JP2814523B2 - Signal processing method of thermal flow sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow sensor for detecting a flow rate of a fluid, and more particularly to a signal processing method for improving responsiveness to a flow rate change.

[Conventional technology]

As a conventional thermal flow sensor, a thermal air flow sensor that detects an intake air flow rate of an internal combustion engine is well known, and as a typical example, a temperature of a platinum wire disposed in an intake passage is constant. A hot wire type air flow sensor is known which suppresses a current flowing through a platinum wire so as to obtain an air flow signal in accordance with the current value. In addition, a thermal air flow sensor in which platinum is deposited on an alumina substrate or film instead of the platinum wire has recently attracted attention as a low-cost version of the hot wire air flow sensor.

By the way, in these thermal air flow sensors,
Since the air flow is measured by detecting the current flowing through the temperature-dependent resistor controlled to a constant temperature, the air flow to be measured changes due to the temperature-dependent resistance and heat conduction and heat storage to the holding member. It is known that the time output response is delayed, causing an error in detection characteristics.

FIG. 6A shows a thermal air flow sensor of this type (1).
(11) is a tubular housing which also serves as a passage through which air flows, and the direction of air flow is indicated by arrows. R _H is a temperature-dependent resistance for detecting an air flow rate, and is formed by printing or depositing platinum on an alumina substrate (14) and then trimming it as shown in FIG. 6 (b). resistor R _K, are arranged with R _M in the air passage. R _H , R _M , R _K , R ₁ , and R ₂ form a resistance detecting device by a well-known bridge circuit configuration, and form a closed loop by a differential amplifier (12) to form a temperature or resistance of R _H. The value is controlled to be constant. Therefore, current supplied R _H is determined in accordance with the air flow rate, it is possible to obtain an output voltage from the product of the resistance value of the current value and R _M (13).

Next, the response delay of the thermal air flow sensor (1) when the air flow rate changes will be described. FIG. 7 is a diagram showing the response of the thermal air flow sensor when the air flow rate is changed stepwise, and its characteristic shows a response substantially equal to a polygonal line with the point A as a node. Here, the horizontal axis indicates the elapsed time after the step change, and the vertical axis indicates the air flow rate change rate. The time delay to the point A is mainly caused by the thermal response of the platinum resistor R _H and the response delay of the circuit. The target value and the deviation at the point A and the time from the point A to the target are mainly the platinum resistance R _H It is generated by heat conduction and heat storage to the alumina substrate (14) as a holding member. FIG. 8 is a diagram for explaining the above operation, and shows a temperature distribution on the alumina substrate (14) when the distance is plotted on the horizontal axis with respect to the position of the platinum resistance _RH relative to the alumina substrate (14). Show. The temperature in the vicinity of the platinum resistance _RH is controlled to a constant temperature sufficiently higher than the air temperature by the above-described circuit. Here, heat generated in the platinum resistance R _H will be heat transfer, heat storage from platinum resistance R _H portion to the alumina substrate (14) while being discharged into the air. The closed loop circuit compensates for this heat loss and limits the current to the platinum resistor _RH .
Therefore, the output of the thermal air flow sensor (1) for a predetermined air flow rate includes the heat transfer heat storage component to the alumina substrate (14), but the heat on the alumina substrate (14) is balanced. Characteristics in the state, that is, accurate flow characteristics in the steady state can be obtained. However, when the air flow rate changes, an error occurs in the flow rate characteristic because the above thermal equilibrium is not achieved.
In FIG. 8, l ₁ is the temperature distribution when the air flow rate is small, and l ₂
Indicates when the air flow rate is high. Here, the cooling effect of the alumina substrate (14) by the air flow through the l ₂ becomes lower l ₁ are different. Small flow from the large flow rate when the air flow rate was changed step the temperature distribution becomes l ₂ eventually, the initial temperature distribution and becomes platinum resistance of l ₁ to an air flow rate corresponding to l ₂ R _The power supplied to _H , that is, the output of the thermal air flow sensor (1) is smaller than the original output. That is, when the air flow rate changes, an initial flow rate error corresponding to the difference between the temperature distribution corresponding to the air flow rate before the change and the temperature distribution corresponding to the air flow rate after the change occurs, and the air flow after the temperature distribution changes. The time error until the steady state with respect to the flow rate is continued for a while while being reduced. In the thermal air flow sensor (1) shown in FIG. 6, the degree of this effect is so great that the heat transfer and heat storage of the alumina substrate (14) as the holding member is large, and the thermal air flow sensor (1) can be practically used in a fuel injection device of an internal combustion engine. The initial flow rate deviation is up to 30% and the duration of the deviation is about 500ms even if the sensor is manufactured taking into account the area of the platinum resistance _RH and the thickness of the alumina substrate (14) in order to make the sensor responsive and durable. ,
Such a response delay is unacceptable in fuel control of the internal combustion engine.

As a method of improving such a defect, for example,
A device using a temperature-dependent resistor as disclosed in -26823 has been proposed. FIG. 9 shows this temperature-dependent resistance. A platinum thin film is deposited on the outer surface of the annular alumina substrate (14), and a platinum resistor _RH is formed on the entire alumina substrate (14) by laser trimming. A lead wire (15) made of a wire is inserted through openings at both ends of the alumina base (14), and is fixed with a conductive paste (16). By increasing the area of the platinum resistance _RH with respect to the alumina substrate in this way, it is possible to reduce the influence on the temperature characteristics of the holding member when the flow rate changes, and to improve the responsiveness.

[Problems to be solved by the invention]

However, such a conventional thermal air flow sensor has a problem in that the structure of the sensor itself is complicated, making it difficult to manufacture, or increasing the price.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a signal processing method that uses a thermal flow sensor having a simple structure and is inexpensive to improve responsiveness by signal processing. It is.

[Means for solving the problem]

The present invention provides a thermal flow sensor including a temperature-dependent resistor and a holding member that supports the resistor, wherein a correction coefficient corresponding to the flow rate of the fluid when the flow rate is in an equilibrium state while maintaining a steady state. A certain first calculation value is set in advance, and the first calculation value is obtained from the flow value obtained from the output of the thermal flow sensor, and the first calculation value obtained when the flow rate of the fluid fluctuates. A second calculation value that is a correction coefficient that follows the change of the amount, and that determines the speed of the follow-up by using a correction ratio value that changes according to the flow rate change amount,
The output of the flow sensor is corrected based on the difference between the first and second calculated values.

[Operation] In the signal processing method according to the present invention, the first operation value which is a correction coefficient set corresponding to the flow rate of the fluid in the equilibrium state and the first operation value when the flow rate of the fluid changes Is configured to correct the output of the flow rate sensor by a difference from a second calculated value that is a correction coefficient that follows the change of the temperature. It is possible to eliminate it.

〔Example〕

Hereinafter, a fuel injection device using a thermal air flow sensor according to an embodiment of the present invention will be described. In FIG. 1, (1) is a thermal air flow sensor of the type shown in FIG. 6, (2) is an intake passage accommodating the air flow sensor (1), and (3) regulates an intake air amount. Throttle valve,
(4) is a surge tank, (5) is an intake manifold, (6) is an engine, (7) is an injector attached to an intake manifold for each cylinder in the engine (6), and (8) is a cam of the engine (6). A crank angle sensor provided in a distributor attached to the shaft to detect a rotational position of the crank shaft; (9)
Is a signal for controlling the injection pulse width of the injector (7) by performing a correction calculation mainly by various sensors (not shown) based on the air flow rate signal from the air flow rate sensor (1) and the engine speed signal from the crank angle sensor (8). An A / D converter (91) for digitally converting the output voltage signal of the thermal air flow sensor (1) and a digital for shaping the output signal of the crank angle sensor (8) as shown in FIG. An interface (92), a central processing unit (CPU) (93) for performing arithmetic processing by receiving these outputs, a ROM (94) storing programs and data, and a RAM (95) for temporarily storing data And a drive circuit (96) for generating an output signal. As a basic calculation processing method, an air flow rate correction calculation described later is performed by using an A / D value of an air flow rate sensor, a rotation speed signal from a crank angle sensor, and the like. The injection pulse width is calculated and the injector (7) is controlled by the drive circuit (96).

Incidentally, the thermal air flow sensor (1) used in such a fuel injection device has a response delay inevitable due to the heat transfer and heat storage characteristics of the alumina substrate (14) as described above. The property improvement processing is required.

Hereinafter, a signal processing method according to an embodiment of the present invention will be described in a third embodiment.
This will be described with reference to FIG. 4, FIG. 4 and FIG. First, in step 101 of FIG. 3 (a), the signal processor (9) performs A / D conversion of the output voltage of the air flow sensor (1) at predetermined time intervals, based on a flow rate characteristic measured in advance. the above
To previously obtain the flow rate Q _m corresponding to A / D conversion value (for 4-cylinder engines, during the rotation of 1000rpm in each 30 msec) interrupt signal by the crank angle sensor (8) is input, at these times average calculating the air flow rate Q _a of between rotation signal from the integrated value of the measured air flow rate Q _m and the number of integrations n, RAM (9
Write in 5).

Hereinafter, a repetitive processing routine by interruption at a fixed time interval different from the interruption signal will be described with reference to FIG. 3 (c). In step 301, the average air flow rate Q _a which is calculated by the routine of FIG. 3 (a) read from RAM (95).
Air flow sensor obtained by referring to the first correction calculation value data C _Qmax table to the average air flow rate Q _a which has been determined in advance corresponding to the thermal equilibrium state at step 302. This table shows that when the practical air flow rate measurement range used for the internal combustion engine is about several g / sec to 100 g / sec, the minimum flow rate is 0.3, and the medium flow rate is 0 or more, as shown in FIG. It is configured to have a value that decreases with an increase in the air flow rate Qa in _a low flow rate range.

The first calculated value C _Qmax represents a temperature characteristic of the alumina substrate (14) that changes with respect to the air flow rate Q.

Next, in step 303, the second calculation value C _Q calculated by the previous calculation of the iterative process routine shown in FIG. 3 (c) read from RAM (95). Then, in step 304, the average air flow rate Q obtained by the previous repetitive calculation
calculating a variation with respect to _a, and temporarily stores it as the flow rate change amount Delta] Q _a per unit time. Then determine the correction ratio value ΔC to determine by referring to the magnitude of the flow rate variation Delta] Q _a In step 305, further C _Qmax and C _Q in step 306
Are determined to be equal to each other, and when they match, the value C _Qmax is held as the second calculated value C _Q assuming that the two are in an equilibrium state.

Also, if both do not match, if the C _Q is larger than C _Qmax at step 307 is set in advance from C _Q delta
Only C is subtracted, and if the magnitude relation is opposite, it is added. In this way, the second calculated value C _{Q is changed} to the first calculated value every fixed time.
Calculation processing is performed so as to follow C _Qmax . By wherein obtaining the correction ratio value ΔC from the average air flow rate Q _a variation Delta] Q _a per unit time, it becomes possible to correct value reflecting the amount of change per holding member unit temperature time.

Then calculating a correction factor C in step 310, the average air flow rate Q _a correction air flow rate is corrected by multiplying the coefficient C Q _a ^* is determined in step 311.

Figure 4 is such an air flow sensor (1) air flow rate used is intended to indicate a rapid time chart when increased or decreased, the opening state of rapidly opening the throttle valve (3) to time t ₀ (high flow conditions) is maintained, after which illustrates a case where to return the t ₃ at the throttle valve (3) to suddenly closed. Here, the solid line of FIG. 4 (a) shows the change in the actual intake air flow rate Q, the dotted line indicates the change in the average air flow rate Q _a as indicated by an air flow sensor (1). That is, the output Q _a of air flow rate sensor (1) After changing the response characteristics of the sensor itself, at point A (time t _1), is accompanied by the temperature characteristic of the alumina substrate as shown in FIG. 7 (14) Te decreases responsiveness, the actual time delay until t ₂ the signal is obtained indicating the air flow rate occurs. This t _{1 to} t ₂
When time is not negligible compared to several 100m 1 second and t ₁ ~t ₂ o'clock 50m sec. Meanwhile, an air flow sensor (1)
The first calculated value C _Qmax along with the output Q _a of FIG.
The changes as shown by the dotted line, also the second calculation value C _Q changes as shown by the solid line is accompanied on the calculation shown in FIG. 3 (c). Accordingly, the correction coefficient C varies according to the deviation between the first and second calculated values C _Qmax and C _Q , as shown in FIG. 4 (c). it is possible to obtain the actual intake air flow rate Q signal representing the intake air flow rate that approximates the Q _a ^* by multiplying the output Q _a of).

FIG. 5 shows a time chart when the air flow rate changes gradually. The flow rate change per unit time ΔQ _a is smaller than the stepwise flow rate change shown in FIG. Accordingly, the correction ratio value ΔC is reduced, and the second
The calculation value C _Q becomes possible to gradually follow the first calculation value C _Qmax, this result, the air flow rate Q _a corrected ^* may be an actual value close to the air flow rate Q.

As described above, in the present invention, the first calculated value C _Qmax generated when the output is in an equilibrium state is stored in advance with respect to the output of the air flow sensor (1), and the first calculated value is calculated. depending on the magnitude relationship between the change in C _Qmax and the first calculated value C _Qmax, and together to form a second calculation value C _Q using a correction ratio had values ΔC which varies according to the flow rate change amount Delta] Q _a The correction coefficient C is calculated based on these calculated values, and the output of the air flow sensor (1) is multiplied by the correction coefficient C for correction. Therefore, the thermal effect of the holding member that supports the temperature-dependent resistance is eliminated. It is possible,
It is possible to improve the response characteristics when detecting the air flow rate.

In the above-described embodiment, the first calculation value is set in advance according to the output of the air flow sensor (1). However, the first calculation value is a value corresponding to the air flow rate. The first calculation value may be obtained from the boost value and the rotation speed or the throttle opening and the rotation speed used as parameters representing the air flow rate in the internal combustion engine. Although the air flow sensor of the internal combustion engine has been described as the thermal flow sensor, the temperature-dependent resistance and the temperature or temperature distribution of the holding member thereof deviate from the equilibrium value for the flow with respect to the change in the flow of the fluid, and the flow characteristic has Any thermal flow sensor that causes an error may be used. For example, the present invention can be applied to an EGR gas flow sensor for an internal combustion engine.

Further, as the signal processing method, in the embodiment, the flow rate value of the thermal air flow rate sensor is configured to be corrected, but the output value of the flow rate sensor or a value obtained by A / D converting the output value may be used. .

〔The invention's effect〕

As described above, according to the present invention, it is possible to correct the temperature-dependent resistance in the thermal type flow sensor and the thermal response delay of the holding member by the signal processing, and furthermore, the correction ratio that changes according to the flow rate change amount. Since the calculation is performed using the values, it is possible to measure the flow rate with good responsiveness by using an inexpensive thermal type flow sensor having a simple structure.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram showing a fuel injection device for an internal combustion engine according to one embodiment of the present invention, FIG. 2 is a block diagram showing a signal processor of the fuel injection device in FIG. 1, and FIG. 4 and 5 are time charts, FIG. 6 is a block diagram showing a thermal air flow sensor for an internal combustion engine, and FIG.
The figure shows the air flow rate change rate of the sensor when the air flow rate is changed stepwise, FIG. 8 is a view for explaining the thermal response delay of the sensor, and FIG. 9 is a schematic view showing a conventional temperature-dependent resistance. is there. In the figure, (1) is an air flow sensor, (3) is a throttle valve, (6) is an engine, (7) is an injector,
(8) is a crank angle sensor, (9) is a signal processor, _RH is a temperature-dependent resistor, (14) is an alumina substrate as a holding member,
C _Qmax indicates a first calculated value, C _Q indicates a second calculated value, and ΔC indicates a correction ratio value.

Claims (1)

(57) [Claims] A temperature-dependent resistor whose resistance value varies depending on temperature; and a holding member for supporting the temperature-dependent resistor.
A device provided with a thermal type flow sensor for detecting a flow rate of a fluid based on an output signal formed through the temperature-dependent resistance, wherein the flow rate of the fluid is in an equilibrium state where a steady state is maintained. A first calculation value, which is a correction coefficient corresponding to the flow rate, is set in advance, and the first calculation value is obtained from the flow value obtained from the output of the thermal flow sensor, and the flow rate of the fluid is determined. A correction coefficient that follows a change in the first calculated value when the value fluctuates, and
A second operation value for determining the following speed is determined by using a correction ratio value that changes according to the flow rate change amount per unit time, and the flow rate sensor is determined by a difference between the first and second operation values. A signal processing method for a thermal flow sensor, wherein the output of the thermal flow sensor is corrected.