The top priorities for design of power-assisted steering,
especially for heavy commercial vehicles, are traffic safety and
driving comfort. Legal limits of steering-assistance attempt to
define safety standards; more power assistance eases control of the
vehicle, but excessive assistance leads to lack of "feel"
for the road.
Analysis of steering forces and tests of vehicles, both
conducted for varying driving speeds and conditions, indicated two
factors which are critical for the evaluation of sudden failure of
power-assistance: the steering force, and the assistance factor. In
general, the assistance component is most needed at low speeds.
Results identify driving condition limits for maintenance of
vehicle control upon loss of steering assistance. Nevertheless,
power-assistance must be limited in order to reduce the surprise
factor should a system failure occur. Current power-assistance
designs which reduce the assistance factor as driving speed
increases are well suited to meet these needs.
Wilhelm Falkner, Karl Feitzelmayer
17th FISITA Congress (1978), Budapest, Hungary