Hydraulic system of an industrial vehicle

Abstract

The hydraulic system (1) includes: a variable capacity type steering pump (21) that supplies working fluid to a steering actuator (11); a variable capacity type loading / unloading pump (31) that supplies working fluid to at least one loading / unloading actuator (12); a merging line (71) that branches from a steering supply line (22) and is connected to a loading / unloading supply line (32); and a priority valve (72) provided in the merging line (71). Furthermore, the hydraulic system (1) includes: a loading / unloading regulator (5) that inputs a loading / unloading demand command pressure, and the greater the loading / unloading demand command pressure, the greater the capacity of the loading / unloading pump (31) is increased; and a steering regulator (4) that inputs the higher one of a steering demand command pressure and the loading / unloading demand command pressure as a signal pressure, and the greater the signal pressure, the greater the capacity of the steering pump (21) is increased.

Description

Technical Field

[0001] This disclosure relates to hydraulic systems for industrial vehicles. Background Technology

[0002] Industrial vehicles such as wheel loaders and forklifts are equipped with hydraulic systems, which include steering circuits for changing the direction of travel and loading / unloading circuits for moving the bucket and forklift.

[0003] For example, Patent Document 1 discloses a hydraulic system for a forklift that uses a variable-capacity steering pump in the steering circuit and a variable-capacity cargo pump in the loading / unloading circuit. In the steering circuit, working fluid is supplied from the steering pump to the steering actuator via a steering supply line and a steering valve. In the loading / unloading circuit, working fluid is supplied from the cargo pump to two loading / unloading actuators via a loading / unloading supply line and two loading / unloading control valves.

[0004] Furthermore, in the hydraulic system disclosed in Patent Document 1, a merging line branches off from the steering supply line and is connected to the loading / unloading supply line. A switching valve is provided on the merging line. The switching valve blocks the merging line when no loading / unloading operation is performed and opens the merging line when a loading / unloading operation is performed. That is, when the merging line is released through the switching valve, the working fluid discharged from the loading / unloading pump and the working fluid discharged from the steering pump merge and are supplied to the loading / unloading actuator. Additionally, when loading / unloading and steering operations are performed simultaneously, the working fluid discharged from the steering pump is supplied to both the steering actuator and the loading / unloading actuator.

[0005] The capacity of the steering pump is changed by the steering regulator, and the capacity of the loading / unloading pump is changed by the loading / unloading regulator. From the perspective of merging the working fluid discharged from the loading / unloading pump with the working fluid discharged from the steering pump, as described above, the capacities of the steering pump and the loading / unloading pump are controlled in the same way. Patent Document 1 uses load sensing control as its control method.

[0006] More specifically, the higher of the load pressures of the two loading / unloading actuators, i.e., the highest load pressure, is input into the loading / unloading regulator as the load sensing pressure. The loading / unloading regulator controls the capacity of the loading / unloading pump by making the pressure difference between the load sensing pressure and the discharge pressure of the loading / unloading pump a constant.

[0007] On the other hand, the higher of the load pressure of the steering actuator and the maximum load pressure of the loading / unloading actuator is input into the steering adjuster as the load sensing pressure. The steering adjuster controls the capacity of the steering pump by making the pressure difference between the load sensing pressure and the discharge pressure of the steering pump constant. Therefore, when steering and loading / unloading operations are performed simultaneously, the capacity of the steering pump is changed according to the higher requirement.

[0008] Existing technical documents:

[0009] Patent documents:

[0010] Patent document 1: Japanese Patent Application Publication No. 2017-226492. Summary of the Invention

[0011] The problem the invention aims to solve:

[0012] However, as a method for controlling the capacity of the loading and unloading pump, it would be desirable to use positive control, where the capacity increases with the magnitude of the loading and unloading operation, instead of load-sensing control. However, this raises the question of how to control the capacity of the steering pump.

[0013] Therefore, the purpose of this disclosure is to provide a hydraulic system for an industrial vehicle that can positively control the capacity of the loading and unloading pump and appropriately control the capacity of the steering pump.

[0014] Solution methods:

[0015] This disclosure provides a hydraulic system for an industrial vehicle, comprising: a variable-capacity steering pump that supplies working fluid to a steering actuator via a steering supply line and a steering valve; a variable-capacity loading / unloading pump that supplies working fluid to at least one loading / unloading actuator via a loading / unloading supply line and at least one loading / unloading control valve; a merging line that branches off from the steering supply line and connects to the loading / unloading supply line; a priority valve located on the merging line that blocks the merging line when no loading / unloading operation is performed and opens the merging line when a loading / unloading operation is performed; a loading / unloading demand command pressure that is positively correlated with the amount of operation of the loading / unloading operation, wherein the larger the loading / unloading demand command pressure, the greater the capacity of the loading / unloading pump; and a steering regulator that inputs the higher of the steering demand command pressure and the loading / unloading demand command pressure, which is negatively correlated with the pressure difference between the upstream and downstream sides of the throttling section in the steering valve that determines the amount of working fluid supplied to the steering actuator, wherein the larger the signal pressure, the greater the capacity of the steering pump.

[0016] Invention effects:

[0017] According to this disclosure, the capacity of the loading and unloading pump can be controlled in a positive control manner, and the capacity of the diverting pump can be appropriately controlled. Attached Figure Description

[0018] Figure 1 This is a schematic structural diagram of the hydraulic system of an industrial vehicle according to one embodiment.

[0019] Figure 2 This is an enlarged view of the steering circuit of the hydraulic system;

[0020] Figure 3 This is an enlarged view of the loading and unloading circuit of the hydraulic system.

[0021] Figure 4 This is the operating system circuit diagram of the loading and unloading circuit;

[0022] Figure 5 It is a graph showing the relationship between the amount of work involved in loading and unloading operations and the loading and unloading requirement command pressure;

[0023] Figure 6 It is a graph showing the relationship between the pressure difference between the upstream and downstream sides of the throttle section in the steering valve and the steering command pressure. Detailed Implementation

[0024] Figure 1 The hydraulic system 1 of an industrial vehicle according to one embodiment is shown. In this embodiment, the industrial vehicle is a wheeled loader including a hoist (also called a boom) and a bucket. However, the industrial vehicle may also be a forklift or the like.

[0025] 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 the wheel loader, the front side of the vehicle body, including the front wheels, and the rear side of the vehicle body, including the rear wheels, are horizontally swayingly connected. Furthermore, the hoist is vertically swayingly connected to the front side of the vehicle body, and the bucket is vertically swayingly connected to the tip of the hoist.

[0026] Steering circuit 2, for example Figure 2 As shown, the system includes a steering pump 21, a steering valve 23, and a steering actuator 11. The steering pump 21 supplies working fluid to the steering actuator 11 via the steering supply line 22 and the steering valve 23. The steering actuator 11 consists of a pair of hydraulic cylinders located on the left and right sides of the connection between the front and rear sides of the vehicle body. Alternatively, when the industrial vehicle is a forklift, the steering actuator 11 may consist of a single two-bar hydraulic cylinder.

[0027] Specifically, the steering pump 21 is connected to the steering valve 23 via the steering supply line 22, and the steering valve 23 is connected to the steering actuator 11 via a pair of supply and discharge lines 24. Furthermore, the steering valve 23 is connected to the tank via the tank line 25.

[0028] The steering valve 23 has a throttling section 23a that determines the amount of working fluid supplied to the steering actuator 11. Furthermore, the steering valve 23 is connected to both ends of an intermediate line 27 located between the steering supply line 22 and the supply discharge line 24. A check valve 28 is provided on the intermediate line 27.

[0029] When the steering valve 23, located in the cab of the industrial vehicle, is operated by the steering wheel, it shifts from the neutral position to a right-hand or left-hand 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 position, the steering supply line 22 connects to one of the supply discharge lines 24 via the intermediate line 27, and the other supply discharge line 24 connects to the tank line 25. In the right-hand or left-hand position, the opening area of ​​the throttling section 23a increases with the amount of steering wheel operation.

[0030] More specifically, the steering valve 23 has a pair of pilot ports connected to the steering unit (orbitrol; registered trademark) 26 via pilot lines 26a and 26b. The steering unit 26 is connected to the steering wheel, and a pilot pressure corresponding to the amount of steering wheel operation is output to the pilot ports of the steering valve 23 via pilot lines 26a or 26b in the direction of steering wheel rotation.

[0031] In addition, the directional valve 23 is also connected to the load pressure line 64 and the tank line 68. When the directional valve 23 is in the neutral position, the load pressure line 64 is connected to the tank line 68. When the directional valve 23 is in the right-hand or left-hand position, the pressure downstream of the throttling section 23a is introduced into the load pressure line 64.

[0032] A compensator 61 is provided on the steering supply line 22. The compensator 61 opens the steering supply line 22 in the neutral position, and the opening area of ​​the compensator 61 decreases as the compensator 61 moves from the neutral position. On the compensator 61, the upstream pressure and the downstream pressure of the throttling section 23a in the steering valve 23 act in opposite directions.

[0033] The pressure downstream of the throttling section 23a in the steering valve 23 is introduced to the compensator 61 through the aforementioned load pressure line 64, acting on the compensator 61 in a manner that shifts in the direction of increasing opening area. On the other hand, the pressure upstream of the throttling section 23a in the steering valve 23 is introduced to the compensator 61 through the supply pressure line 62, acting on the compensator 61 in a manner that shifts in the direction of decreasing opening area. The supply pressure line 62 branches off from the steering supply line 22 on the downstream side of the compensator 61. In this embodiment, throttles 63 and 65 are respectively provided on the supply pressure line 62 and the load pressure line 64, but throttles 63 and 65 may be omitted.

[0034] According to this structure, the opening area of ​​the compensator 61 decreases as the pressure difference between the upstream and downstream sides of the throttling section 23a in the steering valve 23 increases. Furthermore, the relief line 66 branches from the load pressure line 64, and the pressure of the load pressure line 64 is maintained below a specified value by a relief valve 67 located in the relief line 66.

[0035] The aforementioned 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 the loading / unloading pump 31 and the auxiliary pump 15, which will be described later.

[0036] The steering pump 21 is a variable capacity pump. In this embodiment, the steering pump 21 is a swashplate pump with a swashplate 21a. However, the steering pump 21 may also be a swashplate pump. Furthermore, although not shown in the figure, the overflow line branches off from the steering supply line 22 or the confluence line 71 described later, closer to the upstream side than the priority valve 72, and the overflow valve provided in this overflow line maintains the discharge pressure of the steering pump 21 below a predetermined value.

[0037] The capacity of the steering pump 21 is changed by the steering adjuster 4. In this embodiment, the steering adjuster 4 performs flow control using the flow control piston 46 and horsepower control using the horsepower control piston 47. However, the steering adjuster 4 may also perform only flow control.

[0038] The steering adjuster 4 receives an input signal pressure for flow control. In the steering adjuster 4, a higher signal pressure results in a higher capacity of the steering pump 21. In this embodiment, the steering adjuster 4... Figure 2 The structure shown is not limited to this, but the structure of the steering adjuster 4 can be modified as appropriate.

[0039] More specifically, in addition to the flow control piston 46 and the horsepower control piston 47, the steering adjuster 4 also includes a servo piston 41 connected to the swashplate 21a of the steering pump 21 and a regulating valve 42 for driving the servo piston 41. Furthermore, the steering adjuster 4 includes a housing that slidably holds the flow control piston 46, the horsepower control piston 47, and the servo piston 41. A portion of the housing can be integrally formed with the housing of the steering pump 21.

[0040] The steering adjuster 4 has a first pressure chamber 4a for introducing the discharge pressure of the steering pump 21 and a second pressure chamber 4b for introducing control pressure. The servo piston 41 has a first end exposed in the first pressure chamber 4a and a second end exposed in the second pressure chamber 4b, which has a larger diameter than the first end.

[0041] The regulating valve 42 is used to regulate the control pressure introduced into the second pressure chamber 4b. Specifically, the regulating valve 42 includes: a direction for reducing the control pressure (capacity increase direction), Figure 2 (From center to left) and the direction that causes the control pressure to rise (direction of capacity reduction), Figure 2 A valve core 43 that moves from center to right; and a sleeve 44 that accommodates the valve core 43.

[0042] The valve core 43 is connected to the flow control piston 46 via rod 46a and to the horsepower control piston 47 via rod 47a. As the flow control piston 46 advances, the valve core 43 moves in the direction of increasing capacity; as the flow control piston 46 retracts, it moves in the direction of decreasing capacity. Similarly, as the horsepower control piston 47 advances, the valve core 43 moves in the direction of decreasing capacity; as the flow control piston 46 retracts, it moves in the direction of increasing capacity. Furthermore, the flow control piston 46 and the horsepower control piston 47 are configured such that the one with the smaller capacity limitation (i.e., the one commanding less capacity) preferentially moves the valve core 43. This structure is known technology, therefore detailed description is omitted.

[0043] Sleeve 44 is connected to servo piston 41 via feedback rod 45. Sleeve 44 has a pump port, a tank port, and an output port (the output port communicates with the second pressure chamber 4b). Depending on the relative position of sleeve 44 and valve core 43, the output port may be blocked from both the pump port and the tank port, or connected to either the pump port or the tank port. Furthermore, when valve core 43 moves in the direction of increasing or decreasing capacity, the relative position of valve core 43 and sleeve 44 is determined by balancing the forces (pressure × servo piston pressure area) acting from both sides of servo piston 41, thereby adjusting the control pressure.

[0044] Furthermore, a working chamber 4c is formed on the steering adjuster 4 to apply the aforementioned signal pressure to the flow control piston 46. That is, the flow control piston 46 moves forward when the signal pressure is high and moves backward when the signal pressure is low.

[0045] Furthermore, a working chamber 4d is formed on the steering adjuster 4, which causes the output pressure of the steering pump 21 to act on the horsepower control piston 47. That is, the horsepower control piston 47 moves forward when the output pressure of the steering pump 21 is high and moves backward when the output pressure is low.

[0046] Loading and unloading circuit 3, etc. Figure 3 As shown, it includes a loading / unloading pump 31, two loading / unloading control valves 33, and two loading / unloading actuators 12. The loading / unloading pump 31 supplies working fluid to the two loading / unloading actuators 12 via the loading / unloading supply line 32 and the two loading / unloading control valves 33.

[0047] The two loading / unloading actuators 12 are a bucket actuator 13 and a lifting actuator 14. The bucket actuator 13 consists of a single hydraulic cylinder, and the lifting actuator 14 consists of a pair of hydraulic cylinders. The two loading / unloading control valves 33 are a bucket control valve 34 and a lifting control valve 35.

[0048] Specifically, the loading / unloading pump 31 is connected to the bucket control valve 34 and the lifting control valve 35 via the loading / unloading supply line 32. That is, the loading / unloading supply line 32 includes: a common passage 32a extending from the loading / unloading pump 31; a bucket branch passage 32b extending from the downstream end of the common passage 32a to the bucket control valve 34; and a lifting branch passage 32c extending from the downstream end of the common passage 32a to the lifting control valve 35. Check valves 32d and 32e are respectively installed on the bucket branch passage 32b and the lifting branch passage 32c.

[0049] Furthermore, a bucket priority valve 32f is provided on the lifting branch 32c, which is used to restrict the supply of working fluid to the lifting actuator 14 when bucket operation and lifting operation are performed simultaneously. The bucket priority valve 32f opens the lifting branch 32c in the neutral position, and its opening area decreases as it moves from the neutral position. In this embodiment, the bucket priority valve 32f is pilot-operated and has a pilot port. The higher the pilot pressure at the pilot port of the bucket priority valve 32f, the smaller its opening area. However, the bucket priority valve 32f could also be electromagnetic.

[0050] The aforementioned bucket control valve 34 is connected to the bucket actuator 13 via a pair of supply and discharge lines 36, and the lifting control valve 35 is connected to the lifting actuator 14 via a pair of supply and discharge lines 37. Furthermore, the bucket control valve 34 and the lifting control valve 35 are connected to the tank via tank lines 38.

[0051] The bucket control valve 34 shifts from the neutral position to either the first or second working position. In the neutral position, the loading / unloading supply line 32, the pair of supply discharge lines 36, and the tank line 38 are all blocked. In the first or second working position, the loading / unloading supply line 32 is connected to one of the supply discharge lines 36, and the other supply discharge line 36 is connected to the tank line 38.

[0052] In this embodiment, the bucket control valve 34 is pilot-operated and has a pair of pilot ports. When pilot pressure is introduced into one pilot port, the bucket control valve 34 shifts from a neutral position to a first working position; the higher the pilot pressure, the larger the opening area of ​​the bucket control valve 34. Conversely, when pilot pressure is introduced into the other pilot port, the bucket control valve 34 shifts from a neutral position to a second working position; the higher the pilot pressure, the larger the opening area of ​​the bucket control valve 34. However, the bucket control valve 34 can also be electromagnetic.

[0053] The lift control valve 35 shifts from the neutral position to either the first or second operating position. Furthermore, the lift control valve 35 shifts between the second and third operating positions. In the neutral position, the loading / unloading supply line 32, the pair of supply discharge lines 37, and the tank line 38 are all blocked. In the first or second operating position, the loading / unloading supply line 32 is connected to one of the supply discharge lines 37, and the other supply discharge line 37 is connected to the tank line 38. In the third operating position, the supply discharge lines 37 are interconnected within the lift control valve 35.

[0054] In this embodiment, the lift control valve 35 is pilot-operated and has a pair of pilot ports. When pilot pressure is introduced into one pilot port, the lift control valve 35 shifts from a neutral position to a first operating position; the higher the pilot pressure, the larger the opening area of ​​the lift control valve 35. Conversely, when pilot pressure is introduced into the other pilot port, the lift control valve 35 shifts from a neutral position to a second operating position; the higher the pilot pressure, the larger the opening area of ​​the lift control valve 35. When the pilot pressure introduced into the other pilot port further increases, the lift control valve 35 shifts from the second operating position to a third operating position. However, the lift control valve 35 can also be electromagnetic.

[0055] Furthermore, in this embodiment, a central bypass line 39 branches off from the common passage 32a of the loading / unloading supply line 32. This central bypass line 39 extends to the tank via a bucket control valve 34 and a lift control valve 35. The opening area on the central bypass line 39 decreases as the bucket control valve 34 and the lift control valve 35 shift from the neutral position to the first working position or the second working position.

[0056] like Figure 4 As shown, the pilot port of the bucket control valve 34 is connected to a pair of bucket solenoid proportional valves 94 and 95 via a pair of pilot lines, and the pilot port of the lifting control valve 35 is connected to a pair of lifting solenoid proportional valves 96 and 97 via a pair of pilot lines. The bucket solenoid proportional valves 94 and 95 and the lifting solenoid proportional valves 96 and 97 are connected to the auxiliary pump 15 (see reference) via the primary pressure line 16. Figure 1 (Connection). Additionally, although the diagram is omitted, an overflow line branches off from the primary pressure line 16, and an overflow valve located on this overflow line maintains the discharge pressure of the auxiliary pump 15 at a specified value.

[0057] In this embodiment, the solenoid proportional valves 94 and 95 for the bucket and the solenoid proportional valves 96 and 97 for the hoisting are positively proportional types, where the command current and secondary pressure are positively correlated. However, the solenoid proportional valves 94 and 95 for the bucket and the solenoid proportional valves 96 and 97 for the hoisting can also be inversely proportional types, where the command current and secondary pressure are negatively correlated.

[0058] return Figure 3In the cab of the industrial vehicle, in addition to the aforementioned steering wheel, a bucket operating device 92 and a lifting operating device 93 are also provided. The bucket operating device 92 includes an operating lever for bucket operation, and the lifting operating device 93 includes an operating lever for lifting operation.

[0059] In this embodiment, the bucket operating device 92 and the lifting operating device 93 are electric control levers that output electrical signals corresponding to the tilting direction and tilting angle (i.e., the amount of operation of the bucket operation or the lifting operation). The electrical signals output from the bucket operating device 92 and the lifting operating device 93 are input to the control device 91.

[0060] However, the bucket operating device 92 and the lifting operating device 93 can also be pilot operating valves that output pilot pressure corresponding to the tilting direction and tilting angle of the operating lever. In this case, the solenoid proportional valves 94 and 95 for the bucket and the solenoid proportional valves 96 and 97 for the lifting can be omitted. The pilot port of the bucket control valve 34 is connected to the bucket operating device 92, which serves as the pilot operating valve, through a pair of pilot lines, and the pilot port of the lifting control valve 35 is connected to the lifting operating device 93, which serves as the pilot operating valve, through a pair of pilot lines.

[0061] When the operating lever of the bucket operating device 92 is operated by the bucket, the control device 91 sends a command current to the bucket solenoid proportional valve 94 or 95 corresponding to the tilting direction of the operating lever. Furthermore, in the control device 91, the larger the amount of bucket operation, the larger the command current. Additionally, the secondary pressure output from the bucket solenoid proportional valve 94 on one side (the side that tilts the bucket upwards) is... Figure 4 The pilot port of the bucket priority valve 32f mentioned above is also shown.

[0062] Similarly, when the operating lever of the lifting device 93 is lifted, the control device 91 sends a command current to the lifting solenoid proportional valve 96 or 97 corresponding to the tilting direction of the operating lever. Furthermore, in the control device 91, the larger the lifting operation, the larger the command current.

[0063] Regarding control device 91, the functions of the elements disclosed in this specification can be executed using a general-purpose processor, special-purpose processor, integrated circuit, ASIC (Application Specific Integrated Circuits), existing circuitry, and / or combinations thereof that are configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it contains transistors or other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs or is programmed to perform the listed functions. The hardware can be the hardware disclosed in this specification or other known hardware programmed or configured to perform the listed functions. When the hardware is considered a processor, a type of circuit, the circuit, means, or unit is a combination of hardware and software used in the configuration of the hardware and / or processor.

[0064] The loading / unloading pump 31 described above is a variable capacity pump. In this embodiment, the loading / unloading pump 31 is a swashplate pump with a swashplate 31a. However, the loading / unloading pump 31 may also be a swashplate pump. Furthermore, although not shown in the figure, an overflow line branches off from the loading / unloading supply line 32, and an overflow valve provided on this overflow line maintains the discharge pressure of the loading / unloading pump 31 below a predetermined value.

[0065] The capacity of the loading / unloading pump 31 is changed by the loading / unloading regulator 5. In this 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 also perform only flow control.

[0066] The loading / unloading regulator 5 is used for flow control and inputs a loading / unloading requirement command pressure. The loading / unloading requirement command pressure will be explained in detail later. The higher the loading / unloading requirement command pressure of the loading / unloading regulator 5, the greater the capacity of the loading / unloading pump 31. In this embodiment, the loading / unloading regulator 5, as... Figure 3 The configuration shown is not limited to this, but the structure of the loading and unloading regulator 5 can be modified as appropriate.

[0067] More specifically, in addition to the flow control piston 56 and the horsepower control piston 57, the loading / unloading regulator 5 also includes a servo piston 51 connected to the ramp 31a of the loading / unloading pump 31 and a regulating valve 52 for driving the servo piston 51. Furthermore, the loading / unloading 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 can be integrally formed with the housing of the loading / unloading pump 31.

[0068] The loading / unloading regulator 5 has a first pressure chamber 5a for introducing the discharge pressure of the loading / unloading pump 31 and a second pressure chamber 5b for introducing the control pressure. The servo piston 51 has a first end exposed in the first pressure chamber 5a and a second end exposed in the second pressure chamber 5b, which has a larger diameter than the first end.

[0069] The regulating valve 52 is used to regulate the control pressure introduced into the second pressure chamber 5b. Specifically, the regulating valve 52 includes: a direction for reducing the control pressure (capacity increase direction), Figure 3 (From center to left) and the direction that causes the control pressure to rise (direction of capacity reduction), Figure 3 A valve core 53 that moves from center to right; and a sleeve 54 that accommodates the valve core 53.

[0070] The valve core 53 is connected to the flow control piston 56 via rod 56a and to the horsepower control piston 57 via rod 57a. As the flow control piston 56 advances, the valve core 53 moves in the direction of increasing capacity; as the flow control piston 56 retracts, it moves in the direction of decreasing capacity. Conversely, as the horsepower control piston 57 advances, the valve core 53 moves in the direction of decreasing capacity; as the flow control piston 56 retracts, it moves in the direction of increasing capacity. Furthermore, the flow control piston 56 and the horsepower control piston 57 are configured such that the one with the smaller capacity limitation (i.e., the one commanding less capacity) preferentially moves the valve core 53.

[0071] Sleeve 54 is connected to servo piston 51 via feedback rod 55. Sleeve 54 has a pump port, a tank port, and an output port (the output port communicates with the second pressure chamber 5b). Depending on the relative position of sleeve 54 and valve core 53, the output port may be blocked from both the pump port and the tank port, or connected to either the pump port or the tank port. Furthermore, when valve core 53 moves in the direction of increasing or decreasing capacity, the relative position of valve core 53 and sleeve 54 is determined by balancing the forces (pressure × servo piston pressure area) acting from both sides of servo piston 51, thereby adjusting the control pressure.

[0072] Furthermore, the loading / unloading regulator 5 has a working chamber 5c formed therein, which applies the aforementioned loading / unloading command pressure to the flow control piston 56. That is, the flow control piston 56 advances when the loading / unloading command pressure increases and retracts when the loading / unloading command pressure decreases.

[0073] Furthermore, the loading / unloading regulator 5 has a working chamber 5d formed therein, which causes the discharge pressure of the loading / unloading pump 31 to act on the horsepower control piston 57. That is, the horsepower control piston 57 moves forward when the discharge pressure of the loading / unloading pump 31 increases and moves backward when the discharge pressure decreases.

[0074] In this embodiment, the working chamber 5c is connected to the electromagnetic proportional valve 81 via the command pressure line 82. The electromagnetic proportional valve 81 is connected to the auxiliary pump 15 via the aforementioned primary pressure line 16. In this embodiment, the electromagnetic proportional valve 81 is a positively proportional type where the command current and secondary pressure are positively correlated. However, the electromagnetic proportional valve 81 can also be an inversely proportional type where the command current and secondary pressure are negatively correlated.

[0075] The electromagnetic proportional valve 81 is controlled by the aforementioned control device 91, and outputs secondary pressure to the working chamber 5c as a loading / unloading requirement command pressure. During loading / unloading operations (bucket operation or lifting operation), the control device 91 sends a command current to the electromagnetic proportional valve 81. Furthermore, in the control device 91, the larger the operation amount of the loading / unloading operation, the larger the command current. That is, if... Figure 5 As shown, the loading and unloading requirement command pressure is positively correlated with the amount of loading and unloading operations.

[0076] On the other hand, the steering adjuster 4's working chamber 4c, such as Figure 2 As shown, the output port of the high-pressure selector valve 84 is connected via the command pressure line 85. One of the two input ports of the high-pressure selector valve 84 is connected to the pressure reducing valve 75 via input line 79, and the other is connected to the command pressure line 82 via input line 83 (see reference). Figure 3 Alternatively, input line 83 can be connected to the working chamber 5c of loading / unloading regulator 5, instead of the command pressure line 82. Pressure reducing valve 75 is connected to auxiliary pump 15 via the aforementioned primary pressure line 16.

[0077] The pressure reducing valve 75 is driven by the pressure difference between the upstream and downstream sides of the throttling section 23a in the steering valve 23. It outputs a secondary pressure as the steering command pressure, where a larger pressure difference results in a lower secondary pressure. That is, as... Figure 6 As shown, the steering command pressure is negatively correlated with the pressure difference between the upstream and downstream sides of the throttle section 23a in the steering valve 23.

[0078] More specifically, the pressure reducing valve 75 includes a piston 76 for regulating secondary pressure. Pressure on the upstream side of the throttling section 23a and pressure on the downstream side of the throttling section 23a act on the piston 76 in an opposing manner. The pressure on the upstream side of the throttling section 23a is introduced into the piston 76 via a pilot line 78 branching from the steering supply line 22, and the pressure on the downstream side of the throttling section 23a is introduced into the piston 76 via a pilot line 77 branching from the load pressure line 64.

[0079] The high-pressure selector valve 84 selects the higher of the secondary pressure from the pressure reducing valve 75 (i.e., the steering requirement command pressure) and the secondary pressure from the solenoid proportional valve 81 (i.e., the loading / unloading requirement command pressure) and outputs it to the steering adjuster 4. In other words, the higher of the steering requirement command pressure and the loading / unloading requirement command pressure is used as the signal pressure input to the steering adjuster 4.

[0080] like Figures 1-3 As shown, the merging line 71 branches off from the steering supply line 22 near the upstream side of the compensator 61, and this merging line 71 is connected to the loading / unloading supply line 32. A priority valve 72 is provided on the merging line 71.

[0081] Priority valve 72 blocks the merging line 71 when no loading or unloading operation is performed, and opens the merging line 71 when loading or unloading operation is performed. In this embodiment, priority valve 72 is pilot-operated and has a first pilot port 72a and a second pilot port 72b. However, priority valve 72 can also be electromagnetic.

[0082] More specifically, the priority valve 72 blocks the confluence line 71 in the neutral position, and the opening area of ​​the priority valve 72 increases as it moves from the neutral position. The priority valve 72 has a spring 72c for maintaining the priority valve 72 in the neutral position (see reference). Figure 3 The first pilot port 72a is used to shift the priority valve 72 in the direction of decreasing opening area, and the second pilot port 72b is used to shift the priority valve 72 in the direction of increasing opening area.

[0083] The first pilot port 72a of the priority valve 72 is connected to the input line 79 via the pilot line 73, and the second pilot port 72b is connected to the command pressure line 82 via the pilot line 74. That is, the steering requirement command pressure is introduced into the first pilot port 72a through the pilot line 73, and the loading / unloading requirement command pressure is introduced into the second pilot port 72b through the pilot line 74. Therefore, the steering requirement command pressure and the loading / unloading requirement command pressure act on the priority valve 72 in a mutually opposing manner.

[0084] When the loading / unloading command pressure is less than the steering command pressure plus a reference pressure (the pressure corresponding to the applied force of spring 72c), the priority valve 72 blocks the merging line 71. On the other hand, when the loading / unloading command pressure is greater than the reference pressure, the priority valve 72 changes its opening area to correspond to the pressure difference between the loading / unloading command pressure and the reference pressure.

[0085] As explained above, in the hydraulic system 1 of this embodiment, the loading / unloading demand command pressure input to the loading / unloading regulator 5 is positively correlated with the operation quantity of the loading / unloading operation, so the capacity of the loading / unloading pump 31 can be controlled positively. On the other hand, the steering demand command pressure input to the steering regulator 4 is the higher of the steering demand command pressure and the loading / unloading demand command pressure, which is negatively correlated with the pressure difference between the upstream and downstream sides of the throttling section 23a in the steering valve 23. When the steering operation is performed alone, the steering demand command pressure is input to the steering regulator 4, so the smaller the pressure difference between the upstream and downstream sides of the throttling section 23a in the steering valve 23, the greater the capacity of the steering pump 21 can be increased. Furthermore, when the steering operation and the loading / unloading operation are performed simultaneously, the capacity of the steering pump 21 is changed according to the higher demand. Therefore, the capacity of the steering pump 21 can be appropriately controlled.

[0086] Furthermore, this embodiment employs a pressure reducing valve 75 driven by the pressure difference between the upstream and downstream sides of the throttling section 23a in the steering valve 23, so the pressure difference between the upstream and downstream sides of the throttling section 23a in the steering valve 23 can be converted into a steering command pressure by the pressure reducing valve 75.

[0087] Furthermore, in this embodiment, a compensator 61 is installed on the steering supply line 22 near the downstream side at the branch position of the merging line 71. Therefore, the supply flow rate of the working fluid to the steering actuator 11 can be adjusted to the necessary flow rate by the compensator 61, and the remaining working fluid can be introduced into the loading and unloading supply line 32 through the merging line 71.

[0088] Furthermore, in this embodiment, the priority valve 72 provided in the confluence line 71 is pilot-operated, so the priority valve 72 can be mechanically operated. Moreover, depending on the change in the opening area of ​​the priority valve 72, the working fluid discharged from the steering pump 21 can be preferentially supplied to the steering actuator 11.

[0089] (Modified Example)

[0090] This disclosure is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of this disclosure.

[0091] For example, depending on the type of industrial vehicle, the number of loading / unloading actuators 12 and loading / unloading control valves 33 in the loading / unloading circuit 3 of the hydraulic system 1 can be one or more.

[0092] Alternatively, when the bucket operating device 92 and the lifting operating device 93 are both pilot operating valves, the electromagnetic proportional valve 81 is omitted. The highest pilot pressure between the pilot pressure output from the bucket operating device 92 and the pilot pressure output from the lifting operating device 93 is used as the loading and unloading requirement command and is introduced into the working chamber 5c of the loading and unloading regulator 5 and the high-pressure selection valve 84.

[0093] Furthermore, priority valve 72 can be a simple switching valve.

[0094] (Summarize)

[0095] This disclosure provides a hydraulic system for an industrial vehicle, comprising: a variable-capacity steering pump supplying working fluid to a steering actuator via a steering supply line and a steering valve; a variable-capacity loading / unloading pump supplying working fluid to at least one loading / unloading actuator via a loading / unloading supply line and at least one loading / unloading control valve; a confluence line branching from the steering supply line and connected to the loading / unloading supply line; a priority valve located on the confluence line, blocking the confluence line when no loading / unloading operation is performed, and opening the confluence line when a loading / unloading operation is performed; a loading / unloading regulator inputting a loading / unloading request command pressure positively correlated with the operation amount of the loading / unloading operation, wherein a larger loading / unloading request command pressure increases the capacity of the loading / unloading pump; and a steering regulator inputting the higher of the steering request command pressure and the loading / unloading request command pressure, which is negatively correlated with the pressure difference between the upstream and downstream sides of the throttling section in the steering valve that determines the amount of working fluid supplied to the steering actuator, wherein a larger signal pressure increases the capacity of the steering pump.

[0096] Based on the above structure, the loading / unloading demand command pressure input to the loading / unloading regulator is positively correlated with the operational quantity of the loading / unloading operation, thus allowing positive control of the loading / unloading pump capacity. On the other hand, the steering regulator input is the higher of the steering demand command pressure and the loading / unloading demand command pressure, which is negatively correlated with the pressure difference between the upstream and downstream sides of the throttling section in the steering valve. When the steering operation is performed alone, the steering demand command pressure is input to the steering regulator, so the smaller the pressure difference between the upstream and downstream sides of the throttling section in the steering valve, the greater the increase in the steering pump capacity. Furthermore, when the steering operation and the loading / unloading operation are performed simultaneously, the steering pump capacity varies according to the higher demand. Therefore, the steering pump capacity can be appropriately controlled.

[0097] Alternatively, the hydraulic system described above may also include: a pressure-reducing valve, driven by the pressure difference between the upstream and downstream sides of the throttling section in the steering valve, which outputs a secondary pressure as the steering requirement command pressure in a manner where the greater the pressure difference, the lower the secondary pressure; and a high-pressure selection valve, which selects the higher of the steering requirement command pressure and the loading / unloading requirement command pressure to output to the steering adjuster. According to this structure, the pressure difference between the upstream and downstream sides of the throttling section in the steering valve can be converted into a steering requirement command pressure via the pressure-reducing valve.

[0098] Alternatively, the hydraulic system described above may also include: a compensator located on the downstream side of the steering supply line, closer to the branch of the merging line, wherein the opening area decreases as the pressure difference between the upstream and downstream sides of the throttling section in the steering valve increases. According to this structure, the supply flow rate of the working fluid to the steering actuator can be adjusted to the necessary flow rate via the compensator, and the remaining working fluid can be introduced into the loading / unloading supply line through the merging line.

[0099] Alternatively, the priority valve may have a first pilot port for introducing the steering requirement command pressure and a second pilot port for introducing the loading / unloading requirement command pressure. When the loading / unloading requirement command pressure is less than a reference pressure equal to the steering requirement command pressure plus a predetermined value, the merging line is blocked. When the loading / unloading requirement command pressure is greater than the reference pressure, the opening area changes to correspond to the pressure difference between the loading / unloading requirement command pressure and the reference pressure. With this structure, the priority valve can operate mechanically. Furthermore, based on the change in the opening area of ​​the priority valve, the working fluid discharged from the steering pump can be preferentially supplied to the steering actuator.

[0100] Symbol explanation:

[0101] 1 Hydraulic System

[0102] 11 Steering actuator

[0103] 12 Loading and unloading actuators

[0104] 2 Steering circuit

[0105] 21 Steering Pump

[0106] 22-way steering supply line

[0107] 23 Steering valve

[0108] 23a Throttling section

[0109] 3 Loading and unloading circuits

[0110] 31 Loading and unloading pump

[0111] 32 Loading and unloading supply lines

[0112] 33 Loading and unloading control valve

[0113] 4 Steering Adjusters

[0114] 5 Loading and unloading regulators

[0115] 71 merging lines

[0116] 72 Priority Valve

[0117] 72a First Pilot Port

[0118] 72b second pilot port

[0119] 75 pressure reducing valve

[0120] 84 High-pressure selector valve.

Claims

1. A hydraulic system for an industrial vehicle, characterized in that, have: A variable capacity steering pump supplies working fluid to the steering actuator via a steering supply line and a steering valve; A variable capacity loading / unloading pump supplies working fluid to at least one loading / unloading actuator via a loading / unloading supply line and at least one loading / unloading control valve; The merging line branches off from the turning supply line and connects to the loading / unloading supply line; A priority valve is provided at the merging line, which blocks the merging line when no loading or unloading operation is performed, and opens the merging line when loading or unloading operation is performed. The loading and unloading regulator receives a loading and unloading requirement command pressure that is positively correlated with the amount of the loading and unloading operation. The larger the loading and unloading requirement command pressure, the greater the capacity of the loading and unloading pump. and The steering regulator uses the higher of the steering requirement command pressure and the loading / unloading requirement command pressure, which is negatively correlated with the pressure difference between the upstream and downstream sides of the throttling section in the steering valve, as the signal pressure input. The larger the signal pressure, the greater the capacity of the steering pump. The throttling section determines the amount of working fluid supplied to the steering actuator.

2. The hydraulic system for industrial vehicles according to claim 1, characterized in that, It also has: The pressure reducing valve is driven by the pressure difference between the upstream and downstream sides of the throttling section in the steering valve, and outputs a secondary pressure as the steering command pressure in the form that the greater the pressure difference, the lower the secondary pressure. and The high-pressure selector valve selects the higher of the steering requirement command pressure and the loading / unloading requirement command pressure to output to the steering regulator.

3. The hydraulic system for industrial vehicles according to claim 1, characterized in that, It also has: The compensator is located on the downstream side of the merging line branch, and the opening area decreases as the pressure difference between the upstream and downstream sides of the throttling section in the directional valve increases.

4. The hydraulic system of an industrial vehicle according to any one of claims 1 to 3, characterized in that, The priority valve has a first pilot port for introducing the diversion requirement command pressure and a second pilot port for introducing the loading / unloading requirement command pressure. When the loading / unloading requirement command pressure is less than the reference pressure after adding a predetermined value to the diversion requirement command pressure, it blocks the merging line. When the loading / unloading requirement command pressure is greater than the reference pressure, it changes to an opening area corresponding to the pressure difference between the loading / unloading requirement command pressure and the reference pressure.

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