JPH01195326A - Hot-wire air flowmeter - Google Patents

Abstract

PURPOSE:To detect the air quantity with sufficient accuracy even if the storage capacity required for a table is small by substructing in advance a prescribed value from the respective pulses of a detecting signal, thereafter, executing a table retrieval. CONSTITUTION:When a flip-flop 4 is set by a signal from a crank angle sensor 15, its output -Q terminal goes to LOW, a transistor Tr 7 is turned off and a transistor Tr 8 is turned on. On the other hand, when the flip-flop 4 is reset by an output of a comparator 3, the -Q terminal goes to HIGH, the Tr 7 is turned on and the Tr 8 is turned off. As a result, from the output Q terminal of the flip-flop 4, a pulse signal corresponding to the air flow rate Qa is obtained. Subsequently, the pulse signal of the Q terminal of the flip-flop 4 inputted to a microcomputer 23 through an arithmetic circuit 16, in which an air quantity Qa/an engine rotational frequency N is calculated by a retrieval arithmetic processing of a two-dimensional table, and used for controlling an engine fuel supply quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an intake air flow meter for an internal combustion engine such as a gasoline engine, and particularly to a hot wire air flow meter suitable for an automobile gasoline engine.

[Conventional technology]

In order to improve the performance of automobiles and fully comply with exhaust gas regulations,
Systems that detect the intake air flow rate and control the engine based on the detection results have been widely put into practical use.
In response to this, various types of air flow meters have been proposed, each of which is used on the continent, and one type of these is a hot wire air flow meter, a so-called hot wire air flow sensor.

By the way, since most electronic control devices for automobiles are composed of microcomputers, the detection signals of devices such as air flow meters that generate input signals need to be digitized and input to the control device. Therefore, as an air flow meter for automobiles, it is desirable that the output signal can be directly obtained in a form suitable for digitization. As shown in the figure, the current supplied to the hot wire is intermittent in synchronization with the rotation of the engine, and the time taken for the temperature of the hot wire to reach a predetermined value is a predetermined function of the air flow rate. A so-called pulse-width modulation air flow meter that directly converts the flow rate into a pulse width and outputs the pulse width has been disclosed. To explain with a diagram, in Fig. 2, 1 is a hot wire (hot wire probe).
2 is a temperature-compensated resistance wire (temperature probe) called a cold wire), 3 is a comparator, 4 is a flip-flop, 5 is a switch, and 6 is a constant current source. be.

The set terminal of the flip-flop 4 receives a so-called crank angle signal that is generated at each predetermined rotation angle each time the engine rotates.When this signal is input, the set terminal of the flip-flop 4 The output Q terminal of becomes HIGH level, and as a result, the switch 5 is turned on and current is supplied from the constant current source 6 to the hot wire 1. Therefore, the temperature of the hot wire 1 rises, and its resistance value increases.

When the heat 'fIA1 reaches a predetermined temperature, the comparator 3
The output of the flip-flop 4 becomes HIGH level, this signal is input to the reset terminal of the flip-flop 4, and the output Q terminal of the flip-flop 4 becomes LOW level. This turns off the switch 5 and cuts off the current supply to the hot wire l. This interruption of the current supply to the hot wire 1 continues until the next crank signal is input to the set terminal of the flip-flop, and during this time the hot wire 1 is cooled by the intake air flow.

Therefore, when the air flow rate is large, the degree to which the hot wire 1 is cooled during the heating current interruption period described above becomes stronger, and the current supply time required to heat the hot wire 1 to a predetermined temperature becomes longer. Become.

Therefore, the air flow IQ can be determined as a function of the current supply time T and the period T0 of the crank angle signal (corresponding to the transmission of the engine rotational speed N), as shown in FIG.

By the way, in terms of engine control, the air flow rate Q is less than 1.
Amount of air taken into the cylinder during the intake stroke Q, /N (
Q: Air flow rate, N: Engine rotation speed) are required. Figure 4 shows this air IQ.

The relationship between /N, current supply time T, and engine rotation speed N is shown.

Therefore, in order to obtain this air IQ,/N, in the prior art, a three-dimensional table shown in FIG. 4 is stored in a computer, and the current supply time T and engine rotational speed N are
The table shown in FIG. 4 was searched based on the above, and the air IQ, /N was determined by interpolation calculation.

[Problem to be solved by the invention]

As described above, the air quantities Q and /N required for engine control can be determined by interpolation from the three-dimensional table shown in FIG. However, storing the three-dimensional table shown in FIG. 4 in a computer requires an extremely large storage capacity. If the storage capacity is reduced, the error will increase when determining the air IQ,/N by interpolation calculation.

In the above-mentioned conventional technology, no consideration was given to the storage capacity required for this table, and there was a problem in that it was difficult to increase accuracy without increasing cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a hot-wire air flowmeter that can detect the air amount with sufficient accuracy even if the storage capacity required for a table for calculating the air amount is small.

Another object of the present invention is to provide a hot wire air flow meter that can easily accommodate variations in air amount detection characteristics based on variations in resistance value and surface area of hot wire probes.

[Means to solve the problem]

The above purpose is to use a hot-wire air flow meter that detects air flow rate as the pulse width of a pulse synchronized with the rotation of the engine. This is accomplished by subtracting , and searching the table based on the pulse signal after this subtraction to find the air IQ,/N. Another purpose is to be able to adjust the constant current supplied to the hot wire probe. This is achieved by configuring.

[Effect]

If a table search is performed using a pulse from which a predetermined constant value has been subtracted in advance, the contents of the table can be a two-dimensional table, which greatly reduces the increase in storage capacity and improves accuracy without increasing costs. Can be done.

Further, by adjusting the heating current of the hot wire probe, the detection characteristics can be changed, so that the detection characteristics can be made uniform despite variations in the hot wire probe.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The hot wire air flow meter according to the present invention will be explained in detail below using illustrated embodiments.

FIG. 1 shows an embodiment of the present invention, in which l
is a hot wire, 2 is a resistance wire, 3.11 is a comparator, 4 is a flip-flop, 7.8 is a transistor, 9, 10, 1
2, 14, 18.20 are resistors, 13.21 is variable resistor,
15 is a crank angle sensor, 16 is an arithmetic circuit, and 23 is a control microcomputer.

When the flip-flop 4 is set by the signal from the crank angle sensor 15, its output C terminal becomes LOW, which turns off the transistor 7 and turns off the transistor 8.
turns on.

On the other hand, when the flip-flop 4 is reset by the output of the comparator 3, the output terminal becomes II I G II, the transistor 7 is on, and the transistor 8 is off.

As a result, the transistor 8 functions as the switch 5 in the conventional example shown in FIG. 2, and a pulse signal whose pulse width changes depending on the air flow rate Q is obtained from the output Q terminal of the flip-flop 4.

By the way, when the transistor 8 is on, the base current of the transistor 8 is supplied from the comparator 11, and this comparator 11 is provided by dividing the voltage from a constant voltage source by a resistor 12 and a variable resistor 13. A predetermined reference voltage (2) is compared with the voltage effect IRQ caused by the resistor 9, and a current corresponding to the difference between them is output. As a result, the heating current I supplied from the power source to the hot wire (1) increases.
is to be made a constant current to a predetermined value determined by the reference voltage (2), so that the heating current I of the hot wire 1 is sufficiently made constant.

Next, the pulse signal of the output Q terminal of the flip-flop 4 is taken into the microcomputer 23 via the arithmetic circuit 16, in which the air amount Q/N is calculated by searching and calculating a two-dimensional table. The table is used to control the amount of fuel supplied to an engine, and the reason why it is possible to use a two-dimensional table instead of the three-dimensional table shown in FIG. 4 in the conventional example will be explained below.

The heat balance at the hot wire l is expressed by equation (11).

12Rt, ・T/TO=(a +b turtle)'(T, -T,
)-S・・・・・・・・・・・・ (1) Here, I: Current Rh flowing through hot wire 1: Resistance value of hot wire 1 T: Supply time of heating current I To: Period of crank angle signal a, b: Constant Q8: Air flow rate To: Temperature of hot wire 1 T1: Air temperature S: Surface area of hot wire 1 (In equation 11, when Ql-0, if T=T', then 1"Rh-'r'/'rO=a (Tw Ta)
・S・・・・・・・・・・・・ (2) From equations (1) and (2), 12Rh・(T-T')To#bi';W・(T, -T
,) ・s・・・・・・・・・・・・ (3) Substitute T o = i / N into equation (3).

Here, N: Engine rotation speed (T-T':) #b i / I''Rh・(T, -T
, ) ・S ・＜F77K＞ ylW・・・・・・・・・
...(4) Here, bi/IzR,. (T, -T
, ) ・Since S can be regarded as a constant, equation (4) becomes equation (5) below.

``・(T-T')ccσfu7 ・・・・・・・・・・・・
・(5) As shown in Figure 5, the relationship of this equation (5) is 2
It can be expressed as a dimensional table, and therefore, if the heating current supply time T, the air flow rate Q, and the heating current supply time 1' and the engine rotational speed N are known, then qK・(T-T ') and use the two-dimensional table in Figure 5 to determine air IQ.

/N can be calculated by interpolation calculation.

Here, the above-mentioned time T' can be determined in advance as a constant. Therefore, as in the above embodiment, the pulse signal obtained from the output Q terminal of the flip-flop 4 is transmitted to the arithmetic circuit 1.
6 and subtract a predetermined width corresponding to time T' from time T given by the width of this pulse signal, we get
The data (T-T') can be obtained by the microcomputer 23 and air IQ simply by using a secondary table.

/N can be calculated.

Returning to FIG. 1, as mentioned above, the pulse width of the signal ■ at the output Q terminal of the flip-flop 4 corresponds to time T, as shown in FIG.

Therefore, the signal input to the arithmetic circuit 16 is
, a capacitor 19, and a diode 17, and as shown in FIG. 6, a signal (2) whose rise is given a slope is obtained. Due to the action of the diode 17, a delay is added only to the rise. Next, this signal ■
is input to the comparator 22, and is compared with the constant voltage vf set by the resistor 20 and the variable resistor 21.
The signal shown in the figure becomes ◎. At this time, the constant voltage V is applied to the (-) input terminal of the comparator 22 so that the HIGH level time of the signal O corresponds to (T-T').
is adjusted by trimming the dividing resistors 20 and 21.

Therefore, from this arithmetic circuit 16, the pulse width is (T-T
') is obtained, and this is input to the microcomputer 23. At this time, in order to prevent the pulse width (T-T') from being influenced by the power supply voltage, the constant power supply for obtaining the constant voltage VL and the power supply for the flip-flop 4 should be made common. is desirable.

Next, (T-T') in the microcomputer 23
The procedure for obtaining Q, /N from will be explained with reference to FIG.

First, in step 30, a counter built in the computer 23 detects the high level of the output signal of the arithmetic circuit 16.
Count the time for the level. Next, in step 31, the engine rotation speed N is read. In step 32, a surface is determined from N. This calculation may be performed using a computer, or as shown in FIG. 8, a table of N and N may be stored in advance and N may be determined by table lookup. In step 33, N (T-
N(T-T′) is performed in step 34.
) is used to find Q and /N using the table shown in FIG.

Next, a description will be given of means for correcting variations in flowmeter characteristics due to variations in the resistance value and surface area of the hot wire 1.

As can be easily understood from equation (4), variations in the resistance value Rh, temperature T8, and surface area S of the hot wire 1 can be offset by adjusting the current value I. Therefore, the resistor 12 determines the reference voltage of the comparator 11 which determines the current value supplied to the hot wire 1.
．． 13 and adjust the current value I.

Furthermore, in order to reduce the variation in the flowmeter characteristics, as shown in FIG. 9, the air ffi (Q-/N) I.

Dividing resistors 12 and 13 determine the current value ■, and dividing resistor 20 of the arithmetic circuit 16 so that the value of (T-T') matches the reference characteristic at the two points of (Q, /N)2. All you have to do is trim .21 repeatedly.

An example of the detection characteristics according to the above embodiment is shown in FIG. In this example, T'-0 is used in equation (5), and the engine rotational speed N is 60ORPM and 600ORPM.
Although there is a slight deviation between the two, they are generally in agreement as a whole, and sufficient accuracy is obtained for practical use. In addition,
The slight discrepancy is because the values of T' and T in equation (4) change as the engine rotational speed N changes, but despite this, a good agreement is obtained. , T' and T appear in directions that cancel each other out.

By the way, in a normal automobile, high accuracy is required in air amount measurement under light load (low Q, /N).

Therefore, in order to create an example in which the air star measurement characteristics match when the engine rotational speed N is 60 ORPM and 600 ORPM in a region where air 11Qa/N is small, Fig. 10 is rewritten with the vertical axis f・(T+C). Figure 11 shows this. However, C is a constant with a plus or minus sign.

A flowchart of the calculation of air HQ, /N in this embodiment is shown in FIG. That is, first, read the engine speed N and the air flow meter signal T, and then read ".
T+C) is calculated, and the air IQ, /N is determined from the value of -■·(T+C) using the table shown in FIG.

Next, FIG. 13 shows another embodiment of the present invention, in which the above-mentioned
The calculation of T+C is performed by the time width adjustment circuit 24.

In the embodiment shown in FIG. 13, the arithmetic circuit 16 in the embodiment shown in FIG. 1 is simply changed to a time width adjustment circuit 24. Explain using.

The signal ■ inputted from the flip-flop 4 to the time width adjustment circuit 24 is connected to a diode 17, a resistor 18, and a capacitor 1.
9 is changed to the signal [F], and then the comparator 2
2, it is compared with constant voltage 7, and becomes [F] times signal F].

Therefore, the pulse width of this signal [F] is T+C.

Incidentally, the time width increment C can be arbitrarily adjusted by trimming the resistor 21 and the resistor 18.

Next, yet another embodiment of the present invention is shown in FIG.

The embodiment shown in FIG.
The present invention is applied to the hot wire anemometer drive circuit disclosed in Publication No. 16026, and a comparator 25 is added.
This makes it possible to use the same resistance value and shape as the heating wire 1 and the resistance wire 2 for temperature detection.

When a crank angle signal is input to the set terminal of the flip-flop 4, its output σ terminal becomes a LOW level, and the transistor 7 is turned off and the transistor 8 is turned on. As a result, a current is supplied to the hot wire l, the temperature rises and the resistance increases. When the comparator 3 detects that the resistance value of the hot wire 1 has reached a predetermined value, an I (IGH level signal) is input to the R terminal of the flip-flop 4. As a result, each output The terminal becomes HIGH level, transistor 7 is turned on, transistor 8 is turned off, and current supply to hot wire 1 is cut off.

Therefore, in this embodiment as well, a pulse signal whose pulse width represents the time T is obtained from the output Q terminal of the flip-flop 4, as in the embodiment shown in FIG. By providing the time width adjustment circuit 24), the microcomputer 23 can calculate the air fiQ,/N simply by using a two-dimensional table.

〔Effect of the invention〕

According to the invention, memory records to be used for the table j1
7. It requires less capacity and has the advantage of being able to detect air IQ, /N at low cost.

Further, according to the present invention, even if there are variations in the heat wires used, detection characteristics with sufficiently suppressed variations can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the hot wire air flow meter according to the present invention, Fig. 2 is a circuit diagram of a conventional example, Fig. 3 is a waveform diagram for explaining operation, and Fig. 4 is a three-dimensional table. 5 is an explanatory diagram of a two-dimensional table, FIG. 6 is a waveform diagram for explaining the operation, FIG. 7 is a flowchart for explaining the operation, and FIG. 8 is a diagram for explaining the operation.
FIG. 9 is an explanatory diagram of the dimensional table, FIG. 9 is an explanatory diagram of the trimming operation, and FIGS. 10 and 11 are characteristic diagrams of one embodiment, respectively.
FIG. 12 is a flowchart for explaining the operation, FIG. 13 is a circuit diagram showing another embodiment of the present invention, FIG. 14 is a waveform diagram for explaining the operation, and FIG. 15 is yet another embodiment of the present invention. FIG. 3 is a circuit diagram showing an example. 1...Hot wire (hot wire probe), 2...
Resistance wire (temperature probe), 3, 11.22...
Comparator, 4...Flip-flop, 15
...... Crank angle sensor, 16... Arithmetic circuit, 23... Engine Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Figure 9 IN@(T-7 Figure 10 Qo/2N Figure 11 0 (1/2N Figure 12 Figure 14 Hikiga) ■ ■ [

Claims (1)

[Claims] 1. By intermittent supply of heating current to the hot wire for flow rate detection in synchronization with engine rotation, a signal for flow rate detection is directly generated as a pulse width signal, and this pulse width signal is In a hot-wire air flow meter that detects the flow rate per unit engine rotation by searching a predetermined data map based on the data map, a signal processing circuit is provided that adds or subtracts a predetermined constant value from the width of each pulse of the pulse width signal. A hot wire air flowmeter characterized in that the data map is searched based on the output signal of the signal processing circuit. 2. In claim 1, the signal processing circuit comprises an integrating circuit that receives the pulse width signal as an input, and a comparison circuit that receives the output of the integrating circuit and a predetermined reference voltage as inputs. , a hot wire air flowmeter characterized in that the reference voltage is configured to be adjustable. 3. In claim 1, a comparison circuit is provided for detecting the magnitude of the heating current supplied to the heating wire and comparing it with a predetermined reference value, and the heating current is adjusted according to the output of the comparison circuit. A hot wire air flow meter configured to be controlled. 4. The hot wire air flow meter according to claim 3, wherein the predetermined reference value is configured to be adjustable.