Metal working – Method of mechanical manufacture – Gear making
Reexamination Certificate
2000-01-10
2001-11-20
Echols, P. W. (Department: 3726)
Metal working
Method of mechanical manufacture
Gear making
C072S370040, C072S398000
Reexamination Certificate
active
06317979
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a hollow rack bar, wherein a flat portion is formed in a steel pipe and rack teeth are formed in the flat portion.
BACKGROUND OF THE INVENTION
In a conventional rack-and-pinion steering system for motor vehicles and the like, a rack bar has been employed. Recently, it has been tried to hollow the rack bar so as to make it more lightweight. In a method of manufacturing such a hollow rack bar, as disclosed in Publication of Examined Japanese Patent Application No. Hei 3-5892, an electric resistance welded tube or an extrusion molded steel pipe is employed and a flat portion is formed in the periphery of the tube or the steel pipe by press working. In the flat portion are formed rack teeth by placing the steel pipe having the flat portion in a tooth profile forming die-and forcibly inserting a mandrel into the steel pipe, thereby extruding the flat portion from the inside.
However, such a conventional method has a problem that the rack teeth configuration of the tooth profile forming die, particularly the central portion of the rack teeth configuration, is continuously subjected to an excessive load. Also, transverse end portions of the rack teeth cannot be formed precisely. Furthermore, resistance by processing imposed on the mandrel is significant.
SUMMARY OF THE INVENTION
Wherefore, an object of the present invention is to provide a manufacturing method of a hollow rack bar wherein the load imposed on the rack teeth configuration of a tooth profile forming die is reduced and precision level of the formation of rack teeth is improved.
This and other objects of the invention are achieved in a manufacturing method of a hollow rack bar by flattening a steel pipe to form a flat portion and forming rack teeth in the flat portion, wherein, subsequent to the formation of the flat portion, the rack teeth are formed by placing the steel pipe in a tooth profile forming die having rack teeth configuration and sequentially inserting a plurality of mandrels having extruding portions of different sizes into the steel pipe, thereby extruding the flat portion from the inside thereof toward the rack teeth configuration. In the method, a mandrel having a planar extruding portion is firstly inserted, and then a mandrel having an extruding portion with an approximately central depression in the longitudinal direction is inserted.
Since the mandrel having an extruding portion with an approximately central depression in the longitudinal direction is inserted for extrusion toward the rack teeth configuration, the load imposed on the rack teeth configuration is reduced and also the resistance by processing imposed on the mandrel is reduced.
In another aspect of the invention, there is provided a hollow rack bar manufacturing apparatus which comprises pressing means for forming a steel pipe having a flat portion, placing means for placing the steel pipe having a flat portion formed by the pressing means in a forming die having a rack teeth configuration, and inserting means for inserting at least one mandrel having an extruding portion with an approximately central depression into the steel pipe placed in the forming die.
In further aspect of the invention, there is provided a mandrel for manufacturing a hollow rack bar by forming rack teeth in a flat portion formed in a steel pipe by flattening, the mandrel comprising an extruding portion to be inserted into the steel pipe placed in a forming die having a rack teeth configuration and an approximately central depression formed in the extruding portion.
REFERENCES:
patent: 1983584 (1934-12-01), Urschel
patent: 3670555 (1972-06-01), Fredericks
patent: 4598451 (1986-07-01), Ohki
patent: 137335 (1989-11-01), None
patent: 35892 (1991-01-01), None
Echols P. W.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
TRW Automotive Japan Co. LTD
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