JP2004353453A - Fuel supply system of cylinder direct injection cng engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimally switch between a stratified combustion and a homogeneous combustion according to the operating state of an engine by maximally making use of the merit of the injection of high-pressure fuel. <P>SOLUTION: This fuel supply system of a CNG engine comprises an injector 17, a delivery pipe 13, and a pressure sensor 13a detecting pressure in the delivery pipe 13, and is formed to be switchable between the stratified combustion and the homogeneous combustion. A pressure reduction system (high-pressure regulator) for reducing the pressure of the CNG fuel is eliminated from a fuel supply line 14 and, based on the pressure in the delivery pipe 13, a pre-determined combustion map area is selected and, based on a control method pre-determined in the combustion map area, combustion is switched between the stratified combustion and the homogeneous combustion. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel supply system for an in-cylinder direct injection CNG engine having a stratified lean burn operation region by directly injecting compressed natural gas (CNG) into a cylinder, and more particularly to the advantages of high-pressure fuel injection. The present invention relates to a fuel supply system for an in-cylinder direct injection CNG engine capable of optimally switching between stratified combustion and homogeneous combustion in accordance with the operating state of the CNG engine by making the most of the above.
[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 having a lean burn operation region (hereinafter, appropriately referred to as CNG engines) have been actively developed, and various technologies have been proposed.
[0003]
Such an in-cylinder direct injection CNG engine usually includes a CNG fuel cylinder for storing CNG fuel, a fuel injection valve for directly injecting CNG fuel into each cylinder, and a high pressure accumulating CNG fuel for each fuel injection valve. A delivery pipe for distributing, a pressure sensor for detecting the pressure in the delivery pipe, and a high-pressure regulator (a pressure reducing system) provided in the middle of a fuel supply pipe connecting the CNG fuel cylinder and the delivery pipe, for reducing the pressure of the CNG fuel to a predetermined pressure. ), And can be switched between stratified combustion and homogeneous combustion.
[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 a low pressure of 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]
In addition, as another related art, for example, a gas fuel injection device that injects gas fuel into an intake port, that is, a gas fuel injection device that adjusts a fuel pressure guided to a fuel injection valve stepwise according to engine operating conditions is known. It has been proposed (see Patent Document 1). Further, a technique has been proposed that can maintain a stable combustion state even when the fuel injection pressure changes (see Patent Document 2).
[0007]
[Patent Document 1]
JP-A-8-284703 [Patent Document 2]
Japanese Patent Application Laid-Open No. H11-271313
[Problems to be solved by the invention]
However, in the above-described prior art, since the CNG fuel discharged from the CNG fuel cylinder is depressurized by the high-pressure regulator, the merit of directly injecting the CNG fuel into the cylinder at a high pressure cannot be maximized. In other words, if CNG fuel can be injected at high pressure, the fuel injection period can be shortened and compression stroke injection can be performed, so that stratified combustion can be expanded to achieve high fuel efficiency. The advantage that the output increases even in combustion cannot be used to the utmost.
[0009]
When the pressure of the CNG fuel is regulated at a relatively high pressure, the advantage of the high pressure injection described above can be obtained. Due to the shortage, combustion when the injection amount is small may not be established.
[0010]
Further, in the pressure reducing system using the high-pressure regulator and the opening and closing of the electromagnetic valve, the fuel supply system becomes complicated, and there is a possibility that responsiveness to a transient state or the like cannot be secured.
[0011]
The present invention has been made in view of the above, and has the advantage of high-pressure fuel injection to the utmost, and is capable of optimally switching between stratified combustion and homogeneous combustion in accordance with the operating condition of a CNG engine. An object of the present invention is to provide a fuel supply system for a CNG engine.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a fuel supply system for a direct injection CNG engine according to the present invention includes a fuel injection valve provided in a combustion chamber for injecting CNG fuel, and the CNG pressure-fed from a CNG fuel cylinder. Fuel supply for an in-cylinder direct injection CNG engine including a delivery pipe for distributing fuel to the fuel injection valve, and a pressure sensor for detecting a pressure in the delivery pipe, and configured to be able to switch between stratified combustion and homogeneous combustion. In the system, a pressure reducing system for reducing the pressure of the CNG fuel is eliminated in a fuel supply line from the CNG fuel cylinder to the fuel injection valve, and a predetermined combustion map area is selected based on the pressure in the delivery pipe. And switching between stratified combustion and homogeneous combustion based on a control method predetermined in the combustion map area. It is characterized in that the form.
[0013]
Therefore, according to the present invention, since there is no pressure reducing system, the advantages of high pressure fuel injection can be maximized, and stratified combustion and homogeneous combustion can be optimized based on the combustion map area according to the operating condition of the CNG engine. You can switch to
[0014]
Further, the fuel supply system for a direct injection CNG engine according to the present invention is provided with a plurality of fuel injection valves in the combustion chamber, and selectively uses some or all of the fuel injection valves based on the pressure in the delivery pipe. The CNG fuel is injected using the fuel injection valve of (1).
[0015]
Therefore, according to the present invention, even if the fuel injection valves have a narrow dynamic range, the required fuel injection amount can be ensured by selectively using them based on the pressure in the delivery pipe. It can handle a wide range from low pressure to high pressure.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a fuel supply system 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]
Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing a fuel supply system of a direct injection CNG engine according to Embodiment 1 of the present invention. As shown in FIG. 1, the CNG engine 10 is a direct injection type in which CNG fuel is directly injected into a combustion chamber 10a by an injector (fuel injection valve) 17, and is configured to be capable of switching between stratified combustion and homogeneous combustion. The injector 17 has a wide dynamic range covering a required minimum injection amount to a maximum injection amount.
[0018]
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.
[0019]
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 (fuel supply line) 14.
[0020]
The delivery pipe 13 is for distributing the CNG fuel pumped by the fuel supply pipe 14 to each of the injectors 17, and includes a pressure sensor 13a for detecting the pressure in the delivery pipe 13 and a temperature sensor for detecting the temperature. The sensor 13b is provided.
[0021]
The fuel supply pipe 14 is not provided with a high-pressure regulator (decompression system) for adjusting the CNG fuel pressure-fed from the CNG fuel cylinder 12 to the delivery pipe 13 to a predetermined pressure. This point is greatly different from the fuel supply system of the conventional in-cylinder direct injection CNG engine.
[0022]
The fuel supply pipe 14 immediately before the delivery pipe 13 is provided with a shut-off valve 16 that is normally opened and closed when necessary, such as during depressurization control. The reason for performing this pressure release control is as follows.
[0023]
That is, when the CNG engine 10 is stopped (ignition switch is turned off), pollutants (compressor oil and the like) contained in the CNG fuel adhere to the inside of the injector 17 and the seal portion, and the malfunction of the injector 17 and the start of the CNG engine 10 are started. This is because there is a possibility that a defect may occur, and in order to suppress this, it is necessary to extract the CNG fuel remaining in the delivery pipe 13 after the CNG engine 10 stops.
[0024]
Therefore, in this pressure release control, after the CNG engine 10 is stopped, the shutoff valve 16 is closed, new fuel supply to the delivery pipe 13 is shut off, and the CNG engine 10 is rotated for a predetermined time, and the pressure in the delivery pipe 13 is reduced. The remaining CNG fuel may be injected into the combustion chamber 10a by the injector 17 and consumed. By providing the shut-off valve 16 in this manner, the pressure release control of the delivery pipe 13 can be easily performed.
[0025]
The CNG engine 10, the injector 17, the shutoff valve 16, and the like are controlled by an electronic control unit (ECU) (not shown) based on various types of sensor information such as the pressure sensor 13a and the temperature sensor 13b.
[0026]
Next, a control method of the fuel supply system of the CNG engine 10 will be described with reference to FIGS. Here, FIG. 2 is a flowchart illustrating a control method of the fuel supply system of the CNG engine 10, and FIG. 3 is a map diagram illustrating a combustion map area prepared according to the pressure in the delivery pipe 13.
[0027]
FIG. 4 is a conceptual diagram showing an example of control contents in a selected combustion map area. FIG. 5 is a graph showing the ranges of stratified combustion and homogeneous combustion established for each combustion map area. FIG. 5 (1) shows an example of the combustion range of the combustion map area A, and FIG. An example of the combustion range of the map area B is shown.
[0028]
As shown in FIG. 2, first, the pressure in the delivery pipe 13 is measured by the pressure sensor 13a (Step S10). Next, a combustion map area (A, B, C,...) Corresponding to the measured pressure value is selected from the map shown in FIG. 3 (step S11).
[0029]
As shown in FIG. 3, the combustion map areas (A, B, C,...) Are finely set in advance in a range which is corrected but basically achieved by the same control. That is, the fuel injection pressure (the pressure in the delivery pipe 13) gradually decreases as the fuel in the CNG fuel cylinder 12 is consumed, so that various pressures (for example, 20 MPa to 19 MPa, 19 MPa to 18 MPa, 18 MPa to 17 MPa,. ..) are set for the combustion map areas (A, B, C,...).
[0030]
Further, as shown in FIG. 4, for each of the combustion map areas (A, B, C,...), Control for switching between stratified combustion and homogeneous combustion, and each parameter map (for example, fuel The map of injection period, fuel injection timing, ignition timing, etc.) is previously set finely. With this setting, stratified charge combustion with poor robustness (for example, if the fuel injection amount is changed and the injection timing, ignition timing, etc. are not changed, combustion is not achieved) can be accurately controlled.
[0031]
In the related art, as described above, since the pressure in the delivery pipe is reduced to a constant pressure (for example, a low pressure of about 5 MPa) by the high-pressure regulator, a combustion map corresponding to the one pressure value is set in advance. This does not mean that many combustion map areas are set for each pressure as in the present invention.
[0032]
Next, following step S11, the control logic in the selected combustion map area switches between stratified combustion and homogeneous combustion (step S12). That is, optimal combustion control is performed by using a preset parameter map (for example, a map of a fuel injection period, a fuel injection timing, an ignition timing, etc.) for each combustion according to the load and the rotation state of the CNG engine 10. (See FIG. 4).
[0033]
Further, as described above, the fuel supply pipe 14 is not provided with the high-pressure regulator for reducing the pressure of the CNG fuel sent from the CNG fuel cylinder 12 to the delivery pipe 13. Therefore, the high-pressure CNG fuel pressure-fed from the CNG fuel cylinder 12 can be directly injected from the injector 17 into the combustion chamber 10a.
[0034]
That is, as the injection pressure is higher, a larger amount of CNG fuel can be injected in a compression stroke in a shorter injection period, so that stratified charge combustion can be achieved up to a high load and high revolution range (for example, FIG. 5 (1)). See), and fuel efficiency can be improved.
[0035]
Further, when CNG fuel is directly injected into the combustion chamber 10a during the intake stroke, the intake of fresh air is hindered by the injected CNG fuel, and the amount of fresh air intake is reduced accordingly. Decreases.
[0036]
On the other hand, in the first embodiment, since the injection pressure can be increased as described above, injection can be performed in a wide range at an early stage of the compression stroke, the intake air amount can be secured, and the output can be improved even in homogeneous combustion. Can be done.
[0037]
As described above, according to the fuel supply system of the in-cylinder direct injection CNG engine according to the first embodiment, the advantages of the high-pressure fuel injection are maximized, and the stratified combustion and the homogeneous The combustion can be switched optimally.
[0038]
In particular, stratified charge combustion with poor robustness can be achieved up to a high load and high speed range, and fuel efficiency can be improved. Further, since the injection pressure can be increased, it is possible to perform injection in a wide range at an early stage of the compression stroke, to secure an intake air amount, and to improve output even in homogeneous combustion.
[0039]
Further, according to the fuel supply system of the in-cylinder direct injection CNG engine, although the software aspects such as adaptation of control and combustion parameters are more complicated than those of the prior art, the hardware aspects of the fuel supply system are not. Since no pressure reducing system such as a high-pressure regulator is provided, the entire system can be simplified.
[0040]
That is, since the pressure reducing system is not provided, the residual pressure of the CNG fuel cylinder 12 can be effectively used, and the cruising distance can be extended. In addition, it is possible to ensure responsiveness to transitions (for example, during deceleration and acceleration) in combustion control, and to achieve cost reduction by greatly reducing the number of parts.
[0041]
In the first embodiment, the shut-off valve 16 is provided so that the supply of the CNG fuel can be shut off when necessary. However, since the pressure release control using the shut-off valve 16 is not performed, If there is, the injector 17 itself has a fuel shut-off function, so that the shut-off valve 16 is not necessarily provided.
[0042]
Further, in the first embodiment, the present invention is applied to the four-cylinder CNG engine 10 as an example. However, the present invention is not limited to this, and may be applied to a CNG engine having a number of cylinders other than four. The same effect can be expected.
[0043]
Embodiment 2 FIG.
FIG. 6 is a schematic diagram showing a fuel supply system for a direct injection CNG engine according to Embodiment 2 of the present invention. In the following description, members that are the same as or correspond to those already described are denoted by the same reference numerals, and redundant description is omitted.
[0044]
As shown in FIG. 6, a pair of a first injector 17a and a second injector 17b are arranged in each combustion chamber 10a to face each other, and a fuel supply pipe 14, a delivery pipe 13, and the like for supplying CNG fuel thereto are provided. It was done. In the combustion chamber 10a, for example, the first injector 17a is arranged on the intake side, and the second injector 17b is arranged on the exhaust side.
[0045]
This fuel supply system uses either one of the pair of opposed injectors 17a and 17b based on the pressure in the delivery pipe 13 as shown below, or uses both of them to provide the required fuel. The configuration is such that the injection amount can be secured.
[0046]
That is, first, a control example in the case of performing fuel injection on the low pressure side will be described. For example, when the first injector 17a can inject from the minimum injection amount to the maximum injection amount at a predetermined low pressure and the second injector 17b can inject at a lower injection amount than the first injector 17a, the delivery pipe 13 Is higher than the predetermined low pressure value, the minimum injection amount by the first injector 17a is too large. Therefore, the minimum injection amount is secured by switching from the first injector 17a to the second injector 17b.
[0047]
Next, a control example in the case of performing fuel injection on the high pressure side will be described. For example, when the first injector 17a is capable of injecting a minimum injection amount to a maximum injection amount at a predetermined high pressure and the second injector 17b is capable of injecting a higher injection amount, the pressure in the delivery pipe 13 is reduced to the predetermined value. If the pressure drops below the high pressure value, the first injector 17a cannot perform the injection with the maximum injection amount, so that the required injection amount cannot be injected within the predetermined time. Therefore, the required injection amount is secured by switching from the first injector 17a to the second injector 17b, or the use is switched to use of both the injectors 17a, 17b, and the required injection amount is appropriately shared by the two injectors 17a, 17b to perform injection. As a result, the required injection amount is secured.
[0048]
As described above, by selectively using one of the two injectors 17a and 17b based on the pressure in the delivery pipe 13 or using both of them, the required fuel injection amount can be secured, and the low pressure can be maintained. Can handle a wide range up to high pressure.
[0049]
The control operation of the whole system is the same as that of the first embodiment except that the two injectors 17a and 17b are selectively used, and thus the duplicated description will be omitted.
[0050]
As described above, according to the fuel supply system of the in-cylinder direct injection CNG engine according to the second embodiment, one of the two injectors 17a and 17b is selectively used based on the pressure in the delivery pipe 13. Alternatively, by using both, the required fuel injection amount can be secured, and a wide range from low pressure to high pressure can be handled.
[0051]
Therefore, even if the injectors 17a and 17b have a narrow dynamic range, the injectors 17a and 17b can cope with a wide range from a low pressure to a high pressure, and the installation of the injector having a wide dynamic range is not required. Downsizing can be achieved, and the same effect as in the first embodiment can be expected.
[0052]
In the second embodiment, in the combustion chamber 10a, one of the two injectors 17a and 17b is disposed on the intake side, and the other second injector 17b is disposed on the exhaust side. However, the present invention is not limited to this. For example, two injectors may be provided near the intake side of the combustion chamber 10a and near the center of the ignition plug, and three or more injectors may be provided. It may be arranged on any one of the intake side, the central part, and the exhaust side of the combustion chamber 10a. Also in these cases, each injector is selectively used based on the pressure in the delivery pipe 13 and the required fuel injection amount is ensured in the same manner as in the second embodiment, thereby reducing the low pressure. From high pressure to high pressure.
[0053]
【The invention's effect】
As described above, according to the fuel supply system of the in-cylinder direct injection CNG engine according to the present invention, the CNG fuel pressure reducing system is eliminated in the fuel supply line from the CNG fuel cylinder to the fuel injection valve, and the pressure in the delivery pipe is reduced. The selected combustion map area is selected on the basis of the above, the stratified combustion and the homogeneous combustion are switched based on a predetermined control method in the combustion map area, so that the merit of the high-pressure fuel injection is maximized. Thus, it is possible to optimally switch between stratified combustion and homogeneous combustion in accordance with the operating conditions of the CNG engine.
[0054]
In particular, stratified charge combustion with poor robustness can be achieved up to a high load and high speed range, and fuel efficiency can be improved. Further, since the injection pressure can be increased, the compression stroke injection can be performed over a wide range, and the output can be improved even in homogeneous combustion.
[0055]
Further, regarding the hardware aspect of the fuel supply system, since a pressure reducing system such as a high pressure regulator is not provided, the residual pressure of the CNG fuel cylinder can be effectively used, and the cruising distance can be extended. Further, since the entire system can be simplified, responsiveness to a transition time or the like in combustion control can be ensured, and cost can be reduced by drastically reducing the number of parts.
[0056]
Further, according to the fuel supply system of the direct injection CNG engine according to the present invention, a plurality of fuel injection valves are provided in the combustion chamber, and these fuel injection valves are selectively used based on the pressure in the delivery pipe. Since the fuel injection valve is configured to perform the fuel injection, the required fuel injection amount can be ensured even for a fuel injection valve having a narrow dynamic range, and a wide range from low pressure to high pressure can be handled. Further, since it is not required to install a fuel injection valve having a wide dynamic range, the design of the fuel injection valve is facilitated, and the cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a fuel supply system of a direct injection CNG engine according to Embodiment 1 of the present invention.
FIG. 2 is a flowchart illustrating a control method of a fuel supply system of a CNG engine.
FIG. 3 is a map diagram showing a combustion map area prepared according to the pressure in a delivery pipe.
FIG. 4 is a conceptual diagram showing an example of control contents in a selected combustion map area.
FIG. 5 is a graph showing ranges of stratified combustion and homogeneous combustion established for each combustion map area.
FIG. 6 is a schematic diagram showing a fuel supply system of an in-cylinder direct injection CNG engine according to Embodiment 2 of the present invention.
[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 (fuel supply line)
16 shut-off valve 17 injector (fuel injection valve)
17a 1st injector (fuel injection valve)
17b 2nd injector (fuel injection valve)

Claims (2)

A fuel injection valve provided in the combustion chamber for injecting CNG fuel;
A delivery pipe for distributing the CNG fuel pumped from a CNG fuel cylinder to the fuel injection valve;
A pressure sensor for detecting the pressure in the delivery pipe,
In a fuel supply system of an in-cylinder direct injection CNG engine configured to be capable of switching between stratified combustion and homogeneous combustion,
Eliminate a pressure reducing system for reducing the pressure of the CNG fuel in a fuel supply line from the CNG fuel cylinder to the fuel injection valve,
It is configured to select a predetermined combustion map area based on the pressure in the delivery pipe, and to switch between stratified combustion and homogeneous combustion based on a control method predetermined in the combustion map area. A direct fuel injection CNG engine fuel supply system. A plurality of fuel injection valves are provided in the combustion chamber, and some of the fuel injection valves are selectively used based on the pressure in the delivery pipe, or the CNG fuel is injected using all the fuel injection valves. The fuel supply system for an in-cylinder direct injection CNG engine according to claim 1, wherein:

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