Abstract:
A method and a system for assisting a vehicle operator to parallel park a vehicle. The method and system use only a single proximity sensor to detect a suitable parallel parking space and monitor the position of the vehicle when backing into the parallel parking space. Assistance to parallel park the vehicle may be as little as providing indications or warning to a vehicle operator while the vehicle operator backs the vehicle into the parallel parking space, or may be as much as taking complete control of the vehicle away from the vehicle operator, and autonomously parallel parking the vehicle.

Description:
TECHNICAL FIELD OF INVENTION 
       [0001]    The invention generally relates to a system and method for assisting a vehicle operator to parallel park a vehicle, and more particularly relates to a system and method for finding a suitable parallel parking place and providing parallel parking assistance using only a single proximity sensor. 
       BACKGROUND OF INVENTION 
       [0002]    Some vehicles are equipped with parallel parking guidance or parallel parking assistance systems to either autonomously operate the steering and braking of the vehicle to parallel park the vehicle, or to provide the vehicle operator with audible and/or visual cues to assist the vehicle operator to parallel park the vehicle. However such systems are equipped with cameras and/or multiple sensors, and correspondingly complex controllers that undesirably increase the cost of such systems. 
       SUMMARY OF THE INVENTION 
       [0003]    In accordance with one embodiment of this invention, a method for assisting a vehicle operator to parallel park a vehicle is provided. The method includes the step of determining parallel parking space requirements based on a travel path defined by a vehicle length, a vehicle width, a minimum turning radius, and a minimum arc radius of a front corner of the vehicle. The method further includes the step of providing a single proximity sensor configured to output a clearance signal indicative of a clearance distance beside the vehicle. The method also includes the step of providing a controller configured to perform a plurality of steps. The steps performed by the controller include storing the parallel parking space requirements. The steps performed by the controller further include receiving the clearance signal from the single proximity sensor and detecting a parallel parking space suitable for parallel parking the vehicle based on the clearance signal. The steps performed by the controller also include indicating when to start a first backing maneuver, indicating when to start a second backing maneuver, and indicating when to end the second backing maneuver. 
         [0004]    In another embodiment of the present invention, a vehicle parallel parking system for assisting a vehicle operator to parallel park a vehicle is provided. The system includes a single proximity sensor and a controller. The single proximity sensor is configured to output a clearance signal indicative of a clearance distance beside the vehicle. The controller is configured to store parallel parking space requirements based on a vehicle length, a vehicle width, a minimum turning radius, and a minimum arc radius of a front corner of the vehicle. The controller is further configured to receive the clearance signal from the single proximity sensor and detect a parallel parking space suitable for parallel parking the vehicle based on the clearance signal. The controller is also configured to indicate when to start a first backing maneuver, indicate when to start a second backing maneuver, and indicate when to end the second backing maneuver. 
         [0005]    In yet another embodiment of the present invention, a controller for a vehicle parallel parking system that assists a vehicle operator to parallel park a vehicle is provided. The controller includes a memory device, an input, and a processor. The memory device is configured to store parallel parking space requirements that are based on a vehicle length, a vehicle width, a minimum turning radius, and a minimum arc radius of a front corner of the vehicle. The input is configured to receive the clearance signal from the single proximity sensor that is configured to output a clearance signal indicative of a clearance distance beside the vehicle. The processor is configured to detect a parallel parking space suitable for parallel parking the vehicle based on the clearance signal. The processor is also configured to indicate when to start a first backing maneuver, indicate when to start a second backing maneuver, and indicate when to end the second backing maneuver. 
         [0006]    Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]    The present invention will now be described, by way of example with reference to the accompanying drawings, in which: 
           [0008]      FIG. 1  is a top view diagram of a travel path of a vehicle in accordance with one embodiment; 
           [0009]      FIG. 2  is a top view diagram of a vehicle equipped with a vehicle parallel parking system detecting a parallel parking space in accordance with one embodiment; 
           [0010]      FIG. 3  is a top view diagram of two paths of travel of a vehicle in accordance with one embodiment; 
           [0011]      FIG. 4  is a top view diagram of a vehicle parallel parking in accordance with one embodiment; 
           [0012]      FIG. 5  is a cut-away section of a vehicle equipped with a vehicle parallel parking system in accordance with one embodiment; 
           [0013]      FIG. 6  is a flowchart of a method for detecting a parallel parking space in accordance with one embodiment; and 
           [0014]      FIG. 7  is a flow chart of a method for parallel parking a vehicle in accordance with one embodiment. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0015]      FIG. 1  illustrates a travel path  8  for a vehicle  10  when the vehicle is moved and a steering angle of the steering wheels  12  is held constant at the steering angle illustrated. The four innermost circles illustrate a path for the steering wheels  12  and the non-steering wheels. In this non-limiting example illustrated, two of the four vehicle wheels have variable steering angles, and the other two have fixed steering angles and so are characterized as non-steering wheels. The description below is generally directed to the steering wheels being at the front of the vehicle, but it will be appreciated that the teachings herein could be applied to vehicles with rear steering. Alternatively, the vehicle  10  could be equipped with four-wheel steering and so all four wheels would have variable steering angles. The outer circle illustrates an arc radius  14  of a path traveled by a front corner  16  of the vehicle. Accordingly, any object located within the travel path  8 , e.g.—inside the arc radius  14  and outside of the innermost circle  18 , may come into contact with the vehicle  10  if the vehicle moves in the travel path  8  illustrated. As described in more detail below, the vehicle  10  may be equipped with a vehicle parallel parking system  50  ( FIG. 5 ) for assisting a vehicle operator  52  with the task of parallel parking the vehicle  10 .  FIG. 1  may be useful for determining parallel parking space requirements so that it can be determined if a parallel parking space is large enough to accommodate the vehicle  10 . The parallel parking space requirements may be based on a vehicle length  20 , a vehicle width  22 , a minimum turning radius corresponding to the innermost circle  18  when the steering wheels  12  are at a maximum steering angle relative to a straight ahead travel steering angle, and a minimum arc radius  14  of a front corner  16  of the vehicle corresponding to the arc radius traced by the front corner  16  when the steering wheels  12  are at a maximum steering angle relative to a straight ahead travel steering angle. 
         [0016]      FIG. 2  illustrates a vehicle  10  equipped with a single proximity sensor  24 . As used herein, a proximity sensor is a device suitable to measure a distance or range to an object, for example the distance from the proximity sensor  24  to a first other vehicle  30  or a second other vehicle  32  located alongside the vehicle  10 , or a distance to a curb  34  alongside the vehicle  10 . Suitable devices for the single proximity sensor  24  include, but are not limited to, radar based range sensing devices, ultrasonic based range sensing devices, and laser based range sensing devices. Furthermore, cameras and other such optical imaging devices that create a two dimensional map of a scene are not within the meaning of a proximity sensor as used herein. Such optical imaging devices are specifically excluded from the list of devices suitable to use as the single proximity sensor  24  as such devices require complicated signal processing to determine a distance to an object, and so undesirably increase the cost and complexity of the vehicle  10 . 
         [0017]    In general, the single proximity sensor  24  is configured to output a clearance signal  54  ( FIG. 5 ) indicative of a clearance distance beside the vehicle  10 . The vehicle  10  is equipped with only the single proximity sensor  24  because, as will become apparent in the description below, the method for assisting a vehicle operator to parallel park a vehicle, and the vehicle parallel parking system for assisting a vehicle operator to parallel park a vehicle, only requires a single proximity sensor to operate. The vehicle  10  may also be equipped with a controller  26  configured to receive the clearance signal  54  from the single proximity sensor  24 . The controller  26  may also be configured to store the parallel parking space requirements described above, and receive and send signals to other vehicle systems such as a braking system  56  and a steering system  58  ( FIG. 5 ) as will be described in more detail below. Signals to and from the controller  26  may be sent through a vehicle wiring harness as is well known, or may be communicated wirelessly. 
         [0018]    The method of parallel parking the vehicle  10  may be generally divided into two distinct processes for reasons of simplifying an explanation of the method. Those distinct processes may be generally defined as a) determining that a parallel parking space is suitable, i.e.—large enough for the vehicle  10 , and b) parallel parking the vehicle  10 . It should be appreciated that the two processes are generally practiced together. However, it will also be appreciated that determining if a parallel parking space is suitable may be repeated multiple times on multiple parallel parking spaces found to be unsuitable until a suitable parallel parking space is actually found, and then executing the process of parallel parking the vehicle  10 . 
         [0019]      FIGS. 2A-2D  illustrate a progression of the vehicle  10  moving in the direction indicated by arrow  28  to detect a parallel parking space  36  suitable for parallel parking the vehicle  10  based on the clearance signal  54 .  FIG. 6  illustrates a method  600  that describes steps that may be taken by the vehicle parallel parking system  50  that generally correspond to  FIGS. 2A-2D . Step  610 , MOVE VEHICLE FORWARD, may include moving the vehicle  10  in a direction substantially parallel to the parallel parking space  36  while the controller  26  performs the steps described below. As used herein, substantially parallel to the parallel parking space  36  means that a first distance between the vehicle  10  and the first other vehicle  30  illustrated in  FIG. 2A  is about equal to a second distance between the vehicle  10  and the second other vehicle  32  illustrated in  FIG. 2D , for example the first distance and the second distance differing by less than 0.5 meters. If the first distance and the second distance differ by more than 0.5 meters, then it may indicate that the parking space is not parallel to the path traveled when the vehicle  10  moved from the location illustrated in  FIG. 2A  to the location illustrated in  FIG. 2D . A similar determination of the path traveled by the vehicle  10  may be based on a steady change in the distance to the curb  34  when the vehicle is moving forward. 
         [0020]    When the single proximity sensor  24  is mounted on the front corner  16  of the vehicle  10 , it is preferable that detecting the parallel parking space  36  be initiated when the vehicle is at or behind the location beside the first other vehicle  30  illustrated in  FIG. 2A . By starting at this location, when a suitable parallel parking space is detected, the vehicle  10  will then be near the location beside the second other vehicle  32  from where parallel parking can be initiated. Initiating the process of detecting the parallel parking space  36  may include the vehicle operator  52  pressing a button or issuing a voice command to activate the vehicle parallel parking system  50 . 
         [0021]    Step  620 , DETECT REAR BOUNDARY, may include the controller  26  detecting a rear boundary  38  of the parallel parking space  36  when the clearance signal  54  indicates a clearance distance  40  greater than a predetermined depth threshold, for example greater than 2.5 meters. It will be appreciated that the depth threshold may be adjusted based on the vehicle width, and/or a typical vehicle width for the region or country in which the vehicle parallel parking system  50  is being used. The clearance distance  40  may be a distance from the single proximity sensor  24  to the curb  34  as illustrated, or in the case where no curb or other object is present, the clearance distance  40  recorded by the controller  26  may be limited to some value relative to the distance between the vehicle  10  and the first other vehicle  30 . 
         [0022]    Step  630 , DETECT PARKING SPACE DEPTH, may include the controller  26  recording a number of clearance signal  54  values as the vehicle moves forward so that at a later time a minimum parking space depth value can be determined. By way of example and not limitation, if no curb  34  is present and a tree or fire hydrant is present alongside the parallel parking space  36  (not shown), then these objects may determine the minimum parking space depth value. 
         [0023]    Step  640 , DETECT FRONT BOUNDARY, may include the controller  26  receiving a clearance signal  54  indicating that the clearance distance is less than the depth threshold. As illustrated in  FIG. 2D , a front boundary  42  may be indicated by an abrupt decrease in the clearance distance corresponding to the back end of the second other vehicle  32 . Alternatively, the change in clearance distance may be gradual, for example caused by an angled section of the curb  34 , or the second other vehicle  32  being parked at an angle. Also, if the second other vehicle is not present and the curb  34  continues straight as illustrated, the vehicle parallel parking system  50  may be configured to designate a location as the front boundary  42  after the vehicle  10  has moved a distance greater than a minimum parallel parking space length. 
         [0024]    Step  650 , DETERMINE PARALLEL PARKING SPACE DEPTH, may include determining a parallel parking space depth  43  based on a minimum clearance distance detected in step  630  above while the clearance distance  40  is greater than the depth threshold. Alternatively, if no curb  34  or other objects are detected in step  630 , the vehicle parallel parking system  50  may be configured to set the parallel parking space depth  43  to a predetermined value based on the vehicle width  22  ( FIG. 1 ). 
         [0025]    Step  660 , DETERMINE PARALLEL PARKING SPACE LENGTH, may include determining a parallel parking space length  44  based on a distance traveled by the vehicle  10  between detecting the rear boundary  38  and the front boundary  42  of the parallel parking space  36 . 
         [0026]    Step  670 , STOP THE VEHICLE, may be performed by the vehicle operator  52  in response to a signal from the controller  26 , or may be performed by the controller  26  if the vehicle parallel parking system  50  is equipped for autonomous parallel parking. 
         [0027]    Step  680 , SUITABLE PARALLEL PARKING SPACE?, may include the controller processing data received from the clearance signal  54  and a wheel rotation sensor  70 , and determining if the parallel parking space  36  is large enough for parallel parking the vehicle  10 . If the parallel parking space is not suitable, for example not large enough to accommodate the vehicle  10 , then the method  600  may start again to search for a parallel parking space  36  that is suitable by moving the vehicle  10  forward past the second other vehicle  32  in search of another parallel parking space. If the parallel parking space  36  is suitable, then step  680  may include activating an audible indication such as a tone or voice announcement, or may include illuminating an indicator to indicate that the parallel parking space  36  is large enough for parallel parking the vehicle  10 . The suitability is generally based on the parallel parking space length  44  and the parallel parking space depth  43 . Then vehicle operator  52  or the controller  26 , depending on the configuration of the vehicle parallel parking system  50 , may proceed with the process of parallel parking the vehicle  10  by proceeding to method  700  ( FIG. 7 ) to parallel park the vehicle. 
         [0028]      FIG. 3  illustrates a first travel path  8 A for a vehicle  10 A when the vehicle  10 A is moved and the steering angle of the steering wheels is held constant at the steering angle illustrated for vehicle  10 A.  FIG. 3  also illustrates a second travel path  8 B for a vehicle  10 B when the vehicle  10 B is moved and the steering angle of the steering wheels is held constant at the steering angle illustrated for vehicle  10 B. By overlapping the first travel path  8 A and the second travel path  8 B, the location where the steering angle should be changed to parallel park the vehicle  10  should be evident. 
         [0029]      FIG. 7  illustrates a method  700  that assumes that the vehicle  10  is starting near the location suggested in  FIG. 4A .  FIG. 4A-4D  illustrate the progressive motion of the vehicle  10  during parallel parking into the parallel parking space  36 . While not specifically illustrated, it will be appreciated that the progressive motion of the vehicle  10  may also include moving the vehicle  10  forward within the parallel parking space  36  so as to center the vehicle  10  within the parallel parking space  36 . Centering the vehicle  10  may be performed by the operator or by the vehicle  10  if so equipped. 
         [0030]    Step  710 , START FIRST BACKING MANEUVER, may occur following step  680  ( FIG. 6 ) as described above, and may include notifying the vehicle operator  52  that the vehicle  10  is about to start parallel parking if the vehicle parallel parking system  50  is configured for autonomous parallel parking of the vehicle  10 , and so may include instructing the vehicle operator  52  to release the brake pedal  62  and/or shift a transmission  64  ( FIG. 5 ) into a specific gear. 
         [0031]    Step  720 , OPERATE STEERING MECHANISM TO FIRST POSITION, may include instructing the vehicle operator  52  to rotate the steering wheel  60  ( FIG. 5 ) in a direction until the steering system  58  indicates that the steering system  58  has been operated to a first position, such as illustrated in  FIG. 4A . If the vehicle parallel parking system  50  is equipped for autonomous operation, the vehicle operator  52  may be instructed to release control of the steering wheel, for example by instructing the vehicle operator  52  to remove the operator&#39;s hands from the steering wheel  60  so the controller  26  can operate the steering system  58  to the first position. 
         [0032]    Step  730 , BACK THE VEHICLE, may include the vehicle operator  52  or the controller  26  operating the braking system  56  to control the speed of the vehicle  10  while backing. 
         [0033]    Step  740 , ABORT PARALLEL PARKING?, may include the controller  26  determining that the vehicle operator  52  did not hold the steering system  58  in the first position, and so it will not be possible to properly parallel park the vehicle  10 . This determination is indicated by the YES response indicating that the operator should not continue to try and parallel park the vehicle, as illustrated by END PARKING. If the parallel parking maneuver is aborted, the vehicle operator may return the vehicle to a location near that indicated in  FIG. 4A  and attempt parallel parking the vehicle  10  again. It will be appreciated that step  740  may be repeated throughout the method  700  and is illustrated here as a non-limiting example. 
         [0034]    Step  750 , END FIRST BACKING MANEUVER?, is generally based on determining when the vehicle  10  has backed far enough with the steering system in the first position. The distance that the vehicle  10  has backed may be indicated by the wheel rotation sensor  70  ( FIG. 5 ) and communicated to the controller  26 . If NO, the vehicle continues to back-up and the vehicle  10  is monitored to see if parking should be aborted. If YES, the vehicle  10  may be stopped in preparation for step  760 . 
         [0035]    After the vehicle  10  backs to a location similar to that shown in  FIG. 4B , an embodiment of the method  700  may include a step of indicating when to start the second backing maneuver, followed a step of operating a steering mechanism such as a steering wheel  60  or a steering system  50  to a second position, and then actually backing the vehicle  10  as describe below. Depending on the configuration of the vehicle parallel parking system  50 , the steps of operating the steering mechanism to a second position and then backing the vehicle may be performed by the vehicle operator  52 , or the controller  26 . 
         [0036]    Step  760 , OPERATE STEERING MECHANISM TO SECOND POSITION, may include the vehicle operator  52  or the controller  26  operating the steering system  58  so the steering wheels are at a second position corresponding to that illustrated in  FIG. 4B . Operating the steering mechanism may also include adjusting vehicle speed based on the rate at which the steering is being adjusted. For example, stop the vehicle  10  if the steering mechanism is not operating or move the vehicle  10  slowly if steering is operating slowly. Method  700  may be continued by executing step  770 , BACK THE VEHICLE, to continue to move the vehicle into the parallel parking space  36 . 
         [0037]    Step  780 , MINIMUM ARC RADIUS CLEARS FRONT BOUNDARY?, may include the controller  26  monitoring the clearance signal to determine if the front corner  16  of the vehicle  10  will clear the second other vehicle  32 , as illustrated in  FIG. 4C . If NO, parallel parking may be stopped, and may include moving the vehicle  10  forward to a location similar to that illustrated in  FIG. 4A  so parallel parking of the vehicle  10  may be attempted again. If YES, parallel parking may continue and so the vehicle  10  continues to back. In one embodiment, the controller  26  may determine that the minimum arc radius will clear the front boundary of the parallel parking space, and that determination may include the controller  26  determining that the clearance signal  54  indicates a clearance distance greater than a clearance threshold, for example a clearance distance greater than 0.2 meters. 
         [0038]    Step  790 , ABORT PARALLEL PARKING?, may be similar to step  740  described above and may stop or end the parallel parking process if, for example, it is determined that the vehicle operator  52  did not hold the steering mechanism in the second position. If YES, then END PARKING stops the parallel parking process. If NO, then the parallel parking process may continue. 
         [0039]    Step  800 , END SECOND BACKING MANEUVER?, may include the controller  26  determining that the vehicle has backed far enough while the steering system  58  is in the second position. If NO, then the vehicle  10  continues to back. If YES, then the second backing maneuver is completed. 
         [0040]    Step  810 , CENTER THE VEHICLE, is an optional step that may be performed so a first separation between the vehicle  10  and the first other vehicle  30  and a second separation between the vehicle  10  and the second other vehicle  32  may be about the same. Depending on the configuration of the vehicle parallel parking system  50 , centering the vehicle may be performed by the vehicle operator  52  or the controller  26 . By centering the vehicle  10  in the parallel parking space  36 , it may make it more convenient for the first other vehicle  30  and/or the second other vehicle  32  to exit their respective parallel parking spaces without contacting the vehicle  10 . 
         [0041]      FIG. 5  illustrates an embodiment of the vehicle parallel parking system  50  for assisting a vehicle operator  52  to parallel park a vehicle  10 . In one embodiment, the vehicle parallel parking system  50  may include a single proximity sensor  24  configured to output a clearance signal  54  indicative of a clearance distance beside the vehicle  10 . The vehicle parallel parking system  50  may include a controller  26  configured to store parallel parking space requirements based on a vehicle length  20  ( FIG. 1 ), a vehicle width  22 , an innermost circle  18  or a minimum turning radius  18 , and a minimum arc radius of a travel path  8  of a front corner  16  of the vehicle  10 . The controller  26  may also be configured to receive the clearance signal  54  from the single proximity sensor  24 , detect a parallel parking space  36  suitable for parallel parking the vehicle  10  based on the clearance signal  54 . 
         [0042]    Continuing to refer to  FIG. 5 , the controller  26  may also be configured to indicate when to start a first backing maneuver based on a suitable parallel parking space  36  being detected. An example of the first backing maneuver is illustrated as beginning with the vehicle  10  in a position illustrated in  FIG. 4A  and backing to a position illustrated in  FIG. 4B . The controller  26  may also be configured to indicate when to stop or finish the first backing maneuver which may be followed or temporally coincident with indicating to start a second backing maneuver. An example of a second backing maneuver is illustrated as beginning with the vehicle in a position illustrated in  FIG. 4B , backing through a position illustrated in  FIG. 4C , and backing to a position illustrated in  FIG. 4D . The controller  26  may also be configured to indicate when to end the second backing maneuver, for example when the vehicle  10  reaches the position illustrated in  FIG. 4D . The indications provided by the controller  26  may include activating an audible tone or voice command to notify the vehicle operator  52 . For case where the vehicle parallel parking system  50  is configured to autonomously parallel park the vehicle  10 , the indications provided by the controller may be signals to the steering system  58  and or the braking system  56  to control movement of the vehicle  10   
         [0043]    In one embodiment of the vehicle parallel parking system  50 , the single proximity sensor  24  may is preferably mounted on a front corner  16  of the vehicle  10 , as this location is particularly convenient for typical situations where the vehicle  10  is traveling forward while searching for a parallel parking space  36  that is suitable. 
         [0044]    An embodiment of the vehicle parallel parking system  50  may also include a transmission  64  configured to receive a gear selection signal  66  from the controller  26  for controlling vehicle direction, and a brake system  56  configured to receive a brake signal  68  from the controller  26  for stopping the vehicle. The vehicle parallel parking system  50  may also include a distance traveled sensing means for measuring a distance traveled by the vehicle  10 . A non-limiting example of distance traveled sensing means is a wheel rotation sensor  70 , as illustrated in  FIG. 5 . Alternatively, the distance traveled sensing means may be a GPS system or a system that determines vehicle motion based on inertial guidance. The vehicle parallel parking system  50  may also include a steering angle sensor within the steering system  58  configured to output a steering angle signal  72  indicative of a steering angle of the steering wheels  12  of the vehicle  10 . 
         [0045]    While not specifically illustrated, the controller  26  may a memory device to store parallel parking space requirements and an input configured to receive the clearance signal  54  from the single proximity sensor  24 . The controller may also include a processor configured to detect a parallel parking space  36  suitable for parallel parking the vehicle  10 , indicate when to start a first backing maneuver, indicate when to stop or end the first backing maneuver followed by or coincident with indicating when to start a second backing maneuver, and indicate when to end the second backing maneuver. 
         [0046]    Accordingly, a vehicle parallel parking system  50 , a controller  26  for the vehicle parallel parking system  50 , and a method  600 , 700  for assisting a vehicle operator to parallel park a vehicle  10  is provided. The system and method relies on only a single proximity sensor  24  to detect a suitable parallel parking space  36  and parallel park the vehicle  10 . The single proximity sensor  24  only need indicate distance or range, and as such cameras and other such devices that add undesirable complexity and cost to the vehicle are avoided. Detecting a suitable parking space  36  and parallel parking the vehicle  10  may have the vehicle operator  52  operate the vehicle  10  relying on the vehicle parallel parking system  50  provide indications of when to change steering wheel angle and back the vehicle  10 , or may be an autonomous system that controls the vehicle  10  without any intervention on the part of the vehicle operator  52 . 
         [0047]    While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.