Pipes and tubular conduits – Plural duct – Longitudinally extending common wall
Reexamination Certificate
1998-12-10
2001-09-04
Hook, James (Department: 3752)
Pipes and tubular conduits
Plural duct
Longitudinally extending common wall
C138S111000, C138SDIG001
Reexamination Certificate
active
06283159
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a double-walled pipe structure comprising a plurality of pipes of different cross-sectional shapes combined for increased mechanical strength and reduced weight.
2. Description of the Related Art
Various pipes have been used as structural parts for automobiles, for example. In various applications, pipes of different pipe diameters and wall thicknesses are selected to meet demands for different mechanical strengths and weights. If one pipe material is used in an application where it is subject to different loads at different positions, then it is the general practice to determine a pipe diameter and a wall thickness based on the mechanical strength of a pipe portion subject to a maximum load, or to join a pipe having a larger diameter or a greater wall thickness and a pipe having a smaller diameter or a smaller wall thickness to each other by welding or the like.
Even if the mechanical strength of a pipe should be varied directionally, it is customary to determine a pipe diameter and a wall thickness based on the mechanical strength of the pipe with respect to the direction in which a maximum load is applied.
According to the conventional practice of determining a pipe diameter and a wall thickness based on either the mechanical strength of a pipe portion subject to a maximum load or the mechanical strength of the pipe with respect to the direction in which a maximum load is applied, the resultant pipe tends to be too heavy as a whole and also too strong in pipe portions that are not required to be so strong.
Furthermore, it is time-consuming and expensive to carry out the process of joining a pipe having a larger diameter or a greater wall thickness and a pipe having a smaller diameter or a smaller wall thickness to each other by welding or the like.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a double-walled pipe structure suitable for use in applications where different loads are applicable at different positions or in different directions.
According to an aspect of the present invention, there is provided a double-walled pipe structure defined in claim
1
comprising a hollow pipe and a deformed pipe having a deformed cross-sectional shape and press-fitted in said hollow pipe. The deformed pipe has a plurality of ridges projecting radially outwardly and having respective vertexes held in contact with an inner circumferential surface of said hollow pipe.
There is also provided a double-walled pipe structure defined in claim
2
comprising a hollow pipe and a deformed pipe being a flat pipe and press-fitted in said hollow pipe. The deformed pipe has a plurality of vertexes held in contact with an inner circumferential surface of said hollow pipe.
Since the ridges are held in contact with the inner circumferential surface of said hollow pipe, the double-walled pipe structure has an increased mechanical strength in radial directions where the ridges are present. Therefore, the mechanical strength of the double-walled pipe structure depends on the radial direction thereof.
The hollow pipe may have a circular cross-sectional shape, an angular cross-sectional shape such as a rectangular cross-sectional shape, or any of various polygonal cross-sectional shapes.
The deformed pipe may have two, three, four, or more ridges that are circumferentially spaced at equal intervals. The ridges are spaced equally from the central axis of the deformed pipe, and hence are equally held in contact with the inner circumferential surface of said hollow pipe.
The hollow pipe and the deformed pipe are fixedly joined, preferably arc-welded, to each other at axially spaced locations.
The deformed pipe may be inserted longitudinally partly in said hollow pipe. With the deformed pipe inserted longitudinally partly in said hollow pipe, the mechanical strength of the portion of the double-walled pipe structure where the deformed pipe is present is higher than that of the portion of the double-walled pipe structure which is devoid of the deformed pipe. The double-walled pipe structure may be used in applications where different loads are applied at different positions. This double-walled structure can be produced simply by inserting the deformed pipe into the hollow pipe, rather than joining pipes of different diameters or wall thicknesses.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.
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patent: 1242473 (1917-10-01), Prentice
patent: 2386159 (1945-10-01), Elder
patent: 2756032 (1956-07-01), Dowell
patent: 2929408 (1960-03-01), Weatherwax et al.
patent: 3000495 (1961-09-01), Downing
patent: 3585910 (1971-06-01), Brown et al.
patent: 4163474 (1979-08-01), MacDonald et al.
patent: 4397304 (1983-08-01), Villain
patent: 4743329 (1988-05-01), Hata
Bestex Kyoei Co., Ltd.
Hook James
Merchant & Gould P.C.
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