Hydraulic drive device for industrial vehicle

Abstract

To provide a hydraulic drive device for an industrial vehicle capable of stabilizing a loading / unloading speed even when an inertial force is input for a certain period of time during loading / unloading operation.SOLUTION: A hydraulic drive device 20 is disposed between a hydraulic pump 22, a tank 21, and an attachment cylinder 14, and is equipped with a counterbalance valve 25 that allows the flow of hydraulic oil from the attachment cylinder 14 to the tank 21 when the supply pressure of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 is equal to or higher than the valve opening pressure, and blocks the flow of hydraulic oil to the tank 21 when the supply pressure of the hydraulic oil is lower than the valve opening pressure, a pressure sensor 47 that detects the supply pressure of the hydraulic oil, and a motor rotation increase control unit 53 that controls the loading motor 23 to increase the flow rate of hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 when the supply pressure of the hydraulic oil detected by the pressure sensor 47 drops from a state equal to or higher than the valve opening pressure to a preset specified pressure P1.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a hydraulic drive system for an industrial vehicle. [Background technology]

[0002] As a hydraulic drive system for an industrial vehicle, for example, the technology described in Patent Document 1 is known. The hydraulic drive system described in Patent Document 1 is mounted on a forklift, which is one of the industrial vehicles. The hydraulic drive system includes a hydraulic pump that supplies hydraulic oil to the lift cylinder and the tilt cylinder, an electric motor that rotates the hydraulic pump, a directional control valve disposed between the hydraulic pump and the tilt cylinder, a pressure sensor that detects the lift cylinder holding pressure, a tilt angle sensor that detects the tilt angle, and a controller that obtains the tilt cylinder holding pressure based on the detection values ​​of the pressure sensor and the tilt angle sensor and controls the motor according to the tilt cylinder holding pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-31344 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, an example of an attachment for a forklift is a fork that tilts via a hinge (hinged fork). In a forklift equipped with such a hinged fork, a counterbalance valve is sometimes provided in the hydraulic circuit to prevent negative pressure due to inertial inputs such as the load and traveling speed other than hydraulic pressure. However, when the hinged fork is tilted forward by the attachment cylinder, if excessive inertial force due to the load and traveling speed is input for a certain period of time, the extension speed of the attachment cylinder increases, causing a shortage of hydraulic oil supplied to the attachment cylinder, and the pressure (supply pressure) of the hydraulic oil supplied to the attachment cylinder decreases. As a result, the counterbalance valve repeatedly opens and closes, causing the loading speed to become unstable, which is called hunting.

[0005] An object of the present invention is to provide a hydraulic drive system for an industrial vehicle that can stabilize the loading / unloading speed even when an inertial force is input for a certain period of time during loading / unloading operation. [Means for solving the problem]

[0006] (1) One aspect of the present invention is a hydraulic drive system for an industrial vehicle having a fork for holding luggage, the system comprising: a hydraulic cylinder for actuating the fork; a tank for storing hydraulic oil; a hydraulic pump for supplying hydraulic oil to the hydraulic cylinder; a prime mover for rotating the hydraulic pump; a pressure control valve disposed between the hydraulic pump, the tank, and the hydraulic cylinder, the pressure control valve allowing the flow of hydraulic oil from the hydraulic cylinder to the tank when the supply pressure of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder is equal to or higher than the valve opening pressure, and blocking the flow of hydraulic oil from the hydraulic cylinder to the tank when the supply pressure of the hydraulic oil is lower than the valve opening pressure; a pressure detection unit for detecting the supply pressure of the hydraulic oil; and an increase control unit for controlling the prime mover to increase the flow rate of hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder when the supply pressure of the hydraulic oil detected by the pressure detection unit drops from a state equal to or higher than the valve opening pressure to a predetermined specified pressure.

[0007] In such a hydraulic drive system for an industrial vehicle, when the fork is operated by the hydraulic cylinder, hydraulic oil is supplied from the hydraulic pump to the hydraulic cylinder, and the hydraulic oil is returned from the hydraulic cylinder to the tank by allowing the hydraulic oil to flow from the hydraulic cylinder to the tank in the pressure control valve. At this time, the supply pressure of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder is detected. Then, when the supply pressure of the hydraulic oil drops from a state equal to or higher than the valve opening pressure to a preset specified pressure, the prime mover is controlled to increase the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder. Therefore, even if the supply pressure of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder drops due to an excessive inertial force due to the load, traveling speed, etc. being input for a certain period of time, the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder increases. Therefore, since the supply pressure of the hydraulic oil increases, the pressure control valve maintains a state in which the hydraulic oil is allowed to flow from the hydraulic cylinder to the tank. As a result, even when an inertial force is input for a certain period of time during a loading operation, the loading speed is stabilized.

[0008] (2) In the above (1), the hydraulic drive device may further include a quantity reduction control unit that controls the prime mover to reduce the flow rate of hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder after executing the processing of the quantity increase control unit. In such a configuration, the flow rate of hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder increases, and after the supply pressure of the hydraulic oil increases, the flow rate of hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder decreases, thereby suppressing wasteful use of hydraulic oil.

[0009] (3) In the above (2), the reduction control unit may control the prime mover to reduce the flow rate of hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder when the supply pressure of the hydraulic oil detected by the pressure detection unit rises to a target pressure higher than the specified pressure. In this configuration, when the supply pressure of the hydraulic oil rises to a target pressure higher than the specified pressure, the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder is reduced.

[0010] (4) In the above (2), when a specified time has elapsed since the start of the execution of the processing by the increment control unit, the prime mover may be controlled so as to decrease the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder. In such a configuration, when a certain time has elapsed after the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder has increased, the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder will decrease.

[0011] (5) In the above (2), the hydraulic drive device further includes an operation unit for performing an operation of operating the fork, and the decrement control unit may control the prime mover so as to decrease the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder when the operation of operating the fork by the operation unit is released. In such a configuration, when the operation of operating the fork by the operation unit is released, the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder will decrease.

[0012] (6) In any of the above (1) to (5), the hydraulic drive device further includes a storage unit that stores a plurality of parameters in the increment data regarding the increase in the flow rate of the hydraulic oil, and an input unit for selectively inputting any of the plurality of parameters stored in the storage unit. When the supply pressure of the hydraulic oil has decreased from a state where it is equal to or higher than the valve opening pressure to a specified pressure, the increment control unit may control the prime mover so as to increase the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder according to the parameter selectively input by the input unit. In such a configuration, when the supply pressure of the hydraulic oil has decreased from a state where it is equal to or higher than the valve opening pressure to a specified pressure, the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder increases according to the parameter of the increment data selectively input by the input unit. Therefore, depending on the type and usage state of the industrial vehicle or the user's usage environment, etc., the amount of increase change and increase time of the flow rate of the hydraulic oil supplied to the hydraulic cylinder can be easily changed.

[0013] (7) In any of (1) to (6) above, the hydraulic cylinder may be an attachment cylinder that tilts the forks via a hinge, and the amount-increasing control unit may control the prime mover to increase the flow rate of hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder when the supply pressure of the hydraulic oil drops from a state equal to or higher than the valve opening pressure to a specified pressure when the attachment cylinder tilts the forks forward. In this configuration, the extension / contraction speed of the attachment cylinder can be stabilized during forward tilting of the forks, which is prone to input of excessive inertial force due to the load, traveling speed, etc. Effect of the Invention

[0014] According to the present invention, even when an inertial force is input for a certain period of time during a loading / unloading operation, the loading / unloading speed can be stabilized. [Brief description of the drawings]

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0017] Fig. 1 is a side view showing a forklift as an industrial vehicle equipped with a hydraulic drive system according to one embodiment of the present invention. In Fig. 1, the forklift 1 is an electric forklift. The forklift 1 includes a traveling device 2 and a loading device 3 that is disposed in front of the traveling device 2 and performs loading and unloading.

[0018] The running gear 2 has a vehicle body 5 having a driver's cab 4, front wheels 6 which are steered wheels arranged at the front end of the vehicle body 5, and rear wheels 7 which are drive wheels arranged at the rear end of the vehicle body 5.

[0019] The cargo handling device 3 includes a mast 8 erected at the front end of the vehicle body 5, two forks 10, one on the left and one on the right, which are attached to the mast 8 via a lift bracket 9 so as to be able to rise and fall and hold cargo M, a lift cylinder 11 which raises and lowers the forks 10 via the lift bracket 9, and a tilt cylinder 12 which tilts the mast 8. The lift cylinder 11 and the tilt cylinder 12 are hydraulic cylinders.

[0020] As shown in Fig. 2, the fork 10 is a hinged fork that can tilt via a hinge 13 attached to the lift bracket 9. The hinged fork is one of the attachments. The fork 10 can rotate around a shaft 13a provided at the tip of the hinge 13. Fig. 2(a) shows the neutral state of the fork 10. Fig. 2(b) shows the forward tilted state of the fork 10. The fork 10 is tilted by an attachment cylinder 14. The attachment cylinder 14 is a hydraulic cylinder.

[0021] 3 is a diagram showing a hydraulic circuit of a hydraulic drive system according to an embodiment of the present invention, together with the fork 10. This hydraulic circuit is a hydraulic circuit that drives the attachment cylinder 14.

[0022] In FIG. 3, the hydraulic drive system 20 of this embodiment includes the attachment cylinder 14, a tank 21, a hydraulic pump 22, a loading motor 23, an oil control valve 24, a counterbalance valve 25, and a check valve .

[0023] The tank 21 stores hydraulic oil. The hydraulic pump 22 draws in the hydraulic oil in the tank 21 and supplies the hydraulic oil to the attachment cylinder 14. The loading motor 23 is an electric motor (prime mover) that drives the hydraulic pump 22 to rotate.

[0024] The oil control valve 24 is disposed between the hydraulic pump 22 / tank 21, and the attachment cylinder 14. The oil control valve 24 is connected to the discharge port 22a of the hydraulic pump 22 and the tank 21 via hydraulic oil passages 27, 28, respectively, and is connected to the bottom chamber of the attachment cylinder 14 via a hydraulic oil passage 29. The oil control valve 24 is an electromagnetic directional control valve that switches the direction in which hydraulic oil flows between the hydraulic pump 22 / tank 21, and the attachment cylinder 14.

[0025] Although not shown, the oil control valve 24 switches between a neutral position, a forward tilt position, and a backward tilt position. The neutral position is a position that blocks the hydraulic oil passages 27, 28 from the hydraulic oil passage 29, and also blocks the hydraulic oil passages 27, 28 from the hydraulic oil passage 30 (described later). The forward tilt position is a position (position shown) that connects the hydraulic oil passage 27 to the hydraulic oil passage 29, and also connects the hydraulic oil passage 28 to the hydraulic oil passage 30. The backward tilt position is a position that connects the hydraulic oil passage 27 to the hydraulic oil passage 30, and also connects the hydraulic oil passage 28 to the hydraulic oil passage 29.

[0026] The counterbalance valve 25 is disposed between the oil control valve 24 and the attachment cylinder 14. Therefore, the counterbalance valve 25 is disposed between the hydraulic pump 22 / tank 21, and the attachment cylinder 14. The counterbalance valve 25 is connected to the oil control valve 24 via a hydraulic oil passage 30, and is also connected to the rod chamber of the attachment cylinder 14 via a hydraulic oil passage 31.

[0027] The counterbalance valve 25 is a pressure control valve that allows the flow of hydraulic oil from the attachment cylinder 14 to the tank 21 when the pressure (supply pressure) of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 is equal to or higher than the valve opening pressure, and blocks the flow of hydraulic oil from the attachment cylinder 14 to the tank 21 when the supply pressure of the hydraulic oil is lower than the valve opening pressure.

[0028] The counterbalance valve 25 switches between an open position 25a having an oil passage 32 that connects the hydraulic oil passage 30 and the hydraulic oil passage 31, and a closed position 25b that blocks the hydraulic oil passage 30 and the hydraulic oil passage 31. A throttle valve 33 is provided in the oil passage 32 in the open position 25a. A pilot operation unit 34a is provided at one end side (open position 25a side) of the counterbalance valve 25. A spring 35 and a pilot operation unit 34b are provided at the other end side (closed position 25b side) of the counterbalance valve 25.

[0029] The pilot operating unit 34a is connected to the hydraulic oil passage 29 via a pilot passage 36. A throttle valve 37 is provided in the pilot passage 36. A pilot passage 38 is connected in parallel to the pilot passage 36 so as to bypass the throttle valve 37. A spring-loaded check valve 39 that allows hydraulic oil to flow only from the hydraulic oil passage 29 side to the pilot operating unit 34a side is provided in the pilot passage 38.

[0030] The pilot operating section 34b is connected to the hydraulic oil passage 30 via a pilot passage 40. A throttle valve 41 is provided in the pilot passage 40.

[0031] The opening pressure of the counterbalance valve 25 is determined by the biasing force of the spring 35. Specifically, when the pilot pressure in the pilot flow path 36 is equal to or greater than the combined force of the biasing force of the spring 35 and the pilot pressure in the pilot flow path 40, the position of the counterbalance valve 25 is in an open position 25a. When the pilot pressure in the pilot flow path 36 is smaller than the combined force of the biasing force of the spring 35 and the pilot pressure in the pilot flow path 40, the position of the counterbalance valve 25 is in a closed position 25b. The pilot pressure in the pilot flow path 36 corresponds to the pressure (supply pressure) of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14. The combined force of the biasing force of the spring 35 and the pilot pressure in the pilot flow path 40 corresponds to the opening pressure of the counterbalance valve 25.

[0032] The check valve 26 is disposed in a hydraulic oil passage 42 that connects the upstream and downstream sides of the counterbalance valve 25. One end of the hydraulic oil passage 42 is connected to the hydraulic oil passage 30, and the other end of the hydraulic oil passage 42 is connected to the hydraulic oil passage 31. The check valve 26 allows the flow of hydraulic oil from the hydraulic pump 22 side to the attachment cylinder 14 side, and blocks the flow of hydraulic oil from the attachment cylinder 14 side to the tank 21 side.

[0033] When the oil control valve 24 is in the neutral position, no hydraulic oil is supplied from the hydraulic pump 22 to the attachment cylinder 14, so the attachment cylinder 14 does not extend or retract. Therefore, as shown in Figure 2(a), the fork 10 does not tilt.

[0034] With the oil control valve 24 in the forward tilted position, hydraulic oil discharged from the hydraulic pump 22 flows through the hydraulic oil passage 27, the oil control valve 24, and the hydraulic oil passage 29, and is supplied to the bottom chamber of the attachment cylinder 14. At this time, when the supply pressure of the hydraulic oil is equal to or higher than the valve opening pressure of the counterbalance valve 25, the counterbalance valve 25 is in the open position 25a.

[0035] In this state, the attachment cylinder 14 extends, causing the fork 10 to tilt forward via the hinge 13, as shown in Fig. 2(b). At this time, the hydraulic oil in the rod chamber of the attachment cylinder 14 flows through the hydraulic oil passage 31, the counterbalance valve 25, the hydraulic oil passage 30, the oil control valve 24, and the hydraulic oil passage 28, and returns to the tank 21.

[0036] With the oil control valve 24 in the rearward tilted position, hydraulic oil discharged from the hydraulic pump 22 flows through the hydraulic oil passage 27, the oil control valve 24, and the hydraulic oil passages 30, 42, and 31, and is supplied to the rod chamber of the attachment cylinder 14. Then, the attachment cylinder 14 contracts, causing the fork 10 to tilt rearward via the hinge 13. At this time, the hydraulic oil in the bottom chamber of the attachment cylinder 14 flows through the hydraulic oil passage 29, the oil control valve 24, and the hydraulic oil passage 28, and returns to the tank 21.

[0037] 4 is a block diagram showing the configuration of a control system of a hydraulic drive device according to one embodiment of the present invention. In FIG. 4, the hydraulic drive device 20 includes an attachment operation lever 46, a pressure sensor 47, a storage unit 48, an input device 49, and a controller 50.

[0038] The attachment operation lever 46 is a manually operated lever that is used by the operator to tilt the forks 10. The attachment operation lever 46 constitutes an operation unit that is used to operate the forks 10.

[0039] The pressure sensor 47 is a sensor that detects the pressure of the hydraulic oil passage 29. The pressure sensor 47 constitutes a pressure detection unit that detects the pressure (supply pressure) of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14. The pressure sensor 47 may detect the pressure of the pilot passage 36 connected to the hydraulic oil passage 29.

[0040] The memory unit 48 stores a plurality of parameters (numerical values) in the increase data relating to the increase in the flow rate of hydraulic oil when the flow rate of hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 is increased (increased) by increasing the rotation speed of the loading motor 23. Examples of the increase data include the target rotation speed value of the loading motor 23, the time for the rotation speed to increase, and the amount of change in the rotation speed (slope). A plurality of parameters are set for each of these increase data. The increase amount, the increase time, and the amount of increase change in the flow rate of hydraulic oil change by changing the target rotation speed value, the time for the rotation speed to increase, and the amount of change in the rotation speed of the loading motor 23.

[0041] The input device 49 constitutes an input unit for selectively inputting any one of a plurality of parameters for each increase data stored in the memory unit 48. For example, a selection button or a selection switch is used as the input device 49. The parameters for each increase data set and input by the input device 49 are stored in the internal memory of the controller 50.

[0042] The controller 50 is composed of a CPU, a RAM, a ROM, an input / output interface, etc. The controller 50 has a forward tilt control unit 51, a pressure drop determination unit 52, a motor rotation increase control unit 53, a reduction determination unit 54, and a motor rotation decrease control unit 55.

[0043] When the fork 10 is tilted forward by the attachment operating lever 46, the forward tilt control unit 51 controls the oil control valve 24 so that the fork 10 is tilted forward by the attachment cylinder 14, and also controls the loading motor 23 so as to increase the rotation speed of the loading motor 23.

[0044] The pressure drop determination unit 52 determines whether the supply pressure of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 has dropped from a state equal to or higher than the valve opening pressure of the counterbalance valve 25 to a preset specified pressure, based on the detection value of the pressure sensor 47. The specified pressure may be equal to the valve opening pressure of the counterbalance valve 25, or may be higher than the valve opening pressure of the counterbalance valve 25.

[0045] The motor rotation increase control unit 53 controls the loading motor 23 to increase the rotation speed of the loading motor 23 when the pressure drop determination unit 52 determines that the supply pressure of the hydraulic oil has dropped from a state equal to or higher than the opening pressure of the counterbalance valve 25 to a specified pressure.

[0046] The pressure drop determination unit 52 and the motor rotation increase control unit 53 constitute an increase control unit that controls the loading motor 23 to increase the flow rate of hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 when the supply pressure of hydraulic oil detected by the pressure sensor 47 drops from a state equal to or higher than the opening pressure of the counterbalance valve 25 to a preset specified pressure.

[0047] The reduction determination unit 54 determines whether or not it is necessary to reduce the flow rate (supply amount) of hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14, based on the operation signal of the attachment operation lever 46, the detection value of the pressure sensor 47, and a timer built into the controller 50.

[0048] The motor rotation reduction control unit 55 controls the loading motor 23 to reduce the rotation speed of the loading motor 23 when the reduction determination unit 54 determines that the amount of hydraulic oil supplied needs to be reduced.

[0049] The reduction determination unit 54 and the motor rotation reduction control unit 55 constitute a reduction control unit that controls the loading motor 23 to reduce the flow rate of hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 after executing the processing of the increase control unit.

[0050] 5 is a flowchart showing the procedure of the forward tilt control process executed by the controller 50. This process is executed by the forward tilt control unit 51 when the forklift 1 is started.

[0051] 5, the controller 50 first acquires an operation signal of the attachment operating lever 46 (step S101). Then, the controller 50 determines whether the attachment operating lever 46 has been operated to tilt forward based on the operation signal of the attachment operating lever 46 (step S102). If the controller 50 determines that the attachment operating lever 46 has not been operated to tilt forward, it executes the above-mentioned step S101 again.

[0052] When the controller 50 determines that the attachment operating lever 46 has been operated to tilt forward, it controls the oil control valve 24 so that the attachment cylinder 14 tilts the fork 10 forward (step S103). At this time, the controller 50 controls the oil control valve 24 so that the position of the oil control valve 24 is switched from the neutral position to the forward tilt position.

[0053] Further, the controller 50 controls the loading motor 23 so as to increase the rotation speed of the loading motor 23 (step S104). At this time, the controller 50 increases the motor rotation speed command value output to the loading motor 23 to a set value A (see FIG. 7) corresponding to the operation amount of the attachment operation lever 46.

[0054] Fig. 6 is a flowchart showing the procedure of the hydraulic oil supply amount control process executed by the controller 50. This process is executed by the pressure drop determination unit 52, the motor rotation increase control unit 53, the amount reduction determination unit 54, and the motor rotation reduction control unit 55 after the forward tilt control process shown in Fig. 5 is executed.

[0055] At the start of this process, the supply pressure of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 is higher than the opening pressure of the counterbalance valve 25, so that the counterbalance valve 25 is in the open position 25a.

[0056] 6, the controller 50 first acquires a detection value of the pressure sensor 47 (step S111). Then, the controller 50 determines whether the supply pressure of the hydraulic oil has decreased to a preset specified pressure P1 (see FIG. 7) based on the detection value of the pressure sensor 47 (step S112).

[0057] When the controller 50 determines that the supply pressure of the hydraulic oil has not decreased to the specified pressure P1, it executes the above-mentioned step S111 again. When the controller 50 determines that the supply pressure of the hydraulic oil has decreased to the specified pressure P1, it reads the parameters for each increase data stored in the built-in memory (described above) (step S113).

[0058] Then, the controller 50 controls the loading motor 23 so as to increase the rotation speed of the loading motor 23 in accordance with the parameters for each increase data (step S114). Specifically, the controller 50 controls the loading motor 23 so that the rotation speed of the loading motor 23 increases by a set and input amount of change (gradient) for a set and input time. At this time, the motor rotation speed command value output to the loading motor 23 increases to a set value A+α or a set value A×α.

[0059] Next, the controller 50 acquires an operation signal of the attachment operation lever 46 (step S115). Then, the controller 50 determines whether the forward tilt operation of the attachment operation lever 46 has been released based on the operation signal of the attachment operation lever 46 (step S116).

[0060] When the controller 50 determines that the forward tilt operation of the attachment operating lever 46 has been released, it controls the loading motor 23 to reduce the rotation speed of the loading motor 23 (step S117). At this time, the controller 50 controls the loading motor 23, for example, so that the rotation speed of the loading motor 23 is reduced to the rotation speed in the state before the forward tilt operation of the attachment operating lever 46 was performed.

[0061] When the controller 50 determines that the forward tilt operation of the attachment operating lever 46 has not been released, it acquires the detection value of the pressure sensor 47 (step S118). Then, the controller 50 determines whether the supply pressure of the hydraulic oil has increased to a target pressure P2 (see FIG. 7) based on the detection value of the pressure sensor 47 (step S119). The target pressure P2 is a pressure higher than the specified pressure P1.

[0062] When the controller 50 determines that the supply pressure of the hydraulic oil has increased to the target pressure P2, it controls the loading motor 23 to reduce the rotation speed of the loading motor 23 (step S120). At this time, the controller 50 controls the loading motor 23, for example, to reduce the rotation speed of the loading motor 23 to a set value A corresponding to the operation amount of the attachment operation lever 46.

[0063] When the controller 50 determines that the supply pressure of the hydraulic oil has not risen to the target pressure P2, it determines whether a specified time has elapsed since controlling the loading motor 23 to increase the rotation speed of the loading motor 23 in step S114 (step S121).

[0064] When the controller 50 determines that the specified time has elapsed, it controls the cargo handling motor 23 to reduce the rotation speed of the cargo handling motor 23 (step S120). When the controller 50 determines that the specified time has not elapsed, it executes the above-mentioned step S115 again.

[0065] When the rotation speed of the cargo-handling motor 23 is decreased in steps S117 and S120, similarly to when the rotation speed of the cargo-handling motor 23 is increased in step S114, the rotation speed of the cargo-handling motor 23 may be decreased according to the parameters selectively input by the input device 49. In this case, a plurality of parameters are set for each weight loss data.

[0066] Here, the pressure drop determination unit 52 executes steps S111 and S112. The motor speed increase control unit 53 executes steps S113 and S114. The reduction determination unit 54 executes steps S115, S116, S118, S119, and S121. The motor speed drop control unit 55 executes steps S117 and S120.

[0067] In the hydraulic drive system 20 as described above, when the attachment operating lever 46 is tilted forward by the operator, the oil control valve 24 switches from the neutral position to the open position, and the RPM of the loading motor 23 increases (see t0 in the figure) as shown in Fig. 7. Then, as shown in Fig. 3, the hydraulic oil discharged from the hydraulic pump 22 flows through the hydraulic oil passages 27, 29 and is supplied to the bottom chamber of the attachment cylinder 14.

[0068] At this time, the pressure in the hydraulic oil passage 29 rises and becomes higher than the valve opening pressure of the counterbalance valve 25, so that the counterbalance valve 25 opens to the open position 25a as shown in Fig. 3(a). Therefore, the hydraulic oil in the rod chamber of the attachment cylinder 14 flows through the hydraulic oil passages 31, 30, and 28 and returns to the tank 21, causing the attachment cylinder 14 to extend and the fork 10 to tilt forward.

[0069] Here, when the forks 10 holding the load M tilt forward, if excessive inertial force due to the load, traveling speed, etc. is input for a certain period of time, the extension speed of the attachment cylinder 14 increases, causing a shortage of hydraulic oil supplied to the attachment cylinder 14 and a drop in pressure in the hydraulic oil passage 29. When the pressure in the hydraulic oil passage 29 becomes lower than the opening pressure of the counterbalance valve 25, the position of the counterbalance valve 25 switches from the open position 25a to the closed position 25b as shown in Figure 3(b), and the extension operation of the attachment cylinder 14 stops.

[0070] Then, the pressure in the hydraulic oil passage 29 rises and becomes higher than the opening pressure of the counterbalance valve 25, so that the position of the counterbalance valve 25 switches from the closed position 25b to the open position 25a as shown in Figure 3(a), and the attachment cylinder 14 extends again. Because the counterbalance valve 25 repeats opening and closing operations in this way, the extension speed of the attachment cylinder 14 becomes unstable, causing so-called hunting.

[0071] 7, when the pressure in the hydraulic oil passage 29 (the supply pressure of the hydraulic oil) falls to a specified pressure P1, the loading motor 23 is controlled so as to increase its rotation speed (see t1 in the figure). Then, the flow rate of the hydraulic oil discharged from the hydraulic pump 22 increases, and the pressure in the hydraulic oil passage 29 rises. Therefore, the position of the counterbalance valve 25 is maintained in the open position 25a, and the extension speed of the attachment cylinder 14 is prevented from becoming unstable.

[0072] 7, when the pressure in the hydraulic oil passage 29 rises to the target pressure P2, the lifting motor 23 is controlled so as to decrease its rotation speed (see t2 in the figure). Then, the flow rate of the hydraulic oil discharged from the hydraulic pump 22 decreases, and the pressure in the hydraulic oil passage 29 decreases.

[0073] As described above, in this embodiment, when the fork 10 is operated by the attachment cylinder 14, hydraulic oil is supplied from the hydraulic pump 22 to the attachment cylinder 14, and the counterbalance valve 25 allows the hydraulic oil to flow from the attachment cylinder 14 to the tank 21, so that the hydraulic oil returns from the attachment cylinder 14 to the tank 21. At this time, the supply pressure of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 is detected. Then, when the supply pressure of the hydraulic oil drops from a state equal to or higher than the valve opening pressure of the counterbalance valve 25 to a preset specified pressure P1, the loading motor 23 is controlled to increase the flow rate of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14. Therefore, even if the supply pressure of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 drops due to an excessive inertial force due to the load, traveling speed, etc. being input for a certain period of time, the flow rate of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 increases. Therefore, the supply pressure of the hydraulic oil increases, and the counterbalance valve 25 maintains a state in which the hydraulic oil is permitted to flow from the attachment cylinder 14 to the tank 21. This stabilizes the loading / unloading speed even when an inertial force is input for a certain period of time during loading / unloading operation.

[0074] Therefore, even if there is a risk of unstable loading speed, it can be dealt with simply by rewriting the software, eliminating the need to replace hardware parts. As a result, there is no need to order parts, which reduces the cost of the problem and shortens the time it takes to fix it.

[0075] Furthermore, in this embodiment, the flow rate of hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 increases, and after the supply pressure of the hydraulic oil rises, the flow rate of hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 decreases, thereby suppressing wasteful use of hydraulic oil.

[0076] Further, in the present embodiment, when the supply pressure of the hydraulic oil rises to a target pressure P2 that is greater than the specified pressure P1, the flow rate of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 will decrease.

[0077] Further, in the present embodiment, when a certain period of time has elapsed after the flow rate of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 has increased, the flow rate of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 will decrease.

[0078] Further, in the present embodiment, when the operation of operating the fork 10 by the attachment operation lever 46 is released, the flow rate of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 will decrease.

[0079] Further, in the present embodiment, when the supply pressure of the hydraulic oil drops from a state where it is equal to or higher than the valve opening pressure of the counterbalance valve 25 to the specified pressure P1, the flow rate of the hydraulic oil supplied from the hydraulic pump 22 to the attachment cylinder 14 increases according to the parameters of the increment data selected and input by the input device 49. Therefore, depending on the type and usage state of the forklift 1 or the user's usage environment, etc., it is possible to easily change the amount of increase and the increase time of the flow rate of the hydraulic oil supplied to the attachment cylinder 14.

[0080] Further, in the present embodiment, during the forward tilting operation of the fork 10 where excessive inertial forces due to the load capacity and traveling speed are likely to be input, the extension speed of the attachment cylinder 14 can be stabilized.

[0081] Note that the present invention is not limited to the above embodiment. For example, in the above embodiment, the cargo handling motor 23 is controlled to increase the supply amount of the hydraulic oil according to the parameters of the increment data selected and input by the input device 49, but it is not particularly limited to that form, and the supply amount of the hydraulic oil may be increased according to the parameters of predetermined increment data.

[0082] In the above embodiment, the loading motor 23 is controlled to reduce its rotation speed when the supply pressure of the hydraulic oil rises to the target pressure P2 or when a certain time has elapsed since the flow rate of the hydraulic oil increased, but this is not particularly limited to the embodiment. While the forward tilt operation of the attachment operating lever 46 continues, the rotation speed of the loading motor 23 may remain constant without being reduced.

[0083] In the above embodiment, the hydraulic pump 22 is driven by the cargo motor 23, but the present invention can also be applied to an engine-type forklift in which the hydraulic pump 22 is driven by an engine as a prime mover. In this case, when the forklift is stopped and the supply pressure of the hydraulic oil drops to a specified pressure P1, the engine is controlled so that the engine speed increases to a speed lower than that during full throttle.

[0084] In the above embodiment, the rotation speed of the hydraulic pump 22 is controlled when the hinged fork 10 is tilted forward by the attachment cylinder 14. However, the present invention is also applicable to a case where a normal fork is tilted forward by, for example, the tilt cylinder 12.

[0085] Furthermore, although the hydraulic drive system 20 of the above embodiment is provided on the forklift 1, the present invention can also be applied to industrial vehicles other than the forklift, so long as a pressure control valve is installed to prevent negative pressure generated by inertial input during loading and unloading operations. [Explanation of symbols]

[0086] 1...forklift (industrial vehicle), 10...fork, 13...hinge, 14...attachment cylinder (hydraulic cylinder), 20...hydraulic drive unit, 21...tank, 22...hydraulic pump, 23...loading motor (prime mover), 25...counterbalance valve (pressure control valve), 46...attachment operation lever (operation unit), 47...pressure sensor (pressure detection unit), 48...memory unit, 49...input device (input unit), 52...pressure drop determination unit (increase control unit), 53...motor rotation increase control unit (increase control unit), 54...decrease determination unit (decrease control unit), 55...motor rotation decrease control unit (decrease control unit), P1...specified pressure, P2...target pressure.

Claims

1. A hydraulic drive device for an industrial vehicle having forks for holding a load, comprising: a hydraulic cylinder for operating the forks; a tank for storing hydraulic oil; a hydraulic pump for supplying hydraulic oil to the hydraulic cylinder; a prime mover for rotationally driving the hydraulic pump; a pressure control valve disposed between the hydraulic pump, the tank, and the hydraulic cylinder, which allows the flow of hydraulic oil from the hydraulic cylinder to the tank when the supply pressure of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder is equal to or higher than the valve opening pressure, and blocks the flow of hydraulic oil from the hydraulic cylinder to the tank when the supply pressure of the hydraulic oil is lower than the valve opening pressure; a pressure detection unit for detecting the supply pressure of the hydraulic oil; an increment control unit for controlling the prime mover to increase the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder when the supply pressure of the hydraulic oil detected by the pressure detection unit drops from a state equal to or higher than the valve opening pressure to a preset specified pressure. A hydraulic drive device for an industrial vehicle comprising the above components.

2. The hydraulic drive device for an industrial vehicle according to claim 1, further comprising a decrement control unit for controlling the prime mover to decrease the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder after the process of the increment control unit is executed.

3. The hydraulic drive device for an industrial vehicle according to claim 2, wherein the decrement control unit controls the prime mover to decrease the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder when the supply pressure of the hydraulic oil detected by the pressure detection unit rises to a target pressure higher than the specified pressure.

4. The hydraulic drive device for an industrial vehicle according to claim 2, wherein the decrement control unit controls the prime mover to decrease the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder when a specified time has elapsed since the start of the execution of the process of the increment control unit.

5. further comprising an operation unit for performing an operation for operating the forks, The hydraulic drive device for an industrial vehicle according to claim 2, wherein the decrement control unit controls the prime mover to decrease the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder when the operation of operating the forks by the operation unit is released.

6. a storage unit for storing a plurality of parameters in increment data regarding the increase in the flow rate of the hydraulic oil An input unit for selectively inputting any one of the plurality of parameters stored in the memory unit is further provided. The increment control unit controls the prime mover so as to increase the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder according to the parameter selectively input by the input unit when the supply pressure of the hydraulic oil drops from a state where it is equal to or higher than the valve opening pressure to the specified pressure. The hydraulic drive device for an industrial vehicle according to claim 1. **Claim 7** The hydraulic cylinder is an attachment cylinder that tilts the fork via a hinge. The increment control unit controls the prime mover so as to increase the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder when the fork is tilted forward by the attachment cylinder and the supply pressure of the hydraulic oil drops from a state where it is equal to or higher than the valve opening pressure to the specified pressure. The hydraulic drive device for an industrial vehicle according to claim 1.

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