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] The hydraulic brake system 10 includes a master cylinder 12, a brake device 13, and a master cylinder oil passage. The system also includes an actuator 15, a control valve 14, 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, a controller 28, and a situation detection sensor connected to the controller 28 that detects whether or not there is a braking need situation requiring braking. The controller 28 controls the actuator 15 to drive, and also controls the second solenoid valve 36 to open and the first solenoid valve 34 to close, based on the detection of a braking need situation by the situation detection sensor.

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 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 that can be manned is made capable of unmanned automatic driving, means for automatically generating braking force with respect to a brake device that generates braking force by operating a brake pedal is required. That is, in an industrial vehicle configured to switch between manned driving and automatic driving, a hydraulic brake system that applies both the braking force by operating the brake pedal and the 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 driving, but the actuator hinders the operation of the brake pedal in manned driving. 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 having a brake pedal, a master cylinder that discharges 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 mechanism, wherein the system comprises an actuator that outputs hydraulic pressure, a control valve interposed in the master cylinder oil passage, 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 that opens and closes the master cylinder oil passage, a second solenoid valve provided in the control valve that opens and closes the actuator oil passage, a controller that controls the first solenoid valve and the second solenoid valve, and a situation detection sensor connected to the controller that detects whether or not there is a braking necessity situation requiring braking, wherein the controller controls the actuator to drive based on the detection of the braking necessity situation by the situation detection sensor, and controls the second solenoid valve to open and the first solenoid valve to close.

[0007] In this invention, when the situation detection sensor detects a braking requirement, the controller controls the actuator to drive based on the sensor's detection, opens the second solenoid valve, and closes the first solenoid valve. As a result, hydraulic fluid is supplied from the actuator, and braking force is generated in the braking system. Therefore, when a braking requirement arises during driving, braking force can be automatically generated in the braking system.

[0008] Furthermore, in the above-described hydraulic brake system for industrial vehicles, the system may include a brake pedal sensor for detecting the depression of the brake pedal, a first hydraulic pressure sensor for detecting the hydraulic pressure of the master cylinder oil passage, and a second hydraulic pressure sensor for detecting the hydraulic pressure of the actuator oil passage. When hydraulic fluid is supplied from the actuator to the brake device, if the brake pedal sensor detects the depression of the brake pedal, the controller compares the hydraulic pressure of the master cylinder oil passage detected by the first hydraulic pressure sensor with the hydraulic pressure of the actuator oil passage detected by the second hydraulic pressure sensor. If the hydraulic pressure of the master cylinder oil passage is greater than or equal to the hydraulic pressure of the actuator oil passage, the controller controls the system to open the first solenoid valve. If the hydraulic pressure of the master cylinder oil passage is less than the hydraulic pressure of the actuator oil passage, the system may continue to supply hydraulic fluid from the actuator to the brake device.

[0009] In this case, when the brake pedal sensor detects that the brake pedal has been pressed, the controller compares the hydraulic pressure of the master cylinder oil passage detected by the first hydraulic pressure sensor with the hydraulic pressure of the actuator oil passage detected by the second hydraulic pressure sensor. When the hydraulic pressure of the master cylinder oil passage is greater than or equal to the hydraulic pressure of the actuator oil passage, the first solenoid valve opens and the second solenoid valve closes. Therefore, when the brake pedal is pressed while braking is being performed by the actuator, the braking force of the brake system can be switched from the hydraulic pressure of the actuator to the hydraulic pressure of the master cylinder. Also, when the hydraulic pressure of the master cylinder oil passage is less than the hydraulic pressure of the actuator oil passage, the supply of hydraulic fluid from the actuator to the brake system continues, so that the actuator can generate the braking force of the brake system.

[0010] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the controller may be configured to stop the operation of the actuator after a preset time has elapsed since the first solenoid valve was opened.

[0011] In this case, when the brake pedal is pressed and the hydraulic pressure in the master cylinder oil passage is greater than or equal to the hydraulic pressure in the actuator oil passage, the first solenoid valve opens and the second solenoid valve closes. However, the controller controls the system to stop the actuator's operation after a preset time. Therefore, by preventing the second solenoid valve from closing immediately when the brake pedal is pressed, a temporary drop in hydraulic pressure in the braking system due to a decrease in actuator hydraulic pressure can be prevented. As a result, the operator can obtain a natural and appropriate braking feel.

[0012] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the controller may be configured to stop the actuator after the second solenoid valve has been closed when it commands the actuator to stop operating while the actuator is generating braking force for the brake device.

[0013] In this case, the controller controls the actuator to stop after the second solenoid valve closes, which prevents a decrease in braking pressure in the braking system compared to the case where the actuator is stopped immediately. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a hydraulic brake system for industrial vehicles that can properly operate the brakes whether the vehicle is being driven by a human or by an autonomous driver. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram showing a hydraulic brake system for a forklift as an embodiment of the present invention. [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]It is a schematic configuration diagram showing a hydraulic brake system for explaining a state in which braking force is generated by a master cylinder. [Figure 5] It is a graph showing the relationship between the hydraulic pressure of the master cylinder, the opening degrees of the first solenoid valve, the second solenoid valve, the first check valve, and the second check valve, and time. [Figure 6] It is a schematic configuration diagram showing a hydraulic brake system for explaining a state in which the second solenoid valve is opened by the operation of an actuator. [Figure 7] It is a graph showing the relationship between the hydraulic pressure of the actuator, the opening degrees of the first solenoid valve, the second solenoid valve, the first check valve, and the second check valve, and time. [Figure 8] It is a graph showing the relationship between the hydraulic pressures of the master cylinder and the actuator when the brake pedal is depressed during braking of the actuator, the opening degrees of the first solenoid valve, the second solenoid valve, the first check valve, and the second check valve, and time. [Figure 9] It is a graph showing the relationship between the driving and stopping of the electric motor when holding the braking pressure of the braking device during braking of the actuator, the hydraulic pressure of the braking device, the opening degrees of the first solenoid valve, the second solenoid valve, the first check valve, and the second check valve, and time.

Mode for Carrying Out the Invention

[0016] Hereinafter, a hydraulic brake system for an industrial vehicle according to an embodiment of the present invention will be described with reference to the drawings. The industrial vehicle in this embodiment is a forklift, and the hydraulic brake system of the forklift will be described.

[0017] As shown in FIG. 1, the hydraulic brake system (hereinafter referred to as "hydraulic brake system") 10 of the forklift has 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 for storing hydraulic oil. The master cylinder 12 is connected to the hydraulic oil tank 11 by a pipe 16 and is also connected to the control valve 14 by a pipe 17. The control valve 14 is connected to the brake device 13 by a pipe 18.

[0018] The master cylinder 12 includes a brake pedal 19 and outputs hydraulic pressure according to the depression amount of the brake pedal 19. When the forklift is manned and traveling, the master cylinder 12 outputs hydraulic pressure to the brake device 13 via the control valve 14 by the operation of the brake pedal 19 by the operator, and generates braking force in the brake device 13.

[0019] The brake device 13 generates a braking force that stops the rotation of the wheels (not shown) of the forklift according to the hydraulic pressure output by the master cylinder 12 or the actuator 15. The brake device 13 of the forklift is, for example, a wet brake provided on the front axle mounted on the vehicle body, but it may also be a drum brake.

[0020] 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 air 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. The piston 26 moves forward when the electric motor 22 rotates in the forward direction and moves backward when the electric motor 22 rotates in the reverse direction. 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. Although not shown in the diagram, the controller 28 includes a central processing unit (CPU) that performs various processes, a memory unit that stores programs and data, and controls various parts of the forklift, as well as receiving signals from various sensors.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 chamber 40, valve hole 41, and through hole 42 constitute a part of the first passage 33.

[0026] 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.

[0027] 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.

[0028] 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. A through hole 59 is formed in the valve body 54 so as to communicate the through hole 57 with the passage portion 35A. The valve chamber 55, through hole 57, valve hole 58 and through hole 59 constitute a part of the second passage 35.

[0029] 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 spring force of coil spring 66 is determined by the product of the spring constant of coil spring 66 and the displacement of coil spring 66 from its natural length.

[0030] 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.

[0031] 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.

[0032] 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, allowing the valve hole 75 to 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. 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, plus the hydraulic pressure of the brake device 13.

[0033] 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.

[0034] 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.

[0035] 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 no 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 no braking hydraulic pressure is 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.

[0036] In this embodiment, the hydraulic brake system 10 is equipped with a limit switch 90 on the brake pedal 19, which acts as a brake pedal sensor to detect the depression of the brake pedal 19. When the limit switch 90 detects the depression of the brake pedal 19, it transmits a signal to the controller 28. The piping 17 is equipped with a first hydraulic pressure sensor 91 that detects the hydraulic pressure of the piping 17. The first hydraulic pressure sensor 91 transmits a signal indicating the detected hydraulic pressure to the controller 28. The piping 21 is equipped with a second hydraulic pressure sensor 92 that detects the hydraulic pressure of the piping 21. The second hydraulic pressure sensor 92 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 92 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.

[0037] The hydraulic brake system 10 of this embodiment includes an accelerator pedal 93, an accelerator pedal sensor 94 that detects the degree to which the accelerator pedal 93 is pressed, and an obstacle sensor 95. The accelerator pedal 93 can be pressed by an operator during manned operation, as well as automatically during unmanned operation. The speed of the forklift changes according to the degree to which the accelerator pedal 93 is pressed. The accelerator pedal sensor 94 detects whether or not the accelerator pedal 93 is pressed and transmits a detection signal to the controller 28. The obstacle sensor 95 is a sensor that detects obstacles that may hinder driving, and transmits a signal to the controller 28 when an obstacle is detected. The accelerator pedal sensor 94 and the obstacle sensor 95 correspond to situation detection sensors that detect whether or not there is a situation requiring braking, and are sensors that detect whether or not braking force is required when the forklift is running and allow the controller 28 to recognize this.

[0038] 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.

[0039] When the brake pedal 19 is pressed, the hydraulic pressure in the piping 17 rises to above a threshold. The controller 28 receives signals from the limit switch 90 indicating the amount the brake pedal 19 is pressed and signals from the first hydraulic sensor 91 indicating the hydraulic pressure in the piping 17, and therefore detects that hydraulic fluid is being discharged from the master cylinder 12. 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. 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 in the control valve 14. In the brake device 13, braking force is generated by the hydraulic fluid supplied from the master cylinder 12, and the forklift decelerates or stops due to the braking force of the brake device 13.

[0040] Here, we will explain in detail the process by which braking pressure is generated in the brake system 13 by the master cylinder 12. As shown in Figure 5, in the relationship between the hydraulic pressure of the master cylinder 12 and time, the first check valve 71 opens a short time after the brake pedal 19 is pressed down ts. The hydraulic fluid from the master cylinder 12 increases the hydraulic pressure in the master cylinder oil passage, causing the first check valve 71 to open. Meanwhile, the first solenoid valve 34 remains open, and the second solenoid valve 36 and the second check valve 81 are closed. The hydraulic pressure of the master cylinder 12 begins to rise from the time the first check valve 71 starts to open, exceeds the target hydraulic pressure Pt, and after a period of hydraulic pressure adjustment where it increases or decreases relative to the target hydraulic pressure Pt, it becomes almost constant at the target hydraulic pressure Pt. When the hydraulic pressure of the master cylinder 12 becomes almost constant at the target hydraulic pressure Pt, the brake system 13 can obtain the necessary hydraulic pressure. The first check valve 71 closes after the hydraulic pressure adjustment period.

[0041] 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.

[0042] 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 according to the amount of actuator 15 is activated, thereby generating braking force in the brake device 13. Therefore, during 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. The operation of the actuator 15 is based on an operation command sent from the controller 28 when the accelerator pedal sensor 94 stops detecting the depression of the accelerator pedal 93 or when the obstacle sensor 95 detects an obstacle.

[0043] When the accelerator pedal sensor 94 stops detecting the depression of the accelerator pedal 93, or when the obstacle sensor 95 detects an obstacle, the controller 28 issues a drive command to the actuator 15, and at the same time issues an open command for the second solenoid valve 36 and a close command for the first solenoid valve 34. When the actuator 15 is activated, the controller 28 receives a signal indicating the hydraulic pressure of the piping 21 detected by the second hydraulic pressure sensor 92. The controller 28 feeds back the hydraulic pressure of the piping 21 detected by the second hydraulic pressure sensor 92 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. The controller 28 also energizes the first solenoid valve 34 to close and the second solenoid valve 36 to open. Therefore, the second check valve 81 opens immediately after the second solenoid valve 36 begins to open, and hydraulic fluid is supplied to the brake device 13. Then, delayed after the opening of the second check valve 81, the second solenoid valve 36 opens completely. As shown in Figure 6, when the second solenoid valve 36 is fully open, the hydraulic fluid supplied from the actuator 15 is supplied to the brake device 13 through the piping 21, the second passage 35, a part of the passage section 33B, and the piping 18. In the brake device 13, a braking force is generated by the hydraulic fluid supplied from the actuator 15, and the forklift slows down or stops due to the braking force of the brake device 13.

[0044] Here, we will explain in detail the process by which the actuator 15 generates braking pressure in the brake device 13. As shown in Figure 7, in the relationship between the hydraulic pressure of the actuator 15 and time, the second solenoid valve 36 begins to open from the time tc when the operation of the actuator 15 is commanded by the controller 28, and the first solenoid valve 34 begins to close with a delay after the opening of the second solenoid valve 36. The hydraulic fluid from the actuator 15 increases the hydraulic pressure in the actuator oil passage, causing the second check valve 81 to open. The second check valve 81 opens when the first solenoid valve 34 has finished closing. Almost simultaneously with the closing of the first solenoid valve 34 and the opening of the second check valve 81, the hydraulic pressure of the actuator 15 begins to rise, and the opening of the second solenoid valve 36 is completed while the hydraulic pressure of the actuator 15 is rising. Then, the hydraulic pressure of the actuator 15 exceeds the target hydraulic pressure Pt, and after a period of hydraulic pressure adjustment where it increases or decreases relative to the target hydraulic pressure Pt, it becomes almost constant at the target hydraulic pressure Pt. When the hydraulic pressure of actuator 15 becomes nearly constant at the target hydraulic pressure Pt, the brake device 13 can obtain the required hydraulic pressure.

[0045] When releasing the braking pressure of the brake device 13 by the actuator 15, 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.

[0046] Incidentally, when the actuator 15 generates braking force in the brake device 13, it is conceivable that the operator will press down on the brake pedal 19. When the actuator 15 generates braking force in the brake device 13 and the brake pedal 19 is pressed down, the controller 28 compares the hydraulic pressure Pm (hereinafter referred to as "first hydraulic pressure Pm") detected by the first hydraulic pressure sensor 91 with the hydraulic pressure Pn (hereinafter referred to as "second hydraulic pressure Pn") detected by the second hydraulic pressure sensor 92. The first hydraulic pressure Pm increases in proportion to the amount the brake pedal 19 is pressed down. If the first hydraulic pressure Pm is greater than or equal to the second hydraulic pressure Pn, the controller 28 controls the system to start opening the first solenoid valve 34 and starting to close the second solenoid valve 36.

[0047] As shown in Figure 8, after the brake pedal 19 is pressed down at time ts, the first solenoid valve 34 opens, the second solenoid valve 36 closes, and the first check valve 71 opens. The opening of the first solenoid valve 34, the closing of the second solenoid valve 36, and the opening of the first check valve 71 all occur at approximately the same time t1. At time t2, when the second solenoid valve 36 has finished closing, the first solenoid valve 34 is still open, and after time t2, when the second solenoid valve 36 has finished closing, time t3 occurs when the first solenoid valve 34 has finished opening. In Figure 8, for the sake of explanation, the hydraulic pressure A of the actuator 15 is shown by a dashed line on the graph of the hydraulic pressure of the master cylinder 12. The hydraulic pressure A is approximately equal to the second hydraulic pressure Pn detected by the second hydraulic pressure sensor 92.

[0048] On the other hand, if the first hydraulic pressure Pm is less than the second hydraulic pressure Pn, the supply of hydraulic fluid from the actuator 15 is maintained with the first solenoid valve 34 closed. For example, even if the limit switch 90 detects that the brake pedal 19 has been pressed, if the brake pedal 19 has only been pressed lightly or has been immediately released, the first hydraulic pressure Pm will be lower than the second hydraulic pressure Pn, and the braking force of the brake device 13 will be maintained by the hydraulic pressure of the actuator 15. Therefore, the first solenoid valve 34 will not open due to a light press of the brake pedal 19 or the release of the brake pedal 19, thus preventing a decrease in the operating pressure of the brake device 13 due to the opening of the first solenoid valve 34.

[0049] The controller 28 is configured with a set time Tm to delay the stopping of the actuator 15 so that the actuator 15 continues to operate from time t1, when the second solenoid valve 36 starts closing, to time t2, when it is completed. In this embodiment, the set time Tm corresponds to the time between time t1 and time t3 (for example, 50 ms). It is preferable to set the set time Tm considering the detection errors of the first hydraulic pressure sensor 91 and the second hydraulic pressure sensor 92 and the change in viscosity due to the temperature of the hydraulic fluid. By setting the set time Tm in the controller 28, a decrease in hydraulic pressure of the actuator 15 between time t1 and time t2 is prevented. As a result, a decrease in braking force due to a decrease in braking pressure can be prevented before the master cylinder 12 reaches the target hydraulic pressure Pt, and the operator does not feel any discomfort during braking. Incidentally, if the set time Tm to delay the stopping of the actuator 15 is not set, the braking pressure will decrease between time t1 and time t2, so the operator will feel an discomfort as the feeling of deceleration temporarily disappears even though it is braking.

[0050] Furthermore, in this embodiment, it is conceivable to maintain the braking pressure of the brake device 13 by closing the second solenoid valve 36 while the actuator 15 is operating. If the electric motor 22 of the actuator 15 is continuously driven to maintain the braking pressure of the brake device 13, there is a risk of the electric motor 22 overheating. For this reason, it would be sufficient to stop the driving of the electric motor 22 when closing the second solenoid valve 36 while the actuator 15 is operating. However, if the electric motor 22 is stopped before the second solenoid valve 36 has finished closing, the braking pressure in the brake device 13 will decrease. Therefore, in this embodiment, as shown in Figure 9, the controller 28 is set to a set time Tn for delayed stopping of the electric motor 22.

[0051] As shown in Figure 9, if we consider time t1 as the start of closing the second solenoid valve 36 and time t2 as the completion of closing the second solenoid valve 36, then by setting a set time Tn, the drive of the electric motor 22 will be stopped at time t3, which is after time t2 when the second solenoid valve 36 is completed to close. The set time Tn is the time from time t1 when the second solenoid valve 36 starts closing to time t2 when it is completed to close, plus a certain amount of additional time. Therefore, if the controller 28 controls the system to close the second solenoid valve 36 and stop the drive of the electric motor 22 while the actuator 15 is operating, the second solenoid valve 36 will be closed, but the electric motor 22 will stop driving at time t3, which is after the set time Tn has elapsed from time t1 when the second solenoid valve 36 starts closing. As a result, the hydraulic pressure of the brake device 13 will not decrease while the second solenoid valve 36 is closed. Note that the hydraulic pressure in the brake device 13 is approximately equal to the hydraulic pressure of the actuator 15.

[0052] The hydraulic brake system 10 according to this embodiment provides the following effects. (1) When the situation detection sensor detects a braking requirement, the controller 28 controls the actuator 15 to drive based on the detection by the situation detection sensor, and also controls the second solenoid valve 36 to open and the first solenoid valve 34 to close. As a result, hydraulic fluid is supplied from the actuator 15, and braking force is generated in the brake device 13. Therefore, when a braking requirement arises while the forklift is in motion, braking force can be automatically generated in the brake device 13. The situation detection sensor is at least one of the accelerator pedal sensor 94 and the obstacle sensor 95.

[0053] (2) When the actuator 15 is generating braking force in the brake device 13, if the limit switch 90 detects that the brake pedal 19 has been pressed, the controller 28 compares the first hydraulic pressure Pm, which is the hydraulic pressure of the master cylinder oil passage detected by the first hydraulic pressure sensor 91, with the second hydraulic pressure Pn, which is the hydraulic pressure of the actuator oil passage detected by the second hydraulic pressure sensor 92. When the first hydraulic pressure Pm is greater than or equal to the second hydraulic pressure Pn, the first solenoid valve 34 is opened and the second solenoid valve 36 is closed. Therefore, when the brake pedal 19 is pressed while braking is being performed by the actuator 15, the braking force of the brake device 13 can be switched from the hydraulic pressure of the actuator 15 to the hydraulic pressure of the master cylinder 12. Also, when the first hydraulic pressure Pm is less than the second hydraulic pressure Pn, the supply of hydraulic fluid from the actuator 15 to the brake device 13 continues, so that the actuator 15 can generate braking force in the brake device 13.

[0054] (3) When the brake pedal 19 is pressed and the hydraulic pressure in the master cylinder oil passage is greater than or equal to the hydraulic pressure in the actuator oil passage, the first solenoid valve 34 is opened and the second solenoid valve 36 is closed. The controller 28 controls the operation of the actuator 15 to stop after a preset time. Therefore, by preventing the second solenoid valve 36 from closing immediately when the brake pedal 19 is pressed, a temporary drop in the hydraulic pressure of the brake system 13 due to a drop in the hydraulic pressure of the actuator 15 can be prevented. As a result, the operator can obtain an appropriate brake feeling without any discomfort even when pressing the brake pedal 19 while braking by the actuator 15. In particular, the controller 28 is set to a preset time Tm that delays the stopping of the actuator 15's operation so that the actuator 15 continues to operate from the time t1 when the second solenoid valve 36 starts closing until the time t2 when it is completed. The preset time Tm in the controller 28 ensures that a drop in the hydraulic pressure of the actuator 15 is prevented between time t1 and time t2, and prevents the occurrence of an uncomfortable brake feeling due to a drop in hydraulic pressure.

[0055] (4) When the controller 28 commands the actuator 15 to stop operating while the actuator 15 is generating braking force for the brake device 13, it controls the actuator 15 to stop after the second solenoid valve 36 has closed. Since the controller 28 controls the actuator 15 to stop after the second solenoid valve 36 has closed, a decrease in braking pressure in the brake device 13 can be prevented compared to the case where the actuator 15 is stopped immediately. In particular, the controller 28 has a set time Tn for delayed stopping of the electric motor 22, so a decrease in braking pressure in the brake device 13 can be reliably prevented.

[0056] (5) 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, even if a power outage occurs while the forklift is in motion, braking force can be generated in the brake device 13 by operating the brake pedal 19.

[0057] 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.

[0058] ○ In the above embodiment, an accelerator pedal sensor and an obstacle sensor were used as examples of situation detection sensors to detect whether braking force is required when the forklift is in motion, but the system is not limited to these. The situation detection sensor may be, for example, a vibration detection sensor to detect abnormal vibrations of the vehicle body, or a tilt detection sensor to detect significant tilting of the vehicle body. The type and format of the sensor are not limited as long as it can perform the function of detecting whether braking force is required. In addition, for example, when a maximum speed is determined for each location in the factory, the system may communicate with an area sensor as a situation detection sensor to apply the brakes when the speed is exceeded. Alternatively, the system may detect the steering angle using a steering angle sensor as a situation detection sensor during sharp turns and apply the brakes to prevent rollover. ○ In the above embodiment, when hydraulic fluid is supplied from the actuator to the brake device and the brake pedal is depressed, the controller compares the hydraulic pressure in the master cylinder oil passage with the hydraulic pressure in the actuator oil passage, but it is not limited to this. For example, when hydraulic fluid is supplied from the actuator to the brake device and the brake pedal is depressed, the controller does not have to compare the hydraulic pressure in the master cylinder oil passage with the hydraulic pressure in the actuator oil passage. ○ In the above embodiment, when braking is performed by the actuator, the controller detects the depression of the brake pedal and controls the controller to open the first solenoid valve when the hydraulic pressure in the master cylinder oil passage is equal to or greater than the hydraulic pressure in the actuator oil passage. After the first solenoid valve is opened, the operation of the actuator is stopped after a preset time, but this is not limited to this. For example, if there is no decrease in the hydraulic pressure of the actuator, the controller may stop the operation of the actuator immediately after the first solenoid valve is opened. ○ In the above embodiment, the first solenoid valve is a normally open type solenoid valve and the second solenoid valve is a normally closed type solenoid valve, but the embodiment is not limited to this. For example, both the first and second solenoid valves may be normally closed type solenoid valves. ○ In the above embodiment, the second check valve is opened simultaneously with the closing of the first solenoid valve when the actuator is operated, but the embodiment is not limited to this. For example, the valve bore of the first solenoid valve may be set to a diameter that causes a pressure loss so that hydraulic pressure does not escape to the actuator before the first solenoid valve closes. In this case, the second check valve can be opened before the first solenoid valve closes when the actuator is operated, and hydraulic fluid can be supplied to the brake device. Similarly, the valve bore of the second solenoid valve may be set to a diameter that causes a pressure loss so that hydraulic pressure does not escape to the master cylinder before the second solenoid valve closes. In this case, when the master cylinder is operated, the first check valve can be opened before the opened second solenoid valve closes, and hydraulic fluid can be supplied to the brake device. ○ In the above embodiment, a hydraulic brake system for a forklift as an industrial vehicle was illustrated, 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]

[0059] 10. Hydraulic Brake System 11. Hydraulic oil tank 12 Master Cylinder 13 Brake system 14 Control valve 15 Actuators 19 Brake pedal 22 Electric motors 28 Controllers 33 1st aisle 34. First solenoid valve 35 2nd aisle 36. Second solenoid valve 70 First Bypass Passage 71 First check valve 80 Second Bypass Passage 81. Second check valve 90 Limit Switch 91. First hydraulic sensor 92. Second hydraulic sensor 93 Accelerator pedal 94 Accelerator pedal sensor 95 Obstacle Sensor Pm 1st Hydraulic Pn 2nd Hydraulic Tm, Tn setting time

Claims

1. The brake pedal and A master cylinder that 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, An actuator that outputs hydraulic pressure, A control valve interposed in the master cylinder oil passage, 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, A controller for controlling the first solenoid valve and the second solenoid valve, The controller is connected to a situation detection sensor that detects whether or not there is a situation requiring braking, The hydraulic brake system for an industrial vehicle is characterized in that the controller controls the actuator to drive based on the detection of the braking requirement by the situation detection sensor, and also controls the second solenoid valve to open and the first solenoid valve to close.

2. A brake pedal sensor that detects the depression of the brake pedal, A first hydraulic pressure sensor for detecting the hydraulic pressure in the master cylinder oil passage, A second hydraulic pressure sensor for detecting the hydraulic pressure in the actuator oil passage, It has, When hydraulic fluid is supplied from the actuator to the brake device, and the brake pedal sensor detects that the brake pedal has been pressed, The controller compares the hydraulic pressure of the master cylinder oil passage detected by the first hydraulic sensor with the hydraulic pressure of the actuator oil passage detected by the second hydraulic sensor. When the hydraulic pressure in the master cylinder oil passage is equal to or greater than the hydraulic pressure in the actuator oil passage, the first solenoid valve is controlled to open. The hydraulic brake system for an industrial vehicle according to claim 1, characterized in that when the hydraulic pressure in the master cylinder oil passage is less than the hydraulic pressure in the actuator oil passage, the supply of hydraulic fluid from the actuator to the brake device is continued.

3. The hydraulic brake system for an industrial vehicle according to claim 2, characterized in that the controller controls the operation of the actuator to stop after a preset time period has elapsed since the first solenoid valve was opened.

4. The hydraulic brake system for an industrial vehicle according to claim 1 or 2, characterized in that when the controller commands the actuator to stop operating while the actuator is generating braking force for the brake device, it controls the actuator to stop after the second solenoid valve is closed.

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