The Torque Sensor at Delphi Automotive Systems

Delphi Automotive Systems was completely separated from its parent company, General Motors, in the Spring of 1999.  Delphi supplies the automotive industry with "automotive systems" in:  Electronics & Mobile Communication, Safety, Thermal & Electrical Architecture, and Dynamics & Propulsion.  Delphi Research Labs, in Shelby MI, is the central research and development organization for Delphi Automotive Systems Corporation.

The project that I worked on at Delphi was part of a larger project of Delphi's Saginaw Steering Systems called "E-Steer."  Today's standard power steering is a cumbersome and fuel inefficient hydraulic power steering system.  These systems include a hydraulic pump that runs continuously whether or not power assist is needed as well as a complex and heavy system of hydraulic hoses and clamps.  E-Steer is an Electronic Power Steering system (EPS) that senses the need for power assist electronically and then assists the driver's efforts to steer with motors attached to the axle of the car.

The system depends on finding some way of sensing the torque that a driver applies to the steering column when he turns the steering wheel of the car. (Torque is a type of force that tends to twist an object rather than push it along a line.)   The torque sensor converts the mechanical forces within the steering shaft into a magnetic force which is in turn converted into an electrical voltage.  The steering controller then instructs small motors to assist in steering until the torque in the steering column is no longer present.

The method that we are attempted to use to measure torque consists of a ring of material attached directly to the steering column.  This material is very special in that it undergoes what is called "magnetostriction."  This material creates a magnetic field ("magneto-") when it is strained or squeezed ("-striction").  In theory...  When the driver turns the wheel of the car, there is some resistance from the road.  The twisting force applied by the driver to the steering wheel along with the reaction twisting force applied by the road creates a torque within the steering column.  Our magnetostrictive material is strained (or squeezed) and it creates a magnetic field.  A special sensor reads this magnetic field and coverts it into an electrical signal which instructs the motors to assist in turning the wheel.  When the turn is complete, the driver no longer applies the torque to the steering wheel and the magnetostrictive material no longer creates a magnetic field and the motors are no longer instructed to assist.

Eventually, the entire conventional steering system will be replaced by true "Steer-by-Wire."  All of the steering will be accomplished by use of electric motors and all mechanical connections between the steering wheel and tires will be completely removed.  Similar advances in other areas like "Brake-by-Wire," "Shift-by-Wire," and "Accelerate-by-Wire" will remove all mechanical links between the driver and the road and replace them with electrical systems and sub-systems.  It will then be possible to integrate all of these systems into a centralized brain within the car in a system that has been termed "Drive-by-Wire."  The car will be able to adjust things like brakes, acceleration, and steering based on information that it receives from a host of sensors along with the instructions from the driver.  The next step would then be to remove the control of all of these systems (steering, braking, accelerating) from within the automobile and transfer them to a centralized controller which could control many cars on one roadway.  This could enable "automated freeways" which could maximize the efficiency of traffic in densely populated areas.