Patent Description:
The project leading to this application has received funding from the European Union's Horizon <NUM> research and innovation program under grant agreement No. <NUM>.

In known vehicle brake systems, in order to brake the vehicle a brake pad is forced against a body, e.g. a brake disk, which rotates along with a wheel of the vehicle. Due to the friction between the brake pad and the body, the wheel is slowed down. Therewith, also the vehicle slows down or even comes to a full stop. It is known to move the brake pad to the body by means of a piston, e.g. a hydraulic piston, when the vehicle brake is applied and to move the brake pad away from the body by a spring, e.g. a Belleville spring, when the vehicle brake is released.

This known system has several problems. The first problem is associated with the wear of the brake pad and/or of the body. The brake pad is usually moved towards and against the brake disk by means of a piston. When the brake pad and/or the body wear, the stroke over which the brake pad has to travel before it contacts the body increases. Therewith, the driver experiences that the brake pedal has to be pushed further down before the brakes engage. This may pose a safety risk.

A further problem is that the return stroke of the brake pad away from the body when the brake is released is often not fully executed, e.g. due to the accumulation of dirt in the brake system. This may cause the brake pad to still slightly engage the body during normal running of the vehicle, even when the brake is not applied. This causes friction between the brake pad and the body during the running of the vehicle, which leads to increased power consumption or fuel consumption. In particular for highly efficient cars, electric cars, in particular electric cars that are at least partly charged by solar power, this additional friction is undesired as it reduces the power efficiency of the vehicle, and therewith it reduces the range that can be travelled on a single charge of the batteries.

<CIT> discloses a brake system in which each wheel brake cylinder is provided with an adjuster which includes a spring acting upon an abutment movable with respect to the piston whereby inward movement of the piston into its respective cylinder beyond a desired normal position is resisted by the spring and when the pressure urging the piston inwardly is removed, the spring will act to automatically remove the piston to its normal position.

<CIT> discloses a brake system in which normally, under operation, the braking elements are actuated within the predetermined limits or clearance space until such time as the brake wear becomes so great that the brake will not set up tightly within the predetermined limits of movement. Under such conditions, the actuating pressure applied to the brake piston causes relative movement beyond the predetermined limits as the result of exerting a force which is greater than the friction holding force applied to the auxiliary piston. The auxiliary piston is then moved to take up for the brake wear, and upon release of the brake, the piston will again be withdrawn by means of a compression spring to again establish the operation with normal brake clearance.

<CIT> discloses a system that is similar to the system of <CIT>, and which is provided with an anti knock back system.

<CIT> discloses a sliding-caliper disc brake assembly includes grip-and-slip retraction and knockback control mechanism, involving a spring washer and a friction ring, effective between the caliper piston and the caliper housing, and additionally grip-and-slip retraction and knockback control mechanism, involving a spring washer and a friction ring, effective between the caliper housing and a fixed mounting bolt for the caliper, to provide zero brake lining drag in the brake-released condition, without undue lost pedal travel.

<CIT> discloses a brake system which comprises a brake pad and a brake disk. When the brake is engaged, the brake pad is moved into contact with the brake disk by a hydraulic piston. A Belleville spring is arranged in the piston. When the brake pad is forced against the brake disk, the Belleville spring is flattened. When the brake is released, the hydraulic pressure on the piston drops, and the Belleville spring restores its original conical shape, therewith retracting the brake pad from the brake disk. The length of the return stroke of the piston with the brake pad therefore is determined by the Belleville spring, with the endpoint of the return stroke of the piston being reached when the Belleville spring is in its unloaded, entirely relaxed state.

In case wear of the brake pad and/or brake disk occurs in the brake system of <CIT>, the Belleville spring is not only flattened when the brake is engaged, but also moved towards the brake disk to a new position. In this new position, the Belleville spring again relaxes to withdraw the piston with the brake pad when the hydraulic pressure on the piston drops when the brake is released. The length of the return stroke remains the same as before, because the length of the return stroke is determined by the fully relaxed length of the Belleville spring.

Although the known brake system of <CIT> is designed to keep the stroke of the brake pad constant despite wear of the brake pad and/or brake disk, this system has several problems with respect to the predictability of the system for the driver. The Belleville spring does not work linearly over its range of motion between fully relaxed and fully compressed. Therewith, the force that the driver experiences over the downward stroke of the brake pedal will vary. In addition, because the length of the stroke of the piston is rather short, the chance that the brake pad will touch the brake disk during normal non-braked running of the vehicle is significant. This problem is increased when dirt like mud or rust accumulates in the brake system.

The invention aims to provide an improved vehicle brake system, which reacts to the actions by the driver and/or by a brake related driver assistance system (such as a brake booster, ABS/ESP system, adaptive cruise control, automated emergency braking), in a way that is predictable.

This object is obtained by a vehicle brake system, which comprises:.

wherein the stop is moveable by the piston device in the direction of the operational stroke of the piston device.

In the vehicle brake system according to the invention, a brake pad is present which is moveable relative to a frame. The frame is for example a brake caliper or a part thereof. The brake pad is moveable relative to the frame between a braking position and a retracted position.

In the braking position, the vehicle brake system is active, so the wheel that is associated with the vehicle brake system is subjected to a braking action. In the braking position, the brake pad is for example positioned to engage a brake disk or other rotatable wheel part which rotates along with the wheel. In case an in-wheel electrical motor is used to drive the wheel on which the vehicle brake system is arranged to operate, in the braking position, the brake pad is for example positioned to engage a rotor of the in-wheel motor.

In the retracted position, the vehicle brake system is not active, so the wheel that is associated with the vehicle brake system is not subjected to a braking action. In the retracted position, the brake pad is at the largest distance from the brake disk or other rotatable wheel part that the brake pad engaged when the brake pad is in the braking position. So, if the total distance that the brake pad travels from the braking position away from the brake disk or other rotatable wheel part of the wheel with which the vehicle brake system 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 does not travel further away from the brake disk or rotatable wheel part than the retracted position. Any position of the brake pad between the braking position and the retracted position is referred to as an "intermediate position" of the brake pad.

The vehicle brake system according to the invention further comprises a piston device. The piston device is or comprises for example a hydraulic piston, 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.

The piston device is moveable over an operational stroke to move the brake pad from the retracted position into the braking position. Optionally, the piston device is connected to the brake pad. The operational stroke of the piston device may extend parallel or even coaxial with the brake pad stroke, or the operational stroke of the piston device may extend at an angle relative to the brake pad stroke. The operational stroke of the piston device may have the same length or a different length than the brake pad stroke. The operational stroke of the piston device has a start point and an end point. If the piston device is located somewhere between the start point and the end point of the operational stroke, it is in an intermediate position.

The piston device comprises a first engagement surface. The first engagement surface is for example located at a piston or at a piston rod of the piston device.

The vehicle brake system according to the invention further comprises 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. The return stroke of the piston device has a start point and an end point. If the piston device is located somewhere between the start point and the end point of the return stroke, it is in an intermediate position. The retractor is or comprises for example one or more springs and/or one or more magnets, and/or functions hydraulically. The retractor may for example engage the brake pad and/or the piston device.

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

The stop is moveable by the piston device in the direction of the operational stroke of the piston device.

The stop optionally comprises a first stop surface and a second stop surface. If present, the first stop surface is arranged to engage the first engagement surface of the piston device.

In the vehicle brake system according to the invention, it is the stop which determines the location of the end point of the return stroke of the piston device, instead of that the length of the return stroke is determined by the retractor as in the prior art. Therewith, in the vehicle brake system according to the invention, non-linear or other suboptimal parts in the range of motion of the retractor can be avoided. As in the vehicle brake system of the invention, the length of the return stroke is dependent from the position of the stop instead of from the behavior, e.g. the dynamic behavior, of the retractor, the vehicle brake system behave in a more predictable manner for the driver and/or for the driver assistance system (such as a brake booster, ABS/ESP system, adaptive cruise control, automated emergency braking) of the vehicle which contains the vehicle brake system.

Furthermore, that the stop is in engagement with the first engagement surface of the piston device at the end of the return stroke makes that the retracted position of the brake pad is accurately defined, as the deformation of the brake pad due to the piston device being located, and optionally forced, against the stop is minimal. If a stop would be used which would be at a different location, the brake pad may be subjected to bending, which may cause the brake pad to bulge out towards the brake disk or other rotatable part of the wheel that is associated with the vehicle brake system, which in turn may lead to contact and friction between the brake pad and the brake disk or other rotatable part of the wheel that is associated with the vehicle brake system. This problem is significantly reduced by making that the stop is in engagement with the first engagement surface of the piston device at the end of the return stroke.

In addition, the stop being moveable in the direction of the operational stroke of the piston device allows the length of the return stroke to be kept constant, even in case of wear of the brake pad, and optionally of any brake disk or other rotatable wheel part which with the vehicle brake system cooperates. This further contributes to the predictable behavior of the brake system.

The stop being moveable by the piston device in the direction of the operational stroke of the piston device makes that the displacement of the stop, which serves to compensate for wear of e.g. the brake pad, is accurately adapted to the amount of wear on e.g. the brake pad. In a vehicle brake system, large forces may occur during braking, leading to significant deformation of parts of the vehicle brake system. By moving the stop directly by the piston device, the distance over which the stop is moved to compensate for the wear is closely linked to the additional distance the piston device has to travel in the operational stroke to bring the brake pad into the braking position. There will be little influence from deformation of brake system parts between the brake pad and the stop, as there generally are not many parts present between the brake pad and the piston device. This further contributes to the predictable behavior of the brake system.

In an embodiment of the vehicle brake system according to the invention, the piston device further comprises a second engagement surface. The second engagement surface is adapted to engage the stop at the end of the operational stroke. At the end of the operational stroke of the piston device, the brake pad is in the braking position.

The second engagement surface is arranged at a distance from the first engagement surface.

The second engagement surface allows to further control the length of the operational stroke of the piston independent of the retractor.

Optionally, the distance between the first engagement surface and the second engagement surface is equal to the length of the return stroke. Alternatively, the distance between the first engagement surface and the second engagement surface is equal to the length of the return stroke plus a predetermined run-in allowance. Alternatively, 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.

In a variant of this embodiment, 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.

The operational stroke being longer than the return stroke may occur due to wear of the brake pad and/or any brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use. Due to this wear, the brake pad has to be moved further before it engages any brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use.

When the distance between the first engagement surface and the second engagement surface is equal to the length of the return stroke, the second engagement surface of the piston device engages the stop during the operational stroke at the point when the piston device has travelled over the length of the return stroke. When the operational stroke is longer than the return stroke, in this variant the second engagement surface from that point on picks up the stop and moves it along until the brake pad has reached its braking position, i.e. until the piston device has reached the end of its operational stroke. When the driver or brake related the driver assistance system (such as a brake booster, ABS/ESP system, adaptive cruise control, automated emergency braking) releases the brake, the retraction means move the brake pad back into the retracted position and the piston device is moved over the return stroke. Because the stop has now been moved by the secondary engagement surface, the length of the return stroke is the same as it was before.

In an embodiment of this variant, the distance between the first engagement surface and the second engagement surface is equal to the length of the return stroke plus a predetermined run-in allowance. In this case, the secondary engagement surface only moves the stop when the length of the operational stroke is equal to the length of the return stroke plus the predetermined run-in allowance, for example when the wear of the brake pad and/or any brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use has exceeded the predetermined run-in allowance.

In an embodiment of the vehicle brake system according to the invention, the stop optionally comprises a first stop surface and a second stop surface. The first stop surface is arranged to engage the first engagement surface of the piston device. The second stop surface is arranged to engage the second engagement surface of the piston device if such a second engagement surface is present on the piston device.

Optionally, 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 first stop surface and a second stop surface. In this case, the second engagement surface of the piston device engages the stop during the operational stroke at the point when the piston device has travelled over the length of the return stroke. When the operational stroke is longer than the return stroke, in this variant the second engagement surface from that point on picks up the stop and moves it along until the brake pad has reached its braking position, i.e. until the piston device has reached the end of its operational stroke. When the driver or brake related the driver assistance system (such as a brake booster, ABS/ESP system, adaptive cruise control, automated emergency braking) releases the brake, the retraction means move the brake pad back into the retracted position and the piston device is moved over the return stroke. Because the stop has now been moved by the secondary engagement surface, the length of the return stroke is the same as it was before.

In an embodiment of the vehicle brake system according to the invention, 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.

In this embodiment, the first engagement surface is only in contact with the stop at the end of the return stroke of the piston device, which coincides with the beginning of the operational stroke of the piston device. As soon as the piston device leaves this position, the first engagement surface no longer engages the stop. This way, the presence of the stop does not influence the motion of the piston device. Therewith, no additional power consumption of the system occurs due to the presence of the stop.

In an embodiment of the vehicle brake system according to the invention, 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.

Making the first engagement surface of the piston device come to bear against the stop under a pre-tensioning force has several advantages. One advantage is that the piston device is biased towards the position at the end of the return stroke and that a threshold force is required to move it out of that position, and therewith to move the brake pad towards any brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use. This reduces the risk of undesired contact between the brake pad and any brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use during normal running of the vehicle, when the brake is not applied.

In addition, many types of retractors have a non-linear part or other unfavorable part in their range of motion. For example, most springs (coil springs as well as Belleville springs) have a part in their range of motion in which the applied force and the resulting deformation do not have a linear relationship. As usually the piston device has to overcome the force of the retractor when it travels through the operational stroke, and the driver senses this force as he applies the brake. It may also be detrimental for the functioning of a brake related driver assistance system (such as a brake booster, ABS/ESP system, adaptive cruise control, automated emergency braking), or make such a system more complicated. If the retractor then has a non-linear part in its range of motion, the driver will perceive this as by variation of the force feedback he gets through the brake pedal.

By making the first engagement surface of the piston device come to bear against the stop under a pre-tensioning force, the range of motion of the retractor that is actually used in the return stroke and in the operational stroke of the piston device will be only a part of a larger full range of motion of the retractor. This allows to select an advantageous part from this full range of motion, for example a part that has a linear relationship between the applied force and the resulting deformation of the retractor. This further increases the predictability of the brake system for the driver and for any brake related driver assistance system (such as a brake booster, ABS/ESP system, adaptive cruise control, automated emergency braking),.

In an embodiment of the vehicle brake system according to the invention, 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. In this embodiment, the retractor is further adapted to apply a retraction force onto the brake pad and/or on the piston device during the return stroke, and the drive force is larger than the retraction force.

This embodiment provides a practical way to achieve that the stop is moved by the piston device only in the direction of the operational stroke and not in the direction of the return stroke.

In a variant of this embodiment, the stop is slidably mounted in a housing, and a static friction force is present between the stop and the housing. In this variant, the static friction force is smaller than the drive force and larger than the retraction force.

The static friction force is the force that needs to be overcome to get the stop sliding within the housing. Once the stop is sliding in the housing, a dynamic friction force is present between the stop and the housing. According to accepted friction theory, the dynamic friction force is normally lower than the static friction force.

The static friction force being smaller than the drive force and larger than the retraction force makes that the drive force can cause the stop to slide within the housing, but the retraction force cannot. This way, the stop can be moved by the piston device in the direction of the operational stroke, but not in the direction of the return stroke.

The housing can for example be mounted to the frame or form an integral part of the frame.

Optionally, the stop is mounted in the housing in a such a way that the stop can be returned to its initial position when a worn brake pad has been replaced by a new brake pad. For example, a sleeve can be arranged between the stop and the housing which allows the stop to slide back to its initial position when sufficient force is applied to the stop.

In an embodiment of the vehicle brake system according to the invention, the vehicle brake system further comprises a locking device to prevent movement of the stop in the direction of the return stroke.

The locking device may for example be or comprise 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.

For example, 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.

Optionally, the locking device is releasable so that the stop can be returned to its initial position when a worn brake pad has been replaced by a new brake pad.

In an embodiment of the vehicle brake system according to the invention, the retractor is or comprises a spring, a hydraulic device, a pneumatic device a magnetic device, an electric device and/or an electromagnetic device.

If the retractor is a spring, it can for example be a coil spring or a Belleville spring.

If the retractor is a hydraulic device, it for example comprises a hydraulic channel which opens into a hydraulic chamber which is delimited by a piston wall. The piston wall may be part of the piston device comprising the first engagement surface, or the piston wall may be part of a secondary piston device which is present in addition to the piston device which comprises the first engagement surface.

In an embodiment of the vehicle brake system according to the invention, the retractor comprises a plurality of springs, for example a plurality of springs which are arranged in parallel, for example two springs which are parallel to each other or two pairs of springs in which at least the springs that together form a pair are parallel to each other.

In an embodiment of the vehicle brake system according to the invention, 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.

For example, the brake pad guide comprises a plurality of mutually parallel guide rods, which are connected to the brake pad and extend through at least a part of the frame.

Optionally, the brake pad guide comprises at least one guide rod, and the retractor comprises at least one spring, and spring extends parallel to and/or coaxial with the guide rod.

In this embodiment, the piston device extends into a housing. The housing for example is mounted to or forms part of the frame. The stop comprises a ring having a central annular opening. The ring is friction mounted inside the housing and onto an inner wall of the housing.

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.

In this embodiment, 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 to the first annular surface. The 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.

Optionally, the housing further comprises a hydraulic chamber for accommodating a hydraulic fluid, an inlet port for allowing hydraulic fluid to be supplied to the hydraulic chamber, and an outlet port for allowing discharge of hydraulic fluid from the hydraulic chamber. Instead of an inlet port and an outlet pot, a combined inlet/outlet port may be present, which allows hydraulic fluid to be supplied to the hydraulic chamber as well as allowing discharge of hydraulic fluid from the hydraulic chamber.

Optionally, in this embodiment, the retractor is arranged in the housing. In this case, the retractor is for example a spring which is arranged in the housing, for example in the hydraulic chamber of the housing if such a hydraulic chamber is present.

According to the invention, the piston device further comprises a second engagement surface. The second engagement surface is adapted to engage the stop at the end of the operational stroke. At the end of the operational stroke of the piston device, the brake pad is in the braking position.

According to the invention, the vehicle brake system further comprises an intermediate element, which intermediate element comprises the stop. The intermediate element is moveably, e.g. slidably, arranged into a housing. The housing for example is mounted to or forms part of the frame.

The intermediate element may help to reduce the risk of dirt, rust and/or other contaminants to reach the first engagement surface, second engagement surface and/or the stop. Accumulation of dirt, rust and/or similar contaminants could inhibit an optimal functioning of the movable stop.

Alternatively or in addition, the intermediate element may facilitate easy assembly of the brake system according to the invention, by allowing pre-assembly of a large part of the system before mounting it to or in the frame.

Optionally, the intermediate element is adapted to move along with the stop.

Optionally, the retractor is arranged between the piston device and the intermediate element. The retractor for example is or comprises a spring and/or a magnet which operates by attracting and/or repelling.

Optionally, a static friction force is present between the intermediate element and the housing. The static friction force is smaller than the drive force and larger than the retraction force. The static friction force is the force that needs to be overcome to get the intermediate element sliding within the housing.

The static friction force being smaller than the drive force and larger than the retraction force makes that the drive force can cause the intermediate element together with the stop, to slide within the housing, but the retraction force cannot. This way, the stop can be moved by the piston device in the direction of the operational stroke, but not in the direction of the return stroke.

Optionally, a sleeve is provided around the intermediate element. The sleeve is fixed to the intermediate element. A static friction force is present between the sleeve and the housing. The static friction force is smaller than the drive force and larger than the retraction force. The static friction force is the force that needs to be overcome to get the sleeve sliding within the housing.

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, together with the intermediate element and the stop, to slide within the housing, but the retraction force cannot. This way, the stop can be moved by the piston device in the direction of the operational stroke, but not in the direction of the return stroke.

Optionally, the piston device has an outer diameter and a length, and the intermediate element extends along the outer diameter of the piston device over at least a part of the length of the piston device.

Optionally, the intermediate element has an opening in which at least the first engagement surface and the second engagement surface of the piston device are accommodated. Optionally, the intermediate element has an opening in which at least the first engagement surface and the second engagement surface of the piston device are accommodated during the entire operational stroke and/or during the entire return stroke of the piston device, and/or when the brake pad is in the retracted position and/or when the brake pad is in the braking position. Optionally, the piston device comprises a first end facing towards the brake pad and a second end, which is opposite to the first end, and the intermediate element has an opening in which at least the second end of the piston device is accommodated in the opening of the intermediate element.

According to the invention, the intermediate element is cup-shaped and has a central opening, and the at least part of the piston device is accommodated in the central opening.

Optionally, the intermediate element 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 is accommodated in the central opening.

Optionally, the intermediate element is provided with at least one opening to allow hydraulic fluid to pass through.

In an embodiment of the vehicle brake system according to the invention, the vehicle brake system further comprises a rotatable wheel part. In the braking position, the brake pad engages the rotatable wheel part. The rotatable wheel part is for example a brake disk or a rotor of an in-wheel motor.

In an embodiment of the vehicle brake system according to the invention, the piston device comprises a plurality of pistons, each of the pistons being connected to the brake pad. Each of the pistons is moveable over an operational stroke. The plurality of pistons is arranged to move the brake pad from the retracted position into the braking position. At least one of the pistons, or a piston rod which is connected to at least one of the pistons, comprises the first engagement surface.

Optionally, the at least one of the pistons, or the piston rod which is connected to at least one of the pistons, which comprises the first engagement surface, further comprises a second engagement surface adapted to engage the stop at the end of the operational stroke. Optionally, the second engagement surface is arranged at a distance from the first engagement surface, which distance is equal to the length of the return stroke. Optionally, 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. For example, 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 invention further pertains to a vehicle, which vehicle comprises:.

wherein in the braking position the brake pad engages the rotor of the in-wheel motor.

For example, the vehicle brake system is a vehicle brake system in accordance with any of the embodiments of the vehicle brake system according to the invention as described above.

In-wheel motors are generally used in high efficiency vehicles, e.g. electric vehicles, in particular electric vehicles which are at least partly chargeable by solar power. As the vehicle brake system according to the invention reduces the risk that the brake pad is in contact with the rotor of the in-wheel motor when the brake is not applied, the vehicle brake system helps to obtain a good power efficient operation of the vehicle, and therewith contributes to a large range of travel before recharging of the batteries is required.

The invention further pertains to a vehicle,.

The invention further pertains to a trailer, which comprises a vehicle brake system according to the invention.

The invention will be described in more detail below under reference to the drawing, in which in a non-limiting manner exemplary embodiments of the invention will be shown. The drawing shows in:.

<FIG> shows a first embodiment of the vehicle brake system <NUM>. In <FIG>, the brake pad is in the retracted position. <FIG> again shows the embodiment of <FIG>, but now with the brake pad in the braking position.

In the embodiment of <FIG>, the vehicle brake system <NUM> comprises a frame <NUM>. The frame <NUM> is for example a brake caliper or a part thereof.

The vehicle brake system <NUM> of <FIG> further comprises a brake pad <NUM>. In this embodiment, the brake pad <NUM> comprises a brake pad body <NUM> which is arranged on a brake pad holder <NUM>. The brake pad holder <NUM> which has a relatively high rigidity, so it can withstand the forces that occur during braking without too much deformation. The brake pad body <NUM> comprises typical brake pad material.

The brake pad <NUM> is moveable relative to the frame <NUM> between a braking position (which is shown in <FIG>) and a retracted position (which is shown in <FIG>).

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

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

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

In the retracted position, the brake pad <NUM> 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 <NUM> travels from the braking position away from the brake disk or other rotatable wheel part of the wheel with which the vehicle brake system <NUM> 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 <NUM> does not travel further away from the brake disk or rotatable wheel part than the retracted position. Any position of the brake pad <NUM> between the braking position and the retracted position is referred to as an "intermediate position" of the brake pad <NUM>.

The vehicle brake system of <FIG> further comprises a piston device <NUM>. In the embodiment of <FIG>, the piston device <NUM> is formed by a hydraulic piston <NUM>. 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.

The piston <NUM> is optionally connected to the brake pad <NUM>. In this embodiment, the piston <NUM> is attached to the brake pad holder <NUM>. The piston <NUM> is moveable over an operational stroke to move the brake pad <NUM> from the retracted position into the braking position. In the embodiment of <FIG>, the operational stroke of the piston <NUM> extends parallel or even coaxial with the brake pad stroke. In <FIG>, arrow <NUM> indicates the direction of the operational stroke. In the embodiment of <FIG>, the operational stroke of the piston <NUM> 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 <NUM> is associated.

The operational stroke of the piston <NUM> (which in this embodiment forms the piston device <NUM>) has a start point and an end point. If the piston <NUM> is located somewhere between the start point and the end point of the operational stroke, it is in an intermediate position.

The piston <NUM> comprises a first engagement surface <NUM>.

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

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

The vehicle brake system according to the invention further comprises a stop <NUM>. This stop <NUM> is in engagement with the first engagement surface <NUM> of the piston <NUM> at the end of the return stroke, so the position the piston <NUM> is in when the brake pad <NUM> is in the retracted position. The stop <NUM> is arranged to prevent movement of the first engagement surface <NUM> past the stop <NUM> in the direction of the return stroke.

The stop <NUM> is moveable by the piston <NUM> in the direction of the operational stroke of the piston <NUM>, so in the direction of arrow <NUM> in <FIG>.

In the embodiment of <FIG>, the hydraulic chamber <NUM> and the inlet/outlet port <NUM> form part of a hydraulic drive which is adapted to apply a drive force on the piston <NUM> that forms the piston device <NUM> in order to move the piston <NUM> over the operational stroke. The retractor <NUM> is adapted to apply a retraction force onto the brake pad <NUM>, and therewith upon the piston <NUM> during the return stroke. The drive force is larger than the retraction force.

In the embodiment of <FIG>, the stop <NUM> comprises a plug <NUM>. The plug <NUM> is slidably arranged in a plug housing <NUM>. In the embodiment of fig. and <FIG>, the plug <NUM> and the plug housing <NUM> are located inside the hydraulic chamber <NUM>. This has the advantage that the stop <NUM> and the combination of the plug <NUM> and the plug housing <NUM> are shielded from dirt, rust and other contamination, which ensures proper functioning.

A static friction force is present between the plug <NUM> of the stop <NUM> and the plug housing <NUM>. The static friction force is smaller than the drive force and larger than the retraction force.

The static friction force is the force that needs to be overcome to get the plug <NUM> of the stop <NUM> sliding within the plug housing <NUM>.

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 <NUM> of the stop <NUM> to slide within the plug housing <NUM>, but the retraction force cannot. This way, the stop can be moved by the piston <NUM> in the direction of the operational stroke as indicated by arrow <NUM> in <FIG>, but not in the direction of the return stroke as indicated by arrow <NUM> in <FIG>.

The plug housing <NUM> can for example be mounted to the frame <NUM> or form an integral part of the frame <NUM>.

In the embodiment of <FIG>, the stop <NUM> has a first stop surface <NUM> and a second stop surface <NUM>. The first stop surface <NUM> is arranged to engage the first engagement surface <NUM> of the piston <NUM> when the piston <NUM> is at the end of the return stroke. The second stop surface <NUM> is arranged to engage the second engagement surface <NUM> of the piston <NUM> when the piston <NUM> is at the end of the operational stroke, or when the second engagement surface <NUM> engages the stop <NUM> in order to move the stop <NUM> in the direction of the operational stroke.

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 <NUM> with a sleeve <NUM> which is in contact with the plug housing <NUM>. The sleeve <NUM>, which forms part of the plug <NUM> and moves along with the stop <NUM>, allows the stop <NUM> to slide back to its initial position when sufficient force is applied to the stop <NUM>.

In the embodiment of <FIG>, the piston <NUM> that forms the piston device <NUM> further comprises a second engagement surface <NUM>. The second engagement surface <NUM> is adapted to engage the stop <NUM> at the end of the operational stroke, as can be seen in <FIG>. At the end of the operational stroke of the piston <NUM>, the brake pad <NUM> is in the braking position.

The second engagement surface <NUM> is arranged at a distance from the first engagement surface <NUM>.

In the embodiment of <FIG>, the distance between the first engagement surface <NUM> and the second engagement surface <NUM> is for example equal to the length of the return stroke or - as is shown in <FIG> - 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.

In this embodiment, the stop <NUM> is moveable by the second engagement surface <NUM> of the piston <NUM> in the direction of the operational stroke when the operational stroke is longer than the return stroke.

In the embodiment of <FIG>, the first engagement surface <NUM> of the piston <NUM> that forms the piston device <NUM> is spaced apart from the stop <NUM> 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 <NUM> is only in contact with the stop <NUM> at the end of the return stroke of the piston <NUM>, which coincides with the beginning of the operational stroke of the piston <NUM>. As soon as the piston <NUM> leaves this position, the first engagement surface <NUM> no longer engages the stop <NUM>.

In the embodiment of <FIG>, the retractor <NUM> is adapted to force the first engagement surface <NUM> of the piston <NUM> against the stop <NUM> with a pre-tensioning force and to maintain this pre-tensioning force while the piston <NUM> is at the end of the return stroke.

The embodiment of <FIG> works as follows. When the vehicle is running without the brake being applied, the vehicle brake system <NUM> is in the position as shown in <FIG>. The brake pad <NUM> does not engage a brake disk or other rotatable part of a wheel that is associated with the vehicle brake system <NUM>. Dashed line <NUM> in <FIG> indicates the position of the brake disk or other rotatable part of a wheel that is associated with the vehicle brake system <NUM>.

The springs <NUM> of the retractor <NUM> force the first engagement surface <NUM> of the piston <NUM> against the stop <NUM>. The first engagement surface <NUM> cannot move past the stop <NUM>, and the force that is applied by the retractor <NUM> is less than the static friction between the plug <NUM> of the stop <NUM> and the plug housing <NUM>. 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 <NUM> in <FIG>.

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

The springs <NUM> of the retractor <NUM> are stretched to an elongated state when the brake pad <NUM> is in the braking position. The stop <NUM> engages the second engagement surface <NUM> of the piston <NUM>.

If wear of the brake pad <NUM> has occurred, the thickness of the brake pad body <NUM> has been reduced. As a result, the brake pad <NUM> 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.

In this case, the operational stroke of the piston <NUM> gets longer than it was before. As soon as the piston <NUM> reaches the position which previously was the end point of the operational stroke, the second engagement surface <NUM> of the piston <NUM> engages the stop <NUM>. However, the piston <NUM> continues to travel in the direction of the operational stroke until the brake pad <NUM> 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 <NUM>, the piston <NUM> moves the stop <NUM> relative to the plug housing <NUM> in the direction of the operational stroke.

When the brake is released, the pressure in the hydraulic chamber <NUM> drops and the piston starts its return stroke under the influence of the retractor <NUM>. The brake pad <NUM> disengages from the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use. The stop <NUM> disengages from the second engagement surface <NUM> of the piston <NUM>.

The piston <NUM> stops moving in the direction of the return stroke when the first engagement surface <NUM> of the piston engages the stop <NUM>. The first engagement surface <NUM> of the piston <NUM> does not move beyond the stop <NUM> in the direction of the return stroke.

In case the stop <NUM> has been moved by the piston <NUM>, in particular by the second engagement surface <NUM> of the piston <NUM>, the end point of the return stroke is at a different position relative to the frame <NUM> than it was before the wear of the brake pad <NUM> 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.

<FIG> shows a second embodiment of the vehicle brake system <NUM>. In <FIG>, the brake pad is in the retracted position. <FIG> again shows the embodiment of <FIG>, but now with the brake pad in the braking position.

The piston <NUM> is connected to the brake pad <NUM>. In this embodiment, the piston <NUM> is attached to the brake pad holder <NUM>. The piston <NUM> is moveable over an operational stroke to move the brake pad <NUM> from the retracted position into the braking position. In the embodiment of <FIG>, the operational stroke of the piston <NUM> extends parallel or even coaxial with the brake pad stroke. In <FIG>, arrow <NUM> indicates the direction of the operational stroke. In the embodiment of <FIG>, the operational stroke of the piston <NUM> 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 <NUM> is associated.

The operational stroke of the piston <NUM> (which in this embodiment forms the piston device <NUM>) has a start point and an end point. If the piston <NUM> is located somewhere between the start point and the end point of the operational stroke, it is in an intermediate position.

The vehicle brake system according to <FIG> further comprises a retractor <NUM> which is adapted to move the piston <NUM> which in this embodiment forms the piston device <NUM> over a return stroke, thereby moving the brake pad <NUM> from the braking position into the retracted position. The direction of the return stroke is indicated in <FIG> by arrow <NUM>. In the embodiment of <FIG>, the retractor <NUM> comprises a spring <NUM>, which is for example a coil spring. In the embodiment of <FIG>, the spring <NUM> is arranged inside the frame <NUM>. In this embodiment, the retractor <NUM> engages the piston device <NUM>. Alternatively or in addition, the retractor may engage the brake pad <NUM>.

In the embodiment of <FIG>, the piston device <NUM> (which is formed by piston <NUM> in this embodiment) extends into a housing <NUM>, which forms part of the frame <NUM>. The stop <NUM> comprises a ring <NUM> having a central annular opening. The ring <NUM> is friction mounted inside the housing <NUM> and onto an inner wall of the housing <NUM>.

A part of the piston <NUM> extends through the annular opening of the ring <NUM>, with the ring being arranged between the first engagement surface <NUM> of the piston <NUM> and the second engagement surface <NUM> of the piston <NUM>.

In this embodiment, the ring <NUM> comprises a first stop surface <NUM> in the form of an first annular surface, which is arranged to engage the first engagement surface <NUM><NUM> of the piston <NUM> at the end of the return stroke. The ring <NUM> further comprises second stop surface <NUM> in the form of a second annular surface on the opposite side of the ring <NUM> with regard the first annular surface. The second annular surface is arranged to engage the second engagement surface <NUM> of the piston <NUM> at the end of the operational stroke when the operational stroke is longer than the return stroke.

In the embodiment of <FIG>, the ring <NUM> is slidably arranged in the housing <NUM>.

A static friction force is present between the ring <NUM> of the stop <NUM> and the housing <NUM>. The static friction force is smaller than the drive force and larger than the retraction force.

The static friction force is the force that needs to be overcome to get the ring <NUM> sliding within the housing <NUM>.

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 <NUM> of the stop <NUM> to slide within the housing <NUM>, but the retraction force cannot. This way, the ring <NUM> of the stop <NUM> can be moved by the piston <NUM> in the direction of the operational stroke as indicated by arrow <NUM> in <FIG>, but not in the direction of the return stroke as indicated by arrow <NUM> in <FIG>.

Optionally, the way in which the ring <NUM> of the stop <NUM> is mounted in the housing <NUM> is such that the ring <NUM> of the stop <NUM> 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 <NUM> with a sleeve which is in contact with the housing <NUM>, similar to what is shown with respect to the sleeve <NUM> in the embodiment of <FIG>.

In the embodiment of <FIG>, the distance between the first engagement surface <NUM> and the second engagement surface <NUM> is for example equal to the length of the return stroke, or - as is shown in <FIG> - 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 spring <NUM> of the retractor <NUM> forces the first engagement surface <NUM> of the piston <NUM> against the stop <NUM>. The first engagement surface <NUM> cannot move past the stop <NUM>, and the force that is applied by the retractor <NUM> is less than the static friction between the ring <NUM> of the stop <NUM> and the housing <NUM>. Therefore, the force that is exerted by the retractor is not able to move the stop <NUM> in the direction of the return stroke, which is indicated by arrow <NUM> in <FIG>.

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

The spring <NUM> of the retractor <NUM> is stretched to an elongated state when the brake pad <NUM> is in the braking position. The stop <NUM> engages the second engagement surface <NUM> of the piston <NUM>.

When the brake is released, the pressure in the hydraulic chamber <NUM> drops and the piston <NUM> starts its return stroke under the influence of the retractor <NUM>. The brake pad <NUM> disengages from the brake disk or other rotatable wheel part with which the vehicle brake system cooperates during use. The stop <NUM> disengages from the second engagement surface <NUM> of the piston <NUM>.

<FIG> shows a first embodiment of the vehicle brake system <NUM> according to the invention. In <FIG>, the brake pad is in the retracted position. <FIG> again shows the embodiment of <FIG>, but now with the brake pad in the braking position.

The embodiment of <FIG> is a variant of the embodiment of <FIG>, and operates generally in the same way.

In the embodiment of <FIG>, an intermediate element <NUM> is provided. In this embodiment, the ring <NUM> of the stop <NUM> is mounted in the intermediate element <NUM>. The intermediate element <NUM> is moveably, e.g. slidably, arranged into the housing <NUM>, which housing <NUM> forms part of the frame <NUM>. Optionally, the intermediate element <NUM> is provided with at least one opening to allow hydraulic fluid to pass through.

The intermediate element <NUM> moves along with the ring <NUM> of the stop <NUM> in case of wear of the brake pad body <NUM>.

A sleeve <NUM> is provided around the intermediate element <NUM>. The sleeve <NUM> is fixed to the intermediate element <NUM>. A static friction force is present between the sleeve <NUM> and the housing <NUM>. The static friction force is smaller than the drive force and larger than the retraction force.

The static friction force is the force that needs to be overcome to get the sleeve <NUM> sliding within the housing <NUM>.

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 <NUM>, together with the intermediate element <NUM> and the ring <NUM> of the stop <NUM>, to slide within the housing <NUM>, but the retraction force cannot. This way, the ring <NUM> of the stop <NUM> can be moved by the piston <NUM> in the direction of the operational stroke as indicated by arrow <NUM> in <FIG>, but not in the direction of the return stroke as indicated by arrow <NUM> in <FIG>.

In the embodiment of <FIG>, optionally the retractor <NUM> is arranged between the piston <NUM> and the intermediate element <NUM>.

Optionally, and shown in <FIG>, the piston device <NUM> has an outer diameter and a length, and the intermediate element <NUM> extends along the outer diameter of the piston device <NUM> over at least a part of the length of the piston device <NUM>.

Optionally, and shown in <FIG>, the intermediate element <NUM> has an opening in which at least the first engagement surface <NUM> and the second engagement surface <NUM> of the piston device <NUM> are accommodated. Optionally, and shown in <FIG>, the intermediate element <NUM> in this opening at least the first engagement surface <NUM> and the second engagement surface <NUM> of the piston device <NUM> are accommodated during the entire operational stroke and/or during the entire return stroke of the piston device <NUM>, and/or when the brake pad <NUM> is in the retracted position and/or when the brake pad <NUM> is in the braking position. Optionally, and shown in <FIG>, the piston device <NUM> comprises a first end facing towards the brake pad <NUM> and a second end, which is opposite to the first end, and the intermediate element <NUM> has an opening in which at least the second end of the piston device <NUM> is accommodated in the opening of the intermediate element <NUM>.

As shown in <FIG>, the intermediate element <NUM> is cup-shaped and has a central opening, and the at least part of the piston device <NUM> is accommodated in the central opening.

Optionally, and shown in <FIG>, the intermediate element <NUM> 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 <NUM> is accommodated in the central opening.

<FIG> shows a second embodiment of the vehicle brake system <NUM> according to the invention. In <FIG>, the brake pad is in the braking position.

The main difference between the embodiment of <FIG> and the embodiment of <FIG> is in the retractor <NUM>. While in the embodiment of <FIG>, the retractor comprises a spring <NUM>, in the embodiment of <FIG>, the retractor comprises two magnets <NUM>, <NUM>.

In the embodiment of <FIG>, the magnets <NUM>, <NUM> attract each other. When the brake is engaged, the pressure in the hydraulic chamber <NUM> increases and the drive force which is exerted on the piston <NUM> overcomes the magnetic attraction force of the magnets <NUM>, <NUM>.

When the brake is released, the hydraulic pressure in the hydraulic chamber <NUM> decreases. The magnetic attraction force between the magnets <NUM>, <NUM> moves the piston <NUM> over its return stroke to disengage the brake pad <NUM> from the brake disk or other rotatable wheel part of the wheel that is associated with the vehicle brake system.

<FIG> shows a third embodiment of a vehicle brake system, in the braking position. The embodiment of <FIG> is a variant of the embodiment of <FIG>, and works generally in the same way.

In the embodiment of <FIG>, the stop <NUM> does not comprise a stop plug <NUM> which is arranged in a plug housing <NUM>. Instead, the stop <NUM> comprises a stop rod <NUM>.

In the embodiment of <FIG>, a locking device <NUM> is provided to prevent movement of the stop in the direction of the return stroke.

In the embodiment of <FIG>, the locking device <NUM> 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.

In the embodiment of <FIG>, the stop rod <NUM> extends outside the frame <NUM>. A seal <NUM> is provided to prevent leakage of hydraulic fluid from the hydraulic chamber <NUM> while still allowing the stop rod to move relative to the frame <NUM>.

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

In the embodiment of <FIG>, the locking device <NUM> is releasable by pivoting the louvres <NUM> outwards and away from the stop rod <NUM>, out of engagement with the stop rod <NUM>. This way, the stop <NUM> can be returned to its initial position when a worn brake pad has been replaced by a new brake pad.

<FIG> shows a fourth embodiment of a vehicle brake system in the retracted position. The embodiment of <FIG> is based on the embodiment of <FIG>. Alternatively, it can be based on any of the other embodiments described above.

In the embodiment of <FIG>, the piston device comprises a plurality of pistons <NUM>, each of the pistons being connected to the brake pad <NUM>. Each of the pistons i21 s moveable over an operational stroke. The plurality of pistons <NUM> is arranged to move the brake pad <NUM> from the retracted position into the braking position. In the embodiment shown in <FIG>, all pistons <NUM> comprise a first engagement surface <NUM> and a second engagement surface <NUM>.

In the embodiment of <FIG>, the second engagement surface <NUM> is arranged at a distance from the first engagement surface <NUM>, which distance is for example equal to the length of the return stroke, or - as is shown in <FIG> - 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 <NUM> are moveable by the second engagement surface <NUM> of the associated piston <NUM> in the direction of the operational stroke when the operational stroke is longer than the return stroke.

In an embodiment of <FIG>, 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 <NUM>, which are connected to the brake pad and extend through at least a part of the frame <NUM>.

In the embodiment of <FIG>, the retractor comprises multiple springs 31a, 31b. Alternatively, only one or more springs 31a are present between the brake pad <NUM> and the frame <NUM>, or only one or more springs 31b are provided which engage on the pistons <NUM>.

In the embodiment of <FIG>, the brake pad guide comprises a plurality of guide rods <NUM>, and springs 31a of the retractor extend parallel to and coaxial with an associated guide rod <NUM>.

Claim 1:
Vehicle brake system, which comprises:
- a frame (<NUM>),
- a brake pad (<NUM>), which is moveable relative to the frame (<NUM>) between a braking position and a retracted position,
- a piston device (<NUM>) which is moveable over an operational stroke to move the brake pad (<NUM>) from the retracted position into the braking position, which piston device (<NUM>) comprises a first engagement surface (<NUM>),
- a retractor (<NUM>) which is adapted to move the piston device (<NUM>) over a return stroke, thereby moving the brake pad (<NUM>) from the braking position into the retracted position,
- a stop (<NUM>) which is in engagement with the first engagement surface (<NUM>) of the piston device (<NUM>) at the end of the return stroke, which stop (<NUM>) is arranged to prevent movement of the first engagement surface (<NUM>) past the stop (<NUM>) in the direction of the return stroke, and
wherein the stop (<NUM>) is moveable by the piston device (<NUM>) in the direction of the operational stroke of the piston device (<NUM>),
wherein the piston device (<NUM>) further comprises a second engagement surface (<NUM>) adapted to engage the stop (<NUM>) at the end of the operational stroke,
characterised in that,
the vehicle brake system further comprises an intermediate element (<NUM>), which intermediate element (<NUM>) comprises the stop (<NUM>),
which intermediate element (<NUM>) is moveably arranged into a housing (<NUM>, <NUM>),
wherein the intermediate element is cup-shaped and has a central opening, and at least part of the piston device is accommodated in the central opening.