JPH0615838B2 - Engine fuel controller - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fuel control device for an engine.

[Prior art]

Recently, in a vehicle engine, there is a tendency to employ a fuel control device that supplies fuel in accordance with the output of an intake air amount sensor. Various types of intake air amount sensors used in this type of fuel control device have been conventionally known. One example is a hot-wire intake air amount sensor, which is called a hot wire. It is intended to detect the intake air amount by utilizing the heat radiation phenomenon of the so-called heat ray. By the way, with this hot-wire intake air amount sensor, if the operating time becomes long and foreign matter such as dust in the air adheres to the hot wire, the heat radiation characteristics of the hot wire will change and the detection accuracy will decrease. It is required to deal with deterioration.

As a method of coping with such deterioration of the hot wire with time, conventionally, as shown in JP-A-55-139939, the zero point output of the intake air amount sensor in the initial state of the engine is stored in a memory. Then, there is a method of calculating the actual intake air amount from this and the output of the intake air amount sensor in the normal operating state of the engine.

However, there is generally a relationship between the output of the hot-wire intake air amount sensor and the actual intake air amount as shown by the curve a in FIG. 7, and when the intake air amount is small, the sensor output changes abruptly. It is difficult to accurately detect the zero output of the sensor as described above, and therefore the method described in the above-mentioned prior art may cause a substantial error.

Further, as another method for dealing with the deterioration with time of the hot wire, conventionally, the hot wire is heated at a predetermined timing to burn off foreign matter adhering to the hot wire.
There is a method of keeping the heat radiation characteristics of the hot wire constant by turning off), that is, by burning.

However, in this burn-off processing method, oil blown back from the engine side and fine stones in the air may adhere to the hot wire together,
Since such a foreign matter cannot be burned off even if it is heated, the heat dissipation characteristics of the hot wire cannot be kept constant, and it is not possible to completely deal with deterioration with time of the hot wire. Therefore, since the foreign matter attached to the hot wire acts as a heat insulating material, the heat dissipation is deteriorated, and the amount of air detected by the hot wire becomes smaller than the actual intake air amount.

[Object of the Invention]

In view of the above problems, the present invention aims to provide an engine fuel control device capable of guaranteeing detection accuracy by completely dealing with deterioration of a hot wire over time.

[Structure of Invention]

The inventors of the present invention have earnestly studied to develop a method capable of completely coping with the above-described deterioration of the hot wire over time, and as a result, if the above-mentioned burn-off process and the correction of the sensor output are successfully combined, We have found that we can deal with deterioration completely.

That is, when the burn-off treatment is performed on the hot wire as described above, the hot wire has a high temperature of about 1000 ° C., but after the treatment, the temperature of the hot wire is different from that of the hot wire and the atmosphere. It drops sharply due to heat conduction between them. The degree of temperature decrease at this time depends on the amount of foreign matter that remains on the hot wire and cannot be burned off, and decreases as the amount of foreign matter increases. Therefore, if the rate of temperature decrease with time of the hot wire immediately after the burn-off is detected, the deterioration can be known due to the adhesion of foreign matter that cannot be burned off,
By using this temperature decrease rate, the sensor output can be corrected to an accurate value.

Therefore, according to the present invention, as shown in the functional block diagram of FIG. 6, fuel is supplied by the fuel control means 24 in accordance with the output of the hot-wire intake air amount sensor 25, and the hot-wire type is supplied by the heating means 20. While heating the hot wire part of the intake air amount sensor 25 when the engine is stopped, the deterioration detecting means 21 detects the temperature decrease rate of the hot wire part after heating with time, and the deterioration correction amount setting means 22 detects the temperature decrease rate. Set a larger amount of deterioration correction as it gets smaller,
The deterioration correction unit 23 corrects the output of the hot-wire intake air amount sensor 25 according to the output of the deterioration correction amount setting unit 22.

〔Example〕

Prior to the description of the embodiments of the present invention, the principle of the hot-wire intake air amount sensor will be described first.

When a current is passed through the resistance wire to heat it and the resistance wire is placed in a gas, heat is taken away by the flow of the gas, and the value of decrease in the resistance wire changes. The hot-wire intake air amount sensor measures the flow velocity of gas by utilizing this change in resistance value.

The cooling law of the hot wire is shown by the following equation (1) by King.

H: Amount of heat lost from the heat wire every second K: Thermal conductivity of gas T: Temperature of heat wire To: Temperature of gas l: Length of heat wire d: Diameter of heat wire ρ: Density of gas Cp: Constant pressure specific heat of gas v: Gas The flow rate of is calculated by keeping the heat wire of a given size at a constant temperature.
(1) can be transformed into the following equation (2).

C1, C2: Constants On the other hand, the amount of heat H lost from the heating wire is equal to the amount of heat I ² · R / J generated by heating with an electric current, and the formula (2) is expressed by the following formula (3).

I: current value flowing in hot wire R: resistance value of hot wire J: work equivalent of heat Here, when the hot wire is kept at a constant temperature as described above, both J and R become constants, and equation (3) is given by the following equation (4). Can be written as

C3: Constant Qm: Mass flow rate However, Qm = S · ρ · v S: Pipe area of heat wire The mass flow rate can be measured by detecting the current flowing through the heat wire from this equation (4).

Next, an embodiment of the present invention will be described with reference to the drawings.

1 and 2 show an engine fuel control apparatus according to an embodiment of the present invention. In the drawing, reference numeral 1 denotes an engine, a fuel injection valve 4 is arranged in a downstream side of a throttle valve 3 in an intake passage 2 of the engine 1, and an upstream end of the intake passage 2 reaches an air cleaner 5. Exhaust passage 6
An O ₂ sensor 7 is provided in the.

A hot-wire intake air amount sensor 8 is arranged downstream of the air cleaner 5 in the intake passage 2. The hot-wire intake air amount sensor 8 comprises a bridge 9 and a control circuit 10 for controlling the energization of the bridge 9, and the bridge 9 is a hot wire (heat-wire portion) 1 arranged in the intake passage 2.
1, bridge resistors 12, 13, 14 and temperature compensation resistor 1
It is composed of 5.

In FIG. 1, 16 is a rotation speed sensor for detecting the engine rotation speed, 17 is a water temperature sensor for detecting the water temperature of the engine cooling water, 18 is an engine control circuit including a microcomputer, etc. Sensor 7,8,1
The fuel injection control is performed by receiving the outputs of 6 and 17 and creating a fuel injection pulse and adding it to the fuel injection valve 4. Further, the engine control circuit 18 controls the control circuit 10 of the hot-wire intake air amount sensor 8 when the burn-off processing condition is satisfied.
A burn-off signal B is applied to the hot wire 11 to heat the hot wire 11 and burn off foreign matter adhering to the hot wire 11. Further, the engine control circuit 18 detects the temperature decrease rate of the hot wire 11 with the lapse of time after completion of the burn-off, and sets a larger deterioration correction amount as the temperature decrease rate becomes smaller, and in the fuel injection control thereafter. Control is performed to correct the output of the sensor 8 with this deterioration correction amount.

In the above structure, the control circuit 10 is the heating means 20 shown in FIG. 6, and the engine control circuit 18 is the deterioration detection means 21, deterioration correction amount setting means 22, deterioration correction means shown in FIG. 23 and the fuel control means 24 are realized.

Next, the operation will be described with reference to FIGS. Here, FIG. 3 shows changes in sensor outputs a and b after burn-off after deterioration and before deterioration, FIG. 4 is a flowchart of correction operation of sensor output, and FIG. 5 is a timing chart of correction operation of sensor output. Show.

When the engine operates, the oxygen concentration in the exhaust gas is measured by the O ₂ sensor 7, the intake air amount is measured by the intake air amount sensor 8, the engine speed is measured by the rotation speed sensor 16, and the water temperature of the engine cooling water is measured by the water temperature sensor 17. Detected, each sensor 7,8,1
The signals 6 and 17 are applied to the engine control circuit 18.
When the engine is cold, the engine control circuit 18 obtains the basic fuel injection pulse from the engine speed and the intake air amount, and the basic fuel injection pulse is corrected according to the output of the water temperature sensor 17. The actual fuel injection pulse is applied to the fuel injection valve 4. As described above, during cold, the amount of fuel corrected according to the cooling water temperature is injected and supplied.

Further, after the engine is warmed up, when the engine is in the middle or low load state, the basic fuel injection pulse in the engine control circuit 18 depends on the output of the Q ₂ sensor 7 and is lean when the air-fuel ratio is rich, When lean, it is corrected to be rich, and this is added to the fuel injection valve 4 as an actual fuel injection pulse. In this way, the fuel injection amount is feedback-controlled when the load is medium or low.

Further, after the engine is warmed up, when the engine is in a high load state, the engine control circuit 18 creates the basic fuel injection pulse, which is directly applied to the fuel injection valve 4 as an actual fuel injection pulse. . Thus, at high load, the fuel injection amount is controlled according to the operating state of the engine.

Here, the operation of the intake air amount sensor 8 will be described. In the intake air amount sensor 8, the power source I flowing through the hot wire 11 is feedback-controlled so as to keep the temperature change TB of the hot wire 11 from the intake air temperature TA constant,
The intake air amount Q is measured by detecting the current I as the voltage VQ by the resistor 14.

The resistance value RB of the hot wire 11 and the resistance value RC of the temperature compensating resistor 14 have the relationships as shown in equations (5) and (6), respectively. Here, the resistance value of the bridge resistor 12 is R1, and RB,
The resistance temperature coefficient of (RC + R1) is made equal.

RB∝TA + TB (5) (RC + R1) ∝TA (6) Therefore, controlling the temperature rise TB at the intake air temperature TA to be constant is to control the current I so as to satisfy the equation (7). Is. Here, the resistance values of the bridge resistors 13 and 14 are R2 and R3.

(RC + R1): R2 = RB: R3 (7) In FIG. 2, the control circuit 10 controls the voltage Vo so that the voltage VQ = VR can achieve the above. Here, the resistance value is set so that I >> i.

Then, when the fuel injection control is being performed as described above, the key switch is turned off, for example, 5 seconds have passed, and if the burn-off processing condition that the engine is stopped without intake air flow rate is satisfied, the engine control is performed. A burn-off signal B is applied from the circuit 18 to the control terminal 10a of the control circuit 10 of the intake air amount sensor 8, a large current flows from the control circuit 10 to the bridge 9, and the hot wire 11 is heated.
The foreign matter attached to the hot wire 11 is burned off.

When the burn-off process is completed at time T1 as shown in FIG. 5 (a) (see steps 30 and 31 in FIG. 4), as shown by curves a and b (curve b is in the initial state) in FIG. The temperature of the hot wire, and thus the sensor output VQ, drops to room temperature at a speed according to the deterioration state. At that time, the engine control circuit 18 starts the correction operation as shown in FIG. 5 (b), and the voltage VQ between the output terminals 8a and 8b of the sensor 8 is changed to the reference voltage VST as shown in FIG. 5 (c). T2 is measured until the time reaches (see steps 32 to 35 in FIG. 4), and at time T2, FIG.
When the measurement is completed as shown in FIG. 5, C = K · t1 / t2 from the measured value t2 and the measured value t1 similarly obtained in the initial state (without deterioration) as shown in FIG. 5 (d).
Correction coefficient (deterioration correction amount) using the equation (K: constant)
Is calculated, and the value in the correction coefficient memory is rewritten with this value (see step 37 in FIG. 4).
The power is turned off in step 3 (step 38 in FIG. 4).
reference).

Therefore, in the subsequent fuel injection control, the output VQ of the intake air amount sensor 8 is the correction coefficient C (= Kt) in the memory.
Multiply correction is performed with 1 / t2), and the fuel injection pulse is created using this. As a result, even if the foreign matter attached to the hot wire 11 impedes heat dissipation and the intake air amount is detected to be smaller than the actual amount, this can be corrected.

In the apparatus of the present embodiment as described above, the foreign matter of the hot wire is burned off by the burn-off treatment, so that the deterioration of the hot wire can be suppressed. For hot wire deterioration due to foreign matter that does not burn out, the temperature decrease rate after burn-off is checked to detect the deterioration state and the sensor output is corrected accordingly, so the sensor output can be accurately calibrated. The detection accuracy of the intake air amount can be guaranteed for a long time. In the present embodiment, the deterioration is detected by the time to reach the reference voltage, but the deterioration is similarly detected by the voltage when a predetermined time has elapsed after burn-off or by the rate of decrease of the voltage per unit time. Can be done.

〔The invention's effect〕

As described above, according to the engine fuel control device of the present invention, the hot wire intake air amount sensor is heated, the temperature decrease rate of the hot wire after heating is detected, and the sensor output is corrected accordingly. Therefore, there is an effect that the detection accuracy can be guaranteed for a long time.

[Brief description of drawings]

FIG. 1 is a block diagram of a fuel control system for an engine according to an embodiment of the present invention, FIG. 2 is a block diagram of a hot-wire intake air amount sensor in the system, and FIG. 3 is a diagram for explaining the operation of the system. FIG. 4 is a diagram showing a change with time of the sensor output after burn-off, FIG. 4 is a diagram showing a flowchart for explaining a correction operation of the sensor output in the above apparatus, and FIG.
(d) is a diagram showing a timing chart of the burn-off signal B, the correction period, the end of measurement, and the rewriting of the correction coefficient in the correction operation of the sensor output. FIG. 6 is a functional block diagram showing the configuration of the present invention. FIG. 4 is a diagram showing a relationship between an intake air amount and a sensor output for explaining a drawback of the conventional device. 8 ... Heat ray type intake air amount sensor, 10 ... Control circuit, 1
DESCRIPTION OF SYMBOLS 1 ... Hot wire (hot wire part), 18 ... Engine control circuit, 20 ... Heating means, 21 ... Deterioration detection means, 22
... Deterioration correction amount setting means, 23 ... Deterioration correction means, 24
...... Fuel control means 25 ...... Hot wire type intake air amount sensor.

Claims (1)

[Claims] 1. A fuel control means for supplying fuel according to an output of a hot-wire intake air amount sensor, and a heating means for heating a hot-wire portion of the hot-wire intake air amount sensor when the engine is stopped.
Deterioration detection means for detecting a temperature decrease rate of the hot wire portion after heating with time, and deterioration correction amount setting means for receiving an output of the deterioration detection means and setting a larger deterioration correction amount as the temperature decrease rate decreases. And a deterioration correction means for correcting the output of the hot-wire intake air amount sensor according to the output of the deterioration correction amount setting means.