JPH03189352A - Fuel injection device for independent suction engine - Google Patents

Abstract

PURPOSE:To equalize a fuel injection amount of each cylinder by controlling a fuel feed pressure to a fuel injection valve by using only the pressure of a single intake air pipe, and correcting a fuel injection time amount of each cylinder by means of a correction factor set based on displacement in time of a pressure fluctuation cycle between cylinders. CONSTITUTION:An ECU 20 controls a fuel feed pressure to fuel injection valves 6a-6d of all cylinders based on an intake air pipe pressure P1 of a single cylin der, for example, a cylinder 1 as a representative so that a specified differential pressure P0 therebetween is kept. In this case, a pressure in the intake air pipe of each cylinder during injection of fuel of each cylinder and a pressure in the intake air pipe of a current representative cylinder 1 are previously measured under various conditions. From the values, a difference Pi between a fuel feed pressure during injection of fuel of each cylinder and a pressure in an intake air pipe is calculated. Further, based on the calculating result, a fuel injection correction factor alphai=(P0/ Pi) of each cylinder under each operation condition is calculated, a calculating result is stored in an ROM 22, and based on the correction factor, a fuel injection time of each cylinder is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel injection device for an engine, and more particularly to a fuel injection device for an independent intake engine having an independent throttle valve for each intake pipe of each cylinder. .

[Conventional technology]

Conventionally, in a fuel injection system for a common intake engine that has a common throttle valve for all cylinders at the intake pipe assembly section of each cylinder, the pressure downstream of the throttle valve (engine side) at the intake pipe assembly section is guided to a pressure regulator, and each A method is used to adjust the fuel supply pressure to the fuel injection valve of the cylinder. This is because in an electronically controlled fuel injection system, the fuel injection amount is controlled by adjusting the fuel injection time t from the injection valve. ) This is because it is necessary to keep Q constant. That is, the fuel injection amount W from the fuel injection valve is expressed as -=Qxt, but Q must be kept constant in order to adjust the fuel injection amount by controlling the injection time t according to the engine load. Must be. However, the injection flow rate Q is a function of the fuel supply pressure P1 to the fuel injection valve and the pressure at the nozzle outlet of the fuel injection valve (i.e. engine intake pipe pressure) P2, and q=c, /TV
- lower r/ρ (where C is the nozzle flow coefficient and ρ is the fuel density) where the engine intake pipe pressure P
1 varies greatly depending on the operating conditions of the engine, so in order to keep Q constant, it is necessary to control the difference (pz p+) between the fuel supply pressure P2 and the engine intake pipe pressure P to be constant.

For this reason, in a conventional common intake engine, the intake pipe pressure P downstream of the throttle valve is guided to a pressure regulator that controls the fuel supply pressure, and the fuel supply pressure P2 is adjusted so that the difference between P2 and the intake pipe pressure P is constant. It is controlled by

However, in an independent intake engine having a throttle valve for each intake pipe of each cylinder, the intake pipe pressures downstream of each throttle valve fluctuate in cycles different from each other in time. For this reason, if the intake pipe pressure leading to the pressure regulator is taken from one cylinder, the fuel supply pressure to all fuel injection valves will be adjusted according to only the intake pipe pressure fluctuation cycle of that one cylinder,
With the fuel injection valves of other cylinders, the differential pressures P and -P between the fuel supply pressure and the intake pipe pressure do not reach appropriate values during fuel injection, resulting in variations in the fuel injection amount.

Therefore, in other cylinders, a proper air-fuel ratio cannot be obtained, resulting in a problem of decreased output and deterioration of exhaust gas components.

On the other hand, instead of taking the intake pipe pressure that leads to the pressure regulator from one cylinder, it is also possible to introduce the intake pressure to the pressure regulator through piping that communicates with each intake pipe, but in this case, each intake pipe There is a problem in that the advantages of independent intake are lost because the pipes are connected and pressure fluctuations in each intake pipe influence each other. In order to solve the above problem, the present applicant proposed a fuel supply pressure adjustment position in Japanese Utility Model Application Publication No. 61-157168, which uses a communication pipe equipped with a negative pressure delay valve to adjust the fuel pressure of an independent intake engine. is advocating.

The device described in the publication has an intake negative pressure take-out boat on the downstream side of the throttle valve of each cylinder, and each of these negative pressure take-off boats serves as an orifice and a check valve that opens in response to the negative pressure in the intake pipe. The fuel pressure regulator is connected to the fuel pressure regulator via a negative pressure delay valve.

20 By communicating each cylinder via a negative pressure delay valve, the pressure in the communication pipe is not subject to sudden changes in the intake pressure of a specific cylinder, and the pressure regulator has a constant average value of the intake pressure of all cylinders. Pressure is applied.

Therefore, the pressure supplied to the fuel injection valve is not affected by fluctuations in the intake pipe pressure of a particular cylinder, and the conditions are the same for each cylinder, thereby eliminating variations in the amount of fuel injected in each cylinder. Furthermore, since the negative pressure delay valve can prevent pressure fluctuations in each intake pipe from propagating to the intake pipes of other cylinders, the independence of each intake pipe is not affected. Furthermore, in Japanese Patent Application Laid-Open No. 61101868, when there is a large variation in the amount of intake air in each cylinder, a boost sensor is provided in the intake pipe of each cylinder to detect the intake pipe pressure, and the signal from this boost sensor is used to detect the pressure in each cylinder. A fuel injection device is described in which the fuel injection amount is individually adjusted to increase or decrease the amount of fuel depending on the amount of air filled in each cylinder.

[Problems to be Solved by the Invention] However, the device described in the above-mentioned Japanese Utility Model Application Publication No. 157168/1983 provides a negative pressure take-out boat downstream of the throttle valve of each intake pipe, and Must be connected to a communication pipe. This negative pressure delay valve is composed of a very small check valve and an orifice, and requires precision in mounting and processing, which causes an increase in man-hours. Further, it is necessary to connect the intake pipes of each cylinder with a communicating pipe, which causes a problem that the configuration becomes complicated.

Furthermore, since the intake pressure applied to the pressure regulator passes through a negative pressure delay valve, its response is poor (it tends to be delayed in response to sudden changes in engine operating conditions).

On the other hand, although the invention described in JP-A No. 62-101868 does not cause the above problem, it requires precise pressure measurement for each intake pipe of each cylinder, and requires the use of expensive pressure sensors. , there is a problem that the control program is also complicated. SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a fuel injection device for an independent intake engine that can uniformly control the amount of fuel injected into each cylinder with a simple configuration.

[Means for Solving the Problem] The present invention controls the fuel supply pressure to the fuel injection valve using only the pressure of one intake pipe, and controls the fuel supply pressure to the fuel injection valve based on the time lag of the pressure fluctuation cycle between each cylinder in advance. The present invention is characterized in that the fuel injection time amount of the fuel injection valve of each cylinder is corrected using a correction coefficient set to eliminate an imbalance in the fuel injection amount of each cylinder.

That is, according to the present invention, in a fuel injection system for an independent intake engine having an independent throttle valve for each intake pipe of each cylinder, the representative intake air pressure is detected in the intake pipe downstream of the throttle valve of one of the cylinders. a pressure detection means; a fuel supply pressure adjustment means for controlling the fuel supply pressure to all the cylinders so as to produce a predetermined pressure difference from the representative intake pressure detected as described above; Using a representative fuel injection time setting means for setting the fuel injection time and a correction coefficient previously set for each cylinder when injecting fuel into each cylinder, each of the representative fuel injection times is set from the representative fuel injection time set by the representative fuel injection time setting means. A fuel injection device for an independent intake engine is provided, which is characterized by comprising a fuel injection time correction means for setting a fuel injection time for each cylinder.

[For production]

The fuel supply pressure adjusting means controls the fuel supply pressure to the fuel injection valves of all cylinders based on the intake pipe pressure of one cylinder (hereinafter referred to as "representative cylinder"). Therefore, the fuel supply pressure fluctuates according to the intake pipe pressure fluctuation cycle of the representative cylinder mentioned above. Therefore, the fuel supply pressure when fuel injection is performed in each cylinder is different, and the value deviates from the appropriate pressure in cylinders other than the representative cylinder. become.

In the present invention, the fuel supply pressure at the time of fuel injection for each cylinder is determined in advance by actual measurement or the like, and the deviation from the appropriate value is stored in the fuel injection time correction means as a correction coefficient for each cylinder.

The fuel injection amount of each cylinder can be made uniform by controlling the fuel injection time from the fuel injection valve of each cylinder according to the correction coefficient.

〔Example〕 FIG. 1 shows a schematic diagram of a first embodiment of the invention.

In the figure, 1 is an engine cylinder, 2 is an intake valve, 3 is an exhaust valve, 4 is an intake pipe, and 5 is a throttle valve provided for each intake pipe of each cylinder. Moreover, 6a to 6d are fuel injection valves provided at the intake ports of each cylinder. Fuel is supplied from a fuel supply pump (not shown) through a fuel pipe 8, and after its pressure is regulated by a pressure regulator 9, it is distributed to the fuel injection valves 6a to 6d of each cylinder. The pressure regulator 9 is supplied with the pressure of the intake pipe 4 from an intake pressure boat 10 provided downstream of the throttle of the intake pipe 4 of the representative cylinder.
The pressure regulator 9 is connected to each fuel injection valve 6a to 6.
The fuel pressure P2 supplied to the intake pressure port 10 is adjusted to be higher than the pressure P of the intake pressure port 10 by a constant pressure ΔP. That is, the relationship P, -P, = ΔP (constant) is maintained.

Further, 20 is an electronic control unit consisting of a digital computer that controls the engine, and ROM (read only memory) 2 interconnected by a bidirectional bus 21.
2, RAM (Random Access Memory) 23, CPU
(microprocessor) 24, an input port 25, and an output port 26.

Engine control data such as engine speed and load are input to the input port 25, and fuel injection pulses are sent from the output port 26 to each of the fuel injection valves 6a to 6d via the drive circuit 27, depending on the pulse width. to open the fuel injection valve. That is, the ECU 20 controls the fuel injection time (valve opening time) of the fuel injection valves 6a to 6d according to the operating conditions of the engine, and controls the amount of fuel supplied to each cylinder.

Next, FIG. 2 shows the relationship between pressure fluctuations in the intake pipes of each cylinder.

In the figure, the vertical axis shows the intake pipe internal pressure and fuel supply pressure, and the horizontal axis shows the crank angle, and the curves in the figure show each intake pipe internal pressure fluctuation in the case of an independently intake four-cylinder engine. Since this is an independent intake engine, each intake pipe is not affected by pressure changes in other intake pipes, and the pressure changes in the intake pipes of each cylinder have a waveform of - between paths, resulting in four pressure fluctuations with a period of 720 degrees. They are lined up with a phase difference of 180 degrees at the crank angle. Also, in the figure 1. ~I4 is the timing of fuel injection in each cylinder.

Now, as mentioned above, the fuel supply pressure P2 to each fuel injection valve
is controlled to maintain a constant differential pressure ΔP0 with the intake pipe pressure P of one representative cylinder (Nα1 cylinder in this figure), so P2 is the same as the intake pressure fluctuation of No. 1 cylinder as shown in the figure. Shows changes in waveform. Therefore, the difference ΔP6 between each cylinder and the intake pipe internal pressure at the time of fuel injection
(i=l~4) is ΔP1-ΔP in the first cylinder
0, but it is smaller than ΔP0 in the second to fourth cylinders.

As mentioned above, since the injection flow rate Q of the fuel injection valve is proportional to f r, it can be seen that in this case, the injection flow rate of the fuel injection valves of the second to fourth cylinders is each smaller than the injection flow rate of the first cylinder. . Therefore, if the fuel injection time of each cylinder's fuel injection valve is the same as in a normal engine, there will be large variations in the fuel injection amount in each cylinder, and it will be difficult to obtain the required air-fuel ratio in cylinders other than the first in the figure. Can not.

In the fuel injection device of the present invention, the pressure inside the intake pipe of each cylinder at the time of fuel injection and the pressure inside the first cylinder intake pipe at that time are measured in advance under various operating conditions, and the fuel injection of each cylinder is determined based on these values. The difference ΔP between the fuel supply pressure and the inside of the intake pipe (Fig. 2) is calculated in advance. Furthermore, based on these, fuel injection correction coefficients are determined for each cylinder under each operating condition.

The present invention is characterized in that ρ■Babin-Nkari-=α is calculated and stored in the ROM 22 of the ECU 20 in the form of a numerical table, and the fuel injection time of each cylinder is corrected based on this correction coefficient. That is, the fuel injection time of the representative cylinder is t. When closed, the fuel injection amount W is W=C(τ[Xto
For other cylinders, if the injection time is t, then the fuel injection amount W is W, =~ζ9? x t . Here, the fuel injection time for each cylinder is 1. is the correction coefficient α,
Using 1. =αi x t.

Toru(!: grin Wi =cI■[x ti =C
9rN Otsu) (α = X to ) = Palanquin F■4X
P P = X to, H8 = C7TP〒X
t. =W, so the amount of fuel W in each cylinder can be made equal to W. FIG. 3 is a flowchart showing the above fuel injection control by ECII 20.

In the figure, after starting ECLI 20, step 101
Enter engine control data such as engine speed, intake air amount, and crank angle via the input boat 25 and store it in the RAM.
23. Next, in step 102, the required fuel injection amount W is determined based on these data, and in step 103
The fuel injection time t, = ty/c7T1τ, of the representative cylinder (first cylinder in this embodiment) is set. Next, from the crank angle read in step 101, the cylinder number i to which the next fuel injection is to be performed is determined (step 104), based on the operating conditions such as engine speed and intake air amount,
A lookup is performed on the table of injection time correction coefficients stored in 23 to determine the correction coefficient α1 for that cylinder (step 105).

Next, from the fuel injection time to of the representative cylinder obtained in step 103 and the correction coefficient α8 obtained in step 105, the fuel injection time of that cylinder is 1. =1°Xα, step 106), and perform fuel injection (step 107).
. This operation is performed for each fuel injection of each cylinder, that is, twice per revolution of the engine.

4 and 5 show another embodiment of the invention. In this embodiment, the intake pipe of each cylinder includes a bypass passage 31 that bypasses the throttle valve and a solenoid-driven on-off valve 3.
2 is provided. Further, the embodiment shown in FIG. 1 has an intake pressure boat 10 provided downstream of the throttle valve 5 of the first cylinder, and adjusts the fuel supply pressure with a pressure regulator 9 based on the pressure of the first cylinder intake pipe 4. It is similar to

In this embodiment, the bypass passage 31 is used to improve the air filling rate when the engine is idling. In a normal independent intake engine, when the throttle valve 5 is fully closed during idling operation, there will be a large negative pressure downstream of the throttle valve 5. Therefore, when the intake valve 2 opens during the engine intake stroke, the burned gas remains in the cylinder 1. flows back into the intake pipe 5. Particularly in high-output engines and other engines in which the valve overlap between the intake valve 2 and the exhaust valve 3 is large, the amount of burned gas that flows backward is large. This burnt gas is sucked into the cylinder again during the intake stroke of the engine, and as a result, the amount of burnt gas remaining in the cylinder increases, deteriorating combustion conditions.

The bypass passage 31 of this embodiment is provided to prevent burnt gas from flowing back into the intake pipe during idle operation, and the valve 32 of the bypass passage 31 is opened only for a certain period of time before the intake valve is opened during idle operation. By doing so, the negative pressure inside the intake pipe is rapidly lowered (the pressure inside the intake pipe is increased), and the backflow of burned gas when the intake valve is opened is reduced. Figure 5 shows the change in intake pressure during idling operation of this engine.
It can be seen that with respect to the change in intake pressure of an engine without the bypass passage 31 (shown by a dotted line in the figure), there is a large pressure increase prior to the opening of the intake valve. In such an engine, the difference between the intake pipe pressure at the time of fuel injection in each cylinder and the intake pipe pressure in the representative cylinder during idling is larger than in a normal engine. Therefore, when the fuel supply pressure is controlled by the intake pipe pressure of the representative cylinder, the difference ΔP' between the fuel supply pressure and the intake pressure of each cylinder is smaller than that of a normal engine (ΔP in the figure), so each cylinder has a fuel injection flow rate of will vary widely. Therefore, the use of the fuel injection device of the present invention is particularly effective for such engines.

〔Effect of the invention〕

As described above, the present invention controls the fuel supply pressure using the intake pipe negative pressure of one cylinder of an independently aspirated engine, and corrects each cylinder's fuel injection time using a preset correction coefficient. Since variations in the amount of fuel injected between cylinders are eliminated, complicated configurations such as communication pipes and negative pressure delay valves are not required, and control with excellent responsiveness and precision is possible with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of the fuel injection device of the present invention, FIG. 2 is a diagram showing intake pipe pressure fluctuations of each cylinder in FIG. 1, and FIG. 3 is a diagram showing the fuel injection system of the present invention. FIG. 4 is a flowchart showing the control of the device, FIG. 4 is a schematic diagram showing another embodiment of the present invention, and FIG. 5 is a diagram showing intake pipe pressure fluctuations of each cylinder in FIG. 4. 4... Intake pipe, 5... Throttle valve,
6a to 6d...Fuel injection valve, 9...Pressure regulator, 10...Intake pressure boat, 20...ECU, 31...
...Intake bypass passage, 32...Solenoid valve. Fig. 1 20... ECU Fig. 3 Fig. 32... Solenoid valve

Claims (1)

[Scope of Claims] 1. In a fuel injection system for an independent intake engine having an independent throttle valve for each intake pipe of each cylinder, a representative system for detecting the pressure inside the intake pipe downstream of the throttle valve of one of the cylinders. intake pressure detection means; fuel supply pressure adjustment means for controlling the fuel supply pressure to all cylinders so as to produce a predetermined pressure difference from the representative intake pressure detected as described above; From the representative fuel injection time set by the representative fuel injection time setting means, using a representative fuel injection time setting means for setting the fuel injection time and a correction coefficient set in advance for each cylinder when injecting fuel into each cylinder. 1. A fuel injection device for an independent intake engine, comprising: fuel injection time correction means for setting fuel injection time for each cylinder.