JP2017036776A - Electric parking brake - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric parking brake that can effectively work a piston rotation-prevention function by a simple structure.SOLUTION: The electric parking brake 10 has a rotation-linear motion mechanism constituted of a feed screw mechanism. In the electric parking brake 10, a rotation center d of a male screw 54 is aligned with a center OT of an abutment surface 39a where the piston 38 and a brake pad 36 abut on each other, while the rotation center d of the male screw 54 is offset from an outer diameter center OP of the piston 38.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electric parking brake.

  A conventional electric parking brake device has a speed reduction means between a motor and a rotation / linear motion conversion means (hereinafter also referred to as a rotation / linear motion mechanism) composed of a feed screw mechanism, and doubles the rotational torque of the motor by the speed reduction means. The rotation torque is converted into thrust by the rotation / linear motion conversion means. A braking force is generated by pressing the brake disc through the piston and the brake pad by this thrust (see, for example, Patent Document 1).

JP, 2014-101973, A

However, when the rotation / linear motion mechanism generates a high thrust and presses the piston, the piston may rotate along the rotation direction of the rotation shaft. For example, when a sliding screw mechanism is used as the rotation-linear motion mechanism, when the thrust is increased, the friction coefficient of the screw surface may increase and the screw and the nut may rotate together.
An object of the present invention is to provide an electric parking brake capable of effectively functioning a piston detent function with a simple configuration.

  In the electric parking brake having a rotation-linear motion mechanism composed of a feed screw mechanism, the center of the feed screw and the center of the abutting surface on which the piston and the pad come into contact with each other, and the center of the feed screw and the piston The center is offset.

  According to the present invention, by aligning the center of the screw portion of the feed screw mechanism with the center of the contact surface with respect to the pad of the piston, the piston moves directly with the rotation of the screw portion and rotates around the screw portion. try to.

  However, the center of the piston is offset from the screw shaft. For this reason, even if the piston tries to rotate around the threaded portion, the piston located radially outside interferes with the housing by the offset amount, and the piston itself exhibits the function of preventing rotation.

  In addition, the contact surface of the piston that contacts the pad is a circular shape smaller than the outer diameter of the piston, and the center of the contact surface is made to coincide with the center of the feed screw. According to this, since no lateral force is generated with respect to the rotational moment of the lead screw center, it is possible to reduce the influence that the outer diameter center of the piston is separated from the rotational center of the male screw by a predetermined dimension.

  According to the present invention, it is possible to provide an electric parking brake capable of effectively functioning a piston detent function with a simple configuration.

1 is a schematic diagram illustrating an overall outline of an electric parking brake according to an embodiment of the present invention. 1 is an exploded perspective view showing a schematic configuration of a piston and a feed screw in an electric parking brake according to an embodiment of the present invention. In the electric parking brake according to one embodiment of the present invention, (a) is a cross-sectional view of the main part, (b) is a side view showing a state in which the center of the outer diameter of the piston is offset with respect to the contact surface of the piston. It is. It is a mimetic diagram explaining signs that a piston does not rotate with an electric parking brake concerning one embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[Schematic configuration of electric parking brake system]
FIG. 1 shows an electric parking brake 10 according to the present embodiment. The electric parking brake 10 is mounted on a vehicle 1 that employs, for example, a vehicle brake system that performs a normal brake operation during traveling and a brake system 12 that also serves as a parking brake system. ing.

  Further, the vehicle 1 includes a brake pedal 14, a pedal stroke sensor 16 that detects the amount of depression of the brake pedal 14 by a user, an ignition switch 24, a vehicle speed sensor 26, a parking brake operation switch 28, an ECU (Electronic Control). And a control unit 30 such as (Unit).

  The electric parking brake 10 includes a wheel brake 18, an electric motor 20 that electrically operates or releases the wheel brake 18, and a brake system 22 (rotational linear motion conversion means) from the electric motor 20 to the wheel brake 18. The electric parking brake 10 that converts into the braking force using the rotational driving force of the electric motor 20 in this way is also called a motor direct acting parking brake system.

  In addition, the control unit 30 performs a parking brake operation by the user when the ignition switch 24 is on and the vehicle speed detected by the vehicle speed sensor 26 is 0 (when the engine is operating and the vehicle 1 is stopped). In response to the operation of the switch 28 or according to the depression amount of the brake pedal 14 detected by the pedal stroke sensor 16, an operation command is sent to the electric motor 20 (the electric motor 20 is energized to put the wheel brake 18 in a braking state). Or a release command (a signal for energizing the electric motor 20 to release the braking state of the wheel brake 18).

  Further, the control unit 30 detects that the wheel brake 18 is operated or released from a speaker (not shown) until a predetermined time elapses from the start of the braking state or until a predetermined time elapses after the braking state is released. A notification sound indicating this may be output.

[About the configuration of the electric parking brake]
The electric parking brake 10 exerts a continuous braking force when the vehicle 1 is stopped. For this reason, even if the electric motor 20 is energized by the operation command from the control unit 30 and the wheel brake 18 is operated, the operation command from the control unit 30 is stopped and the electric motor 20 is in a non-energized state. The braking state of the wheel brake 18 can be maintained.

  That is, in the electric parking brake 10, the wheel brake 18 accommodates the brake disc 34, the piston 38 that presses and brakes the brake disc 34 via the brake pad 36, and the piston 38 that can be moved forward and backward with respect to the brake disc 34. Housing 40.

  The brake system 22 includes a worm gear mechanism 44 that is a reduction mechanism connected to the output shaft 42 of the electric motor 20, a rotary shaft 46 that is connected to the output side (wheel brake 18 side) of the worm gear mechanism 44, and a rotary shaft. And a thrust conversion mechanism 48 connected to 46.

  Among these, the worm gear mechanism 44 includes a worm 50 provided on the output shaft 42 side and a worm wheel 52 provided on the rotating shaft 46. The worm gear mechanism 44 has a reverse input blocking function that prevents the electric motor 20 from being driven by the rotational force from the rotating shaft 46 on the output side. Here, the reverse input blocking function allows power transmission (transmission of rotational motion (rotational force, torque)) from the input side (electric motor 20) to the output side (wheel brake 18), while from the output side. A function that prevents power transmission to the input side.

  The thrust conversion mechanism 48 includes a male screw 54 formed on the rotary shaft 46 and a nut 56 screwed to the male screw 54, and has a rotation-linear motion mechanism that is a feed screw mechanism. The nut 56 is attached to the piston 38 to restrict relative rotation and sliding movement.

The male screw 54 and the nut 56 are preferably multi-threaded screws having high leads so that transmission efficiency is good.
The rotating shaft 46 is supported by the gear housing 58 in a state where the rotating shaft 46 can rotate and the sliding movement is restricted.

[Piston operating principle]
3A and 3B show the electric parking brake 10 according to the present embodiment, in which FIG. 3A is a cross-sectional view of the main part, and FIG. It is a side view which shows a mode that predetermined dimension (delta) is offset.
The rotation center of the male screw 54 coincides with the center OT of the contact surface 39a of the piston 38.

  That is, from the center of rotation of the feed screw mechanism including the male screw 54 (in this embodiment, the same as the center OT of the contact surface 39a of the piston 38) d, the outer diameter center of the piston 38 is out of the wheel shaft in the outer diameter direction. Is separated by a predetermined dimension δ.

  Even if the center of the outer diameter of the piston 38 is separated from the wheel shaft by the predetermined dimension δ in the outer diameter direction out, the rotation of the piston 38 can be suppressed. However, when the piston 38 tries to rotate around the rotation center of the male screw 54, a lateral force against the rotational moment is generated in the male screw 54. This lateral force generates a bending moment in the male screw 54. Since the bending stress due to this bending moment is added to the male screw 54 in addition to the shearing stress due to torsion, strength consideration is required.

  In the embodiment of the present invention, as shown in FIG. 2, the center OT of the area of the contact surface 39 a of the piston 38 that contacts the brake pad 36 coincides with the rotation center d of the male screw 54 of the male feed screw mechanism. It is configured.

  Thereby, even if the rotation center d of the male screw 54 is offset from the outer diameter center OP of the piston 38 by the predetermined dimension δ, the rotational moments generated at the respective angles around the center OT are equalized. For this reason, a lateral force with respect to the rotational moment is not generated in the male screw 54. Therefore, it is possible to reduce the influence of separating the outer diameter center of the piston 38 from the rotation center of the male screw 54 by a predetermined dimension δ.

  Then, by causing the rotation center d of the male screw 54 of the feed screw mechanism to coincide with the area center OT of the contact surface 39a of the piston 38 with the brake pad 36, the piston 38 is rotated around the center of the screw portion. Bring. The outer diameter center OP of the piston 38 is offset from the rotation center d of the male screw 54 by a predetermined dimension δ.

  For this reason, even if the piston 38 tries to rotate around the male screw 54, the outer peripheral surface of the piston 38 located radially outward by the offset δ interferes with the inner peripheral surface of the housing 40, and the piston 38 itself is prevented from rotating. The function can be demonstrated.

  Furthermore, a pin portion 39 is formed integrally with the large-diameter portion of the piston 38 on the surface of the piston 38 facing the brake pad 36 of the present embodiment. The pin portion 39 has a certain height direction dimension, and has an outer diameter dimension DTN smaller than the outer diameter dimension DPL of the piston 38, and is configured to have a circular shape in front view. A contact surface 39 a is formed on the surface of the pin portion 39 facing the brake pad 36.

  Then, the area center (here, the same as the center of the circle) OT of the contact surface 39a of the circular pin portion 39 is offset from the outer diameter center OP of the piston 38 by a predetermined dimension δ in the outer diameter direction out. . As a result, a pin portion 39 in which the center OT of the circle is shifted from the center of the large diameter portion having the outer diameter dimension DPL of the piston 38 in the outer diameter direction out is formed.

Even if the center OT of the circle is deviated from the front view, the pin portion 39 has an outer shape within the area of the outer diameter DPL, and has a desired circular shape, for example, a circular shape close to a perfect circle. can do.
With this configuration, the circular pin portion 39 does not protrude outward from the outer peripheral edge of the piston 38 in a front view, and the inner surface of the housing 40 and the pin portion 39 do not interfere with each other. Therefore, even if the pin portion 39 is offset by the predetermined dimension δ, the linear movement of the piston 38 is not hindered.
[Comparative example]

In addition, for example, a method of stopping the rotation of the piston 38 by using a method of increasing the friction coefficient of the contact surface between the piston 38 and the brake pad 36 is known.
In such a rotation prevention method of the piston 38, a stable friction state can be maintained at the initial stage of assembly, but when an actual running, foreign matter such as oil or water adheres or the surface wears out durablely, It may be difficult to maintain the coefficients.

Furthermore, a method of preventing rotation of the piston 38 by providing a rotation stop mechanism between the piston 38 and the brake pad 36 is known.
Such a detent method has a structure in which, for example, a pin is provided on the brake pad 36 and a groove for fitting the pin is provided on the piston side. However, in order to allow a dimensional tolerance between the pin and the groove, the fitting groove on the piston side must be set large.

For this reason, the pin and the fitting groove have a backlash from the beginning. For this reason, depending on the size of the backlash between the pin and the fitting groove, the piston rotates by the backlash.
When the parking brake is repeatedly braked / released, the piston repeatedly slides within the backlash range, and wear of the piston and brake pad surfaces occurs.

As a result, when the brake contact surface treatment or the like is applied to the piston contact surface of the pad, the performance cannot be maintained, and the merchantability may be deteriorated.
In view of the above, the present embodiment provides an electric parking brake capable of suppressing the rotation of the piston 38 with a simple structure.

[Piston rotation suppression]
On the other hand, in the electric parking brake of this embodiment, the outer diameter of the piston 38 is larger than that of the pin portion 39, and the hole diameter of the housing 40 (caliper side) that holds the piston 38 is formed to be substantially the same size. As a result, as an anti-rotation between the piston 38 and the housing 40, the area when the outer surface of the piston 38 abuts on the inner surface of the housing 40 holding the piston 38 can be set large.

  For this reason, in this embodiment, the surface pressure per unit area between the piston 38 and the housing 40 generated by the rotation stop can be reduced. As a result, the durability and wear resistance are improved, so that an increase in the piston sliding angle due to wear of the contact surface portion can be suppressed.

  Further, the piston 38 is allowed to swing only for a gap (clearance) formed between the piston 38 and the housing 40. For this reason, the piston 38 hardly rotates in the circumferential direction. Therefore, the wear of the contact surface 39a between the piston 38 and the brake pad 36 is small, the occurrence of brake squeal can be suppressed, the durability is good, and the commercial value can be maintained for a long time.

  Furthermore, the piston 38 of this embodiment hardly rotates in the circumferential direction. For this reason, the twist to the roll-back spring (not shown) holding the piston 38 can be suppressed. Thereby, the characteristics of the rollback spring can be secured over a long period of time. Therefore, the return of the piston 38 becomes good, and the brake drag can be suppressed.

  Since the piston 38 itself has a function of stopping rotation, the friction coefficient on the pad side can be set freely. For this reason, the options for the members constituting the pad are expanded, and it is possible to select a treatment material or the like for measures against brake noise.

  Further, since the piston 38 itself has a function of stopping rotation, even if foreign matter is mixed between the brake pad 36 and the piston 38, a braking force can be stably applied. This improves the disturbance toughness.

  Furthermore, in the electric parking brake of the present embodiment, slip between the brake pad 36 and the piston 38 does not occur in a region where the torque is high. For this reason, generation | occurrence | production of a sliding sound can be suppressed. Further, in the region where the torque at the time of releasing the brake is low, it is possible to reduce or prevent the contact noise between the piston and the non-rotating pin as in the comparative example described above. Therefore, merchantability can be improved.

[Modification]
The present invention is not limited to the above-described embodiments, and various modifications can be made. The above-described embodiments are illustrated for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Further, it is possible to delete a part of the configuration of each embodiment, or to add or replace another configuration. Examples of possible modifications to the above embodiment are as follows.

In the above-described embodiment, the contact surface 39a of the pin portion 39 shown in FIG. 2 is formed to have a circular shape in a front view in which the outer diameter dimension DTN is smaller than the piston outer diameter dimension DPL.
However, the outer diameter dimension DTN of the contact surface 39a is not particularly limited to the shape of the pin portion 39 forming the contact surface 39a in front view, the height direction dimension, and the area. Any type may be used as long as it matches the center OT of the contact surface 39a of the piston 38.

Further, the dimensional amount is not particularly limited with respect to the predetermined offset δ.
Furthermore, although it is offset by a predetermined dimension δ from the wheel shaft in the outer diameter direction out, the present invention is not limited to this, and may be a smaller predetermined dimension. What is necessary is just to make the center OT of the surface 39a coincide.
Also, the direction to be offset is not limited to the outer diameter direction out, and may be a direction other than the outer diameter direction out.
[Function and effect]
FIG. 4 is a schematic diagram illustrating how the piston 38 does not rotate in the electric parking brake 10 according to the embodiment of the present invention.

  When the outer diameter center OP of the piston 38 is offset by a predetermined dimension δ with respect to the center OT of the contact surface 39a of the piston 38, the rotation center d of the male screw 54 contacts the piston 38 and the brake pad 36. The center OT of the contact surface 39a of the pin portion 39 is made to coincide.

By setting in this way, the piston 38 does not attempt to rotate about the piston outer diameter center OP as an axis, but tries to swing around the rotation center d of the male screw 54.
This is because the contact surface 39a of the piston 38 rotates around the rotation center d and rotates around the rotation center d of the male screw 54 rather than revolving around the piston outer diameter center OP. This is because the energy required is small.

  The piston 38 swings while reducing the clearance with respect to the outer housing 40. When the clearance becomes zero, the piston 38 receives a reaction force from the inner surface of the housing 40 and stops. The force balanced with the reaction force is generated on the contact surface between the contact surface 39a of the piston 38 and the brake pad 36, and the lateral force is prevented from being input to the male screw 54.

  In this way, since the generation of the lateral force with respect to the rotational moment at the center of the male screw 54 is suppressed, the lateral force generated when the outer diameter center OP of the piston 38 is separated from the rotational center d of the male screw 54 by a predetermined dimension δ. The impact of will decrease. For this reason, strength consideration is unnecessary.

  Therefore, the anti-rotation function of the piston 38 can effectively function with a simple configuration in which the outer diameter center OP of the piston 38 is offset by a predetermined dimension δ from the rotation center d that is the area center of the contact surface 39a of the piston 38. Can do.

As described above, the contact surface 39a of the piston 38 that contacts the brake pad 36 has a circular shape having an outer diameter DTN smaller than the piston outer diameter DPL, and the center OT of the contact surface 39a is rotated by the male screw 54. It is made to coincide with the center d.
According to this, since no lateral force is generated with respect to the rotational moment of the rotation center d of the male screw 54, the influence of the outer diameter center OP of the piston 38 being separated from the rotation center d of the male screw 54 by a predetermined dimension δ is reduced. be able to.
Therefore, in the electric parking brake of this embodiment, it is possible to effectively function the piston detent function with a simple configuration.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Electric parking brake 12 Brake system 14 Brake pedal 16 Pedal stroke sensor 18 Wheel brake 20 Electric motor 22 Brake system 24 Ignition switch 26 Vehicle speed sensor 28 Parking brake operation switch 30 Control part 34 Brake disk 36 Brake pad 38 Piston 39 Pin part 39a Contact surface 40 Housing 42 Output shaft 44 Worm gear mechanism 46 Rotating shaft 48 Thrust conversion mechanism 50 Worm 52 Worm wheel 54 Male thread 56 Nut 58 Gear housing DTN Outer diameter DPL Piston outer diameter OP Outer diameter center OT center d Rotation center out Outer diameter direction

Claims (2)

In the electric parking brake having a rotation-linear motion mechanism composed of a feed screw mechanism,
An electric parking brake characterized in that the center of the feed screw is coincident with the center of the contact surface where the piston and the pad come into contact, and the center of the feed screw and the center of the piston are offset.   2. The contact surface of the piston that contacts the pad has a circular shape smaller than the outer diameter of the piston, and the center of the contact surface coincides with the center of the feed screw. The described electric parking brake.

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