Friction braking system for a vehicle

Abstract

Friction brake system (1) for a vehicle, comprising a brake element which is connectable to at least one brake pad (8, 9) and is designed to press the brake pad (8, 9) against a friction surface and a transmission unit configured to convert a rotary movement generated by an actuator (2) into a braking movement of the brake pad (8, 9), the transmission unit comprising a ball ramp arrangement comprising: a first plate (12) with at least one groove (26), a second plate (13) having at least one groove facing the groove (26) of the first plate (12), and at least one ball (14) arranged between the first plate (12) and the second plate (13), the ball (14) being held by the groove (26) of the first plate (12) and the groove of the second plate (13), wherein the ball ramp arrangement is arranged to convert a rotational movement of the first plate (12) into a longitudinal movement of the second plate (13) relative to the first plate (12), wherein the second plate (13) is mechanically coupled to the braking element, so that rotation of the first plate (12) causes the braking movement of the braking element, wherein the friction brake system (1) further comprises a spindle (4), wherein the spindle (4) has spindle threads which engage with threads on an inner surface of the first plate (12), wherein the spindle (4) is arranged to be rotated by the actuator (2) through a first angular range in order to effect the rotational movement of the first plate (12) and thereby the braking movement of the braking element, wherein the spindle (4) is adapted to be rotated beyond the first angular range in order to effect a longitudinal movement of the first plate (12) relative to the spindle (4) for adjusting the lining wear, characterized by a lock nut (17) with an internal thread which engages in the spindle thread, wherein the lock nut (17) is adapted to prevent a longitudinal movement of the first plate (12) when the spindle (4) is rotated through the first angular range.

Description

[0001] The application relates to a friction brake system for a vehicle. Furthermore, the application relates to a service brake for a vehicle. More specifically, the application relates to a friction brake system with a brake element that is connectable to at least one brake pad and is designed to press the brake pad against a friction surface, and a transmission unit that is designed to convert a rotational movement generated by an actuator into a braking movement of the brake pad. The friction brake system is suitable for compensating for pad wear.

[0002] Such friction brake systems, particularly electromechanically actuated wheel brakes, are well known. Such brake types can be used, for example, as integrated parking brakes or as service brakes. In order to achieve a braking movement with sufficient clamping force within a specific time using an electromechanically actuated wheel brake, a specific motor power or force must be delivered. For example, the use of a non-linear transmission can reduce the required motor power. The non-linear transmission can be a toggle or angle lever transmission. However, such a transmission type is relatively bulky and difficult to integrate into a housing arranged next to the wheel brake. Another problem that can arise with known friction brake systems is the effort required to compensate for lining wear.Therefore, there is a need for a cost-effective, robust, and compact alternative to the known friction brake systems. Related prior art is described in the publications DE 102 39 793 A1, DE 10 2015 214 547 A1, and US 2012 / 0 292 141 A1.

[0003] Against the background of the above-mentioned aspects, it is an object of the present application to provide an improved friction braking system for a vehicle. In particular, it is an object of the application to provide a friction braking system that is compact, cost-effective, and particularly robust. Furthermore, it is an aim of the application to provide a service brake that offers these advantages.

[0004] This object is achieved by a friction braking system for a vehicle having the features of independent claim 1. Optional further features and developments will become clear from the dependent claims and the specific description in conjunction with the accompanying figures.

[0005] The proposed friction braking system for a vehicle comprises a braking element that is connectable to at least one brake pad and configured to press the brake pad against a friction surface. The friction surface can be, for example, a surface of a brake disc, in particular of a wheel brake. The friction braking system also comprises a transmission unit configured to convert a rotational movement generated by an actuator into a braking movement of the brake pad. When the braking element executes the braking movement, the brake pad is typically pressed against the friction surface. The transmission unit consists of a ball ramp arrangement. The ball ramp arrangement comprises a first plate with at least one groove, a second plate with at least one groove facing the groove of the first plate, and at least one ball arranged between the first plate and the second plate.The ball is held by the groove of the first plate and the groove of the second plate. The ball ramp arrangement is configured to convert a rotational movement of the first plate into a longitudinal movement of the second plate relative to the first plate. This allows an axial distance between the first plate and the second plate to be changed. Typically, when a brake of the vehicle is applied, an axial distance between the first plate and the second plate is increased to create a braking movement that exerts a force on the friction surface. To release the brake, an axial distance between the first plate and the second plate can be reduced. The second plate is mechanically coupled to the braking element such that rotation of the first plate causes the braking movement of the braking element. The friction braking system also includes a spindle.The spindle has spindle threads that engage threads on an inner surface of the first plate. The first plate can be screwed onto the spindle. The spindle is configured to be rotated by the actuator through a first angular range to effect rotational movement of the first plate and thereby braking movement of the braking element. The spindle is further configured to be rotated beyond the first angular range to effect longitudinal movement of the first plate relative to the spindle for adjusting lining wear. During longitudinal movement of the first plate relative to the spindle, the spindle can rotate relative to the first plate. In most embodiments, the first plate does not rotate during longitudinal movement of the first plate relative to the spindle. Typically, the first plate performs the longitudinal movement along a spindle axis.

[0006] This results in a simple, robust, and compact mechanism that enables reliable braking and pad wear adjustment. The spindle, in conjunction with the actuator, can thus enable reliable braking and pad wear adjustment.

[0007] In typical embodiments, the friction brake system comprises a first stop. The first stop can be configured to prevent further rotation of the first plate when the spindle is rotated beyond the first angular range in a first rotational direction, resulting in longitudinal movement of the first plate relative to the spindle in a first axial direction. When the first plate moves in the first axial direction, the first plate can move, for example, towards the brake disc. In this way, the air gap between the brake pad and the brake disc can decrease. The first stop can be formed by part of a housing of the friction brake system. The friction brake system can, for example, comprise a brake caliper housing. The first stop can be formed by the brake caliper housing.

[0008] In some embodiments, the friction brake system includes a second stop. The second stop may be configured to prevent further rotation of the first plate when the spindle is rotated beyond the first angular range in a second rotational direction opposite to the first rotational direction, resulting in longitudinal movement of the first plate relative to the spindle in a second axial direction opposite to the first axial direction. When the first plate moves in the second axial direction, the first plate may, for example, move away from the brake disc. In this way, the air gap between the brake pad and the brake disc may increase.

[0009] The friction brake system includes a locknut having an internal thread that engages the spindle thread. The locknut can be screwed onto the spindle. The locknut is configured to prevent longitudinal movement of the first plate, e.g., toward the locknut and / or away from the locknut, when the spindle is rotated through the first angular range. In this way, the reliability of the braking process is improved. The locknut can rest on the spindle such that the first plate is arranged between the locknut and the actuator and / or such that the locknut is arranged closer to the brake disc and / or the brake pad than the first plate.

[0010] The locknut may be configured to rotate relative to the spindle when the spindle is rotated beyond the first angular range to adjust pad wear. In this way, movement of the locknut may enable longitudinal movement of the first plate to adjust pad wear. The friction brake system may include a locknut end stop configured to prevent further rotation of the locknut when the spindle is rotated beyond the first angular range in the first angular direction to enable longitudinal movement of the first plate relative to the spindle in the first axial direction.

[0011] The end stop of the lock nut can be formed at least partially by the second plate of the ball ramp assembly. The second plate can be rotationally fixed and / or limited in its ability to rotate. The friction braking system can, for example, include a brake caliper housing. The second plate of the ball ramp assembly can be connected to the brake caliper housing by a torque arm, which can prevent or limit rotational movement of the second plate.

[0012] In some embodiments, the end stop of the lock nut is configured to prevent further rotation of the lock nut when the spindle is rotated beyond the first angular range in the first angular direction before further rotation of the first plate is prevented by the first stop, resulting in a longitudinal movement of the lock nut away from the first plate prior to the longitudinal movement of the first plate relative to the spindle in the first axial direction. In this way, the lock nut can reliably release its locking function.

[0013] In most embodiments, the first plate and the locknut are connected by a spring, e.g., a torque spring. The spring can be designed to pull the locknut and the first plate together. In this way, the locknut can be preloaded by the spring. In this way, efficient locking of the first plate can be achieved when the spindle is rotated through the first angular range to effect the braking movement. Furthermore, the spring can achieve reliable locking of the first plate after adjusting for pad wear.

[0014] The ball ramp arrangement may comprise at least three grooves, in particular at least five grooves, of the first plate. Furthermore, the ball ramp arrangement may have at least three, in particular at least five grooves of the second plate. Accordingly, the ball ramp arrangement may comprise at least three, in particular at least five balls held by pairs of the grooves of the first and second plates. Typically, each of the balls is held by a pair of grooves, the pair comprising a groove of the first plate and a groove of the second plate. Any or all of the grooves of the first and / or second plates may have any or all of the features or properties described above or below with respect to each of the grooves. The embodiment with at least three pairs of grooves and at least three balls provides a mechanically stable arrangement.The embodiment with at least five pairs of grooves and at least five balls enables a compact arrangement with a low installation height. In further embodiments, the grooves of the first plate and the grooves of the second plate can have an identical shape, at least in sections. In some embodiments, the grooves of the first and second plates are completely identical in shape.

[0015] The depth of the groove of the first and / or second plate may increase in a non-linear manner between a first section and a second section of the groove, such that a path defined by the groove is steeper in the first section than in the second section. Since the path is steeper in the first section, a certain angular momentum exerted by the actuator is initially converted into a comparatively large relative travel of the first and second plates and into a large travel of the brake pad when the brake is initially applied. After the brake pad has traveled a certain distance, in particular after contact of the brake pad with the friction surface, the certain angular momentum is converted into a smaller relative travel of the brake pad. Therefore, the proposed friction braking system achieves a low gear ratio at the start of the ramp.In this way, a sufficiently high clamping force can be achieved in a short time with low actuator power required. When the brake is applied, the ball can move, specifically roll, from the first section of the groove to the second section.

[0016] Furthermore, the ball ramp arrangement may be configured such that the ball is disposed in the second portion of the groove when the spindle is rotated beyond the first angular range to effect longitudinal movement of the first plate relative to the spindle to adjust lining wear.

[0017] This allows for a lower clamping force. In some embodiments, the depth of the groove is neutral in the second part. The groove can therefore have a neutral inclination in the second part. When adjusting for pad wear, the ball is usually accommodated in the second part of the groove.

[0018] The braking element may include a piston connectable to the brake pad and, in some embodiments, may be referred to as the first brake pad. The piston may transmit the longitudinal movement of the second plate to the brake pad. The friction braking system may include the brake caliper housing. The brake caliper housing may be connected to a second brake pad. Further, the brake caliper housing and the piston may each be coupled to the first or second plate such that the brake caliper housing and the piston are configured to press the first and second brake pads against opposing surfaces of a brake rotor when the braking element executes the braking movement. Typically, the piston and the caliper housing move in opposite directions during braking.

[0019] In some embodiments, the friction braking system includes a coil spring. The first plate may be supported by the coil spring. The coil spring may be disposed between the first plate and the caliper housing. The coil spring may be configured to compress against the first plate toward the second plate and / or the brake pad. In typical embodiments, the spindle rests on a rotatable support plate. The support plate may be rotatable by the actuator. The support plate may be rigidly connected to the spindle. In some embodiments, the friction braking system includes a bearing, e.g., an axial needle bearing. The bearing may be disposed between the support plate and the caliper housing.

[0020] The friction brake system may also include the actuator. The actuator may include an electric motor that rotates the spindle. The actuator may also include a gearbox. The spindle may be coupled to the electric motor via the gearbox. In some embodiments, the actuator is rigidly connected to the brake caliper housing.

[0021] The present application further relates to a vehicle brake that is a service brake for a vehicle. The service brake may consist of a friction brake system having one or all of the features described above or below. Typically, the friction brake system is configured to reduce the rotational speed of a wheel by pressing the brake pad against the friction surface. In other embodiments, the application may relate to a vehicle brake that is a parking brake for a vehicle. The parking brake may consist of the friction brake system described above or below. In this embodiment, the friction brake system is configured to hold the vehicle stationary by pressing the brake pad against the friction surface.

[0022] Exemplary embodiments are described in connection with the following figures. Fig. 1 shows a cross-sectional view of a friction braking system for a vehicle, Fig. 2 shows another cross-sectional view of the friction brake system, and Fig. 3 shows a schematic sectional view of a groove and a ball of a ball ramp arrangement.

[0023] Fig. 1 shows a friction brake system 1 for a vehicle. The friction brake system 1 can be part of a service brake or a parking brake of the vehicle. The friction brake system 1 comprises an actuator 2 with gears and a rotatable output shaft 3. The rotatable output shaft 3 is rigidly connected to a rotatable spindle 4 via a rotatable carrier plate 5. The carrier plate 5 is supported on an axial needle bearing 6, which is arranged between the carrier plate 5 and a brake caliper housing 7 of a brake element. The rotational movement generated by the actuator 2 is converted into a braking movement, in which a first brake pad 8 and a second brake pad 9 are pressed against friction surfaces of a brake disc 10 of a wheel brake.To achieve the braking movement, a gear unit converts the rotational movement generated by the actuator 2 into a longitudinal movement of a piston 11 of the braking element holding the first brake pad 8 relative to the brake caliper housing 7 holding the second brake pad 9.

[0024] The transmission unit comprises a ball ramp assembly with a first plate 12 and a second plate 13 and balls 14, 14', e.g., a set of five balls, arranged between the first plate 12 and the second plate 13. The balls 14, 14' are arranged between the first plate 12 and the second plate 13 and are each held by a pair of grooves arranged on the surfaces of the first plate 12 and the second plate 13. The first plate 12 rests on the spindle 4 and has a thread on an inner surface that engages the spindle thread. In some embodiments, the plates 12, 13 are pressed against each other by a compression spring. Furthermore, the restoring torque of the ball ramp assembly can be increased by a torsion spring acting between the plates 12, 13. When the braking movement is executed, i.e., when the brake is applied, the first plate 12 rotates due to rotation of the spindle 4.The rotation of the first plate 12 is converted by the ball in the ramp into a longitudinal movement of the second plate 13. The second plate 13 is connected to the piston 11. When the brake is applied, the second plate 13 moves to the left relative to the caliper housing 7 to press the brake pads 8, 9 against the friction surfaces of the brake disc 10. The first plate 12 is also supported on the caliper housing 7 by a coil spring 15 arranged between a surface of the caliper housing 7 and a surface of the first plate 12. The second plate 13 is connected to the caliper housing 7 via a torque arm 16. The torque arm 16 is formed in part by a projection of the second plate 13, which engages in a recess in the caliper housing 7 and thereby prevents rotation of the second plate 13. In addition, a lock nut 17 is screwed onto the spindle 4.The lock nut 17 is connected to the first plate 12 via a torsion spring (not shown) and locks the first plate 12 relative to the spindle 4 during the braking movement.

[0025] In order to be able to adjust the pad wear, the first plate 12 is connected to the brake caliper housing 7 via a first stop 18. The first stop 18 is partially formed by a projection of the first plate 12, which engages in a recess in the brake caliper housing 7 when the spindle 4 is rotated beyond the angular range intended for braking. In this case, the first stop 18 prevents further rotation of the first plate 12 upon further rotation of the spindle 4 by the actuator 2, which leads to a translational movement of the first plate 12 with respect to the spindle 4. This longitudinal movement is used to enlarge or decrease the air gap between the brake pads 8, 9 and the brake disc 10 in order to adjust the pad wear. In order to enable the longitudinal movement of the first plate 12 for adjusting the pad wear, the lock nut 17 can also execute a longitudinal movement.To enable the longitudinal movement of the locknut 17, a locknut end stop 19 is provided, which is partially formed by a projection of the locknut 17 that is designed to engage a recess in the second plate 13. The locknut end stop 19 is designed to prevent rotational movement of the locknut 17 when the spindle 4 is rotated to adjust the lining wear, resulting in a longitudinal movement of the locknut 17 that allows the first plate 12 to move translationally to adjust the lining wear.

[0026] Fig. 2 shows a further cross-sectional view of the friction brake system 1. Corresponding and recurring features in the various figures are identified by the same reference numerals. The first stop 18, which connects the first plate 12 to the brake caliper housing 7, comprises a projection 20 formed on an outer surface of the first plate 12. The first stop 18 is formed by a first stop surface 21 machined into the surface of the housing. When the spindle 4 is rotated clockwise beyond the point at which the projection 20 comes into contact with the first stop surface 21, further rotation of the first plate 12 is prevented, and the first plate 12 performs a longitudinal movement to adjust the pad wear, e.g. to reduce the air gap between the brake pads 8, 9 and the brake disc 10. To adjust the pad wear in the opposite direction, e.g.To increase the air gap, a second stop is formed by a second stop surface 22 and the projection 20 of the first plate 12. The second stop is designed to prevent further counterclockwise rotation of the first plate 12.

[0027] The torque support 16 of the second plate 13 is formed by a projection 23 on an outer surface of the second plate 13. The projection 23 of the second plate 13 engages a recess in the brake caliper housing 7 and prevents rotation of the second plate 13. The lock nut end stop 19 is formed by a projection 24 on an outer surface of the lock nut 17 and a first lock nut surface 25 formed by an inner surface of the second plate 13. The lock nut end stop 19 is designed such that when the spindle 4 is rotated clockwise, the projection 24 of the lock nut 17 engages the first lock nut surface 25 shortly before the first plate 12 is prevented from further rotation due to the engagement of the projection 20 with the first stop surface 21.

[0028] Fig.3 shows a schematic view of a groove 26 of the first plate 12. The other grooves of the first plate 12 as well as the grooves of the second plate 13 are shaped accordingly. The ball 14 is held in the groove 26 of the first plate 12 and a corresponding groove in the second plate 13. The depth of the groove 26 decreases from a first section 27 of the groove 26 to a second section 28 of the groove 26. The depth of the groove 26 increases non-linearly, so that it is steeper in the first section 27 than in the second section 28. The depth of the groove 26 is constant in the second section 28, e.g. for the parking or holding function. The first part 27 of the groove 26 holds the ball 14 when the brake is not applied, and the second part 28 of the groove 26 holds the ball when the brake is applied. When adjusting the lining wear, e.g. B. to reduce the air gap between the brake pads 8, 9 and the brake disc 10, the ball 14 is held in the second section 28 of the groove 26.

[0029] According to the present application, a simple mechanism for compensating lining wear can be provided to drive the ball ramp assembly indirectly via a spindle drive rather than directly through the actuator. If the air gap is too large, the actuator can move the spindle drive with the ball ramp assembly from its initial position toward full braking against a stop between the housing and the ball ramp assembly, creating a relative movement between the nut and spindle that leads to lining wear compensation. This is possible because the friction torque caused by a lock nut is also canceled out by the actuator.If the air gap is too small, the actuator can move the spindle drive with the ball ramp assembly from its initial position in the opposite direction against a first stop between the housing and the ball ramp assembly, causing a relative movement between the nut and spindle and also opening the lock nut. In both cases, the change in the air gap can be controlled by a position control of the actuator.

[0030] Features of the various embodiments that are disclosed only in the exemplary embodiments can be combined with one another and also claimed individually.

Claims

[1] Friction brake system (1) for a vehicle, comprising a brake element which is connectable to at least one brake pad (8, 9) and is designed to press the brake pad (8, 9) against a friction surface and a transmission unit configured to convert a rotary movement generated by an actuator (2) into a braking movement of the brake pad (8, 9), the transmission unit comprising a ball ramp arrangement comprising: a first plate (12) with at least one groove (26), a second plate (13) having at least one groove facing the groove (26) of the first plate (12), and at least one ball (14) arranged between the first plate (12) and the second plate (13), the ball (14) being held by the groove (26) of the first plate (12) and the groove of the second plate (13), wherein the ball ramp arrangement is arranged to convert a rotational movement of the first plate (12) into a longitudinal movement of the second plate (13) relative to the first plate (12), wherein the second plate (13) is mechanically coupled to the braking element, so that rotation of the first plate (12) causes the braking movement of the braking element, wherein the friction brake system (1) further comprises a spindle (4), wherein the spindle (4) has spindle threads which engage with threads on an inner surface of the first plate (12), wherein the spindle (4) is arranged to be rotated by the actuator (2) through a first angular range in order to effect the rotational movement of the first plate (12) and thereby the braking movement of the braking element, wherein the spindle (4) is arranged to be rotated beyond the first angular range in order to effect a longitudinal movement of the first plate (12) relative to the spindle (4) for adjusting the lining wear, characterized by a lock nut (17) having an internal thread engaging the spindle thread, the lock nut (17) being configured to prevent longitudinal movement of the first plate (12) when the spindle (4) is rotated through the first angular range. [2] Friction brake system (1) according to claim 1, characterized by a first stop (18), wherein the first stop (18) is configured to prevent further rotation of the first plate (12) when the spindle (4) is rotated beyond the first angular range in a first direction of rotation, resulting in longitudinal movement of the first plate (12) relative to the spindle (4) in a first axial direction. [3] Friction brake system (1) according to claim 2, characterized bya second stop, the second stop being configured to prevent further rotation of the first plate (12) when the spindle (4) is rotated beyond the first angular range in a second direction of rotation opposite to the first direction of rotation, resulting in longitudinal movement of the first plate (12) relative to the spindle (4) in a second axial direction opposite to the first axial direction. [4] Friction brake system (1) according to one of claims 1 to 3, characterized by a locknut end stop (19) configured to prevent further rotation of the locknut (17) when the spindle (4) is rotated beyond the first angular range in the first angular direction to enable longitudinal movement of the first plate (12) relative to the spindle (4) in the first axial direction. [5] Friction brake system (1) according to claim 4, characterized byin that the locknut end stop (19) is arranged to prevent further rotation of the locknut (17) when the spindle (4) is rotated beyond the first angular range in the first angular direction before further rotation of the first plate (12) is prevented by the first stop (18), thereby causing longitudinal movement of the locknut away from the first plate (12) prior to longitudinal movement of the first plate (12) relative to the spindle (4) in the first axial direction. [6] Friction brake system (1) according to one of claims 4 or 5, characterized by that the lock nut end stop (19) is formed by the second plate (13) of the ball ramp arrangement. [7] Friction brake system (1) according to one of claims 3 to 6, characterized by that the first plate (12) and the lock nut (17) are connected to each other by a spring. [8] Friction brake system (1) according to one of claims 1 to 7, characterized byin that a depth of the groove (26) of the first plate (12) and / or the second plate (13) increases in a non-linear manner between a first section (27) and a second section (28) of the groove (26), so that a path defined by the groove (26) is steeper in the first section (27) than in the second section (28), wherein the ball ramp arrangement is arranged such that when the spindle (4) is rotated beyond the first angular range for causing the longitudinal movement of the first plate (12) relative to the spindle (4) for lining wear adjustment, the ball is arranged in the second section (28) of the groove. [9] Friction brake system (1) according to claim 8, characterized by that a depth of the groove (26) in the second section (28) is neutral. [10] Friction brake system (1) according to one of claims 1 to 9, characterized bya brake caliper housing (7), wherein the second plate (13) of the ball ramp arrangement is coupled to the brake caliper housing (7) via a torque support (16). [11] Friction brake system (1) according to one of claims 1 to 10, characterized by in that the braking element comprises a piston (11) which can be connected to a first brake pad (8), and a brake calliper housing (7) which can be connected to a second brake pad (9), wherein the brake calliper housing (7) and the piston (11) are each coupled to one of the first plate (12) and the second plate (13), so that the brake calliper housing (7) and the piston (11) are configured to press the first and the second brake pad (8, 9) against opposite surfaces of a brake disc (10) when the braking element executes the braking movement. [12] Service brake for a vehicle, comprising the friction brake system (1) according to one of the preceding claims, wherein the friction brake system (1) is designed to reduce a rotational speed of a wheel by pressing the brake pad (8, 9) against the friction surface.

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