6 reaches the lowest stop ( Figure 4c ). With a conventional industrial truck 2 (cf. Figure 3c ) after this time interval the load handling device 6 is still at the upper stop of the first mast lifting stage 41.

Wie ein Vergleich der Fig. 3 und 4 zeigt, wird bei dem Flurförderzeug 2 gemäß einem Ausführungsbeispiel das Lastaufnahmemittel 6 wesentlich schneller abgesenkt. Es wird genau dasjenige Zeitintervall eingespart, welches das Lastaufnahmemittel 6 bei einem herkömmlichen Flurförderzeug 2 braucht, um entlang einer Masthubstufe 41, 42 abgesenkt zu werden.Like comparing the Fig. 3 and 4th shows, in the case of the industrial truck 2 according to an exemplary embodiment, the load handling device 6 is lowered significantly more quickly. Exactly that time interval is saved which the load suspension means 6 in a conventional industrial truck 2 needs in order to be lowered along a mast lifting step 41, 42.

Es ist gemäß einem weiteren Ausführungsbeispiel vorgesehen, dass die Steuerung 24 derart eingerichtet ist, dass das Absenken des Hubmastes 4 und der Freihubstufe, welche das Lastaufnahmemittel 6 bewegt, so gesteuert oder geregelt wird, dass die Masthubstufen 41, 42 und das Lastaufnahmemittel 6 den unteren Anschlag zumindest näherungsweise gleichzeitig erreichen. So kann ein homogener Absenkvorgang erreicht werden, was die Bedienung des Flurförderzeugs 2 für die Bedienperson vereinfacht.According to a further exemplary embodiment, it is provided that the controller 24 is set up in such a way that the lowering of the lifting mast 4 and the free lift stage, which moves the load handling device 6, is controlled or regulated in such a way that the mast lifting steps 41, 42 and the load handling device 6 the lower Reach the stop at least approximately at the same time. A homogeneous lowering process can thus be achieved, which simplifies the operation of the industrial truck 2 for the operator.

Um das Lastaufnahmemittel 6 im Lasthubbetrieb anheben zu können, umfasst das hydraulische System 10 des Flurfahrzeugs 2 eine Hydraulikpumpe 26, welche Hydraulikflüssigkeit 14 aus dem Vorratsbehälter 16 über eine hydraulische Zuleitung 28 entnimmt. Die Hydraulikpumpe 26 ist in die hydraulische Zuleitung 28 integriert. Im Lasthubbetrieb dient die Hydraulikpumpe 26 zum Beaufschlagen des Masthubzylinders 12 und des Freihubzylinders 8 mit unter Druck stehender Hydraulikflüssigkeit 14.In order to be able to lift the load handling device 6 in the load lifting mode, the hydraulic system 10 of the industrial truck 2 comprises a hydraulic pump 26 which draws hydraulic fluid 14 from the storage container 16 via a hydraulic supply line 28. The hydraulic pump 26 is integrated into the hydraulic supply line 28. In the load lifting mode, the hydraulic pump 26 is used to pressurize the mast lifting cylinder 12 and the free lifting cylinder 8 with pressurized hydraulic fluid 14.

Die hydraulische Zuleitung 28 gabelt sich zwischen der Hydraulikpumpe 26 und den Hubzylindern, d.h. dem Freihubzylinder 8 und dem Masthubzylinder 12, in einen ersten Versorgungsast 31 und in einen zweiten Versorgungsast 32. Der erste Versorgungsast 31 führt zu dem Freihubzylinder 8, der zweite Versorgungsast 32 führt zu dem Masthubzylinder 12. Die beiden Versorgungsäste 31, 32 werden ebenfalls als Teil der hydraulischen Zuleitung 28 aufgefasst. In den ersten Versorgungsast 31 ist ein Hubventil 34 integriert, welches als Proportionalventil ausgestaltet sein kann. Das Hubventil 34 kann ebenso wie die Hydraulikpumpe 26 über die Steuerung 24 gesteuert oder geregelt werden.The hydraulic supply line 28 forks between the hydraulic pump 26 and the lifting cylinders, ie the free lift cylinder 8 and the mast lift cylinder 12, into a first supply branch 31 and a second supply branch 32. The first supply branch 31 leads to the free lift cylinder 8, the second supply branch 32 leads to the mast lifting cylinder 12. The two supply branches 31, 32 are also perceived as part of the hydraulic feed line 28. A lift valve 34, which can be designed as a proportional valve, is integrated into the first supply branch 31. Like the hydraulic pump 26, the lift valve 34 can be controlled or regulated via the controller 24.

Über die Einstellungen des Hubventils 34 kann ein Verhältnis zwischen den Volumenströmen im ersten und zweiten Versorgungsast 31, 32 verändert werden. Der Freihubzylinder 8 weist einen ersten Querschnitt auf und der Masthubzylinder 12 weist einen zweiten Querschnitt auf, wobei der erste Querschnitt größer ist als der zweite Querschnitt. Aus diesem Grund wird der Freihubzylinder 8 bei einem ersten Druck p1 aktiviert, wobei der Druck p1 kleiner ist als der Druck p2, bei dem der Masthubzylinder 12 aktiviert wird. Über die Einstellungen des Hubventils 34 kann der wirksame hydraulische Strömungsquerschnitt der Hubzylinder 8, 12 variabel eingestellt werden, so dass es möglich ist, beide Hubzylinder 8, 12 gleichzeitig auszufahren. Dies erfolgt in der ersten Schaltstellung 34a des Hubventils 34. In der zweiten Schaltstellung 34b kann der Freihub gesperrt werden, so dass ausschließlich der Masthubzylinder 12 betätigt wird. Es ist außerdem durch die dynamische Einstellung des Hubventils 34 möglich, einen sanften Übergang zwischen einem von dem Freihubzylinder 8 bewerkstelligten Hub des Lastaufnahmemittels 6 und einem von dem Masthubzylinder 12 bewirkten Hub desselben zu erreichen.A ratio between the volume flows in the first and second supply branches 31, 32 can be changed via the settings of the lift valve 34. The free lift cylinder 8 has a first cross section and the mast lift cylinder 12 has a second cross section, the first cross section being larger than the second cross section. For this reason, the free lift cylinder 8 is activated at a first pressure p1, the pressure p1 being lower than the pressure p2 at which the mast lift cylinder 12 is activated. The effective hydraulic flow cross-section of the lifting cylinders 8, 12 can be variably adjusted via the settings of the lifting valve 34, so that it is possible to extend both lifting cylinders 8, 12 at the same time. This takes place in the first switch position 34a of the lift valve 34. In the second switch position 34b, the free lift can be blocked so that only the mast lift cylinder 12 is actuated. The dynamic setting of the lift valve 34 also makes it possible to achieve a smooth transition between a lift of the load-bearing means 6 effected by the free lift cylinder 8 and a lift of the same effected by the mast lift cylinder 12.

Um ein Rückfließen der Hydraulikflüssigkeit 14 in dem ersten und zweiten Versorgungsast 32, 32 zu vermeiden, ist jeweils ein Rückschlagventil 36 in den jeweiligen Versorgungsast integriert.In order to prevent the hydraulic fluid 14 from flowing back into the first and second supply branches 32, 32, a check valve 36 is integrated into the respective supply branch.

Alle genannten Merkmale, auch die den Zeichnungen allein zu entnehmenden sowie auch einzelne Merkmale, die in Kombination mit anderen Merkmalen offenbart sind, werden allein und in Kombination als erfindungswesentlich angesehen. Erfindungsgemäße Ausführungsformen können durch einzelne Merkmale oder eine Kombination mehrerer Merkmale erfüllt sein. Im Rahmen der Erfindung sind Merkmale, die mit "insbesondere" oder "vorzugsweise" gekennzeichnet sind, als fakultative Merkmale zu verstehen.All features mentioned, including those that can be taken from the drawings alone as well as individual features that are combined with other features are disclosed are considered to be essential to the invention alone and in combination. Embodiments according to the invention can be fulfilled by individual features or a combination of several features. In the context of the invention, features that are identified with “in particular” or “preferably” are to be understood as optional features.

BezugszeichenlisteList of reference symbols

22
FlurförderzeugIndustrial truck
44th
HubmastMast
66th
LastaufnahmemittelLoad handling equipment
88th
FreihubzylinderFree lift cylinder
1010
hydraulisches Systemhydraulic system
1212th
MasthubzylinderMast lift cylinder
1414th
HydraulikflüssigkeitHydraulic fluid
1616
VorratsbehälterStorage container
1818th
hydraulische Rückleitunghydraulic return
2121
erstes Senkventilfirst lowering valve
2222nd
zweites Senkventilsecond lowering valve
21a, 22a, 34a21a, 22a, 34a
erste Schaltstellungfirst switch position
21b, 22b, 34b21b, 22b, 34b
zweite Schaltungsecond circuit
2424
Steuerungsteering
2626th
Hydraulikpumpehydraulic pump
2828
ZuleitungSupply line
3131
erster Versorgungsastfirst supply branch
3232
zweiter Versorgungsastsecond supply branch
3434
HubventilLift valve
3636
Rückschlagventilcheck valve
4141
erste Masthubstufefirst mast lift stage
4242
zweite Masthubstufesecond mast lift stage
181181
erste hydraulische Rückleitungfirst hydraulic return line
182182
zweite hydraulische Rückleitungsecond hydraulic return line

Claims (11)

  1. An industrial truck (2) with a lift mast (4) with at least one mast lift stage (41, 42) driven by at least one mast lift cylinder (12) and with a free lift stage driven by at least one free lift cylinder (8) with which a load receiving means (6) can be displaced along the lift mast (4), characterized by a hydraulic system (10) for supplying the at least one mast lift cylinder (12) and the at least one free lift cylinder (8) with a hydraulic fluid (14), wherein the hydraulic system (10) is configured to at least at times simultaneously actuate the at least one mast lift cylinder (12) and the at least one free lift cylinder (8) in load lowering operation, wherein the hydraulic system (10) comprises separate hydraulic return lines (18) for unloading the at least one mast lift cylinder (12) and the at least one free lift cylinder (8) in load lowering operation, the hydraulic system (10) comprises a first hydraulic return line (181) that runs between the at least one free lift cylinder (8) and a reservoir (16) for the hydraulic fluid (14) and the hydraulic system (10) further comprises a second hydraulic return line (182) that runs between the at least one mast lift cylinder (12) and the reservoir (16), wherein a first lowering valve (21) is integrated in the first return line (181) and a second lowering valve (22) is integrated in the second return line (182) and comprising a control (24) that is configured to open the lowering valves (21, 22) simultaneously in load lowering operation when the load receiving means (6) is being lowered.
  2. The industrial truck (2) according to claim 1, characterized in that the lowering valves (21, 22) are proportional valves and the control (24) is further configured to control or regulate a first volumetric flow through the first lowering valve (21) and a second volumetric flow through the second lowering valve (22) so that the at least one mast lift stage (41, 42) and the load receiving means (6) reach a lower end position at least approximately simultaneously in load lowering operation when the load receiving means (6) is being lowered.
  3. The industrial truck (2) according to claim 1 or 2, characterized in that the hydraulic system (10) comprises a hydraulic pump (26) that is integrated in a hydraulic feed line (28) and is configured to apply the at least one mast lift cylinder (12) and the at least one free lift cylinder (8) to pressurized hydraulic fluid (14) in load lifting operation, wherein the hydraulic feed line (28) branches between the hydraulic pump (26) and the lift cylinders (8, 12) into a first and a second supply branch (31, 32) and the first supply branch (31) runs to the free lift cylinder (8) and the second supply branch (32) runs to the mast lift cylinder (812), wherein a lifting valve (34) designed as a proportional valve is integrated in the hydraulic feed line (28) with which a ratio between the volumetric flows in the first and in the second supply branch (31, 32) can be changed.
  4. The industrial truck (2) according to claim 3, characterized in that the free lift cylinder (8) has a first cross-section and the lift cylinder (12) has a second cross-section, wherein the first cross-section is larger than the second cross-section and the lifting valve (34) is integrated in the first supply branch (31).
  5. The industrial truck (2) according to claim 3 or 4, characterized by a control (24) that is configured to activate the lifting valve (34) such that the free lift cylinder (8) and the mast lift cylinder (12) can be at least at times simultaneously extended in load lifting operation.
  6. A hydraulic system (10) for an industrial truck (2) with a lift mast (4) with at least one mast lift stage (41, 42) and with a free lift stage with which a load receiving means (6) can be displaced along the lift mast (4), wherein the hydraulic system (10) comprises at least one mast lift cylinder (12) for driving the at least one mast lift stage (41, 42) and at least one free lift cylinder (8) for driving the at least one free lift stage, characterized in that the hydraulic system (10) is configured to at least at times simultaneously supply the at least one mast lift cylinder (12) and the at least one free lift cylinder (8) with a hydraulic fluid (14) in load lowering operation, wherein the hydraulic system (10) comprises a first hydraulic return line (181) that runs between the at least one free lift cylinder (8) and a reservoir (16) for the hydraulic fluid (14) and the hydraulic system (10) further comprises a second separate hydraulic return line (182) that runs between the at least one mast lift cylinder (12) and the reservoir (16), wherein a first lowering valve (21) is integrated in the first return line (181) and a second lowering valve (22) is integrated in the second return line (182).
  7. The hydraulic system (10) according to claim 6, characterized in that the hydraulic system (10) further comprises a hydraulic pump (26) that is integrated in a hydraulic feed line (28) and is configured to apply the at least one mast lift cylinder (12) and the at least one free lift cylinder (8) to pressurized hydraulic fluid (14) in load lifting operation, wherein the hydraulic feed line (28) branches between the hydraulic pump (26) and the lift cylinders (8, 12) into a first and a second supply branch (31, 32) and the first supply branch (31) runs to the free lift cylinder (8) and the second supply branch (32) runs to the mast lift cylinder (12), wherein a lifting valve (34) designed as a proportional valve, with which a ratio between the volumetric flows in the first and in the second supply branch (31, 32) can be changed, is integrated in the hydraulic feed line (28).
  8. A method for operating a hydraulic system (10) of an industrial truck (2) with a lift mast (4) with at least one mast lift stage (41, 42) and with a free lift stage with which a load receiving means (6) can be displaced along the lift mast (4), wherein the hydraulic system (10) comprises at least one mast lift cylinder (12) for driving the at least one mast lift stage (41, 42) and at least one free lift cylinder (88) for driving the free lift stage, characterized in that the hydraulic system (10) is operated such that the at least one mast lift cylinder (12) and the at least one free lift cylinder (8) are at least at times simultaneously actuated in load lowering operation, wherein the hydraulic system (10) comprises a first hydraulic return line (181) that runs between the at least one free lift cylinder (8) and a reservoir (16) for the hydraulic fluid (14) and the hydraulic system (10) further comprises a separate second hydraulic return line (182) that runs between the at least one mast lift cylinder (12) and the reservoir (16), wherein a first lowering valve (21) is integrated in the first return line (181) and a second lowering valve (22) is integrated in the second return line (182), and wherein the first lowering valve (21) and the second lowering valve (22) are opened simultaneously in load lowering operation when the load receiving means (6) are let down.
  9. The method according to claim 8, characterized in that the lowering valves (21, 22) are proportional valves and a first volumetric flow through the first lowering valve (21) and a second volumetric flow through the second lowering valve (22) are controlled or regulated so that the at least one mast lift stage (41, 42) and the load receiving means (6) reach a lower end position at least approximately simultaneously when the load receiving means (6) is lowered.
  10. The method according to claim 8 or 9, characterized in that the hydraulic system (10) comprises a hydraulic pump (26) that is integrated in a hydraulic feed line (28) and with which the at least one mast lift cylinder (12) and the at least one free lift cylinder (8) are exposed to pressurized hydraulic fluid (14) in load lifting operation, wherein the hydraulic feed line (28) branches between the hydraulic pump (26) and the lift cylinders (8, 12) into a first and a second supply branch (31, 32) and the first supply branch (31) runs to the free lift cylinder (8) and the second supply branch (32) runs to the mast lift cylinder (12), wherein a lifting valve (34) designed as a proportional valve, with which a ratio between a volumetric flow in the first and in the second supply branch (31, 32) can be changed, is integrated in the hydraulic feed line (28), wherein the free lift cylinder (8) has a first cross-section and the mast lift cylinder (12) has a second cross-section, wherein the first cross-section is larger than the second cross-section and the lifting valve (34) is integrated in the first supply branch (31), and wherein the lifting valve (34) is activated such that the free lift cylinder (8) and the mast lift cylinder (12) are at least at times simultaneously extended.
  11. The method according to claim 10, characterized in that, depending on an operating mode of the industrial truck (2) and/or depending on a preselected lifting height of the load receiving means (6), the lifting valve (34) is brought in a first position for a sequential extension of the free lift cylinder (8) and the mast lift cylinder (12) or in a second position for an at least occasional simultaneous extension.
EP18194815.9A 2017-09-20 2018-09-17 Industrial truck, hydraulic system for an industrial truck and method of operating a hydraulic system Active EP3459904B1 (en)

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USD940989S1 (en) * 2019-05-17 2022-01-11 Doosan Industrial Vehicle Co., Ltd. Forklift
USD960484S1 (en) * 2019-11-27 2022-08-09 Hangzhou Hikrobot Technology Co., Ltd. Forklift
KR102385239B1 (en) * 2020-06-19 2022-04-11 두산산업차량 주식회사 Forklift truck
USD1004245S1 (en) * 2020-08-07 2023-11-07 Hangzhou Hikrobot Co., Ltd. Forklift
USD981077S1 (en) * 2020-12-17 2023-03-14 Doosan Industrial Vehicle Co., Ltd. Forklift
USD1021316S1 (en) * 2021-10-18 2024-04-02 Robopac S.P.A. Lift truck
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CN109534238B (en) 2022-01-04
US11427451B2 (en) 2022-08-30
EP3459904A1 (en) 2019-03-27
US20220348447A1 (en) 2022-11-03
US11905153B2 (en) 2024-02-20
US20190084816A1 (en) 2019-03-21
DE102017121818A1 (en) 2019-03-21

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