The technical field of this invention is a vehicle suspension control system.
The applications cited above describe a method and apparatus for controlling vehicle suspension dampers which applies an enhanced body damping command to promote vehicle stability during a vehicle turn. This enhanced body damping command is applied according to a sensed vehicle lateral acceleration; and it is dependent, in its application to specific vehicle dampers, on the direction of the sensed vehicle lateral acceleration, which is an indication of the turning direction of the vehicle. Typically, the enhancement provides enhanced firmness in compression on the side of the vehicle on the outside of the turn (the side opposite the direction of lateral acceleration) and enhanced firmness in rebound on the side of the vehicle on the inside of the turn.
In some turning situations, however, the vehicle operator may turn the steering wheel back in the opposite direction while the vehicle is accelerating laterally in the direction of the turn. If the steering wheel is turned back past the center position, the steering angle of the vehicle will be opposite in direction or sign to the lateral acceleration of the vehicle. This condition is termed xe2x80x9csteering crossover.xe2x80x9d As the oppositely turned wheels have their effect on the turning movement of the vehicle, the original lateral acceleration will slow and pass through zero so that it is again in the direction of the steering angle. At the end of the steering crossover conditionxe2x80x94that is, the point where the lateral acceleration changes from a direction opposite that of the steering angle to a direction the same as that of the steering anglexe2x80x94the switching of enhanced body damping commands from one vehicle side to the other may generate a step change in perceived body damping.
The method and apparatus of this invention provide improved suspension control through steering crossover events. In particular, the method and apparatus sense a vehicle lateral acceleration and a vehicle steering angle and store, for each direction of sensed vehicle lateral acceleration, first and second sets of enhanced body damping commands for the suspension dampers of the vehicle. Responsive to the sensed vehicle lateral acceleration and sensed vehicle steering angle, the method and apparatus apply the first set of enhanced damping commands to the suspension dampers if the sensed steering angle is in the same direction as the sensed lateral acceleration and alternatively apply the second set of enhanced body damping commands to the suspension dampers if the sensed steering angle is in the opposite direction as the sensed lateral acceleration.
In a preferred embodiment of the invention, the first set of enhanced body damping commands provides enhanced damping in compression for the suspension dampers on the side of the vehicle opposite the direction of indicated vehicle lateral acceleration (on the outside of the turn) and enhanced damping in rebound for the suspension dampers on the side of the vehicle in the direction of indicated vehicle lateral acceleration (on the inside of the turn) and the second set of enhanced body damping commands provides enhanced damping in compression and rebound for the suspension dampers on both sides of the vehicle.
In a preferred embodiment of the invention, the suspension control also determines a relative velocity of each of the suspension dampers, derives from the determined relative velocities a demand force command for each of the dampers and applies each of the derived demand force commands to its respective damper only when a comparison of the direction of the demand force command with the sensed relative velocity of the damper indicates that a force corresponding to the demand force command can be effectively exerted by the damper. In this embodiment, the enhanced body damping commands are applied to the suspension dampers without regard for the application of the demand force command.
The result of the invention is that improved handling stability is provided in turns due to more predictable handling during the steering crossover event and fewer changes in individual damper characteristics at the end of the crossover event.