JPH0629748B2 - How to measure fluid temperature of thermal flow meter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fluid temperature measuring method for a thermal type flow meter, and is particularly suitable for measuring a temperature of intake air introduced into a cylinder of an engine. Is.

[Conventional technology]

Recently, comprehensive control of an engine using a microcomputer has been performed for the purpose of improving the control function of the engine. One of these controls is air-fuel ratio control, and one of its parameters is the intake air amount of the engine.

The thermal type flow meter utilizes a heat transfer phenomenon between a heating resistor and air, and is widely used in an engine control system because a mass flow rate can be accurately obtained.

When using another volumetric flow meter as the intake air flow rate detector to perform highly accurate air-fuel ratio control, it is necessary to detect and correct the air temperature and pressure. Therefore, since the thermal type flow meter does not require the temperature and pressure detectors, the system can be inexpensively constructed.

However, since the intake air temperature of the engine can change from −30 ° C. to 80 ° C., it is necessary to detect the intake air temperature when attempting to perform more accurate engine control.

As a thermal type flow meter for detecting an intake air flow rate of an engine, a generally known constant temperature measuring method is used.

The constant temperature circuit has a bridging circuit in which a heating resistor is connected to one of the bridge branches and a temperature compensating resistor whose resistance value changes according to the fluid temperature is connected to the other branch of the bridge. It is connected to the input terminal of the heating current control amplifier, and the heating current is controlled so that the temperature difference between the heating resistor and the temperature compensating resistor becomes substantially constant.

Therefore, it is difficult to detect the resistance value of the temperature compensating resistor in the bridge circuit, and it is necessary to separate the temperature compensating resistor from the bridge circuit in order to detect the fluid temperature.

The following methods have been used for this type of thermal flowmeter. FIG. 2 shows the construction of a conventional thermal type flow meter disclosed in, for example, Japanese Patent Laid-Open No. 55-114911.

In FIG. 2, reference numeral 1 is a flow path, and 2 is a heating resistor disposed in the flow path 1 and having temperature dependency.

The heating resistor 2 and the fixed resistors 4 to 6 form a bridge circuit. The connection point between the heating resistor 2 and the fixed resistor 4 is connected to the output end of the controller 12, and the fixed resistors 5 and 6 are connected. The connection point is grounded and the diagonal branches A and B of the bridge circuit are connected.
Is connected to the input end of the controller 12. A power supply 9A is connected to the controller 12.

The power source 9B is connected to the constant current source 8, and the temperature compensating resistor 3 is connected between the constant current source 8 and the ground. The temperature compensating resistor 3 is arranged in the flow path 1, and a constant current is supplied from the constant current source 8 to the temperature compensating resistor 3 in the flow path 1.

Proportional operating elements 13 are connected to both ends of the temperature compensating resistor 3. Reference numeral 10 is a flow rate detection signal for detecting the heating current, and 11 is a fluid temperature detection signal.

Next, the operation will be described. A heating resistor 2 made of a temperature-dependent resistor and a temperature compensating resistor 3 for detecting a fluid temperature are arranged in the flow path 1. A constant current of about 1 to 3 mA is supplied to the temperature compensating resistor 3 from the power source 9B and the constant current circuit 8.

The proportional operating element 13 outputs a voltage proportional to the voltage across the temperature compensating resistor 3.

Further, the diagonal branch points A and B of the bridge circuit of the heating resistor 2 and the fixed resistors 4 to 6 and the output of the proportional action element 13 are input to the controller 12.

The controller 12 supplies an electric current to the bridge so that the temperature difference between the fluid temperature and the heating resistor becomes substantially constant even if the fluid temperature changes. When configuring such a constant temperature control circuit, the current flowing through the heating resistor 2 becomes a function of the flow rate.

[Problems to be solved by the invention]

When detecting the fluid temperature with the conventional constant temperature type thermal flow meter, it is necessary to configure the temperature compensating resistor 3 separately from the bridge circuit as described above, and the temperature of the heat generating resistor 2 and the fluid temperature. There has been a problem that the controller 12 for keeping the difference constant becomes complicated.

The present invention has been made to solve such a problem, and to obtain a fluid temperature measuring method for a thermal type flow meter capable of obtaining a fluid temperature signal at the same time as a flow rate signal without changing the configuration of a bridge circuit. To aim.

[Means for solving problems]

A fluid temperature detecting method for a thermal type flow meter according to the present invention constitutes a bridge circuit together with a heating resistor, a temperature compensating resistor and a fixed resistor, and is proportional to the resistance value of the heating resistor in addition to a flow rate detection signal. The fluid temperature is detected by detecting the voltage and performing arithmetic processing.

[Action]

In the present invention, the resistance value of the heating resistor is derived from the voltage at the two points of the bridge circuit by arithmetic processing, and the fluid temperature is detected from the value.

〔Example〕

An embodiment of a fluid temperature measuring method for a thermal type flow meter according to the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of a thermal type flow meter applied to the embodiment.
In FIG. 1, the same parts as those in FIG. 2 are described with the same reference numerals.

In FIG. 1, a heat generating resistor 2 composed of a temperature-dependent resistor and a temperature compensating resistor 3 for detecting a fluid temperature are arranged in an intake passage 1 of an intake pipe. And the fixed resistor 6 are connected in series between the output terminal A1 of the current supply amplifier 7 and the ground.

Similarly, a series circuit of the temperature compensating resistor 3 and the fixed resistors 4 and 5 is connected between the output terminal A1 of the current supply amplifier 7 and the ground. Thus, the heat generating resistor 2, the temperature compensating resistor 3, and the fixed resistors 4 to 6 form a bridge circuit. The current supply amplifier 7 supplies a heating current to the bridge circuit and receives the output of the bridge circuit as an input.

The connection point C between the fixed resistors 4 and 5 and the connection point B1 between the fixed resistor 6 and the heating resistor 2 are connected to the input end of the current supply amplifier 7. The current supply amplifier 7 has a power supply 9C
More power is being supplied. Reference numeral 10 is a flow rate detection signal, and 14 is a heat generation resistance value detection signal.

Next, the fluid temperature measuring method of the present invention will be described with reference to FIG. Heating resistor 2, temperature compensating resistor 3,
The resistance values of the fixed resistors 4 to 6 are set to R _H , R _K , R ₄ ,
Let them be R ₅ and R ₆ . When the bridge circuit is in equilibrium,
The following equation holds.

On the other hand, if the voltage of the flow rate detection signal 10 is V ₁₀ and the voltage of the heating element resistance detection signal 14 is V ₁₄ , then V ₁₀ = IR ₆ (2) V ₁₄ = I (R ₆ + _RH ) ... … (3).

From these equations (2) and (3), Substituting equation (4) into equation (1), Becomes

If the resistance values R ₅ and R ₄ are known, the flow rate detection signal V
The resistance value of the temperature compensating resistor 3 can be derived from ₁₀ and the voltage V _{14 of the} heating resistance detecting signal 14.

Therefore, the flow rate can be measured and at the same time the fluid temperature can be detected by performing arithmetic processing after capturing the above two signals into the microcomputer via the A / D converter.

In the above embodiment, the output terminal A1 of the current supply amplifier 7 is used as the heating resistance detection signal 14, but when the input voltage range of the A / D converter is exceeded, the output terminal A1 point and the connection point B1 point are used. Can be used as the input of the differential amplifier, and the output of this differential amplifier can be used as the heating element resistance detection signal to perform arithmetic processing in the same manner as in the above embodiment to detect the fluid temperature.

〔The invention's effect〕

As described above, the present invention detects the voltage proportional to the resistance value of the heating resistor of the constant temperature type thermal flow meter and the voltage proportional to the heating current, and calculates the voltage without changing the bridge circuit. Since the air temperature can be detected at the same time, it is extremely useful when applied to engine control in which fluid temperature changes greatly.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a thermal type flow meter applied to an embodiment of a method for measuring a fluid temperature of a thermal type flow meter of the present invention, and FIG. 2 is applied to a conventional fluid temperature measuring method of a thermal type flow meter. FIG. 3 is a circuit diagram of a thermal type flow meter. 1 ... Flow path, 2 ... Heating resistor, 3 ... Temperature compensation resistor, 4-6 ... Fixed resistor, 7 ... Current supply amplifier, 9
C ... power supply. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A bridging branch is connected to a temperature-dependent heating resistor, which is arranged in the air flow of an intake pipe and generates heat by a heating current, and a fixed resistance, and the other bridging branch is connected to a fluid temperature. A bridge circuit is formed by connecting a temperature compensating resistor whose resistance value changes according to the diagonal line branch of the bridge circuit is connected to an input terminal of a current supply amplifier for controlling a heating current, and the heating resistor In a thermal type flow meter that controls the heating current so that the temperature difference between the temperature compensating resistor and the temperature compensating resistor becomes substantially constant, the voltage across the fixed resistor connected to the heating resistor is proportional to the resistance value of the heating resistor. A method for measuring a fluid temperature, which comprises detecting the applied voltage and performing arithmetic processing to detect the fluid temperature.