Brake unit arranged on wheel of motor vehicle

Abstract

The invention relates to a brake unit (42) which is arranged on a wheel of a motor vehicle, comprising an axially displaceable brake element (28), which is an axially displaceable brake piston (44), and a drive device (64) which selectively displaces the brake element, the brake piston is coupled to the drive (64) in a force-transmitting manner by means of a hydraulic transmission (82).

Description

Technical Field

[0001] The present invention relates to a brake unit arranged on a wheel of a motor vehicle, the brake unit comprising an axially displaceable brake element and a drive device for selectively displacing the brake element axially. The invention also relates to the use of such a brake unit on a wheel of a motor vehicle. Background Art

[0002] In motor vehicles such as motorcycles, passenger vehicles, or trucks, it is common to use a central hydraulic brake unit, typically located in the motor compartment of the vehicle. This central brake unit comprises a hydraulic assembly that is hydraulically connected to a brake pedal operated by the driver. When the brake pedal is operated, a piston, typically guided in a master brake cylinder, moves, thereby transmitting the mechanical pressure of the brake pedal to the hydraulic system of the brake unit. The brake fluid present there is then hydraulically transferred via brake lines to the wheel brakes of at least one associated wheel by volumetric displacement. This provides brake pressure at the wheel.

[0003] Specifically, the wheel brake on a wheel is equipped with at least one piston arranged in a brake caliper pawl as an axially movable brake element. Under the action of brake pressure, the piston moves toward a radially movable friction element fastened to the wheel. Such a friction element is a brake disc or brake drum. In this case, the piston presses against the brake lining, which in turn presses against the friction element. This generates a friction force that brakes the rotational movement of the friction element and the coupled wheel. When the pressure is relieved, the piston moves back into the brake caliper pawl, completing the braking process.

[0004] In modern brake systems with such a central hydraulic brake unit, during normal operation, the brake pedal, along with the master brake cylinder, is typically used only to detect the driver's braking request. In this case, the master brake cylinder is decoupled from the wheel brakes. Instead, the brake pressure at the respective wheel brakes is generated using pressure medium from an electronically controllable pressure-building device. In most cases, the brake system can be operated in a hydraulic fallback mode using pressure medium from the master brake cylinder. Such a brake system is known from document DE 10 2014 222 759 A1. In this case, during normal braking, the braking request is forwarded to the electronically controllable pressure-building device via an electrical signal. The brake pedal is no longer directly connected to the brake unit.

[0005] Recent vehicle developments, with their increasing degree of automation, have completely eliminated the need for a brake pedal. This places new demands on the braking system, but also creates new possibilities. Electromechanical brakes, which are arranged directly on the wheels, are known as brake units. These typically have an electric motor as a converter that converts electrical energy into mechanical energy. Using this mechanical energy, an axially movable brake element presses against a radially movable friction element in the form of a pressure head. To achieve the required braking force, a high conversion ratio between the converter and the brake element is required. Summary of the Invention

[0006] The object of the present invention is to provide a brake unit which is optimized in terms of force and space, in particular for recent vehicle developments, and which also enables a particularly safe and long-lasting braking operation.

[0007] According to the present invention, a brake unit, more precisely a wheel brake unit, arranged on a wheel of a motor vehicle is provided, which has an axially movable brake element and a drive device for selectively axially moving the brake element. The brake element is an axially movable brake piston, which is force-coupled to a drive device or actuator by means of a hydraulic transmission mechanism. In particular, the brake piston is guided in an axially or translationally movable manner in an associated piston housing or brake housing. Furthermore, a brake fluid as a pressure medium is preferably accommodated or contained in the brake housing. The brake piston is guided in an axially movable manner in the brake housing by means of the volumetric displacement of the brake fluid. Compared to the axially movable brake elements (e.g., pressure heads) of conventional electromechanical brake units, the force required to move this brake piston is significantly less. In particular, the component friction forces that need to be overcome are significantly smaller.

[0008] Furthermore, the hydraulic transmission significantly improves the conversion ratio between the drive and the brake piston compared to conventional electromechanical brake units. This, combined with the brake element being designed as a brake piston, significantly reduces the loads and forces required in the brake unit and the entire brake system. This allows for the use of simpler, more cost-effective components, while also extending their service life.

[0009] The brake piston preferably has an end face that is moved out of the brake housing by means of a drive. When moved out of the brake housing, the brake piston applies a compressive force in the axial direction to a friction element fastened to the wheel. A compressive element, such as a brake caliper, is preferably arranged on the end face that is thus located outward. A brake lining is particularly preferably mounted on the caliper and is pressed against the friction element. If the pressure applied to the brake piston by the drive decreases, the brake piston moves back into the brake housing and is no longer pressed against the friction element. The braking effect ends. The friction element is of a simple design and is preferably a brake disc or, in the case of good force transmission, a brake drum.

[0010] Furthermore, the drive device is preferably coupled to an electronic control device or an electronic controller via signal transmission. The electronic control device is adapted to detect a braking request by the driver or, in the case of automated driving, a braking demand from an associated vehicle control system, and to forward the corresponding signal to the drive device. The drive device causes the brake piston to undergo a corresponding translational movement in response to the braking request.

[0011] With the brake unit according to the invention, a hydraulic unit can be formed which is in particular closed in itself and arranged directly on the wheel of a motor vehicle. The closed wheel brake unit with a hydraulic transmission is therefore a single decentralized brake unit arranged on the wheel, in particular an electrohydraulic brake. In order to achieve particularly uniform, well-controllable, adaptable and redundant braking, at least two such brake units are preferably arranged, and particularly preferably one such decentralized brake unit is arranged for each wheel. In contrast to conventional central hydraulic brake units, each brake unit in the decentralized brake unit does not take up any space in the motor compartment. Furthermore, no brake lines are required from the motor compartment to the respective wheel brake. This saves material and valuable installation space.

[0012] According to the present invention, the hydraulic transmission is advantageously formed using a drive piston, which is arranged in addition to the brake piston and is guided axially displaceably in a drive housing, in which brake fluid is to be or is contained. The drive piston can be hydraulically moved by the brake fluid, which can also be used to hydraulically move the brake piston. While the drive piston is moving into its drive housing, the brake piston can, in particular, be moved out of its brake housing by the brake fluid. This hydraulic transmission using two pistons is particularly energy-efficient. In particular, very low friction losses occur. Overall, the load requirements on the affected components are further reduced.

[0013] Furthermore, according to the invention, the drive piston advantageously has a drive piston diameter and the brake piston has a brake piston diameter that differs from the drive piston diameter. This allows the hydraulic transmission to be varied as required and adapted to the respective requirements.

[0014] Preferably, the brake piston diameter is larger than the drive piston diameter. Therefore, while the pressure in the brake fluid remains roughly constant, the larger diameter of the brake piston allows the brake piston to exert a greater force on the friction element than the force transmitted to the drive piston by the transmission, thereby achieving hydraulic pressure conversion. During braking, this hydraulic conversion ratio allows the brake piston to transmit a relatively large braking force to the friction element using a relatively small force from the drive piston.

[0015] Advantageously, according to the present invention, the drive piston can be selectively moved into and out of the drive housing by means of a drive device. This allows the drive piston to be actively reciprocated as required by means of the drive device. To build up pressure by means of the brake piston, the drive piston is actively moved into the drive housing in the driving direction, thereby causing the brake piston to be moved out of the brake housing. To reduce or release pressure, the drive piston is actively retracted by means of the drive device in the opposite direction of the driving direction. Here, the brake piston is also retracted by means of a hydraulic coupling, and the braking process is terminated. Preferably, the drive device comprises a structurally simple spindle drive connected to the drive piston.

[0016] Alternatively or additionally, according to the present invention, the drive piston can advantageously be moved in the opposite direction of the drive by means of a spring element. Here, after the drive piston moves into the drive housing along the drive direction, the spring element uses its deformation force to reset the drive piston. After the force of the drive device acting in the drive direction disappears, the drive piston moves back in the opposite direction of the drive by means of the spring element. The brake piston is also reset by means of a hydraulic coupling. Thus, the spring element acts as a reset spring. The spring element is preferably a low-cost mechanical spring element, particularly preferably a metal spring element, such as a coil spring or a compression spring. Alternatively or additionally, the spring element preferably comprises an elastomer. Furthermore, it is preferred that the spring element be simple in structure and be the only reset element acting on the drive piston. Particularly preferably, the spring element is provided in addition to the drive device that resets the drive piston. Thus, even in the event of a malfunction, such as a power outage causing a malfunction of the drive device during the braking process, the spring element can be used to reset the drive piston and thus retract the brake piston. This prevents residual pressure from accumulating in the system due to friction.

[0017] Furthermore, according to the present invention, the drive device advantageously comprises a drive motor or electric motor and a transmission device that can be driven by the electric motor. The electric motor is preferably controlled by an electric controller and is particularly preferably configured as an electric motor. Due to the hydraulic transmission mechanism, the electric motor can be designed to have a relatively low torque. This electric motor requires very little installation space and material. This particularly saves valuable raw materials such as copper and magnets.

[0018] The transmission preferably includes a rotary mechanical transmission. In this case, the torque of the rotational motion of a motor element (e.g., a motor shaft) is first converted by a mechanical transmission into a higher torque of the rotational motion of the transmission. Thus, the torque of the motor is initially transmitted in a rotational / rotational manner. To this end, the transmission includes a rotation mechanism that can be designed in various embodiments. This rotation mechanism is preferably a planetary gear mechanism, a spur gear mechanism, or a worm gear mechanism. The rotational / translational transmission is then performed by a translation mechanism associated with the transmission, preferably a ball screw mechanism or, more preferably, a screw-nut mechanism. The resulting translational motion causes a translational motion of a brake piston hydraulically coupled to the transmission. The drive piston is preferably positioned between the brake piston and the transmission and is axially displaced by the transmission. This type of transmission has a simple and space-saving design, thereby saving installation space and material. It has been shown that this simple mechanical transmission mechanism in the drive mechanism, combined with a hydraulic transmission mechanism between the drive mechanism and the brake piston, ensures a labor-saving and reliable buildup of brake pressure.

[0019] The transmission is preferably provided with a ball screw drive. Here, a thread surrounds the screw, on which at least one nut is provided, and balls circulate in a closed system in the nut. This results in rolling friction, which reduces friction losses compared to a screw-nut drive or sliding friction in a screw drive. However, it is particularly preferred to design the transmission using a more cost-effective screw drive. Here, the rotational motion generated by the electric motor is transmitted via a coupling to the screw or a nut meshing with the thread of the screw, more precisely a screw nut, so that the rotational motion is converted into linear motion by means of the screw nut. This provides a drive with a particularly simpler structure, lower cost, and higher precision, which requires relatively few parts. Since there are correspondingly fewer parts, the clearances in the transmission are also correspondingly smaller, which increases the precision and service life of the transmission.

[0020] Furthermore, according to the present invention, a pressure compensation device is advantageously provided, which is particularly hydraulically connected to the drive unit. For this purpose, a fluid line is preferably arranged between the drive unit and the pressure compensation device. In particular, the fluid line connects the drive housing to a pressure compensation vessel. Braking fluid is to be contained or is contained in the drive housing and the pressure compensation vessel. Thus, the pressure compensation device serves to compensate for the brake fluid in the fully enclosed hydraulic system of the brake unit. Otherwise, undesirable braking forces could arise in the enclosed hydraulic system due to heat generation and the resulting pressure increase. The pressure compensation device allows for thermal volume compensation if such heat generation occurs, thus preventing such undesirable braking forces.

[0021] Preferably, the fluid line is arranged in the area of the drive housing where the drive piston is located when in the unactuated state. The fluid line is provided with a so-called probe hole. Depending on the position of the drive piston, the pressure compensation device connects or disconnects the conducting fluid, preferably by means of a special geometry on the drive piston. Particularly preferably, this special geometry is formed on the end face of the drive piston facing the driving direction. In particular, the drive piston has a groove on its end face for this purpose, which, when in its unactuated position, is arranged in the area of the fluid line. This provides a connection between the hydraulic area, in particular the drive housing, and the pressure compensation device, thereby compensating for the pressure in the brake fluid. When the drive piston is inserted into the drive housing with its end face, the fluid line is preferably sealed by the drive piston abutting the drive housing over its entire circumference. Alternatively, the drive piston preferably does not abut the drive housing over its entire circumference, but is provided with a sealing device radially surrounding the drive piston. When the fluid line is sealed in this manner, a brake pressure acting toward the brake piston is established, unaffected by the pressure compensation device. According to the invention, the pressure compensation device is preferably provided with a pressure compensation membrane, which is arranged in a sealing manner in a pressure compensation reservoir. This creates a tight separation between atmospheric pressure and the brake fluid in the drive housing, which at the same time reacts particularly flexibly to pressure changes.

[0022] To seal the hydraulic area from its surroundings, the brake piston is preferably provided with a seal radially surrounding the brake piston, which seal is preferably designed as a sealing ring. It is particularly preferred to arrange two such seals axially one after the other on the brake piston. This ensures greater safety against leakage.

[0023] According to the present invention, a first sensor and a second sensor coupled to the drive device are advantageously provided. Preferably, the second sensor is coupled to the brake piston. Particularly preferably, the second sensor is coupled to a brake chamber arranged in the brake housing upstream of the brake piston in the driving direction. Alternatively, the second sensor is preferably coupled to a pressure chamber in the drive housing belonging to the drive device. This allows the required braking force to be determined using various methods. The aforementioned sensors are preferably pressure sensors and / or force sensors. Furthermore, the calculation is preferably performed using the motor current or motor position determined by the rotor position sensor. In particular, the two sensors are coupled to a controller in a signal-transmitting manner, which controls the drive device and, in particular, the electric motor therein, based on the signals.

[0024] Particularly preferably, the first sensor is a rotor position sensor, and the second sensor is particularly a pressure sensor. This provides redundancy for determining the braking force using the rotor position sensor on the drive motor and the pressure sensor in the hydraulic transmission. Different approaches are used to provide redundancy, thus making it possible to cope with a variety of faults. Furthermore, due to the hydraulics, measurement using the pressure sensor is particularly easy to implement. Particularly preferably, the electric motor is equipped with a power pack connected to the pressure sensor.

[0025] The present invention also relates to the use of at least one such brake unit, each for use on a wheel of a motor vehicle or as a component of a wheel brake of a motor vehicle. Preferably, such a brake unit is arranged and used on at least two wheels of the motor vehicle, and particularly preferably on each wheel of the motor vehicle. Accordingly, the present invention also relates to a braking system for a motor vehicle, in which such a brake unit is arranged on at least one wheel of the motor vehicle. Preferably, such a brake unit and a corresponding controller are arranged on each wheel of the motor vehicle. To brake one or more wheels of the motor vehicle, an electrical signal is sent to the controller of the corresponding brake unit. The controller controls an associated electric motor, which transmits torque to a rotary mechanical transmission, which, via a hydraulic transmission, causes a translational movement of the brake piston.

[0026] Therefore, according to the invention, at least one decentralized brake unit is advantageously used, which in particular does not take up any installation space in the motor compartment of the motor vehicle. In order to achieve a particularly uniform braking effect, at least two such decentralized brake units are arranged on the corresponding wheels. Particularly preferably, such a brake unit is arranged on each wheel of the motor vehicle. As a result, there are no space problems in the motor compartment compared to a conventional central brake unit arranged in the motor compartment. In addition, brake lines from the motor compartment to the individual wheel brakes are no longer required. In addition, no second brake unit is required for automated driving, since a separate brake unit is already arranged, in particular, on each wheel according to the technical solution according to the invention. The required redundancy is preferably provided by means of at least two brake units according to the invention, which are connected to two independent power supplies. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The following is a more detailed explanation of an embodiment of the technical solution according to the present invention with reference to the attached schematic diagram.

[0028] Figure 1 shows a schematic diagram of a brake unit according to the prior art;

[0029] Figure 2 A first embodiment of a brake unit according to the invention with a first drive piston variant is shown. Figure 1 Schematic diagram drawn in this way;

[0030] Figure 3 shows a schematic longitudinal section of a first embodiment with a second drive piston variant;

[0031] Figure 4 A second embodiment of a brake unit according to the invention with a first drive piston variant is shown. Figure 1 Schematic diagram drawn in this way;

[0032] Figure 5 A second embodiment with a second drive piston variant is shown according to Figure 3 The view drawn in this way;

[0033] Figure 6 The diagram shows the braking unit according to the third embodiment of the present invention when the driving piston is in different positions. Figure 2 Details VI shown; and

[0034] Figure 7 Shown according to Figure 6 Detail shown VII. DETAILED DESCRIPTION

[0035] Figure 1A simplified schematic diagram shows an electromechanical brake 10 designed as a disc brake. Brake 10 comprises a brake unit 12, which is arranged on a wheel (not shown) of a motor vehicle. Fastened to the wheel is a wheel-side brake element 14 or friction element belonging to brake 10, which rotates during operation and is designed as a brake disc 16. The fastening is not shown in the figure. Brake disc 16 is only partially shown. When the wheel and brake unit 12 are mounted on the vehicle, brake unit 12 is arranged above the radial circumference of brake disc 16 and surrounds it, with a gap 18 between them.

[0036] Brake shoes or calipers 20 and 22 are arranged on either side of the brake disc 16 in the gap 18. Brake linings 24 are provided on the side of each shoe or caliper facing the brake disc. One of the brake calipers 20 is mounted on a carrier element, specifically a caliper pawl 26, while the other caliper 22 is fastened to an axially displaceable brake element 28. The axially displaceable brake element 28 is a pressure plunger 29, which is moved back and forth in translation within a housing 32 integral with the caliper pawl 26 by means of a transmission 30. The transmission 30 is a screw-type transmission assembly (not shown in detail) that can be driven by a drive motor or electric motor 34. The electric motor 34 and the transmission 30 form a drive unit 36, wherein the electric motor 34 is coupled to an electronic control unit 38 via signal transmission. Based on the signal, the electric motor 34 is controlled accordingly, which causes the electric motor 34 to generate a rotational motion. Here, the electric motor 34 is coupled to the transmission 30, converting the rotational motion of the electric motor 34 into the translational motion of the ram 29. When the ram 29 is controlled to move out of the housing 32 via the transmission 30, the brake calipers 20, 22, and thus the brake lining 24, are pressed against the brake disc 16. Each brake caliper 20, 22, with its brake lining 24, forms a friction pair with the brake disc 16, which serves as a rotating friction element. This friction pair brakes the rotational motion of the wheel. When the ram 29 moves back, the brake lining 24 disengages the brake disc 16, and braking is terminated.

[0037] Unlike this electromechanical brake 10, Figure 2 and Figure 3 , an electrohydraulic brake 40 is shown. The brake 40 comprises a brake unit 42 having a brake piston 44 as an axially displaceable brake element 28. The brake piston 44 is guided in a translationally displaceable manner in a brake housing 46 arranged in the brake caliper jaw 26. An end face 48 of the brake piston 44 is located axially outside the brake housing 46 and is force-transmittingly coupled to the brake caliper 22 and the brake lining 24 located thereon.

[0038] An end face 50, located on the brake piston 44 and axially opposite the end face 48, encloses, together with the brake housing 46, a variable-volume brake chamber 52 containing brake fluid 54. To seal the brake chamber 52 from its surroundings outside the brake housing 46 or the brake caliper jaws 26, two axially arranged seals 56 are provided. These seals are sealing rings and each radially surround the brake piston 44. The brake chamber 52, located axially between the end face 50 and a wall 58 delimiting the brake housing 46, is hydraulically connected to a pressure chamber 62 filled with the brake fluid 54 via a fluid line 60. The pressure chamber 62 is part of a drive device 64, which also includes a drive housing 66 surrounding the pressure chamber 62 and a drive piston 68 guided axially displaceably in the drive housing 66.

[0039] The drive piston 68 is guided axially and reciprocally by a transmission 70 associated with the drive unit 64. The transmission 70 is force-coupled to a drive motor 72, or electric motor 72, which is in turn coupled to a control unit 74 for signal transmission. The electric motor 72, designed as an electric motor, is controlled in its rotational motion based on the signal. When rotated in one direction, a planetary gear 76, associated with the transmission 70 and coupled to the electric motor 72, rotates accordingly. A spindle drive 78 associated with the transmission 70 is coupled to the planetary gear 76, which converts the rotation into axial movement of the drive piston 68, which is coupled to the spindle drive 78. When the drive piston 68 is introduced into the drive housing 66 along a drive direction 80, the brake fluid 54 in the pressure chamber 62 flows out of the pressure chamber 62 through the fluid line 60 and is displaced into the brake chamber 52. This volumetric displacement of the brake fluid 54 causes the brake piston 44, with its end face 48, to move out of the brake housing 46. As a result, the brake caliper 22 arranged on the end face 48 presses with its brake lining 24 against the wheel-side rotating brake element 14, which is designed as a brake disk 14. The rotation of the brake disk 16 and the associated wheel is braked.

[0040] If the electric motor 72 is driven in the reverse direction of rotation under the action of a corresponding signal, the planetary gear 76 rotates accordingly. This reverse rotation is then converted into a reverse translational movement of the drive piston 68 via the spindle drive 78. The drive piston 68 is then moved out of the drive housing 66 counter to the drive direction 80 and actively reset by the drive 64. During the reset, the movement of the drive piston 68 creates a suction force in the pressure chamber 62, which draws the brake fluid 54 from the brake chamber 52 via the fluid line 60 and moves it back into the pressure chamber 62. This creates a corresponding suction force in the brake chamber 52, which causes the brake piston 44 to move counter to the drive direction 80 into the brake housing 46. Consequently, the brake caliper 22, which is positioned on the brake piston 44, retracts its brake lining 24 from the brake disc 16. The braking effect is thereby released.

[0041] Thus, a hydraulic transmission 82 is provided, in particular, by the brake fluid 54, the drive piston 68 guided axially displaceably in the drive housing 66, the brake piston 44 guided axially displaceably in the brake housing 46, and the fluid line 60 connecting the two housings 46, 66. The hydraulic transmission 82 also includes a brake piston diameter 84 that is larger than a drive piston diameter 86 of the drive piston 68. This applies correspondingly to the associated cross-sectional diameters of the brake housing 46 and the drive housing 66. Thus, the hydraulic transmission 82 enables a relatively high braking force to be transmitted to the brake disk 16 via the brake piston 44 using a relatively low force of the drive piston 68 during a braking operation.

[0042] Braking unit 42 is a closed hydraulic system in which thermal volume compensation is achieved by means of a pressure compensation device 88, which is connected to drive housing 66 via a fluid line 90. Fluid line 90 leads from a region 92 of drive housing 66, where the drive piston is located when in the unactuated state, and into a pressure compensation reservoir 94. Braking fluid 54 is contained in drive housing 66 and in a space 96 in pressure compensation reservoir 94 adjacent to fluid line 90. A pressure compensation membrane 98 is secured to pressure compensation reservoir 94 to delimit space 96. This membrane seals space 96, which is filled with brake fluid 54, from space 100, which is filled with air pressure.

[0043] Depending on the position of the drive piston 68, the fluid line 90 is either closed or connected in a fluid-conducting manner to the drive housing 66. For this purpose, the drive piston 68 has a special design. Figure 2 (and Figure 4 ) shows a first variant, and Figure 3 (and Figure 5 ) shows a second variant. Figure 2 (and Figure 4 ) and shown in Figure 6 and Figure 7 In a first variant of the detail shown in FIG, the drive piston 68 has an inclined groove 104 on its end face 102 facing the drive direction 80. When the drive piston 68 is in the unactuated position, the groove 104 is arranged in the region 92 of the fluid line 90. This establishes a connection between the drive housing 66 and the pressure compensation device 88. When the drive piston 68 is inserted into the drive housing 66 with its end face 102 and the groove 104 arranged therein, the fluid line 90 is closed because the drive piston 68 rests against the inner side of the drive housing 66 over its entire circumference. Furthermore, a seal 106 is provided on each axial side of the fluid line 90, radially surrounding the drive piston 68 and resting thereon in a sealing manner. In a variant embodiment (not shown), the drive piston 68 does not necessarily rest against the drive housing 66, but only against the seals 106.

[0044] according to Figure 3 (and Figure 5 ), the drive piston 68 has a through-opening 107 which opens into the cup-shaped end face 102 of the drive piston 68 which is open in the drive direction 80 . In the non-actuated state, the through-opening 107 is located on the fluid line 90 .

[0045] For control purposes, a first sensor 108 is provided, coupled to the electric motor 72 of the drive 64. This first sensor is a rotor position sensor. Sensor 108 detects the rotor position of the electric motor 72. For redundancy, a second sensor 110 is provided, which acts as a pressure sensor and detects the pressure of the brake fluid 54 in the brake chamber 52 of the brake housing 46. Both sensors 108 and 110 are coupled to the control device 74 in a signal-transmitting manner. Based on the signals, the control device 74 controls the electric motor 72 and, therefore, the drive 64.

[0046] exist Figure 4 and Figure 5 An embodiment of an electro-hydraulic brake 40 is shown in FIG. Figure 2 and Figure 3 Compared to the embodiment shown in FIG, a spring element 112 is arranged in the pressure chamber 62. This spring element 112 is a return spring and is designed here as a metal coil spring. Furthermore, the spring element 112 is arranged axially between the end face 102 of the drive piston 68 and an axially opposite wall 114 of the drive housing 66. When the drive piston 68 moves into the drive housing 66, the spring element 112 deforms and, when the drive force generated by the electric motor 72 is removed, it resets the drive piston 68 in the opposite direction of the drive direction 80.

[0047] In the present embodiment, the spring element 112 acts in addition to the transmission 70, which returns the drive piston 68 by means of the electric motor 72. Thus, even in the event of a fault, such as a power failure, in which the electric motor 72 cannot be driven, the drive piston 68 can still be returned by means of the additionally returning spring element 112, and the brake piston 44 can also be returned by means of the hydraulic transmission.

[0048] In another advantageous embodiment (not shown here), the drive piston 68 can be reset solely by means of a spring element 112 as the sole restoring element.

[0049] Figure 6 The various positions of the drive piston 68 in the drive housing 66 are shown. Here, the first position 116 shows the non-actuated position of the drive piston 68. Figure 7 is shown in detail in cross section in FIG. The inclined groove 104 provided on the end face 102 is shown, by which a fluid-conducting connection is established between the fluid line 90 and the pressure chamber 62 in the drive housing 66. The second position 118 of the drive piston 68 shows how the drive piston 68 is moved into the drive housing 66 in the drive direction 80 to begin the pressure buildup. In the third position 120, the drive piston 68 is in its pressure-building position, while in the fourth position 122, the drive piston 68 is moved out of the drive housing 66 in a direction 124 opposite to the drive direction 80 to reduce the pressure.

Claims

1. A brake unit (42) arranged on a wheel of a motor vehicle, comprising an axially displaceable brake element (28) and a drive (64) for selectively displacing the brake element (28). It is characterized in that The brake element (28) is an axially displaceable brake piston (44) which is force-transmittingly coupled to the drive device (64) by means of a hydraulic transmission (82).

2. The brake unit according to claim 1, It is characterized by: The hydraulic drive (82) is formed by means of a drive piston (68) which is arranged in addition to the brake piston (44) and is guided in an axially displaceable manner in a drive housing (66).

3. The brake unit according to claim 2, It is characterized by: The drive piston (68) has a drive piston diameter (86), and the brake piston (44) has a brake piston diameter (84) that is different from the drive piston diameter (86), wherein in particular the brake piston diameter (84) is larger than the drive piston diameter (86).

4. The brake unit according to claim 2 or 3, It is characterized by: The drive piston (68) can be selectively moved into and out of the drive housing (66) by means of the drive device (64).

5. The brake unit according to any one of claims 2 to 4, It is characterized in that The drive piston (68) is movable counter to the drive direction (80) by means of a spring element (112).

6. The brake unit according to any one of claims 1 to 5, It is characterized by: The drive device (64) includes a drive motor (72) and a transmission device (70) that can be driven by the drive motor (72).

7. The brake unit according to any one of claims 1 to 6, It is characterized by: A pressure compensation device (88) is provided, which is in particular hydraulically connected to the drive device (64).

8. The brake unit according to claim 7, It is characterized by: The pressure compensation device (88) is provided with a pressure compensation membrane (98).

9. The brake unit according to any one of claims 1 to 8, It is characterized in that A first sensor (108) and a second sensor (110) are provided which are coupled to the drive device (64).

10. Use of at least one brake unit (42) according to any one of claims 1 to 9, respectively on a wheel of a motor vehicle.

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