Electrical resistors – Mounted on wheels or vehicle
Reexamination Certificate
2002-11-06
2004-06-08
Easthom, Karl D. (Department: 2832)
Electrical resistors
Mounted on wheels or vehicle
C338S220000, C338S221000, C338S051000, C338S053000, C338S058000, C338S048000, C338S239000, C338S260000, C338S325000
Reexamination Certificate
active
06747543
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resistor for driving a motor for an air conditioner blower for use in an air ventilation unit for an automobile in order to control a rotational speed of the blower motor, and more particularly, to an air conditioner blower motor driving resistor in which resistance bodies made of metal thin plates are separated into two or more sheets of resistance bodies and stacked over one after another together with insulation plates, and a temperature fuse is externally disposed.
2. Description of the Related Art
Various types of resistors for driving a motor for an air conditioner blower are known.
FIG. 1
is a perspective view showing an example of a conventional resistor for driving a motor for an air conditioner blower.
FIG. 2
is an exploded perspective view of the
FIG. 1
conventional resistor.
FIG. 3
is a perspective view showing another example of a conventional resistor for driving a motor for an air conditioner blower.
FIG. 4
is an exploded perspective view of the
FIG. 3
conventional resistor.
FIG. 7C
illustrates a resistance body of a single plate structure for use in a conventional air conditioner blower motor driving resistor.
FIG. 12B
schematically shows a resistance body realized in a conventional air conditioner blower motor driving resistor.
Referring to
FIGS. 1 through 4
,
7
C and
12
B, a conventional air conditioner blower motor driving resistor includes a connector
20
for connecting to an air ventilation unit and a resistor
10
having a resistance body
11
.
The resistor
10
includes a thermal radiator
13
for emitting heat of the resistance body
11
, a cover member
14
for covering the resistor
10
, and insulation plates
12
installed at both sides of the resistance body
11
in order to insulate the resistance body
11
, in which a soldering portion
30
being an overheat prevention unit is soldered and connected between the lower terminals.
The resistance body
11
in the resistor
10
includes a common terminal
21
and three select terminals
22
,
23
and
24
, in which a resistance circuit is formed so that respectively different resistance values exist between the terminals
22
,
23
and
24
.
Hereinafter, a resistor between the common terminal
21
and the first select terminal
22
is denoted as R
3
, a resistor between the first select terminal
22
and the second select terminal
23
is denoted as R
2
, and a resistor between the second select terminal
23
and the third select terminal
24
is denoted as R
1
. Also, the rotational speed of the blower motor is called a first step speed, a second step speed and a third step speed from the lowest speed.
That is, if the common terminal
21
and the third select terminal
24
are selected, the resistance value becomes R
1
+R
2
+R
3
. As a result, since the resistance value becomes the largest, the rotational speed of the blower motor becomes the lowest speed, that is, the first step speed. If the common terminal
21
and the second select terminal
23
are selected, the resistance value becomes R
3
+R
2
. As a result, the rotational speed of the blower motor becomes the second step speed. If the common terminal
21
and the third select terminal
22
are selected, the resistance value becomes R
3
. As a result, the rotational speed of the blower motor becomes the three step speed which is the highest speed.
In the case of the conventional resistance body, the respective resistance values are formed on only a single metal thin plate. As a result, as shown, the line width of the resistance body
11
is very narrow and the interval between the resistance circuits is also narrow. Accordingly, the short circuit phenomenon frequently occurs to raise an out-of-trouble. Also, the intensity is lowered to make it difficult to fabricate a resistor.
That is, as shown in
FIGS. 7C and 12B
, in order to have a resistance value in a limited area, a portion denoted as “a” has an extremely narrow line width in case of R
1
. As illustrated in the following equation,
R
=&rgr;×(
L/A
)[&OHgr;]
(R: resistance, &rgr;: specific resistance, A: cross-sectional area, and L: the length of a circuit), since a resistance is proportional with a length, and inversely proportional with a cross-sectional area, a portion “a” having a cross-sectional area of such a narrow line width can be easily overheated. Accordingly, the resistance value can be varied due to the heat. As a result, the resistance value becomes a resistance value differing from a design resistance value, to thus raise an operational error.
Meanwhile, a heat generated from a resistor circuit will be described with reference to the following equation.
H
=0.24
×I
2
RT[cal]
(I: current, R: resistance, and T: unity time)
A heat generated during operation of a resistor, called a Joule's heat is proportional with a square of current. As described above, the Joule's heat is inversely proportional with a cross-sectional area of the circuit. In order to reduce a current density per a unity area, a circuit width should be increased to dissipate the generated heat. This should be reflected on designing and fabricating a circuit and a heat radiator.
That is, as the width of a thin plate forming a resistance circuit is narrower, a possibility of breaking of wires becomes higher. As the width of a thin plate forming a resistance circuit is wider, a possibility of breaking of wires becomes lower. Thus, a structural change necessary for improving the line width of each resistor has been required.
As illustrated in the Table of
FIG. 13
, an electric power of the resistance in each resistance body is 10.6 W for R
3
, 18.2 W for R
2
and 30 W for R
1
in case of a first step speed, 35 W for R
3
, 60 W for R
2
and 0 W for R
1
in case of a second step speed, and 140 W for R
3
, 0 W for R
2
and R
1
in case of a three step speed. In this case, it can be seen that the electric power at the R
1
and R
2
sides becomes much smaller than that at the R
3
side. In order to thermally radiate the entire resistance body, a thermally radiating structure without considering a heat generating quantity for each resistance body may cause a loss of materials for fabricating components.
In particular, as shown in
FIGS. 3 and 4
, a cylindrical temperature fuse has been used as an overheat preventive unit in the conventional art. However, since such a resistor structure adopts a structure of soldering and connecting the resistance bodies at the state where the outer upper portion of the cover member is cut, it may cause a short circuit with the inner wall of the thermal radiator. Also, since dispersion of a resistance value R
3
is large, the structure of the resistor is complicated, and the fabrication process is difficult, a production cost becomes high and a failure rate level is high.
Also, since a conventional resistance body of a copper-nickle alloy needs a high material cost. It is nearly impossible to be applied as a semiconductor material since dispersion of the resistance value is high. Also, since a temperature characteristic is inferior and a mechanical strength is not good in the processes of the film etching and the resistor assembly.
SUMMARY OF THE INVENTION
To solve the above problems of the conventional air conditioner blower motor driving resistor, it is an object of the present invention to provide an air conditioner blower motor driving resistor, in which resistance bodies are separated into a number of metal thin plates and stacked over one after another, to thereby obtain a desired resistance value and reduce volume of the resistor to be more compact, and to thereby secure line widths in resistance circuits and intervals between the resistance circuits in order to reduce a short circuit frequency during overheat and suppress a failure rate.
It is another object of the present invention to provide an air conditioner blower motor driving resistor in which a thermal radiator is minimized and removed in a resis
Dong
Easthom Karl D.
F. Chau & Associates LLP
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