Engine-powered industrial vehicles

Abstract

The objective is to provide an engine-powered industrial vehicle that can reduce engine load when releasing the braking force of the automatic parking brake system. [Solution] The automatic parking brake device includes a parking brake unit and an actuator 62 which is equipped with a biasing member that applies a biasing force to generate braking force to the parking brake unit and which can release the braking force by operating hydraulic pressure. The engine-driven industrial vehicle has an actuator supply oil passage which is branched from the oil passage that supplies hydraulic fluid to the hydraulic actuator in the hydraulic fluid circuit and supplies hydraulic fluid to the actuator 62, a switching valve 73 provided in the actuator supply oil passage, and a controller 53 that controls the switching valve 73. The controller 53 closes the switching valve 73 so that hydraulic fluid is not supplied to the actuator 62 when the vehicle speed is 0, and opens the switching valve 73 so that hydraulic fluid is supplied to the actuator 62 when the accelerator pedal 50 is pressed while braking force is generated.

Description

Technical Field

[0001] The present invention relates to an engine-powered industrial vehicle.

Background Art

[0002] As a prior art of engine-powered industrial vehicles, for example, the engine-powered industrial vehicle disclosed in Patent Document 1 is known. The engine-powered industrial vehicle includes a vehicle body, an engine mounted on the vehicle body, a controller that controls the output of the engine based on the operation amount of an accelerator pedal, and an automatic parking brake controlled by the controller that generates braking force when the vehicle is stopped and releases the braking force in response to the operation of the accelerator pedal. The output shaft of the engine is connected to a torque converter, and the output shaft of the torque converter is connected to a speed reducer.

[0003] An automatic parking brake is provided at a rear portion of the speed reducer. The automatic parking brake is a wet multi-plate brake that automatically generates a braking force on the output shaft when the forklift stops. A hydraulic oil pipe connecting the automatic parking brake and the torque converter is provided, and the hydraulic oil pipe is provided with a solenoid on-off valve that opens and closes the hydraulic oil pipe. This solenoid on-off valve is controlled by the controller. When the solenoid on-off valve is closed, the automatic parking brake enters a state of generating and maintaining braking force. On the other hand, when the solenoid on-off valve is opened, hydraulic oil is supplied to the automatic parking brake, and the braking force is released by the hydraulic pressure. The controller controls to open the solenoid on-off valve when the accelerator pedal is operated. A hydraulic oil pump operated by driving the engine is provided, and the hydraulic oil pump and the torque converter are connected by a hydraulic oil pipe.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

[0005] However, in the engine-driven industrial vehicle disclosed in Patent Document 1, the relatively high hydraulic pressure of the torque converter is used to release the braking force of the automatic parking brake, which leads to a problem in that the load on the engine that drives the hydraulic fluid pump increases. This increased engine load may, for example, lead to a decrease in fuel efficiency.

[0006] This invention has been made in view of the above-mentioned problems, and the object of this invention is to provide an engine-powered industrial vehicle that can reduce the engine load when releasing the braking force of the automatic parking brake device. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides an engine-driven industrial vehicle comprising: a vehicle body; a hydraulic actuator provided on the vehicle body and operated by the supply and discharge of hydraulic fluid; a hydraulic fluid circuit that enables the supply and discharge of hydraulic fluid to the hydraulic actuator; an engine mounted on the vehicle body; a hydraulic fluid pump provided in the hydraulic fluid circuit and pumping hydraulic fluid by the engine's drive; an accelerator pedal for increasing or decreasing the engine's rotational speed; and an automatic parking brake device that releases the braking force when the accelerator pedal is pressed while braking force is generated, wherein the automatic parking brake device comprises a parking brake unit capable of generating braking force and an attachment that generates the braking force of the parking brake unit. The device includes an actuator equipped with a biasing member that imparts force, and an actuator that can release the braking force from the biasing member by operating hydraulic pressure; an actuator supply oil passage that branches off from the oil passage that supplies hydraulic fluid to the hydraulic actuator in the hydraulic fluid circuit and supplies hydraulic fluid to the actuator; a switching valve provided in the actuator supply oil passage; and a controller that controls the switching valve, wherein the controller closes the switching valve so that hydraulic fluid is not supplied to the actuator when the vehicle speed is 0, and opens the switching valve so that hydraulic fluid is supplied to the actuator when the accelerator pedal is pressed while braking force is generated in the parking brake section.

[0008] In this invention, the engine drives a hydraulic fluid pump to draw up hydraulic fluid. The actuator supply oil passage is branched from the oil passage that supplies hydraulic fluid to the hydraulic actuation device in the hydraulic fluid circuit, and a portion of the hydraulic fluid drawn up by the hydraulic fluid pump is supplied to the actuator. The controller closes a switching valve to prevent the supply of hydraulic fluid to the actuator when the vehicle speed is 0. The controller also opens the switching valve when the accelerator pedal is pressed while braking force is applied to the parking brake. When the switching valve is opened, hydraulic fluid is supplied through the actuator supply oil passage. When braking force is applied to the parking brake, the actuator receives the supply of hydraulic fluid and operates against the biasing force of the biasing member, releasing the braking force of the parking brake. Since the actuator is operated using the hydraulic pressure generated by the pressure loss in the hydraulic actuation device, it is possible to reduce the engine load when releasing the braking force of the automatic parking brake device.

[0009] Furthermore, in the above-described engine-driven industrial vehicle, the vehicle may include a driver's seat, a seating sensor for detecting when a person sits on the driver's seat, a direction lever that can be switched to one of the following positions: forward, reverse, or neutral, and a lever sensor for detecting the position of the direction lever. The controller may be configured to detect when a person sits on the seat using the seating sensor, when the lever sensor detects either the forward or reverse position, and when the accelerator pedal is pressed, open the switching valve so that hydraulic fluid is supplied to the actuator supply oil passage. In this case, the controller detects that the driver is seated using the seat sensor, and when the lever sensor detects either the forward or reverse position, and the accelerator pedal is pressed, it opens a switching valve to supply hydraulic fluid to the actuator oil passage. Therefore, the braking force of the automatic parking brake is not released when the driver is not seated in the driver's seat. Furthermore, even when the driver is seated in the driver's seat, the braking force will not be released unless the lever sensor is in the forward or reverse position and the accelerator pedal is pressed.

[0010] Furthermore, in the above-described engine-driven industrial vehicle, the controller may be configured to close the switching valve after a predetermined time has elapsed, when the vehicle speed is 0, so that hydraulic fluid is not supplied to the actuator. In this case, when the vehicle speed is 0, the switching valve is closed after a predetermined time has elapsed so that hydraulic fluid is not supplied to the actuator. Therefore, even if the vehicle speed momentarily becomes 0 while driving, the switching valve will not be closed immediately. Consequently, even when frequently moving forward and backward, braking force will not be generated in the automatic parking brake system until a predetermined time has elapsed.

[0011] Furthermore, in the above-described engine-driven industrial vehicle, the vehicle may also have a brake pedal, a master cylinder that receives hydraulic fluid from the hydraulic fluid circuit and generates hydraulic pressure corresponding to the amount the brake pedal is pressed, a wheel cylinder provided in the parking brake section and operated by hydraulic fluid, and a service brake fluid passage connecting the master cylinder and the wheel cylinder, wherein the parking brake section is configured to operate the wheel cylinder when the brake pedal is pressed during driving, and to generate braking force as a service brake device corresponding to the amount the brake pedal is pressed. In this case, the parking brake unit generates braking force as a service brake in proportion to the pressure applied to the brake pedal while driving, so the automatic parking brake can also be used as a service brake. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an engine-powered industrial vehicle that can reduce the engine load when releasing the braking force of the automatic parking brake device. [Brief explanation of the drawing]

[0013] [Figure 1] This is a side view of an engine-powered forklift according to the first embodiment. [Figure 2]This is a plan view of an engine-powered forklift according to the first embodiment. [Figure 3] This is a schematic diagram illustrating the general configuration of an engine-powered forklift. [Figure 4] This is a schematic diagram illustrating the general configuration of an automatic parking brake system. [Figure 5] This is a flowchart showing the procedure for releasing the automatic parking brake. [Figure 6] This is a flowchart illustrating the procedure for generating braking force in the automatic parking brake system. [Figure 7] This flowchart shows the procedure for generating braking force in the modified automatic parking brake system. [Modes for carrying out the invention]

[0014] (First Embodiment) Hereinafter, an engine-powered industrial vehicle according to an embodiment of the present invention will be described with reference to the drawings. The engine-powered industrial vehicle of this embodiment is an engine-powered forklift used as a material handling vehicle. The directions "front and back," "left and right," and "up and down" are indicated based on the state in which the forklift operator is seated in the driver's seat and facing the forward direction of the forklift.

[0015] As shown in Figures 1 and 2, the engine-powered forklift (hereinafter simply referred to as "forklift") 10 is equipped with a cargo handling device 12 at the front of the vehicle body 11. A driver's seat 13 is located near the center of the vehicle body 11. Front wheels 14 are located at the front of the vehicle body 11, and rear wheels 15 are located at the rear of the vehicle body 11. The front wheels 14 are drive wheels, and the rear wheels 15 are steering wheels. A counterweight 16 is located at the rear of the vehicle body 11, and the counterweight 16 is used to adjust the vehicle weight and balance the weight of the vehicle body 11. The vehicle body 11 is equipped with a head guard 17 that covers the top of the driver's seat 13.

[0016] The cargo handling device 12 includes a mast 18 having an outer mast 19 and an inner mast 20. The pair of left and right outer masts 19 are provided with a pair of left and right inner masts 20 that can be lifted and lowered inside the outer masts 19. The cargo handling device 12 includes a lift bracket 21 that lifts and lowers along the inner mast 20, and the lift bracket 21 is provided with a pair of left and right forks 22 and a backrest 23. The left and right forks 22 scoop up and support cargo. The backrest 23 supports the rear surface of the cargo supported by the pair of left and right forks 22.

[0017] Between the vehicle body 11 and the mast 18, a tilt cylinder 24 that is actuated by hydraulic oil is installed. The mast 18 tilts in the front-rear direction about the lower end of the mast 18 as a fulcrum by the actuation of the tilt cylinder 24. The outer mast 19 is provided with a lift cylinder 25 that is actuated by supply and discharge of hydraulic oil (see FIG. 1). By the actuation of the lift cylinder 25, the inner mast 20 lifts and lowers inside the outer mast 19, and the lift bracket 21 also lifts and lowers. The tilt cylinder 24 and the lift cylinder 25 included in the cargo handling device 12 correspond to hydraulic actuators that are actuated by supply and discharge of hydraulic oil.

[0018] An instrument panel 26 is provided in front of the driver's seat 13. The instrument panel 26 is provided with a steering column 27 that supports a steering wheel 28. In addition to a key cylinder (not shown) into which a key is inserted, the instrument panel 26 is provided with a cargo handling lever 29 and a direction lever 30. The cargo handling lever 29 includes a lift lever and a tilt lever. The lift lever is an operation lever for lifting and lowering the forks 22. The tilt lever is an operation lever for tilting the mast 18 back and forth. The direction lever 30 is a lever that is operated by switching according to forward or reverse travel, and can be switched to any one of three positions: forward, reverse, and neutral. An engine 31 is mounted on the vehicle body 11, and the vehicle body 11 includes an openable / closable engine hood 32 that covers the engine 31. A driver's seat 33 is provided on the engine hood 32.

[0019] As shown in Figure 3, the forklift 10 includes a steering device 34 that steers the rear wheels 15 by operating the steering wheel 28. The steering device 34 includes a power steering cylinder (not shown) that is actuated by supplying and discharging hydraulic oil, and the power steering cylinder corresponds to a hydraulic actuator. An output shaft 35 of the engine 31 is connected to a torque converter 36, and an output shaft 37 of the torque converter 36 is connected to a speed reducer 38. The speed reducer 38 has a differential mechanism (not shown) that distributes the rotational force input from the torque converter 36 to left and right axles 39. The axles 39 are provided with front wheels 14. The engine 31 is provided with a vehicle speed sensor 40 that detects vehicle speed. The vehicle speed is detected based on the number of rotations of the output shaft 35. Note that the torque converter 36 corresponds to a hydraulic actuator similarly to the cargo handling device 12 and the steering device 34.

[0020] The forklift 10 includes a hydraulic oil circuit 41 that enables supply and discharge of hydraulic oil to and from the cargo handling device 12 and the steering device 34. The hydraulic oil circuit 41 includes a hydraulic oil pump 42 that is actuated by driving of the engine 31. A vehicle body 11 is provided with a hydraulic oil tank 43 that stores hydraulic oil. The hydraulic oil pump 42 is actuated by driving of the engine 31 and pumps up hydraulic oil from the hydraulic oil tank 43. The hydraulic oil circuit 41 includes a control valve 44 that distributes hydraulic oil at a required pressure to the cargo handling device 12 and the steering device 34. The control valve 44 supplies and discharges hydraulic oil to and from the cargo handling device 12 in accordance with an operation of a cargo handling lever 29, and also supplies and discharges hydraulic oil to and from the steering device 34 in accordance with an operation of the steering wheel 28.

[0021] The hydraulic fluid circuit 41 includes a hydraulic fluid pipe 45 connecting the hydraulic fluid pump 42 and the control valve 44, a hydraulic fluid pipe 46 connecting the control valve 44 and the cargo handling device 12, and a hydraulic fluid pipe 47 connecting the control valve 44 and the steering device 34. The control valve 44 supplies and discharges hydraulic fluid to the hydraulic fluid system according to the driver's operation, etc. The hydraulic fluid pipe 45 corresponds to the oil passage that supplies hydraulic fluid to the hydraulic actuation device in the hydraulic fluid circuit 41. The hydraulic fluid circuit 41 also includes a hydraulic fluid pipe 48 that branches off from the hydraulic fluid pipe 45 and connects to the master cylinder 74 of the brake pedal 51, which will be described later. In addition, there is a hydraulic fluid pipe 49 that returns hydraulic fluid from the control valve 44 to the hydraulic fluid tank 43.

[0022] As shown in Figure 3, the forklift 10 is equipped with an accelerator pedal 50 and a brake pedal 51. The accelerator pedal 50 is a pedal that increases or decreases the rotational speed of the engine 31. An accelerator pedal sensor 52 is provided to detect the amount of operation by pressing the accelerator pedal 50. The accelerator pedal sensor 52 is connected to the controller 53. When the accelerator pedal 50 is pressed down, the accelerator pedal sensor 52 is ON, and when the accelerator pedal 50 is not pressed down, the accelerator pedal sensor 52 is OFF. In addition to the accelerator pedal sensor 52, an accelerator pedal switch may also be used to detect the ON / OFF state of the accelerator pedal 50.

[0023] The controller 53 is mounted in the vehicle body 11 directly below the driver's seat 33 (see Figure 1). The controller 53 controls various parts of the forklift 10. For example, when the accelerator pedal 50 is pressed, the controller 53 controls the engine 31 according to the amount of operation of the accelerator pedal 50. As shown in Figure 3, the controller 53 that controls various parts of the forklift 10 includes a CPU 54, a memory unit 55 consisting of RAM and ROM, etc.

[0024] The controller 53 may include dedicated hardware, such as an application-specific integrated circuit (ASIC), that performs at least some of the various processes. The controller 53 can be configured as a circuit including one or more processors, one or more dedicated hardware circuits such as ASICs, or a combination thereof, that operate according to a computer program. The storage unit 55 stores program code or instructions configured to cause the CPU 54 to execute processes. The storage unit 55 stores various programs for controlling the various parts of the forklift 10.

[0025] As shown in Figure 3, the controller 53 is electrically connected to a seat sensor 56 that detects when the driver is seated in the driver's seat 33, a seat belt sensor 58 that detects when the seat belt 57 provided on the driver's seat 33 is fastened, and a lever sensor 59 that detects the position of the direction lever 30. The seat sensor 56 is located on the seat of the driver's seat 33 and emits an ON signal when the driver is seated and an OFF signal when the driver is not seated. The seat belt sensor 58 emits an ON signal when the driver is fastening the seat belt 57 and an OFF signal when the driver is not fastening. The lever sensor 59 emits a signal indicating the position according to the forward, reverse, and neutral positions of the direction lever 30.

[0026] As shown in Figure 3, the brake pedal 51 is a pedal for generating braking force for drum brakes 60 provided on the left and right axles 39. The forklift 10 has a master cylinder 74 that receives hydraulic fluid from a hydraulic fluid circuit 41 and generates hydraulic pressure corresponding to the amount the brake pedal 51 is pressed. The drum brake 60 in this embodiment is a known dry drum brake comprising a brake drum (not shown) provided on the axle 39 and brake shoes (not shown) that are in conjunction with the brake pedal 51 and face the inner surface of the brake drum. The drum brake 60 is equipped with a wheel cylinder 75 that is operated by hydraulic pressure and presses the brake shoes against the brake drum. The wheel cylinder 75 is connected to the master cylinder 74 via a hydraulic fluid pipe 61 which serves as a service brake fluid passage. Therefore, the brake shoes are pressed against the brake drum in response to the operation of the brake pedal 51.

[0027] In this embodiment, a service brake system is configured having a brake pedal 51, a drum brake 60, a master cylinder 74, a wheel cylinder 75, and hydraulic fluid piping 61. The drum brake 60 is part of the service brake system that generates braking force in response to the depression of the brake pedal 51, but it also functions as part of the automatic parking brake system described next.

[0028] In this embodiment, the forklift 10 has an automatic parking brake device. The automatic parking brake device has the function of automatically generating braking force when the vehicle speed becomes 0 [km / h] and releasing the braking force when the accelerator pedal 50 is pressed while the braking force is generated. The automatic parking brake in this embodiment has a drum brake 60 as a parking brake unit that is capable of generating braking force, and an actuator 62 that can release the braking force by operating hydraulic pressure. As shown in Figure 4, the actuator 62 has a cylindrical body 63, a movable part 64 that can move back and forth relative to the body 63, an operating oil chamber 65 formed in the body 63, and a coil spring 66 that biases the movable part 64. The movable part 64 includes a piston 64A and a rod 64B connected to the piston 64A.

[0029] As shown in Figure 4, one end of the movable part 64 protrudes from the main body 63, and this protruding end of the movable part 64 is connected to one end of a link member 67. The link member 67 is a member that can rotate with respect to the pivot axis 68. The link member 67 comprises a long arm portion 69 and a short arm portion 70. The distance from the tip of the long arm portion 69 to the center of the pivot axis 68 is greater than the distance from the tip of the short arm portion 70 to the center of the pivot axis 68. The protruding end of the movable part 64 is pivotally supported at the tip of the long arm portion 69. One end of the parking brake cable 71 is connected to the tip of the short arm portion 70. The other end of the parking brake cable 71 is connected to the drum brake 60. The link member 67 acts as a power assist mechanism, increasing the force input from the rod 64B and outputting it to the parking brake cable 71.

[0030] The coil spring 66 is a biasing member that biases the movable part 64 in the direction of pulling it towards the main body 63. The hydraulic fluid chamber 65 is a space into which hydraulic fluid is introduced. When hydraulic fluid is supplied to the hydraulic fluid chamber 65, the movable part 64 moves in a direction that is pushed out against the coil spring 66 by the hydraulic pressure. By providing the link member 67, the movable part 64 can be extended even when the pressure in the hydraulic fluid chamber 65 is low, and the tension of the parking brake cable 71 can be increased.

[0031] As shown in Figure 4, the hydraulic fluid chamber 65 is connected to a hydraulic fluid pipe 72 that branches off from the hydraulic fluid pipe 45. The hydraulic fluid pipe 72 corresponds to the actuator supply oil passage that supplies hydraulic fluid from the hydraulic fluid pipe 45 to the actuator 62. The hydraulic fluid pipe 72 is equipped with a switching valve 73 controlled by the controller 53. The switching valve 73 is a normally closed electromagnetic valve that is closed under normal conditions, and opening the switching valve 73 allows hydraulic fluid to be supplied to the hydraulic fluid chamber 65.

[0032] The hydraulic pressure generated by the pressure loss in the cargo handling device 12 and steering device 34, which act as hydraulic operating devices in the hydraulic fluid circuit 41, is utilized to supply hydraulic fluid to the actuator 62 through the hydraulic fluid piping 72. The hydraulic pressure in the hydraulic fluid piping 72 is at its minimum when the engine 31 is idling, but the actuator 62 is able to extend the rod 64B even with the minimum hydraulic pressure at the engine 31's idling.

[0033] When the forklift 10 stops (vehicle speed 0 [km / h]), the controller 53 controls the drum brake 60 to function as the braking unit of the automatic parking brake system. Specifically, the controller 53 closes the switching valve 73, causing the parking brake cable 71 to be pulled by the actuator 62, thereby generating braking force for the drum brake 60.

[0034] The braking force generated in the automatic parking brake system is released according to a series of steps shown in the flowchart of Figure 5. First, the controller 53 determines whether the engine 31 is running or not (see step S101). If it is determined that the engine 31 is running, the controller 53 determines whether the seat occupancy sensor 56 is ON or not (see step S102). If it is determined that the seat occupancy sensor 56 is ON, the controller 53 determines whether the seat belt sensor 58 is ON or not (see step S103).

[0035] When the seat belt sensor 58 is detected as ON, the system proceeds to the next step. The system then determines whether the lever sensor 59 is ON or not (see step S104). The controller 53 determines that the lever sensor 59 is ON if the direction lever 30 is in a position other than neutral (forward or reverse) due to the driver's operation. When the lever sensor 59 is detected as ON, the controller 53 determines whether the accelerator pedal sensor 52 is ON or not (see step S105). The controller 53 determines that the accelerator pedal sensor 52 is ON if the accelerator pedal 50 is pressed down by the driver. When the accelerator pedal sensor 52 is detected as ON, the controller 53 opens the switching valve 73 (see step S106). When the switching valve 73 is opened, the rod 64B of the actuator 62 extends (see step S107). The extension of the rod 64B rotates the link member 67, reducing the tension of the parking brake cable 71. As a result, the braking force of the drum brake 60 is released (see step S108).

[0036] On the other hand, when it is determined in step S101 that the engine 31 is not running, the controller 53 maintains the closed state of the switching valve 73 (see step S109). By maintaining the closed state of the switching valve 73, the braking force of the drum brake 60 is maintained (see step S110). Similarly, when it is determined in step S102 that the seat sensor 56 is not ON, and when it is determined in step S103 that the seat belt sensor 58 is not ON, the controller 53 maintains the closed state of the switching valve 73. Furthermore, when it is determined in steps S104 and S105 that the sensors are not ON, the controller 53 also maintains the closed state of the switching valve 73.

[0037] Furthermore, the braking force of the automatic parking brake device is generated according to a series of steps shown in the flowchart of Figure 6. First, the driver of the forklift 10 presses down on the brake pedal 51 while it is in motion (see step S201). Pressing down on the brake pedal 51 causes the forklift 10 to decelerate. The controller 53 determines whether the vehicle speed is 0 [km / h] or not (see step S202). If it is determined that the vehicle speed is 0 [km / h], the controller 53 switches the switching valve 73 from open to closed (see step S203).

[0038] When the switching valve 73 is switched to the closed position, hydraulic fluid is no longer supplied to the hydraulic fluid chamber 65 of the actuator 62. As a result, the rod 64B of the actuator 62 is subjected to the biasing force of the coil spring 66 and contracts relative to the main body 63 (see step S204). As the rod 64B contracts, the link member 67 rotates, and the tension of the parking brake cable 71 increases. As a result, braking force is generated in the drum brake 60. The hydraulic fluid in the hydraulic fluid chamber 65 is returned to the hydraulic fluid tank 43 as the rod 64B contracts.

[0039] On the other hand, if it is determined in step S202 that the vehicle speed is not 0 [km / h], the controller 53 maintains the open position of the switching valve 73 (see step S206). Therefore, the state in which the braking force of the drum brake 60 is released is maintained (see step S207).

[0040] Next, the operation of the forklift 10 will be explained. When the forklift 10 is stationary, the switching valve 73 is closed, and no hydraulic fluid is supplied to the actuator 62. As a result, the rod 64B is retracted by the biasing force of the coil spring 66 of the actuator 62, and a braking force is generated in the drum brake 60 as an automatic parking brake device.

[0041] When a driver intends to operate the forklift 10, they sit in the driver's seat 33, insert the key into the key cylinder, and turn on the key switch to start the engine 31. Furthermore, the driver puts on the seat belt 57 and positions the direction lever 30 in the forward or reverse position. When the driver presses the accelerator pedal 50, the controller 53 switches the switching valve 73 from closed to open, supplying hydraulic fluid to the actuator 62. As a result, the rod 64B of the actuator 62 extends against the biasing force of the coil spring 66 due to the hydraulic pressure. The extension of the rod 64B reduces the tension of the parking brake cable 71 by the link member 67, thus releasing the braking force of the drum brake 60. In other words, the braking force of the automatic parking brake device is released when the driver presses the accelerator pedal 50. Furthermore, the braking force of the drum brake 60 is not released when the engine 31 is stopped, when the driver is not seated in the driver's seat 33, or when the driver is not wearing the seat belt 57.

[0042] On the other hand, when the driver presses the brake pedal 51 while the forklift 10 is in motion, a braking force as a service brake is generated in the drum brake 60 in proportion to the amount the brake pedal 51 is pressed. As a result, the forklift 10 decelerates according to the amount of braking force. When the speed of the forklift 10 decelerates to 0 [km / h], the vehicle speed sensor 40 transmits a signal indicating that the vehicle speed is 0 [km / h] to the controller 53, and the controller 53 closes the switching valve 73. Because the switching valve 73 is closed, hydraulic fluid is not supplied to the actuator 62. As a result, the rod 64B is contracted by the biasing force of the coil spring 66 of the actuator 62, and a braking force as an automatic parking brake is generated in the drum brake 60. When the braking force is generated in the drum brake 60 due to the operation of the actuator 62, the forklift 10 maintains its stop. Note that the braking force as an automatic parking brake of the drum brake 60 is not released regardless of whether the driver presses the brake pedal 51 or not.

[0043] As long as the driver remains seated in the driver's seat 33 and wearing the seat belt 57, and the engine 31 is running, pressing the accelerator pedal 50 releases the braking force of the drum brake 60 as a parking brake. The forklift 10 increases in speed according to the amount the accelerator pedal 50 is pressed.

[0044] The forklift 10 according to this embodiment provides the following effects. (1) The engine 31 drives the hydraulic oil pump 42 to pump up hydraulic oil. The hydraulic oil piping 72 is branched from the hydraulic oil piping 45 that supplies hydraulic oil to the cargo handling device 12 and the steering device 34 in the hydraulic oil circuit 41. A portion of the hydraulic oil pumped up by the hydraulic oil pump 42 is supplied to the actuator 62 through the hydraulic oil piping 72. The controller 53 closes the switching valve 73 so that hydraulic oil is not supplied to the actuator 62 when the vehicle speed is 0 [km / h]. The controller 53 also opens the switching valve 73 when the accelerator pedal 50 is pressed while braking force is generated in the drum brake 60 as an automatic parking brake device. When the switching valve 73 is opened, hydraulic oil is supplied through the hydraulic oil piping 72. When braking force is generated in the drum brake 60 as a parking brake, the actuator 62 receives the supply of hydraulic oil and operates against the biasing force of the coil spring 66, releasing the braking force of the drum brake 60. Since the actuator 62 is operated using the hydraulic pressure generated by the pressure loss in the cargo handling device 12 and the steering device 34, the load on the engine 31 can be reduced when the braking force of the automatic parking brake is released.

[0045] (2) The controller 53 detects the driver's seating position using the seating sensor 56, and when the lever sensor 59 detects either the forward or reverse position and the accelerator pedal 50 is pressed, it opens the switching valve 73 to supply hydraulic fluid to the hydraulic fluid piping 72. For this reason, the braking force of the drum brake 60 as a parking brake is not released when the driver is not seated in the driver's seat 33. Furthermore, even when the driver is seated in the driver's seat 33, the braking force is not released unless the lever sensor 59 is in the forward or reverse position and the accelerator pedal 50 is pressed.

[0046] (3) The forklift 10 includes a brake pedal 51, a master cylinder 74 that receives hydraulic fluid from a hydraulic fluid circuit 41 and generates hydraulic pressure corresponding to the amount the brake pedal 51 is pressed, a wheel cylinder 75 provided in the parking brake section and operated by hydraulic fluid, and a hydraulic fluid pipe 61 connecting the master cylinder 74 and the wheel cylinder 75. The drum brake 60 generates braking force as a service brake device in response to the pressing of the brake pedal 51 during driving, corresponding to the amount the brake pedal 51 is pressed. For this reason, the automatic parking brake device can also be used as a service brake device.

[0047] (4) The extension of the rod 64B of the actuator 62 reduces the tension of the parking brake cable 71 via the link member 67, and the presence of the link member 67 as a power assist mechanism allows the rod 64B to be extended at low operating hydraulic pressure. This allows the spring force of the coil spring 66 to be reduced, making it possible to miniaturize the actuator 62. Furthermore, even at the minimum operating hydraulic pressure when the engine 31 is idling, this minimum operating hydraulic pressure is sufficient to extend the rod 64B against the biasing force of the coil spring 66. Since the minimum operating hydraulic pressure when the engine 31 is idling is less than or equal to the pressure loss hydraulic pressure generated in the cargo handling device 12 and the steering device 34, the load on the engine 31 can be significantly reduced by providing the hydraulic oil piping 72 and the switching valve 73 in the hydraulic oil circuit 41.

[0048] (modified version) Next, a modified example will be described. As shown in the flowchart of Figure 7, in the modified example, a step S303, "elapsed predetermined time T," is added between steps S302 and S304 in the series of steps until braking force as an automatic parking brake device is generated. Therefore, when the vehicle speed sensor 40 detects a vehicle speed of 0 [km / h] while driving, the controller 53 closes the switching valve 73 so that hydraulic fluid is not supplied to the actuator 62 after a predetermined time T has elapsed. The predetermined time T may be, for example, 2, 3 seconds or a few seconds, and is stored in the memory unit 55. The elapsed time T is determined using the timer function provided by the controller 53.

[0049] In the modified version, even if the vehicle speed momentarily drops to 0 km / h while driving, the switching valve 73 does not immediately close. Therefore, even when frequently moving forward and backward, braking force is not generated in the automatic parking brake system until a predetermined time T has elapsed. As a result, unintended braking by the driver due to the automatic parking brake system can be prevented.

[0050] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the invention. For example, the following modifications may be made.

[0051] ○ In the above embodiment, a forklift was used as an example to describe an engine-powered industrial vehicle, but the invention is not limited to this. An engine-powered industrial vehicle may be, for example, an industrial vehicle having a steering mechanism that includes a power steering cylinder as a hydraulic actuation device. ○ In the above embodiment, the engine-driven industrial vehicle is assumed to have a link member as a power assist mechanism, but it is not limited to this. For example, it may be an engine-driven industrial vehicle that does not have a link member. In this case, the movable member of the actuator is connected to the parking brake cable. ○ In the above embodiment, a dry drum brake was used as an example for the parking brake section, but the invention is not limited to this. The parking brake section may be, for example, a hydraulic disc brake. ○ In the above embodiment, the hydraulic pressure of the hydraulic oil pump was used as the hydraulic power source for the actuator, but this is not the only option. For example, the hydraulic pressure of the torque converter may be used as the hydraulic power source for the actuator. In the above embodiment, the controller determines whether or not the seat belt sensor is ON as part of a series of steps to release the braking force generated in the automatic parking brake device, but it is not limited to this. For example, the step of determining whether or not the seat belt sensor is ON may be omitted. [Explanation of Symbols]

[0052] 10 Forklifts 11 Car body 12. Cargo handling equipment (hydraulic devices) 13. Driver's seat 22 Forks 29. Loading lever 30 Direction lever 31 Engine 33 Driver's seat 34. Steering system (hydraulic actuation system) 36. Torque converter (hydraulic actuation device) 40. Vehicle speed sensor 41. Hydraulic fluid circuit 42. Hydraulic oil pump 44 Control valve 45, 46, 47, 48, 49 Hydraulic oil piping 50 Accelerator pedal 51 Brake pedal 52 Accelerator pedal sensor 53 Controllers 56. Seat occupancy sensor 57 Seat belts 58 Seat belt sensor 59 Lever Sensor 60 Drum brake (brake section) 61. Hydraulic fluid piping (service brake fluid passage) 62 Actuators 66. Coil spring (biasing member) 67 Link member 72. Hydraulic fluid piping (actuator supply oil passage) 73 Switching valve 74 Master Cylinder 75 Wheel Cylinder T predetermined time

Claims

1. The car body and, A hydraulic actuator is provided on the vehicle body and operates by supplying and discharging hydraulic fluid, A hydraulic fluid circuit that enables the supply and discharge of hydraulic fluid to the hydraulic actuator, The engine mounted on the aforementioned vehicle body, The hydraulic fluid circuit is provided with a hydraulic fluid pump that draws up hydraulic fluid when driven by the engine, An accelerator pedal for increasing or decreasing the rotational speed of the aforementioned engine, In an engine-powered industrial vehicle, there is an automatic parking brake device that releases the braking force when the accelerator pedal is pressed while braking force is being applied, The aforementioned automatic parking brake device, A parking brake unit that can generate braking force, The system includes a biasing member that applies a biasing force to generate braking force in the parking brake section, and an actuator that allows the braking force from the biasing member to be released by hydraulic pressure. In the aforementioned hydraulic fluid circuit, a branch is made from the oil passage that supplies hydraulic fluid to the hydraulic actuator, and an actuator supply oil passage that supplies hydraulic fluid to the actuator, A switching valve is provided in the actuator supply oil passage, The system includes a controller that controls the switching valve, The controller is characterized in that it closes the switching valve so that no hydraulic fluid is supplied to the actuator when the vehicle speed is 0, and opens the switching valve so that hydraulic fluid is supplied to the actuator when the accelerator pedal is pressed while braking force is generated in the parking brake section.

2. The driver's seat and, A seating sensor that detects the person sitting in the driver's seat, A direction lever that can be switched to one of the following positions: forward, reverse, or neutral, It includes a lever sensor that detects the position of the direction lever, The engine-driven industrial vehicle according to claim 1, characterized in that the controller detects seating by the seating sensor, the lever sensor detects either a forward or reverse position, and when the accelerator pedal is pressed, the controller opens the switching valve so that hydraulic fluid is supplied to the actuator supply oil passage.

3. The engine-driven industrial vehicle according to claim 1 or 2, characterized in that the controller closes the switching valve so that hydraulic fluid is not supplied to the actuator after a predetermined time has elapsed when the vehicle speed is 0.

4. The brake pedal and A master cylinder that receives hydraulic fluid from the hydraulic fluid circuit and generates hydraulic pressure corresponding to the amount the brake pedal is pressed, The aforementioned parking brake section includes a wheel cylinder that is operated by hydraulic fluid, It has a service brake fluid passage connecting the master cylinder and the wheel cylinder, The engine-driven industrial vehicle according to claim 1 or 2, characterized in that the parking brake unit operates the wheel cylinder when the brake pedal is pressed during driving, and generates a braking force as a service brake device corresponding to the degree to which the brake pedal is pressed.

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