EP0063025A1 - Hydraulic control circuit for an hydraulic ram - Google Patents
Hydraulic control circuit for an hydraulic ram Download PDFInfo
- Publication number
- EP0063025A1 EP0063025A1 EP82301825A EP82301825A EP0063025A1 EP 0063025 A1 EP0063025 A1 EP 0063025A1 EP 82301825 A EP82301825 A EP 82301825A EP 82301825 A EP82301825 A EP 82301825A EP 0063025 A1 EP0063025 A1 EP 0063025A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- hydraulic
- ram
- valve
- lowering
- relief valve
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- 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
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- 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
- F15B13/00—Details of servomotor systems ; Valves for servomotor systems
- F15B13/01—Locking-valves or other detent i.e. load-holding devices
- F15B13/015—Locking-valves or other detent i.e. load-holding devices using an enclosed pilot flow valve
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- 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
- F15B2211/30—Directional control
- F15B2211/305—Directional control characterised by the type of valves
- F15B2211/30505—Non-return valves, i.e. check valves
- F15B2211/30515—Load holding valves
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- 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
- F15B2211/40576—Assemblies of multiple valves
- F15B2211/40584—Assemblies of multiple valves the flow control means arranged in parallel with a check valve
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- 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
- F15B2211/415—Flow control characterised by the connections of the flow control means in the circuit
- F15B2211/41527—Flow control characterised by the connections of the flow control means in the circuit being connected to an output member and a directional control valve
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- 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
- F15B2211/50—Pressure control
- F15B2211/505—Pressure control characterised by the type of pressure control means
- F15B2211/50509—Pressure control characterised by the type of pressure control means the pressure control means controlling a pressure upstream of the pressure control means
- F15B2211/50518—Pressure control characterised by the type of pressure control means the pressure control means controlling a pressure upstream of the pressure control means using pressure relief valves
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- 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
- F15B2211/50—Pressure control
- F15B2211/515—Pressure control characterised by the connections of the pressure control means in the circuit
- F15B2211/5153—Pressure control characterised by the connections of the pressure control means in the circuit being connected to an output member and a directional control valve
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- 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
- F15B2211/50—Pressure control
- F15B2211/52—Pressure control characterised by the type of actuation
- F15B2211/528—Pressure control characterised by the type of actuation actuated by fluid pressure
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- 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
- F15B2211/50—Pressure control
- F15B2211/56—Control of an upstream pressure
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- 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
- F15B2211/50—Pressure control
- F15B2211/575—Pilot pressure control
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- 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
- F15B2211/60—Circuit components or control therefor
- F15B2211/635—Circuits providing pilot pressure to pilot pressure-controlled fluid circuit elements
- F15B2211/6355—Circuits providing pilot pressure to pilot pressure-controlled fluid circuit elements having valve means
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- 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
- F15B2211/75—Control of speed of the output member
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- 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
- F15B2211/80—Other types of control related to particular problems or conditions
- F15B2211/86—Control during or prevention of abnormal conditions
- F15B2211/863—Control during or prevention of abnormal conditions the abnormal condition being a hydraulic or pneumatic failure
- F15B2211/8636—Circuit failure, e.g. valve or hose failure
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- 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
- F15B2211/80—Other types of control related to particular problems or conditions
- F15B2211/875—Control measures for coping with failures
- F15B2211/8752—Emergency operation mode, e.g. fail-safe operation mode
Definitions
- This invention relates to a hydraulic control circuit for a hydraulic ram (cylinder + piston) controlling raising and lowering of a mechanical member, more particularly but not exclusively for ram cylinder control of the boom of a hydraulic excavator.
- the over-centre valve is a pilot operated relief valve and is mounted on a ram cylinder.
- the pilot pressure used to control the valve is obtained from the feed line to the lowering side of the boom cylinders.
- An object of the present invention is to overcome or substantially reduce the abovementioned disadvantage.
- the present invention consists in an hydraulic control circuit for a hydraulic ram controlling raising and lowering of a mechanical member, comprising a source of hydraulic pressure, a selector valve for selectively connecting the hydraulic source to opposite sides of the ram whereby actuation of the selector valve operates the ram to raise or lower the mechanical member, a load control valve disposed adjacent to the ram and connected between the raising side of the ram and the selector valve, said load control valve comprising non-return valve means via which hydraulic pressure is applied to the raising side of the ram and hydraulically operated relief valve means for controlling the outlet of hydraulic fluid from said raising side when applying hydraulic fluid pressure to the lowering side and means responsive to a predetermined hydraulic fluid pressure or flow applied to the lowering side for supplying hydraulic fluid pressure to operate the relief valve means at a sufficient pressure to retain the relief valve means open as the lowering speed increases above that determined by the supply of hydraulic fluid pressure to the lowering side.
- the boom In hydraulic circuits constructed in accordance with the invention for boom ram control, the boom is either locked and prevented from falling after a hose burst or continues the selected movement in a controllable manner depending upon which hose bursts, the maximum speed of lowering of the boom under normal conditions is controlled at a speed faster than would be determined by the flow of oil into the lowering side of the ram cylinder, and boom-drift, i.e. lowering of the boom due to any leakage in the system, is prevented by the load control valve.
- the circuit shown in Figure 1 is used to control two hydraulic excavator boom rams 1 each comprising a respective cylinder 2 and piston 3. Although two rams 1 have been shown, one larger ram may alternatively be used.
- the circuit incorporates, for each ram 1, a load control valve 4 with a respective separate ram cylinder relief valve 5 and associated hydraulic lines and connections which are the same in each case. Thus, for simplicity, one ram only will be referred to as if there is only one ram and its associated load control valve 4, relief valve 5 and connecting lines in the hydraulic circuit.
- the load control valve 4 has good metering characteristics i.e. progressive opening in response to pilot operating pressure, and comprises a non-return valve 6 and a pilot operated relief valve 7.
- valve pilot pressure used to control the opening of the load control valve 4 i.e. the relief valve 7 is obtained from a boom lowering feed line 8 connected to the lowering side 9 of the ram cylinder 2,via a pilot line 10.
- a sequence valve 11 is located in the lowering feed line 8 between where the point/valve pilot pressure is taken off through line 10 and the lowering side 9 of the ram cylinder.
- a main hydraulic pump 12 with reservoir 13 is connected to a selector valve 14 having a directional flow control function which controls the main pump flow through the circuit and which, itself, is controlled remotely via control lines 15 by a servo hand controller 16 with its own pump 17.
- selector valve 14 When the selector valve 14 is operated to raise the boom, fluid flows along a feed line 18 to the raising side 19 of the ram cylinder via the non-return valve 6 with minimal restriction on flow. Return flow from the cylinder lowering side 9 will also pass with minimal restriction through a non-return valve 20 connected to feed line 8 in parallel with the sequence valve 11.
- the load control valve 4 and the sequence valve 11 have little effect on the raising of the boom. Should a hose break occur in the feed line 18 to the cylinder raising side 19, the non-return valve 6 ensures that the boom cannot suddenly fall.
- sequence valve 11 in parallel with the orifice 21 is to limit the maximum level of pressure at the upstream side of the orifice 21 as a protection for the pipe work and load control valve 4. Since the non-return valve 20 is also in parallel there is unimpeded return flow from the cylinder 2 when boom raise is selected.
- the separate ram cylinder mounted relief valve 5 ensures that transient pressures within the ram cylinder 2 are limited in magnitude, thus giving protection to the structure.
- the load control valve 4 could provide this feature when used with a selector valve having an open centre spool, (the selector valve 14, has a closed centre spool necessitating the inclusion of the relief valve 5 for operational reasons).
- Fig. 2 this differs from Fig. 1 in that the sequence valve 11, non-return valve 20 and orifice 21 are replaced by a hydraulic intensifier lla.
- advantage is taken of the pressure signal from the servo-hand controller 16 for remotely activating the selector valve 14 to cause lowering of the excavator boom by feeding this pressure signal from the appropriate line 15 into the input 24 of the hydraulic intensifier lla.
- the output signal from the hydraulic intensifier is fed at its output 25 to the pilot line 10 for the relief valve 7 of the load control valve 4.
- sufficient pilot pressure is obtained to give an acceptable boom lowering speed whilst using a low- pressure energy source.
- the pilot line 10 from the intensifier lla to the body of the load control valve 4 would normally be a closed line in which entrained air would not be flushed out. This could critically effect the operation of the relief valve 7 since, if sufficient in quantity, the amount of compression required would exceed the available displacement of the intensifier output piston 26.
- the circuit includes an automatic bleed system operative when boom lowering is not selected, to flush the pilot line 10 from the load control valve body and through the intensifier lla.
- This bleed system includes a non-return valve 27 and line 28 connected into the pilot port of the relief valve 7 and a non-return valve 29 in the intensifier lla which is unseated when the intensifier is inoperative, such that flow will be induced in the pilot line 10 from the relief valve to the intensifier, thus purging the lines and cavities within the relief valve pilot section and the intensifier.
- FIG. 3 the circuit of Figure 3 differs from that of Figure 1 in that the sequence valve 11, valve 20 and orifice 21 are omitted and a venting valve 30 is incorporated in a pilot line 31 connected to a port 32 in the relief valve 7 and to the servo-hand controller 16 and one of the lines 15.
- the load-control valve 4 consists of the relief valve 7 and non-return valve 6 which are independent of each other but which are contained within a common valve body 33.
- the relief valve 7 has a hollow-cylindrical valve plunger 34 which is slidingly and sealingly mounted within the valve body 33, the annular seals 35 dividing the valve body into four chambers 36, 37, 38 and 39 which are connected respectively through ports 40, 41, 42 and 32 to the raising side 19 of the ram cylinder 2, the raising feed line 18 to the selector valve 14, the pilot line 10 connected to the lowering feed line 8, and the pilot line 31 to the vent valve 30.
- the left-hand end of the valve plunger 34 is normally biased into a position in which it engages a valve seat 43 on the valve body 33 by means of a compression spring 44 in the valve chamber 39 and acting between the opposite end of the valve body and valve plunger.
- balancingholes 47 are provided through the plunger 34 to feed this pressure into the spring chamber 39 and thus balance the effects of back pressure on the plunger.
- the balancing holes 47 must be carefully selected to ensure that the venting valve 30 may be quite small. This valve 30 is set to ensure that only when the servo signal to the selector valve 14 has reached a certain level, predetermined by tests, will the valve 30 open to vent the spring chamber 39 and thus fully open the relief valve 7.
- the non-return valve 6 comprises a valve plunger 47a which is urged into engagement at one of its ends with a mating seat 48 on the valve body 33 by a spring 49 disposed in a chamber 50. Passages 51, and 52 in the valve body communicate with the port 40 to the raising side of the ram cylinder 2, with the spring chamber 50 and an annular chamber 53 adjacent the valve seat 48 respectively.
- pump flow through port 41 is connected to raising feed line 18 and the interior of valve plunger 34 causes the valve plunger 47a to be moved to the left as illustrated in Fig. 4 disengaging the latter from its seat and opening the valve 6 against the spring pressure so that flow passes through valve chamber 48 and passage 52 to port 40. Any hose burst in the feed raising line 18 will result in the valve plunger 47a immediately re-engaging the seat 48 and thus closing the non-return valve 6.
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Fluid-Pressure Circuits (AREA)
Abstract
An hydraulic control circuit for the hydraulic rams (1) of the boom of an excavator includes a servo-controlled hydraulic selector valve (14) for selectively connecting a source of hydraulic pressure (12, 13) to the rams for raising or lowering the boom. Load control valves (4) connected to the raising sides of the rams include pilot-operated relief valves (7) for controlling the outlet of hydraulic fluid from the rams during lowering of the boom. In order to provide for a fast rate of descent of the boom, when required, the relief valves (7) are controlled by an hydraulic intensifier (11a) which is responsive to operation of the servo hand controller (16) upon lowering of the boom. The hydraulic pressure signal from the appropriate line (15) connecting the servo controller to the selector valve (14) is applied to the input (24) of the hydraulic intensifier, upon selection of the lowering mode, and its output signal is fed to the pilot lines (10) of the relief valves (7).
Description
- This invention relates to a hydraulic control circuit for a hydraulic ram (cylinder + piston) controlling raising and lowering of a mechanical member, more particularly but not exclusively for ram cylinder control of the boom of a hydraulic excavator.
- Where hydraulic excavators are used in situations such that men may be working in close proximity to the machine boom and bucket, such as when the excavator is used for craning operations, lowering pipes, shuttering etc., it is highly desirable, and is likely to be mandatory in the future, that the boom should be prevented from sudden uncontrollable lowering in the event of an hydraulic system failure,such as a hose break, by the incorporation of some form of load control valve in the hydraulic circuit. Similarly, in such situations, accurate control and positioning of the load becomes of utmost importance.
- It is known to incorporate over-centre valves in such hydraulic control circuits, which valves react quickly, have good control, a low level of leakage, and protect the structure and ram cylinders from the effects of transient pressure which could occur when stopping downward movement of the boom. Essentially, the over-centre valve is a pilot operated relief valve and is mounted on a ram cylinder. The pilot pressure used to control the valve is obtained from the feed line to the lowering side of the boom cylinders. With this arrangement, the boom may not lower at a faster rate than that determined by the flow of oil into the lowering side of the ram cylinder, since any tendancy to over-run the pump flow will cause the feed line pressure, and hence the over-centre valve pilot pressure, to fall leading to closing of the valve. This feature, while giving good control after a hose break in the feed line supplying the full area of the ram cylinder, unduly restricts the lowering speed of the boom.
- This is a disadvantage since it is common practice for the boom of an hydraulic excavator to be lowered at a speed faster than would be determined by the flow of oil into the lowering side of the boom cylinder, the deficiency of flow being made up from a low pressure source through a non-return valve. A fast rate of descent of the boom is required since, during a typical digging cycle in which earth is dug from beneath the ground level and dumped above, the lowering of the boom into the hole is essentially a non-productive part of the operation and, as such, should be executed rapidly, consistent with machine stability.
- An object of the present invention is to overcome or substantially reduce the abovementioned disadvantage.
- To this end, the present invention consists in an hydraulic control circuit for a hydraulic ram controlling raising and lowering of a mechanical member, comprising a source of hydraulic pressure, a selector valve for selectively connecting the hydraulic source to opposite sides of the ram whereby actuation of the selector valve operates the ram to raise or lower the mechanical member, a load control valve disposed adjacent to the ram and connected between the raising side of the ram and the selector valve, said load control valve comprising non-return valve means via which hydraulic pressure is applied to the raising side of the ram and hydraulically operated relief valve means for controlling the outlet of hydraulic fluid from said raising side when applying hydraulic fluid pressure to the lowering side and means responsive to a predetermined hydraulic fluid pressure or flow applied to the lowering side for supplying hydraulic fluid pressure to operate the relief valve means at a sufficient pressure to retain the relief valve means open as the lowering speed increases above that determined by the supply of hydraulic fluid pressure to the lowering side.
- In hydraulic circuits constructed in accordance with the invention for boom ram control, the boom is either locked and prevented from falling after a hose burst or continues the selected movement in a controllable manner depending upon which hose bursts, the maximum speed of lowering of the boom under normal conditions is controlled at a speed faster than would be determined by the flow of oil into the lowering side of the ram cylinder, and boom-drift, i.e. lowering of the boom due to any leakage in the system, is prevented by the load control valve.
- In order that the invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:-
- Figure 1 shows, diagrammatically, one embodiment of hydraulic control circuit for hydraulic rams controlling raising and lowering of the boom of an hydraulic excavator,
- Figures 2 and 3 show, diagrammatically, two other embodiments respectively, and
- Figure 4 is a cross-section of one form of load-control valve suitable for incorporation in the circuit of Figure 3.
- In the drawings like reference characters are used to designate the same or similar parts.
- The circuit shown in Figure 1 is used to control two hydraulic
excavator boom rams 1 each comprising arespective cylinder 2 andpiston 3. Although tworams 1 have been shown, one larger ram may alternatively be used. The circuit incorporates, for eachram 1, aload control valve 4 with a respective separate ramcylinder relief valve 5 and associated hydraulic lines and connections which are the same in each case. Thus, for simplicity, one ram only will be referred to as if there is only one ram and its associatedload control valve 4,relief valve 5 and connecting lines in the hydraulic circuit. Theload control valve 4 has good metering characteristics i.e. progressive opening in response to pilot operating pressure, and comprises anon-return valve 6 and a pilot operatedrelief valve 7. The valve pilot pressure used to control the opening of theload control valve 4 i.e. therelief valve 7 is obtained from a boom loweringfeed line 8 connected to the lowering side 9 of theram cylinder 2,via apilot line 10. Asequence valve 11 is located in the loweringfeed line 8 between where the point/valve pilot pressure is taken off throughline 10 and the lowering side 9 of the ram cylinder. - A main
hydraulic pump 12 withreservoir 13 is connected to aselector valve 14 having a directional flow control function which controls the main pump flow through the circuit and which, itself, is controlled remotely viacontrol lines 15 by aservo hand controller 16 with itsown pump 17. When theselector valve 14 is operated to raise the boom, fluid flows along afeed line 18 to the raisingside 19 of the ram cylinder via thenon-return valve 6 with minimal restriction on flow. Return flow from the cylinder lowering side 9 will also pass with minimal restriction through anon-return valve 20 connected tofeed line 8 in parallel with thesequence valve 11. Thus, theload control valve 4 and thesequence valve 11 have little effect on the raising of the boom. Should a hose break occur in thefeed line 18 to thecylinder raising side 19, thenon-return valve 6 ensures that the boom cannot suddenly fall. - When the
selector valve 14 is operated to lower the boom, pressure is raised in the boom loweringfeed line 8 due to therelief valve 7 of theload control valve 4 remaining closed initially. This pressure is also applied to thepilot line 10 causing therelief valve 7 to open, this being identical in operation to that of the normal over-center valve previously described. However, in Figure 1, when the servo-hand controller is fully selected to boom lower to obtain a high rate of descent, the pump flow through an orifice 21 connected in parallel with thesequence valve 11 andnon-return valve 20 creates a pressure drop across the orifice sufficient for therelief valve 7 of theload control valve 4 to be piloted fully open from the upstream side of the orifice 21 and ensure that relief valve remains fully open as the boom lowering speed is increased above that determined by the pump flow into the cylinder lowering side 9, while the downstream pressure at theram cylinder 2 falls low enough to permit flow from a make-upnon-return valve 22 to supplement the orifice flow to nake up any flow deficiency in the cylinder lowering side 9. The make-upvalve 22 is fed off a low pressure gallery by pump flow returning from the selector valve, the pressure of which is controlled.by a make-upgallery relief valve 23. This ensures that cavitation does not occur within theram cylinder 2. - At lower rates of boom descent, i.e. when the flow of fluid into the lowering
feed line 8 is metered by theselector valve 14, the pressure drop across the orifice 21 will not be sufficient for therelief valve 7 to be piloted fully open. This will result in restriction of flow from theram cylinder 2 through therelief valve 7 such that the pressure in theboom lowering line 8 will increase. This increase will prevent any make-up flow through thevalve 22 supplementing the pump flow into the cylinder lowering side 9. Thus, the lowering of the boom will be controlled by theload control valve 4 in response to the metered flow infeed line 8. It will be evident that, under these conditions, the failure of a hose in theboom raising line 18 will have a negligible effect on this control. - The purpose of the
sequence valve 11 in parallel with the orifice 21 is to limit the maximum level of pressure at the upstream side of the orifice 21 as a protection for the pipe work andload control valve 4. Since thenon-return valve 20 is also in parallel there is unimpeded return flow from thecylinder 2 when boom raise is selected. - In the event of sudden arrest of lowering of the boom, the separate ram cylinder mounted
relief valve 5 ensures that transient pressures within theram cylinder 2 are limited in magnitude, thus giving protection to the structure. Alternatively, theload control valve 4 could provide this feature when used with a selector valve having an open centre spool, (theselector valve 14, has a closed centre spool necessitating the inclusion of therelief valve 5 for operational reasons). - Whilst the circuit of Figure 1 operates satisfactorily, it has been found that in order to obtain a reasonably high speed of descent, the sequence valve setting is necessarily of the order of 2,500 psi. This can cause power loss in the hydraulic system with heat build-up and, when using power compensated pumps, can result in reduction in flow with consequent slowing of other system functions which may be operated simultaneously with the lowering of the boom.
- The circuits of Figs. 2 and 3 avoid these possible problems.
- Referring now to Fig. 2, this differs from Fig. 1 in that the
sequence valve 11,non-return valve 20 and orifice 21 are replaced by a hydraulic intensifier lla. In this embodiment, advantage is taken of the pressure signal from the servo-hand controller 16 for remotely activating theselector valve 14 to cause lowering of the excavator boom by feeding this pressure signal from theappropriate line 15 into theinput 24 of the hydraulic intensifier lla. The output signal from the hydraulic intensifier is fed at itsoutput 25 to thepilot line 10 for therelief valve 7 of theload control valve 4. By this means, sufficient pilot pressure is obtained to give an acceptable boom lowering speed whilst using a low- pressure energy source. - The
pilot line 10 from the intensifier lla to the body of theload control valve 4 would normally be a closed line in which entrained air would not be flushed out. This could critically effect the operation of therelief valve 7 since, if sufficient in quantity, the amount of compression required would exceed the available displacement of theintensifier output piston 26. Thus, to guard against this occuring, the circuit includes an automatic bleed system operative when boom lowering is not selected, to flush thepilot line 10 from the load control valve body and through the intensifier lla. This bleed system includes anon-return valve 27 andline 28 connected into the pilot port of therelief valve 7 and anon-return valve 29 in the intensifier lla which is unseated when the intensifier is inoperative, such that flow will be induced in thepilot line 10 from the relief valve to the intensifier, thus purging the lines and cavities within the relief valve pilot section and the intensifier. - It will be appreciated from Fig. 2, that the point where the line 28 -connects into the
pilot line 10 is inside the body of the load control valve. This ensures that the bleed flow which exists when boom lower is not selected- enters the load control valve body by one port and leaves by another port, thus purging the body cavity of any air. - . Referring now to Figures 3 and 4, the circuit of Figure 3 differs from that of Figure 1 in that the
sequence valve 11,valve 20 and orifice 21 are omitted and aventing valve 30 is incorporated in apilot line 31 connected to aport 32 in therelief valve 7 and to the servo-hand controller 16 and one of thelines 15. The load-control valve 4 consists of therelief valve 7 andnon-return valve 6 which are independent of each other but which are contained within a common valve body 33. Therelief valve 7 has a hollow-cylindrical valve plunger 34 which is slidingly and sealingly mounted within the valve body 33, theannular seals 35 dividing the valve body into fourchambers ports side 19 of theram cylinder 2, the raisingfeed line 18 to theselector valve 14, thepilot line 10 connected to the loweringfeed line 8, and thepilot line 31 to thevent valve 30. The left-hand end of thevalve plunger 34 is normally biased into a position in which it engages avalve seat 43 on the valve body 33 by means of acompression spring 44 in the valve chamber 39 and acting between the opposite end of the valve body and valve plunger. - The action of pressure due to the loaded
ram cylinder 2 acting on a smallannular area 45 defined by the outside diameter of thevalve plunger 34 and the mating seat. engaging diameter of the plunger end disengages the plunger end from itsseat 43 against the action of thespring 44 to openvalve 7. This action is aided by the application of a pilot pressure throughline 10 andport 42 to a further annular area 46 which generally is of larger area than thearea 45 acted on by the cylinder load pressure. Disengagement of the cylinder end from thevalve seat 43 allows flow from the loaded cylinder through the valve body, theport 41 andline 18 to theselector valve 14. Since back pressure in theport 41 will act on anarea defined by the diameter of the left-hand plunger end, balancingholes 47 are provided through theplunger 34 to feed this pressure into the spring chamber 39 and thus balance the effects of back pressure on the plunger. By venting the pressure within the spring chamber 39 to drain, the back pressure can be used to fully open the valve (disengagement of plunger from valve seat 43), allowing minimum restriction to the flow out of thecylinder 2 through theport 32. The balancing holes 47 must be carefully selected to ensure that the ventingvalve 30 may be quite small. Thisvalve 30 is set to ensure that only when the servo signal to theselector valve 14 has reached a certain level, predetermined by tests, will thevalve 30 open to vent the spring chamber 39 and thus fully open therelief valve 7. This ensures that the relief valve offers a minimum of resistance to the flow of fluid from the cylinder with no extra energy consumption imposed on the circuit. Thus, therelief valve 7 is maintained fully open to provide acceptable boom lowering speed rates when boom lower is fully selected by the servo-hand controller 16. - The
non-return valve 6 comprises avalve plunger 47a which is urged into engagement at one of its ends with amating seat 48 on the valve body 33 by aspring 49 disposed in achamber 50.Passages port 40 to the raising side of theram cylinder 2, with thespring chamber 50 and anannular chamber 53 adjacent thevalve seat 48 respectively. Thus, when the selector valve is operated to boom raise, pump flow throughport 41 is connected to raisingfeed line 18 and the interior ofvalve plunger 34 causes thevalve plunger 47a to be moved to the left as illustrated in Fig. 4 disengaging the latter from its seat and opening thevalve 6 against the spring pressure so that flow passes throughvalve chamber 48 andpassage 52 toport 40. Any hose burst in thefeed raising line 18 will result in thevalve plunger 47a immediately re-engaging theseat 48 and thus closing thenon-return valve 6. - An additional feature of the circuit described with reference to Figure 3 is that since at low servo pressures the venting
valve 30 is inoperative, then after a hose failure in the boom raisingfeed line 18, the lowering of the boom remains under the control of the pump flow since, any tendancy to run-away, leads to loss of pressure within the loweringfeed line 8 and hence in thepilot line 10, causing therelief valve 7 to shut. Thus, under these conditions, the circuit operates as described previously for the over-centre valve. - Although particular embodiments have been described with reference to boom control ram cylinders, it should be appreciated that the invention is also applicable to the control of the ram cylinders of other mechanical members, such as bucket arm and handle control cylinders and wrist control cylinders.
Claims (10)
1. An hydraulic control circuit for an hydraulic ram (1) controlling raising and lowering of a mechanical member, characterised by a selector valve (14) for selectively connecting a source of hydraulic fluid pressure to opposite sides of the ram, whereby actuation of the selector valve operates the ram to raise or lower the mechanical member, a load control valve (4) connected between the raising side (19) of the ram and the selector valve (14), said load control valve comprising non-return valve means (6), via which hydraulic pressure is applied to the raising side of the ram, and pilot-operated relief valve means (7) for controlling discharge of hydraulic fluid from the raising side of the ram in response to application of hydraulic fluid pressure to the lowering side (9) thereof, and means (21,11a,30) for. retaining the relief valve means (7) open as the lowering speed of the ram increases above the maximum speed determined by the available hydraulic fluid supply.
2• An hydraulic circuit as claimed in claim 1, characterised in that the relief valve means (7) is hydraulically actuated and has a pilot line (10) connected to the lowering side (9) of the ram, and the means (20,21) for retaining the relief valve means open is disposed between the connection of said pilot line (10) and the lowering side (9) of the ram and is adapted to constrict flow of hydraulic fluid to said ram upon lowering movement thereof, thereby to maintain at least a predetermined minimum hydraulic pressure applied to the pilot line (10) so as to maintain the relief valve means open, whilst permitting unrestricted discharge of hydraulic fluid from said ram upon raising movement of the latter.
3. An hydraulic circuit as claimed in claim 2, characterised in that the means for retaining the relief valve means (7) open comprises a flow restricting orifice (21) connected in parallel with a non-return valve (20) permitting unrestricted discharge of fluid from the ram.
4. An hydraulic circuit as claimed in claim 2 or 3, characterised in that the means for retaining the relief valve means (7) open includes valve means (11) for limiting the hydraulic pressure on the side of said retaining means (20,21) remote from the ram to a predetermined maximum.
5. An hydraulic circuit as claimed in claim 1, characterised in that the selector valve (14) is hydraulically actuated and is remotely controlled by a servo selector valve (16), the relief valve means (7) is hydraulically actuated, and the means for retaining the relief valve means open comprises hydraulic intensifier means (lla) which is responsive to actuation of the servo selector valve (16) to lower the ram so as to apply hydraulic pressure to the pilot circuit (10) of the relief valve means.
6. An hydraulic circuit as claimed in claim 5, characterised by purging means (27,28) for automatically flushing the pilot circuit of the relief valve means (7) and the intensified means (11a) when lowering movement of the ram is not selected.
7. An hydraulic circuit as claimed in claim 1, characterised in that the relief valve means (7) is hydraulically actuated and has a pilot line (10) connected to the lowering side (9) of the ram, the relief valve means including a valve member (34) moveable to connect an inlet port (40) of the relief valve means to an outlet port (41) and permit discharge of hydraulic fluid from the raising side (19) of the ram, whereby an hydraulic back pressure is applied to one side of said valve member, and means (47) for applying said back pressure to the opposite side of said valve member to balance the effect of said back pressure thereon, and further characterised in that said means for retaining the relief valve means open comprises venting valve means (30) connected to said opposite side of said valve member to vent hydraulic fluid pressure therefrom in response to actuation of the selector valve (14) to maximise the lowering speed of the ram,whereby said back pressure retains said relief valve means open.
8. An hydraulic circuit as claimed in claim 7, characterised in that the selector valve (14) is hydraulically actuated and is remotely controlled by a servo selector valve (16), and the vent valve means (30) is hydraulically actuated and is responsive to actuation of the servo selector valve (16) to maximise the lowering speed of the ram.
9. An hydraulic circuit as claimed in any one of the preceding claims, characterised by means (22) for supplying make-up hydraulic fluid to the lowering side (9) of the ram in response to the decrease below a predetermined minimum pressure of the hydraulic pressure applied to said lowering side.
10. An hydraulic circuit as claimed in any one of the preceding claims, including pilot-operated relief valve means (5) connected in parallel with said load control valve (4) and responsive to the hydraulic pressure at the raising side (19) of the ram for limiting the hydraulic pressure of the raising side to a predetermined maximum, whereby to protect the circuit against overload pressure.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8110699 | 1981-04-06 | ||
GB8110699 | 1981-04-06 |
Publications (1)
Publication Number | Publication Date |
---|---|
EP0063025A1 true EP0063025A1 (en) | 1982-10-20 |
Family
ID=10520960
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP82301825A Withdrawn EP0063025A1 (en) | 1981-04-06 | 1982-04-06 | Hydraulic control circuit for an hydraulic ram |
Country Status (1)
Country | Link |
---|---|
EP (1) | EP0063025A1 (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2541735A1 (en) * | 1983-02-25 | 1984-08-31 | Same Spa | HYDRAULIC ACTUATOR SUPPLY CIRCUIT |
US5191826A (en) * | 1990-07-05 | 1993-03-09 | Heilmeier & Weinlein Fabrik Fur Oel-Hydraulik | Hydraulic control device |
US6422804B1 (en) * | 2000-02-18 | 2002-07-23 | Deere & Company | Inertia load dampening hydraulic system |
DE102008053061A1 (en) * | 2008-10-24 | 2010-04-29 | Hydac System Gmbh | Hydromechanical support device, particularly for holding working platforms erected on floor space in desired alignment position, comprises hydraulic system which has preselection valve which is upstream hydraulic cylinders |
EP2739128B1 (en) | 2011-08-05 | 2016-07-20 | Precision Planting LLC | Apparatus, systems and methods for row unit downforce control |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB929481A (en) * | 1961-04-03 | 1963-06-26 | New York Air Brake Co | Hydraulic mechanism |
DE1550452A1 (en) * | 1966-06-15 | 1969-08-21 | Martin Presch | Controlled hydraulic check valve |
DE1600970A1 (en) * | 1967-02-25 | 1970-06-18 | Berlin Spezialfahrzeugwerk | Broken pipe and holding valve with return throttle |
DE2424973A1 (en) * | 1974-05-22 | 1975-12-04 | Montan Hydraulik Gmbh & Co Kg | Hydraulic drive control - has sealing valve, consisting of pilot and return valve |
US3943825A (en) * | 1972-04-17 | 1976-03-16 | Caterpillar Tractor Co. | Hydraulic control system for load supporting hydraulic motors |
-
1982
- 1982-04-06 EP EP82301825A patent/EP0063025A1/en not_active Withdrawn
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB929481A (en) * | 1961-04-03 | 1963-06-26 | New York Air Brake Co | Hydraulic mechanism |
DE1550452A1 (en) * | 1966-06-15 | 1969-08-21 | Martin Presch | Controlled hydraulic check valve |
DE1600970A1 (en) * | 1967-02-25 | 1970-06-18 | Berlin Spezialfahrzeugwerk | Broken pipe and holding valve with return throttle |
US3943825A (en) * | 1972-04-17 | 1976-03-16 | Caterpillar Tractor Co. | Hydraulic control system for load supporting hydraulic motors |
DE2424973A1 (en) * | 1974-05-22 | 1975-12-04 | Montan Hydraulik Gmbh & Co Kg | Hydraulic drive control - has sealing valve, consisting of pilot and return valve |
Cited By (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2541735A1 (en) * | 1983-02-25 | 1984-08-31 | Same Spa | HYDRAULIC ACTUATOR SUPPLY CIRCUIT |
US5191826A (en) * | 1990-07-05 | 1993-03-09 | Heilmeier & Weinlein Fabrik Fur Oel-Hydraulik | Hydraulic control device |
US6422804B1 (en) * | 2000-02-18 | 2002-07-23 | Deere & Company | Inertia load dampening hydraulic system |
DE102008053061A1 (en) * | 2008-10-24 | 2010-04-29 | Hydac System Gmbh | Hydromechanical support device, particularly for holding working platforms erected on floor space in desired alignment position, comprises hydraulic system which has preselection valve which is upstream hydraulic cylinders |
EP2739128B1 (en) | 2011-08-05 | 2016-07-20 | Precision Planting LLC | Apparatus, systems and methods for row unit downforce control |
US9955623B2 (en) | 2011-08-05 | 2018-05-01 | Precision Planting Llc | Apparatus, systems and methods for row unit downforce control |
US10238023B2 (en) | 2011-08-05 | 2019-03-26 | Precision Planting Llc | Apparatus, systems and methods for row unit downforce control |
EP3106012B1 (en) | 2011-08-05 | 2019-12-11 | Precision Planting LLC | Agricultural planter having a plurality of row units, system and method for row unit downforce control |
US10834863B2 (en) | 2011-08-05 | 2020-11-17 | Precision Planting Llc | Apparatus, systems and methods for row unit downforce control |
EP3106012B2 (en) † | 2011-08-05 | 2023-10-11 | Precision Planting LLC | Agricultural planter having a plurality of row units, with a system for row unit downforce control |
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