Electronically Controlled Steering Systems for Line Haul Vehicles

A commercial vehicle power steering system with driver selectable electronically controlled efforts, designated by TRW as the X-4, was designed and tested on Class 8 trucks. The TRW X-4 system is a variable-flow power assist concept. Prototypes of the system proved successful in installations on highway line-haul tractors from several manufacturers. The X-4 system provides increased steering road feel at highway speeds, without a reduction in power assist at low speeds. In addition to enhanced steering and handling performance, test results indicate that the X-4 system significantly reduces the power consumption as compared to the production OEM power steering system.