Industrial vehicle braking systems

Abstract

To provide a brake system of an industrial vehicle which can achieve stable braking regardless of a battery charging rate.SOLUTION: A brake system 1 comprises: an opening control valve 18 which is arranged between a hydraulic pump 7 and a brake unit 12; a selector valve 16 which is arranged between the brake unit 12 and a master cylinder 14 and the opening control valve 18; and a brake control part 78 which controls a motor 4 for traveling to perform regenerative braking in which the motor 4 for traveling works as a generator when the charging rate of a battery 5 storing electric power supplied to the motor 4 for traveling is a threshold value or less, and which controls the opening control valve 18 so that the opening control valve 18 opens according to the control input of a brake pedal 11 when the charging rate of the battery 5 is higher than the threshold value, and which controls the selector valve 16 so that hydraulic fluid flows from the hydraulic pump 7 to the brake unit 12 to supply the brake unit 12 with brake fluid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Known braking systems for industrial vehicles include the technology described in Patent Document 1. In the braking system described in Patent Document 1, when the driver presses the brake pedal while the forklift is traveling, the power supply from the battery to the traveling motor is stopped, and the traveling motor operates as a generator, performing regenerative braking. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-280178 Summary of the Invention [Problem to be solved by the invention]

[0004] Industrial vehicles such as forklifts are equipped with both mechanical and regenerative brakes. When the contribution of the mechanical brakes is high, the regenerative energy during normal operation is reduced, resulting in energy loss. On the other hand, when the contribution of the regenerative brakes is high, regenerative braking becomes difficult, resulting in a longer braking distance and an uncomfortable feeling for the driver.

[0005] On the other hand, in recent years, in order to promote environmental friendliness worldwide, the use of lithium-ion batteries, similar to those used in automobiles, as an energy source for electric forklifts has been increasing.However, in an electric forklift equipped with a lithium-ion battery, if large regenerative braking is performed when the battery is highly charged, the battery's current voltage may temporarily reach its upper limit voltage, making it difficult to perform regenerative braking.

[0006] An object of the present invention is to provide a braking system for an industrial vehicle that can achieve stable braking regardless of the charging rate of the battery. [Means for solving the problem]

[0007] One aspect of the present invention is a braking system for an industrial vehicle that brakes drive wheels that are rotationally driven by a traveling motor, the braking system including a brake pedal operated by a driver of the industrial vehicle, a brake unit that applies a mechanical braking force to the drive wheels, a master cylinder that is mechanically connected to the brake pedal and is driven by hydraulic oil, a hydraulic source that supplies hydraulic oil, an opening adjustment valve that is arranged between the hydraulic source and the brake unit, a switching valve that is arranged between the brake unit and the master cylinder and the opening adjustment valve, a charge rate detection unit that detects the charge rate of a battery that stores power to be supplied to the traveling motor, an operation amount detection unit that detects the operation amount of the brake pedal, and a brake control unit that detects the brake pedal operation amount based on the brake pedal operation amount detected by the operation amount detection unit. and a braking control unit that controls the travel motor, the aperture adjustment valve, and the switching valve to brake the drive wheels based on the battery charge rate detected by the charging rate detection unit when the brake operation state determination unit determines that the brake pedal has been operated. When the battery charge rate is equal to or lower than a threshold, the braking control unit controls the travel motor to perform regenerative braking in which the travel motor operates as a generator, and when the battery charge rate is higher than the threshold, controls the aperture adjustment valve to open at an aperture corresponding to the amount of brake pedal operation, and controls the switching valve to allow hydraulic oil to flow from the hydraulic power source toward the brake unit, thereby supplying liquid oil to the brake unit.

[0008] In such a braking system, the battery's charging rate is detected, and the amount of brake pedal operation is detected. When the battery's charging rate is equal to or lower than a threshold, the system is controlled to perform regenerative braking, in which the traction motor operates as a generator. When the battery's charging rate is higher than the threshold, the opening adjustment valve is controlled to open at an opening corresponding to the amount of brake pedal operation, and the opening adjustment valve controls the switching valve so that hydraulic oil flows from the hydraulic source toward the brake unit, thereby supplying fluid to the brake unit. As a result, the brake unit applies mechanical braking force to the drive wheels. In this way, when the battery's charging rate is equal to or lower than the threshold, regenerative braking is performed by the traction motor. On the other hand, when the battery's charging rate is higher than the threshold, mechanical braking using hydraulic pressure is performed by the brake unit. This achieves stable braking regardless of the battery's charging rate.

[0009] When the battery charge rate is below a threshold, the braking control unit may control the travel motor to perform regenerative braking when the amount of brake pedal operation is below a specified amount, and may control the travel motor to perform regenerative braking when the amount of brake pedal operation is greater than the specified amount, and may also control the switching valve so that fluid oil is supplied from the master cylinder to the brake unit.

[0010] In this configuration, when the battery's charging rate is below a threshold and the brake pedal operation amount is below a specified amount, regenerative braking is performed. When the battery's charging rate is below a threshold and the brake pedal operation amount is greater than a specified amount, regenerative braking is performed and hydraulic oil is supplied from the master cylinder to the brake unit, causing the brake unit to apply mechanical braking force to the drive wheels. In this way, when the battery's charging rate is below a threshold and the brake pedal operation amount is greater than a specified amount, regenerative braking and mechanical braking by the brake unit are performed. Therefore, even more stable braking is achieved.

[0011] The opening adjustment valve has a variable braking position that allows hydraulic oil to flow from the hydraulic power source toward the brake unit and a return position that returns the hydraulic oil to the tank, and when the battery's charging rate is higher than a threshold, the braking control unit controls the opening adjustment valve so that it opens at an opening that corresponds to the amount of brake pedal operation while the opening adjustment valve is in the braking position, and controls the switching valve so that hydraulic oil is supplied to the brake unit, and then determines whether the brake pedal operation has been released based on the amount of brake pedal operation detected by the operation amount detection unit, and when the brake pedal operation has been released, controls the opening adjustment valve so that it switches from the braking position to the return position.

[0012] In this configuration, when the battery's charge rate is higher than the threshold, the brake unit applies mechanical braking using hydraulic pressure, and then when the brake pedal is released, the valve switches from the braking position to the return position, returning the hydraulic oil to the tank, thereby smoothly releasing the mechanical braking using hydraulic pressure.

[0013] The hydraulic source may have a hydraulic pump and an accumulator that accumulates hydraulic oil discharged from the hydraulic pump, and an on-off valve may be disposed between the hydraulic pump and the opening adjustment valve, and the accumulator may be connected between the on-off valve and the opening adjustment valve.

[0014] In this configuration, hydraulic oil is stored in the accumulator, and the opening adjustment valve controls the hydraulic oil to flow from the accumulator to the brake unit, thereby supplying the hydraulic oil to the brake unit, thereby efficiently performing mechanical braking using hydraulic pressure.

[0015] The braking system may further include a pressure detection unit that detects the pressure of the accumulator, and a pressure accumulation control unit that controls the on-off valve to open when the brake operation state determination unit determines that the brake pedal is not being operated and the pressure of the accumulator detected by the pressure detection unit is equal to or lower than a specified pressure.

[0016] In this configuration, when the brake pedal is not operated and the pressure in the accumulator is equal to or lower than a specified pressure, hydraulic oil discharged from the hydraulic pump is stored in the accumulator, and therefore, when the brake pedal is subsequently operated, the hydraulic oil stored in the accumulator can be used.

[0017] The braking system further includes a switchback detection unit that detects whether the industrial vehicle is about to switch back, and a switchback control unit that, when the switchback detection unit detects that the industrial vehicle is about to switch back, controls the travel motor, the aperture adjustment valve, and the switching valve to decelerate the drive wheels based on the battery charge rate detected by the charging rate detection unit, and the switchback control unit controls the travel motor to perform regenerative braking when the battery charge rate is below a threshold, and controls the aperture adjustment valve to open when the battery charge rate is higher than the threshold, and may also control the switching valve so that hydraulic oil flows from the hydraulic power source toward the brake unit via the aperture adjustment valve, thereby supplying liquid oil to the brake unit.

[0018] In this configuration, when the industrial vehicle switches back, if the battery's charge rate is below a threshold, regenerative braking is performed by the travel motor. If the battery's charge rate is higher than the threshold, the opening adjustment valve is controlled to open, and the opening adjustment valve controls the switching valve so that hydraulic oil flows from the hydraulic power source toward the brake unit, thereby supplying hydraulic oil to the brake unit, thereby causing the brake unit to apply mechanical braking force to the drive wheels. In this way, when the battery's charge rate is below the threshold, deceleration is performed using regenerative braking. On the other hand, if the battery's charge rate is higher than the threshold, mechanical deceleration is performed using hydraulic pressure. Therefore, stable switchback operation is achieved regardless of the battery's charge rate.

[0019] The switching valve has a first position in which the hydraulic oil is supplied from the master cylinder to the brake unit, and a second position in which the hydraulic oil is supplied from the opening adjustment valve side to the brake unit, and when no power is supplied to the switching valve, the position of the switching valve may be the first position.

[0020] In this configuration, even if a break or the like occurs in the electrical signal line of the switching valve, hydraulic oil is supplied from the master cylinder to the brake unit, so that mechanical braking by the brake unit is performed. [Effects of the Invention]

[0021] According to the present invention, stable braking can be achieved regardless of the charging rate of the battery. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a configuration diagram showing a braking system according to an embodiment of the present invention; [Figure 2] FIG. 2 is a control system configuration diagram of the braking system shown in FIG. [Figure 3] 4 is a graph showing the relationship between the depression amount of the brake pedal and the braking force of the drive wheels. [Figure 4] 3 is a flowchart showing the procedure of a running state determination process executed by a running state determination unit shown in FIG. 2. [Figure 5] 3 is a flowchart showing the procedure of a pressure accumulation control process executed by a pressure accumulation control unit shown in FIG. 2. [Figure 6] 2 is a configuration diagram showing the operation when pressure accumulation control processing is executed in the braking system shown in FIG. 1. FIG. [Figure 7] 3 is a flowchart showing a procedure of a braking control process executed by a braking control unit shown in FIG. 2. [Figure 8] 2 is a configuration diagram showing the operation when the brake pedal is depressed in the case where the charging rate of the battery is low when the braking control process is executed in the braking system shown in FIG. 1; FIG. [Figure 9]2 is a configuration diagram showing the operation when the brake pedal is depressed in the case where the charging rate of the battery is high when the brake control process is executed in the brake system shown in FIG. 1. FIG. [Figure 10] FIG. 10 is a configuration diagram showing the operation when the brake pedal is released from the state shown in FIG. 9. [Figure 11] 3 is a flowchart showing the procedure of a switchback control process executed by a switchback control unit shown in FIG. 2. [Figure 12] FIG. 2 is a state transition diagram of the operation of the braking system shown in FIG. 1. [Figure 13] 2 is a table showing braking operations when a break occurs in an electric signal line in the braking system shown in FIG. 1. [Figure 14] 1 is a graph showing the relationship between the state of charge (SOC) and the open-circuit voltage of a lithium-ion battery. [Figure 15] FIG. 10 is a block diagram showing a modified example of the operation of the braking system shown in FIG. 9. [Figure 16] FIG. 2 is a hydraulic circuit diagram showing a modified example of the degree of opening adjustment valve shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0024] Fig. 1 is a configuration diagram showing a braking system according to one embodiment of the present invention. The configuration diagram shown in Fig. 1 includes a block diagram and a hydraulic circuit diagram. In Fig. 1, the braking system 1 of this embodiment is mounted on an electric forklift 2, which is one type of industrial vehicle.

[0025] The forklift 2 includes a traveling motor 4 that rotates and drives the drive wheels 3, and a battery 5 that stores the power supplied to the traveling motor 4. The battery 5 may be, for example, a lithium-ion battery.

[0026] The traction motor 4 also functions as a generator. When the traction motor 4 operates as a generator, regenerative braking is applied to the drive wheels 3, and electric power is generated from the traction motor 4. The electric power generated from the traction motor 4 is then supplied to the battery 5.

[0027] The forklift 2 also includes a cargo handling cylinder 6, a hydraulic pump 7 that supplies hydraulic oil to the cargo handling cylinder 6, a tank 8 that stores the hydraulic oil, a control valve 9 that is arranged between the cargo handling cylinder 6 and the hydraulic pump 7 and tank 8, and a cargo handling motor 10 that drives the hydraulic pump 7. Although not shown, the cargo handling cylinder 6 has a lift cylinder that raises and lowers the forks that hold the load, and a tilt cylinder that tilts the forks.

[0028] The braking system 1 is a system that brakes the drive wheels 3 that are rotated by a travel motor 4. The braking system 1 includes a brake pedal 11, a brake unit 12, a reserve tank 13, a master cylinder 14, a fluid conversion mechanism 15, an electromagnetic switching valve 16, the hydraulic pump 7 and tank 8, an accumulator 17, an electromagnetic opening adjustment valve 18, and an electromagnetic opening / closing valve 19.

[0029] The brake pedal 11 is operated by the driver of the forklift 2 by stepping on it with his foot. The brake unit 12 applies mechanical braking force to the drive wheels 3. The brake unit 12 has, for example, a brake disc or a brake drum. The reserve tank 13 stores brake fluid, which is liquid oil.

[0030] The master cylinder 14 is mechanically connected to the brake pedal 11. The master cylinder 14 is driven by brake fluid.

[0031] The master cylinder 14 has a cylinder tube 21, a piston 22 arranged in the cylinder tube 21, a piston rod 23 fixed to the piston 22, and a spring 24 arranged in a rod chamber 21a in the cylinder tube 21. The spring 24 sets a specified amount A (see FIG. 3) when the brake pedal 11 is depressed. The rod chamber 21a is an area on the piston rod 23 side in the cylinder tube 21. The bottom chamber 21b is an area on the opposite side of the cylinder tube 21 from the piston rod 23.

[0032] The piston rod 23 is connected to the brake pedal 11 via a link 25. When the brake pedal 11 is depressed, the link 25 is pulled, causing the piston 22 to move toward the tip of the piston rod 23 against the biasing force of the spring 24, causing the brake fluid to flow out of the rod chamber 21a.

[0033] The fluid conversion mechanism 15 converts the flow of hydraulic oil and the flow of brake fluid. The fluid conversion mechanism 15 has master cylinders 26 and 27 and a connecting portion 28 disposed between the master cylinders 26 and 27.

[0034] The master cylinder 26 is driven by hydraulic fluid. The master cylinder 26 has a cylinder tube 31, a piston 32 arranged in the cylinder tube 31, a piston rod 33 fixed to the piston 32, and a spring 34 arranged in a rod chamber 31a inside the cylinder tube 31. The rod chamber 31a is an area inside the cylinder tube 31 on the piston rod 33 side. The bottom chamber 31b is an area inside the cylinder tube 31 on the opposite side to the piston rod 33.

[0035] The master cylinder 27 is driven by brake fluid. The master cylinder 27 has a cylinder tube 36, a piston 37 arranged in the cylinder tube 36, a piston rod 38 fixed to the piston 37, and a spring 39 arranged in a rod chamber 36a inside the cylinder tube 36. The rod chamber 36a is an area inside the cylinder tube 36 on the piston rod 38 side. The bottom chamber 36b is an area inside the cylinder tube 36 on the opposite side from the piston rod 38.

[0036] The master cylinders 26, 27 are arranged so that the tips of the piston rods 33, 38 face each other. The connecting part 28 is arranged between the piston rods 33, 38. One end of the connecting part 28 is fixed to the piston rod 33, and the other end of the connecting part 28 is fixed to the piston rod 38.

[0037] The switching valve 16 is disposed between the brake unit 12 and the master cylinder 14 and fluid conversion mechanism 15. The switching valve 16 is disposed between the brake unit 12 and the master cylinder 14 and the opening adjustment valve 18. The switching valve 16 is a valve that switches the direction in which the brake fluid flows. The switching valve 16 is provided with a solenoid operating unit 41 to which a control signal is input.

[0038] The bottom chamber 36b of the master cylinder 27 and the switching valve 16 are connected via a liquid oil flow path 42. The rod chamber 21a of the master cylinder 14 and the switching valve 16 are connected via a liquid oil flow path 43. The bottom chamber 21b of the master cylinder 14 and the reserve tank 13 are connected via a liquid oil flow path 44. The switching valve 16 and the brake unit 12 are connected via a liquid oil flow path 45. The switching valve 16 and the reserve tank 13 are connected via a liquid oil flow path 46.

[0039] The switching valve 16 has a first position 16a (shown) that connects the liquid oil flow paths 43, 45 and also connects the liquid oil flow paths 42, 46, and a second position 16b that connects the liquid oil flow paths 42, 45 and also connects the liquid oil flow paths 43, 46.

[0040] The first position 16a is a position where brake fluid is supplied from the master cylinder 14 to the brake unit 12. The second position 16b is a position where brake fluid is supplied from one of the master cylinder 27 and the brake unit 12 to the other. In other words, the second position 16b corresponds to a position where brake fluid is supplied from the opening adjustment valve 18 side to the brake unit 12.

[0041] In a normal state where no power is supplied to the solenoid operating unit 41, the switching valve 16 is in the first position 16a (illustrated) due to the spring 47. When power is supplied to the solenoid operating unit 41, the solenoid operating unit 41 is energized, and the switching valve 16 switches from the first position 16a to the second position 16b.

[0042] A check valve 48 is disposed in the liquid oil passage 44, which allows brake fluid to flow only from the reserve tank 13 side to the master cylinder 14 side. A liquid oil passage 49 is also connected to the liquid oil passage 44 in parallel with the check valve 48. A throttle valve 50 is disposed in the liquid oil passage 49.

[0043] An on-off valve 51 is disposed in the liquid oil flow path 46. The on-off valve 51 is normally kept open (as shown) by a spring 52. When the pressure of the brake fluid flowing through the liquid oil flow path 46 reaches or exceeds a predetermined pressure, the on-off valve 51 closes.

[0044] The accumulator 17 accumulates pressure in the hydraulic oil discharged from the hydraulic pump 7. The accumulator 17 is connected between the opening adjustment valve 18 and the on-off valve 19. The accumulator 17 and the hydraulic pump 7 constitute a hydraulic pressure source.

[0045] The opening adjustment valve 18 is disposed between the hydraulic pump 7 and accumulator 17 and the master cylinder 26 of the fluid conversion mechanism 15. Therefore, the opening adjustment valve 18 is disposed between the hydraulic pump 7 and accumulator 17 and the brake unit 12. The opening adjustment valve 18 is provided with a solenoid operating unit 55 to which a control signal is input.

[0046] The accumulator 17 and the opening adjustment valve 18 are connected via a hydraulic oil flow path 56. A pressure reducing valve 57 that adjusts the pressure of the hydraulic oil flowing through the hydraulic oil flow path 56 is disposed in the hydraulic oil flow path 56. The opening adjustment valve 18 and the tank 8 are connected via a hydraulic oil flow path 58. The opening adjustment valve 18 and the master cylinder 26 are connected via a hydraulic oil flow path 59.

[0047] The opening adjustment valve 18 has a variable braking position 18a that connects the hydraulic oil flow paths 56, 59 and blocks the hydraulic oil flow paths 58, 59, and a return position 18b (shown) that connects the hydraulic oil flow paths 58, 59 and blocks the hydraulic oil flow paths 56, 59.

[0048] The braking position 18a is a position where hydraulic oil is supplied from the hydraulic pump 7 or the accumulator 17 to the master cylinder 26. In other words, the braking position 18a corresponds to a position where hydraulic oil flows from the hydraulic pump 7 or the accumulator 17 toward the brake unit 12. The return position 18b is a position where hydraulic oil is returned from the master cylinder 26 to the tank 8.

[0049] In a normal state where no power is supplied to the solenoid operation unit 55, the opening adjustment valve 18 is in the return position 18b (illustrated) due to the spring 60. When power is supplied to the solenoid operation unit 55, the solenoid operation unit 55 is energized, and the opening adjustment valve 18 switches from the return position 18b to the braking position 18a. When the opening adjustment valve 18 is in the braking position 18a, the opening of the opening adjustment valve 18 changes in accordance with a control signal (e.g., a current value) supplied to the solenoid operation unit 55.

[0050] The on-off valve 19 is disposed between the hydraulic pump 7 and the accumulator 17. Therefore, the on-off valve 19 is disposed between the hydraulic pump 7 and the opening adjustment valve 18. The on-off valve 19 is provided with a solenoid operation unit 61 to which a control signal is input.

[0051] The hydraulic pump 7 and the on-off valve 19 are connected via a hydraulic oil flow path 62. The on-off valve 19 and the accumulator 17 are connected via a hydraulic oil flow path 63. The on-off valve 19 has a closed position 19a (shown) that blocks the hydraulic oil flow paths 62, 63, and an open position 19b that connects the hydraulic oil flow paths 62, 63.

[0052] In a normal state where no power is supplied to the solenoid operating unit 61, the on-off valve 19 is in a closed position 19a (illustrated) due to the spring 64. When power is supplied to the solenoid operating unit 61, the solenoid operating unit 61 is energized, and the on-off valve 19 switches from the closed position 19a to the open position 19b.

[0053] As also shown in FIG. 2, the braking system 1 includes a potentiometer 71, a voltage sensor 72, a pressure sensor 73, a traveling direction sensor 74, and a controller .

[0054] The potentiometer 71 detects the depression amount of the brake pedal 11 as the operation amount of the brake pedal 11. The potentiometer 71 constitutes an operation amount detection unit that detects the operation amount of the brake pedal 11.

[0055] The voltage sensor 72 detects the voltage of the battery 5. The pressure sensor 73 constitutes a pressure detection unit that detects the pressure of the accumulator 17. The traveling direction sensor 74 detects the traveling direction (forward and reverse) of the forklift 2. The traveling direction sensor 74 detects, for example, the operating state of a forward / reverse lever.

[0056] The controller 70 is connected to the solenoid operation unit 41 of the switching valve 16 via an electric signal line 66. The controller 70 is connected to the solenoid operation unit 55 of the opening adjustment valve 18 via an electric signal line 67. The controller 70 is connected to the solenoid operation unit 61 of the on-off valve 19 via an electric signal line 68.

[0057] The controller 70 is configured with a CPU, RAM, ROM, an input / output interface, etc. The controller 70 has a charging rate calculation unit 75, a running state determination unit 76, a pressure accumulation control unit 77, a braking control unit 78, and a switchback control unit 79.

[0058] The charging rate calculation unit 75 calculates the charging rate (SOC: State of charge) of the battery 5 based on the voltage of the battery 5 detected by the voltage sensor 72. At this time, the charging rate calculation unit 75 estimates the open circuit voltage of the battery 5 based on the detected value of the voltage sensor 72, for example, and obtains the charging rate of the battery 5 from the open circuit voltage of the battery 5 (see FIG. 14). The charging rate calculation unit 75 constitutes a charging rate detection unit that detects the charging rate of the battery 5 in cooperation with the voltage sensor 72.

[0059] The traveling state determination unit 76 determines the traveling state of the forklift 2 based on the depression amount of the brake pedal 11 detected by the potentiometer 71 and the traveling direction of the forklift 2 detected by the traveling direction sensor 74. As the traveling state of the forklift 2, the traveling state determination unit 76 determines whether the brake pedal 11 has been operated and detects whether the forklift 2 is performing a switchback.

[0060] The pressure accumulation control unit 77 controls the on-off valve 19 to open when the driving state determination unit 76 determines that the brake pedal 11 is not being operated and when the pressure in the accumulator 17 detected by the pressure sensor 73 is equal to or lower than a specified pressure.

[0061] When the driving state determination unit 76 determines that the brake pedal 11 has been operated, the braking control unit 78 controls the driving motor 4, the opening adjustment valve 18, and the switching valve 16 to brake the drive wheels 3 based on the charging rate of the battery 5.

[0062] Specifically, when the charging rate of the battery 5 is equal to or lower than a threshold, the braking control unit 78 controls the traveling motor 4 to perform regenerative braking in which the traveling motor 4 operates as a generator (see solid line P in FIG. 3). When the charging rate of the battery 5 is higher than a threshold, the braking control unit 78 controls the opening adjustment valve 18 to open at an opening corresponding to the depression amount of the brake pedal 11, and also controls the switching valve 16 so that the opening adjustment valve 18 causes hydraulic oil to flow from the hydraulic pump 7 or the accumulator 17 toward the brake unit 12, thereby supplying brake fluid to the brake unit 12 (see dash-dotted line R in FIG. 3).

[0063] More specifically, when the charging rate of the battery 5 is equal to or lower than a threshold value and the depression amount of the brake pedal 11 is equal to or lower than a specified amount A, the braking control unit 78 controls the traveling motor 4 to perform regenerative braking (see solid line P in FIG. 3). When the charging rate of the battery 5 is equal to or lower than a threshold value and the depression amount of the brake pedal 11 is greater than the specified amount A, the braking control unit 78 controls the traveling motor 4 to perform regenerative braking (see solid line P in FIG. 3), and also controls the switching valve 16 to supply brake fluid from the master cylinder 14 to the brake unit 12 (see dashed line Q in FIG. 3).

[0064] When the traveling state determination unit 76 detects that the forklift 2 is performing a switchback, the switchback control unit 79 controls the traveling motor 4, the opening adjustment valve 18, and the switching valve 16 to decelerate the drive wheels 3 based on the charging rate of the battery 5.

[0065] Specifically, when the charging rate of the battery 5 is equal to or lower than a threshold value, the switchback control unit 79 controls the travel motor 4 to perform regenerative braking. When the charging rate of the battery 5 is higher than a threshold value, the switchback control unit 79 controls the opening adjustment valve 18 to open, and also controls the switching valve 16 so that the opening adjustment valve 18 causes hydraulic oil to flow from the hydraulic pump 7 or the accumulator 17 toward the brake unit 12, thereby supplying brake fluid to the brake unit 12.

[0066] 4 is a flowchart showing the procedure of the traveling state determination process executed by the traveling state determination unit 76. This process is executed when an ignition switch (not shown) of the forklift 2 is turned on.

[0067] 4, the running state determination unit 76 first acquires the detection value of the potentiometer 71 (step S101). Then, the running state determination unit 76 determines whether the brake pedal 11 has been depressed based on the detection value of the potentiometer 71 (step S102). When the running state determination unit 76 determines that the brake pedal 11 has been depressed, it outputs an instruction signal to the braking control unit 78 to execute braking control processing (step S103).

[0068] When it is determined that the brake pedal 11 is not depressed, the traveling state determination unit 76 acquires the detection value of the traveling direction sensor 74 (step S104). Then, the traveling state determination unit 76 determines whether or not the forklift 2 will perform a switchback based on the detection value of the traveling direction sensor 74 (step S105). A switchback includes both a traveling operation from forward to reverse and a traveling operation from reverse to forward.

[0069] When the traveling state determination unit 76 determines that the forklift 2 will switch back, it outputs an instruction signal to execute switch back control processing to the switch back control unit 79 (Step S106).When the traveling state determination unit 76 determines that the forklift 2 will not switch back, it outputs an instruction signal to execute pressure accumulation control processing to the pressure accumulation control unit 77 (Step S107).

[0070] In the above, steps S101 and S102 constitute a brake operation state determination unit that determines whether the brake pedal 11 has been operated based on the operation amount of the brake pedal 11 detected by the potentiometer 71. Steps S104 and S105 constitute a switchback detection unit that detects whether the forklift 2 is about to switchback.

[0071] Fig. 5 is a flowchart showing the procedure of the pressure accumulation control process executed by the pressure accumulation control unit 77. In Fig. 5, the pressure accumulation control unit 77 first acquires the detection value of the pressure sensor 73 (step S111). Then, the pressure accumulation control unit 77 determines whether the pressure in the accumulator 17 is equal to or lower than a predetermined specified pressure based on the detection value of the pressure sensor 73 (step S112).

[0072] When the pressure accumulation control unit 77 determines that the pressure in the accumulator 17 is equal to or lower than the specified pressure, it controls the solenoid operation unit 61 of the on-off valve 19 so that the on-off valve 19 switches from the closed position 19a to the open position 19b (step S113). At this time, the pressure accumulation control unit 77 energizes the solenoid operation unit 61, for example, by supplying a predetermined current value to the solenoid operation unit 61.

[0073] Next, the pressure accumulation control unit 77 determines whether the cargo handling motor 10 and the hydraulic pump 7 are not being driven (step S114). At this time, whether the cargo handling motor 10 and the hydraulic pump 7 are being driven may be determined from a control signal to the cargo handling motor 10 inside the controller 70, or may be determined by detecting whether the cargo handling motor 10 and the hydraulic pump 7 are rotating using a tachometer or the like.

[0074] When the pressure accumulation control unit 77 determines that the cargo handling motor 10 and the hydraulic pump 7 are not being driven, it controls the cargo handling motor 10 to start (step S115). As a result, the cargo handling motor 10 rotates, and the hydraulic pump 7 is driven to rotate. When the pressure accumulation control unit 77 determines that the cargo handling motor 10 and the hydraulic pump 7 are being driven, it does not execute step S115.

[0075] Thereafter, the pressure accumulation control unit 77 again acquires the detection value of the pressure sensor 73 (step S116). Then, the pressure accumulation control unit 77 determines whether the pressure in the accumulator 17 is higher than the specified pressure based on the detection value of the pressure sensor 73 (step S117). When the pressure accumulation control unit 77 determines that the pressure in the accumulator 17 is equal to or lower than the specified pressure, it executes the above-described step S116 again.

[0076] When the pressure accumulation control unit 77 determines that the pressure in the accumulator 17 is higher than the specified pressure, it controls the solenoid operation unit 61 of the on-off valve 19 so that the on-off valve 19 switches from the open position 19b to the closed position 19a (step S118). At this time, the pressure accumulation control unit 77 stops the supply of current to the solenoid operation unit 61, for example, to stop the flow of current to the solenoid operation unit 61. Then, the pressure accumulation control unit 77 executes the above-mentioned step S111 again.

[0077] When the pressure accumulation control unit 77 determines in step S112 that the pressure in the accumulator 17 is higher than the specified pressure, it does not execute steps S113 to S118, and executes the above step S111 again.

[0078] When the pressure in the accumulator 17 drops while the driver is not depressing the brake pedal 11, the solenoid operating unit 61 of the on-off valve 19 is energized. Then, as shown in FIG. 6, the on-off valve 19 switches from the closed position 19a to the open position 19b, and the hydraulic oil flow paths 62 and 63 are connected. At this time, the opening adjustment valve 18 is in the return position 18b. Therefore, the hydraulic oil discharged from the hydraulic pump 7 flows through the hydraulic oil flow paths 62 and 63 and is supplied to the accumulator 17. As a result, the accumulator 17 accumulates pressure.

[0079] Fig. 7 is a flowchart showing the procedure of the braking control process executed by the braking control unit 78. In Fig. 7, the braking control unit 78 first obtains the charging rate of the battery 5 calculated by the charging rate calculation unit 75 (step S121).

[0080] Next, the braking control unit 78 determines whether the charging rate of the battery 5 is equal to or lower than a predetermined threshold (step S122). The threshold at this time is a braking threshold. When the braking control unit 78 determines that the charging rate of the battery 5 is equal to or lower than the threshold, the braking control unit 78 controls the traveling motor 4 to perform regenerative braking in which the traveling motor 4 operates as a generator (step S123). Specifically, the braking control unit 78 stops the rotational drive of the traveling motor 4, thereby causing the traveling motor 4 to operate as a generator. At this time, the braking force of the regenerative braking is set to increase as the depression amount of the brake pedal 11 increases, as shown by the solid line P in FIG. 3, and to be substantially saturated when the depression amount of the brake pedal 11 exceeds a certain value. Then, the braking control unit 78 executes the above-described step S121 again.

[0081] When the braking control unit 78 determines that the charging rate of the battery 5 is higher than the threshold, it controls the solenoid operation unit 61 of the on-off valve 19 so that the on-off valve 19 switches from the closed position 19a to the open position 19b (step S124).

[0082] Furthermore, the braking control unit 78 controls the solenoid operation unit 41 of the switching valve 16 so that the switching valve 16 switches from the first position 16a to the second position 16b (step S125). At this time, the braking control unit 78 energizes the solenoid operation unit 41, for example, by supplying a predetermined current value to the solenoid operation unit 41.

[0083] Next, the braking control unit 78 controls the solenoid operation unit 55 of the opening adjustment valve 18 so that the opening adjustment valve 18 opens at an opening corresponding to the depression amount of the brake pedal 11 (step S126). At this time, the braking control unit 78 energizes the solenoid operation unit 55, for example, by supplying a current value to the solenoid operation unit 55. The braking control unit 78 increases the current value supplied to the solenoid operation unit 55 according to the depression amount of the brake pedal 11. This enables mechanical braking using hydraulic pressure by the brake unit 12.

[0084] Thereafter, the braking control unit 78 acquires the detection value of the potentiometer 71 (step S127). Then, the braking control unit 78 determines whether the driver has released the brake pedal 11, thereby releasing the brake pedal 11, based on the detection value of the potentiometer 71 (step S128). When the braking control unit 78 determines that the driver has not released the brake pedal 11, it executes the above step S127 again.

[0085] When the braking control unit 78 determines that the driver has released the brake pedal 11, it controls the solenoid operation unit 55 of the opening adjustment valve 18 so that the opening adjustment valve 18 switches from the braking position 18a to the return position 18b (step S129). At this time, the braking control unit 78 stops the supply of current to the solenoid operation unit 55, for example, to stop the flow of current to the solenoid operation unit 55.

[0086] Next, the braking control unit 78 again acquires the charging rate of the battery 5 calculated by the charging rate calculation unit 75 (step S130). Then, the braking control unit 78 determines whether the charging rate of the battery 5 is equal to or lower than the threshold value (step S131).

[0087] When the braking control unit 78 determines that the charging rate of the battery 5 is equal to or lower than the threshold, it controls the solenoid operation unit 41 of the switching valve 16 so that the switching valve 16 switches from the second position 16b to the first position 16a (step S132). At this time, the braking control unit 78 stops the supply of current to the solenoid operation unit 41, for example, to stop the flow of current to the solenoid operation unit 41.

[0088] The braking control unit 78 also controls the solenoid operation unit 61 of the on-off valve 19 so that the on-off valve 19 is switched from the open position 19b to the closed position 19a (step S133). This enables regenerative braking in which the traveling motor 4 operates as a generator. The braking control unit 78 then executes the above step S121 again.

[0089] When the braking control unit 78 determines that the charging rate of the battery 5 is higher than the threshold, it executes the above-described step S130 again. As a result, the switching valve 16 is maintained in the second position 16b and the on-off valve 19 is maintained in the open position 19b, so that the state in which mechanical braking using hydraulic pressure by the brake unit 12 is possible continues.

[0090] When the driver depresses the brake pedal 11 while the battery 5 is at a low charging rate, the traction motor 4 operates as a generator, and regenerative braking is performed by the traction motor 4, as shown in Fig. 8. Therefore, the electric power generated by the traction motor 4 is supplied to the battery 5, and the battery 5 is charged.

[0091] Furthermore, due to the mechanical structure of the link 25 and adjustments to the brake mechanism of the brake unit 12, the brake unit 12 is set to apply mechanical braking when the depression amount of the brake pedal 11 reaches a specified amount A (see FIG. 3). Therefore, when the depression amount of the brake pedal 11 exceeds the specified amount A, mechanical braking by the brake unit 12 is applied in addition to regenerative braking by the travel motor 4.

[0092] On the other hand, when the battery 5 has a high charge rate and the driver depresses the brake pedal 11, regenerative braking by the travel motor 4 is not performed, as shown in FIG. 9 . When the solenoid operating unit 61 of the on-off valve 19 is energized, the on-off valve 19 switches from the closed position 19a to the open position 19b, thereby opening the hydraulic oil passages 62 and 63. When the solenoid operating unit 41 of the selector valve 16 is energized, the selector valve 16 switches from the first position 16a to the second position 16b, thereby opening the hydraulic oil passages 42 and 45 and the hydraulic oil passages 43 and 46. When the solenoid operating unit 55 of the opening adjustment valve 18 is energized, the opening adjustment valve 18 switches from the return position 18b to the braking position 18a, thereby opening the hydraulic oil passages 56 and 59. At this time, the opening adjustment valve 18 opens to an opening degree corresponding to the depression amount of the brake pedal 11.

[0093] Then, hydraulic oil discharged from the hydraulic pump 7 or the accumulator 17 flows through the hydraulic oil flow path 56, the opening adjustment valve 18, and the hydraulic oil flow path 59, and is supplied to the bottom chamber 31b of the master cylinder 26. Then, in the master cylinder 26, the piston 32 moves toward the master cylinder 27 against the biasing force of the spring 34. Then, the piston rod 33 of the master cylinder 26 pushes the piston rod 38 of the master cylinder 27 via the connecting portion 28. Then, in the master cylinder 27, the piston 37 moves to the opposite side of the piston rod 38 against the biasing force of the spring 39 (see the thick solid line).

[0094] As a result, the brake fluid in the bottom chamber 36b of the master cylinder 27 flows through the hydraulic oil passage 42, the switching valve 16, and the hydraulic oil passage 45 and is supplied to the brake unit 12. Therefore, mechanical braking is performed by the brake unit 12 using hydraulic pressure (see the thick solid line).

[0095] At this time, the brake fluid in the reserve tank 13 flows through the liquid oil flow path 44 and is supplied to the bottom chamber 21b of the master cylinder 14, and the brake fluid in the rod chamber 21a of the master cylinder 14 flows through the liquid oil flow path 43, the switching valve 16 and the liquid oil flow path 46 and returns to the reserve tank 13 (see thick dashed line).

[0096] When the brake pedal 11 is depressed to a certain extent or more, the pressure of the brake fluid flowing through the hydraulic fluid passage 42 reaches the set pressure of the on-off valve 51, causing the on-off valve 51 to close. As a result, the brake fluid cannot return to the reserve tank 13, and the piston 22 of the master cylinder 14 cannot move. As a result, the brake pedal 11 cannot be depressed any further.

[0097] Thereafter, when the driver releases the brake pedal 11, the opening adjustment valve 18 is de-energized, and the opening adjustment valve 18 switches from the braking position 18a to the return position 18b, as shown in Figure 10. As a result, the hydraulic oil passages 56 and 59 are blocked, and the hydraulic oil passages 58 and 59 are opened. Then, the brake fluid in the brake unit 12 flows through the hydraulic oil passage 45, the selector valve 16, and the hydraulic oil passage 42, and is supplied to the bottom chamber 36b of the master cylinder 27.

[0098] Then, in the master cylinder 27, the piston 37 moves toward the master cylinder 26 against the biasing force of the spring 39. Then, the piston rod 38 of the master cylinder 27 pushes the piston rod 33 of the master cylinder 26 via the connecting portion 28. Then, in the master cylinder 26, the piston 32 moves to the opposite side of the piston rod 38 against the biasing force of the spring 34. As a result, the hydraulic oil in the bottom chamber 31b of the master cylinder 26 flows through the hydraulic oil flow path 59, the opening adjustment valve 18, and the hydraulic oil flow path 58 and returns to the tank 8 (see the thick solid line).

[0099] At this time, the brake fluid in the reserve tank 13 flows through the fluid oil passage 46, the selector valve 16, and the fluid oil passage 43 to be supplied to the rod chamber 21a of the master cylinder 14, and the brake fluid in the bottom chamber 21b of the master cylinder 14 flows through the fluid oil passages 44 and 49 to return to the reserve tank 13 (see the thick dashed line). Therefore, when the brake pedal 11 is not depressed, the piston 22 of the master cylinder 14 returns to its initial position.

[0100] 11 is a flowchart showing the procedure of the back-and-forth control process executed by the back-and-forth control unit 79. In FIG. 11, the back-and-forth control unit 79 first acquires the charging rate of the battery 5 calculated by the charging rate calculation unit 75 (step S141).

[0101] Next, the switchback control unit 79 determines whether the charging rate of the battery 5 is equal to or lower than a predetermined threshold value (step S142). This threshold value is a switchback threshold value. When the switchback control unit 79 determines that the charging rate of the battery 5 is equal to or lower than the threshold value, it controls the travel motor 4 to perform regenerative braking in which the travel motor 4 operates as a generator (step S143). This decelerates the forklift 2 using regenerative braking. Then, the switchback control unit 79 executes the above-described step S141 again.

[0102] When the switchback control unit 79 determines that the charging rate of the battery 5 is higher than the threshold, it controls the solenoid operation unit 61 of the on-off valve 19 so that the on-off valve 19 switches from the closed position 19a to the open position 19b (step S144). The switchback control unit 79 also controls the solenoid operation unit 41 of the switching valve 16 so that the switching valve 16 switches from the first position 16a to the second position 16b (step S145). Next, the switchback control unit 79 controls the solenoid operation unit 55 of the opening adjustment valve 18 so that the opening adjustment valve 18 opens to a predetermined opening (step S146). This enables mechanical deceleration of the forklift 2 using hydraulic pressure.

[0103] Next, the switchback control unit 79 determines whether the switchback operation of the forklift 2 has ended (step S147). Whether the switchback operation of the forklift 2 has ended is determined from a detection value of, for example, a rotary encoder that detects the rotation direction of the drive wheels 3 or a vehicle speed sensor that detects the traveling speed of the forklift 2.

[0104] When the switchback control unit 79 determines that the switchback operation of the forklift 2 has ended, it controls the solenoid operation unit 55 of the opening adjustment valve 18 so that the opening adjustment valve 18 switches from the braking position 18a to the return position 18b (step S148).

[0105] Next, the switchback control unit 79 again acquires the charging rate of the battery 5 calculated by the charging rate calculation unit 75 (step S149). Then, the switchback control unit 79 determines whether the charging rate of the battery 5 is equal to or lower than the threshold value (step S150).

[0106] When the switchback control unit 79 determines that the charging rate of the battery 5 is equal to or lower than the threshold, it controls the solenoid operation unit 41 of the switching valve 16 so that the switching valve 16 switches from the second position 16b to the first position 16a (step S151). The switchback control unit 79 also controls the solenoid operation unit 61 of the on-off valve 19 so that the on-off valve 19 switches from the open position 19b to the closed position 19a (step S152). This enables the forklift 2 to be decelerated using regenerative braking. The switchback control unit 79 then executes step S141 again.

[0107] When the switchback control unit 79 determines that the charging rate of the battery 5 is higher than the threshold, it executes the above-described step S149 again. As a result, the switching valve 16 is maintained in the second position 16b and the on-off valve 19 is maintained in the open position 19b, so that the state in which the forklift 2 can be mechanically decelerated using hydraulic pressure continues.

[0108] In the braking system 1 described above, as shown in FIG. 12, when the charging rate of the battery 5 is below a threshold, the low SOC mode is implemented, and when the charging rate of the battery 5 is higher than the threshold, the high SOC mode is implemented.

[0109] In the low SOC mode, when the depression amount of the brake pedal 11 is equal to or less than the specified amount A, only regenerative braking is performed in which the traveling motor 4 operates as a generator, and when the depression amount of the brake pedal 11 is greater than the specified amount A, regenerative braking by the traveling motor 4 and mechanical braking by the brake unit 12 are performed. In mechanical braking, the brake unit 12 is driven by brake fluid supplied from the master cylinder 14. Furthermore, in the low SOC mode, when a switchback is performed, regenerative braking by the traveling motor 4 is performed.

[0110] On the other hand, in the high SOC mode, regenerative braking by the travel motor 4 is not performed, and mechanical braking is performed by the brake unit 12. At this time, hydraulic oil is sent from the hydraulic pump 7 or the accumulator 17 to the fluid conversion mechanism 15, and the brake unit 12 is driven by the brake fluid supplied from the fluid conversion mechanism 15. In other words, mechanical braking is performed using the hydraulic pressure that drives the cargo cylinder 6. Furthermore, in the high SOC mode, mechanical braking using the hydraulic pressure is also performed when a switchback is performed.

[0111] In addition, in both the low SOC mode and the high SOC mode, when the remaining amount of oil in the accumulator 17 decreases and the pressure in the accumulator 17 drops, hydraulic oil is charged from the hydraulic pump 7 to the accumulator 17.

[0112] Fig. 13 is a table showing braking operations when the electrical signal lines 66-68 are broken. In Fig. 13, when the electrical signal line 66 connecting the controller 70 and the solenoid operation unit 41 of the switching valve 16 is broken, the solenoid operation unit 41 is not energized. As a result, the switching valve 16 is maintained in the first position 16a. Therefore, brake fluid is supplied from the master cylinder 14 to the brake unit 12, and mechanical braking by the brake unit 12 is performed.

[0113] Even if the electric signal line 66 is not broken, if the electric signal line 67 connecting the controller 70 and the solenoid operation unit 55 of the degree of opening adjustment valve 18 is broken, the solenoid operation unit 55 will not be energized. As a result, the degree of opening adjustment valve 18 will be maintained in the return position 18b. Therefore, by setting the position of the selector valve 16 to the first position 16a, brake fluid will be supplied from the master cylinder 14 to the brake unit 12, and mechanical braking will be performed by the brake unit 12.

[0114] Even if the electric signal lines 66 and 67 are not broken, if the electric signal line 68 connecting the controller 70 and the solenoid operating unit 61 of the on-off valve 19 is broken, the solenoid operating unit 61 will not be energized, and the on-off valve 19 will be maintained in the closed position 19a.

[0115] In this case, when there is hydraulic oil remaining in the accumulator 17, the solenoid operation unit 55 of the opening adjustment valve 18 is energized to switch the opening adjustment valve 18 from the return position 18b to the braking position 18a, and the solenoid operation unit 41 of the switching valve 16 is energized to switch the switching valve 16 from the first position 16a to the second position 16b. Therefore, hydraulic oil flows from the accumulator 17 toward the brake unit 12, supplying brake fluid to the brake unit 12, and hydraulic mechanical braking is performed by the brake unit 12. At this time, mechanical braking is performed in accordance with the amount of operation of the brake pedal 11.

[0116] On the other hand, when there is no hydraulic oil remaining in the accumulator 17, the solenoid operating unit 55 of the degree of opening adjustment valve 18 and the solenoid operating unit 41 of the switching valve 16 are not energized. As a result, the degree of opening adjustment valve 18 is maintained in the return position 18b, and the switching valve 16 is maintained in the first position 16a. Therefore, brake fluid is supplied from the master cylinder 14 to the brake unit 12, and mechanical braking by the brake unit 12 is performed.

[0117] Incidentally, the open-circuit voltage of a lithium-ion battery changes depending on the state of charge (SOC), as shown in Figure 14. Specifically, the open-circuit voltage of a lithium-ion battery increases as the state of charge of the lithium-ion battery increases. Also, a lithium-ion battery has an upper limit voltage V0 that limits the use of the cell.

[0118] One of the characteristics of such lithium-ion batteries is the conduction voltage drop. Conduction voltage drop occurs when the conduction voltage (the cell's internal resistance multiplied by the current) changes relative to the open-circuit voltage when the lithium-ion battery is conducting current. Specifically, when charging, the conduction voltage rises above the open-circuit voltage (see X in the diagram), and when discharging, the conduction voltage drops below the open-circuit voltage. As the lithium-ion battery deteriorates, the amount of change (drop) in the conduction voltage increases.

[0119] In a forklift 2 that uses a lithium-ion battery as its energy source, if the lithium-ion battery is highly charged and large regenerative braking is performed on the traveling motor 4, the voltage of the lithium-ion battery will temporarily reach the upper limit voltage V0 of the cell due to a voltage drop (see X in the diagram). In this case, the lithium-ion battery will not be able to absorb the regenerative current generated by the traveling motor 4, and regenerative braking will no longer be effective.

[0120] Furthermore, the forklift 2 has two braking methods: mechanical braking and regenerative braking. When the contribution of mechanical braking is large, the regenerative energy during normal operation is small, leading to energy loss. On the other hand, when the contribution of regenerative braking is large, regenerative braking becomes difficult, resulting in a longer braking distance and an uncomfortable feeling for the driver.

[0121] To address this issue, in this embodiment, the state of charge of the battery 5 is detected, and the depression amount of the brake pedal 11 is detected. When the state of charge of the battery 5 is equal to or lower than a threshold, the traveling motor 4 is controlled to perform regenerative braking, operating as a generator. When the state of charge of the battery 5 is higher than the threshold, the opening adjustment valve 18 is controlled to open at an opening corresponding to the depression amount of the brake pedal 11, and the switching valve 16 is controlled so that the opening adjustment valve 18 causes hydraulic oil to flow from the hydraulic pump 7 or the accumulator 17 to the brake unit 12, thereby supplying brake fluid to the brake unit 12. Therefore, the brake unit 12 applies mechanical braking force to the drive wheels 3. As described above, when the state of charge of the battery 5 is equal to or lower than the threshold, regenerative braking is performed by the traveling motor 4. On the other hand, when the state of charge of the battery 5 is higher than the threshold, mechanical braking using hydraulic pressure is performed by the brake unit 12. This achieves stable braking regardless of the state of charge of the battery 5. As a result, braking force equivalent to that during normal operation can be ensured even when regeneration of power to the battery 5 is difficult. Moreover, by increasing the amount of power regenerated to the battery 5 as much as possible, energy efficiency can be improved.

[0122] Furthermore, in this embodiment, when the charging rate of the battery 5 is equal to or lower than a threshold value and the depression amount of the brake pedal 11 is equal to or lower than a specified amount A, regenerative braking is performed. When the charging rate of the battery 5 is equal to or lower than a threshold value and the depression amount of the brake pedal 11 is greater than the specified amount A, regenerative braking is performed and brake fluid is supplied from the master cylinder 14 to the brake unit 12, so that the brake unit 12 applies mechanical braking force to the drive wheels 3. In this way, when the charging rate of the battery 5 is equal to or lower than a threshold value and the depression amount of the brake pedal 11 is greater than the specified amount A, regenerative braking and mechanical braking by the brake unit 12 are performed. Therefore, even more stable braking is achieved.

[0123] Furthermore, in this embodiment, when the charging rate of the battery 5 is higher than a threshold, after the brake unit 12 performs mechanical braking using hydraulic pressure, when the brake pedal 11 is released, the opening adjustment valve 18 switches from the braking position 18a to the return position 18b, and the hydraulic oil returns to the tank 8. Therefore, the mechanical braking using hydraulic pressure is smoothly released.

[0124] In this embodiment, hydraulic oil is stored in the accumulator 17, and the opening adjustment valve 18 causes hydraulic oil to flow from the accumulator 17 toward the brake unit 12, thereby supplying brake fluid to the brake unit 12. Therefore, mechanical braking using hydraulic pressure is performed efficiently.

[0125] In addition, in this embodiment, when the brake pedal 11 is not depressed and the pressure in the accumulator 17 is equal to or lower than a specified pressure, the hydraulic oil discharged from the hydraulic pump 7 is stored in the accumulator 17. Therefore, when the brake pedal 11 is subsequently depressed, the hydraulic oil stored in the accumulator 17 can be used.

[0126] Furthermore, in this embodiment, when the forklift 2 switches back, if the charging rate of the battery 5 is equal to or lower than a threshold, regenerative braking is performed by the travel motor 4. If the charging rate of the battery 5 is higher than the threshold, the opening adjustment valve 18 is controlled to open, and the opening adjustment valve 18 controls the switching valve 16 to supply brake fluid to the brake unit 12 by causing hydraulic oil to flow from the hydraulic pump 7 or the accumulator 17 toward the brake unit 12, thereby causing the brake unit 12 to apply mechanical braking force to the drive wheels 3. In this way, when the charging rate of the battery 5 is equal to or lower than the threshold, deceleration is performed using regenerative braking. On the other hand, when the charging rate of the battery 5 is higher than the threshold, mechanical deceleration is performed using hydraulic pressure. Therefore, stable switchback operation is achieved regardless of the charging rate of the battery 5.

[0127] In this embodiment, the switching valve 16 is in the first position 16a when no power is supplied to the switching valve 16. Therefore, even if a break or the like occurs in the electrical signal line 66 of the switching valve 16, brake fluid is supplied from the master cylinder 14 to the brake unit 12, and mechanical braking by the brake unit 12 is performed.

[0128] The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, when the charging rate of the battery 5 is higher than a threshold, the on-off valve 19 opens, causing hydraulic oil to flow from the hydraulic pump 7 toward the brake unit 12. However, the present invention is not particularly limited to such an embodiment. For example, as shown in FIG. 15 , even when the charging rate of the battery 5 is higher than the threshold, the on-off valve 19 may be closed if there is hydraulic oil remaining in the accumulator 17. In this case, hydraulic oil flows from the accumulator 17 toward the brake unit 12, supplying brake fluid to the brake unit 12, and mechanical braking using hydraulic pressure is performed by the brake unit 12.

[0129] Furthermore, in the above embodiment, the degree of opening adjustment valve 18 is configured from one valve, but this is not a particular limitation, and for example, an degree of opening adjustment valve 80 configured from two valves may be used, as shown in Fig. 16. The degree of opening adjustment valve 80 has a pressure increase on-off valve 81 and a pressure decrease on-off valve 82.

[0130] The pressure-increasing on-off valve 81 is provided with a solenoid operating unit 83 to which a control signal is input. The solenoid operating unit 83 is connected to the controller 70 via an electric signal line 84. The pressure-increasing on-off valve 81 has a closed position 81a at which the hydraulic oil flow paths 56, 59 are blocked, and an open position 81b at which the hydraulic oil flow paths 56, 59 are connected. In a normal state, the pressure-increasing on-off valve 81 is in the closed position 81a (illustrated) due to a spring 85. When the solenoid operating unit 83 is energized, the pressure-increasing on-off valve 81 switches from the closed position 81a to the open position 81b.

[0131] The pressure reducing on-off valve 82 is provided with a solenoid operating unit 86 to which a control signal is input. The solenoid operating unit 86 is connected to the controller 70 via an electric signal line 87. The pressure reducing on-off valve 82 has a closed position 82a at which the hydraulic oil passages 58, 59 are blocked, and an open position 82b at which the hydraulic oil passages 58, 59 are open. In a normal state, the pressure reducing on-off valve 82 is in the closed position 82a (illustrated) due to a spring 88. When the solenoid operating unit 86 is energized, the pressure reducing on-off valve 82 switches from the closed position 82a to the open position 82b.

[0132] In such an opening adjustment valve 80, the solenoid operating units 83, 86 are controlled by the controller 70 so that when the pressure-increasing on-off valve 81 is in the closed position 81a, the pressure-reducing on-off valve 82 is in the open position 82b, and when the pressure-reducing on-off valve 82 is in the closed position 82a, the pressure-increasing on-off valve 81 is in the open position 81b.

[0133] In the above embodiment, the flow of hydraulic oil used to drive the cargo cylinders 6 and the flow of brake fluid used to drive the brake units 12 are converted by the fluid conversion mechanism 15, but this is not a particular limitation, and the hydraulic oil used to drive the cargo cylinders 6 may also be used to drive the brake units 12. In other words, hydraulic oil may be used as the liquid oil supplied to the brake units 12. In this case, the fluid conversion mechanism 15 is not necessary.

[0134] In addition, in the above embodiment, hydraulic oil stored in the accumulator 17 flows toward the brake unit 12, thereby performing mechanical braking using hydraulic pressure from the brake unit 12, but such an accumulator 17 may not be necessary. In this case, only the hydraulic pump 7 serves as the hydraulic pressure source.

[0135] Furthermore, the braking system 1 of the above embodiment is equipped with a controller 70 that controls the travel motor 4, the switching valve 16, the opening adjustment valve 18, and the on-off valve 19 using software, but the controller 70 is not limited to a particular form and may be configured as hardware using an electric circuit.

[0136] Furthermore, in the above embodiment, the battery 5 is a lithium ion battery, but the type of battery 5 is not particularly limited to a lithium ion battery.

[0137] Furthermore, in the above embodiment, the braking system is for the driver to manually drive the forklift 2, but the present invention is also applicable to forklifts equipped with an automatic driving system or a collision prevention system.

[0138] Furthermore, although the braking system 1 of the above embodiment is mounted on the forklift 2, the present invention can also be applied to industrial vehicles other than forklifts (for example, towing tractors, etc.) as long as they are equipped with a brake pedal. [Explanation of symbols]

[0139] 1...Braking system, 2...Forklift (industrial vehicle), 3...Drive wheel, 4...Travel motor, 5...Battery, 7...Hydraulic pump (hydraulic source), 8...Tank, 11...Brake pedal, 12...Brake unit, 14...Master cylinder, 16...Switching valve, 16a...First position, 16b...Second position, 17...Accumulator (hydraulic source), 18...Opening adjustment valve, 18a...Braking position, 18b...Return position, 19...Opening / closing valve, 19a...Closed position , 19b...open position, 71...potentiometer (operation amount detection unit), 72...voltage sensor (charge rate detection unit), 73...pressure sensor (pressure detection unit), 74...traveling direction sensor (switchback detection unit), 75...charge rate calculation unit (charge rate detection unit), 76...driving state determination unit (brake operation state determination unit, switchback detection unit), 77...pressure accumulation control unit, 78...braking control unit, 79...switchback control unit, 80...opening adjustment valve, A...specified amount.

Claims

1. In a braking system for an industrial vehicle that brakes drive wheels that are rotationally driven by a travel motor, a brake pedal operated by a driver of the industrial vehicle; a brake unit that applies a mechanical braking force to the drive wheels; a master cylinder mechanically connected to the brake pedal and driven by hydraulic oil; a hydraulic source for supplying hydraulic oil; an opening adjustment valve disposed between the hydraulic power source and the brake unit; a switching valve disposed between the brake unit and the master cylinder and between the brake unit and the opening adjustment valve; a charging rate detection unit that detects a charging rate of a battery that stores power to be supplied to the traveling motor; an operation amount detection unit that detects an operation amount of the brake pedal; a brake operation state determination unit that determines whether the brake pedal is operated based on the operation amount of the brake pedal detected by the operation amount detection unit; a braking control unit that controls the travel motor, the opening adjustment valve, and the switching valve so as to brake the drive wheels based on the charge rate of the battery detected by the charge rate detection unit when the brake operation state determination unit determines that the brake pedal has been operated, the braking control unit controls the travel motor to perform regenerative braking in which the travel motor operates as a generator when the charging rate of the battery is equal to or lower than a threshold value, and controls the opening adjustment valve to open at an opening corresponding to an operation amount of the brake pedal when the charging rate of the battery is higher than the threshold value, and controls the switching valve to supply the hydraulic oil to the brake unit by causing the opening adjustment valve to flow from the hydraulic power source toward the brake unit; The braking control unit controls the travel motor to perform regenerative braking when the battery's charging rate is below the threshold and the amount of operation of the brake pedal is below a specified amount, and controls the switching valve to prevent the supply of fluid from the master cylinder to the brake unit, and when the battery's charging rate is below the threshold and the amount of operation of the brake pedal is greater than the specified amount, controls the travel motor to perform regenerative braking and controls the switching valve to allow the fluid to be supplied from the master cylinder to the brake unit.

2. In a braking system for an industrial vehicle that brakes drive wheels that are rotationally driven by a travel motor, a brake pedal operated by a driver of the industrial vehicle; a brake unit that applies a mechanical braking force to the drive wheels; a master cylinder mechanically connected to the brake pedal and driven by hydraulic oil; a hydraulic source for supplying hydraulic oil; an opening adjustment valve disposed between the hydraulic power source and the brake unit; a switching valve disposed between the brake unit and the master cylinder and between the brake unit and the opening adjustment valve; a charging rate detection unit that detects a charging rate of a battery that stores power to be supplied to the traveling motor; an operation amount detection unit that detects an operation amount of the brake pedal; a brake operation state determination unit that determines whether the brake pedal is operated based on the operation amount of the brake pedal detected by the operation amount detection unit; a braking control unit that controls the travel motor, the opening adjustment valve, and the switching valve so as to brake the drive wheels based on the charge rate of the battery detected by the charge rate detection unit when the brake operation state determination unit determines that the brake pedal has been operated, the braking control unit controls the travel motor to perform regenerative braking in which the travel motor operates as a generator when the charging rate of the battery is equal to or lower than a threshold value, and controls the opening adjustment valve to open at an opening corresponding to an operation amount of the brake pedal when the charging rate of the battery is higher than the threshold value, and controls the switching valve to supply the hydraulic oil to the brake unit by causing the opening adjustment valve to flow from the hydraulic power source toward the brake unit; the opening adjustment valve has a variable braking position that allows the hydraulic oil to flow from a tank toward the brake unit via the hydraulic power source, and a return position that returns the hydraulic oil to the tank, When the charging rate of the battery is higher than the threshold, the braking control unit controls the aperture adjustment valve so that the aperture adjustment valve opens at an aperture corresponding to the amount of operation of the brake pedal while the aperture adjustment valve is in the braking position, and controls the switching valve so that the liquid oil is supplied to the brake unit.Thereafter, based on the amount of operation of the brake pedal detected by the operation amount detection unit, it determines whether the operation of the brake pedal has been released, and when the operation of the brake pedal has been released, controls the aperture adjustment valve so that the aperture adjustment valve switches from the braking position to the return position.

3. In a braking system for an industrial vehicle that brakes drive wheels that are rotationally driven by a travel motor, a brake pedal operated by a driver of the industrial vehicle; a brake unit that applies a mechanical braking force to the drive wheels; a master cylinder mechanically connected to the brake pedal and driven by hydraulic oil; a hydraulic source for supplying hydraulic oil; an opening adjustment valve disposed between the hydraulic power source and the brake unit; a switching valve disposed between the brake unit and the master cylinder and between the brake unit and the opening adjustment valve; a charging rate detection unit that detects a charging rate of a battery that stores power to be supplied to the traveling motor; an operation amount detection unit that detects an operation amount of the brake pedal; a brake operation state determination unit that determines whether the brake pedal is operated based on the operation amount of the brake pedal detected by the operation amount detection unit; a braking control unit that controls the travel motor, the opening adjustment valve, and the switching valve so as to brake the drive wheels based on the state of charge of the battery detected by the state of charge detection unit when the brake operation state determination unit determines that the brake pedal has been operated; a switchback detection unit that detects whether the industrial vehicle is performing a switchback; a switchback control unit that controls the travel motor, the opening adjustment valve, and the switching valve so as to decelerate the drive wheels based on the charge rate of the battery detected by the charge rate detection unit when the switchback detection unit detects that the industrial vehicle is to be switched back, the braking control unit controls the travel motor to perform regenerative braking in which the travel motor operates as a generator when the charging rate of the battery is equal to or lower than a braking threshold, and controls the opening adjustment valve to open at an opening corresponding to an operation amount of the brake pedal when the charging rate of the battery is higher than the braking threshold, and controls the switching valve to supply the hydraulic oil to the brake unit by causing the opening adjustment valve to flow from the hydraulic power source toward the brake unit; the switchback control unit controls the travel motor to perform the regenerative braking when the charging rate of the battery is equal to or lower than a threshold value for switchback, and controls the opening adjustment valve to open when the charging rate of the battery is higher than the threshold value for switchback, and controls the switching valve so that the hydraulic oil flows from the hydraulic power source toward the brake unit via the opening adjustment valve, thereby supplying the liquid oil to the brake unit; The braking control unit controls the travel motor to perform regenerative braking when the battery's charging rate is equal to or lower than the braking threshold and the amount of operation of the brake pedal is equal to or lower than a specified amount, and controls the switching valve so that the fluid oil is not supplied from the master cylinder to the brake unit, and when the battery's charging rate is equal to or lower than the braking threshold and the amount of operation of the brake pedal is greater than the specified amount, controls the travel motor to perform regenerative braking and controls the switching valve so that the fluid oil is supplied from the master cylinder to the brake unit.

4. The hydraulic pressure source includes a hydraulic pump and an accumulator that accumulates pressure in the hydraulic oil discharged from the hydraulic pump, an on-off valve is disposed between the hydraulic pump and the degree of opening adjustment valve; 4. The braking system for an industrial vehicle according to claim 1, wherein the accumulator is connected between the on-off valve and the degree of opening / closing valve.

5. a pressure detection unit that detects the pressure of the accumulator; 5. The braking system for an industrial vehicle according to claim 4, further comprising a pressure accumulation control unit that controls the on-off valve to open when the brake operation state determination unit determines that the brake pedal is not being operated and when the pressure in the accumulator detected by the pressure detection unit is equal to or lower than a specified pressure.

6. the switching valve has a first position for supplying the fluid oil from the master cylinder to the brake unit, and a second position for supplying the fluid oil from the opening adjustment valve side to the brake unit, 6. The braking system for an industrial vehicle according to claim 1, wherein the switching valve is in the first position when no power is supplied to the switching valve.

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