WO2001083277A1 - Method for controlling the handling stability of a vehicle - Google Patents

Abstract

The invention relates to a method for controlling the handling stability of a vehicle. According to said method, a float-angle velocity is determined in accordance with input variables and said float-angle velocity is taken into consideration during the determination of pressures for the individual brakes of the vehicle, in such a way that the handling stability is increased by the intervention of the brakes on individual wheels. The invention is characterized in that a dynamic lane-change manoeuvre is detected using a valuation of variables which reflect the desired and actual handling behaviour of the vehicle, in addition to a control situation and that an intervention of the brakes is undertaken, based on the result of the valuation, said intervention reducing the float angle.

Description

Method for controlling the driving stability of a vehicle

The invention relates to a method for regulating the driving stability of a vehicle in which in dependence upon input variables a slip angular velocity is calculated, and this slip angular velocity is taken into account in the calculation of pressures for the individual brakes of the vehicle, so that increased by wheel-specific braking _{interventions,} the driving stability ,

A large number of driving stability regulations have become known in order to counteract vehicle instabilities automatically. The term driving stability control combines four principles for influencing the driving behavior of a vehicle by means of predeterminable pressures or braking forces in or on individual wheel brakes and by intervening in the engine management of the drive motor. These are brake slip control (ABS), which is intended to prevent individual wheels from locking during braking, traction control (ASR), which prevents the driven wheels from spinning, and electronic braking force distribution (EBV), which determines the ratio of braking forces between the front and rear axle of the vehicle and a yaw moment control (ESP), which ensures stable driving conditions when yawing the vehicle around the vertical axis. In this context, a vehicle means a motor vehicle with four wheels, which is equipped with a hydraulic, electro-hydraulic or electromechanical brake system. In the hydraulic brake system, the driver can build up brake pressure using a pedal-operated master cylinder, while the electro-hydraulic and brake systems build up a braking force that is dependent on the sensed driver braking request. In the following, reference is made to a hydraulic brake system. Each wheel has a brake, which is assigned an inlet valve and an outlet valve. The wheel brakes are connected to the master cylinder via the inlet valves, while the outlet valves lead to an unpressurized container or low-pressure accumulator. Finally, there is an auxiliary pressure source, which is able to build up pressure in the wheel brakes regardless of the position of the brake pedal. The inlet and outlet valves can be actuated electromagnetically for pressure control in the wheel brakes.

Four speed sensors, one for each wheel, are used to record dynamic driving conditions

Yaw rate meter, a lateral accelerometer and at least one pressure sensor for the brake pressure generated by the brake pedal. The pressure sensor can also be replaced by a pedal travel or pedal force meter if the auxiliary pressure source is arranged in such a way that a brake pressure built up by the driver cannot be distinguished from that of the auxiliary pressure source. In the case of a driving stability control, the driving behavior of a vehicle is influenced in such a way that the driver can control it better in critical situations. A critical situation here is an unstable driving condition in which, in extreme cases, the vehicle does not follow the driver's instructions. The function of the

Driving stability control therefore consists in giving the vehicle the vehicle behavior desired by the driver within the physical limits in such situations.

While the longitudinal slip of the tires on the road is of primary importance for the brake slip control, the traction control and the electronic brake force distribution, further variables are included in the yaw moment control (GMR), for example the yaw rate, lateral acceleration and the slip angle speed. Depending on the speed of the vehicle and the steering angle set by the driver, the yaw moment control determines a (target or) reference yaw rate which is compared with the actual yaw rate. Due to the deviation of these two values, an additional torque is calculated so that an additional yaw moment is realized by individually controlling the brakes. To determine a corrected additional torque, the measured or derived from the available parameters of the slip angle speed of the vehicle is used.

During driving maneuvers, such as when changing lanes u. Like. With violent steering and counter steering actions, swimming angles can be built up. The yaw moment control (ESP control) cannot detect this slip angle build-up due to the highly dynamic load change maneuvers, since the filtered measured variables actual yaw rate (Ψ _Mωs ) and lateral acceleration on the rear axle of the vehicle {a _QlιaHA ) the signals reference _yaw rate

(Ψ _Re ), steering angle (δ) and slip angle speed on the rear axle (ß _HA ) lag behind in time, and the conditions required for calculating an additional torque on the basis of the slip angle speed therefore exist at a time when the maximum slip angle is usually already has built up.

It would be desirable to provide the driver with unstable driving situations that are highly dynamic

Going out, supporting or counteracting load change maneuvers in such a way that critical driving situations cannot arise at all.

The invention has for its object to provide a method for controlling the driving stability, which enables a torque size to be determined even in highly dynamic maneuvers.

According to the invention, this object is achieved in that a generic method is carried out in such a way that a highly dynamic lane change situation is determined on the basis of the evaluation of variables which reflect the desired and actual driving behavior of the vehicle and a control situation, and that an intervention in depending on the evaluation result the brake is carried out, which leads to a reduction in the float angle.

As a result, a torque variable is formed on the basis of the slip angle speed at a time when the ESP controller is active and a torque variable may be calculated from the difference between the reference and actual yaw angle variable, but no additional yaw moment is generated in the wheel brakes of the vehicle, since the Direction of the yaw rate difference has already changed. This applies to e.g. highly dynamic lane changes, in which the vehicle is stabilized during the first oversteer control intervention after the reverse or Countersteering, however, oversteered more in the opposite direction and the control intervention then takes place too late.

The intervention in the brakes is carried out according to the method according to the invention at a point in time at which a rest band around the change of direction is traversed by a difference variable which is formed from an actual and reference yaw rate or no additional yaw moment is permitted in the wheel brakes from the calculated difference variable at a time when the "yaw rate control" does not intervene in the driving behavior of the vehicle independently of the driver.

The method according to the invention determines the driving situation (e.g. highly dynamic lane change), namely whether a reverse or Counter steering situation exists, based on the direction of movement of the following variables

Actual yaw rate

Reference yaw rate Steering angle or steering wheel angle

Swimming angular velocity

Lateral acceleration Is the direction of movement of the yaw rate,

Reference yaw rate, steering angle or steering wheel angle and floating angle speed on the rear axle are the same and the direction of movement of the lateral acceleration on the rear axle differs from these values and their amount is greater than one

Threshold value S ( ^a QιιerHA> S), is a highly dynamic

Lane change before. In addition, a status quo ante of the yaw rate controller is determined on the basis of a control situation, namely whether with active yaw rate control without. - brake intervention, e.g. when passing through the rest band of the difference between the reference and

Actual yaw rate, before yaw rate control occurred before entering the rest band.

It is expedient that a torque value is calculated at an early stage from a difference value, which is formed from the float angle speed and a limit value of the float angle speed, which serves to determine the pressures for the brakes, which are only introduced into the brakes when a previous yaw rate control has been carried out Turn in is determined.

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

Show it Figure 1 is a block diagram for describing the controller. to calculate the torque size

Figure 2 block diagram for describing a low-pass filter

Figure 3 evaluated signal sequences according to the invention

FIG. 4 shows a flow chart with a decision logic within the float angle speed control

A measure of the stability of a driving state, namely the driving stability, is the predominant float angle & and its time derivative, the

Angular velocity ß. Using the filtered vehicle _{reference speed} v _Re f _Fι i, the. measured vehicle lateral _acceleration a _transverse and the measured

_{Yaw rate} Ψ _MΘSS , a _slip angle speed determination is made.

The slip angle velocity ß is determined from the measured values or from variables calculated on the basis of measured values as follows, based on purely physical considerations:

The acceleration a _que r of the vehicle's center of gravity transverse to the longitudinal axis in the plane of movement is measured. The center of gravity of the vehicle moves with the speed vector v relative to an inertial system: F 1.1

cosfΨ + Z?) v = v sinfψ + y?)

Here denotes the yaw angle and & the float angle. The acceleration vector a is derived from time t as:

F 1.2

∞s (Ψ + ß) sinfΨ + ^ j a - v = v + v (Ψ + ß) dt sin ψ + ö cosCΨ + yÖ)

The acceleration sensor measures the projection of the acceleration vector onto the transverse axis of the vehicle:

F 1.3

sinΨ

* quer = a cosΨ

F 1.4 a _ψιeι = v sin /? + v (Ψ + ß) cos /?

kann man die Gleichung umformulieren zuAfter linearization of the trigonometric functions

you can reformulate the equation too

ß ₌ £ =. _ ψ _ - ^V ß VV

F 1.5

The float angle velocity β can now be calculated according to the differential equation above. In addition to the lateral acceleration, the measured variable is a _que r

Yaw rate Ψ, the scalar vehicle speed v and their time derivative v a. To determine & / ", the ß of the previous calculation can be integrated numerically, assuming v = 0 for the first ß determination. A simplification results if the last term is generally neglected, so that no a ^ has to be determined ,

FIG. 1 describes the β regulator 10, which is part of the yaw moment regulator. The program uses two input variables to calculate the additional torque M _G around the vertical axis of the vehicle, which is necessary in order to maintain stable vehicle behavior, especially when cornering. The calculated torque M _G is the basis for the calculations of the pressures to be controlled in the wheel brakes. As input variables are available disposal

at input 11: Ψ Dpsip at input 12: ß at input 13: ^a QιιaHA at input 14: δ at input 15: Ψ ^x Re at input 16: Ψ ¹ Maas at input 28: Ψ ISnsin

The value at input 11 is the difference between the measured (actual) yaw rate Ψ _MΘ SS and the reference yaw rate Ψ _Re calculated using a known vehicle reference model.

The value at the input 11, namely Ψ _D , is first fed to a low-pass filter 17.

The input variable 20 of the low-pass filter according to FIG. 2 is denoted by u and the output variable 21 by y. The output variable 21 is fed to a register 22 and is available in the next calculation as the previous value y (k-l). The output value 21 for the calculation loop is then calculated using the following formula

y (k) = λ * (kl) + (lλ) * u * k _p

F 1.6 where ^ can have values between 0 and 1. ^ & describes the value of the low-pass filter. For the Limit value "fl = 0, the recursion function is eliminated: the previous values y (kl) have no significance for the calculation of the new output value 21. The closer" t ⁾ approaches the value 1, the stronger the previous values work, so that the current input value 20 is only slowly asserted as output value 21.

k _p is a linear weighting factor.

The low-pass filtering just described takes place for the input value 11 and leads to the filtered value 18.

The same low-pass filtering 19 in a first-order low-pass filter takes place for the input variable 12, namely for β. The filtered value 23 is fed to a non-linear filter 24. The purpose of this filter is to set the output value to 0 for small input values and to forward an input value reduced by the limit value for input values that are above a certain limit value. The limitation takes place both in the negative and in the positive range. The limit /? _t h can be a fixed quantity implemented in the program, but also quantities that depend on other parameters, for example the coefficient of friction between the tires and the road. In this case, the limit value is calculated separately as a linear function of the coefficient of friction.

The two quantities, namely 18 and 23, are weighted in a further step 25 and 26, each with a linear factor.

These factors are usually fixed in the calculation system implemented. They can be calculated on the order of magnitude from corresponding vehicle models, but generally require fine-tuning through driving tests. In this way, a corresponding set of linear factors is determined for each vehicle or for each vehicle type. The factors can also depend on other parameters, such as the coefficient of friction between the tire and the road. In this case, after fine-tuning, the factors are calculated separately as a linear function of the coefficient of friction. The thus weighted inputs 11, 12 are added, wherein (addition element 27), the additional torque M _G obtained, which is based on the further ^'calculation process of the program. The additional torque is implemented via brake pressures on the vehicle. The program works continuously in order to always have current control variables at hand. However, whether this torque is passed on to the brakes depends on an activation logic. '' If the vehicle is reversing, the transmission is interrupted by the M _G. The same applies if vehicle standstill is detected or if neither

Angular velocity ß is still the default for the

_{Yaw rate difference} Ψ _Dpslp reach an amount that requires control.

FIG. 3 shows a time course of the signals Ψ _{0 ())} (input 28), ß _HA (input 12), _ϋlιerHA (input 13), δ (input 14), Ψ _Re (input 15) and Ψ _measurement (input 16) in a highly dynamic load change maneuver, such as a lane change, in a schematic representation. The zero crossing at which there is a change of direction is it 29 and the only schematically shown thresholds for the Ψ control with 30, 31 and the only schematically shown thresholds for the ß control with 60 and 61 respectively. In the rest band 32 delimited by the thresholds 30, 31 around the zero crossing 29, there is no regulation of the additional torque M _G on the basis of a yaw angular velocity difference. As the

Signal sequence of the yaw rate difference Ψ _{D /) S //} , shows as an example, the

Yaw rate difference Ψ _{D / BI} - _p at

Exceeding threshold 30 at time Ti until falling below threshold 30 at time T _{2 is} controlled by calculating torque quantity M _G , which is used to determine pressure quantities. The pressure variables generate an additional yaw moment * via the wheel brakes of the vehicle, which leads the measured yaw angle variable to the calculated yaw angle variable. Accordingly, the slip angle speed difference between the determined slip angle speed and the limit value is included in the torque size

/? ,,, the float angle speed when the limit is exceeded. The regulation can be, for example, an oversteer regulation, in which the vehicle turns faster about the vertical axis than corresponds to a calculated reference yaw rate. In this case, the lateral force on the front front wheel on the outside of the curve must be reduced. This is done by controlling higher slip values on this wheel. The pressure in the wheel is regulated in such a way that a coefficient is determined for the wheel that relates the relationship between the change in pressure and the calculated one represents additional torque M _G. The signal sequence of the

_{Yaw rate} difference Ψ _{D / Mή} , shows that the

Vehicle is stabilized after the first oversteer control intervention because the

Yaw rate difference at time T ₂ enters the resting band 32. The signal curve of the yaw angular velocity difference changes the direction towards the zero crossing 29 compared to the first maneuver where the

Yaw rate change from zero crossing 29 removed. If the yaw rate difference occurs in the rest band 32, the control is still activated, but no additional yaw moment is applied to the brakes. After reversing or countersteering, the vehicle oversteers, which leads to the regulation at time T ₄ . As shown, the exceeds

Float angle speed on the rear axle ß _{HA in} front

Entry into the Ψ _{0 l);} -Regulation threshold 60. The associated _{build-up of the slip} angle is prevented by a situation _detection 33 (FIG. 1), which activates an early ß ,, _urjj , -regulation. For this, in the

Situation detection 33 determines the driving situation “highly dynamic lane change” because, owing to the high dynamics, the

/? - Regulation too late, namely at time T ₅ , enters the regulation. The highly dynamic lane change is determined on the basis of the actual yaw rate, reference yaw rate, steering angle or steering wheel angle, slip angle speed and lateral acceleration. This is preferably done by observing conditions. The logic 34 of the situation detection 33 determines whether the Direction of movement (the sign) of the sizes yaw rate,

Reference yaw rate, steering angle or steering wheel angle and floating angle speed is the same. FIG. 3 shows that these observed quantities pass through zero crossing 29 in a time band 50. If the directions of movement of these variables are the same, the logic 34 sets a bit (1) in the output logic 35. In the comparison logic 36 with the inputs 12 and 13, the

The slip angle speed ß and the lateral acceleration at the rear wheel a _{QμaRA are compared} in accordance with the direction of movement. If the directions of movement are the same, the switch 41 is closed. The ^ control is entered by multiplying the filtered (24) output variable in the multiplier 38

The slip angle velocity difference is multiplied by 1.

Are the directions of movement of ß and a _{Qu <: rIiA} , as in Figure

3, not the same, the comparison logic _sets a bit (1) in the output logic 35 when the lateral acceleration o _QuaVA on the rear axle

Threshold S exceeds. In addition, it is determined in the logic 37 with the input 28 of the situation detection 33 whether the torque control or Ψ _D control before the entry into the rest band 29 was active during steering, ie a control situation with a first control intervention in the brakes has taken place , This intervention is determined by observing the condition that occurs with a Ψ _{H control} when entering the resting band 29 is still activated. If a counter is used, the counter is reduced after entry into the idle band 29, ie the Ψ "control is still activated. On the other hand, if the counter reading is zero, no override control intervention took place before entry into the idle band 29.

The logic 37 also starts in the output logic 35

Bit (1) if the Ψ _{H j} , control continues to operate. If the conditions in the logic 34, 36 and 37 are met, the output logic 35 switches the switch 39 to the position shown in FIG. 2. The switches 39, 40, 41 merely represent a switching function schematically, which can be implemented by means of electronic elements or as a software function. Entry into the ß ^ -

Regulation is activated. The filtered (24) output variable of the slip angle speed difference is multiplied by 1. At the same time the linear factor (k_?)

26 of the /? Regulation changed. The factors k__? are calculated as a linear function of the coefficient of friction according to the relationship k_ß * k_corr. k_corr increases with increasing coefficient of friction, so that the ß _{early control is} not only for high friction values in the range from μ -6 to μ -. , 2, but can also be used with a low coefficient of friction of less than 0.6.

On the basis of the slip angle speed difference, an additional torque M _{G is} formed on the addition element 27, which is used as a basis for the further calculation process of the program. After an entry dead time (e.g. 5 loops), a torque based on the Schwi m angular velocity difference calculated at a time T _δ at which the rest band 29 around the change of direction from the difference between the difference between the actual and

Reference yaw rate is traversed. The torque is used to determine the pressures for the brakes.

Output 42 of situation detection 33 sets a bit (0) if the conditions for a β and β ^ control are not met. The switch 40 is closed. The output value of the filter 24 is multiplied by zero in the multiplication element 38.

In Figure 4 are the logical in the form of a flow chart

Processes in the ß _Farly regulation shown. logical

Branches are in the flowchart as. Diamonds. Based on a given situation, diamond 50 determines whether the entry conditions into the ß _Early -

Regulation are met or not. If one of the entry conditions is a) Ψ _wj , regulation is active b) The quantities ß, δ, Ψ _Re Ψ _MeM differ in sign (the movement direction c) attitude from a _υιll „. _HA c) the amount of a _ϋlιerHA is not greater than a threshold S before, the entry conditions of the ß regulation are determined. If these are fulfilled, a known / Ϊ control takes place. Will this Entry conditions are not met, a stable driving condition is assumed. Switch 40 is closed, there is no regulation.

If all the entry conditions for a β ^ control are present, then in step 51 the linear factor k_ß (see FIGS. 1, 24) becomes k_ß = k_ / 3 * k_corr, with k_ß = linear factor

/ ^ - control and k_corr = correction value, calculated. In diamond 52, a query is made as to whether the entry dead time and the limit value β _tl , the slip angle speed, has been exceeded, that is to say whether the current slip angle speed on the rear axle ß_ra is greater than the entry threshold β _{lh in} . Is the

If the entry threshold is exceeded, it is checked in diamond 53 whether the control deviation lies in a hysteresis band. There is a ß _early regulation. If the

Conditions in diamond 52 in step 54, the additional torque from the ^• difference of

Float angle velocity ß and the limit value ß _{lh ml} multiplied by the corrected factor k_ß. Thus, if the vehicle has built up a slip angle, it is determined in diamond 55 whether the torque from the yaw angle speed difference and the slip angle speed difference is not equal or the same, and in the latter case, in step 57, no additional torque from the

Floating angle velocity difference formed. On the other hand, if the torques are unequal, the formation of an additional torque is permitted in step 56. The Condition in diamond 55 represents only one exemplary embodiment. It goes without saying that an additional torque can also be calculated, which takes the torque from the yaw rate difference into account.

Claims

Expectations 1. Procedure for controlling the driving stability of a Vehicle in which a float angle speed is determined as a function of input variables and this float angle speed is taken into account when determining the pressures for the individual brakes of the vehicle, so that driving stability is increased by wheel-specific brake interventions, characterized in that a highly dynamic lane change situation is based on the evaluation from variables that reflect the desired and actual driving behavior of the vehicle and a control situation, and that, depending on the evaluation result, an intervention is made in the brakes, which leads to a reduction in the float angle. 2. The method according to claim 1, characterized in that the intervention in the brakes is carried out at a time at which a rest band (30, 31) for the change of direction (29) of a difference variable from the deviation between an actual and reference yaw rate becomes. 3. The method according to claim 1 or 2, characterized in that the intervention in the brakes is carried out at a time at which a difference variable from the deviation between an actual and the reference yaw rate is determined, but no wheel-specific brake interventions are carried out in accordance with the difference. 4. The method according to any one of claims 1 to 3, characterized in that the highly dynamic lane change is evaluated on the basis of the direction of movement of the following variables: yaw rate reference yaw rate Steering angle or steering wheel angle Floating angle speed lateral acceleration. 5. The method according to any one of claims 1 to 4, characterized in that the direction of movement of the sizes Yaw angle speed Reference yaw angle speed Steering angle or steering wheel angle Floating angle speed must be the same. 6. The method according to claim 4 or 5, characterized in that the direction of movement of the lateral acceleration different from Direction of movement of the sizes yaw rate, reference yaw rate, steering angle or steering wheel angle and float rate must be. 7. The method according to any one of claims 1 to 6, characterized in that the highly dynamic lane change in Dependence on a threshold value of the lateral acceleration on the rear axle is detected. Method according to one of claims 1 to 7, characterized in that a torque value is calculated from the difference in the slip angle speed with a limit value, which is used to determine the pressures for the brakes which are only introduced into the brakes when yaw rate control is active.