Friction brake system for a vehicle

Abstract

A friction brake system comprises a first gear unit having a first member and a second member, the first gear unit is configured for converting a rotary motion of the first member into a braking motion of the second member, the first member is configured such that the rotary motion may be driven by an electric motor, the brake system further comprises a second gear unit having a spindle and nut for converting a rotary motion into a linear motion for pad wear compensation, the spindle is connectable to a brake pad, the second member of the first gear unit and the nut of the second gear unit are or may be mechanically coupled such that, during the braking motion, the second member of the first gear unit pushes against the nut of the second gear unit to press the brake pad against a friction surface.

Claims

1. A friction brake system for a vehicle, comprising: a first gear unit having a first member and a second member, wherein the first gear unit is configured for converting a rotary motion of the first member into a braking motion of the second member, wherein the first member is configured such that the rotary motion is configured to be driven by an electric motor; and a second gear unit having a spindle and nut for converting a rotary motion into a linear motion for pad wear compensation, wherein the spindle is connectable to a brake pad, wherein the second member of the first gear unit and the nut of the second gear unit are mechanically coupled such that, during the braking motion, the second member of the first gear unit pushes against the nut of the second gear unit to press the brake pad against a friction surface, wherein the first gear unit and the second gear unit are arranged such that the second gear unit penetrates the first gear unit at least partially, and wherein the friction brake system further comprises a hydraulic chamber and a piston arranged between the hydraulic chamber and the first gear unit and/or the second gear unit, and wherein the piston is configured to push the first gear unit and/or the second gear unit toward the friction surface upon pressurization of the hydraulic chamber to press the brake pad against the friction surface in a hydraulic fallback mode.

2. The friction brake system of claim 1, wherein the nut of the second gear unit is connected to the spindle of the second gear unit via a threaded surface of the nut, wherein the threaded surface of the nut has an axial overlap with the first gear unit.

3. The friction brake system of claim 1, wherein the second member of the first gear unit and the nut of the second gear unit are rotatably coupled such that the nut of the second gear unit is allowed to rotate with respect to the second member of the first gear unit during pad wear compensation.

4. The friction brake system of claim 1, wherein the first gear unit comprises at least one ball arranged and retained between the first member of the first gear unit and the second member of the first gear unit to convert a rotary motion of the first member into the braking motion of the second member.

5. The friction brake system of claim 4, wherein the ball of the first gear unit has an axial overlap with the second gear unit.

6. The friction brake system of claim 4, wherein the first gear unit is a ball in ramp gear, wherein the first member is a first plate with at least one groove, the second member is a second plate with at least one groove facing the groove of the first plate, wherein the at least one ball is arranged between the first plate and the second plate, wherein the ball is retained by the groove of the first plate and the groove of the second plate, wherein the ball in ramp gear is configured to convert a rotary motion of the first plate into a translational motion of the second plate with respect to the first plate.

7. The friction brake system of claim 4, wherein the first gear unit is a ball screw, wherein the first member is a ball screw nut and the second member is a ball screw shaft surrounded by the ball screw nut.

8. The friction brake system of claim 1, wherein the first gear unit has a travel dependent gear ratio in such a way that a travel distance corresponding to the braking motion is longer for a given rotation angle of the rotary motion when the brake pad is further away from the friction surface as compared to when the brake pad is in contact with the friction surface.

9. The friction brake system of claim 1, wherein the first gear unit is arranged such that the second member is closer to the brake pad than the first member, in particular when the braking motion is applied by the electric motor.

10. The friction brake system of claim 1, comprising the electric motor, wherein the electric motor is mechanically coupled to the first member of the first gear unit to drive the rotary motion of the first member of the first gear unit.

11. The friction brake system of claim 1, further comprising: a brake caliper arrangement configured to press another brake pad against a surface opposite the friction surface during the braking motion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments will be described in conjunction with the following figures.

(2) FIG. 1 shows a perspective view of a friction brake system for a vehicle,

(3) FIG. 2 shows a side view of the friction brake system,

(4) FIG. 3 shows an exploded view of components of the friction brake system including a ball in ramp gear,

(5) FIG. 4 shows a cross-sectional view of a first gear unit and a second gear unit of the friction brake system,

(6) FIG. 5 shows a cross-sectional view of the friction gear unit, and

(7) FIG. 6 shows a schematic view of a first and second gear unit according to another embodiment.

DETAILED DESCRIPTION

(8) FIG. 1 shows a friction brake system 1 for a vehicle. The friction brake system 1 comprises a brake caliper arrangement 2 having two brake pads configured to press against a brake disk of a wheel of the vehicle for braking the vehicle. The system 1 further comprises a housing 3. A part of the housing 3 for covering an electric motor of the system 1 is not shown in this figure to facilitate view of a motor shaft 4. The electric motor forms a part of an electro-mechanical actuator, which can press and release the brake pads to and from the brake disk. The motor shaft 4 is connected to a belt 5 for driving a rotation of a rotary connector 6. As it is explained below, the rotary connector 6 is connected to a first gear unit, more precisely to a first member of the first gear unit, for converting the rotational motion generated by the electric motor into a linear braking motion for pressing the brake pads from opposing sides against the brake disk of the wheel.

(9) FIG. 2 shows the friction brake system 1 in a side view. Corresponding and reoccurring features shown in the different figures are denoted using the same reference numerals. The part 7 of the housing covering the electric motor and the belt 5 is shown in this figure. In addition, a connector 8 for electrically connecting the system 1 to a vehicle control unit and power source is shown. A line with reference sign 9 indicates a cross-sectional plane used for FIGS. 4, 5, and 6 below.

(10) FIG. 3 shows an exploded view of components of the friction brake system 1. The friction brake system 1, according to the embodiment shown, comprises a ball in ramp gear 10 as the first gear unit. The first gear unit has a first plate 11 as the first member, a second plate 12 as the second member and a set of balls 13, 13′, 13″ arranged between the first plate 11 and the second plate 12. The balls 13, 13′, 13″ are each retained by a pair of grooves in inner surfaces of the first plate 11 and the second plate 12. While the grooves 14, 14′ of the second plate 12 are shown, the first plate 11 comprises corresponding grooves that are not visible in the figure. The balls and corresponding grooves are shaped such that the ball in ramp gear 10 converts a rotary motion of the first plate 11 driven by the electric motor into a translational motion of the second plate 12 for pressing the brake pads against the brake disk. In some embodiments, the grooves 14, 14′ are shaped such that the first gear unit 10 has a travel dependent gear ratio in such a way that a travel distance is longer for a given rotation angle of the motor shaft 4 when the plates 11, 12 are closer together. To allow smooth rotation of the first plate 11, the first plate 11 rests against a piston 18 via a roller bearing 19. A part 17 of the rotary connector 6 transmits the rotary motion from the motor shaft 4 to the first plate 11 of the first gear unit. The plates 11, 12 and balls 13, 13′, 13″ of the ball in ramp gear 10 surround a second gear unit 15 for pad war compensation. The second gear unit 15 has a nut 16. The second gear unit 15 is arranged radially closer to a main axis of the system 1 as compared with the first gear unit 10. A spring may be arranged between the first plate 11 and the second plate 12 to ensure that in case of a failure the caliper arrangement 2 is releasing fast. The first and second gear units may be arranged in parallel and may have a common main axis.

(11) FIG. 4 is a cross-sectional view showing the first gear unit 10 and the second gear unit 15 in detail. As shown, the second gear unit 15 is arranged within the first gear unit 10 such that the second gear unit 15 penetrates the first gear unit 10. The second gear unit 15 comprises the nut 16 and a spindle 20. The nut 16 and spindle 20 comprise complementary threaded surfaces 21 such that the spindle 20 may be rotated with respect to the nut 16 to compensate pad wear. The spindle 20 has a threaded portion 22 to be received within the nut 16 and a widened portion 23 arranged closer to the brake disk. The brake pad is attached to the widened portion 23 such that it is arranged between the spindle 20 and the brake disk.

(12) When the brake is applied using the electric motor, the rotation of the first plate 11 leads to a translation of the second plate 12 to the left. The second plate 12 may be fixed with regard to rotational motion and movably held with respect to linear motion. When the second plate 12 moves to the left it pushes the nut 16 of the second gear unit 15 to the left, so that the spindle 20 moves to the left together with the brake pad to perform the braking motion. The nut 16 of the second gear unit 15 is rotatable with respect to the second plate 12 to allow for pad wear adjustment. To compensate for pad wear, the nut 16 may be rotated, so that the spindle 20 moves to the left. The nut 15 may, e.g., be connected to the second plate 12 via a ratchet mechanism.

(13) The system 1 also has a small hydraulic chamber 24 arranged between the piston 18 and an end plane part 25 of the housing. When the hydraulic chamber is not pressurized, as shown in the figure, the piston 18 may be in contact with the end plane part 25 of the housing. The hydraulic chamber 24 is fluidly connected with a brake cylinder and may be pressurized by actuating a brake pedal in a fallback mode of operation. When the hydraulic chamber 24 is pressurized, hydraulic fluid within the hydraulic chamber forces the roller bearing 19, the part 17 of the rotary connector 6, the first gear unit 10, and the second gear unit 15 to the left, so that the brake pad is pushed against the brake disk. A spring may be provided to directly or indirectly push back the piston after a hydraulic braking operation has been performed.

(14) FIG. 5 shows the friction brake system 1 in less detail. As can be seen, the brake caliper arrangement 2 comprises a set of brake pad holders 26, 26′ configured to hold the brake pads. When the braking motion is performed, the brake pad holders 26, 26′ move inward together with the brake pads so that a force is applied to the brake disk (not shown) from opposing sides. As can be seen, the arrangement shown is particularly compact, because the second gear unit 15 is received within the first gear unit 10.

(15) FIG. 6 shows a detailed view of a system 1′ according to another embodiment. This system 1′ comprises all of the features of the system 1 described above. However, the first gear unit 10 according to the embodiment shown in FIG. 6 is a ball screw. The ball screw 10 comprises a ball screw nut 27 as a first member and a ball screw shaft 28 as a second member. Further, a set of balls 13, 13′ is arranged between the ball screw shaft 28 and the ball screw nut 27 to convert a rotary motion of the ball screw nut 27 into a translational motion of the ball screw shaft 28. The ball screw nut 27 and the ball screw shaft 28 are essentially of a tubular shape and are arranged such that they are concentric. The ball screw nut 27 surrounds the ball screw shaft 28 and is rotatable using the electric motor and the rotary connector 6. The rotation of the ball screw nut 27 when the brake is applied leads to a translation of the ball screw shaft 28 to the left, thereby pushing the ball screw shaft closer to the brake disk. In this case, the ball screw shaft 28 pushes against the nut 16 of the second gear unit 15 such that the second gear unit 15 moves to the left and the brake pads press against the brake disk.

(16) Features of the different embodiments which are merely disclosed in the exemplary embodiments may be combined with one another and may also be claimed individually.