Abstract:
A device for regulating the driving dynamics of a motor vehicle. A setpoint variable (ψ) for regulating the transverse dynamics of the vehicle is predefined and limited to a maximum value that is set in such a way that the transverse acceleration (a y ) of the vehicle does not exceed a predefined threshold value (a y   max ). In this way, the vehicle is prevented from driving in too tight a curve radius and rolling over.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a device for regulating the driving dynamics of a vehicle and a corresponding method for regulation. 
         [0003]    2. Description of Related Art 
         [0004]    Known vehicle dynamics control systems, such as ESP, normally regulate the yaw rate and the float angle of a vehicle. To that end, it must be determined how the vehicle should behave (setpoint values) and how it actually behaves (actual values). The setpoint values are normally calculated in such a way that the vehicle follows as closely as possible the trajectory specified by the driver via the steering wheel and accelerator pedal position (driver input). It is problematic in this connection that the vehicle dynamics control system also regulates the vehicle based on the trajectory intended by the driver even in critical rollover situations. As a result, the vehicle may experience an excessively high transverse acceleration and roll over. 
         [0005]    Separate devices which intervene in vehicle operation in the case of an excessively high transverse acceleration and stabilize the vehicle, for example, by automatic brake or steering interventions, are known for preventing a vehicle from rolling over. For example, it is known from published international patent application document WO 99/37516 to determine the rollover tendency of a vehicle and to use that to regulate the vehicle&#39;s transverse dynamics in such a way that the vehicle does not roll over. It is known from published international patent application document WO 2006/018439 A1 to detect a rollover based on various predefined driving states for a vehicle. However, all systems have in common that in addition to the vehicle dynamics control system, they are implemented as a separate device having its own sensors and its own signal processing and therefore entail a considerable additional expense. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    It is thus the object of the present invention to provide a device and a method, making it possible to implement a rollover prevention function in a substantially simpler manner. 
         [0007]    An essential aspect of the present invention is that the rollover prevention function is integrated into a conventional vehicle dynamics control system, e.g. ESP, and the modified vehicle dynamics control system is used to force the vehicle onto a trajectory having a greater curve radius than intended by the driver. This limits the transverse acceleration acting on the vehicle. According to the present invention, a setpoint value generator which, taking the driver input into consideration, ascertains at least one setpoint value for the control system is provided for this purpose. In critical driving situations in which the transverse acceleration acting on the vehicle would become too great—if the vehicle dynamics control system were to follow the driver input—the setpoint value according to the present invention is limited to a maximum value. The maximum value must be set in such a way that the transverse acceleration of the vehicle does not exceed a threshold value, and thus the vehicle at least does not roll over. In critical situations in which the driver specifies too small a curve radius at an excessively high speed, the vehicle does not follow precisely the trajectory intended by the driver but instead follows a trajectory having a larger radius and completes a yawing motion having a lower yaw rate. In this manner, the buildup of an excessively high transverse acceleration is counteracted very early and harmonically so that the vehicle no longer rolls over. A simple limitation of the control system setpoint value thus makes it possible to implement a rollover prevention function together with a standard vehicle dynamics control system. 
         [0008]    The transverse acceleration threshold value may, e.g., be defined as the value at which the vehicle would roll over. However, a lower value may also be selected. 
         [0009]    A “vehicle dynamics control system” according to the present invention is preferably a system that regulates at least one driving dynamics state variable, such as the yaw rate and/or the float angle of the vehicle. The associated setpoint value generator preferably includes a mathematical vehicle model (algorithm) which calculates the setpoint value from various measured variables, such as the steering angle or the vehicle speed, and from estimated variables if necessary. 
         [0010]    According to one preferred specific embodiment of the present invention, the setpoint value is calculated as a function of the transverse force acting on the front wheel and/or the rear wheel. In this connection, at least one of the transverse forces is limited to a value that is set in such a way that the transverse acceleration of the vehicle does not exceed the allowed threshold value. Preferably, the transverse force of the front wheels is limited. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention will be explained in greater detail below by way of example with reference to the appended drawing. 
           [0012]      FIG. 1  shows a block diagram of a vehicle dynamics control system of a vehicle. 
           [0013]      FIG. 2  shows a schematic view of a single track model for a vehicle. 
           [0014]      FIG. 3   a  shows a diagram for a steering angle over time. 
           [0015]      FIG. 3   b  shows exemplary time characteristics for the roll angle of a vehicle with and without a setpoint value generator according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 1  shows a vehicle dynamics control system  100  for regulating the transverse dynamics of a vehicle having a control loop. Vehicle dynamics control system  100  includes a setpoint value generator  110  which in this case calculates a setpoint yaw rate {dot over (ψ)} for actual control system  130 . Setpoint value generator  110  includes a mathematical vehicle model (algorithm), such as a single track model known from the related art, which calculates setpoint yaw rate {dot over (ψ)} while taking into consideration steering angle δ f  and longitudinal speed v x  of the vehicle. The named variables are preferably measured. 
         [0017]    Regulation difference e is calculated from setpoint yaw rate {dot over (ψ)} and actual yaw rate {dot over (ψ)} actual  at node  120 , the regulation difference being output to vehicle dynamics control system  130 . In the case of too high a regulation difference, vehicle dynamics control system  130  calculates an individual brake intervention s for each wheel, the brake intervention being implemented by the wheel brakes. The vehicle is shown schematically as a controlled system as block  140 . 
         [0018]    In contrast to conventional vehicle dynamics control systems, setpoint value {dot over (ψ)} is limited here to a value having a maximum amount such that the vehicle&#39;s transverse acceleration never increases above a threshold value. The transverse acceleration threshold value must be set in such a way that the vehicle at least does not roll over. 
         [0019]    The vehicle model of setpoint value generator  110  is shown in  FIG. 2 . The associated model equations for determining setpoint yaw rate {dot over (ψ)} are: 
         [0000]    
       
         
           
             
               
                 
                   
                     
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         [0020]    In addition to vehicle-specific variables, such as vehicle inertia J z  on the z axis, vehicle mass m and wheel spacings l F , l R  of the front and rear wheels from vehicle center of gravity R, setpoint value generator  110  also requires measured variables, such as steering angle δ F  and longitudinal speed v x , for calculating setpoint yaw rate {dot over (ψ)}. Also required are time-dependent variables such as transverse force F y,F  of the front wheels (index F) and transverse force F y,R  of the rear wheels (index R), which may be calculated from measured variables and previous solutions of model equations (1), (2). An additional sensor for determining these variables is not absolutely necessary. 
         [0021]    Transverse forces F y,F , F y,R  are a non-linear function of respective slip angle α F , α R  of the individual wheels. They may be determined, e.g., using a characteristic curve. Slip angles α F , α R  are in turn a non-linear function of setpoint yaw rate {dot over (ψ)} and transverse speed v y . 
         [0022]    Using model equations (1), (2) in addition to setpoint yaw rate {dot over (ψ)}, setpoint value generator  110  also calculates transverse speed v y  and transverse acceleration a y  of the vehicle. 
         [0023]    For determining instantaneous setpoint yaw rate {dot over (ψ)}, setpoint value generator  110  initially calculates instantaneous slip angle α F , α R  based on the most recently calculated setpoint yaw rate {dot over (ψ)} and the most recently calculated transverse speed v y  and looks up associated transverse forces F y,F , F y,R  on the individual wheels in the corresponding characteristic curve. If transverse forces F y,F , F y,R  are so great that the transverse acceleration of the vehicle exceeds a maximum value a y   max , at least one transverse force is limited. Setpoint yaw rate {dot over (ψ)} is then calculated based on limited transverse force F max . The setting of this setpoint yaw rate using the vehicle dynamics control system ensures that the vehicle does not roll over. 
         [0024]    The transverse acceleration of the reference model is determined by 
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         [0025]    In the present exemplary embodiment, transverse force F y,F  of the front wheels is limited. If a y   max  is the maximum allowed transverse acceleration, maximum allowed transverse force F y,F   max  is derived from (3) as follows: 
         [0000]        F   y,F   max   =m·a   y   max   −|F   y,R |  (4)
 
         [0026]    Setpoint value generator  110  now ascertains transverse force F y,F  of the front wheels and checks if it exceeds maximum transverse force F y,F   max . If so, it uses limited value F y,F   max  as a basis in model equations (1), (2), otherwise it uses actually ascertained value F y,F . 
         [0027]      FIGS. 3   a  and  3   b  show the curve of various measured values in a vehicle which is regulated in one case with limitation and in one case without limitation of the setpoint yaw rate. As seen from diagram  210  for steering angle δ F , the vehicle drives in an S-like curve. 
         [0028]    Without limitation of setpoint yaw rate {dot over (ψ)}, the vehicle rolls over when driving in the S-like curve (see dashed line  222  in diagram  220 ). Initially the vehicle rocks 10° in one direction, then moves back into the neutral position and then rocks in the other direction, the roll angle being so great that the vehicle rolls over. 
         [0029]    When setpoint yaw rate {dot over (ψ)} is limited, the vehicle does rock in the same driving maneuver (see continuous line  221 ) in both directions, but the roll angle in both cases remains less than 10° and the vehicle does not roll over.