Industrial vehicle hydraulic systems

Abstract

To provide a hydraulic system of an industrial vehicle which can control a capacity of a cargo handling pump by positive control and properly control a capacity of a steering pump.SOLUTION: A hydraulic system 1 includes: a variable capacity type steering pump 21 which supplies hydraulic fluid to a steering actuator 11; a variable capacity type cargo handling pump 31 which supplies hydraulic fluid to at least one cargo handling actuator 12; a confluence line 71 which is branched from a steering supply line 22 and is connected to a cargo handling supply line 32; and a priority valve 72 which is provided in the confluence line 71. Furthermore, the hydraulic system 1 includes: a cargo handling regulator 5 to which cargo handling request command pressure is input and which increases a capacity of the cargo handling pump 31 as the cargo handling request command pressure is increased; and a steering regulator 4 to which higher one of steering request command pressure and the cargo handling request command pressure is input as signal pressure and which increases a capacity of the steering pump 21 as the signal pressure is increased.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to hydraulic systems for industrial vehicles. [Background technology]

[0002] Industrial vehicles such as wheel loaders and forklifts are equipped with hydraulic systems that include a steering circuit for changing the direction of travel and a loading / unloading circuit for moving the bucket and forks.

[0003] For example, Patent Document 1 discloses a hydraulic system for a forklift truck in which a variable displacement steering pump is used in the steering circuit and a variable displacement cargo handling pump is used in the cargo handling circuit. In the steering circuit, hydraulic oil is supplied from the steering pump to the steering actuator via a steering supply line and a steering valve, and in the cargo handling circuit, hydraulic oil is supplied from the cargo handling pump to two cargo handling actuators via a cargo handling supply line and two cargo handling control valves.

[0004] Furthermore, in the hydraulic system disclosed in Patent Document 1, a merging line branches off from the steering supply line, and this merging line is connected to the cargo handling supply line. A switching valve is provided in the merging line. The switching valve shuts off the merging line when no cargo handling operations are being performed and opens the merging line when a cargo handling operation is being performed. In other words, when the switching valve opens the merging line, the hydraulic oil discharged from the cargo handling pump is merged with the hydraulic oil discharged from the steering pump and supplied to the cargo handling actuator. Note that when a cargo handling operation is performed simultaneously with a steering operation, the hydraulic oil discharged from the steering pump is supplied to both the steering actuator and the cargo handling actuator.

[0005] The displacement of the steering pump is changed by a steering regulator, and the displacement of the cargo pump is changed by a cargo regulator. As described above, from the viewpoint of merging the hydraulic oil discharged from the steering pump with the hydraulic oil discharged from the cargo pump, the displacement of the steering pump and the displacement of the cargo pump are controlled by the same method. In Patent Document 1, load sensing control is adopted as the control method.

[0006] More specifically, the maximum load pressure, which is the higher of the load pressures of the two cargo actuators, is input to the cargo regulator as the load sensing pressure. The cargo regulator controls the displacement of the cargo pump so that the differential pressure between the load sensing pressure and the discharge pressure of the cargo pump is constant.

[0007] Meanwhile, the steering regulator receives the higher of the load pressure of the steering actuator or the maximum load pressure of the cargo handling actuator as the load sensing pressure. The steering regulator controls the displacement of the steering pump so that the differential pressure between the load sensing pressure and the steering pump discharge pressure remains constant. Therefore, when steering and cargo handling operations are performed simultaneously, the displacement of the steering pump changes depending on which is the higher demand. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2017-226492 Summary of the Invention [Problem to be solved by the invention]

[0009] However, there is a demand for a positive control system for controlling the capacity of the cargo handling pump, which increases the capacity as the amount of cargo handling operation increases, instead of load sensing control. However, in this case, the problem arises as to how to control the capacity of the steering pump.

[0010] Therefore, an object of the present disclosure is to provide a hydraulic system for an industrial vehicle that can control the displacement of a cargo pump through positive control and also appropriately control the displacement of a steering pump. [Means for solving the problem]

[0011] The present disclosure provides a hydraulic system for an industrial vehicle, comprising: a variable displacement steering pump that supplies hydraulic oil to a steering actuator via a steering supply line and a steering valve; a variable displacement cargo handling pump that supplies hydraulic oil to at least one cargo handling actuator via a cargo handling supply line and at least one cargo handling control valve; a merging line that branches off from the steering supply line and connects to the cargo handling supply line; a priority valve that is provided in the merging line and that blocks the merging line when a cargo handling operation is not being performed and opens the merging line when a cargo handling operation is being performed; a cargo handling regulator that receives as input a cargo handling demand command pressure that is positively correlated with the amount of cargo handling operation, and that increases the capacity of the cargo handling pump as the cargo handling demand command pressure increases; and a steering regulator that receives as input as a signal pressure either the steering demand command pressure that is negatively correlated with the differential pressure upstream and downstream of a throttle section in the steering valve that determines the amount of hydraulic oil to be supplied to the steering actuator, or the cargo handling demand command pressure, and that increases the capacity of the steering pump as the signal pressure increases. [Effects of the Invention]

[0012] According to the present disclosure, the displacement of the cargo pump can be controlled by positive control, and the displacement of the steering pump can also be appropriately controlled. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic configuration diagram of a hydraulic system of an industrial vehicle according to an embodiment; [Figure 2] FIG. 2 is an enlarged view of a steering circuit of the hydraulic system. [Figure 3]FIG. 2 is an enlarged view of a loading / unloading circuit of the hydraulic system. [Figure 4] FIG. 2 is a circuit diagram of an operation system of the cargo handling circuit. [Figure 5] 10 is a graph showing the relationship between the operation amount of a cargo handling operation and a cargo handling request command pressure. [Figure 6] 4 is a graph showing the relationship between the differential pressure between the upstream side and the downstream side of a throttle portion in the steering valve and the steering demand command pressure. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1 shows a hydraulic system 1 for an industrial vehicle according to one embodiment. In this embodiment, the industrial vehicle is a wheel loader including a hoist (also called an arm or boom) and a bucket. However, the industrial vehicle may also be a forklift or the like.

[0015] The hydraulic system 1 includes a steering circuit 2 for changing the direction of travel and a loading / unloading circuit 3 for moving the bucket. In a wheel loader, a front body including the front wheels and a rear body including the rear wheels are connected so that they can swing horizontally. A hoist is connected to the front body so that it can swing vertically, and a bucket is connected to the tip of the hoist so that it can swing vertically.

[0016] 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 hydraulic oil to the steering actuator 11 via a steering supply line 22 and the steering valve 23. The steering actuator 11 is composed of a pair of hydraulic cylinders provided on both the left and right sides of the connection between the front and rear vehicle bodies described above. Note that if the industrial vehicle is a forklift, the steering actuator 11 is composed of a single double-rod hydraulic cylinder.

[0017] Specifically, the steering pump 21 is connected to a steering valve 23 by a steering supply line 22, and the steering valve 23 is connected to the steering actuator 11 by a pair of supply and discharge lines 24. In addition, the steering valve 23 is connected to a tank by a tank line 25.

[0018] The steering valve 23 has a throttle portion 23a that determines the amount of hydraulic oil supplied to the steering actuator 11. The steering valve 23 is also connected to both ends of an intermediate line 27 that is interposed between the steering supply line 22 and the supply / discharge line 24. A check valve 28 is provided in the intermediate line 27.

[0019] When a steering wheel provided in the driver's cab of the industrial vehicle is operated, the steering valve 23 shifts from a neutral position to a right-turn position or a left-turn position. In the neutral position, the steering supply line 22, both ends of the intermediate line 27, the pair of supply and discharge lines 24, and the tank line 25 are all blocked. In the right-turn position or the left-turn position, the steering supply line 22 communicates with one of the supply and discharge lines 24 via the intermediate line 27, and the other supply and discharge line 24 communicates with the tank line 25. In the right-turn position or the left-turn position, the opening area of the throttle portion 23a increases as the amount of operation of the steering wheel increases.

[0020] More specifically, the steering valve 23 has a pair of pilot ports, which are connected to the Orbitroll (registered trademark) 26 by pilot lines 26a and 26b. The Orbitroll 26 is connected to the steering wheel, and outputs a pilot pressure corresponding to the amount of operation of the steering wheel to the pilot port of the steering valve 23 through the pilot line 26a or 26b in the rotational direction of the steering wheel.

[0021] Furthermore, a load pressure line 64 and a tank line 68 are also connected to the steering valve 23. 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 in the right turn position or the left turn position, the pressure downstream of the throttle portion 23a is introduced into the load pressure line 64.

[0022] A compensator 61 is provided in the steering supply line 22. The compensator 61 opens the steering supply line 22 when in a neutral position, and the opening area of the compensator 61 decreases as the compensator 61 shifts from the neutral position. Pressures on the upstream side and downstream side of the throttle portion 23a of the steering valve 23 act on the compensator 61 in a manner opposing each other.

[0023] The pressure downstream of the throttle portion 23a in the steering valve 23 is led to the compensator 61 through the load pressure line 64 described above, and acts on the compensator 61 so as to shift the opening area in an increasing direction. On the other hand, the pressure upstream of the throttle portion 23a in the steering valve 23 is led to the compensator 61 through the supply pressure line 62, and acts on the compensator 61 so as to shift the opening area in a decreasing direction. The supply pressure line 62 branches off from the steering supply line 22 downstream of the compensator 61. In this embodiment, throttles 63, 65 are provided in the supply pressure line 62 and the load pressure line 64, respectively, but the throttles 63, 65 may be omitted.

[0024] With this configuration, the opening area of the compensator 61 decreases as the differential pressure between the upstream and downstream sides of the throttle portion 23a in the steering valve 23 increases. A relief line 66 branches off from the load pressure line 64, and a relief valve 67 provided in this relief line 66 keeps the pressure in the load pressure line 64 below a predetermined value.

[0025] The steering pump 21 is driven by a prime mover, which may be an internal combustion engine or an electric motor, and also drives a cargo pump 31 and an auxiliary pump 15, which will be described later.

[0026] The steering pump 21 is a variable displacement pump. In this embodiment, the steering pump 21 is a swash plate pump having a swash plate 21a. However, the steering pump 21 may also be a bent-axis pump. Although not shown, a relief line branches off from the steering supply line 22 or a joining line 71 (described later) upstream of a priority valve 72, and a relief valve provided in this relief line keeps the discharge pressure of the steering pump 21 at or below a predetermined value.

[0027] The capacity of the steering pump 21 is changed by the steering regulator 4. In this embodiment, the steering regulator 4 performs flow rate control using a flow rate control piston 46 and horsepower control using a horsepower control piston 47. However, the steering regulator 4 may perform only flow rate control.

[0028] A signal pressure is input to the steering regulator 4 for flow rate control. The steering regulator 4 increases the capacity of the steering pump 21 as the signal pressure increases. In this 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 changed as appropriate.

[0029] More specifically, the steering regulator 4 includes a servo piston 41 connected to the swash plate 21a of the steering pump 21, in addition to a flow rate control piston 46 and a horsepower control piston 47, and an adjustment valve 42 for driving the servo piston 41. The steering regulator 4 also includes a housing that slidably holds the flow rate control piston 46, the horsepower control piston 47, and the servo piston 41. A part of the housing may be integrated with the casing of the steering pump 21.

[0030] The steering regulator 4 is formed with a first pressure receiving chamber 4a to which the discharge pressure of the steering pump 21 is introduced and a second pressure receiving chamber 4b to which the control pressure is introduced. The servo piston 41 has a first end exposed to the first pressure receiving chamber 4a and a second end exposed to the second pressure receiving chamber 4b and having a larger diameter than the first end.

[0031] The adjusting valve 42 adjusts the control pressure introduced into the second pressure-receiving chamber 4b. Specifically, the adjusting valve 42 includes a spool 43 that moves in a direction to decrease the control pressure (a direction to increase the capacity, leftward in FIG. 2) and a direction to increase the control pressure (a direction to decrease the capacity, rightward in FIG. 2), and a sleeve 44 that accommodates the spool 43.

[0032] The spool 43 is connected to the flow rate control piston 46 via a lever 46a, and is connected to the power control piston 47 via a lever 47a. The spool 43 moves in the direction of increasing capacity as the flow rate control piston 46 advances, and moves in the direction of decreasing capacity as the flow rate control piston 46 moves backward. The spool 43 also moves in the direction of decreasing capacity as the power control piston 47 advances, and moves in the direction of increasing capacity as the flow rate control piston 46 moves backward. The flow rate control piston 46 and the power control piston 47 are configured so that whichever piston limits the capacity to a small value (i.e., whichever piston commands a small capacity) has priority in moving the spool 43. This configuration is a well-known technique, so a detailed description will be omitted.

[0033] The sleeve 44 is connected to the servo piston 41 by a feedback lever 45. A pump port, a tank port, and an output port (the output port communicates with the second pressure receiving chamber 4b) are formed in the sleeve 44, and depending on the relative position of the sleeve 44 and the spool 43, the output port is either blocked from both the pump port and the tank port, or the output port is communicated with either the pump port or the tank port. When the spool 43 is moved in the direction of increasing or decreasing the capacity, the relative position of the spool 43 and the sleeve 44 is determined so that the forces acting from both sides of the servo piston 41 (pressure × servo piston pressure receiving area) are balanced, and the control pressure is adjusted.

[0034] Furthermore, the steering regulator 4 is formed with an operating chamber 4c that applies the above-mentioned signal pressure to the flow control piston 46. In other words, the flow control piston 46 moves forward when the signal pressure increases, and moves backward when the signal pressure decreases.

[0035] The steering regulator 4 also has an operating chamber 4d that applies the discharge pressure of the steering pump 21 to the horsepower control piston 47. That is, the horsepower control piston 47 moves forward when the discharge pressure of the steering pump 21 increases, and moves backward when the discharge pressure decreases.

[0036] 3, the cargo handling circuit 3 includes a cargo handling pump 31, two cargo handling control valves 33, and two cargo handling actuators 12. The cargo handling pump 31 supplies hydraulic oil to the two cargo handling actuators 12 via a cargo handling supply line 32 and the two cargo handling control valves 33.

[0037] The two cargo handling actuators 12 are a bucket actuator 13 and a hoist actuator 14. The bucket actuator 13 is composed of a single hydraulic cylinder, and the hoist actuator 14 is composed of a pair of hydraulic cylinders. The two cargo handling control valves 33 are a bucket control valve 34 and a hoist control valve 35.

[0038] Specifically, the cargo handling pump 31 is connected to the bucket control valve 34 and the hoist control valve 35 by a cargo handling supply line 32. That is, the cargo handling supply line 32 includes a common path 32a extending from the cargo handling pump 31, a bucket branch path 32b extending from the downstream end of the common path 32a to the bucket control valve 34, and a hoist branch path 32c extending from the downstream end of the common path 32a to the hoist control valve 35. Check valves 32d and 32e are provided in the bucket branch path 32b and the hoist branch path 32c, respectively.

[0039] Furthermore, the hoist branch passage 32c is provided with a bucket priority valve 32f for limiting the supply of hydraulic oil to the hoist actuator 14 when bucket operation and hoist operation are performed simultaneously. The bucket priority valve 32f opens the hoist branch passage 32c in the neutral position, and the opening area of the bucket priority valve 32f decreases as the bucket priority valve 32f shifts from the neutral position. In this embodiment, the bucket priority valve 32f is pilot-operated 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 also be electromagnetic.

[0040] The bucket control valve 34 is connected to the bucket actuator 13 by a pair of supply and discharge lines 36, and the hoist control valve 35 is connected to the hoist actuator 14 by a pair of supply and discharge lines 37. In addition, the bucket control valve 34 and the hoist control valve 35 are connected to a tank by a tank line 38.

[0041] The bucket control valve 34 shifts from a neutral position to a first operating position or a second operating position. In the neutral position, the cargo 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 cargo supply line 32 communicates with one of the supply and discharge lines 36, and the other supply and discharge line 36 communicates with the tank line 38.

[0042] In this embodiment, the bucket control valve 34 is pilot-operated and has a pair of pilot ports. When pilot pressure is introduced to one of the pilot ports, the bucket control valve 34 shifts from the neutral position to the first operating position, and the opening area of the bucket control valve 34 increases as the pilot pressure increases. Conversely, when pilot pressure is introduced to the other pilot port, the bucket control valve 34 shifts from the neutral position to the second operating position, and the opening area of the bucket control valve 34 increases as the pilot pressure increases. However, the bucket control valve 34 may be electromagnetic.

[0043] The hoist control valve 35 shifts from a neutral position to a first operating position or a second operating position. The hoist control valve 35 also shifts between the second operating position and a third operating position. In the neutral position, the cargo 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 cargo supply line 32 communicates with one of the supply and discharge lines 37, and the other supply and 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 hoist control valve 35.

[0044] In this embodiment, the hoist control valve 35 is pilot-operated and has a pair of pilot ports. When pilot pressure is introduced into one of the pilot ports, the hoist control valve 35 shifts from the neutral position to the first operating position, and the opening area of the hoist control valve 35 increases as the pilot pressure increases. Conversely, when pilot pressure is introduced into the other pilot port, the hoist control valve 35 shifts from the neutral position to the second operating position, and the opening area of the hoist control valve 35 increases as the pilot pressure increases. When the pilot pressure introduced into the other pilot port further increases, the hoist control valve 35 shifts from the second operating position to the third operating position. However, the hoist control valve 35 may be electromagnetic.

[0045] Furthermore, in this embodiment, a center bypass line 39 branches off from the common path 32a of the cargo supply line 32, and this center bypass line 39 passes through the bucket control valve 34 and the hoist control valve 35 and extends to the tank. The bucket control valve 34 and the hoist control valve 35 reduce the opening area of the center bypass line 39 as they shift from the neutral position to the first operating position or the second operating position.

[0046] As shown in Fig. 4, the pilot port of bucket control valve 34 is connected to a pair of bucket electromagnetic proportional valves 94, 95 by a pair of pilot lines, and the pilot port of hoist control valve 35 is connected to a pair of hoist electromagnetic proportional valves 96, 97 by a pair of pilot lines. Bucket electromagnetic proportional valves 94, 95 and hoist electromagnetic proportional valves 96, 97 are connected to auxiliary pump 15 (see Fig. 1) by primary pressure line 16. Although not shown, a relief line branches off from primary pressure line 16, and the discharge pressure of auxiliary pump 15 is maintained at a predetermined value by a relief valve provided in this relief line.

[0047] In this embodiment, each of the bucket electromagnetic proportional valves 94, 95 and the hoist electromagnetic proportional valves 96, 97 is a direct proportional type in which the command current and the secondary pressure show a positive correlation. However, each of the bucket electromagnetic proportional valves 94, 95 and the hoist electromagnetic proportional valves 96, 97 may also be an inverse proportional type in which the command current and the secondary pressure show a negative correlation.

[0048] Returning to Figure 3, in addition to the handles described above, the driver's cab of the industrial vehicle is provided with a bucket operating device 92 and a hoist operating device 93. The bucket operating device 92 includes an operating lever for operating the bucket, and the hoist operating device 93 includes an operating lever for operating the hoist.

[0049] In this embodiment, bucket operating device 92 and hoist operating device 93 are each electric joysticks that output electric signals according to the tilt direction and tilt angle of the operating lever (i.e., the operation amount of bucket operation or hoist operation). The electric signals output from bucket operating device 92 and hoist operating device 93 are input to control device 91.

[0050] However, bucket operation device 92 and hoist operation device 93 may each be a pilot-operated valve that outputs a pilot pressure according to the tilt direction and tilt angle of the operation lever. In this case, bucket electromagnetic proportional valves 94, 95 and hoist electromagnetic proportional valves 96, 97 may be omitted, and the pilot port of bucket control valve 34 may be connected to bucket operation device 92, which is a pilot-operated valve, by a pair of pilot lines, and the pilot port of hoist control valve 35 may be connected to hoist operation device 93, which is a pilot-operated valve, by a pair of pilot lines.

[0051] When the operating lever of bucket operating device 92 is subjected to bucket operation, control device 91 sends a command current to bucket electromagnetic proportional valve 94 or 95 that corresponds to the tilting direction of the operating lever. Furthermore, control device 91 increases the command current as the amount of bucket operation increases. Note that the secondary pressure output from one bucket electromagnetic proportional valve 94 (the one that swings the bucket upward) is also introduced to the pilot port of bucket priority valve 32f described above, as shown in FIG. 4.

[0052] Similarly, when the operating lever of the hoist operating device 93 is subjected to a hoist operation, the control device 91 supplies a command current to the hoist electromagnetic proportional valve 96 or 97 corresponding to the tilting direction of the operating lever. Also, the control device 91 increases the command current as the amount of hoist operation increases.

[0053] With respect to the controller 91, the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, application-specific integrated circuits (ASICs), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where the hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor.

[0054] The cargo pump 31 described above is a variable displacement pump. In this embodiment, the cargo pump 31 is a swash plate pump having a swash plate 31a. However, the cargo pump 31 may also be a bent-axis pump. Although not shown, a relief line branches off from the cargo supply line 32, and a relief valve provided in this relief line keeps the discharge pressure of the cargo pump 31 at or below a predetermined value.

[0055] The capacity of the cargo pump 31 is changed by the cargo regulator 5. In this embodiment, the cargo regulator 5 performs flow rate control using a flow rate control piston 56 and horsepower control using a horsepower control piston 57. However, the cargo regulator 5 may perform only flow rate control.

[0056] A cargo handling demand command pressure is input to the cargo handling regulator 5 for flow rate control. The cargo handling demand command pressure will be described in detail later. The cargo handling regulator 5 increases the capacity of the cargo handling pump 31 as the cargo handling demand command pressure increases. In this embodiment, the cargo handling regulator 5 is configured as shown in FIG. 3, but the configuration of the cargo handling regulator 5 is not limited to this and can be changed as appropriate.

[0057] More specifically, the cargo regulator 5 includes a servo piston 51 connected to the swash plate 31a of the cargo pump 31, in addition to a flow rate control piston 56 and a horsepower control piston 57, and an adjustment valve 52 for driving the servo piston 51. The cargo regulator 5 also includes a housing that slidably holds the flow rate control piston 56, the horsepower control piston 57, and the servo piston 51. A part of the housing may be integrated with the casing of the cargo pump 31.

[0058] The cargo handling regulator 5 is formed with a first pressure receiving chamber 5a to which the discharge pressure of the cargo handling pump 31 is introduced, and a second pressure receiving chamber 5b to which the control pressure is introduced. The servo piston 51 has a first end exposed to the first pressure receiving chamber 5a, and a second end exposed to the second pressure receiving chamber 5b and having a larger diameter than the first end.

[0059] The adjusting valve 52 adjusts the control pressure introduced into the second pressure-receiving chamber 5b. Specifically, the adjusting valve 52 includes a spool 53 that moves in a direction to decrease the control pressure (a direction to increase the capacity, leftward in FIG. 3) and a direction to increase the control pressure (a direction to decrease the capacity, rightward in FIG. 3), and a sleeve 54 that accommodates the spool 53.

[0060] The spool 53 is connected to the flow rate control piston 56 via a lever 56a, and is connected to the power control piston 57 via a lever 57a. The spool 53 moves in the direction of increasing capacity as the flow rate control piston 56 advances, and moves in the direction of decreasing capacity as the flow rate control piston 56 moves backward. The spool 53 also moves in the direction of decreasing capacity as the power control piston 57 advances, and moves in the direction of increasing capacity as the flow rate control piston 56 moves backward. The flow rate control piston 56 and the power control piston 57 are configured so that whichever piston limits the capacity to a smaller value (i.e., whichever piston commands a smaller capacity) has priority in moving the spool 53.

[0061] The sleeve 54 is connected to the servo piston 51 by a feedback lever 55. A pump port, a tank port, and an output port (the output port communicates with the second pressure receiving chamber 5b) are formed in the sleeve 54, and depending on the relative position of the sleeve 54 and the spool 53, the output port is either blocked from both the pump port and the tank port, or the output port is communicated with either the pump port or the tank port. When the spool 53 is moved in the direction of increasing or decreasing the capacity, the relative position of the spool 53 and the sleeve 54 is determined so that the forces acting from both sides of the servo piston 51 (pressure × servo piston pressure receiving area) are balanced, and the control pressure is adjusted.

[0062] Furthermore, the cargo handling regulator 5 is formed with an operating chamber 5c that applies the above-mentioned cargo handling demand command pressure to the flow rate control piston 56. That is, the flow rate control piston 56 moves forward when the cargo handling demand command pressure increases, and moves backward when the cargo handling demand command pressure decreases.

[0063] The cargo regulator 5 is also formed with an operating chamber 5d that applies the discharge pressure of the cargo pump 31 to the horsepower control piston 57. In other words, the horsepower control piston 57 moves forward when the discharge pressure of the cargo pump 31 increases, and moves backward when the discharge pressure decreases.

[0064] In this embodiment, the working chamber 5c is connected to a solenoid proportional valve 81 via a command pressure line 82. The solenoid proportional valve 81 is connected to the sub-pump 15 via the above-mentioned primary pressure line 16. In this embodiment, the solenoid proportional valve 81 is a direct proportional type in which the command current and the secondary pressure show a positive correlation. However, the solenoid proportional valve 81 may also be an inverse proportional type in which the command current and the secondary pressure show a negative correlation.

[0065] The electromagnetic proportional valve 81 is controlled by the above-mentioned control device 91, and outputs secondary pressure to the operating chamber 5c as a cargo handling request command pressure. When a cargo handling operation (bucket operation or hoist operation) is performed, the control device 91 supplies a command current to the electromagnetic proportional valve 81. Furthermore, the control device 91 increases the command current as the operation amount of the cargo handling operation increases. In other words, as shown in Figure 5, the cargo handling request command pressure shows a positive correlation with the operation amount of the cargo handling operation.

[0066] On the other hand, as shown in Fig. 2, the working chamber 4c of the steering regulator 4 is connected to the output port of the high-pressure selection valve 84 by a command pressure line 85. One of a pair of input ports of the high-pressure selection valve 84 is connected to the pressure reducing valve 75 by an input line 79, and the other is connected to the command pressure line 82 by an input line 83 (see Fig. 3). It should be noted that the input line 83 may be connected to the working chamber 5c of the cargo handling regulator 5 instead of the command pressure line 82. The pressure reducing valve 75 is connected to the auxiliary pump 15 by the above-mentioned primary pressure line 16.

[0067] The pressure reducing valve 75 is driven by the differential pressure between the upstream and downstream sides of the throttle section 23a in the steering valve 23, and outputs the secondary pressure as the steering demand command pressure so that the secondary pressure decreases as the differential pressure increases. In other words, as shown in Fig. 6, the steering demand command pressure shows a negative correlation with the differential pressure between the upstream and downstream sides of the throttle section 23a in the steering valve 23.

[0068] More specifically, the pressure reducing valve 75 includes a piston 76 for adjusting the secondary pressure. The pressure upstream of the throttle portion 23a and the pressure downstream of the throttle portion 23a act on the piston 76 so as to face each other. The pressure upstream of the throttle portion 23a is led to the piston 76 through a pilot line 78 branching off from the steering supply line 22, and the pressure downstream of the throttle portion 23a is led to the piston 76 through a pilot line 77 branching off from the load pressure line 64.

[0069] The high-pressure selection valve 84 selects the higher of the steering demand command pressure, which is the secondary pressure of the pressure reducing valve 75, and the cargo unloading demand command pressure, which is the secondary pressure of the electromagnetic proportional valve 81, and outputs it to the steering regulator 4. In other words, the higher of the steering demand command pressure and the cargo unloading demand command pressure is input to the steering regulator 4 as the above-mentioned signal pressure.

[0070] 1 to 3, a junction line 71 branches off from the steering supply line 22 upstream of the compensator 61, and this junction line 71 is connected to the cargo handling supply line 32. A priority valve 72 is provided in the junction line 71.

[0071] The priority valve 72 shuts off the merging line 71 when no loading / unloading operations are being performed, and opens the merging line 71 when loading / unloading operations are being performed. In this embodiment, the priority valve 72 is a pilot-operated valve having a first pilot port 72a and a second pilot port 72b. However, the priority valve 72 may also be an electromagnetic valve.

[0072] More specifically, the priority valve 72 shuts off the merging line 71 in a neutral position, and the opening area of the priority valve 72 increases as the priority valve 72 shifts from the neutral position. The priority valve 72 has a spring 72c (see FIG. 3) for maintaining the priority valve 72 in the neutral position. The first pilot port 72a shifts the priority valve 72 in a direction that decreases the opening area, and the second pilot port 72b shifts the priority valve 72 in a direction that increases the opening area.

[0073] A first pilot port 72a of the priority valve 72 is connected to an input line 79 via a pilot line 73, and a second pilot port 72b is connected to a command pressure line 82 via a pilot line 74. That is, a steering request command pressure is introduced to the first pilot port 72a via the pilot line 73, and a cargo operation request command pressure is introduced to the second pilot port 72b via the pilot line 74. Therefore, the steering request command pressure and the cargo operation request command pressure act on the priority valve 72 in opposing directions.

[0074] When the cargo handling request command pressure is smaller than a reference pressure obtained by adding a predetermined value (pressure corresponding to the biasing force of the spring 72c) to the steering request command pressure, the priority valve 72 shuts off the merging line 71. On the other hand, when the cargo handling request command pressure is larger than the reference pressure, the opening area of the priority valve 72 corresponds to the differential pressure between the cargo handling request command pressure and the reference pressure.

[0075] As described above, in the hydraulic system 1 of this embodiment, the cargo unloading demand command pressure, which has a positive correlation with the operation amount of the cargo unloading operation, is input to the cargo unloading regulator 5, so that the displacement of the cargo unloading pump 31 can be controlled by positive control. On the other hand, the steering regulator 4 receives the higher of the steering demand command pressure and the cargo unloading demand command pressure, which have a negative correlation with the differential pressure upstream and downstream of the throttle section 23a of the steering valve 23. When a steering operation is performed alone, the steering demand command pressure is input to the steering regulator 4, so that the displacement of the steering pump 21 can be increased as the differential pressure upstream and downstream of the throttle section 23a of the steering valve 23 decreases. Furthermore, when a steering operation and a cargo unloading operation are performed simultaneously, the displacement of the steering pump 21 changes depending on which of the two is higher. Therefore, the displacement of the steering pump 21 can be appropriately controlled.

[0076] Moreover, in this embodiment, a pressure reducing valve 75 is used that is driven by the pressure difference between the upstream and downstream sides of the throttling section 23a in the steering valve 23, so the pressure reducing valve 75 can convert the pressure difference between the upstream and downstream sides of the throttling section 23a in the steering valve 23 into a steering request command pressure.

[0077] In addition, in this embodiment, a compensator 61 is provided in the steering supply line 22 downstream of the position where the merging line 71 branches off, so that the flow rate of hydraulic oil supplied to the steering actuator 11 can be adjusted to the required flow rate by the compensator 61, and excess hydraulic oil can be guided to the cargo handling supply line 32 through the merging line 71.

[0078] Furthermore, in this embodiment, the priority valve 72 provided in the merging line 71 is a pilot type, so it is possible to mechanically operate the priority valve 72. Moreover, by changing the opening area of the priority valve 72, it is possible to supply the hydraulic oil discharged from the steering pump 21 to the steering actuator 11 with priority.

[0079] (Variation) The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present disclosure.

[0080] For example, depending on the type of industrial vehicle, the number of cargo handling actuators 12 and the number of cargo handling control valves 33 in the cargo handling circuit 3 of the hydraulic system 1 may be one, or three or more.

[0081] Furthermore, when the bucket operating device 92 and the hoist operating device 93 are each a pilot-operated valve, the electromagnetic proportional valve 81 may be omitted, and the highest pilot pressure out of the pilot pressure output from the bucket operating device 92 and the pilot pressure output from the hoist operating device 93 may be led to the operating chamber 5c of the cargo handling regulator 5 and the high-pressure selection valve 84 as the cargo handling request command pressure.

[0082] Moreover, the priority valve 72 may be a simple switching valve.

[0083] (summary) The present disclosure provides a hydraulic system for an industrial vehicle, comprising: a variable displacement steering pump that supplies hydraulic oil to a steering actuator via a steering supply line and a steering valve; a variable displacement cargo handling pump that supplies hydraulic oil to at least one cargo handling actuator via a cargo handling supply line and at least one cargo handling control valve; a merging line that branches off from the steering supply line and connects to the cargo handling supply line; a priority valve that is provided in the merging line and that blocks the merging line when a cargo handling operation is not being performed and opens the merging line when a cargo handling operation is being performed; a cargo handling regulator that receives as input a cargo handling demand command pressure that is positively correlated with the amount of cargo handling operation, and that increases the capacity of the cargo handling pump as the cargo handling demand command pressure increases; and a steering regulator that receives as input as a signal pressure either the steering demand command pressure that is negatively correlated with the differential pressure upstream and downstream of a throttle section in the steering valve that determines the amount of hydraulic oil to be supplied to the steering actuator, or the cargo handling demand command pressure, and that increases the capacity of the steering pump as the signal pressure increases.

[0084] According to the above configuration, the cargo handling regulator receives a cargo handling demand command pressure that is positively correlated with the amount of cargo handling operation, allowing the displacement of the cargo handling pump to be controlled by positive control. Meanwhile, the steering regulator receives the higher of the steering demand command pressure and the cargo handling demand command pressure, which are negatively correlated with the pressure difference between the upstream and downstream sides of the throttle in the steering valve. When a steering operation is performed alone, the steering demand command pressure is input to the steering regulator, allowing the displacement of the steering pump to be increased as the pressure difference between the upstream and downstream sides of the throttle in the steering valve decreases. Furthermore, when a steering operation and a cargo handling operation are performed simultaneously, the displacement of the steering pump changes depending on which of the two is higher. Therefore, the displacement of the steering pump can be appropriately controlled.

[0085] The hydraulic system may further include a pressure reducing valve that is driven by a pressure difference between the upstream side and the downstream side of the throttle portion in the steering valve and outputs a secondary pressure as the steering demand command pressure so that the secondary pressure decreases as the pressure difference increases, and a high-pressure selection valve that selects the higher of the steering demand command pressure and the cargo handling demand command pressure and outputs the selected pressure to the steering regulator. According to this configuration, the pressure difference between the upstream side and the downstream side of the throttle portion in the steering valve can be converted into the steering demand command pressure by the pressure reducing valve.

[0086] The hydraulic system may further include a compensator provided in the steering supply line downstream of the branching position of the merging line, the compensator having an opening area that decreases as the differential pressure between the upstream and downstream sides of the throttle section in the steering valve increases. With this configuration, the supply flow rate of hydraulic oil to the steering actuator can be adjusted to a required flow rate by the compensator, and excess hydraulic oil can be guided to the cargo supply line through the merging line.

[0087] The priority valve may have a first pilot port to which the steering demand command pressure is introduced and a second pilot port to which the cargo unloading demand command pressure is introduced, and may shut off the merging line when the cargo unloading demand command pressure is smaller than a reference pressure obtained by adding a predetermined value to the steering demand command pressure, and may have an opening area corresponding to a pressure difference between the cargo unloading demand command pressure and the reference pressure when the cargo unloading demand command pressure is larger than the reference pressure. With this configuration, the priority valve can be mechanically operated. Moreover, by changing the opening area of the priority valve, hydraulic oil discharged from the steering pump can be preferentially supplied to the steering actuator. [Explanation of symbols]

[0088] 1 Hydraulic system 11 Steering actuator 12 Loading actuator 2 Steering Circuit 21 Steering pump 22 Steering supply line 23 Steering valve 23a Constriction section 3. Loading and unloading circuit 31 Loading pump 32 Cargo Handling Supply Line 33 Loading control valve 4 Steering regulator 5. Loading regulator 71 Merging Line 72 Priority valve 72a No. 1 pilot port 72b Second pilot port 75 Pressure reducing valve 84 High pressure selection valve

Claims

1. a variable displacement steering pump that supplies hydraulic fluid to a steering actuator via a steering supply line and a steering valve; a variable displacement cargo pump supplying hydraulic fluid to at least one cargo actuator via a cargo supply line and at least one cargo control valve; a junction line branching from the steering supply line and connecting to the cargo handling supply line; a priority valve provided in the merging line, which shuts off the merging line when no loading / unloading operation is being performed and opens the merging line when a loading / unloading operation is being performed; a cargo handling regulator that receives a cargo handling demand command pressure that is positively correlated with the operation amount of the cargo handling operation, and increases the capacity of the cargo handling pump as the cargo handling demand command pressure increases; a steering regulator that receives as input as a signal pressure one of a steering demand command pressure that shows a negative correlation with a differential pressure between an upstream side and a downstream side of a throttle portion that determines the amount of hydraulic oil supplied to the steering actuator in the steering valve and the cargo handling demand command pressure, and that increases the capacity of the steering pump as the signal pressure increases; A hydraulic system for an industrial vehicle.

2. a pressure reducing valve that is driven by a pressure difference between the upstream side and the downstream side of the throttle portion in the steering valve, and outputs a secondary pressure as the steering request command pressure so that the secondary pressure decreases as the pressure difference increases; 2. The hydraulic system for an industrial vehicle according to claim 1, further comprising a high-pressure selection valve that selects the higher of the steering demand command pressure and the cargo handling demand command pressure and outputs the selected pressure to the steering regulator.

3. 2. The hydraulic system for an industrial vehicle according to claim 1, further comprising a compensator provided in the steering supply line downstream of the position where the merging line branches, the compensator having an opening area that decreases as the pressure difference between the upstream side and the downstream side of the throttle portion in the steering valve increases.

4. 4. The hydraulic system for an industrial vehicle according to claim 1, wherein the priority valve has a first pilot port to which the steering request command pressure is introduced and a second pilot port to which the cargo unloading request command pressure is introduced, and when the cargo unloading request command pressure is smaller than a reference pressure obtained by adding a predetermined value to the steering request command pressure, the priority valve blocks the merging line, and when the cargo unloading request command pressure is larger than the reference pressure, the priority valve has an opening area corresponding to a pressure difference between the cargo unloading request command pressure and the reference pressure.

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