Automotive steering system

An automotive power-assisted steering system comprising:

• a steering wheel;
• a steering shaft carrying the steering wheel and a steering linkage drivingly connected to steered road wheels;
• a hydromechanical leverage unit mechanically connected to the steering linkage and movable between a right-turn positional range to drive the steering linkage into a condition effecting right-turn of the steered road wheels and a left-turn positional range to drive the steering linkage into a condition effecting left-turn of the steered road wheels;
• a rotary piston-valve rotatable about a longitudinal axis thereof and longitudinally movable between first and second positional ranges across an equilibrium position depending upon its rotational position about said axis, the rotary piston-valve being hydraulically connected to said leverage unit for moving the leverage unit into the right-turn or left-turn positional range when moved to the first or second positional range, respectively, thereof or holding the leverage unit in a locked condition when moved to said equilibrium position;
• a valve re-set mechanism operatively connected between the leverage unit and the rotary piston-valve and operative to be driven by the leverage unit for longitudinally moving the rotary piston-valve from the first or second positional range back to the equilibrium when the leverage unit is moved by the piston-valve to the right-turn or left-turn positional range, respectively, thereof;
• a drive source having an output shaft drivingly connected to the rotary-valve for driving the piston-valve about said axis when actuated;
• and
• an electric control circuit including means responsive to turning of the steering wheel for producing a first signal related to the angle and direction of turning of the steering wheel, means responsive to the velocity of the vehicle for producing a second signal related to the velocity of the vehicle, means responsive to an external force imparted sideways to the vehicle for producing a third signal related to the intensity of the force, a control module receiving the first second and third signals from the means for thereby producing an output signal representative of a desired angle of steering, means for producing a fourth signal representative of the rotational position of the output shaft of the said drive source, a comparator operative to compare the output signal from said control module with the fourth signal for producing an output signal representative of a difference between the two signals which are introduced thereto, an analog-to-digital converter for converting the output signal from the comparator into a pulsating signal, and a drive pulse generator for supplying to said drive source a pulsating current in accordance with the pulsating signal from the analog-to-digital converter, whereby the drive source is actuated to have its output shaft rotated in a direction and through an angle dictated by the pulsating current from the pulse generator.