Hydraulic brake systems for industrial vehicles

Abstract

The objective is to provide a hydraulic brake system for industrial vehicles that minimizes the size of the electric motor as much as possible and can quickly supply hydraulic fluid from the actuator to the brake device during braking. [Solution] The actuator 13 includes an electric motor 32, a ball screw 35, a first cylinder 42, a first piston 43, a first hydraulic fluid chamber 51, a second cylinder 45 having a smaller inner diameter than the first cylinder 42, a second piston 46, a second hydraulic fluid chamber 54, a first brake oil passage 55 connecting the first hydraulic fluid chamber 51 to a brake device, a second brake oil passage 56 connecting the second hydraulic fluid chamber 54 to a brake device, a first return oil passage 57 connecting the hydraulic fluid tank 11 to the first hydraulic fluid chamber 51, a first check valve 58 that opens when the hydraulic pressure is equal to or greater than a first threshold A, and a second check valve 62 that opens when the hydraulic pressure is equal to or greater than a second threshold B, wherein the second threshold B is set to be greater than the first threshold A.

Description

Technical Field

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

Background Art

[0002] As a prior art related to the hydraulic brake system of industrial vehicles, a drive device disclosed in Patent Document 1 is known. The drive device of Patent Document 1 includes an axle shaft, a speed reducer that reduces the rotational speed and outputs it, a hub attached to this speed reducer, a wet brake that brakes the rotation of the axle shaft, and a housing that houses the axle shaft and the wet brake. The wet brake has a plurality of fixed brake disks, a plurality of rotating brake disks, and a pressing member. The fixed brake disks are spline-coupled to the inner peripheral surface of the housing so as to be movable in the axial direction of the axle. The rotating brake disks are spline-coupled to the outer peripheral surface of the axle shaft so as to be movable in the axial direction of the axle. The pressing member presses the fixed brake disks and the rotating brake disks toward the hub side. The fixed brake disks and the rotating brake disks are alternately arranged along the axial direction of the axle. The inside of the housing is filled with hydraulic oil for operating the pressing member. In the drive device of Patent Document 1, when the brake pedal is operated, the pressing member is pushed outward of the axle by the hydraulic pressure of the hydraulic oil. Then, since the fixed brake disks and the rotating brake disks come into contact, a braking force is generated on the axle shaft.

[0003] By the way, in an industrial vehicle capable of automatic driving, an actuator that outputs hydraulic pressure to the wet brake may be used instead of operating the brake pedal. This type of actuator may output hydraulic pressure to the wet brake using, for example, an electric cylinder disclosed in Patent Document 2.

[0004] The electric cylinder disclosed in Patent Document 2 comprises a cylindrical casing, an operating rod, a ball spline nut, a ball screw nut, an electric motor, and a rotational force transmission gear. The operating rod is disposed within the cylindrical casing so as to be able to move back and forth in the front-rear direction, and has a ball spline shaft portion and a ball screw portion at its front and rear ends. The ball spline nut is fixedly housed in the front part of the cylindrical casing, slidably supporting the ball spline shaft portion and restricting its rotation. The ball screw nut is rotatably housed in the rear part of the cylindrical casing, and screws into the ball screw portion to impart a linear force to the operating rod. The electric motor is mounted on the outer circumferential surface of the cylindrical casing. The rotational force transmission gear transmits the rotational force of the electric motor from its output shaft to the ball screw nut. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-199361 [Patent Document 2] Registered Utility Model No. 3027795 Publication [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In a hydraulic brake system for an industrial vehicle having a wet brake as disclosed in Patent Document 1 and an actuator using an electric cylinder as disclosed in Patent Document 2, increasing the supply speed of hydraulic fluid to the wet brake inevitably requires increasing the size of the electric motor. When the electric motor is enlarged, the distance between the axis of the electric motor of the actuator and the axis of the operating rod increases, which presents a problem as it increases the space required to mount the actuator.

[0007] The present invention has been made in view of the above-mentioned problems, and the object of the present invention is to provide a hydraulic brake system for industrial vehicles that can miniaturize the electric motor as much as possible and quickly supply hydraulic fluid from the actuator to the brake device during braking. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides a hydraulic brake system for an industrial vehicle having a hydraulic oil tank for storing hydraulic oil, a brake device for braking the wheels by hydraulic pressure, and an actuator for outputting hydraulic pressure to the brake device, wherein the actuator comprises an electric motor, a ball screw, a conversion mechanism for converting the rotational force of the electric motor into the reciprocating motion of the ball screw, a first cylinder, a first piston that reciprocates within the first cylinder by the reciprocating motion of the ball screw, a first hydraulic oil chamber partitioned by the first cylinder and the first piston and for storing hydraulic oil, a second cylinder having an inner diameter smaller than the inner diameter of the first cylinder, a second piston that reciprocates within the second cylinder by the reciprocating motion of the ball screw, and the second cylinder The device comprises a second hydraulic fluid chamber partitioned by the second piston, a first brake fluid passage connecting the first hydraulic fluid chamber and the brake device, a second brake fluid passage connecting the second hydraulic fluid chamber and the brake device, a first return fluid passage connecting the hydraulic fluid tank and the first hydraulic fluid chamber, a first check valve provided in the first brake fluid passage which opens when the hydraulic pressure of the first brake fluid passage is equal to or greater than a first threshold, allowing hydraulic fluid to pass from the first hydraulic fluid chamber to the brake device, and a second check valve provided in the first return fluid passage which opens when the hydraulic pressure of the first return fluid passage is equal to or greater than a second threshold, allowing hydraulic fluid to be returned from the first hydraulic fluid chamber to the hydraulic fluid tank, wherein the second threshold is set to be greater than the first threshold.

[0009] In this invention, the inner diameter of the first cylinder is larger than the inner diameter of the second cylinder. Furthermore, it includes a first brake oil passage, a second brake oil passage, a first return oil passage, a first check valve, and a second check valve, with the second threshold value set higher than the first threshold value. This allows for a reduction in the torque of the electric motor required to advance the first and second pistons. As a result, the electric motor can be miniaturized as much as possible, and the hydraulic fluid required for braking can be quickly supplied from the actuator to the brake device.

[0010] Furthermore, in the hydraulic brake system for the industrial vehicle described above, when the first piston moves forward, the first check valve may be configured to open to supply hydraulic fluid from the first hydraulic fluid chamber to the brake device, and to close together with the opening of the second check valve. In this case, opening the first check valve allows low-pressure hydraulic fluid to be supplied from the first hydraulic fluid chamber to the brake system. Additionally, opening the second check valve simultaneously with closing the first check valve allows the hydraulic fluid from the first hydraulic fluid chamber to be returned to the hydraulic fluid tank, and high-pressure hydraulic fluid from the second hydraulic fluid chamber to be supplied to the brake system.

[0011] Furthermore, the hydraulic brake system for the industrial vehicle described above may also be configured to include a first tank connecting oil passage that connects the first hydraulic oil chamber and the hydraulic oil tank, and a second tank connecting oil passage that connects the second hydraulic oil chamber and the hydraulic oil tank. In this case, hydraulic fluid can be supplied from the hydraulic fluid tank to the first hydraulic fluid chamber through the first tank oil passage, and hydraulic fluid can also be supplied from the hydraulic fluid tank to the second hydraulic fluid chamber through the second tank oil passage.

[0012] Furthermore, in the hydraulic brake system for the industrial vehicle described above, the brake device may be configured as a wet brake comprising: a rotating body rotatable with the wheel; a brake housing housing the rotating body; a plurality of rotating brake plates that rotate with the rotating body and are movable in a direction along the axis of the rotating body; a plurality of non-rotating brake plates provided in the brake housing and arranged alternately with the plurality of rotating brake plates; and a pressing member capable of pressing the rotating brake plates and the non-rotating brake plates in a direction along the axis by hydraulic pressure from the actuator. In this case, a large amount of hydraulic fluid at a low pressure necessary for the pressing member to contact the rotating brake plate or the non-rotating brake plate can be supplied to the brake device by the forward movement of the first piston. In addition, high-pressure hydraulic pressure necessary for the pressing member to press against the multiple rotating brake plates and the multiple non-rotating brake plates can be supplied to the brake device by the forward movement of the second piston. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a hydraulic brake system for industrial vehicles that minimizes the size of the electric motor as much as possible and can quickly supply hydraulic fluid from the actuator to the brake device during braking. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of a hydraulic brake system according to an embodiment of the present invention. [Figure 2] This is a longitudinal cross-sectional view showing an overview of the wet brake in a hydraulic brake system according to an embodiment of the present invention. [Figure 3] This is an explanatory diagram showing graph G1, which illustrates the relationship between the actuator's discharge pressure and the piston's displacement; graph G2, which illustrates the relationship between the opening and closing of the first check valve and the piston's displacement; graph G3, which illustrates the relationship between the opening and closing of the second check valve and the piston's displacement; and graph G4, which illustrates the relationship between the amount of hydraulic fluid discharged from the actuator and the piston's displacement. [Modes for carrying out the invention]

[0015] (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 a forklift will be described as an example.

[0016] As shown in Figure 1, the hydraulic brake system 10 of the forklift (hereinafter simply referred to as the "hydraulic brake system") comprises a hydraulic oil tank 11, a wet brake device 12 as a braking device, and an actuator 13. The hydraulic oil tank 11 is mounted on the body of the forklift (not shown) and is a tank for storing hydraulic oil.

[0017] As shown in Figure 2, the wet brake device 12 includes an axle 14 as a rotating body, a number of rotating brake plates 15 provided on the axle 14, a brake housing 16, and non-rotating brake plates 17 provided on the brake housing 16. The axle 14 receives rotational force from the drive source and transmits it to the wheels (not shown). In this embodiment, the axle 14 is used as an example of a rotating body, but other rotating bodies besides the axle 14 may be, for example, hubs that support the wheels. The rotating brake plates 15 are annular and spline-fitted to the outer circumferential surface of the axle 14, and are movable in a direction along the axis P of the axle 14. The inner circumferential surface of the brake housing 16 is provided with a number of non-rotating brake plates 17, which are annular discs arranged in a row along the axis P. The number of non-rotating brake plates 17 are movable axially relative to the brake housing 16. The rotating brake plates 15 and non-rotating brake plates 17 are arranged to be positioned alternately. In Figure 2, the right side represents the vehicle's center in the vehicle width direction, and the left side represents the wheels in the vehicle width direction.

[0018] The brake housing 16 houses the axle 14, the rotating brake plate 15, and the non-rotating brake plate 17. A recess 18 for housing the pressing member 19 is provided at a portion of the brake housing 16 that faces the rotating brake plate 15. The pressing member 19 in the recess 18 is movable forward and backward in the direction along the axis P of the axle 14. An oil chamber 20 partitioned by the brake housing 16 and the pressing member 19 is formed in the brake housing 16. An oil passage 21 communicating from the oil chamber 20 to the outside is formed in the brake housing 16. A return spring 23 for retracting the pressing member 19 and a recess 22 for housing the spring receiving member 24 are formed in the brake housing 16. The spring receiving member 24 and the pressing member 19 are connected by a plate member 25. Therefore, when the hydraulic pressure in the oil chamber 20 rises, the pressing member 19 moves forward against the biasing force of the return spring 23. When the hydraulic pressure in the oil chamber 20 is released, the pressing member 19 moves backward by the biasing force of the return spring 23. The brake housing 16 is provided with a retainer 26 so as to face the rotating brake plate 15 located closest to the wheel side. The inside of the brake housing 16 is filled with hydraulic oil. Note that in FIG. 1, the wet brake device 12 is schematically illustrated.

[0019] Next, the actuator 13 will be described. As shown in FIG. 1, the actuator 13 has an electric cylinder section 30 and a hydraulic cylinder section 31. The electric cylinder section 30 has an electric motor 32 as a drive source, an actuator housing 33, a ball screw nut 34, and a ball screw 35. The electric motor 32 is capable of forward and reverse rotation, and a drive gear 37 is provided on the output shaft 36 of the electric motor 32. The electric motor 32 is controlled by a controller (not shown) that controls each part of the forklift. The controller has an arithmetic processing unit (CPU) and a storage unit, and controls the electric motor 32 under preset conditions.

[0020] In the actuator housing 33, a ball screw nut 34 is rotatably supported by a plurality of bearings 38. A ball screw 35 is inserted through the center of the ball screw nut 34, and a ball screw hole 39 is formed. The ball screw nut 34 is provided with a driven gear 40 so as to mesh with the drive gear 37. A through hole 41 is formed at the center of the driven gear 40, and the ball screw nut 34 is inserted into and fixed to the through hole 41. Therefore, the driven gear 40 is concentric with the ball screw nut 34 and rotates integrally with the ball screw nut 34.

[0021] The ball screw 35 is housed together with the ball screw nut 34 in the actuator housing 33. The ball screw 35 moves forward and backward with respect to the ball screw nut 34 due to the rotation of the ball screw nut 34. The drive gear 37, the ball screw nut 34, and the driven gear 40 correspond to a conversion mechanism that converts the rotational force of the electric motor 32 into the forward and backward movement of the ball screw 35. Although not shown in the figure, a detent member is provided in the actuator housing 33 so that the ball screw 35 does not rotate together with the ball screw nut 34.

[0022] In the electric cylinder unit 30, when the electric motor 32 rotates forward, the ball screw nut 34 is rotated in one direction via the drive gear 37 and the driven gear 40, and the ball screw 35 moves forward (moves to the left in FIG. 1). When the electric motor 32 rotates reversely, the ball screw nut 34 is rotated in the other direction via the drive gear 37 and the driven gear 40, and the ball screw 35 moves backward (moves to the right in FIG. 1). The axis Q1 of the output shaft 36 and the axis Q2 of the ball screw 35 are parallel, and the distance between the axis Q1 and the axis Q2 is the axial distance L. The axial distance L depends on the size of the electric motor 32. The smaller the size of the electric motor 32, the smaller the axial distance L, and the larger the size of the electric motor 32, the larger the axial distance L.

[0023] Next, the hydraulic cylinder section 31 will be described. As shown in Figure 1, the hydraulic cylinder section 31 includes a first cylinder 42, a first piston 43, a first piston rod 44, a second cylinder 45, a second piston 46, and a second piston rod 47. The cylindrical first cylinder 42 is connected to the front end of the actuator housing 33. Inside the first cylinder 42 is a first piston 43 that is capable of reciprocating movement. The first piston 43 is connected to one end of the first piston rod 44. The first piston 43 includes a cylindrical first piston body 48 and an annular sealing member 49 attached to the outer circumferential surface of the first piston body 48. The other end of the first piston rod 44 is connected to the tip of the ball screw 35. Inside the first cylinder 42, a first hydraulic oil chamber 51 is formed, which is partitioned by the first cylinder 42 and the first piston 43 and filled with hydraulic fluid.

[0024] A second cylinder 45 is connected to the front end of the first cylinder 42. In other words, the second cylinder 45 is connected in series with the first cylinder 42. In this embodiment, the inner diameter of the first cylinder 42 is set to 2.5 times the inner diameter of the second cylinder 45, and the cross-sectional area of ​​the first cylinder 42 is 6 times or more the cross-sectional area of ​​the second cylinder 45. A reciprocating second piston 46 is provided inside the second cylinder 45. The second piston 46 is connected to one end of the second piston rod 47. The second piston 46 comprises a cylindrical second piston body 52 and an annular sealing member 53 attached to the outer circumferential surface of the second piston body 52. ​​The other end of the second piston rod 47 passes through the first cylinder 42 and is connected to the first piston 43. The second piston rod 47 is coaxial with the first piston rod 44. Therefore, the first piston 43, the first piston rod 44, the second piston 46, and the second piston rod 47 are integrated and move back and forth as a single unit. A second hydraulic fluid chamber 54 is formed inside the second cylinder 45, partitioned by the second cylinder 45 and the second piston 46, and filled with hydraulic fluid.

[0025] The hydraulic cylinder section 31 includes a first brake oil passage 55, a second brake oil passage 56, and a first return oil passage 57. The first brake oil passage 55 is an oil passage connecting the first hydraulic oil chamber 51 and the wet brake device 12, and a first check valve 58 is interposed in the first brake oil passage 55. The first check valve 58 is a check valve that allows the flow of hydraulic oil from the first hydraulic oil chamber 51 to the wet brake device 12, but does not allow the flow of hydraulic oil from the wet brake device 12 to the first hydraulic oil chamber 51. The first check valve 58 is equipped with a first coil spring 61 that biases the valve body 60 in the direction of closing the valve hole 59. Therefore, if the hydraulic pressure at which the valve body 60 opens the valve hole 59 against the spring force of the first coil spring 61 is defined as the first threshold A, then the first check valve 58 opens when the hydraulic pressure in the first hydraulic oil chamber 51 exceeds the first threshold A.

[0026] The second brake oil passage 56 is an oil passage connecting the second hydraulic fluid chamber 54 and the wet brake device 12. In this embodiment, the second brake oil passage 56 is connected between the first check valve 58 in the first brake oil passage 55 and the wet brake device 12. The first return oil passage 57 is an oil passage connecting the hydraulic fluid tank 11 and the first hydraulic fluid chamber 51. A second check valve 62 is interposed in the second brake oil passage 56. The second check valve 62 is a check valve that allows the flow of hydraulic fluid from the first hydraulic fluid chamber 51 to the hydraulic fluid tank 11, but does not allow the flow of hydraulic fluid from the hydraulic fluid tank 11 to the first hydraulic fluid chamber 51. The second check valve 62 is equipped with a second coil spring 65 that biases the valve body 64 in the direction of closing the valve hole 63. Therefore, if the hydraulic pressure at which the valve body 64 opens the valve hole 63 against the spring force of the second coil spring 65 is defined as the second threshold B, then the first check valve 58 opens when the hydraulic pressure in the first hydraulic fluid chamber 51 exceeds the second threshold B. The spring constants of the first coil spring 61 and the second coil spring 65 are set such that the second threshold B is greater than the first threshold A.

[0027] The hydraulic cylinder section 31 has a first tank oil passage 66 connecting the first hydraulic oil chamber 51 to the hydraulic oil tank 11, and a second tank oil passage 67 connecting the second hydraulic oil chamber 54 to the hydraulic oil tank 11. The first cylinder 42 has a first brake port 68 communicating with the first brake oil passage 55, a return port 69 communicating with the first return oil passage 57, and a first tank port 71 communicating with the first tank oil passage 66. The first brake port 68 and the return port 69 are positioned so that they communicate with the first hydraulic oil chamber 51 even when the first piston 43 is at its furthest forward position. The first tank port 71 is positioned so that it communicates with the first hydraulic oil chamber 51 when the first piston 43 is at its furthest backward position in the first cylinder 42, and does not communicate with the first hydraulic oil chamber 51 when the first piston 43 is at its furthest forward position. Therefore, when the first piston 43 is retracted to its original position before moving forward, the first hydraulic fluid chamber 51 is filled with hydraulic fluid from the hydraulic fluid tank 11.

[0028] The second cylinder 45 has a second brake port 72 that communicates with a second brake oil passage 56 and a second tank port 73 that communicates with a second tank oil passage 67. The second brake port 72 is positioned so as to communicate with the second hydraulic oil chamber 54 even when the second piston 46 is in its furthest forward position. The second tank port 73 is positioned so as to communicate with the second hydraulic oil chamber 54 when the second piston 46 is in its furthest retracted position before moving forward, and not communicate with the second hydraulic oil chamber 54 when the second piston 46 is moving forward. Therefore, when the second piston 46 is in its retracted position before moving forward, the second hydraulic oil chamber 54 is filled with hydraulic oil from the hydraulic oil tank 11.

[0029] In this embodiment, the inner diameter of the first cylinder 42 is set to 2.5 times the inner diameter of the second cylinder 45. The first piston rod 44 and the second piston rod 47 move together as the ball screw 35 moves back and forth. Therefore, even if the strokes of the first piston 43 and the second piston 46 are the same, the amount of hydraulic fluid discharged from the first hydraulic fluid chamber 51 and the amount of hydraulic fluid and hydraulic pressure discharged from the second hydraulic fluid chamber 54 are different. The amount of hydraulic fluid discharged from the first hydraulic fluid chamber 51 due to the advance of the first piston 43 is lower in pressure and larger in volume compared to the amount of hydraulic fluid discharged from the second hydraulic fluid chamber 54 due to the advance of the second piston 46, but the time required for discharge is shorter.

[0030] Next, the operation of the hydraulic brake system 10 of this embodiment will be described. When the forklift is moving and no braking force is being generated in the wet brake device 12, the ball screw 35 is in its most retracted position. Therefore, the first piston 43 is in its most retracted position relative to the first cylinder 42. Also, the second piston 46 is in its most retracted position relative to the second cylinder 45. The first hydraulic fluid chamber 51 is filled with hydraulic fluid through the first tank oil passage 66. The second hydraulic fluid chamber 54 is filled with hydraulic fluid through the second tank oil passage 67.

[0031] When conditions are met that require braking while the forklift is in motion, the electric motor 32 rotates in the forward direction. The forward rotation of the electric motor 32 causes the ball screw nut 34 to rotate in one direction via the drive gear 37 and the driven gear 40. The rotation of the ball screw nut 34 in one direction causes the ball screw 35 to advance relative to the ball screw nut 34. The advancement of the ball screw 35 causes the first piston rod 44 and the second piston rod 47 to advance. The first piston 43 advances, increasing the hydraulic pressure of the hydraulic fluid in the first hydraulic fluid chamber 51, and the second piston 46 also advances, increasing the hydraulic pressure in the second hydraulic fluid chamber 54.

[0032] In graph G1 shown in Figure 3, when the hydraulic pressure of the actuator 13 (first hydraulic oil chamber 51) exceeds the first threshold A, the first check valve 58 opens, as shown in graph G2. When the first check valve 58 opens, the amount of hydraulic oil discharged from the actuator 13 (first hydraulic oil chamber 51 and second hydraulic oil chamber 54) increases in section S1, as shown in graph G4. In graph G4, section S1 is defined as the period until the pressing member 19 contacts the rotating brake plate 15, and section S2 is defined as the period from when the rotating brake plate 15 and the non-rotating brake plate 17 are pressed by the pressing member 19 and braking force is generated. Also, the piston displacement in Figure 3 is the displacement of the first piston 43 and the second piston 46. In section S1, it is sufficient to generate low-pressure hydraulic pressure that allows the pressing member 19 to displace against the sliding resistance during displacement, and it is preferable to have a large amount of hydraulic oil so that the displacement time of the pressing member 19 is shortened. In section S2, the pressing member 19 presses against the rotating brake plate 15 and the non-rotating brake plate 17, and high-pressure hydraulic pressure is required to obtain braking force through the frictional force between the rotating brake plate 15 and the non-rotating brake plate 17.

[0033] When the first check valve 58 opens, a large amount of hydraulic fluid is discharged from the first hydraulic fluid chamber 51 at low pressure, and this large amount of low-pressure hydraulic fluid quickly brings the pressing member 19 in the wet brake device 12 into contact with the rotating brake plate 15. Since the inner diameter of the first cylinder 42 is larger than the inner diameter of the second cylinder 45, the torque of the electric motor 32 required to discharge a large amount of low-pressure hydraulic fluid from the first hydraulic fluid chamber 51 can be reduced. As the piston continues to move forward, the hydraulic pressure of the wet brake device 12 rises above the hydraulic pressure of the first hydraulic fluid chamber 51, and when the hydraulic pressure of the first hydraulic fluid chamber 51 exceeds the second threshold B, the first check valve 58 closes and the second check valve 62 opens. In other words, when the piston moves forward, the first check valve 58 opens to supply hydraulic fluid from the first hydraulic fluid chamber 51 to the wet brake device 12, and when the hydraulic pressure in the first hydraulic fluid chamber 51 exceeds the second threshold B, it closes together with the opening of the second check valve 62.

[0034] Even if the piston continues to move forward due to the closing of the first check valve 58 and the opening of the second check valve 62, the hydraulic fluid in the first hydraulic fluid chamber 51 is discharged to the hydraulic fluid tank 11. On the other hand, as the piston moves forward, the hydraulic pressure in the second hydraulic fluid chamber 54 rises sharply at the timing of the closing of the first check valve 58 and the opening of the second check valve 62. Then, the hydraulic fluid discharged from the actuator 13 is only the hydraulic fluid discharged from the second hydraulic fluid chamber 54, and as the piston continues to move forward, the amount of hydraulic fluid discharged from the actuator 13 (second hydraulic fluid chamber 54) increases in section S2, as shown in graph G4.

[0035] As shown in graph G4, the hydraulic fluid discharged in section S2 is a small amount compared to the hydraulic fluid discharged from actuator 13 in section S1, but as shown in graph G1, it is at high pressure. Therefore, the hydraulic pressure of the wet brake device 12 is such that the hydraulic fluid discharged from the second hydraulic fluid chamber 54 is at high pressure and in small volume. This high-pressure, small amount of hydraulic fluid presses the pressing member 19 against the rotating brake plate 15 and the non-rotating brake plate 17 in the wet brake device 12. Because the inner diameter of the second cylinder 45 is sufficiently small, the torque of the electric motor 32 required to discharge high-pressure hydraulic fluid from the second hydraulic fluid chamber 54 can be reduced. The discharge of high-pressure hydraulic fluid causes the rotating brake plate 15 and the non-rotating brake plate 17 to slide against each other, generating a braking force. As a result of the braking force generated in the wet brake device 12, the forklift slows down or stops due to the braking force.

[0036] Incidentally, when discharging hydraulic fluid with a single cylinder and piston, the amount of hydraulic fluid discharged is determined by the cylinder's inner diameter and the piston's displacement. If a specific hydraulic pressure is set and the cylinder's inner diameter is set accordingly, the amount of hydraulic fluid discharged can only be adjusted by the piston's displacement, and the hydraulic fluid discharge time is set by default. This embodiment has a first cylinder 42 and a second cylinder 45 with different inner diameters, and the first piston 43 and the second piston 46 reciprocate as a single unit, so it is possible to set the desired hydraulic pressure and discharge time for the hydraulic fluid.

[0037] When releasing the braking force, the electric motor 32 is controlled to rotate in the reverse direction, and the reverse rotation of the electric motor 32 causes the ball screw 35 to retract relative to the ball screw nut 34. As the ball screw 35 retracts, the piston retracts, and hydraulic fluid is recovered from the wet brake device 12 into the second hydraulic fluid chamber 54, causing the hydraulic pressure of the wet brake device 12 to decrease and the braking pressure to be released. Note that some of the hydraulic fluid recovered into the second hydraulic fluid chamber 54 due to the piston's retraction is recovered into the hydraulic fluid tank 11 and then into the first hydraulic fluid chamber 51.

[0038] The hydraulic brake system 10 according to this embodiment provides the following effects. (1) The inner diameter of the first cylinder 42 is larger than the inner diameter of the second cylinder 45. It also has a first brake oil passage 55, a second brake oil passage 56, a first return oil passage 57, a first check valve 58, and a second check valve 62, and the second threshold B is set to be larger than the first threshold A. As a result, the torque of the electric motor 32 required to advance the first piston 43 and the second piston 46 can be reduced. As a result, the electric motor 32 can be made as small as possible, and the hydraulic fluid required for braking can be quickly supplied from the actuator 13 to the wet brake device 12.

[0039] (2) When the ball screw 35 moves forward, the opening of the first check valve 58 allows low-pressure hydraulic fluid to be supplied from the first hydraulic fluid chamber 51 to the wet brake device 12. In addition, the opening of the second check valve 62 and the closing of the first check valve 58 allow the hydraulic fluid from the first hydraulic fluid chamber 51 to be returned to the hydraulic fluid tank 11, and also allow high-pressure hydraulic fluid from the second hydraulic fluid chamber 54 to be supplied to the wet brake device 12.

[0040] (3) When the first piston 43 is retracted, hydraulic fluid can be supplied from the hydraulic fluid tank 11 to the first hydraulic fluid chamber 51 through the first tank oil passage 66. Also, when the second piston 46 is retracted, hydraulic fluid can be supplied from the hydraulic fluid tank 11 to the second hydraulic fluid chamber 54 through the second tank oil passage 67.

[0041] (4) A large amount of hydraulic fluid at a low pressure necessary for the pressing member 19 to contact the rotating brake plate 15 can be supplied to the wet brake device 12 by the forward movement of the first piston 43. In addition, high-pressure hydraulic pressure necessary for the pressing member 19 to press against the multiple rotating brake plates 15 and the multiple non-rotating brake plates 17 can be supplied to the wet brake device 12 by the forward movement of the second piston 46.

[0042] (5) The first cylinder 42 and the second cylinder 45 have different inner diameters, and the first piston 43 and the second piston 46 reciprocate integrally. Even if the amount of movement of the first piston 43 and the second piston 46 is the same, the inner diameter of the first cylinder 42 is larger than the inner diameter of the second cylinder 45, so the amount of hydraulic fluid discharged from the first hydraulic fluid chamber 51 can be increased by the forward movement of the first piston 43, and discharge can be performed in a short time. In addition, the force required to move the first piston 43 and the second piston 46 forward can be reduced, and the torque required for the electric motor 32 can be reduced, so the electric motor 32 can be made smaller and the distance L between the shafts can be suppressed.

[0043] 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.

[0044] ○ In the above embodiment, a wet brake system was used as an example of a brake system, but the system is not limited to this. The brake system may be, for example, a drum brake system that generates braking force by pressing a brake shoe against a brake drum. In this case, the advance of the ball screw supplies low-pressure hydraulic fluid from the first and second hydraulic fluid chambers necessary for the brake shoe to press against the drum, and high-pressure hydraulic fluid is supplied from the second hydraulic fluid chamber to press the brake shoe against the brake drum. ○ In the above embodiment, the conversion mechanism that converts the rotational force of the electric motor into the forward and backward movement of the ball screw is configured with a drive gear, a ball screw nut, and a driven gear, but it is not limited to this configuration. The conversion mechanism is not particularly limited in terms of the conversion method or means for conversion, as long as it is capable of converting the rotational force of the electric motor into the forward and backward movement of the ball screw. ○ In the above embodiment, the first and second pistons are returned to their original positions by the retraction of the ball screw due to the reverse rotation of the electric motor, but this is not limited to this. For example, a return spring may be provided inside the first cylinder (second cylinder) to bias the first piston (second piston) in the direction of returning it to its original position. In this case, the biasing force of the return spring makes it easier to retract the ball screw. ○ In the above embodiment, a hydraulic brake system for a forklift as an industrial vehicle was used as an example, but the invention is not limited to this. 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 actuator is acceptable. [Explanation of Symbols]

[0045] 10. Hydraulic Brake System 11. Hydraulic oil tank 12. Wet Brake System (Brake System) 13 Actuators 14. Axle (rotating body) 15 Rotating Brake Plates 16 Brake Housing 17 Non-rotating brake plate 19 Pressing member 30 Electric Cylinder Section 31 Hydraulic Cylinder Section 32 Electric motors 34 Ball screw nuts 35 Ball screw 42 First Cylinder 43 First Piston 45 Second Cylinder 46. ​​Second piston 51. First hydraulic oil chamber 54. Second hydraulic oil chamber 55 First brake fluid passage 56 Second brake fluid passage 57 First return oil channel 58. First check valve 62. Second check valve 66. No. 1 Tank Oil Passage 67 Second Tank Oil Passage A, B threshold G1, G2, G3, G4 graphs L Center distance S1, S2 section

Claims

1. A hydraulic oil tank for storing hydraulic fluid, A braking system that uses hydraulics to brake the wheels, In a hydraulic brake system for an industrial vehicle, which includes an actuator that outputs hydraulic pressure to the brake device, The actuator is Electric motor and Ball screw and A conversion mechanism that converts the rotational force of the electric motor into the forward and backward movement of the ball screw, First cylinder and The first piston moves back and forth within the first cylinder as the ball screw moves forward and backward, A first hydraulic fluid chamber is partitioned by the first cylinder and the first piston, and hydraulic fluid is stored in it. A second cylinder having an inner diameter smaller than the inner diameter of the first cylinder, The second piston moves back and forth within the second cylinder as the ball screw moves forward and backward, A second hydraulic fluid chamber partitioned by the second cylinder and the second piston, A first brake fluid passage connecting the first hydraulic fluid chamber and the brake device, A second brake fluid passage connecting the second hydraulic fluid chamber and the brake device, A first return oil passage connecting the hydraulic oil tank and the first hydraulic oil chamber, A first check valve is provided in the first brake fluid passage, which opens when the hydraulic pressure in the first brake fluid passage is equal to or greater than a first threshold, allowing hydraulic fluid to pass from the first hydraulic fluid chamber to the brake device. The system includes a second check valve provided in the first return oil passage, which opens when the hydraulic pressure in the first return oil passage is equal to or greater than a second threshold, allowing hydraulic fluid to be returned from the first hydraulic fluid chamber to the hydraulic fluid tank. A hydraulic brake system for industrial vehicles, characterized in that the second threshold is set to be greater than the first threshold.

2. The hydraulic brake system for an industrial vehicle according to claim 1, characterized in that when the first piston moves forward, the first check valve opens to supply hydraulic fluid from the first hydraulic fluid chamber to the brake device, and closes together with the opening of the second check valve.

3. A first tank oil passage connecting the first hydraulic oil chamber and the hydraulic oil tank, A hydraulic brake system for an industrial vehicle according to claim 1 or 2, characterized in that it has a second tank oil passage connecting the second hydraulic oil chamber and the hydraulic oil tank.

4. The aforementioned brake device, A rotating body that can rotate together with the aforementioned wheel, A brake housing that houses the rotating body, A plurality of rotating brake plates that rotate together with the rotating body and are movable in a direction along the axis of the rotating body, The brake housing is provided with a plurality of non-rotating brake plates arranged alternately with the plurality of rotating brake plates, A hydraulic brake system for an industrial vehicle according to claim 1 or 2, characterized in that it is a wet brake having a pressing member capable of pressing the rotating brake plate and the non-rotating brake plate in a direction along the axis by hydraulic pressure from the actuator.

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