DE102004044599A1 - Brake control process for a motor vehicle having an electric regenerative brake has generator and hydraulic friction brakes and uses auxiliary pressure unit - Google Patents

Abstract

A brake control process for a motor vehicle comprises using a generator (4) and hydraulically driven friction brakes (2) whose delay combines the friction and electric brake delays. When releasing the electric brake moment the desired total delay is partly maintained, when an auxiliary support provides additional brake pressure. Independent claims are also included for the following: (a) a brake system for the above;and (b) an operating process for the above system.

Description

The The invention relates to a method for the control of a brake system, especially for the regulation of a regenerative braking system with a number of Friction brakes and an electric regenerative brake for a motor vehicle.

Of the Purpose of regenerative braking systems in motor vehicles consists in it, at least part of the energy applied during braking to save in the vehicle and for to reuse the drive of the vehicle. This can reduce energy consumption of the vehicle lowered overall, the efficiency increased and the Operation to be made more economical. motor vehicles with a regenerative braking system usually have different Types of brakes, which are also called brake actuators.

there are usually hydraulic friction brakes, as they are ordinary Vehicles are known, and an electric regenerative brake used. The brake pressure for the friction brakes over a conventional friction brakes Brake pressure generating means or over applied the brake pedal movement. The electric-regenerative Brake is usually designed as an electrical generator over the at least part of the total braking power is applied. The recovered electrical energy is stored in a storage medium For example, an on-board battery fed or fed back and for the drive of the motor vehicle over reused a suitable drive.

Generally can regenerative braking systems are designed as so-called serial regenerative concepts, in which the proportion of the braking torque applied by the generator will, if possible is high. In contrast, parallel and so-called drag torque-based regenerative concepts known in which the braking torque on the Brake actuators is divided in predetermined proportions. Farther Mixing concepts of these brake concepts are known. All systems is common that at least in some areas of the applied Braking torque simultaneously braked with several brake actuators is, so that the total delay from the delay components composed of brake actuators.

The Distribution of braking energy in shares of the friction brakes and in shares the electric generator is, especially in serial concepts, usually the desired braking torque, the state of charge of the battery and especially the operating area and other special features of the generator. In regenerative braking systems, the brake pressure therefore because of the Bremsenergiteilung at least partially independent built up by the hydraulic influence of the brake pedal.

at On the other hand, conventional brake systems, which have only one friction brake, becomes the hydraulic brake pressure depending on the position of the brake pedal built up. It is about the position of the brake pedal with or without auxiliary energy the pressure constructed of a braking means, which is received by the friction brake becomes. The pedal position thus corresponds to the braking behavior of the Motor vehicle. Exceptions are possible the inserts of electronic security systems such as one electrical stability program (ESP), the devices for self-developed brake pressure, regardless of the brake pedal position, may include.

in the Compared to this conventional braking behavior is the braking behavior a regenerative braking system consisting of the combination an electrically regenerative brake and a conventional, hydraulically operated Friction brake, disadvantageous that the position of the brake pedal is not necessarily corresponds to the braking behavior of the motor vehicle. So For example, during an increase the braking delay the position of the brake pedal remain constant, which is for the driver a very unfamiliar brake feel represents, so that sets only insufficient braking comfort.

As a solution to this problem, so-called "brake-by-wire" systems can be used.These braking systems use electronic sensors to detect the braking demand of the driver on the brake pedal, whereby the brake fluid is sent from a high-pressure accumulator to the friction brakes via electronically controlled valves In such "brake-by-wire" - systems, the required brake pressure is applied to the friction brakes with the exception of a failure of system components exclusively from the Hochdruckdrucki cher, so that the brake pedal is inherently decoupled from the friction brakes, since the control or the brake fluid delivery to the friction brakes is electronically controlled and controlled. By decoupling the brake pedal from the friction brakes, a pedal control suitable for a regenerative braking system can be integrated with the brake system to establish an acceptable brake pedal feel. However, "brake-by-wire" systems such as the electronic brake (EHB) or electromechanical brake (EMB) are very costly and only with increased effort realizable.

Therefore can be used in an alternative braking system to produce an acceptable braking system pedal feel be provided in a regenerative braking system, brake means when braking with an electric regenerative brake in one Pressure accumulator, in particular a low-pressure accumulator, derive. This will be an additional Braking the friction brakes simulated to a driving behavior corresponding To obtain pedal movement or pedal force.

One Such braking system can be controlled by passing it over a electronic control unit via controls electrically controllable hydraulic valves accordingly. Next suitable low-pressure accumulators is also a further pressure generating means, such as a motor pump unit, used to the pedal pressure accordingly build or regulate and brake means from the low-pressure accumulator via suitable To transport hydraulic lines to the friction brakes. The braking system will regulated with predetermined control processes, wherein the brake fluid pressure the friction brakes and the position and pressure of the brake pedal as Controlled variables are used. The hydraulic unit of the brake system is in contrast to aware of a "brake-bywire" system kept coupled to the brake pedal to this according to the delay request and the realized delay to be able to adjust.

For a high System dynamics are in a further embodiment of the brake system described above a number of high-pressure accumulators are provided in the hydraulic system, at a strong braking torque request increase, such as in so-called "Nachtreten", the higher demand for braking request to be able to meet with sufficient speed. The same applies for situations in which the driver releases the brake pedal quickly, resulting in a sudden Reduction of the current brake pressure requirement results. At a such situation, the brake pedal on the high-pressure accumulator in his original Situation pushed back.

Around Pressure pulsations on the low pressure side of motor pump units to smooth the brake system may as well still a number of extra Have low pressure storage, which act to dampen.

Problematic on the braking system described above, which is a high Achieve system dynamics with a decent pedal feel that However, the system has a very high complexity. This leads to, that in particular the control of the brake system is complicated, and, for example, control technology problematic control transitions occur can.

The Brake system is due to the high complexity or the numerous system components, especially the extra High and low pressure storage, relatively expensive and therefore has an unfavorable Cost-effectiveness on, allowing a use in larger numbers so far not realized.

Of the The invention is therefore based on the object of a regenerative braking system and a method for specify the control of a braking system, which at a high braking comfort and a high system dynamics in particular has a favorable cost-benefit ratio.

These The object is achieved according to the invention by in a braking system of a motor vehicle, which is an electrical-regenerative Brake, in particular a generator and a number of a brake pressure generating means via a Has brake means driven hydraulic friction brakes, whose total delay from delay shares the friction brakes and the electric regenerative brake, on release of braking torque of the electrically regenerative brake the desired total delay is at least partially upheld by additional Brake pressure build-up for the friction brakes with another assisted brake pressure generating means he follows.

The Invention is based on the consideration, that if from the premise A serial regenerative concept deviates from the requirements for the Significantly reduce the braking system. This leads in principle to lower Cost of the brake system and thus to a better cost-benefit ratio. Conceivable is for that a parallel, a drag-based or a hybrid of these brake systems. Although these braking systems can not be optimal Brake Energy Regeneration reach for that But fewer system components and control processes are necessary.

Thus, the braking behavior, in particular the brake pedal feeling in non-serial regenerative braking systems over the largest part of the deceleration range is unproblematic. Only at low speeds, especially at speeds below about 15 km / h is a strong braking torque drop of the electric regenerative brake problematic. To be in this speed To achieve the same delay as in the hitherto effected braking, the driver would have to step abruptly, which is very disturbing in so-called target braking and has a safety-critical effect.

Around in this speed range the declining braking torque of to compensate for the electric regenerative brake is additional brake pressure according to the invention via a another supportive Brake pressure generating means for the friction brakes applied. The decreasing braking torque of the electric regenerative Brake is therefore of a stronger Braking torque of the friction brakes compensated, with the necessary additional Brake pressure applied by the further brake pressure generating means becomes.

For a simple one Process and cost-effective Brake system is advantageously additional brake pressure for the friction brakes only at a vehicle speed below a maximum speed built up. It means that in others or higher Speed ranges the brake system substantially unregulated can be, or no additional Regulations take place.

there this maximum speed is set at a limit the braking torque and the braking power of the electric regenerative brake particularly strong, preferably at a maximum speed of about 15 km / h.

The for the Brake booster the friction brakes necessary brake is from the auxiliary power assisting Brake pressure generating means expediently in the friction brakes leading Transported hydraulic lines. The required brake fluid can in a storage container the actual brake pressure generating means are kept.

Around to prevent this increase in pressure on the brake pressure generating means, which is connected to a brake pedal affects, is the hydraulic Connection between the actual brake pressure generating means and a friction brake, expediently while an additional one Brake pressure build-up for the friction brakes with another assisted brake pressure generating means done, throttled. This can be over a throttled hydraulic valve done.

Around after a braking process again represent the brake feel on the friction brakes to be able to is preferably after a braking operation by the controlled opening of a Hydraulic valve pressure equalization between a Hydrauliklei device, which leads to a friction brake, and a pressure generating means. It can be a valve for one Pressure equalization first slowly opened and then for another braking operation also remain open.

Around the brake feel while braking with an electric regenerative brake and the friction brakes not too much of the actual braking behavior or the motor vehicle delay, by varying in the course of the speed braking torque of the decoupling electrically regenerative brake is advantageously the braking torque of the electric regenerative brake on a given Maximum value limited. In particular, the performance and Brake torque peaks of the electric regenerative brake filtered out. Depending on the state of charge of the on-board battery, in which the of the electrical-regenerative Brake generated energy is stored, is the limiting given maximum braking torque at different vehicle speeds reached.

For a suitable Braking torque limitation The electric regenerative brake becomes the maximum value for the electric regenerative brake Brake expediently predetermined such that the achievable by this delay contribution does not exceed about 0.07 g.

Around To prevent that when reaching the given maximum Braking torque of the electric regenerative brake not too abrupt delay variation when the maximum value is reached, the electric regenerative brake is activated preferably a smoothing function given when their braking torque to the above maximum value approaches.

In order to the varying braking torque of the electric regenerative brake in the course of the speed or by the variable Braking torque entering varying delay fraction not so strong is that change in terms of brake feel In the course too strong negative effect, the braking torque of the electric regenerative Brake preferably limited such that the change of the delay component the electric regenerative brake at a change in the vehicle speed does not exceed a predetermined maximum value. Mathematically equivalent This is the specification of a maximum derivative for the braking torque curve of electrically regenerative brake according to the speed or the time.

In an additional or alternative advantageous embodiment, the smoothing can also be provided such that not only the change of the delay component of the electrical-regenerative Brake, but also the change of this change in a change of the vehicle speed does not exceed a predetermined maximum value. Thus, not only the first, but also the second derivative of the braking torque curve is kept limited according to the vehicle speed or time.

For the scheme the brake system has this in addition to the components already described Advantageously, a hydraulic unit with controllable hydraulic valves and hydraulic lines on which are the components of the braking system connect with each other, the brake system advantageously with the control unit over the controllable hydraulic valves can be regulated.

For an exact one Determining the desired braking is a desired braking torque or a desired brake pressure on the Brake pedal of the brake system determined. This is indicated by the brake pedal preferably a pedal travel transmitter and / or a pressure sensor, in leading to the pressure generating means or the brake pedal Hydraulic line is positioned. The pressure sensor and the pedal travel sensor can do it for one high reliability be advantageously designed redundant. From a determination of the position of the brake pedal, via the encoder takes place, and the applied brake pedal pressure, over the Pressure sensors results, leaves determine the desired braking torque or the target brake pressure.

Around the intended pressure generating processes with the brake pressure generating means to be able to raise is expediently the one brake pressure generating means is an auxiliary power operated Master cylinder, especially tandem master cylinder and the other Pressure generating means an electrically controllable hydraulic pump.

Around the for a Bremsvorgung and in particular for the regulation of this the brake pressure of To be able to detect braking means on the friction brakes is advantageous in a number leading to the friction brakes hydraulic lines a pressure sensor positioned to measure the pressure of a brake fluid. About the Detecting the brake fluid pressure, the required additional brake pressure calculated and be regulated.

To can the electrically controllable hydraulic valves preferably such be controlled that made a pressure control via a hydraulic valve can be.

For a high Operational safety is expediently another pressure generating means output or input side assigned a check valve, that only in Bremsmittelförderrichtung Flowed through by the brake fluid of the pressure generating means can. In case of failure of the further brake pressure generating means there is no brake fluid pressure loss in the hydraulic lines of the Friction brakes and the brake system can continue to operate.

By the additional, provided with the shut-off hydraulic line is another direct connection of the active components of the brake system with made the brake fluid reservoir. In case of failure of individual components and in particular the additional one Shut-off valve or the upstream of this check valve could thus Leaks and unwanted Media backflow enter. To effectively prevent this is preferably in Operation of the braking system the regular execution of test cycles to detect any existing or imminent leaks intended.

The execution such a test cycle is preferably only in the absence of a driver's request to the brake system, so that no impairment of the driving feel occur can. Alternatively or in addition the implementation takes place such a test cycle, without requiring an active intervention or start by the driver would be automated and advantageously in a global test phase for the motor vehicle, preferably before departure (so-called "Pre Drive Check") or after completion of the journey (so-called "post Drive Check ").

The achieved with the invention, in particular consist in the Possibility, a regenerative braking system with a high system dynamics and one the delay behavior appropriate pedal feel to disposal to provide a simple structure with few system components having. Due to the simple structure are also the necessary Control processes comparatively simple and without the occurrence of rule problems feasible. The braking system is therefore relatively inexpensive, so that it has an acceptable cost-benefit ratio.

One embodiment is explained with reference to a drawing. Show:

1 the block diagram of a brake system and

2 an example of the braking torque curve of an electrical generator of the brake system according to 1 depending on the speed of a motor vehicle.

In 1 is a schematic diagram of a brake system 1 represented for a motor vehicle. In the brake system 1 it is a regenerative braking system 1 , in addition to the four friction brakes 2 also an electric generator 4 for generating electrical energy, which is stored in a not shown on-board battery for driving the motor vehicle. The brake system 1 is there as a non-serial brake system 1 designed so that not the maximum possible amount of braking torque through the generator 4 is applied. For this, the brake system 1 be designed comparatively simple, which will be described below.

To the main braking torque for the friction brakes 2 to apply is the braking system 1 equipped with a brake booster as a tandem master cylinder 8th is designed with a helper and with a brake pedal 6 connected is. This is the tandem master cylinder 8th applied brake pressure via hydraulic lines 10 with a braking means B to the friction brakes 2 passed.

To the braking system 1 It has an electronic control unit, in particular for the most comfortable brake feel possible and for normal driving stability functions 28 on, with the brake system 1 and in particular the hydraulic system of the brake system 1 can be adjusted by means of suitable, electronically controllable hydraulic valves. The valves 14 and 16 are referred to whether they are normally open - ie without electrical control - open or closed. The SO valve 14 is normally open and the SG valve 16 closed normally. The EU valve 18 corresponds to an electronic switching valve.

The following is the sequence of a braking operation based on 1 explained in more detail, this being only a part of the braking system 1 on each of a friction brake 2 with the associated system components. The system components of the other friction brakes 2 work accordingly.

As input and control variables for the control of the brake system serve the desired braking torque and the brake fluid pressure at the friction brakes 2 , As it turned out 1 recognizes, is first about a Weggeber 24 on the brake pedal 6 is positioned, and a pressure sensor 26 , who at the to the tandem master cylinder 8th leading hydraulic line 10 is, the target braking torque via the electronic control unit 28 certainly. The brake fluid pressure at the friction brakes 2 results from a pressure sensor 26 which is in a hydraulic line of a friction brake 2 is positioned.

In 2 is in line 1 the braking torque curve of a generator 4 when braking from 130 km / h shown. The delay component or the braking torque of the simultaneously acting on the generator friction brakes 2 is not shown in the figure. At the generator 4 it is an asynchronous generator, which identifies a characteristic of the type shown. The theoretically achievable braking torque of this generator in the braking process at sufficiently discharged on-board battery 4 is in line 2 shown and theoretically achievable generator power is in line 3 demonstrated. The change in the generator braking torque occurs by the speed change in the speed reduction of the motor vehicle and falls regardless of the state of charge of the on-board battery below a speed of about 15 km / h to zero back.

In order to obtain the highest possible braking comfort in this braking operation and not to decouple the pedal feel too much from the actual deceleration behavior, the generator braking torque is limited to a maximum braking torque corresponding to a proportionate generator delay of 0.07 g, as from line 1 evident. Thus, the change in the braking torque or the delay fraction achieved by this does not change too much during the deceleration of the motor vehicle, which would adversely affect the braking comfort, the generator braking torque is limited such that the change in the delay component of the generator with a change in vehicle speed does not exceed a predetermined maximum value. line 1 is limited by a maximum slope.

In addition, the generator braking torque with a smoothing function slowly approaches the maximum braking torque, which corresponds to 0.07 g, so that there is a smooth transition to the maximum braking torque of the generator 4 established.

At the beginning of the braking process, at 130 km / h, braking means B is first applied to the brake pedal when the desired brake torque is increased 6 or the tandem master cylinder 8th over the open ASR valve 20 and the opened SO valve 14 in the hydraulic line 10 the friction brake 2 given.

When the vehicle is braked to 25 km / h, the braking torque of the generator 4 slowly reduced to mitigate the abrupt drop in the generator braking torque at 15 km / h or to obtain a smooth transition. At the same time, the entire braking torque is applied to the friction brakes 2 relocated. This is done via an additional shut-off valve 21 into a hydraulic line connected directly to the brake fluid reservoir 10 is switched, with the provided in this case as a motor pump unit, as an additional Brake pressure generating agent acting hydraulic pump 22 additional brake fluid B from the reservoir of the tandem master cylinder 8th in the hydraulic line 10 a friction brake 2 pumped. So that no too strong reaction to the brake pedal 6 occurs or this is not pushed back, the ASR valve 20 Temporarily throttled or kept closed.

The additional shut-off valve 21 is through to him in the hydraulic line 10 series-connected check valve 40 hedged.

When the vehicle is stationary or even before the ASR valve 20 controlled open to a pressure equalization between the friction brake pressure and the pressure of the tandem master cylinder 8th restore, with the ASR valve 20 is throttled open. Upon completion of the braking process, the brake pedal 6 pushed back to its original position and unnecessary brake fluid B in the reservoir of the tandem master cylinder 8th returned.

The brake system 1 is designed for a particularly high operational safety. In particular, the knowledge is taken into account that by the additional, with the shut-off valve 21 provided hydraulic line 10 another direct connection of the active components of the braking system 1 is made with the brake fluid reservoir, so that in case of failure of individual components and in particular the shut-off valve 21 or the upstream of this check valve 40 Leaks and unwanted media reflux could occur. To effectively prevent this is preferably in the operation of the brake system 1 the regular execution of test cycles to detect any existing or imminent leaks planned.

The implementation of such a test cycle is preferably carried out only in the absence of a driver request to the brake system 1 , so that no impairment of the driving feeling can occur. Alternatively or additionally, the execution of such a test cycle, without an active intervention or start by the driver would be necessary, automated and advantageously in a global test phase for the motor vehicle, preferably before driving (so-called "Pre Drive Check") or after driving completion ( so-called "Post Drive Check").

In carrying out such a test cycle, first a state is established in which the hydraulic pump 22 not fed with brake fluid B and therefore should not be able to brake pressure on the friction brakes 2 build. For this purpose, the supply lines to the pressure generating means or to the hydraulic pump 22 closed by pressing the appropriate valves. For complete input-side decoupling from Bremsmittelreservoir also the ASR valve 20 closed. Subsequently, the hydraulic pump 22 triggered, as a result of the decoupling designed by no brake pressure on the friction brakes 2 should build up. If still a pressure build-up on the friction brakes 2 should be noted, so can be a leak in the supply system and in particular in the shut-off valve 21 getting closed.

1

braking system

2

friction brake

4

generator

6

brake pedal

8th

Tandem master cylinder

10

hydraulic line

12

accumulator

14

SO valve

16

SG-valve

18

EU-valve

20

ASR-valve

21

Valve

22

hydraulic pump

24

encoder

26

pressure sensor

28

control unit

40

check valve

B

braking means

Claims (26)

Method for controlling a braking system ( 1 ) of a motor vehicle having an electric regenerative brake, in particular a generator ( 4 ) and a number of hydraulic friction brakes (B) driven by a brake pressure generator (B) 2 ) whose total deceleration is made up of deceleration fractions of the friction brakes ( 2 ) and the electric regenerative brake, wherein upon release of braking torque of the electrically regenerative brake, the desired total deceleration is at least partially maintained by additional brake pressure build-up for the friction brakes ( 2 ) takes place with another assisted brake pressure generating means. Method according to Claim 1, in which additional brake pressure for the friction brakes ( 2 ) is built only at a vehicle speed below a maximum speed Method according to Claim 1 or 2, in which the maximum speed a speed of about 25 km / h is given. Method according to one of claims 1 to 3, wherein for the additional brake pressure build-up for the friction brakes ( 2 ) Brake means (B) from a power assisting brake pressure generating means in the friction brakes ( 2 ) leading hydraulic lines ( 10 ). Method according to one of claims 1 to 4, wherein in the additional brake pressure build-up for the friction brakes ( 2 ) With the further assisted brake pressure generating means, the hydraulic connection of the actual brake pressure generating means with the friction brakes is temporarily throttled. Method according to one of claims 1 to 5, wherein at the end and / or after a braking operation by the controlled opening of a hydraulic valve ( 20 ) a pressure equalization between a hydraulic line ( 10 ) leading to a friction brake ( 2 ), and a pressure generating means is performed. Method according to one of claims 1 to 6, wherein the braking torque the electric regenerative brake limited to a predetermined maximum value becomes. Method according to Claim 7, in which the maximum value for the electrically regenerative brake is specified such that the through this achievable delay contribution does not exceed about 0.1 g, preferably about 0.07 g. The method of claim 7 or 8, wherein the electrically Regenerative brake a smoothing function is given when its braking torque to the above maximum value approaches. Method according to one of claims 7 to 9, wherein the braking torque the electric regenerative brake is limited so that the change the delay portion the electric regenerative brake at a change in the vehicle speed does not exceed a predetermined maximum value. Method according to one of claims 7 to 10, wherein the change the delay part of the electrically regenerative brake is subjected to a smoothing. Method according to one of claims 7 to 11, wherein the braking torque the electric regenerative brake is limited so that the change the change the delay portion the electric regenerative brake at a change in the vehicle speed does not exceed a predetermined maximum value. Brake system ( 1 ) of a motor vehicle, in particular for carrying out the method according to one of claims 1 to 12, which has a brake pressure generating means with or without auxiliary power, which is used to generate hydraulic brake pressure via a brake means (B) for friction brakes ( 2 ) of the braking system ( 1 ) with a brake pedal ( 6 ), an electronically controllable electrically regenerative brake, in particular a generator ( 4 ) for generating electrical energy from the kinetic energy of the motor vehicle, an electronic control unit ( 28 ), a hydraulic unit with electrically controllable hydraulic valves ( 14 . 16 . 18 . 20 . 21 ), and hydraulic lines ( 10 ) connecting the hydraulic valves ( 14 . 16 . 18 . 20 . 21 ), Brake pressure generating means and the friction brakes ( 2 ), wherein upon release of braking torque of the electrically-regenerative brake, an additional brake pressure build-up for the friction brakes ( 2 ) can be done with another assisted brake pressure generating means. Brake system ( 1 ) according to claim 13, wherein the brake means (B) for the additional brake pressure build-up via a hydraulic line ( 10 ) and an additional shut-off valve ( 21 ) can be removed directly from the brake fluid reservoir. Brake system ( 1 ) according to claim 14, in which in the hydraulic line ( 10 ) in series with the shut-off valve ( 21 ) a check valve ( 40 ) is switched. Brake system ( 1 ) according to one of claims 13 to 15, of which one brake pressure generating means is an auxiliary power operated master cylinder, in particular tandem master cylinder ( 8th ), and the further pressure generating means an electrically controllable hydraulic pump ( 22 ). Brake system ( 1 ) according to one of Claims 13 to 16, in which a number of friction brakes ( 2 ) leading hydraulic lines ( 10 ) a pressure sensor ( 26 ) is positioned to measure the pressure of a braking means (B). Brake system ( 1 ) according to one of claims 13 to 17, in which electrically controllable hydraulic valves ( 14 . 16 . 18 . 20 . 21 ) can be controlled so that a pressure control via a hydraulic valve ( 14 . 16 . 18 . 20 . 21 ) can be made. Brake system ( 1 ) according to one of claims 13 to 18, the brake pedal ( 6 ) a number of encoders ( 24 ) having. Brake system ( 1 ) according to one of claims 13 to 19, comprising a number of pressure sensors ( 26 ), for measuring the pressure of a braking means (B), wherein a pressure sensor ( 26 ) in a hydraulic line ( 10 ), which leads to a Bremsdru leads cuber. Method for operating a brake system ( 1 ) according to one of claims 13 to 20, in which the shut-off valve ( 21 ) is subjected to regular test cycles. The method of claim 21, wherein a test cycle exclusively then done if there is no driver request. A method according to claim 21 or 22, wherein a test cycle automated, preferably in a global test phase before departure or after completion of the journey, carried out becomes. Method according to one of Claims 21 to 23, in which, in the case of a test cycle, the inlets to the pressure generating means ( 22 ) switched valves and the ASR valve ( 20 ) and then the pressure generating means ( 22 ) is controlled, wherein at a detected pressure build-up on the friction brakes ( 2 ) is closed to a leak in the supply system, Method according to one of Claims 21 to 24, in which, in the case of a test cycle, the feeds into the supply lines to the pressure generating means ( 22 ) switched valves and the ASR valve ( 20 ) and then the pressure generating means ( 22 ) is driven, wherein at a detected increased power consumption in the pressure generating means ( 22 ) is closed to a leak in the supply system. Method according to one of Claims 21 to 23, in which, in the case of a test cycle, the inlets to the pressure generating means ( 22 ) connected valves and as an inlet valve for the friction brake ( 2 ) provided SO valve ( 14 ) and the ASR valve ( 20 ) are throttled if necessary and then the pressure generating means ( 22 ) is driven, wherein at a detected increased power consumption in the pressure generating means ( 22 ) is closed to a leak in the supply system.