DE102020215965A1 - Wear monitoring method and electrically actuated motor vehicle brake - Google Patents

Abstract

The invention relates to a method for monitoring wear on an electrically actuated motor vehicle brake along a travel path of an actuator, a zero point being determined when the air play is initialized and a global correction value being able to monitor the wear over an entire period of use of brake pads. The invention also relates to an electrically operated motor vehicle brake for carrying out such a method.

Description

The invention relates to a method for monitoring wear, in particular lining wear, of an electrically actuated motor vehicle brake along a travel path of an actuator and an associated electrically actuated motor vehicle brake.

Electrically actuated motor vehicle brakes can be designed, for example, as disc brakes or as drum brakes. Typically, a clamping force is generated by means of an electric motor, a primary gear and a rotation/translation gear. To measure clamping forces, a clamping force sensor mounted in a clamping module housing is typically used, which delivers a signal that corresponds to the force with which the brake linings are pressed onto a brake disc or brake drum.

In the case of electrically actuated motor vehicle brakes, the thickness of a brake pad naturally decreases during operation. As a result, a contact position, in which a brake pad touches a brake disk or a brake drum, shifts along a travel path of the actuator. This can be referred to as wear and tear. It can also happen that this shift goes so far that reliable braking is no longer possible or the brake pads have to be replaced.

It is therefore an object of the invention to provide a method for monitoring wear of an electrically actuated motor vehicle brake along a travel path of an actuator, which is designed alternatively or better than known designs. It is also an object of the invention to provide an electrically actuated motor vehicle brake for carrying out such a method.

According to the invention, this is achieved by a method and a motor vehicle brake according to the respective main claims. Advantageous configurations can be found, for example, in the respective dependent claims. The content of the claims is made part of the content of the description by express reference.

• - Durchführen einer anfänglichen Lüftspielinitialisierung, dabei Setzen eines globalen Korrekturwerts auf einen ersten Startwert, eines Initialisierungskorrekturwerts auf einen zweiten Startwert und eines aktuellen Korrekturwerts auf einen dritten Startwert, und Setzen eines Nullpunkts entlang des Verfahrwegs des Aktuators, dann
• - bei jeder Bremsbetätigung oder bei einigen Bremsbetätigungen Bestimmen einer temporären Kontaktposition relativ zum Nullpunkt und jeweiliges Aktualisieren des aktuellen Korrekturwerts basierend auf der temporären Kontaktposition, und dann Setzen des globalen Korrekturwerts auf die Summe aus Initialisierungskorrekturwert und aktuellem Korrekturwert, und
• - bei jeder weiteren Lüftspielinitialisierung Setzen des Initialisierungskorrekturwerts auf den globalen Korrekturwert, Setzen des aktuellen Korrekturwerts auf null und Aktualisieren des Nullpunkts.

The invention relates to a method for monitoring wear of an electrically operated motor vehicle brake along a travel path of an actuator. The procedure has the following steps:

• - performing an initial clearance initialization, thereby setting a global correction value to a first starting value, an initialization correction value to a second starting value and a current correction value to a third starting value, and setting a zero point along the travel of the actuator, then
• - at each brake application or at some brake applications, determining a temporary contact position relative to the zero point and respectively updating the current correction value based on the temporary contact position, and then setting the global correction value to the sum of the initialization correction value and the current correction value, and
• - With each further clearance initialization, setting the initialization correction value to the global correction value, setting the current correction value to zero and updating the zero point.

An electrically operated motor vehicle brake and in particular its wear can be monitored in a simple manner by means of such a method. This can in particular be wear on the brake pads. In particular, an aggregated displacement of a position at which the brake pads and brake disk or brake drum come into contact with one another can be tracked in a simple manner, even over a longer period of time.

Initial slack initialization is typically performed immediately after brake pad replacement. It provides a zero point along the traversing path of the actuator, which from then on initially serves as the zero point of a coordinate system to be used. The global correction value is a value that typically increases between two brake pad changes and indicates how much a position at which the brake pads are in contact has changed compared to the last brake pad change. The initialization correction value typically indicates a value of such a change up to the last clearance initialization. A clearance initialization is in particular a process which is carried out independently of an actual brake actuation in order to determine a new zero point. Such a new zero point is in particular that position along the travel path of the actuator at which contact of the brake linings just occurs. It will be described below as a Such a zero point can be determined. The current correction value is typically the one that indicates changes since the last clearance initialization.

The first starting value, the second starting value and/or the third starting value can preferably be zero. This enables a particularly simple design. In this case, all three correction values start with the value zero.

A brake actuation is typically an actuation which is carried out on the basis of a clamping force request from a driver or vehicle electronics in order to actually brake a motor vehicle. Measurements can be carried out in accordance with a clearance initialization.

As mentioned, the temporary contact position, which is determined when the brake is actuated, is to be seen relative to the zero point, specifically relative to the currently valid zero point. Here, the origin represents a starting point of a coordinate system, and a value of the temporary contact position is measured relative to this origin. On the other hand, when the clearance is initialized, the zero point can be shifted because a new point for the contact of the brake pads has been determined along the travel path of the actuator.

According to one embodiment, the current correction value is updated by multiplying it by a predetermined factor and adding thereto the temporary contact position multiplied by a difference between the value one and the factor. This allows the current correction value to be adjusted smoothly, so that a possible one-off outlier in a measurement does not have a significant impact on the calculation. The specified factor acts as a filter. Basically, the currently valid current correction value is received and updated, i.e. it is changed relative to the zero point, taking into account the specified factor and the temporary contact position just determined. If the specified factor is high, the change is rather slow. If the specified factor is low, the current correction value changes more quickly.

The current correction value can also be updated by adding a specified change value to the correction value. The previously applicable current correction value is therefore taken and the specified change value is added to it. The predefined change value can thus be the largest possible step in which the current correction value is updated after a brake actuation. A delayed response and thus a filter function can also be achieved in this way. However, if the correction value is to be changed by less than the specified change value, the specified change value is typically not exhausted and the correction value is only updated to the extent necessary.

According to one embodiment, the current correction value can be updated by setting it to the temporary contact position. This corresponds to an immediate change of the current correction value to a new value without a filter function.

Generally speaking, the current correction value can be updated, in particular using a filter function. This makes it possible to ensure that individual values that may be incorrect when measuring the temporary contact position only have a limited effect and that the current correction value is adjusted smoothly.

According to one embodiment, the current correction value is only updated if a difference between the temporary contact position and the current correction value is at least as great as an update threshold. In this way it can be specified that an update only takes place if there is also a significant change. The calculation effort can be reduced as a result.

The global correction value, the initialization correction value and/or the current correction value can be stored in a non-volatile memory in particular. This ensures that these are still available even after a power failure or other events. The global correction value and/or the initialization correction value and/or the current correction value can be stored in particular after it has changed by at least a predetermined threshold value and/or immediately before the motor vehicle brake is switched off. It can thereby be ensured that a respective storage takes place in the case of relevant changes and/or that a storage takes place before an expected power failure in order to be able to continue the calculations reliably after the power failure.

An initial clearance initialization can be carried out in particular immediately after a brake pad change. For example, it can be entered into a control of a motor vehicle that such a brake pad change has taken place, and an initial clearance initialization can be carried out in response thereto. A further clearance initialization can be carried out in particular for some or all startups. Such a start-up can be, for example, starting a motor vehicle from a parked state, with further clearance initializations during a journey, for example when stopping at a traffic light, also being possible in principle.

The zero point may be set to a contact position upon initial clearance initialization, and/or updated to a contact position upon further clearance initialization. This is a contact position, which is determined, for example, as described below, in which case the contact position does not necessarily have to be measured relative to the zero point as mentioned above, but is measured or fixed along the entire travel path of the actuator. The new zero point provides a new reference in the coordinate system for all further calculations.

• - Zuspannen der Kraftfahrzeugbremse ausgehend von einer unbetätigten Position, dabei Überwachen einer Spannkraft,
• - wenn die Spannkraft einen Spannkraftschwellenwert erreicht, Bestimmen einer aktuellen Position, und
• - Bestimmen der Kontaktposition basierend auf der aktuellen Position.

A respective contact position can be determined in particular as follows:

• - Application of the motor vehicle brake starting from an unactuated position, monitoring a clamping force,
• - when the clamping force reaches a clamping force threshold, determining a current position, and
• - Determine contact position based on current position.

This enables a simple and reliable determination of a contact position, with the motor vehicle brake only being applied and the acting force being monitored. The current position, which is the position of the actuator at which the clamping force threshold value is reached, can be determined by a simple threshold value comparison. In principle, the procedure can be used both for the contact position and for the temporary contact position.

In particular, the contact position can be determined by subtracting a distance value from the current position. Such a distance value can be determined empirically, for example, and can indicate how far away the current position is typically from the actual contact position. This has proven to be a reliable practice.

In particular, a position of the actuator can be determined based on a measured motor angle. In this case, in particular, a transmission factor can be used, in which case the position can be determined in particular as the product of the motor angle and transmission factor.

In particular, the method allows the use of a motor angle sensor that does not require a global reference. By using the global correction value, the wear of the pads can still be tracked over a long period of time, even if the zero point is updated with each additional clearance initialization. In particular, this measure ensures that the actuator remains within its position limits if the actuator speed, which leads from the sign in the direction of the position limit, is reduced to zero the closer its position is to the limits. This is particularly important when these position limits are defined by the actuator's available working space and exceeding these limits means that the actuator moves against its mechanical stop.

According to one development, it is provided that an actuator speed is limited as a function of a position of the actuator. In particular, the actuator speed can be limited to a lower value the closer the position of the actuator approaches a limit. Typically, the position is bounded by two boundaries. It can thereby be ensured that when a predefined limit value is approached, the actuator only runs more slowly and thus a displacement of brake pads on a brake disk or a brake drum also takes place more slowly. This can prevent you from building up strength too quickly. In particular, the position can be seen in absolute terms along a maximum working range and can be determined taking into account a zero point, in particular also an updated zero point, and/or the global correction value and/or the initialization correction value, so that such a limitation is advantageous in the context of the procedure described herein can be carried out.

An alarm message is preferably issued if the global correction value exceeds a safety threshold value. Such a safety threshold value can indicate, for example, that the brake linings have already worn too far and should therefore be replaced in the near future. This alarm message can, for example, be displayed optically and/or acoustically to a driver of the motor vehicle so that he can change the brake pads or visit a workshop.

The invention also relates to a motor vehicle brake that is configured to carry out a method described herein. With regard to the method, all of the versions and variants described herein can be used. The advantages already described above can be achieved accordingly.

An electrically actuated motor vehicle brake according to the invention can in particular have one or more brake linings and a brake disk or a brake drum. It can also have an actuator which has an electric motor to drive it and which is designed to press the brake shoes against the brake disc or against the brake drum. Furthermore, the motor vehicle brake can typically have at least one clamping force sensor. It can also in particular have an electronic control device which is configured to carry out a method according to the invention.

• 1: einen Verfahrweg eines Aktuators und zugehörige Kräfte,
• 2: eine Bestimmung einer Kontaktposition,
• 3: eine Verschiebung von Kraftverläufen mit der Zeit,
• 4: beispielhafte Berechnungen, und
• 5: eine Vorgehensweise zur Begrenzung einer maximalen Winkelgeschwindigkeit.

The person skilled in the art will derive further features and advantages from the exemplary embodiment described below with reference to the attached drawing. show:

• 1 : a travel of an actuator and associated forces,
• 2 : a determination of a contact position,
• 3 : a shift in force curves over time,
• 4 : exemplary calculations, and
• 5 : an approach to limiting a maximum angular velocity.

1 shows schematically a travel of an actuator and associated clamping forces.

The travel distance, also referred to as the working range, of an electrically operated motor vehicle brake is typically limited and structurally determined by the mechanical structure. It is typically selected in such a way that a thickness of a brake disc or brake drum, a thickness of friction linings, a lining clearance to be set and a sufficient position reserve can be taken into account. 1 shows an example of an arrangement for a case in which an electrically operated motor vehicle brake is equipped with new pads. A position X _actuator of the actuator along a travel path is specified on the horizontal axis and a clamping force F _SP is specified along the vertical axis. The maximum possible working range MAB runs between the limits X _Mech,Min and X _Mech,Max . Within this area there is an available working range VAB between the limits which are drawn by the distances ΔX _Min,Reserve and ΔX _Max,Reserve . At a distance ΔX _Min from the left end, there is a standby position SP at a position X _Standby . A contact position KP is located at a further distance X _LS , which indicates the clearance. This defines the zero point of a coordinate system of a clamping position X _SP in the horizontal direction, ie X _SP =0. How out 1 It is easy to see that the clamping force F _SP is zero to the left of the contact position KP and increases more than linearly to the right of it. This clamping force F _SP can be measured and also used to determine the contact position KP.

To determine the position X _actuator or clamping position X _SP , a motor angle sensor is available, which provides an angle signal φ _motor . Such a motor angle sensor is typically already present, particularly in the case of electrically commutated motors, for the purpose of motor control. The motor angle φ _motor and the position X _actuator are multiplicatively linked to each other via a gear ratio factor i: $${\text{X}}_{\text{actuator}}=\text{i *}{\mathrm{\phi }}_{\text{engine}}.$$

Such a motor angle sensor is typically a sensor that can only measure relative motor rotations, but not in relation to an absolute reference point. Thus, for example, a position relative to an ad hoc defined reference point, such as a specific contact position. The method described herein is implemented in such a way that such a motor angle sensor without an absolute reference point is sufficient. A motor angle sensor with an absolute reference point can thus advantageously be dispensed with.

The standby position X _standby is the position with a defined distance X _LS from the lining to the brake disc or brake drum, to which the actuator is moved when there is no force request. It is also referred to as the air play position. The contact position KP represents the position of the actuator at which the linings are just in contact with the brake disc or brake drum and, with regard to the actuation of a wheel brake, represents the transition from the non-forced to the non-positive movement. Knowing this contact position KP is typically important for a force control system so that, for example, the standby position X _standby can be approached correctly and a defined distance between the brake pads and the brake disc or brake drum can be set in this position.

2 shows an advantageous procedure for determining a contact position. The motor vehicle brake is applied so that the position, starting from the standby position, first traverses the clearance and then contact between the brake lining and the brake disc or brake drum is achieved at the contact position KP. However, this cannot yet be measured directly. For this reason, clamping continues until the clamping force F _SP reaches a clamping force threshold value F ₁ . If such a threshold value exceeding is detected, then the actuator is at a current position X ₁ . A distance value is now subtracted from this, which indicates a typical, for example empirically determined, distance between the current position X ₁ and the contact position KP. This allows an exact determination of the contact position KP. In this way, a new zero point can be determined when an air gap is initialized, and a temporary contact position can be determined relative to a zero point when the brake is actuated.

The process just described can be carried out, for example, during an initial clearance initialization. In this case, a zero point X ₀ is defined, which, from its determination, serves as the zero point of the coordinate system for the clamping position X _SP and in particular also for a temporary contact position. This process is also possible for further clearance initializations.

As in 3 As can be seen, during operation of a motor vehicle brake there is a displacement of the force build-up along the horizontal axis. An initial force characteristic is shown in dashed lines, which can be valid, for example, immediately after a brake pad change. After several braking operations, this curve shifts further to the right, with an associated curve being shown as a solid line. The curve is shifted to the right by an amount ΔX. Such a shifting of curves is fundamentally dependent on the use of the motor vehicle brakes, it being assumed that ultimately every braking operation leads to at least minor wear. As will be described below, a resulting change in the behavior of the motor vehicle brake can be detected.

For this purpose, an initial clearance initialization is always carried out, namely immediately after the brake pads have been changed. In this case, a zero point is determined along the travel path of the actuator, as described above with reference to FIG 2 was described. A global correction value X _{SP,Korr,Summe} is initially set to a first start value S1, typically to the value zero. Using this global correction value, changes can be tracked over a longer period of time. Furthermore, an initialization correction value X _{SP,Corr,Summe,Last LS} is initially set to a second start value S2, typically to the value zero, with this initialization correction value _{XSP,Corr,Summe,Last LS} being used for a respective change to to track another initialization. Furthermore, a current correction value X _SP,Korr is initially set to a third starting value S3, typically to the value zero, with this current correction value X _SP,Korr being used to indicate a change since the respective last further initialization, or initially as well since initial airplay initialization. For clarity, these initializations are in 4a shown.

In principle, a motor vehicle brake can be actuated regularly during operation of a vehicle in order to generate a braking force and thus brake or even stop the vehicle. In the case of such a brake actuation, a respective determination of a temporary contact position relative to the zero point can take place, specifically in the manner described further above in principle with reference to FIG 2 was described. This temporary contact position relative to the zero point is denoted by ΔX because it indicates the displacement relative to the last determined zero point.

The current correction value X _SP,Corr is then updated. According to a preferred embodiment, the current correction value X _SP,Korr is not immediately completely updated to the temporary contact position ΔX, but as part of a filter function f can be implemented using a given factor λ as follows: $${\text{X}}_{\text{SP}\text{,corr}}=\mathrm{\lambda }*X_{\text{SP}\text{,corr}}+\left(1-\mathrm{\lambda }\right)*\mathrm{\Delta }\text{X}$$

The definition of the parameter λ can in particular be between zero and one. It can thus be specified whether errors are to be filtered rather or whether high adaptation dynamics are to be achieved. In the first case λ can be large or close to one, in the second case λ can be small or close to zero. As an alternative to this, an immediate update of the current correction value X _SP,Korr to the temporary contact position ΔX is also possible, or the update can take place in predetermined maximum steps.

Simultaneously with the update of the current correction value X _SP,Corr to a new value as just described, the global correction value X _{SP,Corr,Summe} is also recalculated, namely to a sum from the currently valid initialization correction value X _{SP,Corr,Summe,Last LS} and the current correction value X _SP,Corr . The global correction value X _{SP,Korr,Summe} is therefore included in each recalculation of a current correction value X _SP,Korr . For clarity, the calculations are in 4b shown.

If a further clearance initialization takes place, for example if the vehicle is put into operation after it has been stationary, a new zero point is first determined. This is done as with reference to 2 described, wherein a determined contact position along the travel path represents the new zero point of a coordinate system. The initialization correction value X _{SP,Corr,Summe,Last LS} is set to the global correction value X _{SP,Corr,Summe} in such a further clearance initialization, so that it determines the shift in the zero point that is already present when the further clearance initialization is carried out relative to the initial clearance initialization indicates the zero point. The current correction value X _SP,Korr is set to zero at the same time. When the brakes are actuated, a calculation can then be carried out again, which updates the values as described in the previous paragraph. For clarity, the calculations are in 4c shown.

The procedure just described enables uninterrupted tracking of a change in the zero point due to abrasion, with the global correction value X _SP,Corr,Sum typically being stored in a non-volatile memory and ensuring uninterrupted monitoring. It is therefore also available if the vehicle has been switched off in the meantime or even if the power has failed. The initialization correction value X _{SP,Corr,Summe,Last LS} and the current correction value X _SP,Corr , on the other hand, do not necessarily have to be stored in a non-volatile memory, since they are only used between two further clearance initializations, for example during normal operation of a vehicle . However, if, for example, the current correction value X _SP,Korr is also to be retained during a rest phase of the vehicle, since no further clearance initialization is carried out when it is restarted, for example, this can also be stored in a non-volatile memory.

5 shows a procedure for limiting an actuator speed ω, which can be specified, for example, as an angular speed or as revolutions per minute. It can be seen here that at a position X _actuator which approaches a right-hand end, a maximum actuator speed ω _Max within a range ΔX _Max,ε decreases towards the end down to the value 0. The actuator can therefore no longer be operated at its maximum possible angular velocity within this range ΔX _Max,ε , but moves more slowly in order to achieve slower clamping at this end range. In addition, reducing the maximum possible angular velocity down to the value zero means that the actuator does not exceed the available working range VAB in the direction of application. Depending on the position of the contact, this can also mean that a requested clamping force cannot be set. The same applies to the left-hand side, with a range ΔX _Min,ε being provided at this point, within which the maximum actuator speed in the opposite direction, referred to here as ω _Min , decreases towards the end to the value zero. It should be mentioned that instead of the linear curves shown here, more complex curves are also possible. Safety can be increased because overloading of the motor vehicle brake at its limit areas is avoided.

Furthermore, in 5 the meaning of the global correction value X _SP,Corr,Sum is also shown. Compared to the situation of 1 the force characteristic is shifted considerably further to the right. It is therefore considerably closer to the right limit of the available working area. This offset is given by the global correction value X _SP,Corr,Sum .

The described limitation of the actuator speed can therefore be carried out particularly advantageously in connection with the calculation of the global correction value as described, since the global correction value can be used to track the position of the actuator during braking and thus also to approach limits over a longer period of time.

Mentioned steps of the method according to the invention can be carried out in the order given. However, they can also be executed in a different order, as far as this is technically reasonable. In one of its implementations, for example with a specific combination of steps, the method according to the invention can be carried out in such a way that no further steps are carried out. In principle, however, further steps can also be carried out, including those which are not mentioned.

It should be noted that in the claims and in the description features can be described in combination, for example to facilitate understanding, although they can also be used separately. The person skilled in the art recognizes that such features can also be combined independently of one another with other features or combinations of features.

Back-references in dependent claims can identify preferred combinations of the respective features, but do not exclude other combinations of features.

Reference List

FSP

resilience

F1

Tension Threshold

X1

actual position

MAB

Maximum working area

VAB

Available workspace

XMech,Min, XMech,Max.

Limits of the work area

ΔXMin,reserve, ΔXMax,reserve

distances

ΔXMin

Distance of the standby position

SP

standby position

XSP

clamping position

X0

zero point

CP

contact position

Xactuator

position

φmotor

motor angle

X0

zero point

ω

angular velocity

ΔX

temporary contact position

XSP,Corr,Total

global correction value

XSP,Corr,Sum,Load LS

initialization correction value

XSP, corr.

current correction value

f

filter function

S

starting values

ω

actuator speed

ωmax, ωmin

maximum actuator speed

ΔXMax,ε, ΔXMin,ε

areas

Claims (19)

Method for monitoring wear of an electrically operated motor vehicle brake along a travel path of an actuator, the method having the following steps: - Carrying out an initial clearance initialization, setting a global correction value (X _{SP, Korr, Sum} ) to a first starting value (S1), one Initialization correction value (X _{SP,Korr,Summe,Last LS} ) to a second start value (S2) and a current correction value (X _SP,Korr ) to a third start value (S3) and setting a zero point along the travel path of the actuator, then - at each Brake application or in some brake applications determining a temporary contact position (ΔX) relative to the zero point and respectively updating the current correction value (X _SP,Korr ) based on the temporary contact position (ΔX), and then setting the global correction value (X _SP,Korr,Sum ) to the sum of the initialization correction value (X _{SP,Corr,Summe,Last LS} ) and the current correction ture value (X _SP,Corr ), and - with each further clearance initialization, setting the initialization correction value (X SP,Corr,Summe _{,Last LS} ) to the global correction value (X _SP,Corr,Sum ), setting the current correction value (X _SP,Corr ) to zero and updating the zero point. procedure after claim 1 , - whereby the current correction value (X _SP,Korr ) is updated by - multiplying it by a predetermined factor (λ), and - to this the temporary contact position (ΔX) multiplied by a difference between the value 1 and the factor ( λ), is added. procedure after claim 1 , - the current correction value (X _SP,Korr ) being updated in that a predetermined change value is added to the current correction value (X _SP,Korr ). procedure after claim 1 , - where the current correction value (X _SP,Korr ) is updated by setting it to the temporary contact position (ΔX). Method according to one of the preceding claims, - the current correction value (X _SP,Korr ) being updated using a filter function. Method according to one of the preceding claims, - wherein the current correction value (X _SP,Korr ) is only updated if a difference between the temporary contact position (ΔX) and the current correction value (X _SP,Korr ) is at least as large as an update threshold value . Method according to one of the preceding claims, - wherein the first starting value (S1) is zero and/or the second starting value (S2) is zero and/or the third starting value (S3) is zero. Method according to one of the preceding claims, - wherein the global correction value (X _{SP,Korr,Summe} ), the initialization correction value (X _{SP,Korr,Summe,Last LS} ) and/or the current correction value (X _SP,Korr ) in a non-volatile memory get saved. Method according to one of the preceding claims, - the global correction value (X _SP,Corr,Sum ) and/or the initialization correction value (X _{SP,Corr,Sum, Last LS} ) and/or the current correction value (X _SP,Corr ) being stored after it has changed by at least a predetermined threshold value, and/or immediately before the motor vehicle brake is switched off. Method according to one of the preceding claims, - wherein an initial clearance initialization is carried out immediately after a brake lining change. Method according to one of the preceding claims, - with further clearance initialization being performed on some or all startups. Method according to one of the preceding claims, - wherein the zero point is set to a contact position (KP) at the initial clearance initialization, and/or is updated to a contact position (KP) at a further clearance initialization. Method according to one of the preceding claims, wherein a respective contact position (KP) is determined as follows: - applying the motor vehicle brake starting from an unactuated position, monitoring a clamping force (F _SP ), - if the clamping force (F _SP ) exceeds a threshold value (F ₁ ) reached, determining a current position (X ₁ ), and - determining the contact position (KP) based on the current position (X ₁ ). procedure after Claim 13 , - where the contact position (KP) is determined by subtracting a distance value from the current position (X ₁ ). Method according to one of the preceding claims, - wherein a position (X _actuator ) of the actuator is determined based on a measured motor angle. Method according to one of the preceding claims, - wherein an actuator speed (ω) depending on a position (X _actuator ) of the actuator is limited. procedure after Claim 16 , - whereby the actuator speed (ω) is limited to a lower value the closer the position (X _actuator ) of the actuator approaches a limit (X _Mech,Min , X _Mech,Max ). Method according to one of the preceding claims, - an alarm message being output if the global correction value (X _SP,Corr,Sum ) exceeds a safety threshold value. Motor vehicle brake configured to carry out a method according to any one of the preceding claims.

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