DE102013018766A1 - A method of removing a lubricating film from a friction surface of a brake disk of a vehicle - Google Patents

Abstract

A method of removing a lubricating film from a friction surface of a brake disc of a vehicle, the vehicle comprising a brake system comprising the at least one brake disc having at least one associated friction pad having a variable surface pressure (p) on the friction surface of the brake disc for generating a vehicle negative longitudinal acceleration (a) can be pressed, as well as means for detecting the longitudinal acceleration and means for lubricating film detection, wherein the means for lubricating film detection can be made that at least one friction lining on the friction surface automatically for a cleaning period (r) with a surface pressure ( p), which generates a negative longitudinal acceleration (a) below a threshold of visibility, can be pressed on the friction surface, wherein at an instigation by the means for lubricating film detection intermittently during an upstream period (v) without Flächenpres Sung (p) and at a longitudinal acceleration (a) within a tolerance band lying around 0 g (T) the average longitudinal acceleration (av) is detected, ...

Description

The present invention relates to a method for removing a lubricating film from a friction surface of a brake disc of a vehicle, wherein the vehicle is a brake system comprising the at least one brake disc with at least one associated friction lining having a variable surface pressure on the friction surface of the brake disc for generating a on the Vehicle acting negative longitudinal acceleration can be pressed, as well as means for detecting the longitudinal acceleration and means for lubricating film detection, wherein the means for lubricating film detection can cause the at least one friction lining on the friction surface automatically for a cleaning period with a surface pressure, the negative longitudinal acceleration generated below a perception threshold, can be pressed on the friction surface.

Such methods are used in vehicles with disc brakes having brake system. Usually, each wheel is associated with a brake disk with two opposing friction surfaces. The brake disk rotates with the wheel. Each friction surface is assigned a friction lining, also called a brake pad or brake pad, which can be brought into frictional contact with the friction surface as required by electromechanical, electromagnetic, pneumatic or hydraulic means. One problem is that, among other things by the wheel rim dirt and moisture can reach the brake disc and in particular to the friction surfaces, which forms a lubricating film there. If the friction lining does not rub over the friction surface, a particularly pronounced lubricating film can build up, which significantly worsens the coefficient of friction between the friction surface and the friction lining during a subsequent braking operation. Since this represents a safety risk, a process for removing the lubricating film from the friction surface of the brake disk is started (so-called "brake wiping") in a recognized or expected film formation (for example, using a rain sensor of the windscreen wiper system). In this case, the friction lining is pressed at intervals with little pressure against the friction surface, so that the lubricant film is wiped off. The pressure is so low that the driver does not perceive this brake wiping as possible. The difficulty is to find a suitable intensity for the brake disc wiper, which represents a compromise between safety, efficiency and comfort.

The DE 100 35 179 A1 describes a method for detecting lubricating film on brake discs and / or the measurement of the friction coefficient of the brake pad on the brake disc, wherein a time course and / or a current ratio of the achieved braking effect compared to the brake pressure of the vehicle is evaluated in terms of increasing ratio. With each braking of the vehicle, therefore, the time course of the brake pressure and the actual braking deceleration is measured. In order to obtain the brake deceleration by the brake pressure, adjusted for any downgrade accelerations, the acceleration of the vehicle immediately before the onset of braking, possibly taking into account the instantaneous engine power, must be estimated or calculated. This method has the disadvantage that it is dependent on brake actuations by the driver and, in particular with very long constant driving, does not permit any precise conclusions about the condition of the lubricating film on the friction surfaces.

The DE 103 22 451 A1 discloses a method for improving the coefficient of friction of brake linings of a friction brake of a vehicle, wherein the brake is actuated automatically in response to a predetermined first parameter according to a predetermined program and in response to a predetermined second parameter preferably second measured value, the program is terminated by the program the brake is operated automatically at intervals. This method is designed to be relatively rigid and must therefore be set exactly to each vehicle type, which is not readily possible in practice.

The DE 199 47 903 A1 shows a method of controlling a friction brake of a wheel of a vehicle having two friction linings movable relative to a brake disc, comprising tensioning the brake by exerting a frictional force over the friction linings on the brake disc for decelerating the speed of the vehicle, releasing the brake for adjustment a desired deceleration and / or adjustment of a clearance between the brake disc and each of the friction linings, wherein an automatic, cyclic and active brake actuation for drying or cleaning a friction surface of the brake disc takes place without substantial deceleration of the vehicle. The braking force and / or the braking stroke ratio for drying, keeping dry or cleaning the brake disc is adjusted depending on a measured speed of the vehicle, deceleration of the vehicle, windshield wiper frequency of the vehicle and / or amount of rain. Also, this method offers only limited adaptability to the actual lubricating film on the friction surfaces.

The object of the present invention is therefore a method for removing a lubricating film from a friction surface of a brake disk to provide self-learning optimization of the intensity of the braking interventions used to remove the lubricating film during operation.

This object is solved by the features of patent claim 1.

A method of removing a lubricating film from a friction surface of a brake disk of a vehicle, the vehicle comprising a brake system comprising the at least one brake disk having at least one associated friction lining pressed against the friction surface of the brake disk with a variable surface pressure to produce a negative longitudinal acceleration acting on the vehicle can be caused by the means for detecting the lubricant film, that the at least one friction lining on the friction surface automatically for a cleaning period with a surface pressure that generates a negative longitudinal acceleration below a perception threshold, can be pressed onto the friction surface, wherein at an instigation by the means for lubricating film detection intermittently during an upstream period without surface pressure and at a length acceleration within a tolerance band lying around 0 g, the average longitudinal acceleration is detected, wherein the preceding period directly follows the cleaning period and during this the surface longitudinal compression resulting average pressure is detected, the actual difference of the longitudinal accelerations during the upstream period and the Cleaning period is compared with a desired difference range and wherein by adjusting the interval length between the cleaning periods and / or duration of the cleaning period and / or the amount of surface pressure, the actual difference can be continuously maintained within the desired differential range.

In the case of a lubricant film formation detected or expected by the lubricant film detection means on the friction surface of the brake disk, the method steps for determining the average longitudinal acceleration of the vehicle in an upstream period with a longitudinal acceleration within a tolerance band lying around 0 g at an interval, for determining the average longitudinal acceleration of the vehicle in an immediately following cleaning period with a defined surface pressure of the at least one friction lining on the corresponding friction surface ("brake wiping"), forming the actual difference between the two determined longitudinal accelerations and the comparison of the actual difference with a desired difference range can be performed by the derivable adjustment of the interval length between the cleaning periods and / or duration of the cleaning period and / or the amount of surface pressure a continuous optimization of Procedure can be achieved. With the method according to the invention, the best possible compromise of safety, efficiency and comfort can thus be found and permanently maintained in a short time. The initial parameter settings are limited to basic values for the tolerance band, the target differential range, interval length between the cleaning periods, duration of the cleaning periods and the amount of surface pressure. Based on this, the method automatically develops the optimum parameters for the vehicle and the ambient conditions by calling this step sequence at intervals. The surface pressure should be kept as constant as possible during the cleaning period by the brake system with electromechanical, electromagnetic, hydraulic or pneumatic power generation. It should be noted that the longitudinal acceleration of the vehicle, at least during the preceding period, but preferably during the upstream period and the cleaning period, remains constant, so no additional longitudinal acceleration of the vehicle is performed by a drive unit, no switching operations of a speed change gearbox or a change in the Impact force acting on the vehicle. The means for detecting the lubricant film can either detect the lubricating film on the friction surface on the basis of discrete measured values or, by way of further boundary conditions (eg, windscreen wiper switched on), infer the presence of moisture with the risk of film formation. The means for detecting the longitudinal acceleration are already present in modern vehicles as part of the ESP system anyway. The perceptibility threshold is the negative longitudinal acceleration that a majority of vehicle drivers would already perceive as disruptive. Exceeding this threshold should always be avoided.

In a preferred embodiment, if the actual difference is too small outside of the desired difference range, the interval length between the cleaning periods is increased step by step and / or the duration of the cleaning period is increased and / or the amount of surface pressure is increased. Too small an actual difference is an indication that the surface pressure applied during the cleaning period leads to almost no slowing of the vehicle (negative longitudinal acceleration) and is therefore ineffective. For the sake of safety, therefore, measures must be taken to enhance the removal of the lubricating film.

In a preferred embodiment, if the actual difference is too large outside the desired difference range, the interval between the cleaning periods is reduced step by step and / or the duration of the cleaning period is shortened and / or the amount of surface pressure is reduced. Too large an actual difference is an indication that the surface pressure exerted during the cleaning period leads to a noticeable slowing of the vehicle (negative longitudinal acceleration) and can therefore be perceived by the driver. For convenience and efficiency, therefore, measures must be taken to reduce the removal of the lubricating film.

In a preferred embodiment, the cleaning period comprises two sub-periods, the longitudinal acceleration being detected only in the later sub-period. By only determining the average longitudinal acceleration acting on the vehicle in the later sub-period of the cleaning period, the complete set-up of the required surface pressure by the brake system can be awaited and consequently measured with improved accuracy.

In a preferred embodiment, the lubricant film detection means comprises a humidity sensor. The moisture sensor can be arranged in the wheel area or serve as a rain sensor for a windshield wiper system of the vehicle.

Further details and advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the drawings.

Show:

1 a part of the brake system of a vehicle;

2 a diagram section of the method.

According to the 1 includes a brake system 1 for a vehicle, not shown, several assemblies of brake disc 2 and friction linings 3 In this case, by way of example, only one brake disk 2 with friction lining 3 is shown. The brake disc 2 has a pot and a friction ring, the friction ring on both sides opposite friction surfaces 2a having. One friction lining each 3 superimposes the friction surface assigned to it 2a at least partially and may (by a brake caliper of known type not shown), if necessary, power-operated with a variable surface pressure against the friction surface 2a be pressed, thereby increasing the angular velocity of the rotating brake disc 2 decreases and leads to a negative longitudinal acceleration on the vehicle. On the friction surface 2a In particular, in the case of rain, a lubricating film can form, which is wiped off by a defined surface pressure, which leads to a negative longitudinal acceleration below a perceptibility threshold (so-called "brake wiping").

The 2 shows a diagram for a method according to the invention for brake wiper, so to remove the lubricating film on the in 1 shown friction surface 2a the brake disc 2 , The time t is plotted on the abscissa, while the ordinate is dimensionless. The lower graph represents the course of the amount of the surface pressure p over the time t and the upper graph the course of the longitudinal acceleration a over the time t. If a brake wipe is requested, the method starts at intervals with the first method step, as soon as the longitudinal acceleration a during an upstream period v continuously within a tolerance band T, which lies around 0 g longitudinal acceleration a remains. The determined mean longitudinal acceleration av, which is likely to be very close to 0 g by the required constant travel, is stored internally and started after the expiry of the upstream period v with the structure of the surface pressure p to the defined extent. When the desired surface pressure p is reached, it is maintained constant for the cleaning period r. The cleaning period r can be subdivided into two sub-periods r1 and r2, wherein first the earlier under-time period r1 and then the subsequent lower-time period r2 then takes place. Only during the later sub-time interval r2, in turn, the average longitudinal acceleration ar is determined and stored internally, which in this case should have a negative sign. From the two longitudinal accelerations av and ar an actual difference D is formed and compared with a stored desired difference range. If the actual difference D lies within the desired differential range, then no adaptation of the process parameters is necessary. If the actual difference D lies outside the desired difference range in the sense of an excessively small actual difference D, then the interval length between the cleaning periods r is increased step by step and / or the duration of the cleaning period r is increased and / or the amount of the surface pressure p is increased. If the actual difference D lies outside the desired difference range in the sense of an excessively large actual difference D, then the interval length between the cleaning periods r is reduced in a stepwise manner and / or the duration of the cleaning period r is shortened and / or the amount of the surface pressure p is reduced.

LIST OF REFERENCE NUMBERS

a

longitudinal acceleration

ar

mean longitudinal acceleration during the cleaning period

av

mean longitudinal acceleration during the preceding period of time

D

Actual difference

p

surface pressure

r

Cleaning period

r1

earlier sub-period span

r2

later sub time span

T

tolerance band

t

Time

v

upstream time span

1

braking system

2

brake disc

2a

friction surface

3

friction lining

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10035179 A1 [0003]
• DE 10322451 A1 [0004]
• DE 19947903 A1 [0005]

Claims (5)

Method for removing a lubricating film from a friction surface ( 2a ) a brake disc ( 2 ) of a vehicle, wherein the vehicle is a brake system ( 1 ), comprising the at least one brake disc ( 2 ) with at least one associated friction lining ( 3 ), with a variable surface pressure (p) on the friction surface ( 2a ) of the brake disc ( 3 ) for generating a negative longitudinal acceleration (a) acting on the vehicle, as well as means for detecting the longitudinal acceleration and means for identifying the lubricant film, whereby the means for detecting the lubricant film can cause the at least one friction lining ( 3 ) on the friction surface ( 2a ) automatically for a cleaning period (r) with a surface pressure (p), which generates a negative longitudinal acceleration (a) below a perception threshold, on the friction surface ( 2a ) can be pressed, characterized in that at an instigation by the means for lubricating film detection intermittently during an upstream period (v) without surface pressure (p) and at a longitudinal acceleration (a) within a lying around 0 g tolerance band (T) the mean Longitudinal acceleration (av) is detected, wherein the upstream period (v) immediately follows the cleaning period (r) and during this by the surface pressure (p) resulting average longitudinal acceleration (ar) is detected, wherein the actual difference (D) the Longitudinal accelerations (av, ar) during the preceding period (v) and the cleaning period (r) is compared with a target differential range and wherein by adjusting the interval length between the cleaning periods (r) and / or duration of the cleaning period (r) and / or the amount of surface pressure (p), the actual difference (D) is continuously within the desired differential range s can be kept. A method according to claim 1, characterized in that at too small an actual difference (D) outside the target differential range gradually increases the interval length between the cleaning periods (r) and / or extends the duration of the cleaning period (r) and / or the amount the surface pressure (p) is increased. A method according to claim 1, characterized in that at too large an actual difference (D) outside the target difference range gradually reduces the interval length between the cleaning periods (r) and / or the duration of the cleaning period (r) and / or shortened the amount the surface pressure (p) is reduced. Method according to one of claims 1 to 3, characterized in that the cleaning period (r) comprises two sub-periods (r1, r2), wherein only in the later sub-period (r2) the longitudinal acceleration (a) is detected. Method according to one of claims 1 to 4, characterized in that the means for lubricating film detection comprise a moisture sensor.

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