JP2004353460A - Fuel injection timing control method for cylinder direct injection cng engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection timing control method for a cylinder direct injection CNG engine capable of minimizing a time in which an inoperable area is produced by injecting fuel in a compression stroke wherever possible. <P>SOLUTION: In this fuel injection timing control method for the cylinder direct injection CNG engine capable of switching between a stratified combustion and a homogeneous combustion according to the operating conditions of an engine, when an injection pressure lowers below a target fuel pressure (step S11 Yes), combustion is switched to an all area homogeneous combustion (steps S12, 13), and an injection completion crank angle A is calculated by using a minimum interval map for the completion of injection and ignition (step S14), an injection completion crank angle B at the present time is calculated by using a cylinder pressure map defined by rotational speed and load beforehand and the pressure of fuel (step S15). The calculated both angles A and B are compared with each other, and one nearer a spark-advance side is used as a crank angle (step S16), and based on the angle and the fuel pressure at present, an injection start crank angle is calculated and fuel is injected (step S17). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for controlling the fuel injection of a direct injection CNG engine having a stratified combustion operation region by directly injecting compressed natural gas (CNG) into a cylinder, and more particularly, to a method for compressing as much as possible. The present invention relates to a fuel injection timing control method for a direct injection CNG engine that can minimize the time during which an area in which operation is not possible due to fuel injection is generated.
[0002]
[Prior art]
In recent years, from the viewpoint of energy and environmental measures, compressed natural gas (CNG) has been used as fuel for internal combustion engines for automobiles, and CNG fuel has been injected into cylinders to improve fuel efficiency and output. In-cylinder direct injection CNG engines (hereinafter, appropriately referred to as CNG engines) for direct injection have been actively developed, and various technologies have been proposed.
[0003]
Such an in-cylinder direct injection CNG engine usually has a CNG fuel cylinder for storing CNG fuel, a fuel injection valve for directly injecting CNG fuel into each cylinder, and accumulating and distributing the CNG fuel to each fuel injection valve. A delivery pipe, and a high-pressure regulator that is provided in the middle of a fuel supply pipe that connects the CNG fuel cylinder and the delivery pipe and that reduces the pressure of the CNG fuel to a predetermined pressure, and is configured to be capable of switching between stratified combustion and homogeneous combustion. I have.
[0004]
The CNG fuel is stored at a high pressure (for example, about 20 MPa) in the CNG fuel cylinder. When the CNG fuel is pressure-fed from the CNG fuel cylinder, the CNG fuel is supplied at a constant pressure (for example, by the high pressure regulator) before being supplied to the delivery pipe. The pressure is reduced to about 5 MPa).
[0005]
Therefore, conventionally, a combustion map corresponding to the above-mentioned constant pressure value is set in advance, and based on this map, control for switching between stratified combustion and homogeneous combustion according to the engine speed and load condition has been performed. .
[0006]
That is, such an in-cylinder direct-injection CNG engine attempts to improve its performance by injecting fuel in the compression stroke to improve the filling efficiency and the like. Therefore, it is necessary to inject fuel into the combustion chamber at high pressure. Further, it is known that when the residual gas pressure in the CNG fuel cylinder becomes equal to or less than the above-mentioned fixed pressure value, the CNG fuel cannot be regulated and supplied by the high-pressure regulator, so that the cruising distance does not increase.
[0007]
For this reason, when the pressure of the CNG fuel is lower than the reference pressure, the valve closing timing of the intake valve is advanced, and control is performed such that in-cylinder injection is performed in the first half of the intake stroke or the compression stroke (immediately after the intake dead center). A technology has been disclosed in which fuel injection can be performed even when the pressure is low, and the cruising distance can be extended (see Patent Document 1).
[0008]
[Patent Document 1]
JP 2000-328997 A
[Problems to be solved by the invention]
However, when the fuel pressure drops below the pressure of the high-pressure regulator, if the operation is immediately switched to the intake stroke injection, the engine performance is reduced due to the insufficient amount of air compared to the compression stroke injection, and an area where operation is not possible occurs. There were challenges.
[0010]
Further, a specific means for injecting fuel in the first half of the compression stroke immediately after the intake bottom dead center is not disclosed in the above document.
[0011]
The present invention has been made in view of the above, and it is possible to minimize the time during which a region in which operation cannot be performed by injecting fuel in a compression stroke occurs as much as possible, and to start the injection in an exhaust stroke. It is another object of the present invention to provide a method for controlling the fuel injection timing of a direct injection CNG engine, which can cope with the problem, and can further suppress misfires or the like generated when only the fuel injection timing is changed without switching stratified combustion. I do.
[0012]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, a fuel injection timing control method for a direct injection CNG engine according to the present invention provides a fuel injection method for a direct injection CNG engine that switches between stratified combustion and homogeneous combustion in accordance with engine operating conditions. In the timing control method, when the pressure in the delivery pipe for distributing CNG fuel to the fuel injection valve becomes lower than the target fuel pressure, the combustion is switched to homogeneous combustion in all areas, and the injection is performed from the minimum interval map of ignition and injection. The end crank angle is calculated, the injectable crank angle at the present time is calculated from the in-cylinder pressure map and the fuel pressure defined in advance by the rotation speed and the load, and the calculated both crank angles are compared, and the more advanced angle is calculated. The injection start crank angle is calculated based on the final injection end crank angle and the current fuel pressure. The one in which the features.
[0013]
Therefore, according to the present invention, fuel can be injected in the compression stroke as much as possible, so that the time during which an inoperable region occurs can be minimized.
[0014]
Further, it is possible to cope with the case where the fuel pressure is considerably low, the fuel injection period is long in a region where the load is large, and the start of the injection is the exhaust stroke.
[0015]
Further, misfire or the like that occurs when only the fuel injection timing is changed without switching stratified combustion can be suppressed.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a fuel injection timing control method for a direct injection CNG engine according to the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited by the embodiment.
[0017]
FIG. 1 is a flowchart showing a fuel injection timing control method for an in-cylinder direct injection CNG engine according to an embodiment of the present invention, and FIG. 2 is a map showing an example of a minimum ignition-injection interval map. FIG. 3 is a map diagram showing an example of the in-cylinder pressure map, and is a graph (1) and a map (2) showing the relationship between the in-cylinder pressure and the crank angle.
[0018]
FIG. 4 is a schematic diagram showing the concept of the operating region when the fuel pressure changes, and shows the case where the fuel pressure is normal (1), the case of the prior art when the fuel pressure is low (2), and the present invention when the fuel pressure is low. The case (3) is shown so that it can be compared with the case (3). FIG. 5 is a schematic diagram showing a fuel supply system of a direct injection CNG engine to which the present invention is applied.
[0019]
First, a fuel supply system for a direct injection CNG engine to which the present invention is applied will be described with reference to FIG. As shown in FIG. 5, the CNG engine 10 is of a direct injection type in which CNG fuel is directly injected into a combustion chamber 10a by an injector (fuel injection valve) 17.
[0020]
The CNG engine 10 has basically the same configuration as a normal direct-injection gasoline engine. However, in order to supply CNG fuel, the configuration of a fuel supply system is different from that of the gasoline engine. Is different. The illustration of the configuration of the exhaust system is omitted.
[0021]
The CNG fuel cylinder 12 is for storing the CNG fuel at a high pressure (for example, about 20 MPa at maximum). Although not shown, the CNG fuel cylinder 12 includes a pressure sensor for detecting the pressure in the cylinder and a temperature sensor for detecting the temperature. The CNG fuel cylinder 12 and the delivery pipe 13 of the CNG engine 10 are connected by a fuel supply pipe 14.
[0022]
The delivery pipe 13 is for distributing CNG fuel pressure-fed through a high-pressure regulator 15 described later to each injector 17, and a pressure sensor 13 a for detecting a pressure in the delivery pipe 13, a temperature sensor for detecting a temperature, and the like. The temperature sensor 13b is provided.
[0023]
The fuel supply pipe 14 extending from the CNG fuel cylinder 12 to the injector 17 is provided with a high-pressure regulator 15 for reducing the pressure of the CNG fuel pumped from the CNG fuel cylinder 12 to a predetermined pressure (for example, about 5 MPa). .
[0024]
The CNG engine 10, the injector 17, the high-pressure regulator 15, and the like are based on various sensor information such as a pressure sensor 13a and a temperature sensor 13b of the delivery pipe 13, and a pressure sensor and a temperature sensor (not shown) of the CNG fuel cylinder 12. , And is controlled by an electronic control unit (ECU) (not shown).
[0025]
Next, a method for controlling the fuel injection timing according to the present invention will be described with reference to FIG. As shown in FIG. 1, first, when the CNG engine 10 is started (step S10), it is determined whether or not the injection pressure, which is the pressure in the delivery pipe 13, is lower than the target fuel pressure, which is the pressure of the high-pressure regulator 15. (Step S11).
[0026]
If the injection pressure exceeds the target fuel pressure (No at step S11), the pressure is regulated at a constant pressure by the high-pressure regulator 15 and is controlled based on a preset adaptation value. (Step S18).
[0027]
However, this determination value is set with a certain width in consideration of pressure fluctuations and the like. For example, when the fuel pressure by the high-pressure regulator 15 is 5 MPa, the determination pressure is 4.5 MPa.
[0028]
On the other hand, when the fuel in the CNG fuel cylinder 12 is low and the injection pressure is lower than the target fuel pressure (Yes at Step S11), it is determined whether or not the engine is in the stratified combustion region (Step S12).
[0029]
That is, in such a case, the injection pressure decreases step by step, and a preset normal control value cannot be used. Particularly during stratified combustion, since the injection period and the penetration force of the sprayed fuel change, inconveniences such as misfire easily occur.
[0030]
Therefore, when the injection pressure becomes lower than the target fuel pressure (Yes at Step S11), the occurrence of the above-described trouble such as misfire is suppressed by switching all the combustion regions to the homogeneous combustion (Step S12, Step S13). .
[0031]
Next, the following control is performed so that the fuel can be injected in the compression stroke as much as possible even in the state where the homogeneous combustion is switched as described above.
[0032]
{Circle around (1)} The ignition timing is determined by the rotation speed and load (intake pipe pressure and fuel amount) of the CNG engine 10, and is not affected by the fuel pressure.
[0033]
{Circle around (2)} If the injection end timing and the ignition timing do not have a certain interval, the injected fuel and air are not sufficiently mixed. Also in this case, there is no relation to the fuel pressure.
[0034]
Since the CNG fuel is a gas and does not require a vaporization time, the minimum interval between the end of ignition and the injection is adjusted by a map (see FIG. 2) defined by the rotation speed and the fuel amount, and an electronic control unit (ECU) not shown ).
[0035]
Then, a possible injection end crank angle A is calculated from the injection end-ignition minimum interval map and the injection-ignition interval obtained from the above (1) (step S14).
[0036]
(3) Next, based on the in-cylinder pressure map (see FIG. 3) at the time of motoring and the fuel pressure (injection pressure) defined in advance by the rotation speed and the intake pipe pressure, the injection end crank angle B (injection possible) The crank angle is calculated (step S15).
[0037]
(4) Next, the injection end crank angle A is compared with the injection end crank angle B, and the more advanced angle is defined as the injection end crank angle (final injection end crank angle) (step S16). .
[0038]
(5) Then, an injection start crank angle is calculated from the injection end crank angle and the current fuel pressure (injection pressure), and fuel injection is performed based on the injection start crank angle (step S17).
[0039]
By such control, as shown in FIG. 4, when the fuel pressure is normal (see FIG. 4A), when the fuel pressure is reduced, the control is immediately switched to the first half of the intake stroke injection or the compression stroke injection. , As follows:
[0040]
That is, in the case of the prior art, as shown in FIG. 4 (2), the engine performance is reduced at once due to the shortage of the air amount and the output is reduced as compared with the normal compression stroke injection due to insufficient air volume.
[0041]
On the other hand, in the case of the present invention, as shown in FIG. 4 (3), since the fuel can be injected in the compression stroke as much as possible, the homogeneous combustion region is reduced step by step, and the time during which the inoperable region occurs is reduced. Can be minimized.
[0042]
As described above, according to the fuel injection timing control method for the direct injection CNG engine according to this embodiment, fuel can be injected in the compression stroke as much as possible, so that the time during which an inoperable region occurs is minimized. it can.
[0043]
Further, it is possible to cope with a case where the fuel pressure is considerably low and the fuel injection period is long in a region where the load is large, and the start of the injection is the exhaust stroke.
[0044]
Further, misfire or the like that occurs when only the fuel injection timing is changed without switching stratified combustion can be suppressed.
[0045]
【The invention's effect】
As described above, according to the method for controlling the fuel injection timing of the in-cylinder direct injection CNG engine according to the present invention, fuel can be injected in the compression stroke as much as possible, and the time during which an inoperable region occurs can be minimized. Further, it is possible to cope with a case where the fuel pressure is considerably low and the fuel injection period is long in a region where the load is large, and the start of the injection is the exhaust stroke. Further, misfire or the like that occurs when only the fuel injection timing is changed without switching stratified combustion can be suppressed.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a fuel injection timing control method for a direct injection CNG engine according to an embodiment of the present invention.
FIG. 2 is a map diagram showing an example of a minimum interval map of ignition-injection.
FIG. 3 is a map diagram showing an example of an in-cylinder pressure map.
FIG. 4 is a schematic diagram showing a concept of an operation region when a fuel pressure changes.
FIG. 5 is a schematic diagram showing a fuel supply system of the in-cylinder direct injection CNG engine.
[Explanation of symbols]
Reference Signs List 10 CNG engine 10a Combustion chamber 12 CNG fuel cylinder 13 Delivery pipe 13a Pressure sensor 13b Temperature sensor 14 Fuel supply pipe 15 High pressure regulator 17 Injector (fuel injection valve)

Claims (1)

A fuel injection timing control method for a direct injection CNG engine that switches between stratified combustion and homogeneous combustion according to engine operating conditions,
When the pressure in the delivery pipe for distributing the CNG fuel to the fuel injection valve becomes lower than the target fuel pressure, while switching to homogeneous combustion throughout,
Calculate the injection end crank angle from the minimum interval map of ignition and injection,
Calculate the current injectable crank angle from the in-cylinder pressure map and fuel pressure defined in advance by the rotational speed and load,
By comparing the calculated two crank angles, the more advanced side as the final injection end crank angle,
A fuel injection timing control method for an in-cylinder direct injection CNG engine, comprising calculating an injection start crank angle based on the final injection end crank angle and the current fuel pressure and performing fuel injection.

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