Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2002-04-26
2004-08-24
Thompson, Gregory (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C165S080200, C165S080300, C165S185000, C174S016300, C257S719000, C257S726000, C257S727000, C361S690000, C361S710000
Reexamination Certificate
active
06781840
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a fastening mechanism, for example, for a circuit unit in a control device for an automobile.
There are now an increasing number of motor vehicles carrying a control device for driving a large-current actuator for an automobile motor and lamp by means of a semiconductor or a circuit unit such as an inverter using a semiconductor. Semiconductors are used for carrying out a duty-control of such a large-current actuator or the switching circuit of an inverter, or for increasing the useful lifetime of the device or to make the whole device lighter.
Such a circuit unit typically has a casing for covering its surface, made of a thermally conductive material such as aluminum or an aluminum alloy, and includes a heat sink of a similar thermally conductive material attached to the inner surface of the casing. The aforementioned semiconductor is attached onto the surface of this heat sink such that the heat generated when the likes of a large-current actuator are being driven by this semiconductor will be quickly led away from the unit. It is also commonly done to attach such a heat sink to a circuit board, or to fasten the semiconductor to the circuit board through the heat sink, such that the semiconductor, and in particular its connecting part, can be fastened to the circuit board securely and protected from the mechanical stress.
FIGS. 2A and 2B
show an example of such a circuit unit, including a circuit board
1
, a field effective transistor (FET)
2
, a heat sink
3
, a casing
4
and screws
5
serving as fastening devices. The heat sink
3
has a plurality of holes
3
a
prepared on its front, back and bottom surfaces for accepting therein a tapping screw
5
(or a rivet throughout herein) such that the FET
2
, the casing
4
and the circuit board
1
can be affixed to the heat sink
3
. Explained more in detail, the bottom surface of the heat sink
3
is attached to the upper surface of the circuit board
1
and the heat sink
3
is fastened to the circuit board
1
by means of a screw
5
passed through the circuit board
1
and inserted from below into a prepared hole
3
a
on the bottom surface of the heat sink
3
. The FET
2
is attached to the front of the heat sink
3
and secured to it by means of another screw
5
inserted into a corresponding hole
3
a
from the front. The heat sink
3
is further fastened to the casing
4
by means of still another screw
5
inserted into still another hole
3
a
on the back side of the heat sink
3
. In some examples, a plurality of FETs
2
may be required, say, for forming a bridge circuit for driving a motor. In such a case, the heat sink
3
becomes an elongated member extending in the direction of their arrangement, having a plurality of holes
3
a
on its front surface for attaching the FETs therethrough.
In summary, prior art circuit units were structured such that a plurality of independent holes with a circular sectional shape had to be prepared on each surface of a heat sink to which other components were to be attached. Thus, their productivity was low and their production cost could not be reduced easily. These holes must be prepared by machining as a secondary process after the heat sink is prepared in its basic form. Thus, the preparation of these holes involves a number of extra steps. For example, the heat sink is preliminary produced by extrusion molding of aluminum in its basic form without any holes, and then it is set on a drilling machine for each surface to prepare the individual holes. Thus, the production of a heat sink cannot be accomplished in a single step.
Such a problem related to the drilling of holes for fastening is not limited to the production of a circuit unit for an automobile but is also present with regard to fastening mechanisms of many sorts using a fastening device such as a screw or a rivet.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a fastening mechanism using a fastening component such as a screw or a rivet having a shaft to be screwed or pushed into a target object to be fastened but requiring no drilling (as secondary process) for preparing holes for accepting the tips of these fastening components.
A fastening mechanism embodying this invention with which the above and other objects can be accomplished may be characterized not only as comprising one or more objects (“first objects”) to be fastened by this mechanism, a target object (“second object”) to which the first objects are to be fastened and one or more fastening members such as tapping screws and rivets each having a shaft with which the first object or objects are to be fastened to the second object, but also wherein the second object has a groove or grooves formed thereon and each of the first objects is fastened to the second object by having the shaft of at least one of these fastening members to pass penetratingly therethrough and inserted into the groove and affixed to the second object. Since such a groove can be formed when the second object is produced by a molding process, there is no need to drill holes for accepting tapping screws and/or rivets as a secondary process. Thus, the present invention has the merits of improving productivity and reducing production costs of products using such a fastening mechanism. The invention is particularly advantageous if the second object is produced as a member having a uniform cross-sectional shape along a specified direction and the groove is over the entire length of the member in that direction because such a member can be produced in a single production step by a molding process with the groove in the direction of releasing the molded product from the mold.
The present invention is particularly useful where the aforementioned target (second) object is a heat sink used in a circuit unit and the first objects are various components of the circuit unit such as circuit elements, a circuit board and a casing. The circuit unit may typically be a control circuit unit for a system of a different kind to be carried on a motor vehicle such as an AC inverter, an electrical power steering (EPS) system, a daytime running light (DRL) system, a power slide door system and an anti-skid braking (ABS) system.
REFERENCES:
patent: 4288839 (1981-09-01), Prager et al.
patent: 4471407 (1984-09-01), Sleder
patent: 4695924 (1987-09-01), Wozniczka
patent: 5191512 (1993-03-01), Ogura et al.
patent: 5414592 (1995-05-01), Stout et al.
patent: 5461541 (1995-10-01), Wentland, Jr. et al.
patent: 6046908 (2000-04-01), Feng
patent: 1-304800 (1989-01-01), None
patent: 4-96296 (1992-03-01), None
Ikushima Yoshihiro
Ohkubo Yutaka
Yoshikawa Hidetoshi
Beyer Weaver & Thomas LLP
Omron Corporation
Thompson Gregory
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