1. Field of the Invention
This invention relates generally to automotive vehicle steering systems, and more particularly to a steering system that includes an electric actuator having a shaft that translates linearly to turn a vehicle wheel.
2. Background Information
A preliminary novelty search in connection within this invention developed various U.S. Patents that are identified on an attachment to an accompanying Information Disclosure Statement. Also identified on that attachment are two U.S. Patents relating to electric motor powered linear actuators.
The state of the art shows that it is known to utilize an electric powered actuator in an automotive vehicle steering system to aid in turning steered wheels on opposite sides of a vehicle, such as right and left front wheels of a four wheeled vehicle. The steered wheels are turned by a steering wheel that is coupled through a steering column shaft to a pinion of a mechanical steering gear that imparts linear motion to a steering rack that is coupled to the steered wheels. As the steering wheel is turned, a shaft of the electric powered actuator translates linearly to aid the motion of the rack by supplying a major share of the force that turns the wheels. This type of system is referred to by various names such as electrically assisted steering or electric power steering.
The state of the art also reveals another type of steering system, one in which a steering wheel is not mechanically coupled to the steered wheels, but rather is electrically coupled by wires to an electric actuator for turning a single wheel or a pair of wheels, such as right and left wheels. Such a steering system lacks a steering column shaft that is coupled to the wheels through a mechanical steering gear that operates a rack. This type of system is sometimes referred to as a steer-by-wire system. In a four wheel vehicle, front wheels alone may be steered, or all four wheels may be steered.
A steered wheel of a vehicle imposes certain requirements on linear force that a shaft of an electric actuator must exert in order to turn the wheel. The mechanism of one type of electric actuator that is suitable for use in a steering system of one of the types described above converts electric energy into rotational motion and the rotational motion into linear motion for translating the actuator shaft. The force that is imposed on the actuator shaft by the wheel or wheels that the actuator turns is therefore reflected as torque load imposed on a rotary portion of the actuator.