DE19607050A1 - Method for determining variables that describe the driving behavior of a vehicle - Google Patents

Abstract

Ensuring stability and good yawing moment adjustment even in case of road surface cross slope and/or if the vehicle rolls requires cross slope detection. This is done by calculating the cross slope alpha q. At a certain cross slope angle, the vehicle computer can be set to counteract the cross slope vigorously. Calculation of the cross slope angle alpha q is based on a co-ordinate transformation. The value aqm measured by the lateral acceleration gauge fixed relative to the vehicle is related to a value aq (the lateral ground acceleration determined by signals from other sensors) by the equation aqm = aq cos alpha q - g sin alpha q. The solution to this equation gives the cross slope angle alpha q.

Description

The present invention relates to a method for determining of sizes that determine the driving behavior of a four-wheeler Describe vehicle, according to the preamble of claim 1.

Such a method is described in DE 42 26 749 A1. Signals are supplied to a computing device which represent the longitudinal acceleration a _x , the vehicle speed in the longitudinal direction v _x , the lateral acceleration a _y and the yaw rate, with at least the float angle β being derived on the basis of these measured variables in the computing device using a vehicle model . In the course of the calculation, pitch and roll movements of the vehicle are assumed to be negligible in order to be able to set the rotational speeds around the vehicle's longitudinal and transverse axes to zero and thus to simplify a complex system of equations. The lateral vehicle acceleration is also assumed to be that which is detected by lateral accelerometers fixed to the vehicle, so that lateral road inclinations are also assumed to be lateral accelerations. This inevitably leads to errors in the calculation of the float angle. Therefore, it cannot be guaranteed that the regulation leads to the desired driving behavior even when driving with a bank without taking the bank angle into account.

To the stability or good quality of the yaw moments regulation also with a roadway bank and / or with  Ensuring a rolling movement of the vehicle is one Bank detection necessary. This is done by a Calculation of the bank angle. With a recognized The controller, ie the computing device, can bank be interpreted that it is robust against bank is working.

The present invention is based on the object To create methods of the type mentioned, which in is able to bank the vehicle from a real one To distinguish lateral acceleration of the vehicle and amount to be stated.

This task is combined with the characteristic Features of claim 1 solved. The calculation of the cross egg angle is based on one Coordinate transformation. That of the vehicle-fixed Lateral accelerometer value becomes one other sensor signals calculated value of the earth-related Lateral acceleration related. Earth-related means that the z-axis of the coordinate system in gravitational direction runs, while the x and y axes are vertical point in the vehicle's longitudinal and transverse directions.

The earth-related lateral acceleration of the vehicle can for example from a measured or calculated yaw angle speed and the vehicle's longitudinal speed or off the individual wheel speeds of one right and one left vehicle wheel can be calculated.  

If desired, a portion of the Bank angle can be shown as roll angle by the measured, vehicle-related lateral acceleration with a vehicle-specific, load-dependent factor is multiplied, preferably once by in advance Test measurements determined and in the vehicle's own Computing device is stored.

A more detailed explanation of the inventive concept is now given with the help of a drawing.

The only figure shows the relationship of the vehicle-related Coordinate system (x ′, y ′, z ′) for earth-related coordinates system (x, y, z), assuming in this example that the vehicle does not make a longitudinal inclination to the horizontal takes (x = x ′). The transformation can be seen from the figure represented by the following equation.

a _qm = a _q cos α _q - g sin α _q (1)

The variables used in the figure are defined as follows:
a _q lateral acceleration with respect to the original coordinate system;
a _qm measured lateral acceleration with respect to the vehicle coordinate system;
g gravitational acceleration;
α _b road bank angle;
X roll angle;
α _q = α _b + X vehicle bank angle with respect to the original coordinate system.
From (1) follows:

in which

After (2) and the figure applies:

From (2) and (3) follows:

To reduce the computing effort or in integer too can program this calculation either by approxi after Taylor series development or after Newton iteration procedures are performed.

The approximations after the Taylor series expansion

read: These approximations then result in the Equation:

With

and

The Newton iteration method is known and is therefore not pursued further here.  

The lateral acceleration a _q with respect to the original coordinate system can either by

or by one of the equations below

are reproduced using the following names:
v vehicle _{reference speed} ;
Angular velocity;
Yaw rate;
v _vr wheel speed front right;
v _vl wheel speed front left;
v _hr rear right wheel speed;
v _hl wheel speed rear left;
S gauge of the vehicle.

In the following, one way of determining the roll angle is given. As described in the literature, e.g. B. in Mitschke, Dynamics of Motor Vehicles, Volume C, Springer Verlag 1990, the lateral acceleration a _{q is} dependent on the original coordinate system of the vehicle speed and the radius of curvature of the trajectory R. It is calculated using the following equation:

The roll angle is proportional to the lateral acceleration as long as the vehicle parameters are constant. According to the literature, the roll angle is 8 ° / g when the vehicle is empty and 11 ° / g when the vehicle is loaded. If a _qm <0 then X <0, then for a _qm <0 X <0 and for a _qm = 0 X = 0. This means that your own roll motion when the vehicle is empty

and when the vehicle is loaded

can be estimated. The factor k can be determined by a driving test on a level road with the help of a special roll angle measuring system can be determined vehicle-specifically, namely:

where X _{m is} the roll angle measured by the measuring system.

The bank detection was made during a driving test in  a test steep curve without switching on the Yaw moment controller used for testing. The Root calculation using the Newton iteration method performed because the root function is already in the integer programming is available.

It could be seen from the measurement results that the cross acceleration with respect to the original coordinates systems according to equation (4) on the vehicle speed is dependent. The effect of your own roll motion was over a comparison of the measurement results at different Determine vehicle speeds because the Lane inclination known and the same for all runs was. The Querbe is at low vehicle speeds acceleration small and causes a small own Roll. At a higher lateral acceleration that is Rolling motion unmistakable. With the help of the roll angle measuring system the actual value of the bank angle can be determined be used as a reference value for an investigation of the Driving test results is available. By comparison between the measured and the calculated cross egg angle has been found that the calculation at least satisfactory on an almost stationary journey Delivers results.

Claims (6)

1. A method for determining the characteristics of the driving behavior of a vehicle, wherein the vehicle with a vehicle-mounted lateral accelerometer (a _qm ) and per vehicle wheel with a wheel sensor for detecting the wheel speed (v _vl , v _vr , v _hl , v _hr ) and at least as single-track vehicle is equipped with a yaw rate sensor for detecting the yaw angular velocity (), characterized in that a value of the lateral acceleration (a _qm ) of the vehicle measured in vehicle coordinates (x ′, y ′, z ′) to a value in earth coordinates (x, y, z) the calculated value (a _q ) of the lateral acceleration is related and by solving the equation a _qm = a _q cos α _q - g sin α _q the bank (α _q ) of the vehicle with respect to the earth coordinates (x, y, z) is determined, with g being the gravitation. 2. The method according to claim 1, characterized in that the calculation of the earth-related lateral acceleration (a _q ) according to the formula takes place, where v _{fzg is} the vehicle speed measured or determined from individual wheel speeds and the measured or calculated yaw rate of the vehicle. 3. The method according to claim 1, characterized in that the calculation of the earth-related lateral acceleration (a _q ) according to one of the formula takes place, where v _{fzg is} the vehicle speed measured or determined from individual wheel _speeds , the measured or calculated yaw rate of the vehicle and the measured or calculated slip angle speed of the vehicle. 4. The method according to claim 1, wherein it is a two-lane vehicle, characterized in that the calculation of the earth-related lateral acceleration (a _q ) according to one of the formulas takes place, where v _{xr denotes} the wheel speed of a right vehicle wheel, v _{xl denotes} the wheel speed of a left vehicle wheel and S the track width of the vehicle. 5. The method according to any one of the preceding claims, characterized in that the roll angle (X) of the vehicle according to the formula X ≅ - a _qm is determined, where k is a load-dependent, vehicle-specific determined factor. 6. The method according to claim 5, characterized in that the factor k by a measurement of in vehicle coordinates (x ', y', z ') measured lateral acceleration (a _qm ) and simultaneous test measurement of the roll angle (X _m ) once according to the formula is determined and stored in a computing device in the vehicle.