Variable steering ratio control apparatus with backlash adjustment structure

A variable steering ratio control apparatus comprising:

• a differential gear unit comprising a first bevel gear fixedly connected to a steering input shaft, a second bevel gear fixedly connected to a steering output shaft coaxially aligned with the input shaft, a third and a fourth bevel gears rotatably supported by gear supporting shafts respectively for being in meshed-engagement with the first and the second bevel gears, and a differential gear casing supporting the gear supporting shafts of the third and the fourth bevel gears and rotatable about a common axis of the input and output shafts for varying a steering ratio;
• a worm wheel rotatable together with the differential gear casing and driven by a motor through a worm gear;
• a housing unit separatable into a first housing rotatably supporting the second bevel gear, the output shaft and the differential gear casing, and a second housing rotatably supporting the first bevel gear and the input shaft and axially movably engaged with the first housing in a manner so as to be movable in a direction of the common axis when assembling the first and second housing;
• supporting means for supporting the gear supporting shafts of the third and the fourth bevel gears movably in a direction of the common axis;
• relative-position adjustment means formed in an engaging portion of the first and second housing, for permitting axial movement of the second housing relative to the first housing in the direction of the common axis while being engaged with the first housing through the engaging portion;
• and
• the supporting means and the relative-position adjustment means being configured to cooperate with each other for backlash adjustment between each meshing pair of the four bevel gears by way of axial movement of each of the gear supporting shafts, caused by the axial movement of the second housing relative to the first housing, without affecting a meshed-engagement relationship between the worm wheel and the worm gear.