CN118103573A

CN118103573A - Hydraulic system for industrial vehicle

Info

Publication number: CN118103573A
Application number: CN202280067083.9A
Authority: CN
Inventors: 小寺裕康; 松尾政浩; 三木崇; 藤本祐介
Original assignee: Kawasaki Jukogyo KK
Current assignee: Kawasaki Motors Ltd
Priority date: 2021-11-24
Filing date: 2022-11-21
Publication date: 2024-05-28
Also published as: JP2023076907A; WO2023095739A1

Abstract

The hydraulic system (1) comprises: a variable displacement steering pump (21) for supplying a working fluid to the steering actuator (11); a variable capacity type loading/unloading pump (31) for supplying the working fluid to at least one loading/unloading actuator (12); and a converging line (71) which branches from the steering supply line (22) and is connected to the loading/unloading supply line (32). Furthermore, the hydraulic system (1) comprises: a loading/unloading regulator (5) which inputs a loading/unloading request command pressure and increases the capacity of the loading/unloading pump (31) as the loading/unloading request command pressure increases; and a steering regulator (4) which controls the capacity of the steering pump (21) so that the higher one of the steering load pressure and the loading/unloading load pressure is inputted as a load sensing pressure and the pressure difference between the load sensing pressure and the discharge pressure of the steering pump (21) is constant.

Description

Hydraulic system for industrial vehicle

Technical Field

The present disclosure relates to hydraulic systems for industrial vehicles.

Background

Industrial vehicles such as wheel loaders and forklifts are equipped with a hydraulic system including a steering circuit for changing the traveling direction and a loading and unloading circuit for moving the bucket and the forklift.

For example, patent document 1 discloses a hydraulic system for a forklift that uses a variable capacity steering pump for a steering circuit and a variable capacity loading and unloading pump (cargo pump) for an unloading circuit. In the steering circuit, the working fluid is supplied from the steering pump to the steering actuator via the steering supply line and the steering valve, and in the loading and unloading circuit, the working fluid is supplied from the loading and unloading pump to the two loading and unloading actuators via the loading and unloading supply line and the two loading and unloading control valves.

Further, in the hydraulic system disclosed in patent document 1, a merging line branches from a steering supply line, and the merging line is connected to a loading and unloading supply line. The switching valve is arranged on the combining line. The switching valve blocks the merging line when the loading and unloading operation is not performed, and opens the merging line when the loading and unloading operation is performed. That is, when the switching valve releases the confluence line, the working fluid discharged from the loading and unloading pump and the working fluid discharged from the steering pump are merged and supplied to the loading and unloading actuator. In addition, when the loading and unloading operation and the steering operation are performed simultaneously, the working fluid discharged from the steering pump is supplied to both the steering actuator and the loading and unloading actuator.

The capacity of the steering pump is changed by the steering regulator, and the capacity of the loading pump is changed by the loading regulator. As described above, the capacity of the steering pump and the capacity of the loading and unloading pump are controlled in the same manner from the viewpoint of merging the working fluid discharged from the loading and unloading pump with the working fluid discharged from the steering pump. In patent document 1, load sensing control is adopted as a control method thereof.

More specifically, the higher load pressure of the two load actuators, that is, the highest load pressure, is input into the load adjuster as the load sensing pressure. The loading/unloading regulator controls the capacity of the loading/unloading pump in such a way that the pressure difference between the load sensing pressure and the discharge pressure of the loading/unloading pump is constant.

On the other hand, the higher one of the load pressure of the steering actuator and the highest load pressure of the loading/unloading actuator is input into the steering regulator as the load sensing pressure. The steering regulator controls the capacity of the steering pump so that the pressure difference between the load sensing pressure and the discharge pressure of the steering pump is constant. Therefore, when the steering operation and the loading and unloading operation are performed simultaneously, the capacity of the steering pump is changed according to the higher-demand side.

Prior art literature:

Patent literature:

patent document 1: japanese patent application laid-open No. 2017-226492.

Disclosure of Invention

Problems to be solved by the invention:

However, as a control method of the capacity of the loading and unloading pump, it is desirable to use positive control in which the capacity increases as the operation amount of the loading and unloading operation increases, instead of the load sensing control. However, at this time, how the capacity of the steering pump is controlled becomes a problem.

It is therefore an object of the present disclosure to provide a hydraulic system of an industrial vehicle that can control the capacity of a steering pump appropriately with positive control of the capacity of the steering pump.

Means for solving the problems:

The present disclosure provides a hydraulic system for an industrial vehicle, comprising: a variable displacement steering pump for supplying the working fluid to the steering actuator via a steering supply line and a steering valve; a variable capacity type loading/unloading pump for supplying the working fluid to the at least one loading/unloading actuator through the loading/unloading supply line and the at least one loading/unloading control valve; a converging line branched from the steering supply line and connected to the loading/unloading supply line; a priority valve provided in the merging line, blocking the merging line when the loading and unloading operation is not performed, and opening the merging line when the loading and unloading operation is performed; a loading/unloading regulator which inputs a loading/unloading request command pressure which is positively correlated with the operation amount of the loading/unloading operation, and increases the capacity of the loading/unloading pump as the loading/unloading request command pressure is increased; and a steering regulator that controls the capacity of the steering pump so that a pressure difference between the load sensor pressure and the discharge pressure of the steering pump becomes constant, the higher one of a steering load pressure, which is a pressure on a downstream side of a throttle portion of the steering valve that determines a supply amount of the working fluid to the steering actuator, and a loading/unloading load pressure, which is a pressure on an upstream side of the at least one loading/unloading control valve in the loading/unloading supply line, is inputted as a load sensor pressure.

The invention has the following effects:

According to the present disclosure, the capacity of the steering pump can be controlled and the capacity of the loading and unloading pump can be appropriately controlled with positive control.

Drawings

FIG. 1 is a schematic block diagram of a hydraulic system of an industrial vehicle according to an embodiment;

FIG. 2 is an enlarged view of a steering circuit of the hydraulic system;

FIG. 3 is an enlarged view of a load and unload circuit of the hydraulic system;

fig. 4 is an operating system loop diagram of the loading and unloading loop.

Detailed Description

Fig. 1 shows a hydraulic system 1 of an industrial vehicle of an embodiment. In the present embodiment, the industrial vehicle is a wheel loader including a hoist (also called an arm or a boom) and a bucket. However, the industrial vehicle may be a forklift or the like.

The hydraulic system 1 comprises a steering circuit 2 for changing the direction of travel and a loading and unloading circuit 3 for moving the bucket. In a wheel loader, a front vehicle body including front wheels and a rear vehicle body including rear wheels are swingably coupled in a horizontal direction. The hoist is swingably coupled to the front-side vehicle body in the vertical direction, and the bucket is swingably coupled to the tip end of the hoist in the vertical direction.

As shown in fig. 2, the steering circuit 2 includes a steering pump 21, a steering valve 23, and a steering actuator 11. The steering pump 21 supplies the working fluid to the steering actuator 11 through a steering supply line 22 and a steering valve 23. In the present embodiment, the steering actuator 11 is configured by a pair of hydraulic cylinders provided on both left and right sides of the connecting portion between the front-side vehicle body and the rear-side vehicle body. However, depending on the size of the wheel loader, the steering actuator 11 may be formed of a single hydraulic cylinder. When the industrial vehicle is a forklift, the steering actuator 11 is composed of a single two-rod hydraulic cylinder.

Specifically, the steering pump 21 is connected to a steering valve 23 through a steering supply line 22, and the steering valve 23 is connected to the steering actuator 11 through a pair of supply/discharge lines 24. The steering valve 23 is connected to the tank via a tank line 25.

The steering valve 23 has a throttle portion 23a that determines the amount of the hydraulic fluid supplied to the steering actuator 11. The steering valve 23 is also connected to both ends of an intermediate line 27 interposed between the steering supply line 22 and the supply/discharge line 24. The intermediate line 27 is provided with a check valve 28.

When a steering wheel provided in a cab of an industrial vehicle is operated, the steering valve 23 is displaced (shift) from a neutral position to a right-hand or left-hand turning position. In the neutral position, both ends of the steering supply line 22, the intermediate line 27, the pair of supply/discharge lines 24, and the tank line 25 are all blocked. In the right-hand or left-hand turning position, the steering supply line 22 communicates with one supply/discharge line 24 via an intermediate line 27, and the other supply/discharge line 24 communicates with the tank line 25. In the right-hand or left-hand turning position, the opening area of the throttle portion 23a increases as the steering wheel operation amount increases.

More specifically, the steering valve 23 has a pair of pilot ports, and these pilot ports are connected to a steering main unit (orbitrol; registered trademark) 26 via pilot lines 26a and 26 b. The steering main unit 26 is coupled to the steering wheel, and a pilot pressure corresponding to the operation amount of the steering wheel is output to a pilot port of the steering valve 23 through a pilot line 26a or 26b in the rotation direction of the steering wheel.

The steering valve 23 is also connected to a load pressure line 64 and a tank line 68. When the steering valve 23 is in the neutral position, the load pressure line 64 communicates with the tank line 68. When the steering valve 23 is located at the right-hand or left-hand position, a steering load pressure, which is the pressure on the downstream side of the throttle portion 23a, is introduced into the load pressure line 64.

The steering supply line 22 is provided with a compensator 61. The compensator 61 opens the steering supply line 22 at the neutral position, and the opening area of the compensator 61 decreases as the compensator 61 is displaced from the neutral position. The compensator 61 is operated so as to face each other, and the pressure on the upstream side of the throttle portion 23a in the steering valve 23 and the steering load pressure described above are applied.

The steering load pressure is introduced into the compensator 61 through the load pressure line 64, and acts on the compensator 61 so as to be displaced in the direction in which the opening area increases. On the other hand, the pressure on the upstream side of the throttle portion 23a in the steering valve 23 is introduced into the compensator 61 through the supply pressure line 62, and acts on the compensator 61 so as to be displaced in the direction in which the opening area decreases. The supply pressure line 62 branches from the steering supply line 22 on the downstream side of the compensator 61. In the present embodiment, the supply pressure line 62 and the load pressure line 64 are provided with the throttles 63 and 65, respectively, but the throttles 63 and 65 may be omitted.

According to such a structure, the opening area of the compensator 61 decreases as the pressure difference between the upstream side of the throttle portion 23a in the steering valve 23 and the steering load pressure increases. A relief line 66 branches from the load pressure line 64, and the pressure of the load pressure line 64 is maintained at or below a predetermined value by a relief valve 67 provided in the relief line 66.

The steering pump 21 is driven by a prime mover. The prime mover is, for example, an internal combustion engine or an electric motor. The prime mover also drives a loading and unloading pump 31 and a sub-pump 15, which will be described later.

The steering pump 21 is a variable capacity pump. In the present embodiment, the steering pump 21 is a swash plate pump having a swash plate 21 a. However, the steering pump 21 may be a tilt-axis pump. In the present embodiment, the relief line 17 branches from an upstream side portion of the merging line 71 described later than the priority valve 72, and the relief valve 17a provided in the relief line 17 keeps the discharge pressure of the steering pump 21 at a predetermined value or less. The overflow line 17 may also branch from the diverting supply line 22.

The capacity of the steering pump 21 is changed by the steering regulator 4. In the steering regulator 4, a load sensing pressure is input through a load sensing line 99. The steering regulator 4 controls the capacity of the steering pump 21 so that the pressure difference between the load sensing pressure and the discharge pressure of the steering pump 21 becomes constant. In the present embodiment, the steering regulator 4 is configured as shown in fig. 2, but the configuration of the steering regulator 4 is not limited to this, and can be adaptively changed.

More specifically, the steering adjuster 4 includes a spring 41 that biases the swash plate 21a in the capacity increasing direction, and a piston 42 that presses the swash plate 21a in the capacity decreasing direction against the spring 41. In the steering regulator 4, a pressure receiving chamber 43 for applying a control pressure to the piston 42 is formed.

Further, the steering regulator 4 includes a load sensing valve 45 connected to the pressure receiving chamber 43 through a control pressure line 44, and a shutoff valve 48, む provided on the control pressure line 44. However, the shut-off valve 48 may be omitted.

The load sensing valve 45 is connected to the steering supply line 22 via a pump line 46 and to the tank via a tank line 47. The load sensing pressure and the discharge pressure of the steering pump 21 described above act on the load sensing valve 45 so as to oppose each other. The load sensing valve 45 operates so that the pressure difference between the load sensing pressure and the discharge pressure of the steering pump 21 becomes constant, and the control pressure thus regulated is introduced into the pressure receiving chamber 43 through the control pressure line 44.

The shutoff valve 48 is used to introduce the discharge pressure of the steering pump 21 into the pressure receiving chamber 43 when the discharge pressure of the steering pump 21 exceeds a predetermined value, so that the capacity of the steering pump 21 is minimized.

As shown in fig. 3, the loading/unloading circuit 3 includes a loading/unloading pump 31, two loading/unloading control valves 33, and two loading/unloading actuators 12. The loading and unloading pump 31 supplies the working fluid to the two loading and unloading actuators 12 via the loading and unloading supply line 32 and the two loading and unloading control valves 33.

The two loading actuators 12 are a bucket actuator 13 and a lift actuator 14. In the present embodiment, the bucket actuator 13 is constituted by a single hydraulic cylinder, and the lift actuator 14 is constituted by a pair of hydraulic cylinders. However, the bucket actuator 13 is sometimes constituted by a pair of hydraulic cylinders. The two loading and unloading control valves 33 are a bucket control valve 34 and a lift control valve 35.

Specifically, the loading and unloading pump 31 is connected to a bucket control valve 34 and a lift control valve 35 via a loading and unloading supply line 32. That is, the loading/unloading supply line 32 includes: a common passage 32a extending from the attachment/detachment pump 31; a bucket branch line 32b extending from a downstream end of the common passage 32a to the bucket control valve 34; and a lift sub-branch 32c extending from the downstream end of the common passage 32a to the lift control valve 35. The bucket branch 32b and the lift branch 32c are provided with check valves 32d and 32e, respectively.

Further, a bucket priority valve 32f for restricting the supply of the working fluid to the lift actuator 14 when the bucket operation and the lift operation are performed simultaneously is provided on the lift branch line 32 c. The bucket priority valve 32f opens the lift branch line 32c at the neutral position, and the opening area of the bucket priority valve 32f decreases as the bucket priority valve 32f is displaced from the neutral position. In the present embodiment, the bucket priority valve 32f is a pilot type, and has a pilot port. The opening area of the bucket priority valve 32f decreases as the pilot pressure introduced into the pilot port of the bucket priority valve 32f increases. However, the bucket priority valve 32f may be electromagnetic.

The bucket control valve 34 is connected to the bucket actuator 13 through a pair of supply/discharge lines 36, and the lift control valve 35 is connected to the lift actuator 14 through a pair of supply/discharge lines 37. Bucket control valve 34 and lift control valve 35 are connected to the tank via tank line 38.

Bucket control valve 34 is displaced from the neutral position to either the first operating position or the second operating position. In the neutral position, the loading and unloading supply line 32, the pair of supply and discharge lines 36, and the tank line 38 are all blocked. In the first operating position or the second operating position, the loading/unloading supply line 32 communicates with one supply/discharge line 36, and the other supply/discharge line 36 communicates with the tank line 38.

In the present embodiment, bucket control valve 34 is a pilot type, and has a pair of pilot ports. When pilot pressure is introduced to one of the pilot ports, bucket control valve 34 is displaced from the neutral position to the first operating position, and the opening area of bucket control valve 34 increases as the pilot pressure increases. Conversely, when the pilot pressure is introduced to the other pilot port, bucket control valve 34 is displaced from the neutral position to the second operating position, and the opening area of bucket control valve 34 increases as the pilot pressure increases. However, bucket control valve 34 may also be electromagnetic.

The lift control valve 35 is displaced from the neutral position to the first operating position or the second operating position. Further, the lift control valve 35 is also displaced between the second operating position and the third operating position. In the neutral position, the loading and unloading supply line 32, the pair of supply and discharge lines 37, and the tank line 38 are all blocked. In the first operating position or the second operating position, the loading/unloading supply line 32 communicates with one supply/discharge line 37, and the other supply/discharge line 37 communicates with the tank line 38. In the third operating position, the supply and discharge lines 37 communicate with each other within the lift control valve 35.

In the present embodiment, the lift control valve 35 is a pilot type, and has a pair of pilot ports. When pilot pressure is introduced into one pilot port, the lift control valve 35 is displaced from the neutral position to the first operation position, and the opening area of the lift control valve 35 increases as the pilot pressure increases. Conversely, when the pilot pressure is introduced into the other pilot port, the lift control valve 35 is displaced from the neutral position to the second operation position, and the opening area of the lift control valve 35 increases as the pilot pressure increases. When the pilot pressure introduced to the other pilot port further increases, the lift control valve 35 is displaced from the second operation position to the third operation position. However, the lift control valve 35 may be electromagnetic.

In the present embodiment, a center bypass line 39 is branched from the common passage 32a of the loading/unloading supply line 32, and the center bypass line 39 extends to the tank through the bucket control valve 34 and the lift control valve 35. Bucket control valve 34 and lift control valve 35 reduce the open area on center bypass line 39 as they shift from the neutral position to the first or second operating positions.

As shown in fig. 4, the pilot port of bucket control valve 34 is connected to a pair of bucket electromagnetic proportional valves 94 and 95 via a pair of pilot lines, and the pilot port of lift control valve 35 is connected to a pair of lift electromagnetic proportional valves 96 and 97 via a pair of pilot lines. The bucket electromagnetic proportional valves 94 and 95 and the lift electromagnetic proportional valves 96 and 97 are connected to the sub-pump 15 (see fig. 1 and 3) via the primary pressure line 16. Although not shown, a relief line branches from the primary line 16, and the relief valve provided in the relief line keeps the discharge pressure of the sub-pump 15 at a predetermined value. The primary line 16 may be connected to the steering supply line 22 instead of the sub-pump 15, and a pressure reducing valve may be provided in the primary line 16, so that the discharge pressure of the steering pump 21 may be reduced and used as the primary pressure.

In the present embodiment, the bucket electromagnetic proportional valves 94 and 95 and the lift electromagnetic proportional valves 96 and 97 are respectively in a positive proportion in which the command current and the secondary pressure are positively correlated. However, the bucket electromagnetic proportional valves 94 and 95 and the lift electromagnetic proportional valves 96 and 97 may be inverse proportional valves in which the command current and the secondary pressure are inversely related to each other.

Returning to fig. 3, in the cab of the industrial vehicle, a bucket operating device 92 and a lift operating device 93 are further provided in addition to the steering wheel. The bucket operating device 92 includes an operating lever that receives a bucket operation, and the lift operating device 93 includes an operating lever that receives a lift operation.

In the present embodiment, the bucket operating device 92 and the lift operating device 93 are electric levers that output electric signals corresponding to the tilting direction and tilting angle (i.e., the operation amount of the bucket operation or the lift operation) of the levers, respectively. The electric signals output from the bucket operating device 92 and the lift operating device 93 are input to the control device 91.

However, the bucket operating device 92 and the lift operating device 93 may be pilot operated valves that output pilot pressures corresponding to the tilting direction and the tilting angle of the operation lever, respectively. In this case, the bucket electromagnetic proportional valves 94 and 95 and the lift electromagnetic proportional valves 96 and 97 may be omitted, the pilot port of the bucket control valve 34 may be connected to the bucket operating device 92 as a pilot operating valve through a pair of pilot lines, and the pilot port of the lift control valve 35 may be connected to the lift operating device 93 as a pilot operating valve through a pair of pilot lines.

When the bucket operation device 92 is operated by the bucket, the control device 91 sends a command current to the bucket electromagnetic proportional valve 94 or 95 corresponding to the tilting direction of the bucket operation device. Further, the control device 91 increases the command current as the operation amount of the bucket operation increases. The secondary pressure output from the bucket electromagnetic proportional valve 94 on the one hand (the one that swings the bucket upward) is also introduced into the pilot port of the bucket priority valve 32f as shown in fig. 4.

Similarly, when the lever of the lift operation device 93 is subjected to a lift operation, the control device 91 sends a command current to the lift electromagnetic proportional valve 96 or 97 corresponding to the tilting direction of the lever. Further, in the control device 91, the instruction current increases as the operation amount of the lifting operation increases.

The functions of the elements disclosed in the present specification may be performed by the control device 91 using a circuit or a processing circuit including a general-purpose processor, a special-purpose processor, an integrated circuit, an ASIC (Application SPECIFIC INTEGRATED Circuits), an existing circuit, and/or a combination thereof, which are configured or programmed to perform the disclosed functions. A processor is considered to be a processing circuit or circuits since it includes transistors or other circuits. In this disclosure, a circuit, unit, or means is hardware that performs the recited function or is programmed to perform the recited function. The hardware may be the hardware disclosed in this specification or other known hardware programmed or configured to perform the recited functions. When hardware is considered to be a processor of one of the circuits, a circuit, means or unit is a combination of hardware and software, the software being used for the constitution of the hardware and/or the processor.

The loading and unloading pump 31 is a variable capacity pump. In the present embodiment, the loading and unloading pump 31 is a swash plate pump having a swash plate 31 a. However, the loading pump 31 may be a tilt-axis pump. The relief line 18 branches from the loading/unloading supply line 32, and the discharge pressure of the loading/unloading pump 31 is kept at a predetermined value or less by a relief valve 18a provided in the relief line 18. When the priority valve 72 described later is opened, the relief valve 18a also plays a role of maintaining the discharge pressure of the steering pump 21 at or below a predetermined value.

The capacity of the loading pump 31 is changed by the loading regulator 5. In the present embodiment, the loading/unloading regulator 5 performs flow control using the flow control piston 56 and horsepower control using the horsepower control piston 57. However, the loading/unloading regulator 5 may perform only flow control.

The loading/unloading regulator 5 receives a loading/unloading request command pressure as a flow rate control. The loading and unloading request command pressure will be described in detail later. The greater the loading and unloading request command pressure of the loading and unloading regulator 5, the greater the capacity of the loading and unloading pump 31. In the present embodiment, the loading/unloading regulator 5 is configured as shown in fig. 3, but the configuration of the loading/unloading regulator 5 is not limited to this, and the suitability can be changed.

More specifically, the loading and unloading regulator 5 includes, in addition to the flow rate control piston 56 and the horsepower control piston 57, a servo piston 51 coupled to the swash plate 31a of the loading and unloading pump 31, and a regulator valve 52 for driving the servo piston 51. The attachment/detachment regulator 5 includes a housing that slidably holds the flow control piston 56, the horsepower control piston 57, and the servo piston 51. A portion of the housing may be formed integrally with the housing of the loading and unloading pump 31.

The loading/unloading regulator 5 has a first pressure receiving chamber 5a into which the discharge pressure of the loading/unloading pump 31 is introduced and a second pressure receiving chamber 5b into which the control pressure is introduced. The servo piston 51 has a first end portion exposed to the first pressure receiving chamber 5a and a second end portion exposed to the second pressure receiving chamber 5b and having a larger diameter than the first end portion.

The regulator valve 52 is used to regulate the control pressure introduced into the second pressure receiving chamber 5 b. Specifically, the regulator valve 52 includes: a spool 53 that moves in a direction (a capacity increasing direction, left in fig. 3) in which the control pressure decreases and in a direction (a capacity decreasing direction, right in fig. 3) in which the control pressure increases; and a sleeve 54 accommodating the spool 53.

The spool 53 is coupled to the flow control piston 56 via a rod 56a, and is coupled to the horsepower control piston 57 via a rod 57 a. The valve element 53 moves in the capacity increasing direction with the advance of the flow control piston 56, and moves in the capacity decreasing direction with the retreat of the flow control piston 56. The valve body 53 moves in the capacity decreasing direction with the advance of the horsepower control piston 57, and moves in the capacity increasing direction with the retreat of the flow control piston 56. The flow rate control piston 56 and the horsepower control piston 57 are configured such that the valve element 53 is preferentially moved by the side in which the capacity is limited to be small (i.e., the side in which the smaller capacity is commanded).

The sleeve 54 is coupled to the servo piston 51 via a feedback rod 55. The sleeve 54 is formed with a pump port, a tank port, and an output port (the output port communicates with the second pressure receiving chamber 5 b), and the output port is blocked from both the pump port and the tank port or communicates with either the pump port or the tank port depending on the relative positions of the sleeve 54 and the valve body 53. When the spool 53 moves in the capacity increasing direction or the capacity decreasing direction, the relative position of the spool 53 and the sleeve 54 is determined so that forces (pressure×servo piston pressure receiving area) acting from both sides of the servo piston 51 are balanced, and the control pressure is adjusted.

The loading/unloading regulator 5 is provided with a working chamber 5c for applying the loading/unloading demand pressure to the flow rate control piston 56. That is, the flow control piston 56 advances when the loading and unloading request command pressure becomes high, and retreats when the loading and unloading request command pressure becomes low.

The attachment/detachment regulator 5 is provided with a working chamber 5d for allowing the discharge pressure of the attachment/detachment pump 31 to act on the horsepower control piston 57. That is, the horsepower control piston 57 advances when the discharge pressure of the loading and unloading pump 31 becomes high, and retreats when the discharge pressure becomes low.

In the present embodiment, the working chamber 5c is connected to the electromagnetic proportional valve 81 through the command pressure line 82. The electromagnetic proportional valve 81 is connected to the sub-pump 15 (the steering supply line 22 in the case of the modification described above) through the primary pressure line 16 described above. In the present embodiment, the electromagnetic proportional valve 81 is a proportional valve in which the command current and the secondary voltage are positively correlated. However, the electromagnetic proportional valve 81 may be of an inverse proportional type in which the command current and the secondary voltage are inversely correlated.

The electromagnetic proportional valve 81 is controlled by the control device 91, and outputs a secondary pressure to the working chamber 5c as a loading and unloading request command pressure. When the control device 91 performs a loading/unloading operation (bucket operation or lifting operation), it sends a command current to the electromagnetic proportional valve 81. Further, in the control device 91, the command current increases as the operation amount of the loading and unloading operation increases. That is, the load demand command pressure is positively correlated with the operation amount of the load operation.

Next, the load sensing pressure input to the steering regulator 4 will be described. The load sensing line 99 is connected to an output port of the high-pressure selector valve 98 as shown in fig. 2. One of the pair of input ports of the high-pressure selector valve 98 is connected to the load pressure line 64 via an input line 88, and the other is connected to the loading/unloading supply line 32 via an input line 89 (see fig. 3).

The high-pressure selector valve 98 selects the pressure on the upstream side of the loading/unloading control valve 33 in the loading/unloading supply line 32, that is, the higher one of the loading/unloading load pressure and the steering load pressure, and outputs the selected pressure to the steering regulator 4. In other words, the higher one of the load pressure for loading and unloading and the steering demand command pressure is input to the steering regulator 4 as the load sensing pressure.

As shown in fig. 1 to 3, the merging line 71 is branched from the turn supply line 22 upstream of the compensator 61, and the merging line 71 is connected to the loading/unloading supply line 32. The merging line 71 is provided with a priority valve 72.

The priority valve 72 blocks the merging line 71 when the loading and unloading operation is not performed, and opens the merging line 71 when the loading and unloading operation is performed. In the present embodiment, the priority valve 72 is a pilot type, and has a first pilot port 72a and a second pilot port 72b. However, the priority valve 72 may be electromagnetic.

More specifically, the priority valve 72 blocks the merging line 71 at the neutral position, and the opening area of the priority valve 72 increases as the priority valve 72 is displaced from the neutral position. The priority valve 72 has a spring 72c (see fig. 2) for maintaining the priority valve 72 in the neutral position. The first pilot port 72a is connected to the tank via a pilot line 73. The pilot line 73 is provided with a check valve 74, and is connected to a bypass line 75 bypassing the check valve 74. A restrictor 76 is provided in the bypass line 75. The second pilot port 72b is used to displace the priority valve 72 in the direction in which the opening area increases.

That is, when the priority valve 72 is displaced from the neutral position, the outflow of the working fluid from the first pilot port 72a is restricted by the restrictor 76, so that the priority valve 72 is slowly operated. Conversely, when the priority valve 72 returns to the neutral position, the hydraulic fluid smoothly flows into the first pilot port 72a through the check valve 74, and therefore the priority valve 72 operates rapidly. In addition, the check valve 74, bypass line 75, and restrictor 76 may be omitted.

The second pilot port 72b of the priority valve 72 is connected to the switching valve 84 via a pilot line 77. The switching valve 84 is connected to the command pressure line 82 via a pilot line 83, and is connected to a tank via a tank line 85. The pilot line 83 may be connected to the working chamber 5c of the loading/unloading regulator 5, instead of being connected to the command pressure line 82.

The switching valve 84 switches whether or not to output a loading/unloading request command, which is the secondary pressure of the electromagnetic proportional valve 81, to the second pilot port 72b of the priority valve 72. In the present embodiment, the switching valve 84 is a pilot type, and has a first pilot port 84a and a second pilot port 84b. However, the switching valve 84 may be electromagnetic.

More specifically, the switching valve 84 is shifted between a neutral position in which the pilot line 77 communicates with the tank line 85 and an operating position in which the pilot line 77 communicates with the pilot line 83. The switching valve 84 has a spring 84c for maintaining the switching valve 84 in the neutral position. The first pilot port 84a is located on the same side of the spring 84c and the second pilot port 84b is located on the opposite side of the spring 84c.

The first pilot port 84a is connected to the load pressure line 64 via a pilot line 86. That is, the steering load pressure is introduced into the first pilot port 84 a. In the present embodiment, a part of the pilot line 86 and a part of the input line 88 form a common flow path. The second pilot port 84b is connected to the loading/unloading supply line 32 via a pilot line 87. That is, the second pilot port 84b guides the loading/unloading load pressure. In the present embodiment, a part of the pilot line 87 and a part of the input line 89 form a common flow path.

The switching valve 84 is located at the neutral position and does not output the loading/unloading request command pressure to the second pilot port 84b when the loading/unloading load pressure is smaller than the reference pressure obtained by adding a predetermined value (pressure corresponding to the urging force of the spring 84 c) to the steering load pressure. On the other hand, when the loading and unloading request command pressure is greater than the reference pressure, the switching valve 84 is displaced to the operating position and the loading and unloading request command pressure is output to the second pilot port 84 b.

As described above, in the hydraulic system 1 of the present embodiment, the loading and unloading demand command pressure that is positively correlated with the operation amount of the loading and unloading operation is input to the loading and unloading regulator 5, so that the capacity of the loading and unloading pump 31 can be positively controlled. On the other hand, the higher one of the steering load pressure and the loading load pressure is input to the steering regulator 4 as a load sensing pressure. When the steering operation is performed alone, the steering load is input to the steering regulator 4, so the capacity of the steering pump 21 varies according to the steering load pressure. When the loading and unloading operation is performed alone, the loading and unloading load is input to the steering regulator 4, and therefore the capacity of the steering pump 21 is changed according to the loading and unloading load pressure, and the working fluid is supplied from the loading and unloading pump 31 and the steering pump 21 to the loading and unloading actuator 12. When the steering operation and the loading and unloading operation are performed simultaneously, the capacity of the steering pump 21 changes according to the higher-demand side. Therefore, the capacity of the steering pump 21 can be appropriately controlled.

In the present embodiment, the priority valve 72 provided in the merging line 71 is a pilot type, and therefore the priority valve 72 can be mechanically operated. Further, the loading and unloading request command pressure output to the second pilot port 82b of the priority valve 72 is positively correlated with the operation amount of the loading and unloading operation, so that the smaller the operation amount of the loading and unloading operation is, the smaller the opening area of the priority valve 72 is. Therefore, the hydraulic fluid discharged from the steering pump 21 can be preferentially supplied to the steering actuator 11.

(Modification)

The present disclosure is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present disclosure.

For example, the number of the loading/unloading actuators 12 and the number of the loading/unloading control valves 33 in the loading/unloading circuit 3 of the hydraulic system 1 may be one or three or more, respectively, depending on the type of industrial vehicle.

When the bucket operating device 92 and the lift operating device 93 are pilot operated valves, the electromagnetic proportional valve 81 may be omitted, and the highest pilot pressure of the pilot pressures outputted from the bucket operating device 92 and the lift operating device 93 may be introduced as the loading and unloading request command to the working chamber 5c of the loading and unloading regulator 5.

The switching valve 84 does not have to be an on-off valve, and may have a function of a pressure reducing valve capable of reducing the pressure of the command pressure required for the loading and unloading operation.

(Summary)

The present disclosure provides a hydraulic system for an industrial vehicle, comprising: a variable displacement steering pump for supplying the working fluid to the steering actuator via a steering supply line and a steering valve; a variable capacity type loading and unloading pump for supplying working fluid to at least one loading and unloading actuator through a loading and unloading supply line and at least one loading and unloading control valve; a merging line branched from the steering supply line and connected to the loading/unloading supply line; a priority valve provided in the confluence line, blocking the confluence line when the loading and unloading operation is not performed, and opening the confluence line when the loading and unloading operation is performed; a loading/unloading regulator for inputting a loading/unloading request command pressure which is positively correlated with the operation amount of the loading/unloading operation, wherein the capacity of the loading/unloading pump increases as the loading/unloading request command pressure increases; and a steering regulator that controls the capacity of the steering pump so that a pressure difference between a steering load pressure, which is a pressure on a downstream side of a throttle portion in the steering valve that determines a supply amount of the working fluid to the steering actuator, and a discharge load pressure, which is a pressure on an upstream side of the at least one discharge control valve in the discharge/supply line, is constant, is inputted as a load sensing pressure.

According to the above configuration, since the loading and unloading request command pressure that is positively correlated with the operation amount of the loading and unloading operation is input to the loading and unloading regulator, the capacity of the loading and unloading pump can be positively controlled. On the other hand, the higher one of the steering load pressure and the loading/unloading load pressure is input to the steering regulator as a load sensing pressure. When the steering operation is performed alone, the steering load is pressed toward the steering regulator input, so the capacity of the steering pump varies according to the steering load pressure. When the loading and unloading operation is performed alone, the loading and unloading load is input to the steering regulator, and therefore, the capacity of the steering pump is changed according to the loading and unloading load pressure, and the working fluid is supplied from the loading and unloading pump and the steering pump bidirectional loading and unloading actuator. When the steering operation and the loading and unloading operation are simultaneously operated, the capacity of the steering pump changes according to the higher-demand side. Therefore, the capacity of the steering pump can be appropriately controlled.

For example, the hydraulic system may further include a high-pressure selector valve for selecting the higher one of the steering load pressure and the loading/unloading load pressure to be output to the steering regulator.

The priority valve may block the merging line at a neutral position and may have a pilot port for displacing the priority valve in a direction in which an opening area increases, and the hydraulic system may further include a switching valve for switching whether or not to output the loading/unloading request command pressure to the pilot port, wherein the loading/unloading request command pressure is not output when the loading/unloading load pressure is lower than a reference pressure obtained by adding a predetermined value to the steering load pressure, and the loading/unloading request command pressure is output when the loading/unloading load pressure is higher than the reference pressure. According to this structure, the priority valve can be mechanically operated. Further, since the loading and unloading request command pressure output to the pilot port of the priority valve is positively correlated with the operation amount of the loading and unloading operation, the smaller the operation amount of the loading and unloading operation is, the smaller the opening area of the priority valve is, and the working fluid discharged from the steering pump can be preferentially supplied to the steering actuator.

Symbol description:

1 Hydraulic System

11-Turn actuator

12 Handling actuator

2 Steering circuit

21 Steering pump

22 Turn supply line

23 Steering valve

23A throttle part

3 Loading and unloading loop

31 Loading and unloading pump

32 Loading and unloading supply line

33 Loading and unloading control valve

4 Steering regulator

5 Assembling and disassembling regulator

71 Confluence line

72 Priority valve

72A first pilot port

72B second pilot port

84 Switching valve

98 High pressure selector valve.

Claims

1. A hydraulic system for an industrial vehicle, characterized in that,

A variable displacement steering pump for supplying the working fluid to the steering actuator via a steering supply line and a steering valve;

a variable capacity type loading and unloading pump for supplying working fluid to at least one loading and unloading actuator through a loading and unloading supply line and at least one loading and unloading control valve;

A merging line branched from the steering supply line and connected to the loading/unloading supply line;

A priority valve provided in the confluence line, blocking the confluence line when the loading and unloading operation is not performed, and opening the confluence line when the loading and unloading operation is performed;

a loading/unloading regulator for inputting a loading/unloading request command pressure which is positively correlated with the operation amount of the loading/unloading operation, wherein the capacity of the loading/unloading pump increases as the loading/unloading request command pressure increases; and

And a steering regulator that controls a capacity of the steering pump so that a pressure difference between a load sensor pressure and a discharge pressure of the steering pump becomes constant, the higher one of a steering load pressure, which is a pressure on a downstream side of a throttle portion of the steering valve that determines a supply amount of the working fluid to the steering actuator, and a loading/unloading load pressure, which is a pressure on an upstream side of the at least one loading/unloading control valve in the loading/unloading supply line, is inputted as the load sensor pressure.

2. The hydraulic system of an industrial vehicle of claim 1, wherein the hydraulic system is configured to control the hydraulic system,

The steering control device further includes a high-pressure selector valve for selecting the higher one of the steering load pressure and the loading/unloading load pressure to be outputted from the steering regulator.

3. The hydraulic system of an industrial vehicle according to claim 1 or 2, wherein,

The priority valve blocks the merging line at a neutral position and has a pilot port for displacing the priority valve in a direction in which an opening area increases;

The steering control device is further provided with a switching valve for switching whether or not to output the loading/unloading request command pressure to the pilot port, wherein the loading/unloading request command pressure is not output when the loading/unloading load pressure is smaller than a reference pressure obtained by adding a predetermined value to the steering load pressure, and the loading/unloading request command pressure is output when the loading/unloading load pressure is larger than the reference pressure.