JPS586415A - Thermal flow meter - Google Patents

Abstract

PURPOSE:To obtain a thermal flow meter which can measure both the flow rate and the temperature of a fluid at one time with a simple constitution of circuit, by providing separately a terminal to draw out an output in accordance with the resistance value of a temperature compensating resistor. CONSTITUTION:A terminal is provided separately to draw out an output corresponding to the resistance value of a temperature compensating resistor 3. For instance, a terminal is connected through a joint 10 between the resistor 3 in bridge branch of temp. compensating side, and a resistance R3 to draw out the aspirated temperature signal T. An output corresponding to the resistance value of the resistor 3 can be drawn out at the joint 10. The resistance value of the resistor 3 varies by the temperature of the fluid that flows within a path 1 and shows the value corresponding to the temperature of the fluid. Thus the temperature of the fluid can be detected by the signal T.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal flow meter, and in particular, it has a temperature-dependent temperature-sensitive resistor and a temperature-compensating resistor installed in a flow path, and the temperature difference between these two resistors is In a thermal flowmeter of the type that obtains a flow rate detection signal while balancing the control current of the temperature-sensitive resistor to maintain a constant flow rate, an improvement has been made so that a fluid temperature detection signal can be extracted at the same time as the flow rate detection signal. The present invention provides a thermal flow meter.

In the engine control of automobiles, etc., ignition timing.

Air fuel ratio, EGR (exhaust gas recirculation system), or l5
Various types of controls such as O (idle speed control) are implemented, and these engine controls are normally performed while detecting the engine state based on detection signals of the engine rotation speed, intake flow rate, or intake negative pressure. Furthermore, depending on the specifications of the engine, the temperature of the cooling water, the temperature of the intake air, etc. are also detected, and corrections are made based on these detection signals to perform engine control that can respond to specific operating conditions. In particular, when starting the engine cold, it is necessary to temporarily control the air-fuel ratio to be rich in order to supply a sufficiently rich air-fuel mixture to facilitate starting. A thermal flow meter is widely used as a means for detecting the intake air flow rate. This thermal flow meter obtains an output signal based on the control current value (or voltage) to the temperature-sensitive resistor installed in the intake passage when the amount of heat generated by the resistor and the amount of heat dissipated are balanced. It is. In addition, since automobile engines are used in a wide temperature range from -20tll' to 120C, it is necessary to temperature-compensate the intake air amount detection value, and for this purpose, a separate temperature-compensating resistor that is also temperature-dependent is used. The control current to each resistor is balanced so that the temperature difference between the temperature-sensitive resistor and the temperature-compensating resistor becomes constant. - Thermal flowmeters with a temperature-sensitive resistor and a temperature-compensating resistor of this type have a temperature-dependent temperature-sensitive resistor installed in the flow path in one bridge branch and heated by the control current. A bridge circuit is installed in which a temperature-compensating resistor whose resistance value changes depending on the fluid temperature is connected to the other bridge branch.
A diagonal branch of the bridge circuit is connected to an input terminal of an amplifier for controlling current supply, and the current of the temperature-sensitive resistor is controlled so that the temperature difference between the temperature-sensitive resistor and the temperature-compensating resistor becomes constant by 5 degrees. It is configured like this.

Conventional thermal flowmeters of this type have been designed to detect the intake air flow rate, and have not been equipped with a function to extract the intake air temperature as an output signal. Therefore, when it is necessary to detect the intake air temperature, it is necessary to separately provide an independent temperature sensing element.

An object of the present invention is to provide a thermal flowmeter that can simultaneously measure not only the original flow rate but also the fluid temperature (intake temperature, etc.) with an extremely simple and compact circuit configuration.

A feature of the present invention is that in the conventional thermal flowmeter as described above, a separate terminal is provided for taking out an output corresponding to the resistance value of the temperature compensating resistor.

That is, according to the present invention, a temperature-dependent temperature-sensitive resistor installed in the flow path and heated by a control current is connected to one bridge branch, and a temperature-dependent temperature-sensitive resistor whose resistance value changes depending on the fluid temperature is connected to the other bridge branch. A diagonal branch of the bridge circuit is connected to an input terminal of an amplifier for supplying a control current, and the temperature difference between the temperature-sensitive resistor and the temperature-compensating resistor is In a thermal flowmeter that controls the current of the temperature-sensitive resistor in a closed loop so that the current is constant, a terminal is provided to take out an output according to the resistance value of the temperature-compensating resistor, and the temperature of the fluid can also be detected. A thermal flow meter is provided which is characterized by:

The present invention will be described in detail below with reference to FIGS. 1 to 5.

FIG. 1 is a circuit diagram showing an embodiment of a thermal flowmeter according to the present invention.

In FIG. 1, a temperature-sensitive resistor having a predetermined resistance value formed of a temperature-dependent resistor is installed in a flow path (for example, an engine intake passage) 1 through which the fluid to be measured flows in the direction of arrow F. There is. A temperature compensating resistor 3 composed of a temperature-dependent resistor is also installed in the flow path 1.

A control voltage is applied from the power source 4 to the branch point A via the collector and emitter of the transistor 5. At one of the bridge branches leading from the branch point A to the connection points B and C, the temperature-dependent temperature-sensitive resistor 2, which is installed in the flow path and heated by the control current, and a fixed resistor R3 are connected in series. It is connected to the. Further, a voltage dividing resistor in which two resistors r1'+r2 are connected in series is connected in series with the temperature-sensitive resistor. By adjusting the resistance value of any one of the voltage dividing resistors r, , r2, the voltage at the connection point Z can be adjusted according to the voltage dividing ratio.

The other bridge branch is connected from the connection point C to the resistor R3 to the connection point 10. It is constituted by a branch path leading to the connection point A through the connection point A, the temperature compensating resistor 3, and the resistor 8. The connection point AI is connected to the output side of the amplifier 7, the connection point B is connected to the positive phase of the amplifier 7, and the connection point B is connected to the negative phase of the amplifier 7. There is. Therefore, the voltage at the connection point A1 has a constant ratio to the voltage at the branch point A and changes in accordance with the voltage change at the point A. Further, the connection point B and the connection point 1 form diagonal branch points of the bridge circuit.

A connection point Z of the voltage dividing resistor 'l+'2 is connected to the positive phase of the amplifier 6 via a delay circuit 9.

The connection point A1 is connected to the negative phase of the amplifier 6. The output side of the amplifier 6 is connected to the base of the transistor 5.

According to the circuit configuration described above in FIG. The current value in the flow path 1, that is, heat dissipation from the temperature-sensitive resistor 1, is controlled by the current value (control current) that makes the temperature of the temperature-sensitive resistor 2 constant, that is, the temperature of the temperature-sensitive resistor 2 in a balanced state. The flow rate corresponding to the amount can be detected.

This detection signal is taken out from the diagonal branch point B of the output bridge branch and can be detected as an output signal V.

When the fluid temperature changes, the amount of heat dissipated from the temperature-sensitive resistor 2 also changes. Temperature compensation can be performed by controlling the temperature difference with the temperature compensation resistor 3 to be constant. In this way, the output signal V can accurately detect the flow rate flowing through the flow path 1 regardless of temperature changes.

Furthermore, in the circuit configuration shown in FIG. 1, a terminal for taking out the intake air temperature signal T is connected to a connection point 10 between the temperature compensation resistor 3 and the resistor R8 in the bridge branch on the temperature compensation side. This connection point 10 is a point from which an output corresponding to the resistance value of the temperature compensation resistor 3 can be taken out. The resistance value of this temperature compensating resistor changes depending on the temperature of the fluid flowing in the flow path 1 and shows a value corresponding to the fluid temperature, so the fluid temperature can be detected from the output signal T. That is, the first
According to the circuit configuration of the thermal flowmeter shown in the figure, it is possible to obtain the intake air temperature signal T as well as the flow rate detection signal V,
Flow rate and fluid temperature can be detected simultaneously.

FIG. 2 is a circuit diagram showing a modified embodiment of the thermal flowmeter according to the present invention.

In the embodiment shown in FIG. 2, an intake temperature signal stabilization circuit is connected to the bridge branch on the temperature compensation side of the bridge circuit portion of the circuit shown in FIG. 1, and the intake temperature signal T is taken out through this stabilization circuit. This embodiment differs from the embodiment shown in FIG. 1 in this respect, and all other configurations are substantially the same as in the embodiment shown in FIG. In FIG. 2, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In the embodiment shown in FIG. 2, a voltage dividing resistor consisting of a resistor 12 and a resistor 13 is connected to a connecting point 11 having the same potential as the connecting point A, and the connecting point between these voltage dividing resistors is connected to the negative phase of the amplifier 14. It is connected to the.

On the other hand, the connection point 10, which is the same as the diagonal branch of the bridge branch on the temperature compensation side, is connected to the positive phase of the amplifier 14. A terminal for taking out an intake air temperature signal T is connected to the output side of the amplifier 14. Note that a parallel resistor 15 is connected between the negative phase input side of the amplifier 14 and the output side of the amplifier.

According to the configuration shown in FIG. 2, the connection point 1o, where a voltage corresponding to the resistance value of the temperature compensation resistor 3 is obtained, is connected to the terminal T via the amplifier 14. A signal obtained by appropriately amplifying and correcting the output can be extracted as the intake temperature signal T.

Therefore, compared to the intake temperature signal obtained in FIG. 1, a signal that has been amplified to a predetermined level and whose output has been stabilized can be extracted as the intake temperature signal T.

In the embodiment shown in FIGS. 1 and 2, the temperature-sensitive resistor 2
The connection point Z between the voltage dividing resistor r and r2 connected in parallel with
is connected to the positive layer of the amplifier 6 via a delay circuit 9. The reason for connecting this delay circuit will be explained below.

FIG. 3 is a diagram illustrating the operation of the drive circuit of the thermal flowmeter shown in FIGS. 1 and 2. When the flow rate Q changes stepwise as shown, the flow rate detection signal V is as shown in FIG. As shown by the solid line, at the rising point, the flow rate changes smoothly due to the delay in closed loop control, etc., but at the falling point, the flow rate Q changes more than the yloJ-like stage. That is, there is a response delay at the rising point and no response delay at the falling point.

FIG. 4 is also a diagram showing the same characteristics as FIG. 3, and is a diagram showing the responsiveness at the rising and falling points of the detected flow rate signal Q. corresponds to the solid line. That is, at the -rise point, as shown by the curve S1, there is a delay in response to the stepwise change in the flow rate Q, and it changes gently, but at the -fall point, the flow rate changes smoothly. As shown in fM S 2, it changes rapidly in response to a stepwise change in the flow rate Q.

As shown by the solid lines in Figures 3 and 4, if the responsiveness of the detection signal to the flow rate is different at the rising and falling points and is asymmetrical, there is a change in the magnitude of the flow pulsation in the flow path. A detection error will occur due to the measurement difference. That is, when the pulsation is relatively small, the integral area of the detection signal V becomes relatively large, and as a result, the detected value shows a value higher than the reference flow rate. On the other hand, when the pulsation is large, the influence of slow response at the rising point becomes significant, and the value of the detection signal V becomes relatively small compared to when the pulsation is small. In other words, depending on the magnitude of the pulsation,
Even when the flow rate is the same, the values of the detection signals are different, making it impossible to perform stable measurements and causing errors.

Furthermore, as the pulsation rate increases, the value of the detection signal for the same flow rate becomes smaller, and the same detection signal is formed when the pulsation is small and when the pulsation is large, even though the flow rates are different. A binary problem arises. This binary problem must also be solved in order to improve measurement accuracy.

The delay circuit 9 is provided to reduce detection errors that occur when such pulsations are present or large. That is, the first
By using the delay circuit having the configuration shown in FIG. 5 as the delay circuit 9 in FIG. The responsiveness at the point can be similarly delayed. That is, by making the responsiveness at the falling point similar to that at the rising point as shown by the dotted line in FIGS. 3 and 4, it is possible to eliminate the detection error caused by the presence or absence of pulsation and its magnitude. .

FIG. 5 is a diagram showing the internal structure of the delay circuit in FIGS. 1 and 2. In FIG. 5, the delay circuit 9 consists of two amplifiers 16, 17 and 8 connected in parallel between these amplifiers.
0 circuit and a rectifying element 18. A connection point Z in FIGS. 1 and 2 is connected to the positive phase of an amplifier 16, and the output side of the amplifier 16 is connected to the positive phase of an amplifier 17 via a rectifying element 18. The output side of the amplifier 17 is connected to the negative phase of the amplifier, and is also connected to the negative phase of the amplifier 16 via a resistor 20 after branching at a branch point 19 . The negative phase of the amplifier 16 is grounded via a resistor 21. The rectifying element 18 and the amplifier 17
A delay circuit element consisting of a resistance ratio and a capacitance C is connected in parallel between the capacitor C and the capacitor C when the voltage at the connection point Z rises. The response to sudden changes at the connection point Z is delayed only at the time of falling. This response delay is due to a time constant determined by the values of capacitance C and resistance ratio, and the response can be adjusted by changing these values. For example, in actual circuit design, when the resistance R is 120 Ω, the capacitance C is 0.0
By selecting an appropriate value within the range of 15 to 0.1 μF, it is possible to delay the response only at the falling edge, and as shown by the dotted lines in Figures 3 and 4, the response can be delayed at the rising edge and at the rising edge. We were able to make the response delay at the lower position the same level and create a bilaterally symmetrical design. In this way, by selecting the responsiveness at the rise and fall in the same way, the flow rate can be adjusted when the pulsation of the flow in the flow path is large or small, and when there is or is not pulsation. Detection accuracy can be stabilized.

Since each embodiment of the thermal flowmeter according to the present invention has the configuration and operation described above, it is possible to simultaneously extract the intake air temperature (fluid temperature) detection signal in addition to the flow rate detection signal, unlike the conventional thermal flowmeter. Furthermore, by providing a delay circuit in the closed loop, it is possible to improve the temperature characteristics of the flow rate detection signal.

For example, in the microcomputer control of a turbocharged automobile engine, the intake air is adiabatically compressed during supercharging, so the
The intake air temperature rises at a rapid rate of about 200 m, and it is necessary to correct the ignition timing accordingly to prevent non-king. In order to prevent such knocking, it is necessary to delay the ignition timing, and at this time, it is necessary to immediately detect not only the intake air amount but also the intake air temperature and execute engine control that delays the ignition timing. In addition, even if the engine is controlled by a microcomputer without a turbo, the atomization state and combustion state of the fuel will be different in cold weather or high-temperature idling than in normal operation, and uniform control cannot cover the situation. However, engine control is required to detect the intake air temperature and adjust the air-fuel ratio.

According to each embodiment of the thermal flowmeter of the present invention, not only the intake air flow rate but also the intake air temperature can be detected at the same time.
It is extremely effective when applied to such engine control.

Furthermore, according to each of the embodiments described above, the responsiveness is delayed only at the time of falling into the closed loop circuit that controls the current supplied to the temperature-sensitive resistor, and this is corrected to the same responsiveness as at the time of rising. By providing this means, it is possible to reduce detection errors, especially in the pulsating operation region, and to perform stable measurements.In addition, it is also possible to solve the binary problem, which is a problem unique to this thermal flowmeter. can. That is, by providing a delay circuit in the closed loop circuit for driving the temperature-sensitive resistor, the temperature characteristics of the temperature-sensitive resistor can be improved.

As is clear from the above description, according to the present invention, it is possible to provide a thermal flow meter that can simultaneously extract not only a flow rate detection signal but also an intake air temperature detection signal.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram illustrating the circuit configuration of one embodiment of the thermal flowmeter according to the present invention, FIG. 2 is an explanatory diagram illustrating the circuit configuration of another embodiment of the thermal flowmeter according to the present invention, and FIG. Fig. 3 is a graph illustrating the change characteristics of the flow rate detection signal V corresponding to a stepwise change in the flow rate Q, and Fig. 4 is a graph showing the response of the flow rate detection signal at rising and falling times corresponding to a stepwise change in the flow rate. The graph illustrating the characteristics, FIG. 5, is an explanatory diagram illustrating the circuit configuration of the delay circuit in FIGS. 1 and 2. DESCRIPTION OF SYMBOLS 1... Flow path, 2... Temperature sensitive resistor, 3... Temperature compensation resistor, 4... Power supply, 6, 7... Amplifier, 9...
Delay circuit, 14...Amplifier, A, B, C, D...Bridge circuit branch point, F...Flow direction, Q...Flow rate, Q,...Flow rate detection signal, T...・Intake air temperature detection signal, ■... formation amount detection signal. 1st figure 2nd figure 3 closed Q-''-1-shim-y''' No. 40 2

Claims (1)

[Claims] 1. A temperature-dependent temperature-sensitive resistor installed in the flow path and heated by a control current is connected to one bridge branch, and the resistance value changes depending on the fluid temperature to the other bridge branch. A diagonal branch of the bridge circuit is connected to an input terminal of an amplifier for supplying a control current, and the temperature difference between the temperature-sensitive resistor and the temperature-compensating resistor is approximately constant. In a thermal flowmeter that controls the current of the temperature-sensitive resistor in a closed loop so that Features of thermal flowmeter. 2. The thermal flow meter according to claim 1, characterized in that a rise delay circuit for a flow rate detection signal is interposed in the closed loop that controls the current of the temperature-sensitive resistor.