Fork lift

Abstract

To provide a fork lift having an auxiliary mechanism of steering operation capable of reducing bouncing of a voltage generated in a control circuit at the time of power off.SOLUTION: A fork lift includes an auxiliary mechanism having an auxiliary motor assisting an operation of a steering by a liquid pressure. The auxiliary motor is a pump motor driving a liquid pressure pump, a control circuit of the auxiliary motor has a switch (SW) capable of cutting off input of a power source voltage, and a first switching element (Q1) and a second switching element (Q2) that are connected in series between a pair of terminals (t1 and t2) to which the power source voltage is applied, an auxiliary motor (M3) is connected between an intermediate node (n1) of the first switching element (Q1) and the second switching element (Q2) and a terminal (t2), when the switch (SW) is switched to OFF, the first switching element (Q1) is alternately switched between ON and OFF, and the second switching element (Q2) is kept OFF.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a forklift. [Background technology]

[0002] Patent Document 1 describes a forklift equipped with an electric power steering device that assists steering operation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Publication No. 2003-118606 Summary of the Invention [Problem to be solved by the invention]

[0004] In some cases, the power steering device of a forklift truck is equipped with a mechanism that generates auxiliary force by hydraulic pressure. In such cases, depending on the control circuit of the motor of the hydraulic pump, a back electromotive force may be generated in the hydraulic motor when the power is turned off, causing the voltage of the control circuit to jump up.

[0005] An object of the present invention is to provide a forklift equipped with a steering operation assist mechanism that can reduce a voltage spike that occurs in a control circuit when the power is turned off. [Means for solving the problem]

[0006] The forklift according to the present invention comprises: A forklift including a steering mechanism, an auxiliary motor for assisting the steering operation, and a control unit for controlling the auxiliary motor, the assist mechanism is a mechanism that assists the steering operation by hydraulic pressure, the auxiliary motor is a pump motor that drives a hydraulic pump, The control unit has a control circuit disposed on a substrate, the control circuit has a switch capable of cutting off an input of a power supply voltage, and a first switching element and a second switching element connected in series between a pair of terminals to which the power supply voltage is applied, the pump motor being connected between an intermediate node between the first switching element and the second switching element and one of the pair of terminals, When the switch is turned off, the first switching element alternates between on and off, and the second switching element is maintained off. Effect of the Invention

[0007] According to the present invention, it is possible to obtain an effect of reducing a voltage jump occurring in a control circuit when the power is turned off. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing a forklift according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a configuration of an operation unit of the forklift shown in FIG. [Diagram 3] 1 is a block diagram showing the configuration of an electrical system and a mechanical system of a forklift. [Figure 4] FIG. 4 is a diagram showing a control circuit for an auxiliary motor. [Diagram 5] 11A and 11B are diagrams illustrating a voltage jump caused by a counter electromotive force in a comparative example. [Figure 6] 5 is a flowchart showing the procedure of a discharge process executed by a controller. [Figure 7] 7 is a diagram for explaining the operation of the discharge process in FIG. 6. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a diagram showing a forklift 300 according to an embodiment of the present invention. Fig. 2 is a diagram showing a configuration of an operation unit of the forklift 300.

[0010] As shown in Fig. 1, the forklift 300 of this embodiment includes a vehicle body 302 including wheels 610, 612 and a driver's seat 301, a fork 303 extending forward of the vehicle body 302, a backrest 304 located behind the fork 303, and a fork drive unit 201 for driving the fork 303. As shown in Fig. 2, the driver's seat 301 includes a steering wheel 704 for steering, a forward / reverse lever 712 for switching between forward and reverse travel, a lift lever 706 for raising and lowering the fork 303, an accelerator pedal 708 for accelerating the vehicle, a brake pedal 710 for braking the vehicle, and an ignition switch 702 for switching between supplying and cutting off power supply voltage to each drive unit.

[0011] 3 is a block diagram showing the configuration of an electrical system and a mechanical system of the forklift 300. The forklift 300 includes a steering wheel 704, an assist mechanism 118 having an assist motor M3 that assists the operation of the steering wheel 704, and a control unit 800 that controls the assist motor M3. The assist mechanism 118 is a mechanism that assists the operation of the steering wheel 704 by hydraulic pressure (e.g., hydraulic pressure), and the assist motor M3 is a pump motor that drives a hydraulic pump PM.

[0012] Specifically, the assist mechanism 118 has a hydraulic actuator that applies a rotational force to the steering wheel 704. The rotational force serves as an assist force for the steering operation. The assist mechanism 118 changes the magnitude of the rotational force by the pressure of a liquid (e.g., hydraulic oil). Furthermore, the assist mechanism 118 can switch the direction in which the assist force is applied by mechanically interlocking with the rotation direction of the steering wheel 704. That is, it can switch between applying an assist force for left rotation and applying an assist force for right rotation.

[0013] The auxiliary motor M3 is an electric motor that is driven in one direction by a direct current flowing in the same direction. When a large torque is output from the auxiliary motor M3, the hydraulic pressure delivered from the hydraulic pump PM increases, and the assist force of the steering operation of the auxiliary mechanism 118 increases.

[0014] The control unit 800 has a control circuit 810 arranged on a substrate 802. The control unit 800 further includes a controller 110 and an encoder 122 that detects the rotational position and rotational speed of the steering wheel 704. The controller 110 is a microcomputer and operates according to a control program. The controller 110 receives a detection signal from the encoder 122, and controls the control circuit 810 based on the detection signal so as to generate an assist force whose magnitude changes according to the rotational speed of the steering wheel 704, etc.

[0015] The fork driving device 201 has a lifting mechanism 606 that supports the fork 303 so that it can be raised and lowered, a hydraulic actuator 116 that powers the lifting mechanism 606, a hydraulic motor M2 that supplies hydraulic pressure to the hydraulic actuator, and a control circuit 102 that controls the drive of the hydraulic motor M2. The controller 110 drives the hydraulic motor M2 via the control circuit 102 based on operation information of a lift lever 706, and raises and lowers the fork 303.

[0016] The forklift 300 further includes a traveling motor M1, a gear box 112 and a drive shaft 114 which transmit the power of the traveling motor M1 to the wheels 610, and a control circuit 200 which drives the traveling motor M1. The controller 110 drives the traveling motor M1 via the control circuit 200 based on operation information of a forward / reverse lever 712 and an accelerator pedal 708, to cause the vehicle body 302 to travel.

[0017] The forklift 300 further includes a battery 100 that supplies a DC power supply voltage. The battery 100 supplies the power supply voltage to the control circuits 810, 102, and 200.

[0018] <Control circuit> 4 is a diagram showing a control circuit 810 for the auxiliary motor M3. The control circuit 810 has a first switching element Q1 and a second switching element Q2 connected in series between a pair of terminals t1, t2 to which a power supply voltage is applied. The auxiliary motor M3, which is a pump motor, is connected between an intermediate node n1 between the first switching element Q1 and the second switching element Q2 and one terminal t2 of the pair of terminals t1, t2.

[0019] Specifically, the power supply voltage applied to terminals t1 and t2 is the output voltage of the battery 100, and terminal t2 is a ground terminal. The first switching element Q1 and the second switching element Q2 are FETs (Field Effect Transistors) that are turned on / off by controlling a control terminal (gate terminal), but similar switching elements such as bipolar transistors may also be used. Hereinafter, the terminal to which a control signal that switches the open / closed state of the switching element is input is referred to as the "control terminal," and both ends of the current path opened / closed by the switching element are referred to as the "current terminals."

[0020] The second switching element Q2 has a parasitic diode d2. The parasitic diode d2 is a diode that passes a current from the cathode side to the anode side of the pair of terminals t1 and t2. The first switching element Q1 also has a parasitic diode d1 that passes a current in the same direction.

[0021] The control circuit 810 also includes an input capacitor C1 that stabilizes the power supply voltage input to terminals t1 and t2, a main switch (corresponding to an example of a "switch" according to the present invention) SW that can cut off the input of the power supply voltage at a stage preceding the input capacitor C1, and drive circuits D1 and D2 that receive control signals from the controller 110 and drive control terminals of the first switching element Q1 and the second switching element Q2, respectively. Power supply lines Lp and Ln from the battery 100 are connected to the terminals t1 and t2, respectively. The board on which the main switch SW is mounted and the board 802 on which the control circuit 810 is mounted may be different boards.

[0022] The main switch SW is a contactor or a relay, and is switched off (that is, open) in conjunction with the ignition switch 702 being turned off.

[0023] With this configuration, the controller 110 drives and controls the auxiliary motor M3 by operating the first switching element Q1 and the second switching element Q2 as follows. That is, the controller 110 alternately repeats a first state in which the first switching element Q1 is ON and the second switching element Q2 is OFF, and a second state in which the first switching element Q1 is OFF and the second switching element Q2 is ON. As a result, in the first state, the power supply voltage is applied to the coil of the auxiliary motor M3, and torque is generated in the auxiliary motor M3. Subsequently, in the second state, a current path is formed that circulates from the ground point, the second switching element Q2, the auxiliary motor M3, and the ground point, and the current flowing through the coil of the auxiliary motor M3 is not interrupted. The controller 110 controls the torque generated by the auxiliary motor M3 by changing the time ratio between the first state and the second state.

[0024] Then, the controller 110 operates the control circuit 810 so that the torque of the assist motor M3 becomes large when a large assist force is required for the operation of the steering wheel 704, for example, at a high rotation speed, based on the output of the encoder 122 representing the rotation speed of the steering wheel 704. On the other hand, when a small assist force is required for the operation of the steering wheel 704, for example, at a low rotation speed, the controller 110 operates the control circuit 810 so that the torque of the assist motor M3 becomes small. Furthermore, the direction of the assist force is switched by mechanical interlocking based on the rotation direction of the steering wheel 704. Through such control and operation, a rotation force that appropriately assists the operation of the steering wheel 704 by the driver can be applied to the steering wheel 704.

[0025] Furthermore, according to the control method of the control circuit 810 as described above, the first switching element Q1 and the second switching element Q2 are switched between open and closed states in synchronization, so that the above-mentioned first state current and second state current flow. That is, synchronous rectification can be realized. To generate the first state current and the second state current, the second switching element Q2 can be replaced with a diode. However, a switching element in the on state can pass current with less loss than a diode. Therefore, the synchronous rectification of the control circuit 810 can reduce losses and achieve high efficiency of the control circuit 810.

[0026] <Voltage jump in discharge control in the comparative example> Fig. 5 is a diagram for explaining a voltage jump caused by a back electromotive force in a comparative example. Next, a voltage jump when the discharge control of the comparative example is performed in the control circuit 810 of the embodiment will be explained with reference to Fig. 5. Note that the back electromotive force V1 and the currents I2 and I3 shown in Fig. 5 indicate voltages and currents occurring at different times.

[0027] When the ignition switch 702 is turned off and the main switch SW is turned off, the auxiliary motor M3 continues to rotate due to inertia, and a counter electromotive force V1 is generated in the coil of the auxiliary motor M3 (step S1). At this time, the first switching element Q1 and the second switching element Q2 are turned off, and no current due to the counter electromotive force V1 flows.

[0028] Next, the first switching element Q1 and the second switching element Q2 are alternately switched on and off to release the charge remaining in the input capacitor C1. At this time, the second switching element Q2 is turned on, so that a circular path is generated that passes through the coil of the auxiliary motor M3, the second switching element Q2, and the ground point in this order, and a current I2 corresponding to the back electromotive force V1 flows through the circular path (step S2). Then, energy is stored in the coil of the auxiliary motor M3 by the current I2.

[0029] Subsequently, when the second switching element Q2 is turned off, the current I3 is input to the input capacitor C1 via the first switching element Q1 due to an action that tries to keep the current flowing through the coil of the auxiliary motor M3 (step S3).

[0030] By the actions of steps S1 to S3, the input capacitor C1 is charged, and the voltage across the input capacitor C1 jumps up.

[0031] <Discharge treatment of this embodiment> FIG. 6 is a flowchart showing the procedure of the discharge process executed by the controller 110. The discharge process is started by the controller 110 when the ignition switch 702 is turned off and the main switch SW is turned off. When the discharge process is started, the controller 110 turns off the second switching element Q2 (step T1), and while maintaining the second switching element Q2 off, controls the first switching element Q1 to be alternately switched on and off (step T2). Then, the controller 110 determines whether the end condition is satisfied (step T3), and if satisfied, turns off the first switching element Q1 (step T4) and ends the discharge process. On the other hand, if not satisfied, the controller 110 returns the process to step T2 and repeats the process from step T2. The end condition of step T3 may be set appropriately, for example, when the voltage of the input capacitor C1 drops or when a predetermined processing time has elapsed.

[0032] FIG. 7 is a diagram for explaining the discharge process of FIG. 6. The currents I11 and I12 shown in FIG. 6 indicate currents generated at different timings. According to the above discharge process, first, the first switching element Q1 is turned on and the second switching element Q2 is turned off, so that the voltage remaining in the input capacitor C1 is applied to the auxiliary motor M3, and a forward current I11 flows through the auxiliary motor M3 (step S11). Next, when the first switching element Q1 is turned off while the second switching element Q2 is kept off, a forward current I12 flows through a circular path passing through the auxiliary motor M3, the parasitic diode d2 of the second switching element Q2, and the ground point in this order (step S12). Then, the actions of steps S11 and S12 are repeated. As a result of this action, the energy stored in the input capacitor C1 is consumed by the rotation of the auxiliary motor M3, and the discharge of the input capacitor C1 is achieved. In addition, the rotation speed of the auxiliary motor M3 converges to zero due to the load of the hydraulic pump PM.

[0033] As described above, according to the forklift 300 of this embodiment, the control circuit 810 having the first switching element Q1 and the second switching element Q2 enables synchronous rectification operation, and the efficiency of the control circuit 810 can be improved. On the other hand, when a normal discharge process is performed in the control circuit 810 configured as described above, the voltage of the control circuit 810 may jump up, but the discharge process of this embodiment can reduce the voltage jump up.

[0034] Furthermore, according to the forklift 300 of this embodiment, the second switching element Q2 has a parasitic diode d2. Therefore, by utilizing the parasitic diode d2 during the discharge process, it is possible to reduce the voltage jump with easy control.

[0035] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. For example, in the above embodiments, the power supply voltage input to the terminals t1 and t2 is the output voltage of the battery 100, but the power supply voltage may be a voltage sent from the battery 100 via other circuits such as a filter circuit or a voltage conversion circuit. Other details shown in the embodiments can be modified as appropriate without departing from the spirit of the invention. [Explanation of symbols]

[0036] 100 batteries 110 Controller 116 Hydraulic Actuator 118 Auxiliary mechanism 102, 200 Control circuit 201 Fork drive unit 300 Forklift 301 Driver's seat 302 Body 303 Fork 606 Lifting mechanism 610, 612 wheels 712 Forward / reverse lever 702 Ignition Switch 704 Steering 706 Lift Lever 708 Accelerator Pedal 710 Brake pedal 800 Control section 802 Substrate 810 Control circuit M1 Drive motor M2 Hydraulic Motor M3 Auxiliary Motor PM hydraulic pump Q1 First switching element Q2 Second switching element t1, t2 terminals n1 intermediate node

Claims

1. A forklift including a steering mechanism, an auxiliary motor for assisting the steering operation, and a control unit for controlling the auxiliary motor, the assist mechanism is a mechanism that assists the steering operation by hydraulic pressure, the auxiliary motor is a pump motor that drives a hydraulic pump, The control unit has a control circuit disposed on a substrate, the control circuit has a switch capable of cutting off an input of a power supply voltage, and a first switching element and a second switching element connected in series between a pair of terminals to which the power supply voltage is applied, the pump motor being connected between an intermediate node between the first switching element and the second switching element and one of the pair of terminals, When the switch is turned off, the first switching element alternates between on and off, and the second switching element is maintained off. forklift.

2. The second switching element includes a parasitic diode.

2. The forklift according to claim 1.

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