Abstract:
Described is a device for stabilizing a vehicle in critical driving situations, including a vehicle dynamics control system having a control unit, including a vehicle dynamics control algorithm, and at least one actuator and an additional vehicle stability system having an associated actuator. Vehicle dynamics control may be executed in a particularly simple and trouble-free manner when the vehicle dynamics control algorithm is retrofitted with a distribution function which derives an actuating request for an actuator of the vehicle dynamics control system as well as an actuating request for at least one actuator of the vehicle stability system from a controller output variable.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a vehicle dynamics control system.  
       BACKGROUND INFORMATION  
       [0002]     Vehicle dynamics control systems, such as the ESP (electronic stability program), are used to improve the controllability of motor vehicles in critical driving situations, e.g., during oversteering when cornering, and to stabilize the vehicle. Known vehicle dynamics control systems include a control unit which includes a control algorithm for executing a float angle regulation and/or a yaw speed regulation, as well as a series of sensors which provide measured values about the vehicle&#39;s current driving state. Different setpoint variables are calculated from the driver inputs, in particular the steering wheel position, the accelerator pedal position, and the brake operation. If the deviation of the vehicle&#39;s actual behavior from its setpoint behavior is too great, the vehicle dynamics control system intervenes in the driving operation and creates a compensating yaw moment which counters the vehicle&#39;s yaw motion. For this purpose, the vehicle dynamics control system normally uses the vehicle brakes and/or the engine management as actuators.  
         [0003]     In addition to a vehicle dynamics control system, modern vehicles oftentimes also include other systems which may also intervene in the driving operation for the purpose of vehicle stabilization, such as an active steering system AFS (active front steering), an active chassis ARC (active roll compensation), or a system for actively influencing the tire properties. Such systems are referred to in the following as “vehicle stability systems.” They normally include their own control electronics (control unit) and their own actuators, such as a steering actuator, via which the steering angle may be adjusted, an active spring-and-shock-absorber unit for influencing the tire contact forces, or other actuators via which the vehicle&#39;s handling properties may be influenced.  
       SUMMARY OF THE INVENTION  
       [0004]     The mentioned vehicle stability systems also determine different setpoint values of driving state variables, such as a setpoint yaw rate or a setpoint float angle, and calculate from the deviation a necessary stabilizing intervention, such as a change in the steering angle or a change in the wheel contact force on predefined wheels. The calculated values are implemented via the appropriate actuators and influence the vehicle&#39;s handling properties. Since the vehicle dynamics control system ESP as well as the other vehicle stability systems (e.g., AFS, ARC) execute stabilizing interventions, it is possible for the systems to constrain or block one another.  
         [0005]      FIG. 1  shows a controller structure for a stability system known from the related art which has an active steering system AFS and an active chassis ARC in addition to a vehicle dynamics control system ESP. Systems ESP, AFS, and ARC each include a separate control unit  1 ,  2 ,  3  which each include a control algorithm  4 ,  5 ,  6 . Algorithms  4 - 6  each include in a known manner an “observer” B in which different state variables, such as the float angle or the wheel slip angle, are estimated, a unit So for calculating setpoint values of the regulation, a setpoint yaw rate for example, and a state controller ZR which generates a controller output variable y which is converted into an actuating request for different actuators  8 . Controller output variables ya-yc are transferred to appropriate actuators  8  or associated electronics  1 ,  3  via interfaces  7 . Vehicle  10  forms the control path of the control system.  
         [0006]     The driving state is recorded by different sensors which are combined here in a block  11 . The corresponding sensor signals are supplied as actual values to algorithms  4 - 6  of control systems AFS, ESP, ARC.  
         [0007]     Such a parallel controller structure has the disadvantage that multiple control algorithms  4 - 6  are present, at least partially. This is an expensive proposition since, in addition to the control algorithms, the necessary security software must also be implemented several times. Moreover, individual control systems AFS, ESP, ARC may pursue different control targets, thereby constraining or blocking one another.  
         [0008]     Therefore, it is the object of the present invention to create a method and a device for stabilizing a vehicle in critical driving situations which have a particularly simple design and operate reliably.  
         [0009]     The object of the present invention is achieved by the features specified in Claim  1  and Claim  8 . Further embodiments of the present invention are the object of the subclaims.  
         [0010]     A fundamental aspect of the present invention is to create an advanced vehicle dynamics control system (VDM) which, in addition to the brake system and the engine management, is able to also address other actuators, and to provide this system with only one single control algorithm which generates one controller output variable (e.g., a yaw moment) from which an actuating request for an actuator (i.e., the brake system or the engine management) of the vehicle dynamics control system as well as for an actuator (e.g., a steering actuator or an active spring-and-shock-absorber unit) of at least one additional vehicle stability system is derived. This has the substantial advantage that only one central control algorithm is present, and its controller output variable is implemented by one or multiple actuators. Such a central control is particularly easily implementable and particularly safe and reliable.  
         [0011]     The appropriate control algorithm may be implemented, for example, in the control unit of the vehicle dynamics control system (e.g., ESP). The previously present vehicle dynamics control algorithm (ESP) needs to be only marginally retrofitted and adjusted for this purpose. No separate stability control is to be carried out in the additional vehicle stability systems, such as AFS or ARC.  
         [0012]     The control algorithm of the advanced vehicle dynamics control system (VDM) preferably includes a distribution unit which generates from a controller output variable an actuating request for an actuator (i.e., the brake system or the engine management) of the vehicle dynamics control system as well as an actuating request for an actuator of an additional vehicle stability system.  
         [0013]     The vehicle stability system may include, for example, an active steering system (AFS), an active chassis system (ARC), and/or another system which, for vehicle stabilization purposes, may actively intervene in the driving operation.  
         [0014]     The control algorithm preferably includes a yaw rate controller; in this case, the controller output variable would be a yaw moment or a variable proportional thereto.  
         [0015]     According to a preferred embodiment of the present invention, the distribution unit is implemented in such a way that an actuating request for a first actuator (e.g., an active spring-and-shock-absorber unit) is derived from the controller output variable, and that a residual value of the controller output variable is determined from the controller output variable and the actuating request actually implementable by the actuator, and that an actuating request for a second actuator (e.g., a steering actuator) is generated from the residual value. This means that the part of the control intervention which cannot be implemented by the first actuator (e.g., an active spring-and-shock-absorber unit) is implemented by a second actuator (e.g., an active steering system or an active brake system) or by additional actuators if needed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  shows a vehicle dynamics control system known from the related art having control algorithms which operate in parallel.  
         [0017]      FIG. 2  shows an advanced vehicle dynamics control system having additional actuators.  
         [0018]      FIG. 3  shows a detailed view of the vehicle dynamics control system of  FIG. 2 .  
         [0019]      FIG. 4  shows an exemplary embodiment of a unit for distributing the controller output variable.  
         [0020]      FIG. 5  shows the calculation of a superimposed steering angle from the controller output variable.  
         [0021]      FIG. 6  shows an example of a hardware architecture for an advanced vehicle dynamics control system. 
     
    
     DETAILED DESCRIPTION  
       [0022]     Regarding the explanation of  FIG. 1 , reference is made to the preamble of the description.  
         [0023]      FIG. 2  shows an advanced vehicle dynamics control system VDM which has the ability, for vehicle stabilization purposes, to control additional actuators—steering actuator  8   a  of an active steering system and spring-and-shock-absorber unit  8   c  of an active chassis in this case—in addition to the vehicle&#39;s engine management and brake systems. The vehicle dynamics control system includes a control algorithm which is schematically depicted by blocks  4   d - 6   d.    
         [0024]     Reference numeral  4   d  indicates an “observer,” reference numeral  5   d  indicates a unit for the setpoint value calculation which determines a setpoint yaw rate in particular, and reference numeral  6   d  indicates a state controller whose controller output variable ΔM GiSo  is a yaw moment or a variable proportional thereto.  
         [0025]     The control algorithm also includes a distribution unit  9  which converts controller output variable ΔM GiSo  into different actuating requests ΔF Nstab , δ stab , M stab , where ΔF Nstab  is a change in the wheel contact force, δ stab  is a superimposed steering angle, and P wheelsetpoint  is a brake force. The individual actuating requests are transferred to control units  1 ,  3  of active steering system AFS, active chassis ARC, and the electronics of an active brake system  8   b  via interfaces  7   a - 7   c . Control units  1 ,  2  subsequently control corresponding actuators  8   a ,  8   c . The modified actual state of vehicle  10  is recorded via a sensor  11 .  
         [0026]     Unlike known vehicle dynamics control algorithms (e.g., ESP), this advanced system VDM may address one or multiple different actuators  8  without coming into conflict with other systems. The vehicle&#39;s handling properties may be influenced by controlling steering actuator  8   a  or an active spring-and-shock-absorber unit  8   c.    
         [0027]     Since the additional stability systems (AFS, ARC, etc.) influence the vehicle&#39;s handling properties, information about the state of these actuators  8 , such as information about the actual steering angle or information about the calibration of spring-and-shock-absorber unit  8   c , must be supplied to control algorithm  4   d - 6   d . Vehicle dynamics control algorithm  4   d - 6   d  would otherwise carry out the control on the basis of wrong parameters (e.g., only based on the steering wheel angle, but not based on the steering angle at the wheel), which may result in erroneous brake and engine interventions.  
         [0028]      FIG. 3  shows an advanced vehicle dynamics control system VDM in detail. The overall system includes vehicle  10  as the control path, sensors  12  for determining the controller input variables, actuators  18   a - 18   e  for influencing the handling properties, as well as a hierarchically structured controller  4 ,  5 ,  6 ,  9   a ,  13 ,  14  including a superimposed vehicle dynamics controller  6  (state controller) and a subordinate brake and drive slip controller  14 . The controller functions are implemented in control unit  2  of vehicle dynamics control system ESP in the form of software.  
         [0029]     The configuration and the function of such a vehicle dynamics controller are widely known from the related art so that only the essential functions and in particular the differences with respect to known controllers are discussed in the following. The actual values of the regulated state variables (yaw speed, float angle) are determined in “observer”  4 . The setpoint values of the state variables are calculated in a unit  5  for the setpoint value calculation.  
         [0030]     Superimposed controller  6  carries out a yaw speed and/or float angle regulation in a known manner and generates a controller output variable ΔM GiSo  in the form of a yaw moment or a variable proportional thereto. Part of controller output variable ΔM GiSo  is converted into a setpoint slip λ So  and supplied to subordinate brake and drive slip controller  14 . Setpoint slip λ So , calculated for the individual wheels, is converted into corresponding instructions P wheelsetpoint , M SoMot  for the actuators “brake hydraulics”  18   a  and “engine management”  18   b  which adjust the required brake and drive forces on the individual wheels. Another part of controller output variable ΔM GiSo , is converted into moments ΔM zx  which are implemented by actuators  18   c - 18   e  of additional subsystems (AFS, SRC, etc.). The distribution of controller output variable ΔM GiSo  to individual subsystems  1 ,  3 ,  15 - 18   e  may basically be adjusted in any way, depending on how forceful the intervention of the individual subsystems should be. The vehicle dynamics control system is designed in such a way that the control intervention may be implemented by one or multiple subsystems  18   a -  18   e.    
         [0031]     In this case, the subsystems include an active steering system AFS having a control unit  1  and a steering actuator  18   e , an active chassis having a control unit  3  and an actuator  18   d , a further optional subsystem having a control unit  17  and an associated actuator  18   c , an engine management having a control unit (Motronic)  16  and an actuator  18   b , and a brake system having electronics  15  and brake hydraulics  18   a  as actuators.  
         [0032]     Unlike known vehicle dynamics control systems, the vehicle dynamics controller includes a function block  9   a - 9   e  which is used to distribute controller output variable ΔM GiSo  to subsystems  1 ,  3 ,  15 - 18   e . For this purpose, block  9   a  initially generates partial variables ΔM zx  from controller output variable ΔM GiSo , partial variables ΔM zx  being implemented by actuators  18   a - 18   c  of subsystems AFS, ESP, ARC, etc. Partial variables ΔM zx  are calculated by units  9   b - 9   e  into corresponding actuating requests, such as a change in wheel contact force ΔF Nstab  for a wheel, a superimposed steering angle δ stab , a steering torque M stab , or another control value ΔX for another optional subsystem  17 ,  18   c.    
         [0033]     Individual actuating requests P wheelsetpoint , M SoMot , ΔX, ΔF Nstab , δ stab , M stab  are supplied to control units  1 ,  3 ,  17  and control electronics  15 ,  16  via predefined interfaces (not shown). Actuating requests P wheelsetpoint , M SoMot , ΔX, ΔFN stab , δ stab , M stab  are subsequently converted into corresponding electrical control signals for individual actuators  18   a - 18   e.    
         [0034]     Necessary control intervention ΔM GiSo  may basically be distributed in any way to the different subsystems  1 ,  3 ,  15 - 18   e . However, a larger part of the overall control intervention is preferably assigned to individual systems, such as an active suspension ARC, than to other systems.  
         [0035]      FIG. 4  shows a preferred embodiment of a distribution unit  9  which converts controller output variable ΔM GiSo  into multiple actuating requests ΔFN stab , δ stab , Δλ for different subsystems  1 ,  3 ,  15 . Controller output variable ΔM GiSo  is initially converted into wheel contact forces F for the individual wheels of vehicle  10  using a unit  31 . Downstream unit  32  limits calculated values F if the values are not able to be implemented directly for reasons of the efficiency of active suspension ARC  3 . For this purpose, values F and/or their gradient are/is reduced when predefined limits are exceeded. Resulting actuating request ΔFN stab  may thus accept only values which are able to be implemented by actuator  18   d  of the active suspension.  
         [0036]     Value ΔFN stab  is conveyed to active suspension  3  where a corresponding control intervention is effected. The part of controller output variable ΔM GiSo  which is not able to be implemented by active chassis  3  is determined as a residual value ΔM GiSo     —     AFS . A unit  33  is provided for this purpose which converts the implementable actuating request ΔFN stab  back into a variable ΔM GiSo     —     ARCO  of the unit of controller output variable ΔM GiSo . At node  39 , the difference between controller output variable ΔM GiSo  and estimated variable ΔM GiSo     —     ARCO  is calculated and residual value ΔM GiSo     —     AFS  is formed.  
         [0037]     Residual value ΔM GiSo     —     AFS  in turn is subsequently converted into an actuating request δ stab  for steering actuator  18   e  of an active steering system AFS  1  via a unit  34 . If needed, this value δ stab  is limited via a unit  35 . Actuating request δ stab  (in this case a superimposed steering angle) is supplied to active steering system  1  and to a unit  36  which determines the part which is able to be implemented by active steering system AFS  1 .  
         [0038]     A residual value ΔM GiSo     —     AB , which is supplied to active brake system  15 , is in turn calculated from setpoint request ΔM GiSo     —     AFS  and the actually implementable request ΔM GiSo     —     AFSO . This residual moment ΔM GiSo     —     AB  is converted into a wheel slip λ via a unit  37  and limited via unit  38 . Resulting setpoint slip λ stab  is finally converted by active brake system  15  into a corresponding brake intervention.  
         [0039]     The distribution of controller output variable ΔM GiSo  is illustrated here as an example for only three different subsystems  1 ,  3 ,  15 . The control intervention may basically be distributed to any number of subsystems in any sequence.  
         [0040]     Another embodiment of a distribution unit  9  may be implemented, for example, in such a way that controller output variable ΔM GiSo  is supplied to multiple subsystems  1 ,  3 ,  15 - 18   e  and implemented in a weighted manner. Depending on the preference, subsystems  1 ,  3 ,  15 - 18   e  may take on different portions, e.g., 60% by the active suspension ARC, 30% by the active steering system AFS, and 10% by brake system  15 .  
         [0041]      FIG. 5  shows the calculation of superimposed steering angle δ stab  from controller output variable ΔM GiSo  as it may be carried out in control unit  2 , for example. Controller output variable ΔM GiSo  is initially supplied to a low-pass filter  21  and a filtered variable ΔM GiSof  is generated. This variable ΔM GiSof  is converted into a steering angle δ Raw  via a unit  22 . This raw value δ Raw  is again bandwidth-limited in downstream unit  23  and a value δ ToZo  is generated. The bandwidth of filter  23  is dependent on friction factor μ which is incorporated in filter function F via a characteristic curve  25 . Block  25  generates a parameter P ToZo  which changes filter function F as a function of friction factor μ.  
         [0042]     Filtered steering angle δ ToZo  is finally scaled using a unit  24 , whereby the superimposed steering angle, i.e., steering angle change δ stab  to be set, is maintained. The scaling is in turn dependent on friction factor μ which is incorporated in scaling function  24  via a characteristic curve  26 .  
         [0043]      FIG. 6  shows a possible hardware architecture for the advanced vehicle dynamics control system VDM. The system includes two data buses  19 ,  20 , multiple sensors  27 - 30  as well as different control units  1 ,  2 ,  3  being connected to first bus  19 , also known as the chassis CAN. Indicated control units  1 ,  2 ,  3  are also connected to the other data bus  20 , also known as the power train CAN. An engine management (Motronic)  16  and a control unit  31  for a speed controller ACC are additionally connected to data bus  20 .  
         [0044]     The sensors include redundantly embodied yaw speed and transverse acceleration sensors  27 , a steering wheel angle sensor  28 , and a steering angle sensor  29 , as well as additional optional sensors  30 . Actuating requests ΔF Nstab , δ stab , Δλ for active steering system AFS  1 , active chassis ARC  3 , and possibly additional subsystems  17  generated by VDM control unit  2  are preferably conveyed via bus  19 , since this bus is typically less overloaded and carries fewer interference signals than power train CAN  20 .  
       LIST OF REFERENCE NUMERALS  
       [0000]    
       
           1  AFS control unit  
           2  VDM control unit  
           3  ARC control unit  
           4  observer  
           5  setpoint value calculation  
           6  state controller  
           7  interfaces  
           8  subsystems  
           9  distribution unit  
           10  vehicle  
           11  sensor signals  
           12  sensors  
           13  setpoint slip and blocking moment calculation  
           14  brake and drive slip controller  
           15  hydraulic control  
           16  motronic  
           17  control unit  
           18  actuators  
           19  chassis CAN  
           20  power train CAN  
           21  low-pass filter  
           22  conversion unit  
           23  filter  
           24  scaling unit  
           25  characteristic curve  
           26  characteristic curve  
           27  yaw speed and transverse acceleration sensors  
           28  steering wheel angle sensor  
           29  steering angle sensor  
           30  optional sensor  
           31  conversion unit  
           32  limiting unit  
           33  estimator  
           34  conversion unit  
           35  limiting unit  
           36  estimator  
           37  conversion unit  
           38  limiting unit  
          Y controller output variable  
          M GiSo  yaw setpoint moment  
          ΔF Nstab  change in the wheel contact force  
          δ stab  steering angle change  
          M stab  steering moment  
          ΔX actuating request