JP2004092540A - Fuel supply control device of gaseous fuel for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively utilize gaseous fuel in a fuel storage vessel. <P>SOLUTION: A fuel feed control device is provided with a fuel injection valve to inject gaseous fuel directly in a cylinder. When a gaseous fuel pressure P in a fuel cylinder is higher than a set pressure PR of a regulator, fuel injection is effected in a compression stroke (a step 101). When the gaseous fuel pressure P is lower than the set pressure PR and higher than a lower limit pressure PL, fuel injection is effected in a compression stroke with the fuel injection time being corrected (a step 104). When the gaseous fuel pressure P is reduced to a value lower than the lower limit pressure PL, fuel injection is effected in a suction stroke with the fuel injection time being corrected (a step 105). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel supply control device for a gas-fueled internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an internal combustion engine using a gas fuel such as compressed natural gas (hereinafter, referred to as CNG) has been known.
[0003]
[Problems to be solved by the invention]
However, compared to liquid fuels, gas fuels are gaseous and therefore have a large volume in the first place, and a small amount of heat generated per unit volume. Therefore, the amount of fuel required to obtain a certain engine output is large. Therefore, when the gas fuel is supplied to the intake passage, the air cannot be sucked to that extent, that is, the intake charging efficiency decreases.
[0004]
This problem can be solved by providing a fuel injection valve for directly injecting gas fuel into the cylinder, and injecting gas fuel from the fuel injection valve into the cylinder during the compression stroke.
[0005]
However, a relatively high injection pressure is required to inject gas fuel into the cylinder during the compression stroke. Therefore, when the gas fuel pressure in the fuel cylinder gradually decreases as the gas fuel is consumed, the gas fuel cannot be finally supplied to the internal combustion engine, and as a result, the gas fuel in the fuel cylinder is effectively used. There is a problem that can not be. For example, when the capacity of the fuel cylinder is 20 MPa and the minimum allowable pressure is 5 MPa, 25% of the gas fuel filled in the fuel cylinder cannot be used, that is, the fuel cylinder has a dead volume of 25%. It is the same as having.
[0006]
Therefore, an object of the present invention is to provide a fuel supply control device for a gas-fueled internal combustion engine that can effectively use gas fuel in a fuel storage container.
[0007]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a fuel injection valve for directly injecting gas fuel into a cylinder, and the gas fuel is injected from the fuel injection valve into the cylinder during a compression stroke. In a gas-fueled internal combustion engine, the fuel injection timing is advanced when the gas fuel pressure in the fuel storage container is low as compared to when the gas fuel pressure is high.
[0008]
According to a second aspect, in the first aspect, when the gas fuel pressure in the fuel storage container becomes lower than a predetermined lower limit pressure, the gas fuel is injected from the fuel injector during the intake stroke. I have to.
[0009]
According to a third aspect, in the first aspect, an additional fuel injection valve for injecting gas fuel into the intake passage is provided, and the gas fuel pressure in the fuel storage container is lower than a predetermined lower limit pressure. When it becomes low, gas fuel is injected into the intake passage from an additional fuel injection valve during the intake stroke.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake port, 8 is an exhaust port, 9 Indicates spark plugs, respectively. The intake port 7 is connected to a surge tank 11 via a corresponding intake branch 10, and the surge tank 11 is connected to an air cleaner 13 via an intake duct 12. A throttle valve 15 driven by a step motor 14 is arranged in the intake duct 12. On the other hand, the exhaust port 8 is connected to a catalytic converter 18 via an exhaust manifold 16 and an exhaust pipe 17.
[0011]
As shown in FIG. 1, the ignition plug 9 is disposed substantially at the center of the inner wall surface of the cylinder head 3. On the other hand, the fuel injection valve 6 is arranged on the peripheral portion of the inner wall surface of the cylinder head 3.
[0012]
The fuel injection valve 6 is for directly injecting gas fuel into the cylinder. As shown in FIG. 1, each fuel injection valve 6 is connected to a common fuel delivery pipe 19, and the fuel delivery pipe 19 is connected to a gas fuel storage container or a fuel cylinder 21 via a regulator 20. The gas fuel in the fuel cylinder 21 is supplied to the fuel delivery pipe 19 after being reduced to a predetermined set pressure PR by the regulator 20, and then injected into the cylinder from the fuel injection valve 6 at the set pressure PR. In the internal combustion engine shown in FIG. 1, CNG is used as gas fuel. However, other gas fuels can be used.
[0013]
The electronic control unit 30 is composed of a digital computer, and is connected to a ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, and a power supply, which are mutually connected by a bidirectional bus 31. It has a B-RAM (backup RAM) 35, an input port 36, and an output port 37. A pressure sensor 40 for generating an output voltage representing an intake pressure in the surge tank 11 is attached to the surge tank 11, and a gas fuel for generating an output voltage representing a gas fuel pressure P in the fuel cylinder 21 is provided in the fuel cylinder 21. The pressure sensor 41 is attached. Output signals of these sensors 40 and 41 are input to the input port 36 via the corresponding AD converter 38. The input port 36 is connected to a crank angle sensor 42 that generates an output pulse each time the crankshaft rotates, for example, 30 °. In the CPU 34, an intake air amount Q is calculated based on an output signal from the pressure sensor 40, and an engine speed N is calculated based on an output pulse from the crank angle sensor 42. On the other hand, the output port 37 is connected to the fuel injection valve 6, the ignition plug 9, and the step motor 14 via the corresponding drive circuit 39.
[0014]
In the embodiment according to the present invention, at the fuel injection timing θF during the compression stroke, gas fuel is injected into the cylinder from the fuel injection valve 6 for the fuel injection time TAU. In this case, the fuel injection timing θF and the fuel injection time TAU are functions of the engine operating state, for example, engine load Q / N (intake air amount Q / engine speed N) and engine speed N, as shown in FIGS. 2 (B) is stored in the ROM 32 in advance in the form of a map shown in FIG. The fuel injection time TAU is a fuel injection time required to inject the required amount of gaseous fuel under the set pressure PR at the fuel injection timing θF.
[0015]
As the gas fuel is consumed and the remaining fuel amount in the fuel cylinder 21 decreases, the gas fuel pressure P in the fuel cylinder 21 gradually decreases. Next, when the gas fuel pressure P becomes lower than the set pressure PR, the regulator 20 no longer operates, and gas fuel must be injected at the gas fuel pressure P at this time.
[0016]
However, as described at the beginning, in order to inject gas fuel into the cylinder during the compression stroke, a relatively high injection pressure is required. As a result, when the gas fuel pressure P becomes lower than the set pressure PR, the gas is discharged during the compression stroke. It becomes difficult to inject fuel well. If the gas fuel pressure P is higher than the in-cylinder pressure PC, it is possible to perform a certain amount of fuel injection. However, as the gas fuel pressure P decreases and the difference from the in-cylinder pressure PC (= P−PC) decreases, The fuel injection time required to inject the required amount of gas fuel is undesirably long. On the other hand, the in-cylinder pressure PC in the intake stroke is relatively low, and fuel injection can be performed with a relatively low injection pressure in a short time.
[0017]
Therefore, in the embodiment according to the present invention, when the gas fuel pressure P is lower than the set pressure PR set by the regulator 20, the gas fuel is injected during the intake stroke. Or, generally speaking, the fuel injection timing is advanced when the gas fuel pressure P is low as compared to when it is high.
[0018]
However, even if the gas fuel pressure P becomes lower than the set pressure PR, this does not necessarily mean that good fuel injection cannot be performed in all engine operating states. For example, in an engine operating state in which the fuel injection timing θF is relatively advanced and the in-cylinder pressure PC at the time of fuel injection is relatively low, it is possible to perform good fuel injection during the compression stroke.
[0019]
Therefore, in the embodiment according to the present invention, the lower limit pressure PL at which a good fuel injection can be performed during the compression stroke is set in advance, and even if the gas fuel pressure P is lower than the set pressure PR, the lower limit pressure PL is set lower than the lower limit pressure PL. When the fuel pressure is high, fuel injection is performed during the compression stroke, and when the gas fuel pressure P becomes lower than the lower limit pressure PL, fuel injection is performed during the intake stroke.
[0020]
Various methods can be considered for setting the lower limit pressure PL. In the embodiment according to the present invention, as shown in FIG. 3A, the lower limit pressure PC is set to be larger than the in-cylinder pressure PC by a constant value ΔP. (PL = PC + ΔP).
[0021]
Here, the in-cylinder pressure PC when the fuel injection is performed is determined according to the fuel injection timing θF, and the fuel injection timing θF is determined according to the engine operating state as described above. Therefore, in the embodiment according to the present invention, the lower limit value PL is obtained in advance as a function of the engine operating state, for example, the engine load Q / N and the engine speed N, and is stored in advance in the ROM 32 in the form of a map shown in FIG. I try to remember.
[0022]
FIG. 4 shows a change in the fuel injection timing with respect to a change in the gas fuel pressure P in a constant engine operating state. Referring to FIG. 4, when the gas fuel pressure P is higher than the set pressure PR, fuel injection is performed in the compression stroke. At this time, the fuel injection timing θF and the fuel injection time TAU can be obtained from the map shown in FIG. 2 as described above.
[0023]
When the gas fuel pressure P is lower than the set pressure P but higher than the lower limit pressure PL, the fuel injection is performed during the compression stroke while maintaining the fuel injection timing θF. Next, when the gas fuel pressure P further decreases and becomes lower than the lower limit pressure PL, fuel injection is performed in the intake stroke.
[0024]
In this case, as the gas fuel pressure P decreases, the differential pressure between the injection pressure and the in-cylinder pressure PC gradually decreases. Therefore, when the fuel injection is performed only by TAU shown in FIG. Is less than required. Therefore, in the embodiment according to the present invention, the fuel injection time is made longer as the gas fuel pressure P becomes lower. In other words, when the gas fuel pressure P is lower than the set pressure PR, the fuel injection time is corrected based on the gas fuel pressure P so that the actually injected fuel amount matches the required amount.
[0025]
As described above, in the embodiment according to the present invention, even if the gas fuel pressure P becomes lower than the set pressure PR, fuel can be continuously supplied to the engine, and the gas fuel in the fuel cylinder 21 is effectively used. be able to. This also means that the travelable distance of the gas-fueled internal combustion engine vehicle is increased.
[0026]
FIG. 5 shows a fuel injection control routine according to the embodiment of the present invention. This routine is executed by interruption every predetermined crank angle.
[0027]
Referring to FIG. 5, first, at step 100, it is determined whether or not the gas fuel pressure P is lower than the set pressure PR. When P ≧ PR, the routine proceeds to step 101, where fuel injection is performed during the compression stroke for the fuel injection time TAU described above. On the other hand, when P <PR, the routine proceeds to step 102, where the lower limit pressure PL is calculated from the map of FIG. In the following step 103, it is determined whether or not the gas fuel pressure P is lower than the lower limit pressure PL. When P ≧ PL, the routine proceeds to step 104, where fuel injection is performed during the compression stroke while correcting the fuel injection time TAU. On the other hand, when P <PL, the routine proceeds to step 105, where fuel injection is performed during the intake stroke while correcting the fuel injection time TAU.
[0028]
FIG. 6 shows another embodiment according to the present invention.
[0029]
In another embodiment according to the invention, in addition to the fuel injection valve 6 for injecting gas fuel into the cylinder during the compression stroke, an additional fuel injection valve for injecting gas fuel into the intake port 7 during the intake stroke 6A is provided. Each additional fuel injection valve 6A is connected to a common additional fuel delivery pipe 19A, and the additional fuel delivery pipe 19A is connected to the fuel cylinder 21 via an additional regulator 20A. The regulator 20 and the additional regulator 20A are connected to the fuel cylinder 21 via the three-way valve 22.
[0030]
The three-way valve 22 is for connecting the fuel cylinder 21 to one of the fuel injection valve 6 and the additional fuel injection valve 6A. That is, the fuel cylinder 21 is connected to the fuel injection valve 6 when gas fuel is to be injected into the cylinder during the compression stroke, and additional fuel injection is performed when gas fuel is to be injected into the intake port 7 during the intake stroke. Connected to valve 6A. The three-way valve 22 is controlled based on an output signal from the electronic control unit 30.
[0031]
Another embodiment according to the present invention will be described in detail with reference to a fuel injection control routine shown in FIG. This routine is executed by interruption every predetermined crank angle.
[0032]
Referring to FIG. 7, first, at step 120, it is determined whether the gas fuel pressure P is lower than the set pressure PR. When P ≧ PR, the routine proceeds to step 121, where in-cylinder injection is performed by the fuel injection valve 6 in the compression stroke for the above-described fuel injection time TAU. On the other hand, when P <PR, the routine proceeds to step 122, where the lower limit pressure PL is calculated from the map of FIG. In the following step 123, it is determined whether or not the gas fuel pressure P is lower than the lower limit pressure PL. When P ≧ PL, the routine proceeds to step 124, in which the fuel injection valve 6 performs in-cylinder injection during the compression stroke while correcting the fuel injection time TAU. On the other hand, when P <PL, the routine proceeds to step 125, where the additional fuel injection valve 6A performs intake port injection during the intake stroke while correcting the fuel injection time TAU.
[0033]
【The invention's effect】
The gas fuel in the fuel storage container can be effectively used.
[Brief description of the drawings]
FIG. 1 is an overall view of a gas-fueled internal combustion engine.
FIG. 2 is a diagram showing a fuel injection timing and a fuel injection time.
FIG. 3 is a diagram showing a lower limit pressure.
FIG. 4 is a diagram showing a change in fuel injection timing in a constant engine operating state.
FIG. 5 is a flowchart for executing fuel injection control.
FIG. 6 is a diagram showing another embodiment according to the present invention.
FIG. 7 is a flowchart for executing fuel injection control of another embodiment according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine body 6 ... Fuel injection valve 6A ... Additional fuel injection valve 7 ... Intake port 21 ... Fuel cylinder 41 ... Gas fuel pressure sensor

Claims (3)

In a gas-fueled internal combustion engine having a fuel injection valve for directly injecting gas fuel into a cylinder and injecting gas fuel from the fuel injection valve into the cylinder during a compression stroke, the gas fuel pressure in a fuel storage container is reduced. A fuel supply control device for a gas-fueled internal combustion engine in which the fuel injection timing is advanced when the fuel injection timing is low compared to when it is high. 2. The fuel supply system according to claim 1, wherein when the gas fuel pressure in the fuel storage container becomes lower than a predetermined lower limit pressure, the gas fuel is injected from the fuel injection valve during the intake stroke. Control device. An additional fuel injection valve for injecting gas fuel into the intake passage is provided. When the gas fuel pressure in the fuel storage container becomes lower than a predetermined lower limit pressure, the intake fuel is supplied from the additional fuel injection valve during the intake stroke. The fuel supply control device for a gas-fueled internal combustion engine according to claim 1, wherein gas fuel is injected into the passage.

Images