VEHICLE BRAKE SYSTEM

Abstract

A vehicle brake system, comprising: a brake pad (10), being moveable between a braking position and a retracted position, a piston device (20) which is moveable over an operational stroke to move the brake pad from the retracted position into the braking position, which piston device comprises a first engagement surface (25), a retractor (30) which is adapted to move the piston device over a return stroke, thereby moving the brake pad from the braking position into the retracted position, a stop (40) which is in engagement with the first engagement surface (25) of the piston device (20) at the end of the return stroke, which stop (40) is arranged to prevent movement of the first engagement surface 825) past the stop in the direction of the return stroke, and wherein the stop (40) is moveable by the piston device (20) in the direction of the operational stroke of the piston device.

Claims

1. A vehicle brake system, which comprises: a frame, a brake pad, which is moveable relative to the frame between a braking position and a retracted position, a piston device which is moveable over an operational stroke to move the brake pad from the retracted position into the braking position, which piston device comprises a first engagement surface, a retractor which is adapted to move the piston device over a return stroke, thereby moving the brake pad from the braking position into the retracted position, a stop which is in engagement with the first engagement surface of the piston device at the end of the return stroke, which stop is arranged to prevent movement of the first engagement surface past the stop in the direction of the return stroke, and wherein the stop is moveable by the piston device in the direction of the operational stroke of the piston device.

2. The vehicle brake system according to claim 1, wherein the piston device further comprises a second engagement surface adapted to engage the stop at the end of the operational stroke.

3. The vehicle brake system according to claim 2, wherein the stop is moveable by the second engagement surface of the piston device in the direction of the operational stroke when the operational stroke is longer than the return stroke.

4. The vehicle brake system according to claim 1, wherein the first engagement surface of the piston device is spaced apart from the stop when the piston device is in an intermediate position in the return stroke, an intermediate position in the operational stroke, and at the end of the operational stroke.

5. The vehicle brake system according to claim 1, wherein the retractor is adapted to force the first engagement surface of the piston device against the stop with a pre-tensioning force and to maintain this pre-tensioning force while the piston device is at the end of the return stroke.

6. The vehicle brake system according to claim 1, wherein the vehicle brake system further comprises a drive which is adapted to apply a drive force on the piston device in order to move the piston device over the operational stroke, and wherein the retractor is adapted to apply a retraction force onto the brake pad and/or on the piston device during the return stroke, and wherein the drive force is larger than the retraction force.

7. The vehicle brake system according to claim 6, wherein the stop is slidably mounted in a housing, wherein a static friction force is present between the stop and the housing, which static friction force is smaller than the drive force and larger than the retraction force.

8. The vehicle brake system according to claim 1, wherein the vehicle brake system further comprises a locking device which is adapted to prevent movement of the stop in the direction of the return stroke.

9. The vehicle brake system according to claim 8, wherein the locking device is or comprises one of the following: a wedge, a double louvre, a linear backstop, a one way freewheel clutch, a rod having one-directional self-locking thread, a flexible seal.

10. The vehicle brake system according to claim 1, wherein the retractor is or comprises a spring, a hydraulic device, a pneumatic device, a magnetic device, an electric device and/or an electromagnetic device.

11. The vehicle brake system according to claim 2, wherein the piston device extends into a housing, and wherein the stop comprises a ring having a central annular opening, which ring is friction mounted inside the housing and onto an inner wall of the housing, wherein a part of the piston device extends through the annular opening of the ring, with the ring being arranged between the first engagement surface of the piston device and the second engagement surface of the piston device, wherein the ring comprises a first annular surface which is arranged to engage the first engagement surface of the piston device at the end of the return stroke and a second annular surface on the opposite side of the ring with regard the first annular surface, which second annular surface is arranged to engage the second engagement surface of the piston device at the end of the operational stroke when the operational stroke is longer than the return stroke.

12. The vehicle brake system according to claim 11, wherein the retractor is arranged in the housing.

13. The vehicle brake system according to claim 2, wherein the vehicle brake system further comprises an intermediate element, which intermediate element comprises the stop, which intermediate element is moveably arranged into a housing.

14. The vehicle brake system according to claim 13, wherein the retractor is arranged between the piston device and the intermediate element.

15. The vehicle brake system according to claim 1, wherein the vehicle brake system further comprises a rotatable wheel part, and wherein in the braking position the brake pad engages the rotatable wheel part.

16. A vehicle, which vehicle comprises: a wheel which is provided with an in-wheel motor, which in-wheel motor comprises a rotor, a vehicle brake system according to claim 1, wherein in the braking position the brake pad engages the rotor of the in-wheel motor.

17. A vehicle, which vehicle comprises: a wheel which is provided with a brake disk, a vehicle brake system according to claim 1, wherein in the braking position the brake pad engages the brake disk.

18. A trailer, which comprises a vehicle brake system according to claim 1.

Description

[0119] FIG. 1 shows a first embodiment of the vehicle brake system 1 according to the invention. In FIG. 1, the brake pad is in the retracted position. FIG. 2 again shows the embodiment of FIG. 1, but now with the brake pad in the braking position.

[0120] In the embodiment of FIG. 1 and FIG. 2, the vehicle brake system 1 comprises a frame 5. The frame 5 is for example a brake caliper or a part thereof.

[0121] The vehicle brake system 1 of FIG. 1 and FIG. 2 further comprises a brake pad 10. In this embodiment, the brake pad 10 comprises a brake pad body 12 which is arranged on a brake pad holder 11. The brake pad holder 11 which has a relatively high rigidity, so it can withstand the forces that occur during braking without too much deformation. The brake pad body 12 comprises typical brake pad material.

[0122] The brake pad 10 is moveable relative to the frame 5 between a braking position (which is shown in FIG. 2) and a retracted position (which is shown in FIG. 1).

[0123] In the braking position, which is shown in FIG. 2, the vehicle brake system 1 is active, so the wheel that is associated with the vehicle brake system 1 is subjected to a braking action. In the braking position, the brake pad 10 is for example positioned to engage a brake disk or other rotatable wheel part which rotates along with the wheel. In FIG. 1, the position of a brake disk or other rotatable wheel part of the wheel that is associated with the vehicle brake system 1 is indicated by dashed line 2.

[0124] In case an in-wheel electrical motor is used to drive the wheel on which the vehicle brake system 1 is arranged to operate, in the braking position, the brake pad 10 is for example positioned to engage a rotor of the in-wheel motor.

[0125] In the retracted position, which is shown in FIG. 1, the vehicle brake system 1 is not active, so the wheel that is associated with the vehicle brake system 1 is not subjected to a braking action. In FIG. 1, the position of a brake disk or other rotatable wheel part of the wheel that is associated with the vehicle brake system 1 is indicated by dashed line 2.

[0126] In the retracted position, the brake pad 10 is at the largest distance from the brake disk or other rotatable wheel part that the brake pad engages when the brake pad is in the braking position. So, if the total distance that the brake pad 10 travels from the braking position away from the brake disk or other rotatable wheel part of the wheel with which the vehicle brake system 1 is associated is referred to as the brake pad stroke, the braking position and the retracted position are located at opposite ends of the brake pad stroke. The brake pad 10 does not travel further away from the brake disk or rotatable wheel part than the retracted position. Any position of the brake pad 10 between the braking position and the retracted position is referred to as an “intermediate position” of the brake pad 10.

[0127] The vehicle brake system of FIG. 1 and FIG. 2 further comprises a piston device 20. In the embodiment of FIG. 1 and FIG. 2, the piston device 20 is formed by a hydraulic piston 21. Alternatively, a hydraulic piston with a piston rod, a pneumatic piston, a pneumatic piston with a piston rod, a magnetically operated piston, a magnetically operated piston with a piston rod, a piston which is driveable by a linear motor, or a combination of a piston and piston rod which is driven by a linear motor could be applied.

[0128] The piston 21 is optionally connected to the brake pad 10. In this embodiment, the piston 21 is attached to the brake pad holder 11. The piston 21 is moveable over an operational stroke to move the brake pad 10 from the retracted position into the braking position. In the embodiment of FIG. 1 and FIG. 2, the operational stroke of the piston 21 extends parallel or even coaxial with the brake pad stroke. In FIG. 1, arrow 3 indicates the direction of the operational stroke. In the embodiment of FIG. 1 and FIG. 2, the operational stroke of the piston 21 has the same length as the brake pad stroke as long a no wear occurs on the brake pad or on the brake disk or other rotatable wheel part of the wheel with which the vehicle brake system 1 is associated.

[0129] The operational stroke of the piston 21 (which in this embodiment forms the piston device 20) has a start point and an end point. If the piston 21 is located somewhere between the start point and the end point of the operational stroke, it is in an intermediate position

[0130] The piston 21 comprises a first engagement surface 25.

[0131] The vehicle brake system according to FIG. 1 and FIG. 2 further comprises a retractor 30 which is adapted to move the piston 21 which in this embodiment forms the piston device 20 over a return stroke, thereby moving the brake pad 10 from the braking position into the retracted position. The direction of the return stroke is indicated in FIG. 2 by arrow 4 in the embodiment of FIG. 1 and FIG. 2, the retractor 30 comprises a plurality of springs 31, which are for example coil springs. In this embodiment, the retractor 30 engages the brake pad 10 as the springs 31 engage the brake pad holder 11. Alternatively in or addition, the retractor may engage the piston device 20. Because the springs 31 engage the brake pad holder, the piston 21 is optionally not fixedly connected to the brake pad 10, but only engages the brake pad 10 under the influence of the hydraulic pressure on the piston 21 and/or of the springs 31.

[0132] In the embodiment of FIG. 1 and FIG. 2, the hydraulic piston 21 extends in a hydraulic chamber 22 within the frame 5. The hydraulic chamber 22 can be filled with a hydraulic fluid. An inlet/outlet port 23 is provided which allows hydraulic fluid to be supplied to and discharged from the hydraulic chamber 22. The hydraulic chamber is sealed by piston seal 24. Piston seal 24 can be a rigid seal through which the piston 21 can move back and forth, or it can be a flexible seal of which the inner wall (which is the wall of the seal 24 that contacts the piston 21) at least partly moves along with the piston 21 when the piston 22 is moved over its operational stroke and its return stroke. In case of a flexible seal, the flexible seal may bias the piston 21 towards the end of its return stroke Optionally, such a flexible seal may form part of the retractor 30.

[0133] The vehicle brake system according to the invention further comprises a stop 40. This stop 40 is in engagement with the first engagement surface 25 of the piston 21 at the end of the return stroke, so the position the piston 21 is in when the brake pad 10 is in the retracted position. The stop 40 is arranged to prevent movement of the first engagement surface 25 past the stop 40 in the direction of the return stroke.

[0134] The stop 40 is moveable by the piston 21 in the direction of the operational stroke of the piston 21, so in the direction of arrow 3 in FIG. 1.

[0135] In the embodiment of FIG. 1 and FIG. 2, the hydraulic chamber 22 and the inlet/outlet port 23 form part of a hydraulic drive which is adapted to apply a drive force on the piston 21 that forms the piston device 20 in order to move the piston 21 over the operational stroke. The retractor 30 is adapted to apply a retraction force onto the brake pad 10, and therewith upon the piston 21 during the return stroke. The drive force is larger than the retraction force.

[0136] In the embodiment of FIG. 1 and FIG. 2, the stop 40 comprises a plug 41. The plug 41 is slidably arranged in a plug housing 42. In the embodiment of fig. and FIG. 2, the plug 41 and the plug housing 42 are located inside the hydraulic chamber 22. This has the advantage that the stop 40 and the combination of the plug 41 and the plug housing 42 are shielded from dirt, rust and other contamination, which ensures proper functioning.

[0137] A static friction force is present between the plug 41 of the stop 40 and the plug housing 42. The static friction force is smaller than the drive force and larger than the retraction force.

[0138] The static friction force is the force that needs to be overcome to get the plug 41 of the stop 40 sliding within the plug housing 42.

[0139] The static friction force being smaller than the drive force and larger than the retraction force makes that the drive force can cause the plug 41 of the stop 40 to slide within the plug housing 42, but the retraction force cannot. This way, the stop can be moved by the piston 21 in the direction of the operational stroke as indicated by arrow 3 in FIG. 1, but not in the direction of the return stroke as indicated by arrow 4 in FIG. 2.

[0140] The plug housing 42 can for example be mounted to the frame 5 or form an integral part of the frame 5.

[0141] In the embodiment of FIG. 1 and FIG. 2, the stop 40 has a first stop surface 44 and a second stop surface 45. The first stop surface 44 is arranged to engage the first engagement surface 25 of the piston 21 when the piston 21 is at the end of the return stroke. The second stop surface 45 is arranged to engage the second engagement surface 26 of the piston 21 when the piston 21 is at the end of the operational stroke, or when the second engagement surface 26 engages the stop 40 in order to move the stop 40 in the direction of the operational stroke.

[0142] Optionally, the way in which the stop is mounted in the housing is such that the stop can be returned to its initial position when a worn brake pad has been replaced by a new brake pad. This can for example be achieved by providing the plug 41 with a sleeve 43 which is in contact with the plug housing 42. The sleeve 43, which forms part of the plug 41 and moves along with the stop 40, allows the stop 40 to slide back to its initial position when sufficient force is applied to the stop 40.

[0143] In the embodiment of FIG. 1 and FIG. 2, the piston 21 that forms the piston device 20 further comprises a second engagement surface 26. The second engagement surface 26 is adapted to engage the stop 40 at the end of the operational stroke, as can be seen in FIG. 2. At the end of the operational stroke of the piston 21, the brake pad 10 is in the braking position.

[0144] The second engagement surface 26 is arranged at a distance from the first engagement surface 25.

[0145] In the embodiment of FIG. 1 and FIG. 2, the distance between the first engagement surface 25 and the second engagement surface 26 is for example equal to the length of the return stroke or—as is shown in FIG. 1 and FIG. 2—the distance between the first engagement surface and the second engagement surface is equal to the length of the return stroke plus the distance between the location on the stop where the first engagement surface contacts the stop and the location on the stop where the second engagement surface contacts the stop, this distance being measured in the direction of the return stroke.

[0146] In this embodiment, the stop 40 is moveable by the second engagement surface 26 of the piston 21 in the direction of the operational stroke when the operational stroke is longer than the return stroke.

[0147] In the embodiment of FIG. 1 and FIG. 2, the first engagement surface 25 of the piston 21 that forms the piston device 2 is spaced apart from the stop 40 when the piston device is in an intermediate position in the return stroke, an intermediate position in the operational stroke, and at the end of the operational stroke. The first engagement surface 25 is only in contact with the stop 40 at the end of the return stroke of the piston 21, which coincides with the beginning of the operational stroke of the piston 21. As soon as the piston 21 leaves this position, the first engagement surface 25 no longer engages the stop 40.

[0148] In the embodiment of FIG. 1 and FIG. 2, the retractor 30 is adapted to force the first engagement surface 25 of the piston 21 against the stop 40 with a pre-tensioning force and to maintain this pre-tensioning force while the piston 21 is at the end of the return stroke.

[0149] The embodiment of FIG. 1 and FIG. 2 works as follows. When the vehicle is running without the brake being applied, the vehicle brake system 1 is in the position as shown in FIG. 1. The brake pad 10 does not engage a brake disk or other rotatable part of a wheel that is associated with the vehicle brake system 1. Dashed line 2 in FIG. 1 indicates the position of the brake disk or other rotatable part of a wheel that is associated with the vehicle brake system 1.

[0150] The springs 31 of the retractor 30 force the first engagement surface 25 of the piston 21 against the stop 40. The first engagement surface 25 cannot move past the stop 40, and the force that is applied by the retractor 30 is less than the static friction between the plug 41 of the stop 40 and the plug housing 42. Therefore, the force that is exerted by the retractor is not able to move the stop in the direction of the return stroke, which is indicated by arrow 4 in FIG. 2.

[0151] When the brake is applied, the pressure in the hydraulic chamber 22 is increased so that a drive force is exerted on the piston 21 and the piston 21 leaves the position that is shown in FIG. 1 and moves over its operational stroke into a position in which the brake pad 10 engages the brake disk or other rotatable part of a wheel that is associated with the vehicle brake system 1. When brake pad 10 engages the brake disk or other rotatable part of a wheel that is associated with the vehicle brake system 1, the brake pad 10 is in its braking position. This position of the piston 21 and the brake pad 10 is shown in FIG. 2.

[0152] The springs 31 of the retractor 30 are stretched to an elongated state when the brake pad 10 is in the braking position. The stop 40 engages the second engagement surface 26 of the piston 21.

[0153] If wear of the brake pad 10 has occurred, the thickness of the brake pad body 12 has been reduced. As a result, the brake pad 10 will have to travel over a longer distance from the retracted position to reach the braking position in which it engages the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use. The same happens when the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use has suffered wear.

[0154] In this case, the operational stroke of the piston 21 gets longer than it was before. As soon as the piston 21 reaches the position which previously was the end point of the operational stroke, the second engagement surface 26 of the piston 21 engages the stop 40. However, the piston 21 continues to travel in the direction of the operational stroke until the brake pad 10 engages the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use. During this continued travel of the piston 21, the piston 21 moves the stop 40 relative to the plug housing 42 in the direction of the operational stroke.

[0155] When the brake is released, the pressure in the hydraulic chamber 22 drops and the piston starts its return stroke under the influence of the retractor 30. The brake pad 10 disengages from the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use. The stop 40 disengages from the second engagement surface 26 of the piston 21.

[0156] The piston 21 stops moving in the direction of the return stroke when the first engagement surface 25 of the piston engages the stop 40. The first engagement surface 25 of the piston 21 does not move beyond the stop 40 in the direction of the return stroke.

[0157] In case the stop 40 has been moved by the piston 21, in particular by the second engagement surface 26 of the piston 21, the end point of the return stroke is at a different position relative to the frame 5 than it was before the wear of the brake pad 10 and/or the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use occurred. This makes that the length of the return stroke is kept constant regardless of wear that occurs.

[0158] FIG. 3 shows a second embodiment of the vehicle brake system 1 according to the invention. In FIG. 3, the brake pad is in the retracted position. FIG. 4 again shows the embodiment of FIG. 3, but now with the brake pad in the braking position.

[0159] In the embodiment of FIG. 3 and FIG. 4, the vehicle brake system 1 comprises a frame 5. The frame 5 is for example a brake caliper or a part thereof.

[0160] The vehicle brake system 1 of FIG. 3 and FIG. 4 further comprises a brake pad 10. In this embodiment, the brake pad 10 comprises a brake pad body 12 which is arranged on a brake pad holder 11. The brake pad holder 11 which has a relatively high rigidity, so it can withstand the forces that occur during braking without too much deformation. The brake pad body 12 comprises typical brake pad material.

[0161] The brake pad 10 is moveable relative to the frame 5 between a braking position (which is shown in FIG. 4) and a retracted position (which is shown in FIG. 3).

[0162] In the braking position, which is shown in FIG. 4, the vehicle brake system 1 is active, so the wheel that is associated with the vehicle brake system 1 is subjected to a braking action. In the braking position, the brake pad 10 is for example positioned to engage a brake disk or other rotatable wheel part which rotates along with the wheel. In FIG. 3, the position of a brake disk or other rotatable wheel part of the wheel that is associated with the vehicle brake system 1 is indicated by dashed line 2.

[0163] In case an in-wheel electrical motor is used to drive the wheel on which the vehicle brake system 1 is arranged to operate, in the braking position, the brake pad 10 is for example positioned to engage a rotor of the in-wheel motor.

[0164] In the retracted position, which is shown in FIG. 3, the vehicle brake system 1 is not active, so the wheel that is associated with the vehicle brake system 1 is not subjected to a braking action. In FIG. 3, the position of a brake disk or other rotatable wheel part of the wheel that is associated with the vehicle brake system 1 is indicated by dashed line 2.

[0165] In the retracted position, the brake pad 10 is at the largest distance from the brake disk or other rotatable wheel part that the brake pad engages when the brake pad is in the braking position. So, if the total distance that the brake pad 10 travels from the braking position away from the brake disk or other rotatable wheel part of the wheel with which the vehicle brake system 1 is associated is referred to as the brake pad stroke, the braking position and the retracted position are located at opposite ends of the brake pad stroke. The brake pad 10 does not travel further away from the brake disk or rotatable wheel part than the retracted position. Any position of the brake pad 10 between the braking position and the retracted position is referred to as an “intermediate position” of the brake pad 10.

[0166] The vehicle brake system of FIG. 3 and FIG. 4 further comprises a piston device 20. In the embodiment of FIG. 3 and FIG. 4, the piston device 20 is formed by a hydraulic piston 21. Alternatively, a hydraulic piston with a piston rod, a pneumatic piston, a pneumatic piston with a piston rod, a magnetically operated piston, a magnetically operated piston with a piston rod, a piston which is driveable by a linear motor, or a combination of a piston and piston rod which is driven by a linear motor could be applied.

[0167] The piston 21 is connected to the brake pad 10. In this embodiment, the piston 21 is attached to the brake pad holder 11. The piston 21 is moveable over an operational stroke to move the brake pad 10 from the retracted position into the braking position. In the embodiment of FIG. 3 and FIG. 4, the operational stroke of the piston 21 extends parallel or even coaxial with the brake pad stroke. In FIG. 3, arrow 3 indicates the direction of the operational stroke. In the embodiment of FIG. 3 and FIG. 4, the operational stroke of the piston 21 has the same length as the brake pad stroke as long a no wear occurs on the brake pad or on the brake disk or other rotatable wheel part of the wheel with which the vehicle brake system 1 is associated.

[0168] The operational stroke of the piston 21 (which in this embodiment forms the piston device 20) has a start point and an end point. If the piston 21 is located somewhere between the start point and the end point of the operational stroke, it is in an intermediate position.

[0169] The piston 21 comprises a first engagement surface 25.

[0170] The vehicle brake system according FIG. 3 and FIG. 4 further comprises a retractor 30 which is adapted to move the piston 21 which in this embodiment forms the piston device 20 over a return stroke, thereby moving the brake pad 10 from the braking position into the retracted position. The direction of the return stroke is indicated in FIG. 4 by arrow 4. In the embodiment of FIG. 3 and FIG. 4, the retractor 30 comprises a spring 31, which is for example a coil spring. In the embodiment of FIG. 3 and FIG. 4, the spring 31 is arranged inside the frame 5. In this embodiment, the retractor 30 engages the piston device 20. Alternatively or in addition, the retractor may engage the brake pad 10.

[0171] In the embodiment of FIG. 1 and FIG. 4, the hydraulic piston 21 extends in a hydraulic chamber 22 within the frame 5. The hydraulic chamber 22 can be filled with a hydraulic fluid. An inlet/outlet port 23 is provided which allows hydraulic fluid to be supplied to and discharged from the hydraulic chamber 22. The hydraulic chamber is sealed by piston seal 24. Piston seal 24 can be a rigid seal through which the piston 21 can move back and forth, or it can be a flexible seal of which the inner wall (which is the wall of the seal 24 that contacts the piston 21) at least partly moves along with the piston 21 when the piston 22 is moved over its operational stroke and its return stroke. In case of a flexible seal, the flexible seal may bias the piston 21 towards the end of its return stroke Optionally, such a flexible seal may form part of the retractor 30.

[0172] The vehicle brake system according to the invention further comprises a stop 40. This stop 40 is in engagement with the first engagement surface 25 of the piston 21 at the end of the return stroke, so the position the piston 21 is in when the brake pad 10 is in the retracted position. The stop 40 is arranged to prevent movement of the first engagement surface 25 past the stop 40 in the direction of the return stroke.

[0173] The stop 40 is moveable by the piston 21 in the direction of the operational stroke of the piston 21, so in the direction of arrow 3 in FIG. 3.

[0174] In the embodiment of FIG. 3 and FIG. 4, the hydraulic chamber 22 and the inlet/outlet port 23 form part of a hydraulic drive which is adapted to apply a drive force on the piston 21 that forms the piston device 20 in order to move the piston 21 over the operational stroke. The retractor 30 is adapted to apply a retraction force onto the brake pad 10, and therewith upon the piston 21 during the return stroke. The drive force is larger than the retraction force.

[0175] In the embodiment of FIG. 3 and FIG. 4, the piston device 20 (which is formed by piston 21 in this embodiment) extends into a housing 46, which forms part of the frame 5. The stop 40 comprises a ring 47 having a central annular opening. The ring 47 is friction mounted inside the housing 46 and onto an inner wall of the housing 46.

[0176] A part of the piston 21 extends through the annular opening of the ring 47, with the ring being arranged between the first engagement surface 25 of the piston 21 and the second engagement surface 26 of the piston 21.

[0177] In this embodiment, the ring 47 comprises a first stop surface 44 in the form of an first annular surface, which is arranged to engage the first engagement surface 25 of the piston 21 at the end of the return stroke. The ring 47 further comprises second stop surface 45 in the form of a second annular surface on the opposite side of the ring 47 with regard the first annular surface. The second annular surface is arranged to engage the second engagement surface 26 of the piston 21 at the end of the operational stroke when the operational stroke is longer than the return stroke.

[0178] In the embodiment of FIG. 3 and FIG. 4, the ring 47 is slidably arranged in the housing 46.

[0179] A static friction force is present between the ring 47 of the stop 40 and the housing 46. The static friction force is smaller than the drive force and larger than the retraction force.

[0180] The static friction force is the force that needs to be overcome to get the ring 47 sliding within the housing 46.

[0181] The static friction force being smaller than the drive force and larger than the retraction force makes that the drive force can cause the ring 47 of the stop 40 to slide within the housing 46, but the retraction force cannot. This way, the ring 47 of the stop 40 can be moved by the piston 21 in the direction of the operational stroke as indicated by arrow 3 in FIG. 3, but not in the direction of the return stroke as indicated by arrow 4 in FIG. 4.

[0182] Optionally, the way in which the ring 47 of the stop 40 is mounted in the housing 46 is such that the ring 47 of the stop 40 can be returned to its initial position when a worn brake pad has been replaced by a new brake pad. This can for example be achieved by providing the ring 47 with a sleeve which is in contact with the housing 46, similar to what is shown with respect to the sleeve 43 in the embodiment of FIG. 1 and FIG. 2.

[0183] In the embodiment of FIG. 3 and FIG. 4, the piston 21 that forms the piston device 20 further comprises a second engagement surface 26. The second engagement surface 26 is adapted to engage the stop 40 at the end of the operational stroke, as can be seen in FIG. 4. At the end of the operational stroke of the piston 21, the brake pad 10 is in the braking position.

[0184] The second engagement surface 26 is arranged at a distance from the first engagement surface 25.

[0185] In the embodiment of FIG. 3 and FIG. 4, the distance between the first engagement surface 25 and the second engagement surface 26 is for example equal to the length of the return stroke, or—as is shown in FIG. 3 and FIG. 4—the distance between the first engagement surface and the second engagement surface is equal to the length of the return stroke plus the distance between the location on the stop where the first engagement surface contacts the stop and the location on the stop where the second engagement surface contacts the stop, this distance being measured in the direction of the return stroke.

[0186] In this embodiment, the stop 40 is moveable by the second engagement surface 26 of the piston 21 in the direction of the operational stroke when the operational stroke is longer than the return stroke.

[0187] In the embodiment of FIG. 3 and FIG. 4, the first engagement surface 25 of the piston 21 that forms the piston device 2 is spaced apart from the stop 40 when the piston device is in an intermediate position in the return stroke, an intermediate position in the operational stroke, and at the end of the operational stroke. The first engagement surface 25 is only in contact with the stop 40 at the end of the return stroke of the piston 21, which coincides with the beginning of the operational stroke of the piston 21. As soon as the piston 21 leaves this position, the first engagement surface 25 no longer engages the stop 40.

[0188] In the embodiment of FIG. 3 and FIG. 4, the retractor 30 is adapted to force the first engagement surface 25 of the piston 21 against the stop 40 with a pre-tensioning force and to maintain this pre-tensioning force while the piston 21 is at the end of the return stroke.

[0189] The embodiment of FIG. 3 and FIG. 4 works as follows. When the vehicle is running without the brake being applied, the vehicle brake system 1 is in the position as shown in FIG. 3. The brake pad 10 does not engage a brake disk or other rotatable part of a wheel that is associated with the vehicle brake system 1. Dashed line 2 in FIG. 3 indicates the position of the brake disk or other rotatable part of a wheel that is associated with the vehicle brake system 1.

[0190] The spring 31 of the retractor 30 forces the first engagement surface 25 of the piston 21 against the stop 40. The first engagement surface 25 cannot move past the stop 40, and the force that is applied by the retractor 30 is less than the static friction between the ring 47 of the stop 40 and the housing 46. Therefore, the force that is exerted by the retractor is not able to move the stop 40 in the direction of the return stroke, which is indicated by arrow 4 in FIG. 4.

[0191] When the brake is applied, the pressure in the hydraulic chamber 22 is increased so that a drive force is exerted on the piston 21 and the piston 21 leaves the position that is shown in FIG. 3 and moves over its operational stroke into a position in which the brake pad 10 engages the brake disk or other rotatable part of a wheel that is associated with the vehicle brake system 1. When brake pad 10 engages the brake disk or other rotatable part of a wheel that is associated with the vehicle brake system 1, the brake pad 10 is in its braking position. This position of the piston 21 and the brake pad 10 is shown in FIG. 4.

[0192] The spring 31 of the retractor 30 is stretched to an elongated state when the brake pad 10 is in the braking position. The stop 40 engages the second engagement surface 26 of the piston 21.

[0193] If wear of the brake pad 10 has occurred, the thickness of the brake pad body 12 has been reduced. As a result, the brake pad 10 will have to travel over a longer distance from the retracted position to reach the braking position in which it engages the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use. The same happens when the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use has suffered wear.

[0194] In this case, the operational stroke of the piston 21 gets longer than it was before. As soon as the piston 21 reaches the position which previously was the end point of the operational stroke, the second engagement surface 26 of the piston 21 engages the stop 40. However, the piston 21 continues to travel in the direction of the operational stroke until the brake pad 10 engages the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use. During this continued travel of the piston 21, the piston 21 moves the stop 40 relative to the plug housing 42 in the direction of the operational stroke.

[0195] When the brake is released, the pressure in the hydraulic chamber 22 drops and the piston 21 starts its return stroke under the influence of the retractor 30. The brake pad 10 disengages from the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use. The stop 40 disengages from the second engagement surface 26 of the piston 21.

[0196] The piston 21 stops moving in the direction of the return stroke when the first engagement surface 25 of the piston engages the stop 40. The first engagement surface 25 of the piston 21 does not move beyond the stop 40 in the direction of the return stroke.

[0197] In case the stop 40 has been moved by the piston 21, in particular by the second engagement surface 26 of the piston 21, the end point of the return stroke is at a different position relative to the frame 5 than it was before the wear of the brake pad 10 and/or the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use occurred. This makes that the length of the return stroke is kept constant regardless of wear that occurs.

[0198] FIG. 5 shows a third embodiment of the vehicle brake system 1 according to the invention. In FIG. 5, the brake pad is in the retracted position. FIG. 6 again shows the embodiment of FIG. 5, but now with the brake pad in the braking position.

[0199] The embodiment of FIG. 5 and FIG. 6 is a variant of the embodiment of FIG. 3 and FIG. 4, and operates generally in the same way.

[0200] In the embodiment of FIG. 5 and FIG. 6, an intermediate element 50 is provided. In this embodiment, the ring 47 of the stop 40 is mounted in the intermediate element 50. The intermediate element 50 is moveably, e.g. slidably, arranged into the housing 46, which housing 46 forms part of the frame 5. Optionally, the intermediate element 50 is provided with at least one opening to allow hydraulic fluid to pass through.

[0201] The intermediate element 50 moves along with the ring 47 of the stop 40 in case of wear of the brake pad body 12.

[0202] A sleeve 51 is provided around the intermediate element 50. The sleeve 51 is fixed to the intermediate element 50. A static friction force is present between the sleeve 51 and the housing 46. The static friction force is smaller than the drive force and larger than the retraction force.

[0203] The static friction force is the force that needs to be overcome to get the sleeve 51 sliding within the housing 46.

[0204] The static friction force being smaller than the drive force and larger than the retraction force makes that the drive force can cause the sleeve 51, together with the intermediate element 50 and the ring 47 of the stop 40, to slide within the housing 46, but the retraction force cannot. This way, the ring 47 of the stop 40 can be moved by the piston 21 in the direction of the operational stroke as indicated by arrow 3 in FIG. 5, but not in the direction of the return stroke as indicated by arrow 4 in FIG. 6.

[0205] In the embodiment of FIGS. 5 and 6, optionally the retractor 30 is arranged between the piston 21 and the intermediate element 50.

[0206] Optionally, and shown in FIG. 5 and FIG. 6, the piston device 20 has an outer diameter and a length, and the intermediate element 50 extends along the outer diameter of the piston device 20 over at least a part of the length of the piston device 20.

[0207] Optionally, and shown in FIG. 5 and FIG. 6, the intermediate element 50 has an opening in which at least the first engagement surface 25 and the second engagement surface 26 of the piston device 20 are accommodated. Optionally, and shown in FIG. 5 and FIG. 6, the intermediate element 50 in this opening at least the first engagement surface 25 and the second engagement surface 26 of the piston device 20 are accommodated during the entire operational stroke and/or during the entire return stroke of the piston device 20, and/or when the brake pad 10 is in the retracted position and/or when the brake pad 10 is in the braking position. Optionally, and shown in FIG. 5 and FIG. 6, the piston device 20 comprises a first end facing towards the brake pad 10 and a second end, which is opposite to the first end, and the intermediate element 50 has an opening in which at least the second end of the piston device 20 is accommodated in the opening of the intermediate element 50.

[0208] Optionally, and shown in FIG. 5 and FIG. 6, the intermediate element 50 is cup-shaped and has a central opening, and the at least part of the piston device 20 is accommodated in the central opening.

[0209] Optionally, and shown in FIG. 5 and FIG. 6, the intermediate element 50 is has a U-shaped cross section and has a central opening which extends in the axial direction of the intermediate direction, and the at least part of the piston device 20 is accommodated in the central opening.

[0210] FIG. 7 shows a fourth embodiment of the vehicle brake system 1 according to the invention. In FIG. 7, the brake pad is in the braking position.

[0211] The embodiment of FIG. 7 is a variant of the embodiment of FIG. 5 and FIG. 6, and operates generally in the same way.

[0212] The main difference between the embodiment of FIG. 7 and the embodiment of FIG. 5 and FIG. 6 is in the retractor 30. While in the embodiment of FIG. 5 and FIG. 6, the retractor comprises a spring 31, in the embodiment of FIG. 7, the retractor comprises two magnets 32, 33.

[0213] In the embodiment of FIG. 7, the magnets 32, 33 attract each other. When the brake is engaged, the pressure in the hydraulic chamber 22 increases and the drive force which is exerted on the piston 21 overcomes the magnetic attraction force of the magnets 32, 33.

[0214] When the brake is released, the hydraulic pressure in the hydraulic chamber 22 decreases. The magnetic attraction force between the magnets 32, 33 moves the piston 21 over its return stroke to disengage the brake pad 10 from the brake disk or other rotatable wheel part of the wheel that is associated with the vehicle brake system.

[0215] FIG. 8 shows a fifth embodiment of a vehicle brake system according to the invention, in the braking position. The embodiment of FIG. 8 is a variant of the embodiment of FIG. 1 and FIG. 2, and works generally in the same way.

[0216] In the embodiment of FIG. 8, the stop 40 does not comprise a stop plug 41 which is arranged in a plug housing 42. Instead, the stop 40 comprises a stop rod 48.

[0217] In the embodiment of FIG. 8, a locking device 60 is provided to prevent movement of the stop in the direction of the return stroke.

[0218] In the embodiment of FIG. 8, the locking device 60 is a mechanical device which allows movement in one direction but not in the direction opposite thereto, e.g. by shape locking and/or by force locking. Alternatively or in addition, the locking device may be or comprise a hydraulic, pneumatic, electric and/or magnetic device which allows movement in one direction but not in the direction opposite thereto.

[0219] In the embodiment of FIG. 8, the stop rod 48 extends outside the frame 50. A seal 62 is provided to prevent leakage of hydraulic fluid from the hydraulic chamber 22 while still allowing the stop rod to move relative to the frame 5.

[0220] In the embodiment of FIG. 8, the locking device 60 comprises two louvres 61. The louvres are moveable, in particular pivotable, around pivots 63. The distance between the pivots is less than twice the length of a louvre 61 plus the diameter of the stop rod 48. In addition, each louvres 61 points towards the piston 21 as seen from its associated pivot 63. This makes that the louvres allow movement of the stop rod 48 in the direction of the operational stork of the piston 21, but not in the direction of the return stroke.

[0221] In the embodiment of FIG. 8, the locking device 60 is releasable by pivoting the louvres 61 outwards and away from the stop rod 48, out of engagement with the stop rod 48. This way, the stop 40 can be returned to its initial position when a worn brake pad has been replaced by a new brake pad.

[0222] FIG. 9 shows a sixth embodiment of a vehicle brake system according to the invention, in the retracted position. The embodiment of FIG. 9 is based on the embodiment of FIG. 3 and FIG. 4. Alternatively, it can be based on any of the other embodiments described above.

[0223] In the embodiment of FIG. 9, the piston device comprises a plurality of pistons 21, each of the pistons being connected to the brake pad 10. Each of the pistons 21 is moveable over an operational stroke. The plurality of pistons 21 is arranged to move the brake pad 10 from the retracted position into the braking position. In the embodiment shown in FIG. 9, all pistons 21 comprise a first engagement surface 25 and a second engagement surface 26.

[0224] In the embodiment of FIG. 9, the second engagement surface 26 is arranged at a distance from the first engagement surface 25, which distance is for example equal to the length of the return stroke, or—as is shown in FIG. 9—the distance between the first engagement surface and the second engagement surface is equal to the length of the return stroke plus the distance between the location on the stop where the first engagement surface contacts the stop and the location on the stop where the second engagement surface contacts the stop, this distance being measured in the direction of the return stroke. The stop 40 are moveable by the second engagement surface 26 of the associated piston 21 in the direction of the operational stroke when the operational stroke is longer than the return stroke.

[0225] In an embodiment of FIG. 9, the vehicle brake system further comprises a brake pad guide, which is adapted to guide the brake pad in its movement from the retracted position to the braking position and/or vice versa. In the embodiment, the brake pad guide comprises a plurality of mutually parallel guide rods 70, which are connected to the brake pad and extend through at least a part of the frame 5.

[0226] In the embodiment of FIG. 9, the retractor comprises multiple springs 31a, 31b. Alternatively, only one or more springs 31a are present between the brake pad 10 and the frame 5, or only one or more springs 31b are provided which engage on the pistons 21.

[0227] In the embodiment of FIG. 9, the brake pad guide comprises a plurality of guide rods 70, and springs 31a of the retractor extend parallel to and coaxial with an associated guide rod 70.

[0228] In the embodiments of the vehicle brake system described above, in the braking position, the brake pad engages a rotatable wheel part. The rotatable wheel part is for example a brake disk or a rotor of an in-wheel motor. Optionally, the rotatable wheel part forms part of the vehicle brake system.