Abstrict
An electric heater apparatus for automobiles is disclosed. A sheathed
heater (14a) constituting a heat generating member of a heater assembly
(14) generates heat by power supplied from a main power supply for
generating a DC high voltage through an inverter. A thermal fuse
(15) has a temperature detecting element (15a) (low-melting alloy)
adapted to fuse when a set temperature is reached. The temperature
detecting element (15a) is connected to the power circuit of the
sheathed heater (14a) through lead wires (15b, 15c). The thermal
fuse (15) is arranged in such a position that the longitudinal direction
of the temperature detecting element (15a) accommodated in the casing
(17) is coincident with the longitudinal direction of the heater
assembly 14, and mounted in surface-to-surface contact with the
body (aluminum body (14c)) of the heater assembly (14). Also, the
interior of the casing (17) is sealed with a material (such as cement
or a silicon caulking material) higher in heat conductivity than
air.
Claims
The invention claimed is:
1. An automotive electric heater apparatus comprising an electric
heater for generating heat with power supplied from a high voltage
power supply, and a thermal fuse including a temperature detecting
element connected in series to the electric heater through lead
wires, the temperature detecting element fusing and turning off
the power circuit of the electric heater when the electric heater
is abnormally overheated, wherein the thermal fuse includes a casing
accommodating the temperature detecting element and the lead wires
therein and mounted on a body surface of the electric heater, and
the interior of the casing is filled up with a material being higher
in heat conductivity than air; the casing of the thermal fuse is
arranged in such a manner that the longitudinal direction of the
temperature detecting element coincides with the longitudinal direction
of the electric heater, and one of the lead wires connected to an
end of the temperature detecting element is bent in the shape of
U in the casing on a plane generally parallel to the body surface
of the electric heater and led out in the same direction as the
other lead wire connected to the other end of the temperature detecting
element; and the casing is mounted in surface-to-surface contact
with the body of the electric heater.
2. An automotive electric heater apparatus according to claim 1,
wherein said material having a higher heat conductivity than air
contains ceramic or cement as a main component.
3. An automotive electric heater apparatus according to claim 1,
wherein the casing of the thermal fuse is fixed on the body of the
electric heater through a bracket.
4. An automotive electric heater apparatus according to claim 1,
wherein the temperature detecting element is encased in an insulating
container.
5. An automotive electric heater apparatus according to claim 4,
wherein the insulated container and the lead wires are fixed in
place by the material being higher in heat conductivity than the
air.
6. An automotive electric heater apparatus according to claim 1,
wherein the lead wires are fixed in place by the material being
higher in heat conductivity than the air.
7. An automotive electric heater apparatus according to claim 1,
wherein the material being higher in heat conductivity is disposed
between the temperature detecting element and the electric heater.
8. An automotive electric heater apparatus according to claim 1,
wherein the electric heater includes a sheathed heater and a hot
water pipe, the sheathed heater being arranged adjacent to one of
two straight portions of a U-shaped lead wire and the hot water
pipe being arranged adjacent to the other of the two straight portions
of the U-shaped lead wire, and the temperature detecting element
is arranged at a straight portion of the hot water pipe side.
9. An automotive electric heater apparatus according to claim 1,
wherein the electric heater includes a sheathed heater and a hot
water pipe, both of the sheathed heater and the hot water pipe being
embedded in an aluminum body.
10. An automotive electric heater apparatus comprising an electric
heater for generating heat with power supplied from a high voltage
power supply, and a thermal fuse including a temperature detecting
element connected in series to the electric heater through lead
wires, the temperature detecting element fusing and turning off
the power circuit of the electric heater when the electric heater
is abnormally overheated, wherein the thermal fuse includes a casing
accommodating the temperature detecting element and the lead wires
therein and mounted on a body surface of the electric heater, the
casing is arranged in such a manner that the longitudinal direction
of the temperature detecting element coincides with the longitudinal
direction of the electric heater, and one of the lead wires connected
to an end of the temperature detecting element is bent in the shape
of U in the casing on a plane generally parallel to the body surface
of the electric heater and led out in the same direction as the
other lead wire connected to the other end of the temperature detecting
element; and the casing is mounted in surface-to-surface contact
with the body of the electric heater.
11. An automotive electric heater apparatus according to claim
10, wherein said material higher in heat conductivity than air contains
ceramic or cement as a main component.
12. An automotive electric heater apparatus according to claim
10, wherein the casing of the thermal fuse is fixed on the body
of the electric heater through a bracket.
13. An automotive electric heater apparatus according to claim
10, wherein the electric heater includes a sheathed heater and a
hot water pipe, the sheathed heater being arranged adjacent to one
of two straight portions of a U-shaped lead wire and the hot water
pipe being arranged adjacent to the other of the two straight portions
of the U-shaped lead wire, and the temperature detecting element
is arranged at a straight portion of the hot water pipe side.
14. An automotive electric heater apparatus according to claim
10, wherein the electric heater includes a sheathed heater and a
hot water pipe, both of the sheathed heater and the hot water pipe
being embedded in an aluminum body.
15. An automotive electric heater apparatus comprising: an electric
heater; a thermal fuse including a temperature detecting element
and a casing accommodating the temperature detecting element and
lead wires connecting the temperature detecting element in series
with the electric heater; and a material being higher in heat conductivity
than air disposed between the temperature detecting element and
the electric heater; wherein the material is disposed between the
lead wires and the electric heater; and one of the lead wires is
bent in the shape of a U in the casing on a plane generally parallel
to a body surface of the electric heater.
16. An automotive electric heater apparatus according to claim
15, wherein the electric heater includes a sheathed heater and a
hot water pipe, the sheathed heater being arranged adjacent to one
of two straight portions of a U-shaped lead wire and the hot water
pipe being arranged adjacent to the other of the two straight portions
of the U-shaped lead wire, and the temperature detecting element
is arranged at a straight portion of the hot water pipe side.
17. An automotive electric heater apparatus according to claim
15, wherein the electric heater includes a sheathed heater and a
hot water pipe, both of the sheathed heater and the hot water pipe
being embedded in an aluminum body.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automotive electric heater
apparatus utilizing a high voltage power supply of 200 V to 400
V DC.
2. Description of the Related Art
Automotive vehicles such as a fuel cell-powered vehicle, an electric
car and a hybrid car with little waste heat are designed to employ
an electric heater as a heating system by using a high-voltage power
supply together with a thermal fuse for protecting the electric
heater (Japanese Unexamined Patent Publication No. 2002-324653).
The thermal fuse, as shown in FIGS. 4A, 4B, includes a temperature
detecting element 120 (low-melting alloy) connected to an electric
heater 110 through lead wires 100. A ceramic container 130 accommodating
the temperature detecting element 120 is inserted into an insulating
tube 140 together with the lead wires 100, and the insulating tube
140 is mounted in contact with an aluminum body 150 of the electric
heater 110. In the case where the electric heater 110 is abnormally
overheated, heat is transmitted from the aluminum body 150 to the
lead wires 100 in the insulating tube 140, and when the temperature
detecting element 120 which has received the heat from the lead
wires 100 reaches a set temperature, the thermal fuse fuses and
turns off the power circuit of the electric heater 110.
In the thermal fuse described above, however, only a peripheral
part of the insulating tube 140 is in contact with the surface of
the aluminum body 150 of the electric heater 110 as shown in FIG.
4B and, therefore, the contact area between the insulating tube
140 and the aluminum body 150 is very small. Also, an air layer
(an air layer in the insulating tube 140) low in heat conductivity
in the path of the heat transmitted from the aluminum body 150 to
the lead wires 100 causes a considerable length of time to be consumed
before the temperature detecting element 120 blows (the thermal
fuse has a low temperature sensitivity). As a result, the surface
temperature of the aluminum body 150 increases greatly (to, say,
400.degree. C. or higher) before the temperature detecting element
120 actually fuses, thereby posing a safety problem.
Also, in the thermal fuse shown in FIGS. 4A, 4B, the two lead wires
100 connected to the temperature transducer 120 are led out in opposite
directions. Therefore, a harness (not shown) connected to one of
the lead wires 100 is required to be laid in U-turn form, and the
resulting detour-connection of harness reduces the working efficiency.
SUMMARY OF THE INVENTION
This invention has been achieved in view of the situation described
above, and the object thereof is to provide an automotive electric
heater apparatus in which the temperature sensitivity of the thermal
fuse is improved, for a higher safety, while, at the same time,
improving the connection of the harness to the lead wires of the
thermal fuse.
According to one aspect of the invention, there is provided an
automotive electric heater apparatus comprising an electric heater,
for generating heat with power supplied from a high voltage power
supply of 200 V to 400 V DC, and a thermal fuse including a temperature
detecting element connected in series to the electric heater through
lead wires, wherein the temperature detecting element is adapted
to blow and turn off the power circuit of the electric heater when
the electric heater is abnormally overheated, and wherein the thermal
fuse includes a casing accommodating the temperature detecting element
and the lead wires therein and mounted on the body surface of the
electric heater, and the interior of the casing is sealed with a
material higher in heat conductivity than air.
In this configuration, as described above, the interior of the
casing accommodating the temperature detecting element and the lead
wires is sealed with a material higher in heat conductivity than
the air. As compared with a case in which the interior of the casing
is filled with air, therefore, the temperature sensitivity of the
thermal fuse is improved and, when the electric heater is abnormally
overheated, therefore, the temperature detecting element fuses within
a shorter time. As a result, in the case where the electric heater
is abnormally overheated, the temperature detecting element fuses
and turns off the power circuit of the electric heater at an early
time to assure a higher safety.
Also, the periphery of the temperature detecting element and the
lead wires is fixedly covered with a material high in heat conductivity.
Should the casing be broken, therefore, the lead wires (blown portion)
are not exposed and the power circuit of the electric heater is
positively turned off when the temperature detecting element fuses.
According to another aspect of the invention, there is provided
an automotive electric heater apparatus comprising an electric heater,
for generating heat with power supplied from a high voltage power
supply of 200 V to 400 V DC, and a thermal fuse including a temperature
detecting element connected in series to the electric heater through
lead wires, wherein the temperature detecting element is adapted
to fuse and turn off the power circuit of the electric heater when
the electric heater is abnormally overheated, and wherein the thermal
fuse includes a casing accommodating the temperature detecting element
and the lead wires therein and mounted on the body surface of the
electric heater, the casing is arranged in such a manner that the
longitudinal direction of the temperature detecting element coincides
with the longitudinal direction of the electric heater, and one
of the lead wires connected to an end of the temperature detecting
element is bent in the shape of U in the casing and led out in the
same direction as the other lead wire connected to the other end
of the temperature detecting element.
In this configuration the two lead wires connected to the temperature
detecting element are led out of the casing in the same direction.
Therefore, the harness connected to the lead wires is not required
to be laid in U-turn fashion, thereby improving the harness connection
for an improved working efficiency.
As the thermal fuse is of such a type that the longitudinal direction
of the temperature detecting element is arranged in the longitudinal
direction of the electric heater, the width of the casing can be
reduced as compared with the type in which the lead wires are led
out in the direction at right angles to the temperature detecting
element. Thus, the casing is not exposed outside the body of the
electric heater and can be arranged efficiently.
According to still another aspect of the invention, there is provided
an automotive electric heater apparatus, wherein the casing of the
thermal fuse is arranged in such a manner that the longitudinal
direction of the temperature detecting element coincides with the
longitudinal direction of the electric heater, and one of the lead
wires connected to an end of the temperature detecting element is
bent in the shape of U in the casing and led out in the same direction
as the other lead wire connected to the other end of the temperature
detecting element.
In the automotive electric heater apparatus according to this invention,
a material containing ceramic or cement, as a main component having
a higher heat conductivity than air, can be used.
In the automotive electric heater apparatus according to this invention,
the casing is mounted in surface-to-surface contact with the body
of the electric heater.
With this configuration, as compared with the prior art (Japanese
Unexamined Patent Publication No. 2002-324652) in which an insulating
tube is arranged in contact with the body surface of the electric
heater, the contact area between the casing and the body surface
of the electric heater is increased and, therefore, the temperature
sensitivity of the thermal fuse increases. In the case where the
electric heater is abnormally overheated, the temperature detecting
element fuses and turns off the power circuit of the electric heater
earlier for a further improved safety.
In the automotive electric heater apparatus according to this invention,
the casing of the thermal fuse is fixed on the body of the electric
heater through a bracket.
The thermal fuse according to the invention is not fixed by solder
or the like on a control board, for example, but on the body of
the electric heater through a bracket which is screwed and securely
fixed.
The present invention may be more fully understood from the description
of preferred embodiments of the invention, as set forth below, together
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1A is a perspective view of an electric heater apparatus having
a thermal fuse, and FIG. 1B a sectional view of a heater assembly.
FIG. 2 is a perspective view showing a method of fixing the thermal
fuse and is a sectional view of a casing accommodating a temperature
detecting element.
FIG. 3 is a schematic diagram showing a configuration of an air
conditioning system.
FIGS. 4A, 4B are a diagram for explaining the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Next, an embodiment of the invention will be explained with reference
to the accompanying drawings.
This embodiment represents an example of application of the electric
heater apparatus according to the invention to the air conditioning
system of a fuel cell-powered vehicle driven with an electric motor
as a power source. FIG. 1A is a perspective view of the electric
heater apparatus, and FIG. 3 a schematic diagram showing a configuration
of the air conditioning system.
The air conditioning system includes a duct 1 for introducing the
air into the passenger compartment, a blower 2 for introducing and
supplying the air from inside or outside the passenger compartment
into the duct 1, an evaporator 3 and a heater core 4 arranged in
the duct 1, and an air mix door 5 for adjusting the temperature
of the air blown into the passenger compartment. The air conditioning
system is controlled by an electronic control unit (ECU) 6.
The evaporator 3 is a well-known heat exchanger used in a refrigeration
cycle and cools the blown air by exchanging heat with a low-temperature
refrigerant supplied by the operation of a compressor 7.
The compressor 7 is driven by an AC motor, and the rotational speed
of the AC motor (i.e. the amount of the refrigerant discharged from
the compressor 7) is controlled by the ECU 6 through an inverter
8. The inverter 8 is supplied with DC current from a main power
supply 9 (the high voltage power supply according to the invention)
mounted on the vehicle. The main power supply 9 is charged by a
fuel cell not shown and generates a high voltage of 200 V to 400
V DC.
The heater core 4 is arranged downstream of the evaporator 3 along
the air flow in the duct 1, is connected with a cooling water circuit
10, and heats the blown air by exchanging heat with the hot water
flowing in the heater core 4.
The cooling water circuit 10 includes a pump 11 for circulating
the cooling water, an electric heater apparatus 12 according to
the invention for heating the cooling water, and a water temperature
sensor 13 for detecting the temperature of the cooling water supplied
to the heater core 4.
The air mix door 5 is arranged rotatably between a position of
the lowest temperature (position indicated by dashed line in FIG.
3) where the air inlet side of the heater core 4 is closed up and
a position of the highest temperature (position indicated by solid
line in FIG. 3) where the detour circuit of the heater core 4 is
closed up. The air mix door 5 thus adjusts the ratio between the
air passing through the heater core 4 and the air detouring the
heater core 4 (the air flowing in the detour circuit) thereby to
change the blown air temperature.
The air adjusted in temperature by the air mix door 5 is blown
into the passenger compartment by way of an air outlet (not shown)
selected in accordance with the air outlet mode.
Next, the electric heater apparatus 12 is explained.
The electric heater apparatus 12 comprises, as shown in FIGS. 1A,
1B, a heater assembly 14 for heating the cooling water, and a thermal
fuse 15 constituting a protection device of the heater assembly
14.
The heater assembly 14, as shown in FIG. 1B, is configured of a
sheathed heater 14a making up a heat generating member embedded
in an aluminum body 14c together with a hot water pipe 14b.
The sheathed heater 14a is connected to the inverter 8 and heated
by the power supplied from the main power supply 9 through the inverter
8.
The duty cycle of the power supplied to the sheathed heater 14a
is controlled by the ECU 6 through the inverter 8 in such a manner
that the cooling water temperature detected by the water temperature
sensor 13 is held at a predetermined level (say, 80.degree. C. at
maximum).
The hot water pipe 14b has an end thereof connected to the outlet
of the pump 11, and the other end thereof connected to the hot water
inlet of the heater core 4, thus constituting a part of the cooling
water path.
The thermal fuse 15 includes a temperature detecting element 15a
(low-melting alloy) adapted to fuse when a set temperature (say,
180.degree. C.) is reached. The temperature detecting element 15a
is connected to the power circuit of the sheathed heater 14a through
two lead wires 15b15c. (Specifically, the lead wire 15b is connected
to the inverter 8, and the other lead wire 15c is connected in series
with the sheathed heater 14a.)
The thermal fuse 15 has a casing 17 for accommodating the temperature
detecting element 15a encased in the insulating container 16 and
the two lead wires 15b, 15c.
The lead wire 15b connected to an end of the temperature detecting
element 15a is bent in the shape of U in the casing 17 and, together
with the other lead wire 15c connected to the other end of the temperature
detecting element 15a, is led out in the same direction from one
side of the casing 17.
The casing 17 is formed of an insulating material, such as a ceramic,
high in heat conductivity and is screwed, through a bracket 18 (FIG.
2), to an aluminum body 14c of the heater assembly 14. The casing
17, as shown in FIG. 1A, is arranged so that the longitudinal direction
of the temperature detecting element 15a is coincident with the
longitudinal direction of the heater assembly 14 and is mounted
in surface contact with the body of the heater assembly 14.
Also, the interior of the casing 17 is sealed (filled up) with
a material being higher in heat conductivity than air and having
stiffness capable of enduring breaking energy when the thermal fuse
15 is fused (such as cement or a silicon caulking agent).
As described above, the electric heater apparatus 12 has the interior
thereof sealed with a material having a higher heat conductivity
than air. Therefore, heat is transmitted more quickly from the body
surface of the heater assembly 14 through the lead wires 15b, 15c
to the temperature detecting element 15a. The casing 17, which is
formed of a ceramic high in heat conductivity, is mounted in surface
contact on the body of the heater assembly 14, and, therefore, the
thermal resistance thereof is reduced. As a result, the temperature
sensitivity of the thermal fuse 15 is improved. As compared with
the prior art (Japanese Unexamined Patent Publication No. 2002-324653),
therefore, the temperature detecting element 15a fuses within a
shorter time when the sheathed heater 14a is abnormally overheated.
The earlier fusing of the temperature detecting element 15a turns
off the power circuit of the sheathed heater circuit 14a earlier.
Thus, the surface temperature of the heater assembly 14 (the surface
temperature of the aluminum body 14c) is prevented from increasing
excessively (say, 400.degree. C. or higher) thereby to assure an
improved safety.
The interior of the casing 17 is sealed with a material high in
heat conductivity (i.e. the surroundings of the insulating container
16 and the lead wire 15b are fixed by a material high in heat conductivity),
as described above. Should the casing 17 be broken, therefore, the
temperature detecting element 15a which may fuse is not exposed
to the exterior. Thus, the fused part of the temperature detecting
element 15a is kept out of contact with the body surface of the
heater assembly 14 and prevented from being grounded. In this way,
the power circuit of the sheathed heater 14a can be turned off safely
and positively.
Further, the lead wire 15b of the thermal fuse 15 connected to
an end of the temperature detecting element 15a is bent in the shape
of U in the casing 17, and together with the other lead wire 15c
connected to the other end of the temperature detecting element
15a, is led out in the same direction from one side of the casing
17. As shown in FIG. 1A, therefore, the harness 19 connected to
the lead wires 15b, 15c is not required to be laid in U-turn fashion.
Thus, the connection of the harness 19 is improved for an improved
working efficiency.
Also, in view of the fact that the length of the temperature detecting
element 15a is arranged along the length of the heater assembly
14, the width of the casing 17 (horizontal width in FIG. 2) can
be reduced as compared with the thermal fuse of the type in which
the lead wires are led in the direction at right angles to the temperature
detecting element. As a result, the casing 17 can be arranged in
an efficient way without being exposed from the heater assembly
14.
The bracket 18 for fixing the casing 17 of the thermal fuse 15
to the heater assembly 14 may be fixed by other than the screw (by
a clamp, for example).
According to this embodiment, the electric heater apparatus 12
according to the invention is applied to the air conditioning system
of the fuel cell-powered vehicle. Nevertheless, the electric heater
apparatus 12 according to the invention may be used for the heating
system of other vehicles (such as an electric car and a hybrid car),
with little waste heat, with equal effect.
While the invention has been described by reference to specific
embodiments chosen for purposes of illustration, it should be apparent
that numerous modifications could be made thereto by those skilled
in the art without departing from the basic concept and scope of
the invention. |