Transmission shift fork, and manufacturing method thereof

Details Transmission shift fork, and manufacturing method thereof Transmission shift fork, and manufacturing method thereof

1998-11-24

2001-01-30

Lin, Kuang Y (Department: 1722)

Metal founding

Process

Shaping liquid metal against a forming surface

C164S132000, C164S900000

Reexamination Certificate

active

06179040

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a shift fork used in a manual transmission.
BACKGROUND OF THE INVENTION
A shift fork used to move a coupling sleeve in an axial direction when a transmission gear shift is performed, is manufactured for example by aluminum diecasting. During manufacture, an engaging part which engages with an engaging groove of the coupling sleeve is formed at the tip of the fork main body.
Conventionally, ADC12 was chiefly used as a diecasting material in aluminum diecasting. Recently, high silicon aluminum diecasting materials with superior wear-resistant properties to those of ADC12 have also come into use. Such materials are used to mold the fork main body and the engaging part in a one-piece construction so as to decrease costs and achieve a lightweight construction.
As shown in
FIG. 5
, a claw-shaped engaging part
52
is usually molded integrally at the tip of a fork main body
51
, and the engaging part
52
slides on a rotating coupling sleeve
54
. In order to obtain high wear-resistant properties in the engaging part of high silicon aluminum shift forks, a casting surface is cut by 50 &mgr;m or more so as to cause pro-eutectic silicon to form on the surface.
FIG. 6
is a view from the direction of the arrow VI in FIG.
5
. Flat engaging surfaces
53
L,
53
R are formed on the engaging part
52
by the above process.
However, in the prior art shift fork, because there is a space between the engaging part
52
and coupling sleeve
54
, when the shift fork bends and the engaging part
52
inclines, the engaging surfaces
53
L,
53
R and coupling sleeve
54
do not come into contact evenly. For instance, when the shift fork
50
moves to the right of
FIG. 6
, the rotating coupling sleeve
54
and the upper right corner of the engaging part
52
will come in contact. As a result, the surface pressure increases, the wear of the engaging part
52
increases, and the engaging part
52
wears unevenly as shown by the dotted line in the figure.
As shown in
FIG. 5
, ideal points P
1L
, P
1R
, at which the coupling sleeve
54
should be pushed, lie on a straight line which passes through the center O of the coupling sleeve
54
. However, when the engaging part
52
inclines and comes in contact with the coupling sleeve
54
, the positions at which the engaging part
52
pushes the coupling sleeve are points P
2L
, P
2R
which are offset upwards in the figure above the ideal points P
1L
, P
1R
.
When the contact point of the engaging part
52
and coupling sleeve
54
shifts from the ideal points P
1L
, P
1R
in this way, a force acts on the coupling sleeve
54
in a direction other than axial and operating performance decreases.
Tokkai Hei 5-340471 issued by the Japanese Patent Office in 1993 and Tokkai Hei 6-117451 issued in 1994 disclose a method regarding wear-resistant properties of the engaging part wherein a wear-resistant member is made to adhere to the engaging part, and deformation of the engaging part is prevented.
Further, Tokkai Hei 8-49035 published by the Japanese Patent Office in 1996 discloses an engaging part integrally molded with the fork main body from an wear-resistant aluminum alloy, and shot peening is performed.
However, in all these cases, additional machining is necessary after diecasting.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a low cost shift fork for a transmission having high wear-resistant properties and high operational performance.
In order to achieve the above object, this invention provides a shift fork engaging with an engaging groove of a coupling sleeve of a transmission, the shift fork comprising a fork main body, and an engaging part having an engaging surface which comes in contact with an inner wall of the engaging groove and integrally molded with the fork main body, wherein the engaging surface is formed in a bulging shape.
According to an aspect of this invention, this invention provides a method for casting a shift fork engaging with an engaging groove of a coupling sleeve of a transmission, the shift fork comprising a fork main body, and an engaging part having an engaging surface which comes in contact with an inner wall of the engaging groove and integrally molded with the fork main body. The method comprises a step for pouring molten metal into a mold with no draft slope comprising a fixed die and a movable die, the mold forming the engaging surface in a bulging shape, and a step for opening the mold and removing the shift fork therefrom while the shift fork therein is in a semi-solid state.
The details as well as other features and advantages of this invention are set fourth in the remainder of the specification and are shown in the accompanying drawings.


REFERENCES:
patent: 4548253 (1985-10-01), Funatani et al.
patent: 5201237 (1993-04-01), Berndtson
patent: 4-4961 (1992-01-01), None
patent: 5-340471 (1993-12-01), None
patent: 6-117451 (1994-04-01), None
patent: 8-49035 (1996-02-01), None

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