Metal working – Method of mechanical manufacture – Assembling or joining
Reexamination Certificate
1997-12-08
2003-05-13
Echols, P. W. (Department: 3726)
Metal working
Method of mechanical manufacture
Assembling or joining
C029S235000, C029S432200, C029S451000, C029S900000, C029S714000, C082S118000, C082S147000, C082S148000
Reexamination Certificate
active
06560846
ABSTRACT:
This application is based on Japanese Patent Application No. 8-340288 filed Dec. 20, 1996, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to techniques for effecting an interference fit of two parts.
2. Discussion of the Related Art
One example of known techniques for effecting an interference fit of two parts is disclosed in JP-U-63-144136 (Japanese Utility Model Application as published on Sep. 22, 1988), wherein a first part
200
is held stationary, and a second part
202
is forced by a rigid pressure head
204
, into engagement with the first part
200
, as shown in
FIG. 12
, to thereby achieve an interference fit of the first and second parts
200
,
202
.
In the known technique shown in
FIG. 12
, a mechanical force F is applied to the second part
202
by abutting contact of the pressure head
204
with one of the opposite ends of the second part
202
which is remote from the first part
200
. According to this arrangement, the compressive stress acting on the second part
202
in its axial direction as a result of the abutting contact of the second part
202
with the first part
200
is substantially evenly distributed over the entire length of the second part
202
, as indicated in the graph given in the lower part of FIG.
12
. Thus, this conventional technique suffers from a problem that the axial portion of the second part
202
other than its end portion which engages the first part
200
for the interference fit is subject to the axial compressive stress.
In an effort to solve the above problem, the assignee of the present application developed a technique wherein at least one of the two parts is accelerated toward the other or each other in a direction that permits the interference fit of the two parts, to apply a kinetic energy to the above-indicated at least one part, for thereby achieving the interference fit of the two parts, as disclosed in co-pending Application, Ser. No. 08/670,743 filed Jun. 21, 1996. According to this technique, the axial compressive stress acting on the second part
202
as a result of the abutting contact with the first part
200
continuously decreases in the axial direction from the axial end of the second part
202
abutting on the first part
200
toward the other axial end of the second part
202
, at which the stress is zero, as indicated in FIG.
13
.
The present applicants had the following finding as a result of continued research of the technique as disclosed in the above-identified co-pending application. That is, it was found that the thrust force applied to the second part immediately after the initiation of the acceleration of the second part tends to vary or fluctuate unless the thrust force to be applied upon the initiation of the acceleration is positively controlled. The variation of the initial thrust force applied to the second part causes a variation in the velocity of the second part upon abutting contact of the second part with the first part, leading to deteriorated stability in the accuracy of the interference fit of the two parts.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a method of effecting an interference fit of a first and a second part by accelerating the second part into abutting contact with the first part, which method permits improved stability of the thrust force to be applied to the second part upon initiation of acceleration of the second part.
This first object may be achieved according to a first aspect of the present invention, which provides a method of effecting an interference fit of a first part and a second part, comprising: a thrust force applying step of applying a thrust force to the second part in a direction toward the first part to thereby accelerate the second part for applying a kinetic energy to the second part to cause abutting contact of the second part with the first part for achieving the interference fit of the first and second parts; and an acceleration initiation inhibiting and permitting step of inhibiting initiation of acceleration of the second part by the thrust force until the thrust force has been increased to a predetermined threshold, and permitting the initiation of the acceleration when the thrust force has been increased to the predetermined threshold.
In the present method of effecting the interference fit of the two parts, the initiation of the acceleration of the second part is positively inhibited until the thrust force applied to the second part has been increased to the predetermined threshold or lower limit, so that the actual thrust force applied to the second part upon initiation of the acceleration is stabilized at a sufficient value, whereby the velocity of movement of the second part immediately before the abutting contact of the second part with the first part is accordingly stabilized to assure improved stability in the accuracy of the interference fit of the first and second parts.
The first and second parts may both have mutually fitting portions that are rigid. Alternatively, one and the other of these mutually fitting portions of the two parts may be rigid and elastic, respectively.
Where one of the two parts has an end portion in the form of a rod or shaft while the other part has a hole in which the end portion of the above-indicated one part is fitted with an interference, the above-indicated one part having the rod-shaped end portion or the other part having the hole may be accelerated. In other words, the above-indicated second part may be a part having a rod-shaped end portion or a hole. The second part may be accelerated by direct application of a force based on a pressure of a gas or liquid, or by indirect application of a force such as a magnetic force, a gravitational force or a centrifugal force. In one form of the method wherein the acceleration of the second part is effected by a pressurized gas, the pressurized gas delivered from a high-pressure source is introduced through a suitable gas passage into a rear space formed at the rear of the second part which is accommodated in a guide passage such that the second part may be guided toward the first part. The above-indicated rear space is defined by at least the rear end face of the second part remote from the first part and a rear end portion of the guide passage remote from the first part. It is desirable to terminate the acceleration of the second part to permit a constant-velocity or uniform motion of the second part immediately before the abutting contact of the second part with the first part, in order to assure that the axial compressive stress at the rear end of the second part remote from the first part is substantially zero upon abutting contact of the second part with the first part.
In one preferred form of the method of the invention, the acceleration initiation inhibiting and permitting step comprises inhibiting the initiation of the acceleration of the second part by engagement of a stop member with the second part.
In another preferred form of the present method, the acceleration initiation inhibiting and permitting step comprises inhibiting the initiation of the acceleration of the second part by clamping the second part.
In a further preferred form of the present method, the acceleration initiation inhibiting and permitting step comprises inhibiting the initiation of the acceleration of the second part by forcing the second part onto a stationary member to thereby generate a force of friction between the second part and the stationary member.
A second object of the present invention is to provide an apparatus for effecting an interference fit of a first and a second part by accelerating the second part into abutting contact with the first part, which apparatus permits improved stability of the thrust force to be applied to the second part upon initiation of acceleration of the second part.
The above second object may be achieved according to a second aspect of the invention, which provides an apparatus for effectin
Fuwa Wataru
Shioya Shigemi
Echols P. W.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Hong John
Toyota Jidosha & Kabushiki Kaisha
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