Braking system for a motor vehicle

Abstract

The present invention relates to a braking system (110) for a motor vehicle, comprising at least two electrical braking devices (1) that have at least two electric servomotors (41, 42), and comprising at least two mutually independent voltage sources (P1, P2), wherein, in order to supply voltage, a first of the at least two servomotors (41) is assigned to a first voltage source (P1) and a second of the at least two servomotors (42) is assigned to a second voltage source (P2). In order to enable a higher degree of operational safety, the invention proposes that each braking device (1) has a braking actuator (4, BM1, BM2, BM3, BM4) that has at least a first servomotor (41) and a second servomotor (42).

Description

[0001] Braking system for a motor vehicle

[0002] State of the art

[0003] The invention relates to a braking system for a motor vehicle, comprising at least two electric braking devices which have at least two electric servomotors, and comprising at least two mutually independent voltage sources, wherein for the voltage supply at least one of the servomotors is assigned to a first voltage source, and at least one of the servomotors is assigned to a second voltage source.

[0004] Such a braking system comprises at least two electromotive braking devices, each assigned to a wheel of a motor vehicle to be braked. An electromotive braking device, also referred to as a brake unit or wheel brake, has an electromotive brake actuator supported on the chassis relative to the rotation of the wheel to be braked, which actuator has at least one electric servomotor. This acts via an actuator on a braking part, for example a brake pad, which can be brought into braking engagement with a counter-braking part attached to the wheel to be braked, for example a brake disc, by driving the servomotor. During braking engagement, frictional contact is generated between the braking part and the counter-braking part, whereby the braking torque generated by friction increases the higher the adjusting force exerted by the actuator in the adjustment direction.

[0005] The braking system is controlled electrically. An electrical braking command to initiate braking can be generated manually by an input device such as a brake pedal or a parking brake switch, and additionally or alternatively by an automated input device such as an anti-lock braking system (ABS) or an automatic drive system (ADS). To activate the braking devices, the servomotors of the brake actuators are controlled by a voltage source to energize or release the brake.

[0006] To increase operational reliability, a redundant power supply is proposed in the prior art in DE 195 37 464 A1. This describes a braking system of the type mentioned above, which has four electric braking devices assigned to the wheels to be braked, each of the braking devices having an electric servomotor. Redundant operation is enabled by providing two independent voltage sources, for example, batteries, of which a first voltage source is assigned to supply power to at least one of the servomotors in order to energize it as needed, and at least one second voltage source is assigned to supply power to at least one other servomotor.For example, the two braking devices assigned to the wheels on the front axle of the vehicle can be supplied from the first voltage source, and the two braking devices assigned to a rear axle from the second voltage source. This means that if one of the two voltage sources fails, the braking devices assigned to the other, intact voltage source can continue to be actuated, making it possible to brake at least those vehicle wheels whose braking devices are assigned to the intact voltage source. The disadvantage of this, however, is that if one voltage source fails, only some of the vehicle wheels can be braked, for example the two front wheels or rear wheels, or even a front and rear wheel of a wheel diagonal. This can impair driving and braking safety.

[0007] In view of the problems explained above, it is an object of the present invention to enable greater operational reliability.

[0008] Description of the invention

[0009] This object is achieved according to the invention by the braking system having the features of claim 1. Advantageous further developments emerge from the subclaims.

[0010] In a braking system for a motor vehicle, comprising at least two electric braking devices which have at least two electric servomotors, and comprising at least two mutually independent voltage sources, wherein for the purpose of supplying power at least one of the servomotors is assigned to a first voltage source and at least one of the servomotors is assigned to a second voltage source, it is provided according to the invention that at least one braking device has a brake actuator which has a first servomotor and a second servomotor.

[0011] Where reference is made below to the two voltage sources, this formulation comprises the first and second voltage sources together, and accordingly the first and second servomotors are referred to together as the two servomotors. In the invention, one, preferably each vehicle wheel to be braked, also referred to as a wheel for short, can have a braking device, each with a brake actuator that has at least two servomotors. The brake actuator can comprise a first servomotor and a second servomotor, wherein the first servomotor is assigned to the first voltage source and can be energized by it, and the second servomotor can be energized independently from the second voltage source, or vice versa. This represents a significant difference from the prior art, in which a braking device of a vehicle wheel only has a single servomotor that is assigned to one of the two voltage sources.

[0012] One advantage of the invention is that a braking device remains functional even if one of the two voltage sources is impaired or fails. In this case, only one of the two servomotors fails, and the other remains fully functional to generate sufficient braking effect. As a result, each wheel interacting with a braking device according to the invention remains brakeable even if one of the two voltage sources fails and one of the servomotors cannot be controlled. In contrast, in the prior art, a braking device becomes completely inoperable if the associated voltage source fails. Accordingly, the invention can achieve greater redundancy, thus enabling greater braking and driving safety.

[0013] It is possible for each braking device assigned to a wheel to be braked in a braking system to be designed according to the invention and connected to the two voltage sources. This ensures that all braking devices remain fully functional in the event of a voltage source failure, creating a fully redundant system.

[0014] Alternatively, it can be provided that only some of the braking devices of a braking system have two servomotors assigned to the two voltage sources, while the servomotors of the remaining braking devices are each assigned to only one voltage source. Individual braking devices can be assigned to different voltage sources. The latter embodiment has the advantage of lower complexity, allowing for the implementation of adequate, adequate redundancy. This advantageously allows for flexible design adaptation to the required safety level.

[0015] In a braking system according to the invention, at least two braking devices preferably each have two servomotors. Particularly preferably, each braking device is configured such that, for example, a braking system with four wheels to be braked has a total of at least eight servomotors. As explained above, the two servomotors for each of the braking devices can be assigned to the two voltage sources, or only some of the braking devices can be configured according to the invention.

[0016] It can be provided that at least one brake actuator is designed as a front-wheel brake actuator, and at least one brake actuator is designed as a rear-wheel brake actuator. Preferably, two front-wheel brake actuators can be provided, which are assigned in pairs to the or a front axle of the motor vehicle. Correspondingly, two rear-wheel brake actuators can be provided, which are assigned in pairs to the or a rear axle of the motor vehicle. In this case, it is possible for preferably both front-wheel brake actuators, and additionally or alternatively both rear-wheel brake actuators, to be designed according to the invention. This allows for flexible adaptation to the required degree of redundancy.

[0017] It may be advantageous for the first servomotor of a front-wheel brake actuator to be connected to the first voltage source, and for the second servomotor of this front-wheel brake actuator to be connected to the second voltage source. Preferably, the two front-wheel brake actuators assigned to a front axle can be configured in this way according to the invention. This ensures that the braking function of the vehicle's front wheels, which generally have the greatest braking effect due to the inertial forces acting during vehicle braking, can be fully redundantly protected.

[0018] It is possible for the first servomotor of a rear-wheel brake actuator to be connected to the first voltage source, and the second servomotor of this rear-wheel brake actuator to be connected to the second voltage source. Preferably, the two rear-wheel brake actuators assigned to a rear axle can be configured according to the invention in this way. This allows fully redundant protection of all wheels to be braked to be realized, particularly when the front-wheel brake actuators are configured according to the invention according to the aforementioned embodiment. The advantage of this is that all braking devices remain functional even if a voltage source or individual servomotors fail.

[0019] Alternatively, it can be provided that the first servomotor and the second servomotor of a rear-wheel brake actuator are connected to a common voltage source. Because the two servomotors of a rear-wheel brake actuator are connected in parallel to the first or second voltage source, they can only be energized and thus activated together, but this results in the advantage of simplified control. Due to the generally lower braking effect of the rear wheels, the associated reduced redundancy of the entire braking system can be accepted, particularly if the front-wheel braking devices are designed according to the invention, whereby the greater part of the overall braking effect is already redundantly secured.

[0020] In the latter embodiment, it can be provided that, with two brake devices assigned to a rear axle, the brake actuator of one brake device is assigned to the first voltage source and can be energized by it, and the brake actuator of the other brake device is assigned to the second voltage source. This ensures that, in the event of a voltage source failure, at least one of the rear wheels remains brakeable. In this way, greater redundancy can be achieved than with a parallel connection of all servomotors of the rear wheel brake actuators to just one of the voltage sources.

[0021] An advantageous further development can provide for at least a third voltage source. Accordingly, the braking system can have three or more voltage sources. Where reference is made below to a third or further voltage source, this can mean any voltage source in addition to the first and second voltage sources, for example also a fourth or nth voltage source. A third or further voltage source can achieve an even higher degree of redundancy than two voltage sources. This means that redundancy can be maintained even if one voltage source fails, so that sufficient braking action can be guaranteed even in the unlikely event of a further voltage source failing.

[0022] It can be provided that the first servomotor of a front wheel brake actuator is connected to the first voltage source or the second voltage source, and the second servomotor of a front wheel brake actuator is connected to a third voltage source.

[0023] This ensures that at least one of the front wheels can still be braked even if the power sources fail. This enables fully redundant protection of the front axle brakes. Even in designs with three or more power sources, it can be advantageous for the first servomotor of a front-wheel brake actuator to be connected to the first power source, and the second servomotor of a front-wheel brake actuator to be connected to the second power source. This already enables redundant protection of the front axle brakes.

[0024] It may be advantageous for the first servomotor of a rear-wheel brake actuator to be connected to the first voltage source or the second voltage source, and for the second servomotor of this rear-wheel brake actuator to be connected to the third voltage source. This ensures that both rear-wheel brake actuators remain functional if the first and / or second voltage source fails.

[0025] An advantageous embodiment can provide for the first actuator or the second actuator of a rear-wheel brake actuator to be connected to a third voltage source, and the other actuator of this rear-wheel brake actuator to be connected to the first or second or a further voltage source. As a result, the rear-wheel brake actuator, preferably the two rear-wheel brake actuators assigned to a rear axle, remains functional even in the unlikely event that the first and second voltage sources fail, and, for example, the front-wheel brake actuators powered by them fail completely.

[0026] It can further be provided that the first servomotor and the second servomotor of a rear-wheel brake actuator are connected to a common voltage source. In this case, both servomotors of a rear-wheel brake actuator can be powered by the first, second, or third voltage source. Due to the parallel connection, the two servomotors of a rear-wheel brake actuator can only be activated together. The advantage lies in simplified control. Due to the generally lower braking effect of the rear wheels, the associated reduced redundancy of the entire braking system can be accepted, especially if the front-wheel braking devices are designed according to the invention, whereby the greater part of the overall braking effect is already redundantly secured.

[0027] In the latter embodiment, it can advantageously be provided that, with two brake devices assigned to a rear axle, both servomotors of one brake device are assigned to a voltage source and can be energized by this source, and both servomotors of the other brake device are assigned to a different voltage source. This ensures that, in the event of a voltage source failure, at least one of the rear wheels remains brakeable. In this way, greater redundancy can be achieved than with a parallel connection of all servomotors of the rear wheel brake actuators to only one of the voltage sources.

[0028] The voltage sources and the servomotors can preferably be connected to a central control unit (ECU = electronic control unit). This determines, according to a predefined control algorithm, the control currents delivered to the servomotors of all brake actuators, which are required to generate defined wheel braking torques. Furthermore, this can preferably record the operating status of the servomotors and the voltage sources. If one of the voltage sources or a servomotor fails, the braking force of the intact voltage sources and servomotors can be increased, for example, by appropriate control. For example, if a voltage source fails, the servomotors connected to a voltage source that is still intact can be controlled with a higher current to compensate for the braking force of failed servomotors.

[0029] The optimum braking torque, which enables the shortest possible braking distance, ideally without locking the wheels, can be determined from the target values ​​issued with the braking command and other actual parameters relevant to the braking process, such as wheel position, wheel speed, electric current of the servo motor, braking force, vehicle speed, and the like. In the cited prior art, it is known to feed at least the values ​​for the braking command and, if necessary, other values ​​into the central control unit (ECU). The braking system can have at least two wheel brake control units separate from the ECU. These can be electrically controlled by the central control unit using control signals.

[0030] In other words, by providing at least two wheel brake control units, each of which is assigned to a braking device and connected to a brake actuator, it is provided that at least two braking devices each have their own wheel brake control unit, which is connected to the central control unit and to the brake actuator.

[0031] Each wheel brake control unit can be controlled by the ECU with target braking values ​​generated from a braking command received from the input devices. The inventive combination of the central control unit with at least two decentralized wheel brake control units assigned to the wheels enables decentralized brake control. This enables simpler and shorter cabling, for example, from a wheel sensor, such as a wheel position sensor, which is assigned to a wheel and can be connected directly to the wheel brake control unit of the braking device also assigned to the wheel. This advantageously reduces manufacturing and assembly costs. Furthermore, sensitivity to external interference can be reduced.The decentralized design of the brake control according to the invention also allows for greater redundancy, so that operational reliability can be increased.

[0032] A wheel brake control unit can preferably be integrated with the braking device. This allows for a compact, safe, and easy-to-install design.

[0033] Preferably, each of the braking devices has a wheel brake control unit, for example, in a 4-wheeled vehicle with four braking devices, correspondingly four wheel brake control units can be provided, or in a 2-wheeled vehicle with two braking devices, correspondingly two wheel brake control units can be provided.

[0034] It is preferred that a wheel brake control unit is connected to at least one brake actuator. A wheel brake control unit ensures the control of the brake actuator(s) with a defined target control signal in order to generate a defined braking torque for the wheel assigned to the respective braking device.

[0035] It is possible for each of the wheel brake control units to be connected to an electric actuator. The wheel brake control unit can control the actuator with electrical target control values ​​of the control current. Two or more actuators of a braking device can also be connected to a wheel brake control unit.

[0036] Preferably, each wheel brake control unit can be connected to a sensor device. The sensor device can preferably comprise a wheel sensor assigned to the respective wheel to be braked. This can be designed to detect parameters (actual values) relevant to a braking operation, such as wheel position, wheel speed, vehicle speed, slip, and the like, and to forward them to the wheel brake control unit. Furthermore, a sensor device can be provided for detecting the electric current of the servomotor, the braking force, and the like. Preferably, each of the braking devices has a sensor device, preferably at least one wheel sensor. One advantage is that the sensor unit, in particular a wheel sensor assigned to the respective braking unit, can be connected with less effort.The fact that relevant parameters can be measured on the wheel to be braked and fed directly to the wheel brake control unit without the need for the central control unit means that operational reliability and redundancy can be increased.

[0037] It can be provided that each wheel brake control unit has a control unit.

[0038] The electrical control unit compares the actual values ​​of a wheel sensor or other sensor device with the target values ​​of a brake command transmitted from the central control unit to the wheel brake control unit and controls the servomotor(s) of the brake actuator accordingly in order to achieve the target values.

[0039] In a braking device for a motor vehicle, which comprises a brake actuator with an electric servo motor and a wheel sensor, it can be provided that the braking device has a wheel brake control unit which can be connected to the brake actuator and the wheel sensor.

[0040] The braking device can preferably be used in a braking system of the type described above, wherein all of the features described in this context can be implemented.

[0041] The wheel sensor, also referred to as wheel position sensor, can be designed as described above.

[0042] The wheel brake control unit is designed for connection to the central control unit and to at least one wheel sensor. The at least one servomotor of the brake actuator can be electrically controlled by the wheel brake control unit.

[0043] The wheel brake control unit can preferably be designed to be integrated with the braking device, for example by structural integration in a housing of the braking device.

[0044] In a method for controlling a braking system of a motor vehicle having at least two braking devices, each with a brake actuator, wherein each of the brake actuators has an electric servomotor, and wherein the braking devices are connected to a central control unit which is designed for connection to at least one input device, wherein a braking command is input into the central control unit by at least one input device, which controls the brake actuators with control signals, it can be provided that the central control unit outputs control signals to at least two wheel brake control units, each assigned to a braking device, which each control a brake actuator of the respective braking device.

[0045] To implement the method, all features and procedures described above in connection with the braking system and the braking device can be used.

[0046] One advantage of the method is that the decentralized control architecture allows for improved operational reliability, for example, through the robust design that is less susceptible to external interference and the possibility of redundantly distributing control functions between the central control unit and the wheel brake control units according to the invention. For example, anti-lock braking (ABS) can be controlled by the wheel brake control unit together with the associated wheel sensor in a decentralized manner and independently of the central control unit. This allows for increased operational reliability.

[0047] It is advantageous for each of the wheel brake control units to receive actual signals from a wheel sensor of the respective braking device. According to a control algorithm, the control of the respective brake actuator is regulated in the respective wheel brake control unit, taking into account the actual signals from the wheel sensor, such as wheel position and / or wheel speed, so that the target values ​​specified by the braking command are realized. The wheel sensor preferably provides the actual signals of the measured parameters in real time. Actual values ​​provided by other sensor devices can also be considered and processed, such as the electric current of the servo motor, braking force, vehicle speed, and the like.

[0048] An advantage of the method according to the invention is that the processing of the signals supplied by the wheel sensor (wheel position sensor) can take place virtually in real time in the decentralized wheel brake control units of the braking devices. This allows for increased processing speed and operational reliability, as well as a redundant control design.An advantageous embodiment of the braking system according to the invention can provide that the braking device comprises an actuating device and a braking part connected thereto, which can be adjusted along an axis by the actuating device and brought into braking engagement with a counter-braking part, wherein the actuating device has a first actuating drive and a second actuating drive coupled in series thereto, wherein the first actuating drive has a first drive wheel that can be driven in rotation, and the second actuating drive has a second drive wheel that can be driven in rotation and is coaxial with the first drive wheel, wherein a coupling device is arranged between the first drive wheel and the second drive wheel.

[0049] The actuating device can be driven by at least one electric actuator. This actuator is preferably in gear engagement with at least one drive wheel. Preferably, one actuator can be provided for each of the first and second drive wheels. According to the invention, the actuator(s) can be controlled by a wheel brake control unit assigned to the braking device.

[0050] In the last-mentioned embodiment, it can be provided that the clutch device is designed as a friction clutch with a friction element that can be frictionally connected to a counter friction element in the clutch engagement.

[0051] In the following, the first and second drive wheels are referred to together as the two drive wheels or simply as the drive wheels.

[0052] The drive wheels can each be designed as a gear, for example as a spur gear, or as a belt or toothed belt wheel or worm wheel, so that generally a gear wheel is provided via which a drive torque from an electric actuator can be coupled into the actuator.

[0053] A friction clutch is implemented between the drive wheels. This comprises a friction element, which is torque-locked to one of the drive wheels, and a corresponding counter-friction element, which is torque-locked to the other drive wheel. The friction element can be brought into frictional engagement with the counter-friction element in any relative angular position. This creates a purely force-locking coupling, as opposed to a positive locking connection. This allows the relative position of the drive wheels to be continuously specified, in contrast to the discrete locking steps of a locking connection. Accordingly, a uniform, continuous adjustment of the second actuator relative to the first actuator is possible, and a continuous adjustment of the air gap can be achieved.This is particularly advantageous with regard to the consistent adjustment of the braking system's optimal operating point to the continuous wear of the braking component during operation, i.e., the continuous wear of the brake pad. Compared to a purely incremental adjustment option, a consistently improved braking system response can be achieved, thus increasing operational reliability and greater ease of use.

[0054] A further advantage over a locking clutch is that, to engage and disengage the clutch device, essentially no axial relative movement is required between the clutch elements engaged in the clutch, for example, between the drive gears or the locking elements, which must necessarily be movable relative to one another to create and release the lockable positive locking. In contrast, the pure frictional connection between the friction and counter-friction elements according to the invention can be simply determined by the applied axial actuation force, whereby the friction and counter-friction elements do not need to be moved axially relative to one another. This enables a simpler and more reliable design of the clutch device.

[0055] It is preferably provided that the friction clutch has a defined, predeterminable clutch torque. The clutch torque indicates the maximum differential torque that can be transmitted force-lockingly between the friction element and the counter-friction element due to the frictional engagement during clutch engagement. If the clutch torque is exceeded, the clutch device slips, causing the two drive wheels to rotate relative to each other. One advantage of this is that the friction clutch according to the invention slips continuously in a sliding manner, enabling improved, uniform readjustment of the air gap. Furthermore, there is no need to design for axial evasive movements of locking elements, as is the case with the known locking clutch, and thus compensate for these.

[0056] It is advantageous for the friction element and the counter-friction element to be arranged coaxially. This coaxial arrangement corresponds to the coaxial arrangement of the drive wheels. The friction element and the counter-friction element can be arranged in a simple and compact design in the area of ​​the axially opposing end faces of the drive wheels. Due to the above-described generation of the pure frictional connection of the clutch, no moving parts are required. In an advantageous embodiment, the friction element and the counter-friction element can be conical.The friction element can have a conical section with a conical friction surface that converges at least partially in the axial adjustment direction and can be designed as an outer cone or inner cone, and which has a corresponding conical section on the counter friction element, which is designed in the opposite direction as an inner cone or outer cone and has a conical counter friction surface. To generate the clutch engagement, the outer cone dips into the inner cone, with the conical friction and counter friction surfaces being frictionally loaded against one another by an axial actuating force of the clutch. One advantage of this is that the cone can convert the axially acting actuating force of the clutch into the normal force acting between the conical friction surfaces in frictional contact.Thus, a flatter pitch allows a relatively small axial actuating force to be converted into a larger normal force in the frictional contact, whereby a high clutch torque can be achieved even with a relatively small axial actuating force of the clutch.

[0057] Alternatively or in addition to the aforementioned embodiment, the friction element and the counter friction element can be designed as planar surfaces. The corresponding friction surfaces are designed, at least in sections, as flat axial surfaces, similar to a disc clutch. This enables a space-saving arrangement, especially when only a relatively small clutch torque is to be achieved.

[0058] It can preferably be provided that the friction element and the counter-friction element are preloaded against each other. Preferably, the friction element and the counter-friction element are elastically or resiliently preloaded against each other. The friction and counter-friction surfaces are pressed against each other in frictional engagement with a predetermined axial preload force. To generate the preload force, an elastic preload element, for example a spring element or the like, can preferably be provided. The clutch torque of the friction clutch is determined by the actuating force acting perpendicular to the frictional contact, i.e. the force applied axially between the friction and counter-friction elements, whereby the clutch torque is greater the greater the preload force. This opens up the advantageous possibility of simply specifying the clutch torque through the preload force exerted by the preload element.For example, in the case of a spring element that is elastic in the axial direction, such as a compression spring, the applied preload force can be simply specified and adjusted by the spring constant and the compression of the spring. The aforementioned embodiment can advantageously be implemented in such a way that the friction element and / or the counter-friction element are axially displaceable and supported against the first drive wheel or the second drive wheel via an axially acting spring element. The friction element or the counter-friction element are connected to one drive wheel in a torque-locking and axially displaceable manner, for example via radially projecting drivers that create a positive connection effective in the circumferential direction.The spring element axially clamped between the friction element or the counter-friction element and one drive wheel, which is preferably designed as an axially acting compression spring, ensures that the friction or counter-friction element is axially pre-tensioned against the corresponding counter-friction or friction element axially supported on the other drive wheel, i.e. is pressed axially against it in frictional contact. The corresponding counter-friction or friction element is rotationally connected to the other drive wheel. It is also possible, alternatively or additionally, that the counter-friction element is supported on one of the drive wheels via a spring element. An advantage of this arrangement is that this friction clutch can be integrated between the drive wheels in a structurally simple and space-saving manner.

[0059] In an advantageous development, it is possible for the friction element and / or the counter-friction element to be arranged in the first drive wheel or the second drive wheel. For example, it is possible to design one drive wheel essentially drum-shaped, so that the friction or counter-friction element can be arranged in an interior space enclosed by the rotating gear or gear ring. This enables a compact design that is protected against external influences. For example, the drive wheel of the first actuator can have a conical friction element that engages axially in a counter-friction element designed as an inner cone, which is arranged at least partially within the second drive wheel.

[0060] A particularly compact design can be achieved - especially in the last-mentioned embodiment - by arranging the drive wheels within the axial extension of the actuators, i.e. by not being mounted axially protruding on one side.

[0061] It is preferred that the friction element and / or the counter-friction element have a friction lining. The friction and counter-friction elements preferably have a metallic base body, for example, made of steel. To prevent metal-to-metal contact, a coating or lining can preferably be applied to create a friction pairing with a defined friction force, for example, made of sintered, metal and / or ceramic friction materials, composite materials, or the like. This ensures a defined, reproducible clutch torque.

[0062] An actuator can be provided with a spindle drive. In this case, a threaded spindle engages a spindle nut in a conventional manner, and a relative rotating drive is provided via a drive wheel connected to the threaded spindle or the spindle nut. It is possible for the spindle nut to form the drive-side drive element of the actuator, and the threaded spindle to form the output-side output element, which is linearly adjustable relative to it, or vice versa.

[0063] It is possible for an actuator to have a ball ramp arrangement, a wedge disk arrangement, or a tilt pin arrangement. In a ball ramp arrangement, also known as a ramp bearing, the drive and output elements preferably have cam disks with raceways or ramps inclined relative to the axis, between which balls that can roll in the circumferential direction are arranged. A relative rotation leads to the output element being axially displaced relative to the drive element due to the ball rolling on the ramps. In a tilt pin arrangement known per se, tilt pins are arranged between the drive and output elements and each supported in the circumferential direction in such a way that, depending on the direction of rotation, they are inclined more or less towards the axis during a relative rotation, whereby the distance between the drive and output elements can also be adjusted.

[0064] In the actuating device, two similarly acting actuators can be combined as first and second actuators, for example, two spindle drives. It is also possible to combine two different designs, for example, a ball ramp arrangement as the first actuator and a spindle drive as the second actuator for adjusting the air gap. The respective characteristic properties of each design can be optimally utilized. For example, with a ball ramp arrangement, a non-linear adjustment characteristic can be realized with little effort, and / or self-locking properties at least in sections, and / or a defined dead center or extended position that enables a defined adjustment path. The realization of the aforementioned positive properties can at least partially require a precise specification of the air gap, which can be easily achieved with the friction clutch according to the invention.

[0065] A braking device according to the invention can comprise an actuating device and a braking part connected thereto, which can be adjusted along an axis by the actuating device and brought into braking engagement with a counter-braking part, wherein the actuating device has a first actuating drive and a second actuating drive coupled in series therewith, wherein the first actuating drive has a first drive wheel that can be driven in rotation, and the second actuating drive has a second drive wheel that can be driven in rotation and is coaxial with the first drive wheel, wherein a coupling device is arranged between the first drive wheel and the second drive wheel.

[0066] The actuating device can be driven by at least one electric actuator. This actuator is preferably in gear engagement with at least one drive wheel. Preferably, one actuator can be provided for each of the first and second drive wheels. According to the invention, the actuator(s) can be controlled by a wheel brake control unit assigned to the braking device.

[0067] In the last-mentioned embodiment of the braking device, it can preferably be provided that the coupling device is designed as a friction clutch with a friction element that can be frictionally connected to a counter friction element in the clutch engagement.

[0068] This makes it possible to realize the advantages previously explained in connection with the braking system.

[0069] To implement the method, it can be provided that the braking device has an actuating device which can be coupled to a servomotor and comprises a first actuating drive and a second actuating drive coupled in series therewith, and which acts on a braking part which can be brought into braking engagement with a counter-braking part in the direction of an axis, wherein the first actuating drive has a rotatably drivable first drive wheel to which a first drive torque can be applied for actuation, and the second actuating drive has a rotatably drivable second drive wheel which is coaxial with the first drive wheel and to which a second drive torque can be applied for actuation, wherein a clutch device is arranged between the first drive wheel and the second drive wheel, wherein the invention provides that the clutch device is designed as a friction clutch and has a predeterminable clutch torque,When this value is exceeded, the first drive wheel slips relative to the second drive wheel. To actuate the first actuator, the first drive wheel and the second drive wheel are driven synchronously, so that the second actuator remains unactuated. To actuate the second actuator, the second drive wheel is driven, and the first drive wheel is stopped relative to it, so that the friction clutch slips and the first actuator remains unactuated. The features mentioned above in connection with the braking device according to the invention can be used individually and in combination to implement the method.

[0070] To adjust the first actuator, an actuating torque can be coupled into the first drive wheel by means of a first electric actuator motor, and accordingly the second actuator can be driven by a second electric actuator motor.

[0071] During normal braking operation, the first and second drive wheels rotate synchronously. This can be achieved by driving the first and second drive wheels with synchronized drive torques by the first and second actuators. Alternatively, the second drive wheel can be driven synchronously by the clutch device when the first drive wheel is driven, as long as the transmitted drive torque remains below the clutch torque. In this operating mode, the second actuator remains unactuated and rotates freely as a whole, together with the braking element.

[0072] In the method, the clutch device can slip continuously and smoothly when the clutch torque is exceeded to adjust the air gap. This can be achieved, for example, by immobilizing the drive wheel of the first actuator, for example, by a brake or a corresponding control of the first drive motor, while the second drive motor applies a second drive torque to the second drive wheel that is greater than the clutch torque. This rotates the second drive wheel relative to the first drive wheel, and by actuating the second actuator, the air gap can be continuously and sensitively adjusted, so that continuously advancing wear of the brake element or brake pad can be optimally compensated.

[0073] It is possible for the first drive wheel and the second drive wheel to be torque-locked by the friction clutch to generate a synchronous drive.

[0074] This eliminates the need for synchronous drive of the two drive wheels by the servomotors. Any torque differences can be compensated within specified tolerances.

[0075] It can advantageously be provided that a higher clutch torque is specified when the first actuator is actuated than when the second actuator is actuated. The first actuator is actuated by synchronous drive of the first and second drive wheels. The friction element and the counter-friction element are preloaded against each other by the spring force of the spring element, and in addition, the adjusting force of the first actuator acts opposite to the spring force. This results in a relatively high clutch torque. If, on the other hand, only the second drive wheel is rotated to adjust the air gap, the spring force alone acts, so that a lower clutch torque is set. This facilitates the adjustment of the air gap.

[0076] Description of the drawings

[0077] Advantageous embodiments of the invention are explained in more detail below with reference to the drawings. In detail:

[0078] Figure 1 shows a braking system of a motor vehicle according to the invention in a schematic representation,

[0079] Figure 2a shows a structural diagram of a braking system according to the invention in a first embodiment,

[0080] Figure 2b shows an electrical connection diagram of the braking system according to Figure 2a,

[0081] Figure 2c shows a structural diagram of a braking system according to the invention in a second embodiment,

[0082] Figure 3 shows a braking device according to the invention in a schematic perspective view,

[0083] Figure 4 is a side view of the braking device according to Figure 3,

[0084] Figure 5 shows a section QQ through the braking device according to Figure 3,

[0085] Figure 6 shows the first actuator of the braking device according to Figure 1 in a schematic perspective view,

[0086] Figure 7 is an enlarged detailed view of the adjusting device from Figure 5. Embodiments of the invention

[0087] In the various figures, identical parts are always provided with the same reference symbols and are therefore usually named or mentioned only once.

[0088] Fig. 1 shows a schematic, isolated, perspective partial view of a chassis 100 of a motor vehicle. This comprises steerable wheels (vehicle wheels) 101, which are mounted on pivotable steering knuckles 103 on a frame part of the body 102 of the motor vehicle.

[0089] The two wheels 101 shown in Figure 1 are the two front wheels 101V of the front axle of the vehicle.

[0090] A steering system comprises a steering shaft 104, at the rear end of which, in the direction of travel, a steering wheel 105 is mounted for manual steering input. The steering shaft 104 is connected to a steering gear 106, which is connected to the steering knuckles 103 via tie rods 107 to generate a steering angle.

[0091] A braking system 110 has a braking device 1 for each of the two wheels (vehicle wheels) 101, wherein the braking device 1 of one front wheel 101V is designated as BU1, and the braking device 1 of the other front wheel 101V is designated as BU2. Each of these has a brake caliper 2, which is attached to and supported on the motor vehicle body 102. A brake disc 3 is rotatably mounted on each wheel 101, which is gripped by the brake caliper 2, which is fixed relative to the wheel. The braking devices BU1 and BU2 are of identical design.

[0092] The braking devices 1, i.e., BU1 and BU2, are connected to a central control unit 112 (ECU) via electrical control lines 111. A schematically illustrated brake pedal 113, mounted on the body 102 and representing a manual input device, is also connected to the ECU 112.

[0093] Furthermore, an automated input device 114 can be connected to the ECU 112, which can output external control signals to the ECU 112 for controlling the braking system 110. The braking system has a first voltage source P1 and a second voltage source P2, which can be configured as batteries or accumulators. The two voltage sources P1 and P2 are each connected to the two braking devices BU1 and BU2.

[0094] Figure 2a shows a schematic diagram of the chassis 100 with a braking system 110. The vehicle has four wheels 101, each of which is assigned a braking device 1 according to the invention.

[0095] Of the total of four wheels 101 of the vehicle, two front wheels 101V are on the front axle and two rear wheels 101H are on the rear axle of the vehicle.

[0096] A total of four braking devices 1 are provided, of which the braking devices BU1 and BU2 are assigned to the two front wheels 101V, and the two braking devices BU3 and BU4 are assigned to the two rear wheels 101H.

[0097] Each of the braking devices BU1, BU2, BU3 and BU4 has a brake actuator 4, which is designated as BM1, BM2, BM3 and BM4 according to the assignment.

[0098] Each of the braking devices BU1, BU2, BU3, and BU4 can optionally further comprise a wheel brake control unit 120, which is designated BC1, BC2, BC3, and BC4, respectively. A wheel sensor 121 (S1, S2, S3, S4) can be connected to each wheel brake control unit 120, which is preferably designed as a wheel position sensor and transmits actual values ​​of the rotational position to the wheel brake control unit 120 in real time while driving.

[0099] The wheel brake control unit 120 can preferably be integrated with the braking device 1 and electrically connected to the brake actuator 4.

[0100] According to the invention, each of the brake actuators BM1, BM2, BM3 and BM4 has two electric servomotors 41, 42, specifically a first servomotor 41 and a second servomotor 42. According to the invention, these are assigned to the voltage sources P1 and P2 and can be supplied with current from them.

[0101] Figure 2b shows an exemplary electrical diagram for an inventive assignment of the first servomotors 41 and the second servomotors 42 of the four brake actuators BM1, BM2, BM3, and BM4 to the voltage sources P1 and P2. For each brake actuator BM1, BM2, BM3, and BM4, the first servomotor 41 is assigned to the first voltage source P1, and the second servomotor 41 is assigned to the second voltage source P2. In this way, a fully redundant arrangement is created that continues to ensure the braking of each wheel 101 in the event of the failure of one of the voltage sources P1 or P2. This arrangement can be summarized schematically as follows, with the arrow indicating the connection of a servomotor 41, 42 to one of the voltage sources P1, P2, P3:

[0102] Figure 2c shows a further embodiment of a braking system 101 according to the invention in a view similar to Figure 2a. This system has an additional third voltage source P3.

[0103] In the arrangement of Figure 2c, the two brake actuators BM1 and BM2 of the front wheels 101V are connected to the two voltage sources P1 and P2, as in Figures 2a and 2b, respectively. The two first servomotors 41 of the two rear brake actuators BM3 and BM4 are connected to the third voltage source P3 and can be energized by it. The second servomotor 42 of the brake actuator BM3 is connected to the first voltage source P1, and the second servomotor 42 of the brake actuator BM4 is connected to the second voltage source P1. This ensures that the two rear wheels remain brakeable even in the unlikely event that the two voltage sources P1 and P2 fail simultaneously. If the third voltage source P3 fails, all four wheels 101 remain brakeable.

[0104] This arrangement can be represented schematically as follows:

[0105] As an alternative to the examples shown in Figures 2a, 2b, and 2c, all combinations of the servomotors 41 and 42 of the brake actuators BM1, BM2, BM3, and BM4 mentioned in the description, which are not explicitly shown in the figures, can also be implemented. For example, it is possible for the two servomotors 41 and 42 of a brake actuator BM1, BM2, BM3, or BM4 to be connected in parallel and assigned to one of the voltage sources P1, P2, or P3, with the two servomotors 41 and 42 of another brake actuator BM1, BM2, BM3, or BM4 being assigned to two of the voltage sources P1, P2, or P3. For example, the following schematically illustrated arrangements can be implemented: or or

[0106] Other combinations not explicitly shown here are conceivable and possible.

[0107] It is also conceivable and possible to provide at least one additional voltage source.

[0108] Each of the four braking devices 1 shown in the example has its own wheel brake control unit 120, which can exchange electrical control signals with the wheel sensor 121 and the ECU 112 and, depending on these signals, can control the brake actuator 4. The servo motors 41, 42 can be energized by the respective wheel brake control unit 120 to generate a predetermined braking effect.

[0109] An embodiment of the brake actuator 4 is shown in detail below in Figures 3, 4, and 5. It has a housing 45 in which the wheel brake control unit 120 is arranged, as can be seen in Figure 5. This has an electrical circuit connected to the servomotors 41, 42 and the ECU 112. As a result, the wheel brake control unit 120 is integrated with the braking device 1. For connecting the wheel sensor 121, which is indicated schematically in Figures 4 and 5, the brake actuator 4 has a connection device 46, for example an electrical plug connection arranged on the housing 45 or the like.

[0110] Figure 3 shows an embodiment of the braking device 1 according to the invention as a whole, which is designed as a disc brake. This comprises a brake disc 2, which forms a counter-braking part and is connected to a vehicle wheel 101 (not shown here) that is rotatable about a wheel axis R. A brake caliper 3 engages the two axial end faces of the brake disc 2.

[0111] Brake disc 2 is designed as a non-ventilated brake disc made of solid material. Alternatively, it can also be designed as an internally ventilated brake disc.

[0112] An electric brake actuator 4 according to the invention is attached to the brake caliper 3.

[0113] The brake actuator 4 comprises an adjusting device 5 which extends axially in the direction of an axis A which is parallel to the wheel axis R and indicates the adjustment direction V of the adjusting device 5.

[0114] Figure 4 shows a view of the brake caliper 3 seen from the brake disc 2.

[0115] As can be seen in the sectional view of Figure 5 along axis A, the brake disc 2 is arranged axially between two brake pads 31 and 32. One brake pad 31 is firmly supported on the brake caliper 3 on the side facing away from the brake actuator 4. The other brake pad 32, which forms a braking part within the meaning of the invention, is attached to the adjusting device 5 and can be adjusted by it in the axial adjustment direction V defined by the axis A to generate the braking engagement on the brake disc 2, as indicated by the arrow in Figure 5.

[0116] In the unactuated state of the braking device 1, there is an axial air gap L between the brake disc 2 and the adjustable brake pad 32, which is shown schematically in Figure 4 as exaggeratedly wide.

[0117] The structure of the actuating device 5 is shown in Figure 5 and in the enlarged section thereof in Figure 7. The actuating device 5 comprises a first actuating drive 6, which has a ramp bearing, and a second actuating drive 7, which is axially coupled thereto (with respect to the axis A) and has a spindle drive.

[0118] The first actuator 6, which in the example shown is designed as a ramp bearing, comprises a drive-side cam disc 61 and an output-side cam disc 62, which are axially and rotationally fixedly supported on the brake actuator 4. Balls 63 are arranged between the cam discs 61 and 62. As can be seen in the schematically isolated view of Figure 6, the cam discs 61 and 62 have axially opposite, ramp-like raceways 64, which are inclined to the axis A and between which balls 63 can roll. A rotation of the output-side cam disc 62, in Figure 6 above, relative to the fixed drive-side cam disc 61 - as schematically indicated by the curved arrows - leads to a linear adjustment of the output-side cam disc 62 in the adjustment direction V parallel to the axis A. As a result, the brake pad 32 can be brought into braking engagement by actuating the first actuator 6, as shown in Figure 4.

[0119] The cam disc 62 is connected to a coaxial gear 65, which is designed as a spur gear and forms a drive wheel in the sense of the invention.

[0120] The gear 65 is in gear engagement with a first electric actuator 41. This enables the rotating drive of the cam disc 62 and thus the actuation of the first actuator 6.

[0121] The second actuator 7, which in the example shown is designed as a spindle drive, has a threaded spindle 71 on the output side, which engages the internal thread of a drive-side spindle nut 72. This internal thread is formed in the output-side cam disc 62 of the first actuator 6, so that the functions of the output-side cam disc 62 and the drive-side spindle nut 72 are combined in one component.

[0122] The threaded spindle 71 is connected via a hub part 74 to a coaxial gear 75, which is axially fixed and rotatably mounted in the brake actuator 4. The threaded spindle is coupled to the gear 75 in a torque-locking but axially displaceable manner via drivers 73, which may, for example, have radially projecting projections or teeth that engage axially displaceably in axial slots of the hub part 74. Like the gear 65, the gear 75 can be designed as a spur gear and is arranged coaxially adjacent to it. This gear 75 is in gear engagement with a second electric actuator 42. This enables the rotating drive of the threaded spindle 71 and thus actuation of the second actuator 7.

[0123] The threaded spindle 71 is axially connected via a thrust bearing 43, for example, an axial roller bearing as shown, to a thrust piece 44, to which the movable brake pad 32 is attached, as can be seen in Figure 4. The thrust piece 44 can also be referred to as a piston.

[0124] The clutch device according to the invention comprises a friction element 8, which is designed as a coaxial, conical extension extending from the cam disc 62 toward the second actuator 7. The conical extension has a conical friction surface 81 arranged externally on an outer cone. The friction element 81 can preferably be formed integrally with the cam disc 62 / spindle nut 72.

[0125] In clutch engagement, the friction element 8 is frictionally coupled to a counter friction element 9. The conical projection axially engages a corresponding conical opening of the counter friction element 9, which has a conical friction surface 91 arranged in an inner cone. In clutch engagement, the friction surface 81 and the counter friction surface 91 are in frictional contact with each other, as can be clearly seen in Figure 7.

[0126] The counter friction element 9 is coupled to the gear 75 in a torque-locking but axially displaceable manner via drivers 92 which engage axially displaceably in corresponding slots 76 in the hub part 74 or the gear 75.

[0127] A spring element 93 is arranged between the gear 75 or the hub part 74 connected thereto and the counter friction element 9. Its axially acting spring force elastically braces the counter friction element 9 against the friction element 8. This generates a defined clutch torque of the friction clutch according to the invention formed by the friction element 8 and the counter friction element 9.

[0128] To actuate the braking device 1, the gears 65 and 75 rotate synchronously, causing the first actuator 6 to execute a working stroke in the adjustment direction V, causing the brake pad 32 to pass through the air gap L and engage the brake disc 2. The synchronous drive of the gears 65 and 75 can be achieved by synchronizing the drive speeds of the actuator motors 41 and 42, or by driving only one of the actuator motors 41 or 42, while the other actuator motor 42 or 41 runs idle. The frictional coupling engagement between the friction element 8 and the counter friction element 9 then ensures synchronous rotation of the gears 65 and 75.

[0129] To adjust the width of the air gap L, the gear 65 is fixed or blocked, for example, by appropriately controlling the first servomotor 41. The second servomotor 42 rotates the gear 75 relative to the gear 65, causing the friction clutch to slip continuously. Accordingly, the second actuator 7 is adjusted evenly, allowing the width of the air gap L to be continuously adjusted and adapted, for example, to compensate for wear on the brake pad 32.

[0130] Because the friction element 8 and the counter friction element 9 are arranged entirely or at least partially within the gear wheels 65 and 75, a particularly compact design can be realized.

[0131] The braking devices illustrated in Figures 3 to 7 are designed as floating caliper brakes, also referred to as floating caliper brakes. The brake pad 32 is pressed against the brake disc 2 by the pressure piece 44, and the brake pad 31 is pressed against the brake disc 2 by the brake caliper 3, which is movable relative to the brake disc 2 in the direction of the axis A. Alternatively, the solution according to the invention can also be used with a fixed caliper brake.

[0132] List of reference symbols

[0133] 1 ,BU1 , BU2, BU3, BU4 braking device

[0134] 100 chassis

[0135] 101 Wheel (vehicle wheel)

[0136] 101V front wheel

[0137] 101 H rear wheel

[0138] 102 Body

[0139] 103 Steering knuckles

[0140] 104 Steering shaft

[0141] 105 Steering wheel

[0142] 106 steering gear

[0143] 107 Tie rod

[0144] 110 Brake system

[0145] 111 Control line

[0146] 112 Central control unit (ECU

[0147] 113 Brake pedal

[0148] 114 Input device

[0149] 120 Wheel brake control unit (BC1, BC2, BC3, BC4)

[0150] 121 Wheel sensor

[0151] 2 brake discs

[0152] 3 brake caliper

[0153] 31, 32 brake pad

[0154] 4, BM1, BM2, BM3, BM4 brake actuator

[0155] 41, 42 Actuator

[0156] 43 thrust bearings

[0157] 44 Pressure piece

[0158] 45 housings

[0159] 46 Connection device

[0160] 5 Adjusting device

[0161] 6 first actuator

[0162] 61 cam disc

[0163] 62 cam disc (integrated with spindle nut 72)

[0164] 63 ball

[0165] 64 Career

[0166] 65 gear

[0167] 7 second actuator 71 threaded spindle

[0168] 72 spindle nut (integrated with cam disc 62)

[0169] 73 drivers

[0170] 74 Hub part 75 Gear

[0171] 76 slot

[0172] 8 Friction element

[0173] 81 Friction surface

[0174] 9 Counter friction element 91 Counter friction surface

[0175] 92 drivers

[0176] 93 spring element

[0177] A Axle R Wheel axle

[0178] V Adjustment direction

[0179] L Air gap

[0180] P1, P2, P3 voltage source

Claims

PATENT CLAIMS 1. Braking system (110) for a motor vehicle, comprising at least two electric braking devices (1) which have at least two electric servomotors (41, 42), and comprising at least two mutually independent voltage sources (P1, P2), wherein for the voltage supply at least one of the servomotors (41, 42) is assigned to a first voltage source (P1), and at least one of the servomotors (41, 42) is assigned to a second voltage source (P2), characterized in that a braking device (1) each has a brake actuator (4, BM1, BM2, BM3, BM4) which has at least a first servomotor (41) and a second servomotor (42).

2. Brake system according to claim 1, characterized in that at least one brake actuator (4, BM1, BM2, BM3, BM4) is designed as a front wheel brake actuator (BM1, BM2), and at least one brake actuator (4, BM1, BM2, BM3, BM4) is designed as a rear wheel brake actuator (BM3, BM4).

3. Braking system according to claim 2, characterized in that the first servomotor (41) of a front wheel brake actuator (BM1, BM2) is connected to the first voltage source (P1), and the second servomotor (42) of this front wheel brake actuator (BM1, BM2) is connected to the second voltage source (P2).

4. Braking system according to one of the preceding claims 2 or 3, characterized in that the first servomotor (41) of a rear wheel brake actuator (BM3, BM4) is connected to the first voltage source (P1), and the second servomotor (42) of this rear wheel brake actuator (BM3, BM4) is connected to the second voltage source (P2).

5. Braking system according to one of the preceding claims 2 or 3, characterized in that the first servomotor (41) and the second servomotor (42) of a rear wheel brake actuator (BM3, BM4) are connected to a common voltage source (P1, P2).

6. Braking system according to one of the preceding claims, characterized in that at least one third voltage source (P3) is provided.

7. Braking system according to claim 6, characterized in that the first servomotor (41) of a front wheel brake actuator (BM1, BM2) is connected to the first voltage source (P1) or the second voltage source (P2), and the second servomotor (42) of a front wheel brake actuator (BM1, BM2) is connected to the third voltage source (P3).

8. Braking system according to claim 6, characterized in that the first servomotor (41) of a front wheel brake actuator (BM1, BM2) is connected to the first voltage source (P1), and the second servomotor (42) of a front wheel brake actuator (BM1, BM2) is connected to the second voltage source (P2).

9. Braking system according to one of the preceding claims 6 to 8, characterized in that the first servomotor (41) or the second servomotor (42) of a rear wheel brake actuator (BM3, BM4) is connected to a third voltage source (P3), and the respective other servomotor (41, 42) of this rear wheel brake actuator (BM3, BM4) is connected to the first or second or a further voltage source (P1, P2).

10. Braking system according to one of the preceding claims 6 to 8, characterized in that the first servomotor (41) of a rear wheel brake actuator (BM3, BM4) is connected to the first voltage source (P1), and the second servomotor (42) of a rear wheel brake actuator (BM3, BM4) is connected to the second voltage source (P2).

11. Braking system according to one of the preceding claims 6 to 8, characterized in that the first servomotor (41) and the second servomotor (42) of a rear wheel brake actuator (BM3, BM4) are connected to a common voltage source (P1, P2, P3).

12. Braking system according to one of the preceding claims, characterized in that the braking devices (1, B11) are connected to a central control unit (112) which is designed for connection to at least one input device (113, 114), wherein at least two wheel brake control units (120, BC) are provided, which are each connected to a brake actuator (4) and which are connected to the central control unit (112).

13. Braking system according to one of the preceding claims, characterized in that the braking device (1) comprises an adjusting device (5) and a Brake part (32) which is adjustable by the adjusting device (5) along an axis (A) and can be brought into braking engagement with a counter-brake part (2), wherein the adjusting device (5) has a first actuating drive (6) and a second actuating drive (7) coupled in series therewith, wherein the first actuating drive (6) has a first drive wheel (65) which can be driven in rotation, and the second actuating drive (7) has a first drive wheel (65) which can be driven in rotation and which is connected to the first The drive wheel has a coaxial second drive wheel (75), wherein a coupling device (8, 9) is arranged between the first drive wheel (65) and the second drive wheel (75).

14. Braking system according to one of the preceding claims, characterized in that the braking device (1) has a wheel brake control unit (120) that can be connected to the brake actuator (4) and a wheel sensor (121).

Images