Hollow rack bar and method of manufacturing the hollow rack bar

Abstract

Provided is a hollow rack bar including a rack portion that is engaged with a pinion gear and faces supported by a yoke. The hollow rack bar includes: the rack portion engaged with the pinion gear; and the supported faces provided on a back side of teeth of the rack portion and supported by the yoke. The rack portion is formed by locating a toothed mold on an outer face of a circular tube material, and inserting a cored bar into the circular tube material to pressurize an inner face, thereby transferring a shape of the toothed mold. The supported faces are formed by removal processing or deformation processing of a back side of the teeth rack portion of the circular tube material.

What is claimed is: 
     
         1 . A hollow rack bar, comprising:
 a rack portion engaged with a pinion gear; and   supported faces provided on a back side of the rack teeth portion and supported by a yoke,   wherein the supported faces are flat and provided to form portions thinner than surrounding areas, and a circularly continuous heat-treated layer is made by quenching and tempering in an area where the rack portion and the supported faces are provided.   
     
     
         2 . The hollow rack bar as set forth in  claim 1 , wherein the heat-treated layer is provided over an entire thickness of a portion where the rack portion and the supported faces are provided. 
     
     
         3 . The hollow rack bar as set forth in  claim 1 , further comprising:
 a ball screw,   wherein a rotating part of an assist mechanism is assembled to the ball screw at a different position in an axial direction with respect to the rack portion and the supported faces.   
     
     
         4 . The hollow rack bar as set forth in  claim 2 , further comprising:
 a ball screw,   wherein a rotating part of an assist mechanism is assembles to the ball screw at a different position in an axial direction with respect to the rack portion and the supported faces.