DE102018201461A1 - Estimation method for the coefficient of friction of a hydraulic brake system - Google Patents

Abstract

The invention relates to a system and a method for estimating the coefficient of friction of a hydraulic brake system of a motor vehicle. Moreover, the invention relates to a system and a method for adapting the desired yaw moment of a motor vehicle generated by a hydraulic brake system in order to obtain a desired actual yaw moment.

Description

The invention relates to a system and a method for estimating the coefficient of friction of a hydraulic brake system of a motor vehicle. Moreover, the invention relates to a system and a method for adapting the desired yaw moment of a motor vehicle generated by a hydraulic brake system in order to obtain a desired actual yaw moment.

The coefficient of friction (also known as Cp value) of a hydraulic brake system between brake pad and brake disc determines the generation of braking torque and is proportional to the brake pressure. Since only the brake pressure can be measured, it is important for accurate knowledge of the braking torque at the wheels to estimate the coefficient of friction as accurately as possible. By measuring the vehicle deceleration and brake pressure and knowing the vehicle parameters, e.g. the vehicle mass, can be calculated back to the coefficient of friction. There is also a method for friction coefficient estimation, which does not require knowledge of the vehicle mass, in which the longitudinal deceleration is compared by the friction brake with that by an electric motor whose moment is precisely known.

The DE 35 02 050 A1 proposes to measure as a parameter for the braking torque in the brake torque generating the braking device resulting temperature and evaluated in an evaluation.

The DE 100 11 270 A1 discloses a method and apparatus for determining a characteristic of a wheel brake that represents the relationship between brake torque and brake pressure. The determination of the brake characteristic value takes place on a wheel-by-cylinder basis on the basis of wheel-specific variables such as wheel slip, wheel contact force, wheel brake pressure and wheel radius.

The DE 10 2014 226 290 A1 teaches a method for adjusting or controlling a brake actuation quantity BR (FZ), which is either the application force F or the brake pressure PR or the application path X (xs) of a motor vehicle brake with at least one braked wheel R, within an electro-hydraulic or electromechanical vehicle brake a chassis of the vehicle is mounted with a brake holder and brake friction on the wheel in accordance with the brake actuation size BR (FZ) braking, which resulting from contact of the braked wheel with a road surface Radumfangskraft F (FU) measured and influencing the braking force F (FU ) is performed as a function of the gradient of the wheel peripheral force F (.DELTA.FU / .DELTA.s), in which the actual value of the control is the slope of the wheel peripheral force F (.DELTA.FU / .DELTA.s) and this by adjusting the brake actuation quantity BR (FZ) to a predetermined desired value TVR (OP (ΔFU / Δs)) or a setpoint range TUR (OP (ΔFU / Δs) +/- R (ΔFU / Δs)) is adjusted.

From the DE 10 2010 043 320 A1 are known an apparatus and a method for determining a measure of an effective frictional force on a disc brake of a motor vehicle. A sensor device arranged on the disk brake measures a displacement of the brake holder caused by the braking force effect in a direction perpendicular to the axial direction of the brake disk. A measure of the braking torque acting is determined on the basis of the friction force caused by the deformation of the brake holder in a direction tangential to the brake disc surface.

Against this background, the object was to provide a new system and method for estimating the coefficient of friction of a hydraulic brake system of a motor vehicle, which make do without the use of vehicle parameters, such as a vehicle mass.

In the context of the present invention, a new system for estimating a coefficient of friction of a hydraulic brake system of a motor vehicle with the features of claim 1 is presented. Embodiments result from the dependent claims and the description. In addition, a method for estimating a coefficient of friction of a hydraulic brake system of a motor vehicle with the features of claim 4 is presented. Embodiments result from the dependent claims and the description.

In addition, a method with the features of claim 7 for adapting a desired yaw moment of a motor vehicle generated by a hydraulic brake system to obtain a desired actual yaw moment, and a system suitable for this purpose with the features of claim 8 are presented. Embodiments emerge from the dependent claims and the description and the drawings.

• 1 ein Flussdiagramm des erfindungsgemäßen Verfahrens zur Schätzung des Reibwerts eines hydraulischen Bremssystems eines Kraftfahrzeugs, in dem die Verfahrensschritte und Datenflüsse illustriert sind;
• 2 ein Flussdiagramm des erfindungsgemäßen Verfahrens zur Anpassung des von einem hydraulischen Bremssystem erzeugten Soll-Giermoments eines Kraftfahrzeugs, um ein gewünschtes Ist Giermoment zu erhalten, in dem die Verfahrensschritte und Datenflüsse illustriert sind.

The invention is schematically illustrated by means of embodiments in the drawings and will be described schematically and in detail with reference to the drawings. It shows:

• 1 a flowchart of the method according to the invention for estimating the coefficient of friction of a hydraulic brake system of a motor vehicle, in which the method steps and data flows are illustrated;
• 2 a flowchart of the inventive method for adjusting the desired yaw moment of a motor vehicle generated by a hydraulic brake system to obtain a desired actual yaw moment, in which the method steps and data flows are illustrated.

The invention provides a solution for estimating the coefficient of friction of a hydraulic brake system of a motor vehicle that manages without the use of vehicle parameters, for example the vehicle mass. Within the scope of the invention adjusting and measuring systems can be used, which are usually present in the vehicle. Further advantages and embodiments of the invention will become apparent from the following description.

The system according to the invention comprises at least one hydraulic brake system with the possibility of a wheel-specific pressure build-up, which acts on at least one wheel of the motor vehicle; and at least one further actuator system, which can apply a torque to at least one wheel with a higher positioning accuracy than the hydraulic brake system, which generates a yaw moment on the motor vehicle. Furthermore, the system according to the invention comprises at least one sensor and a unit for calculating an estimated coefficient of friction from the sensor data.

Hydraulic brake systems usually have the possibility of a wheel-specific pressure build-up via e.g. an ESP pump and suitable valve switching. By building up pressure on individual wheels, a yaw moment can be applied to the vehicle, which improves the driving dynamics or produces driving stability. This is called Brake Torque Vectoring (BTV).

In one embodiment, the further actuator system comprises at least one EM single-wheel motor. The EM single-wheel motor can also be operated as a generator. So he can set both a positive and a negative moment on the wheel and thus generate a yaw moment. In another embodiment, the further actuator system comprises at least one sport differential, i. H. a differential which can set a differential moment of the wheels on an axle.

In the system according to the invention at least one suitable sensor is included. In one embodiment, the system includes at least one yaw rate sensor. The method according to the invention for estimating the coefficient of friction of a hydraulic brake system of a motor vehicle comprises the following steps: A braking torque (desired braking torque = actual braking torque) is set on at least one wheel of the motor vehicle via an actuator system with high positioning accuracy, thereby generating a yawing moment on the vehicle , which measures the yaw reaction caused by the yaw moment and determines the transmission behavior between yawing moment and yaw reaction. It is applied via the hydraulic brake system, a target yaw moment on the vehicle and measured the yaw reaction. Thus, with the inverse transmission behavior between yaw moment and yaw reaction, the actual yaw moment can be calculated. From the yawing moments on the vehicle, the braking moments at the wheels and thus the actual coefficient of friction of the hydraulic brake system can be calculated by means of the vehicle dimensions.

To clarify the sequence of the method according to the invention in 1 Also shown as a flowchart in which the individual process steps and the data flows are located.

Alternativ kann über eine Messung des Bremsdrucks der Ist-Reibwert berechnet werden: $$\text{Ist}-\text{Reibwert}=\text{ Ist}-\text{Giermoment}/\text{Bremsdruck}.$$

Due to the unknown coefficient of friction of the braking system, the desired yawing moment mostly deviates from the actual yawing moment. There are other actuator systems (eg EM single-wheel motors, Sportdifferenziale) known which can apply a yaw moment on the vehicle with a higher positioning accuracy than the brake system. The desired yaw moment thus corresponds well to the actual yaw moment. It is made via an actuator system with high positioning accuracy a braking torque on the wheel that generates a yaw moment on the vehicle (target yaw moment = actual yaw moment) and measured the yaw response and determines the transmission behavior between yaw moment and wheel deceleration. It is applied via the hydraulic brake system, a target yaw moment on the vehicle and measured the yaw reaction and closed with the inverse transfer behavior between yaw moment and yaw reaction to the actual torque of the friction brake on the wheel. Knowing the setpoint torque and the rated friction value, it is possible to deduce the actual coefficient of friction: $$\text{is}-\text{friction}=\text{is}-\text{yaw moment}/\text{Should}-\text{yaw moment}*\text{Nennreibwert},$$

Alternatively, the actual friction coefficient can be calculated by measuring the brake pressure: $$\text{is}-\text{friction}=\text{is}-\text{yaw moment}/\text{brake pressure},$$

Another object solved in the context of the present invention is to set a desired actual yaw moment on the vehicle via at least one wheel with a hydraulic brake system. In this case, one is not interested in the coefficient of friction, but in the relationship between the desired and actual yawing moment generated by the hydraulic braking system. With this factor, you can then multiply the target yaw moment generated by the hydraulic brake system to get the desired yaw moment on the vehicle. For this purpose, as described above, the actual yaw moment generated via the brake system is determined and it relates to the desired yawing moment on the vehicle generated via the brake system.

The invention therefore also relates to a system and a method for adapting the desired yaw moment generated by a hydraulic brake system of a motor vehicle to achieve a desired actual yaw moment on the motor vehicle. The desired actual yaw moment corresponds to the original desired yaw moment. The method comprises setting a yaw moment on the motor vehicle via an actuator system which has a higher positioning accuracy than the hydraulic brake system and the measurement of the yaw moment caused by the yaw moment of the motor vehicle with subsequent determination of the transmission behavior between yaw moment and yaw reaction. Furthermore, the method comprises applying a desired yaw moment to the motor vehicle via the hydraulic brake system, measuring the yaw moment caused by the yaw moment and estimating the actual yaw moment via the inverse of the transmission behavior between yaw moment and yaw reaction. Then, the ratio between the target and actual yaw momentes generated by the hydraulic brake system is calculated, and the target yaw moment generated by the hydraulic brake system is multiplied by the obtained factor to obtain a target yaw moment that produces an actual yaw moment. which corresponds to the original target yaw moment.

To clarify the sequence of the method according to the invention in 2 Also shown as a flowchart in which the individual process steps and the data flows are located.

Furthermore, the invention provides a system for adapting the desired yaw moment generated by a hydraulic brake system of a motor vehicle to obtain a desired actual yaw moment. The desired actual yaw moment corresponds to the original desired yaw moment. The system comprises at least one hydraulic brake system acting on at least one wheel of the motor vehicle, and at least one further actuator system which can apply a yaw moment to the vehicle with a higher positioning accuracy than the hydraulic brake system. The system also includes at least one sensor, a unit for calculating an actual yaw moment from the sensor data, and a unit for changing the target yaw moment generated by the hydraulic brake system.

Examples of suitable other actuator systems include sport differential and EM single-wheel engines. Suitable sensors are, for example, yaw rate sensors.

It is understood that the above-mentioned features can be used not only in the respectively specified combination, but also in other combinations or in isolation, without departing from the scope of the present invention.

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 3502050 A1 [0003]
• DE 10011270 A1 [0004]
• DE 102014226290 A1 [0005]
• DE 102010043320 A1 [0006]

Claims (10)

System for estimating a coefficient of friction of a hydraulic braking system of a motor vehicle, comprising: at least one hydraulic braking system acting on at least one wheel of the motor vehicle; at least one further actuator system, which can provide a torque at at least one wheel with a higher positioning accuracy than the hydraulic brake system, which causes a yaw moment on the vehicle; at least one sensor; a unit for calculating an estimated coefficient of friction from the sensor data. System after Claim 1 in which the further actuator system comprises at least one EM single-wheel motor or a differential which can set a differential torque between the wheels of an axle ("sport differential"). System after Claim 1 or 2 comprising at least one yaw rate sensor. Method for estimating a coefficient of friction of a hydraulic brake system of a motor vehicle, comprising the steps: a) setting a yaw moment on the motor vehicle via an actuator system which has a higher positioning accuracy than the hydraulic brake system; b) measuring the yaw moment caused by the yaw moment of the vehicle; c) determining the transmission behavior between yaw moment and yaw response of the vehicle; d) applying a desired yaw moment to the motor vehicle via the hydraulic brake system; e) measuring the yaw moment caused by the yaw moment of the vehicle; f) estimating the actual yaw moment via the inverse of the transmission behavior between yaw moment and yaw response of the vehicle determined in step c); g) Calculation of the actual coefficient of friction of the hydraulic brake system. Method according to Claim 4 in which the friction coefficient is calculated from the target yaw moment and the actual yaw moment and the rated friction value of the hydraulic brake system according to $$\text{friction}=\text{is}-\text{yaw moment}/\text{Should}-\text{yaw moment}*\text{Nennreibwert},$$

Method according to Claim 4 in which the coefficient of friction is calculated from the actual braking torque and the brake pressure of the hydraulic braking system according to $$\text{friction}=\text{is}-\text{braking torque}/\text{brake pressure},$$

A method of adjusting a desired yaw moment of a motor vehicle generated by a hydraulic braking system to achieve a desired actual yaw moment, comprising the steps of: a) setting a yaw moment on the motor vehicle via an actuator system which has a higher positioning accuracy than the hydraulic brake system; b) measuring the yaw moment caused by the yaw moment of the vehicle; c) determining the transmission behavior between yaw moment and yaw response of the vehicle; d) applying a desired yaw moment to the motor vehicle via the hydraulic brake system; e) measuring the yaw moment caused by the yaw moment of the vehicle; f) estimating the actual yaw moment via the inverse of the transmission behavior between yaw moment and yaw response of the vehicle determined in step c); g) calculating the ratio between the desired and actual yawing moment generated by the hydraulic braking system; h) multiplying the desired yaw torque generated by the hydraulic brake system with the factor obtained to obtain a desired yaw moment corresponding to the desired actual yaw moment. A system for adjusting a desired yaw moment of a motor vehicle generated by a hydraulic brake system to a desired actual yaw moment, comprising: at least one hydraulic brake system acting on at least one wheel of the motor vehicle; at least one further actuator system which can apply a torque to at least one wheel with a higher positioning accuracy than the hydraulic brake system, which causes a yaw moment on the vehicle; at least one sensor; a unit for calculating an actual yaw moment from the sensor data; and a unit for changing the target yaw moment generated by the hydraulic brake system. System after Claim 8 in which the further actuator system comprises at least one EM single-wheel motor and / or at least one sports differential. System after Claim 9 comprising at least one yaw rate sensor.

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