Method and apparatus for braking and stopping vehicles having an electric drive

Abstract

A method and apparatus are provided for braking and stopping a vehicle whose powertrain includes an electric drive. The electric drive is used to generate braking torque which is used to decelerate the vehicle down to a full stop. The braking torque is achieved using any of several closed loop speed control systems. The system can be used as a substitute for or as a supplement to conventional friction bakes.

1 . A method of braking and stopping a vehicle having at least one traction wheel driven by an electric motor, comprising the steps of: 
 sensing a speed parameter related to the speed of the vehicle;    sensing a commanded braking rate;    generating a motor control signal to achieve a desired braking action;    producing a negative torque using the electric motor;    applying a braking force to the traction wheel using the negative torque produced by the electric motor; and,    controlling the amount of negative torque produced by the electric motor using the motor control signal to achieve the commanded braking rate.    
   
   
       2 . The method of  claim 1 , wherein the motor control signal is a torque command signal.  
   
   
       3 . The method of  claim 1 , wherein, the motor control signal is a speed command signal  
   
   
       4 . The method of  claim 1 , wherein, the motor control signal is a power command signal.  
   
   
       5 . The method of  claim 1 , wherein, the motor control signal is a force command signal.  
   
   
       6 . The method of  claim 1 , wherein the motor control signal is generated using the sensed speed parameter and the commanded braking rate.  
   
   
       7 . The method of  claim 1 , wherein the step of applying braking force is continued until the vehicle is stopped.  
   
   
       8 . The method of  claim 1 , wherein the step of generating the motor control signal comprises: 
 producing a torque command signal used to control the motor until the vehicle decelerates to a preselected speed, and    producing a speed control signal used to control the motor after the vehicle has decelerated to the preselected speed.    
   
   
       9 . The method of  claim 1 , wherein the step of applying braking force is continued until the vehicle decelerates to a stop.  
   
   
       10 . The method of  claim 1 , wherein the step of generating the motor control signal comprises producing a torque control signal based on the positions of the vehicle's brake and accelerator pedals.  
   
   
       11 . The method of  claim 1 , wherein the step of generating the motor control signal comprises: 
 generating a negative torque control signal used to control the amount of negative torque produced by the electric motor until the sensed speed parameter reaches a preselected value, and    then, generating a speed control signal used to control the speed of the electric motor after the sensed speed reaches the preselected value.    
   
   
       12 . The method of  claim 1 , wherein the step of sensing the speed parameter comprises: 
 sensing the speed of the motor, and    sensing the speed of at least one wheel of the vehicle.    
   
   
       13 . The method of  claim 1 , wherein the step of sensing the commanded braking rate comprises sensing a parameter related to the operation of the brake pedal.  
   
   
       14 . The method of  claim 1 , wherein the step of generating the motor control signal comprises: 
 generating a torque command signal,    generating a speed command signal,    modifying the speed command signal using the torque command signal.    
   
   
       15 . The method of  claim 14 , wherein; 
 the step of sensing the speed parameter comprises generating a motor speed signal representing the speed of the electric motor, and    the step of generating the motor control signal comprises feeding back the motor speed signal in a motor control feedback loop, and controlling the motor using the feedback signal and the modified speed command signal.    
   
   
       16 . A method of braking and stopping a vehicle powered by an electric motor driving at least one traction wheel, comprising the steps of: 
 sensing a speed parameter related to the speed of the vehicle;    sensing a commanded braking rate;    generating a commanded motor speed signal;    generating a torque limiting signal using the commanded braking rate;    generating a torque command signal using the commanded motor speed signal and torque limiting signal;    controlling the motor using the torque command signal to produce negative torque; and,    applying a braking force to the traction wheel using the negative torque.    
   
   
       17 . The method of  claim 16 , wherein the step of sensing the speed parameter comprises sensing the speed of the motor.  
   
   
       18 . A method of  claim 16 , wherein the step of sensing the speed parameter comprises sensing the speed of at least one wheel of the vehicle.  
   
   
       19 . The method of  claim 16 , wherein the step of sensing the commanded braking rate comprises sensing a parameter related to the operation of a brake pedal on the vehicle.  
   
   
       20 . The method of  claim 16 , wherein the step of generating the torque command signal comprises using the sensed speed parameter as a feedback signal in a closed feedback loop, and performing dynamic compensation of the torque command signal using the feedback signal.  
   
   
       21 . The method of  claim 16 , wherein the step of generating the torque command signal comprises modifying the torque command signal using the torque limiting signal.  
   
   
       22 . The method of  claim 16 , wherein the torque limiting signal is determined by at least one of the brake pedal or accelerator pedal inputs.  
   
   
       23 . The method of  claim 16 , further comprising the steps of: 
 controlling the motor using the torque command signal to produce positive torque; and,    applying a braking force to the traction wheel using the positive torque.    
   
   
       24 . A system for braking and stopping a vehicle powered by an electric motor driving at least one traction wheel, comprising: 
 a torque command signal generator for generating a torque command signal used to drive the motor and produce negative torque for braking the traction wheel; and,    a torque limiting signal generator for converting brake pedal and accelerator pedal position values into torque limiting signals used to modify the torque command signal.    
   
   
       25 . The system of  claim 24 , wherein the torque command signal generator comprises a dynamic compensator for compensating for the effects of changes in motor speed.  
   
   
       26 . The system of  claim 24 , wherein the torque command signal generator comprises a closed speed control loop.  
   
   
       27 . The system of  claim 26 , wherein the torque limiting signal generator includes a bipolar signal generator.