DE19909453A1 - Method of improving the driving behavior of a vehicle when driving on a curved path with a change in vehicle dynamic behavior especially engine torque - Google Patents

Abstract

The method improves the driving of a vehicle by maintaining the actual driving characteristics which exist before or on changing engine torque, for a given period of time. Preferably, the curved path is determined by input parameters such as speed and heading and a target value for the change in curve per unit time is determined. An actual value for the change in curve per unit time is also determined. The brake pressure is varied in dependence on the results of a comparison between the target and actual values. The target value is varied over a period of time towards the actual value in dependence on the results of the comparison. Independent claims also cover a control system for carrying out the method.

Description

The invention relates to a method and control system for Improving the driving behavior of a vehicle when Driving through a curved path according to the generic term of Claims 1 and 9.

Such methods and control systems are used to targeted interventions on the individual brakes of a vehicle to create an additional torque, which over the actually measured yaw angle change per unit of time (actual Yaw rate) of a vehicle to that influenced by the driver Yaw angle change per unit time (target yaw rate). Such a method and control system is effective especially then supportive in the steering behavior of the Vehicle if due to circumstances (e.g. too high Speed, smooth road) that of the vehicle actually covered cam track not with that of the Driver matches without additional torque desired. Such procedures and control systems to improve In principle, driving stability has already been extensively described and are therefore not intended to be discussed again here in detail are explained.  

In such methods and control systems, input variables which result from the curved path desired by the driver (for example steering wheel angle, driving speed) are always fed to a vehicle model circuit which, based on a known single-track model or another driving model, uses these input variables and parameters characteristic of the driving behavior of the vehicle but also a target yaw rate (ψ _target ), which is compared with the measured actual yaw rate (ψ _actual ), is determined by the properties of the environment predetermined variables (coefficient of friction of the road). The difference between the yaw angles (Δψ _Diff ) is converted by means of a so-called yaw moment controller into an additional yaw moment M _G , which forms the input variable of a distribution logic.

The distribution logic itself determines, if necessary, in Dependence on the one particular brake pressure to the Wheel braking request from the driver to the brake pressure to be applied to individual brakes. This should in addition to the braking effect that may be desired generate additional torque on the vehicle which the driving behavior of the vehicle in the direction of the desired steering supported by the driver.

Occurrence of changes in the vehicle's dynamic driving behavior (e.g. changes in the coefficient of friction), particularly a change in the engine torque, e.g. B. by accelerating or a gas surge, the driving behavior of the vehicle changes, because by the interaction of several influences, such as tire influences, kinematic influences and elastokinematic influences, among other things, a change in the axle load and thus the forces. Figures 1a and 1b show a situation that can arise in a curve before and after the gas is removed:
The driving forces F _a act on the drive wheels when driving through a curved path before the gas is removed. Due to the lateral deformation of the tire contact patch, the longitudinal drive force F _A = 2 × F _a acts somewhat outside the wheel center plane depending on the lateral forces. The driving longitudinal force F _A , which acts asymmetrically to the longitudinal axis of the vehicle, creates an understeering yaw moment (ψ _below ).

After the throttle is removed, the engine (and other resistances) brakes the vehicle, the drive (longitudinal) forces F _b , F _B become negative. At the same time, the deceleration creates the mass force mx in the center of gravity SP, which increases the axle load on the front wheels and reduces it by the same amount on the rear wheels. This changes the distribution of transferable lateral forces. The change in lateral force (lateral force on the front axle increases slightly and drops sharply on the rear axle) creates an oversteering yaw moment (ψ _over ), the slip angle on the rear axle increases and the vehicle turns into the curved path. When the engine torque changes from driving force to braking force, a reversal of these moments leads to a change in the driving behavior of the vehicle from an oversteering to an understeering driving behavior.

An important goal in improving driving behavior of a vehicle is to adjust the driving behavior so that the vehicle's response to steering, braking and The driver's accelerator pedal inputs are always predictable and good is controllable. As a result, have already been Regulatory principles provided the under- and oversteering Recognize operating states of the vehicle and by a Correct the corresponding brake intervention.  

A simplified known control principle consists in using a direct measure for understeering / oversteering driving behavior of a vehicle as a controlled variable. According to a definition of the steering behavior of a vehicle, the mean slip angles of the front and rear axles (α _v , α _h ) are compared. At larger slip angles at the front, the vehicle then has an understeering behavior, in the opposite case an oversteering behavior. By definition, neutral behavior is when the slip angles at the front and rear are the same. Therefore:

<0: understeering
α _v - α _h = 0: neutral
<0: oversteering

On the basis of the slip angle difference, it is therefore possible to directly determine the current driving state of the vehicle. If the single-track vehicle model is used as an approach, the slip angle depending on the steering wheel angle δ, the float angle β, the yaw rate ψ and the vehicle speed v can be derived as follows:

Since the skew angle cannot be measured directly or is easy to calculate, the individual skew angle cannot be calculated explicitly. However, if their difference is formed, it is possible to calculate this variable on the basis of the available measured variables (steering wheel angle, yaw rate), the vehicle reference speed v _Ref known from the ABS controller and the constant wheelbase 1.

So there is a size available that is a measure of Understeer / oversteer can be used.

If we further consider the known relationship between the current curve radius R of the curve path of the vehicle's center of gravity and the slip angle difference

it can be seen that assuming

α _v - α _h = 0

of a neutral driving state, the curve radius R is only determined by the steering wheel angle α, namely

The known control therefore uses the as the controlled variable directly calculated slip angle difference. Default for this The rule is to keep the controlled variable small, around a neutral driving behavior of the vehicle to reach.

The object of the invention is a method and a Control system to improve the driving behavior of a Vehicle traveling through a curved path with changing vehicle dynamic driving behavior, in particular changing Engine torque, to indicate the driving behavior of a Influence the vehicle so that it is adapted to the situation Driver is always predictable and well controlled. About that In addition, the responsiveness of the control system should be increased become.

This task is carried out with the characteristics of the independent Claims resolved, dependent claims are preferred Embodiments of the claims of the invention directed.

The following is the invention with changing engine torque described as an activation variable. Other that activation variables that change vehicle dynamic driving behavior, such as B. changes in coefficient of friction, are by the invention includes.

The fact that in the process for improving the Driving behavior of a vehicle when driving through a Cam track with changing vehicle dynamic Driving behavior, in particular changing engine torque Actual existing before or when changing the engine torque Driving behavior of the vehicle over a period of time is maintained, oversteer or understeer states of the Vehicle "frozen" depending on time. For this, the calculated target value for changing the cam track per Time unit (target driving behavior) depending on the previous or when changing z. B. the existing engine torque Difference between the calculated target value and the measured actual value for the change of the cam track pro Time unit (actual driving behavior) changed. Through the Shift of the target value for the calculated driving behavior  of the vehicle to the before or when the Engine torque measured actual value for the driving behavior of the Vehicle, the responsiveness of the Control system because the control difference between which is a neutral Target value representing the driving behavior and the actual value can no longer be followed in the control difference must, but the regulation in a predetermined tolerance range immediately because the derived target value for the Driving behavior of the vehicle before or when the Engine torque to the actual value at the start of control for the driving behavior of the vehicle. Hereby sets the control after passing the input threshold immediately.

The change in engine torque is preferred over a Activation size of the motor control, for example a Activation signal from the Motronic system posed. Of course there are others too Activation variables based on a changing engine torque let close to determine a changing To use engine torque, for example by means of a sensor monitored accelerator pedal travel or corresponding other sizes which can be derived from a change in engine torque.

By maintaining the understeering or oversteering Driving behavior of the vehicle over a period of time the driver does not additionally change the engine torque a driving behavior of the vehicle that is not surprising based on the driver's request, he can react optimally. The Delay times are minimized.

An advantageous development of the method provides that the curve path of the vehicle is determined from input variables, such as driving speed and steering wheel angle, that an actual value and a target value for the change in the curve path is determined per unit of time, that the brake pressure, if applicable Brake of a wheel or on several wheels depending on a comparison of the target value with the actual value for the cam track is influenced and that the target value depending on a before or when a change in the engine torque from the comparison between the target value and Actual value formed difference value from the change in vehicle dynamic driving behavior, for. B. the engine torque, is changed over a period of time in the direction of the actual value. When selecting the definition of the cam track, vehicle models are preferably selected that can determine a target yaw rate (ψ _target ) from the available input variables, for example the steering wheel angle and the driving speed, as well as the variables specified by the properties of the environment, such as the linear one dynamic single-track model or that of the stationary circular drive.

An actual value (ψ _actual ) for the yaw rate is determined by means of sensors. By changing the target value (ψ _target ) depending on the existing difference value (Δψ _Diff ) between the target value and the actual value in the direction of the actual value, an understeer or oversteer state of the vehicle remains.

The fact that the difference value (Δψ _Diff ) before or when changing the vehicle dynamic driving behavior, for. B. the engine torque, is stored and the difference (Δψ _Diff ) between the target value and the stored difference value (Δψ _Diff ) is formed over a period of time and as a derived target value (Δψ _{target / diff} ) with the actual value ( ψ _If ) is compared, the driving behavior of the vehicle is retained with measures that require a low computing capacity and lead the driving behavior of the vehicle to the neutral driving behavior of the vehicle by means of a flat control curve after the time period has elapsed.

Practical tests have shown that a maximum period of 7 Seconds, preferably 4 seconds, in which the target value of the Yaw angle change towards the before or when changing the vehicle dynamic driving behavior, e.g. B. the engine torque, existing driving behavior of the vehicle is changed, covers all driving situations that require maintaining the Driving behavior of the vehicle require the vehicle for the driver is always predictable and easy to control do.

When the vehicle turns to the inside of the curve, the Brake pressure modified so that at least one outside wheel the brake pressure is raised and / or on is lowered at least one inside wheel, whereby an additional yaw moment is generated that the Counteracts over-tax effect.

When the vehicle turns to the outside of the curve, the Brake pressure modified so that at least one Brake pressure raised and / or on inside wheel at least one outer wheel is lowered, thereby a additional yaw moment is generated that the Counteracts the under-tax effect.

The brake pressures are on the wheels of the rear axle modified because the rear wheels do not have one with the Steering wheel directly connected steering axle. This will a modification of the brake pressures possible by the driver is not perceived.  

The modification of the brake pressures is not or will be canceled or undone if one with the Modification of the brake pressures taking place further reduction the cornering forces of the wheel or wheels to one leads to unstable driving behavior of the vehicle.

A control system to improve the driving behavior of a Vehicle when cornering with changing vehicle dynamic driving behavior, in particular changing Engine torque, has a detection device that a or in the event of a change in the actual driving behavior of the Detects the vehicle and activates a storage device that the recognized actual driving behavior of the vehicle is saved and used Provides and an influencing device that the Driving behavior of the vehicle over a period of time like this influences that it saves the actual driving behavior of the Vehicle maintains. Such a control system is simple built and requires only a small computing capacity.

Due to the features of claim 10, the response sensitivity of the control system much higher, because before or at the change in vehicle dynamic driving behavior, e.g. B. of Motor torque, the setpoint by which the control takes place the actual value recorded before or during the change in engine torque Value is placed on the driving behavior of the vehicle is maintained and the regulation applies directly.

The fact that the memory provides the difference value (Δψ _Diff ) for 7 seconds, preferably 4 seconds, covers all critical driving situations that require the driving behavior of the vehicle to be maintained so that the driving behavior of the vehicle is always predictable and easy to control for the driver close.

An embodiment of the invention is in the drawing shown and is described in more detail below.

Show it:

FIG. 1a + b an example of an over- and under-control state of a vehicle on changes in engine torque,

Fig. 2 shows a control system for improving the Fahrver behavior of a vehicle during cornering with changing engine torque,

Fig. 3 according to the invention the displacement of the course of the set value of the change of the yaw angle per unit time,

Fig. 4 shows the profile of the brake pressure over time,

Fig. 5 shows the course of the driver's torque over time.

FIG. 2 shows a control system 10 for improving the vehicle behavior of a vehicle when cornering with a changing engine torque. This control system has the task of forcing the vehicle onto the curved path determined by the steering wheel angle δ set by the driver and the existing driving speed v by forming an additional yaw moment M _G if this is not possible without such an additional yaw moment M _G. The yawing moments are brought about by targeted braking processes on the individual wheels, the course of the braking processes and the selection of the wheels to be braked depending on the necessary additional yawing moment. The direction of travel desired by the driver is determined by a corresponding angular adjustment of the steering wheel, which leads to a corresponding angular position of the steering wheels.

In the control system 10 , a vehicle model circuit 12 is provided, to which input data, such as driving speed v, steering wheel angle δ, are fed, which define the curved path desired by the driver. In the vehicle model circuit 12 , the input variables are used to calculate how large the change in the yaw angle per unit of time ψ _should be, which is determined by the driver through the input variables of the vehicle model circuit. In a comparator 13 the target value of the change of the yaw angle ψ ψ _target per unit time with the actually measured by a corresponding measuring device 11 the actual value of the change of the yaw angle per unit time _is compared with a constant engine torque. As the output signal, the comparator 13 outputs an output variable Δψ _Diff , which corresponds to the difference between ψ _target and ψ _actual . The difference value Δψ _{Diff determined in this way} between the desired and the actual change in the yaw angle per unit of time is fed to a yaw moment controller 14 for controlling the yaw moment. The GMR controller 14 calculates an additional yaw moment M _G based on Δψ _Diff , which is fed to a distribution logic 15 . The distribution logic 15 , based on the additional yaw moment M _G and possibly a driver's request for pressure build-up in the brakes (B _F ) (driver's braking request), defines output variables which correspond to the pressure values required on the individual brakes and which via a hydraulic circuit 16 the individual Brakes are applied to the wheels of the vehicle. The pressure changes thus achieved on the brakes of the individual wheels lead to a new actual value ψ _actual yaw angle, which in turn is compared with ψ _target in comparator 13 .

React when cornering at excessive driving speed usually take the accelerator away first. This A change in the engine torque causes the transition from the drive a reversal of direction of the vehicle for engine braking the peripheral forces acting and a Shifting the wheel load from the rear wheels to the front wheels.

The axle load change ΔF _z results from

ΔF _z = | F _zVa + ΔF _zVi | ΔF _zHa + ΔF _zHi | = mh / l × Δ ³ _F.

Here, the vehicle mass M, the center of gravity h, the wheel base L and the acceleration difference Δ ³ _F. This results in different degrees of changes in the slip angle on the front and rear wheels and a change in the tire return torque on the two front wheels. The increase in the slip angle on the rear wheels causes a yaw rotation and a course deviation of the vehicle from the outside of the curve to the inside of the curve. This can be seen from the course of the measured ψ _actual , which is greater than the associated target value ψ _target . The invention prevents the change in the vehicle behavior by detecting the difference between ψ _target and ψ _actual at a time which lies before the change or in the change in the engine torque. Z serves as an activation variable. B. a control signal output via the engine control, which switches a connection between the comparator 13 and the memory 17 , in which the yaw angle difference ψ _Diff generated in the comparator is stored. In Fig. 2, the switching of the memory 17 is shown schematically by a switch 18 which is controlled by a trigger circuit 20 via a control line 19 . The memory 17 is connected via a line 23 to a further switch 21 with the comparator 22 . Switch 21 is also controlled by trigger circuit 20 via control line 24 when the change in engine torque meets the conditions for setting memory 17 . The difference Δψ _{Diff of} the yaw angle existing before or during the change in the engine torque is compared in the comparator 22 with the target value ψ _{target of} the yaw angle. The difference Δψ _{target / diff} generated in the comparator 22 changes the size ψ _target to the value ψ _actual at the time before or when the engine torque changes. The difference Δψ _{setpoint / diff} is fed to the comparator 13 , where the setpoint value Δψ _{setpoint / diff of} the yaw angle, which is changed by the amount of the yaw angle difference ψ _diff at the time before or when the engine torque changes, is compared with the actual value ψ _actual yaw angle . This difference value Δψ _{target / diff,} which is now shifted on the course of the actual value of the yaw angle change, prevents a change in the driving behavior of the vehicle over a maximum period of 7 seconds, since the amount of the yaw angle difference Δ dessen _Diff over its period with that generated in the vehicle model circuit 12 ψ _{Should be} compared before it _is compared with ψ _actual . ψ _Should be adjusted over a preferred period of 4 seconds.

The amount | Δψ _{Diff / Diff} | The Δψ _{target / diff} value compared in the comparator 13 with the actual value ψ _actual is supplied to the GMR controller 14 . The GMR controller calculates on the basis of | Δψ _{Diff / Diff} | the additional yaw moment M _G as a function of the Δψ _Diff present before the change in the engine torque, which is supplied to the distribution logic 15 . The distribution logic 15 determines a brake pressure based on the additional yaw moment M _{G / Diff} and possibly a driver's request for pressure build-up in the brakes B _F or modifies the brake pressure in such a way that in a vehicle which is in oversteering mode, on the outside of the curve Rear wheel, the brake pressure is modified so that a counter-yaw moment builds up, which generates a rotation of the vehicle to the outside of the curve.

Accordingly, when the vehicle turns Outside of the curve the brake pressure modified so that at at least one rear wheel inside the brake pressure is raised so as to generate a counter-yaw moment which causes the vehicle to turn toward the inside of the curve.

The modification of the brake pressures is not or will be canceled or undone if one with the Modification of the brake pressures taking place Cornering forces to an unstable driving behavior of the Vehicle leads. Since the oversteering vehicle modified brake pressures on the outside rear wheel low friction coefficients generate slip enemas that Reduce cornering forces of the wheel and one Favor oversteer behavior, the brake pressure is therefore in its height limited by a value, from the brake pressure is reduced in favor of higher cornering forces.

In FIGS. 3 to 5, the course is _is ψ, ψ and Δψ _{target setpoint / Diff,} the modified brake pressure and the driver torque plotted over time. As shown in FIG. 3, the difference Δψ _Diff between ψ _actual and ψ _target that exists before the change in engine torque at time t1 is stored when the engine torque changes at time t ₂ and compared with ψ _target . The driver torque shown in FIG. 5, which is composed of the driving torque Ma and the decelerating torque Mv of the engine and corresponds to the engine torque requested by the driver, is "zero" at the time t ₂ , which is the time of the gas removal, since from Driver no vehicle driving forces are requested. Through the comparison, the calculated target value ψ _target , which represents a neutral driving behavior, is reset by the amount Δψ _Diff in the direction of the respective actual value ψ _actual . The now "current" target value Δψ _{target / diff} , which has been changed from the calculated target value (dashed line) by the amount Δψ _Diff , _is compared with the actual value ψ _actual over a predetermined period of time. Via the compared amount Δψ _{Diff / Diff} , an additional yaw moment M _{G is} generated by modifying the brake pressure of at least one rear wheel according to FIG. 4, which leads from time t ₂ to a new ψ _actual yaw angle, which is based on the Δψ _{target / diff} value regulated course leads to maintaining the oversteering or understeering driving behavior of the vehicle.

Claims (11)

1. A method for improving the driving behavior of a vehicle when driving through a curved path with a change in vehicle dynamic driving behavior, in particular with a change in engine torque, characterized in that an existing driving behavior of the vehicle before or during the change is maintained over a period of time. 2. The method according to claim 1, characterized in that the curve path of the vehicle is determined from input variables such as driving speed (v) and steering wheel angle (δ) and a target value (ψ _target ) for changing the curve path is determined per unit of time,
that an actual value (ψ _actual ) for the change in the cam track per unit of time is determined,
that the brake pressure of a brake on one wheel or on several wheels may be influenced as a function of a comparison of the target value (ψ _target ) with the actual value (ψ _actual ) for cornering,
and that the target value (ψ _target ) as a function of a difference value (Δψ _Diff ) formed before or during the change from the comparison between the target value (ψ _target ) and the actual value (ψ _actual ) over a period of time in Direction of the actual value (ψ _actual ) is changed. 3. The method according to claim 1 or 2, characterized in that the difference value (Δψ _Diff ) is stored before or during the change and over a period of time the difference between the target value (ψ _target ) and the stored difference value (Δψ _Diff ) formed and compared as a derived target value (Δψ _{target / diff} ) with the actual value (ψ _actual ). 4. The method according to any one of claims 1 to 3, characterized characterized that the time span is a maximum of 7 seconds, preferably 4 seconds. 5. The method according to any one of claims 1 to 4, characterized characterized in that when the vehicle rotates Inside the curve the brake pressure is modified in such a way that on at least one outside wheel of the Brake pressure raised and / or on at least one inner wheel is lowered. 6. The method according to any one of claims 1 to 4, characterized characterized in that when the vehicle rotates Outside the curve the brake pressure is modified in such a way that the brake pressure on at least one inside wheel raised and / or on at least one outside of the curve Wheel is lowered. 7. The method according to any one of claims 1 to 6, characterized characterized in that the brake pressures on the wheels of the Rear axle to be modified. 8. The method according to any one of claims 1 to 7, characterized characterized in that the modification of the brake pressures omitted or canceled or undone will when a with the modification of the brake pressures taking place of the corner executives to one leads to unstable driving behavior of the vehicle.   9. control system for improving the driving behavior of a vehicle when driving through a curved path with a change in vehicle dynamic driving behavior, in particular with a change in engine torque, characterized in that a detection device ( 20 ) detects an existing driving behavior of the vehicle before or during the change, that a storage device ( 17 ) stores and detects the detected actual driving behavior of the vehicle and that an influencing device ( 22 ) influences the driving behavior of the vehicle in such a way that it retains the stored actual driving behavior of the vehicle from the change over a period of time . 10. Control system according to claim 9, characterized in that in a vehicle model circuit ( 12 ) the sizes for determining the curve path of the vehicle, such as speed (V) and steering wheel angle (δ), which are entered due to a circuit in the vehicle model ( 12 ) located, which simulates the properties of the vehicle under simplified boundary conditions, for example, determines a target value (ψ _target ) for the yaw rate change per unit time (target yaw rate) and a comparator ( 13 ) compares this target yaw rate with a measured yaw rate change per unit time ( ψ _actual ) (actual yaw rate), a yaw moment controller ( 14 ) calculating a control yaw moment as a function of the difference (Δψ _diff ) between the target yaw rate and the actual yaw rate, which is used to determine pressure variables that are applied to the brakes of the vehicle generate an additional yaw moment (M _G ), which the actual yaw rate (ψ _actual ) to the target yaw rate (ψ _{So ll} ) leads, and the detection device ( 20 ) before or during the change recognizes the difference value (Δψ _Diff ) between the target yaw rate (ψ _target ) and the actual yaw rate (ψ _actual ), and unlocks the memory device ( 17 ) in which the Differential value (Δψ _Diff ) is stored and an influencing device ( 22 ) is made available, which compares the difference value (Δψ _Diff ) with the target yaw rate (ψ _target ) over a period of time and the comparator ( 13 ) this tracked target yaw rate (Δψ _{target / diff} ) with the actual yaw rate (ψ _actual ). 11. Control circuit according to claim 9 or 10, characterized in that the memory ( 17 ) provides the difference value (Δψ _Diff ) for a maximum of 7 seconds, preferably 4 seconds.