Hydraulic brake systems for industrial vehicles

Abstract

The objective is to provide a hydraulic brake system for industrial vehicles that can properly operate the braking system regardless of whether braking is performed by the master cylinder or the actuator. Furthermore, the objective is to provide a hydraulic brake system for industrial vehicles that can achieve both improved braking system responsiveness and miniaturization of the control valve. [Solution] The controller 28 controls the first solenoid valve 34 to open the master cylinder oil passage when braking by the master cylinder 12, and controls the second solenoid valve 36 to close the actuator oil passage. When braking by the actuator 15, the controller 28 controls the second solenoid valve 36 to open the actuator oil passage, and controls the first solenoid valve 34 to close the master cylinder oil passage. When releasing the hydraulic pressure of the brake device 13, the controller 28 controls the third solenoid valve 75 to open the return oil passage.

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 is provided with 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 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 the braking force by operating the brake pedal to the brake device 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 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 switched to manned or automated driving. Furthermore, the object of this invention is to provide a hydraulic brake system for industrial vehicles that can achieve both improved responsiveness of the brake device and miniaturization of the control valve. [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 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 hydraulic fluid tank for storing hydraulic fluid, 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 return oil passage for returning hydraulic fluid from the brake device to the hydraulic fluid tank, a first solenoid valve provided in the control valve for opening and closing the master cylinder oil passage, and a control valve The hydraulic fluid tank is connected to the master cylinder oil passage and the actuator oil passage, and the controller controls the first solenoid valve, the second solenoid valve and the third solenoid valve to open and close the actuator oil passage when braking by the master cylinder, 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 when braking by the actuator, the second solenoid valve to open the actuator oil passage and the first solenoid valve to close the master cylinder oil passage when releasing the hydraulic pressure of the brake device, and controls the third solenoid valve to open the return oil passage.

[0007] This invention includes a third solenoid valve that opens and closes a return oil passage. When the hydraulic pressure of the brake system is released, the return oil passage is opened by the third solenoid valve, which reduces the force required to open the first solenoid valve when returning hydraulic fluid to the hydraulic fluid tank through the master cylinder, and also reduces the force required to open the second solenoid valve when returning hydraulic fluid to the hydraulic fluid tank through the actuator. Therefore, even if the valve holes of the first and second solenoid valves are enlarged, the force required to open the valve holes of the first and second solenoid valves can be reduced, and the size of the first and second solenoid valves can be reduced. Furthermore, when the hydraulic pressure of the brake system is released, the return oil passage is opened by the third solenoid valve, which, combined with the return of hydraulic fluid from the brake system to the hydraulic fluid tank through the control valve, allows the hydraulic fluid to be quickly returned to the hydraulic fluid tank through the return passage. In other words, it is possible to improve the responsiveness of the brake system by increasing the diameter of the valve holes of the first and second solenoid valves, and to miniaturize the control valve.

[0008] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the control valve may be provided with a bypass passage that bypasses the first solenoid valve in the master cylinder oil passage, and a fourth solenoid valve provided with the control valve that opens and closes the bypass passage under the control of the controller, wherein the controller may be configured to control the fourth solenoid valve to close the bypass passage when braking is performed by the actuator. In this case, the fourth solenoid valve opens and closes a bypass passage that bypasses the first solenoid valve in the master cylinder oil passage, but the controller controls the fourth solenoid valve to close the bypass passage when braking in automatic driving. Even if the first, second, and third solenoid valves fail to open due to malfunction or other reasons when the braking system is braking, hydraulic fluid can still be passed to the master cylinder through the fourth solenoid valve, and the hydraulic pressure (braking pressure) of the braking system can be released.

[0009] Furthermore, in the hydraulic brake system of the industrial vehicle described above, the fourth solenoid valve may be configured as a normally open type solenoid valve. In this case, since the fourth solenoid valve is a normally open type solenoid valve, even if a power outage occurs during braking of the brake system and the first, second, and third solenoid valves become unable to open, hydraulic fluid can still be passed through the fourth solenoid valve towards the master cylinder, and the hydraulic pressure (braking pressure) of the brake system can be released.

[0010] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the first solenoid valve may have a first valve hole and a first valve body for opening and closing the first valve hole, the second solenoid valve may have a second valve hole and a second valve body for opening and closing the second valve hole, and the third solenoid valve may have a third valve hole and a third valve body for opening and closing the third valve hole, with the first and second valve holes having a larger diameter than the third valve hole. In this case, since the first and second valve holes are set to have larger diameters than the third valve hole, a larger amount of hydraulic fluid can be passed through by opening the first or second solenoid valve compared to the third solenoid valve.

[0011] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the diameters of the first valve hole and the second valve hole may be configured to be 1.5 to 90 times the diameter of the third valve hole. In this case, since the diameters of the first and second valve holes are 1.5 to 90 times that of the third valve hole, a larger volume of hydraulic fluid can be passed through by opening the first or second solenoid valve compared to the third solenoid valve. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a hydraulic brake system for industrial vehicles that can properly operate the brake device regardless of whether braking is performed by a master cylinder or an actuator. Furthermore, it is possible to provide a hydraulic brake system for industrial vehicles that can achieve both improved responsiveness of the brake device and miniaturization of the control valve. [Brief explanation of the drawing]

[0013] [Figure 1]This is a schematic diagram showing a hydraulic brake system for a forklift according to 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 third solenoid valve, and (b) is a schematic diagram of the fourth solenoid valve. [Figure 4] This is a schematic diagram illustrating a hydraulic brake system in which braking force is generated by the master cylinder. [Figure 5] This is a schematic diagram illustrating a hydraulic brake system that explains the state in which the braking force from the master cylinder is released. [Figure 6] This is a schematic diagram illustrating a hydraulic brake system in which braking force is generated by an actuator. [Figure 7] This is a schematic diagram illustrating a hydraulic brake system that explains the state in which the braking force is released by the actuator. [Figure 8] This is a schematic diagram illustrating a hydraulic brake system that releases the hydraulic pressure (braking pressure) of the brake device in the event of a power failure. [Figure 9] This is a schematic diagram showing a control valve related to a modified example. [Modes for carrying out the invention]

[0014] (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.

[0015] As shown in FIG. 1, a hydraulic brake system (hereinafter referred to as "hydraulic brake system") 10 of a 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.

[0016] 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 forkl operation is performed on the forklift, the master cylinder 12 outputs hydraulic pressure to the brake device 13 via the control valve 14 by an operator's operation of the brake pedal 19, and generates a braking force in the brake device 13.

[0017] The brake device 13 generates a braking force to stop 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 a front axle provided on the vehicle body, but may also be a drum brake or a disc brake.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] The first solenoid valve 34 is a normally closed solenoid valve that opens the first passage 33 when energized and closes 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 and a valve body 40. The valve housing 39 and the valve body 40 form a valve chamber 41. A through hole 42 is formed in the upper part of the valve housing 39, which communicates with the passage section 33B of the first passage 33.

[0024] A through hole 43 is formed in the center of the valve body 40 so as to communicate with the valve chamber 41. A valve hole 44, which serves as the first valve hole, is formed on the valve chamber 41 side of the through hole 43. The valve hole 44 is a tapered surface whose inner diameter widens from the through hole 43 towards the opening. A through hole 45 is formed in the valve body 40 so as to communicate the through hole 43 with the passage portion 33A. The valve chamber 41, through hole 43, valve hole 44, and through hole 45 constitute a part of the first passage 33. In addition, a through hole 46 is formed in the valve body 40 so as to penetrate from the through hole 43 to the outer circumference at a different position from the through hole 45.

[0025] The solenoid section 38 comprises a fixed core 47, a movable core 48, and an electromagnetic coil 49. A rod insertion hole 51 is formed in the center of the fixed core 47 through which a rod 50 is inserted. One end (lower) of the rod 50 is connected to the movable core 48. The movable core 48 is movable in the axial direction of the rod 50. The electromagnetic coil 49 is provided so as to surround the fixed core 47 and the movable core 48. When the electromagnetic coil 49 is energized, the movable core 48 approaches the fixed core 47, and the rod 50 rises. The other (upper) end of the rod 50 is provided with a spherical valve body 52, which serves as a first valve body capable of closing the valve hole 44. Note that the valve body 52 is not limited to a spherical shape and may be a conical valve body. A coil spring 53 is interposed between the valve housing 39 and the valve body 52 in the valve chamber 41 as a biasing member. The coil spring 53 imparts a biasing force (spring force) to the valve body 52 in the direction of closing the valve hole 44. The spring force of the coil spring 53 is determined by the product of the spring constant of the coil spring 53 and the displacement of the coil spring 53 from its natural length.

[0026] The second solenoid valve 36 is a normally closed solenoid valve that opens the second passage 35 when energized and closes the second passage 35 when de-energized. As shown in Figure 2(b), the second solenoid valve 36 comprises a valve section 57 embedded in the lower part of the control valve 14 and a solenoid section 58 connected to the valve section 57 and protruding from the lower part of the control valve 14. The valve section 57 comprises a cylindrical valve housing 59 and a valve body 60. The valve housing 59 and the valve body 60 form a valve chamber 61. A through hole 62 is formed in the upper part of the valve housing 59, which communicates with the passage section 35B of the second passage 35.

[0027] A through-hole 63 is formed in the center of the valve body 60 so as to communicate with the valve chamber 61. A valve hole 64, which serves as a second valve hole, is formed on the valve chamber 61 side of the through-hole 63. The valve hole 64 has a tapered surface whose inner diameter widens from the through-hole 63 towards the opening. A through-hole 65 is formed in the valve body 60 so as to communicate the through-hole 63 with the passage portion 35A. The valve chamber 61, through-hole 63, valve hole 64, and through-hole 65 constitute a part of the second passage 35.

[0028] The solenoid section 58 comprises a fixed core 67, a movable core 68, and an electromagnetic coil 69. A rod insertion hole 71 is formed in the center of the fixed core 67 through which a rod 70 is inserted. One end (lower) of the rod 70 is connected to the movable core 68. The movable core 68 is movable in the axial direction of the rod 70. The electromagnetic coil 69 is provided so as to surround the fixed core 67 and the movable core 68. When the electromagnetic coil 69 is energized, the movable core 68 approaches the fixed core 67, and the rod 70 rises. The other (upper) end of the rod 70 is provided with a spherical valve body 72, which serves as a second valve body capable of closing the valve hole 64. The valve body 72 is not limited to a spherical shape; it may also be a conical valve body. A coil spring 73 is interposed between the valve housing 59 and the valve body 72 in the valve chamber 61 as a biasing member. The coil spring 73 imparts a biasing force (spring force) to the valve body 72 in the direction of closing the valve hole 64. The spring force of the coil spring 73 is determined by the product of the spring constant of the coil spring 73 and the displacement of the coil spring 73 from its natural length.

[0029] Incidentally, in addition to the first solenoid valve 34 and the second solenoid valve 36, the hydraulic brake system 10 of this embodiment also has a third solenoid valve 75 and a fourth solenoid valve 76. Furthermore, the hydraulic brake system 10 has a return oil passage for returning hydraulic fluid from the brake device 13 to the hydraulic fluid tank 11. The return oil passage includes a pipe 77 connecting the brake device 13 and the third solenoid valve 75, and a pipe 78 connecting the third solenoid valve 75 and the pipe 20 (see Figure 1).

[0030] The third solenoid valve 75 is a normally closed solenoid valve that opens the return oil passage when energized and closes when de-energized, and is provided independently of the control valve 14 (see Figure 1). As shown in Figure 3(a), the third solenoid valve 75 comprises a valve section 81 and a solenoid section 82 connected to the valve section 81. The valve section 81 comprises a cylindrical valve housing 83 and a valve body 84, and the valve housing 83 and valve body 84 form a valve chamber 85. A through hole 86 is formed in the upper part of the valve housing 83, which communicates with the return oil passage piping 78.

[0031] A through-hole 87 is formed in the center of the valve body 84 so as to communicate with the valve chamber 85. A valve hole 88, which serves as a third valve hole, is formed on the valve chamber 85 side of the through-hole 87. The valve hole 88 is a tapered surface whose inner diameter expands from the through-hole 87 towards the opening. The diameter of the valve hole 88 of the third solenoid valve 75 is set to be smaller than the valve hole 44 of the first solenoid valve 34 and the valve hole 64 of the second solenoid valve 36. Specifically, it is about 1 / 3 of the diameter of the valve holes 44 and 64, but it is acceptable if it is 2 / 3 to 1 / 90 of the diameter of the valve holes 44 and 64. In other words, the diameter of the valve holes 44 and 64 is about 3 times the diameter of the valve hole 88, but it is acceptable if it is 1.5 to 90 times. Preferably, the diameter of the valve holes 44 and 64 is 3 to 15 times the diameter of the valve hole 88. The valve body 84 has a through hole 89 that connects the through hole 87 to the piping 77. The valve chamber 85, through hole 87, valve hole 88, and through hole 89 constitute part of the return oil passage.

[0032] The solenoid section 82 comprises a fixed core 90, a movable core 91, and an electromagnetic coil 92. A rod insertion hole 94 is formed in the center of the fixed core 90 through which a rod 93 is inserted. One end (lower) of the rod 93 is connected to the movable core 91. The movable core 91 is movable in the axial direction of the rod 93. The electromagnetic coil 92 is provided so as to surround the fixed core 90 and the movable core 91. When the electromagnetic coil 92 is energized, the movable core 91 approaches the fixed core 90, and the rod 93 rises. The other (upper) end of the rod 93 is provided with a valve body 95, which serves as a third valve body capable of closing the valve hole 88. The valve body 95 is spherical. Note that the valve body 95 is not limited to spherical; it may also be conical. The valve chamber 85 houses a coil spring 96, which acts as a biasing member that applies a biasing force (spring force) to the valve body 95. The coil spring 96 applies a biasing force (spring force) to the valve body 95 in the direction of closing the valve hole 88. The spring force of the coil spring 96 is determined by the product of the spring constant of the coil spring 96 and the displacement of the coil spring 96 from its natural length.

[0033] The hydraulic brake system 10 has a third solenoid valve 75, which allows the opening hydraulic pressure required to open the first solenoid valve 34 to be reduced even if the diameter of the valve bore 44 of the first solenoid valve 34 is increased. The opening hydraulic pressure required to open the first solenoid valve 34 when no braking hydraulic pressure is generated in the brake device 13 can be calculated by dividing the spring force of the coil spring 53 by the area of ​​the valve bore 44. The opening hydraulic pressure required to open the first solenoid valve 34 when braking hydraulic pressure is generated in the brake device 13 is the hydraulic pressure obtained by dividing the spring force of the coil spring 53 by the area of ​​the valve bore 44 and adding the hydraulic pressure of the brake device 13. The third solenoid valve 75 releases the braking pressure of the brake device 13 by opening the return passage, thereby reducing the hydraulic pressure received by the valve body 52. ​​As a result, the opening hydraulic pressure is reduced, and the thrust of the rod 50 that pushes up the valve body 52 can be reduced, allowing the solenoid portion 38 of the first solenoid valve 34 to be reduced. The thrust of the rod 50 is proportional to the number of turns of the electromagnetic coil 49. The solenoid section 58 of the second solenoid valve 36 can also be made smaller, similar to the first solenoid valve 34. Both the first solenoid valve 34 and the second solenoid valve 36 are configured to reduce the opening hydraulic pressure by combining a large bore diameter with a small spring force.

[0034] Next, the fourth solenoid valve 76 will be described. The control valve 14 has a bypass passage 97 connected to the passage section 33B via the through hole 46 of the first solenoid valve 34, and a fourth solenoid valve 76 interposed in the bypass passage 97. The fourth solenoid valve 76 is a normally open type solenoid valve that closes the bypass passage 97 when energized and is normally open when de-energized, opening the bypass passage 97.

[0035] As shown in Figure 3(b), the fourth solenoid valve 76 comprises a valve section 98 embedded in the lower part of the control valve 14, and a solenoid section 99 connected to the valve section 98 and protruding from the lower part of the control valve 14. The valve section 98 comprises a cylindrical valve housing 100. A valve chamber 101 is formed inside the valve housing 100. A valve hole 102, which serves as the fourth valve hole, is formed in the upper part of the valve housing 100, and a through hole 103 is formed on the side of the valve housing 100 that communicates with the first solenoid valve 34 side of the bypass passage 97. The valve hole 102 communicates with the passage section 33B side of the bypass passage 97. The valve hole 102 is smaller in diameter than the valve hole 44 of the first solenoid valve 34 and the valve hole 64 of the second solenoid valve 36, similar to the valve hole 88 of the third solenoid valve 75. In this embodiment, the diameter of the valve bore 102 is the same as the diameter of the valve bore 88, but it does not have to be the same as the diameter of the valve bore 88. The valve chamber 101, valve bore 102, and through hole 103 constitute a part of the bypass passage 97.

[0036] The solenoid section 99 comprises a fixed core 104, a movable core 105, and an electromagnetic coil 106. A rod insertion hole 108 is formed in the center of the fixed core 104 through which a rod 107 is inserted. One end (lower) of the rod 107 is connected to the movable core 105. The movable core 105 is movable in the axial direction of the rod 107. The electromagnetic coil 106 is provided so as to surround the fixed core 104 and the movable core 105. When the electromagnetic coil 106 is energized, the movable core 105 approaches the fixed core 104, and the rod 107 rises. The other (upper) end of the rod 107 is provided with a valve body 109, which serves as a fourth valve body capable of closing the valve hole 102. The valve body 109 is a conical valve body whose outer diameter decreases towards the tip. The rod 107 is provided with a spring receiver 110. In the valve chamber 101, a coil spring 111 is interposed between the spring receiver 110 and the valve housing 100 as a biasing member. The coil spring 111 imparts a biasing force (spring force) to the rod 107 in the direction of opening the valve hole 102. The spring force of the coil spring 111 is determined by the product of the spring constant of the coil spring 111 and the displacement of the coil spring 111 from its natural length.

[0037] In this embodiment, for example, as shown in Table 1, if the diameters of the valve bore 44 of the first solenoid valve 34 and the valve bore 64 of the second solenoid valve 36 are 3.0 mm, then with the installation of the third solenoid valve 75, the hydraulic pressure (braking pressure) received by the valve body 52 becomes 0.2 MPa, and the required thrust of the rod 50 becomes 1.4 N. In Comparative Example 1, which does not provide the third solenoid valve 75, even if the diameters of the valve bore of the first and second solenoid valves are 1.1 mm, the hydraulic pressure (braking pressure) received by the valve body becomes 5.0 MPa, and the required thrust of the rod becomes 4.7 N. In other words, Comparative Example 1 requires more than 3.36 times the thrust. Furthermore, in Comparative Example 2, which does not provide the third solenoid valve 75 and uses the same valve bore diameter of 3.0 mm as in this embodiment, the required thrust of the rod for the first and second solenoid valves becomes 35.3 N, which is more than 25 times that of this embodiment. Therefore, even if the diameters of the valve bore 44 of the first solenoid valve 34 and the valve bore 64 of the second solenoid valve 36 are, for example, approximately three times the diameter of the valve bore of the third solenoid valve 75, the thrust required by the first solenoid valve 34 and the second solenoid valve 36 can be reduced as shown in Table 1. Note that the values ​​for hydraulic pressure (braking pressure) and required thrust in Table 1 may vary slightly depending on measurement errors and measurement conditions. In Table 1, the diameters of the valve bores 44 and 64 were set to 2.27 times the diameter of the valve bore of Comparative Example 1, but the diameters of the valve bore 44 of the first solenoid valve 34 and the valve bore 64 of the second solenoid valve 36 should be 1.5 to 90 times the diameter of the valve bore 88 of the third solenoid valve 75, preferably 3 to 15 times the diameter.

[0038] [Table 1]

[0039] Furthermore, as a comparative example separate from Comparative Examples 1 and 2 in Table 1, for example, the diameter of the common valve bore for maintaining and releasing hydraulic pressure during braking is set to 1.1 mm, the hydraulic pressure received by the valve body is set to 10 MPa, and the thrust of the rod required to release the hydraulic pressure during braking is set to 9.5 N. Compared to this other comparative example, by setting the diameter of the valve bore 88 of the third solenoid valve 75 in this embodiment to 0.1 to 0.6 mm, the diameter of the valve bore 88 becomes 9 to 55% of the diameter of the valve bore in the other comparative example. As a result, the thrust of the rod 93 of the third solenoid valve 75 required to release the hydraulic pressure during braking can be reduced from 9.5 N in the other comparative example to 0.1 to 2.8 N, making it possible to miniaturize the third solenoid valve 75.

[0040] In this case, the diameters of the valve holes 44 of the first solenoid valve 34 and 64 of the second solenoid valve 36 can be increased to 2.0 to 3.0 mm, and the diameters of the valve holes 44 and 64 can be 180 to 270% of the diameter of the valve holes in another comparative example. When the hydraulic pressure during braking is released by the third solenoid valve 75, it drops from 10 MPa to 0.5 MPa, so the thrust required by the rods 50 and 70 can be reduced from 9.5 N in another comparative example to 1.6 to 3.5 N. In this case, the diameter of the valve hole 102 of the fourth solenoid valve 76 for power failure can be 0.6 to 0.8 mm, and the diameter of the valve hole 102 can be 55 to 73% of the diameter of the valve hole in comparative example 1. The thrust of the rod 107 required to maintain the hydraulic pressure during braking can be reduced from 9.5 N in another comparative example to 2.8 to 5.0 N, and the fourth solenoid valve 76 can be made more compact.

[0041] In the hydraulic brake system 10 of this embodiment, a first hydraulic pressure sensor 112 is provided to detect the hydraulic pressure of the piping 17. The first hydraulic pressure sensor 112 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 113 to detect the hydraulic pressure of the piping 21. The second hydraulic pressure sensor 113 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 feeds back the hydraulic pressure of the piping 21 detected by the second hydraulic pressure sensor 113 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. Alternatively, instead of the first hydraulic pressure sensor 112, a stroke sensor that detects the amount the brake pedal 19 is pressed and transmits a detection signal to the controller 28 may be provided on the brake pedal 19.

[0042] 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.

[0043] 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 112. 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 and the second solenoid valve 36 are normally closed solenoid valves, the controller 28 commands the first solenoid valve 34 to open. On the other hand, the controller 28 controls the second solenoid valve 36 and the third solenoid valve 75 to close. The fourth solenoid valve 76 is a normally open solenoid valve with a small diameter valve bore 102. However, even if the supply of hydraulic fluid to the brake device 13 by the fourth solenoid valve 76 is delayed, the enlarged valve body 52 opens the valve bore 44, allowing the hydraulic fluid to be supplied to the brake device 13 immediately. As a result, a braking delay in the brake device 13 is prevented.

[0044] As shown in Figure 4, when the first solenoid valve 34 is opened, the hydraulic fluid discharged from the master cylinder 12 is supplied to the brake device 13 through piping 17, the first passage 33, and piping 18. In addition, hydraulic fluid is supplied to the brake device 13 through the bypass passage 97 and the fourth solenoid valve 76. 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. When maintaining the hydraulic pressure (braking pressure) of the brake device 13, the controller 28 controls the first solenoid valve 34 and the fourth solenoid valve 76 to close.

[0045] When the braking pressure of the brake device 13 is released by releasing the brake pedal 19, the controller 28 controls the opening of the first solenoid valve 34, the third solenoid valve 75, and the fourth solenoid valve 76, as shown in Figure 5. At this time, when the third solenoid valve 75 is opened, the hydraulic fluid of the brake device 13 is recovered into the hydraulic fluid tank 11 via the third solenoid valve 75 and the return oil passage. As a result, the hydraulic pressure in the valve chamber 41 acting on the valve body 52 of the first solenoid valve 34 decreases, so less force is required to open the first solenoid valve 34. When the first solenoid valve 34 is opened, the hydraulic fluid returns to the master cylinder 12 via the first solenoid valve 34 and the master cylinder oil passage, and any excess hydraulic fluid is recovered from the master cylinder 12 into the hydraulic fluid tank 11. Furthermore, when the fourth solenoid valve 76 is opened, the hydraulic fluid flows to the master cylinder 12 via the bypass passage 97. When the braking pressure of the brake device 13 is released in this manner, the hydraulic fluid in the brake device 13 is quickly recovered into the hydraulic fluid tank 11, resulting in high responsiveness to the release of the braking pressure.

[0046] 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, hydraulic fluid should be discharged according to the amount of actuator 15 is activated, and braking force should be generated in the brake device 13. Therefore, when braking under autonomous driving conditions, the second solenoid valve 36 should open the second passage 35, the first solenoid valve 34 should close the first passage 33, and the fourth solenoid valve 76 should close the bypass passage 97.

[0047] When braking in autonomous driving, the controller 28 issues a drive command to the actuator 15, and simultaneously issues an open command to the second solenoid valve 36 and a close command to the fourth solenoid valve 76. 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 sensor 113. The controller 28 feeds back the hydraulic pressure of the piping 21 detected by the second hydraulic sensor 113 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 maintains the closed position of the first solenoid valve 34, closes the fourth solenoid valve 76, and energizes the second solenoid valve 36 to open it.

[0048] As shown in Figure 6, when the second solenoid valve 36 is opened and the fourth solenoid valve 76 is closed, the hydraulic fluid discharged from the actuator 15 is supplied to the brake device 13 through the piping 21, the second passage 35, and the piping 21. The enlarged valve body 72 opens the valve hole 64, allowing the hydraulic fluid to be supplied to the brake device 13 immediately. As a result, a braking delay in the brake device 13 is prevented. The hatching shown in Figure 6 indicates the hydraulic fluid in the control valve 14. In the brake device 13, a 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. When maintaining the braking pressure of the brake device 13, the controller 28 controls the second solenoid valve 36 to close.

[0049] When releasing the braking pressure of the brake device 13, the controller 28 controls the second solenoid valve 36 and the third solenoid valve 75 to open, as shown in Figure 7. When the third solenoid valve 75 opens, the hydraulic fluid of the brake device 13 is recovered into the hydraulic fluid tank 11 via the third solenoid valve 75 and the return oil passage. As a result, the hydraulic pressure in the valve chamber 61 acting on the valve body 72 of the second solenoid valve 36 decreases, so less force is required to open the second solenoid valve 36. When the second solenoid valve 36 opens, the hydraulic fluid returns to the actuator 15 via the second solenoid valve 36 and the actuator oil passage, and any excess hydraulic fluid is recovered from the actuator 15 into the hydraulic fluid tank 11. In this way, when the braking pressure of the brake device 13 is released, the hydraulic fluid in the brake device 13 is quickly recovered into the hydraulic fluid tank 11, resulting in high responsiveness to the release of the braking pressure. The hatching shown in Figure 7 indicates the hydraulic fluid in the control valve 14.

[0050] Incidentally, in the hydraulic brake system 10, even if a power outage occurs while the braking pressure of the brake device 13 is being maintained, it is possible to release the braking pressure. For example, the braking pressure of the brake device 13 is maintained by first generating the braking pressure of the brake device 13 with the master cylinder 12 and then closing the first solenoid valve 34 and the fourth solenoid valve 76. If a power outage occurs in this state, the first solenoid valve 34 and the third solenoid valve 75 cannot be opened, but the fourth solenoid valve 76 becomes de-energized and opens. As shown in Figure 8, when the fourth solenoid valve 76 opens, the hydraulic fluid of the brake device 13 returns to the master cylinder 12 through the bypass passage 97, the fourth solenoid valve 76, and the piping 17, and any excess hydraulic fluid is recovered from the master cylinder 12 into the hydraulic fluid tank 11.

[0051] On the other hand, even if a power outage occurs while the braking pressure of the brake device 13 is maintained by closing the second solenoid valve 36 and the fourth solenoid valve 76 after the actuator 15 has generated the braking pressure of the brake device 13, the fourth solenoid valve 76 will be de-energized and open. As shown in Figure 8, when the fourth solenoid valve 76 opens, the hydraulic fluid of the brake device 13 returns to the master cylinder 12 through the bypass passage 97, the fourth solenoid valve 76, and the piping 17, and any excess hydraulic fluid is recovered from the master cylinder 12 into the hydraulic fluid tank 11. The hatching shown in Figure 8 indicates the hydraulic fluid inside the control valve 14.

[0052] The hydraulic brake system 10 according to this embodiment provides the following effects. (1) The hydraulic brake system 10 has a third solenoid valve 75 that is provided separately from the control valve 14 and opens and closes the return oil passage. When the hydraulic pressure of the brake device 13 is released, the return oil passage is opened by the third solenoid valve 75. As a result, the force required to open the first solenoid valve 34 when returning hydraulic fluid to the hydraulic fluid tank 11 through the master cylinder 12 can be reduced, and the force required to open the second solenoid valve 36 when returning hydraulic fluid to the hydraulic fluid tank 11 through the actuator 15 can also be reduced. As a result, even if the valve holes of the first solenoid valve 34 and the second solenoid valve 36 are enlarged, the force required to open the valve holes of the first solenoid valve 34 and the second solenoid valve 36 can be reduced, and the size of the first solenoid valve 34 and the second solenoid valve 36 can be reduced. Therefore, in conjunction with the return of hydraulic fluid from the brake device 13 to the hydraulic fluid tank 11 through the control valve 14, the hydraulic fluid can be quickly returned to the hydraulic fluid tank 11 through the return passage. In other words, the responsiveness of the brake device 13 can be improved by increasing the diameter of the valve holes of the first solenoid valve 34 and the second solenoid valve 36, and the control valve 14 can be made smaller.

[0053] (2) The fourth solenoid valve 76 opens and closes a bypass passage 97 that bypasses the first solenoid valve 34 in the master cylinder oil passage, but the controller 28 controls the fourth solenoid valve 76 to close the bypass passage 97 when braking in automatic operation. Even if the first solenoid valve 34, the second solenoid valve 36, and the third solenoid valve 75 fail to open due to malfunction or the like when the brake device 13 is braking, hydraulic fluid can still be passed through the fourth solenoid valve 76 toward the master cylinder 12, and the hydraulic pressure (braking pressure) of the brake device 13 can be released.

[0054] (3) The fourth solenoid valve 76 is a normally open type solenoid valve. Even if a power outage occurs during braking of the brake device 13 and the first solenoid valve 34, the second solenoid valve 36, and the third solenoid valve 75 become unable to open, the fourth solenoid valve 76 will open. As a result, hydraulic fluid can be passed through the fourth solenoid valve 76 toward the master cylinder 12, and the braking pressure of the brake device 13 can be released.

[0055] (4) The first solenoid valve 34 has a valve hole 44 and a valve body 52 that opens and closes the valve hole 44, and the second solenoid valve 36 has a valve hole 64 and a valve body 72 that opens and closes the valve hole 64. The third solenoid valve 75 has a valve hole 88 and a valve body 95 that opens and closes the valve hole 88. The valve holes 44 and 64 are set to have a larger diameter than the valve hole 88. For this reason, the first solenoid valve 34 and the second solenoid valve 36 can pass a larger amount of hydraulic fluid when the first solenoid valve 34 or the second solenoid valve 36 is opened compared to the third solenoid valve 75.

[0056] (5) Since the diameters of valve holes 44 and 64 are 1.5 to 90 times the diameter of valve hole 88, the first solenoid valve 34 and the second solenoid valve 36 can pass a larger amount of hydraulic fluid when either the first solenoid valve 34 or the second solenoid valve 36 is opened compared to the third solenoid valve 75. Preferably, the diameters of valve holes 44 and 64 are 3 to 15 times the diameter of valve hole 88, in which case practical effects such as improved ease of manufacture of each solenoid valve become significant.

[0057] (6) Simply increasing the diameter of the valve bore of the first solenoid valve 34 would increase the flow rate of the hydraulic fluid, but the hydraulic pressure that the valve body 52 receives from the brake device 13 would increase. Consequently, the force pushing up the valve body 52 would increase, leading to the problem that it would be unavoidable to enlarge the solenoid unit 38. On the other hand, it is possible to miniaturize the solenoid unit 38 by reducing the diameter of the valve bore of the first solenoid valve 34, but in that case, the valve bore 44 would become smaller, resulting in a decrease in the flow rate of the hydraulic fluid, which would delay the supply of hydraulic fluid to the brake device 13 and reduce the responsiveness of the brake device 13. However, in this embodiment, the presence of the third solenoid valve 75 allows for a reduction in the force required to open the valve bore 44 of the first solenoid valve 34, even if the valve bore 44 of the first solenoid valve 34 is enlarged. As a result, the thrust of the rod 50 that pushes up the valve body 52 can be reduced compared to the size of the valve bore 44, and the solenoid unit 38 of the first solenoid valve 34 can be miniaturized. Furthermore, the solenoid section 58 of the second solenoid valve 36 can also be miniaturized in the same way as the first solenoid valve 34. Therefore, when braking begins, the valve hole 44 (64) is immediately opened, and hydraulic fluid is quickly supplied to the brake device 13, ensuring the hydraulic pressure necessary for braking. In addition, the hydraulic pressure of the brake device 13 can be increased or decreased by maintaining the conductivity of the first solenoid valve 34 (second solenoid valve 36). Also, when returning the hydraulic fluid of the brake device 13 to the master cylinder 12, the return of the hydraulic fluid is slow due to the small diameter valve hole 102 of the fourth solenoid valve 76, but by releasing the hydraulic pressure of the brake device 13 with the third solenoid valve 75, the large diameter valve hole 44 (64) is opened, and the hydraulic fluid can be quickly returned to the master cylinder 12.

[0058] (modified version) Next, a modified control valve 141 will be described. In the modified example shown in Figure 9, the master cylinder port 30 and actuator port 32 of the control valve 141 are located on the side of the control valve 141 instead of the top. This modified example provides the same effects as the embodiment. Furthermore, by providing the master cylinder port 30 and actuator port 32 on the side of the control valve 141, the number of passages in the control valve 14 can be reduced, making the control valve 141 more compact.

[0059] 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.

[0060] ○ In the above embodiments (including modified examples), a fourth solenoid valve and a bypass passage are provided, but the system is not limited thereto. The hydraulic brake system does not necessarily have a fourth solenoid valve and a bypass passage, and in this case as well, the responsiveness of the brake device can be improved by increasing the diameter of the valve bores of the first and second solenoid valves, and the control valve can be made smaller. ○ In the above embodiments (including modified examples), the fourth solenoid valve is a normally open type solenoid valve, but the invention is not limited to this. The fourth solenoid valve may be, for example, a normally closed type solenoid valve, and the third solenoid valve may be opened by energizing when the hydraulic fluid is returned from the brake device to the master cylinder. ○ In the above embodiments (including modified versions), the third solenoid valve is provided separately from the control valve, but the invention is not limited to this. For example, the third solenoid valve may be provided in the control valve. In this case as well, the first and second solenoid valves can be miniaturized. ○ In the above embodiments (including modified examples), when releasing the hydraulic pressure (braking pressure) of the brake system, the opening of the first or second solenoid valve and the opening of the third solenoid valve were performed simultaneously, but this is not limited to this. For example, the third solenoid valve may be opened first, and then the first or second solenoid valve may be opened a short time later. ○ In the above embodiments (including modifications), 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. ○ The above embodiments (including modifications) illustrate a hydraulic brake system for a forklift as an industrial vehicle, but are 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]

[0061] 10. Hydraulic Brake System 11. Hydraulic oil tank 12 Master Cylinder 13 Brake system 14, 141 Control valve 15 Actuators 19 Brake pedal 28 Controllers 30 Master Cylinder Ports 31 Brake Ports 32 actuator ports 33 1st aisle 34. First solenoid valve 35 2nd aisle 36. Second solenoid valve 44 Valve opening (first valve opening) 52 Valve body (first valve body) 64 Valve opening (second valve opening) 72 Valve body (second valve body) 75. Third solenoid valve 76. Fourth Solenoid Valve 77 Piping (return oil passage) 78 Piping (return oil passage) 88 Valve opening (3rd valve opening) 95 Valve body (third valve body) 97 Bypass Passage 102 Valve opening (4th valve opening) 109 Valve body (4th valve body)

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 hydraulic oil tank for storing hydraulic fluid, 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 return oil passage for returning hydraulic fluid from the brake device to the hydraulic fluid tank, 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 third solenoid valve that opens and closes the aforementioned return oil passage, The system includes a controller that controls the first solenoid valve, the second solenoid valve, and the third solenoid valve, The hydraulic fluid tank is connected to the master cylinder oil passage and the actuator oil passage, The aforementioned controller, The first solenoid valve is controlled to open the master cylinder oil passage when braking is performed by the master cylinder, and the second solenoid valve is controlled to close the actuator oil passage. The second solenoid valve is controlled to open the actuator oil passage when braking is performed by the actuator, and the first solenoid valve is controlled to close the master cylinder oil passage. A hydraulic brake system for an industrial vehicle, characterized in that when the hydraulic pressure of the brake device is released, the third solenoid valve is controlled to open the return oil passage.

2. The control valve is provided with a bypass passage that bypasses the first solenoid valve in the master cylinder oil passage, The control valve is provided with a fourth solenoid valve that opens and closes the bypass passage under the control of the controller, The hydraulic brake system for an industrial vehicle according to claim 1, characterized in that the controller controls the fourth solenoid valve to close the bypass passage when braking is performed by the actuator.

3. The hydraulic brake system for an industrial vehicle according to claim 2, characterized in that the fourth solenoid valve is a normally open type solenoid valve.

4. The first solenoid valve has a first valve hole and a first valve body that opens and closes the first valve hole. The second solenoid valve has a second valve hole and a second valve body that opens and closes the second valve hole. The third solenoid valve has a third valve hole and a third valve body that opens and closes the third valve hole. The hydraulic brake system for an industrial vehicle according to claim 1 or 2, characterized in that the first valve hole and the second valve hole are set to have a larger diameter than the third valve hole.

5. The hydraulic brake system for an industrial vehicle according to claim 4, characterized in that the diameters of the first valve hole and the second valve hole are 1.5 to 90 times the diameter of the third valve hole.

Images