Abstract:
In a method and an apparatus for affecting the cornering performance of a motor vehicle, a transverse acceleration of the motor vehicle is determined, a desired transverse tilt of the motor vehicle defined based on the determined transverse acceleration, at least one actuator of an active suspension system of the motor vehicle is adjusted so that the motor vehicle assumes the desired transverse tilt, and an additional actuator intervening in the steering system of the motor vehicle. A yaw movement of the motor vehicle caused by the adjustment of the at least one actuator of the active suspension system is at least partially compensated by the additional actuator.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of German Patent Application, Serial No. 10 2011 010 845.9, filed Feb. 10, 2011, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a method and an apparatus for affecting the cornering performance off a motor vehicle. The invention also relates to a motor vehicle with such an apparatus. 
         [0003]    The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
         [0004]    Motor vehicles with active suspension system and/are stabilizers are known as Active Body Control (ABC), wherein their controllable suspension characteristics enable a specific compensation of pitch and roll movements. Typically, the vertical position of each wheel can be electro-hydraulically adjusted. In this way, the driving characteristics of a motor vehicle can be improved, in particular when driving along turns, for example in that the motor vehicle actively leans into the turn. 
         [0005]    Disadvantageously, roll movements when negotiating turns typically cause feedback for the cornering performance of the motor vehicle. In particular, with active rolling, the axles of the motor vehicle are operated at an unfavorable operating point, causing the motor vehicle to steer into the turn when cornering, which must typically be compensated by a manual steering movement from the vehicle operator. 
         [0006]    It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved method and an apparatus, which can improve the driving comfort for the occupants of the motor vehicle and which leads to a more natural steering characteristic of the motor vehicle in turns. 
       SUMMARY OF THE INVENTION 
       [0007]    According to one aspect of the present invention, a method for affecting a cornering performance of a motor vehicle includes the steps of determining a transverse acceleration of the motor vehicle, defining a desired transverse tilt of the motor vehicle as a function of the transverse acceleration, adjusting at least one actuator of an active suspension system of the motor vehicle, so that the motor vehicle assumes the desired transverse tilt, and adjusting at least one additional actuator cooperating with a steering system of the motor vehicle so as to at least partially compensate a yaw movement of the motor vehicle caused by the adjustment of the at least one actuator of the active suspension system. 
         [0008]    According to another aspect of the invention, an apparatus for affecting cornering performance of a motor vehicle includes a determination device configured to determine a transverse acceleration of the motor vehicle and to define a desired transverse tilt of the motor vehicle as a function of the determined transverse acceleration, at least one actuator of an active suspension system of the automobile, said at least one actuator coupled with the determination device and operating to adjust a transverse tilt of the motor vehicle so that the adjusted transverse tilt corresponds to the desired transverse tilt defined by the determination device; and at least one additional actuator coupled with the determination device and configured to cause an intervention in a steering system of the motor vehicle, said intervention at least partially compensating a yaw movement of the motor vehicle caused by operating the at least one actuator. 
         [0009]    A motor vehicle according to the invention includes the aforedescribed apparatus according to the invention. 
         [0010]    Advantageous embodiments of the invention may include one or more of the following features. 
         [0011]    The transverse acceleration may be determined by measuring the current acceleration or the instantaneous transverse acceleration. Alternatively, the transverse acceleration of the motor vehicle may also be predetermined for a future time. This may be done, for example by using suitable vehicle models through calculation and/or within the context of a provided roadway preview. An expected transverse acceleration may also be estimated based on available data. 
         [0012]    The term transverse tilt refers, in particular, to a rotation of the motor vehicle about its roll axis. Such rotary movements, also referred to as rolling, predominantly occur when the motor vehicle travels through turns, where transverse accelerations cause the motor vehicle to rotate and/over roll due to the centrifugal force. In particular, the desired transverse tilt may be defined so as to produce for the occupants of the motor vehicle a particularly comfortable and largely undisturbed driving experience when the motor vehicle rotates about the roll axis. This is particularly the case when the transverse accelerations subjectively experienced by the occupants are at least partially compensated. In particular, a desired transverse tilt curve may be defined, for example depending on the transverse acceleration. In the absence of transverse accelerations on the motor vehicle, this desired transverse tilt angle is 0°. Conversely, when transverse accelerations occur on the motor vehicle, this transverse tilt angle is different from 0°. The desired transverse tilt may particularly be a function of the transverse acceleration. The functional relationship may be provided by stored characteristic curves or by mathematically equations. 
         [0013]    According to an advantageous feature of the present invention, the actuators of the active suspension system may include electro-hydraulic actuator systems, which act on the individual wheels of the automobile and control their vertical positions. The active suspension system may be an active spring system, for example an Active Body Control system and/or a system with active stabilizers. The individual actuators of the corresponding wheels can then be controlled such that only certain wheels are raised or lowered, thereby adjusting the predetermined desired transverse tilt of the motor vehicle. 
         [0014]    According to an advantageous feature of the present invention, the at least one actuator which causes a steering intervention in a steering system of the motor vehicle may be adjusted so as to that at least partially compensate a yaw movement of the motor vehicle caused by the adjustment of the at least one actuator of the active suspension system. Adjusting the at least one actuator at step c) may affect not only the rolling performance, but also the cornering performance of the motor vehicle. Adjustment of the at least one actuator which causes the intervention in the steering system may at least partially, more particularly completely, affect the cornering performance. 
         [0015]    With this method, a motor vehicle can be urged to actively tilt when travelling through a turn, thereby reducing uncomfortable transverse accelerations for the vehicle occupants. The subjective driving comfort increases considerably. In addition, the motor vehicle maintains the familiar steering characteristic almost unchanged when traveling through turns. The actively produced rolling of the motor vehicle then does not or only insignificantly change of the cornering performance of the motor vehicle, requiring no or only slight counter steering from the vehicle operator. In particular, the familiar steering characteristic of the motor vehicle remains almost unchanged. Driving comfort and driving safety are increased and the vehicle operator receives the familiar haptic feedback from the steering wheel. 
         [0016]    According to an advantageous feature of the present invention, by adjusting the at least one actuator which causes the intervention in the steering system of the motor vehicle, a superimposed steering angle is superimposed on a first steering angle such that the radius of curvature of the turn traveled by the motor vehicle caused by the resulting steering angle corresponds substantially to the radius of curvature which would have resulted without the adjustment of the at least one actuator of the active suspension system at the first steering angle. Accordingly, a steering actuator actively intervenes in the steering movement of the motor vehicle. For this purpose, a generally existing steering system of the motor vehicle may be used to which the additional actuators for active steering intervention have been added. A vehicle operator then no longer needs to compensate the additional yaw movement of the motor vehicle caused by the active rolling along turns through manual counter steering, because the steering actuator performs this intervention automatically. The vehicle operator then experiences in turns the familiar steering characteristic of the motor vehicle. This obviates the need for manual counter steering which is viewed as annoying and which affects the driving safety. 
         [0017]    According to another advantageous feature of the present invention, a vehicle operator may at least partially manually define the first steering angle, on which the superimposed steering angle is superimposed. Alternatively or in addition, this first steering angle may be defined by a system for semi-automatic vehicle guidance, in particular a lane assist system. However, the vehicle may also be guided autonomously or fully automatically, wherein the vehicle operator no longer actively intervenes in steering the vehicle. The invention is particularly advantageous when the steering angle is at least partially predefined by the vehicle operator, meaning that the motor vehicle is steered into a turn manually. When a vehicle guided semi-automatically, for example by a Heading Control, a number of driving-related operations are no longer performed by the vehicle operator himself, but instead by systems of the motor vehicle. These systems may, for example, correct the steering operation of the vehicle operator and intervene in critical situations. 
         [0018]    According to yet another advantageous feature of the present invention, the at least one actuator which causes the intervention in the steering system of the motor vehicle is adjusted depending on the defined desired transverse tilt and/or the transverse tilt. A suitable steering actuator setting may be provided for each predetermined desired transverse tilt, with which an undesirable cornering performance of the motor vehicle can be compensated to a significant degree. The functional cooperation then guarantees very good results for yaw movement compensation. 
         [0019]    According to an advantageous feature of the present invention, a superimposed steering angle may be adjusted with the at least one actuator which causes the intervention in the steering system of the motor vehicle. According to another advantageous feature of the present invention, the superimposed steering angle may be calculated from the desired transverse tilt and/or the adjusted transverse tilt with a mathematical function and/or from a characteristic curve. Advantageously, the functional relationship may be defined so as to at least partially compensate an additional yaw angle of the motor vehicle caused by the at least one actuator of the active suspension system by superimposing a steering angle in the opposite direction. Advantageously, a suitable compensating superimposed steering angle may be predetermined for all possible actively adjustable roll angles or transverse tilt angles. This allows excellent compensation for many feasible curve shapes. 
         [0020]    According to an advantageous feature of the present invention, a future transverse acceleration of the motor vehicle may be determined with a device for automatic roadway preview and the desired transverse tilt of the motor vehicle may be defined with this device. Many different input parameters may be considered in the automatic roadway preview. For example, the respective transverse acceleration may be determined based on the instantaneous speed of the motor vehicle and the current steering wheel angle. Alternatively, map data may be provided which show the course of the roadway. For example, the current vehicle position may then be determined with a satellite signal sensor (e.g. a GPS [Global Positioning System]-Sensor), and the expected transverse acceleration may be determined based on the map material indicating the turns ahead of the vehicle. Data obtained from an environmental sensor (e.g. video camera, ultrasound sensors, etc.) may also be used for predicting the roadway. Data relating to the slope of the roadway may also be important input parameters for determining the expected transverse acceleration. With such a device for automatic roadway preview, the transverse tilt of the motor vehicle can be adjusted not only in response to an actual measured transverse acceleration, but the expected transverse accelerations may be determined before they actually occur. In this way, the transverse tilt can be optimally adapted to the prevailing conditions quickly and without time delay. The adjustment of the transverse tilt as well as the interventions of the steering actuator can then be designed to be even smoother and less abrupt, thus increasing the driving comfort for the occupants of the motor vehicle. 
         [0021]    According to an advantageous feature of the present invention, the transverse acceleration may also be determined by using a signal from at least one sensor. This sensor may be, for example, an acceleration sensor (g-sensor) measuring the instantaneous transverse acceleration. Such sensors enable a particularly accurate measurement of the respective transverse acceleration. 
         [0022]    According to yet another advantageous feature of the present invention, the at least one actuator for affecting the transverse tilt of the motor vehicle may be provided in an active suspension system or in an active stabilizer. Such suspension systems and/or stabilizer systems allow a particularly dynamic control of the vehicle tilt and a rapid adaptation to the respective situation commensurate with the requirements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0023]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
           [0024]      FIG. 1  shows a schematic top view on a motor vehicle with an active suspension system and an actuator for influencing the steering movement; 
           [0025]      FIG. 2  shows a schematic rear view of a motor vehicle with an active suspension system; 
           [0026]      FIG. 3  shows a schematic top view on a motor vehicle with three possible travel paths; and 
           [0027]      FIG. 4  shows a schematic illustration of a steering unit for determining a superimposed steering angle according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0028]    Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
         [0029]    Turning now to the drawing, and in particular to  FIG. 1 , there is shown a motor vehicle  10  moving in a driving direction indicated by the arrow  14 . The motor vehicle  10  has two front wheels  16   a  and  16   b  arranged proximate to its front side  12 . These are connected with each other by way of a front axle  24 . The motor vehicle also includes two rear wheels  16   c  and  16   d . Vertical actuators  18   a  to  18   d , which are part of an ABC (Active Body Control) actuator system, are associated with each of the wheels  16   a  to  16   d  in one to one correspondence. The vertical actuators  18   a  to  18   d  are controlled by an ABC control device  20 . In this way, the vertical lift of each individual wheel can be individually adjusted. For example, the vertical actuators  18   a  can affect the vertical wheel position of wheel  16   a . The ABC control device  20  is connected with a control device  22  which controls a semi-automatic vehicle guidance system. Alternatively, the ABC control device  20  and the control device  22  may also form part of a common control device. The motor vehicle  10  also includes a sensor  32  configured for measurement of the instantaneous transverse acceleration of the motor vehicle  10 . The sensor  32  is connected with the control device  22  and transmits to the control device  22  the measurement information about the transverse acceleration. 
         [0030]    The front wheels  16   a  to  16   d  can be steered via a steering system  26 , i.e. the steering angle b can be adjusted with the steering system  26 . In particular, the steering system  26  includes a steering wheel that can be operated by a driver  30 . In addition to manual steering, the motor vehicle  10  also includes a steering actuator  28 , with which the steering angle b of the wheels  16   a  and  16   b  can be automatically adjusted. To this end, the steering actuator  28  is connected with the control device  22 . In particular, the steering actuator  28  is constructed so that a superimposed steering angle Δb can be superimposed on the steering angle b adjusted by the driver  30  with the steering system  26 , resulting in a steering angle b+Δb. However, the steering wheel angle c of the steering wheel of the steering system  26  should continue to be the angle corresponding to the steering angle b. The driver  30  then does not receive a haptic feedback on the steering wheel relating to the superimposed steering angle Δb. 
         [0031]      FIG. 2  shows a schematic rear view of a motor vehicle with a conventional roll control. In the exemplary embodiment, the motor vehicle  10  travels through a left-hand turn. To enhance the driving comfort for the occupants of the motor vehicle  10 , the vertical actuators  18   a  to  18   d  are controlled such that the body of the motor vehicle  10  tilts into the left-hand turn. The tilt is accomplished by a rotation about the roll axis W, which extends parallel to a roadway  34 . When traveling in a straight line, no transverse forces act on the motor vehicle  10 , so that its body is oriented substantially parallel to a plane E 1 . In a left-hand turn, the body is actively tilted by the vertical actuators  18   a  to  18   d  by a roll angle a. The body is then substantially parallel to a plane E 2  which is no longer parallel to the roadway  34 . The plane E 2  then encloses the roll angle a with the plane E 1 . Because the vehicle body now leans into the turn, the transverse acceleration experienced by the driver  30  is improved. 
         [0032]      FIG. 3  shows three possible trajectories T 1 , T 2  and T 3  along which the motor vehicle moves, depending on which systems affecting the driving dynamics are activated. The motor vehicle travels along the trajectory T 1  when the steering angle b is set by the driver  30 . In this example, neither does the motor vehicle  10  actively lean into the turn (see  FIG. 2 ), nor does the steering actuator  28  actively intervene in the steering. 
         [0033]    The situation illustrated in  FIG. 2  will now be described, where the motor vehicle  10  tilts actively into the left-hand turn shown in  FIG. 3  by the roll angle a. The motor vehicle  10  then no longer travels along the trajectory T 1 , although the steering angle b is set, but travels instead on the trajectory T 2 , which is tighter, i.e. has a smaller radius of curvature than the trajectory T 1 . Active rolling produces a yaw moment towards the left into the turn. The active rolling increases the yaw angle of the motor vehicle  10  in relation to the yaw angle associated with the trajectory T 1 , although the steering angle b remains the same. This corresponds to the situation known in the art. In order to be nevertheless able to travel along the trajectory T 1 , the driver  30  must correctively intervene in the steering system  26  by moving the steering wheel further to the right, i.e. by reducing the steering angle b. The driving characteristics of the motor vehicle  10  then it appears unfamiliar to the driver  30 . The driver  30  may be surprised that he must steer back to the right which may endanger the driving safety. 
         [0034]    The corrective steering intervention is therefore performed automatically. The situation is illustrated again in  FIG. 4 . The control device  22  computes a superimposed steering angle Δb which is applied on the steering system  26  by way of the steering actuator  28 , thereby producing an effective steering angle b+Δb. The steering wheel angle c remains unchanged and keeps the value corresponding to the steering angle b. The control device  22  uses several input variables to compute the superimposed steering angle Δb. These are, in particular, the roll angle a, the steering angle b, and optionally the speed v of the motor vehicle  10 . The superimposed steering angle Δb and the roll angle a are functionally correlated by way of a curve K. A roll angle a of 5° causes, for example, a superimposed steering angle Δb of −1°. Rolling to the left causes a superimposed steering angle Δb to the right and vice versa. 
         [0035]    As a result, the actual trajectory T 3  traveled by the motor vehicle  10  runs on the right of the trajectory T 2 . The radius of curvature associated with T 3  is greater than the radius of curvature associated with T 2 . Ideally, the superimposed steering angle Δb is selected so that the trajectories T 1  and T 3  coincide. The driver  30  then experiences the familiar cornering performance of the motor vehicle  10 . Correlating automatic rolling and automatic counter steering is particularly advantageous when the motor vehicle  10  is steered manually, or in the so-called chauffeur mode. The system composed of control device  22  and steering actuator  28  can also be referred to as superimposed steering system and may be constructed as an ADS. 
         [0036]    The roll angle a is adjusted by acquiring with the control device  22  signals from the sensor  32  and determining with the control device  22  the transverse acceleration from these signals. Depending on the respective value of the transverse acceleration, the control device  22  now determines a suitable transverse tilt with the roll angle a and a suitable superimposed steering angle Δb. The transverse tilt is adjusted by transmitting signals from the control device  22  to the ABC control device  20 , wherein the latter controls the corresponding lift of the individual vertical actuators  18   a  to  18   d . The superimposed steering angle is adjusted by transmitting corresponding signals from the control device  32  to the steering actuator  28  which intervenes in the steering system  26  so as to define a particular steering angle for the wheels  16   a  and  16   b.    
         [0037]    While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.