JP4439284B2 - Electric brake device - Google Patents

Abstract

A motor-driven brake device having excellent responsivenesses to the application and release of a brake and preventing these responsivenesses from being lowered even if a brake member is worn. When a screw shaft (8) is moved forward by rotating the nut (6) of a ball screw mechanism by an electric motor when the brake is applied, a tension shaft (14) pressingly energized to the base end side by a compression coil spring (18) is moved, while rotating, to the base end side relative to the screw shaft (8) since a serration-like screw with a large lead angle alpha is loosened until it touches a stopper screw (19) to pressingly support the screw shaft (8) so that the screw shaft is not returned rearward. Accordingly, even if brake pads (3a) and (3b) are worn, the excellent responsiveness to the application of the brake can be naturally secured by always holding a pressing member (9) near a pressing position, and also when the brake is released, an excellent responsiveness can be secured by separating the pressing member (9) from the brake pads (3a) by the axial clearance of the serration-like screw by merely stopping the electric motor.

Description

  The present invention relates to an electric brake device that converts rotation of an electric motor into linear motion by a ball screw mechanism and presses a brake member against a member to be braked.

  Although many hydraulic brake devices have been adopted as a vehicle brake device, in recent years, with the introduction of advanced brake control such as ABS (Antilock Brake System), these controls can be performed without complicated hydraulic circuits. Electric brake devices that can be designed compactly are drawing attention. The electric brake device operates an electric motor in response to a depression signal of a brake pedal, converts rotation of the electric motor into a linear motion, and presses a brake member against a member to be braked.

  Usually, since an electric brake device is attached under the spring of a vehicle, it is desired that a compact and lightweight design is possible. As an electric brake device capable of such a design, the nut of the ball screw mechanism is rotated integrally with the rotor of the electric motor, and the screw shaft screwed to the nut via the ball is linearly moved to be heavy and bulky. There has been proposed a type in which the rotation of an electric motor is directly converted into a linear motion by a ball screw mechanism without using a gear reduction mechanism (see, for example, Patent Documents 1 and 2).

  In the electric brake device described in Patent Document 1, an elastic member such as a synthetic rubber material is interposed between a shaft end portion of a screw shaft of a ball screw mechanism that moves linearly and a brake member, and the electric motor rotates when the brake is operated. Thus, the brake member is pressed by the screw shaft through the elastic member, the electric motor is stopped when the brake is released, and the screw shaft is pushed back by the elastic restoring force of the elastic member.

  The electric brake device described in Patent Document 2 rotates the electric motor forward when the brake is operated, moves the screw shaft of the ball screw mechanism to the brake member pressing side, and reversely rotates the electric motor when the brake is released. The screw shaft is moved to the side for retracting from the brake member. In this electric brake device, after the screw shaft is retracted, the electric motor is rotated forward to return the screw shaft to the standby position.

Japanese Unexamined Patent Publication No. 2002-213504 (page 2-4, FIG. 1-3) JP 2002-213505 A (page 2-4, FIG. 1-2)

  In the electric brake device described in Patent Document 1 described above, since the elastic member is interposed between the shaft end portion of the screw shaft of the ball screw mechanism that moves linearly and the brake member, only the elastic deformation of the elastic member. There is a problem that it is necessary to move the screw shaft excessively, and the response of the brake effect becomes slow. Further, the elastic member may deteriorate due to repeated elastic deformation, and the screw shaft may not be pushed back when the brake is released.

  On the other hand, since the electric brake device described in Patent Document 2 needs to reversely rotate the electric motor when releasing the brake, there is a problem in that the timing of releasing the brake is delayed and the driver feels uncomfortable. In addition, when a brake member such as a brake pad is worn, there is a problem that the moving distance until the screw shaft presses the brake member becomes long, and the response of the brake effect becomes slow. In order to eliminate this delay in response, it is only necessary to detect the amount of wear of the brake member and change the stand-by position of the screw shaft. It becomes.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electric brake device that has excellent braking effectiveness and responsiveness for releasing a brake, and that does not deteriorate these responsiveness even if the brake member is worn.

  In order to solve the above-described problems, the present invention includes an electric motor and a ball screw mechanism, a ball screw mechanism that rotates a nut of the ball screw mechanism integrally with a rotor of the electric motor, and is screwed into the nut via the ball. An electric brake that linearly moves the screw shaft of the screw mechanism and presses the brake member against the member to be braked by a pressing portion provided on the front end side of the screw shaft by the output of the electric motor converted into the linear motion of the screw shaft. In the apparatus, an axial through hole is provided in a screw shaft of the ball screw mechanism, and a projecting shaft having a male screw provided at a tip portion of the through hole is fitted and inserted toward a front end side of the screw shaft. A male screw of the shaft is screwed into a screw hole provided on the front end side of the through hole, a lead angle α of the male screw is increased, and a pressing means for pressing and urging the projecting shaft to the base end side is provided, This It is biased pressed by pressing means, adopting a configuration in which the provided stoppers for stopping the large lead angle 突張 shaft the screw shaft and the relative movement in the proximal side while rotating loose screws in alpha.

  That is, in this electric brake device, when the electric motor is rotated during brake operation and the screw shaft of the ball screw mechanism is moved forward to the brake member pressing side, the tension shaft also moves together with the screw shaft. The projecting shaft pressed and urged toward the base end by the pressing means moves relative to the screw shaft toward the base end while rotating with the screw with a large lead angle α loosening when it moves away from the stopper. Stretch and support so that it does not return backwards. Therefore, when the brake member wears, the pressing position gradually changes so as to move forward. With this change in the pressing position, the tension support position of the screw shaft by the tension shaft also changes forward, and the screw shaft is pressed. The portion can always be held near the pressing position of the brake member, and excellent responsiveness of the brake effect can be naturally secured.

  Further, when releasing the brake, the screw shaft escapes from the brake member pressing side by the axial clearance of the screw having a large lead angle α only by stopping the electric motor, so that excellent responsiveness can be ensured. . In addition, the screw shaft pressing portion can be sufficiently released from the brake member by providing an appropriate gap between the male and female screws in the screw having a large lead angle α.

The male screw of the tension shaft is a serrated screw whose flank angle θ _{F on the} front surface of the thread facing the distal end of the tension shaft is larger than the flank angle θ _B on the rear surface of the thread facing the proximal end of the tension shaft; Therefore, when the projecting shaft that is screwed with the serrated screw engages with the female screw on the front surface of the male screw thread facing the tip with the large flank angle θ _F , the screw will loosen even if the lead angle α is large. Since it is locked first, it moves relative to the screw shaft of the ball screw mechanism only to the proximal end side and does not move relative to the distal end side. Therefore, when the brake member is not worn, as a matter of course, even if the brake member is worn, the pushing portion of the screw shaft can be stretched and supported more reliably so as not to return near the pushing position. In addition, the screw thread front side of the male thread facing the tip side of the projecting shaft with a large flank angle θ _F further increases the axial clearance of the screw. I can escape.

  The lead angle α of the male screw is preferably 8 to 20 °. Grease is often used for screw lubrication, but the friction coefficient μ of the screw when grease is lubricated is about 0.08 to 0.12. FIG. 5 is a graph obtained by calculation of a limit curve where the screw starts to loosen when an axial force is applied when the friction coefficient μ is 0.08 and 0.12. It can be seen that the lower side of each limit curve is a slack region, and the upper side is a lock region. The larger the lead angle α and the smaller the flank angle θ, the larger the slack region. Since the flank angle θ of a normal screw is 30 ° on both the front and back surfaces of the thread, the lead angle α is set to 8 ° or more so that a loose region exists even if the flank angle θ is 30 °. In addition, the upper limit of the lead angle α was set to 20 ° in consideration of practicality as a screw.

It is desirable that the flank angle θ _{F on the} front surface of the thread of the male screw and the flank angle θ _{B on the} back surface of the thread are set within the ranges of the following expressions using the lead angle α as a parameter.
θ _F ≧ 1.5α + 50 (°) (1)
θ _B ≦ 3.0α + 11 (°) (2)
Equation (1) regulates the lock side of the screw, and represents the upper side of the approximate straight line F in which the limit curve of μ = 0.08 shown in FIG. 5 is provided with a margin on the lock region side. Further, the expression (2) regulates the loose side of the screw, and represents the lower side of the approximate straight line B in which the margin curve of μ = 0.12 shown in FIG. .

  The pressing means is a compact design by providing a compression elastic member between a seat plate provided on the front end side of the through hole and a seat provided on the front end surface of the extension shaft. The thrust shaft can be pressed and biased. In addition, by forming the end surface of the compression elastic member on the side in contact with the seat of the tension shaft with a small diameter, the rotation restraint moment caused by the pressing force is reduced, and the rotation due to the looseness of the tension shaft screw is smoothed. Can be.

  The pressing portion on the front end side of the screw shaft is formed by a separate pressing member, and a screw hole into which the male screw of the tensioning shaft is screwed is provided in the pressing member, thereby incorporating the tensioning shaft and its pressing means. Can be easily.

  When the electric brake device of the present invention rotates the electric motor at the time of brake operation and moves the screw shaft of the ball screw mechanism forward to the brake member pressing side, the tension shaft also moves together with the screw shaft. The projecting shaft pressed and urged toward the base end by the pressing means moves relative to the screw shaft toward the base end while the screw with a large lead angle α is loosened and rotated, and again hits the stopper so that the screw shaft does not return backward. Even if the brake member wears and its pressing position changes, the pressing part of the screw shaft is always kept close to the pressing position to naturally ensure excellent braking effectiveness responsiveness. Can do. Further, even when the brake is released, the screw shaft escapes from the brake member pressing side by the axial clearance of the screw having a large lead angle α only by stopping the electric motor, so that excellent responsiveness can be ensured.

The male screw of the tension shaft is a serrated screw whose flank angle θ _{F on the} front surface of the thread facing the distal end of the tension shaft is larger than the flank angle θ _B on the rear surface of the thread facing the proximal end of the tension shaft; By doing so, the projecting shaft that is screwed with the saw-toothed screw moves relative to the screw shaft of the ball screw mechanism only to the proximal end side and does not move relative to the distal end side, and the brake member is not worn. Of course, even if the brake member is worn, it is possible to more securely support the screw shaft so that the pressing portion of the screw shaft does not return near the pressing position. In addition, the screw thread front side of the male thread facing the tip side of the projecting shaft with a large flank angle θ _F further increases the axial clearance of the screw. I can escape.

  The pressing means has a compact design with a compression elastic member disposed between a seat plate provided on the front end side of the through hole and a seat provided on the front end surface of the extension shaft. The shaft can be pressed and biased. In addition, by forming the end face of the compression elastic member on the side that contacts the seat of the tension shaft with a small diameter, the rotation restraint moment due to the pressing force is reduced, and the rotation due to the looseness of the tension shaft screw is smooth. Can be.

  The push shaft on the front end side of the screw shaft is formed by a separate press member, and a screw hole into which the male screw of the stretch shaft is screwed is provided in the press member, thereby making it easy to incorporate the stretch shaft and its pressing means. Can be.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, this electric brake device is a disc brake in which brake pads 3 a and 3 b as brake members are opposed to each other on both sides of a disc rotor 2 as a braked member inside a caliper 1. A stator 5 of an electric motor is fixed to an inner peripheral surface of a motor casing 4 attached to 1, and a nut 6 of a ball screw mechanism formed integrally with the rotor is rotated by a pair of bearings 10 on the caliper 1 and the motor casing 4. A separate pressing member 9 that presses the brake pad 3 a against the disc rotor 2 is attached to the front end side of the screw shaft 8 that is freely supported and screwed into the nut 6 via the ball 7. The interior of the motor casing 4 is sealed with a boot 11 attached between the caliper 1 and the pressing member 9.

  A through-hole 12 is provided in the center of the screw shaft 8 of the ball screw mechanism, and a screw hole 13 is provided in the pressing member 9 so as to be continuous with the through-hole 12, and the through-hole 12 is provided on the front end side of the screw shaft 8. The projecting shaft 14 fitted and inserted is screwed into the screw hole 13 with a male screw 15 provided at the tip.

  A seat plate 16 is attached to the front end surface of the pressing member 9, and a compression coil spring 18 as a compression elastic member is disposed between the pressing member 9 and a boring seat 17 provided on the front end surface of the projecting shaft 14. The tension shaft 14 is pressed and urged toward the proximal end side. The compression coil spring 18 is formed with a small diameter on the end surface that comes into contact with the boring seat 17, and the rotation restraint moment caused by the pressing force is reduced, and the rotation of the tension shaft 14 due to the loosening of a saw-tooth screw (described later). It comes to be smooth. The base end of the tension shaft 14 is stopped by a stopper screw 19 screwed to the motor casing 4. Further, a notch portion 16 a that engages with a protrusion on the brake pad 3 a side and prevents the screw shaft 8 from rotating is provided on the front surface of the seat plate 16.

The male screw 15 of the projecting shaft 14 has a lead angle α as large as 11 °. As shown in FIG. 2, the flank angle θ _F of the thread front surface 15a facing the distal end side of the projecting shaft 14 of the male screw 15 is set as follows. The sawtooth screw is 75 ° (≧ 1.5α + 50) and the flank angle θ _B of the thread rear surface 15b is 15 ° (≦ 3.0α + 11). The serrated screw is grease lubricated.

Therefore, as described with reference to the graph of FIG. 5, when the thrust shaft 14 is pressed and urged by the compression coil spring 18, it engages with the internal thread of the screw hole 13 at the thread rear surface 15b having a small flank angle θ _B. The serrated screw to be loosened is moved relative to the screw shaft 8 and the pressing member 9 while rotating to the proximal end side and hits the stopper screw 19. The screw thread front surface 15 a having a large flank angle θ _{F is formed on} the screw hole 13. The sawtooth screw is locked in the opposite direction to engage with the female screw and does not move relatively. In addition, since the saw-toothed screw has a large lead angle α, the axial clearance is originally large for the gap between the male and female screws, but the axial clearance δ of the thread front 15a having a large flank angle θ _F is further increased. Yes.

  The operation of the above-described electric brake device will be described below. FIG. 1 shows a case where the brake pads 3a and 3b are not worn, and FIG. 3 shows a case where the brake pads 3a and 3b are worn. In either case, when the brake is operated, the electric motor is activated by a depression signal of a brake pedal (not shown), the nut 6 of the ball screw mechanism rotates, and the screw shaft 8 moves forward on the brake pad 3a side. To do. When the pressing member 9 on the front end side of the screw shaft 8 presses the brake pad 3a, the brake pad 3b attached to the caliper 1 is also pressed by the disc rotor 2 by the reaction force, so that the brake is effective.

When the screw shaft 8 moves forward during the operation of the brake, the tension shaft 14 also moves together with the screw shaft 8. However, the tension shaft 14 pressed against the proximal end side by the compression coil spring 18 has a stopper screw. When moving away from 19, the serrated screw engaging with the female screw of the screw hole 13 is loosened at the thread rear face 15b having a large lead angle α and a small flank angle θ _B, and moves relative to the screw shaft 8 toward the proximal end while rotating. Then hit the stopper screw 19 again. Even if the electric motor is stopped at the time of releasing the brake, which will be described later, the projecting shaft 14 relatively moved toward the base end side is in the reverse direction in which the thread front surface 15a with a large flank angle θ _F engages with the female screw of the screw hole 13. Does not move relative to each other and supports the screw shaft 8 and the pressing member 9 so as not to return backward.

  Therefore, as shown in FIG. 1, when the brake pads 3a and 3b are not worn, as shown in FIG. 3, even if the brake pads 3a and 3b are worn and the pressing position thereof changes forward, The tension shaft 14 is gradually moved relative to the screw shaft 8 only toward the base end side, and the pressing member 9 is always held near the pressing position, so that excellent braking effectiveness can be ensured.

  On the other hand, when the brake is released, the electric motor is stopped by a brake pedal release signal. When the electric motor is stopped and the rotational driving force of the nut 6 of the ball screw mechanism disappears, the screw shaft 8 and the pressing member 9 escape backward by the axial clearance of the thread front surface 15a of the sawtooth screw, and each brake pad 3a 3b is released. Therefore, this electric brake device does not need to reverse the electric motor, and can release the brake with excellent responsiveness only by stopping the electric motor.

  Next, a replacement procedure when the brake pads 3a and 3b are worn will be described. As shown in FIG. 3, when the brake pads 3 a and 3 b are worn, the projecting shaft 14 moves considerably relative to the base end side with respect to the screw shaft 8, and supports the pressing member 9 in the vicinity of the pressing position. In this state, as shown in FIG. 4, the stopper screw 19 is removed from the motor casing 4, and the driver groove 20 provided on the proximal end surface of the projecting shaft 14 is turned by the driver 21, whereby the screw shaft 8 and the pressing member 9. Can be pulled back to open a space for replacement with the brake pad 3a.

  In the embodiment described above, the pressing portion of the screw shaft of the ball screw mechanism is formed by a separate pressing member, and the pressing member is provided with a screw hole that is screwed with the sawtooth male screw of the tension shaft. The screw shaft may be integrated. Further, the male screw of the tension shaft only needs to have a large lead angle so that the screw is loosened by an axial load on the base end side, and the front and rear surfaces of the thread can be symmetrical. Further, the pushing means and the stopper of the tension shaft are not limited to those in the embodiment, and can be arbitrarily designed.

A longitudinal sectional view showing an embodiment of an electric brake device Sectional drawing which expands and shows the male screw of the tension shaft of FIG. 1, and the screw hole of a pressing member 1 is a longitudinal sectional view showing a state where the brake pad of FIG. 1 is worn FIG. 3 is a longitudinal sectional view for explaining a procedure for replacing the worn brake pad in FIG. Graph showing looseness limit curve for screw lead angle and flank angle

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Caliper 2 Disc rotor 3a, 3b Brake pad 4 Motor casing 5 Stator 6 Nut 7 Ball 8 Screw shaft 9 Pressing member 10 Bearing 11 Boot 12 Through hole 13 Screw hole 14 Strut shaft 15 Male screw 15a Thread front 15b Thread rear surface 16 Seat plate 16a Notch 17 Bore seat 18 Compression coil spring 19 Stopper screw 20 Driver groove 21 Driver

Claims (6)

  An electric motor and a ball screw mechanism are provided, the nut of the ball screw mechanism is rotated integrally with the rotor of the electric motor, and the screw shaft of the ball screw mechanism screwed to the nut via the ball is linearly moved to In an electric brake device that presses a brake member against a member to be braked by a pressing portion provided on a front end side of a screw shaft by an output of an electric motor converted into a linear motion of the shaft, an axial direction is applied to a screw shaft of the ball screw mechanism. A through-hole is provided, and a projecting shaft provided with a male screw at the tip of the through-hole is fitted and inserted toward the front end side of the screw shaft, and the male screw of the projecting shaft is provided on the front end side of the through-hole. Screwing into the screw hole, increasing the lead angle α of this male screw, and providing a pressing means for pressing the thrust shaft toward the proximal end side, and pressing and biasing by the pressing means, Electric brake apparatus characterized in that a stopper for stopping the 突張 shaft the screw shaft and the relative movement in the proximal side while rotating loose screws with a large lead angle alpha. The male screw of the tension shaft is a serrated screw whose flank angle θ _{F on the} front surface of the thread facing the distal end of the tension shaft is larger than the flank angle θ _B on the rear surface of the thread facing the proximal end of the tension shaft; The electric brake device according to claim 1.   The electric brake device according to claim 1 or 2, wherein a lead angle α of the male screw is 8 to 20 °. 4. The electric brake device according to claim 3, wherein the flank angle θ _{F on the} front surface of the thread of the male screw and the flank angle θ _{B on the} rear surface of the thread are set within the ranges of the following expressions using the lead angle α as a parameter.
θ _F ≧ 1.5α + 50 (°)
θ _B ≦ 3.0α + 11 (°)   5. The compression member according to claim 1, wherein the pressing means includes a compression elastic member disposed between a seat plate provided on a front end side of the through hole and a seat provided on a front end surface of the projecting shaft. The electric brake device according to the above.   6. The electric motor according to claim 1, wherein a pressing portion on a front end side of the screw shaft is formed by a separate pressing member, and a screw hole into which the male screw of the projecting shaft is screwed is provided in the pressing member. Brake device.

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