Hydraulic drive system for a goods handling vehicle

Abstract

Hydraulic drive device (16) for a goods handling vehicle (1) comprising: a hydraulic cylinder (4) for use in lifting and lowering, which is designed to lift and lower an object by supplying and releasing hydraulic oil; a hydraulic pump (17) which is configured to supply the hydraulic oil to the hydraulic cylinder (4) and to discharge it from the hydraulic cylinder (4); an internal combustion engine (18) which is connected to the hydraulic pump (17) and is configured to drive the hydraulic pump (17); a tank (19) which is designed to store the hydraulic oil; a first hydraulic oil passage (49) which connects the tank (19) and the hydraulic cylinder (4) and is designed to return the hydraulic oil from the hydraulic cylinder (4) to the tank (19); a first flow control valve (50) which is arranged at the first hydraulic oil passage (49) and is configured to control a flow of hydraulic oil returning from the hydraulic cylinder (4) to the tank (19); a second hydraulic oil passage (47) which connects a branch point (91) between the hydraulic cylinder (4) and the first flow control valve (50) at the first hydraulic oil passage (49) with a suction port (17a) of the hydraulic pump (17) and is configured to convey the hydraulic oil from the hydraulic cylinder (4) to the hydraulic pump (17); and a second flow control valve (80) which is arranged at the second hydraulic oil passage (47) and is configured to control the flow of the hydraulic oil flowing from the hydraulic cylinder (4) to the hydraulic pump (17), wherein the second flow control valve (80) has a throttle position (80c) for adjusting the flow rate of the hydraulic oil, and wherein the second flow control valve (80) is configured, in a case where a rotational speed of the internal combustion engine (18) increases during a lowering operation when an accelerator pedal (79) is pressed, to control the flow of hydraulic oil flowing from the hydraulic cylinder (4) to the hydraulic pump (17) such that the flow of hydraulic oil is suppressed in the throttle position (80c).

Description

TECHNICAL AREA

[0001] The present invention relates to a hydraulic drive device for a goods handling vehicle. STATE OF THE ART

[0002] For example, a hydraulic drive unit for a goods handling vehicle is described in patent application JP 2012-62137A. The hydraulic drive unit described in JP 2012-62137A includes a hydraulic cylinder for lifting and lowering, which raises and lowers an object by supplying and discharging hydraulic oil; a lifting actuation section that actuates the hydraulic cylinder; a hydraulic pump that supplies and discharges hydraulic oil to the hydraulic cylinder; and a motor that drives the hydraulic pump.

[0003] In US 2015 / 0013324A1, an outlet port of a hydraulic pump / motor and a lower chamber of a lifting cylinder are connected by a hydraulic fluid channel. A hydraulic fluid channel connected to a hydraulic fluid tank is configured to branch off from the hydraulic fluid channel. A flow control valve regulates the hydraulic fluid supplied by the lifting cylinder when the forks are lowered, thereby regulating the flow rate of hydraulic fluid to the hydraulic pump / motor and the flow rate of hydraulic fluid to the hydraulic fluid tank. When regenerative operation is possible, the flow control valve closes, and hydraulic fluid is supplied to the hydraulic pump / motor.If regenerative operation cannot be performed, the flow control valve opens and hydraulic fluid is supplied to the hydraulic fluid tank. In any case, the fork can be lowered at a specified speed.

[0004] US 2014 / 0 331 662 A1 also deals with a hydraulic control device that controls the lowering of a fork and the tilting of a lifting frame. SUMMARY OF THE INVENTIONAL PROBLEM

[0005] The existing hydraulic drive system described above exhibits the following problems. Specifically, the hydraulic drive system was activated to deliver hydraulic oil to a tank via the hydraulic cylinder when a fork was lowered, for use during lifting and lowering. This means that the potential energy of the load was transferred to the tank via the hydraulic oil. Consequently, the load's potential energy was effectively wasted. Therefore, there was a need to utilize the load's potential energy more effectively to reduce engine load and fuel consumption.

[0006] One object of the present invention is to provide a hydraulic drive device for a goods handling vehicle that is capable of reducing engine load and fuel consumption. SOLUTION TO THE PROBLEM

[0007] The claimed invention in view of the above problem is defined in the subject matter of independent claim 1, wherein the dependent claims specify preferred embodiments of the invention.

[0008] A hydraulic drive device for a goods handling vehicle in accordance with one aspect of the present invention comprises a hydraulic cylinder for use in lifting and lowering, configured to raise and lower an object by supplying and discharging hydraulic oil; a hydraulic pump configured to supply and discharge hydraulic oil to the hydraulic cylinder; a motor connected to the hydraulic pump and configured to drive the hydraulic pump; a tank configured to store the hydraulic oil; a first hydraulic oil passage connecting the tank and the hydraulic cylinder and configured to return the hydraulic oil from the hydraulic cylinder to the tank; and a first flow control valve arranged at the first hydraulic oil passage and configured to control the flow of hydraulic oil returning from the hydraulic cylinder to the tank.and a second hydraulic oil passage, which connects a branch point between the hydraulic cylinder and the first flow control valve in the first hydraulic oil passage to a suction port of the hydraulic pump and is designed to convey the hydraulic oil from the hydraulic cylinder to the hydraulic pump.

[0009] The hydraulic drive unit for the goods handling vehicle, in accordance with one aspect of the present invention, can include the first hydraulic oil passage, which connects the tank to the hydraulic cylinder and returns the hydraulic oil from the hydraulic cylinder to the tank, and the first flow control valve, which is arranged at the first hydraulic oil passage and is configured to control the flow of hydraulic oil returning from the hydraulic cylinder to the tank. Furthermore, the branch point between the hydraulic cylinder and the first flow control valve at the first hydraulic oil passage is connected to the suction port of the hydraulic pump by the second hydraulic oil passage, which is configured to convey the hydraulic oil from the hydraulic cylinder to the hydraulic pump.In accordance with this design, it is possible to route the hydraulic oil from the hydraulic cylinder to the hydraulic pump's intake port via a second hydraulic oil passage when the forks are lowered. Consequently, the energy of the hydraulic oil, generated by the forks' descent, can be used to drive the hydraulic pump. This reduces the load on the engine that powers the hydraulic pump. With the design described above, it is possible to reduce both engine load and fuel consumption.

[0010] The hydraulic drive unit for the goods handling vehicle, in accordance with a further aspect of the present invention, can further comprise a second flow control valve located at the second hydraulic oil passage and configured to control the flow of hydraulic oil from the hydraulic cylinder to the hydraulic pump. For example, there is a case where the engine rotation speed increases when the accelerator pedal is depressed during the lowering operation. If the second flow control valve restricts the flow of hydraulic oil from the hydraulic cylinder towards the hydraulic pump, it is possible in this case to suppress a sudden increase in the fork lowering speed. With the setup described above, it is possible to appropriately control the fork lowering speed when the accelerator pedal is depressed during the lowering operation.

[0011] Furthermore, in the hydraulic drive unit for the goods handling vehicle, in accordance with another aspect of the present invention, the flow rate of the hydraulic oil, which is controllable by the second flow control valve, can be set higher than the flow rate of the hydraulic oil, which is controllable by the first flow control valve. Comparing the case of maintaining a constant fork lowering speed with respect to a predetermined lowering actuation amount by controlling the second flow control valve with the case of maintaining a constant fork lowering speed with respect to a predetermined lowering actuation amount by controlling the first flow control valve, the fork lowering speed can accordingly be set higher by controlling the second flow control valve.In this case, it is possible to provide a transition section where the fork lowering speed increases partially in line with an increase in the motor rotation speed when the control switches from the first flow control valve to the second flow control valve. Such a transition section makes it possible to suppress a sudden change from control by the first flow control valve to control by the second flow control valve.

[0012] Furthermore, in accordance with another aspect of the present invention, the hydraulic drive unit for the goods handling vehicle can also include an actuating section configured to actuate the hydraulic cylinder, and a proportional valve arranged between the hydraulic cylinder and the branch point in the first hydraulic oil passage, configured to open to a degree corresponding to the actuation force of the actuating section during a lowering operation. The second flow control valve can control the flow of hydraulic oil based on a pressure differential across the proportional valve. Accordingly, the second flow control valve can be controlled by the fork lowering speed, which corresponds to the actuation force of the actuating section during lowering. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0013] In accordance with the present invention, it is possible to reduce engine load and fuel consumption. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a side view illustrating a goods handling vehicle including a hydraulic drive unit in accordance with an embodiment of the present invention. Fig. Figure 2 is a hydraulic circuit diagram illustrating the hydraulic drive device in accordance with the embodiment of the present invention. Fig. 3 is a diagram illustrating a control system of the Fig. 2 illustrated hydraulic drive device illustrated. Fig. 4 is a flowchart that shows the process through a Fig. Figure 3 illustrates the executed control process operations. Fig. Figure 5 is a graph showing a relationship between the amount of accelerator pedal input and the engine rotation speed, and Figure 5 is a graph showing a relationship between the engine rotation speed and the cylinder flow rate. DESCRIPTION OF THE EXECUTION FORMS

[0014] Preferred embodiments of a hydraulic drive device for a goods handling vehicle in accordance with the present invention are described in detail below with reference to the drawings. In the drawings, identical or equivalent elements are identified by the same reference numerals, and repetitive descriptions are omitted.

[0015] Fig. Figure 1 is a side view illustrating the material handling vehicle equipped with the hydraulic drive unit in accordance with the embodiments of the present invention. In the figure, the material handling vehicle 1, in accordance with this embodiment, is a motorized forklift. The material handling vehicle 1 includes a vehicle body frame 2 and a lifting mast 3, which is arranged at the front section of the vehicle body frame 2. The lifting mast 3 is constructed with a pair of outer lifting masts 3a, which are tiltably supported by the vehicle body frame 2, and an inner lifting mast 3b, which is arranged inside the outer lifting masts 3a in order to be raised and lowered relative to the outer lifting masts 3a.

[0016] A lifting cylinder 4, a hydraulic cylinder for use in lifting and lowering, is arranged on the rear side of the lifting frame 3. The front end section of a piston rod 4p of the lifting cylinder 4 is connected to the upper section of the inner lifting frame 3b.

[0017] A lifting support 5 is mounted on the inner lifting frame 3b, which is to be raised and lowered. A fork (object) 6, onto which a load is placed, is attached to the lifting support 5. A sprocket 7 is provided in the upper section of the inner lifting frame 3b, and a chain 8 is suspended over the sprocket 7. One end of the chain 8 is connected to the lifting cylinder 4, and the other end of the chain 8 is connected to the lifting support 5. When the lifting cylinder 4 is extended and retracted, the fork 6, together with the lifting support 5, is raised and lowered via the chain 8.

[0018] Tilting cylinders 9, acting as hydraulic tilting cylinders, are supported on both the right and left sides of the vehicle body frame 2. The front end section of a piston rod 9p of the tilting cylinder 9 is rotatably connected in the vertical direction to the substantially central section of the outer lifting frame 3a. When the tilting cylinder 9 is extended and retracted, the mast 3 is tilted.

[0019] The upper section of the vehicle body frame 2 is equipped with a driver's cab 10. The front section of the driver's cab 10 is equipped with a lifting lever 11 for raising the forks 6 by actuating the lifting cylinder 4 and a tilting lever 12 for tilting the lifting frame 3 by actuating the tilting cylinder 9. Furthermore, the lower section of the driver's cab 10 is equipped with an accelerator pedal 79. The accelerator pedal 79 is used to increase and decrease the rotational speed of a motor 18 based on the amount of pressure applied.

[0020] In the front section of the driver's cab 10, a steering wheel 13 is provided for steering. The steering wheel 13 is a power steering system, and it is possible to control the vehicle manually using a horsepower cylinder 14 (see Fig. 2) to support as a hydraulic power steering cylinder (PS cylinder).

[0021] In addition, the goods handling vehicle 1 includes an additional cylinder 15 (see Fig. 2) as an auxiliary hydraulic cylinder that actuates an auxiliary device (not illustrated). Examples of an auxiliary device include those that move, tilt, and rotate the fork 6 in a horizontal direction. Furthermore, an auxiliary operating lever (not illustrated) is provided on the driver's cab 10 for actuating the auxiliary device by operating the auxiliary cylinder 15.

[0022] Although not particularly illustrated, the driver's cab 10 also features a direction switch for changing between the directions of travel (forward / reverse / neutral) of the goods handling vehicle 1.

[0023] Fig. Figure 2 is a hydraulic circuit diagram illustrating the first embodiment of the hydraulic drive device in accordance with the present invention. The figure shows a hydraulic drive device 16 of this embodiment, which drives the lifting cylinder 4, the tilting cylinder 9, the auxiliary cylinder 15, and the horsepower cylinder 14.

[0024] The hydraulic drive unit 16 includes a single hydraulic motor pump 17 and a single motor 18 for driving the hydraulic motor pump 17. The motor 18 and the hydraulic motor pump 17 are connected by a gearbox 18a. Furthermore, the motor 18 is connected to a drive section to enable the material handling vehicle 1 to move. The drive section is connected to a vehicle wheel and is operated at a suitable speed of the material handling vehicle corresponding to the rotational speed of the motor 18. The motor 17 includes a suction port 17a, which draws in the hydraulic oil, and a discharge port 17b, which discharges the hydraulic oil. The hydraulic motor pump 17 is configured to rotate in one direction.

[0025] A tank 19, which stores the hydraulic oil, is connected to the suction port 17a of the motor-driven hydraulic pump 17 via a hydraulic pipe 20. A check valve 21, which allows the hydraulic oil to flow only in the direction from tank 19 to the motor-driven hydraulic pump 17, is provided in the hydraulic pipe 20. The motor-driven hydraulic pump 17 operates as a pump that supplies the hydraulic oil to the lifting cylinder 4 during lifting operation by the lifting lever 11, and as a hydraulic motor that is driven by the hydraulic oil delivered by the lifting cylinder 4 during lowering operation by the lifting lever 11.

[0026] The discharge port 17b of the motor hydraulic pump 17 and a lower chamber or bottom chamber 4b of the lifting cylinder 4 are connected via a hydraulic pipe 22. A proportional solenoid valve 23 is arranged in the hydraulic pipe 22. The proportional solenoid valve 23 switches between an open position 23a, in which the flow of hydraulic oil from the motor hydraulic pump 17 to the bottom chamber 4b of the lifting cylinder 4 is permitted, and a closed position 23b, in which the flow of hydraulic oil from the motor hydraulic pump 17 to the bottom chamber 4b of the lifting cylinder 4 is blocked.

[0027] The proportional solenoid valve 23 is normally in the illustrated closed position 23b and switches to the open position 23a when an actuation signal, i.e., a fork lift solenoid current setpoint corresponding to an actuation amount of the lift actuation lever 11, is input into a solenoid actuation section 23c. Then, hydraulic oil is supplied by the motor-driven hydraulic pump 17 to the bottom chamber 4b of the lift cylinder 4, causing the lift cylinder 4 to extend and thus raising the fork 6. Simultaneously, the proportional solenoid valve 23 opens to a degree corresponding to the actuation signal in the open position 23a. A check valve 24, which allows hydraulic oil to flow only from the proportional solenoid valve 23 to the lift cylinder 4, is provided in the hydraulic line 22 between the proportional solenoid valve 23 and the lift cylinder 4.

[0028] A tilting proportional solenoid valve 26 is connected via a hydraulic pipe 25 to the branch point between the motor hydraulic pump 17 and the proportional solenoid valve 23 in the hydraulic pipe 22. A check valve 27, which allows the hydraulic oil to flow only in the direction from the motor hydraulic pump 17 to the proportional solenoid valve 26, is provided in the hydraulic pipe 25.

[0029] The proportional solenoid valve 26 is connected via hydraulic pipes 28 and 29 to a rod chamber 9a and a bottom chamber 9b of the tilt cylinder 9, respectively. The proportional solenoid valve 26 switches between an open position 26a, in which the flow of hydraulic oil from the motor hydraulic pump 17 to the rod chamber 9a of the tilt cylinder 9 is permitted, an open position 26b, in which the flow of hydraulic oil from the motor hydraulic pump 17 to the bottom chamber 9b of the tilt cylinder 9 is permitted, and a closed position 26c, in which the flow of hydraulic oil from the motor hydraulic pump 17 to the tilt cylinder 9 is blocked.

[0030] The proportional solenoid valve 26 is normally in the illustrated closed position 26c. It switches to the open position 26a when an actuation signal, i.e., a tilt solenoid current setpoint corresponding to an actuation amount of a backward tilt actuation of the tilt actuation lever 12, is input into a solenoid actuation section 26d on the side of the open position 26a. It switches to the open position 26b when an actuation signal, i.e., a tilt solenoid current setpoint corresponding to an actuation amount of a forward tilt actuation of the tilt actuation lever 12, is input into a solenoid actuation section 26e on the side of the open position 26d. When the proportional solenoid valve 26 switches to the open position 26a, the hydraulic oil is directed from the motor hydraulic pump 17 to the rod chamber 9a of the tilt cylinder 9.Therefore, the tilt cylinder 9 retracts, and consequently the lifting frame 3 tilts backward. When the proportional solenoid valve 26 switches to the open position 26b, hydraulic oil is supplied from the engine hydraulic pump 17 to the bottom chamber 9b of the tilt cylinder 9. Therefore, the tilt cylinder 9 extends, and consequently the lifting frame 3 tilts forward. Additionally, the proportional solenoid valve 26 opens with degrees corresponding to the actuation signals in the open positions 26a and 26b.

[0031] An additional proportional solenoid valve 31 is connected via a hydraulic pipe 30 to the upstream side of the check valve 27 in the hydraulic pipe 25. A check valve 32, which allows the hydraulic oil to flow only towards the motor hydraulic pump 17 and the proportional solenoid valve 31, is provided in the hydraulic pipe 30.

[0032] The proportional solenoid valve 31 is connected, respectively, via hydraulic pipes 33 and 34 to a rod chamber 15a and a bottom chamber 15b of the auxiliary cylinder 15. The proportional solenoid valve 31 switches between an open position 31a, in which the flow of hydraulic oil from the motor hydraulic pump 17 to the rod chamber 15a of the auxiliary cylinder 15 is permitted, an open position 31b, in which the flow of hydraulic oil from the motor hydraulic pump 17 to the bottom chamber 15b of the auxiliary cylinder 15 is permitted, and a closed position 31c, in which the flow of hydraulic oil from the motor hydraulic pump 17 to the auxiliary cylinder 15 is blocked.

[0033] The proportional solenoid valve 31 is normally in the illustrated closed position 31c. It switches to the open position 31a when an actuation signal, i.e., an additional solenoid current setpoint corresponding to the actuation amount of a one-sided actuation of an auxiliary actuation lever, is input into a solenoid actuation section 31d on the side of the open position 31a. It switches to the open position 31b when an actuation signal, i.e., an additional solenoid current setpoint corresponding to the actuation amount of the other side of the auxiliary actuation lever, is input into a solenoid actuation section 31e on the side of the open position 31b. The actuation of the auxiliary cylinder 15 is omitted. Furthermore, the proportional solenoid valve 31 opens with degrees corresponding to the actuation signals in the open positions 31a and 31b.

[0034] A PS proportional solenoid valve 36 is connected via a hydraulic pipe 35 to the upstream side of the check valve 32 in the hydraulic pipe 30. A check valve 37, which allows the hydraulic oil to flow only in the direction from the motor hydraulic pump 17 to the proportional solenoid valve 36, is provided in the hydraulic pipe 35.

[0035] The proportional solenoid valve 36 is connected, respectively, via hydraulic pipes 38 and 39 to a first rod chamber 14a and a second rod chamber 14b of the PS cylinder. The proportional solenoid valve 36 switches between an open position 36a, in which the flow of hydraulic oil from the engine hydraulic pump 17 to the first rod chamber 14a of the PS cylinder 14 is permitted; an open position 36b, in which the flow of hydraulic oil from the engine hydraulic pump 17 to the second rod chamber 14b of the PS cylinder 14 is permitted; and a closed position 36c, in which the flow of hydraulic oil from the engine hydraulic pump 17 to the PS cylinder 14 is blocked.

[0036] The proportional solenoid valve 36 is normally in the illustrated closed position 36c. It switches to the open position 36a when an actuation signal, i.e., a PS solenoid current setpoint corresponding to an actuation speed of a right- or left-hand actuation of the control 13, is input into a solenoid actuation section 36d on the side of the open position 36a. It switches to the open position 36b when an actuation signal, i.e., a PS solenoid current setpoint corresponding to an actuation speed of the other right- and left-hand actuation of the control 13, is input into a solenoid actuation section 36e on the side of the open position 36b. Actuation of the PS cylinder 14 is omitted. Furthermore, the proportional solenoid valve 36 opens with degrees corresponding to the actuation signals in the open positions 36a and 36b.

[0037] The branch point between the motor hydraulic pump 17 and the proportional solenoid valve 23 in the hydraulic pipe 22 is connected to the tank 19 via a hydraulic pipe 40. A relief valve 41 and a filter 42 are provided in the hydraulic pipe 40. The hydraulic pipe 40 is connected to the proportional solenoid valves 26, 31, and 36 via hydraulic pipes 43 to 45. Furthermore, the proportional solenoid valves 23, 26, 31, and 36 are connected to the hydraulic pipe 40 via a hydraulic pipe 46.

[0038] A tank 19 and a lower chamber or floor space 4b of the lifting cylinder 4 are connected by a hydraulic pipe 49 (a first hydraulic oil passage). The hydraulic pipe 49 is a pipe that returns the hydraulic oil from the lifting cylinder 4 to the tank 19. A bypass flow control valve 50 (a first flow control valve) is arranged in the hydraulic pipe 49. The bypass flow control valve 50 controls the flow of hydraulic oil returning from the lifting cylinder 4 to the tank 19. The hydraulic pipe 49 is also equipped with a filter 54.

[0039] A branch point 91 between the lifting cylinder 4 and the bypass flow control valve 50 at the hydraulic pipe 49 and the intake port 17a of the motor hydraulic pump 17 are connected to each other via a hydraulic pipe 47 (a second hydraulic oil passage). The hydraulic pipe 47 delivers the hydraulic oil from the cylinder 4 to the motor hydraulic pump 17. A fork lowering proportional solenoid valve 48 is arranged between the lifting cylinder 4 and the branch point 91 in the hydraulic pipe 49. The proportional solenoid valve 48 is switched between an open position 48a, which allows the flow of hydraulic oil from the bottom space 4b of the lifting cylinder 4 to the suction opening 17a of the motor hydraulic pump 17, and a closed position 48b with an interruption of the flow of hydraulic oil from the bottom space 4b of the lifting cylinder 4 to the suction opening 17a of the motor hydraulic pump 17.

[0040] The proportional solenoid valve 48 is generally located in the closed position 48b, as illustrated in the drawings, and switches to the open position 48a when an actuation signal, i.e., a setpoint current for the fork lowering solenoid, is input into a solenoid actuation section 48c in response to the actuation amount of the lowering action of the lifting actuation lever 11. The fork 6 is then lowered due to its own weight, and the lifting cylinder 4 is thus retracted. Consequently, the hydraulic oil flows out of the bottom chamber 4b of the lifting cylinder 4. Furthermore, the proportional solenoid valve 48 opens to a degree corresponding to the actuation signal at the open position 48a.

[0041] The bypass flow control valve 50 switches between an open position 50a, which allows the flow of hydraulic oil, a closed position 50b, which interrupts the flow of hydraulic oil, and a throttled position 50c, which regulates the amount of hydraulic oil flow. A pilot actuation section on the closed position 50b side of the bypass flow control valve 50 and the upstream (front) side of the proportional solenoid valve 48 are connected by a pilot passage 51. A pilot actuation section on the open position 50a side of the bypass flow control valve 50 and the downstream (rear) side of the proportional solenoid valve 48 are connected by a pilot passage 52. The bypass flow control valve 50 opens to a degree corresponding to the pressure differential across the proportional solenoid valve 48.In particular, the bypass flow control valve 50 is arranged in a closed position in which the proportional solenoid valve 48 is not open. Then, when the proportional solenoid valve 48 opens, the bypass flow control valve 50 opens and its opening degree corresponds to the pressure differential across the proportional solenoid valve 48. The opening degree of the bypass flow control valve 50 decreases as the pressure differential across the proportional solenoid valve 48 increases, and increases as the pressure differential across the proportional solenoid valve 48 decreases.

[0042] An energy recovery flow control valve 80 (a second flow control valve) is arranged in the hydraulic pipe 47. The energy recovery flow control valve 80 controls the flow of hydraulic oil flowing from the lifting cylinder 4 to the motor hydraulic pump 17. The energy recovery flow control valve 80 switches between an open position 80a, which allows the flow of hydraulic oil, a closed position 80b, which interrupts the flow of hydraulic oil, and a throttled position 80c, which adjusts the flow rate of the hydraulic oil. The pilot actuation section on the closed position 80b side of the energy recovery flow control valve 80 and the upstream side (the front side) of the proportional solenoid valve 48 are connected by a pilot passage 81.The pilot actuation section on the open position 80a side of the energy recovery flow control valve 80 and the downstream side (the rear side) of the proportional solenoid valve 48 are connected by a pilot passage 82. The energy recovery flow control valve 80 opens to a degree corresponding to the pressure differential across the proportional solenoid valve 48. Specifically, the energy recovery flow control valve 80 is in a closed position in which the proportional solenoid valve 48 is not open. Then, when the proportional solenoid valve 48 is open, the bypass flow control valve 50 opens and is controlled to a degree corresponding to the pressure differential across the proportional solenoid valve 48.The opening degree of the energy recovery flow control valve 80 decreases as the pressure difference across the proportional solenoid valve 48 increases, and increases as the pressure difference across the proportional solenoid valve 48 decreases.

[0043] Among the cylinders described above, the tilt cylinder 9, the auxiliary cylinder 15, and the power cylinder 14, which perform different actuations than the lifting cylinder 4 (first hydraulic cylinder) for supplying and discharging the hydraulic oil, can be referred to collectively as the "second hydraulic cylinders 70". The tilt actuation lever 12, the control unit 13, and the auxiliary actuation lever for actuating the second hydraulic cylinders 70 can be referred to collectively as the "second actuation sections 73".

[0044] Fig. Figure 3 is a diagram illustrating a control system for the hydraulic drive unit 16. In the figure, the hydraulic drive unit 16 includes a lever actuation amount sensor for a lift actuation 55 (actuation amount detection unit) that detects the actuation amount of the lift actuation lever 11, a lever actuation amount sensor for a tilt actuation 56 that detects the actuation amount of the tilt actuation lever 12, a lever actuation amount sensor for an auxiliary actuation 57 that detects the actuation amount of the auxiliary actuation lever (not illustrated), a control actuation speed sensor 58 that detects the actuation speed of the control 13, a rotation speed sensor 59 that detects the current rotation speed (current motor rotation speed) of the motor 18, an accelerator pedal detent sensor 83 that detects an accelerator pedal detent of the accelerator pedal 79, and a control unit 60.

[0045] The control unit 60 receives the actuation values ​​of the lever actuation magnitude sensors 55 to 57, the control actuation speed sensor 58, the rotation speed sensor 59, and the accelerator pedal actuation magnitude sensor 83, executes predetermined operations, and controls the motor 18 and the proportional solenoid valves 23, 26, 31, 36, and 48. The sensors 56, 57, and 58, which detect the actuation magnitudes of the second actuation sections 73, can also be referred to as "second actuation magnitude detection units 71." Furthermore, the proportional solenoid valves 26, 31, and 36, which are arranged between the discharge port 17b of the motor hydraulic pump 17 and the second hydraulic cylinders to control the flow of hydraulic oil based on the actuations of the second actuation sections, can be referred to as "second control valves 72."

[0046] The engine control unit 65 sets a fuel injection quantity based on a target engine rotation speed, a crankshaft angle sensor, or similar, and performs a control operation so that the engine rotation speed follows the target rotation speed. The engine control unit 65 sets the target engine rotation speed in response to the reading from the accelerator pedal input sensor 83. The target engine rotation speed set by the engine control unit 65 is described in detail below.

[0047] Fig. Figure 4 is a flowchart showing the control process sequences executed by a controller 60. The control process focuses solely on the actuation, which includes lowering the fork 6 (fork lowering). Furthermore, the execution cycle of the control process is appropriately determined through an experiment or similar method.

[0048] In the same drawing, the actuation values ​​of the lift actuation lever 11, the tilt actuation lever 12, and the auxiliary actuation lever, which are detected by the actuation of the lever actuation sensors 55 to 57, are first recorded (procedure S101). Consequently, a fork lowering mode, which is an operating state, can be determined based on the actuation values ​​of the lift actuation lever 11, the tilt actuation lever 12, and the auxiliary actuation lever, which are detected by procedure S101. The fork lowering modes are independent fork lowering actuation, fork lowering actuation + tilt actuation, and fork lowering actuation + auxiliary actuation.

[0049] The following determines a setpoint magnetic current for the proportional solenoid valve, corresponding to the actuation values ​​of the lift actuation lever 11, the tilt actuation lever 12, and the auxiliary actuation lever obtained by procedure S101 (procedure S102). The setpoint magnetic currents for the proportional solenoid valve include the fork lowering setpoint, which corresponds to the actuation value of the lowering actuation of the lift actuation lever 11; a tilting setpoint, which corresponds to the actuation value of the tilt actuation lever 12; and an auxiliary setpoint magnetic current, which corresponds to the actuation value of the auxiliary actuation lever.

[0050] The controller 60 sends a solenoid current setpoint of the proportional solenoid valve, obtained by procedure S102, to the solenoid actuation section of the corresponding proportional solenoid valve (procedure S103). At this point, the solenoid current setpoint for fork lowering is sent to solenoid actuation section 48c of proportional solenoid valve 48. When the solenoid current setpoint for tilting is obtained, the current setpoint is further sent to any one of the solenoid actuation sections 26d and 26e of proportional solenoid valve 26. Then, when the auxiliary solenoid current setpoint is obtained, the current setpoint is sent to any one of the solenoid actuation sections 31d and 31e of proportional solenoid valve 31. When the PS solenoid current setpoint is received, the current setpoint is sent to any one of the solenoid actuation sections 36d and 36e of the proportional solenoid valve 36.

[0051] Meanwhile, the control unit 60 detects the accelerator pedal detent based on the reading from the accelerator pedal detent sensor 83 (procedure S104). The target engine rotation speed is adjusted as the accelerator pedal detent increases. The engine control unit 65 sets the target engine rotation speed (the target engine rotation speed) based on the fork lowering mode determined by procedure S102 and the accelerator pedal detent obtained by procedure S104 (procedure S105).

[0052] Subsequently, the engine control unit 65 outputs the target engine rotational speed value (the target engine rotational speed) set by procedure S105 and controls the amount of fuel injected so that the current engine rotational speed becomes the target engine rotational speed value (procedure S106).

[0053] Next, characteristic data of the motor rotation speed of motor 18 and the cylinder flow rate of the lifting cylinder 4 of the hydraulic drive unit 16 of this embodiment are given with reference to Fig. 5 described. Fig. Figure 5(a) is a graph showing a relationship between the amount of pressure applied to the accelerator pedal 79 and the engine rotational speed. Fig. 5(a) shows a horizontal axis representing the amount of pressure applied to the accelerator pedal 79, and a vertical axis representing the rotational speed of the motor 18. Furthermore, the motor rotational speed is the same as the rotational speed of the motor hydraulic pump 17. As in Fig. As shown in 5(a), the engine rotation speed is set to increase while the amount of pressure applied to the accelerator pedal 79 increases.

[0054] Fig. 5(b) is a graph showing a relationship between the engine rotation speed and the cylinder flow rate. A horizontal axis in Fig. Figure 5(b) shows the motor rotation speed of motor 18, and it can be assumed that the motor rotation speed is the same as the pump rotation speed of the motor hydraulic pump 17. A vertical axis in Fig. Figure 5(b) shows the cylinder flow rate of the lifting cylinder 4, and it can be assumed that the cylinder flow rate is a value that corresponds to the fork lowering speed. Furthermore, it shows Fig. 5(b) a graph L1 showing characteristic data when the actuation amount, referred to hereafter as the lowering actuation amount, of the lift actuation lever 11 is “large”, a graph L2 showing characteristic data when the lowering actuation amount is “medium”, and a graph L3 showing characteristic data when the lowering actuation amount is “small”. As can be seen from graphs L1, L2 and L3, the control is designed such that the cylinder flow, i.e. the fork lowering speed, increases while the lowering actuation amount increases. In addition, the actuation amount can be increased by the lever actuation of the driver, as in Fig. 5(a) shown, continuously adjustable, however, for the description of the Fig. 5(b) the case of the three steps “large”, “medium” and “small” is shown by way of example.

[0055] Furthermore, it shows Fig. 5(b) a graph LP showing a relationship between the engine rotation speed (the pump rotation speed) and the pump flow rate of the engine hydraulic pump 17. As shown in graph LP, a directly proportional relationship is established between the engine rotation speed and the pump flow rate of the engine hydraulic pump 17. When the lowering actuation is performed while the goods handling vehicle 1 is moving, the cylinder flow rate is arranged in graph LP when the accelerator pedal detent corresponds to regions L1b, L2b, and L3b. As an example of adjusting the cylinder flow rate and engine rotation speed, when the lowering actuation is "large," graph L1b is set to a point at the maximum rotational speed R2 or several hundred revolutions lower than the maximum rotational speed R2.

[0056] Here, flow control by the bypass flow control valve 50 is implemented in region E1, where the motor rotation speed is on the negative side (left-hand side) with respect to graph LP. This means that flow control by the bypass flow control valve 50 is implemented in the sections of graphs L1a, L2a, and L3a on the side of region E1, specifically in graphs L1, L2, and L3. At this point, the energy recovery flow control valve 80 is in an "open" state. In region E1, the bypass flow control valve 50 controls the flow of hydraulic oil to be discharged, so that the cylinder flow, i.e., the fork lowering speed, remains constant in response to the lowering actuation amount, as shown in graphs L1a, L2a, and L3a.For example, if the motor rotation speed “R1” is low relative to the lowering actuation amount “large”, a portion of the cylinder flow is diverted to the tank 19 via the bypass flow control valve 50. Specifically, the hydraulic oil is discharged to the tank 19 via the bypass flow control valve 50 at the flow rate indicated by “V1” between graph L1a and graph LP of the pump flow. Since the hydraulic oil flows to the intake port 17a of the motor hydraulic pump 17 at the flow rate indicated by “V2” of graph LP, pressure is applied to the intake port 17a. Because the motor hydraulic pump 17 can use this pressure as energy for rotation, the load on the motor 18 can be reduced to this extent.

[0057] Flow control is performed by the energy recovery flow control valve 80 in region E2 where the motor rotation speed is on the positive side (a right-hand side) with respect to graph LP. This means that flow control by the energy recovery flow control valve 80 is performed in the sections of graphs L1b, L2b, and L3b, and graphs L1c, L2c, and L3c on the side of region E2 in graphs L1, L2, and L3. At this time, the bypass flow control valve 50 is in a "half-open" state in the sections of graphs L1b, L2b, and L3b, and in a "closed" state in the sections of graphs L1c, L2c, and L3c.In area E2, the energy recovery flow control valve 80 controls the flow of hydraulic oil into the intake port 17a of the motor hydraulic pump 17, ensuring that the cylinder flow, i.e., the fork lowering speed, remains constant in response to the lowering actuation amount, as shown in graphs L1c, L2c, and L3c. That is, when the motor rotation speed increases to the level of or greater than the motor rotation speed required for lowering, the pressure differential across the proportional solenoid valve 48 increases. Consequently, the opening degree of the energy recovery flow control valve 80 decreases, thus restricting the flow of hydraulic oil delivered by the lifting cylinder 4 towards the intake port 17a of the motor hydraulic pump 17.In sections of graphs L1c, L2c, and L3c, the difference between the pump flow rate, which corresponds to the motor rotation speed, and the cylinder flow rate, which must be kept constant, is compensated for in such a way that the motor hydraulic pump 17 draws the hydraulic oil from the tank 19 through the hydraulic pipe 20. Consequently, no energy is recovered in sections of graphs L1c, L2c, and L3c. The cylinder flow rate, i.e., the fork lowering speed, in sections of graphs L1c, L2c, and L3c is set to be greater than the cylinder flow rate, i.e., the fork lowering speed, in sections of graphs L1a, L2a, and L3a. This means that the flow rate of the hydraulic oil that can be controlled by the energy recovery flow control valve 80 is set higher than the flow rate of the hydraulic oil that can be controlled by the bypass flow control valve.

[0058] In sections of graphs L1b, L2b, and L3b, the throttling state of the energy recovery flow control valve 80 is adjusted such that the cylinder flow rate increases slightly along graph LP of the pump flow rate with an increase in engine rotation speed. Energy is recovered in sections of graphs L1b, L2b, and L3b. These sections serve as buffer sections when the flow control using the bypass flow control valve 50 switches to the flow control using the energy recovery flow control valve 80.

[0059] An example of a detailed operation will now be described. If, for example, the independent lowering operation is implemented with the lowering operation amount "large" and the goods handling vehicle 1 is in a stopped state, the motor 18 is idling, that is, one rotational speed corresponds to a low rotational speed state and belongs to the range E1, and the cylinder flow rate has a value that corresponds to the one in Fig. This corresponds to point “P3” shown in Figure 5(b). At this point, the pump flow rate is low due to the low motor rotation speed. However, since the bypass flow control valve 50 supplements the flow, i.e., some of the hydraulic oil is discharged to the tank 19, a desired cylinder flow rate (lowering speed) can be achieved. Because the hydraulic oil flowing towards the energy recovery flow control valve 80 on the side of the hydraulic pipe 47 flows towards the suction port 17a of the motor hydraulic pump 17, pressure is applied to the suction port 17a. Since the motor hydraulic pump 17 can use the pressure as rotational energy, the load on the motor 18 can be reduced to this extent.

[0060] For example, if the independent lowering actuation is implemented with the lowering actuation amount "large" and the goods handling vehicle 1 is in a state of motion at medium speed, the motor 18 rotates at medium speed, which corresponds to the accelerator pedal detent, that is, the speed is greater than the motor rotational speed "P3" and belongs to the range E1, and the cylinder flow has a value that corresponds to the one in Fig. This corresponds to point “P2” shown in Figure 5(b). Since the bypass flow control valve 50 supplements the flow at this point (part of the hydraulic oil is discharged to the tank 19), a desired cylinder flow rate (lowering speed) can be achieved. Furthermore, since the hydraulic oil flowing towards the energy recovery flow control valve 80 on the side of the hydraulic pipe 47 flows towards the intake port 17a of the motor hydraulic pump 17, pressure is exerted on the intake port 17a. Because the motor hydraulic pump 17 can use the pressure as rotational energy, the load on the motor 18 can be reduced to this extent.

[0061] For example, if the independent lowering actuation is implemented with the lowering actuation amount "large" and the goods handling vehicle 1 is in a high-speed state of motion, the motor 18 rotates at a high speed corresponding to the accelerator pedal detent (a speed belonging to the range E2), and the cylinder flow has a value corresponding to that in Fig. This corresponds to point “P1” shown in Figure 5(b). At this point, the bypass flow control valve 50 is in a closed state and the energy recovery flow control valve 80 is throttling the flow. Accordingly, it is possible to achieve a desired cylinder flow rate (lowering speed) without excessively increasing the cylinder flow rate, that is, without excessively increasing the lowering speed. In this case, no pressure is applied to the intake port 17a of the motor hydraulic pump 17 and the load on the motor 18 is not reduced.

[0062] As a further example of operation, a case is described in which the goods handling vehicle 1 is in a stationary state and the second hydraulic cylinder 70 is actuated simultaneously with the lowering mechanism. For example, if the second hydraulic cylinder 70 is actuated simultaneously with the lowering mechanism at the "large" lowering threshold while the accelerator pedal is depressed at low speed, a control operation similar to state "P3" is executed. If the second hydraulic cylinder 70 is actuated simultaneously with the lowering mechanism at the "large" lowering threshold while the accelerator pedal is depressed at medium speed, a control operation similar to state "P2" is executed.If the second hydraulic cylinder 70 is actuated simultaneously with the lowering mechanism at the "large" lowering threshold while the accelerator pedal is depressed at a high speed, a control operation similar to state "P1" is executed. Furthermore, if the goods handling vehicle 1 is in motion and the second hydraulic cylinder 70 is actuated simultaneously with the lowering mechanism, a control operation similar to states "P1", "P2", and "P3" is executed by the engine rotation speed, which corresponds to the accelerator pedal depressor.

[0063] Next, an actuation effect of the hydraulic drive device 16 of the goods handling vehicle 1 in accordance with this embodiment is described.

[0064] The hydraulic drive unit 16 of the goods handling vehicle 1, in accordance with this embodiment, includes the hydraulic pipe 49, which connects the tank 19 and the lifting cylinder 4 and is configured to return the hydraulic oil from the lifting cylinder 4 to the tank 19, and the bypass flow control valve 50, which is located at the hydraulic pipe 49 and is configured to control the flow of the hydraulic oil returning from the lifting cylinder 4 to the tank 19. Furthermore, the branch point 91 between the lifting cylinder 4 and the bypass flow control valve 50 at the hydraulic pipe 49 is connected to the suction port 17a of the motor hydraulic pump 17 by the hydraulic pipe 47, which is configured to convey the hydraulic oil from the lifting cylinder 4 to the motor hydraulic pump 17.In accordance with this design, it is possible to guide the hydraulic oil from the lifting cylinder 4 to the intake port 17a of the motor hydraulic pump 17 through the hydraulic pipe 47 at the moment the forks are lowered. Therefore, it is possible to use the energy of the hydraulic oil carried by the lowering of the forks to rotate the motor hydraulic pump 17. This means that the load on the motor 18, which rotates the motor hydraulic pump 17, is reduced. With the design described above, it is possible to reduce both the engine load and fuel consumption. Since there is no need to add an expensive component, such as an energy storage mechanism (unlike, for example, the storage of potential energy in an energy storage device such as a battery), it is possible to avoid an increase in costs.

[0065] The hydraulic drive unit 16 of the material handling vehicle 1, in accordance with this embodiment, further includes the energy recovery flow control valve 80, which is arranged at the hydraulic pipe 47 and is configured to control the flow of hydraulic oil flowing from the lifting cylinder 4 to the motor hydraulic pump 17. For example, there is a case in which the motor rotation speed increases when the accelerator pedal is depressed during the lowering operation. If the energy recovery flow control valve 80, in this case, suppresses or reduces the flow of hydraulic oil flowing from the lifting cylinder 4 towards the motor hydraulic pump 17, it is possible to suppress a sudden increase in the fork lowering speed. With the setup described above, it is possible to appropriately control the fork lowering speed when the accelerator pedal is depressed during the lowering operation.

[0066] In the hydraulic drive unit 16 of the goods handling vehicle 1 in accordance with this embodiment, the flow rate of the hydraulic oil, which can be controlled by the energy recovery flow control valve 80, is set higher than the flow rate of the hydraulic oil, which can be controlled by the bypass flow control valve 50. In the case of maintaining a constant fork lowering speed relative to a predetermined lowering actuation amount (the sections of graphs L1c, L2c and L3c of the Fig. 5) by controlling the energy recovery flow control valve 80, compared with the case where the fork lowering speed is kept constant with respect to the predetermined lowering actuation amount by controlling the bypass flow control valve 50 (the sections of graphs L1a, L2a and L3a of the Fig. 5), the fork lowering speed can be set higher accordingly by controlling the energy recovery flow control valve 80. Accordingly, it is possible to provide a transition section (which is described in Fig.(5 sections of graphs L1b, L2b, and L3b shown), where the fork lowering speed partially increases with an increase in the motor rotation speed when the control by the bypass flow control valve 50 switches to control by the energy recovery flow control valve 80 while the motor rotation speed is increasing. Because such a transition section is provided, it is possible to suppress a sudden change from control by the bypass flow control valve 50 to control by the energy recovery flow control valve 80. For example, there is a case where the motor rotation speed increases slightly due to the influence of a temperature change instead of simultaneous actuation. In such a case, too, the motor load reduction efficiency deteriorates because energy is not recovered at an unnecessary time when the control changes abruptly.However, since the transition section, which serves as a buffer section, is provided, it is possible to suppress a deterioration in engine load reduction efficiency.

[0067] In the hydraulic drive unit 16 of the goods handling vehicle 1 in accordance with this embodiment, the energy recovery flow control valve 80 controls the flow of the hydraulic oil based on the pressure difference via the proportional solenoid valve 48. Accordingly, the energy recovery flow control valve can be controlled with the fork lowering speed, which corresponds to the actuation amount of the lowering actuation.

[0068] Although preferred embodiments of the hydraulic drive device for the goods handling vehicle have been described in accordance with the present invention, the present invention is not limited to the embodiment described above.

[0069] In the embodiment described above, the tilt cylinder, the power steering cylinder, and the auxiliary cylinder are provided as second hydraulic cylinders. However, some of the second hydraulic cylinders can be omitted as long as at least one is provided. For example, in the embodiment described above, the auxiliary device and the power steering are installed, but the hydraulic drive device of the present invention can also be applied to a forklift without the auxiliary device and the power steering. Furthermore, the hydraulic drive device of the present invention can also be used in a material handling vehicle other than a forklift. REFERENCE MARK LIST 1 goods handling vehicle 4 lifting cylinders (hydraulic cylinders) 6 Fork (object) 11 Lifting actuation lever (actuating section) 16 hydraulic drive unit 17 engine hydraulic pump (hydraulic pump) 17a Intake opening 17b Drop-off opening 18 engine 47 Hydraulic pipe (second hydraulic oil passage) 48 Fork lowering proportional solenoid valve (proportional solenoid valve) 49 Hydraulic pipe (first hydraulic oil passage) 50 Bypass flow control valve (first flow control valve) 80 Energy recovery flow control valve (second flow control valve).

Claims

[1] Hydraulic drive unit (16) for a goods handling vehicle (1) comprising: a hydraulic cylinder (4) for use in lifting and lowering, which is designed to lift and lower an object by supplying and releasing hydraulic oil; a hydraulic pump (17) which is configured to supply the hydraulic oil to the hydraulic cylinder (4) and to discharge it from the hydraulic cylinder (4); an internal combustion engine (18) which is connected to the hydraulic pump (17) and is configured to drive the hydraulic pump (17); a tank (19) which is designed to store the hydraulic oil; a first hydraulic oil passage (49) which connects the tank (19) and the hydraulic cylinder (4) and is designed to return the hydraulic oil from the hydraulic cylinder (4) to the tank (19); a first flow control valve (50) which is arranged at the first hydraulic oil passage (49) and is configured to control a flow of hydraulic oil returning from the hydraulic cylinder (4) to the tank (19); a second hydraulic oil passage (47) which connects a branch point (91) between the hydraulic cylinder (4) and the first flow control valve (50) at the first hydraulic oil passage (49) with a suction port (17a) of the hydraulic pump (17) and is configured to convey the hydraulic oil from the hydraulic cylinder (4) to the hydraulic pump (17); and a second flow control valve (80) which is arranged at the second hydraulic oil passage (47) and is configured to control the flow of the hydraulic oil flowing from the hydraulic cylinder (4) to the hydraulic pump (17), wherein the second flow control valve (80) has a throttle position (80c) for adjusting the flow rate of the hydraulic oil, and wherein the second flow control valve (80) is configured, in a case where a rotational speed of the internal combustion engine (18) increases during a lowering operation when an accelerator pedal (79) is pressed, to control the flow of hydraulic oil flowing from the hydraulic cylinder (4) to the hydraulic pump (17) such that the flow of hydraulic oil is suppressed in the throttle position (80c). [2] Hydraulic drive device (16) for a goods handling vehicle (1) according to claim 1, in which the flow rate of the hydraulic oil that can be controlled by the second flow control valve (80) is set higher than the flow rate of the hydraulic oil that can be controlled by the first flow control valve (50). [3] Hydraulic drive device (16) for a goods handling vehicle (1) according to claim 1 or 2, further comprising: an actuating section (11) which is configured to actuate the hydraulic cylinder (4); and a proportional valve (48) which is arranged between the hydraulic cylinder (4) and the branch point (91) in the first hydraulic oil passage (49) and is configured to be open to a degree that corresponds to an actuation amount when lowering the actuating section (11), wherein the second flow control valve (80) controls the flow of the hydraulic oil based on a pressure difference via the proportional valve (48).

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