JPS58187531A - Fuel injection quantity controller of internal- combustion engine - Google Patents

Abstract

PURPOSE:To prevent a fuel-air mixture from diluting, by a method wherein an injection quantity is fixed to a predetermined point in case a detecting value of a suction quantity is clamped at its detectable maximum value by lowering battery voltage to be fed to hot-wire type air flow meter. CONSTITUTION:A suction quantity signal Q by a hot-wire type air flow meter, an ignition signal SF from an ignition coil and a water temperature signal SW are applied to an operating circuit 1, and a basic fuel injection quantity TP is computed through a number of revolutions N of an engine to be obtained by the suction quantity signal Q and the ignition signal SF first of all in a basic injection quantity operating circuit 12. The injection quantity TP is applied to a fuel injection valve driving circuit 5 through a directional control circuit 17 after correction by a correcting circuit 13 through a water temperature signal SW. On this occasion, the suction quantity signal Q is compared 16 with a reference value Vr varying corresponding to a change of the maximum output value of the air flow meter 2 and a fixed pulse signal PC by a fixed pulse generator 14 is applied to a driving circuit 5 by changing the direction control circuit 17 when the signal Q is in Q>=Vr.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a fuel injection amount control device for an internal combustion engine, which controls the fuel injection amount in accordance with the intake air amount and engine rotational speed detected by a hot wire air flow meter.

As a conventional device of this type, for example, there is one described in "Isuzo Technical Report" No. 66 published by Isuzo Jidosha Co., Ltd. on June 1, 1980.

To briefly explain the outline with reference to FIGS. 1 and 2, the arithmetic circuit 1 generates an intake air amount signal Q according to the intake air amount from the hot wire air flow meter 2 installed on the upstream side of the intake manifold IM. , and the engine rotational speed N detected using the ignition signal SF output from the ○ terminal of the ignition coil 6, the basic fuel injection amount TP- is changed to -Q-(K
゛Calculate constants.

Next, this calculation circuit 1 calculates the calculated basic fuel injection amount TP.
The water temperature signal Sw from the water temperature sensor 4 attached to the water jacket WJ of the engine EG and the throttle valve TV
After obtaining the optimum fuel injection amount by performing a correction calculation based on the signal indicating the operating state of the engine EG, such as the opening degree of
It is output to the fuel injection valve drive circuit 5 in synchronization with the injection timing detected based on.

Thereby, the fuel injection valve drive circuit 5 controls the fuel injection valve 6
is opened for a time corresponding to the pulse width of the pulse signal PN, and an appropriate amount of fuel is injected and supplied to the engine EG.

The calculation circuit 1 also calculates the basic fuel injection amount Tp calculated previously.
The ignition timing is determined based on the ignition timing and engine speed N, and the power transistor 7 is turned off to cut off the primary current of the ignition coil 3 at a timing corresponding to the ignition timing. Generates high voltage on the next side.

This high voltage is then distributed by the distributor 8 and sequentially guided to the spark plugs 9 provided for each cylinder of the engine EG, thereby causing ignition.

In addition, in FIG. 1, 10 is an alternator.

The air is regulated and supplied to the battery 11 by a crank pulley attached to the crankshaft of the engine EG via a fan belt.

Further, the voltage VB of the battery 11 is determined by the calculation circuit 1° hot wire air flow meter 2. The voltage is supplied to the ignition coil 3, etc., and serves as a driving voltage for them.

The hot wire air flow meter 2 is constructed as shown in FIG. 2 and operates as follows.

That is, intake air flows around the hot wire probe H made of, for example, platinum wire, which together with the resistors R1 to R3 constitutes a Wheatstone bridge, and heat is removed from the hot wire probe H according to the flow rate, and its resistance value changes.

When the resistance value of the hot-wire globe H changes, the balance of the wheat strike/bridge collapses, and the unbalanced voltage is input to the differential amplifier A configured by the operational amplifier OP and the feedback resistor R6 via the input resistors R4 and R5. Ru.

The differential amplifier A outputs an intake air amount signal Q corresponding to the input unbalanced voltage to the base of the transistor Tr via the resistor R7, thereby changing the heating current flowing through the hot wire probe H.

In this way, it acts so that the resistance value (temperature) of the hot wire probe H becomes constant, that is, the unbalanced voltage becomes zero, so if the amount of intake air flowing around the hot wire probe H changes, the intake air An intake air amount signal Q corresponding to the amount can be obtained from the differential amplifier A.

The differential amplifier A supplies a bias signal to the transistor Tr so that a predetermined heating current flows through the hot wire probe H even when the unbalanced voltage is zero.

In addition to the output of the differential amplifier A, the intake air amount signal Q may also be obtained by detecting a voltage drop due to the heating current of the hot wire probe H, for example.

By the way, the maximum value of the heating current flowing through the hot wire probe H of this hot wire type air flow meter 2 is the same as that of the battery 1 shown in FIG.
It is determined by the voltage VB of 1.

Therefore, the maximum intake flow rate Qmax that can be detected by the hot wire air flow meter 2 also changes depending on the battery voltage VB as shown in FIG.
If a conventional hot wire air flow meter 2 as shown in the figure is used, for example, when the voltage regulator in the alternator breaks down and the battery voltage VB decreases, the engine E
The maximum detectable intake amount Qrn when the intake amount of G is 9
Even if it is larger than ax, the actual intake air amount is detected as Qrnax.

Therefore, the arithmetic circuit 1 calculates a fuel injection amount that is smaller than the actually required amount of fuel, which not only causes the mixture to become lean, resulting in a decrease in output and a tendency to misfire, but also leads to unburned fuel due to misfire. If the air-fuel mixture is discharged as it is,
There was also the problem that the catalyst that purifies exhaust gas could burn out.

As a solution to this problem, the circuit constants of the hot-wire air flow meter 2 should be selected so that the decrease in battery voltage VB can be anticipated in advance and the output corresponding to the engine's maximum intake amount can be obtained even if the voltage decreases. It is possible to leave it there.

However, doing so has the following disadvantages and is not practical.

That is, the maximum energy generated by the hot wire probe H is VB /r, where r is the resistance value of the hot wire probe H.

Therefore, even when the battery voltage VB decreases, VB/r
In order to prevent the resistance value r from becoming less than a required value, there are two methods: making the resistance value r relatively small or making the set temperature of the hot wire probe H relatively low.

In order to reduce the resistance value r, it is possible to increase the wire diameter of the hot wire probe H or shorten the wire length.

However, increasing the diameter of the wire not only significantly increases costs because platinum is expensive, but also deteriorates the thermal conductivity within the hot wire, resulting in poor detection response and difficulty in detecting minute amounts of intake air. It becomes difficult.

′! Furthermore, if the wire length is shortened, the surface area of the hot wire that is in contact with the flow of intake air becomes smaller, and detection accuracy deteriorates when the flow of intake air is uneven.

Furthermore, the accuracy with which the set temperature of the hot wire probe H is lowered becomes worse.

The present invention has been made in view of the above background, and includes a fuel injection amount control device for an internal combustion engine as described above, in which a detection output of a hot wire air flow meter and a battery that supplies power to the hot wire air flow meter are used. When the detection output exceeds the reference value, it is determined that the correct amount of intake air has not been detected, and the fuel injection amount is set to a predetermined constant value. The aim is to solve the conventional problems by fixing the

Hereinafter, embodiments of the present invention will be described with reference to FIG. 4 of the drawings.

FIG. 4 is a block diagram of a main part showing one embodiment of the present invention, and corresponds to the arithmetic circuit 1 in FIG.

In the figure, a basic injection amount calculation circuit 12 receives an intake air amount signal Q from the hot wire air flow meter 2 shown in FIG. 1, and an ignition signal SF.
-Q- (K: constant) is calculated for the basic fuel injection amount TP- based on the engine rotational speed N detected using .

The correction circuit 16 calculates the basic fuel injection amount Tp calculated in the basic injection amount calculation circuit 12 based on the water temperature signal Sw from the water temperature sensor 4 shown in FIG. After performing a correction calculation to obtain the optimum fuel injection amount, a pulse signal PN having a pulse width corresponding to the fuel injection amount is output in synchronization with the injection timing detected based on the ignition signal SF.

The fixed pulse generator 14 generates a fixed pulse signal P having a pulse width corresponding to the amount of fuel injection required at the maximum load of the engine, for example.
c is output in synchronization with the injection timing detected based on the ignition signal SF.

The reference value output circuit 15 receives the voltage value VB of the battery 11 shown in FIG. 1 and outputs the maximum output value Qmaz of the hot wire air flow meter 2 determined as shown in FIG.
A reference straight line Vr that changes in response to changes in is output.

However, this reference value Vr is always the maximum output value Qrnax
For example, the value is set to be about 10 mV smaller.

The comparator 16 receives the reference value Vr from the reference value output circuit 15 and the first . The comparator 16 inputs and compares the intake air amount signal Q from the hot wire airflow meter 2 shown in FIG. 2, and outputs a signal e which becomes a high level "H" when Q≧Vr. A predetermined hysteresis is provided to prevent false detection.

The switching circuit 17 is configured so that the output of the comparator 16 is at a low level.
", that is, when the high level signal e is not input, 1) - c is connected, and when the high level signal e is input, the electronic switch switches so that a - c is connected. Become.

Therefore, the switching circuit 17 receives the signal e (・
When the signal e is not present, the pulse signal PN from the correction circuit 16 is output, and when the signal e is input, the fixed pulse signal Pc from the fixed pulse generator 14 is output to the fuel injection valve drive circuit 5 shown in FIG.

Therefore, if the intake air amount signal Q from the hot-wire air flow meter 2 is smaller than the reference value Vr determined corresponding to the battery voltage VB at that time, the pulse signal PN indicating the fuel injection amount determined according to the intake air amount signal Q is Since the fuel injection valve 6 shown in FIG. 1 is opened, fuel is injected according to the engine required value.

Furthermore, when the intake air amount signal Q from the hot wire airflow meter 2 exceeds the reference value Vr, the fuel injection valve 6 is opened by the fixed pulse signal Pc from the fixed pulse generator 14 instead of the pulse signal PN. Therefore, the required amount of fuel is injected at maximum engine load.

Therefore, even if the actual amount of intake air exceeds the maximum amount of intake air that can be detected by the hot-wire air flow meter at that time due to a drop in battery voltage, the air-fuel mixture will not become lean as in the conventional case. This eliminates the possibility of a drop in output, loss of stability due to misfire, or risk of unburned air-fuel mixture being discharged as it is and causing the catalyst to become sideways.

In FIG. 4, the fixed pulse generator 114 and the switching circuit 17 constitute fuel injection amount fixing means.

Furthermore, in the embodiment described above, nothing may be output to the fuel injection valve drive circuit 5 while the purpose is only to prevent the catalyst from being horizontally damaged due to the discharge of unburned air-fuel mixture.

In this case, fuel injection is cut off, resulting in a decrease in output, but it is possible to prevent horizontal damage to the catalyst due to discharge of unburned air-fuel mixture, as in the above embodiment.

As explained above, in the fuel injection amount control device for an internal combustion engine according to the present invention, when the voltage of the battery that supplies power to the hot wire air flow meter decreases, the detected value of the intake air amount changes to the maximum detectable value at that time. In cases where the fuel injection amount is clamped, the fuel injection amount is fixed at a predetermined constant value.
The air-fuel mixture does not become lean, and therefore the problems caused by this can be prevented.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an example of a conventional fuel injection amount control device for an internal combustion engine, Fig. 2 is a circuit diagram showing an example of the configuration of the hot wire type air flow meter in Fig. 1, and Fig. 3 is a hot wire type air flow meter. A diagram showing the relationship between the maximum value of the intake air amount that can be detected by the air flow meter and the battery voltage. FIG. 4 is a block diagram of main parts showing an embodiment of the present invention. 1... Arithmetic circuit 2... Hot wire air flow meter 5... Fuel injection valve drive circuit 6... Fuel injection valve 1
2... Basic injection amount calculation circuit 13... Correction circuit 14
... Fixed pulse generator 15 ... Reference value output circuit 16 ... Comparator 17
...switching circuit

Claims (1)

[Claims] 1. In a fuel injection amount control device for an internal combustion engine that controls the fuel injection amount according to the intake air amount and engine rotation speed detected by a hot wire air flow meter, the voltage of a battery that supplies power to the hot wire air flow meter is a reference value output means for outputting a reference value that changes accordingly; and a reference value output from the reference value output means and a detected output of the hot wire air flow meter are compared, and the detected output is equal to or greater than the reference value. A fuel for an internal combustion engine, characterized in that the comparison means outputs a signal when the comparison means outputs the signal, and the fuel injection amount fixing means fixes the fuel injection amount to a predetermined constant value when the comparison means outputs the signal. Injection amount control device.