WO2009086979A1

WO2009086979A1 - Device and method for actuating an electric brake system

Info

Publication number: WO2009086979A1
Application number: PCT/EP2008/065713
Authority: WO
Inventors: Stefan Strengert; Peter Blessing; Wolfgang Haas; Werner Harter
Original assignee: Robert Bosch Gmbh
Priority date: 2008-01-10
Filing date: 2008-11-18
Publication date: 2009-07-16
Also published as: EP2231453A1; DE102008003801A1

Abstract

The invention relates to an actuation device for an electric brake system, comprising a first switching element (100, 332, 311), which changes a first signal level (200) present in a first signal line (104) by a first level difference (212) upon actuation, a second switching element (102, 330, 310), which changes a second signal level (202) present in a second signal line (106) by a second level difference (214) upon actuation, said difference having a leading sign opposite that of the first level difference (212), an actuating element (108, 300, 302) actuating the first and the second switching element, a function activator (112) activating a function (ACU11-22, L1) of the brake system if the first signal level changed by the first level difference is present in the first signal line, or if the second signal level changed by the second level difference is present in the second signal line, and a plausibility warning device (110), which outputs a plausibility warning signal (120, 334, 336) based on the signal levels present in the first and second signal lines. The invention further provides an electric brake system for a motor vehicle, comprising such an actuation device and two brake circuits, wherein the first and the second switching elements are part of different brake circuits. According to a further aspect the invention provides a method for actuating an electric brake system.

Description

description

title

Apparatus and method for driving an electrical braking system

STATE OF THE ART

The present invention relates to a drive device for an electric brake system, an electric brake system with two brake circuits for a motor vehicle, and a method for driving an electric brake system.

In automotive braking systems, critical components and functionalities are redundantly designed to ensure that failure of individual components does not result in overall system failure and loss of braking performance. For example, from DE 103 57 373Al an electronic braking system for a vehicle is known, which has at least two brake circuits and a central control unit for all brake circuits. Each of the brake circuits is assigned a brake circuit control. In case of failure of the central control unit, a brake circuit control can autonomously perceive the control of a brake circuit from the central control unit. For this purpose, two autonomous receiving means are provided on a brake pedal or other brake request pick-up device, one of which is connected to the central control unit and the other to the autarkic brake circuit control unit.

In such a redundant design of recording means on a Bremsanforderangsauf- receiving device, such as double provided pedal travel sensors or dual brake lights switches on a brake pedal, however, there is no protection against so-called common-mode errors in which redundant designed components are affected by similar failures. The risk of such failures is particularly increased by the fact that the joint coupling of the redundant receiving means to the Bremsanforderangsaufnahmegerät and the consequent spatial proximity of the recording means to each other favor the simultaneous occurrence of errors that go back to a common cause (so-called common-cause error) , There is therefore a need for further measures that increase the availability and / or safety of the brake system. ADVANTAGES OF THE INVENTION

Accordingly provided is a drive device for an electrical brake system, wherein the drive device comprises: a first switching element which, when actuated, modifies a first signal level applied to a first signal line by a first level difference, a second switching element, when actuated, a second signal level applied to a second signal line changing a second level difference having a sign inverse to the first level difference, an actuator actuating the first and second switching elements, a function activator that activates a function of the brake system when the first signal level changed by the first level difference on the first signal line or on the second signal line the second signal level changed by the second level difference is present, and a plausibility warning device which based on the signal levels applied to the first and second signal lines has a plausibility output safety alert.

A significant advantage of the device according to the invention is that it makes it possible, with high availability of the relevant function of the brake system by redundant design of the switching elements in operation to detect errors occurring with improved reliability and thus to increase the safety of the brake system and the entire motor vehicle. The said function of the braking system may be e.g. to act the drive brake of the motor vehicle, the brake light system, an electric parking brake or a roll-back, wherein the actuator with which the driver requests the function, can be configured as a brake pedal or lever, button, rocker switch or the like.

Since the first and second switching element on actuation of the actuating element change the respective signal level applied to the first and the second signal line in opposite directions, by the plausibility warning device a common mode error of both switching elements and / or both signal lines, in which a gleichläufige change of first and second signal level occurs, reliably detected and the plausibility warning signal are output. The plausibility warning signal thus output with increased reliability in turn enables, e.g. warn the driver with a warning lamp or similar to have the braking system repaired, or / and initiate appropriate emergency measures such as the activation of replacement systems, thereby increasing the availability of the braking system.

According to a preferred embodiment, at least the first or the second switching element is designed as a closing contact switching element. This causes, when idle, unconfirmed beta is open, the contact so that no electrical current flows through the switch. Thus, the energy consumption of the drive device, in particular in the Parkierzustand the motor vehicle, with the engine off, advantageously reduced.

According to a preferred refinement, the first signal level, which is changed by the first level difference, is substantially equal to the second signal level, and the second signal level, which is changed by the second level difference, is substantially equal to the first signal level. This has the advantage of being particularly cost-effective, since only two different signal levels need to be generated and processed, so that the use of similar components and evaluation circuits is made possible.

According to a preferred refinement, the plausibility warning device is designed to output the plausibility warning signal if the first signal level is applied to the first signal line and the second signal level changed by the second level difference is applied to the second signal line. This advantageously allows for an implausible state such as to detect damage to the first switching element, when the switching elements are coupled to the actuating element, that they are always operated in the same direction in error-free operation of the drive device, or such that in error-free operation, the second switching element is actuated only in the actuated state of the first switching element.

According to a preferred embodiment, the actuating element is movable along an actuation path, wherein it actuates the first switching element from a first point of the actuation path and the first and second switching element from a second point of the actuation path. For example, the actuating element is designed as a brake pedal that can be moved by the driver along a pedal travel. This allows the plausibility warning device, a state in which the second switching element appears to be operated alone to reliably detect as an error, since this state does not occur in error-free operation, even if the first and / or second point along the actuation only within predetermined tolerance limits ,

Preferably, one or more displacement sensors are furthermore provided which each output a displacement signal which is equivalent to a position of the actuating element on the actuating travel. In this case, the function activator is designed to activate the function of the brake system only if in addition the path signal of one of the displacement sensors has a level equivalent to a movement of the actuator to at least a predetermined threshold position on the actuation path, or if both the first signal line is applied to the first signal level changed by the first level difference and to the second signal level, which is changed by the second level difference, on the second signal line. This causes a particularly high availability, since at Failure of one of the switching elements to replace the information provided by this information derived from the path signal of the displacement sensor information is used. The function activator makes a majority decision about the information provided by the switching elements and the displacement sensors.

According to another preferred embodiment, at least one further switching element is provided, which is actuated by the actuating element. In this case, the function activator is designed to activate the function of the brake system only if additionally one of the further switching elements is actuated, or if the first signal level changed by the first level difference as well as on the second signal line both at the first signal line the second level difference is applied to changed second signal levels. This also causes a particularly high availability, since in case of failure of one of the switching elements to replace the information provided by this information provided by the further switching element information is used. The function activator makes a majority decision about the information provided by the switching elements.

According to a preferred development, a function deactivator is furthermore provided which deactivates the function of the brake system when the plausibility warning signal is output. This advantageously allows a function of the brake system, which is not absolutely necessary for the motor vehicle, to be used, for example. a rollback inhibit, to deactivate when an error occurs and thus to avoid possible damage due to a malfunctioning function.

In a further aspect, the invention provides an electric braking system for a motor vehicle having one of the above-described driving devices and two brake circuits, wherein the first and second switching elements belong to different ones of the brake circuits. This has the particular advantage that the function remains available even in the event of complete failure of one of the brake circuits, since each of the brake circuits has one of the shifting elements.

DRAWINGS

The invention will be explained in more detail with reference to the exemplary embodiments indicated in the schematic figures of the drawings. It shows:

1 shows a schematic representation of a brake system with an embodiment of a drive device according to the invention;

FIGS. 2A-B are each a function graph showing a function of an operation path-dependent signal in the embodiment of FIG. 1; and Fig. 3 is a schematic representation of an embodiment of the invention

Braking system.

DESCRIPTION OF THE EMBODIMENTS

In all figures of the drawings, identical or functionally identical elements - unless otherwise stated - have been provided with the same reference numerals.

FIG. 1 shows a schematic illustration of a brake system for a motor vehicle, with a drive device according to an embodiment of the invention. For example, the motor vehicle has four wheels, of which only a single wheel R1 is shown here for the sake of clarity. On the shown wheel Rl 1 a wheel brake actuator RAl 1 is arranged, which can exert on the associated wheel Rl 1 by means of brake calipers or the like an adjustable braking force. The power transmission to the brake calipers may e.g. done by mechanical or hydraulic means. The wheel brake actuator RAl 1 is actuated by an associated wheel brake actuator control unit ACU1, which contains the electronics that are necessary for the safe operation of the wheel brake actuator RA11. The brake system further comprises a brake light system Ll with e.g. two or three brake lights, of which the sake of clarity here only a single brake light Ll is shown. Both the wheel brake actuator RA1 with associated wheel brake actuator control unit ACU1 and the brake light system L1 provide different components of the brake system as components of the brake system.

The drive device of the brake system has a central control unit SCU1. The wheel brake actuator control unit ACUI 1 is connected to the central control unit SCU1 via a data bus AB1. The data bus AB1 can be designed as a CAN, LIN or FlexRay bus or the like. The brake light system Ll is also connected to the central control unit SCUl, e.g. over a similar data bus or simple supply lines. The central control unit SCUl comprises a function activator 112 for activating the brake function ACUI 1 and the brake light function Ll of the brake system. The function activator 112 may comprise both hardware and software elements executed on a processor, not shown, of the central controller SCU1.

Furthermore, the drive device has a brake pedal 108 as an actuating element 108, which is designed to be actuated by the driver of the motor vehicle with his foot and thereby moved along an actuating path 114 in order to control both the wheel brake function ACUI 1 and the brake light. To request function Ll of the brake system. The brake pedal 108 is rotatably mounted at a suspension point 126 around which it rotates upon actuation by the driver. The brake pedal 108 is connected via a mechanical coupling 128 with two pedal travel sensors 122, 124 which determine a position of the brake pedal 108 along the actuation path 114 during operation of the drive device and in each case emit a signal equivalent to the position to the central control unit SCU1. The coupling 128 is shown here purely by way of example mechanically, but can also be implemented, for example, in a magnetic, hydraulic, pneumatic, optical manner. The pedal travel sensors 122, 124 themselves may, for example, be designed as potentiometers, Hall sensors, magnetoresistive sensors or voice coils, which either directly determine the actuation path 114 or an equivalent value to it, such as the deflection angle of the pedal or the actuation force. Preferably, the pedal travel sensors 122, 124 are implemented in various technologies to avoid both sensors 122, 124 becoming ineffective due to common mode or common cause errors.

The drive device further has a first 100 and a second 102 switching element, which are connected via respective couplings 130, 132 with the brake pedal 108 such that the first switching element 100 is actuated when the brake pedal 108 at a first position 116 on the actuation path 114, and the second shift element 102 is actuated when the brake pedal 108 is at a second position 118 on the actuation path 114. The first position 116 is located on the actuation path 114 in front of the second position 118, that is to say reached on actuation of the brake pedal in front of the second position 118. In order for proper, trouble-free operation of the drive device is excluded that only the second switching element 102, but not the first switching element 100 is actuated.

As in the case of the coupling 128 of the pedal travel sensors 122, 124, the couplings 130, 132 of the switching elements are mechanically illustrated by way of example, but may also be applied to e.g. be implemented magnetic, hydraulic, pneumatic or optical way. In this case, the switching elements 100, 102 may be inexpensively connected to the pedal travel sensors 122, 124, e.g. by the brake pedal 108 moving a permanent magnet whose magnetic field actuates both a pedal travel sensor 122 implemented as a Hall angle sensor and a switching element 100 implemented as a reed contact.

Both switching elements 100, 102 are formed as a closing contacts, which are each arranged between two resistors 136, 138 and 140, 142. In each case, the free end of one resistor 138, 142 is connected to a ground potential 144 and the free end of the other resistor to an operating voltage potential 146. In the closed state of the closing contacts 100, 102, each of the pairs of resistors 136, 138 and 140, 142 thus forms a voltage divider. The values of the resistors 140, 142 are set such that when the second switching element 102 is closed, a predetermined first signal level is established between the resistors 140, 142. The values of Resistors 136, 138 are set such that when the first switching element 100 is closed, a predetermined second signal level, which is higher than the first signal level, ie, further from the ground potential 144 than the first signal level, is established between the resistors 136, 138.

The first switching element 100 is connected at its one end, which connects the resistor 138 to the ground potential 144, via a first signal line 104 to the central control unit SCUl. When the closing contact is closed, the first signal line 104 therefore transmits the second, higher signal level to the central control unit SCU1. When the first switching element 100 is open, the first signal line 104, on the other hand, transmits to the central control unit SCU1 a lower signal level, which is close to the ground potential 144 when the central control unit SCU1 has a high input impedance.

The second switching element 102 is connected at the end, which connects the resistor 140 with the operating potential 146, via a second signal line 106 to the central control unit SCUl. When the contact closure is closed, the second signal line 106 therefore transmits to the central control unit SCU1 the first, lower signal level. When the second switching element 102 is open, on the other hand, the second signal line 106 transmits to the central control unit SCU1 a higher signal level, which is close to the operating potential 146 at a high input impedance of the central control unit SCU1.

The function activator 112 of the central controller SCUl is configured to activate the brake light function Ll of the brake system when the first signal line 104 has the higher second signal level or the second signal line 106 has the lower first signal level. when at least one of the signal lines 104, 106 indicates that the associated switching element 100, 102 has been closed. As a result, the brake light function Ll remains available even if an error occurs on one of the switching elements 100, 102 or on one of the signal lines 104, 106.

The central control unit SCU1 furthermore has a plausibility warning device 110 which, like the function activator 112, may comprise hardware and / or software components and is designed to issue a warning signal via a suitable output device 120 based on the signal levels applied to the first 104 and second signal lines 106 output if the signal levels are not plausible, ie in error-free operation possible signal level combination correspond.

The operation of the drive device shown in FIG. 1 will be described by way of example with reference to FIGS. 2A to 2D, which indicate the change in the signals output by the pedal travel sensors 122, 124 and the switching elements 100, 102 as a function of the position of the brake pedal 108 on the actuation path 114 be explained in more detail. FIG. 2A shows, by way of example, the profile of the signal 208 output by the first pedal travel sensor 122 to the central control unit SCU1, plotted along the vertical tension axis 218, as a function of the position of the brake pedal 108 on the actuation path 114 plotted along the horizontal axis as a distance from the latter Position of the unactuated brake pedal 108. The signal 208 rises from a voltage value of 0 V with progressive actuation of the brake pedal to a maximum value 204 of eg 5 V, thus showing a monotonically increasing dependence on the position.

FIG. 2B shows by way of example the course of the signal 210 output by the second pedal travel sensor 124 to the central control unit SCU1, plotted along the vertical tension axis 218, as a function of the position of the brake pedal 108 on the actuation path 114, plotted along the horizontal axis as a distance from the latter Position of the unactuated brake pedal 108. The signal 210 falls from a maximum voltage value 206 of eg 5 V with progressive actuation of the brake pedal 108 to a minimum value of 0 V, thus showing a monotonically decreasing dependence on the position.

FIG. 2C shows the profile of the signal output by the first switching element 100 to the central control unit SCU1, which is located at the first, lower signal level 200 up to the first position 116, and abruptly when reaching the first position 116 by a first level difference 212 second, higher signal level 202 increases.

FIG. 2D shows the profile of the signal output by the second switching element 102 to the central control unit SCU1, which is at the second, higher signal level 202 up to the second position 118 and, when the second position 118 is reached, abruptly by a second level difference 214, that of the first Level difference 212 is exactly opposite, falls to the first, lower signal level 200.

3 shows a schematic illustration of an embodiment according to the invention of a brake system with two brake circuits 304, 306. The first brake circuit 304 comprises a first system control unit SCU1, which is connected to a wheel brake actuator control unit ACU1 for a left front wheel via a first brake circuit data bus AB1 is connected to a wheel brake actuator control unit ACUl 2 for a right rear wheel to control for these wheels a regular braking function while driving, a parking brake function and a roll-back. The second brake circuit 306 includes a second system controller SCU2 connected to a wheel brake actuator controller ACU21 for a right front wheel and a wheel brake actuator controller ACU22 via a second brake circuit data bus AB2 is connected for a left rear wheel to control for the said wheels, the driving brake function, the parking brake function and the Rückrollsperrfünktion.

The brake system includes, for requesting the service brake function, a drive brake request unit 324 with a driver-operable brake pedal 108, a parking brake request unit 328 with a driver-actuated rocker switch 302 requesting the park brake function, and a roll-back request unit 326 with a driver-to-operator request for the roll-back function Button 300 on. The request units 324, 326, 328 are each connected to the transmission of function request signals with two system control units SCUl, SCU2. Each of the system controllers SCU1, SCU2 has a function activator 112, which activates the corresponding function in accordance with the request of the vehicle driver in dependence on the transmitted request signals.

Each of the system controllers SCU1, SCU2 has a plausibility warning device 110 which checks the transmitted request signals for plausibility and for a signal combination that is implausible, i. is not expected in trouble-free operation, emits a warning signal. For outputting the warning signal, the first system control unit SCU1 is connected to a first warning light 334, and the second system control unit SCU2 is connected to a second warning light 336 in the dashboard of the vehicle. Both warning lights are e.g. designed so that they together illuminate a visible warning surface for the driver on the dashboard.

Two central data buses CB1, CB2 provide redundant communication paths between the system controllers SCU1, SCU2. A first CB1 of the central data buses CB1, CB2 is furthermore connected to a dashboard control unit CSG for text display on the dashboard, a driver assistance system ESP and an engine control unit MSG. Electrical protection elements EPE at connection points of the system control units SCU1, SCU2 with the central data buses CB1, CB2 protect the system control units SCU1, SCU2 from undesired influence by the respective other participants of the relevant data bus.

The driving brake requesting unit 102 includes a brake pedal 108 as the actuator 108, four pedal sensors 122-125 coupled to the brake pedal 108, which output a continuous signal depending on the degree of operation of the brake pedal, and two switching elements 100, 102 coupled to the brake pedal 108 Deliver threshold signal. For the sake of clarity, the mechanical coupling between the actuating element 108, the sensors 122-125 and the switching elements 100, 102 is implicitly represented by a frame surrounding these elements 100, 102, 108, 122-125. Two 122, 124 of the pedal sensors and a first 100 of the switching elements are the first brake circuit 304, the other two pedal sensors 123, 125 and the second switching element 102 associated with the second brake circuit 306.

As in the embodiment of FIG. 1, the first 100 and second 102 switching element each have a closing contact which, when actuated, forms a voltage divider formed between two resistors 136, 138 and 140, 142 between an operating potential 146 and 147 of the respective brake circuit and a Ground potential 140 switches. As in the embodiment of FIG. 1, respective signal lines 104, 106, which connect the switching elements 100, 102 to the system control units SCU1, SCU2, are connected to different ends of the switching elements 100, 102, so that in the unactuated state of the brake pedal 108 The first switching element 100 transmits a low signal level and the second switching element 102 transmits a high signal level to the associated system control unit SCU1 or SCU2. The resistors 136, 138 and 140, 142 are selected such that in the actuated state of the brake pedal 108, the first switching element 100 transmits a high signal level and the second switching element 102 a low signal level to the associated system controller SCUl or SCU2.

During operation of the brake system, the two system control units SCU1, SCU2 exchange the data for the current pedal position determined by the respectively associated pedal sensors 122, 124 or 123, 125 and the threshold value signals of the switching elements 100 and 102 respectively obtained via the data lines 104 and 106 , The plausibility monitoring devices 110 of each system control unit SCU1, SCU2 constantly check all six signals for plausibility and issue a warning signal via the respective connected warning light 334 or 336 as soon as a non-plausible signal combination is detected. If the six transmitted signals or the signals still received in the event of a partial failure indicate different pedal positions to a function activator 112 of one of the system controllers SCU1, SCU2, then the respective function activator 112 activates the driving brake function according to a majority decision on the received signals.

The parking brake request unit 328 has a parking brake switch 302 for selectively activating and deactivating a parking brake function of the brake system. The parking brake switch 302 as an actuating element 302 is coupled to four individual switching elements 309-312, of which two 311, 312 are associated with the first brake circuit 304 and two 309, 310 with the second brake circuit 306. For the sake of clarity, the mechanical coupling between the actuating element 302 and the individual switching elements 309-312 is implicitly represented by a frame surrounding these elements 302, 309-312.

The parking brake switch 302 is adapted to be pulled 320 for activating the parking brake function and 322 for deactivating the parking brake function to be pressed, wherein it is automatically in each case a neutral position returns. It transmits the following signals to the respective central control units SCU1, SCU2 of the brake circuits 304, 306, which subject these to a plausibility check.

In the neutral position of the parking brake switch all the closing contacts of the switching elements 309- 312 are interrupted, so that at a high input impedance of the controllers SCUl, SCU2 no or almost no electrical power is taken from the electrical system 146, 147 of the respective brake circuit when the vehicle is e.g. parked with the ignition off. For each of the brake circuits 304, 306, the associated switching elements 311, 312 and 309, 310 are connected to each other in a complementary manner with the operating potential 146 or 147 and the ground potential 144. Thereby, each of the system controllers SCU1, SCU2 receives a low (0V) and a high (12V) signal level in the neutral position of the parking brake switch 302.

During operation of the brake system, the two system control units SCU1, SCU2 exchange the data determined by means of the respectively associated switching elements 311, 312 or 309, 310 for the current actuation state of the parking brake switch 302. The plausibility monitoring devices 110 of each system control unit SCU1, SCU2 continuously check all four signals for plausibility and issue a warning signal via the respectively connected warning light 334 or 336 as soon as a non-plausible signal combination is detected. If the four transmitted signals or the partial failure signals still indicate different pedal positions to a function activator 112 of one of the system controllers SCU1, SCU2, the respective function activator 112 activates the parking brake function according to a majority decision on the received signals.

The rollback request unit 326 includes a button 300 for selectively enabling and disabling a rollback function of the brake system. The push button 300 as an actuating element 300 is coupled to two individual switching elements 332, 330, of which one 332 is assigned to the first brake circuit 304 and one 330 to the second brake circuit 306. For the sake of clarity, the mechanical coupling between the actuating element 300 and the two switching elements 332, 330 is implicitly represented by a frame surrounding these elements 300, 332, 330. The two switching elements 332, 330 are connected in the same way as the threshold value switching elements 100, 102 of the driving brake request unit 324 or the switching elements 100, 102 of the embodiment of FIG. 1. The signal levels of the signals transmitted by one of the switching elements 332, 330 to the associated system control unit are therefore in the actuated state as well as in the non-actuated state of the push button 300 complementary to each other. The design with closing contacts ensures that the button 300 in the idle state of the vehicle no current from the brake system of the respective brake circuit 304, 306 takes.

The roll-back blocking function is not indispensable as a so-called comfort function in contrast to the driving brake and parking brake function for operating the vehicle. On the other hand, the rollback inhibit function can be a hindrance or a nuisance in certain driving situations. The system control units SCU1, SCU2 therefore each have a function deactivator 314 which deactivates the roll-back function in the event of a defect.

During operation of the brake system, the two system control units SCU1, SCU2 exchange the data determined by means of the respectively associated switching element 332 or 330 for the current actuation state of the pushbutton 300. The plausibility monitoring devices 110 of each system control unit SCU1, SCU2 constantly check both signals for plausibility. As soon as a plausibility monitoring device 110 of a system control unit SCU1, SCU2 detects a non-plausible signal combination, it issues a warning signal via the respectively connected warning light 334 or 336 and deactivates the roll-back blocking function for the relevant one via the function deactivator 314 of the same system control unit SCU1 or SCU2 Brake circuit 304 or 306.

Claims

claims

1. Drive device for an electric brake system with:

a first switching element (100, 332, 311) which, when actuated, modifies a first signal level (200) applied to a first signal line (104) by a first level difference (212);

- a second switching element (102, 330, 310) which, when actuated, modifies a second signal level (202) applied to a second signal line (106) by a second level difference (214) having a sign inverse to the first level difference (212); - An actuating element (108, 300, 302) which actuates the first (100, 332, 311) and the second (102, 330, 310) switching element;

a function activator (112) which activates a function (ACU1 1-22, L1) of the brake system when, on the first signal line (104), the first signal level (200) changed by the first level difference (212) or on the second signal line ( 106) is applied to the second signal level (202) modified by the second level difference (214); and

- A plausibility warning device (110), which outputs a plausibility warning signal (120, 334, 336) based on the voltage applied to the first (104) and second (106) signal line signal levels (200, 202).

2. Control device according to claim 1, characterized in that at least the first (100, 332, 311) or the second (102, 330, 310) switching element as a closing contact switching element (100, 332, 311, 102, 330, 310) is formed is.

3. Drive device according to claim 1, characterized in that the first signal level (200) changed by the first level difference (212) is substantially equal to the second signal level (202), and the second signal level (214) changed by the second level difference (214). 202) is substantially equal to the first signal level (200).

4. Drive device according to one of the preceding claims, characterized in that the plausibility warning device (110) is adapted to the plausibility warning signal (120,

334, 336) when, on the first signal line (104), the first signal level (200) and on the second signal line (106) the second one changed by the second level difference (214) Signal level (202) is present.

5. Drive device according to one of the preceding claims, characterized in that the actuating element (108) along an actuation path (114) is movable, wherein from a first point (116) of the actuation path (114), the first switching element (100) and from a second point (118) of the actuating path (114) actuates the first (100) and second (102) switching element.

6. Drive device according to one of the preceding claims, characterized in that further one or more displacement sensors (122, 124) are provided which each output a path signal (208, 210) which a position of the actuating element (108) on the actuation path (114 ) is equivalent, wherein the function activator (112) is adapted to activate the function (ACUl 1-22, Ll) of the brake system only if in addition the path signal (208, 210) of one of the displacement sensors (122, 124) a level (211) which is equivalent to a movement of the

Actuator (108) is at least to a predetermined threshold position (216) on the actuation path (214), or if on both the first signal line (104) to the first level difference (212) changed first signal level (200) and at the second Signal line (106) of the second level difference (214) changed second signal level (202) is applied.

7. Drive device according to one of the preceding claims, characterized in that at least one further switching element (309, 312) is provided, which is actuated by the actuating element (302), wherein the function activator (112) is adapted to the function (ACUl -22) of the brake system only to be activated when additionally one of the further switching elements (309, 312) is actuated, or if both on the first signal line

(104) the first signal level (200) changed by the first level difference and the second signal level (202) changed by the second level difference on the second signal line (106).

8. Drive device according to one of the preceding claims, characterized in that there is further provided a function deactivator (314) which deactivates the function (ACUl 1-22) of the brake system when the plausibility warning signal (334, 336) is output.

9. An electric brake system for a motor vehicle, comprising: - a drive device according to at least one of claims 1 to 8; and

two brake circuits (304, 306); wherein the first (100, 332, 311) and second (102, 330, 311) switching elements belong to different ones of the brake circuits (304, 306).

10. A method for driving an electric braking system, comprising the steps of: - actuating an actuating element (108, 300, 302) which actuates a first (100, 332, 311) and a second (102, 330, 310) switching element, wherein the in that the first switching element (100, 332, 311) is designed, upon actuation, to change a first signal level (200) applied to a first signal line (104) by a first level difference (212), and the second switching element (102, 330, 310) configured to change, when actuated, a second signal level (202) applied to a second signal line (106) by a second level difference (214) having a sign inverse to the first level difference (212);

- Activating a function (ACUl 1-22, Ll) of the brake system, when on the first signal line (104) by the first level difference (212) changed first signal level (200) or on the second signal line (106) by the second level difference (214) applies altered second signal levels (202); and

Outputting a plausibility warning signal (120, 334, 336) based on the signal levels applied to the first (104) and second signal lines (106).