JPS63231269A - Wind speed measuring instrument for air conditioning equipment for vehicle - Google Patents

Abstract

PURPOSE:To secure sufficient heat generation even when the temperature of an air flow is low and to suppress the supply of excessive electric power even when the air flow temperature is high by driving a thermosensitive element with a constant current. CONSTITUTION:Thermistors 2 for correction are provided in an air passage oppositely to wind speed thermistors 1. The wind speed thermistors 1 are applied with a voltage Ea through a constant current driving circuit 5 and the thermistor 2 for correction are applied with a voltage Ec through a resistance Rc. The outputs of the wind speed thermistors 1 and thermistors 2 for correction are connected to a voltage measuring instrument 4 through a switching circuit 3. The output of the voltage measuring instrument 4 is supplied to an arithmetic controller 6, which calculates a wind speed from the output of the voltage measuring instrument 4.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a wind speed measuring device for a vehicle air conditioner, and particularly to a vehicle air conditioner suitable for measuring the airflow temperature of a vehicle air conditioner over a wide range. Related to wind speed measuring device for aircraft.

[Conventional technology]

A low-cost, highly reliable measurement system is needed to control the air velocity at the outlet of a heater or cooler in a vehicle air conditioner. Therefore, as a device to measure the wind speed of a vehicle air conditioner, a heating wire such as a platinum or nichrome wire is heated by passing an electric current through it, and then placed in the airflow, and the heating wire is cooled by the airflow. Devices that measure wind speed from temperature changes in hot wires, such as hot wire anemometers and thermoelectric anemometers, are known. In addition, a self-heating heat-sensitive resistor such as a thermistor is used as a sensing part, and a constant voltage is applied to a circuit consisting of a resistor arranged in series with this sensing part to cause the self-heating heat-sensitive resistor to generate heat. There are also known measuring devices that detect changes in heat transfer coefficient due to airflow as changes in resistance.

In addition, as wind speed detectors that can handle a wide range of airflow temperatures, Japanese Patent Publication No. 46-26278 and Japanese Patent Publication No. 49-3
A detection body for a thermoelectric anemometer as described in Japanese Patent No. 1355 is known. Furthermore, there is known a device for controlling the dryness of refrigerant in an air conditioner by driving a self-heating type heat-sensitive resistor at a constant voltage, as described in Japanese Patent Publication No. 1663/1983.

[Problem that the invention seeks to solve]

Some of the above-mentioned conventional techniques have excellent measurement accuracy and responsiveness, but there are problems in that the reliability of the sensing section is poor and the circuit is complex, resulting in high cost. In addition, as shown in Fig. 3, in the conventional device, the wind speed is measured by driving the self-heating type heat-sensitive resistor 1 at a constant voltage. There was a problem in that the resistance value changed, making it impossible to measure the airflow temperature over a wide range. That is, as shown in FIG.
When the airflow temperature decreases, the resistance value of the heat-sensitive resistor 1 increases, and accordingly, the flowing current decreases, making it impossible for the resistor 1 to generate sufficient heat, and the accuracy of wind speed measurement decreases significantly.

Conversely, when the airflow temperature increases, the resistance value of resistor 1 decreases rapidly, resulting in damage or deterioration of characteristics.
There was a problem that temperature measurement was not possible.

An object of the present invention is to provide a wind speed measuring device for a vehicle air conditioner that can measure airflow temperature over a wide range.

[Means for solving problems]

In order to achieve the above object, the present invention provides a heat-sensitive element that is sensitive to the temperature of airflow in an air conditioning air passage and outputs a signal according to the temperature, a drive means that drives the heat-sensitive element with a constant current, and a heat-sensitive element that This is a wind speed measuring device for a vehicle air conditioner, which has a measuring means for measuring wind speed from the output of the air conditioner.

[Effect]

When the heat-sensitive element is driven with a constant current, sufficient heat generation can be ensured even when the airflow temperature is low, and even when the airflow temperature is high, it is possible to suppress the supply of excessive power due to a decrease in the resistance of the heat-sensitive element. This makes it possible to measure wind speed over a wide range of airflow temperatures.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows the configuration of a preferred embodiment of the present invention. In FIG. 1, a self-heating heat-sensitive resistor (wind velocity thermistor) 1 is installed as a heat-sensitive element in an air passage for air conditioning so that heat can be exchanged directly with airflow. Thermal resistor for temperature detection (correction thermistor) 2 is thermistor 1 for wind speed
It is provided in the air passage in opposition to the air passage. A voltage Ea is applied to each thermistor 1 for wind speed via a constant current drive circuit 5, and an electric voltage EC is applied to each thermistor 2 for correction via a resistor Re. The correction thermistor 2 is placed at a position where the airflow that hits the wind speed thermistor 1 is not disturbed as much as possible, and where it is not affected by the radiation of the wind speed thermistor 1, and where the airflow temperature that hits the wind speed thermistor 1 can be measured, for example, the air flow. They are placed close to each other at right angles to the direction. The output of each wind measuring thermistor 1 and correction thermistor 2 is connected to a voltage measuring device 4 via a switching circuit 3.
connected to. The output of the voltage measuring device 4 is supplied to the arithmetic and control device 6, and the wind speed is measured from the output of the voltage measuring device 4 in the arithmetic and control device 6.

That is, the arithmetic and control unit 6 functions as a measuring means.

When driving the wind speed thermistor 1, it is possible to connect each wind speed thermistor 1 in series and drive it by a constant current drive circuit 5 as shown in FIG. It is also possible to provide a constant current drive circuit 5 for each connected wind speed thermistor 1. The constant current circuit may be one using a three-terminal regulator as shown in FIG. 6, or an operational amplifier 8 as shown in FIG. transistor 9
．． It is possible to use resistors R2, R3, R4, R5, R6, R7 and a Zener diode D1.

Here, the applied voltage Ea of the thermistor 1 for wind speed, the resistance value Rth of the thermistor 1 for wind speed, the voltage Eth across the thermistor 1 for wind speed, the constant current ■ flowing in the circuit, the air flow temperature Ta, the temperature Tth of the thermistor 1 for wind speed, and the temperature Tth of the thermistor 1 for wind speed, β of thermistor 1
Given the constant β, the resistance value Ra of the thermistor 1 for wind speed at temperature Ta, the heat transfer coefficient α of the thermistor 1 for wind speed during forced convection, and the wind speed V at this time, generally α and V
is expressed by the relationship shown in the following equation (1).

α=aVb...(1) Also,
The relationship between the resistance of the thermistor 1 and the temperature is expressed by the following equation (2).

Rth= Ra exp(β(1/ Tth −1/
T a ))...(2) Therefore, Tth= 1/((1/β)Q n(R, t
h/Ra)+1/Ta)...(3) Here, Ta and Ta are absolute temperatures.

If the amount of heat lost by the wind speed thermistor 1 is Q, then Q=Aa (Tth-Ta)...(4)
It can be expressed as Also, Q = E th · Engineering ... (
5) can also be expressed.

Therefore, from equations (1), ('l), and (5).

V=Ct(Eth”I/(Tth Ta)) −
(6) is obtained.

Based on the above theoretical formula, the wind speed and the voltage E across the thermistor 1 are
When the relationship between th and th was actually measured, the measurement results shown in FIG. 8 were obtained. From FIG. 8, it was confirmed that the measurement results almost matched the theoretical values.

2, in this embodiment, the wind speed thermistor 1
Since it is driven with a constant current, it is possible to ensure sufficient heat generation even when the airflow temperature is low, and even when the airflow temperature is high, it is possible to suppress excessive current due to a decrease in the resistance of the thermistor 1.

Furthermore, in this embodiment, even if multiple wind speed thermistors are connected in series to a single power supply circuit, each thermistor can be operated without interfering with each other, and even in multiple wind speed measurements, it is possible to operate over a wide range. temperature measurement becomes possible. Furthermore, since the thermistor 1 for wind speed is driven with a constant current, even if the airflow temperature becomes low and the resistance of thermistor 1 increases, it is not possible to obtain a sufficient difference between the temperature detected by thermistor 1 and the airflow temperature. can.

〔Effect of the invention〕

According to the present invention, since the heat-sensitive element is driven with a constant current, sufficient heat generation can be guaranteed even when the airflow temperature is low, and even when the airflow temperature is high, excess power is supplied by reducing the resistance of the heat-sensitive element. This makes it possible to suppress wind speed over a wide range of airflow temperatures, making it possible to measure wind speed with high precision.

[Brief explanation of drawings]

Fig. 1 is an overall configuration diagram showing an embodiment of the present invention, Fig. 2 is a drive circuit diagram of the thermistor 1, Fig. 3 is a drive circuit diagram of a conventional example, and Fig. 4 is a diagram of the thermistor 1 for controlling air flow temperature and wind speed. A diagram showing the relationship with temperature rise, FIG. 5 is another configuration diagram of the drive circuit according to the present invention, FIGS. 6 and 7 are respectively other configuration diagrams of the drive circuit according to the present invention, and FIG. 8 is a diagram showing the relationship between wind speed and output voltage. 1...Self-heating type heat-sensitive resistor, 2...Thermal sensitive 1st section for temperature detection Fig. 2 #4 Fig. 50 y, Fig. 4

Claims (1)

[Claims] 1. a heat-sensitive element that is sensitive to the temperature of the airflow in an air conditioning air passage and outputs a signal according to the temperature; a driving means that drives the heat-sensitive element at a constant current; and a measuring means that measures wind speed from the output of the temperature-sensitive element; A wind speed measuring device for a vehicle air conditioner, characterized by having the following.