HYDRAULIC CONTROL SYSTEM

Abstract

Hydraulic control system or drive system, comprising the following: a load line pump device (11L) configured to deliver an operating fluid at a flow rate corresponding to a first load-sensing pressure signal input into the load line pump device (11L); a load line control device connected to a load line actuator (2,3) or a plurality of load line actuators (2,3) and also connected to the load line pump device (11L) via a charging-side passage (17), wherein the load line control device is configured to adjust a flow rate of the operating fluid flowing from the load line pump device (11L) to the single load line actuator (2,3) or the plurality of load line actuators (2,3); a steering line pump device (11R) configured to deliver the operating fluid at a flow rate corresponding to a second load-sensing pressure signal input into the steering line pump device (11R); a steering line control device (12) connected to a steering actuator (4) and also connected to the steering line pump device (11R) via a steering-side passage (16), wherein the steering line control device (12) is configured to adjust a flow rate of the operating fluid flowing from the steering line pump device (11R) to the steering actuator (4); and a switching valve device (15) configured to (i) connect the charging-side passage (17) and the steering-side passage (16) when a charging pressure of one load line actuator (2,3) or at least one of the plurality of load line actuators (2,3) is equal to or higher than a predetermined pressure, and (ii) disconnect the charging-side passage (17) and the steering-side passage (16) when a charging pressure of one load line actuator (2,3) or the plurality of load line actuators (2,3) is less than the predetermined pressure.

Description

Technical area

[0001] The present invention relates to a hydraulic control system or drive system configured to supply an operating fluid to a load line actuator, and a steering actuator for controlling the load line actuator and the steering actuator. Technical background

[0002] An industrial machine, such as a forklift or wheel loader, comprises: a steering actuator configured to change the direction of the industrial machine; and a load line actuator configured to move a fork, bucket, and the like. A hydraulic control system is connected to the steering actuator and the load line actuator and supplies the steering actuator and the load line actuator with operating oil for controlling the steering actuator and the load line actuator. As an example of the hydraulic control system, a hydraulic circuit device of PTL 1 is known. The hydraulic circuit device comprises two fixed-displacement hydraulic pumps.One of the hydraulic pumps is connected to a steering cylinder via a steering-side port, and a switching valve configured to control the flow rate of the operating oil to the steering cylinder is associated with this port. The other hydraulic pump is connected to a load line actuator via a charging port, and a charging valve configured to control the flow rate of the operating oil to the load line actuator is associated with this port. A priority flow control valve is also located on the steering-side port, upstream of the switching valve. The priority flow control valve is configured to supply excess operating oil to the charging port, which is generated when the pump's delivery rate exceeds the flow rate of the operating oil to the steering actuator.

[0003] Relevant prior art is known from JP 2010-76937A. Further relevant prior art is known from US 2011 / 0289908A1. Summary of the invention: Technical problem

[0004] In the hydraulic circuit of PTL 1, fixed-displacement hydraulic pumps are used to circulate the operating oil. Because the fixed-displacement pumps deliver the operating oil at a constant flow rate, the oil is discharged from the pumps at an excessively high flow rate, which negatively impacts energy efficiency. To improve energy efficiency, variable-displacement hydraulic pumps can be used instead of the fixed-displacement pumps. In this case, the two variable-displacement hydraulic pumps are configured to deliver the operating oil at flow rates corresponding to the load pressure of the steering cylinder and the load pressure of the load line actuator.

[0005] In the hydraulic circuit configured as described above, the priority flow control valve preferably directs the operating oil of one of the hydraulic pumps into the steering cylinder. Therefore, if the steering cylinder is actuated in a state where only the load line actuator is engaged, the operating oil of one hydraulic pump is preferentially supplied to the steering cylinder. Since one of the hydraulic pumps delivers the operating oil at a flow rate corresponding to the load pressure of the steering cylinder, it only supplies the amount of operating oil required to drive the steering cylinder. This significantly reduces the flow rate of the operating oil supplied to the charging-side passage via the priority flow control valve. If the actuation force of an actuating lever is large, the required flow rate of operating oil, relative to the actuation force of the actuating lever, cannot be supplied solely by the other hydraulic pump.This results in a low flow rate of operating oil to the load line actuator relative to the actuation force of the operating lever. Consequently, the operating speed of the load line actuator drops significantly, and the required operating speed cannot be guaranteed.

[0006] One objective of the present invention is to provide a hydraulic control system that prevents the operating speed of a load line actuator from decreasing significantly even when a steering actuator is actuated. Solution to the problem

[0007] According to the present invention, a hydraulic drive system with the features of claim 1 is provided. Advantageous embodiments are the subject of the dependent claims.

[0008] According to the present invention, in the operating state of the load line actuator, the connection between the steering-side passage and the charging-side passage is maintained by the switching valve device. Thus, even when the steering actuator is actuated, a portion of the operating oil derived from the steering line pump device can be supplied from the steering-side passage to the charging-side passage. This prevents the steering-side passage and the charging-side passage from being suddenly separated when the steering actuator is actuated in the operating state of the load line actuator, and thus prevents the operating oil from being introduced from the steering line pump device into the charging-side passage. Specifically, this prevents the steering-side passage from being suddenly separated when the steering actuator is actuated or...When the steering actuator is driven in the operating state of the load line actuator, the flow rate of the operating oil supplied to the load line actuator decreases significantly, and thus the operating speed of the load line actuator drops significantly.

[0009] In the above invention, the hydraulic control system can comprise: a plurality of load line load pressure passages connected to the respective plurality of load line actuators; a steering line load pressure passage connected to the steering actuator;and a load sensing device configured to input, in the operating state of the load line actuator, the highest of the pressures from the plurality of load line load pressure passes and the pressure of the steering line load pressure pass as the first load sensing pressure signal to the load line pumping device, and also to input the highest of the pressures from the plurality of load line load pressure passes and the pressure of the steering line load pressure pass to the steering line pumping device as the second load sensing pressure signal, and in the holding state of the load line actuator to input, the highest of the pressures from the plurality of load line load pressure passes as the first load sensing pressure signal to the load line pumping device, and also to input the highest of the pressures from the plurality of load line load pressure passes and the pressure of the steering line pressure pass to the steering line pumping device as the second load sensing pressure signal.

[0010] According to the configuration above, when the load line actuator is in its holding state, the flow rate of the operating oil derived from the load line pump device can be reduced to a minimum. This minimizes the energy loss of the load line pump device. Conversely, when the steering actuator is activated while the load line actuator is in its operating state, the highest of the load line actuator load pressures and the load pressure of the steering actuator are input to the load line pump device as the first load pressure signal, and to the steering line pump device as the second load pressure signal.Even if the load line actuator and the steering actuator are activated simultaneously, and the load pressure of the steering actuator becomes higher than that of the load line actuator, the operating oil can be discharged from the load line hydraulic pump and the steering line pump at a flow rate corresponding to the load pressure of the steering actuator. Therefore, even when the load line actuator and the steering actuator are activated simultaneously, it is possible to prevent a situation in which the flow rate of the operating oil supplied to the load line actuator drops significantly, thus preventing a significant decrease in the operating speed of the load line actuator.

[0011] In the above invention, the hydraulic control system can be configured such that: the load line control device has a plurality of flow control mechanisms, each of which has a pressure compensation function; the plurality of flow control mechanisms is assigned to a corresponding plurality of operating devices; the plurality of flow control mechanisms is assigned to the respective plurality of load line actuators; the plurality of flow control mechanisms has corresponding flow control valves and corresponding compensators; and each of the plurality of flow control mechanisms supplies the operating fluid to the associated load line actuator via the flow control valve and the compensator with a delivery rate that corresponds to an operating command issued by the associated operating device.

[0012] According to the above configuration, the operating oil can be supplied with the flow rate corresponding to the operating command of the operating device even during simultaneous control. of the load line actuator and the steering actuator are supplied to the load line actuator assigned to the operating device.

[0013] In the above invention, the hydraulic control system can be configured such that: the steering line control device has a steering valve and a steering-side compensator; and the steering line control device supplies the operating fluid from the steering line pump device to the steering actuator through the steering valve and the steering-side compensator with a delivery rate that corresponds to an operating rate of an actuating tool.

[0014] According to the configuration above, the steering actuator can also be supplied with operating oil at a delivery rate corresponding to the operating quantity of the actuating tool, even when the load line actuator and the steering actuator are being controlled simultaneously.

[0015] In the above invention, the hydraulic control system can be configured such that: the control line drive device has a pressure relief valve; the steering-side compensator is connected to the pressure relief valve and supplies the pressure relief valve with a portion of the operating fluid flowing through the steering-side passage; when the pressure of the operating fluid flowing through the pressure relief valve becomes excessive, the pressure relief valve discharges the operating fluid flowing through the pressure relief valve into a tank; and the excess pressure is set to be higher than the operating pressure at which the steering actuator operates.

[0016] According to the configuration above, the operating oil can be drained if the operating oil accumulates in the steering-side passage, thereby increasing the hydraulic pressure of the steering-side passage. Advantageous effects of the invention

[0017] According to the present invention, even when a steering cylinder is operated in a state in which a load line actuator is actuated, it is possible to prevent a significant decrease in the operating speed of the load actuator.

[0018] The above-mentioned problem, other problems, features and advantages of the present invention are clarified by the following detailed explanation of the preferred embodiments with reference to the accompanying drawings. Brief description of the drawings Fig. Figure 1 is a circuit diagram illustrating the configuration of a hydraulic control system according to embodiment 1 of the present invention. Fig. Figure 2 is an enlarged circuit diagram showing a steering control device that is integrated into the hydraulic control system of Fig. 1 is integrated. Fig. Figure 3 is an enlarged circuit diagram showing a load line control device that is integrated into the hydraulic control system of Fig. 1 is integrated. Fig. Figure 4 is a circuit diagram illustrating the steering control device of the hydraulic control system according to embodiment 2 of the present invention. Description of the embodiments

[0019] The hydraulic control systems 1 and 1A according to embodiments 1 and 2 of the present invention are explained below with reference to the drawings. It should be noted that the directions indicated in the following explanations are used for clarity and do not restrict the directions and the like of components of the present invention. Furthermore, each of the hydraulic control systems 1 and 1A described below is only one embodiment of the present invention. Therefore, the present invention is not limited to these embodiments, and additions, deletions, and modifications may be made within the scope of the present invention.

[0020] An industrial machine, such as a forklift or wheel loader, can move while changing the direction of a vehicle body via a steering actuator. Furthermore, the industrial machine incorporates an attachment, such as a bucket or forks, and can move the attachment via a load line actuator to perform loading operations. More specifically, the industrial machines can (i) move the attachment via the load line actuator, (ii) load a target object (such as a load, soil, or sand) onto the attachment, (iii) move to a desired position while changing the direction of the vehicle body via the steering cylinder, and (iv) unload the target object there. The industrial machines configured as described above incorporate a hydraulic control system 1, which is integrated into Fig. Figure 1 shows the hydraulic control system 1. This system supplies the actuators 2 to 4 with operating oil to control them. The following describes a case in which a forklift truck, an example of an industrial machine, is equipped with the hydraulic control system 1. forklift

[0021] The forklift truck includes a plurality of actuators 2 to 4. In the present embodiment, the forklift truck has three actuators, which are a lifting actuator 2, a tilting actuator 3, and a steering actuator 4. The lifting actuator 2 consists, for example, of a pair of hydraulic cylinders and raises and lowers a fork, which is a mounting. The tilting actuator 3 consists, for example, of a pair of hydraulic cylinders 3L and 3R and extends and retracts to tilt the fork. The steering actuator 4 consists, for example, of a double-rod hydraulic cylinder and is configured to move a rod 4e to change the direction of the rear wheels and thereby change the forward direction of the vehicle body. These three actuators 2 to 4 are actuated by being supplied with operating oil. To supply the operating oil to the three actuators 2 to 4, the forklift truck includes the hydraulic control system 1. Design 1

[0022] The hydraulic control system 1 of embodiment 1 comprises two pump devices 11L and 11R, a steering line control device 12, a load line control device 13, a load sensing device 14, and a switching valve device 15. The two pump devices 11L and 11R are identical in configuration. The following description focuses primarily on the configuration of a steering line pump device 11R, i.e., pump device 11R. The same reference symbols are used for the components of a load line pump device 11L, i.e., pump device 11L, with "L" instead of "R," and detailed explanations are omitted. Pump device

[0023] The steering line pump device 11R comprises a hydraulic pump 21R and a regulator 22R. The hydraulic pump 21R is a variable displacement swashplate pump and can change its delivery rate according to the tilt angle of a swashplate 21a. The hydraulic pump 21R is equipped with the regulator 22R, and the regulator 22R changes the tilt angle of the swashplate 21a according to a pressure signal input to the regulator 22R. More precisely, the regulator 22R comprises a servo piston 23R and a differential pressure coil 24R.

[0024] The servo piston 23R is coupled to the swashplate 21a, and the differential pressure coil 24R is connected to the servo piston 23R. The differential pressure coil 24R supplies and discharges the pilot oil to and from the servo piston 23R. The servo piston 23R moves forward or backward according to the supply or discharge of the pilot oil to change the tilt angle of the swashplate 21a. An output pressure from the hydraulic pump 21R and a pressure signal described below are applied to the differential pressure coil 24R in opposite directions, and the differential pressure coil 24R changes its position according to an intermediate differential pressure. This switches the supply and discharge of the servo piston 23R and thus sets a movement parameter of the servo piston 23R, i.e., the tilt angle of the swashplate 21a.The steering line pump device 11R, configured as described above, is connected to the steering line control device 12 via a steering-side passage 16, and the load line pump device 11L is connected to the load line control device 13 via a load-side passage 17. Steering line control device

[0025] As in Fig. As shown in Figure 2, the steering line control device 12 has a handle 25, which is an example of an actuating tool. When the handle 25 is actuated, the steering line control device 12 supplies the steering actuator 4 with operating oil to change the direction of travel of the vehicle body. The configuration of the steering line control device 12 is explained in more detail below. The steering line drive device 12 has the handle 25, a pulley 26, and a steering-side compensator 27.

[0026] The rotating roller 26 is connected to the steering-side passage 16 via the steering-side compensator 27 and has a steering valve 28 and a metering mechanism 29. The steering valve 28 has a steering coil 28a. The position of the steering coil 28a is changed by the handle 25 coupled to the steering coil 28a. The steering coil 28a reverses the direction of the operating oil supplied to the steering actuator 4 by changing its position and controls the flow of the operating oil according to its position.

[0027] Specifically, the steering valve 28 is connected to the steering-side passage 16, the metering mechanism 29, two ports 4a and 4b (first and second ports 4a and 4b) of the steering actuator 4, a reservoir 18, and a steering-side load-sensing passage (a load pressure passage of the steering actuator) 30. When the handle 25 is in a neutral position, the steering coil 28a is in a neutral position M0, and both the metering mechanism 29 and the two ports 4a and 4b of the steering actuator 4 are locked. Conversely, the steering-side load-sensing passage 30 is connected to the reservoir 18. This keeps the steering actuator 4 in a neutral position. Thus, the vehicle body moves linearly, and the pressure at the steering-side load-sensing passage 30 is reduced to the reservoir pressure.

[0028] Next, when the handle 25 is actuated in the direction of rotation towards a first side, the steering coil 28a moves to a first offset position M1. This connects the steering-side passage 16 to the metering mechanism 29. The metering mechanism 29 is a so-called hydraulic pump and has two ports 29a and 29b. The metering mechanism 29 is coupled to the handle 25 via a shaft 25a. When the handle 25 is actuated in the direction of rotation towards the first side, the metering mechanism 29 draws the operating oil from port 29a and discharges the operating oil through port 29b at a rate corresponding to the rotational speed of the handle 25. Port 29b is connected to the second port 4b of the steering actuator 4 via the steering coil 28a. This supplies the operating oil discharged from the metering mechanism 29 to a second oil chamber 4d of the steering actuator 4.The first connection 4a of the steering actuator 4 is connected to the tank 18 via the steering coil 28a. The operating oil in a first oil chamber 4c of the steering actuator 4c is drained into the tank 18. This allows the rod 4e of the steering actuator 4e to be moved in a predetermined direction to a first side, thereby changing the direction of the rear wheels.

[0029] When the handle 25 is actuated in the direction of rotation towards a second side, the steering coil 28a moves to a second offset position M2. In doing so, the steering-side passage 16 is connected to the port 29b of the metering mechanism 29. Port 29a is connected to the first port 4a of the steering actuator 4. This supplies the operating oil discharged from the metering mechanism 29 to the first oil chamber 4c of the steering actuator 4. Simultaneously, the second port 4b of the steering actuator 4 is connected via the steering coil 28a to the reservoir 18, and the operating oil in the second oil chamber 4d of the steering actuator 4d is drained into the reservoir 18. This allows the rod 4e of the steering actuator 4e to be moved in the predetermined direction to a second side, thereby changing the direction of the rear wheels.

[0030] When the steering coil 28a, configured as above, is in the neutral position M0, it connects the steering-side load sensing channel 30 to the reservoir 18. When the steering coil 28a is in either of the first or second offset positions M1 or M2, it connects the steering-side load sensing passage 30 to the steering-side passage 16. A steering-side load sensing pressure is then output to the steering-side load sensing passage 30. This steering-side load sensing pressure is an output pressure of the steering valve 28, i.e., a load pressure of the steering actuator 4. Furthermore, the steering-side load sensing passage 30 is connected to the steering-side compensator 27, and the steering-side load sensing pressure is applied to the steering-side compensator 27.

[0031] The steering-side compensator 27 is arranged on the steering-side passage 16. In addition to the steering-side load sensing pressure, the steering-side compensator 27 receives a downstream pressure from the steering-side compensator 28, i.e., an upstream pressure from the steering valve 28, such that the downstream pressure opposes the steering-side load sensing pressure. Specifically, pressures upstream and downstream of the steering coil 28 act on the steering-side compensator 27 and are opposed to each other. In the present embodiment, the pressures upstream and downstream of the steering valve 28 are applied to the steering-side compensator 27 via corresponding throttles. Through the interaction of the steering-side compensator 27 and the steering line control device 12, the operating oil is supplied to the steering actuator 4 with a flow rate corresponding to an actuation value of the handle 25.Therefore, the steering line pump device 11R is controlled according to a second load-sensing pressure signal LS2 described below, such that it is tilted and discharges the operating oil with such a delivery rate that a pressure difference between the upstream and downstream side of the steering valve 28 becomes constant.

[0032] As above, the steering line control device 12 supplies the operating oil from the steering line pump device 11R to the steering actuator 4 for the drive of the steering actuator 4. Load line control device

[0033] As in Fig. As shown in Figure 3, the load line control device 13 supplies the lifting actuator 2 and the tilting actuator 3 with the operating oil for controlling these actuators 2 and 3. In particular, the load line control device 13 has two flow control mechanisms 31 and 32, each with a pressure equalization function. The two flow control mechanisms 31 and 32 are connected in parallel to a hydraulic pump 21L of the load line pump device 11L through the charging-side passage 17.

[0034] The two flow control mechanisms 31 and 32 are arranged to correspond to the respective actuators 2 and 3. Regardless of the load pressures of the actuators 2 and 3, the two flow control mechanisms 31 and 32 supply the operating oil to the respective actuators 2 and 3 at flow rates corresponding to the operating commands of the operating devices 44 and 45 described below. More precisely, flow control mechanism 31 comprises a flow control valve 34 and a compensator 37, and flow control mechanism 32 comprises a flow control valve 35 and a compensator 38. The flow control valve 34 works in conjunction with the compensator 37 to supply the operating oil to the actuator 2 at a flow rate corresponding to an operating command (control pressures p1 and p2 described below) input into the flow control valve 34.The flow control valve 35 works in conjunction with the compensator 38 to supply the actuator 3 with operating oil at a flow rate corresponding to an operating command (control pressures p3 and p4 described below) input into the flow control valve 35. The configurations of the two flow control mechanisms 31 and 32 are explained in more detail below.

[0035] A first flow control mechanism 31, one of the two flow control mechanisms 31 and 32, controls the direction of the operating oil supplied to the stroke actuator 2 to expand or contract the stroke actuator 2. More precisely, the first flow control mechanism 31 comprises a first flow control valve 34 and a first compensator 37. The first flow control valve 34 is connected to the stroke actuator 2 via a stroke passage 40. The first flow control valve 34 is connected to the upstream and downstream ends of a load-side first load-sensing passage 41. The first load-sensing valve 34 is connected to the tank 18 via a tank passage 43. The first flow control valve 34 has a coil 34a and changes the position of the coil 34a to modify the connection state and opening degrees of the passages described above.To change the position of the coil 34a, the stroke actuating device 44 is connected to the first flow control valve 34.

[0036] The stroke actuating device 44 comprises an actuating lever 44a and an actuating valve 44b. The actuating lever 44a is configured to tilt relative to the actuating valve 44b in a predetermined direction in a first and second direction. The actuating valve 44b is configured to output the control pressures p1 and p2 in directions (i.e., two directions) corresponding to the respective tilting directions of the actuating lever 44a. The first flow control valve 34 is connected in parallel to the operating valve 44b configured as above, and the control pressures p1 and p2 are applied to the coil 34a. These two control pressures p1 and p2 are applied to the coil 34a such that they are opposite each other.Therefore, the coil 34a moves in a direction corresponding to the tilting direction of the actuating lever 44a and switches the connection states of the charging-side passage 17 and the lifting channel 40 according to the direction of movement of the coil 34a.

[0037] More precisely, in the first flow control valve 34, when the actuating lever 44a is in the neutral position, the coil 34a is arranged in a neutral position M10. Thus, the first flow control valve 34 blocks the charging-side passage 17, the stroke passage 40, and the upstream end of the charging-side first load-sensing passage 41, and connects the downstream end of the charging-side first load-sensing channel 41 to the tank channel 43. This stops the expansion and contraction of the stroke actuator 2.

[0038] When the actuating lever 44a is inclined to the first side, the control pressure p1 is applied to the coil 34a, and the coil 34a moves into a first offset position M11. In this position, the first flow control valve 34 connects the charging-side channel 17 to the upstream end of the charging-side first load sensing passage 41 and also connects the downstream end of the charging-side first load sensing passage 41 to the lifting passage 40. Due to the connection states of the passages described above, the operating oil flowing from the charging-side passage 17 to the coil 34a is supplied to the lifting actuator 2 via the lifting passage 40. This causes the lifting actuator 2 to expand, and the fork is lifted.

[0039] When the actuating lever 44a is inclined to the second side, the control pressure p2 is applied to the coil 34a, and the coil 34a moves to a second offset position M12. In this position, the first flow control valve 34 disconnects the charging-side channel 17 and the upstream end of the charging-side first load-sensing passage 41 and connects the downstream end of the charging-side first load-sensing passage 41 and the lifting passage 40 to the tank passage 43. This stops the flow of operating oil from the charging-side channel 17 via the coil 34a to the lifting channel 40. Conversely, the operating oil of the lifting actuator 2 is discharged into the lifting channel 40 by the weight of the rods 2a, which are discharged into the tank channel 43 by the first flow control valve 34. This allows the lifting actuator 2 to contract and the fork to be lowered.A mechanism for limiting the lowering speed 46, consisting of a check valve 46a and a throttle 46b, is associated with the lifting channel 40. Without limiting the lifting speed of the fork, only the lowering speed of the fork is limited by the mechanism for limiting the lowering speed 46.

[0040] The stroke actuating device 44 outputs the control pressures p1 and p2 according to the actuation directions of the actuating lever 44a, and the first flow control valve 34 supplies the operating oil in a direction corresponding to the control pressure p1 or p2 to expand or contract the stroke actuator 2. The stroke actuating device 44 outputs the control pressure p1 or p2 according to an actuation amount of the actuating lever 44a. The coil 34a moves to a position corresponding to the control pressure p1 or p2 and connects each passage with an opening degree corresponding to the position. Specifically, the first flow control mechanism 31 acts such that the operating oil is supplied to the stroke passage 40 at a flow rate corresponding to the opening degree of the first flow control valve 34, i.e., a flow rate corresponding to the actuation amount of the actuating lever 44a.Therefore, the load line pump device 11L is controlled according to a first load sensing pressure signal LS1 described below, such that it tilts and discharges the operating oil at a flow rate such that a pressure differential between the upstream and downstream sides of the first throttle valve 34 becomes constant. To ensure that the pressure differential before and after the first flow control valve 34 remains constant even when the lift actuator 2 and the tilt actuator 3, i.e., the other load line actuator, are operating simultaneously, the first flow control mechanism 31 includes the first compensator 37.

[0041] The first compensator 37 is located on the charging side of the first load sensing pass 41. A pressure downstream of the first flow control valve 34 and a first selection pressure signal, described below, are input to the first compensator 37. The first compensator 37 acts such that the pressure differential before and after the first flow control valve 34 becomes essentially constant. Although the first selection pressure signal is described later, it is a pressure signal that is fed as the first load sensing pressure signal LS1 into a differential pressure coil 24L to control a flow rate of the hydraulic pump 21L of the load line pump device 11L. The first selection pressure signal corresponds to an output pressure of the hydraulic pump 21L.This allows the operating oil to be supplied by the first flow control mechanism 31 to the stroke passage 40 with a delivery quantity that corresponds to the degree of opening of each passage, i.e. a delivery quantity that corresponds to the actuation amount of the actuating lever 44a, regardless of a change in the load pressure of the lifting actuator 2.

[0042] As described above, the lifting actuator 2 can be operated at an operating speed corresponding to the actuation of the actuating lever 44a by supplying the operating oil from the flow control mechanism 31 to the lifting actuator 2 at a flow rate corresponding to the actuation of the actuating lever 44a. More precisely, the fork can be raised and lowered at an operating speed corresponding to the actuation of the actuating lever 44a. In addition to the first flow control mechanism 31, which operates as described above, the load line control device 13 also has a second flow control mechanism 32, which is one of the two flow control mechanisms. The second flow control mechanism 32 is connected to the load-side passage 17 in parallel with the first flow control valve 34.

[0043] The second flow control mechanism 32 controls the direction of the flow to the tilting actuator 3. flowing operating oil to operate the tilting actuator 3. To be precise, as described above, the second flow control mechanism 32 comprises the second flow control valve 35 and the second compensator 38. The second flow control valve 35 is connected to the tilting actuator 3. The tilting actuator 3 consists of the cylinder pair 3L and 3R. The second flow control valve 35 is connected via a first tilting passage 47 to the head-side ports 3a of cylinders 3L and 3R and via a second tilting passage 48 also to the rod-side ports 3b of cylinders 3L and 3R. The second flow control valve 35 is connected to the upstream and downstream ends of a second load-side load-sensing passage (a load pressure passage of the load line actuator) 42 and also to the tank 18 via the tank passage 43.

[0044] The second flow control valve 35 has a coil 35a and changes the position of the coil 35a to modify the connection states and opening degrees of the passages described above. To change the position of the coil 35a for modifying the connection states and opening degrees of the passages, the second flow control valve 35 is equipped with the rocker actuator 45.

[0045] The tilting actuating device 45 is identical in configuration to the lifting actuating device 44. The tilting actuating device 45 has an actuating lever 45a and an actuating valve 45b. The actuating valve 45b outputs the control pressures p3 and p4 (operating command) according to the tilting directions of the operating lever 45a, the control pressures p3 and p4 each corresponding to a tilting quantity of the operating lever 45a. The operating valve 45b is connected to the second flow control valve 35, and the control pressures p3 and p4 are applied to the coil 35a opposite each other. Therefore, the coil 35a moves in a direction corresponding to the tilting direction of the actuating lever 45a and connects the loading-side passage 17 to one of the two tilting channels 47 and 48, and the other of the two tilting channels 47 and 48 to the tank 18 according to the direction of movement of the coil 35a.

[0046] More precisely, in the second flow control valve 35, when the actuating lever 45a is in a neutral position, the coil 35a is arranged in a neutral position M20. This blocks the charging-side passage 17, the first and second tilting passages 47 and 48, and the upstream end of the charging-side second load sensing channel 42, thus stopping the operation of the tilting actuator. The downstream end of the charging-side second load sensing passage 42 is connected to the tank passage 43.

[0047] Next, when the actuating lever 45a is tilted to a first side, the control pressure p3 acts on the coil 35a, and the coil 35a moves into a first offset position M21. This connects the charging-side passage 17 and the upstream end of the charging-side second load-sensing passage 42. Furthermore, the downstream end of the charging-side second load-sensing passage 42 is connected to the first tilting passage 47, and the second tilting passage 48 is connected to the tank 18 via the tank passage 43. Due to the above connection states of the passages, the operating oil flowing through the charging-side passage 17 flows through the coil 35a, which is supplied to the end-face ports 3a of the cylinder pair 3L and 3R via the first tilting passage 47.On the other hand, the operating oil in the cylinder pair 3L and 3R flows from the rod-side connections 3b through the second tilting passage 48, which is discharged through the coil 35a and the tank passage 43 to the tank 18. This allows the cylinder pair 3L and 3R to be extended and the fork to be tilted to one side.

[0048] When the actuating lever 45a is tilted towards a second side, the control pressure p4 acts on the coil 35a, and the coil 35a moves into a second offset position M22. This connects the charging-side passage 17 and the upstream end of the charging-side second load-sensing passage 42. Furthermore, the downstream end of the charging-side second load-sensing passage 42 is connected to the second tilting passage 48, and the first tilting passage 47 is connected to the tank 18 via the tank passage 43. Through these connection states, the operating oil flowing from the charging-side passage 17 passes through the coil 35a, which is supplied to the rod-side connections 3b of the cylinder pair 3L and 3R via the second tilting passage 48.On the other hand, the operating oil in the cylinder pair 3L and 3R flows from the end-face connections 3a through the first tilting passage 47, which is discharged to the tank 18 via the slide valve 35a and the tank passage 43. This allows the tilting control 3 to be retracted and the fork to be tilted to a second side. Furthermore, the operating oil of the tilting actuator 3 is introduced into the second load-side load-sensing passage 42 via the second flow control valve 35, and the hydraulic pressure of the second load-side load-sensing passage 42 becomes a hydraulic pressure corresponding to the load pressure of the lifting actuator 2.

[0049] As above, the tilting actuator 45 outputs the control pressures p3 and p4 in directions corresponding to the actuation directions of the actuating lever 45a, and the second flow control valve 35 supplies the operating oil in a direction corresponding to the control pressure p3 or p4 to expand or contract the tilting actuator 3. The tilting actuator 45 outputs the control pressure p3 or p4 according to an actuation value of the actuating lever 45a. The coil 35a moves to a position corresponding to the control pressure p3 or p4 and connects each passage to an opening degree corresponding to the position. Specifically, the second flow control mechanism 32 supplies the first tilting passage 47 or the second tilting passage 48 with a flow rate corresponding to the opening degree, i.e., a flow rate corresponding to the actuation value of the actuating lever 45a.Furthermore, the load line pump device 11L is tilted according to the first load sensing pressure signal LS1 described below and delivers the operating oil at such a flow rate that a pressure differential between the upstream and downstream sides of the second throttle valve 35 becomes constant. To ensure that the pressure differential before and after the second flow control valve 35 remains constant even when the tilting actuator 3 and the lifting actuator 2, i.e., the other load line actuator, are operating simultaneously, the second flow control mechanism 32 includes the second compensator 38. The second compensator 38 is assigned to the second load sensing pass 42 on the charging side and has the same functions as the first compensator. Specifically, a pressure downstream of the second flow control valve 35 and the first selection pressure signal are input into the second compensator 38.The second compensator 38 acts in such a way that the pressure difference before and after the second flow control valve 35 becomes essentially constant. This allows the operating oil to be supplied to the second flow control mechanism 32 and the stroke passage 40 with a delivery rate corresponding to the degree of opening of each passage, i.e., a delivery rate corresponding to the actuation amount of the operating lever 45a, regardless of any change in the load pressure of the tilting actuator 3.

[0050] As described above, the tilting actuator 3 can be operated at an operating speed corresponding to the actuation of the actuating lever 45a by supplying the operating oil from the second flow control mechanism 32 to the tilting actuator 3 at a flow rate corresponding to the actuation of the actuating lever 45a. More precisely, the fork can be tilted to the first side or the second side at an operating speed corresponding to the actuation of the actuating lever 45a.

[0051] As above, the actuators 2 and 3 are operated by the steering line control device 12 and the load control device 13, respectively, according to the hydraulic control system 1, at operating speeds corresponding to the actuation amounts of the actuating levers 44a and 45a in directions corresponding to the actuation directions of the actuating levers 44a and 45a. Furthermore, according to the hydraulic control system 1, a load sensing control is implemented for the pump devices 11R and 11L, so that the operating oil is supplied to the actuators 2 and 3 at flow rates corresponding to the actuation amounts of the actuating levers 44a and 45a. To implement the load sensing control, the hydraulic control system 1 includes the following: Fig. 1 Load sensing device shown 14. load sensing device

[0052] The load sensing device 14 compares and selects the load pressures of the actuators 2 to 4 to obtain the first and second load sensing pressure signals LS1 and LS2. The load sensing device 14 outputs the received first load sensing pressure signal LS1 to the load line pumping device 11L and also outputs the received second load sensing pressure signal LS2 to the steering line pumping device 11R. The load line pumping device 11L operates the regulator 22L to discharge the operating oil at the flow rate corresponding to the pressure signal LS1, and the steering line pumping device 11R operates the regulator 22R to discharge the operating oil at the flow rate corresponding to the pressure signal LS2. The load sensing device 14, configured as described above, has two changeover valves 51 and 52 and the switching valve device 15, and the switching valve device 15 has a switching valve 60.The first changeover valve 51 is connected to the first load-side load sensing pass 41 and the second changeover valve 52, and the second changeover valve 52 is connected to the first load-side load sensing pass 41 and the changeover valve 60 as well as the first changeover valve 51. connected. The switching valve 60 is connected to the loading-side channel 17, the steering-side channel 16, the second changeover valve 52, the steering-side load sensing channel 30 and a third changeover valve 53. When the switching valve 60 is in a neutral position, it blocks the loading-side passage 17 and the loading-side passage 16, connects the second changeover valve 52 to the tank 18, and also connects the third changeover valve 53 to the loading-side load sensing passage 30. If, on the other hand, the switching valve 60 is switched from the neutral position to a switching position, it connects the loading-side passage 17 to the steering-side passage 16, connects the second changeover valve 52 to the steering-side load sensing passage 30, and connects the third changeover valve 53 to the tank 18. The third changeover valve 53 is connected to the first changeover valve 51 in addition to the switching valve 60.The third changeover valve 53 compares an output pressure of the first changeover valve 51 and an output pressure of the switching valve 60 and outputs the higher pressure as the second load sensing pressure signal LS2. The following explains the operation of the switching valve 60 and the load sensing device 14 when the switching valve 60 is in each of its switching positions and neutral positions (i.e., in a switching state and in a neutral state). Actuation of the switching valve, etc., in the switching state

[0053] First, a case is described in which actuator 2 and / or actuator 3 are operating (i.e., an operating state of the load line actuator) and the switching valve 60 is switched from the neutral position to the switching position (during the switching state). The switching valve 60 receives the first selection pressure signal from the first changeover valve 51, which is the output pressure of the first changeover valve 51. When the first selection pressure signal reaches a predetermined pressure or higher, the switching valve 60 is switched from the neutral position to the switching position. More precisely, when actuator 2 and / or actuator 3 are operating (i.e., the load pressure of actuator 2 and / or the load pressure of actuator 3 increases), the switching valve 60 is switched from the neutral position to the switching position. This connects the steering-side load sensing passage 30 and the second changeover valve 52, and the hydraulic pressure (i.e.,The steering-side load sensing pass of the steering-side load sensing pass 30 is input into the second changeover valve 52. At this point, the third changeover valve 53 is connected to the tank 18 via a tank channel 55 through the switching valve 60.

[0054] Furthermore, the second changeover valve 52 is connected to the second load-side load sensing passage 42 and also to the second load-side load sensing channel 42. Specifically, in addition to the hydraulic pressure of the steering-side load sensing channel 30, the hydraulic pressure (i.e., the load pressure of the tilting actuator 3) of the second load-side load sensing passage 42 is also input to the second changeover valve 52. The second changeover valve 52 compares the two input hydraulic pressures, i.e., the hydraulic pressure of the second load-side load sensing passage 42 and the hydraulic pressure of the steering-side load sensing passage 30, and outputs the higher pressure to the first changeover valve 51. The first changeover valve 51 is connected to the first load-side load sensing passage 41, in addition to the second changeover valve 52. Specifically, in addition to the output pressure of the second changeover valve 52, the hydraulic pressure (i.e., the load pressure of the tilting actuator 3) of the second load-side load sensing passage 42 is also input to the second changeover valve 52.The load pressure of the lifting element 2) of the first load-side load-sensing channel 41 is input into the first changeover valve 51. The first changeover valve 51 compares the output pressure of the second changeover valve 52 with the hydraulic pressure of the first load-side load-sensing pass 41 and outputs the higher pressure as the first selection pressure signal. The first selection pressure signal is applied to the switching valve 60 as described above and simultaneously applied to the differential pressure coil 24L of the load line pump device 11L as the first load line pressure signal LS1. Furthermore, the first selection pressure signal is also output to the third changeover valve 53.

[0055] The third changeover valve 53 is connected to the tank 18 via the changeover valve 60, in addition to the first changeover valve 51. The first selection pressure signal and the tank pressure are input to the third changeover valve 53. The third changeover valve 53 selects the higher of the first selection pressure signals and outputs this signal as the second selection pressure signal. This second selection pressure signal is applied to the differential pressure coil 24R of the steering line pump device 11R as the second load sensing pressure signal LS2.

[0056] As described above, the first load pressure signal LS1 is applied to the differential pressure coil 24L of the load line pump device 11L, and the second load pressure signal LS2 is applied to the differential pressure coil 24R of the steering line pump device 11R. The load line pump device 11L then delivers the operating oil at the flow rate corresponding to the first load pressure signal LS1, and the steering line pump device 11R delivers the operating oil at the flow rate corresponding to the second load pressure signal LS2. More precisely, while actuator 2 and / or actuator 3 are in operation, the load line pump device 11L and the steering line pump device 11R supply the operating oil at the required flow rates corresponding to the highest load pressure among the load pressures of actuators 2 to 4.

[0057] The first selection pressure signal is also fed into the control device 13 of the load line, which is applied to the first and second compensators 37 and 38. The first selection pressure signal is applied to the first compensator 37 to counteract the underpressure of the flow control valve 34 (i.e., the hydraulic pressure of the loading-side first load sensing passage 41). The first selection pressure signal is applied to the second compensators 38 to counteract the underpressure of the flow control valve 35 (i.e., the hydraulic pressure of the loading-side second load sensing channel 42). Thus, when actuator 2 and / or actuator 3 are actuated, the flow control mechanism 31 operates such that the pressure differential before and after the flow control valve 34 becomes constant, and the flow control mechanism 32 operates such that the pressure differential before and after the flow control valve 35 becomes constant.

[0058] As above, even if the highest pressure is one of the load pressures of actuators 2 to 4 If the pressure differential before and after the flow control valve 34 and the pressure differential before and after the flow control valve 35 are kept constant, the operating oil can be supplied to actuator 2 with a flow rate corresponding to the actuation amount of actuator 44a of the actuating device 44a, and to actuator 3 with a delivery rate corresponding to the actuation amount of actuator 45a of the actuating device 45a. Specifically, actuator 2 can be actuated independently of the load pressures of actuators 2 to 4 with an actuation speed corresponding to the actuation magnitude of the actuating lever 44a, and actuator 3 with an actuation speed corresponding to the actuation magnitude of the actuating lever 45a. Actuation of the switching valve etc. in the neutral state

[0059] Next, a case is explained in which, for example, actuators 2 and 3 stop (i.e., one load line actuator stops) and the switching valve 60 is in the neutral position (during the neutral state). As described above, when the first selection pressure signal reaches a predetermined pressure or higher, the switching valve 60 operates, i.e., it switches from the neutral position to the switching position. Thus, when actuators 2 and 3 are not operating, the switching valve 60 is held in the neutral position. During this time, the second changeover valve 52 is connected to the tank 18 via the tank passage 55 through the changeover valve 60, and the third changeover valve 53 is connected to the steering-side load sensing passage 30. Therefore, the tank pressure is fed into the second changeover valve 52, and the hydraulic pressure (i.e., the steering-side load sensing pressure) of the steering-side load sensing passage 30 is fed into the third changeover valve 53.

[0060] In addition to the hydraulic pressure of the steering-side load sensing port 30, the first selection pressure signal, which is selected as the higher pressure by the first changeover valve 51, is fed into the third changeover valve 53. At this point, the first selection pressure signal becomes the tank pressure because (i) actuators 2 and 3 are not in operation, (ii) each of the load pressures of actuators 2 and 3 becomes the tank pressure, and (iii) the tank pressure is also fed into the second changeover valve 52 via the switching valve 60. Therefore, when the handle 25, which increases the hydraulic pressure of the steering-side load sensing port 30, is actuated, the third changeover valve 53 outputs the hydraulic pressure of the steering-side load sensing port 30 as the second selection pressure signal. The second selection pressure signal output, as described above, is applied to the differential pressure coil 24R of the steering line pump device 11R as the second load line pressure signal LS2.The steering line pump device 11R delivers the operating oil at a flow rate corresponding to the second load sensing pressure signal LS2 (i.e., the steering-side load sensing pressure). The load line pump device 11L also delivers the operating oil at a flow rate corresponding to the first load sensing pressure signal LS1. As described above, in the neutral state, since actuators 2 and 3 stop and the tank pressure is introduced into the second changeover valve 52, the first selection pressure signal, which is applied as the first load pressure signal LS1, is the tank pressure. Therefore, the first load sensing pressure signal LS1 is in a low state, and the flow rate of the load line pump device 11L is slightly reduced.

[0061] As above, based on the load pressures of the actuators 2 to 4, the load sensing device 14 outputs the first load sensing pressure signal LS1 to the load line pumping device 11L and also the second load sensing pressure signal LS2 to the steering line pumping device 11R via the switching valve 60. Switching valve device

[0062] The switching valve 60, contained in the switching valve device 15, controls the opening and closing of the steering-side passage 16 and the charging-side passage 17 according to the first selection pressure signal input to the switching valve 60. More precisely, when actuator 2 and / or actuator 3 are operating and the first selection pressure signal reaches a predetermined pressure or higher, the steering-side passage 16 and the charging-side passage 17 are connected. This allows the operating oil flowing through the steering-side channel 16 to flow into the charging-side passage 17. Thus, a large quantity of operating oil flows to actuators 2 and 3, enabling them to be moved quickly.

[0063] On the other hand, if, for example, actuators 2 and 3 stop and the first selection pressure signal becomes lower than the specified pressure, the steering-side passage 16 and the loading-side passage 17 are separated from each other. Thus, when only the handle 25 is actuated and the second load-sensing pressure signal LS2, which is the hydraulic pressure of the steering-side load-sensing passage 30, is input into the steering line pump device 11R, the operating oil from the steering line pump device 11R is only delivered with the quantity required to drive the steering actuator 4. Operation of the hydraulic control system

[0064] The functions of the hydraulic control system 1 are explained below. In the hydraulic control system 1, when the actuating lever 44a of the lifting actuating device 44 is actuated, the operating oil is supplied to or discharged from the lifting actuator 2 via the load line control device 13, thereby extending or retracting the lifting actuator 2. Furthermore, when the actuating lever 45a of the tilting actuating device 45 is actuated, the operating oil is supplied to or discharged from the tilting actuator 3 via the load line control device 13, thereby extending or retracting the tilting actuator 3. As above, when at least one of the two actuating levers 44a and 45a (i.e.,When at least one of the two actuators 2 and 3 is actuated, the higher of the load pressures of the two actuators 2 and 3 is selected as the first selection pressure signal by the load sensing device 14 and the first selection pressure signal is output to the switching valve 60. The first selection pressure signal is also output to the differential pressure coil 24L of the load line pump device 11L as the first load line pressure signal LS1.

[0065] When the switching valve 60 receives the first selection pressure signal, it connects the second changeover valve 52 to the steering-side load sensing passage 30. This applies the steering-side load sensing pressure to the second changeover valve 52. If the handle 25 is not actuated, the steering-side load pressure is low, so it is not selected as the first selection pressure signal. More precisely, the higher of the load pressures of the two actuators 2 and 3 is selected as the first selection pressure signal.

[0066] When the switching valve 60 receives the first selection pressure signal, it connects the third changeover valve 53 to the tank 18 through the tank passage 55 to introduce the tank pressure into the third changeover valve 53. In addition to the tank pressure, the first selection pressure signal is applied to the third changeover valve 53. Therefore, the third changeover valve 53 selects the first selection pressure signal as its second selection pressure signal. The third changeover valve 53 then outputs the second selection pressure signal as the second load sensing pressure signal LS2 to the differential pressure coil 24R of the steering line pump device 11R.As described above, when the steering actuator 4 stops and at least one of the two actuators 2 and 3 is in operation, each of the first and second load sensing signals LS1 and LS2 is converted to a hydraulic pressure corresponding to the higher of the load pressures of the two actuators 2 and 3. The hydraulic pumps 21L and 21R of the pump units 11L and 11R then discharge the operating oil at the flow rate corresponding to the higher pressure into the loading-side passage 17 and the steering-side passage 16, respectively. Furthermore, when the switching valve 60 receives the first selection pressure signal, it connects the steering-side passage 16 to the loading-side passage 17. Through this connection, the operating oil discharged by the hydraulic pump 21R into the steering-side passage 16 can flow into the loading-side passage 17. This allows the operating oil to be supplied to the actuators 2 and 3 at a high flow rate.

[0067] Next, a case is explained in which, when at least one of the actuators 2 and 3 is actuated, the handle 25 is actuated, which actuates the steering actuator 4. For example, when the handle 25 is actuated in the direction of rotation towards the first side, the steering slide 28a moves from the neutral position M0 to the first offset position M1. In this case, the steering-side passage 16 is connected to the metering mechanism 29, and the operating oil flowing through the steering-side passage 16 is supplied via the metering mechanism 29 to the second port 4b of the steering actuator 4.

[0068] Simultaneously, the steering-side passage 16 is also connected to the steering-side load sensing passage 30, thus increasing the steering-side load sensing pressure. The steering-side compensator 27 acts such that the pressure difference between the steering-side load sensing pressure and the pressure upstream of the steering valve 28 becomes constant; that is, the pressure difference before and after the steering valve 28 becomes constant. The operating oil flows from the steering valve 28 to the steering actuator 4 with a flow rate corresponding to the actuation force of the handle 25, and the steering actuator 4 operates at an actuation speed corresponding to the actuation force of the handle 25.

[0069] Since at least one of the actuators 2 and 3 is actuated, the switching valve 60 receives the first selection pressure signal and the connection between the steering-side passage 16 and the charging-side passage 17 is maintained. This allows a portion of the operating oil derived from the steering line pump device 11R to be supplied from the steering-side passage 16 to the charging-side passage 17 even when the steering actuator 4 is actuated while at least one of the actuators 2 and 3 is actuated. Thus, even when the steering actuator 4 is actuated while at least one of the actuators 2 and 3 is actuated, it is possible to prevent a situation in which the connection between the steering-side passage 16 and the charging-side passage 17 is suddenly interrupted, and therefore the operating oil is not supplied from the steering line pump device 11R to the charging-side passage 17.Thus, even when steering actuator 4 is being controlled while at least one of actuators 2 and 3 is being controlled, it is possible to prevent a situation in which the operating oil supplied to actuators 2 and 3 decreases significantly and the operating speeds of actuators 2 and 3 decrease significantly.

[0070] The steering-side load sensing channel 30 is connected to the third changeover valve 53 via the switching valve 60. Therefore, if the steering-side load pressure exceeds either of the load pressures of actuators 2 and 3, the steering-side load pressure is selected as the first selection pressure signal by the two changeover valves 51 and 52. Furthermore, the first selection pressure signal is selected by the third changeover valve 53 as the second selection pressure signal, and the second selection pressure signal is output to the steering line pump device 11R as the second load line pressure signal LS2. Thus, even if the steering-side load sensing pressure exceeds either of the load pressures of actuators 2 and 3, the delivery rate of the operating oil from the steering line pump device 11R is ensured, and the steering actuator 4 operates according to the actuation force of the handle 25.

[0071] Furthermore, the first selection pressure signal, which is selected by the two changeover valves 51 and 52, is output as the first load sensing pressure signal LS1 to the load line pump device 11L. This allows the load line pump device 11L to increase the delivery rate according to the first load pressure signal LS1, i.e., the steering-side load pressure, even if the steering-side load pressure becomes higher than either of the load pressures of the actuators 2 and 3. More precisely, if (i) the steering actuator 4 is actuated while at least one of the actuators 2 and 3 is actuated, and (ii) the steering-side load sensing pressure is higher than either of the load pressures of the actuators 2 and 3, the first load sensing pressure signal LS1 (i.e. the steering-side load sensing pressure) is input to the load line pump device 11L and the second load sensing pressure signal LS2 (i.e. the steering-side load sensing pressure) is input to the steering line pump device 11R.For this reason, the delivery rates of both pumps increase. Even if the delivery rate of the operating oil from the steering line pump device 11R is distributed to the actuators 2 and 3 and the steering actuator 4, the operating speeds of the actuators 2 and 3 cannot decrease significantly.

[0072] A further explanation is given of a case in which the handle 25 is actuated alone and the steering actuator 4 is driven alone. When the handle 25 is actuated alone, the steering coil 28a moves into a position corresponding to the direction of rotation of the handle 25, and the rod 4e of the steering actuator 4e moves in a direction corresponding to the direction of rotation. Simultaneously, the load pressure of the steering actuator 4 is introduced into the steering-side load sensing passage 30, and the steering-side compensator 27 controls the flow rate of the operating oil flowing to the steering-side compensator 27 according to the load pressure of the steering actuator 4. Furthermore, the load pressure of the steering actuator 4 is introduced into the switching valve 60 via the steering-side load sensing passage 30.

[0073] When handle 25 is actuated alone, the load pressures of actuators 2 and 3 are low, and the first selection pressure signal is lower than the preset pressure. Therefore, the switching valve 60 connects the second changeover valve 52 to the tank 18 and also the steering-side load sensing passage 30 to the third changeover valve 53. For this reason, the first selection pressure signal output by the first changeover valve 51 is kept low, and the first load sensing pressure signal LS1, also low, is fed into the load line pump device 11L. Thus, the flow rate of the operating oil derived from the load line pump device 11L can be set to a minimum flow rate.On the other hand, the second selection pressure signal, output by the third changeover valve 53, is the load pressure of the steering actuator 4, and the second load pressure signal LS2, corresponding to the load pressure of the steering actuator 4, is input into the steering line pump device 11R. Therefore, the operating oil can be drained from the steering line pump device 11R at the flow rate required by the steering actuator 4. Thus, when only the handle 25 is actuated, the energy loss of the load line pump device 11L during operation of the steering actuator 4 can be minimized by the operating oil supplied by the steering line pump device 11R.According to the load line control device 13 of the hydraulic control system 1 configured as above, since the operating oil is supplied to the actuator 2 via the flow control mechanism 31 and also to the actuator 3 via the flow control mechanism 32, the operating oil can be supplied to the actuator 2 with a delivery rate corresponding to the actuation quantity of the actuator 44a, and to the actuator 3 with a delivery rate corresponding to the actuation quantity of the actuator 45a. For example, if the steering actuator 4 is actuated while at least one of the actuators 2 and 3 is actuated, the operating oil can be supplied to the actuator 2 with a delivery rate corresponding to the actuation quantity of the actuating lever 44a, and also to the actuator 3 with a delivery rate corresponding to the actuation quantity of the actuating lever 45a.Thus, the steering actuator 4 and at least one of the actuators 2 and 3 can be controlled simultaneously without significantly impairing the actuation feel of the actuating devices 44 and 45.

[0074] According to the steering line control device 12, since the operating oil is supplied to the steering actuator 4 via the steering-side compensator 27 and the steering control valve 28, the operating oil can be supplied to the actuators 2 and 3 at a flow rate corresponding to the actuation of the handle 25. Therefore, even if at least one of the actuators 2 and 3 is actuated while the steering actuator 4 is being actuated, the operating oil can still be supplied to the steering actuator 4 at a flow rate corresponding to the actuation of the handle 25. For this reason, the steering actuator 4 and at least one of the actuators 2 and 3 can be actuated simultaneously without significantly affecting the actuation feel of the handle 25. Design 2

[0075] The hydraulic control system 1A of embodiment 2 is similar in configuration to the control system 1 of embodiment 1. Therefore, the following section essentially describes components of the hydraulic control system 1A of embodiment 2 that differ from the components of the hydraulic control system 1 of embodiment 1. The same reference numerals are used for the same components, and repetition of the same explanation is avoided.

[0076] The hydraulic control system 1A of embodiment 2 has a Fig.Figure 4 shows a steering line control device 12A, which includes a priority valve 27A and a safety valve 71. The priority valve 27A is connected to the steering-side passage 16 and the idler pulley 26 and has the same functions as the steering-side compensator 27 of embodiment 1. Specifically, the priority valve 27A is also connected to the steering-side load-sensing passage 30. The hydraulic pressure of the steering-side load-sensing passage 30 and a pressure downstream of the priority valve 27A (i.e., the pressure upstream of the steering valve 28) act against each other on the priority valve 27A. The priority valve 27A functions in such a way that the pressure difference between the hydraulic pressure of the steering-side load sensing passage 30 and the pressure upstream of the steering valve 28 becomes constant, i.e. the pressure difference before and after the steering valve 28 becomes constant.

[0077] The priority valve 27A is also connected to the safety valve 71 and connects the steering-side passage 16 to the safety valve 71 with an opening degree corresponding to the pressure differential before and after the steering valve 28. Specifically, the priority valve 27A can distribute the operating oil flowing through the steering-side passage 16 to the pressure relief valve 71. If the pressure upstream of the safety valve 71 reaches a predetermined overpressure, the safety valve 71 discharges the operating oil distributed from the steering-side passage 16 into the reservoir 18. The overpressure is set to be higher than the maximum load pressure that can act on the steering actuator 4. If the operating oil accumulates in the steering-side channel 16, thereby increasing the hydraulic pressure of the steering-side channel 16, the pressure relief valve 71 can discharge the operating oil.

[0078] The hydraulic control system 1A of embodiment 2, configured as described above, has the same operational advantages as the hydraulic control system 1 of embodiment 1. Other embodiments

[0079] In each of the hydraulic control systems 1 and 1A according to embodiments 1 and 2, the first and second compensators 37 and 38 are arranged on the first and second load-sensing channels 41 and 42 on the charging side, i.e., downstream of the first and second flow control valves 34 and 35. However, the positions of the first and second compensators 37 and 38 are not limited to these. For example, the first and second compensators 37 and 38 can be arranged upstream of the first and second flow control valves 34 and 35. The only requirement is that the pressure differential upstream and downstream of the first flow control valve 34 and the pressure differential upstream and downstream of the second flow control valve 35 remain constant.

[0080] In each of the hydraulic control systems 1 and 1A according to embodiments 1 and 2, the highest of the load pressures of actuators 2 to 4 is selected as the first selection pressure signal. Thus, when the load pressure of steering actuator 4 exceeds any of the load pressures of actuators 2 and 3, and steering actuator 4 is actuated, the load line pump device 11L delivers the operating oil at a flow rate corresponding to the load pressure of steering actuator 4. Since the highest of the load pressures of actuators 2 to 4 is selected as the first selection pressure signal, the flow rate of the load line pump device 11L also increases when the flow rate of the operating oil flowing from the steering-side channel 16 to the charging-side channel 17 decreases. This prevents the operating speeds of actuators 2 and 3 from decreasing.However, the present invention is not necessarily configured as described above, and a higher of the load pressures of actuators 2 and 3 can be selected as the first selection pressure signal. Even if, in this case, the load pressure of the steering actuator 4 becomes higher than either of the load pressures of actuators 2 and 3, and the flow rate of the operating oil flowing from the steering-side channel 16 to the charging-side channel 17 decreases, the flow rate of the load line pump device 11L does not change, so that the operating speeds of actuators 2 and 3 decrease slightly.

[0081] In each of the hydraulic control systems 1 and 1A according to embodiments 1 and 2, the switching valve 60 consists of a pilot switching valve, but need not necessarily be a pilot switching valve. For example, an electromagnetic switching valve is used as the switching valve 60, and a sensor configured to detect the actuations of the actuating levers 44a and 45a, or the first selection pressure signal, is used. Based on the sensor's detection result, the switching valve 60 switches the connection states of the passages. This results in the same operational advantages as in the hydraulic control systems 1 and 1A according to embodiments 1 and 2.

[0082] In each of the hydraulic control systems 1 and 1A according to embodiments 1 and 2, the two actuators 2 and 3 are included as the actuators to be controlled. However, the number of actuators can be one, three, or more, including, for example, a sideshift actuator configured to move the forks laterally. Furthermore, each of the hydraulic control systems 1 and 1A according to embodiments 1 and 2 is not limited to a forklift truck and need only be used in an industrial machine, such as a wheel loader, including a steering actuator and the other load line actuator. Additionally, the hydraulic control systems 1 and 1A according to embodiments 1 and 2 use operating oil as the operating fluid.However, the operating fluid is not limited to oil and simply needs to be a fluid that the steering actuator and the load line actuator can use.

[0083] It is evident from the foregoing explanation that many modifications and other embodiments of the present invention are obvious to a person skilled in the art. Therefore, the foregoing explanation should be interpreted only as an example and serves to convey to a person skilled in the art the best way of carrying out the present invention. The structures and / or functional details can be substantially modified within the scope of the present invention. Reference symbol list LS1 first load line pressure signal LS2 second load-sensing pressure signal 1, 1A hydraulic control system 2 lifting actuators (load line actuators) 3 Tilting actuator (load line actuator) 4 Steering actuator 11L load line pump device 11R Steering line pump device 12 steering line control devices 13 Load line control device 14 Load sensing device 15 Switching valve device 16 steering-side passage 17 loading-side passage 25 handle 27 Steering-side compensator 27A Priority valve (steering-side compensator) 28 Steering valve 30 Steering-side load sensing passage (steering line load pressure channel) 31 First flow control mechanism with pressure equalization function 32 Second flow control mechanism with pressure equalization function 34 Flow control valve 35 Flow control valve 37 first compensator 38 second compensator 41. First load sensing pass on the charging side (load line load pressure pass) 42 Second load-side load sensing pass (load line load pressure pass) 60 Diverter valve 71 Pressure relief valve

Claims

[1] Hydraulic control system or drive system comprising the following: a load line pump device (11L) configured to deliver an operating fluid at a flow rate corresponding to a first load-sensing pressure signal input into the load line pump device (11L); a load line control device connected to a load line actuator (2,3) or a plurality of load line actuators (2,3) and also connected to the load line pump device (11L) via a charging-side passage (17), wherein the load line control device is configured to adjust a flow rate of the operating fluid flowing from the load line pump device (11L) to the single load line actuator (2,3) or the plurality of load line actuators (2,3); a steering line pump device (11R) configured to deliver the operating fluid at a flow rate corresponding to a second load-sensing pressure signal input into the steering line pump device (11R); a steering line control device (12) connected to a steering actuator (4) and also connected to the steering line pump device (11R) via a steering-side passage (16), wherein the steering line control device (12) is configured to adjust a flow rate of the operating fluid flowing from the steering line pump device (11R) to the steering actuator (4); and a switching valve device (15) configured to (i) connect the charging-side passage (17) and the steering-side passage (16) when a charging pressure of one load line actuator (2,3) or at least one of the plurality of load line actuators (2,3) is equal to or higher than a predetermined pressure, and (ii) disconnect the charging-side passage (17) and the steering-side passage (16) when a charging pressure of one load line actuator (2,3) or the plurality of load line actuators (2,3) is less than the predetermined pressure. [2] Hydraulic control system according to claim 1, comprising the following: a multitude of load line load pressure passages connected to the respective multitude of load line actuators (2,3); a pressure passage for the steering line connected to the steering actuator (4); and a load sensing device (14) configured to In the operating state of the load line actuator (2,3), the highest of the pressures from the multitude of load line load pressure passages and a pressure of the steering line load line pressure channel are to be input into the load line pumping device (11L) as the first load-sensing pressure signal, and also the highest of the pressures from the multitude of load line load pressure passages and the pressure of the steering line load line pressure channel are to be input into the load line pumping device (11L) as the second load-sensing pressure signal. In the holding state of the load line actuator (2,3), one of the highest pressures from the multitude of load line load pressure passes is to be entered as the first load sampling pressure signal to the load line pump device (11L), and also the highest pressure from the multitude of load line load pressure passes and the pressure of the steering line load pressure pass are to be entered as the second load sampling pressure signal to the steering line pump device (11R). [3] Hydraulic control system according to claim 2, wherein: the load line control device has a plurality of flow control mechanisms (31,32) each having a pressure equalization function; the multitude of flow control mechanisms (31,32) are assigned to a corresponding multitude of actuating devices; the multitude of flow control mechanisms (31,32) are assigned to the respective multitude of load line actuators (2,3); the multitude of flow control mechanisms (31, 32) includes corresponding flow control valves and corresponding compensators (27, 37, 38); and Each of the multiple flow control mechanisms (31,32) supplies the operating fluid via the flow control valve and the compensator (27,37,38) to the associated load line actuator (2,3) at a flow rate corresponding to an operating command issued by the associated actuating device. [4] Hydraulic control system according to claim 2 or 3, wherein: the steering line control device (12) comprises a steering valve and a steering-side compensator (27); and The steering line control device (12) supplies the operating fluid from the steering line pump device (11R) to the steering actuator (4) via the steering valve (28) and the steering-side compensator (27) with a delivery quantity that corresponds to an actuation quantity of an actuating tool. [5] Hydraulic control system according to claim 4, wherein: the steering line control device (12) has a safety or pressure relief valve (71); the steering-side compensator (27) is connected to the safety valve and supplies the safety valve with a portion of the operating fluid flowing through the steering-side passage; if the pressure of the operating fluid flowing through the safety valve (71) becomes excessive, the safety valve releases the operating fluid flowing through the safety valve into a tank; and the overpressure is set higher than an operating pressure at which the steering actuator (4) operates.

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