DE19751227A1 - Operating procedure for steering system of vehicle - Google Patents

Abstract

The steering system (40a-626) for a car uses a steering drive train in which at least one steerable wheel, one positioning drive, a superimposed gearbox, the driver-operated steering wheel and mechanical turning devices are located. The turning devices have a rotatable input and output shaft and an angular alignment between them. The steering movement initiated by the steering wheel and the movement initiated by the positioning drive to generate the steering movement of the steerable wheels are superimposed through the superimposed gearbox. A parameter representing the yaw movement of the car is determined and a control signal at least dependent on this is generated when a certain travel state exists. The positioning drive is controlled to initiate the movement by this signal. Another parameter representing the braking condition of the car is determined and the existence of the travel state is determined according to this.

Description

State of the art

The invention relates to a method and a device for operating a steering system for a motor vehicle.

Such a steering system is known from DE-OS 40 31 316 (corresponds to US 5,205,371) and, insofar as it is relevant for understanding the present invention, is to be explained with reference to FIGS . 1 and 2. In such a steering system, the steering movements applied by the driver through the steering wheel 11 or 21 , the steering wheel angle δ _L detected by the sensor 28 , in the superposition gear 12 or 22 with the movements, the motor angle δ _M , the actuator bes 13 or 23 overlaid. The resulting total movement δ _L 'is transmitted via the steering gear 14 or the steering linkage 16 to the steerable wheels 15 a and 15 b for setting the steering angle δ _V. The actuator 13 or 23 can be designed as an electric motor. The functional principle of such a steering system is that the motor angle δ _M for influencing the dynamic behavior of the vehicle is determined depending on the steering wheel angle δ _L and depending on signals Sm, the steering wheel angle δ _{L being determined} via the sensor 28 and the signals Sm represent the vehicle movements detected by the sensors 26 . The overall steering angle results from the relationship

δ _L '= δ _L / i _ü + δ _M ,

where the gear ratio can be i _ü = 1 or i _ü ≈ 1.

DE-A1-36 25 392 shows the delivery of a correction signal to an actuator that influences the front wheel steering angle. The correction signal is dependent on a target-actual yaw speed deviation.

The compensation of cross wind influences by an over stored steering angle intervention shows the GB-PS 1,414,206.

DE-OS 40 38 079 (corresponds to US 5,316,379) shows one Superposition of a steering component (compensation steering angle) on Front wheel and / or rear wheel. The compensation steering angle, which is dependent on the brake pressure differences, compensated the yaw movement in so-called µ-split braking, that is, during braking, where the road surface friction significantly ver. on the right and left side of the lane are divorced. However, this can lead to the problem that the brake pressure difference is only an inaccurate measure of that Yaw moment represents, in particular by different Tires left and right, fading, uneven brake ver wear, ABS malfunction or brake circuit failure can be faked.  

In the publication Ackermann et al .: "Driving safety through robust steering control ", automation technology 44 (1996) 5, pages 219 to 225, the Gierdy is suggested namik a motor vehicle by a steering intervention to be influence, in particular an integrating controller (I controller) is provided.

Although for the settlement of large disturbances, like them e.g. B. with µ-split ABS braking or strong cross winds occur with an integrating yaw rate controller high gain is particularly suitable such controller on the other hand for small disturbances, such as. B. slight bumps, frequent steering interventions that are unnecessary and are disturbing.

The object of the present invention is that Yawing behavior of a vehicle due to steering intervention without causing unnecessary frequent steering interventions sen.

This task is carried out by the combinations of features of the independent pending claims resolved.

Advantages of the invention

As already mentioned, the invention is based on a Lenksy stem for a motor vehicle with at least one steerable Wheel, an actuator and a superposition gear. The superimposed gearbox is used by the driver of the vehicle initiated steering movement and the Actuator initiated movement to generate the steering movement steering wheel superimposed. According to the invention  a yaw representing the yaw movement of the vehicle size recorded and in the presence of a certain driving condition a control signal at least dependent on this detected Yaw size formed. The actuator then becomes an initiative tion of the movement by the generated control signal Furthermore, according to the invention, the braking state of the vehicle representative brake size detected and Presence of the driving condition depends on this detected Brake size determined.

The invention enables active steering intervention for ver improvement in yaw behavior that only turned on is detected when an external disturbance of the vehicle movement is tiert.

In particular, it is provided that the detected braking quantity represents a braking state of the vehicle in which a braking operation on a roadway with significantly different road surface friction values takes place on the different vehicle sides. In particular, it is provided that the detected brake quantity is detected as a function of the braking effects, in particular as a function of the wheel brake pressures, of at least two wheel brakes on different sides of the vehicle. The detected brake size can be detected depending on the difference in the wheel brake pressures of at least two wheel brakes on different vehicle sides and / or depending on the ratio of the larger to the smaller of the wheel brake pressures (p _vr , p _vl ) at least two wheel brakes on different vehicle sides. Furthermore, it can be provided that the detected brake quantity depending on an actuation of the brake system of the vehicle, in particular depending on an actuation of the brake lights, is detected.

As already mentioned, such a so-called µ-split brake is used induces a yaw moment, which it is acc counteractive steering intervention. In contrast to Systems such as those mentioned in the introduction DE-OS 40 38 079 (corresponds to US 5,316,379) are, is by the invention even with uneven Brake pad wear, fading, different tires right and left, anti - lock (ABS) malfunction or Brake circuit failure intervened correctly in the steering and counteracted the yaw movement to increase driving safety.

In an advantageous embodiment of the invention is before seen that a target value for the yaw movement of the drive stuff is determined. This target size is particularly from depending on the one initiated by the driver of the vehicle Steering movement and / or depending on the detected vehicle speed determined. The control signal is then little at most depending on the difference between the recorded Yaw size and the determined target size formed.

It is particularly advantageous if the yaw size detected or the difference between the detected yaw rate and the certain setpoint to form the control signal inte is grated (I controller). As already described for the Correction of large disturbances, such as z. B. at the µ-split ABS braking or strong cross winds occur integrating yaw rate controller with high gain especially suitable. The problem that such a regulator for small disturbances, such as B. slight bumps, often Steering interventions that are unnecessary and disruptive solved by the invention. It is therefore an I controller with  high gain found only in the case of certain large interferes.

It is also advantageous that after the presence of the be agreed driving condition, so if this driving condition is not more, the control signal or at least the dependent share of the control signal formed by the yaw size a temporally decreasing behavior towards a predefinable one Value, especially to the value zero. The time Lich decreasing behavior can be done by a ramp or realized by a first-order delay behavior be. In particular, the time-decreasing behavior depend on the vehicle speed. According to this Aus design of the invention, the additional steering angle on the Value zero returned when there is no more external disturbance lies.

An improved detection of external disturbances is there achieved by that the detected brake size continues to depend is from the steering initiated by the driver of the vehicle movement and vehicle speed and / or from one the quantity representing the lateral acceleration of the vehicle eat. With this variant, the µ-split detection becomes too additionally the steering angle and the vehicle speed or the lateral acceleration takes into account µ-split braking and to differentiate between cornering braking better.

Because cross wind also leads to an undesirable yaw movement of the Vehicle, it is also advantageous that represent a cross wind influence on the vehicle tating cross wind size is detected, and the presence of  Driving condition also depending on the detected side wind size is true.

Further advantageous refinements are the dependent claims Chen to take.

drawings

Figs. 1 and 2 schematically show the steering system of the prior art from which the invention proceeds in the embodiment. Fig. 3 illustrates the control or Regelungsstra strategy is of such a steering system. FIG. 4 shows a yaw moment compensation, Fig. 5 control a yaw rate, while the Fig. 6, the combination of the yaw speed controller according to the invention with the μ-split detection shows.

Embodiment

In the following, the invention is to be described with reference to an embodiment are shown in a game. An example of one overlap steering mentioned at the outset.

Fig. 1 and Fig. 2 shows an actuatable by the driver of the vehicle steering wheel by the reference numerals 11 and 21 respectively. By actuating the steering wheel 11 or 21 , the gearbox 12 or 22 is fed through the connection 101 to the steering wheel angle δ _L. At the same time, the motor gear δ _{M of} the actuator 13 or 23 is fed to the superposition gear 12 or 22 via the connection 104 , it being possible for the actuator to be designed as an electric motor. On the output side of the superposition gear 12 or 22 , the total movement δ _L 'is fed via the connection 103 to the steering gear 14 or 24 , which in turn, via the steering linkage 16, corresponds to the total angle δ _L ' of the steerable wheels 15 a and 15 b with the steering angle δ _V acted upon. In FIG. 2 sensors continue to see 28 and 26, wherein the sen sor 28 the steering wheel angle δ _L is detected and the control unit supplies 27, while 26 sensors are gekennzeich net with the reference numerals which the movements of the vehicle 25 (eg. Gierbewe conditions, lateral acceleration, vehicle speed, etc.) sen and supply appropriate output signals Sm to the control unit 27 . The control unit 27 determines, depending on the detected steering wheel angle δ _L and possibly depending on the vehicle movements, a manipulated variable u for controlling the actuator 13 or 23 .

Fig. 3 shows a block diagram of the function of the steering system while driving the vehicle. The setting of the additional steering angle δ _M takes place in that a vehicle controller or a controller 31 determines a target value δ _M for the additional angle. This happens depending on the yaw rate ω of the vehicle detected by the sensor 26 . The target value δ _M, is set by a subordinate position controller 32 and possibly a current controller by the motor 33 and is superimposed on the steering wheel angle δ _L induced by the driver at point 35 (superposition gear). Of course, it can also be provided that the target value δ _{M, should} also contain components for the additional angle which are dependent, for example, on steering assistance for the driver, on the steering wheel angle δ _L.

In FIG. 4, the determination of the target value δ _{M soll,} shown in the case of μ-split braking. In this case, a strong braking process, in particular anti-lock braking (ABS braking), takes place on a road surface that has very different coefficients of friction on the right and left sides of the vehicle. There is a yaw moment in a known manner. In the yaw moment compensation shown in FIG. 4, the brake pressures p _vl and p _vr on the left and right front wheel are either sensed directly or calculated from existing measurement data (e.g. valve opening times, admission pressure) (detection means 40 a and 40 b). These wheel brake pressures are then filtered in filters 41 and 42 to suppress interference. The difference between the brake pressures filtered in this way is then processed in block 43 (proportional amplifier with dead band). The target value δ _M, target for the additional angle is then determined from the difference thus processed by means of a constant and a time-variable gain factor (blocks 44 and 45 ).

In the yaw moment compensation shown in FIG. 4, there is the problem already mentioned that the brake pressure difference is only an inaccurate measure of the yaw moment, which is particularly falsified by various tires left and right, fa ding, uneven brake wear, ABS malfunction or brake circuit failure can be.

Another possibility consists in the OFF control of the Stö stanchions by a yaw speed controller according to Figure 5. In this case, _x from the vehicle speed V, the steering wheel angle δ _L (sensor 28) and possibly further variables _should ω a target value for the yaw rate is calculated (block. 51 ) and compared with the measured yaw rate ω of the vehicle. If it is found in the yaw rate controller 52 that the target and actual values differ from one another, the yaw rate controller 52 determines a suitable target value δ _{M, should} for the additional steering angle in order to reduce the deviation. The position controller 53 and the motor 54 correspond to the blocks 32 and 33 described with reference to FIG. 3.

For µ-split braking, the use of a pure I controller as a yaw rate controller is particularly favorable. This means the rule law:

δ _{M, soll} = K _I .∫ (ω _soll -ω) dt

respectively.

dδ _{M, to} / dt = K _{I. (to} ω -ω)

K _I is a constant gain factor. As he mentioned above, this rule of law leads to frequent minor interventions that are unnecessary and disruptive.

The yaw rate regulation described with reference to FIG. 5 represents the basis for the combination shown in FIG. 6.

The yaw rate controller 61 is supplied with the instantaneous yaw angle rate ω detected by the sensor 26 and the corresponding target value (block 51 , see FIG. 5). The difference (ω _soll -ω) formed in the link 611 _is fed to the amplifier stage 612 (integration gain K _I ). If the switch 615 takes the position shown in FIG. 6, the difference (ω _soll -ω) is passed via the integrator 613 and is processed to the desired variable δ _{M, intended} for the additional steering angle δ _M. If the switch 615 which can be controlled by the signal S has the other position (not shown in FIG. 6), the desired variable δ _{M is to be placed} on the input of the integrator 613 via the amplifier stage 614 .

The integrating yaw rate controller 61 is therefore only switched on when a µ-split braking is recognized by the µ-split detection 62 . The switch 615 has the position shown in FIG. 6. Before a µ-split braking solution is recognized, the manipulated variable is δ _M, target = 0. If the µ-split braking is ended, the additional angle still pending or the corresponding target variable δ _M, target _{is set} again Zero value returned; this is preferably done with a first-order delay behavior. The switch 615 has the position not shown in FIG. 6 Darge.

If the start of the journey is identified by the time t = 0, the control law is described by the following equations:

for t = 0:

δ _{M, should} (t = 0) = 0;

for t <0:

dδ _{M soll (t)} / dt = K _I. (ω _to -ω)
if µ-split braking is present;

dδ _{M, should} (t) / dt = -a.δ _{M, should} (t),
if there is no µ-split braking.

K _I <0 is a constant gain that is approximately as large as the steering ratio i _L. a <0 is a constant factor, where 1 / a is the time constant with which the additional angle or the target variable δ _{M is} to be canceled after the end of the µ-split braking.

The µ-split detection 62 works as follows:
When the brake is actuated, which is determined by means of the brake light switch 63 (signal BLS), it is recognized _from the brake pressures p _vr and p _vl on the front wheels whether there is a μ-split situation or not. The brake pressures can be measured directly or estimated from other parameters such as ABS valve opening times and pre-pressure.

After suppression of the interference by the filters 41 and 42 , the brake pressure difference Δp = (p _vl -p _vr ) is formed in point 625 . If the brake pressure difference Δp exceeds a certain limit value P _G , which can also depend on the total pressure level, it is concluded that the braking is µ-split. The µ-split flag is then set to one, otherwise it is zero.

The limit value P _G is adapted to the total pressure level by increasing the constant value P _Go by the product (block 621 ) of the filtered brake pressures weighted with the constant factor K _G (block 622 ).

The µ-split flag is multiplied with the BLS value in block 626 or logically AND-linked. If it is recognized in this way that braking is currently being carried out on μ-split, the switch 615 is brought into the position shown in FIG. 6 by the signal S, whereby the I controller is switched on. If there is no µ-split braking, the switch 615 is switched over and δ _{M, should be brought} to zero.

In addition to the described consideration of the wheel brake pressure differences, the ratio of the larger to the smaller of the wheel brake pressures (p _vr , p _vl ) of at least two wheel brakes on different sides of the vehicle can be evaluated.

The proposed switchable yaw rate controller enables numerous variants and extensions:

• - After the end of the µ-split braking, the additional angle _is reduced to zero with a deceleration behavior _, rather with a ramp, ie with the constant speed ± dδ _{M, set (0)} / dt.
• - The return to the value zero, ie the factor a or the speed ± dδ _{M, should (0)} / dt, depends on the vehicle speed.
• - When the vehicle is stationary, the additional angle is not changed; if δ _M ≠ 0 or δ _M when the vehicle comes to a standstill _{, soll} 0, the additional angle is only returned to zero when the vehicle starts up again.
• - The steering angle is also shown in the µ-split detection and the vehicle speed or the lateral acceleration taken into account to µ-split braking and cornering braking to differentiate better.
• - Instead of using the µ-split detection according to FIG. 6, a µ-split braking can then be concluded if the so-called µ-split factor
  exceeds a certain limit. P _max = max (p _vl , p _vr ), P _min = min (p _vl , p _vr ); P _off is a constant offset and ay is the vehicle lateral acceleration; P ₀ , P ₁ and P ₂ are constant parameters.
• - Instead of a separate µ-split detection, the µ split flag used, which is generally in a conv tional anti-lock control unit is present.
• - The integrating controller is also switched on in cross winds switches. The fact that there is cross wind is by means of air pressure sensors at various locations on the body de tect, see Tran, V.T .: Crosswind Feedforward Control
• - A Measure to Improve Vehicle Crosswind Behavior; Ve hicle System Dynamics 23 (1993), pp. 165-205.
• - The switchable I controller is replaced by further feedback added, e.g. B. a proportional return of the yaw speed to dampen the yaw movement itself Obtain steering interventions at all times in a way that is understandable can.

In summary, the following can be highlighted as advantages of the invention:

• - It will be an integrating yaw rate controller for presented an active steering intervention, which is only then is switched when there is an external fault in the vehicle motion is detected. If there is no external disturbance, the additional steering angle is reset to zero leads.
• - In contrast to a conventional yaw moment grip is also with uneven brake pad wear, Fading, different tires right and left, ABS malfunction or brake circuit failure correctly in the len intervened.  
• - The fault can also be cross winds with can be detected by means of air pressure sensors.
• - The switchable I controller can be controlled by additional controllers or Controls can be added.

Claims (11)

1. A method for operating a steering system for a motor vehicle with at least one steerable wheel ( 15 ), an actuator ( 13 ; 23 ) and a superposition gear ( 12 ; 22 ), wherein the steering movement initiated by the driver of the vehicle (δ _L ) and the movement (δ _M ) initiated by the actuator ( 13 ; 23 ) for generating the steering movement of the steerable wheel are superimposed, wherein

• a yaw variable (ω) representing the yaw movement of the vehicle is detected,
• - a control signal (δ _{M soll) (is} ω) in the presence of a specific driving state of at least dependent on the detected yaw variable is formed,
• - The actuator ( 13 ; 23 ) is triggered to initiate the movement (δ _M ) by the generated control signal (δ _{M, should} ),
• - A braking quantity (S) representing the braking state of the vehicle is detected, and
• - The presence of the driving condition is determined depending on the detected brake size (S).

2. The method according to claim 1, characterized in that the detected braking quantity (S) is a braking state of the vehicle represents, in which a braking operation on a road with significantly different road friction values on the different vehicle sides takes place (µ-split braking). 3. The method according to claim 1, characterized in that the detected brake variable (S) depending on the braking effects, in particular depending on the wheel brake pressures (p _vr , p _vl ), at least two wheel brakes on different vehicle sides is detected, in particular providing, that the detected brake variable (S) depends on the difference between the wheel brake pressures (p _vr , p _vl ) of at least two wheel brakes on different sides of the vehicle and / or depending on the ratio of the larger to the smaller of the wheel brake pressures (p _vr , p _vl ) of at least two wheel brakes Various vehicle sides is detected. 4. The method according to claim 1, characterized in that the detected brake variable (S) depending on an actuation of the Brake system of the vehicle, in particular depending on one Actuation of the brake lights is detected. 5. The method according to claim 1, characterized is that a target quantity _(to ω) for the yaw motion of the vehicle, in particular depending on the initiated by the driver of the vehicle steering movement (δ _L) and / or depending on which he conceived vehicle speed determined, and the STEU ersignal (δ _{M, soll)} at least dependent _(to ω -ω _is) of the deviation is formed between the detected yaw size and be agreed target size. 6. The method according to claim 1 or 5, characterized in that the detected yaw variable (ω _is ) or the deviation (ω _should -ω _is ) to form the control signal (δ _{M, should} ) is inte grated. 7. The method according to claim 1 or 5, characterized in that after the presence of the specific driving state, the control signal (δ _M, target) or at least the portion of the control signal (δ _M, target) formed depending on the yaw size (ω _is ) with a time-decreasing behavior is led to a predeterminable value, in particular to the value zero, the time-decreasing behavior being realized in particular by means of a ramp or by a deceleration behavior of the first order and / or the time-decreasing behavior depends on the vehicle speed. 8. The method according to claim 3, characterized in that the detected braking variable (S) is further dependent on the steering movement initiated by the driver of the vehicle (δ _L ) and the vehicle speed and / or a variable representing the transverse acceleration of the vehicle. 9. The method according to claim 1, characterized in that which represent a cross wind influence on the vehicle crosswind size is detected, and the presence of the Driving condition also depending on the detected side wind size is true. 10. Device for operating a steering system for a motor vehicle with at least one steerable wheel ( 15 ), an actuator ( 13 ; 23 ) and a superposition gear ( 12 ; 22 ), the steering movement initiated by the driver of the vehicle (δ _L ) and the movement (δ _M ) initiated by the actuator ( 13 ; 23 ) to generate the steering movement of the steerable wheel are superimposed, the following being provided:

• - means ( 26 ) for detecting a yaw variable (ω) representing the yaw movement of the vehicle,
• _(Is ω) means (61) for forming a control signal (δ _{M, soll)} depen at least in the presence of a specific driving condition of the detected yaw gig size -
• - Means ( 27 ) for controlling the actuator ( 13 ; 23 ) for initiating the movement (δ _M ) by the generated control signal (δ _{M, should} ),
• - Means ( 62 ) for detecting a braking quantity (S) and representing the braking state of the vehicle
• - Means ( 615 ) for determining the presence of the driving state depending on the detected brake size (S).

11. The device according to claim 10, characterized in that the detected brake variable (S) depending on the Bremswirkun gene, in particular depending on the wheel brake pressures (p _vr , p _vl ), at least two wheel brakes on different sides of the vehicle is detected, in particular providing, that the detected brake variable (S) depends on the difference in the wheel brake pressures (p _vr , p _vl ) of at least two wheel brakes on different sides of the vehicle and / or depending on the ratio of the larger to the smaller of the wheel brake pressures (p _vr , p _vl ) at least two wheel brakes on un different vehicle sides is detected.