JPH0562932B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an apparatus for measuring fluid flow rate based on a signal from a temperature-sensitive flowmeter using a temperature-sensitive resistor.

<Prior art> This type of temperature-sensitive flow rate measuring device is used to measure the intake air flow rate in internal combustion engines for automobiles, and there is, for example, one shown in Fig. (See No. 78926).

To explain the outline with reference to the figure, a bridge circuit is formed by a temperature-sensitive resistor R _H made of platinum and resistors R _K , R ₁ , R ₂ , and R ₃ arranged in the intake passage of the engine. Resistor from battery B to bridge circuit
The current supplied via R ₄ is based on the difference between the terminal voltage of resistor R ₂ and the terminal voltage of resistor R ₃ , i.e., the unbalanced voltage of the bridge circuit, and is supplied via the differential amplifier _OP and the transistor _Tr . It's becoming controlled. For example, when the intake air flow rate increases, temperature-sensitive resistor R _H is cooled further and its resistance value decreases, but at this time, the terminal voltage of resistor R ₃ increases and the output of differential amplifier O _P decreases. , the base current of the transistor T _r increases and the collector current increases, so the current I supplied to the bridge circuit increases. In other words, the temperature-sensitive flowmeter 1 having the above configuration
By changing the supply current so as to keep the terminal voltage of temperature-sensitive resistor R _H constant in response to changes in flow rate, the terminal voltage of resistor R ₃ proportional to this supply current can be changed.
It outputs U _n as a fluid flow rate signal.

Then, input the terminal voltage U _n to the microcomputer 4 via the A/D (analog-to-digital) converter 3 in the control unit 2,
The microcomputer 4 calculates and measures the flow rate corresponding to the terminal voltage U _n .

In addition, in this type of temperature-sensitive flow rate measuring device, a temperature-compensating resistor _RK placed in the intake passage along with a temperature-sensitive resistor _RH compensates for fluctuations in the flow rate characteristics due to temperature changes in the intake air flow rate. By appropriately selecting the resistance temperature coefficients α ₁ to α ₂ of the other resistors R ₁ , R ₂ , and R ₃ placed on the engine room side, fluctuations in flow characteristics due to temperature changes in the engine room can be compensated for. There is.

Specifically, the unbalanced voltage of the bridge circuit is kept constant even when the temperature changes.

<Problems to be Solved by the Invention> However, in the conventional device, the temperature-sensitive flowmeter 1 and the control unit 2 are mounted at different locations, and the respective ground terminals E ₁ and E ₂ are connected to separate ground terminals. Since it is grounded to the engine body via a ground line (harness), each ground terminal may
The reference ground voltages V _E1 and V _E2 at E _{1 and E 2} are different.

That is, the output voltage U _n from the temperature-sensitive flowmeter 1 is a value based on V _E1 , whereas the A/D converter 3 in the control unit 2 is based on V _E2 , so the output voltage U n is a value based on V E1. A voltage differing by V _E1 −V _E2 from the voltage U _n was input, which sometimes caused a flow rate measurement error.

The present invention was developed in view of the problems of conventional devices, and it measures the flow rate by generating a number of pulses proportional to the voltage signal from a temperature-sensitive flowmeter and measuring the number of pulses. It is an object of the present invention to provide a temperature-sensitive flow rate measuring device that can measure flow rate with high accuracy without being affected by differences in ground voltage levels.

<Means for Solving the Problems> Therefore, the present invention provides a bridge circuit formed by a temperature-sensitive resistor and a plurality of resistors disposed in a fluid passage, and a bridge circuit having a resistance value of the temperature-sensitive resistor depending on the fluid flow rate. A temperature-sensitive flow rate control circuit that controls the supply current to the bridge circuit based on the unbalanced voltage of the bridge circuit that changes due to changes, and outputs a voltage corresponding to the supply current as a fluid flow signal. In a temperature-sensitive flow rate measuring device that measures a fluid flow rate based on a signal from the temperature-sensitive flowmeter, the temperature-sensitive flowmeter includes a reading signal for periodically reading a flow signal voltage from the temperature-sensitive flowmeter. a read signal output circuit that outputs a read signal; a pulse generation circuit that generates a number of pulses proportional to the voltage value of the flow rate signal read in synchronization with the output of the read signal; and a pulse generation circuit that generates the pulse during the read signal output period. The configuration includes a measurement circuit that measures the fluid flow rate corresponding to the counted value by counting the number of pulses generated from the circuit.

<Function> When a read signal is output from the read signal output means, the pulse generation means generates a number of pulses proportional to the voltage value of the flow signal from the temperature-sensitive flowmeter read in synchronization with this signal.

The number of pulses generated during this read signal output period is counted by a measuring circuit, and the fluid flow rate corresponding to the counted value is measured.

Since the flow rate signal has been digitized in this way, the flow rate can be determined with high accuracy without being affected by differences in the ground voltage on the temperature-sensitive flowmeter side and the ground voltage on the measuring circuit side. Measurements can be taken.

<Example> Below, an example of the present invention will be described based on the drawings.

In FIG. 1 showing the configuration of one embodiment, the circuit configuration of the temperature-sensitive flowmeter 1 is the same as the conventional one, so illustration of the internal circuit is omitted.

A control unit 11 containing a microcomputer is provided with a circuit that periodically outputs a read signal based on an internal clock signal.
The read signal is output from the output terminal O.

That is, the control unit 11 includes a read signal output circuit.

The read signal is input to the set terminal S of the flip-flop 12, and the read signal is input to the set terminal S of the flip-flop 12.
outputs from the output terminal Q an actuation signal that is inverted from L level to H level in synchronization with the input of the read signal.

The output terminal Q of the flip-flop 12 is connected to the battery voltage V _B via two resistors R ₁₁ and R ₁₂ and also to one input terminal of an AND circuit 13.

On the other hand, a reference signal generating circuit 14 that generates a pulse every minute unit time is provided, and an output terminal of the reference signal generating circuit 14 is connected to the other input terminal of the AND circuit 13.

The output terminal of the AND circuit 13 is connected to the input terminal of the control unit 11.

The connection point between the two resistors R ₁₁ and R ₁₂ is
It is connected to the base terminal of the transistor T _r11 , and the emitter terminal of the transistor T _r11 is connected to the battery V _B
The collector terminal is connected to the negative input terminal of the amplifier _OP11 via a resistor _R13 . The - side input terminal is connected to the temperature-sensitive flowmeter 1 through the resistor _R14 .
It is connected to ground terminal E, which has the same ground level as .

Further, a capacitor _C11 and a diode _D11 are connected in parallel between the negative input terminal and output terminal of the amplifier _OP11 .

Here, amplifier O _P11 , resistor R ₁₄ and capacitor C ₁₁
A Miller integrator circuit is constructed.

The output terminal of the amplifier O _P11 is connected to the comparator O _P12 .
The + side input terminal of the comparator O _P12 is connected to the output terminal of the temperature-sensitive flowmeter 1 via a resistor R ₁₅ , and the output terminal of the comparator O P12 is connected via a resistor R ₁₆ to the output terminal of the comparator O _P12 . connected to the terminal.

The output terminal of the comparator O _P12 is directly connected to the reset terminal of the flip-flop 12, and when the output level of the comparator O _P12 reaches the H level, the flip-flop 12 is reset and the H level operating signal from the output terminal Q is output. Stop the output (switch to L level).

As described above, the control unit 11 counts the number of pulses output from the output terminal of the AND circuit 13 during the output period of the read signal, and measures the intake air (fluid) flow rate corresponding to the counted value.

Here, as described later, flip-flop 1
2. The Miller integration circuit and reference signal generation circuit 14
And the AND circuit 13 generates a number of pulses proportional to the voltage value of the fluid flow signal for each read signal output. That is, these circuits constitute a pulse generation circuit, and the control unit 11, which counts the number of pulses and measures the fluid flow rate, includes a measurement circuit.

Next, the measurement operation by the circuit according to the present invention will be explained based on the time chart shown in FIG.

The control unit 11 periodically outputs a read signal.

In synchronization with the output of the read signal, the output of the flip-flop 12 becomes H level and output of the actuation signal is started.

As a result, the input voltage at the base terminal of the transistor T _r11 is switched from the L level to the H level, so that the transistor T _r11 is switched from on to off.

As a result, the potential of the negative input terminal of amplifier O _P11 becomes H.
On the other hand, the potential of the + side input terminal of the amplifier _OP11 is switched from the L level to the H level by the output from the flip-flop 12, so a current is output from the output terminal of the amplifier _OP11 . , this current flows into the circuit connecting the capacitor C ₁₁ and the resistor R ₁₄ and charges the capacitor C ₁₁ , so that the voltage at the output terminal gradually increases.
Note that the diode 11 prevents the capacitor _C11 from being charged in the opposite direction and connects the amplifier O _P11 before charging.
This is inserted to keep the connection point with the - side input terminal near the ground level (R ₁₃ ≪ R ₁₄ ).

Here, due to the Miller effect of the Miller integration circuit consisting of amplifier O _P11 , resistor R ₁₄ , and capacitor C ₁₁ , the output voltage of amplifier O _P11 is proportional to the elapsed time after inputting the H level operating signal from flip-flop 12. It becomes the size.

In addition, the resistance _R14 is the temperature-sensitive flowmeter 1 as described above.
It is grounded to the ground terminal with the same ground level as the
Therefore, the output voltage of amplifier O _P11 increases linearly from this ground voltage level as shown in FIG. When the output voltage from the amplifier _OP11 matches the output voltage of the temperature-sensitive flowmeter 1, the output of the comparator _OP12 inputting these two output voltages is switched from the H level to the L level.

As a result, the flip-flop 12 receives an L level reset signal at its reset terminal, so that the output from the output terminal Q is switched from the H level to the L level and the output of the operating signal is stopped.
Then, the input voltage at the base terminal of transistor T _r11 decreases, transistor T _r11 is turned on, and while the input voltage at the negative input terminal of amplifier O _P11 increases, the input voltage at the positive input terminal becomes L level. The output of amplifier O _P11 becomes L level. This results in
The capacitor _C11 is discharged in a short time, and the output level of the comparator _OP12 becomes H level again, returning the input voltage to the reset terminal R of the flip-flop 12 to the H level.

As mentioned above, the output voltage of the amplifier O _P11 is proportional to the operating signal output time, and since the ground level of the amplifier O _P11 and the ground level of the temperature-sensitive flowmeter 1 are equal, the operating signal output The time (pulse width) is a value proportional to the output voltage of the temperature-sensitive flowmeter 1.

On the other hand, since the reference signal generation circuit 14 generates a pulse every minute unit time, and this pulse is input to the AND circuit 13, the AND circuit 13 generates a pulse.
outputs a pulse synchronized with the pulse from the reference signal generation circuit 14 only while the H-level activation signal is input. Therefore, the number of pulses during this period is a value proportional to the activation signal output time, that is, the voltage value of the fluid flow signal from the temperature-sensitive flowmeter 1.

The control unit 11 then measures the flow rate by counting the number of pulses generated from the AND circuit 13 during the output period of the read signal.

That is, even if the grounding levels of the temperature-sensitive flowmeter 1 and the control unit 11 are different, accurate flow rate measurement can be performed without being affected by this difference.

Furthermore, since A/D conversion is not required, other analog signals can be input to the A/D converter in the control unit 11.

<Effects of the Invention> As explained above, according to the present invention, the flow rate signal is digitized by the number of pulses for measurement. Even if the ground level of the circuit being measured is different, the flow rate can be accurately measured without being affected by the ground level.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a time chart showing the signal output of the circuit of the same embodiment, and FIG. 3 is a circuit diagram showing the configuration of a conventional example. 1...Temperature-sensitive flowmeter, 11...Control unit, 12...Flip-flop, 13...AND circuit, 14...Reference signal generation circuit, _C11 ...
Capacitor, O _P11 ... Amplifier, O _P12 ... Comparator, R ₁₁ to R ₁₅ ... Resistor.

Claims (1)

[Scope of Claims] 1. A bridge circuit formed by a temperature-sensitive resistor and a plurality of resistors arranged in a fluid passage, and an unbalanced bridge circuit that changes due to a change in the resistance value of the temperature-sensitive resistor according to the fluid flow rate. a control circuit that controls the current supplied to the bridge circuit based on the voltage, and a temperature-sensitive flowmeter configured to output a voltage corresponding to the supply current as a fluid flow rate signal; A temperature-sensitive flow rate measuring device that measures fluid flow rate based on a signal from a flowmeter, comprising: a read signal output circuit that outputs a read signal for periodically reading a flow rate signal voltage from the temperature-sensitive flowmeter; a pulse generation circuit that generates a number of pulses proportional to the voltage value of the flow rate signal read in synchronization with the output of the read signal, and a pulse generation circuit that generates a number of pulses from the pulse generation circuit during the read signal output period. 1. A temperature-sensitive flow rate measuring device comprising: a measurement circuit that measures a fluid flow rate corresponding to the counted value by counting.