Abstract:
A method controls a parallel parking of a vehicle. A distance between the first object and the second object is remotely sensed. The distance is compared to a first predetermined distance and a second predetermined distance. An autonomous first steering strategy maneuver is performed for parking the vehicle between the first object and second object if the distance is greater than the first predetermined distance. The first steering strategy maneuver consists of a first predetermined number of steering cycles for parking the vehicle. An autonomous second steering strategy maneuver is performed for parking the vehicle between the first and second object if the distance is between the first predetermined distance and the second predetermined distance. The second steering strategy maneuver consists of a second predetermined number of steering cycles for parking the vehicle where the second is greater than the first predetermined number of steering cycles.

Description:
BACKGROUND OF INVENTION 
     The present invention relates generally to a parking strategy for autonomously parallel parking a vehicle. 
     Parallel parking a vehicle between two vehicles is often a difficult task for a driver. Semi-autonomous parking systems are vehicle based systems designed to aid the driver in performing difficult parking maneuvers such as parallel parking. Such systems either guide the driver in steering the vehicle through its intended trajectory path or increase/decrease power steering efforts when the driver of the vehicle has deviated from the intended trajectory path. In such systems, the driver is required to control the steering efforts or make some adjustments to the steering wheel. 
     SUMMARY OF INVENTION 
     An advantage of an embodiment provides a determination of whether an available parking space between a first and second object is sufficient to parallel park the vehicle using a fully autonomous single cycle steering strategy or a fully autonomous two cycle steering strategy. 
     An embodiment contemplates a method of controlling a parallel parking of a vehicle between a first object and a second object in response to an available parking distance therebetween. A distance between the first object and the second object is remotely sensed. The distance is compared to a first predetermined distance and a second predetermined distance where the first predetermined distance is greater than the second predetermined distance. If the distance is greater than the first predetermined distance, then performing an autonomous first steering strategy maneuver for parking the vehicle between the first object and second object. The first steering strategy maneuver consists of a first predetermined number of steering cycles for parking the vehicle. If the distance is between the first predetermined distance and the second predetermined distance, then performing an autonomous second steering strategy maneuver for parking the vehicle between the first and second object. The second steering strategy maneuver consists of a second predetermined number of steering cycles for parking the vehicle where the second predetermined number of steering cycles is greater than the first predetermined number of steering cycles. 
     An embodiment contemplates an autonomous parking system for parallel parking a driven vehicle between a first object and a second object. The system includes a controller for autonomously controlling a steering of the driven vehicle for parallel parking the driven vehicle and a sensing device for detecting objects proximate to the driven vehicle. The sensing device is in communication with the controller to provide signals to the controller for identifying a space between the first object and the second object. A distance is determined between the first object and the second object in response to sensing the detected objects. The controller compares the determined distance to a first predetermined distance and a second predetermined distance. The controller determines that a first steering strategy maneuver may be used to park the vehicle if the determined distance is greater than the first predetermined distance. The first steering strategy maneuver includes a first predetermined number of steering cycles. The controller determines that a second steering strategy maneuver may be used to park the vehicle if the determined distance is between the first predetermined distance and the second predetermined distance. The second steering strategy maneuver includes a second number of steering cycles. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing an autonomous parallel parking system according to an embodiment. 
         FIG. 2  is a geometric schematic illustrating vehicle parameters for applying a first steering strategy maneuver according to an embodiment 
         FIG. 3  is a geometric schematic illustrating vehicle parameters for applying a second steering strategy maneuver according to an embodiment 
         FIG. 4  is a flowchart for a method for parallel parking the vehicle according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     There is shown in  FIG. 1  an embodiment of an autonomous steering system  10  for parallel parking a vehicle. The autonomous steering system  10  includes a steering module  12  and a controller  14  for controlling steerable wheels  16  of the vehicle. The steering module  12  may be an electronic module or similar device that is capable of pivoting the steerable wheels  16  without a driver&#39;s steering demand through a steering wheel of the vehicle. The controller  14  provides control input signals to the steering module  12 , such as a conventional electronic power steering module, for controlling the pivoting of the steerable wheels during a parking maneuver. The controller  14  may be separate from the steering module  12  or may be integrated within the steering module  12  as a single unit. 
     The autonomous steering system  10  further includes a sensing device  18  for detecting objects proximate to the driven vehicle. The sensing device  18  detects the presence and non-presence of objects laterally from the vehicle for determining an available parking space between a first object and a second object. The sensing device  18  may include a radar-based sensing device, an ultrasonic-based sensing device, an imaging-based sensing device, or similar device capable of providing a signal characterizing the available space between the objects. The sensing device  18  is in communication with the controller  14  for providing signals to the controller  14 . The sensing device  18  may be capable of determining the distance between the respective objects and communicating the determined distance to the controller  14  or the sensing device  18  may provide signals to the controller  14  to be used by the controller  14  to determine the distance of the spacing between the objects. 
     In response to the determined spacing between the first and second objects, controller  14  determines whether to apply a first steering strategy maneuver or a second steering strategy maneuver. The first steering strategy maneuver includes a single cycle steering strategy where the steerable wheels are pivoted only in a single direction before returning to a center position for bringing the vehicle to a parked position. The center position being defined when the steerable wheels are in a position where the vehicle if moving would be driving in a straight path. 
       FIG. 2  illustrates a geometric schematic showing vehicle parameters used for determining the minimum spacing required for applying the first steering strategy maneuver for a respective vehicle. The model for determining whether the vehicle can be successfully parked utilizing the single cycle steering strategy is based on the assumption that a vehicle parked at a most rearward position in a parking space of a particular length can leave the parking spot utilizing a single cycle steering strategy with the steerable wheels at full steer. That is, if the vehicle can leave the parking space utilizing only a single maneuver, then the vehicle can be parked in the parking space utilizing only a single steering maneuver. 
     The determination for the single cycle steering maneuver will be discussed as follows. A first object  20  and the second object  22  are shown having a spacing L therebetween. The width of the available parking space is assumed to be a width of the vehicle. A vehicle, illustrated generally by  24 , includes a respective vehicle width, vehicle length, and vehicle turning radius at full steer based on the design of the vehicle chassis. The minimum distance required to apply the first steering strategy maneuver is predetermined and specific to a vehicle based on the vehicle characteristics as described. The formula for determining a first distance L 1  (i.e., minimum spacing for applying the first steering strategy maneuver) is represented by:
 
 L   1 =[( b   2 ) 2 +4( a   1 )( R   1 )] 1/2   +b   1  
 
     where a 1  is half of a width of the vehicle along a rear axle  26 ; b 1  is a longitudinal distance from a rear  28  of the vehicle to the rear axle  26  of the vehicle; b 2  is a longitudinal distance from a front  30  of the vehicle to the rear axle  26  of the vehicle; and R 1  is a distance from a midpoint  32  of the rear axle  26  to a center of the turning radius  34  of the vehicle at full steer to the left as illustrated in  FIG. 2 . The turning radius, herein, is based on the steerable wheels being at a full steer position. Full steer correlates to the steerable wheels being pivoted to the maximum pivotable position in a single direction. The determined distance L 1  is the minimum distance required between the first object  20  and second object  22  for applying the single steering strategy maneuver. If the actual measured distance between the first object  20  and second object  22  is less then the predetermined distance L 1 , then the single steering strategy maneuver is not applied. 
     The second steering strategy maneuver includes a two cycle steering strategy where the steerable wheels are first pivoted in a first direction to a first steering position (i.e., first steering maneuver). Thereafter, the wheels are then pivoted in a direction opposite to the first direction where the steerable wheels pivot past the normal position to a second position (i.e., second steering maneuver). Determining whether the vehicle can be successfully parallel parked utilizing the two cycle steering strategy is modeled on a condition of whether the vehicle parked in the available parking space can leave the parking spot utilizing two steering maneuvers. That is, if the vehicle can leave the parking space utilizing only two steering maneuvers, then the vehicle can be parallel parked in the parking space utilizing only two steering maneuvers. A first steering maneuver includes the driven vehicle moving backward in the available parking space at a respective turning angle where a respective rear corner of the vehicle reaches a respective boundary (i.e., front of the first object). A second steering maneuver includes the vehicle moving forward where a respective front corner of the vehicle reaches a respective rear boundary of the second object (i.e., rear corner of the second object). 
       FIG. 3  illustrates a geometric schematic illustrating vehicle parameters used for determining the minimum spacing required for applying the second steering strategy maneuver for a respective vehicle. The first object  20  and the second object  22  having a spacing L therebetween. The width of the available parking space is assumed to be the width of the vehicle. The minimum space required to apply the second steering maneuver strategy is predetermined based on the respective vehicle&#39;s characteristics such as those described above. The formula for determining a second distance (i.e., minimum spacing for applying the second steering strategy maneuver) is represented by:
 
 L   2 =( R   2   +a   1 )sin ψ+ b   1  cos ψ+ b   2  
 
     where a 1  is half of the width of the vehicle along the rear axle  26 ; b 1  is the longitudinal distance from the rear  28  of the vehicle to the rear axle  26  of the vehicle; b 2  is the longitudinal distance from the front  30  of the vehicle to the rear axle  26  of the vehicle; R 2  is the distance from a midpoint of the rear axle  32  to the center of the turning radius  36  for a vehicle steering to the right as illustrated in  FIG. 3 , and ψ is an angle of the vehicle as a whole that the vehicle must turn before contacting the rearward object  20  in order to complete a two-cycle parking maneuver. That is, the turn angle is the minimum angle that the vehicle should be positioned as a whole after applying the first steering maneuver so that the vehicle may initiate the second steering maneuver in moving forward to exit the parking space without contacting object  22 . The turn angle ψ required to complete the two-cycle parking maneuver may be solved for by the following equation:
 
[ b   2 +( R   1   +R   2 )sin ψ] 2 +[−( R   2   +a   1 )+( R   1   +R   2 )cos ψ] 2   =[−b   2 (1−cos ψ)−( R   2   −a   1 )sin ψ] 2   +b   2 +( R   1   +R   2 )sin ψ] 2   +[b   2  sin ψ−( R   2   −a   1 )(1−cos ψ)−2 a   1 +( R   2   +a   1 )−( R   1   +R   2 )cos ψ] 2  
 
     where R 2  is the distance from a midpoint of the rear axle  32  to the center of the turning radius (C 2 )  36  of the vehicle corresponding to a right vehicle steer. The other variables shown in the equations are the same as described above. In the above equation, the left side of the equation represents the distance from the center of turn radius (C 1 )  34  (i.e., for the driven vehicle in forward motion) to a rear corner of the second object  22  designated as (0,0) coordinate shown in  FIG. 3 . The right side of the equation represents the distance between the center of the turn radius (C 1 )  34  and an outer front corner of the driven vehicle  24  designated as point A. This equation establishes the relationship of the turn radius of the vehicle with respect to the object  22  in order to safely leave the parking spot from a respective position. 
     Once the turn angle ψ has been solved for in the above equation, the turn angle ψ may be substituted in the previous equation to determine the second distance L 2 . The second distance L 2  is the minimum distance required between the first object  20  and second object  22  for applying the second steering strategy maneuver. If the actual measured distance between the first object  20  and second object  22  is less then the second distance L 2 , then the second steering strategy maneuver is not applied. 
     The steering module  12  (shown in  FIG. 1 ) performs a control action for parallel parking the vehicle based on the determination of whether to apply the first steering strategy maneuver or the second steering strategy maneuver given the distance L between the first and second objects. If the determined spacing between the objects is insufficient to perform either the first steering strategy maneuver or the second steering strategy maneuver, then no control action is performed. 
       FIG. 4  illustrates a method of an embodiment for parallel parking the vehicle. In step  40 , the parallel parking routine is started. In step  41 , the distance between a first object and a second object for parallel parking the vehicle is determined. To determine the distance between the first object and the second object, a sensing device is actuated for detecting the proximity of the first object and second object adjacent to the driven vehicle. The presence of the first object is detected as the driven vehicle travels along a side of the first object. Thereafter, a non-presence of the first object is detected as the driven vehicle travels past the first object. The presence of the second object is detected as the driven vehicle travels along side the second object. The distance traveled by the driven vehicle between a point when the first object is no longer detected and a point when the second object is first detected is determined. The distance between the objects may be a calculated or measured determination based on the sensing device utilized. 
     In step  42 , a determination is made as to whether the determined distance is greater than a first predetermined distance. The first predetermined distance is determined from the vehicle parameters as described above. If determination is made that the first determined distance is greater than the first predetermined distance, then in step  43 , the system determines a parking path plan for the first steering strategy maneuver. In step  44 , a control action is performed for autonomously parallel parking the vehicle using the first steering strategy maneuver. The routine proceeds to step  49  where the routine is exited after a successful parking maneuver. 
     In step  42 , if the determination is made that the determined distance is less than the first predetermined distance, then the routine continues to step  45  to determine whether the determined distance is greater than the second predetermined distance. If the determined distance is greater than the second predetermined distance, then the routine proceeds to step  46  where the system determines a parking path plan for the second steering strategy maneuver. In step  47 , a control action is performed for autonomously parallel parking the vehicle using the second steering strategy maneuver. The routine proceeds to step  49  where the routine is exited after a successful parking maneuver. 
     In step  45 , if the determination is made that the predetermined distance is less than the second predetermined distance, then the routine proceeds to step  48  where the search continues for a next available parking space. When a next available parking space is found, the routine returns to step  41  to determine the distance between the objects. 
     While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.