Method and apparatus to control coordinated wheel motors
A method and system providing coordinated torque control and speed control of a vehicle equipped with individual wheel motors, a steering system, and yaw-rate detection to achieve a desired yaw moment for the vehicle, based upon operator input and vehicle operation, is described. This includes determining a commanded steering angle, and a yaw-rate error, based upon the commanded steering angle and detected yaw-rate. A desired wheel motor yaw torque moment is calculated. First and second torque moments are calculated for inner and outer motored wheels, based upon the desired wheel motor yaw torque moment. First and second ideal wheel speeds are calculated for the inner and outer motored wheels, based upon the commanded steering angle. Torque and speed at each inner motored wheel and each outer motored wheel are calculated, based upon the yaw-rate error, the first and second torque moments, and the first and second ideal wheel speeds.
1. Method to control a vehicle equipped with a plurality of individual wheel motors, a steering system, and yaw-rate detection, comprising:
determining a commanded steering angle;
identifying at least one inner motored wheel and at least one outer motored wheel, based upon the commanded steering angle;
determining a yaw-rate error;
calculating a desired wheel motor yaw moment based on a linear range of torque control of the wheel motors;
calculating a first torque for each of the inner motored wheels and calculating a second torque for each of the outer motored wheels, said first and second torques being calculated based on the desired wheel motor yaw moment;
calculating a first ideal wheel speed for each of the inner motored wheels and calculating a second ideal wheel speed for each of the outer wheels; and,
controlling torque and speed of each of the inner motored wheels and each of the outer motored wheels, based upon the yaw-rate error, the first and second torques, and the first and second ideal wheel speeds.
2. The method of claim 1 , further comprising: controlling the speed of each of the inner motored wheels and each of the outer motored wheels, based upon the yaw-rate error and the first and second ideal wheel speeds when the determined yaw-rate error is less than a threshold.
3. The method of claim 1 , wherein calculating a desired wheel motor yaw moment comprises:
determining a linear range of torque control for each individual wheel motor between a propulsion torque limit and a regenerative braking limit; and,
determining the desired wheel motor yaw moment based upon the linear range of torque control for each individual wheel motor.
4. The method of claim 3 , wherein calculating a first torque for each of the inner motored wheels and calculating a second torque for each of the outer motored wheels further comprises:
determining each of the wheel motors to be in an operating mode comprising one of a motoring mode, a regenerative braking mode, and a free-wheeling mode;
determining magnitude and direction of vehicle understeer; and,
calculating magnitude of the first torque and magnitude of the second torque based upon the magnitude and the direction of vehicle understeer and the determined operating mode.
5. The method of claim 4 , wherein calculating a first ideal wheel speed for each of the inner motored wheels and calculating a second ideal wheel speed for each of the outer wheels:
determining an ideal vehicle turning radius based upon the commanded steering angle; and,
calculating an ideal ratio of inner and outer wheel speeds based upon the ideal vehicle turning radius.
6. The method of claim 1 , wherein controlling torque and speed of each of the inner motored wheels and each of the outer motored wheels, based upon the yaw-rate error, the first and second torques, and the first and second ideal wheel speeds, comprises:
balancing proportionally a magnitude of the first torque relative to a magnitude of the first torque needed to achieve ideal wheel speed, based upon the yaw-rate error; and,
balancing proportionally a magnitude of the second torque relative to a magnitude of the second torque needed to achieve ideal wheel speed, based upon the yaw-rate error.
7. The method of claim 1 , wherein determining a commanded steering angle and determining a yaw-rate error, further comprises: identifying a fault in the vehicle steering system.
8. System for controlling motor wheels of a vehicle, comprising:
a plurality of individually controlled wheel motors, comprising at least one wheel motor for an inner wheel and at least one wheel motor for an outer wheel;
a steering system, comprising a steering wheel, a steering command sensor, and a means for steering the vehicle;
a yaw-rate detector; and,
an electronic controller: signally connected to the steering command sensor, and, the yaw-rate detector; and, operably connected to each of the plurality of individually controlled wheel motors; the electronic controller operable to:
determine a commanded steering angle;
identify the at least one inner motored wheel and the at least one outer motored wheel;
determine a yaw-rate error;
calculate a desired wheel motor yaw torque moment;
calculate a first torque for each of the inner motored wheels;
calculate a second torque for each of the outer motored wheels;
calculate a first ideal wheel speed for each of the inner motored wheels;
calculate a second ideal wheel speed for each of the outer wheels; and, control torque and speed of each of the inner motored wheels and each of the outer motored wheels, based upon the yaw-rate error, the first and second torques, and the first and second ideal wheel speeds.