Housing structure and power steering apparatus

1. A housing structure comprising:

a first housing having a fitting inner tubular portion that is formed around an axis of a shaft member and has an inner tubular end surface at a tip of the fitting inner tubular portion, and a first bolt fastening portion that has a first bolt aligning surface formed at a position away from the inner tubular end surface in a radial direction of the shaft member, the first housing supporting a first end side of the shaft member via a first bearing; and

a second housing having a fitting outer tubular portion, into which the fitting inner tubular portion is fitted and which has an outer tubular end surface provided at an uppermost end of the fitting outer tubular portion, and a second bolt fastening portion that has a second bolt aligning surface that mates with the first bolt aligning surface, the second housing supporting a second end of the shaft member via a second bearing,

wherein a first gap is provided between the inner tubular end surface and an inner tubular opposite surface of the second housing that is positioned opposite to the inner tubular end surface in an axial direction of the shaft member, and a second gap is provided between the outer tubular end surface and an outer tubular opposite surface of the first housing that is positioned to the outer tubular end surface in the axial direction of the shaft member, and

when, after a thrust load on the shaft member causes the fitting inner tubular portion and the fitting outer tubular portion to separate from each other in the axial direction of the shaft member, the fitting outer tubular portion return to a position at which the fitting inner tubular portion is fitted into the fitting outer tubular portion, the first gap prevents contact between the inner tubular end surface and the inner tubular opposite surface, and the second gap prevents contact between the outer tubular end surface and the outer tubular opposite surface.

2. The housing structure according to claim 1 , wherein the second gap is formed by positioning the outer tubular opposite surface on same plane as the first bolt aligning surface and by positioning the outer tubular end surface so that the second end of the shaft member is closer from the outer tubular end surface than from the second bolt aligning surface.

3. The housing structure according to claim 1 , wherein the second gap is formed by positioning the outer tubular end surface on same plane as the second bolt aligning surface and by positioning the outer tubular opposite surface so that the first end of the shaft member is closer from the outer tubular opposite surface than from the first bolt aligning surface.

4. A power steering device comprising the housing structure according to claim 1 , wherein the shaft member is an assist shaft to which a worm wheel driven by an assist motor is rotatably attached.

5. A power steering device comprising the housing structure according to claim 2 , wherein the shaft member is an assist shaft to which a worm wheel driven by an assist motor is rotatably attached.

6. A power steering device comprising the housing structure according to claim 3 , wherein the shaft member is an assist shaft to which a worm wheel driven by an assist motor is rotatably attached.

7. The housing structure according to claim 1 , wherein the fitting outer tubular portion has a surface that defines an outermost surface of the second housing in the radial direction.