Abstract:
A device and a method for regulating at least one vehicle dynamics controlled variable (vGi) which describes a motion of a vehicle, is described. At least one vehicle dynamics variable is determined in a determination device. A regulator device with which actuators are triggered for regulating the at least one vehicle dynamics controlled variable is provided, the sensitivity of the regulator device being influenceable. Sensitivity of the regulator device in at least one operating state of the vehicle is determined by at least one of the vehicle dynamics variables thus determined.

Description:
BACKGROUND INFORMATION 
     German Published Patent Application No. 199 49 286 describes a device for regulating at least one vehicle motion variable describing a motion of a vehicle. To this end, the device contains regulator means with which actuators are triggered for regulating the vehicle motion variable. Furthermore, the device contains determination means with which a bad stretch of road variable, which describes the vehicle&#39;s drive on a stretch of bad road, is determined. The regulator means is influenced as a function of the bad stretch of road variable, such that the sensitivity of the regulator means is adapted to the vehicle&#39;s drive on a stretch of bad road. European Patent No. 0 339 056 describes a method of regulating the stability of a vehicle in traveling along a curve, where the vehicle speed and the coefficient of friction between the tires and the road are determined. In this method, the steering angle and the rate of rotation of the vehicle about the vertical axis (yaw rate) are also determined, and a lower limit value characteristic of the yaw rate is determined as a function of the steering angle, taking into account the vehicle speed and the coefficient of friction. The brake pressure is reduced when the measured yaw rate drops below the limit value characteristic. German Published Patent Application No. 199 64 032 describes a method and a device for stabilizing a vehicle. In this method, a transverse dynamics variable which describes the transverse dynamics of the vehicle is regulated to stabilize the vehicle. The transverse dynamics variable is regulated by limiting the float angle of the vehicle to a predetermined value. Regulation of the transverse dynamics variable is altered by input by the driver to allow a larger float angle than the predetermined value. 
     SUMMARY OF THE INVENTION 
     In vehicle dynamics control (VDC) systems (ESP=electronic stability program), the driver selects a desired driving performance by selecting the steering angle. A setpoint for the yaw rate is calculated as a function of the steering angle, the transverse acceleration and the longitudinal speed of the vehicle. If the measured yaw rate does not match the calculated setpoint yaw rate, the vehicle dynamics controller will attempt to adapt the yaw rate to the setpoint, e.g., through changes in brake pressure on the individual wheels or through active steering operations. The phase shift between the change in the steering angle and the change in the yaw rate due to the inherent dynamics of the vehicle is taken into account through suitable filters. It is desirable, especially with certain sporty vehicles, to tolerate an admissible system deviation between the setpoint yaw rate and the actual yaw rate in many cases. Suitable measures are performed to suppress the vehicle controller intervention measures in these cases. 
     With the known implementations, it is impossible to allow greater permanent system deviations between the yaw rate setpoint and the actual yaw rate depending on the situation. Thus, in the case of front-wheel-drive vehicles, for example, it is impossible to steer back in coming out of a turn on a smooth road surface and to straighten out the vehicle again slowly merely by accelerating without any active braking intervention by the vehicle dynamics controller. However, that is precisely what is often desired in the case of sporty vehicles. Stabilizing measures should be taken only when the driver must definitely countersteer (“countersteering” means that the steering angle is rotated in the opposite direction, past the zero position) or when the float angle of the vehicle increases. If the driver steers back only slightly (“steering back” means that the steering angle is reduced but is not rotated in the other direction, past the zero position), then the regulator should assume the stabilization function and should intervene with full sensitivity. If the driver steers back forcefully, this is sufficient with a suitably tuned vehicle to straighten the vehicle out even without a braking intervention measure. It is thus important to prevent the stabilization measure on the part of the driver (due to steering back forcefully) to be superimposed on that of the regulator (through a braking intervention measure on the front wheel which is on the outside of the turn, for example), in which case the stabilization may subjectively appear to be too intense. The present invention described here opens up the possibility of expanding the known vehicle dynamics control (VDC, ESP) in the manner described above. 
     The present invention relates to a device for regulating at least one controlled variable of vehicle dynamics which describes a motion of a vehicle, the device 
     containing the determination means with which at least one vehicle dynamics variable is determined, and 
     containing regulator means for triggering actuators for regulating the at least one vehicle dynamics controlled variable, the sensitivity of the regulator means being influenceable. 
     The advantage of the present invention is that the sensitivity of the regulator means in at least one operating state of the vehicle is influenced by at least one of the vehicle dynamics variables thus determined. 
     The vehicle dynamics variables determined by the determination means may, of course, also include the vehicle dynamics controlled variables. 
     An advantageous embodiment of the present invention is characterized in that at least one transverse acceleration variable and one steering angle variable are determined as vehicle dynamics variables by the determination means, and the sensitivity of the regulator means is influenced 
     when the operating state is driving with a transverse acceleration of the vehicle different from zero and driver-operated steering against the direction of transverse acceleration or 
     when the vehicle is oversteered as the operating state and is traveling with a transverse acceleration of the vehicle different from zero, and driver-operated steering is occurring in the direction of transverse acceleration. 
     Another advantageous embodiment of the present invention is characterized in that at least one transverse acceleration variable and one steering angle variable are determined by the determination means as vehicle dynamics variables, and the sensitivity of the regulator means is influenced 
     when the operating state of the vehicle is traveling with a transverse acceleration which is different from zero and driver-operated steering is occurring against the direction of transverse acceleration, or 
     when the operating state of the vehicle is an oversteered state and the vehicle is traveling with a transverse acceleration which is different from zero and driver-operated steering is occurring in the direction of transverse acceleration, the oversteered state being defined in particular by the actual yaw rate exceeding the setpoint yaw rate in absolute value. 
     It is also possible to define the term “oversteering” as follows: oversteering is when the tire slip angle on the rear axle increases more rapidly than the tire slip angle on the front axle with an increase in transverse acceleration. 
     In an advantageous embodiment, the present invention is characterized in that two different vehicle dynamics variables thus determined are compared, and the sensitivity of the regulator means is influenced differently, depending on the outcome of this comparison. 
     Another advantageous embodiment is characterized in that 
     at least the steering angle and the transverse acceleration are determined by the determination means as vehicle dynamics variables, and 
     the plus or minus signs of the steering angle and the transverse acceleration are compared in this comparison. 
     It is advantageous if the vehicle dynamics variables thus determined include at least one measured yaw rate and one yaw rate determined by a mathematical model in particular. 
     An advantageous embodiment is characterized in that 
     the vehicle dynamics variables thus determined also include the transverse acceleration and the longitudinal speed of the vehicle, and 
     the absolute value of the yaw rate determined by the mathematical model is limited at the upper end by an upper limit value, at least the transverse acceleration and the vehicle longitudinal speed being used in determining the upper limit value. 
     It is advantageous 
     if a driver-independent triggering of the actuators takes place to regulate the at least one vehicle dynamics variable to be regulated if the deviation in the measured yaw rate from the yaw rate determined by a mathematical model, multiplied by a factor, exceeds a maximum allowed limit value, and 
     if the sensitivity of the regulator means is determined by this factor. 
     Multiplying the deviation between the measured yaw rate and the yaw rate determined by a mathematical model is equivalent to scaling. This permits an especially robust, inexpensive, and uncomplicated means of attenuating the stabilization measures. 
     In an advantageous embodiment, the factor has a value between zero and one, 
     the value zero indicating deactivation of the regulator means, and 
     the value one indicating operation of the regulator means at maximum sensitivity. 
     It should be pointed out that the advantageous embodiments mentioned above do not require any additional sensors besides the sensors that are present anyway in a vehicle dynamics control system. This means that no major increase in hardware complexity is required. It should also be pointed out that the vehicle dynamics control system is not completely altered by the present invention. Instead, in many embodiments, the present invention is limited to a variation of intervention threshold values of the vehicle dynamics control system as a function of vehicle dynamics variables. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the structure of the present invention in the form of a block diagram. 
     FIG. 2 shows how the present invention is embedded in the sensors, the actuators, and the vehicle dynamics controller. 
     FIG. 3 shows the structure of the system as in FIG. 2, but subdivided into the blocks “determination means,” “regulator means,” and “actuators.” 
    
    
     DETAILED DESCRIPTION 
     In vehicle dynamics control systems in general, a setpoint yaw rate vGiAck is calculated first from steering angle Lw and vehicle longitudinal speed vx with the help of characteristic speed vch (vch is a vehicle constant). Then, using vehicle transverse acceleration ay, vehicle longitudinal speed vx, and optionally additional variables, the setpoint yaw rate is limited in absolute value toward the upper end. This yields setpoint yaw rate vGiSo. Value vGiBeg=ay/vx supplies a significant portion of the limit of the setpoint yaw rate because it is a stability limit. If the stability limit is exceeded on a flat road surface, the float angle of the vehicle increases and the vehicle becomes unstable. One might imagine the vehicle driving in a circle with a constant radius, where ay=vGi*vx, ay being the transverse acceleration, vGi being the measured yaw rate, and vx being the longitudinal speed of the vehicle. If vGi increases but ay does not increase (and therefore vGiBeg does not increase either), then the float angle increases and the vehicle becomes unstable. This is also confirmed mathematically by the fact that the larger value of vGi then exceeds stability limit ay/vx, which has not increased. 
     The following equations hold for above-mentioned variables vGiAck, vGiBeg and vGiSo:        vGiAck   =       vx   ·   Lw       c   ·     [     1   +       (     vx   ·   vx     )     /     (     vch   ·   vch     )         ]                                
     as well as vGiBeg=ay/vx and vGiSo=f(vGiAck, vGiBeg), where c is the wheelbase. 
     For example, vGiSo may be selected as the minimum of vGiAck and vGiBeg. Thus, yaw rate system deviation DvGi 0  may be determined as follows: 
     
       
           DvGi   0 = vGiSo−vGi,   
       
     
     where vGi is the yaw rate measured by a yaw rate sensor, for example. Then, with the help of a wide variety of regulation methods, it is possible to calculate manipulated variables which will influence the vehicle performance in the desired manner. It is also possible to attenuate system deviation DvGi 0  depending on the situation so that only weak regulator intervention measures or none at all are implemented. This is accomplished by the multiplication DvGi=DvGi 0 *V 1 , which is explained in greater detail below. 
     FIG. 1 illustrates the procedure for attenuation of regulation intervention measures. 
     In a block  1 , a first attenuation factor A 1  for attenuation of the regulation intervention measures between zero and one is predefined by a speed-dependent characteristic line (vx is plotted on the abscissa). At A 1 =0 there is no attenuation due to the contribution of first attenuation factor A 1 ; at A 1 =1 there is a maximum attenuation due to the contribution of first attenuation factor A 1 , i.e., the regulation intervention measures are attenuated or even completely suppressed. Therefore, the attenuation may be implemented only at low speeds, for example. In a particular embodiment, this speed-dependent characteristic line may be a characteristic line having some linear segments. 
     The output signal of block  1  is multiplied by the output signal of block  2  in block  100 . Block  100  is a multiplier. Block  2  contains a characteristic line which depends on the transverse acceleration. An attenuation factor A 2  is calculated there as a function of the absolute value of transverse acceleration ay, i.e., |ay|. Instead of the characteristic line which depends on transverse acceleration, a characteristic line dependent on the coefficient of friction is also conceivable. Then the attenuation factor is determined as a function of the coefficient of friction. The coefficient of friction is a measure of the friction between the tire and the road surface. It depends on variables such as the properties of the road surface, the material of the tires, the wheel contact force or variables representing the vehicle dynamics. In a particular embodiment, block  2  may also include a characteristic curve having some linear segments. In the concrete embodiment, A 2  assumes a value of 1 for small transverse accelerations |ay| and then decreases linearly to a smaller value with an increase in transverse acceleration. 
     Multiplier  100  supplies variable A 1 *A 2  as the output signal. The result of multiplication A 1 *A 2  is subtracted from one in logic block  3 . Output signal V 0  of block  3  thus corresponds to a gain for the regulation intervention measures, because V 0 =1−A 1 *A 2 . This yields the following limiting cases: 
     V 0 =0: maximum or even complete suppression of the regulating intervention measures 
     V 0 =1: no suppression of the regulating intervention measures. 
     V 0 =1 occurs, for example, when A 1  or A 2  is zero. In other words, there is no suppression of regulating intervention measures at high longitudinal speeds of the vehicle or at high transverse accelerations. This is appropriate because potentially hazardous situations might occur then. 
     In the interpretation of the statements with regard to the “maximum suppression of the control measures” and/or “no suppression of the control measures,” it should be kept in mind that V 0  is the output signal generated by logic block  3 . As the method proceeds, additional terms are also added to V 0 , ultimately generating signal V 1 . This signal V 1  is the deciding measure for the sensitivity of the system as a whole. Variable V 0  may be considered an intermediate variable. 
     Output signal V 0  of block  3  is then relayed to two branches: 
     branch A: the driver steers in the direction of turning (this also includes steering back); 
     branch B: the driver steers against the direction of turning (countersteering). 
     The selection of one or the other branch will depend on the position of switch  11 . 
     First, branch A will be considered, which is steering in the direction of the curve. Steering angle Lw and transverse acceleration ay in this case have the same plus or minus sign. The plus or minus signs may be selected, for example, so that in turning right, both the steering angle and the transverse acceleration have a plus sign, whereas in turning left, both have a minus sign (for example, a stable driving state may be assumed both in turning right and in turning left). 
     In block  4 , the absolute value of yaw rate vGi thus determined (vGi is measured by a yaw rate sensor, for example) is evaluated with regard to stability limit vGiBeg (=ay/vx). Variable |vGi| is plotted on the abscissa, and variable V 4  is plotted on the ordinate. If the absolute value of yaw rate |vGi| exceeds the value of |vGiBeg|, then the output of the characteristic curve implemented in block  4  is at 1 (V 4 =1). Therefore, if necessary, the regulator gain is diminished less or even not at all subsequently. At a smaller yaw rate, the output of the characteristic curve in block  4  rapidly drops to zero, because in this case stabilization of the vehicle by the regulator is no longer so urgent. If |vGi| is less than |vGiBeg|, then the vehicle float angle is automatically reduced, i.e., driving becomes more stable. 
     In a block  5 , the dependence on the absolute value of setpoint yaw rate |vGiAck| and thus on the predefined steering angle is evaluated. Variable |vGiAck| is plotted on the abscissa and variable V 5  is plotted on the ordinate. If |vGiAck| is near stability limit |vGiBeg|, then the output of a characteristic curve is in the vicinity of 1. The regulator gain is therefore decreased only slightly. However, if |vGiAck| is much smaller than |vGiBeg|, this means that the driver is steering back, i.e., the driver has taken over the stabilization function. In this case, the regulator gain may be reduced significantly. This also illustrates the statement made previously, namely that the regulator should assume the stabilization function in the case when the driver is steering back slightly (vGiAck is reduced only insignificantly with slight steering back), whereas when the driver steers back forcefully (vGiAck then assumes a small value), the regulator influence is reduced or even eliminated. 
     In particular embodiments, characteristic curves having some linear segments may of course be implemented in blocks  4  and  5 . 
     The output signals of block  4  (output signal V 4 ) and block  5  (output signal V 5 ) are then multiplied in block  101 , yielding a criterion for the change in the regulator gain which depends mainly on the steering angle (preselected by the driver) and the yaw rate (vehicle response). The result of the multiplication V 4 *V 5  is added again to gain V 0  in logic block  6 , i.e., the gain decreased previously may be increased again here. 
     In the case of countersteering (branch B), the output of block  7  is added by logic block  8  to gain V 0 . Block  7  receives the absolute value of setpoint yaw rate vGiAck as an input signal. Block  7  calculates gain factor V 7  (ordinate) as a function of |vGiAck| (abscissa). Up to a predefined value, which depends mainly on the steering angle, the output of block  7  remains at a low value or at zero and then increases continuously. Gain V 0  is thus increased. This means that the previously reduced gain for the system deviation increases again starting at a preselectable threshold. 
     Then through query  9 , a distinction is made between oversteering and not oversteering. Oversteering is detected by the fact that the absolute value of actual yaw rate vGi exceeds that of setpoint yaw rate vGiSo. If the vehicle is not oversteered, the gain in a block  10  is set fixedly at one. This is due to the fact that the gain is to be reduced by this algorithm only when the vehicle does not respond immediately when steered back, i.e., when the actual yaw rate exceeds the setpoint yaw rate. Through query  11 , a distinction is now made between countersteering (Lw*ay&lt;0) and steering into the curve (Lw*ay&gt;0). In countersteering, the output of logic block  8  is relayed (branch B). If the answer to query  11  is in the negative, i.e., there is no countersteering, then the result of query  9  is relayed further (branch A). 
     The output signal of query  11  is then limited between zero and one in block  12 , yielding gain V 1 , which is multiplied by the yaw rate system deviation (vGiSo−vGi) formed in subtraction block  103 . In the characteristic curve stored in block  12 , the output signal of query  11  is plotted on the abscissa (e.g., V 0 +V 4 *V 5  or 1 or V 0 +V 7 ) and V 1  is plotted on the ordinate. 
     The multiplication is performed in multiplier  104 . Normally, V 1  has a value of 1, i.e., system deviation DvGi is equal to vGiSo−vGi and the regulator operates at full gain. Only if the calculation supplies a value of less than one is the system deviation attenuated and hence the stabilization measure attenuated. Therefore, in certain situations, sporty driving is supported with regulator intervention measures that are subjectively less interfering. 
     Signal DvGi is relayed to query block  105 , where the query as to whether DvGi exceeds a threshold value Sw is made. The query is: DvGi&gt;Sw? If DvGi exceeds threshold value Sw, then intervention measures into the vehicle dynamics control system are implemented by block  106 . If DvGi does not exceed threshold value Sw, then no intervention measure into the vehicle dynamics control system is implemented (block  107 ). 
     The input signals of blocks  1 ,  2 ,  4 ,  5  and  7  are summarized below in key words: 
     block  1 : input signal vx 
     block  2 : input signal |ay| 
     block  4 : input signal |vGi| 
     block  5 : input signal |vGiAck| 
     block  7 : input signal |vGiAck| 
     FIG. 2 illustrates how the present invention is embedded in the system composed of sensors, actuators, and the vehicle dynamics controller. The actuators may be, for example, the wheel brakes or the engine control unit. Block  200  contains the “remaining” vehicle dynamics controller functions, i.e., the vehicle dynamics controller functions without the components included in the present invention. 
     Block  201  is referred to as an “additional block” and includes the present invention, as illustrated essentially in FIG.  1 . 
     Block  202  contains the sensors. 
     Block  203  contains the actuators. 
     The following sensors are contained in block  202 , for example: wheel rpm sensors, a yaw rate sensor, a steering angle sensor, a transverse acceleration sensor, brake pressure sensors. 
     The output signals of these sensors are sent to block  200  (remaining vehicle dynamics control functions), some of the output signals also being sent to block  201 , which includes the present invention. The signals which are sent to block  201  in this specific embodiment are vGi, |vGi| and |ay|. 
     Block  201  contains additional input signals of block  200 , namely |vGiAck|, vGiSo and vx. Longitudinal speed vx of the vehicle may then be determined from the wheel rotational speeds. The input signals of block  201  are also shown in FIG. 1, considering the input channels shown at the left edge from top to bottom. 
     In this embodiment, output signal DvGi is generated in block  201  and sent to block  200 . 
     Block  200  controls actuators  203 , which includes the individual wheel brakes, for example, as well as the engine control. The vehicle dynamics control system may thus initiate braking operations or de-braking operations on individual wheels or may intervene in the engine control (e.g., controlling the throttle valve position). 
     The system as a whole is illustrated again in FIG.  3 . In contrast with FIG. 2, the system as a whole here is subdivided into the blocks “determination means,” “regulator means” and “actuators.” 
     Determination means  300  supply output signals vx, ay, vGi, vGIAck, and Lw (and possibly also other variables such as brake pressures). The variables go as input signals to regulator means  301 . The regulator means in turn interact with actuators  302 . 
     Instead of attenuating system deviation DvGi, the control intervention measure may, of course, also be attenuated at many other points in the regulating circuit, e.g., by reducing the regulator gain or by attenuating the manipulated variables (e.g., the changes in setpoint slip). 
     With regard to the present invention, it should be pointed out that the driver&#39;s behavior is also taken into account in this regulation system. This inclusion of the driver&#39;s behavior is accomplished, for example, through the setpoint yaw rate raw value (vGiAck) which is influenced by the driver by selecting steering angle Lw and vehicle longitudinal speed vx. 
     In conclusion, the most important mathematical variables used here shall be summarized for better understandability: 
     Lw=steering angle, 
     vGi=yaw rate, 
     vx=vehicle longitudinal speed, 
     vch=characteristic speed (vehicle constant), 
     ay=vehicle transverse acceleration, 
     vGiAck=setpoint yaw rate raw value, 
     vGiBeg=yaw rate limit value, 
     vGiSo=setpoint yaw rate, 
     DvGi 0 =yaw rate system deviation, 
     DvGi=yaw rate system deviation multiplied by factor V 1 .