WO2008077670A1 - Procédé et dispositif de détermination d'un indice de friction - Google Patents

Procédé et dispositif de détermination d'un indice de friction Download PDF

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Publication number
WO2008077670A1
WO2008077670A1 PCT/EP2007/061783 EP2007061783W WO2008077670A1 WO 2008077670 A1 WO2008077670 A1 WO 2008077670A1 EP 2007061783 W EP2007061783 W EP 2007061783W WO 2008077670 A1 WO2008077670 A1 WO 2008077670A1
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WO
WIPO (PCT)
Prior art keywords
vehicle
acceleration
determined
angle
detected
Prior art date
Application number
PCT/EP2007/061783
Other languages
German (de)
English (en)
Inventor
Ning Bian
Celine Gamulescu
Matthias Kretschmann
Andreas Mayer
Original Assignee
Continental Automotive Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Continental Automotive Gmbh filed Critical Continental Automotive Gmbh
Publication of WO2008077670A1 publication Critical patent/WO2008077670A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
    • B60T8/17—Using electrical or electronic regulation means to control braking
    • B60T8/172—Determining control parameters used in the regulation, e.g. by calculations involving measured or detected parameters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W40/00—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models
    • B60W40/02—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models related to ambient conditions
    • B60W40/06—Road conditions
    • B60W40/068—Road friction coefficient
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T2210/00—Detection or estimation of road or environment conditions; Detection or estimation of road shapes
    • B60T2210/10—Detection or estimation of road conditions
    • B60T2210/12—Friction

Definitions

  • the invention relates to a method and a device for determining a friction coefficient between at least one tire of a vehicle and a roadway.
  • Modern motor vehicles have control systems that intervene in predetermined situations in a control of the motor vehicle.
  • the control system may be, for example, a vehicle dynamics control system and / or a driving dynamics comfort system.
  • an electronic stability system prevents a spin of the motor vehicle in the border area.
  • the electronic stability system may include an anti-lock braking system whereby the braking effect is periodically released and reinserted when the wheels are locked.
  • the electronic stability system may include a traction control system which controls the internal combustion engine of the motor vehicle by temporarily limiting the torque transmitted to the wheels so that the wheels do not spin.
  • DE 39 120 14 Al discloses a method for determining a coefficient of friction between a roadway and tires of a vehicle.
  • values for a steering angle, a driving speed, a yawing angular velocity and a lateral acceleration of the vehicle are respectively detected or determined.
  • a reference or desired yaw angular velocity is determined on the basis of a mathematical vehicle reference model.
  • a difference between the actual yaw rate of the vehicle and the reference or target vehicle yaw rate determined.
  • the value of the lateral acceleration is determined as a measure of the coefficient of friction between the road surface and the tires of the vehicle at which the difference between the actual yaw rate and the reference yaw rate begins to increase sharply.
  • EP 1 627 790 A1 discloses a method for estimating a friction coefficient.
  • a steering angle and a lateral acceleration are recorded.
  • An estimated value of the friction coefficient is determined by means of a table.
  • several areas for different steering angles and transverse accelerations are provided, which are assigned a plurality of friction coefficients.
  • the associated area of the table is selected and the assigned friction coefficient is used as an estimate of the friction coefficient.
  • US 2003/0074127 A1 discloses a system for calculating a road surface friction coefficient. This is estimated depending on a deviation of an estimated longitudinal or lateral acceleration with respect to a measured longitudinal or lateral acceleration of the vehicle.
  • the object of the invention is to provide a method and apparatus for determining a friction coefficient that is reliable.
  • the invention is characterized by a method and a corresponding device for determining a friction index between at least one tire of a vehicle and a roadway. At least one inclination of at least one acceleration sensor with respect to a vehicle-independent predetermined reference plane is determined. At least one acceleration of the vehicle is detected by means of the at least one acceleration sensor in a plane that runs essentially parallel to the roadway. The detected at least one acceleration of the vehicle is corrected as a function of the at least one inclination.
  • the friction coefficient is determined as a function of the corrected at least one acceleration.
  • the invention is based on the finding that in the presence of different inclinations of the road with respect to the predetermined reference plane, the detected at least one acceleration of the vehicle depending on a mounting direction of an acceleration sensor, which is provided for the detection of at least one acceleration, a different size Acceleration error caused by the gravitational acceleration.
  • the acceleration error has a negative effect on the precision of the determined friction coefficient.
  • an inclination of three degrees can lead to an acceleration error of 0.5 meters per second and significantly affect the precision of the determined coefficient of friction.
  • the correction of the at least one acceleration thus takes place in particular with respect to the gravitational acceleration.
  • the friction coefficient is therefore particularly precise and reliably determined.
  • the predetermined reference plane preferably has a fixed relation to the direction of gravitational acceleration.
  • the reference plane is perpendicular or parallel to the direction of gravitational acceleration.
  • the predetermined reference plane is a horizontally extending, horizontal reference plane.
  • the predetermined reference plane can also be specified differently.
  • the at least one acceleration of the vehicle comprises in particular a longitudinal acceleration and / or a lateral acceleration of the vehicle.
  • the at least one inclination of the roadway with respect to the predetermined reference plane comprises in particular a pitch angle and / or a roll angle.
  • the at least one inclination is determined depending on the detected at least one acceleration, a yaw rate, at least one wheel speed and a steering wheel angle or steering angle by means of a predetermined physical vehicle model.
  • a pitch rate and / or a roll rate is detected.
  • the at least one inclination is determined as a function of the pitch rate and / or the roll rate.
  • the pitch angle is determined as a function of the pitch rate and the roll angle as a function of the roll rate.
  • the at least one inclination is determined by integration of the pitch rate or the roll rate.
  • the advantage is that this is very easy.
  • the at least one inclination determined by the predetermined physical vehicle model is assigned to integration as the initialization value.
  • the advantage is that the initialization value contained in the at least one NEN predetermined driving condition is determined, is particularly reliable and by resetting the integration to the initial value diverging the integral can be easily and reliably prevented.
  • the at least one predetermined driving state includes in particular normal driving without skidding or heavy slipping.
  • the invention is characterized by a method and a corresponding device for determining a friction index between at least one tire of a vehicle and a roadway.
  • At least one differential angle is detected between a vehicle body and a chassis.
  • At least one acceleration of the vehicle is detected in a plane that runs essentially parallel to the roadway.
  • the detected at least one acceleration of the vehicle is corrected as a function of the at least one differential angle.
  • the friction coefficient is determined as a function of the corrected at least one acceleration.
  • the invention is based on the finding that, when different differential angles between the vehicle body and the chassis are present, the detected at least one acceleration of the vehicle has a different magnitude of acceleration error as a function of a mounting direction of an acceleration sensor which is provided for detecting the at least one acceleration caused by the gravitational acceleration.
  • the acceleration error has a negative effect on the precision of the determined friction coefficient. Even a difference angle of three degrees can lead to an acceleration error of 0.5 meters per second and significantly affect the precision of the determined coefficient of friction.
  • the correction of the at least one acceleration thus takes place in particular with respect to the gravitational acceleration.
  • the friction characteristics The number is therefore particularly precise and reliably determinable.
  • the at least one acceleration of the vehicle comprises, in particular, a longitudinal acceleration and / or a transverse acceleration of the vehicle.
  • the determination of the friction coefficient is suspended when an amount of the at least one inclination or the at least one differential angle is greater than a predetermined first inclination threshold or differential angle threshold, and resumed when the amount of at least one inclination or the at least one difference angle is smaller than a predetermined second inclination threshold value or difference angle threshold value.
  • the first and the second inclination threshold value or the difference angle threshold value can in particular also be given the same or can be predetermined such that a switching hysteresis results.
  • a slip angle is detected or determined.
  • a lateral coefficient of friction between the at least one tire of the vehicle and the roadway is determined by means of a model in which a functional relationship between the lateral friction value and the slip angle is predetermined in such a way that a nonlinear profile of the lateral friction value is dependent on the slip angle is from a recursively determined estimate of the friction coefficient.
  • a model acceleration corresponding to the at least one acceleration of the vehicle is determined and a deviation between the at least determines an acceleration of the vehicle and the model acceleration.
  • the recursion in determining the estimated value of the friction coefficient comprises that it is adjusted as a function of the determined deviation.
  • FIG. 1 is a plan view of a vehicle
  • FIG. 2 shows a side view of the vehicle on a longitudinally inclined roadway
  • FIG. 3 shows a front view of the vehicle on a transversely inclined roadway
  • FIG. 4 shows a further side view of the vehicle on the longitudinally inclined roadway
  • FIG. 5 shows a first device for determining a friction index
  • FIG. 6 shows a second device for determining the friction index
  • FIG. 7 shows a first flowchart
  • FIG. 9 shows a diagram of a lateral coefficient of friction.
  • a vehicle has an arithmetic unit 1 and sensors (FIG. 1).
  • the sensors are coupled to the arithmetic unit 1.
  • the sensors are in particular designed for detecting driving dynamic measured variables.
  • Such sensors are in particular a longitudinal acceleration sensor 2 for detecting a detected longitudinal acceleration ax sens and / or a lateral acceleration sensor 3 for detecting a detected lateral acceleration ay sens and a yaw rate sensor 4 for detecting a yaw rate w_z and a steering wheel angle sensor 7 for detecting a steering wheel angle ⁇ .
  • a steering angle can be detected at the wheels, in particular in the presence of a superposition steering.
  • a wheel speed sensor 8 is preferably arranged on each wheel of the vehicle for detecting a respective wheel speed rd.
  • a roll rate sensor 5 for detecting a roll rate wx and / or a pitch rate sensor 6 for detecting a pitch rate w_y can also be provided.
  • the sensors are in each case coupled to the arithmetic unit 1 and supply the respectively acquired measured values to them. Furthermore, other sensors may be provided.
  • FIG. 2 shows the vehicle in a side view on a roadway inclined in the longitudinal direction of the vehicle.
  • the roadway is inclined with respect to a vehicle-independent predetermined reference plane BE by a pitch angle ⁇ . Accordingly, the vehicle has an orientation in space that is rotated about a transverse axis of the vehicle.
  • Vehicle also essentially has the pitch angle ⁇ with respect to the predetermined reference plane BE.
  • FIG. 3 shows the vehicle in a front view on a roadway inclined in the transverse direction of the vehicle.
  • the roadway is inclined with respect to the vehicle-independent predetermined reference plane BE by a roll angle ⁇ .
  • the vehicle has an orientation in space that is rotated about a longitudinal axis of the vehicle.
  • the chassis FW of the vehicle also essentially has the roll angle ⁇ with respect to the predetermined reference plane BE.
  • the sensors and in particular the longitudinal acceleration sensor 2 and the lateral acceleration sensor 3 are generally fixedly mounted with a predetermined orientation in the vehicle.
  • the longitudinal acceleration sensor 2 and the lateral acceleration sensor 3 are arranged to detect an actual longitudinal acceleration ax or lateral acceleration a_y of the vehicle assuming a horizontal, horizontally running roadway.
  • the longitudinal acceleration sensor 2 and / or the lateral acceleration sensor 3 detect not only a component of the actual longitudinal or lateral acceleration ax, ay, but also a component of a gravitational acceleration a_g.
  • the predetermined reference plane BE is in particular given with a fixed relation to a direction of the gravitational acceleration a g, for example perpendicular or parallel to it.
  • the predetermined reference plane BE is preferably a plane running at the location of the vehicle perpendicular to the direction of the gravitational acceleration a_g and thus extending horizontally and horizontally.
  • the predetermined reference plane BE can also be specified differently.
  • the longitudinal acceleration sensor 2 and / or the lateral acceleration sensor 3 are preferably arranged in a vehicle body FA of the vehicle.
  • the vehicle body FA and the chassis FW are coupled to one another, for example, via a damping system, which comprises, for example, springs. Because of this non-rigid coupling, the vehicle body FA and the chassis FW can have a pitch difference angle ⁇ diff and / or a Have Wankdifferenzwinkel ⁇ _diff to each other, which can be equal to zero, in particular during acceleration or deceleration of the vehicle, cornering or by loading the vehicle.
  • the pitch difference angle ⁇ _diff and / or the roll difference angle ⁇ _diff may also be referred to as the difference angle.
  • the pitch difference angle ⁇ _diff for the side view of the vehicle.
  • the pitch difference angle ⁇ diff and the roll difference angle ⁇ _diff are small in most driving situations, so that the vehicle body FA therefore has substantially the inclination of the roadway with respect to a pitch or roll of the vehicle.
  • the vehicle preferably has spring travel sensors 9 or level sensors for determining the pitch difference angle ⁇ _diff and the roll difference angle ⁇ _diff.
  • FIG. 5 shows a first embodiment of a device for determining a friction coefficient ⁇ _R.
  • the coefficient of friction ⁇ R characterizes the friction between the tire and the road and is defined as the quotient of a maximum of the tire on the road transferable force in the direction parallel to the road and a Aufstandskraft F_z or as a limit of this quotient for large slip values.
  • the device is formed for example by the arithmetic unit 1 or is a part of this.
  • the device comprises a vehicle observer unit FB, which is designed to determine the inclination of the longitudinal and / or the lateral acceleration sensor 2, 3 with respect to the predetermined reference plane BE, for example as the sum of the pitch angle ⁇ and the pitch difference angle ⁇ diff and / or as the sum of the roll angle ⁇ and the roll difference angle ⁇ _diff.
  • these sums are determined as a function of the detected longitudinal acceleration a_x_sens and / or the detected lateral acceleration ay sens and the wheel speeds rd, the yaw rate wz and the steering wheel angle ⁇ or steering angle by means of a predetermined physical vehicle model.
  • it is to determine pitch angle ⁇ plus pitch difference angle ⁇ _diff and / or roll angle ⁇ plus rolling difference angle ⁇ diff depending on the pitch rate w_y and / or the roll rate w_x.
  • the device further comprises an acceleration error determination unit ERR, which is designed as a function of the detected longitudinal acceleration a_x_sens and / or the detected lateral acceleration ay sens and the sum of the pitch angle ⁇ and the pitch angle ⁇ _diff and / or the sum of the roll angle ⁇ and the roll difference angle ⁇ diff to determine the longitudinal acceleration error a_x_err and / or the lateral acceleration error ay err.
  • ERR acceleration error determination unit
  • the device is furthermore designed to determine the actual longitudinal acceleration a x as a function of the detected longitudinal acceleration a_x_sens and the longitudinal acceleration error a x err and to determine the actual lateral acceleration a_y in accordance with the detected lateral acceleration a y sens and the lateral acceleration error a y err.
  • the device further comprises an estimation unit EST, which is designed to determine the coefficient of friction ⁇ R between the at least one tire of the vehicle and the roadway as an estimated value.
  • the estimation unit EST is supplied with the actual longitudinal or lateral acceleration a_x, a_y. Further, the estimation unit EST is supplied with a slip angle ⁇ , the footing force F_z of the respective tire of the vehicle on the road, and a vehicle speed v.
  • the slip angle ⁇ is defined as an angle between a wheel plane perpendicular to a wheel axis and a moving direction of a touch area in which the tire and the road touch.
  • measured values of the measured quantities are processed before these are sent to the vehicle observer unit FB, the acceleration error determination unit ERR or the Estimation unit EST be supplied.
  • the processing of the respective measured values comprises, for example, a filtering and in particular a low-pass filtering and / or a correction or conversion of the acquired measured values.
  • it may be provided to determine measured variables derived depending on the supplied measured values, for example taking vehicle-dynamics vehicle models into account or by simply calculating two or more of the measured values of different measured variables into a measured value of a measured variable derived therefrom.
  • Such a derived measured variable is, for example, the vehicle speed v, which can be determined as a function of the detected wheel speeds rd, or the contact force F_z, which is exerted perpendicular to the roadway via a wheel of the vehicle. Furthermore, the slip angle ⁇ can be determined as a function of the detected yaw rate w_z. However, the said derived measured variables may also be determined or recorded differently.
  • FIG. 6 shows a second embodiment of the device for determining the coefficient of friction ⁇ R, which differs from the first embodiment essentially in that the vehicle observer unit FB is designed, depending on sensor signals of the spring travel sensors 9 or level sensors, the pitch difference angle ⁇ diff and / or Wankdifferenzwinkel ⁇ _diff to determine, and the Beministerungstalk er accordingsillon ERR is designed to determine depending on these difference angles and depending on the detected longitudinal acceleration ax sens and / or the detected lateral acceleration a_y_sens the longitudinal acceleration error a_x_err and / or the lateral acceleration error ay err.
  • the second embodiment of the device substantially corresponds to the first embodiment of the device.
  • FIG. 7 shows a flow chart of a first program for determining the friction coefficient ⁇ _R.
  • the program is executed by the first embodiment of the device.
  • the program starts in a step Sl.
  • a step S2 the yaw rate wz, the wheel speeds rd and the steering wheel angle ⁇ or the steering angle detected or determined.
  • a step S3 may be provided to detect the pitch rate wy and / or the roll rate w_x.
  • the detected longitudinal acceleration a_x_sens and / or the detected lateral acceleration a_y_sens are detected in a step S4.
  • the sum of the pitch angle ⁇ and the pitch difference angle ⁇ _diff and / or the sum of the roll angle ⁇ and the roll difference angle ⁇ diff is preferably determined by the vehicle observer unit FB as a function of
  • the sum of the pitch angle ⁇ and the pitch angle ⁇ _diff and / or the sum of the roll angle ⁇ and the roll difference angle ⁇ diff are determined by means of the predetermined physical vehicle model.
  • a step S6 it is preferably checked whether an amount of the sum of the pitch angle ⁇ and the pitch difference angle ⁇ diff is greater than a predetermined pitch angle threshold ⁇ _th and / or an amount of the sum of the roll angle ⁇ and the roll difference angle ⁇ diff is greater than a given given roll angle threshold ⁇ _th.
  • the predetermined pitch angle threshold value ⁇ th and the predetermined roll angle threshold value ⁇ _th may also be referred to as predetermined tilt threshold values. These are for example about 20 degrees. However, they can also be larger or smaller than 20 degrees.
  • two predefined tilt threshold values can also be predetermined, in particular a predetermined first and a predetermined second tilt threshold value. If the predetermined first and second tilt threshold values are each given the same size, then they correspond this the predetermined pitch angle threshold ⁇ _th or the predetermined roll angle threshold ⁇ th. However, if the first and second inclination threshold values are predetermined differently, then a switching hysteresis can be specified.
  • the determination of the friction coefficient ⁇ R can thereby be suspended, for example, if the magnitude of the sum of the pitch angle ⁇ and the pitch difference angle ⁇ diff or the sum of the sum of the roll angle ⁇ and the roll difference angle ⁇ _diff is greater than the respective predetermined first tilt threshold, and resumed when the amount of the sum of the pitch angle ⁇ and the pitch difference angle ⁇ diff or the magnitude of the sum of the roll angle ⁇ and the roll difference angle ⁇ _diff is smaller than the respective predetermined second tilt threshold.
  • the friction coefficient ⁇ _R determined last before the preceding suspension of the determination is used as the starting value.
  • step S6 If the condition in step S6 is met, that is, the
  • Amount of the sum of the pitch angle ⁇ and the pitch difference angle ⁇ diff is greater than the predetermined pitch angle threshold ⁇ _th or the sum of the roll angle ⁇ and the roll difference angle ⁇ diff is greater than the predetermined roll angle threshold ⁇ _th, then the program in
  • Step S2 continued. Otherwise, in a step S7 the longitudinal and / or the lateral acceleration error a_x_err, ay err is dependent on the detected longitudinal acceleration a_x_sens and the sum of the pitch angle ⁇ and the pitch difference angle ⁇ diff or dependent on the detected lateral acceleration a_y_sens and the sum of the roll angle ⁇ and the roll difference angle ⁇ diff determined.
  • the actual longitudinal or lateral acceleration a_x, a_y is determined as a function of the longitudinal or lateral acceleration error a_x_err, a_y_err and the detected longitudinal or transverse acceleration a_x_sens, a_y_sens.
  • the actual longitudinal or lateral acceleration ax, ay corresponds to one order the influence of gravitational acceleration corrected longitudinal or lateral acceleration.
  • the coefficient of friction ⁇ R is determined as a function of the actual longitudinal or lateral acceleration a_x, a_y.
  • the program is continued in step S2.
  • the program is preferably continued only after a waiting period T W has elapsed.
  • the waiting period T W corresponds to a sampling interval in which the measured values are detected or determined, or a predetermined time interval for adjusting and thus updating the estimated value of the friction coefficient ⁇ R.
  • the determination of the sum of the pitch angle ⁇ and the pitch difference angle ⁇ _diff and / or the sum of the roll angle ⁇ and the roll difference angle ⁇ diff is preferably carried out in step S5 depending on the pitch rate w_y or the roll rate w x.
  • the pitch rate wy and / or the roll rate w_x is preferably integrated numerically in order to be able to determine changes in the sum of the pitch angle ⁇ and the pitch difference angle ⁇ diff or the sum of the roll angle ⁇ and the roll difference angle ⁇ diff in a particularly precise manner, in particular even if the vehicle is in a particular driving condition, that is, the vehicle, for example, flings or slips heavily.
  • An initialization value for the integration by the predetermined physical vehicle model is preferably determined as a function of the yaw rate w_z, the wheel speeds rd, the steering wheel angle ⁇ or the steering angle and the detected longitudinal or lateral acceleration a_x_sens, ay sens. Furthermore, the integral is preferably reset to the currently determined initialization value in at least one predetermined driving state of the vehicle. This prevents divergence of the integral and the sum of the pitch angle ⁇ and the pitch difference angle ⁇ diff and / or the sum of the roll angle ⁇ and the roll difference angle ⁇ diff are durably reliably and precisely determinable.
  • a corresponding program is provided.
  • the sensor signals of the spring travel sensors 9 or the level sensors are detected in step S2.
  • the pitch difference angle ⁇ diff and / or the roll difference angle ⁇ diff is determined as a function of the detected sensor signals of the spring travel sensors 9 or the level sensors.
  • the step S6 may be provided to check an amount of the pitch difference angle ⁇ _diff and / or the roll difference angle ⁇ diff to the exceeding of a predetermined differential angle threshold.
  • step S7 the longitudinal and / or the lateral acceleration error a_x_err, a_y_err is determined as a function of the detected longitudinal acceleration a x sens and the pitch difference angle ⁇ _diff or dependent on the detected lateral acceleration a y sens and the roll difference angle ⁇ _diff. Otherwise, the program essentially corresponds to that of the first embodiment of the device.
  • FIG. 8 shows a flow chart of a program for determining the friction coefficient ⁇ _R by estimating according to step S9.
  • the program is preferably executed by the estimation unit EST.
  • the determination of the friction coefficient ⁇ _R is shown as an example depending on the actual lateral acceleration a_y. However, it is also possible to determine the coefficient of friction ⁇ R as a function of the actual longitudinal acceleration a_x accordingly.
  • the program starts in a step Sil.
  • the estimated value of the friction coefficient ⁇ _R for a time t-1 is assigned a predetermined value, for example 1.
  • the slip angle ⁇ , the contact force F z, the vehicle speed v are detected or determined as an input variable.
  • a lateral coefficient of friction ⁇ T is determined as a function of the slip angle ⁇ and of the estimated value of the friction coefficient ⁇ _R at time t-1.
  • the lateral friction coefficient ⁇ _T is defined as the quotient of a lateral force F_y acting on the tire and the tire upright force F z on the roadway.
  • a determined lateral acceleration a_y_c is determined as a vehicle dynamic model variable as a function of the determined lateral friction coefficient ⁇ T, and is preferably smoothed by low-pass filtering.
  • the transverse force F_y is determined as the product of the determined lateral coefficient of friction ⁇ _T and the contact force F z.
  • the determined lateral acceleration a_y_c can then be determined as a function of the determined lateral force F y.
  • the actual lateral acceleration a_y is determined or read as an input variable.
  • a step S17 it is preferably checked whether an amount of the detected lateral acceleration a_y is smaller than a predetermined lower transverse acceleration limit value a th.
  • the predefined lower lateral acceleration limit value a_th is, for example, about 0.5 m / s 2 , but may also be greater than or less than 0.5 m / s 2 .
  • the predetermined lower speed limit v_th is for example about 5 m / s, but may also be greater than or less than 5 m / s.
  • step S17 it is preferably checked in step whether the actual lateral acceleration a_y within a predetermined tolerance band around the determined transverse acceleration a c is _Y_.
  • a lower limit of the predetermined tolerance band is specified as a difference between an amount of the determined lateral acceleration a_y_c and a lower acceleration tolerance limit value a min. Accordingly, an upper re limit of the predetermined tolerance band by a sum of the amount of the determined lateral acceleration a_y_c and an upper acceleration tolerance limit a_max given. If the amount of the detected lateral acceleration a_y is within the predetermined tolerance band, then the program is ended in step S20. Otherwise, the estimated value of the friction coefficient ⁇ _R is adjusted in a step S18.
  • the adjustment of the estimated value of the friction coefficient ⁇ R is effected such that the estimated value of the friction coefficient ⁇ _R at a time t is a difference of the estimated value of the friction coefficient ⁇ R at the time t-1 and a product of a factor K and a difference of the magnitude of the determined lateral acceleration a_y_c and the amount of the actual lateral acceleration ay is assigned.
  • the estimated value of the friction coefficient ⁇ _R at time t is also assigned to the estimated value of the friction coefficient ⁇ R at time t-1 for a subsequent adaptation step according to steps S13 to S18.
  • the program is ended in step S20.
  • the step S12 is preferably executed only in a first execution of the program according to Figure 8 as an initialization.
  • the friction coefficient ⁇ R is recursively determined as an estimated value.
  • the factor K is given as about 1.5 s / m • T_W.
  • the factor K can also be specified differently.
  • the estimation unit EST is designed to execute the program according to FIG. 8 and to determine the estimated value of the friction coefficient ⁇ _R between the at least one tire of the vehicle and the roadway, depending on the measured values acquired or determined.
  • the lateral friction value ⁇ _T is determined in step S14 as a function of the detected or determined slip angle ⁇ by means of a model.
  • Coefficient of friction ⁇ T and the slip angle ⁇ in the model is a non-linear functional relationship, in a first curve kl and a second curve k2 for different Estimates of the friction coefficient ⁇ _R in Figure 9 is shown by way of example.
  • the estimated value of the friction coefficient ⁇ _R is, for example, 0.5 for the first curve and k2 for the second curve 1.
  • the functional relationship can also be specified differently.
  • the determination of the actual longitudinal or lateral acceleration ax, ay according to the steps S2 to S8 and the determination of the determined lateral acceleration ayc as the vehicle dynamic model variable according to the steps S13 to S15 is parallel or quasi parallel to each other, that is, on the one hand, the steps S2 to S8 and on the other hand, the steps S13 to S15 are performed in parallel or quasi parallel to each other.
  • the program according to FIG. 8 then does not end in step S20 but instead continues in step S13, if appropriate after expiration of the waiting period T_W.
  • At least one inclination of at least one acceleration sensor with respect to the vehicle-independent predetermined reference plane BE is determined, and at least one acceleration of the vehicle is detected by means of the at least one acceleration sensor in the plane which is substantially parallel to the road surface or substantially parallel to the vehicle body FA , The detected at least one acceleration of the vehicle is corrected as a function of the at least one inclination and the friction coefficient ⁇ R is determined as a function of the corrected at least one acceleration.
  • the at least one inclination comprises the pitch angle ⁇ and / or the roll angle ⁇ .
  • the detected at least one acceleration preferably comprises the detected longitudinal acceleration a_x_sens and / or the detected lateral acceleration a_y_sens.
  • the at least one inclination of the roadway can also be represented by a different angle, and the detected at least one acceleration can also be represented by another acceleration of the vehicle.

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  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Automation & Control Theory (AREA)
  • Mathematical Physics (AREA)
  • Control Of Driving Devices And Active Controlling Of Vehicle (AREA)
  • Regulating Braking Force (AREA)

Abstract

Au moins une inclinaison d'au moins un capteur d'accélération est déterminée par rapport à un plan de référence prédéterminé indépendamment du véhicule. Au moins une accélération du véhicule est détectée au moyen d'au moins un capteur d'accélération dans un plan qui s'étend de manière sensiblement parallèle à la voie de circulation. Au moins une vitesse détectée du véhicule est corrigée en fonction d'au moins une inclinaison. Un indice de friction (μ_R) est déterminé en fonction d'au moins une vitesse corrigée.
PCT/EP2007/061783 2006-12-22 2007-10-31 Procédé et dispositif de détermination d'un indice de friction WO2008077670A1 (fr)

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