Hydraulic brake systems for industrial vehicles

Abstract

The objective is to provide a hydraulic braking system for industrial vehicles that can properly operate the braking system whether the vehicle is being driven by a human or by an autonomous driver. [Solution] In a hydraulic brake system 10 for an industrial vehicle, which includes a master cylinder 12 that discharges hydraulic fluid according to the amount of pressure applied to the brake pedal 19, a brake device 13 that brakes by hydraulic pressure, and a master cylinder oil passage, the system further includes a control valve 14 interposed in the master cylinder oil passage, an actuator 15, an actuator oil passage, a first solenoid valve 34 that opens and closes the master cylinder oil passage, a second solenoid valve 36 that opens and closes the actuator oil passage, and a controller 28 that controls the first solenoid valve 34 and the second solenoid valve 36. The controller 28 opens the first solenoid valve 34 and closes the second solenoid valve 36 when braking in manned operation, and opens the second solenoid valve 36 and closes the first solenoid valve 34 when braking in automated operation.

Description

Technical Field

[0001] This invention relates to a hydraulic brake system for industrial vehicles.

Background Art

[0002] As a prior art related to a hydraulic brake system for industrial vehicles, for example, a brake hydraulic control device disclosed in Patent Document 1 is known. The brake hydraulic control device disclosed in Patent Document 1 includes a control piston that receives the hydraulic pressure generated by a master cylinder, and a control valve that controls the hydraulic pressure of a hydraulic pressure source with respect to the hydraulic pressure acting on the control piston, and has a brake device that is operated by the control hydraulic pressure of the control valve.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A hydraulic brake system as disclosed in Patent Document 1 is known. By the way, when an industrial vehicle capable of manned operation is made capable of unmanned automatic operation, means for automatically generating a braking force with respect to a brake device that generates a braking force by operating a brake pedal is required. That is, in an industrial vehicle configured to switch between manned operation and automatic operation, a hydraulic brake system that applies both a braking force by operating a brake pedal and a braking force by automatic control by an actuator to the brake device must be realized. In this case, for example, it is conceivable to press the brake pedal with an actuator that is automatically controlled in automatic operation, but the actuator becomes an obstacle to the brake pedal operation in manned operation. Further, when the actuator operates the brake pedal, it is difficult to adjust the braking force of the brake device.

[0005] This invention has been made in view of the above-mentioned problems, and the object of this invention is to provide a hydraulic brake system for industrial vehicles that can operate the brake device appropriately whether the vehicle is being driven by a human or by an autonomous driver. [Means for solving the problem]

[0006] To solve the above problems, the present invention provides a hydraulic brake system for an industrial vehicle comprising: a master cylinder equipped with a brake pedal and discharging hydraulic fluid according to the amount the brake pedal is pressed; a brake device that brakes the wheels by hydraulic pressure; and a master cylinder oil passage connecting the master cylinder and the brake device, wherein the system comprises: a control valve interposed in the master cylinder oil passage; an actuator that outputs hydraulic pressure; an actuator oil passage connected from the actuator through the control valve to the master cylinder oil passage; a first solenoid valve provided in the control valve for opening and closing the master cylinder oil passage; a second solenoid valve provided in the control valve for opening and closing the actuator oil passage; and a controller that controls the first solenoid valve and the second solenoid valve, wherein the controller controls the first solenoid valve to open the master cylinder oil passage and the second solenoid valve to close the actuator oil passage during braking in manned operation; and controls the second solenoid valve to open the actuator oil passage and the first solenoid valve to close the master cylinder oil passage during braking in automated operation.

[0007] In this invention, the control valve interposed in the master cylinder oil passage is equipped with a first solenoid valve that opens and closes the master cylinder oil passage and a second solenoid valve that opens and closes the actuator oil passage. Therefore, during braking in manned operation, the first solenoid valve opens the master cylinder oil passage and the second solenoid valve closes the actuator oil passage, thereby generating braking force in the brake system through the hydraulic pressure of the master cylinder. Similarly, during braking in automated operation, the second solenoid valve opens the actuator oil passage and the first solenoid valve closes the master cylinder oil passage, thereby generating braking force in the brake system through the hydraulic pressure of the actuator. Consequently, it is possible to operate the brake system appropriately whether switching between manned and automated operation.

[0008] Furthermore, the hydraulic brake system for the industrial vehicle described above may also have a configuration comprising: a hydraulic fluid tank in which hydraulic fluid is stored; a return passage that returns the hydraulic fluid from the brake device to the hydraulic fluid tank via the control valve without passing through the master cylinder and the actuator; and a third solenoid valve provided in the control valve that opens and closes the return passage under the control of the controller. In this case, the third solenoid valve of the control valve opens the return passage, which, combined with the return of hydraulic fluid to the hydraulic fluid tank through the master cylinder oil passage or actuator oil passage, allows the hydraulic fluid of the brake system to be returned to the hydraulic fluid tank more quickly, thereby improving the responsiveness of the brake system. Furthermore, even if the first and second solenoid valves do not operate, it is possible to return the hydraulic fluid of the brake system to the hydraulic fluid tank via the control valve without passing through the master cylinder and actuator.

[0009] Furthermore, in the hydraulic brake system of the industrial vehicle described above, the hydraulic fluid tank may be configured to be connected to the master cylinder oil passage and the actuator oil passage. In this case, the hydraulic fluid tank is connected to the master cylinder oil passage and the actuator oil passage, and is a common hydraulic fluid tank for both the master cylinder and the actuator. Therefore, even if the hydraulic fluid is biased towards a specific oil passage and returns to the hydraulic fluid tank, the master cylinder and actuator will not experience a shortage of the necessary hydraulic fluid.

[0010] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the control valve may have a master cylinder port in the master cylinder oil passage and an actuator port in the actuator oil passage, and the master cylinder port and the actuator port may be formed on the upper part of the control valve. In this case, since the master cylinder port and actuator port are formed on the top of the control valve, it becomes easier to remove air (bubbles) that tend to be contained in the hydraulic fluid through the master cylinder port and actuator port.

[0011] Furthermore, in the hydraulic brake system for the industrial vehicle described above, a first hydraulic sensor for detecting hydraulic pressure may be provided between the master cylinder and the control valve in the master cylinder oil passage, and a second hydraulic sensor for detecting hydraulic pressure in the actuator oil passage may be provided between the actuator and the control valve in the actuator oil passage, with the first and second hydraulic sensors being connected to the controller. In this case, the first hydraulic sensor detects the hydraulic pressure in the master cylinder oil passage, and the second hydraulic sensor detects the hydraulic pressure in the actuator oil passage, allowing the controller to control the first and second solenoid valves to apply the necessary hydraulic pressure to the braking system.

[0012] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the control valve includes a master cylinder port connected to the master cylinder, an actuator port connected to the actuator, a brake port connected to the brake device, a first passage which is part of the master cylinder oil passage and connects the master cylinder port and the brake port, and in which the first solenoid valve is interposed, a second passage which is part of the actuator oil passage and connects the actuator port and the first passage, and in which the second solenoid valve is interposed, a first bypass passage which bypasses the first passage, a second bypass passage which bypasses the second passage, a first check valve interposed in the first bypass passage which allows the supply of hydraulic fluid from the master cylinder to the brake device, and a second check valve interposed in the second bypass passage which allows the supply of hydraulic fluid from the actuator to the brake device, wherein the opening hydraulic pressure for opening the first check valve and the second check valve may be lower than the opening hydraulic pressure for opening the first solenoid valve and the second solenoid valve. In this case, since the opening hydraulic pressure of the first check valve is lower than that of the first solenoid valve, the first check valve opens before the first solenoid valve opens, allowing the supply of hydraulic fluid from the master cylinder to the brake system. Also, since the opening hydraulic pressure of the second check valve is lower than that of the second solenoid valve, the second check valve opens before the second solenoid valve opens, allowing the supply of hydraulic fluid from the actuator to the brake system. Therefore, the hydraulic pressure of the brake system can be increased by the first or second check valve, which opens before the first or second solenoid valve, thereby suppressing the delay in the generation of braking force at the beginning of braking.

[0013] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the opening hydraulic pressure of the first check valve and the second check valve may be configured to be 0.05 to 10.0% of the opening hydraulic pressure of the first solenoid valve and the second solenoid valve. In this case, the opening hydraulic pressure of the first and second check valves is 0.05 to 10.0% of the opening hydraulic pressure of the first and second solenoid valves, thus more reliably suppressing the delay in the generation of braking force at the initial stage of braking.

[0014] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the first check valve and the second check valve may be arranged in the control valve such that their respective opening directions are vertical. In this case, the first check valve and the second check valve are arranged in the control valve so that their respective opening directions are vertical. Therefore, compared to the case where the first check valve and the second check valve are arranged so that their respective opening directions are horizontal, it becomes easier to remove air (bubbles) from the first check valve and the second check valve.

[0015] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the first solenoid valve may be configured as a normally open type solenoid valve that is normally open when not energized. In this case, since the first solenoid valve is a normally open type solenoid valve that is normally open when de-energized, even in the event of a power outage, the first solenoid valve will open due to the lack of power, allowing the hydraulic pressure of the brake system to be released into the master cylinder oil passage. In other words, the braking pressure of the brake system can be immediately released in the event of a power outage.

[0016] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the valve bore of the first solenoid valve may be set to a diameter that causes a pressure loss so that the hydraulic pressure from the actuator does not escape to the master cylinder until the first solenoid valve closes, and the valve bore of the second solenoid valve may be set to a diameter that causes a pressure loss so that the hydraulic pressure from the master cylinder does not escape to the actuator until the second solenoid valve closes. In this case, even if hydraulic pressure is generated by the actuator, the hydraulic pressure generated by the actuator does not escape to the master cylinder until the first solenoid valve closes due to the pressure loss in the valve hole of the first solenoid valve. Also, even if hydraulic pressure is generated by the master cylinder, the hydraulic pressure generated by the master cylinder does not escape to the actuator until the second solenoid valve closes due to the pressure loss in the valve hole of the second solenoid valve. That is, the hydraulic pressure of the braking device does not decrease even before the first solenoid valve or the second solenoid valve closes.

Effect of the Invention

[0017] According to the present invention, it is possible to provide a hydraulic braking system for an industrial vehicle that can appropriately operate the braking device even when switching between manned driving and autonomous driving.

Brief Description of the Drawings

[0018] [Figure 1] FIG. 15 is a schematic configuration diagram showing a hydraulic braking system of a forklift in a first embodiment. [Figure 2] (a) is a schematic diagram of the first solenoid valve, and (b) is a schematic diagram of the second solenoid valve. [Figure 3] (a) is a schematic diagram of the first check valve, and (b) is a schematic diagram of the second check valve. [Figure 4] FIG. 24 is a schematic configuration diagram showing a hydraulic braking system for explaining a state in which braking force is generated by a master cylinder. [Figure 5] FIG. 27 is a graph showing the relationship between the fuel supply amount of the actuator, the opening degree of the second check valve, the opening degree of the second solenoid valve, and the fuel supply amount to the braking device and time. [Figure 6] FIG. 30 is a schematic configuration diagram showing a hydraulic braking system for explaining a state in which the second check valve is opened by the operation of the actuator. [Figure 7] FIG. 33 is a schematic configuration diagram showing a hydraulic braking system of a forklift in a second embodiment. [Figure 8] FIG. 36 is a graph showing the relationship between the fuel supply amount of the master cylinder, the opening degree of the first check valve, the opening degree of the first solenoid valve, and the fuel supply amount to the braking device and time. [Figure 9] This is a schematic diagram illustrating a hydraulic brake system in which the first check valve is open due to the operation of the master cylinder. [Figure 10] The second embodiment is a schematic diagram showing a hydraulic brake system for a forklift. [Figure 11] This is a schematic diagram illustrating a hydraulic brake system in a state where the first and second solenoid valves are closed and the third solenoid valve is open. [Figure 12] This is a schematic diagram showing a hydraulic brake system for a forklift according to a modified example of the third embodiment. [Modes for carrying out the invention]

[0019] (First Embodiment) The hydraulic brake system for an industrial vehicle according to the first embodiment will be described below with reference to the drawings. The industrial vehicle in this embodiment is a forklift, and the hydraulic brake system for the forklift will be described.

[0020] As shown in Figure 1, the hydraulic brake system 10 of the forklift (hereinafter referred to as the "hydraulic brake system") includes a hydraulic oil tank 11, a master cylinder 12, a brake device 13, a control valve 14, and an actuator 15. The hydraulic oil tank 11 is a tank in which hydraulic oil is stored. The master cylinder 12 is connected to the hydraulic oil tank 11 by piping 16 and also to the control valve 14 by piping 17. The control valve 14 is connected to the brake device 13 by piping 18.

[0021] The master cylinder 12 is equipped with a brake pedal 19 and outputs hydraulic pressure corresponding to the amount the brake pedal 19 is pressed. When the forklift is operated with a person on board, the master cylinder 12 outputs hydraulic pressure to the brake device 13 via the control valve 14 in response to the operator's operation of the brake pedal 19, and the brake device 13 generates braking force.

[0022] The brake system 13 generates a braking force that stops the rotation of the forklift's wheels (not shown) in response to the hydraulic pressure output by the master cylinder 12 or actuator 15. The forklift's brake system 13 is, for example, a wet brake mounted on the front axle of the vehicle body, but it may also be a drum brake or a disc brake.

[0023] The actuator 15 is connected to the hydraulic fluid tank 11 by piping 20 and to the control valve 14 by piping 21. The actuator 15 generates hydraulic pressure by mechanically outputting hydraulic fluid. The actuator 15 in this embodiment is an electrically operated hydraulic cylinder and includes an electric motor 22, a conversion mechanism 23 that converts the rotation of the electric motor 22 into linear motion, a cylinder 24 having an oil chamber 25, and a piston 26 that can reciprocate within the cylinder 24. The oil chamber 25 houses a coil spring 27 as a biasing member that returns the piston 26 to its original position. In the actuator 15, the piston 26 moves forward when driven by the electric motor 22, and the hydraulic fluid is discharged by pressurizing the hydraulic fluid in the oil chamber 25. The electric motor 22 is electrically connected to a controller 28 and controlled by the controller 28. The controller 28, although not shown in the figures, includes a central processing unit (CPU) that performs various processing, a memory unit that stores programs and data, controls various parts of the forklift, and receives signals from various sensors.

[0024] The control valve 14 has a master cylinder port 30 to which piping 17 is connected, a brake port 31 to which piping 18 is connected, and an actuator port 32 to which piping 21 is connected. The master cylinder port 30, brake port 31, and actuator port 32 are all formed on the upper part of the control valve 14. The reason why the master cylinder port 30, brake port 31, and actuator port 32 are formed on the upper part of the control valve 14 is to make it easier to remove air (air bubbles) contained in the hydraulic fluid.

[0025] The control valve 14 has a first passage 33 which connects the master cylinder port 30 and the brake port 31. A first solenoid valve 34 is interposed in the first passage 33 to open and close the first passage 33. The first passage 33 has a passage portion 33A which connects the master cylinder port 30 and the first solenoid valve 34, and a passage portion 33B which connects the first solenoid valve 34 and the brake port 31.

[0026] The control valve 14 has a second passage 35 which connects the actuator port 32 and the first passage 33. A second solenoid valve 36 is interposed in the second passage 35 to open and close it. The second passage 35 is connected to the passage portion 33B of the first passage 33. The second passage 35 has a passage portion 35A which connects the actuator port 32 and the second solenoid valve 36, and a passage portion 35B which connects the second solenoid valve 36 and the passage portion 33B. The first solenoid valve 34 and the second solenoid valve 36 are controlled by the controller 28.

[0027] In the hydraulic brake system 10 of this embodiment, a master cylinder oil passage is formed by piping 17, a first passage 33, and piping 18, connecting the master cylinder 12 and the brake device 13. In addition, in the hydraulic brake system 10, an actuator oil passage is formed by piping 21 and a second passage 35, connecting the actuator 15 to the master cylinder oil passage through the control valve 14.

[0028] The first solenoid valve 34 is a normally open type solenoid valve that closes the first passage 33 when energized and opens the first passage 33 when de-energized. As shown in Figure 2(a), the first solenoid valve 34 comprises a valve section 37 embedded in the lower part of the control valve 14 and a solenoid section 38 connected to the valve section 37 and protruding from the lower part of the control valve 14. The valve section 37 comprises a cylindrical valve housing 39. A valve chamber 40 is formed inside the valve housing 39. A valve hole 41 is formed in the upper part of the valve housing 39, and a through hole 42 communicating with the passage section 33A is formed on the side of the valve housing 39. The valve hole 41 communicates with the passage section 33B. The valve hole 41 of the first solenoid valve 34 is set to a hole diameter (for example, about 1.0 mm) that causes a pressure loss, preventing hydraulic pressure from escaping to the actuator 15 while the first solenoid valve 34 is closing. The diameter of this hole is set according to various conditions such as the viscosity of the hydraulic fluid and the hydraulic fluid passage in the control valve 14, but the smaller the hole diameter, the greater the pressure loss. The valve chamber 40, valve hole 41, and through hole 42 constitute a part of the first passage 33.

[0029] The solenoid section 38 comprises a fixed core 43, a movable core 44, and an electromagnetic coil 45. A rod insertion hole 47 is formed in the center of the fixed core 43 through which a rod 46 is inserted. One end (lower) of the rod 46 is connected to the movable core 44. The movable core 44 is movable in the axial direction of the rod 46. The electromagnetic coil 45 is provided so as to surround the fixed core 43 and the movable core 44. When the electromagnetic coil 45 is energized, the movable core 44 approaches the fixed core 43, and the rod 46 rises. The other (upper) end of the rod 46 is provided with a valve body 48 capable of closing the valve hole 41. The valve body 48 is a conical valve body whose outer diameter decreases towards the tip. The rod 46 is provided with a spring receiver 49. In the valve chamber 40, a coil spring 50 is interposed between the spring receiver 49 and the valve housing 39 as a biasing member. The coil spring 50 imparts a biasing force (spring force) to the rod 46 in the direction of opening the valve hole 41. The spring force of the coil spring 50 is determined by the product of the spring constant of the coil spring 50 and the displacement of the coil spring 50 from its natural length.

[0030] The second solenoid valve 36 is a normally closed solenoid valve that opens the second passage 35 when energized and is normally closed when de-energized, opening the second passage 35. As shown in Figure 2(b), the second solenoid valve 36 comprises a valve section 51 embedded in the lower part of the control valve 14, and a solenoid section 52 connected to the valve section 51 and protruding from the lower part of the control valve 14. The valve section 51 comprises a cylindrical valve housing 53 and a valve body 54, and the valve housing 53 and valve body 54 form a valve chamber 55. A through hole 56 is formed in the upper part of the valve housing 53, which communicates with the passage section 35B of the second passage 35.

[0031] A through-hole 57 is formed in the center of the valve body 54 so as to communicate with the valve chamber 55. A valve hole 58 is formed on the valve chamber 55 side of the through-hole 57. The valve hole 58 is a tapered surface whose inner diameter widens from the through-hole 57 towards the opening. The valve hole 58 of the second solenoid valve 36 is set to a hole diameter (for example, about 1.0 mm) that causes a pressure loss, preventing hydraulic pressure from escaping to the master cylinder 12 until the second solenoid valve 36 closes. This hole diameter is set according to various conditions such as the viscosity of the hydraulic fluid and the hydraulic fluid passage in the control valve 14, but the smaller the hole diameter, the greater the pressure loss. The valve body 54 has a through-hole 59 that connects the through-hole 57 to the passage section 35A. The valve chamber 55, through-hole 57, valve hole 58, and through-hole 59 constitute a part of the second passage 35.

[0032] The solenoid section 52 comprises a fixed core 60, a movable core 61, and an electromagnetic coil 62. A rod insertion hole 64 is formed in the center of the fixed core 60 through which a rod 63 is inserted. One end (lower) of the rod 63 is connected to the movable core 61. The movable core 61 is movable in the axial direction of the rod 63. The electromagnetic coil 62 is provided so as to surround the fixed core 60 and the movable core 61. When the electromagnetic coil 62 is energized, the movable core 61 approaches the fixed core 60, and the rod 63 rises. The other (upper) end of the rod 63 is provided with a valve body 65 capable of closing the valve hole 58. The valve body 65 is spherical, but is not limited to a sphere; for example, it may be conical. A coil spring 66, which acts as a biasing member to impart biasing force (spring force) to the valve body 65, is housed in the valve chamber 55. The coil spring 66 imparts a biasing force (spring force) to the valve body 65 in the direction of closing the valve hole 58. The spring force of the coil spring 66 is determined by the product of the spring constant of the coil spring 66 and the displacement of the coil spring 66 from its natural length.

[0033] The control valve 14 has a first bypass passage 70 that branches off from passage 33A, bypasses the first solenoid valve 34, and connects to passage 33B, and a first check valve 71 interposed in the first bypass passage 70. As shown in Figure 3(a), the first check valve 71 has a housing 72 that forms a valve chamber 73, a valve member 74 having a valve hole 75, and a valve body 76 and a coil spring 77 housed in the valve chamber 73. The housing 72 has a through hole 78 that communicates with the valve chamber 73. The valve body 76 is a spherical valve body and receives a biasing force (spring force) from the coil spring 77 to close the valve hole 75. The diameter of the valve hole 75 is sufficiently larger than the diameter of the valve hole 41 of the first solenoid valve 34, for example, it is set to a diameter about three times that of the valve hole 41. Furthermore, the diameter of the valve hole 75 is not limited to approximately three times the diameter of the valve hole 41, but may be approximately one to five times the diameter of the valve hole 41.

[0034] In the first check valve 71, when the hydraulic pressure on the valve hole 75 side of the first bypass passage 70 rises, the valve body 76 opens the valve hole 75 against the biasing force (spring force) of the coil spring 77, and hydraulic fluid from the master cylinder 12 is supplied toward the brake device 13. The first check valve 71 allows the supply of hydraulic fluid toward the brake device 13 in the first bypass passage 70 when braking begins, but does not allow hydraulic fluid to pass from the brake device 13, where braking hydraulic pressure is generated, toward the master cylinder 12.

[0035] The spring force of the coil spring 77 in the first check valve 71 is determined by the product of the spring constant of the coil spring 77 and the displacement of the coil spring 77 from its natural length. The spring force of the coil spring 77 is sufficiently smaller than the spring force of the coil spring 50 of the first solenoid valve 34, and the valve hole 75 can be opened with sufficiently low hydraulic pressure. The first check valve 71 is set to have a small opening hydraulic pressure by combining a large hole diameter and a small spring force. The opening hydraulic pressure of the first check valve 71 is approximately the same as the opening hydraulic pressure of the second check valve 81, which will be described later. Note that when no braking hydraulic pressure is generated in the brake device 13, the opening hydraulic pressure of the first check valve 71 is determined by dividing the spring force of the coil spring 77 by the area of ​​the valve hole 75. When braking hydraulic pressure is generated in the brake device 13, the opening hydraulic pressure of the first check valve 71 is the hydraulic pressure obtained by dividing the spring force of the coil spring 77 by the area of ​​the valve hole 75 and adding the hydraulic pressure of the brake device 13.

[0036] The control valve 14 has a second bypass passage 80 that branches off from passage 35A, bypasses the second solenoid valve 36, and connects to passage 35B, and a second check valve 81 interposed in the second bypass passage 80. As shown in Figure 3(b), the second check valve 81 has a housing 82 that forms a valve chamber 83, a valve member 84 having a valve hole 85, and a valve body 86 and a coil spring 87 housed in the valve chamber 83. The housing 82 has a through hole 88 that communicates with the valve chamber 73. The valve body 86 is a spherical valve body and receives a biasing force (spring force) from the coil spring 87 to close the valve hole 85. The diameter of the valve hole 85 is sufficiently larger than the diameter of the valve hole 58 of the second solenoid valve 36, for example, it is set to be about three times the diameter of the valve hole 58. Furthermore, the diameter of valve hole 85 is not limited to approximately three times the diameter of valve hole 58, but may be approximately one to five times the diameter of valve hole 58.

[0037] In the second check valve 81, when the hydraulic pressure on the valve hole 85 side of the second bypass passage 80 rises, the valve body 86 opens the valve hole 85 against the biasing force (spring force) of the coil spring 87, and the hydraulic fluid from the actuator 15 is supplied to the brake device 13. The second check valve 81 allows the supply of hydraulic fluid to the brake device 13 in the second bypass passage 80 when braking begins, but it does not allow hydraulic fluid to pass from the brake device 13, where braking hydraulic pressure is generated, to the actuator 15.

[0038] The spring force of the coil spring 87 in the second check valve 81 is determined by the product of the spring constant of the coil spring 87 and the displacement of the coil spring 87 from its natural length. The spring force of the coil spring 87 is smaller than the spring force of the coil spring 66 of the second solenoid valve 36, allowing the valve hole 85 to be opened with a sufficiently low hydraulic pressure. The opening hydraulic pressure of the second check valve 81 is 0.05 to 10.0% of the opening hydraulic pressure of the second solenoid valve 36, preferably 0.06 to 5.0%, and more preferably 0.07 to 1.0%. The second check valve 81 is set to have a smaller opening hydraulic pressure compared to the second solenoid valve 36 by combining a larger hole diameter and a smaller spring force. When no braking hydraulic pressure is generated in the brake device 13, the opening hydraulic pressure of the second check valve 81 can be determined by dividing the spring force of the coil spring 87 by the area of ​​the valve hole 85. When braking hydraulic pressure is generated in the brake device 13, the opening hydraulic pressure of the second check valve 81 is the hydraulic pressure obtained by dividing the spring force of the coil spring 87 by the area of ​​the valve hole 85 and adding the hydraulic pressure of the brake device 13. When braking hydraulic pressure is not generated in the brake device 13, the opening hydraulic pressure of the second solenoid valve 36 is obtained by dividing the spring force of the coil spring 66 by the area of ​​the valve hole 58. When braking hydraulic pressure is generated in the brake device 13, the opening hydraulic pressure of the second solenoid valve 36 is the hydraulic pressure obtained by dividing the spring force of the coil spring 66 by the area of ​​the valve hole 58 and adding the hydraulic pressure of the brake device 13. Then, when hydraulic fluid is supplied from the actuator 15 and the hydraulic pressure in the passage portion 35A of the second passage 35 rises, the second check valve 81 opens before the second solenoid valve 36 opens under the control of the controller 28 and supplies hydraulic fluid to the brake device 13. The first check valve 71 and the second check valve 81 are positioned in the control valve 14 such that their respective opening directions are vertical, in order to prevent air contained in the hydraulic fluid from accumulating in the valve chambers 73 and 83.

[0039] In the hydraulic brake system 10 of this embodiment, a first hydraulic pressure sensor 90 is provided to detect the hydraulic pressure of the piping 17. The first hydraulic pressure sensor 90 transmits a signal indicating the detected hydraulic pressure of the piping 17 to the controller 28. The piping 21 is equipped with a second hydraulic pressure sensor 91 to detect the hydraulic pressure of the piping 21. The second hydraulic pressure sensor 91 transmits a signal indicating the detected hydraulic pressure to the controller 28. The controller 28 simultaneously issues an operation command for the actuator 15 and an opening command for the second solenoid valve 36, but also feeds back the hydraulic pressure of the piping 21 detected by the second hydraulic pressure sensor 91 to the electric motor 22 of the actuator 15, and controls the torque of the electric motor 22 so that the hydraulic pressure of the piping 21 reaches the target hydraulic pressure.

[0040] Next, the operation of the hydraulic brake system 10 according to this embodiment will be described. First, braking when the forklift is operated by a person will be described. When the forklift is operated by a person, no braking force is generated in the brake device 13 unless the operator operates the brake pedal 19. To brake the forklift while it is operated by a person, the operator should press down on the brake pedal 19, and hydraulic fluid corresponding to the amount of pressure should be discharged from the master cylinder 12, thereby generating braking force in the brake device 13. Therefore, when braking while the forklift is operated by a person, the first solenoid valve 34 should open the first passage 33, and the second solenoid valve 36 should close the second passage 35.

[0041] When the brake pedal 19 is pressed, the hydraulic pressure in the piping 17 rises to above a threshold. The controller 28 receives a signal indicating the hydraulic pressure in the piping 17 detected by the first hydraulic pressure sensor 90. Therefore, when the hydraulic pressure in the piping 17 rises to above a threshold, the controller 28 illuminates the brake lamp (not shown). Since the first solenoid valve 34 is a normally open type solenoid valve and the second solenoid valve 36 is a normally closed type solenoid valve, the controller 28 does not control the first solenoid valve 34 and the second solenoid valve 36. Alternatively, a limit switch to detect the degree of depression of the brake pedal 19 or a stroke sensor to detect the amount of depression of the brake pedal 19 may be provided, and the brake lamp may be illuminated when the limit switch or stroke sensor detects the degree of depression of the brake pedal 19. As shown in Figure 4, even if the first solenoid valve 34 and the second solenoid valve 36 are not controlled, the hydraulic fluid discharged from the master cylinder 12 is supplied to the brake device 13 through the piping 17, the first passage 33, and the piping 18. The hatching shown in Figure 4 indicates the hydraulic fluid inside the control valve 14. In the brake system 13, braking force is generated by the hydraulic fluid supplied from the master cylinder 12, and the forklift slows down or stops due to the braking force of the brake system 13.

[0042] When releasing the braking force of the brake device 13, the first solenoid valve 34 and the second solenoid valve 36 are not controlled, and the hydraulic fluid returns to the master cylinder 12 through the first passage 33 and piping 17 by returning the brake pedal 19. As a result, the hydraulic pressure in the brake device 13 decreases, and the braking force of the brake device 13 is released. In other words, the hydraulic pressure on the brake device 13 decreases and the braking force decreases in proportion to the amount the brake pedal 19 is returned. Furthermore, any excess hydraulic fluid is recovered from the master cylinder 12 through piping 16 to the hydraulic fluid tank 11.

[0043] Next, we will explain braking when the forklift is operating under autonomous driving conditions. When the forklift is operating under autonomous driving conditions, no braking force is generated in the brake device 13 unless the actuator 15 is activated. To brake the forklift under autonomous driving conditions, the actuator 15 should be activated, and hydraulic fluid should be discharged in proportion to the amount of actuator 15 is activated, thereby generating braking force in the brake device 13. Therefore, when braking under autonomous driving conditions, the second solenoid valve 36 should open the second passage 35, and the first solenoid valve 34 should close the first passage 33.

[0044] When braking in autonomous driving, the controller 28 issues a drive command to the actuator 15, and at the same time issues a command to open the second solenoid valve 36 and a command to close the first solenoid valve 34. When the actuator 15 is activated, the controller 28 receives a signal indicating the hydraulic pressure in the piping 21 detected by the second hydraulic sensor 91. The controller 28 energizes the first solenoid valve 34 to close and the second solenoid valve 36 to open.

[0045] Figure 5 shows the relationship between the amount of oil supplied from the actuator 15, the opening degree of the second check valve 81, the opening degree of the second solenoid valve 36, the amount of oil supplied to the brake device 13, and time. As the amount of oil supplied from the actuator 15 begins to increase in proportion to time, the second check valve 81 opens from 0% to 100% while the opening degree of the second solenoid valve 36 is at 0%. In other words, as shown in Figure 6, the second check valve 81 opens before the second solenoid valve 36 opens, opening at low pressure and supplying to the brake device 13. Therefore, hydraulic fluid is supplied from the second check valve 81 to the brake device 13 during the opening process of the second solenoid valve 36, and the brake device 13 is prevented from experiencing a braking delay due to the delayed opening of the second solenoid valve 36. Even if the first solenoid valve 34 does not completely close when the second check valve 81 opens, the hydraulic pressure from the actuator 15 does not escape to the master cylinder 12 until the first solenoid valve 34 closes due to pressure loss at the valve hole 41 of the first solenoid valve 34. Then, delayed after the opening of the second check valve 81, the second solenoid valve 36 begins to open and becomes fully open. Because the control valve 14 is equipped with the second check valve 81, the discharge amount of hydraulic fluid from the actuator 15 and the supply amount of hydraulic fluid to the brake device 13 become approximately the same (see Figure 5). Note that in Figure 6, for the sake of explanation, the state in which the first solenoid valve 34 and the second solenoid valve 36 are closed is shown.

[0046] When the second solenoid valve 36 opens fully, the hydraulic fluid supplied from the actuator 15 is supplied to the brake device 13 through the piping 21, the second passage 35, a portion of the passage section 33B, and the piping 18. In the brake device 13, braking force is generated by the hydraulic fluid supplied from the actuator 15, and the forklift decelerates or stops due to the braking force of the brake device 13. Incidentally, since the valve hole 58 of the second solenoid valve 36 is smaller in diameter than the valve hole 85 of the second check valve 81, if the control valve 14 does not have the second check valve 81, the hydraulic fluid will be supplied to the brake device 13 with a delay through the smaller diameter valve hole 58 when the second solenoid valve 36 opens. As a result, the hydraulic pressure in the brake device 13 rises with a delay after the opening of the second solenoid valve 36, causing a braking delay. Note that the hatching shown in Figure 6 indicates the hydraulic fluid in the control valve 14.

[0047] When releasing the braking pressure of the brake device 13, the second solenoid valve 36 remains open, and the piston 26 of the actuator 15 is returned, causing the hydraulic fluid to return to the actuator 15 through the second passage 35 and piping 21, thereby releasing the braking force. In other words, the hydraulic pressure on the brake device 13 decreases in proportion to the amount the brake pedal 19 is returned, and the braking force decreases. Furthermore, any excess hydraulic fluid is recovered from the master cylinder 12 through piping 16 into the hydraulic fluid tank 11.

[0048] Incidentally, for example, it is possible to operate a forklift autonomously while an operator is on board. In this case, the controller 28 generates braking force for the brake device 13 using the actuator 15. If a power outage occurs in this state due to battery over-discharge or harness breakage, the actuator 15 and the first solenoid valve 34 and second solenoid valve 36 in the control valve 14 will no longer receive power. As a result, the actuator 15 will stop operating, the supply of hydraulic fluid by the actuator 15 will cease, and braking force for the brake device 13 will not be obtained. On the other hand, the first solenoid valve 34 will open due to the power outage. Therefore, by pressing the brake pedal 19, the operator can supply hydraulic fluid via the master cylinder 12, and braking force can be generated for the brake device 13. In other words, even if a power outage occurs during autonomous driving, the forklift can be stopped by the operator operating the brake pedal 19.

[0049] The hydraulic brake system 10 according to this embodiment provides the following effects. (1) The control valve 14 interposed in the master cylinder oil passage is equipped with a first solenoid valve 34 that opens and closes the master cylinder oil passage and a second solenoid valve 36 that opens and closes the actuator oil passage. Therefore, when braking in manned operation, the first solenoid valve 34 opens the master cylinder oil passage and the second solenoid valve 36 closes the actuator oil passage, thereby generating braking force in the brake system 13 by the hydraulic pressure of the master cylinder 12. Also, when braking in automated operation, the second solenoid valve 36 opens the actuator oil passage and the first solenoid valve 34 closes the master cylinder oil passage, thereby generating braking force in the brake system 13 by the hydraulic pressure of the actuator 15. Therefore, it is possible to operate the brake system 13 appropriately whether switching to manned or automated operation.

[0050] (2) The hydraulic fluid tank 11 is connected to the master cylinder oil passage and the actuator oil passage, and is therefore a common hydraulic fluid tank for the master cylinder 12 and the actuator 15. For this reason, even if the hydraulic fluid is biased towards a specific oil passage and returns to the hydraulic fluid tank 11, the master cylinder 12 and the actuator 15 will not suffer from a shortage of the necessary hydraulic fluid.

[0051] (3) The control valve 14 has a master cylinder port 30 in the master cylinder oil passage and an actuator port 32 in the actuator oil passage. Since the master cylinder port 30 and the actuator port 32 are formed at the top of the control valve 14, it is easier to remove air (bubbles) that tend to be contained in the hydraulic fluid through the master cylinder port 30 and the actuator port 32.

[0052] (4) A second hydraulic pressure sensor 91 is provided between the actuator 15 and the control valve 14 in the actuator oil passage to detect the hydraulic pressure of the actuator oil passage. The second hydraulic pressure sensor 91 is connected to the controller 28. As a result, when the second hydraulic pressure sensor 91 detects the hydraulic pressure of the actuator oil passage, the controller 28 can control the electric motor 22 of the actuator 15 to apply the necessary hydraulic pressure to the brake device 13.

[0053] (5) Since the opening hydraulic pressure of the second check valve 81 is lower than the opening hydraulic pressure of the second solenoid valve 36, the second check valve 81 opens before the second solenoid valve 36 opens, allowing the supply of hydraulic fluid from the actuator 15 to the brake device 13. As a result, the second check valve 81, which opens before the second solenoid valve 36, can linearly increase the hydraulic pressure of the brake device 13, thereby suppressing the delay in the generation of braking force at the beginning of braking. Furthermore, since the opening hydraulic pressure of the second check valve 81 is 0.05 to 10.0% of the opening hydraulic pressure of the second solenoid valve 36, the delay in the generation of braking force at the beginning of braking can be suppressed more reliably. If the opening hydraulic pressure of the second check valve 81 is set to 0.06 to 5.0% of the opening hydraulic pressure of the second solenoid valve 36, the effect of suppressing the delay in the generation of braking force is further improved, and if the opening hydraulic pressure of the second check valve 81 is set to 0.07 to 1.0% of the opening hydraulic pressure of the second solenoid valve 36, the most desirable effect of suppressing the delay in the generation of braking force can be obtained. In addition, because the first check valve 71 is provided, when hydraulic pressure is generated by the master cylinder 12 from the state in which the first solenoid valve 34 is closed, the first check valve 71 allows the supply of hydraulic fluid to the brake device 13 before the first solenoid valve 34. As a result, the hydraulic pressure of the brake device 13 can be increased linearly by the first check valve 71, and the delay in the generation of braking force at the beginning of braking can be suppressed.

[0054] (6) The first check valve 71 and the second check valve 81 are arranged in the control valve 14 such that their respective opening directions are vertical. Therefore, compared to the case where the first check valve 71 and the second check valve 81 are arranged so that their respective opening directions are horizontal, it becomes easier to remove air from the first check valve 71 and the second check valve 81. As a result, air is less likely to accumulate in the valve chamber 73 of the first check valve 71 and the valve chamber 83 of the second check valve 81. In addition, since the first check valve 71 and the second check valve 81 are arranged in the control valve 14 so that their opening directions are vertical, the length of the control valve 14 in the left-right direction relative to the vertical direction can be suppressed.

[0055] (7) Since the first solenoid valve 34 is a normally open type solenoid valve that is normally open when no power is supplied, even in the event of a power outage, the first solenoid valve 34 will open when no power is supplied, allowing the hydraulic pressure of the brake device 13 to be released into the master cylinder oil passage. In other words, the braking pressure of the brake device 13 can be immediately released in the event of a power outage.

[0056] (8) When hydraulic pressure is generated by the actuator 15, the hydraulic pressure generated by the actuator 15 does not escape to the master cylinder 12 until the first solenoid valve 34 closes due to pressure loss at the valve hole 41 of the first solenoid valve 34. Also, when hydraulic pressure is generated by the master cylinder 12, the hydraulic pressure generated by the master cylinder 12 does not escape to the actuator 15 until the second solenoid valve 36 closes due to pressure loss at the valve hole 58 of the second solenoid valve 36. In other words, the hydraulic pressure of the brake device 13 does not decrease even before the first solenoid valve 34 or the second solenoid valve 36 closes.

[0057] (9) In this embodiment, the control valve 14 is provided with a first solenoid valve 34, a second solenoid valve 36, a first check valve 71, and a second check valve 81, forming a master cylinder oil passage and an actuator oil passage. The hydraulic circuit is a simple hydraulic circuit having a hydraulic oil tank 11, a master cylinder 12, a brake device 13, a control valve 14, an actuator 15, and piping 16, 17, 18, 20, and 21. No other hydraulic equipment is required, and the brake device 13 can be operated appropriately whether switching between manned and automated operation.

[0058] (Second embodiment) Next, a hydraulic brake system according to the second embodiment will be described. The hydraulic brake system of this embodiment differs from the first embodiment in that the first and second solenoid valves are normally closed type solenoid valves, and the opening direction of the first and second check valves is in a direction intersecting the vertical direction. In this embodiment, the same components as in the first embodiment will be referred to in the description of the first embodiment, and common reference numerals will be used.

[0059] As shown in Figure 7, the control valve 101 of the hydraulic brake system 100 of this embodiment has a first passage 102 which is a passage connecting the master cylinder port 30 and the brake port 31. A first solenoid valve 103 is interposed in the first passage 102 to open and close the first passage 102. The first passage 102 has a passage portion 102A which connects the master cylinder port 30 and the first solenoid valve 103, and a passage portion 102B which connects the first solenoid valve 103 and the brake port 31.

[0060] The control valve 14 has a second passage 104 which connects the actuator port 32 and the first passage 102. A second solenoid valve 36 is interposed in the second passage 104 to open and close it. The second passage 104 is connected to the passage portion 102B of the first passage 102. The second passage 104 has a passage portion 104A which connects the actuator port 32 and the second solenoid valve 36, and a passage portion 104B which connects the second solenoid valve 36 and the passage portion 102B. The first solenoid valve 103 and the second solenoid valve 36 are controlled by the controller 28.

[0061] In the hydraulic brake system 100 of this embodiment, a master cylinder oil passage is formed by piping 17, a first passage 102, and piping 18, connecting the master cylinder 12 and the brake device 13. In addition, in the hydraulic brake system 100, an actuator oil passage is formed by piping 21 and a second passage 104, connecting the actuator 15 to the master cylinder oil passage through the control valve 14.

[0062] The first solenoid valve 34 is a normally closed solenoid valve that opens the first passage 33 when energized and is normally closed when de-energized, opening the first passage 33. The structure of the first solenoid valve 103 is the same as that of the second solenoid valve 36.

[0063] The control valve 14 has a first bypass passage 105 that branches off from passage 102A, bypasses the first solenoid valve 34, and connects to passage 102B, and a first check valve 106 interposed in the first bypass passage 105. The structure of the first check valve 106 is the same as that of the first check valve 71, and therefore no further explanation is given. The first check valve 106 allows the supply of hydraulic fluid toward the brake device 13 in the first bypass passage 105, but does not allow hydraulic fluid to pass from the brake device 13 toward the master cylinder 12, and can allow the supply of hydraulic fluid toward the brake device 13 with a sufficiently low hydraulic pressure. The opening hydraulic pressure of the first check valve 106 is 0.05 to 10.0% of the opening hydraulic pressure of the first solenoid valve 103, preferably 0.06 to 5.0%, and more preferably 0.07 to 1.0%. The first check valve 106 is set to have a smaller opening hydraulic pressure compared to the first solenoid valve 103, by combining a larger bore diameter and a smaller spring force. When no braking hydraulic pressure is generated in the brake device 13, the opening hydraulic pressure of the first check valve 106 is calculated by dividing the spring force of the coil spring 77 by the area of ​​the valve bore 75. When braking hydraulic pressure is generated in the brake device 13, the opening hydraulic pressure of the first check valve 106 is the hydraulic pressure obtained by dividing the spring force of the coil spring 77 by the area of ​​the valve bore 75 and adding the hydraulic pressure of the brake device 13. When no braking hydraulic pressure is generated in the brake device 13, the opening hydraulic pressure of the first solenoid valve 103 is calculated by dividing the spring force of the coil spring 66 by the area of ​​the valve bore 58. When braking hydraulic pressure is generated in the brake device 13, the opening hydraulic pressure of the first solenoid valve 103 is the hydraulic pressure obtained by dividing the spring force of the coil spring 66 by the area of ​​the valve bore 58 and adding the hydraulic pressure of the brake device 13.

[0064] The control valve 14 has a second bypass passage 107 that branches off from passage 104A, bypasses the second solenoid valve 36, and connects to passage 104B, and a second check valve 108 interposed in the second bypass passage 107. The structure of the second check valve 108 is the same as that of the second check valve 81, and therefore no further explanation is provided. The second check valve 108 allows the supply of hydraulic fluid toward the brake device 13 in the second bypass passage 107, but does not allow hydraulic fluid to pass from the brake device 13 toward the actuator 15, and can allow the supply of hydraulic fluid toward the brake device 13 with a sufficiently low hydraulic pressure.

[0065] In the hydraulic brake system 10 according to this embodiment, when the forklift is operated by a person, the operator presses the brake pedal 19 when braking the forklift while it is being operated by a person. When the brake pedal 19 is pressed, the controller 28 receives a signal from the first hydraulic sensor 90 and detects that hydraulic fluid is being discharged from the master cylinder 12. Since the first solenoid valve 103 is a normally closed type solenoid valve, the controller 28 energizes the first solenoid valve 103 but does not energize the second solenoid valve 36.

[0066] Figure 8 shows the relationship between the amount of oil supplied from the master cylinder 12, the opening degree of the second check valve 108, the opening degree of the first solenoid valve 103, the amount of oil supplied to the brake device 13, and time. As the amount of oil supplied from the master cylinder 12 begins to increase in proportion to time, the first check valve 106 opens from 0% to 100% while the opening degree of the first solenoid valve 103 is at 0%. In other words, as shown in Figure 9, the first check valve 106 opens before the first solenoid valve 103 opens, and hydraulic fluid is supplied to the brake device 13. Therefore, the brake device 13 is prevented from experiencing a braking delay due to a delay in the opening of the first solenoid valve 103. Then, after the opening of the first check valve 106, the first solenoid valve 103 begins to open and becomes fully open. Because the control valve 101 is equipped with the first check valve 106, the amount of hydraulic fluid discharged from the actuator 15 and the amount of hydraulic fluid supplied to the brake device 13 are approximately the same (see Figure 8). Note that in Figure 9, for the sake of explanation, the first solenoid valve 103 and the second solenoid valve 36 are shown in a closed state.

[0067] As described above, the first check valve 106 is provided so that when hydraulic pressure is generated by the master cylinder 12 while the first solenoid valve 103 is closed, the first check valve 106 opens before the first solenoid valve 103 opens, allowing the supply of hydraulic fluid to the brake device 13. Therefore, the first check valve 106, which opens before the first solenoid valve 103 opens, can cause the hydraulic pressure of the brake device 13 to increase linearly, thereby suppressing the delay in the generation of braking force in the initial stages of braking.

[0068] When releasing the braking force of the brake device 13, the hydraulic fluid returns to the master cylinder 12 through the first passage 102 and piping 17 by releasing the brake pedal 19 with the first solenoid valve 103 open. As a result, the hydraulic pressure in the brake device 13 decreases, and the braking force of the brake device 13 is released. In other words, the hydraulic pressure on the brake device 13 decreases and the braking force decreases in proportion to the amount the brake pedal 19 is released. Furthermore, any excess hydraulic fluid is recovered from the master cylinder 12 through piping 16 to the hydraulic fluid tank 11. Note that the braking when the forklift is operating under automatic driving conditions is the same as in the first embodiment, except that the first solenoid valve 103 is closed and not energized, so a detailed explanation is omitted.

[0069] The hydraulic brake system 100 of this embodiment provides the same effects as those of the first embodiment (1) to (5). In this embodiment, a first hydraulic pressure sensor 90 is provided between the master cylinder 12 and the control valve 101 in the master cylinder oil passage to detect the hydraulic pressure in the master cylinder oil passage. The first hydraulic pressure sensor 90 is connected to the controller 28. Therefore, when the first hydraulic pressure sensor 90 detects an oil pressure in the piping 17 that is above a threshold, the controller 28 can control the first solenoid valve 103 to apply the necessary hydraulic pressure to the brake device 13.

[0070] Furthermore, in this embodiment, the opening directions of the first check valve 106 and the second check valve 108 are intersecting with the vertical direction. Therefore, the vertical dimensions of the control valve 101 can be reduced compared to the case where the opening directions of the first check valve 106 and the second check valve 81 are vertical.

[0071] (Third embodiment) Next, a hydraulic brake system according to a third embodiment will be described. This embodiment differs from the first embodiment in that, in addition to the first and second solenoid valves, it has a third solenoid valve, and does not have a first check valve or a second check valve. In this embodiment, the same configuration as in the first embodiment will be described by referring to the description of the first embodiment, and the same reference numerals will be used.

[0072] As shown in Figure 10, the control valve 201 of the hydraulic brake system 200 in this embodiment has a first passage 202 which is a passage connecting the master cylinder port 30 and the brake port 31. A first solenoid valve 203 is interposed in the first passage 202 to open and close the first passage 202. The first passage 202 has a passage portion 202A which connects the master cylinder port 30 and the first solenoid valve 203, and a passage portion 202B which connects the first solenoid valve 203 and the brake port 31.

[0073] The control valve 14 has a second passage 204 which connects the actuator port 32 and the first passage 202. A second solenoid valve 36 is interposed in the second passage 204 to open and close the second passage 204. The second passage 204 is connected to the passage portion 202B of the first passage 202. The second passage 204 has a passage portion 204A which connects the actuator port 32 and the second solenoid valve 36, and a passage portion 204B which connects the second solenoid valve 36 and the passage portion 202B. The first solenoid valve 203 and the second solenoid valve 36 are controlled by the controller 28.

[0074] In the hydraulic brake system 200 of this embodiment, a master cylinder oil passage is formed by piping 17, a first passage 202, and piping 18, connecting the master cylinder 12 and the brake device 13. In addition, in the hydraulic brake system 200, an actuator oil passage is formed by piping 21 and a second passage 204, connecting the actuator 15 to the master cylinder oil passage through the control valve 14.

[0075] The first solenoid valve 203 is a normally closed solenoid valve that opens the first passage 202 when energized and is normally closed when de-energized, opening the first passage 33. The structure of the first solenoid valve 203 is the same as that of the second solenoid valve 36.

[0076] The hydraulic brake system 200 of this embodiment has a return passage that returns the hydraulic fluid from the brake device 13 to the hydraulic fluid tank 11 via a control valve 201, without passing through the master cylinder 12 and actuator 15. Specifically, the control valve 201 has a return port 205 and a third passage 206 connected to the return port 205 and the passage portion 204B of the second passage 204. A third solenoid valve 207 is interposed in the third passage 206 to open and close the third passage 206. The hydraulic brake system 200 has a pipe 208 that connects the return port 205 to the pipe 20. Therefore, in the hydraulic brake system 200 of this embodiment, the third passage 206 and the pipe 208 constitute a return passage that returns the hydraulic fluid from the brake device 13 to the hydraulic fluid tank 11 via the control valve 201, without passing through the master cylinder 12 and actuator 15.

[0077] The third solenoid valve 207 is a normally closed solenoid valve that opens the third passage 206 when energized and is normally closed when de-energized, opening the third passage 206. The structure of the third solenoid valve 207 is the same as that of the second solenoid valve 36. The third solenoid valve 207 is installed in the control valve 201 and opens and closes the return passage under the control of the controller 28.

[0078] In this embodiment, when releasing the braking force generated in the brake device 13 by the master cylinder 12 or actuator 15, the hydraulic fluid can be returned to the master cylinder 12 or actuator 15 by opening the first solenoid valve 203 or the second solenoid valve 36. Furthermore, by opening the third solenoid valve 207, the hydraulic fluid can be returned to the hydraulic fluid tank 11 through the piping 18, passage section 204B, third passage 206, and piping 208.

[0079] The hydraulic brake system 200 according to this embodiment provides the same effects as those of the first embodiment (1) to (4). In this embodiment, the control valve 201 has a return passage and a third solenoid valve 207, and by opening the third solenoid valve 207, the braking pressure of the brake device 13 can be quickly released, thereby improving the responsiveness of the hydraulic brake system 200. Also, as shown in Figure 11, even if the first solenoid valve 203 and the second solenoid valve 36 become inoperable while the braking pressure of the brake device 13 is maintained, the braking pressure of the brake device 13 can be released by opening the third solenoid valve 207. Furthermore, since the control valve 201 does not have a first check valve and a second check valve, the configuration of the hydraulic brake system 200 can be further simplified, and manufacturing costs can be reduced. Since the return port 205 is formed on the upper part of the control valve 201, it is easier to release air (bubbles) from the hydraulic fluid in the return passage.

[0080] (modified version) Next, a modified example will be described. In this modified example, as shown in Figure 12, the control valve 301 does not have a third passage 206 and a third solenoid valve 207. Therefore, the hydraulic brake system 300 does not have piping 208. In this modified example, the effects (1) to (4) are the same as those of the first embodiment. Furthermore, in this modified example, since the control valve 301 does not have a third passage 206 and a third solenoid valve 207, the control valve 301 can be made smaller, the number of parts can be reduced, and manufacturing costs can be lowered.

[0081] 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.

[0082] ○ In the embodiments described above, the hydraulic fluid tank is a common tank for both the master cylinder and the actuator, but this is not the only option. For example, a dedicated hydraulic fluid tank may be provided for each of the master cylinder and the actuator. ○ In the embodiments described above, an electrically operated hydraulic cylinder driven by an electric motor was used as an example of an actuator, but the invention is not limited to this. The actuator can be of any type or design as long as it is capable of generating hydraulic pressure for the brake system. ○ In the embodiments described above, the master cylinder port and actuator port are formed on the upper part of the control valve, but the invention is not limited to this. The master cylinder port and actuator port may be formed, for example, on the side of the control valve. ○ In each of the embodiments described above, the valve bore of the first solenoid valve is set to a diameter that causes a pressure loss so that the hydraulic pressure from the actuator does not escape to the master cylinder until the first solenoid valve closes, and the valve bore of the second solenoid valve is set to a diameter that causes a pressure loss so that the hydraulic pressure from the master cylinder does not escape to the actuator until the second solenoid valve closes, but the embodiment is not limited thereto. ○ In the first embodiment described above, the second solenoid valve is a normally closed type solenoid valve, but it is not limited to this. The second solenoid valve may be, for example, a normally open type solenoid valve, and it is sufficient to close the second solenoid valve by energizing it when hydraulic fluid is supplied to the brake device by the master cylinder. ○ In the embodiments described above, a hydraulic brake system for a forklift as an industrial vehicle was used as an example, but the invention is not limited thereto. The industrial vehicle may be, for example, a towing vehicle or a towing tractor, and any vehicle equipped with a brake system that can be operated by the hydraulic pressure of a master cylinder and actuators is acceptable. [Explanation of Symbols]

[0083] 10, 100, 200, 300 Hydraulic Brake System 11. Hydraulic oil tank 12 Master Cylinder 13 Brake system 14, 101, 201, 301 Control valves 15 Actuators 19 Brake pedal 28 Controllers 30 Master Cylinder Ports 31 Brake Ports 32 actuator ports 33, 102, 202 1st aisle 34, 103, 203 First solenoid valve 35, 104, 204 2nd aisle 36. Second solenoid valve 41 Valve opening (first solenoid valve) 58 Valve opening (2nd solenoid valve) 70, 105 First Bypass Passage 71, 106 First check valve 80, 107 Second Bypass Passage 81, 108 Second check valve 90. First hydraulic sensor 91. Second hydraulic sensor 207 Third Solenoid Valve

Claims

1. A master cylinder equipped with a brake pedal, which discharges hydraulic fluid in proportion to the amount the brake pedal is pressed, A braking system that uses hydraulics to brake the wheels, A hydraulic brake system for an industrial vehicle having a master cylinder oil passage connecting the master cylinder and the brake device, A control valve interposed in the master cylinder oil passage, An actuator that outputs hydraulic pressure, An actuator oil passage connected from the actuator through the control valve to the master cylinder oil passage, The control valve is provided with a first solenoid valve that opens and closes the master cylinder oil passage, The control valve is provided with a second solenoid valve that opens and closes the actuator oil passage, The system includes a controller that controls the first solenoid valve and the second solenoid valve, The aforementioned controller, The first solenoid valve is controlled to open the master cylinder oil passage during braking in manned operation, and the second solenoid valve is controlled to close the actuator oil passage. A hydraulic brake system for an industrial vehicle, characterized by controlling the second solenoid valve to open the actuator oil passage and the first solenoid valve to close the master cylinder oil passage during braking in automatic driving.

2. A hydraulic fluid tank in which hydraulic fluid is stored, A return passage that returns the hydraulic fluid from the brake device to the hydraulic fluid tank via the control valve without passing through the master cylinder and the actuator, The hydraulic brake system for an industrial vehicle according to claim 1, further comprising a third solenoid valve provided in the control valve, which opens and closes the return passage under the control of the controller.

3. The hydraulic brake system for an industrial vehicle according to claim 2, characterized in that the hydraulic fluid tank is connected to the master cylinder oil passage and the actuator oil passage.

4. The control valve is The master cylinder port in the master cylinder oil passage, The actuator oil passage has an actuator port, The hydraulic brake system for an industrial vehicle according to claim 1 or 2, characterized in that the master cylinder port and the actuator port are formed on the upper part of the control valve.

5. A first hydraulic pressure sensor for detecting hydraulic pressure is provided between the master cylinder and the control valve in the master cylinder oil passage. A second hydraulic pressure sensor for detecting the hydraulic pressure in the actuator oil passage is provided between the actuator and the control valve in the actuator oil passage. The hydraulic brake system for an industrial vehicle according to claim 1 or 2, characterized in that the first hydraulic sensor and the second hydraulic sensor are connected to the controller.

6. The control valve is The master cylinder port connected to the master cylinder, The actuator port connected to the actuator, A brake port connected to the aforementioned brake device, A part of the master cylinder oil passage, comprising a first passage connecting the master cylinder port and the brake port, in which the first solenoid valve is interposed, A part of the actuator oil passage, which connects the actuator port and the first passage, and in which the second solenoid valve is interposed, A first bypass passage that bypasses the first passage, A second bypass passage that bypasses the aforementioned second passage, Interposed in the first bypass passage is a first check valve that allows the supply of hydraulic fluid from the master cylinder to the brake device, The second bypass passage includes a second check valve interposed therein, which allows the supply of hydraulic fluid from the actuator to the brake device, The hydraulic brake system for an industrial vehicle according to claim 1 or 2, characterized in that the opening hydraulic pressure for opening the first check valve and the second check valve is lower than the opening hydraulic pressure for opening the first solenoid valve and the second solenoid valve.

7. The hydraulic brake system for an industrial vehicle according to claim 6, characterized in that the opening hydraulic pressure of the first check valve and the second check valve is 0.05 to 10.0% of the opening hydraulic pressure of the first solenoid valve and the second solenoid valve.

8. The hydraulic brake system for an industrial vehicle according to claim 6, characterized in that the first check valve and the second check valve are arranged in the control valve such that their respective opening directions are vertical.

9. The hydraulic brake system for an industrial vehicle according to claim 1 or 2, characterized in that the first solenoid valve is a normally open type solenoid valve that is normally open when not energized.

10. The valve bore of the first solenoid valve is set to a diameter that causes a pressure loss, preventing the hydraulic pressure from the actuator from escaping to the master cylinder while the first solenoid valve is closing. The hydraulic brake system for an industrial vehicle according to claim 1 or 2, characterized in that the valve bore of the second solenoid valve is set to a bore diameter that causes a pressure loss, preventing the hydraulic pressure from the master cylinder from escaping to the actuator while the second solenoid valve is closed.

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