EP2004466A1

EP2004466A1 - Method and processing unit for determining a performance parameter of a brake

Info

Publication number: EP2004466A1
Application number: EP07704460A
Authority: EP
Inventors: Henry Hartmann; Leopold Krausen
Original assignee: Siemens AG; Continental Automotive GmbH
Current assignee: Continental Automotive GmbH
Priority date: 2006-03-31
Filing date: 2007-02-09
Publication date: 2008-12-24
Also published as: WO2007113033A1; CN101460347A; DE102006015034B4; US20090164172A1; DE102006015034A1

Abstract

The invention relates to a method for determining a performance parameter of a brake having a first (311) and a second (313) brake element which, in order to generate a friction force (FR) and a friction torque (NR), can be placed in interaction, wherein a first quantity (204a, 204b) of friction coefficients (μ) between the first (311) and the second (313) brake element is determined in the field, the first quantity (204a, 204b) of friction coefficients (μ) is compared with a predetermined second quantity (204) of friction coefficients (μ), and the performance parameter is determined on the basis of a deviation of the first (204a, 204b) and the second quantity (204), wherein the deviation is obtained from the comparison. Additionally proposed are a corresponding processing unit, a computer program and computer program product.

Description

description

Method and arithmetic unit for determining a performance parameter of a brake

The invention relates to a method for determining a performance parameter of a brake, a corresponding computing unit, a corresponding computer program and a corresponding computer program product.

State of the art

The prior art has a variety of different brakes. For example, brakes which can be actuated by cable pull, linkage, hydraulic fluid or compressed air are mentioned here. In particular, in motor vehicles in addition to the conventional hydraulically actuated increasingly also electrical or electro-mechanical brakes are used, in which the brake is no longer supplied manually by the driver but electrically or electromechanically by an electric motor or detected and solved, for example. (Self-reinforcing ) electromechanical disc brakes. In such disc brakes, an electric actuator applies an actuating force, which applies the friction lining of the brake to the rotating brake disc. An additional predictable

Selbststarkungseinrichtung in the form of a wedge assembly uses the kinetic energy contained in the rotating brake disc for further delivery of the friction lining, i. the friction lining are pressed against the brake disk with a force which is significantly increased in relation to the actuator force and which is not applied by the electric actuator. The basic principle of such a brake is known from DE 198 19 564.

Allen said brakes have in common that a first non-rotatable brake element cooperates with a second rotatable brake element, for example. Friction brake disc, brake shoe brake cylinder, etc., to generate a friction torque N _R. Of the Interaction can be a normal force F _N , which is perpendicular to the contact surface of the two brake elements, and a frictional force F _R , which counteracts the relative movement between the two brake elements assign. The frictional force is related to the friction torque N _R , N _R = _r F _R via the distance r of the attachment point from the rotational axis and to the normal force, F _R = μ ^• F _N (Coulomb friction), via a friction coefficient μ. It should be noted that for a floating caliper disc brake the relation F _R = 2μ-F _N applies.

DE 101 51 950, the disclosure of which is expressly incorporated herein by reference, describes how the friction torque of an electromechanical wedge brake can be determined and the coefficient of friction (coefficient of friction) can be determined. The result is used to control the braking force in order to prevent, for example, a brake lock.

In braking systems, especially vehicle brakes, there is the problem that the braking performance, i. in particular, the relationship between the amount of expenditure incurred

Force, over time, in particular, deteriorates. The easing of the braking power can be compensated by increased braking force or Aktuatorkraftaufwand a certain time, until finally the safe operation of the brake system is no longer given and it comes to the loss of operability. When using a brake in the field, i. So, for example, when the vehicle after delivery to the customer, a decrease in braking power is usually recognized only when it comes to dangerous situations or even an accident. Also, the examination in a workshop or test center usually can not show all the malfunctions that are possible with a brake. Such investigations usually take place only at long intervals.

The problem therefore arises of determining a performance parameter of a brake system, in particular in the field, more accurately and earlier. This object is achieved by a method, a computing unit, a computer program and a computer program product for determining a performance parameter of a brake having the features of the independent patent claims.

The following explanations and advantages relate to all inventive solutions, unless it is expressly described differently. The arithmetic unit according to the invention has corresponding means for carrying out the steps described.

According to the invention, a performance parameter, in particular the operating or performance, of a brake is determined. The brake has a first and a second brake element, which can be brought into interaction for generating a friction force and a friction torque. A first set of friction coefficients (sliding friction coefficients) between the first and the second brake element is determined in the field. The characteristic "determination in the field" is to be understood as a distinction from a determination by the manufacturer. According to the invention, the determination is not carried out by the manufacturer but, for example, during normal driving, in a workshop or at a test point, for example TUV. In this disclosure, the term "determine" is to be understood in particular as a generic term for "ascertain", "measure", "estimate", "calculate", etc., that is to say for every measure which yields a result. The first set of friction coefficients is compared to a predetermined second set of friction coefficients. The following are the first quantity as well

"Actual Fingerprint" or "Actual Value" and the second set is referred to as "Target Fingerprint" or "Target Value". The performance parameter is finally determined based on a deviation of the first and second quantities, the deviation being obtained from the comparison.

A coefficient of friction can in principle be determined from a comparison between friction force and normal force, as it already is was explained above. The normal force can be determined, for example, by means of a sensor in the force flow. The frictional force can be measured, for example, with a sensor which is arranged between a friction lining of the brake and a component on which the friction lining is braced during braking. The person skilled in the art are aware of other possibilities.

In the following, the relationship between sole fingerprint and deviation is explained. If the sole fingerprint (depending on vehicle type and vehicle axle) is a lower limit of the friction coefficients (friction coefficients), which just allows the safe operation of the brake, a small deviation or a deviation of zero should be used accordingly. If, however, the target fingerprint of mint brake elements, for example. A Reibbelag- / brake disc combination used, the allowable deviation can be set correspondingly higher.

In a simple embodiment, a fingerprint consists of a set of friction coefficients which are considered as a function of their (relative) frequency. Usually a distribution function is obtained from this, which can be approximated with a Gaussian function. In another embodiment, a fingerprint consists of a first set of coefficients of friction as a function of temperature, velocity and force, as described, for example, in the lecture "Method for extracting the spectrum of frictional material performance (fingerprints) using the SAE J2681" by Tim Duncan and Otto Schmitt, 22nd Annual Brake Colloquium & Exhibition, October 2004, Anaheim, CA, USA, SAE Technical Papers Document Number: 2004-01-2768. Reference is made explicitly to this publication, as it discloses how a fingerprint in the context of the present application can be configured in further embodiments. In turn, a frequency distribution of friction coefficients is determined by means of this method. The frequency distribution typically corresponds to a (Gaussian) bell curve. The deviation of the actual fingerprint from the target fingerprint can ability (performance) of the brake system are closed. The deviation can be determined in these examples mentioned, for example, as a flat measure or surface deviation, ie it is determined which portion of the surfaces overlaps under the curve. This procedure for determining fingerprints, which is described in SAE J2681, represents a very detailed method for determining friction coefficients. During normal driving, however, not all braking situations usually occur that correspond to a brake pad test for friction coefficient determination according to this method. Therefore, for example, it is possible to use only test methods that are comparable to the cited Perfomance method. However, it is also possible to carry out the determination of the coefficient of friction on a test stand (for example a roller test stand), for example in a workshop or a TUV station, a comprehensive fingerprint test being possible. As a result, a comprehensive and therefore very accurate test can advantageously be carried out.

However, it is also possible and desirable to perform the procedure during normal driving. To determine the first set of coefficients of friction during normal driving, the individual coefficients of friction should be collected. With each brake ma- nizer, the coefficient of friction on the brake pads together with the associated temperature, wheel speed and clamping force (normal force) are stored in a memory (eg microchip). In addition, to obtain friction coefficients for other combinations of temperature, velocity, and normal force, the brake system may automatically apply brakes to record the missing friction coefficients at certain operating conditions to produce a first set. Such braking, preferably with a small friction torque, can be initiated for a short time during an acceleration phase of the vehicle, for example. In this case, only the acceleration of the vehicle has been reduced, which normally does not involve any danger potential. With a suitable implementation, moreover, the braking effect could be hidden from the driver. The invention provides for a target / actual comparison between a predetermined fingerprint and a determined fingerprint, preferably at regular intervals. The target specification is stored in the brake system, eg in a microchip, and can be read out at any time. Since the brake system, the brakes and thus brake elements (brake pad, brake shoe, brake cylinder, brake drums, brake discs, etc.) for each vehicle (and for each vehicle axle) by the vehicle or brake manufacturer (or in general by the OEM) have been designed individually In principle, an associated sole fingerprint can be determined for each brake element combination. This means that each brake element combination associated with a brake can be characterized by a frequency distribution of friction values predefined by the manufacturer (depending on the type of vehicle and on the vehicle axle).

According to the invention, the target fingerprint (for example, specified by the manufacturer) for each brake of a vehicle is now stored in a memory and can be called up at any time. In order to be able to perform a desired-actual comparison, the vehicle or the brake system must be able to determine an actual fingerprint for each brake element combination. For this purpose, the coefficient of friction between the brake elements, preferably in dependence on the clamping force, the temperature and the relative speed, determined.

If the brake performance drops below a certain desired value, advantageously certain measures can be initiated automatically. For example, the driver can be informed that his brake is in an incorrect condition. By means of the solution according to the invention, insufficient brake elements, for example a lining, can be detected, which no longer achieve desired performance. In addition to normal wear and tear, other physical conditions such as aging or glazing can cause increasing (creeping) deterioration. Even with a repair built-fake pad and / or brake discs, etc. can easily be recognized, which in turn significantly increases the safety of the occupants. Before a main inspection or maintenance, a self-diagnosis of the brake can be carried out in advance, which leads to a time and cost savings. After installing a new brake element (brake pad, brake disc, brake shoe, brake cylinder, etc.), these can be identified and monitored. If the performance no longer meets the criteria of the target fingerprint, a desired action can be taken.

In addition to the target / actual comparison, additionally or alternatively, an actual comparison of all brake elements of a vehicle can be carried out. Here it can be determined whether the brake elements on an axle have a different good (skewing of the vehicle when braking) or whether the braking ratio front to rear axle is correct.

By means of the performance measurement, certain operating points of a brake can be determined, e.g. Beginning of fading, minimum and maximum coefficient of friction, etc.

In addition, similar to a flight recorder, the fingerprints of all brakes can be stored and, in the event of an accident, used for accident analysis.

Advantageous developments are the subject of the subclaims and the following description.

Advantageously, for each coefficient of friction acting between the first and the second brake element normal force F _N , a temperature of the brake elements and a relative speed between the first and the second brake element is determined. Consequently, the coefficients of friction of the first and second quantities are dependent on the parameters mentioned. The sliding friction coefficient is theoretically independent of the sliding speed and therefore constant. In practice, however, is a temperature, speed and Force or pressure dependence determined. Therefore, the friction coefficients are preferably determined as a function of these parameters in order to be able to make a more accurate comparison of the coefficients of friction.

It is expedient if the temperature, in particular at the interface of the two brake elements, is calculated or estimated or measured by means of a sensor. A calculation or estimation can be easily derived and carried out by means of temperature models. The friction heat can be calculated by means of the friction force and the friction distance. The material parameters, in particular heat capacity, etc., of the brake elements are also known. The friction path results from the distance traveled. Overall, the heat introduced into the brake system via the brake friction can thus be estimated and the temperature calculated therefrom. Likewise, it is easily possible to provide a temperature sensor, for example on the brake disk.

Expediently, the relative speed is measured by means of a sensor. For this purpose, for example, the rotational speed of the brake disc can be determined, from which in a simple way the relative speed over the radius can be calculated. It is particularly advantageous to use existing sensors. For example. the speed is also determined by a sensor of the ABS system or by a tachometer. Then, particularly advantageous, no additional sensor is necessary.

Expediently, the normal force by means of an im

Force flow of the normal force arranged force sensor measured. In particular, the components of the normal force are obtained from the determination, for example in Cartesian, cylindrical or spherical coordinates, as well as their amount. For example, the measurement of the normal force in the friction linings themselves or in or on the lining wearers, also on the Abstutzflachen the wedge of the wedge assembly in the brake disc cross-saddle or in the context of the disc brake. In general, a measurement of forces close to the point of origin is advantageous in order to avoid a falsification of the measurement signals by carrying masses. However, the normal force can also be determined indirectly, for. For example, from the extent of the displacement of a wedge of the wedge arrangement of a wedge brake occurring during a given braking. During a braking operation, the normal force leads to a widening of the caliper of the disc brake and to a compression of the friction lining and, to a lesser extent, of the brake disc. These elasticities of the brake are compensated by a corresponding displacement of the wedge in the direction of actuation. If the term "zero position" refers to that position of the friction lining in which the so-called air clearance has just been overcome and the friction lining thus bears against the brake disk without force, the normal force can be calculated directly from the degree of displacement of the wedge in the actuating direction. If the spring characteristic of the brake system is linear, the normal force is directly proportional to the displacement of the wedge. The displacement of the wedge can either be measured directly or determined from operating data of the actuator. For example, it is possible to calculate the displacement path of the wedge from the motor rotation angle of an electric motor associated with the actuator, in particular when the electric motor acts on the wedge via a pitch-accurate feed system. Alternatively or additionally, the widening of the caliper can be determined with a commercially available position measuring system. Since the relationship between the expansion of the caliper and the acting normal force is linear for practical purposes, the measurement of the expansion of the caliper is another way to determine the normal force.

According to a further preferred refinement, the friction coefficient is determined from the friction force and the normal force, and the friction force is measured, in particular, by a force sensor, which in particular detects the stopping force of the brake that occurs during braking. As already explained, the friction coefficient is related to the frictional force over the normal force. By determining the frictional force and the normal force for determining the friction coefficient, the present invention can be used in principle in almost every mechanical friction brake.

In a preferred embodiment, a performance parameter of a self-reinforcing or self-decelerating brake is determined in which an actuator generating an actuator is provided which acts on the first brake element to press the first brake element to the second brake element, wherein a dependence of the normal force of the Aktuatorkraft and the coefficient of friction exists. In this case, a functional relationship between the friction coefficient and components of the normal force and components of the actuator force is determined, the components of the normal force and the actuator force are determined and the friction coefficient is determined from the functional relationship, the specific components of the actuator force and the specific components of the Normal force determined. By means of this preferred embodiment, it is possible to determine a friction coefficient for each self-damping or self-intensifying brake for which a dependence of the normal force on the actuator force and the coefficient of friction exists. The invention is thus not limited to, for example, wedge brakes, but can also be used for power brakes, Duoservobremsen and so on. An actuator normally converts control signals into mechanical work. The actuator may be designed, in particular, as an (electric) motor, hydraulic or pneumatic cylinder, piezoactuator (translator), etc.

According to a preferred embodiment, the

Actuator force or its components measured by means disposed in the power flow of Aktuatorkraft force sensor or determined from operating data of the actuator, in particular from the motor current of an electric actuator zugeho- rigenous electric motor during an operation of the brake. The force sensor can, for. B. detect the reaction force with which an actuator associated with the electric motor on the housing of the actuator and the brake braces. The reaction force speaks up to the sign of Aktuatorkraft. However, the force sensor can also be arranged at the point at which the Aktuatorkraft is introduced into the wedge of the wedge assembly. Likewise, a force sensor can be arranged in or on a force transmission means of the actuator, for example on a spindle or a pull or push rod. However, the Aktuatorkraft does not have to be measured directly, but can be determined indirectly, for example, from the motor current of the electric motor associated with the actuator. The motor current is a measure of the torque output by the engine, which is converted, for example by a spindle drive in an axial force. The motor current is therefore proportional to the actuator force generated. If the accuracy requirements are not too high, such an indirect determination of the actuator force is a suitable and favorable solution. The force sensor can work as a direct force or strain sensor, for example, capacitive (piezo), resistive (DMS) or via a hydraulic pressure transducer. He can also work by means of displacement measurement via eddy current, inductive, capacitive or magnetic. Such force sensors can be made robust but still small and are therefore easy to install on the brake system.

In a further embodiment, the actuator is electrically, the second brake element as a rotatable brake disc and the first brake element as a friction lining on which the electric actuator in an effective angle ß via a wedge assembly with a wedge angle α acts to press the friction lining to the brake disc is formed. The effective angle is to be understood as the angle between the actuator force and the normal force. The proposed method can be used particularly easily in the special case ß = 90 ° for wedge brakes, since in wedge brakes, in which the Aktuatorkraft perpendicular to the normal force and thus acts parallel to the frictional force, the friction coefficient can be determined particularly easily in dependence on the Aktuatorkraft and the wedge angle , Such a determination method is explained in detail in the aforementioned DE 101 51 950, to which reference is again expressly made. Not to to repeat the entire DE 101 51 950 at this point, only the essential results are briefly quoted. The person skilled in the art can consult DE 101 51 950 for clarification of open questions. According to DE 101 51 950, the friction coefficient μ can be determined from the wedge angle α, the normal force F _N and the actuator force F _A to μ = tan α-F _A / F _N. The actuator force can be determined, for example, from the Aktuatorstromaufnahme, the normal force by means of a force sensor. In addition, according to the preferred embodiment already mentioned, the friction temperature prevailing at the boundary surfaces between the brake disk and the friction lining, approximately the temperature of the brake disk, and a rotational speed of the brake disk can be determined for each coefficient of friction. The rotational speed ω of the brake disk is proportional to the sliding speed v (tangential speed) of the friction lining on the brake disk in accordance with v = ωr, as is familiar to any person skilled in the art. r indicates the distance of the friction lining from the axis of rotation. A method for determining a friction coefficient at arbitrary angle β will be explained later with reference to FIG.

Advantageously, the functional relationship becomes too

b ^ e ^~ is true, whereff μ denotes the coefficient of friction, F _N the amount of the normal force and F _A the amount of the actuator force. Thus, the determination of the coefficient of friction for wedge brakes with any angle of action is possible in a particularly simple manner.

An arithmetic unit according to the invention comprises calculating means for performing the steps of a method according to the invention, in particular means for determining a first set of friction coefficients between the first and second braking elements in the field, storage means containing a predetermined second set of friction coefficients, means for comparing the first Amount of coefficients of friction with the second set of coefficients of friction, tel determining a deviation based on the comparison, and means for determining the performance parameter from the deviation. The arithmetic unit can be designed, in particular, as a control unit in a motor vehicle.

Preferably, the method according to the invention and the computing unit according to the invention are used in an embedded system, control unit or ECU in a motor vehicle.

A computer or microprocessor program according to the invention contains program code means for carrying out the method according to the invention when the program is executed on a computer, a microprocessor or a corresponding arithmetic unit, in particular the arithmetic unit according to the invention.

A computer or microprocessor program product according to the invention includes program code means stored on a machine- or computer-readable medium for carrying out a method according to the invention when the program product is executed on a computer, a microprocessor or on a corresponding arithmetic unit, in particular the arithmetic unit according to the invention , Suitable data carriers are in particular floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, u.a.m. It is also possible to download a program via computer networks (Internet, Intranet, etc.) and vehicle networks (body bus, infotainment bus, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention. The invention is illustrated schematically with reference to an exemplary embodiment in the drawing and will be described in detail below with reference to the drawing.

figure description

Figure 1 shows schematically a frequency plot of friction coefficients for a simple form of the first or second set of friction coefficients;

Figure 2a shows a first possibility of a deviation between a first and a second set of friction coefficients;

Figure 2b shows a second example of a possible deviation between a first and a second set of friction coefficients; and

FIG. 3 schematically shows a wedge arrangement of a self-reinforcing electromechanical brake for use with the invention.

In FIG. 1, a diagram showing a relationship between coefficients of friction of a first or second set of coefficients of friction and the associated relative frequency is designated by 100 as a whole. The graph 100 plots friction coefficients for a predetermined combination of normal force, temperature and velocity. The coefficients of friction μ are plotted against the relative frequency on a y-axis 102 on an x-axis 101 comprising values of 0-1.

In the illustration shown, the coefficients of friction are not continuous, but plotted in steps 103 of 1/15. For example, all coefficients of friction from μ = 11/30 (0.37) to μ = 13/30 (0.43) are summarized in one stage. This coefficient of friction μ = 0.4 is assigned a relative frequency of approximately 0.14. The width of the steps, for example, 1/15 in the illustrated illustration, is caused, for example, by the measurement accuracy or the type of application, as will be apparent to one of ordinary skill in the art. The stepped application of the coefficients of friction can be approximated by an enveloping curve 104. The curve shape of the curve 104 essentially corresponds to a Gaussian bell shape. In the present example, the maximum is approximately at a coefficient of friction of μ = 0.42.

FIGS. 2a and 2b show two of the possible deviations of the first and the second set of coefficients of friction. In addition, a variety of other variations is possible, as will be apparent to anyone skilled in the art.

In FIG. 2 a, in turn, the coefficients of friction together with their respective relative frequencies are shown in a diagram 201. The predetermined second set of friction values, the actual fingerprint, is identified by a curve 204. The particular first set of friction values is indicated by a curve 204a. In the figure, the deviation of the first quantity from the second quantity is clearly visible. In the example shown, coefficients of friction with a value μ between approximately 0.25 and 0.52 occur less frequently in the first quantity than in the second quantity, whereas coefficients of friction are less than approximately 0.25 and greater than approximately 0.52 occur more frequently in the first quantity than in the second quantity. From the deviation shown, it can be concluded that the friction lining used does not correspond to the prescribed friction lining from which the target fingerprint was determined. It could be a different guy or a fake.

FIG. 2b shows in a diagram 202 the coefficients of friction and their associated relative frequency of a predetermined second quantity 204 and a specific first quantity 204b. In the illustration shown, the maximum of the relative frequency in the specific first quantity is shifted to smaller coefficients of friction μ. The curve shape of the curve 204b is substantially identical to that of the curve 204. These are deviation is caused for example by a worn friction lining.

FIG. 3 shows a wedge arrangement which is suitable for use in a self-reinforcing, electromechanical brake, as also disclosed in DE 101 51 950. An electric actuator, which usually includes an electric motor and a spindle drive, generates an actuating or actuator force F _A , which is introduced into a wedge 300 at an effective angle β in order to displace the wedge in the x-direction (to the right in the illustration) , A friction lining 311 abuts on one side surface, an abutment 312 for wedge the wedge on another side surface of the wedge 300. The actuator force F _A shifts the wedge 300 having a wedge angle α in the x direction, as a result of which the friction lining 311 comes into contact with a brake disk 313 rotating at a speed v. As soon as the friction lining 311 touches the brake disk 313, a reaction force normal to the brake disk or normal force F _N and a friction force F _R acting in the circumferential direction of the brake disk 313 are produced. These forces are for the most part in the abutment, for example, the housing of the brake, initiated and trimmed there, resulting in a Abstutzkraft F _B.

Taking into account the forces acting on the wedge in the x-direction one obtains: μF _N + F _A sin β - F _B sin a = 0 (1)

Taking into account the forces in the wedge in the y-direction, one obtains:

F _B cos a + F _A cos β - F _N = 0 (2)

By on lots of (2) to F _{_B:)} and insertion in (1): μ F _N + F _A sin β - (F _N - F _A cos /?) tan a = 0

gives the functional relationship for μ:

_ (F _N - F _A cos /?) Tan a - F _A sin ß

μ = tan α - (sin γ + cos β tan α) with the two special fall:

Fβ = 90 °: μ = tan a ^

F

In this way, a first set of coefficients of friction for a wedge brake with arbitrary angles α and β can be determined from the values of the actuator force and the normal force.

Claims

claims

1. A method for determining a performance parameter of a brake having a first (311) and a second (313) braking element, which for generating a frictional force (F _R ) and a

Friction moments (N _R ) can be brought into interaction, with the following steps:

Determining a first amount (204a, 204b) of friction coefficients (μ) between the first (311) and second (313) braking elements in the field,

Comparing the first amount (204a, 204b) of friction coefficients (μ) with a predetermined second amount (204) of friction coefficients (μ), and

Determining the performance parameter based on a deviation of the first (204a, 204b) and the second set (204), the deviation being obtained from the comparison.

2. The method of claim 1, wherein for each coefficient of friction (μ) acting between the first and the second braking element normal force (F _N ), a temperature and / or a relative speed between the first (311) and the second (313) Bremselement is determined.

3. The method according to claim 2, characterized in that the temperature is calculated or estimated or by means of a

Temperature sensor is measured.

4. The method according to claim 2 or 3, characterized in that the relative speed by means of a, in particular already existing, sensor is measured.

5. The method according to any one of the preceding claims, characterized in that the normal force (F _N ) is measured by means of a arranged in the force flow of the normal force sensor.

6. The method according to any one of the preceding claims, characterized in that the friction coefficient (μ) from the friction force (F _R ) and the normal force (F _N ) is determined.

7. The method according to any one of claims 2 to 5, characterized in that the performance parameter of a self-reinforcing or self-slowing brake is determined, in which an actuator force (F _A ) generating actuator is provided, which acts on the first brake element (311) to press the first brake element (311) to the second brake element (313), wherein a dependence of the normal force (F _N ) of the actuator force (F _A ) and the coefficient of friction (μ), a functional relationship between the coefficient of friction (μ ) and components of the normal force (F _N ) and components of the actuator force (F _A ) is determined, the components of the normal force (F _N ) and the actuator force (F _A ) are determined and the friction coefficient (μ) from the functional relationship, the determined Components of the actuator force (F _A ) and the specific components of the normal force (F _N ) is determined.

8. The method according to claim 7, characterized in that the Aktuatorkraft (F _A ) or its components measured by means of a force flow in the Aktuatorkraft force sensor or is determined from operating data of the actuator or, in particular from the motor current of an e-lektrischen actuator associated electric motor during an operation of the brake.

9. The method according to any one of claims 7 or 8, character- ized in that the actuator electrically, the second brake element as a rotatable brake disc (313) and the first brake element as a friction lining (311) on which the electric actuator in an effective angle ß on A wedge arrangement (300) with a wedge angle α acts to press the friction lining (311) against the brake disk (313).

10. The method according to claim 9, characterized in that the functional relationship is determined to F _N tan a - F _A (sin β + cos β tan a) ^{μ =} F ¹ N 'where μ denotes the coefficient of friction, F _N the amount of the normal force and F _A the amount of the actuator force.

11. Arithmetic unit for determining a performance parameter of a brake with a first (311) and a second (313) braking element, which are for generating a frictional force (F _R ) and a friction torque (N _R ) interacting, with:

Means for determining a first amount (204a, 204b) of friction coefficients (μ) between the first (311) and second (313) braking elements in the field,

Storage means containing a predetermined second amount (204) of friction coefficients (μ),

Means for comparing the first set (204a, 204b) of friction coefficients (μ) with the second set (204) of friction coefficients (μ),

Means for determining a deviation based on the comparison and

Means for determining the performance parameter from the deviation.

12. Computer or microprocessor program mit Programmcode- mittein to perform all the steps of a method according to any one of claims 1 to 10, when the program on a computer, a microprocessor or a corresponding arithmetic unit, in particular according to claim 11, is executed.

A computer or microprocessor program product comprising program code means stored on a machine-readable medium for carrying out all the steps of a method as claimed in any one of claims 1 to 10 when the program product is stored on a computer, a microprocessor or on a computer corresponding arithmetic unit, in particular according to claim 11, is executed.