Abstract:
A vehicle control system includes an active steering system having a steerable wheel defining a steering angle and a steering wheel defining a driver input control angle. The active steering system further includes a coupler component, a actuator component, a controller component and a sensory component. The components are operably interconnected such that the controller component can selectively vary the steering angle relative to the driver input control angle. The steering angle defines a desired vehicle path. The sensor component is configured to detect at least a first vehicle operating parameter indicating that the vehicle is off road, and to detect at least a second vehicle operating parameter indicating that the vehicle has encountered an object preventing the vehicle from traveling along the desired vehicle path. The controller component is adapted to oscillate the steerable wheel when the sensor component detects that the vehicle is off road and has encountered an object preventing the vehicle from traveling along the desired path.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a motor vehicle, and in particular to an active front steering system for a motor vehicle.  
         [0002]     Active front steering systems for motor vehicles are used to rotate the wheels of the vehicle at a rate that is independent from the rotation of the steering wheel of the vehicle or without rotation of the steering wheel. The ratio of the rotation of the steering wheel to the rotation of the wheel defines a steering ratio. The active front steering system therefore sets the steering ratio of the vehicle. Without the active front steering system, the steering ratio is typically only determined by the ratio set by the mechanical connections between the steering wheel and the wheel of the vehicle.  
         [0003]     Heretofore, active front steering systems have included a powered actuator operably connected to a pinion of a rack-and-pinion system of a vehicle. The active front steering system assists in pivoting the steerable wheels. In basic operation, the active front steering system typically alters (either positively or negatively) a driver input control angle from the driver as applied to the steering wheel, via the powered actuator, to rotate the wheels according to the steering ratio.  
         [0004]     During off road operation, obstacles may be encountered by a vehicle. If the obstacle is sufficiently large and/or the friction generated by the tire is sufficiently low, the wheel will be unable to climb over the object. Such obstacles impede vehicle progress and may cause difficulty in controlling the vehicle.  
       SUMMARY OF THE INVENTION  
       [0005]     One aspect of the present invention is a vehicle control system including an active steering system having a steerable wheel defining a steering angle and a steering wheel defining a driver input control angle. The active steering system further includes a coupler component, an actuator component, a controller component and a sensory component. The components are operably interconnected such that the controller component can selectively vary the steering angle relative to the driver input control angle. The steering angle defines a desired vehicle path. The sensor component is configured to detect at least a first vehicle operating parameter indicating that the vehicle is off road, and to detect at least a second vehicle operating parameter indicating that the vehicle has encountered an object preventing the vehicle from traveling along the desired vehicle path. The controller component is adapted to oscillate the steerable wheel when the sensor component detects that the vehicle is off road and has encountered an object preventing the vehicle from traveling along the desired path.  
         [0006]     Another aspect of the present invention is a motor vehicle including a chassis, a power train, and a vehicle control system. The chassis includes at least one steerable wheel defining a steering angle, and the power train includes an engine and a transmission coupled thereto. The vehicle control system includes a controller and an active system coupled to the controller. The steering system includes a steerable wheel defining a steering angle and a steering wheel providing a driver input control angle. The active steering system further includes a coupler component, an actuator component, a controller component, and a sensor component. The components of the active steering system are operably interconnected such that the controller is adapted to selectively vary the steering angle relative to the driver input control angle. The steering angle defines a desired vehicle path. The sensor component is adapted to detect a vehicle operating parameter indicating that the vehicle has encountered an object preventing the vehicle from traveling along the desired vehicle path. The controller component oscillates the steerable wheel when the vehicle has encountered an object.  
         [0007]     Yet another aspect of the present invention is a vehicle control system including an active steering system. The active steering system includes a steerable wheel having a steering angle defining a desired direction, an actuator operably coupled to the steerable wheel for powered steering thereof, and a controller adapted to the actuator to steer the steerable wheel. The vehicle control system also includes at least one sensor adapted to sense a vehicle operating parameter indicating that an object has been encountered. The controller selectively varies the steering angle if an object is encountered.  
         [0008]     These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a partially schematic view of a steering system embodying the present invention, wherein a steering angle is 0°;  
         [0010]      FIG. 2  is a partial schematic view of the steering system pivoted to a non-zero steering angle;  
         [0011]      FIG. 3  is a graph illustrating the direction of vehicle travel;  
         [0012]      FIG. 4  is a flow chart illustrating the process for controlling the vehicle control system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     For purposes of description herein, it is to be understood that the invention may assume various alternative orientations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.  
         [0014]     Referring to  FIG. 1 , reference number  10  generally designates a steering system for a motor vehicle embodying the present invention. In the illustrated example, the steering system  10  comprises a steerable wheel  12  defining a steering angle  20  (see  FIG. 2 ), a powered actuator  14  controlling the steering angle and a steering wheel  16  providing a driver input control angle. The ratio of the driver input control angle to the steering angle defines a steering ratio. The steering system  10  also includes a controller  18  for selectively varying the steering ratio based, at least in part, upon road conditions.  
         [0015]     In the illustrated example, the steering system  10  includes a pair of the steerable wheels  12  that pivot about a pivot point  17  with respect to a vehicle frame  19 . Each wheel defines the steering angle  20  ( FIG. 2 ) between the longitudinal axis  22  of the associated vehicle and a central travel axis  24  of each wheel  12 . It should be noted that while the steering angle  20  is defined by the pivotal movement of each of steerable wheels  12 , the steering angle  20  may be defined by pivotable rear wheels if the vehicle is so equipped, and/or any other pivotable wheels.  
         [0016]     The illustrated steering system  10  also includes a steering column  26  rotatable in a direction represented by an arrow  27 , and operable to receive the driver input control angle from an operator of the vehicle via the steering wheel  16 . The steering column  26  is operably linked to the steerable wheels  12  via a rack-and-pinion system  30  that includes a rack  32  and a pinion gear  34 , a pair of drag links  36 , and a steering arm  38 . Although the present example utilizes a rack-and-pinion steering system, it should be noted that other steering systems compatible with the steering system  10  described herein may be utilized.  
         [0017]     The steering system  10  further includes a basic active front steering system  40  that includes the controller  18  in operable communication with the powered actuator  14 . The powered actuator  14  is operably connected to the rack  32  of the rack-and-pinion system  30  via a coupler  46 . The active front steering system  40  assists in pivoting the steerable wheels  12 . Although a particular kind of active front steering system is described herein, other systems known in the art my be utilized. In basic operation, the active front steering system  40  augments the driver input control angle from the driver as applied to the steering wheel  16 , via the powered actuator  14 . The steering angle  20  as defined by the steerable wheel  14  is determined by a combination of the driver input control angle and an additional steering angle supplied by the powered actuator  14 . The additional steering angle supplied by the powered actuator  14  is determined by the following equation: 
 
∝ ASA =δ DICA (( R   A−   R   D )/ R   D ); 
 
 wherein ∝ ASA =the additional steering angle supplied by the powered actuator  14 , δ DICA =the angle change of the steering wheel  16  as determined by the driver input steering angle, R A =the steering ratio of the vehicle without the additional steering angle and R D =the desired steering ratio. For example, if the steering ratio of the steering system  10  without the powered actuator  14  is 1 (e.g., turn the steering wheel  16  five degrees and the steerable wheel  12  will turn five degrees), the desired steering ratio is 5 (i.e., slow change of the steering angle  20  of the steerable wheel  12  compared to the change of angle of the steering wheel  16 ) and the steering wheel  16  has moved five degrees, the powered actuator  14  will move the steerable wheel  12  negative four degrees. Therefore, the steering wheel  16  will rotate five degrees and the steerable wheel  12  will rotate one degree, thereby providing the vehicle with a steering ratio of 5. 
 
         [0018]     With further reference to  FIG. 3 , during off road operation a vehicle will generally travel along a first portion  50  of a desired path. The desired path is the direction of travel that the operator of the vehicle desires. If sufficient traction is available, the desired path  50  may be determined by the steering angle  20  of the steerable wheels  12  either by itself or in conjunction with other driver input control parameters. If the vehicle encounters an object  51 , and there is insufficient traction to maintain the direction of travel along the desired path  50 , the vehicle will generally move in a direction of an undesired path  52 , or may stop completely. The controller  18  evaluates the output of sensors  60  ( FIGS. 1 and 2 ) corresponding to various vehicle operating parameters and compares the operating parameters to the driver input parameters to determine if the vehicle has reached a condition where it does not have sufficient grip to continue traveling along the desired path  50 .  
         [0019]     The operating parameters measured by the sensors  60  could include suspension deflection, as well as wheel slip, vehicle velocity and accelerations. The vehicle velocities and accelerations could include both linear displacements in the XYZ directions, as well as rotation (e.g. pitch, roll, and yaw). Once the controller  18  has utilized the information from the sensors  60  to determine that an object has been encountered, the controller  18  then determines if the driver wants the vehicle to continue down the desired path. To determine if the driver wants to continue down the path, the sensors provide information concerning the clutch, throttle and gear settings, the torques in the drive line, as well as other control signals on the vehicle, such as DSC, ABS or ACE.  
         [0020]     With further reference to  FIG. 4 , if the controller  18  determines that the vehicle is off road, and that an object has been encountered, the controller goes into an object avoidance mode illustrated generally by the portion of the flow chart  56  enclosed by the dashed lines  55 . If the controller  18  determines that the driver wants to continue along the desired path  50 , the controller oscillates the steerable wheel to locate in easier path, or to increase grip by using the sidewalls of the tires or an alternative face or surface portion of the obstacle. During oscillation of the steerable wheels  12 , the controller will generally vary ∝ ASA  at a preselected frequency and magnitude between positive and negative values. Although the precise manner of the oscillations could vary depending upon the particular application and road conditions, in a preferred embodiment ∝ ASA  varies sinusoidally at a preselected frequency and magnitude. Thus, with reference to  FIG. 2 , although the steering wheel  16  may be stationary at a driver input control angle nominally corresponding to the central travel axis  24  of wheel  12  at nominal steering angle  20 , the actual, momentary angle of the wheel  12  will oscillate about the axis  24  between the maximum momentary travel axis  24 A, and a minimum momentary travel axis  24 B. Similarly, the steering angle will vary between the maximum angle  20 A and minimum angle  20 B. For example, the controller  18  may be programmed to vary the steering angle  20  by +/−5° about the nominal steering angle  20 . However, it is anticipated that the oscillation magnitude could be greater in one direction if the sensors  60  determine that an asymmetrical oscillation is required to maintain the vehicle on the desired path  50 . For example, the controller  18  could oscillate the steerable wheels  12  at +5° and 0° relative to the nominal steering angle  20  to increase the amount of steering angle provided at the steerable wheels  12  relative to the input control angle provided by the driver. Also, the magnitude and frequency of the oscillation may be varied depending upon the vehicle speed, co-efficient of friction and wheel slippage, and the like.  
         [0021]     As illustrated in  FIG. 3 , upon encountering the object  51 , the vehicle is temporarily forced off the desired path  50  along a portion of an undesired path  52 . Upon actuation of the object avoidance mode by the controller  18 , the vehicle returns to a second portion of the desired path  53 . Although the second portion  53  of desired path may be displaced slightly from the original desired path  54 , the “new” desired path  53  is substantially closer to the original desired path  54  than if the vehicle had continued along the undesired path  57  due to encountering the object.  
         [0022]     To determine that the vehicle is driving in an off road condition, various vehicle operating parameters may be monitored and evaluated. Examples of methods to determine if the vehicle is off road include determining low speed differences between the vehicle response and driver inputs, both in terms of lateral response and longitudinal response. Detection of low tire and/or road friction at high temperatures may also be utilized. Also, large wheel travel differential may be detected to determine if the vehicle is off road. In order to avoid an erroneous determination that the vehicle is off road upon encountering a curve, the controller  18  may make the determination only if a predetermined number of large wheel travels have occurred within a predetermined time period. Yet another method for determining that the vehicle is in off road condition may include detecting road roughness by use of accelerometers in conjunction with the vehicle speed. Still further, in all wheel drive vehicles, sensors may determine if the differential lock condition or low ratio gear box is actuated, and thereby determine that an off road condition is present. Alternately, dynamic low frequency wheel loads, roll bar deflections. ACE logic signals, air suspension logic, DSC signals, engine management signals, GPS signals, and/or a driver setting an on/off road switch may all be utilized to determine if an off road condition is present.  
         [0023]     To determine if the vehicle has encountered an object, such that it can no longer continue along a desired path, the vehicle ABS or traction control can be utilized to detect low speed wheel slip. Alternately, the detection of low speed, high magnitude longitudinal acceleration oscillation at a particular frequency may also be utilized to indicate that an object has been encountered. Also, suspension travel sensors may be utilized to determine if the wheel position is changed, or returned to the same positions under large wheel travel situations. Also, a manual switch that is actuated by the driver may be utilized by the controller  18  to determine that an object has been encountered. Alternately, optical sensors on the vehicle or GPS signals may also be utilized to determine that an object has been encountered.  
         [0024]     As illustrated in  FIG. 4 , the vehicle will normally operate in the standard operating mode. However, the controller  18  continuously monitors to determine if the vehicle is off road and whether or not an object has been encountered. If the vehicle is off road, and an object has been encountered, the controller will go into the object avoidance mode  55 . The controller  18  will then determine the desired path, and then determine if there is sufficient traction to continue along the desired path. If there is sufficient traction, the controller  18  will return to the standard operating mode. Alternately, if there is insufficient traction to continue along the desired path, the controller will then determine if the driver wants to continue along the desired path. If the driver does not want to continue along the desired path, the controller returns to the standard operating mode. Alternately, if the driver wants to continue along the desired path, the controller  18  oscillates the steering angle while monitoring and controlling vehicle speed in the manner described above. If the vehicle has returned to the desired path, the controller returns to the standard operating mode. Alternately, if the vehicle is still not on the desired path, the controller returns to the step of determining if the driver wants to continue along a desired path.  
         [0025]     In addition to oscillating the steering angle upon encountering an object in an off road condition, the controller  18  may also utilize sensors  60  that are connected to the vehicle ABS or traction control system to actively limit wheel slip during oscillation of the wheels. Also, the system may include a manual switch that is operable by the vehicle operator such that the controller  18  does not go into the object avoidance mode even if the vehicle is off road and an object has been encountered. Alternately, the manual switch may include a position that would cause the controller  18  to go into the object avoidance even if the vehicle is not off road and/or an object has not been encountered. Also, although the controller  18  preferably goes into the object avoidance mode only if off road and an object has been encountered, the controller  18  could be configured to go into the object to avoidance mode upon encountering an object, regardless of whether or not the vehicle is off road.  
         [0026]     In the foregoing description, it will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed herein. Such modifications are to be considered as included in the following claims, unless these claims by their language expressly state otherwise.