WO2009109240A1

WO2009109240A1 - Method for determining the slip angle of a wheel on a vehicle

Info

Publication number: WO2009109240A1
Application number: PCT/EP2008/063339
Authority: WO
Inventors: Oliver Oettgen; Ulrich Blankenhorn; Marco Rajapakse Pathirage; Andreas Schulz; Andreas Reim; Alexander Steinbach
Original assignee: Robert Bosch Gmbh
Priority date: 2007-10-19
Filing date: 2008-10-06
Publication date: 2009-09-11
Also published as: WO2009053233A1; DE102008013102A1

Abstract

The invention relates to a method for determining the slip angle of a wheel on a vehicle, wherein the vehicle acceleration and yaw rate are measured with an inertial sensor system and the vehicle longitudinal speed and the vehicle transverse speed are calculated in the inertia system. The speeds from the inertia system are then transformed into the wheel specific coordinate system and the slip angle determined on the basis of the ratio of vehicle transverse speed to vehicle transverse speed.

Description

title

Method for determining the slip angle on a wheel of a vehicle

The invention relates to a method for determining the slip angle on a wheel of a vehicle

State of the art

Vehicle control systems such as ESP (Electronic Stability Program) use sensor-determined driving state variables that characterize the current vehicle state in terms of longitudinal and lateral dynamics, as well as state variables estimated from mathematical models in order to influence driving behavior with the aid of active actuators. In particular, lateral dynamic variables such as the yaw rate or the lateral acceleration as well as wheel slip values can be inferred from the driving stability of the vehicle, whereby an intervention, for example in the brakes or in the engine management, can be carried out to stabilize the vehicle.

In order to determine whether the vehicle is oversteering or understeering when cornering, the information about the current slip angle at the wheels is of interest, which designates the angle between the wheel center plane and the resulting, projected on the roadway speed vector in the wheel center.

Disclosure of the invention The invention has for its object to determine with simple measures the slip angle on a wheel of a vehicle with high quality. This should be carried out in particular with a sensor arranged in the vehicle for a vehicle control system, which is present for example in an ESP system.

This object is achieved with the features of claim 1. The dependent claims indicate expedient developments.

In the method according to the invention for determining the slip angle on a wheel of a vehicle, different vehicle state variables are measured with the aid of a vehicle-specific sensor system

Differential equation system further processed in order to determine at least one slip angle on a wheel of the vehicle. Already existing sensor platforms in the motor vehicle can be used, whose signals are evaluated. This relates in particular to an inertial sensor system, which is usually present in electronic stability programs (ESP) and can be determined with the vehicle accelerations and yaw rates in the direction of the vehicle axles or about the vehicle axles. The inertial sensor system is located, for example, in the center of gravity of the vehicle or the signals supplied by the inertial sensor system are converted to the vehicle center of gravity.

As an inertial sensor system, a so-called 6D inertial sensor system is preferably used which supplies the vehicle accelerations and the rotation rates in or around all three vehicle axles in the inertial system. This information is needed to calculate the slip angle.

As inertial sensor technology, a 5D

Inertialsensorik off, in which the vehicle accelerations in all three vehicle axles and the yaw rates around the Vehicle longitudinal axis x (roll rate) and around the vehicle's vertical axis z (yaw rate) are measured. The yaw rate about the vehicle transverse axis y (pitch rate) can also be determined from a mathematical model.

From the measured vehicle accelerations and yaw rates can be achieved by integrating a kinematic

Differential equation system, the vehicle longitudinal speed, the vehicle lateral velocity and the attitude angle to all three vehicle axes are calculated relative to the inertial system. In a following step, the vehicle longitudinal speed and the vehicle lateral velocity are transformed from the inertial system into the wheel-own coordinate system taking into account the distance between the inertial system and the axial coordinate system. Subsequently, the slip angle can be calculated based on the ratio of vehicle lateral velocity to vehicle longitudinal velocity in the wheel coordinate system. In this case, both an exact calculation is possible in which the arctangent from the ratio of Fahrzeugquer-

Vehicle longitudinal speed is formed, as well as an approximate determination for small angles by the skew angle is equated without trigonometric conversion with the ratio of vehicle to vehicle longitudinal speed in Radeigen coordinate system.

When transforming the vehicle lateral velocity from the inertial system into the wheel coordinate system, the vehicle geometry must be taken into account. It may be sufficient for reasons of symmetry, only to take into account the measured in the direction of the vehicle longitudinal axis longitudinal distance between the coordinate systems and disregard the transverse offset between the longitudinal center axis and the lateral position of the vehicle wheel. The longitudinal distance between the coordinate systems is multiplied by the yaw rate, which is present as the measured value of the inertial sensor. The yaw rate corresponds to the measured yaw rate about the z-axis (vertical axis). - A -

The yaw angle is determined by integrating the kinematic differential equation system from the measured yaw rates.

The vehicle lateral velocity in the internal coordinate system is determined by adding the vehicle lateral velocity in the inertial system and the product of the yaw rate and the distance between the inertial system and the internal coordinate system.

The vehicle longitudinal speed in the wheel coordinate system is advantageously equated with the vehicle longitudinal speed in the inertial system, which preferably also applies to steered wheels. Thus, the conversion into the wheel coordinate system is limited to the vehicle lateral velocity.

By comparing the slip angle between a front wheel and a rear wheel can be concluded that oversteer or understeer. The conversion of the vehicle lateral velocity to a coordinate system in the

Front wheel or in the rear wheel taking into account the corresponding longitudinal distance and with positive (front wheel) and negative (rear wheel) sign of the term, formed from the product of yaw rate and distance of the coordinate systems. A neutral handling without oversteer or understeer is present when the slip angles at the front wheel and the rear wheel are the same. An oversteering drivability exists if the slip angle at the front wheel is smaller than at the rear wheel and understeering vehicle behavior if the slip angle at the front wheel is greater than at the rear wheel. From the information about oversteer or understeer of the vehicle, a countermeasure can be initiated by applying a vehicle control system, for example by applying the brakes or the engine management or an active suspension actuator. The method for determining the slip angle preferably runs in a control unit in the vehicle, which may be part of a vehicle control system with an actively adjustable actuator. In the control unit or control signals are generated, which are supplied to the actuator for changing the current driving condition of the vehicle.

Further advantages and expedient embodiments can be taken from the further claims, the description of the figures and the drawings. Show it:

1 is a schematic representation of a front wheel and a rear wheel in a vehicle with an inertial system arranged in the center of gravity of the vehicle as well as with wheel-own coordinate systems, in each of which speed vectors are entered,

Fig. 2 is a block diagram, the blocks of different steps to the expiry of the determination of

Symbolize slip angle.

In Fig. 1, a vehicle with a front wheel 1 and a rear wheel 2 is shown, wherein the respective speed vectors vζ at the front wheel 1 and vζ at the rear wheel 2 are also registered. The velocity vectors v ™ and vζ are the respective resulting vectors, which are determined from the vehicle's own coordinate system - which in the case of the steerable front wheel 1 rotates with the steering angle - vehicle speeds vζ _v and v ^w for the front wheel and vζ _h and V ^w _yh composed vectorially for the rear wheel. The angular difference between the resulting speed vector vζ and the respective Radmittellängsachse is referred to as front wheel slip angle α _v and rear wheel slip angle c < _h . An inertial sensor system is available in the motor vehicle which determines the vehicle accelerations a _x , a _y and a _z in the center of gravity in the vehicle longitudinal, vehicle transverse and vehicle vertical direction in accordance with the conventional convention for vehicles in the x, y and z directions. The inertial sensor system can also sense the yaw rates ω _x , ω _y and ω _z about the respective vehicle axles in the center of gravity of the vehicle. From this information, the vehicle longitudinal velocity v _x and the vehicle lateral _velocity v _y in the vehicle center of gravity 3 can be calculated; the yaw rate ψ corresponds to the measured yaw rate ω _z . This information and the geometric distances l _v and l _h between the center of gravity 3 and the center of the front wheel 3 and the center of the rear wheel 2 are basically sufficient to the vehicle speeds v ™ in the front wheel and vζ in the rear wheel with the respective components in x and Determine y-direction in the respective wheel coordinate system from which the slip angle α _v and α _h can be calculated at the front wheel or rear wheel. The distances l _v and I _h between the vehicle center of gravity and the wheel centers are preferably taken into account only in the vehicle longitudinal direction regardless of the transverse offset of the vehicle wheels.

In Fig. 2 is a block diagram for calculating the slip angle is shown. First, the yaw rates ω _x , ω _y and ω _z about all three spatial axes as well as the vehicle longitudinal acceleration a _x , the vehicle lateral acceleration a _y and the vehicle acceleration a _z in the vertical direction are determined by means of inertial sensors. These sizes are required to calculate the slip angles. Accordingly, a 6D inertial sensor is used, with which these sizes can be sensed. If necessary, a 5D inertial sensor system in which the vehicle accelerations and yaw rates about the x and z axes are measured, wherein the yaw rate is computationally determined about the y-axis. From the state variables measured in the inertial sensor system are from a known kinematic relationship, which is described by a differential equation system, which is solved by numerical integration, the

Vehicle speeds v _x , v _y , v _z in all three spatial directions and the attitude angle φ, θ, ψ are determined to all vehicle fixed axis directions, of which the attitude angle φ the roll angle, the attitude angle θ the pitch angle and the attitude angle ψ the yaw angle. The kinematic differential equation system in block 10 can be given in the following form:

where g denotes the gravitational acceleration.

The vehicle longitudinal velocity v _x obtained in the numerical solution of the kinematic differential equation system 10, the vehicle lateral velocity Vy and the measured yaw rate ψ are then fed to a block 11, in which a transformation of these variables from the inertial system into the radeigene coordinate system of the front wheel or Rear wheel is performed.

The transformation from the inertial system into the wheel-own coordinate systems takes place only for the vehicle lateral velocity. The vehicle longitudinal speed vζ _v in the front wheel and vζ _h in the rear wheel, however, are equated with the vehicle longitudinal _speed v _x in the inertial system. In order to determine the transverse components of the vehicle speeds in the front wheel and in the rear wheel, the information about the distance between the inertial system and the wheel-own coordinate system, measured in the vehicle longitudinal direction, is additionally required. This distance is denoted by l _v and l _h for the front wheel and the rear wheel. This can be calculated with the vehicle lateral velocity v _{y of} the inertial system and the yaw rate ψ according to the relationships

the vehicle _lateral ^velocity v _y ^w _v in the front wheel or v _y ^w _h in the rear wheel are calculated.

In the next block 12, the slip angles α _v and c < _{h are} calculated from the respective components of the vehicle longitudinal and lateral speeds in the front wheel or rear wheel. The slip angles are in principle calculated on the basis of the ratio of the transverse component of the speed to the longitudinal component

However, for reasons of simplification, it may be expedient to equate the skew angle directly with the ratio of transverse to longitudinal velocity, which is permissible for small angles with sufficient accuracy:

"y, k α * = vx, h

In the last block 13, a comparison is made between the front wheel slip angle α _v and the rear wheel slip angle c < _h . If the rear wheel slip angle. c < _{h is} greater than the front wheel slip angle α _v , there is oversteer of the vehicle. In the opposite case, ie with a larger front wheel slip angle α _v compared to the rear wheel slip angle α _h , there is an understeer of the vehicle. If the front wheel slip angle α _v and the rear wheel slip angle α _{h are the} same size, there is a neutral driving behavior.

From the comparison of front wheel slip angle α _v with the rear wheel slip angle α _h , a signal S can be generated, which can be subsequently fed to a vehicle control system or an actuator to cause a reaction that contributes to the stabilization of the vehicle. In principle, the signal S can also be used for documentation or be displayed to the driver, for example as a warning signal.

Claims

claims

1. A method for determining the slip angle on a wheel of a vehicle, comprising the following method steps:

Measuring the vehicle accelerations (a _x , a _y , a _z ) in all three vehicle axles and at least the rotation rates (ω _x , ω _z ) about the vehicle longitudinal axis (x) and about the vehicle vertical axis (z) by means of an inertial sensor system,

Calculating the vehicle longitudinal speed (v _x ) and the vehicle lateral velocity (v _y ) and the attitude angle (φ, θ, ψ) about the vehicle axes in the inertial inertial system by integration of a

Differential equation system of the measured vehicle accelerations (a _x , a _y , a _z ) and the rotation rate (ω _x , ω _y , ω _z ), transforming the vehicle longitudinal velocity (v _x ) and the vehicle lateral velocity (v _y ) from the inertial system in the wheel coordinate system on the vehicle wheel and determining the slip angle (OC) based on the ratio of vehicle lateral velocity (V ™) to

Vehicle longitudinal speed (vζ) in the wheel coordinate system.

2. The method according to claim 1, characterized in that the transformation of

Vehicle transverse velocity (vj) of the inertial system in the wheel-own coordinate system on the vehicle wheel (1, 2) by means of the yaw rate (ψ) is performed.

3. The method according to claim 2, characterized in that the transformation according to

is performed, wherein

/ the distance between the inertial system and the wheel coordinate system

designated .

4. The method according to any one of claims 1 to 3, characterized in that the vehicle longitudinal speed (vζ) is equated in the wheel-own coordinate system with the vehicle longitudinal speed (v _x ) in the inertial system:

5. The method according to any one of claims 1 to 4, characterized in that the slip angle (OC) from the vehicle longitudinal speed (vζ) and the

Vehicle lateral velocity (vζ) in the internal coordinate system according to the relationship

v α = arctane L--

is determined.

6. The method according to any one of claims 1 to 5, characterized in that the slip angle (OC) for small angular amounts approximately from the

Vehicle longitudinal speed (vζ) and the Vehicle lateral velocity (vj) in the internal coordinate system according to the relationship

CC =

is determined.

7. The method according to any one of claims 1 to 6, characterized in that for under- or oversteer detection in a vehicle, the front wheel slip angle (GW) and the rear wheel slip angle (0C _h ) are determined and compared with each other, wherein there is an understeer when the front wheel slip angle (OCj is greater than the rear wheel slip angle (OC _H) and oversteering present when the front wheel slip angle (OCj is smaller than the rear wheel slip angle (0C _H).

8. The method according to claim 7, characterized in that when the detected understeer or oversteer a driving condition affecting adjusting system is applied in the vehicle.

9. The method according to any one of claims 1 to 8, characterized in that the rotation rate (ω _y ) about the vehicle transverse axis (y) is also measured using the inertial sensor.

10. The method according to any one of claims 1 to 8, characterized in that the rotation rate (ω _y ) about the vehicle transverse axis ( _y ) is determined from a mathematical model.

11. regulating or control device for carrying out the method according to one of claims 1 to 10.

12. Vehicle control system with a control or control device according to claim 11.