JP2002324653A - Electric heater device and air conditioner for use in vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to use a thermal fuse as a protection for the electric heater driven by DC power of high voltage and high current. SOLUTION: Based on the evaluation result of the reliability of a thermal fuse, the voltage of the DC power source 17 and the resistance value of the electric heater 53a, 53b are set in order to make the maximum actual working power 2 kW or less, and the thermal fuses 80a, 80b are used in that condition of securing high reliability. Hence, the thermal fuse can be used practically as a protection of the electric heater.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric heater provided with an electric heater for heating a fluid by supplying DC power, and is particularly suitable for an air conditioner for a vehicle for air conditioning a vehicle interior.

[0002]

2. Description of the Related Art Conventionally, a vehicle equipped with an electric motor for traveling (for example, a hybrid vehicle, a fuel cell electric vehicle).
In this case, electric power is supplied from a DC power supply of about 300 V to the electric motor for traveling. In such an air conditioner for an automobile, an electric heater is used for heating the conditioned air blown into the passenger compartment, and a high voltage of about 300 V is applied to the electric heater from the DC power supply (Japanese Patent Laid-Open No.
157446).

[0003] In a general-sized passenger car,
When only an electric heater is used as a heat source for heating the conditioned air, an electric heater having a capacity of about 6 kW is required from the viewpoint of heating capacity, and vehicle waste heat (for example, engine cooling water) and electric heater When both are used as heat sources, an electric heater having a capacity of about 3 kW is required.

When an electric heater driven by high-voltage, high-current DC power is provided, a relay for opening and closing an electric circuit of the electric heater, a temperature sensor for detecting the temperature of the electric heater, and this temperature sensor And a control circuit for controlling the relay based on the signal from the controller. When the electric heater is abnormally overheated, the electric circuit is shut off to protect the electric heater.

[0005]

However, in the above-described conventional apparatus, a relay, a temperature sensor, and a control circuit are required for protecting the electric heater, and there is a problem that the configuration is complicated and the cost is increased. . Also,
In the case of high-voltage, high-current DC power, an arc is generated at the contact point of the relay when the energizing circuit is cut off, and the arc causes the relay contact point to be welded, making it impossible to cut off the energizing circuit.

Therefore, it is conceivable to use a thermal fuse to protect the electrical heater by interrupting the energizing circuit when the electrical heater is overheated. The thermal fuse is highly reliable in AC, but is used in DC. Then, it is known that reliability is inferior.

That is, for example, in the case of AC 200 V, 50 or 60 Hz, the voltage applied to the thermal fuse is 3
After applying a high voltage of 00V or more, 5 m
The voltage becomes 0 V within s. Therefore, even if an arc is generated when the thermal fuse is blown, the arc disappears in a short time, so that the thermal fuse is blown without any problem.

However, when the above-mentioned thermal fuse for AC 200 V, 50 or 60 Hz is used at DC 300 V, an arc generated at the time of melting of the thermal fuse easily occurs because the thermal fuse is constantly applied with a high voltage of 300 V. Therefore, the thermal fuse may not be blown, or may be fused again after the blow. Therefore, it has been difficult to use a thermal fuse for protecting an electric heater driven by high-voltage, high-current DC power.

The present invention has been made in view of the above points, and has as its object to enable use of a thermal fuse for protecting an electric heater driven by high voltage and high current DC power.

[0010]

Means for Solving the Problems By the way, the present inventor has proposed:
A thermal fuse of the type shown in FIG.
1 and 802 are connected by a fusible conductor 803) to a direct-current power supply circuit, and the temperature fuse is heated to a temperature equal to or higher than its set temperature (= the fusing temperature of the fusible conductor 803). And the reliability of the thermal fuse (= number of normally operated samples / total number of samples × 100%).
4 and 5 show the results. When the current is 10 A, 100% reliability is obtained at a voltage of 200 V or less (that is, at a power of 2 kW or less), and when the voltage is 300 V, the current is 7 A. It was confirmed that 100% reliability was obtained below (that is, the power was 2.1 kW or less).

The present invention has been made based on the above-mentioned evaluation results. In order to achieve the above object, according to the first aspect of the present invention, a fluid is supplied from a DC power supply (17) via an energizing circuit. Electric heaters (53
a, 53b) are connected in parallel, and electric heaters (53a, 53b) are connected.
b) The temperature fuses (80a, 80b), which are blown when an abnormal overheat occurs and cut off the current-carrying circuit, are connected to the electric heaters (53a,
53b), characterized in that they are connected in series.

According to this, since a plurality of electric heaters are connected in parallel and the temperature fuses are connected in series for each electric heater, the current flowing through one electric heater and one temperature fuse is reduced, and high reliability is achieved. The thermal fuse can be used under the condition that the property can be obtained, and the thermal fuse can be practically used for protecting an electric heater driven by high-voltage, high-current DC power. And, by using thermal fuse, relay for protection of electric heater,
The cost can be reduced by eliminating the need for a temperature sensor and a control circuit.

[0013] In implementing the invention of claim 1,
According to the second aspect of the present invention, the electric heater (53a,
It is desirable to limit the actual maximum power consumption per one of the devices 53b) to 2 kW or less.

Further, as in the third aspect of the present invention, the actual maximum power consumption per electric heater (53a, 53b) can be made 500 W or more.

Further, as in the invention according to claim 4, the thermal fuse (80a, 80b) has a fusible conductor (803) that melts at a set temperature or higher, and the fusible conductor (80b).
According to 3), a type in which two terminals in the energized circuit are connected can be used.

Further, as in the invention according to claim 5, the electric heater device according to any one of claims 1 to 4 can be used for an air conditioner for a vehicle.

The reference numerals in parentheses of the above-mentioned means indicate the correspondence with specific means described in the embodiments described later.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. This embodiment is an example in which the present invention is applied to an air conditioner for an automobile having a not-shown traveling electric motor as a traveling drive source of the vehicle. FIG. 1 shows a schematic configuration of the vehicle air conditioner.

In FIG. 1, a blower 1 for blowing air from a vehicle compartment air taken in from an inside air inlet (not shown) or outside air from a vehicle room taken from an outside air inlet is provided in a ventilation duct 10.
1 is provided, and on the downstream side of the air flow of the blower 11,
Air blown by heat exchange with refrigerant (hereinafter referred to as conditioned air)
The evaporator 12 which cools is provided.

Further, a heater core 13 for reheating the conditioned air cooled by the evaporator 12 by heat exchange with hot water is disposed downstream of the air flow of the evaporator 12. The heater core 13 is disposed so as to close the passage in the ventilation duct 10 by about half.
3, a bypass air passage 14 is formed in parallel. An air mix upstream of the heater core 13 adjusts the ratio of air passing through the heater core 13 and air passing through the bypass air passage 14 to adjust the temperature of the conditioned air blown into the vehicle interior. A damper 15 is provided rotatably.

Although not shown, a defroster outlet for blowing temperature-controlled conditioned air toward the windshield and a face blower for blowing conditioned air toward the upper body of the occupant are provided at the most downstream portion of the air flow in the ventilation duct 10. An outlet and a foot outlet for blowing the conditioned air toward the feet of the occupant are provided respectively.

Electric compressor 16 for compressing and discharging refrigerant
Constitutes a well-known refrigeration cycle together with the evaporator 12, a condenser (not shown), an expansion valve, and the like. The electric compressor 16 includes a compression mechanism that compresses and discharges refrigerant, and an AC motor that drives the compression mechanism. Consists of To the motor of the electric compressor 16, DC power obtained from a DC power supply 17 mounted on the vehicle (a DC power supply with a rated voltage of 300 V in this embodiment) is converted into AC power by an inverter 18 and supplied.

The DC power supply 17 is charged by a fuel cell 30 that generates electric power using a chemical reaction between hydrogen and oxygen.

To adjust the temperature of the fuel cell 30 to a predetermined temperature range, a first cooling water circuit 40 is provided. In the first cooling water circuit 40, a first water pump 41 for circulating cooling water in the direction of arrow a, the fuel cell 3
0, a first coolant temperature sensor 42 for detecting the temperature of the coolant passing through the fuel cell 30, and a first coolant circuit 4 according to the coolant temperature.
A thermostat 43 for opening / closing the cooling water and a radiator 44 for exchanging heat between the cooling water and the outside air are provided.
The first cooling water circuit 40 includes a first water pump 4
The first bypass cooling water circuit 45 connects the cooling water flow upstream of the fuel cell 1 and the cooling water flow downstream of the fuel cell 30.

When the temperature of the cooling water becomes equal to or higher than the set temperature on the high temperature side, the thermostat 43 is opened, and the cooling water flows to the radiator 44 as indicated by an arrow a1 and is cooled. On the other hand, when the temperature of the cooling water becomes equal to or lower than the low temperature set temperature, the thermostat 43 closes,
The flow of the cooling water to the radiator 44 is cut off, and the cooling water is returned to the first water pump 41 via the first bypass cooling water circuit 45 as indicated by an arrow a2. By the operation of the thermostat 43, the temperature of the fuel cell 30 is adjusted to a temperature range in which high power generation efficiency can be obtained.

The cooling water which has become hot water due to the heat of the fuel cell 30 is supplied to the heater core 1 via the second cooling water circuit 50.
3, the heat of the fuel cell 30 is used for air conditioning. One end of the second cooling water circuit 50 is connected to the first cooling water circuit 40 downstream of the flow of the cooling water from the fuel cell 30, and the other end of the second cooling water circuit 20 is connected to the cooling water The first cooling water circuit 40 on the upstream side of the flow
It is connected to the.

In the second cooling water circuit 50, an electric three-way valve 51 for switching the flow of the cooling water in the second cooling water circuit 50, and a second electric motor for circulating the cooling water in the direction of arrow b.
Water pump 52, two electric heaters for heating the cooling water (see FIGS. 2 and 3) 53a, 53b, electric heater 5
A second water temperature sensor 54 for detecting the temperature of the cooling water passing through 3a and 53b, and a heater core 13 are provided. In the second cooling water circuit 50, the heater core 13
From the downstream side of the cooling water flow to the second bypass cooling water circuit 5
The second bypass cooling water circuit 55 is connected to the three-way valve 51.

The air conditioning ECU 19 includes a CPU (not shown),
A well-known microcomputer including an OM, a RAM, and the like is provided. The microcomputer performs arithmetic processing based on an input signal according to a program and a map stored in the microcomputer. A predetermined air-conditioning control is performed based on the arithmetic result. , The air mix damper 15, the inverter 18, the three-way valve 51, the second water pump 52, the first,
The second electric heaters 53a and 53b are controlled.

The vehicle control device (hereinafter referred to as a vehicle ECU) 60 includes a well-known microcomputer including a CPU, a ROM, a RAM, and the like (not shown), and performs calculations based on input information in accordance with programs and maps stored in the microcomputer. The processing is performed. The vehicle ECU 60 controls the traveling electric motor based on the depression amount of an accelerator pedal (not shown) and the like, and controls the fuel cell 30 based on the charging / discharging state of the DC power supply 17.
The power generation amount is controlled. In addition, vehicle EC
Information signals are input and output between the U60 and the air-conditioning ECU 19.

The first and second electric heaters 53a, 53
b is a sheathed heater using a nichrome wire.
The DC power obtained from the DC power supply 17 is supplied to the second electric heaters 53a and 53b under the duty control of the inverter 18.

As shown in FIG. 2, the first and second electric heaters 53a and 53b are connected in parallel to the DC power supply 17, and the electric characteristics of each of the electric heaters 53a and 53b are, in this embodiment, a resistance. The value is set to 60Ω, the rated voltage is set to 300 V, and the rated power is set to 1.5 kW. According to this,
If the actual maximum voltage of the DC power supply 17 is about 350 V or less,
The actual maximum power used per electric heater 53a, 53b is limited to 2 kW or less.

When the first electric heater 53a is abnormally overheated, a first temperature fuse 80a for interrupting a current supply circuit to the first electric heater 53a is connected in series to the first electric heater 53a. Is used to detect the temperature of the first electric heater 53a.
It is attached closely to. Similarly, the second electric heater 5
3b, the second temperature fuse 80b that cuts off the current supply circuit to the second electric heater 53b when the second electric heater 53b is overheated.
3b and the second thermal fuse 80b
Is mounted in close contact with the second electric heater 53b to detect the temperature of the second electric heater 53b.

FIG. 3 shows the structure of the thermal fuses 80a and 80b, in which the ends of two lead wires 801 and 802 forming an energizing circuit are set at a set temperature (about 1 in this example).
70 ° C.), a fusible conductor 80 made of a low melting point alloy
3 are connected. The fusible conductor 803 is covered with a flux, and the fusible conductor 803 and the lead wires 801, 8
02 is a cylindrical insulating case 80 made of ceramic.
4. Further, both ends of the insulating case 804 are closed with a resin layer 805, and the insulating case 804 and the resin layer 805 are covered with an insulating covering material 806.

Next, the inverter 18 will be described with reference to FIG. The DC power of the DC power supply 17 is supplied to the inverter 18 via a fuse 70. The inverter 18 switches the DC power by the compressor drive circuit 18a to generate an AC output (AC power) having a variable frequency, and variably controls the rotation speed of the electric compressor 16 by the AC output.

The inverter 18 switches the DC power by the heater drive circuit 18b to control the duty of the DC output (DC power) supplied to the first and second electric heaters 53a and 53b. By this duty control, a voltage equal to the voltage of the DC power supply 17 is applied to the first and second electric heaters 53a and 53b via the heater drive circuit 18b. Note that transistors (for example, IGBTs) are used as switching elements of the compressor drive circuit 18a and the heater drive circuit 18b.

The inverter 18 has an air conditioning ECU 19
And a control circuit 18c for controlling the operation of the compressor drive circuit 18a and the heater drive circuit 18b according to a command from the controller 17;
9 and a voltage detection circuit 18d that outputs the voltage to the voltage detection circuit 9.

Next, the operation of the vehicle air conditioner having the above configuration will be described.

The air-conditioning ECU 19 receives signals such as an engine cooling water temperature, a temperature inside the vehicle compartment, a temperature outside the vehicle compartment, an amount of solar radiation entering the vehicle compartment, a desired set temperature in the vehicle compartment, and a first water temperature sensor. 42 and a signal from the second water temperature sensor 54 are input.

The air-conditioning ECU 19 obtains a target blow-off temperature of the air blown into the cabin based on these signals, and sets the temperature of the air blown into the cabin (hereinafter referred to as blow-off air temperature) to the target blow-out temperature. The air mix damper 15, the electric compressor 16, the inverter device 1
8. Control the three-way valve 51, the second water pump 52, the first and second electric heaters 53a and 53b, and the like.

First, when an air conditioner switch (not shown) for determining operation and stop of the air conditioner is turned on, the air conditioner ECU 19 activates the second water pump 52 and, based on a signal from the first water temperature sensor 42, activates the three-way valve. The controller 51 controls the flow of the cooling water in the second cooling water circuit 50.

Specifically, when the temperature of the cooling water that has passed through the fuel cell 30 exceeds the set temperature and the conditioned air can be heated, the second cooling water circuit 50 and the second bypass cooling water circuit 55 Is shut off by the three-way valve 51. Thus, the fuel cell 30, the first and second electric heaters 53a, 53
b, a circuit connecting the heater core 13 is formed, and the fuel cell 3
0 is passed through the first and second electric heaters 53a,
The cooling water flowing through the heater core 53 and the heater core 13 and passing through the heater core 13 is returned to the fuel cell 30 as indicated by an arrow b1. In this case, the first and second electric heaters 53
Since the heating of the cooling water by a and 53b is unnecessary, the first and second electric heaters 53a and 53b are not energized.

On the other hand, when the temperature of the cooling water passing through the fuel cell 30 is lower than the set temperature, the second bypass cooling water circuit 5
5 and the upstream side of the cooling water flow of the second water pump 52, and the communication between the second bypass cooling water circuit 55 and the downstream side of the cooling water flow of the fuel cell 30 is shut off. As a result, the cooling water that has passed through the heater core 13 does not flow to the fuel cell 30 side, but returns to the second water pump 52 side via the second bypass cooling water circuit 55, as indicated by an arrow b2. In this case, the power supply to the first and second electric heaters 53a and 53b is controlled based on the signal of the second water temperature sensor 54 to adjust the temperature of the cooling water flowing into the heater core 13 to a predetermined temperature. I do.

When the electric heaters 53a and 53b and the waste heat of the fuel cell 30 are used as a heat source for heating the conditioned air as in this embodiment, about 3 kW is used for a general-sized passenger car. An electric heater of the capacity is required. However, as is clear from the results shown in FIGS. 4 and 5, when a thermal fuse is used to protect an electric heater that exhibits about 3 kW at a DC voltage of 300 V, the thermal fuse has 100% reliability. Absent.

Therefore, in the present embodiment, the necessary heating capacity is secured by using two 1.5 kW electric heaters, the two electric heaters 53a and 53b are connected in parallel, and a temperature fuse is provided for each electric heater. 80a, 80
By connecting b in series, the current flowing through one electric heater and one thermal fuse is reduced so that the thermal fuses 80a and 80b can be used under the condition that 100% reliability can be obtained. I have.

That is, when the DC power supply 17
When 0 V is generated, the current flowing through one thermal fuse is 5 A (that is, the power is 1.5 kW), and the thermal fuses 80 a and 80 b can obtain 100% reliability. Therefore, when the electric heaters 53a and 53b are abnormally overheated, the fusible conductor 803 of the temperature fuses 80a and 80b is reliably blown by receiving the heat of the electric heaters 53a and 53b, and the energizing circuit of the electric heaters 53a and 53b is cut off. Is done.

(Other Embodiments) In the above embodiment, an example was shown in which two electric heaters were used, but three or more electric heaters may be connected in parallel. In this case, a thermal fuse is connected in series for each electric heater, and
By setting the voltage of the DC power supply 17 and the resistance value of the electric heater so that the actual maximum power consumption of the electric heaters is 2 kW or less, the thermal fuse is used under the condition that 100% reliability can be obtained. be able to.

In the above embodiment, the sheathed heater is used as the first and second electric heaters 53a and 53b. However, the present invention may be any heater that generates heat by electricity, for example, a PTC heater using a PTC heater element. May be.

In the above-described embodiment, an example has been described in which the cooling water is heated by the first and second electric heaters 53a and 53b, and the conditioned air is heated by the heater core 13 using the heat of the cooling water. , First and second electric heaters 53a, 53b
Is disposed not in the second cooling water circuit 50 but in a position close to the heater core 13 in the ventilation duct 10, and when the amount of heating of the conditioned air by the heater core 13 is insufficient, the first,
The conditioned air may be directly heated by the second electric heaters 53a and 53b.

In the above embodiment, the electric compressor 16
Although the example in which the air-conditioning air is cooled by the refrigeration cycle constituted by the refrigeration cycle and the evaporator 12 is shown, the present invention is also applicable to a case where a heat pump cycle capable of switching between a cooling function and a heating function is configured as the refrigeration cycle. is there.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a vehicle air conditioner according to an embodiment of the present invention.

FIG. 2 is a block diagram of an electric circuit unit of FIG.

FIG. 3 is a sectional view showing a configuration of the thermal fuse of FIG. 2;

FIG. 4 is a diagram showing evaluation results of the reliability of the thermal fuse.

FIG. 5 is a diagram showing evaluation results of the reliability of the thermal fuse.

[Explanation of symbols]

17: DC power supply, 53a, 53b: Electric heater, 80
a, 80b: Thermal fuse.

Continued on the front page F term (reference) 3K058 AA12 AA22 BA04 CA23 5G502 AA02 BA03 FF06 FF07 5H115 PA08 PG04 QA04 SE10 TO05 TU11 TZ03

Claims (5)

[Claims] A plurality of electric heaters (53a, 53b), which are supplied with electric power from a DC power supply (17) through an energizing circuit to heat a fluid, are connected in parallel, and the electric heater (5) is connected.
An electric heater device characterized in that temperature fuses (80a, 80b) which are blown out when abnormal heating of 3a, 53b) and cut off the energizing circuit are connected in series for each of the electric heaters (53a, 53b). 2. One of the electric heaters (53a, 53b).
The electric heater device according to claim 1, wherein the actual maximum power consumption per unit is limited to 2 kW or less. 3. One of the electric heaters (53a, 53b).
3. The electric heater device according to claim 1, wherein the actual maximum power consumption per unit is 500 W or more. 4. The thermal fuse (80a, 80b)
Has a fusible conductor (803) that melts at a set temperature or higher, and the fusible conductor (803) connects between two terminals in the current-carrying circuit. 4. The electric heater device according to any one of items 3 to 3. 5. A vehicle air conditioner comprising the electric heater device according to claim 1, wherein the electric heater (53a, 53b) is used for heating conditioned air blown into the vehicle interior. An air conditioner for a vehicle, which is used.