Abstract:
A method of monitoring and deactivating a steer-by-wire system capable of several performance levels of a vehicle, including measuring an angle of an actuated road wheel of the vehicle, a steering angle of a steering device of the vehicle, and a velocity of the vehicle; determining and storing an acceptable angle range based on the measured steering angle of the steering device and the measured velocity; comparing the measured angle of the actuated road wheel to the acceptable angle range; and implementing a procedure based on the comparison of the measured angle to the acceptable angle range that complies with a particular set of rules.

Description:
TECHNICAL FIELD 
     This invention relates generally to monitoring systems for steer-by-wire systems. 
     BACKGROUND 
     Consumer demand for lighter weight, more fuel-efficient vehicles coupled with major advances in technology has resulted in the advent of the steer-by-wire system. The steer-by-wire system is able to reduce weight by eliminating the large mechanical linkage associated with conventional steering systems. The steer-by-wire system uses actuators connected to both the wheels of the vehicle and a control unit to turn the wheels and control the angle to which they are turned. While the steer-by-wire system has been successful in reducing the weight of vehicles and, therefore, contributing to greater fuel efficiency, it has also raised concerns about steering accuracy. 
     Whereas conventional steering systems use a mechanical linkage to connect the steering wheel to the road wheels, the steer-by-wire system uses no such device. Much of the concern related to the use of steer-by-wire systems stems from the fact that the system uses no mechanical linkage. A major concern is that the electrical connection used by the steer-by-wire system will result in reduced steering accuracy and the driver of the vehicle will receive no warning of such accuracy reduction. 
     In light of the concerns discussed above, a monitoring and deactivating system for a steer-by-wire system of a vehicle is needed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view schematic of a monitoring system for a steer-by-wire system. 
     FIG. 2 is a flow chart of a method for monitoring and deactivating a steer-by-wire system. 
    
    
     DETAILED DESCRIPTION 
     The following description of the preferred embodiment of the invention and the preferred method of using the invention are not intended to limit the scope of this invention to this preferred embodiment and method, but rather to enable any person skilled in the art of steer-by-wire systems to make and use the invention. 
     As shown in FIG. 1, the invention is a monitoring and deactivating system  10  for a steer-by-wire system of a vehicle  32 , which includes a sensor subsystem  12 , an actuated road wheel  34 , a warning system  16 , and a controller  18 . The monitoring and deactivating system  10  is capable of monitoring an angle of the actuated road wheel  34  and reducing or increasing performance of a steer-by-wire system of the vehicle  32  when appropriate. In addition, the monitoring and deactivating system  10  is capable of warning a driver of the changes in performance of the steer-by-wire system. 
     The sensor subsystem of the preferred embodiment  12  includes a road wheel sensor  22 , a steering device sensor  24 , and a velocity sensor  26 . The purpose of the road wheel sensor  22  is to measure the angle to which the road wheel  20  is turned. Preferably, the road wheel sensor  22  is a conventional sensor. Alternatively, any suitable device capable of measuring the angle of the road wheel  20  and transmitting that information may be used. The purpose of the steering device sensor  24  is to measure the steering angle of a steering device  30 . Preferably, the steering device  30  is a conventional steering wheel and the steering device sensor  24  is a conventional sensor. Alternatively, a joystick, a touch pad, a track ball, or any other suitable steering device may be used. Further, any suitable device capable of measuring the steering angle of the steering device  30  and transferring that information to a controller  18  may be used as the steering device sensor  24 . The purpose of the velocity sensor  26  is to measure the velocity of the vehicle  32 . Preferably, the velocity sensor  26  is a conventional sensor. Alternatively, any suitable device capable of measuring the velocity of the vehicle  32  and transferring that information to the controller  18  may be used. In the preferred embodiment, as shown in FIG. 1, the velocity sensor  26  is coupled to the controller  18  by wiring  28 . However, as discussed above, the connection depends on the type of controller  18  and velocity sensor  26  being used. Alternatively, the velocity sensor  26  may be coupled to the controller  18  by infrared means, radio means, or any other suitable means of transferring information from the velocity sensor  26  to the controller  18 . 
     The actuated road wheel  34  of the preferred embodiment includes an actuator  14  and a road wheel  20 . The purpose of the actuator  14  is to turn the road wheel  20  and the purpose of the road wheel  20  is to direct the vehicle  32 . Preferably, the actuator  14  is a conventional electrical power-assisted steering mechanism connected to the road wheel  20  through conventional electric motors and conventional rack and pinion subsystems. Alternatively, any other suitable device capable of independently turning the road wheel  20  may be used. The road wheel  20  is preferably a conventional road wheel, but any other suitable device capable of directing the vehicle  32  may be used. 
     The purpose of the warning system  16  of the preferred embodiment is to, upon activation of the system, provide warning to a driver of the vehicle  32  that the performance of the steer-by-wire system has been or will be reduced. Similarly, the warning system  16  may be used to warn the driver of the vehicle  32  that the performance of the steer-by-wire system has been or will be increased. Activation of the warning system  16  preferably includes a transmission of audio and visual signals. Alternatively, any signal that is capable of adequately warning the driver of a change in performance of the steer-by-wire system may be used. 
     The purpose of the controller  18  is to control the actuator  14  of the actuated road wheel  34  based on input from the sensor subsystem  12  and to activate the warning system  16  accordingly. The controller  18  is preferably a conventional controller containing, among other things, a processor and a memory bank. Alternatively, any other suitable device capable of controlling the actuator  14  and warning system  16  based on input received from the sensor subsystem  12  may be used. As discussed above, the controller  18  is connected to the road wheel sensor  22 , the steering device sensor  24 , the velocity sensor  26 , the actuator  14 , and the warning system  16  by wiring  28 . Alternatively, the controller  18  may be coupled to the road wheel sensor  22 , the steering device sensor  24 , the velocity sensor  26 , the actuator  14 , and the warning system  16  by infrared means, radio means, or any other suitable means of transferring information from the sensors to the controller  18  and from the controller  18  to the warning system  16  and the actuator  14 . 
     As illustrated in FIG. 2, the preferred method of using the present invention involves: measuring the angle of the road wheel  20 , the steering angle of the steering device  30 , and the velocity of the vehicle  32 ; determining an acceptable angle range; comparing the measured angle of the road wheel  20  to the acceptable angle range; and reducing or increasing the performance of the steer-by-wire system and activating a warning system  16  based on the above comparison when appropriate. 
     The angle of the road wheel  20 , the steering angle of the steering device  30 , and the velocity of the vehicle  32  are measured using the road wheel sensor  22 , the steering device sensor  24 , and the velocity sensor  26 , respectively, as discussed above, and that information may be transmitted to the controller  18  via wiring  28 . 
     The acceptable angle range is determined by the controller  18  based on the measured steering angle of the steering device  30  and velocity of the vehicle  32 . Based on this information, the controller  18  is able to calculate a theoretical maximum acceptable angle for the road wheel  20  and a theoretical minimum acceptable angle for the road wheel  20 . Angles less than or equal to the theoretical maximum angle and greater than or equal to the theoretical minimum angle constitute the acceptable angle range. The velocity of the vehicle  32  is used since acceptable angle differences at parking speeds could be less safe at highway speeds, and since the high degree of accuracy required at highway speeds might not be available at parking speeds due to environmental factors. Preferably, the acceptable angle range associated with various velocities and steering angles is stored within the memory bank of the controller  18  as a look-up table. Alternatively, the controller  18  may calculate the acceptable angle range as input is received from the sensor subsystem  12  or the controller  18  may use any other suitable method for determining the acceptable angle range. 
     Once input has been received from the sensor subsystem  12  and the controller  18  has determined the acceptable angle range, the controller  18  then compares the measured angle of the road wheel  20  to the acceptable angle range. The processor within the controller  18  preferably carries out this comparison, but any other suitable device capable of comparing the measured angle of the road wheel  20  to the acceptable angle range may be used. If the measured angle of the road wheel is outside the acceptable range, then the system gradually reduces the actuation range of the road wheel  34  (the “performance”) of the steer-by-wire system, which allows the system and/or the driver to recover from the situation as discussed below. 
     Depending on the results of the comparison discussed above, the performance of the steer-by-wire system may be reduced, increased, or maintained. There are preferably four levels of performance at which the steer-by-wire system can operate: a full performance level, two intermediate performance levels, and a lowest performance level. Alternatively, any suitable number of performance levels may be used. The preferred performance levels are as follows: the full performance level includes an activation range; a first intermediate performance level includes 90% of the activation range; a second intermediate performance level includes 50% of the activation range; and the lowest performance level includes 0% of the activation range. Alternatively, any other suitable levels of performance may be used. 
     The controller  18  uses input data from the steering device sensor  24  and the road wheel sensor  22  to choose a proper level of performance. For every steering angle of the steering device  30  of a steer-by-wire system at full performance there is a corresponding desired angle of the road wheel  20 . When the steer-by-wire system is at the full performance level, the controller  18  receives input from the steering device sensor  24  regarding the steering angle and it outputs a command to the actuator  14  to turn the road wheel  20  to the corresponding desired angle. However, when the steer-by-wire system is not at the full performance level, the upper limit of the requested actuation is reduced or “truncated” from the full activation range or capability. For example, the controller  18  of the steer-by-wire system at the first intermediate lever (90%) may request an actuation requiring the full actuator capability corresponding to a command current of 100 Amps, but will only receive actuation corresponding to a command current of 90 Amps. On the other hand, at the same performance level, the controller may request an actuation requiring less than the full actuator capability, for example a command current of 60 Amps, and will receive actuation corresponding to a command current of 60 Amps. 
     If the measured angle of the road wheel  20  of the steer-by-wire system at the full performance level is within the acceptable angle range, then the steer-by-wire system remains at the full performance level. However, if the measured angle at the full performance level is outside the acceptable angle range, then the warning system  16  is activated and the performance level is reduced to an intermediate performance level. 
     If the measured angle of the road wheel  20  of the steer-by-wire system at the intermediate performance level is within the acceptable angle range, then the performance is increased to a higher performance level. For example, a steer-by-wire system at the lower intermediate performance level would be increased to the higher intermediate performance level, whereas a steer-by-wire system at the higher intermediate performance level would be increased to the full performance level. However, if the measured angle at the intermediate performance level is outside the acceptable angle range, then the warning system  16  is activated and the performance level is reduced to a lower performance level. For example, a steer-by-wire system at the higher intermediate performance level would be reduced to the lower intermediate performance level, whereas a steer-by-wire system at the lower intermediate performance level would be reduced to the lowest performance level. 
     If the performance of the steer-by-wire system is reduced to the lowest performance level, the warning system  16  is activated and the transmission of signals from the controller  18  to the actuator  14  ceases, which completely deactivates the steer-by-wire system. Restarting the vehicle  32  preferably reactivates the steer-by-wire system. Upon starting the vehicle, the steer-by-wire system is reset to full performance and monitoring of the steer-by-wire system is continued in the same manner as previously discussed. 
     The method and apparatus discussed above is preferably adapted to monitor and deactivate one, two, three, or four actuated road wheels  34 . Alternatively, the method and apparatus for monitoring and deactivating the steer-by-wire system may be adapted to be used with vehicles having any number of actuated road wheels  34 . 
     As any person skilled in the art of steer-by-wire systems will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiment of the invention without departing from the scope of this invention defined in the following claims.