JPH06160141A - Air flow meter - Google Patents

Abstract

PURPOSE:To prevent the infiltration of noises and radio waves to the minimum by forming a circuit board capable of extracting multiple output signals into one board. CONSTITUTION:A current output terminal 36, a voltage output terminal 37, and a frequency output terminal 38 on a hybrid IC board 40 are connected to a control unit and a battery with a connector. A bridge circuit is constituted of a heating resistor 1, a thermosensitive resistor 2, operation amplifiers 3, 4, and resistors 19-23, and the resistor 1 is heat-controlled. The temperature difference between the resistor 1 and the resistor 2 is controlled at a constant value, the current Ih flowing in the resistor 1 is made the function of the air flow Q by the thermosensitive resistor 2, and the voltage, current, and frequency output can be expressed on the same curve as functions of the air flow Q. The air flow detection error is limited to the detection error of the current Ih, and no error occurs among the voltage, current, and frequency signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air flow meter used in an internal combustion engine of an automobile or the like, and more particularly to an air flow meter having a structure capable of extracting a plurality of output signals from one air flow meter and having excellent usability.

[0002]

2. Description of the Related Art In a conventional air flow meter, as described in Japanese Patent Laid-Open No. 59-3142, the output signal of the air flow meter has only one method in accordance with the input circuit of the other side, for example, an engine control unit. It was. However, in recent years, the output method of the air flow meter has the same voltage output as the conventional one, frequency output type (the A / D converter can be a counter) that simplifies the input circuit on the other side, or complicated wiring effects in automobiles. There is an increasing need for a current output type that does not receive power.

[0003]

In the prior art, the circuit board of the air flow meter is selectively used according to the input signal used on the control unit side.

According to the present invention, since several kinds of output signals can be taken out by one air flow meter, it is possible to meet the input specifications of the control unit. Further, it is possible to provide an air flow meter having a structure in which the circuit boards can be unified into one type and which is excellent in cost and productivity.

[0005]

According to the present invention, a current Ih flowing through a heating resistor is maintained so that the heating resistor is maintained at a certain temperature.
(V) -current (I) for converting the voltage output obtained from the drive unit, the amplification unit and the constant voltage circuit unit for controlling the
Voltage (V) for converting the converter and voltage output to frequency output
The circuit board is composed of the circuit configuration of the frequency (F) converter and is capable of taking out a plurality of output signals. Further, the circuit board is formed on a single board so as to minimize the intrusion of noise and radio waves.

[0006]

[Function] The air flow meter is detected only once. That is, the current Ih flowing through the heating resistor is used as a detection signal, and the voltage, current and frequency are obtained from the electronic circuit. Therefore, the air flow rate detection error is only the Ih detection error, and no error occurs between the voltage, current and frequency signals.

[0007]

Embodiments of the air flow meter according to the present invention will be described below with reference to the drawings.

First, FIG. 1 is a circuit diagram of an embodiment of the present invention. A heating resistor 1, a temperature sensitive resistor 2, and operational amplifiers 3-1.
0, transistors 11-13, diodes 14-16,
Capacitors 17, 18, resistors 19 to 34, power supply terminal 3
5, a current output terminal 36, a voltage output terminal 37, a frequency output terminal 38, and a ground terminal 39, and outputs a voltage signal from the drive section, the constant voltage circuit section, and the amplification section. Also VI
It is a circuit configuration that can output a current signal and a frequency signal by the converter and the VF converter, respectively. In addition, the current terminal 35
Is the (+) terminal of the battery, the current output terminal 36, the voltage output terminal 37, the frequency output terminal 38, the input terminal of the control unit that controls the engine using the output signal of the air flow meter is grounded. The (-) terminal of the battery and the ground terminal of the control unit are connected to the terminal 39.

Next, FIGS. 2 and 3 show an embodiment of an air flow meter composed of a hybrid IC substrate 40 formed on a single substrate incorporating the above-mentioned circuit, and a heating resistor installed in an air passage. 1, temperature-sensitive resistor 2, base 41, case 4
2, hybrid IC 40, connector 43, cover 44
It is composed of. Power supply terminal 3 on hybrid IC
5, the current output terminal 36, the voltage output terminal 37, the frequency output terminal 38, and the ground terminal 39 are connected to the control unit and the battery by the connector 43.

Next, the operation will be described. Heating type resistor 1, temperature sensitive resistor 2, operational amplifier 3, 4, resistors 19, 20, 2
A bridge circuit is formed by 1, 22, and 23, and the heating resistor 1 is heated and controlled as in the equation (1). On the other hand, the applied power of the heat generating resistor 1 and the amount of heat transferred from the heat generating resistor 1 to the air are expressed by the King's equation (Equation 2).

[0011]

[Equation 1]

RH: Resistance value of heating resistor 1 RC: Resistance value of temperature-sensitive resistor 2 (varies with air temperature Ta) R19, R20, R23, R22, RC: Resistance value of each resistor

[0013]

## EQU2 ## Ih ² RH = (A + B√Q) (Th-Ta) (Equation 2) Ih: Current flowing to heating resistor 1 A, B: Constant Q: Air flow rate Th: Temperature of heating resistor 1 Ta Since the temperature of the temperature sensitive resistor 2 (Th-Ta) is controlled to a constant value, Ih becomes a function of the air flow rate Q due to the temperature sensitive resistance, and the voltage output,
The current output and frequency output are shown in Fig. 4.

FIG. 5 shows an input circuit of an engine control system using a voltage output. Reference numeral 50 is an air flow meter of the present invention, and 51 is a control unit. In the case of voltage output, an A / D converter 52 is provided in the input circuit of the control unit 51 to convert the voltage signal V into a digital signal and process the signal with Cpu.

FIG. 6 shows an input circuit of the engine control system in the case of current output. The air flow rate signal I is converted into a voltage signal by the input reference resistance Ri, and the A / D converter 5
It is converted into a frequency signal at 2. In this example, the air flow meter 50 and the wiring 55 of the control unit 51 are
Even if there is wiring resistance, the control unit is uniquely taken in as I × Ri, so that the detection error is not reduced.

FIG. 7 shows the input circuit of the engine control system for frequency output. The frequency output is measured by the counter 56, and the air flow rate signal is processed by Cpu. In this example, the counter is cheaper than the A / D, which is advantageous in terms of cost, and the frequency signalization has a strong effect on external noise.

[0017]

According to the present invention described above, one type of circuit board can have correlation with various control units without dividing the circuit board of the air flow meter for each of a plurality of output signals. It is possible to provide an air flow meter excellent in productivity and cost.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view of an air flow meter showing an embodiment of the present invention.

FIG. 3 is a top view of an air flow meter showing an embodiment of the present invention.

FIG. 4 is an output characteristic diagram.

FIG. 5 is a system diagram in which a voltage output is used as an input.

FIG. 6 is a system diagram in which a current output is used as an input.

FIG. 7 is a system diagram in which a frequency output is used as an input.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating resistor, 2 ... Thermal resistor, 3-10 ... Operational amplifier, 11-13 ... Transistor, 14-16 ... Diode, 17-18 ... Capacitor, 19-34 ... Resistor, 35
... power supply terminal, 36 ... current output terminal, 37 ... voltage output terminal, 38 ... frequency output terminal, 39 ... ground terminal, 40 ...
Hybrid IC substrate, 41 ... Base, 42 ... Case,
43 ... Connector, 44 ... Cover.

Claims (3)

[Claims] 1. An air flow rate comprising a heating resistor installed in an air passage for sensing an air flow rate, and a control circuit for controlling a heating temperature of the heating resistor to be constant and outputting a signal corresponding to the air flow rate. Form, voltage (V) output, current (I)
An air flow meter having an output, a frequency (F) output and a plurality of output signals. 2. An air flow meter according to claim 1, wherein all the circuits are formed on a single substrate and housed in a common casing. 3. The drive unit, the amplification unit, the constant voltage circuit unit (voltage output unit) and the voltage for controlling the current Ih flowing through the heating resistor so as to keep the heating resistor at a certain temperature.
(V) -current (I) conversion unit (current output unit) and voltage (V)
An air flow meter characterized by comprising a circuit configuration of a frequency (F) conversion unit (frequency output unit).