METHOD FOR ELECTRONIC CLEARANCE CONTROL OF A VEHICLE WHEEL BRAKE AND ELECTRONIC VEHICLE BRAKE SYSTEM THEREFOR

Description

[0001] The invention relates to a method for electronic brake clearance control, in particular for starting and maintaining a clearance determined electronically by a microprocessor and defined as required, and wherein this individually sensor-supported defined clearance of an electric wheel brake of a motor vehicle is impressed individually as required, as well as to an electronic motor vehicle brake system comprising a plurality of electric wheel brakes for the purpose of carrying out the method of electronically microprocessor-supported impressed brake clearance control.

[0002] Electric wheel brakes are typically used in motor vehicles to decelerate them. Drum brakes and disc brakes are particularly common. Brake shoes, in particular, are used to generate a braking effect. Sometimes, spring means are provided, which can be preloaded and can always act on the brake shoes to pull the brake shoes out of frictional engagement. For example, in hydraulically actuated drum brakes, elastically preloaded tension springs can be used to reset the brake shoes after pressure has built up, creating a clearance between the brake shoes and drum and preventing residual torque. To prevent excessive contraction, i.e., excessive clearance, a mechanical "adjuster" can be used, for example, in simplex drum brakes.At the same time, this adjuster often initiates an automatic readjustment process in the event of pad wear, as a spindle / nut system moves apart depending on the spreading distance, usually actuated by a stepping mechanism. Such adjusters are typically sensitive to tolerances and can be subject to disturbances. If, for example, the air gap is set too small, residual torques can arise. This can, for example, lead to the wheel brake generating braking torque even while driving, thus causing unnecessary wear and unnecessary energy consumption. Another disadvantage of existing systems is that the brake shoes always require special return springs or at least a hardware component with a return spring effect that acts directly or indirectly on the brake shoes, which always increases structural effort and design complexity.The systems or methods known to date do not meet the increased requirements of modern, prefabricated electric wheel brake systems containing electric wheel brake actuators.

[0003] US 2007068237 A1 relates to an electromechanical brake with a method for clamping force estimation, comprising the following steps: providing a motor with at least one recognizable motor signal, the motor being adapted to engage a first non-rotatable body with a second rotating body, determining a first value for the motor signal before the first body engages the second body, determining a second value for the motor signal after the first body engages the second body, and generating a force value based on a comparison of the second value with the first value. The brake is presented without clearance control, as a distinction is made only between a fully retracted initial position, on the one hand, and a fully extended clamping position, on the other.

[0004] It is therefore an object of the invention to provide a method for electronic air gap control which is alternative to or better than the prior art. It is also an object of the invention to provide an electronic motor vehicle braking system with electric wheel brakes for implementing the electronic method. This is achieved according to the invention by a control method and a braking system with electric wheel brakes according to the respective main claims. Advantageous embodiments can be found, for example, in the respective subclaims. The content of the claims is incorporated into the content of the description by express reference, and vice versa.

[0005] The invention relates, more specifically, to a method for electronically controlling the air gap of an electric wheel brake for a motor vehicle. The electric wheel brake comprises, in particular, one or more brake shoes that are provided so that they can be electronically actuated and released by an electric actuator using one or more electronic control units (ECUs). The electronic air gap control or air gap maintenance method primarily comprises the following essential steps: Electrically moving to a (braking) rest position in which a specific clearance is set, and supplying electrical energy to the actuator (rest current supply) so that the approached rest position is maintained.

[0006] In the method according to the invention, the rest position of a vehicle wheel brake is therefore not defined for the first time in a conventional, rigid, mechanical manner, for example via the so-called adjuster device in mandatory combination with elastically pre-tensioned return springs on the basis of hydraulic drum brakes according to a known prior art, but for the first time is defined electrically as needed, ie individually as needed, and electrically regulated by defining an electrical energy individually.Consequently, the present invention makes it possible, surprisingly simply and by a stroke of luck, for the first time to offer a sufficiently robust and also precise as well as efficient, i.e. mass-market-suitable special control for maintaining an individualized, needs-based, rest position of a brake actuator in an electric car wheel brake, without at the same time triggering an uncontrollably high increase in equipment (sensor) expenditure on this highly stressed and safety-relevant car component.

[0007] In In a particularly practical specification, the electrical energy applied according to the invention is in particular an electrical current that is determined for each wheel using a microprocessor and is individually applied to the respective electric brake actuator. This is the so-called holding current according to the invention, which is particularly preferably transmitted as a regulated direct current by the control unit to the electrical actuator, and all of this is present in a direct current electrical system of a motor vehicle. The effect of this defined, regulated energy, in particular the defined holding current, is directed and dimensioned in such a way that, for example, a return effect of one (or more) elastic return springs, return means, roll-back ring, knock-back or similar.- which could directly or indirectly act on a brake shoe in a return direction ("backward") - is reduced at least by a slight, specific amount. Electrical energy individually applied to an electric wheel brake actuator for this adjustment of its rest position therefore causes at least one, possibly even relatively slight, actuator actuation process, which is suitable and intended to compensate for or gradually reduce opposing effects, such as spring-mechanical effects of return means with respect to the respective brake shoe(s), and thus to gradually compensate for this return means effect, so that no purely mechanically arbitrarily predetermined rearward end position of the brake shoes or brake pads applies, but rather a rest position for the respective wheel brake is adjusted as needed and defined by electro-energetic means.This electrically regulated rest position during vehicle operation according to the invention includes the advantageously required and individually controlled air gap or air gap range L for each wheel brake, which takes into account the prevailing or desired operating conditions and / or general conditions. With such controlled approach to the rest position of the friction brake, frictional wear resulting from diminishing wear parts is automatically compensated for and, at the same time, excessive resetting is efficiently prevented. Wear dimensions can be determined and adjusted for each wheel individually using "kiss point detection" (KP) of the respective wheel brake and / or by adjustment using actuator current detection.

[0008] In order to reduce the electrical load on the vehicle's electrical system, it may be determined that the described energetically defined and electrically actively maintained wheel brake rest position with a defined adjusted air gap position applies exclusively to active vehicle driving operation (vehicle driving operation detected - such as ignition on + parking brake released).

[0009] The problems described above, particularly those related to tolerances and dependence on operating parameters, can be avoided by means of wheel-specific electrical control. The electrical energy can be used to maintain the clearance for a period of time during which, in particular, no braking action is taking place. Accordingly, the electrical energy can be supplied continuously. The electrical energy can also be supplied situationally and / or as needed. In other words, the electrical energy is typically supplied as long as the clearance is to be maintained, typically as long as no braking force is to be generated. Interruptions, for example, due to control-related reasons, do not prevent or terminate the supply of electrical energy.

[0010] The electrical energy can be supplied, for example, in the form of a constant quiescent current, which is possible in the case of a simple electric motor. However, the electrical energy can also be supplied in a much more complex form, for example in electronically commutated motors, where, for example, phases are controlled specifically. The phases can be controlled constantly or variably while maintaining the air gap.

[0011] A brake clearance is understood, in particular, to be the distance between a brake shoe and a brake rotor, a brake disc, or a similar element. The clearance should, in particular, be large enough to avoid residual torque, i.e., to prevent braking torque from building up when no braking force is required. However, it should also be small enough to allow the wheel brake to be applied as quickly as possible. The rest position is typically the position along the actuator's travel path in which the clearance range L is set, so that the brake shoe(s) have the desired distance from the brake rotor.

[0012] According to one embodiment, the wheel brake is a drum brake. According to another embodiment, the wheel brake is a disc brake. The method described here has proven particularly effective for such wheel brakes. In principle, however, it can be used for all wheel brakes in which one or more brake shoes are actuated by an electric actuator.

[0013] In particular, the rest position can be continuously updated during wheel brake operation. This allows changes in the wheel brake that may occur over time to be taken into account. For example, wear on the wheel brake, which can be caused by abrasion of the brake pads, can be taken into account. The update can be achieved, for example, by recording force-displacement curves.

[0014] In one design, the wheel brake has a rear end stop for the brake shoe. It is fundamentally possible for such a rear end stop to be electrically actuated by an actuator, for example, to perform a brake shoe change. One or more return means may be present, which may be elastically preloaded spring means, and which can act on the brake shoe. In a drum wheel brake, for example, a return spring means may be clamped between two brake shoes as an elastically preloaded tension spring. This ensures that each brake shoe is, in principle, de-energized and permanently elastically preloaded toward the unactuated position (rear end stop).As a result, brake shoes generally tend to move into this released, unactuated position (rear end stop) in the event that a wheel brake is not to be applied, or in the event of a malfunction, so that no braking torque is generated under any circumstances.

[0015] According to one embodiment, however, the wheel brake has no mechanical return (spring) means / air gap adjustment means at all. Thus, the desired air gap range L / the desired air gap is set and maintained exclusively by the process according to the invention using the aforementioned supply of electrical energy. In particular, the adjuster already described above can be omitted. A mechanical air gap adjustment means could, for example, be designed such that the movement of the brake shoe(s) away from the drum or disc is adjustable and limited. Such a mechanical air gap adjustment means is not absolutely necessary when using the method described herein, but can nevertheless be present. This can save costs and effort if necessary.

[0016] In particular, the supplied electrical energy can have a maximum power of 1 W. Such values ​​have proven successful for typical applications. They are typically easy to accept, as they place little strain on a vehicle's electrical system and its energy balance, and are therefore acceptable for adjusting the clearance in the manner described herein. However, higher power levels can also be used in principle.

[0017] The supplied electrical energy can be regulated, in particular, to maintain the rest position. For example, monitoring of the rest position can be implemented, with the electrical energy being increased or decreased if a deflection from the desired rest position occurs. This can also be done, for example, in more complex motor control systems, such as phase control of an electronically commutated motor.

[0018] The actuator can, for example, be connected to the brake shoes so that it can actively retract the brake shoes. This can also be considered an independent inventive feature. For example, in this case, return means or other mechanical return means can be dispensed with. In other words, the actuator can actively actuate the brake shoes in both directions, so that they can also be removed from a brake rotor or a brake disc using the actuator. In particular, the actuator can be firmly connected to the brake shoes for this purpose, for example via joints.

[0019] The rest position can be adjusted in particular as a function of one or more parameters. Such parameters can be, for example, operating parameters such as temperature or aging. The rest position can be adjusted in particular based on a measured force-displacement characteristic curve or several measured force-displacement characteristic curves. Such force-displacement characteristic curves can, for example, be recorded while the motor vehicle is stationary and / or can be recorded during initialization. For example, the rest position can be redetermined at the start of an ignition cycle. Such an ignition cycle can be started, for example, when the motor vehicle is put back into operation after being parked, i.e. the driver activates the motor vehicle in order to drive off.

[0020] In a further development of the invention, in cooperation with and / or for all conceivable embodiments or variations of the control method and / or vehicle braking system, a mode-dependent air gap adaptation is suitable for a vehicle manufacturer to market an exemplary ecologically advantageous and / or driving pleasure-enhancing sporty added value function entirely without any special additional equipment expenditure, in that braking behavior can be designed in a simple, reproducible - mode-dependent - adaptable manner based on adaptation of the air gap control. The invention enables a mode-dependent definition of differently dimensioned, adaptable air gap positionings, which enables electronically machine-supported, i.e. automatic and / or driver-supported, pre-selectable, air gap adaptation and air gap mode definition.In this context, it is conceivable, for example, that the electronic control unit or a vehicle driver selects a sport mode for the air gap dimensioning, and wherein this sport mode cooperates, for example, with a particularly narrowly defined air gap width, so that on the basis of this sport mode selection, a particularly sporty-accelerated, ergo particularly idle-travel-reduced, safety-focused-accelerated vehicle braking behavior can be reproducibly guaranteed with a narrow air gap dimensioning, which can, for example, always guarantee the shortest stopping distances.In contrast to such a mode, the invention makes it possible, for example, to provide an "Off-Road" and / or "Green Mode," each with a gradually increased air gap, so that brake drag, and in particular gradual residual braking torque, are completely eliminated even in the presence of extreme brake contamination. This allows the advantages of a correspondingly modified braking behavior to be electronically reproduced as desired or when needed. The differentiation between the different air gaps, defined as required, is generally freely programmable and can be modified using software parameters at the lower vehicle level. This also requires manageable effort, but is protected against unauthorized misuse.A clearance mode selection may affect all electric wheel brakes in a braking system, or alternatively, it can be defined that a selective effect is intended only for very specific wheel brakes. For example, a selective effect refers exclusively to wheel brakes grouped in pairs in a brake circuit and / or a vehicle axle, namely, for example, selectively only for the wheel brakes of a front axle. For example, an adaptively adjusted clearance for a so-called Green Mode (vehicle on-road operation) can be dimensioned at least twice as large as in a so-called Sport Mode. A so-called Off-Road Mode (off-road operation, rough road operation), on the other hand, could be implemented with a clearance dimension that is three times higher due to contamination, for example.

[0021] The described adaptive electronic clearance control system and the corresponding electric braking system may finally include a so-called fail-safe mode for the purpose of particularly secure clearance control of its wheel brakes. In this context, the preprogrammed, defined fail-safe mode acts as a fallback for a brake system fault detected, for example. This has the consequence, for example, that all systems, components, and parts detected without errors, such as electric wheel brakes, are addressed with a safety-oriented clearance, which always ensures maximum driving safety while taking the detected fault into account. For safety reasons, any driver-assisted selection of the clearance mode, especially manual selection, is prohibited. This is because safety, i.e., the fail-safe mode, takes priority.

[0022] For the purpose of appropriate cooperation and / or coordination as well as interaction of a vehicle friction brake system with a regenerative vehicle brake system and vice versa, mutual electronic networking between electrical control units is provided. This electronic networking can include a control-related data exchange regarding the status and condition of the various components and systems, such as, in particular, data exchange regarding the air gap control and / or air gap mode selection. This makes it possible, for example, to very effectively mirror a systematically suitable off-road mode, sport mode, and / or green mode drive / regenerative braking configuration into the electrical control unit (ECU) of a parallel drive train / (regenerative) vehicle brake system by means of a comparison together with a specific air gap mode selection starting from the friction brake system, in a somewhat flanking / accompanying manner.

[0023] The invention further relates to an electronic braking system with at least one electronic control unit including a plurality of electric wheel brakes for a motor vehicle. All electric wheel brakes are configured to execute a clearance control method according to the present invention within the system. With regard to the method, all embodiments and variants described herein can be used.

[0024] In particular, such a wheel brake may have a control device configured to execute a method according to the invention. It may, in particular, have an actuator and one or more brake shoes that can be actuated by the electric actuator.

[0025] For example, return devices can still be used. After the actuator has moved to the clearance position, the position can be adjusted or, if necessary, reset by applying a permanent or situationally low current. This can be done particularly if frictional forces due to transmission hysteresis are smaller than the return forces. Low electrical power levels of, for example, a maximum of 1 W or less are permanently acceptable and do not lead to a significant temperature increase in the actuator. Should the clearance increase after "ignition off," it is the task of an algorithm to readjust the clearance, especially after the vehicle is restarted. Should the clearance become unacceptably small after the drum has cooled down, both the temperature model and the spreading force sensor can provide a correction.

[0026] According to one embodiment, return devices can be omitted, and the brake shoes can be coupled, in particular, to a spreading mechanism. Since, unlike with hydraulic actuation, the motor can actively retract the brake shoes upon release, no forces are present after the clearance is adjusted to change the clearance. It may be possible, particularly if the stored spring force is insufficient due to the wheel brake being preloaded, to use springs with reduced spring force. These minimize residual torque in the event of a fault, for example, a power failure, but cannot completely retract the transmission, particularly due to transmission friction.

[0027] Mechanical adjustment devices can be advantageously eliminated. The clearance adjustment can be performed very precisely using the method described here. Incorrect adjustments due to thermal disturbances or high actuation forces can be avoided. The clearance can be adjusted, particularly depending on the situation (mode selection). For example, it can be automatically set very small if a potential collision risk is detected, and it can be set very large for a rapid reduction of residual torques with subsequent adjustment to the ideal position. In particular, residual braking torques can be reduced, ideally to 0 Nm in the shortest possible time.

[0028] The present invention is systematically and, in the broadest sense, particularly predestined to make a particularly important ecological contribution to the required CO2 reduction / reduction of individual transport-related climate effects / i.e., a contribution to the reduction of greenhouse gases, at a reasonable cost through functional system and wheel brake improvements, without interfering with an evolutionarily defined vehicle architecture at an unreasonably costly rate. The invention is open to any cooperation with all energy sources. This applies to the given energy sources, such as combustion engines (liquid, gaseous), HEVs, EVs (battery technology), and even future energy sources such as hydrogen-based fuel cell configurations.

[0029] The method described herein can be used, for example, for electrically operated drum brakes or electrically operated disc brakes. In particular, all designs can be used, for example, Simplex, Duo-Servo, etc. The method can be used for service brakes, parking brakes, and combined service and parking brakes.

[0030] Typical adjusters used in state-of-the-art designs can also typically compensate for lining wear using displacement control and partially prevent unwanted readjustment due to hot drum expansion. These two control types typically represent a compromise between many different system conditions, part tolerances, etc., which are generally designed to prevent the worst-case scenario, such as excessive residual torque or jamming. As a result, such mechanical adjustment devices typically never achieve the ideal clearance.

[0031] The design described here allows the full potential of intelligent control to be exploited. The use of mechanical control structures and unnecessary components can be avoided.

[0032] In particular, the clearance position can be approached, and the permanent, controlled holding of the position can be achieved by means of permanent, particularly very low, actuator current to compensate for a return force or to make a necessary correction due to specific disturbances, such as vibration excitations or a new ignition cycle. The spreading device can also be coupled to the brake shoes, allowing the shoes to be rigidly fixed in both the actuation and release directions. In this case, the return means can be eliminated or at least reduced.

[0033] The invention will now be described with reference to the figure, which shows a schematic outline and essentially simplified example: Fig. 1 : an electric wheel brake in a first state, Fig. 2 : the wheel brake as in Fig. 1 in a second state, Fig. 3 : the wheel brake in a third state, Fig. 4 : Parts of a force-travel characteristic curve KL, KL' for different brake wear conditions Fig. 5 : the actuating force characteristic curve KL obtained by the responsible ESC-ECU, e.g. using force / torque sensor TS, including the actuator current characteristic curve I obtained synchronously with this using actuator current sensing, each plotted over time t, and Fig. 6 : simplified embodiment of an electronic motor vehicle braking system with ESC-ECU in network with an electrically recuperating drive train comprising a drive train ECU (M-ECU)

[0034] Fig. 1 shows a wheel brake 10 according to an exemplary embodiment in a first state. The wheel brake 10 is designed as a drum brake. For this purpose, it has a brake rotor 20, which is connected, in a manner not shown, to a shaft to be braked.

[0035] For actuation, the wheel brake 10 has an electric actuator 30. In this case, this is designed as a spreading unit. The wheel brake 10 further has a first brake shoe 40 and a second brake shoe 45. These are connected to the actuator 30 so that they can be pressed apart by the actuator 30. A first brake pad 50 is applied to the first brake shoe 40. Likewise, a second brake pad 55 is applied to the second brake shoe 45. Furthermore, the wheel brake 10 has a return means 60 which connects the two brake shoes 40, 45 to one another. This preloads the brake shoes 40, 45 in the event of non-actuation so that the brake pads 50, 55 do not contact the brake rotor 20. The build-up of a braking torque in the event that no actuation is to occur or a system error is thus prevented.

[0036] Fig. 1 shows a state in which the actuator 30 is not actuated, i.e., in which the brake shoes 40, 45 are in a maximally retracted position. A clearance L is set, which defines a distance between the brake pads 50, 55 and the brake rotor 20. The clearance L thus ensures that no braking torque is built up.

[0037] Fig. 2 shows a different state of the wheel brake 10. In this case, the clearance range / clearance L is reduced. For this purpose, electrical energy is applied to the actuator 30, so that it partially compensates for the effect of the return means 60. The brake pads 50, 55 are not yet in contact with the brake rotor 20, but in the event of an actuation, they can be applied more quickly than is possible based on the Fig. 1 shown state would be possible.

[0038] While applying a small amount of electrical energy does result in power consumption, this is so low that it plays no significant role in the load on the vehicle's electrical system, the heating of the actuator, or the vehicle's energy balance. However, this has the advantage that mechanical adjusters or similar mechanical devices for adjusting the clearance L can be dispensed with. Furthermore, the clearance L can be adjusted very precisely using the procedure described here.

[0039] Fig. 3 shows a state of the wheel brake 10 in which the brake pads 50, 55 are more worn than in the Fig. 1 und 2 This can be done, for example, by the following conditions with reference to Fig. 4 The clearance L should typically remain constant, however, so that tracking of a rest position is necessary. This can be achieved, for example, by increasing the energy supplied to the electric actuator 30 for adjusting the clearance L.

[0040] Fig. 4 shows a schematic of a force-displacement characteristic curve section KL when applying a wheel brake 10 for the purpose of explaining the adjustment or determination of a rest position within the framework of the control or regulation of an electric wheel brake 10. The uninterrupted solid characteristic curve section KL refers to a virtually unworn, new condition of brake wear parts, or, for example, in the case of an immediate connection to the replacement of all brake wear parts (essentially replacement of the brake pads +, if applicable, the brake rotor). A dotted characteristic curve section KL' documents the conditions associated with an advanced state of brake wear. The abscissa of the diagram shows a distance s along the travel path of an actuator 30. Due to the fundamental, qualitative discussion of the curve, no specific specification of a unit for the delivery path is necessary.The unit could be millimeters, for example. The ordinate represents a braking force F, which is typically measured in Newtons [N], and which can be measured, for example, by a force sensor FS installed in a wheel brake 10 or, alternatively or additionally with a braking torque-based brake control architecture, by a wheel braking torque sensor TS (Torque Sensor).

[0041] On this basis, the characteristic curve KL begins at point 1 in conjunction with a completely unhindered return action, such as a rear brake stop position, i.e., in the fully returned state of the actuator 30 and, for example, in conjunction with elastically unhindered preloaded return means 60. With an applied holding current, this actuator achieves the rest position 2 in the clearance range L. The actuator 30 is then braked, and the brake pads 50, 55 come into frictional engagement with the associated brake rotor 20 (brake disc or, as shown, brake drum) at point 3. This is evident at point 3 in that the measured force F increases very clearly in a quasi-linear manner along a characteristic curve KL.The ideally defined rest position is therefore assigned to the characteristic curve range L before the characteristic curve point 3, with the result that the thus specified clearance range L can be reproducibly located, displayed, and maintained for a subsequent service braking application in the non-actuated vehicle driving state, and this rest position is designated as point 2. Consequently, the electric wheel brake 10 is particularly well conditioned for a subsequent service braking application in the released braking state because the electric actuating device, using the electric actuator 30, does not have to bridge any unnecessarily extended free travel, release, play, etc., until a brake application point / kiss point at 3 is reached.

[0042] The discussion of the curve for KL' gives rise to the following remarks. With progressive wear of the brake wear parts, the characteristic curve KL to KL' is shifted to the right by the additional travel Δ of the actuating device (actuator 30), which is illustrated by the dotted characteristic curve branch KL'. For this case, too, the control unit ECU has the relevant sensor-acquired data (actuator current I + actuating force / braking torque). However, the allocation of the clearance range L' or the defined rest position 4 is offset to the right by the distance Δ due to the wear path. This means that the characteristic curve KL' is verified, measured, or followed during operation with a corresponding offset by Δ. Point 5, at which the new kiss point with its frictional contact, shifted by the additional travel Δ due to wear, manifests itself with a significant increase in force, is present with an "offset by Δ", this meansis very clearly shifted to the right by the distance Δ. Qualitatively as before, the defined decisive clearance range L' for actuator positioning is defined up to point 5, which must be approached and maintained in the brake release state. In other words, the new rest position is defined with point 4 and is approached and maintained.

[0043] Based on recurring, if necessary periodic, execution of the above process, it is now possible for the first time to successively and verifiably update a rest position for air gap calculation in a sufficiently precise and yet rational manner, or to adapt it to advancing brake wear, i.e., to compensate for it as needed and individually. For largely uninterrupted, successive wear adjustment, it is recommended that a rest position of an electric wheel brake 10, which is automatically newly learned or at least recognized by the ECU, for example, be relearned either periodically or at the beginning of each new ignition cycle, in order to operate the actuator on this basis. Accordingly, actual brake wear is taken into account in a clear, simple, yet precise manner.The clearance position can thus be used as the defined rest position for the actuating device / actuator 30 in an electronic control system based on the relevant ESC-ECU during vehicle operation. The rest position 2, 4 is controlled and maintained using a defined electrical energy when the released electric wheel brake 10 is not intended to generate any braking force during normal vehicle operation.

[0044] In addition to Fig. 4 clarified Fig. 5 schematically in the upper part of the figure, an exemplary characteristic curve KL, and with the corresponding actuator current curve I in the lower part of the figure synchronously. The two curves each start from an actively held rest point 1 under a holding current I1, so that the actuator 30, which is relatively low and actively energized for the rest position, counteracts an imposed return spring force via its release clearance range L. At α - corresponding to point 2, brake application begins and a current increase with current peak I 2 symbolizes the start of a brake actuator drive train. From time β corresponding to kiss point KP = 3, the brake application force is noticeably increased, which is accompanied by a quasi-linear current ramp up to a maximum peak in I 3 . This is followed by a gradual, low current reduction phase and a constant current phase without any significant loss of application force, which embodies stationary service braking.A brake release action follows at time γ in that the termination of a service brake request is physically processed with different current gradients (recognizable by three differently reduced, decreasing gradients of the current curve) until the new brake release position is reached with a new brake rest position at time 1' = δ. With and after δ, the holding current is reduced to I1' so that the actuator 30 approaches and holds the new active rest position on this basis, thereby implementing a new clearance setting until further notice.

[0045] The Fig. 6illustrates a largely self-explanatory, electrically networked vehicle braking system with electric wheel brakes and brake sensors TS, which are suitable and intended for implementing the invention, as well as a recuperatively enhanced electric vehicle drive EM including the associated electrical control unit M-ECU, which, among other things, communicates with the electrical control unit of the braking system ESC-ECU. For reasons of functional safety, each electric wheel brake 10 is assigned its own local wheel brake control unit WCU, so that in an emergency if other components fail, emergency braking measures can be carried out without endangering occupant safety.

[0046] The steps mentioned in the method according to the invention can be carried out in the specified order. However, they can also be carried out in a different order, as long as this is technically reasonable. The method according to the invention can be carried out in one of its embodiments, for example, with a specific combination of steps, in such a way that no further steps are carried out. However, in principle, further steps can also be carried out, even those not mentioned.

[0047] It should be noted that features may be described in combination in the claims and the description, for example, to facilitate understanding, although they may also be used separately. Those skilled in the art will recognize that such features may also be combined independently with other features or combinations of features.

[0048] References in subclaims may indicate preferred combinations of the respective features, but do not exclude other combinations of features. List of reference symbols

[0049] 1 Rear end stop / release end stop 2 Rest position (with defined clearance) 3 / KP Kiss point 4 Rest position (with defined clearance) - advanced brake wear condition 5 Kiss point - advanced brake wear condition 10 Wheel brake 20 Brake rotor (brake drum / brake disc) 30 Actuator 40, 45 Brake shoes 50, 55 Brake pad 60 Return means / return spring ECU Electrical control unit EM Electric vehicle (gearbox) motor (with integral regenerative brake) F Force [Newton] FA Vehicle front axle FR Front axle wheel brake, right FL Front axle wheel brake, left HMI Human-machine interface for service brake actuation RR Rear axle wheel brake, right RL Rear axle wheel brake, left TS Wheel brake force and / or wheel brake torque sensor WCU Electrical wheel brake control unit WSS Wheel rotation sensor I Current [A] t Time s (Actuator travel) KL Characteristic curve KP Kiss point L Clearance range / clearance RA Vehicle rear axle α,β,γ,δ Time

Claims

1. Method for electronic air gap control (L) of an electrical wheel brake (10) for a motor vehicle, comprising a brake rotor (20) and a brake stator having an electric actuator (30), and at least one adjustable brake shoe (40, 45) which is activatable in the direction of the brake rotor (20) by the electric actuator (30) and is mounted so as to be restorable, wherein the method comprises the following steps: - electrically adopting a defined resting position in such a manner that a defined air gap range (L) between the brake shoe (40, 45) and the brake rotor (20) is adjusted; and - supplying electric energy to the electric actuator (30) in a defined manner so that the actuator (30) maintains the adopted resting position.

2. Method according to Claim 1, - wherein the air gap (L) is in each case adjusted and maintained in a wheel-specific manner by a control unit (ECU).

3. Method according to Claim 1 or 2, - wherein the wheel brake (10) is a drum brake.

4. Method according to Claim 1 or 2, - wherein the wheel brake (10) is a disk brake.

5. Method according to one or a plurality of the preceding claims, - wherein the resting position is continuously updated during operation of the wheel brake (10).

6. Method according to one or a plurality of the preceding claims, - wherein the resting position is automatically verified and / or updated by means of the control unit (ECU) each time the brake is activated.

7. Method according to one or a plurality of the preceding claims, - wherein the wheel brake (10) has one or a plurality of restoring means (60) which pre-loads / pre-load the brake shoes (40, 45) to a non-activated position.

8. Method according to one or a plurality of the preceding claims, - wherein the wheel brake (10) does not have any mechanical air gap adjustment means.

9. Method according to one or a plurality of the preceding claims, - wherein the electric energy supplied includes an output of, for example, at most approximately 1 W.

10. Method according to one or a plurality of the preceding claims, - wherein the electric energy supplied is controlled to maintain the resting position.

11. Method according to one or a plurality of the preceding claims, - wherein the actuator (30) is connected to the brake shoes (40, 45) in such a way that said actuator (30) can actively retract the brake shoes (40, 45).

12. Method according to one or a plurality of the preceding claims, - wherein the resting position is tracked as a function of one or a plurality of parameters.

13. Method according to Claim 10, - wherein the resting position is tracked based on measured force / displacement characteristic lines (KL).

14. Method according to one or a plurality of the preceding claims, - wherein the resting position is newly determined at the beginning of each ignition run.

15. Method according to one or a plurality of the preceding claims, - wherein an air gap mode selection is provided.

16. Method according to one or a plurality of the preceding claims, - wherein a fail-safe mode is programmed for an identified fault, which has priority over any air gap mode selection.

17. Electronic motor vehicle brake system having at least one electronic control unit (ECU), and comprising a plurality of electrical wheel brakes (10), - which is specified and configured to carry out a method according to one or a plurality of preceding Claims 1 to 16.

18. Electronic motor vehicle brake system according to Claim 17, characterized in that a vehicle powertrain and / or a recuperative motor vehicle brake system is defined having at least one electronic control unit (ECU) and having a motor vehicle drive and / or an actuated powertrain brake, and wherein the electronic control units (ECUs) of the systems are networked and / or cooperate with one another for the purpose of exchanging data and / or for the purpose of exchanging configurations.