Abstract:
A direction determination system particularly useful with a retrofit automatic steering system compares the rate of change of vehicle yaw rate and the rate of change of the steering wheel position. A determination of the direction is made by comparing the sign of the steering wheel angle change and the sign of the yaw rate change. The GPS course can be monitored after the direction has been determined to provide a more rapid response to changing direction. A change in direction is indicated when the vehicle speed transitions to zero and the GPS course generally reverses. Even when the direction is known, the steering wheel angle and yaw rate changes can be monitored to verify that the direction indication is correct.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to automatic steering systems and, more specifically, to determine operational direction of a vehicle from vehicle yaw rate and steering wheel movement.  
       BACKGROUND OF THE INVENTION  
       [0002]     In order to work properly, an automatic steering system for a vehicle must recognize if the vehicle is operating in a forward mode or a reverse mode. To turn the vehicle a given direction, movement of the steering device during operation of the vehicle in a forward mode typically is the opposite of the movement of the device during operation of the vehicle in reverse. Many presently available integrated automatic steering or tracking systems can determine the vehicle gear selected and the direction of travel. However, some non-integrated steering systems lack a transducer or other attachment that can readily communicate the actual vehicle operational direction to the controller. An example of a non-integrated system is a retrofittable steering control with a drive mechanism that attaches to a steering column or contacts an existing steering wheel for automatic steering control such as described in my commonly assigned U.S. patent application Ser. No. 11/019,482 entitled Automatic Steering Control, filed 21 Dec. 2004. Even in systems wherein the selected gear and direction is readily determinable, further verification of the direction is often desired.  
       SUMMARY OF THE INVENTION  
       [0003]     It is therefore an object of the present invention to provide an improved system and method for determining vehicle direction. It is a further object to provide such a system and method which overcomes most or all of the aforementioned problems.  
         [0004]     It is another object to provide an improved system and method for determining vehicle direction which can operate independently of gear select switches and which is particularly useful with retrofittable steering controls.  
         [0005]     A system constructed in accordance with the present invention compares the rate of change of the yaw rate and the rate of change of the steering wheel or steering control position. If the steering wheel is turned to the right and the vehicle is in a forward gear, then the vehicle yaw rate will go to the right. If the steering wheel is turned to the right and the vehicle is in reverse gear, the vehicle yaw rate will go to the left. Upon vehicle start up, the direction is set to unknown. Once vehicle speed, steering wheel turn and vehicle yaw reach preselected thresholds, a determination of the vehicle direction can be made by comparing the sign of the steering wheel angle change and the sign of the yaw rate change. If the signs match, then the vehicle is in a forward gear. If the signs do not match, then the vehicle is in reverse.  
         [0006]     As a further enhancement to this method, the GPS course can be monitored after the direction has been determined to provide a more rapid response to changing direction. A change in direction is indicated when the vehicle speed transitions to zero and GPS course change approaches 180 degrees. Even when the direction is known, the steering wheel angle and yaw rate changes can be monitored to verify that the direction is correct.  
         [0007]     The system provides a direction indication without need for an input from the vehicle transmission or shift control. Therefore, a direction determination input for an automatic steering system, even a system which is retrofitted to an existing vehicle is easily attainable.  
         [0008]     These and other objects, features and advantages of the present invention will become apparent from the description which follows taken with the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a schematic representation of steering structure for converting-a manual steering system to an automatic system, the system including direction determination structure.  
         [0010]      FIG. 2  is an exploded view of a portion of the steering structure of  FIG. 1 .  
         [0011]      FIG. 3  is a flow chart illustrating a method for determining vehicle direction.  
         [0012]      FIG. 4  is a flow chart illustrating a method for continually monitoring the vehicle direction once an initial direction determination has been made.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]     Referring now to  FIG. 1 , therein is shown an off-road vehicle  10  such as a tractor or utility vehicle having an operator station  12  supported for movement over the ground by steerable wheels  14 . The wheels  14  are connected to a conventional steering mechanism or control  16  which includes a rotatable steering shaft  20  supported within a steering column  22  which projects upwardly at the operator station  12 . A steering wheel  30  with a hand grip portion  31  is supported at the upper end of the shaft  20  for manual steering operation by the operator.  
         [0014]     As shown, the steering wheel  30  is part of conversion structure indicated generally at  32  for providing an automatic steering function on a vehicle normally equipped with manual steering only. Alternatively, the original steering wheel of the vehicle may be mounted on the conversion structure  32 . The conversion structure is fully described in my aforementioned co-pending application U.S. patent application Ser. No. 11/019,482 entitled Automatic Steering Control.  
         [0015]     Pulley structure  34  is connected for rotation with the shaft  20  about the shaft axis at a location adjacent the connection of the steering wheel  30  with the shaft  20 . A motor  40  is supported from the column  22 . Pulley structure  44  drivingly connects the motor  40  to the pulley structure  34 . As shown, the pulley structures  34  and  44  are pulleys connected by a chain, conventional drive belt or timing belt arrangement  46 . However, other types of drives such as gear drives may also be used. For example, a motor may be mounted on the end of the steering shaft  20  to provide direct drive to the shaft  20  at a location offset from hand grip portion  31 .  
         [0016]     A processor  50  is located on the vehicle  10  and includes a control output  52  connected through a CAN harness  54  to an input  56  of the motor  40 . A position feedback output  58  on the motor  40  is connected to an input of the processor  50 . As shown, the motor  40  is an electric stepper motor, and the feedback device is an encoder located on the motor  40  and providing signal over a feedback line  58  indicative of the number of steps the motor  40  has moved. The motor  40  remains drivingly connected to the steering shaft  20  in both a manual steering mode and an automatic steering mode so that the encoder is capable of providing a shaft position signal to the processor  50  in both modes.  
         [0017]     The processor  50  is connected to position sensor structure indicated generally at  60  in  FIG. 1 , such as a conventional global positioning system (GPS) with a receiver  61  that receives signals  62  from one or more remote locations. Additional correction inputs such as a RTK ground based differential correction input may be provided from an RTK radio  63 , and a terrain compensation input may be provided from a terrain compensation module (TCM)  65 . The TCM  65  corrects GPS data for roll angle and yaw as the vehicle  10  moves over uneven terrain and provides a yaw rate signal utilized in the direction determination feature discussed in detail below.  
         [0018]     The system  60  is connected through CAN  54  to an input of the processor  50 . A steering system unit (SSU)  70  is connected through a CAN harness  71  and a system connector  72  to the CAN harness  54  and to a system display  73 . The SSU  70  receives control information from the processor  50  and position feedback information via line  58  from the encoder on the motor  50 . An on-off and resume switch  78  is connected to the SSU  70 .  
         [0019]     The processor  50  determines the position of the vehicle and compares the position to a desired position and intended path of the vehicle. An error signal is generated, and the motor  40  is activated to move a preselected number of steps depending on the error signal. Detection devices, such as a ground speed detector and lateral velocity, provide signals utilized by the processor  50  to increase the accuracy of the automatic steering system.  
         [0020]     If the number of steps reported by the motor encoder to the processor  50  outside a range expected by the processor, the system assumes the operator wants control and turns off power to the stepper motor  40 . Also, if the encoder determines there is steering wheel movement when no change in position was requested by the processor, the power to the motor  40  is interrupted.  
         [0021]     An adapter bracket  80  connects the motor  40  to the steering column  22  or other convenient location adjacent the upper end of the steering shaft  20 . The bracket  80  includes a U-clamp  82  secured to the column  22  and having an arm support  84  pivotally connected to ends of a pair of arms  86 . A second pair of arms  88  is pivotally connected to opposite ends of the arms  86  and supports a motor mount  90 . The stepper motor  40  is bolted to the mount  90  and includes a drive shaft  94  which receives the pulley  44 . The pulley structure  34  is supported for rotation on the mount  90  by insert and bearing structure  100  secured by bolts  104  and snap ring  106 . A replaceable insert  110  is captured within the bearing structure  100  for rotation together with the upper end of the shaft  20  and the pulley  34 . The insert  110  has an inner configuration  112  adapted to be received on the splined or keyed end of the steering shaft  20  for the particular vehicle being converted for automatic steering. A cover  118  is secured to the mount  90  and generally encloses the pulley structures  34  and  44 . The structure  32  can be easily positioned by selectively locating the clamp  82  and pivoting the arms  86  and  88 . Once the structure  32  is properly positioned with the insert  110  over the steering shaft  20 , the linkage  80  can be anchored to a fixed surface to prevent rotation of the motor assembly.  
         [0022]     The GPS system  60  provides speed, course, and timing information. The processor  50  uses the speed information to determine when the vehicle  10  has transitioned between moving and stopped states. The course information is used to continually monitor the direction once an initial direction determination has been made. Alternatively, another type of position sensor system indicated by the broken lines at  60 ′ in  FIG. 1  can be used to provide the speed, course and timing information.  
         [0023]     The encoder on the motor  40  provides a steered angle signal via line  58  is used to measure vehicle steered angle. Although this signal is shown as generated from the encoder on the motor  40 , other types of conventional signal generating devices indicated at  40 ′ can be used to measure the steering wheel angle, an actual steered wheel angle, or an articulation angle for a four-wheel drive vehicle  10  to provide the steered angle signal.  
         [0024]     A yaw rate signal is provided to the processor  50  by the TCM  65 . Alternatively, a yaw rate sensor or gyro such as shown by the broken lines at  65 ′ associated with the vehicle  10  may be connected to the processor  50 . Yaw rate signals may be generated by monitoring the rate of change of the GPS course, or by measuring the vehicle attitude using two GPS receivers. The processor  50  performs the necessary comparisons and calculations as described below. As shown in  FIG. 1 , the processor  50  comprises a steering controller. However, other types of processors, such as the processor in the GPS system  60  or in the display  73 .  
         [0025]     Upon initiation of the routine at  100  ( FIG. 3 ), the processor  50  checks the status information sent by the GPS  60  to verify that the GPS is available at step  102 . If GPS is available at  102 , then the processor  50  obtains vehicle speed from the GPS and compares it to a threshold at  104 . Speed can also be obtained from another source such as the wheel speed, radar speed, or other vehicle-indicated speed. The step  104  is performed to verify that the vehicle speed is high enough to guarantee that the speed reading is not merely noise and that the vehicle is actually moving. For example, the system shown uses a speed of one mile per hour as the threshold speed.  
         [0026]     If the speed is greater than the threshold at  104 , the processor then obtains the rate of change of the steering wheel angle or steering control and yaw rate over a period of time at  106  and  108 . The system as shown, for example has an elapsed time threshold of approximately three seconds. The time is obtained from the GPS signal but timing information can also be obtained from an internal timer on the  
         [0027]     At the step  108 , the processor  50  compares the steering wheel angle or steering control change over the time interval of the step  106  to a threshold to determine if there has been enough control motion to cause a change in the yaw rate. By way of example, the current threshold, for steering wheel angle is 45°. If the control angle is greater than the prescribed threshold, the processor  50  compares path curvature change over the time interval to a threshold at  110  to determine if then steering radius has changed. Curvature is calculated using the yaw rate and the ground speed. The sign of the path curvature is compared to the sign of the control motion at step  112 . If curvature and control motion signs are the same, then the direction is set to forward in the processor  50  at  114 . If the curvature and wheel motion signs are not the same, then the direction is set to reverse at  116 .  
         [0028]     The process can be repeated to verify that the direction is correct. If a determination is made during operation that conflicts with the currently stored direction, then the series of questions will be repeated once more to verify that field conditions have not caused a momentary false reading.  
         [0029]     Referring to  FIG. 4 , therein illustrates a method for continually monitoring the direction once a direction determination has been made. This extension of the method described directly above provides fast response to changing direction. A change in direction is indicated when the vehicle speed transitions to zero and the GPS course changes more than a preselected number of degrees.  
         [0030]     The routine is begun at  200 , and once a direction has been established at  202 , the processor  50  compares the speed of the vehicle  10  to a threshold at  204  to determine if the vehicle has come to a stop. The direction may change from forward to reverse, or from reverse to forward, when the vehicle  10  has come to a stop. Once it is determined at  204  that the vehicle has come to a stop, the vehicle course when the transition to zero speed occurred is stored in the processor  50  at  206 . The vehicle speed is then monitored and compared to a threshold at step  208  to determine when the vehicle starts to move again. The threshold of the current system, for example, is 0.5 mph. If the speed is not greater than the threshold; the integral of the yaw rate is calculated at  210  and the stored course is changed by that amount. The integration is necessary because the vehicle may be rotating while traveling below the speed threshold. Such movement is possible, for example, on track tractors which can rotate without moving forward.  
         [0031]     Once the speed becomes greater than the threshold, then the new course is subtracted from the stored course at  212 . If the difference is greater than a preselected angle, which for example is 120°, then a reversal of direction is signaled at  214 , and the direction is toggled at  216  in the processor. If the difference is less than this threshold, then the direction has not changed, and the system returns to the start and monitors for another transition to zero speed.  
         [0032]     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.