JP2007100723A - Disc brake - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow operation by low-pressure liquid pressure source, in a disc brake provided with a hydraulic-assisted parking brake mechanism. <P>SOLUTION: A feed screw 13 and a locking nut 14 are inserted in a cylinder 7, and a drive mechanism 20 is connected with the feed screw 13. A hydraulic unit 28 is connected with a hydraulic pressure supply port 12 through a booster unit 31 and a bypass passage 32. When the brake is used as a normal brake, an electromagnetic open/close valve 31A is closed and an electromagnetic open/close valve 32A is opened to directly supply hydraulic pressure from the hydraulic unit 28 to the cylinder 7 through the bypass passage 32. When the brake is used as a parking brake, the electromagnetic open/close valve 31A is opened and the electromagnetic open/close valve 32A is closed to boost the hydraulic pressure from the hydraulic unit 28 by the booster unit 31, and the boosted pressure is supplied to the cylinder 7 to increase a control force. The feed screw 14 is rotated by a drive mechanism 20, and a piston 9 is pressed by the locking nut 14 to hold a braking state. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hydraulic disc brake having a parking brake mechanism.

2. Description of the Related Art Conventionally, in a hydraulic disc brake mounted on a vehicle such as an automobile, a parking brake mechanism that can maintain a braking state regardless of the hydraulic pressure when the vehicle is stopped is disclosed in Patent Document 1, for example. What you have is known. When the disc brake described in Patent Document 1 is used as a service brake, the piston in the cylinder is actuated by hydraulic pressure, and the brake pad is pressed against the disc rotor to generate a braking force. Also, when used as a parking brake, after supplying hydraulic pressure and generating braking force, an electric motor rotates the screw mechanism via the gear mechanism to maintain the position of the piston. Thereafter, the braking force can be maintained even if the hydraulic pressure is released.
Japanese National Publication No. 5-506196

  The hydraulic disc brake equipped with the parking brake mechanism will be described. When used as a parking brake, hydraulic pressure is supplied into the cylinder by a hydraulic pressure supply source such as a hydraulic pump, and the piston is pushed to release the brake pad. After being pressed against the disc rotor, a hydraulically assisted parking brake mechanism is provided in which a lock mechanism is operated by an electric motor to hold the piston in a braking state. Thereby, the load of the electric motor can be greatly reduced, and the electric motor can be reduced in size and power can be saved.

However, the disc brake provided with the conventional hydraulic assist parking brake mechanism has the following problems. In order to operate the hydraulic pressure assisted parking brake mechanism, a high hydraulic pressure of about 20 MPa is generally required. For example, by applying appropriate braking force to each wheel according to the running state of the vehicle, skidding, etc. In-vehicle hydraulic pumps used for vehicle motion control (VDC) or the like that stabilizes the vehicle by suppressing the vehicle usually cannot obtain a high hydraulic pressure sufficient to operate the parking brake mechanism. For this reason, when the pressure of the hydraulic pump is increased, in addition to the problem of increase in size and weight, it is necessary to ensure the pressure resistance of the hydraulic pipe and the cost.
In order to operate the parking brake mechanism with low hydraulic pressure, it is conceivable to increase the diameter of the disc brake piston. In this case, however, the piston thrust increases during operation with the service brake, causing slipping, etc. May occur and the stability of the service brake will be lost.

  The present invention has been made in view of the above points, and is a hydraulically assisted parking brake mechanism that can be operated by a low-pressure hydraulic pressure supply source and can ensure stability during normal brake operation. It aims at providing the disc brake provided with.

In order to solve the above-mentioned problems, the invention according to claim 1 is directed to a pair of brake pads disposed on both sides via a disk, and a piston slidably fitted to a cylinder so that a liquid from a hydraulic pressure source is fitted. A caliper that slides the piston by pressure supply to bring the pair of brake pads into contact with the disc, a drive mechanism that is arranged outside the cylinder and generates a driving force by an electric actuator, and is arranged inside the cylinder And a pressing mechanism that is driven by the driving mechanism and presses the piston against the brake pad, in response to a parking brake instruction signal, simultaneously with the hydraulic pressure supply from the hydraulic pressure source to the cylinder or hydraulic pressure A pressure regulator for adjusting a hydraulic pressure between the hydraulic pressure source and the cylinder in a disc brake in which the electric actuator operates after supply And a bypass passage for bypassing the pressure regulating mechanism, and a switching means for selectively circulating one of the pressure regulating mechanism or the bypass passage in response to the parking brake instruction signal. brake.
According to a second aspect of the present invention, there is provided the disc brake according to the first aspect, wherein the pressure adjusting mechanism includes a large diameter portion having a pressure receiving surface on the hydraulic pressure source side and a small diameter portion having a pressure receiving surface on the cylinder side. A pressure increasing mechanism that increases the hydraulic pressure supplied from the hydraulic pressure source to the cylinder, and the switching means responds to the parking brake signal, It is characterized by being distributed.
According to a third aspect of the present invention, there is provided the disc brake according to the first aspect, wherein the pressure adjusting mechanism includes a small diameter portion having a pressure receiving surface on the hydraulic pressure source side and a large diameter portion having a pressure receiving surface on the cylinder side. A stepped piston having a communication path for communicating the fluid pressure source side and the cylinder side; and valve means for opening and closing the communication path by the movement of the stepped piston, from the fluid pressure source to the cylinder A pressure reducing mechanism for reducing the supplied hydraulic pressure, wherein the switching means circulates the bypass passage in response to the parking brake signal.

According to the disc brake of the first aspect of the present invention, the hydraulic pressure is supplied from the hydraulic pressure source to the cylinder by the switching means via the pressure regulating mechanism or by bypassing the pressure regulating mechanism. And the supply hydraulic pressure to a cylinder required at the time of parking brake operation | movement can be selected suitably. Thus, the parking brake can be operated even when a low-pressure hydraulic pressure source is used, and an appropriate piston thrust can be generated even when the service brake is used.
According to the disc brake of the second aspect of the invention, the hydraulic pressure is directly supplied from the hydraulic pressure source to the cylinder by the bypass passage when the service brake is operated, and is supplied to the cylinder by the pressure increasing mechanism when the parking brake is operated. The hydraulic pressure can be increased. Thus, the parking brake can be operated even when a low-pressure hydraulic pressure source is used, and an appropriate piston thrust can be generated even when the service brake is used.
According to the disc brake of the third aspect of the invention, the hydraulic pressure supplied to the cylinder is reduced by the pressure reducing mechanism when the normal brake is operated, and the hydraulic pressure is directly supplied from the hydraulic pressure source to the cylinder by the bypass passage when the parking brake is operated. Pressure can be supplied. As a result, even when the diameter of the piston of the disc brake is increased, it is possible to ensure stability when using the service brake, and it is possible to operate the parking brake using a low-pressure hydraulic pressure source.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
A first embodiment of the present invention will be described with reference to FIGS. 1 and 4. As shown in FIG. 1, a disc brake 1 according to the present embodiment is a caliper floating type hydraulic disc brake, and is a pair of disc rotors 2 (discs) disposed on both sides of a disc rotor 2 (disc) that rotates with wheels (not shown). The brake pads 3 and 4, the caliper 5 straddling the disk rotor 2, and the carrier fixed to the non-rotating portion of the vehicle and supporting the brake pads 3 and 4 and the caliper 5 movably along the axial direction of the disk rotor 2. (Not shown).

  In the caliper body 6 of the caliper 5, a cylinder 7 is provided at a portion facing one brake pad 3, and a claw portion 8 is formed across the disk rotor 2 and facing the other brake pad 4. A bottomed cylindrical piston 9 is slidably fitted to the cylinder 7 via a fallback seal 10. A dust seal 11 seals between the piston 9 and the cylinder 7. The caliper body 6 is provided with a hydraulic pressure port 12 that communicates with the cylinder 7. The hydraulic pressure is supplied from the hydraulic pressure port 12 to the cylinder 7 to operate the piston 9.

  A feed screw 13 and a lock nut 14 constituting a pressing mechanism are inserted into the piston 9. The feed screw 13 is formed with a screw portion 15 at the distal end inserted into the piston 9, and a base end portion is inserted into the cylinder 7 in a liquid-tight and rotatable manner so as to extend outside the caliper body 6. ing. A flange portion 16 is integrally formed at an intermediate portion of the feed screw 13, and a thrust bearing 17 is provided between the flange portion 16 and the bottom portion of the cylinder 7.

  The lock nut 14 is screwed into the screw portion 15 of the feed screw 13, and one end thereof is in contact with the bottom portion of the piston 9. The lock nut 14 is provided with a detent 18, and by engaging the detent 18 with the piston 9, the lock nut 14 can move in the axial direction with respect to the piston 9 and rotate around the axis. It is prevented. Note that the piston 9 is prevented from rotating with respect to the caliper body 6 by engaging with a detent 19 formed on the brake pad 3. Thereby, the lock nut 14 can be moved forward or backward by rotating the feed screw 13.

  A drive mechanism 20 is attached to the end of the caliper body 6 on the bottom side of the cylinder 7 (outside of the cylinder 7) with a bolt 21. The drive mechanism 20 has a structure in which a worm wheel 24 is engaged with a worm 23 attached to a shaft 22 of an electric motor (electric actuator). The worm wheel 24 is based on a feed screw 13 extended from the caliper body 6. It is connected to the end. Accordingly, the rotation of the electric motor can be decelerated by the worm 23 and the worm wheel 24 to drive the feed screw 13, and the rotation of the feed screw 13 can be locked when the electric motor is stopped.

Next, a brake hydraulic circuit that uses the disc brake 1 of the present embodiment will be described.
As shown in FIG. 4, the brake hydraulic circuit 25 is an automotive brake hydraulic circuit, and a master cylinder 27 to which a brake pedal 26 is connected is connected to a disc brake of each wheel via a hydraulic unit 28. Has been. A normal disc brake 29 having no parking brake mechanism is connected to the front wheel side, whereas a disc brake 1 of this embodiment having a parking brake mechanism is connected to the rear wheel side. ing. In the disc brake 1 of the present embodiment connected to the rear wheel side, in consideration of the fact that the load applied to the rear wheel is generally smaller than the load applied to the front wheel, the pressure receiving area of the piston 9 is the disc brake on the front wheel side. 29 is set smaller.

  The hydraulic pressure unit 28 supplies the hydraulic pressure generated in the master cylinder 27 by operating the brake pedal 26 to the disc brakes 1 and 29. Further, the hydraulic unit 28 includes a hydraulic pump (hydraulic pressure source), and supplies hydraulic pressure to the disc brakes 1 and 29 of each wheel according to the running state of the vehicle to appropriately apply a braking force. Vehicle motion control (VDC) that suppresses side slip and stabilizes the vehicle can be executed. Furthermore, hydraulic pressure can be supplied to the hydraulic pressure port 12 of the disc brake 1 in order to operate the parking brake.

  The disc brake 1 includes a hydraulic pressure switching unit 30 that switches the hydraulic pressure supplied to the hydraulic pressure port 12. As shown in FIG. 1, the hydraulic pressure switching unit 30 includes a pressure-increasing mechanism 31, a bypass passage 32 that bypasses the pressure-increasing mechanism 31, and a normally open electromagnetic on-off valve 32A that opens and closes the bypass passage 32 (switching means). And a normally closed electromagnetic on-off valve 31A (switching means) arranged on the inlet side of the pressure increasing mechanism 31 is arranged. The pressure increasing mechanism 31 has a large stepped bore consisting of a large diameter bore 34 communicating with the inlet 33 connected to the hydraulic pressure unit 28 side and a small diameter bore 36 communicating with the outlet 35 connected to the hydraulic pressure port 12 side. A stepped piston 39 having a diameter portion 37 and a small diameter portion 38 is slidably fitted. The stepped piston 39 is urged toward the inlet 33 by a return spring 39A.

Next, the operation of the present embodiment configured as described above will be described.
When used as a service brake, a disc on the front wheel side is operated from the master cylinder 27 via the hydraulic unit 28 by operating the brake pedal 26 without energizing the electromagnetic on-off valves 31A and 32A of the hydraulic pressure switching unit 30. Fluid pressure is supplied to the brake 29 and the disc brake 1 on the rear wheel side. At this time, in the hydraulic pressure switching unit 30, the normally open electromagnetic opening / closing valve 32 </ b> A is opened and the normally closed electromagnetic opening / closing valve 31 </ b> A is closed, so that the hydraulic pressure from the master cylinder 27 directly passes through the bypass passage 32. The pressure port 12 is supplied.

  As a result, the piston 9 advances while bending the fallback seal 10, presses one brake pad 3 against the disc rotor 2, and the caliper 5 moves by the reaction force, and the other brake is applied by the claw portion 8. The pad 4 is pressed against the disc rotor 2. The brake pads 3 and 4 pinch the disc rotor 2 to generate a braking force. When the brake pedal 26 is released and the supply of hydraulic pressure is released, the piston 9 is retracted to the original position by the elasticity of the fallback seal 10 and the braking is released. When the brake pads 3 and 4 are worn, the clearance between the brake pads 3 and 4 and the disc rotor 2 can be adjusted to a constant level by slipping between the piston 9 and the fallback seal 10 during braking. it can.

  When used as a parking brake, first, the electromagnetic on / off valve 32A of the hydraulic pressure switching unit 30 is closed by energization, and the electromagnetic on / off valve 31A is opened. Supply hydraulic pressure only to the brake 1. At this time, since the electromagnetic on-off valve 32A is closed and the electromagnetic on-off valve 31A is open, the hydraulic pressure from the hydraulic unit 28 is supplied to the hydraulic pressure port 12 via the pressure increasing mechanism 31.

  In the pressure increasing mechanism 31, the hydraulic pressure supplied to the inlet 33 side is increased and transmitted to the outlet 35 side by the pressure receiving area ratio between the large diameter portion 37 and the small diameter portion 38 of the stepped piston 39. The increased hydraulic pressure is supplied to the hydraulic pressure port 12 to advance the piston 9 and press the brake pads 3 and 4 against the disc rotor 2. Next, in this state, the shaft 22 of the electric motor of the drive mechanism 20 is rotated, the feed screw 13 is rotated, and the lock nut 14 is pressed against the bottom of the piston 9. Thereafter, the supply of the hydraulic pressure from the hydraulic pump of the hydraulic unit 28, the energization of the electromagnetic on-off valves 31A and 32A, and the energization of the electric motor of the drive mechanism 20 are stopped. At this time, the rotation of the feed screw is locked by the frictional force between the screw portion 15 of the feed screw 13 and the lock nut 14 and the engagement between the worm 23 and the worm wheel 24. Thereby, the piston 9 can be held at the braking position, and the braking force as a parking brake can be maintained.

  Thus, when the disc brake 1 is used as a parking brake, the hydraulic pressure supplied to the hydraulic pressure port 12 can be increased by the pressure-increasing mechanism 31, so the load on the hydraulic pump of the hydraulic unit 28 is reduced. Therefore, a necessary hydraulic pressure can be obtained even with a low-pressure hydraulic pump used for vehicle motion control or the like, and a braking force necessary as a parking brake can be ensured. When used as a parking brake, the supply of hydraulic pressure to the hydraulic pressure port 12 and the operation of the electric motor of the drive mechanism 20 may be performed simultaneously.

  When releasing the parking brake, the hydraulic pressure is supplied from the hydraulic pump of the hydraulic pressure unit 28 in the state where the electromagnetic on-off valves 31 and 33 of the hydraulic pressure switching unit 30 are energized, as in the case of the parking brake operation described above. Thus, the piston 9 is urged toward the brake pad 3, and the lock of the rotation of the feed screw 13 due to the frictional force between the screw portion 15 and the lock nut 14 is released. Next, in this state, the shaft 22 of the electric motor of the drive mechanism 20 is reversely rotated, the feed screw 13 is reversely rotated, and the lock nut 14 is moved backward. Thereafter, the supply of the hydraulic pressure from the hydraulic pump of the hydraulic unit 28, the energization of the electromagnetic on-off valves 31A and 32A, and the energization of the electric motor of the drive mechanism 20 are stopped. In this way, the parking brake can be released. The electromagnetic on-off valves 31A and 32A may be a single three-way valve.

  Next, a second embodiment of the present invention will be described with reference to FIGS. In addition, since this embodiment is substantially the same structure as the first embodiment except that the structure of the hydraulic pressure switching unit is different, hereinafter, the same part as the first embodiment will be described. Only the different parts will be described in detail using the same reference numerals.

  In the disc brake according to the present embodiment, a hydraulic pressure switching unit 30A shown in FIG. 2 is provided instead of the hydraulic pressure switching unit 30 of the first embodiment. As shown in FIG. 2, the hydraulic pressure switching unit 30A includes a pressure reducing valve 40, a bypass passage 41 that bypasses the pressure reducing valve 40, and a normally closed electromagnetic opening / closing valve 41A (switching means) that opens and closes the bypass passage 41. I have. The pressure reducing valve 40 includes a small diameter bore 44 communicating with a valve chamber 43 provided on the inlet 42 side connected to the hydraulic pressure unit 28 side and a large diameter bore 46 communicating with an outlet 45 connected to the hydraulic pressure port 12 side. A stepped piston 49 having a small diameter portion 47 and a large diameter portion 48 is slidably fitted in the stepped bore. The stepped piston 49 is provided with a communication passage 50 that allows the valve chamber 43 and the outlet 45 to communicate with each other. The stepped piston 49 is urged toward the outlet 45 by the spring 51. In the valve chamber 43, a valve member 52 (valve means) that opens and closes the communication passage 50 by being seated on the end surface of the small diameter portion 47 of the stepped piston 49 and a valve spring that biases the valve member 52 toward the stepped piston 49 side. 53 is provided.

  In the pressure reducing valve 40, when the fluid pressure on the inlet 42 side is low, the inlet 42 side and the outlet 45 side are communicated with each other by the communication passage 50, and the fluid pressure on the outlet 45 side becomes equal to the inlet 42 side. When the hydraulic pressure rises and reaches a predetermined pressure, the stepped piston 49 moves toward the inlet 42 against the urging force of the spring 51 due to the pressure receiving area difference between the small diameter portion 47 and the large diameter portion 48, and the valve member 52 is moved. The communication path 50 is closed by sitting on the end face of the small diameter portion 47. Thereafter, the stepped piston 49 moves to the outlet 45 side due to the increase of the hydraulic pressure on the inlet side 42, and when the valve member 52 is separated from the end face of the small diameter portion 47 by this movement and the communication passage 50 opens, the stepped piston 49 again. The attached piston 49 moves to the inlet 42 side, and by this repetition, the increase in the hydraulic pressure on the outlet 45 side is suppressed to a lower ratio than the increase in the hydraulic pressure on the inlet 42 side. The relationship between the hydraulic pressure on the inlet 42 side of the pressure reducing valve 40 and the hydraulic pressure on the outlet 45 side is shown by a solid line in FIG.

  Further, in the present embodiment, the pressure receiving area of the piston 9 of the disc brake 1 is set sufficiently large so that a braking force necessary as a parking brake can be obtained even by a low hydraulic pressure from the hydraulic pump of the hydraulic pressure unit 28. .

Next, the operation of the present embodiment configured as described above will be described.
When used as a service brake, the disc brake 29 on the front wheel side is operated from the master cylinder 27 through the hydraulic unit 28 by operating the brake pedal 26 without energizing the electromagnetic on-off valve 41A of the hydraulic pressure switching unit 30A. In addition, hydraulic pressure is supplied to the disc brake 1 on the rear wheel side. At this time, in the hydraulic pressure switching unit 30A, the normally closed electromagnetic on-off valve 41A is closed, so that the hydraulic pressure from the master cylinder 27 is supplied to the hydraulic pressure port 12 via the pressure reducing valve 40.

  As a result, the piston 9 advances while bending the fallback seal 10, presses one brake pad 3 against the disc rotor 2, and the caliper 5 moves by the reaction force, and the other brake is applied by the claw portion 8. The pad 4 is pressed against the disc rotor 2. The brake pads 3 and 4 pinch the disc rotor 2 to generate a braking force.

  At this time, when the hydraulic pressure from the master cylinder 27 rises above a predetermined pressure, the hydraulic pressure supplied to the hydraulic pressure port 12 is reduced by the pressure reducing valve 40 as shown in FIG. Even if the area is set large, the braking force does not increase excessively, and an appropriate braking force is distributed to the rear wheel side, so that the rear wheel is not locked early.

  When used as a parking brake, first, with the electromagnetic on-off valve 41A of the hydraulic pressure switching unit 30A opened by energization, the hydraulic pressure of only the rear wheel side disc brake 1 is applied by the hydraulic pump of the hydraulic pressure unit 28. Supply. At this time, since the electromagnetic opening / closing valve 39 is open, the hydraulic pressure from the hydraulic pressure unit 28 is directly supplied to the hydraulic pressure port 12 by bypassing the pressure reducing valve 40 by the bypass passage 41. Then, the piston 9 moves forward by this hydraulic pressure and presses the brake pads 3 and 4 against the disc rotor 2. At this time, since the pressure receiving area of the piston 9 is set to be sufficiently large, a braking force required as a parking brake can be generated even by a low hydraulic pressure by the hydraulic pump of the hydraulic unit 28.

  Next, in this state, the shaft 22 of the motor of the drive mechanism 20 is rotated, the feed screw 13 is rotated, and the lock nut 14 is pressed against the bottom of the piston 9. Thereafter, the supply of the hydraulic pressure from the hydraulic pump of the hydraulic unit 28, the energization of the electromagnetic on-off valve 41A, and the energization of the electric motor of the drive mechanism 20 are stopped. At this time, the rotation of the feed screw is locked by the frictional force between the screw portion 15 of the feed screw 13 and the lock nut 14 and the engagement between the worm 23 and the worm wheel 24. Thereby, the piston 9 can be held at the braking position, and the braking force as a parking brake can be maintained. When used as a parking brake, the supply of hydraulic pressure to the hydraulic pressure port 12 and the operation of the electric motor of the drive mechanism 20 may be performed simultaneously.

  When releasing the parking brake, the hydraulic pressure is supplied from the hydraulic pump of the hydraulic pressure unit 28 in the state where the electromagnetic on-off valve 41A of the hydraulic pressure switching unit 30A is energized, as in the case of the parking brake operation described above. The piston 9 is urged toward the brake pad 3, and the lock of the rotation of the feed screw 13 due to the frictional force between the screw portion 15 and the lock nut 14 is released. Next, in this state, the shaft 22 of the electric motor of the drive mechanism 20 is reversely rotated, the feed screw 13 is reversely rotated, and the lock nut 14 is moved backward. Thereafter, the supply of the hydraulic pressure from the hydraulic pump of the hydraulic unit 28, the energization of the electromagnetic on-off valve 41A, and the energization of the electric motor of the drive mechanism 20 are stopped. In this way, the parking brake can be released.

1 is a longitudinal sectional view showing a disc brake according to a first embodiment of the present invention. It is the schematic which shows the hydraulic pressure switching unit of the disc brake which concerns on 2nd Embodiment of this invention. It is a figure which shows the characteristic of the pressure-reduction valve of the hydraulic pressure switching unit shown in FIG. It is the schematic which shows the hydraulic brake system of the motor vehicle which applied the disc brake which concerns on this invention.

Explanation of symbols

1 disc brake, 2 disc rotor (disc), 3, 4 brake pad, 5 caliper, 7 cylinder, 9 piston, 13 feed screw (pressing mechanism), 14 lock nut (pressing mechanism), 20 drive mechanism, 31 pressure increasing mechanism (Pressure adjustment mechanism), 41 Bypass passage, 31A, 32A Electromagnetic on-off valve (switching means)

Claims (3)

A pair of brake pads disposed on both sides via a disk, and a piston slidably fitted to a cylinder, and the piston slides due to a hydraulic pressure supply from a hydraulic pressure source so that the pair of brake pads are A caliper that comes into contact with the disk, a drive mechanism that is arranged outside the cylinder and generates a driving force by an electric actuator, and is arranged inside the cylinder and driven by the drive mechanism to press the piston against the brake pad In a disc brake in which the electric actuator is operated simultaneously with or after the hydraulic pressure is supplied from the hydraulic pressure source to the cylinder in response to a parking brake instruction signal, the hydraulic pressure source A pressure adjusting mechanism for adjusting a hydraulic pressure between the cylinder, a bypass passage for bypassing the pressure adjusting mechanism, Disc brake, characterized in that provided the switching means in response to the vehicle brake command signal selectively flowing one of the pressure regulating mechanism or the bypass passage. The pressure adjusting mechanism includes a stepped piston having a large diameter portion having a pressure receiving surface on the hydraulic pressure source side and a small diameter portion having a pressure receiving surface on the cylinder side, and is supplied from the hydraulic pressure source to the cylinder. 2. The disc brake according to claim 1, wherein the switching means causes the pressure regulating mechanism to flow in response to the parking brake signal. The pressure adjusting mechanism includes a small-diameter portion having a pressure-receiving surface on the hydraulic pressure source side, a large-diameter portion having a pressure-receiving surface on the cylinder side, and a communication path that communicates the hydraulic pressure source side with the cylinder side. And a valve mechanism that opens and closes the communication path by the movement of the stepped piston, and is a pressure reducing mechanism that reduces the hydraulic pressure supplied from the hydraulic pressure source to the cylinder. The disc brake according to claim 1, wherein the bypass passage is circulated in response to a parking brake signal.

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