JPH04204119A - Hot wire type air flowmeter - Google Patents

Abstract

PURPOSE:To improve the precision in measurement of an intake air temperature by a method wherein a resistor for compensating the intake air temperature is driven by a constant current and a terminal voltage is measured when a heating current of a heating resistor is interrupted. CONSTITUTION:Outputs obtained at detection points 25 and 26 of a bridge circuit l including a heating resistor 2 and an intake air temperature compensating resistor 3 are subjected to comparison and amplification 8 and fed back to the circuit 1 and thereby a control is made so that a potential difference between the detection points 25 and 26 be minimum. Under this control, an intake air quantity signal subjected to temperature compensation by the resistor 3 is taken out from the detection point 25. On the occasion, the resistor 3 is driven intermittently by a constant-current circuit 19, a terminal voltage of the resistor 3 is supplied to an arithmetic unit 23 when the resistor is driven, and an intake air temperature signal is taken out of an output of the unit. A switch circuit 13 brings into operation alternately an N-P-N transistor 9 for current supply which supplies an operation current to the circuit 1, and the circuit 19 which supplies a current to the resistor 3. In this way, an intake air temperature can be determined with high precision on the basis of a temperature change in the resistance value of the resistor 3.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a thermal air flow meter used in an engine intake air amount detection device for an automobile, and in particular, to a thermal air flowmeter that measures the intake air flow rate and the intake air temperature. This article relates to a thermal air flow meter.

[Prior art] Conventionally, this type of thermal air flow meter was disclosed in Japanese Patent Application Laid-open No. 1983-
A structure as described in No. 206616 was known. In this conventional configuration, a bridge circuit is constructed of a heating resistor and an air temperature compensating resistor placed in the air flow of the intake pipe, and a plurality of fixed resistors, and the detection output of the bridge circuit is compared with an amplifier. This system controls the heating current of the heating resistor so that the temperature difference between the heating resistor and the air temperature compensating resistor becomes constant by feeding back to the bridge circuit via the heating resistor.

The intake air temperature is measured by separately detecting a voltage proportional to the heating current obtained across a fixed resistor connected to the heating resistor and a voltage proportional to the resistance value of the heating resistor. The measured value is obtained by processing the detected voltage values.

[Problems to be Solved by the Invention] The conventional configuration has a voltage proportional to the heating current obtained across a fixed resistor connected to the heating resistor and a voltage proportional to the resistance value of the heating resistor. are detected separately, and from the detected values, the value of the terminal voltage and the value of the conduction current of the heating resistor are determined, and the necessary arithmetic processing is performed to determine the resistance value of the heating resistor. Since it is necessary to go through a complicated calculation process to measure the target intake air temperature, there is a drawback that the accuracy of the measurement of the air temperature cannot be increased. Since it is necessary to supply and control current to the heating resistor, there is also a drawback that the power consumption of the thermal air flowmeter increases.

The present invention has been devised to eliminate these drawbacks, and one of its objects is to provide a thermal air flowmeter with improved accuracy in measuring intake air temperature.

Another object is to provide a thermal air flow meter with reduced power consumption.

[Means for Solving the Problems] In order to achieve the above-mentioned one object, the present invention supplies a driving current from a constant current circuit to the intake air temperature compensation resistor, while supplying the drive current of the intake air temperature compensation resistor to the intake air temperature compensation resistor. A calculator is provided to calculate the terminal voltage, and the intake air temperature is measured based on the result of the calculation.Furthermore, in order to achieve the above-mentioned another object, the present invention operates on a bridge circuit including a heating resistor. A current supply circuit that supplies current and a constant current circuit that supplies a constant value of current to the intake air temperature compensation resistor are provided, and both circuits are operated alternately to reduce the power consumed in the thermal air flowmeter. I'm trying to save money.

[Operation] If the outputs obtained at the two detection points of the bridge circuit including the heating resistor and the intake air temperature compensating resistor are compared and amplified by a comparator amplifier, and the comparison output is fed back to the bridge circuit, the bridge circuit The circuit is controlled so that the potential difference between the two detection points is minimized.

Through this control, a signal representing the amount of intake air whose temperature has been compensated by the intake air temperature compensating resistor is extracted from a detection point on the heating resistor side of the bridge circuit.

Further, the intake air temperature compensation resistor is intermittently driven by a constant current circuit, and during driving, the terminal voltage of the intake air temperature compensation resistor is supplied to a computing unit, and the intake air temperature is determined from the output of the computing unit. The signal that represents this is extracted.

Further, a switching means is provided for alternately operating a current supply circuit that supplies an operating current to the bridge circuit and a constant current circuit that supplies current to the intake air temperature compensation resistor,
When the bridge circuit operates, a signal representing the amount of intake air temperature-compensated by the intake air temperature compensation resistor is extracted, and when the constant current circuit operates, the terminal voltage of the intake air temperature compensation resistor is extracted. By supplying the signal to a computing unit, a signal representing the intake air temperature is extracted from the output of the computing unit.

[Example code] Embodiments of the present invention will be described below with reference to the drawings.

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

In the figure, 1 is a bridge circuit, 2 is a heating resistor, 3 is an intake air temperature compensation resistor, 4 to 6 are fixed resistors, 7 is a diode, 8 is a comparator amplifier, 9 is an NPN transistor for current supply, and 10 is an output 11 is an output terminal, 12 is a logic circuit, i3 is a switch circuit, 14.15 is the first and second switch, 16 is an inverter, 17 is a control signal terminal, 18 is a power supply line, 19 is a constant current circuit, 2
0 is a PNP transistor for current supply, 21 is a bias diode, 22 is an arithmetic circuit, 23 is an arithmetic unit, 24 is a temperature measurement signal output terminal, 25 and 26 are first and second detection points, 27 is an inversion gate, 28 is a non-inverting gate.

Here, the heating resistor 2 and the intake air temperature compensating resistor 3 are as follows.
Both are placed in the engine intake air passage of an automobile.

Further, in the bridge circuit 1, the heating resistor 2 and the fixed resistor 4 constitute a first series branch, and the diode 7, the intake air temperature compensation resistor 3, and the two fixed resistors 5 and 6 constitute a second series branch. The connecting portion between the heat generating resistor 2 and the fixed resistor 4 and 2
The connections of the two fixed resistors 5.6 are each connected to the bridge circuit 1.
forming first and second detection points 25 and 26.

When the current supply NPN transistor 9 is conductive, a heating current Ih flows through the heating resistor 2 and a compensation current Ic flows through the intake air temperature compensation resistor 3 in the bridge circuit 1, and the first and second detections are performed. A voltage is developed at points 25,26.

After these voltages are compared and amplified in a comparison amplifier 8, a comparison output is supplied to the base of the transistor 9. In this case, the feedback control loop from the bridge circuit 1 to the transistor 9 via the comparator amplifier 8 is connected to the comparator amplifier 8.
The current of the transistor 9 is adjusted by the output of the first
The voltage at the second detection point 25 obtained by this control is outputted via the output buffer amplifier 10 as a signal representing the air flow rate. It is taken out from the terminal 11. Note that the configuration of such a feedback control loop and the effects based on the configuration are already known.

In addition to the known configuration, this embodiment connects a switch circuit 13 and a logic circuit 12 between the pressure of the comparison amplifier 8 and the transistor 9, and also connects the intake air temperature compensation resistor 3 and the power supply. Constant current circuit 1 between line 18
9 is connected to the intake air temperature compensating resistor 3, and an arithmetic circuit 22 is further connected to both ends of the intake air temperature compensating resistor 3.

In this case, the switch circuit 13 consists of a first switch 14 and a second switch 14, 15, the control terminal of the first switch 14 is directly connected, and the control terminal of the second switch 15 is connected via an inverter 16, respectively. connected to terminal 17,
When the first switch 14 is on, the second switch 15
is off and the second switch 15 is on, the first
The switch 14 is turned off. Further, the logic circuit 12 includes an inverting gate 27 and a non-inverting gate 28, and matches the polarity of the two outputs of the switch circuit 13. Further, the constant current circuit 19 includes a current supply PNP transistor 2o and a bias diode 21, and causes a constant value of measurement current Ir to flow through the second series branch of the bridge circuit 1 excluding the diode 7. Finally, the arithmetic circuit 22 includes an arithmetic unit 23, and an air temperature compensation resistor 3.
When the measurement current Ir flows through the terminal, the terminal voltage is detected, necessary calculations are performed, and a signal representing the intake air temperature is generated.

Next, the operation of this embodiment will be explained.

Now, when a one-polarity control signal is supplied to the control signal terminal 17, the first switch 14 is turned on and the second switch 14 is turned on.
switch 15 is turned off, and the output of comparison amplifier 8 is coupled to the base of transistor 9 via first switch 14 and non-inverting gate 27 of logic circuit 12. Therefore, an operating current is supplied to the bridge circuit l, and the feedback control loop is formed which passes through the comparator amplifier 8 and reaches the transistor 9. Due to the above-described control operation in the feedback control loop, the current is supplied to the output terminal 11. A signal representing the air flow rate is obtained. During this control operation, the base of the current supplying transistor 2o of the constant current circuit 19 is supplied via the off state of the second switch 15 and the non-inverting gate 27.
Since a control signal with a polarity that cuts off the transistor 20 is supplied, the constant current circuit 19 is placed in a non-operating state, and the bridge circuit 1 is isolated from the constant current circuit 19.

In this state, when the control signal supplied to the control signal terminal 17 is converted to the other polarity, the first switch 14 is turned off and the second switch 15 is turned on, and the output of the comparator amplifier 8 is transferred to the transistor 9. Since the coupling to the base of the transistor 9 is cut off, the transistor 9 is cut off and no longer supplies operating current to the bridge circuit 1, and the bridge circuit 1 becomes inactive. Further, the base of the transistor 2o of the constant current circuit 19 is connected to ground via the non-inverting gate 28 and the second switch 15, and the constant current circuit 19 enters the operating state due to the conduction of the transistor 20. A constant current Ir is supplied to the bridge circuit 1. However, since the diode 7 is connected to the bridge circuit 1 in a direction that blocks the constant current Ir, the constant current r is connected to the intake air temperature compensation resistor 3 and the fixed resistor 5.
．． Flows through 6. At this time, the intake air temperature compensation resistor 3
The arithmetic unit 23 of the arithmetic circuit 22 connected to both ends of the
The terminal voltage of the intake air temperature compensating resistor 3 is detected, a predetermined calculation is performed based on the detected voltage, and a signal representing the intake air temperature is generated at the output terminal 24.

Furthermore, at this time, when the control signal supplied to the control signal terminal 17 is reconverted to one polarity, the first switch 14 is turned on and the second switch 15 is turned off, so that the bridge circuit 1 The feedback control loop control operation is performed, and a signal representing the intake air flow rate is obtained at the output terminal 11, and in the same manner, every time the polarity of the control signal supplied to the control signal terminal 17 changes, The operation of generating a signal representing the intake air flow rate at the output terminal 11 and the operation of generating a signal representing the intake air temperature at the output terminal 24 are alternately and repeatedly performed.

By the way, in a thermal air flow meter that measures the intake air temperature using the intake air temperature compensation resistor 3, the value of the current flowing through the intake air temperature compensation resistor 3 and the value of the current flowing Detect the value of the terminal voltage of the intake air temperature compensation resistor 3 when the intake air temperature is in is obtained by a predetermined conversion, and in the conventional structure described above, the value of the current and the value of the terminal voltage are individually detected by separate circuit means, and after detection, the value of the resistance is calculated from these two values. It performs an operation to obtain a value.

However, in this embodiment, when measuring the intake air temperature, the current flowing through the intake air temperature compensating resistor 3 is a constant value Ir, so the arithmetic unit is used as the circuit for detecting the value of the terminal voltage. It is sufficient to connect 23 between the terminals of the intake air temperature compensation resistor 3, and a circuit for detecting the value of the current can be omitted. Furthermore, the calculation performed by the calculator 23 can be performed by simply performing a predetermined conversion between the value of the terminal voltage and the resistance value.

As described above, this embodiment measures the intake air flow rate and the intake air temperature by alternately operating and inactivating the current supply transistors 9 and 20 depending on the polarity of the supplied control signal. Since these are performed independently, the measurement accuracy can be improved, and it is also useful for reducing the power consumption of the thermal air flowmeter.

FIG. 2 is a concave path diagram showing a second embodiment of the present invention.

Compared to the first embodiment, this embodiment uses an RS flip-flop circuit 29 instead of the output buffer amplifier 10, switch circuit 13, and inverter 16, and also uses an RS flip-flop circuit 29 as a gate constituting the logic circuit 12. gate 3o
, 31 is used, but the rest of the structure is the same.

The control signal from the control input terminal 17 and the output signal of the comparator amplifier 8 are supplied to the set input terminal S and reset input terminal R of the RS flip-flop circuit 29,
A signal representing the intake air flow rate is obtained from the non-inverting output terminal Q, and a feedback output signal is obtained from the inverting output terminal Q.

This embodiment performs the following operations.

When a control signal of positive polarity (hereinafter referred to as "l") is supplied to the control signal terminal 17, a control signal of negative polarity (hereinafter referred to as rOJ) is supplied to the inverting output terminal Q of the RS flip-flop circuit 29.
), "1" is generated at the non-inverting output terminal Q, and among these, "○" is the inverting gate 30.3 of the logic circuit 12.
1, the polarity is inverted to "L", which makes the current supply transistor 9 conductive and the current supply transistor 20 non-conductive.

When the transistor 9 becomes conductive, a heating current Ih is supplied to the heating resistor 2 of the bridge circuit l, a compensation current Ic is supplied to the intake air temperature compensation resistor 3, and a voltage is applied to the first and second detection points 25 and 26. occurs. After these voltages are compared and amplified by the comparison amplifier 8, the comparison output is supplied to the reset terminal R of the RS flip-flop circuit 29, and further,
As in the case of the first embodiment, control is performed such that the potential difference between the first and second detection points 25 and 26 is minimized by being supplied to the transistor 9 via the logic circuit 12. be.

However, in this embodiment, when the potential difference between the first and second detection points 25 and 26 becomes equal to or less than a predetermined value due to the control,
The comparison output of the comparison amplifier 8 is inverted from "0" to "L",
The RS flip-flop circuit 29 is reset. By this reset, "1" is generated at the inverting output terminal Q, and rQJ is generated at the non-inverting output terminal Q. Of these, "1" is inverted in polarity by the inverting gate 30, 31 and becomes rQJ,
It is applied to transistor 9.20, causing transistor 9 to convert from conducting to non-conducting and transistor 20 from non-conducting to conducting. As a result of this conversion, the control operation of the feedback control loop in the bridge circuit 1 is stopped, while the constant current circuit 19 enters the operating state, and the constant current Ir from the constant current circuit 19 is supplied to the bridge circuit l. Similar to the embodiment 1, the intake air temperature compensation resistor 3
The terminal voltage of is detected and a signal representative of the intake air temperature is generated at output terminal 24. In addition, the signal representing the intake air flow rate is set by the RS flip-flop circuit 29.
The period from when "o" is converted to "1" until it is converted from "1" to "O" by reset, that is, the pulse width that is the duration of "1" of the signal represents the air flow rate. Become something.

In this state, when a control signal of "1" is supplied to the control signal terminal 17, the RS flip-flop circuit 2
9 is set again, and both output terminals Q and Q are set to "1".
”, is converted to “0”, and the same operation as described above is performed. Further, thereafter, the above-described operation is repeated every time the control signal is supplied.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

Compared to the second embodiment, this embodiment uses a transistor 32 instead of the diode 7, and furthermore, its base is connected to the inverting gate 3 through bias setting resistors 33 and 34.
The difference is that it is connected to the output of o, but the rest of the configuration is the same.

The transistor 32 of this embodiment is turned on when the current supply transistor 9 is turned on, and turned off when the transistor 9 is turned off, and has the same function as a diode. The operation of this embodiment is the same as that of the second embodiment, so a description of the operation of this embodiment will be omitted.

In this embodiment, a normal transistor is used as the transistor 32, but the type of the transistor 32 is not limited to this, and for example, a field effect type may be used.

Further, in this embodiment, a transistor 32 is used in place of the diode 7 in the second embodiment, but in the first embodiment, the transistor 32 is used in place of the diode 7 used therein. Of course, it is possible.

[Effects of the Invention] According to the present invention, when the heating current 1h of the heating resistor 2 is cut off, the intake air temperature compensation resistor 3 is driven with a constant current Ir, and the intake air temperature compensation resistor 3 is driven with a constant current Ir. Since the terminal voltage of the intake air temperature compensation resistor 3 is measured by the calculator 31, the intake air temperature can be determined based on the temperature change in the resistance value of the intake air temperature compensation resistor 3 by performing a simple calculation. It becomes possible to measure the intake air temperature.

In addition, since the intake air temperature is measured when the heating current Ih of the heating resistor 2 is cut off, the power consumption of the entire air flow meter can be reduced when measuring both the intake air flow rate and the intake air temperature. becomes possible.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a first embodiment of the invention, Fig. 2 is a circuit diagram showing a second embodiment of the invention, and Fig. 3 is a circuit diagram showing a third embodiment of the invention. It is. l...Bridge circuit, 2...Heating resistor, 3...Resistor for intake air temperature compensation,
4.5.6...Fixed resistance, 7...
Diode, 8... Comparison amplifier, 9...
... NPN transistor for current supply, 1o... ・
...Output buffer amplifier, 11...Output terminal, 12......Logic circuit, 13......Switch circuit, 14.15......First and first Switch 2, 16... Inverter, 17...
...Control signal terminal, 18... ...Power line, 19... ...Constant current circuit, 20... ...
PNP' transistor for current supply, 21...
Bias diode, 22... Arithmetic circuit,
23... Arithmetic unit, 24... Temperature measurement signal output terminal, 25.26... First and second detection points, 27.30.31... ・・Inverting gate, 28... ・Non-inverting gate, 29... ・
...RS flip-flop circuit, 32... Switching transistor, 33.34... ... Bias setting resistor. Figure 1 Figure 2

Claims (1)

[Claims] 1. A bridge circuit is configured by a heating resistor and an intake air temperature compensating resistor placed in the intake air flow, and a plurality of fixed resistors, and a comparison amplifier is used to compare the detection output of the bridge circuit. In a thermal air flow meter that controls the temperature difference between the heating resistor and the intake air temperature compensation resistor to be constant by feeding back to the bridge circuit through the A thermal air flowmeter that is driven by a current circuit and measures the intake air temperature by detecting the terminal voltage. 2. A thermal air flowmeter characterized in that the constant current circuit according to claim 1 is turned on and off by a control signal fed back to the bridge circuit. 3. Means for alternately turning on and off the heating resistor and the intake air temperature compensating resistor according to claim 1 by means of a control signal fed back to the bridge circuit is provided, and when the current of the heating resistor is cut off, the intake air temperature is adjusted. A thermal air flow meter that measures intake air temperature by driving a compensating resistor with a constant current circuit and detecting the terminal voltage. 4. A diode or a transistor is connected to the bridge circuit according to any one of claims 1 to 3, and the diode or transistor is configured to prevent the drive current of the constant current circuit from flowing into the heat generating resistor. Thermal air flow meter.