JP5571809B2 - Brake system - Google Patents

Description

  The present invention relates to a brake system used for a hydraulic motor or the like.

  As a friction braking type brake system used for a hydraulic motor, a fixed plate provided on a non-rotating body, a rotating plate provided on the rotating body, and a coil spring that presses the rotating plate against the fixed plate via a piston (For example, refer to Patent Document 1).

  In this brake device, a friction brake force is generated between the rotating plate and the fixed plate by the biasing force of the coil spring to stop the rotating body. Release of the braking force is performed by moving the piston against the urging force of the coil spring using hydraulic pressure.

  For this reason, in Patent Document 1, a brake release hydraulic pressure switching valve for controlling the release of the brake force is provided. The hydraulic pressure switching valve causes the hydraulic pressure from the pump to act on the piston of the brake device according to the position of the spool that moves according to the supplied signal pressure.

  In this way, the brake force is released by compressing the coil spring by the action of the hydraulic switching valve and releasing the frictional force between the rotating plate and the fixed plate.

JP 2002-39047 A

  The pilot pressure passage for supplying the signal pressure to the spool of the hydraulic switching valve is configured such that pressurized hydraulic oil is drained to the tank when the driving pressure from the hydraulic pump is not supplied. However, only one end of the pilot pressure passage is opened in the tank, and so-called air bleeding for removing the air remaining in the pilot pressure passage may be insufficient. If air bleeding is insufficient, the brake force release timing is delayed as the signal pressure rises, and the brake motor is accelerated by the rotation of the hydraulic motor, resulting in a problem that the service life is shortened.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a brake system in which the pilot pressure passage is sufficiently vented.

The present invention releases a braking force by supplying a pressurized working fluid and generates a braking force by draining the pressurized working fluid, and supplies the pressurized working fluid to the brake device. A drive pressure passage, a drain passage for draining pressurized working fluid from the brake device, a hydraulic pressure switching valve for selectively opening the drive pressure passage and the drain passage to the brake device according to the signal pressure, and the hydraulic pressure switching A brake system comprising a pilot pressure passage for guiding a signal pressure to the valve, and the hydraulic switching valve switches from a braking position at which the drain passage opens to a release position at which the drive pressure passage opens as the signal pressure increases. And a pilot drain passage for draining the pressurized working fluid in the pilot pressure passage, and the hydraulic switching valve closes the pilot drain passage at the braking position. Write, and shall be characterized in that for opening the pilot drain passage after releasing the braking force by opening the drive pressure passage in turn switched course the release position from the braking position.

  According to the present invention, air in the pilot pressure passage is sufficiently vented by allowing the pressurized working fluid in the pilot pressure passage to escape through the pilot drain passage together with air at the release position of the hydraulic switching valve. As a result, the rise of the signal pressure is prevented from being delayed due to the air remaining in the pilot pressure passage, and the brake force is released accurately.

  After the braking of the brake device is released by opening the drive pressure passage in the process of switching from the braking position to the release position, the pilot pressure passage is opened by opening the pilot drain passage. Thus, before the braking of the brake device is released, the pressurized hydraulic fluid in the pilot pressure passage is not drained through the pilot drain passage, the signal pressure rises quickly, and the braking force is released. It is done accurately.

1 is a sectional view of a hydraulic motor showing an embodiment of the present invention. Similarly, the hydraulic circuit diagram of the brake system. Similarly, the hydraulic circuit diagram of the brake system. Similarly, a sectional view and a hydraulic circuit diagram of a hydraulic switching valve. Sectional drawing which similarly shows operation | movement of a hydraulic switching valve. Similarly, sectional drawing which shows operation | movement of a hydraulic switching valve. Similarly, sectional drawing which shows operation | movement of a hydraulic switching valve. Sectional drawing and the hydraulic circuit figure of the hydraulic switching valve which show other embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  First, an overall configuration of a hydraulic motor 1 to which the present invention can be applied will be described with reference to FIG. The hydraulic motor 1 is, for example, a swash plate type hydraulic motor used in a turning device such as a construction machine.

  The hydraulic motor 1 includes an output shaft 2 connected to a load (not shown) and a cylinder block 3 connected to the output shaft 2 and rotating integrally with the output shaft 2. The output shaft 2 is rotatably supported by the case 11 and the cover 12 of the hydraulic motor 1 via bearings 17 and 18.

  A plurality of cylinders 4 are opened in parallel with the output shaft 2 on a concentric circle centering on the output shaft 2 in the cylinder block 3. A piston 6 that defines a volume chamber 5 is inserted into each cylinder 4 so as to be slidable back and forth.

  A shoe 9 is connected to the tip of the piston 6 via a spherical seat 10. The shoe 9 is in surface contact with the swash plate 7 fixed to the case 11. As the cylinder block 3 rotates, each shoe 9 comes into sliding contact with the swash plate 7, and each piston 6 reciprocates with a stroke amount corresponding to the tilt angle of the swash plate 7.

  A valve plate 8 with which the base end surface of the cylinder block 3 is in sliding contact is attached to the cover 12. The valve plate 8 has a port communicating with a hydraulic pump (not shown) and a port communicating with the tank side. Each piston 6 protrudes from the cylinder 4 by the hydraulic pressure guided from the hydraulic pump to each volume chamber 5 through each port, and each piston 6 pushes the swash plate 7 through the shoe 9 to rotate the cylinder block 3. Then, the rotation of the cylinder block 3 is transmitted to the load via the output shaft 2.

  The hydraulic motor 1 includes a friction braking type brake device 20. The brake device 20 will be described below.

  The brake device 20 is provided with a plurality of (three in the present embodiment) disk plates 21 that rotate together with the cylinder block 3 and the case 11 so as not to rotate. In this embodiment, a plurality of (two in this embodiment) friction plates 22 as friction members that generate a frictional braking force, and the disk plate 21 and the friction plate 22 are pressed against each other between the plates 21 and 22. And a brake actuating mechanism 25 that can release the friction brake force by releasing the pressing force.

  Each disk plate 21 is spline-engaged with the outer periphery of the cylinder block 3. Each disk plate 21 has an annular shape, and teeth (not shown) are formed on the inner periphery. A spline 3 a formed so as to extend in the axial direction of the output shaft 2 is formed on the outer periphery of the cylinder block 3. When the teeth of the disk plate 21 and the splines 3 a of the cylinder block 3 are engaged with each other, the disk plate 21 rotates with the rotation of the cylinder block 3 and can move in the axial direction of the output shaft 2.

  Each friction plate 22 is spline-engaged with the inner periphery of the case 11 like the disc plate 21. Each friction plate 22 has an annular shape, and is attached to the inner periphery of the case 11 so as not to rotate relative to the case 11 and to be movable in the axial direction of the output shaft 2.

  Each friction plate 22 is disposed so as to be sandwiched between adjacent disk plates 21.

  The brake operating mechanism 25 is supported between the inner periphery of the case 11 and is interposed between the cover 12 and the brake piston 27, and is disposed between the cover 12 and the brake piston 27. The brake piston 27 is attached to the disc plate. When the pressurized hydraulic oil (working fluid) is supplied from a plurality of brake springs 26 as urging members that urge toward 21, and the brake release hydraulic switching valve 30, the urging force of the brake springs 26 is resisted. And a brake release chamber 28 for moving the brake piston 27.

  The brake piston 27 is formed between the sliding portion 27a that slides along the inner peripheral wall 11a of the case 11 and the friction plate 22 by pressing the disk plate 21 that is provided integrally with the sliding portion 27a and faces the sliding plate 27a. It comprises a piston portion 27b that generates a friction brake force. A pin 13 implanted in the cover 12 is inserted into the brake piston 27 and rotation around the output shaft 2 is prevented.

  The piston portion 27b is formed to have a smaller outer diameter compared to the sliding portion 27a, and a space exists between the outer peripheral surface 27c of the piston portion 27b and the inner peripheral wall 11a of the case 11.

  In the space, a ring body 29 is disposed so as to be in contact with both the outer peripheral surface 27c of the piston portion 27b and the inner peripheral wall 11a of the case 11. Thereby, the brake release chamber 28 is defined by the outer peripheral surface 27 c of the piston portion 27 b, the inner peripheral wall 11 a of the case 11, and the base end surface of the ring body 29. Note that a stepped portion 11 b with which the tip of the ring body 29 engages is formed on the inner peripheral wall 11 a of the case 11.

  The sliding portion 27a of the brake piston 27 is formed with a plurality of holes 27d opened on the base end face on the same circle, and the brake springs 26 are accommodated in the holes 27d, respectively.

  The brake release chamber 28 is selectively connected to a tank or a hydraulic supply source (pilot pump 50) (not shown) via a hydraulic switching valve 30. By switching the selection by the hydraulic switching valve 30, pressure oil is supplied to and discharged from the brake release chamber 28, and the brake piston 27 is moved forward and backward accordingly, and the brake operation and release thereof are performed.

  On the inner wall of the case 11, as a restricting member that restricts movement of each disk plate 21 and each friction plate 22 in the axial direction of the output shaft 2 more than a predetermined amount when the brake piston 27 moves forward by the biasing force of the brake spring 26. The receiving portion 11c is formed. In this way, the disc plate 21 and the friction plate 22 are pressed against each other between the brake piston 27 and the receiving portion 11 c, and a friction brake force is generated between the disc plate 21 and the friction plate 22.

  FIG. 2 shows a turning hydraulic circuit of a hydraulic excavator provided with the hydraulic motor 1. In the figure, a hydraulic motor 1 is configured to drive an upper swing body (not shown) of a hydraulic excavator through a reduction gear using a planetary gear mechanism 90 or the like. Further, the hydraulic motor 1 is provided with the above-described brake device 20, and the brake device 20 generates a braking force when the upper swing body stops turning.

  As described above, the pilot pump 50 that supplies the drive pressure to the drive pressure port 39 and the spool 40 of the hydraulic switching valve 30 is provided, and the pressurized hydraulic oil that has been sucked up from the tank 52 is supplied to the hydraulic motor 1. A hydraulic pump 51 is provided. The pilot pump 50 and the hydraulic pump 51 are driven by an engine (not shown) mounted on the vehicle.

  The hydraulic pump 51 is connected to the hydraulic motor 1 through a pair of main pipes 54A and 54B. In the middle of the main pipelines 54A and 54B, a manually-switchable direction switching valve 55 is provided.

  The direction switching valve 55 is switched from the neutral position (A) to the switching position (B) and (C) by the operator operating the operation lever 58, and from the neutral position (A) to the switching position (B). In this case, the discharged pressurized hydraulic oil is supplied to the hydraulic motor 1 from the main pipeline 54A, and is drained to the tank 52 from the main pipeline 54B. On the other hand, when the neutral position (a) is switched to the switching position (c), the discharged pressurized hydraulic fluid is supplied from the main line 54B to the hydraulic motor 1 and drained from the main line 54A to the tank 52. The Further, in the neutral position (A), the pressurized hydraulic oil from the hydraulic pump 51 is drained to the tank 52 without being supplied to the hydraulic motor 1. In this way, the configuration is such that the direction of the pressure oil supplied to and discharged from the hydraulic pump 51 to the hydraulic motor 1 is switched, and the rotational direction of the hydraulic motor 1 is switched or stopped.

  Branch pipes 57A, 57B, 58A and 58B are provided between the hydraulic motor 1 and the direction switching valve 55 to communicate between the main pipes 54A and 54B, and the tank pipe 56 is connected to the branch pipes 57A and 57B. , Connected to the connecting portion with the branch pipes 58A, 58B, and opens to the tank 52.

  Check valves 59A and 59B are arranged in the middle of the branch pipes 57A and 57B, respectively. The check valves 59A and 59B allow pressurized hydraulic fluid to flow from the tank 52 toward the main pipes 54A and 54B. By allowing, the inside of the main pipelines 54A and 54B is prevented from being in a negative pressure state.

  A pair of relief valves 60A and 60B are provided in the middle of the branch pipes 58A and 58B. The relief valves 60A and 60B have a high relief setting pressure Ph determined in advance by pressure setting springs 61A and 61B. The valve opening pressure Pl at the time of low pressure relief is set by 62A and 62B. The relief valves 60A and 60B, for example, when the pressure (excess pressure) higher than the relief set pressure Ph is generated in the main pipeline 54A or 54B when the hydraulic motor 1 is rotated, etc., the valve bodies of the relief valves 60A and 60B are By opening the valve, this pressure (excess pressure) is relieved to the tank line 56 side.

  The accumulators 62A and 62B are provided to the relief valves 60A and 60B. For example, during the inertia rotation of the hydraulic motor 1, the pressurized hydraulic fluid from the main pipelines 54A and 54B is passed through the throttles 67A and 67B and the accumulators 62A and 62B. When supplied to the inside, the pressurized hydraulic oil is temporarily stored, and at this time, the relief valves 60A and 60B perform low pressure relief with the valve opening pressure Pl.

  As a result, the accumulators 62A and 62B provide a shockless function to the relief valves 60A and 60B, and the impact when the relief valves 60A and 60B are opened at the high relief set pressure Ph is reduced.

  Further, the brake device 20 for applying a braking force to the hydraulic motor 1 is provided, and when the pressurized hydraulic fluid in the chamber 28 is drained, the brake piston 27 causes the disc plate 21 to move to the friction plate 22 side by the brake spring 26. The pressing force generates a braking force on the output shaft 2 of the hydraulic motor 1 or the like. When the pressurized hydraulic fluid that serves as a brake release pressure (driving pressure) is supplied from the brake pipe 73 into the chamber 28 from the brake pipe 73 when the hydraulic motor 1 is driven to rotate, The brake of the hydraulic motor 1 is released by compressing the brake spring 26 with pressure.

  The brake release hydraulic pressure switching valve 30 selectively switches the connection destination of the brake line 73 between the pilot pump 50 and the tank 52. Here, when the drain pressure is introduced as the signal pressure of the brake release hydraulic switching valve 30, the pressurized hydraulic fluid in the chamber 28 is drained by the urging force of the return spring 36, and the brake device 20 applies the braking force. The resulting braking position (d) is held. On the other hand, when the brake release hydraulic pressure switching valve 30 is supplied with a driving pressure as its signal pressure, the brake release hydraulic pressure switching valve 30 is switched from the braking position (d) to the release position (e) and from the pilot pump 50. A drive pressure, that is, a brake release pressure is supplied to the chamber 28 of the brake device 20 via the brake line 73.

  In order to switch the signal pressure to the brake release hydraulic pressure switching valve 30, a two-position switching valve pilot pressure switching valve 80 is provided. An operation lever 81 for switching the position of the pilot pressure switching valve 80 is provided, and this operation lever 81 is interlocked with the operation lever 58.

  When the operator operates the operation lever 58 and the pilot pressure switching valve 80 is switched to the release position (f) via the operation lever 81, the driving pressure from the pilot pump 50 is supplied from the driving pressure passage 83. It acts on the spool 40 of the brake release hydraulic pressure switching valve 30 through the branched pilot pressure passage 82, and the hydraulic pressure switching valve 30 switches to the release position (e) against the urging force of the return spring 36.

  On the other hand, when the operator operates the operation lever 58 and the pilot pressure switching valve 80 is switched to the braking position (g) via the operation lever 81, the pilot pressure passage 82 communicates with the tank 52. Thus, the drain pressure acts on the spool 40 of the brake release hydraulic switching valve 30, and the hydraulic switching valve 30 is switched to the braking position (d) by the urging force of the return spring 36.

  As described above, the brake release hydraulic pressure switching valve 30 is disposed in the pilot pressure passage 82 in the operating state in which the pilot pressure passage 82 that guides the signal pressure to the spool 40 is switched to the release position (e) that communicates with the tank 52. The hydraulic oil is drained to the tank 52.

  However, actually, since one end of the pilot pressure passage 82 is closed by the spool 40 of the brake release hydraulic switching valve 30, the hydraulic oil in the pilot pressure passage 82 hardly flows down into the tank 52. There is a problem that the air mixed in the hydraulic oil remains in the pilot pressure passage 82 and the so-called air bleeding is not sufficiently performed. When air remains in the hydraulic oil in the pilot pressure passage 82, the rise of the signal pressure is delayed, and therefore the timing at which the brake release hydraulic switching valve 30 is switched from the braking position (d) to the release position (e) is delayed. In a state where the brake force of the brake device 20 is not released, the hydraulic motor 1 rotates and wear of the brake device 20 progresses, so that the service life is shortened.

  In response to this, as shown in FIG. 3, the present invention includes a pilot drain passage 49 that allows one end of the pilot pressure passage 82 to communicate with the tank 52 at the release position (e) of the brake release hydraulic switching valve 30. The pressurized hydraulic oil in the pilot pressure passage 82 is drained from the drain passage 88 to the tank 52 through the pilot drain passage 49 together with air.

  4A is a sectional view of the brake release hydraulic switching valve 30 of the present invention, and FIG. 4B is a hydraulic circuit diagram of the brake release hydraulic switching valve 30. As shown in FIG. 1, the hydraulic switching valve 30 includes a valve body 31 fastened to the case 11 of the hydraulic motor 1 and a spool 40 slidably received in a hole formed in the central axis direction of the valve body 31. And a pilot port 33 defined by one end of the spool 40 and a return spring 36 for urging the spool 40 in the right direction in the figure.

  When the discharge pressure of the pilot pump 50 is guided to the pilot port 33 through the pilot pressure passage 82 as a signal pressure, the spool 40 moves to the left in the figure against the urging force of the return spring 36.

  The spool 40 is restrained from moving in the right direction by abutment of a collar portion thereof formed on the inner peripheral surface of the valve body 31, while the end surface of the spool 40 abuts on the closing plug 34. Movement in the direction is restricted.

  The valve body 31 includes a drive pressure port 39 to which pressurized hydraulic oil from the pilot pump 50 is supplied through the drive pressure passage 83 shown in FIG. 3, and a brake pipe shown in FIG. A brake release port 38 communicating with the passage 73 and a drain port 37 communicating with the case 11 of the hydraulic motor 1 are provided.

  The cylindrical spool 40 includes holes 40a and 40b formed from both ends along the central axis, an orifice 40c communicating with the holes 40a and 40b, and an annular groove formed on the outer peripheral surface of the spool 40. 41a and 41b and the orifice 42b which connects the hole part 40b and the groove part 41b are formed.

  When the spool 40 is in the braking position (d) shown in FIG. 4, the drain port 37 is communicated with the brake release port 38 via the pair of grooves 41b and the orifice 42b. The pair of groove portions 41b are always in communication with each other through the throttle portion.

  When the spool 40 is in the release position (e) shown in FIGS. 5 to 7, the drive pressure port 39 is communicated with the brake release port 38 via the groove 41a. That is, the groove 41a constitutes a brake drive passage 48 that allows the drive pressure port 39 to communicate with the brake release port 38 at the release position (e).

  The brake release hydraulic switching valve 30 includes a rod 45 slidably fitted in the hole 40 a of the spool 40, and the pilot drain passage 49 is opened and closed via the rod 45.

  A flange 45 a that extends in an annular shape is formed at the base end of the rod 45, and the flange 45 a is fixed in the spool 40 via the stopper ring 46. The rod 45 is formed with a through hole 45b communicating with both sides of the flange 45a.

  The rod 45 is formed with a hole 45c extending from the tip thereof along the central axis and an orifice 45d communicating with the hole 45c and opening on the outer peripheral surface of the rod 45.

  When the spool 40 is at the stroke position shown in FIGS. 4 and 5, the orifice 45d is closed by the spool 40, while when the spool 40 is at the stroke position shown in FIG. 40 opens the pilot drain passage 49.

  The pilot drain passage 49 includes a through hole 45b, an orifice 45d, a hole portion 45c, a hole portion 40b, an orifice 40c, a hole portion 40a, and a spring chamber 47 in which the return spring 36 is accommodated. Lead oil to drain port 37.

  Next, the operation of the brake release hydraulic pressure switching valve 30 will be described according to the operating state of the brake device 20.

  First, when the braking device 20 generates a braking force, the pilot pressure switching valve 80 is switched to the braking position (g). As a result, the drain pressure acts on the end of the spool 40 of the hydraulic switching valve 30, and the hydraulic switching valve 30 is switched to the braking position (d) by the urging force of the return spring 36 as shown in FIG. As a result, the pressurized hydraulic oil in the chamber 28 is drained from the drain port 88 to the tank 52 via the brake release port 38 and the drain port 37, and the urging force of the brake spring 26 becomes larger than the pressure in the chamber 28. For this reason, the brake piston 27 moves, the disk plate 21 presses against the friction plate 22, and a braking force is generated between the disk plate 21 and the friction plate 22.

  At this time, the orifice 45d is closed by the spool 40, and the pilot drain passage 49 is closed.

  On the other hand, when releasing the braking force of the brake device 20, the pilot pressure switching valve 80 is switched to the release position (f). Along with this, the driving pressure supplied from the pilot pump 50 is guided from the pilot pressure switching valve 80 to the pilot port 33 through the pilot pressure passage 82, and the spool 40 moves against the urging force of the return spring 36 to switch the hydraulic pressure. The valve 30 switches to the release position (e). As a result, the pressurized hydraulic fluid introduced into the drive pressure port 39 is supplied from the brake release port 38 to the chamber 28 of the brake device 20, and the brake piston 27 becomes the urging force of the brake spring 26 due to the pressure increase in the chamber 28. Accordingly, the disc plate 21 and the friction plate 22 are disengaged from each other, and the braking force of the brake device 20 is released.

  As described above, when the hydraulic switching valve 30 switches from the braking position (d) to the release position (e) against the urging force of the return spring 36, the spool 40 moves as shown in FIGS. After the brake drive passage 48 is opened, the pilot drain passage 49 is opened, and part of the pressurized hydraulic oil in the pilot pressure passage 82 is drained to the tank 52 through the pilot drain passage 49 together with air.

  As shown in FIG. 5, when the spool 40 moves and the drive pressure port 39 communicates with the brake release port 38 via the groove 41a of the spool 40 and the brake drive passage 48 starts to open, the orifice 45d of the rod 45 is opened. Is closed by the inner peripheral surface of the spool 40 and the pilot drain passage 49 is closed.

  As a result, before the brake piston 27 moves due to the pressure increase in the chamber 28, the pressurized hydraulic oil in the pilot pressure passage 82 does not flow out to the tank 52 through the pilot drain passage 49, and enters the pilot port 33. The induced signal pressure rises quickly. Therefore, the spool 40 of the hydraulic switching valve 30 is quickly switched from the braking position (d) to the release position (e) by the signal pressure, and the braking force can be released quickly.

  Thereafter, as shown in FIG. 6, the spool 40 moves, the orifice 45d of the rod 45 is opened by the inner peripheral surface of the spool 40, and the pilot drain passage 49 is opened.

  As shown in FIG. 7, even if the spool 40 moves to the stroke end where it comes into contact with the closing plug 34, the orifice 45d of the rod 45 is opened by the inner peripheral surface of the spool 40, and the pilot drain passage 49 is opened. Yes.

  In the stroke region from FIG. 6 to FIG. 7, the pilot drain passage 49 is opened, and the pressurized hydraulic fluid in the pilot port 33 is, as indicated by the arrow in the figure, the through hole 45, the orifice 45 d, the hole 40 b, the orifice It flows out into the case 11 of the hydraulic motor 1 through 40 c, the hole 40 a, the spring chamber 47, and the drain port 37, and is returned to the tank 52 through this case 11.

  The flow of hydraulic oil drained through the pilot drain passage 49 is throttled in two stages by the orifice 45d and the orifice 40c, so that the signal pressure of the pilot port 33 is prevented from dropping below the set value, and the spool 40 is As shown in FIG. 7, the state of moving to the stroke end is maintained, and insufficient pilot flow is prevented.

  As a result, the air that has entered the pilot pressure passage 82 is discharged together with the hydraulic oil drained through the pilot drain passage 49, the pressurized hydraulic oil fills the pilot pressure passage 82, and the pilot pressure switching valve 80 is released. As the position is changed to the position (f), the signal pressure is rapidly increased by the pressurized hydraulic fluid supplied from the pilot pump 50. Therefore, the spool 40 of the hydraulic switching valve 30 is quickly switched from the braking position (d) to the release position (e) by the signal pressure, and the braking force can be released quickly. Thereby, it is avoided that the hydraulic motor 1 rotates while braking of the brake device 20 is not released, and wear of the brake device 20 is suppressed.

  In the present embodiment, the brake device 20 that releases the braking force when the pressurized hydraulic oil is supplied and generates the braking force when the pressurized hydraulic fluid is drained, and the brake device 20 is pressurized. A drive pressure passage 83 for supplying oil, a drain passage 88 for draining pressurized hydraulic oil from the brake device 20, and the drive pressure passage 83 and the drain passage 88 for the brake device 20 are selectively selected according to the signal pressure. A hydraulic switching valve 30 to be opened and a pilot pressure passage 82 for guiding a signal pressure to the hydraulic switching valve 30 are provided, and the hydraulic switching valve 30 has a braking position (d) where the drain passage 88 is opened as the signal pressure increases. ) To a release position (e) for opening the drive pressure passage 83, which is a pilot system that drains pressurized hydraulic fluid in the pilot pressure passage 82. A drain passage 49 is provided, and the hydraulic switching valve 30 is configured to close the pilot drain passage 49 at the braking position (d) while opening the pilot drain passage 49 at the release position (e). The pressurized hydraulic oil is allowed to escape through the pilot drain passage 49 together with air, so that the air in the pilot pressure passage 82 is sufficiently vented. As a result, the rise of the signal pressure is prevented from being delayed due to the air remaining in the pilot pressure passage, and the brake force is released accurately.

  In the present embodiment, the hydraulic switching valve 30 is configured to open the pilot drain passage 49 after opening the driving pressure passage 83 in the process of switching from the braking position (d) to the release position (e). After the braking of the brake device 20 is released by opening, the pilot drain passage 49 is opened and the pilot pressure passage 82 is opened. Thus, before the braking of the brake device 20 is released, the pressurized hydraulic fluid in the pilot pressure passage 82 is not drained through the pilot drain passage 49, and the signal pressure rises quickly, and the brake force Is properly released.

  In this embodiment, since the throttle means (orifices 40c and 45d) for restricting the flow of hydraulic oil is provided in the pilot drain passage 49, the hydraulic pressure is released after the braking of the brake device 20 is released by opening the drive pressure passage 83. Even if the pilot drain passage 49 is opened at the release position (e) of the switching valve 30, the signal pressure in the pilot pressure passage 82 is kept high, and air is discharged through the throttle means (orifices 40c and 45d), and the braking force. Is properly released.

  In the present embodiment, the hydraulic switching valve 30 includes a spool 40 that moves according to the signal pressure guided by the pilot pressure passage 82, and a hole 40 b that defines the pilot drain passage 49 is formed in the spool 40. Since the rod 45 slidably fitted in the hole 40b is provided, and the pilot drain passage 49 is opened and closed through the rod 45 as the spool 40 moves, the pilot drain passage 49 is placed inside the spool 40. Therefore, the hydraulic switching valve 30 can be prevented from being enlarged.

  Next, another embodiment shown in FIG. 8 will be described. This basically has the same configuration as that of the embodiment shown in FIG. 4, and only different portions will be described. In addition, the same code | symbol is attached | subjected to the same structure part as the said embodiment.

  8A is a cross-sectional view of the brake release hydraulic switching valve 30, and FIG. 8B is a hydraulic circuit diagram of the brake release hydraulic switching valve 30.

  The pilot drain passage 49 is defined by through holes 31 a, 31 b and 31 c formed in the valve body 31, and the open end of the through hole 31 a is opened and closed by the spool 40.

  As throttling means for restricting the flow of the hydraulic oil to the pilot drain passage 49, orifices 91 and 92 are interposed in the through hole 31b. The flow of the hydraulic oil drained through the pilot drain passage 49 is throttled in two stages by the orifices 91 and 92, so that the signal pressure of the pilot port 33 is prevented from dropping below the set value, and the spool 40 is As shown in FIG. 7, the state of moving to the stroke end is maintained, and insufficient pilot flow is prevented.

  Next, the operation of the brake release hydraulic pressure switching valve 30 will be described according to the operating state of the brake device 20.

  First, when the braking device 20 generates a braking force, the through hole 31a is closed by the spool 40, and the pilot drain passage 49 is closed.

  On the other hand, when releasing the braking force of the brake device 20, when the spool 40 moves from the braking position (d) to the release position (e) against the urging force of the return spring 36, the groove 41a of the spool 40 is obtained. After the brake drive passage 48 is opened via the through hole, the through hole 31a is opened by the spool 40 to open the pilot drain passage 49, and the pressurized hydraulic fluid in the pilot pressure passage 82 passes through the pilot drain passage 49 together with air. Then drain into the tank 52.

  In the present embodiment, the hydraulic switching valve 30 includes a spool 40 that moves according to the signal pressure guided by the pilot pressure passage 82 and a valve body 31 in which the spool 40 is slidably housed. The through holes 31a, 31b, 31c that define the pilot drain passage 49 are formed in the valve body 31 so that the pilot drain passage 49 is opened and closed as the spool 40 moves. It is provided and the freedom degree with respect to arrangement | positioning of the orifices 91 and 92 grade | etc., Is raised.

  Note that a working fluid such as a water-soluble alternative liquid may be used instead of the oil as the working oil.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

DESCRIPTION OF SYMBOLS 1 Hydraulic motor 20 Brake device 30 Hydraulic switching valve 31 Valve body 31a, 31b, 31c Through-hole 33 Pilot port 36 Return spring 37 Drain port 38 Brake release port 39 Drive pressure port 40 Spool 40b Hole 40c, 45d Orifice (throttle means )
48 Brake drive passage 49 Pilot drain passage 50 Pilot pump 52 Tank 82 Pilot pressure passage 83 Drive pressure passage 88 Drain passage 91, 92 Orifice (throttle means)

Claims (4)

A brake device that releases the braking force by supplying the pressurized working fluid and generates the braking force by draining the pressurized working fluid;
A drive pressure passage for supplying pressurized working fluid to the brake device;
A drain passage for draining pressurized working fluid from the brake device;
A hydraulic switching valve that selectively opens the drive pressure passage and the drain passage in response to a signal pressure with respect to the brake device;
A pilot pressure passage for guiding a signal pressure to the hydraulic switching valve,
The hydraulic switching valve is a brake system configured to switch from a braking position at which the drain passage opens to a release position at which the driving pressure passage opens as the signal pressure increases,
A pilot drain passage for draining the pressurized working fluid in the pilot pressure passage;
The hydraulic switching valve closes the pilot drain passage at the braking position, and opens the driving pressure passage in the process of switching from the braking position to the release position to release the braking force, and then the pilot drain passage. Brake system characterized by opening the door.   2. The brake system according to claim 1, wherein throttle means for restricting a flow of the working fluid is provided in the pilot drain passage. The hydraulic switching valve includes a spool that moves in response to a signal pressure guided by the pilot pressure passage;
Forming a hole defining the pilot drain passage in the spool;
Comprising a rod slidably fitted into the hole,
The brake system according to claim 1 or 2, wherein the pilot drain passage is opened and closed with the movement of the spool via the rod. The hydraulic switching valve has a spool that moves according to a signal pressure guided by the pilot pressure passage;
A valve body in which the spool is slidably housed,
Forming a through hole defining the pilot drain passage in the valve body;
The brake system according to any one of claims 1 to 3, wherein the pilot drain passage is opened and closed as the spool moves.

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