JPH0692753B2 - Fuel supply control method for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel supply control method for an internal combustion engine, and more particularly to a plurality of fuel injection valves provided one upstream and one downstream of a throttle valve in the middle of an intake pipe. The present invention relates to a control method when fuel is supplied to the cylinder.

(Technical Background of the Invention and Problems Thereof) As a conventional fuel supply control device of a type in which fuel is distributed and supplied from a common fuel injection valve to a plurality of cylinders of an internal combustion engine, an intake pipe collecting portion is provided when an engine has a medium or high load. There is a type in which fuel is supplied by a fuel injection valve provided on the upstream side of an upstream throttle valve, while fuel is supplied by an auxiliary fuel injection valve provided on the downstream side of the throttle valve when the engine is under a low load (Japanese Patent Laid-Open Publication No. 2000-242242). 47-35422). The auxiliary fuel injection valve having excellent atomization characteristics is used to ensure the distribution of a small amount of fuel to each cylinder when the engine load is low.

According to this method, the fuel supply to the cylinder is not hindered by the throttle valve even during the low load operation in which the throttle valve is fully closed or the opening close to this is achieved.
That is, the responsiveness of fuel supply is improved.

When the engine temperature is high, the atomization of fuel in the intake pipe is good, so in order to improve the responsiveness of the fuel supply to the cylinder and to ensure the control accuracy of the minute flow rate, the discharge amount from the fuel injection valve upstream of the throttle is maintained as usual. It is desirable to inject the fuel from an auxiliary fuel injection valve having a small size.

However, when the engine temperature is low, the injection time of the auxiliary fuel injection valve is long because the fuel amount is increased in the cold state, and the temperature of the intake pipe is also low. Fuel atomization worsens. In order to avoid this deterioration of fuel atomization, if the fuel is injected from the auxiliary fuel injection valve installed on the downstream side of the throttle valve, which is a position near the collecting portion of the intake pipe, the distribution of fuel to a plurality of cylinders deteriorates. There was a problem.

Further, in the above-described conventional fuel supply control method, when the engine temperature is low such as during cold operation, the fuel injection valve that supplies fuel when the low load operating state transitions to the high load operating state is the auxiliary fuel downstream of the throttle valve. When changing from the injection valve to the normal fuel injection valve upstream of the throttle valve, there is a problem that the amount of fuel actually supplied to the engine varies. That is,
In this case, when the auxiliary fuel injection valve downstream of the throttle valve is performing maximum fuel injection, this valve immediately interrupts this fuel injection, and the fuel injection valve upstream of the throttle valve suddenly releases a large amount of fuel. Will start. At this time, the throttle valve and the inner wall of the intake pipe near the throttle valve suddenly become wet due to fuel adhering from a dry state, and the amount of the adhering fuel increases as the temperature of the intake wall pipe becomes lower. As the time elapses, the amount of fuel actually supplied to the engine fluctuates more. As a result, there arises a problem that the accuracy of the fuel supply control deteriorates when the auxiliary fuel injection valve is switched to the normal fuel injection valve.

(Object of the Invention) The present invention has been made in view of the above circumstances, and when the engine temperature is low, the distribution of fuel to a plurality of cylinders becomes poor, or the auxiliary fuel injection valve changes to a normal fuel injection valve. An object of the present invention is to provide a fuel supply control method for an internal combustion engine in which a problem such as a change in fuel supply amount due to switching does not occur.

(Structure of the Invention) In order to achieve the above object, in the present invention, a fuel injection valve installed on each of an upstream side and a downstream side of a throttle valve upstream of an intake pipe collecting portion of an internal combustion engine including a plurality of cylinders. And a fuel supply control method for an internal combustion engine, which supplies fuel from an auxiliary fuel injection valve according to an operating state of the engine, when the engine temperature is lower than a predetermined temperature, fuel is supplied by a fuel injection valve upstream of the throttle valve. The fuel supply control of the internal combustion engine is characterized in that when the engine temperature is higher than the predetermined temperature and the throttle valve opening is equal to or smaller than the predetermined opening, fuel is supplied by an auxiliary fuel injection valve downstream of the throttle valve. A method is provided.

Embodiments of the Invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram of a fuel supply control device to which the method of the present invention is applied. Reference numeral 1 indicates, for example, an internal combustion engine of four cylinders, and an intake pipe 2 is connected to the engine 1 via an intake manifold. There is. A throttle body 3 is provided upstream of the collecting portion of the intake pipe 2, and a throttle valve 3'is provided inside. A throttle valve opening (θ _TH ) sensor 4 is connected to the throttle valve 3 ′ so that the valve opening of the throttle valve 3 ′ is converted into an electric signal and sent to an electronic control unit (hereinafter referred to as “ECU”) 5. Has been

A fuel injection valve 6 is provided slightly upstream of the throttle body 3 of the intake pipe 2 so that fuel is supplied to all cylinders of the internal combustion engine 1 when the engine 1 is operating at medium and high loads. On the other hand, an auxiliary fuel injection valve 6a is provided slightly downstream of the throttle body 3 of the intake pipe 2 and upstream of the intake pipe collecting portion so that the internal combustion engine 1 is fully warmed during low load operation. Fuel is supplied to the cylinders. The fuel injection valve 6 and the auxiliary fuel injection valve 6a are EC
The valve opening time T of each of the fuel injection valve 6 and the auxiliary fuel injection valve 6a is electrically connected to U5 and is controlled by a signal from the ECU5.
_{OUT M} and T _{OUT Ma} are controlled.

An absolute pressure (P _BA ) sensor 8 is provided downstream of the throttle valve 3 ′ of the throttle body 3 via a pipe 7. The absolute pressure signal converted into an electric signal by the absolute pressure sensor 8 is provided. Is sent to the ECU 5.

The fuel injection valve 6 and the auxiliary fuel injection valve 6a are connected to a fuel pump 17 in a fuel tank 16 via a pipe line 21, a strainer 15, and pipe lines 22, 23 and 24. The fuel pump 17 is EC
It is controlled by U5. Also, pipelines 22,2
3 and 24 are pipeline 25, pressure regulator 18 and pipeline 2
It is connected to the fuel tank 16 via 6. The pressure regulator 18 is for adjusting the fuel pressure in the pipe lines 22 to 25 in accordance with the negative pressure (absolute pressure P _BA ) in the intake pipe downstream of the throttle valve 3 ′, and the negative pressure chamber 18 a has a pipe line. It is connected via 31 to the intake pipe 2 downstream of the throttle valve 3 ′. That is, the valve opening pressure of the valve body 18b that opens and closes the opening end 26a of the pipe line 26 is determined by the combined force of the biasing force of the coil spring 18c and the negative pressure in the intake pipe downstream of the throttle valve 3 '.
The difference between the fuel pressure (absolute pressure) within .about.25 and the intake pipe absolute pressure P _BA downstream of the throttle valve _3'is always constant. Therefore,
The discharge pressure of the auxiliary fuel injection valve 6a becomes constant regardless of the size of the intake pipe absolute pressure P _BA, fuel injection amount of the auxiliary fuel injection valve 6a is only by opening time T _{OUT M} a of the auxiliary fuel injection valve 6a Can be determined and accurate fuel metering can be performed.

On the other hand, since the pressure in the intake pipe 2 upstream of the throttle valve 3'is always close to atmospheric pressure, the discharge pressure of the fuel injection valve 6 is the absolute pressure P _{BA in} the intake pipe downstream of the throttle valve 3 '. It changes according to the size. That is, the discharge pressure of the fuel injection valve 6
When the engine has a low load, P _D is connected to the pipes 22 to 25 as the absolute pressure P _{BA in} the intake pipe downstream of the throttle valve 3 ′ decreases.
Since the fuel pressure in the inside becomes low, and when the engine is under high load, the absolute pressure P in the intake pipe downstream of the throttle 3 '
_{As the BA} becomes higher, the fuel pressure in the pipes 22 to 25 becomes higher, and hence becomes higher. Therefore, when the engine has a low load, the valve opening time T _{OUT M} of the fuel injection valve 6 becomes longer when the fuel pressure is lower with respect to the same fuel supply amount, so that it is possible to control the fuel amount control with a minute flow rate. When the load is high, the valve opening time T _{OUT M} of the fuel injection valve 6 becomes short for the same fuel supply amount, so that a large flow rate of the fuel supply amount can be secured and high output can be easily obtained.

The valve opening time T _{OUT M} of the fuel injection valve 6 and the auxiliary fuel injection valve
The respective reference values Ti _M , Ti _M a of the valve opening time T _{OUT M} a of 6a are stored in a map stored in the storage means 5c of the ECU 5 described later, and the intake pipe absolute pressure P _BA and the engine speed The basic valve opening times Ti _M and Ti _Ma are retrieved from the two parameters of Ne. Reference value of opening time T _{OUT M} a of auxiliary fuel injection valve 6a Ti _M a
With respect to, since the reference value corresponding to the required air-fuel ratio A / F is a value proportional to the required fuel supply amount Qf, as in the normal case, accurate measurement is possible even at a minute flow rate. However, regarding the reference value Ti _M of the valve opening time T _{OUT M} of the fuel injection valve 6, the reference value corresponding to the required air-fuel ratio A / F is a value calculated in advance by the following procedure. The discharge pressure P _D of the fuel injection valve 6 is the throttle valve 3'as described above.
Since it changes according to the intake pipe absolute pressure P _BA in the downstream of, the plurality of discharge pressure values P _{D of} the fuel injection valve 6 corresponding to the plurality of predetermined values of the intake pipe absolute pressure P _BA are first determined. A plurality of required fuel supply amount values Qf corresponding to respective combinations of a plurality of predetermined values of the engine speed Ne and the intake pipe absolute pressure P _BA are determined, and a plurality of the discharge pressure value P _D and the required fuel supply amount value Qf are determined. combinations determined respectively corresponding basic valve opening time Ti _M and Ti _M a in the,
And stores it in the map (P _BA -Ne map).

That is, since the discharge pressure P _D is the engine load parameter for determining the basic valve opening time Ti _M and Ti _M a with changes in response to the intake pipe absolute pressure P _BA is also at the intake pipe absolute pressure P _BA, P
_Since two phenomena of the discharge pressure P _D and the charging efficiency for each cylinder can be expressed on the same map on the _BA- Ne map, the basic valve opening times Ti _M and Ti _M a determined from the two phenomena can be set. Good. In other words, P _BA -Ne map of map values Ti _M
And Ti _M a in addition to the charging efficiency corresponding to the conventional P _BA -Ne P _BA
It is set in consideration of the discharge pressure P _D according to.

The engine cooling water temperature sensor (hereinafter “Tw
The sensor 9) is provided, and the Tw sensor 9 is composed of a thermistor or the like, is inserted into the engine cylinder peripheral wall filled with cooling water, and supplies the detected water temperature signal to the ECU 5. An engine speed sensor (hereinafter referred to as "Ne sensor") 10 is mounted around a cam shaft or a crank shaft (not shown) of the engine.
A crank angle position signal (hereinafter referred to as a "TDC signal") at a predetermined crank angle position for every 0 ° rotation, that is, at a crank angle position that is a predetermined crank angle before the top dead center (TDC) at the start of the intake stroke of each cylinder. Is output),
This TDC signal is sent to ECU5.

A three-way catalyst 12 is arranged in the exhaust pipe 11 of the engine 1 to purify HC, CO and NOx components in the exhaust gas. An O ₂ sensor 13 is attached to the exhaust pipe 11 on the upstream side of the three-way catalyst 12, and the sensor 13 detects the oxygen concentration in the exhaust gas and outputs an O ₂ concentration signal.
Supply to ECU5.

Further, another parameter sensor 14 such as an atmospheric pressure sensor is connected to the ECU 5, and the other parameter sensor 14 supplies the detection value signal to the ECU 5.

The ECU 5 shapes the input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, and the like, an input circuit 5a, a central processing circuit (hereinafter, "CPU"). 5b, a storage means 5c for storing various calculation programs executed by the CPU 5b and calculation results, and an output circuit 5d for supplying drive signals to the fuel injection valve 6 and the auxiliary fuel injection valve 6a. It

The CPU 5b executes the fuel supply control program shown in FIG.
It is executed every time a signal is input. A fuel injection valve upstream of the throttle valve (hereinafter referred to as an upstream valve) 6 and an auxiliary fuel injection valve downstream of the throttle valve (based on the engine parameter signals from the above-mentioned various sensors supplied through the programmed input circuit 5a). Hereinafter, each fuel injection time of the downstream valve 6a is calculated, and a valve opening drive signal based on these injection times is output to both the injection valves 6 and 6a.

Hereinafter, the processing procedure of the fuel supply control program of FIG. 2 will be described in detail.

This program is executed every time a TDC signal is generated.

First, in step 1, the engine water temperature Tw is the predetermined temperature Tw.
It is determined whether or not higher than _MA (e.g. 60 ° C.), when the answer is negative (No), i.e. if the engine temperature is lower than the predetermined temperature, the open time T _{OUT M} a downstream valve 6a to 0 Set (step 8). Then, the process proceeds to step 15 and later described below, the basic valve opening time Ti _M is searched from the upstream valve P _BA -Ne map, and the valve opening time T _{OUT M} of the upstream valve 6 is calculated based on the Ti _M value by the following equation ( The calculation is performed according to 1) (step 17), and in step 6, the valve opening drive signal corresponding to the T _{OUT M} value is output to the upstream valve 6.

T _{OUT M} = Ti _M × K _1M + K _2M (1) Here, K _1M and K _2M are correction coefficients and correction constants determined based on the various engine parameter signals described above.

As a result, fuel is supplied from the upstream valve when the engine is cold, so fuel distributability to a plurality of cylinders is ensured.

If the determination result in step 1 is affirmative (Yes), it is determined in the next step 2 whether or not the throttle valve opening θ _TH is smaller than a predetermined low throttle opening Zθ _IDL (for example, 0.39 °). There affirmative (Yes), that is, when the engine temperature is high and the throttle valve opening than the predetermined temperature is equal to or less than a predetermined opening degree, the basic valve opening time from P _BA -Ne map for the downstream valve Ti _M
a, and the downstream valve opening time T _OUT based on the Ti _M a value
The _M a is calculated according to the following equation (2) (Step 3).

T _{OUT Ma} = Ti _Ma × K ₁ a + K ₂ a (2) Here, K ₁ a and K ₂ a are correction coefficients and correction constants determined based on the various engine parameter signals described above.

Next, the η _TDCAM value used in step 9 described later is reset to the initial value η _TDCAM (for example, 3) (step 4),
The valve opening time T _{OUT M} value of the upstream valve is set to 0 (step 5). For this reason, the valve opening drive signal is not output to the upstream valve when the next step 6 is executed. Further, in the next step 7, a valve opening drive signal corresponding to the T _{OUT Ma} value calculated in step 3 is output, and this program is ended.
As a result, the responsiveness of fuel supply to the cylinder is improved.

If the determination result in step 2 is negative (No), the above η
_It is determined whether the _TDCAM value is 0 or not (step 9), and if the answer is negative (No), it is for the downstream valve as in step 3 above.
Search for P _B -Ne map than the basic valve opening time Ti _M a, and calculates the valve opening time T _{OUT M} a downstream valve based on the Ti _M a value (step 10). Then subtract 1 from the η _TDCAM value (step 1
1) Go to step 15 and below.

If the determination result in step 9 is affirmative (Yes), the T _{OUT Ma} value calculated in step 10 is decreased by the decrease degree according to the engine speed Ne in the next step 12,13 or steps 12,14. . That is, it is determined whether or not the engine speed Ne is higher than a predetermined value Z _N e _{A M} (e.g. 900 rpm) at step 12, the subtraction value from the previous T _{OUT M} a value when the answer to this question is affirmative (Yes) delta
Subtract T _{OUT M} a ₂ (for example, 1.0 msec) and confirm that this answer is positive (N
When the o) subtracting the subtraction value ΔT _{OUT M} a ₁ (e.g., 1.0 msec) from the previous T _{OUT M} a value, then proceeds to step 15 below.

In step 15, T calculated in step 10, 13 or 14 is
_It is determined whether or not the _{OUT M} a value is smaller than the lower limit value T _{OUT M} a _LMT (for example, 3.0 msec). If the answer is affirmative (Yes), the T _{OUT M} a value is set to the lower limit value T _{OUT M} a in step 16. a After _LMT , proceed to step 17, and if this answer is negative (No), proceed directly to step 17. In step 17, the basic valve opening time Ti _M is searched from the upstream valve P _B -Ne map, and the upstream valve opening time T _{OUT M} is calculated based on the Ti _M value according to the equation (1).

In the next step 18, it is determined whether or not the T _{OUT M} value calculated in step 17 is larger than a predetermined value Me−T _{OUT LMT} . Here, Me is the generation interval of the TDC signal, which corresponds to the time of the intake stroke. Further, T _OUTLMT is a value obtained by converting the valve opening time of the downstream valve at the time of high load into the valve opening time of the upstream valve, and represents the fuel amount injected by the downstream valve. The predetermined value Me-T _{OUT LMT} represents the amount of fuel actually injected by the upstream valve into the cylinder, and the T _{OUT M} value is the predetermined value Me-T.
_When it exceeds _OUTLMT , the excess fuel first adheres to the throttle valve, etc., then evaporates from the throttle valve and adheres to the inner wall of the intake pipe downstream of the throttle valve. However, if the fuel adhering to the inner wall of the intake pipe on the downstream side of the throttle valve is supplied by the downstream valve, the amount of evaporation from the throttle valve will decrease, so the change in the amount of fuel adhering to the throttle valve will be small and the fuel supply The control accuracy is further improved. Therefore, when the determination result of step 18 is affirmative (Yes), the valve opening time of the downstream valve is calculated by the following equation (3) (step 19).

_{T OUT M a = {T OUT} M - (Me-T OUTLMT)} × K A ux + Tva ... (3) Here, K _A ux is the flow rate of the downstream valve for upstream valve,
Tva is a correction value according to the fluctuation of the battery voltage. After performing step 19, proceed to step 6. Also, step 18
If the result of the determination is negative (No), it means that fuel adhering to the throttle valve or the inner wall of the intake pipe is not required, that is, the engine is in a deceleration state, etc. Go to 6.

Finally, in step 6, the valve opening drive signal corresponding to the T _{OUT M} value is output to the upstream valve, and in step 7, the valve opening drive signal corresponding to the T _{OUT M} a value is output to the downstream valve, and this program ends. To do.

(Effects of the Invention) As described in detail above, according to the fuel supply control method for an internal combustion engine of the present invention, the upstream side and the downstream side of the throttle valve upstream of the intake pipe collecting portion of the internal combustion engine having a plurality of cylinders. In a fuel supply control method for an internal combustion engine, which supplies fuel from a fuel injection valve and an auxiliary fuel injection valve respectively installed in the engine, the upstream side of the throttle valve when the engine temperature is lower than a predetermined temperature. Fuel is supplied by the fuel injection valve, and when the engine temperature is higher than the predetermined temperature and the throttle valve opening is less than the predetermined opening, fuel is supplied by the auxiliary fuel injection valve downstream of the throttle valve. Therefore, even if the engine temperature is low, the fuel can be distributed well to the plurality of cylinders. Further, when the engine temperature is low, it is not necessary to switch from the auxiliary fuel injection valve downstream of the throttle valve to the fuel injection valve upstream of the throttle valve when shifting from the low load operating state to the high load operating state. It is possible to prevent the fluctuation of the fuel supply amount due to the switching. Further, when the engine temperature is high, the fuel injection valve is switched at the moment when the throttle valve is opened, that is, at the moment when the intake flow rate changes, so the fuel supply amount may change due to the change in the intake state in the intake pipe. Can be prevented.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a fuel supply control device for an internal combustion engine that implements the method of the present invention, and FIG. 2 is a flowchart of a fuel supply control program executed by the ECU of FIG. 1 ... Internal combustion engine, 3 '... Throttle valve, 4 ... Throttle valve opening sensor, 5 ... Electronic control unit (ECU), 5b ... CPU, 5c ... Storage means, 6 ... Fuel injection valve, 6a ... Auxiliary fuel injection valve, 8 ... Intake pipe absolute pressure sensor, 10 ... Engine speed sensor.

Claims (1)

[Claims] 1. A fuel injection valve and an auxiliary fuel injection valve, which are respectively installed upstream and downstream of a throttle valve upstream of an intake pipe collecting portion of an internal combustion engine having a plurality of cylinders, according to an operating state of the engine. In a fuel supply control method for an internal combustion engine that supplies fuel by means of an internal combustion engine, fuel is supplied by a fuel injection valve upstream of the throttle valve when the engine temperature is lower than a predetermined temperature, and the engine temperature is higher than the predetermined temperature and the throttle valve A fuel supply control method for an internal combustion engine, wherein fuel is supplied by an auxiliary fuel injection valve downstream of the throttle valve when the opening is equal to or smaller than a predetermined opening.