Method and apparatus for plastic working of hollow rack bar and hollow rack bar

Abstract

A preparatory working device by which a work piece to be fed to a rack bar forging device is obtained. The device is provided with a die sets for obtaining a diameter reduction at a location of a blank pipe, which becomes a toothed part of a rack bar, while the wall thickness being substantially unchanged or slightly increased. The device is further provided with a die set for reducing a wall thickness at a location of the blank pipe, which becomes a connection part of the rack bar. The wall thickness reduction is one half of the initial thickness, which causes the length of the work piece to be elongated. Then a rack bar forging by a die set is done.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of Invention[0002]The present invention relates to a production of rack bar in a steering mechanism of a vehicle from a pipe shaped blank by plastic working, and, more particularly, to its improvement, by which an increased reduction in the weight of the product is obtained in comparison with the prior art.[0003]2. Description of Related Art[0004]A rack bar is a main part of a steering system of a vehicle and has conventionally been produced by machining from a solid bar of a rounded cross-sectional shape by using originally a hobbing machine and recently a broaching machine. However, such a machining from a solid bar of rounded cross-sectional shape makes the product to be heavy. Therefore, a solution has been proposed, wherein the machined product is subjected to a subsequent boring by using a gun drill to obtain a hollow structure, thereby reducing the weight. However, this solution makes the production cost to be increased on one hand an...

AI Technical Summary

Benefits of technology

[0007]The present invention aims to overcome the above difficulties in the prior art and, in particular, to provide a technology, by which an effective use of the material along the entire length of the blank is realized, a desired performance as a rack bar is obtained and increased degrees of a weight reduction, a cost performance, a resource saving and a vehicle performance is realized.

[0011]In a power steering mechanism of an electric operated type, a rack bar of VGR (variable gear ratio) type is usually used. In this type of mechanism, it is needed that values of the pitch as well as the inclination angle of toothed portions are varied along the length. Such a construction of the VGR rack bar makes it difficult that it is machined from a solid work piece. Therefore, a forging from a pipe shaped blank is usually employed. Furthermore, unlike the hydraulic operated type, the electric operated type requires an increased bending strength of toothed portion, i.e., an increased size of tooth part as well as an increased thickness.

[0014]Furthermore, as a result of the ironing after the swaging, a highly improved surface roughness is obtained not only at the inner surface but also at the outer surface, which allows a dimension to be controlled within a tolerance of microns, thereby allowing a increased product quality and precision to be easily obtained.

Problems solved by technology

However, such a machining from a solid bar of rounded cross-sectional shape makes the product to be heavy.

However, this solution makes the production cost to be increased on one hand and, on the other hand, makes the resource consumption efficiency to be reduced.

In the prior art, a blank pipe of a uniform value of wall thickness was used, resulting in an excessive wall thickness at the locations other than the toothed portions.

Thus, the prior art is defective in an increased product weight and reduced material consumption efficiency.

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