Drive train used in a steering apparatus for rear wheels of a vehicle

A drive train of a steering apparatus for steering rear wheels of a vehicle by shifting a steering shaft of the rear wheels in the axial direction by means of a driving force of a rotary motor, for transmitting the driving force of the motor to the steering shaft of the rear wheels, said drive train comprising:

• a reduction mechanism for receiving said driving force from said motor;
• a converting mechanism, driven by said reduction mechanism for converting a rotational motion of said motor to a linear motion for steering the rear wheels;
• said reduction mechanism including a worm for driving connection to said motor, and
• a worm wheel in meshing engagement with said worm;
• said converting mechanism comprising a screw-threaded mechanism;
• said screw-threaded mechanism including a trapezoidally-threaded male screw member having a male screw portion with a trapezoid thread formed in an outer circumference thereof, and
• a trapezoidally-threaded female screw member with a trapezoid thread formed in an inner circumference thereof for engagement with said male screw portion, and
• one of said trapezoidally-threaded male and female screw members being driven by said worm wheel, and the other having means for being fixed to said steering shaft of the rear wheels;
• said converting mechanism in combination with said reduction mechanism having a transmission efficiency equal to zero in transmitting driving force from said steering shaft of the rear wheels to said motor;
• said trapezoidally-threaded female and male screw members being tubular in shape for mounting concentric with the steering shaft of the rear wheels;
• said trapezoidally-threaded female screw member having means for being rotatably supported by a housing of said steering apparatus for steering rear wheels;
• a backlash adjusting mechanism for adjusting a backlash of said screw-threaded mechanism, said backlash adjusting mechanism including an elastic biasing member for biasing said trapezoidally-threaded male screw member toward said trapezoidally-threaded female screw member so that said male and female screw members are elastically pressed against each other with respective portions thereof being engaged;
• said backlash adjusting mechanism further comprising a sliding member placed between said elastic biasing member and a member biased by said elastic biasing member, said sliding member being slidable in a predetermined direction relative to said housing of said steering apparatus;
• said sliding member having a steering shaft rotation preventing means for preventing the steering shaft of the rear wheels from rotating relative to said housing of said steering apparatus;
• and
• said steering shaft rotation preventing means comprising clamping portions for clamping a pair of parallel flat surfaces formed on an outer circumference of the steering shaft of the rear wheels.