JPH02259427A - Heating element type apparatus for measuring flow rate - Google Patents

Abstract

PURPOSE:To average a response speed for a change in an output voltage by giving nonlinearity to the input-output characteristic of a temperature controlling circuit and by decreasing a signal amplification factor thereof in accordance with an increase in the output voltage. CONSTITUTION:A divided-voltage output V2 of a voltage dividing circuit is sent to a constant temperature controlling circuit 3 and a control voltage V1 of the circuit 3 is fed back for control to a heating resistor 1. The output V2 turns to hold a proportional relation with the voltage V1 when the resistance value of the resistor 1 is fixed. In order to keep the resistance value of the resistor 1 fixed, accordingly, the characteristic of the circuit 3 needs to be approximate to that of a DC amplifier 4. A voltage VOS is an offset voltage and it is a factor for determining the transient characteristic of a measuring apparatus. When the input-output characteristic of the circuit 3 is linear, besides, a change in the voltage V1 of the circuit 3 in relation to the amount of a change in the resistance value of the resistor 1 varies in accordance with the amplitude of the output V2 and the rate of the change therein increases as the output V2 increases. In other words, the rate of the change in the voltage V1 of the circuit 3 in relation to the change in the resistance value of the resistor 1 is determined by the voltage VOS and the output V2 and the rate of the change becomes large as the output V2 turns large.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heating element type flow measuring device for measuring the amount of air taken into an internal combustion engine of an automobile or the like.

[Conventional technology]

Generally, methods for measuring the amount of air taken into an internal combustion engine include a pressure sensor method that measures pressure, a vane method that measures the angle of the vane that receives the dynamic pressure of the intake air, and a heating method that measures the angle of the vane that receives the dynamic pressure of the intake air. A heating element method that measures the amount of electricity supplied to a resistor is in practical use.

Demand for the heating element method is increasing because it has good responsiveness, is compact, and is not affected by EGR, etc.

As such a heating element system, Japanese Patent Application Laid-open No. 57-
The one shown in Japanese Patent No. 22563 is known as a typical example.

[Problem to be solved by the invention]

By the way, in the prior art described above, the output characteristic with respect to the amount of air taken in is a nonlinear characteristic.

For this reason, there was a problem in that the average value of the air amount and the average value of the output did not necessarily match, resulting in low measurement accuracy.

It has been found that this problem is caused by the fact that the response characteristics differ depending on the voltage of the current detection resistor, which is the output voltage value of the measuring device.

Therefore, it can be seen that in order to improve the measurement accuracy, it is necessary to reduce the influence of the magnitude of the output voltage value on the rate of change of the output voltage value with respect to the change in the amount of air taken in.

(Means for Solving the Problems) In the present invention, the input/output characteristics of the temperature control circuit that controls the temperature of the heating resistor are made to have nonlinearity, and the signal amplification factor is made smaller as the output voltage becomes larger. This is what I did.

[Effect]

In the present invention, since the signal amplification factor is reduced as the output voltage increases, the rate of change in the output voltage with respect to a change in the resistance value of the heating resistor can be reduced, so that the response speed to changes in the output voltage can be averaged. can.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 1, reference number 1 is a heating resistor made of platinum or the like having temperature-dependent characteristics and placed in the intake air introduction passage of an internal combustion engine.This heating resistor 1 is connected in series with a current detection resistor 2. constitutes a voltage divider circuit.

The divided voltage output V2 of the voltage dividing circuit (this becomes a so-called output voltage and is sent to an arithmetic device such as a microcomputer).
is sent to the constant temperature control circuit 3, and the control voltage Vl of this constant temperature control circuit 3 is further feedback-controlled to the heating resistor 1.

Then, the divided voltage output v2 maintains a proportional relationship with the control voltage Vt when the resistance value RH of the heating resistor 1 is constant.

Therefore, in order to keep the resistance value R)l of the heating resistor 1 constant, the characteristics of the constant temperature control circuit 3 need to be close to those of the DC amplifier 4.

Here, the voltage Vos is called an offset voltage and is an element for determining the transient characteristics of the measuring device.

When the input/output characteristic of the constant temperature control circuit 3 is a linear characteristic, the change in the control voltage v1 of the constant temperature control circuit 3 with respect to the amount of change in the resistance value RH of the heating resistor 1 is the divided voltage output v2
It changes depending on the size of the voltage, and this is the partial pressure output ■
2 is large, the rice malting rate becomes large.

That is, the rate of change in the control voltage v1 of the constant temperature control circuit 3 with respect to the change in the resistance value RH of the heating resistor 1 is determined by the offset voltage Vos and the divided voltage output V2.
The larger the value, the greater the rate of change.

Figure 2 shows the operating characteristics when the input/output characteristics of the constant temperature control circuit 3 are linear, and the operating point moves with respect to the resistance value change of the heating resistor 1 as the divided voltage output Vz increases, that is, the output voltage of the measuring device It can be seen that the change in the divided voltage output V2 becomes large.

On the other hand, according to the embodiment of the present invention, the divided voltage output v2 is input to the multiplication circuit 5, and its output is input to the inverting terminal of the DC amplifier 4.

This multiplier circuit 5 has a function of imparting non-linearity to the input/output characteristics of the constant temperature control circuit 3, and specifically controls the constant temperature by reducing the output of the multiplier circuit 5 from the characteristics of the DC amplifier 4. It acts so that the second derivative of the input/output characteristics of the circuit 3 is always negative.

That is, the amplification factor of the constant temperature control circuit 3 is decreased as the value of the input divided voltage output v2 increases.

Figure 3 shows the operating characteristics of the measuring device when the second derivative of the input/output characteristics of the constant temperature control circuit 3 is always negative, and the resistance value of the heating resistor 1 when the partial pressure output v2 increases. It is understood that the increase in the rate of change of the control voltage v1 with respect to a change in RH can be reduced.

FIG. 4 shows another embodiment of the present invention, in which the multiplication circuit 5 shown in FIG. 1 is made into two stages.

In FIG. 4, a multiplication circuit 5A and a multiplication circuit 5B are provided in series, and the output of the multiplication circuit 5B is input to the inverting terminal of the DC amplifier 4.

Therefore, the output of the quartic function is generated by the two multiplier circuits 5A and 5B, and nonlinearity can be imparted to the input/output characteristics of the constant temperature control circuit 3.

FIG. 5 shows another embodiment of the present invention, in which the divided voltage output v2 is input to an exponential or logarithmic function generating circuit 6, and its output is input to the inverting terminal of the DC amplifier 4.

Therefore, an exponential or logarithmic function output is generated by the exponential or logarithmic function generation circuit 6, and nonlinearity can be imparted to the input/output characteristics of the constant temperature control circuit 3.

As described above, the present invention can improve measurement accuracy by reducing the rate of change in the control voltage as the divided voltage output (2) increases.

FIG. 6 is a diagram showing a specific circuit configuration of FIG. 1.

In FIG. 6, the heating resistor 1 is controlled to be energized by a control transistor 8, and the control transistor 9 is driven by the differential output of a differential amplifier 10. The inverting terminal of the differential amplifier 10 is connected to the heating resistor 1.
It is connected to the connection point of series resistor 7.8 in parallel with .

Further, the connection portion of the voltage dividing circuit is connected to the non-inverting terminal of the differential amplifier 11. Note that a resistor 8 is also connected. Further, the resistor 2 is connected to the inverting terminal of the differential amplifier 11, and a temperature sensing resistor 12 made of platinum or the like is connected between this inverting terminal and the output terminal of the differential amplifier 11. This temperature detection resistor 1
2 is provided in the intake air introduction passage and compensates for the intake air temperature. The output terminal of the differential amplifier 11 is connected to the non-inverting terminal of the differential amplifier 10. resistance 13
, 14, 15, and 16 are adjustment resistors.

The constant temperature control circuit 3 having the above configuration is manufactured by the Japanese Patent Publication Publication No. 61-1.
The operation is explained in detail in Japanese Patent No. 6026, so it is omitted here.

The multiplication circuit 5 is mainly composed of two transistors 17 and 18 and a diode 19, and a control voltage 1 is supplied to the base of each transistor 17 and 18 through the diode 19. In addition, the collectors of each transistor 17 and 18 are connected to each input terminal of the differential amplifier 11, respectively.

Therefore, as shown in FIG. 1, the constant temperature control circuit is operated so that the second derivative of the input/output characteristics is always negative.

FIG. 7 is a diagram showing a specific configuration of FIG. 5, and shows the logarithmic function generator 6. In FIG.

The logarithmic function generator 6 mainly includes an operational amplifier 20 and series-connected diodes 21 and 22. The divided voltage output v2 is input to the non-inverting terminal of the operational amplifier 2o, and the resistor 2 is input to the inverting terminal. Series-connected diodes 21 and 22 are connected between the output terminal and the inverting terminal of the operational amplifier 20. Furthermore, the output terminal is resistor 23
It is connected to the non-inverting terminal of the differential amplifier 11 via.

Note that 24 is an adjustment resistor.

Therefore, in this embodiment as well, non-linearity can be imparted to the input/output characteristics of the constant temperature control circuit 3, as in FIG.

〔Effect of the invention〕

As described above, according to the present invention, the average value of the air amount and the average value of the output voltage match, and measurement accuracy can be improved.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a heating element type flow rate measuring device which is an embodiment of the present invention, Figures 2 and 3 are input/output characteristic diagrams of a constant temperature control circuit, and Figures 4 and 5 are diagrams of the present invention. FIG. 6 is a specific circuit diagram of FIG. 1, and FIG. 7 is a specific circuit diagram of FIG. 5. 1... Heating resistor, 2... Current detection resistor, 3...
- Constant temperature control circuit, 4... DC amplifier, 5... Multiplication circuit, 6... Exponential or logarithmic function circuit. Partial pressure output ■2 O5 Partial pressure output v2 Fig. Fig.

Claims (1)

[Claims] 1.(a) Disposed in an intake air introduction passage of an internal combustion engine,
Heating resistor (1) heated by control output (V_1)
); (b), a current detection resistor (2) connected in series with the heating resistor and generating a divided voltage output (V_2) at its connection part;
(c) generating the control output (V_1) based on the divided voltage output (V_2);
and a temperature control circuit (3) constituted by a circuit in which the input-output relationship of the control output (V_1) is such that the second-order differential value thereof is always negative. 2. (a) disposed in the intake air introduction passage of the internal combustion engine;
Heating resistor (1) heated by control output (V_1)
); (b), a current detection resistor (2) connected in series with the heating resistor and generating a divided voltage output (V_2) at its connection part;
(c) The control output is generated based on the divided voltage output (V_2), and the input/output relationship between the divided voltage output (V_2) and the control output (V_1) is
Non-linearity in which the rate of change of the control output (V_1) is larger on the low partial voltage output side than on the high partial voltage output side, and the control output (V_1) increases as the partial voltage output (V_2) increases. A heating element type flow rate measuring device consisting of a temperature control circuit (3) composed of a circuit having characteristics. 3. In claim 2, the temperature control circuit includes a second-order or higher-order function generation circuit, and the input/output of the divided voltage output (V_2) and the control output (V_1) is performed by the high-order function generation circuit. A heating element flow measurement device configured to impart nonlinearity to the relationship. 4. In claim 2, the temperature control circuit receives at least the divided voltage output (V_2) and outputs the control output (V_2).
_1) is output from the DC amplifier, and the divided voltage output (V_
2) is input and the control output (V_1) of the DC amplifier is
A heating element type flow rate measurement device equipped with a high-order function generation circuit that controls.