JPH04241754A - Cylinder injection type internal combustion engine - Google Patents

Abstract

PURPOSE:To improve emission and to prevent generation of a smoke by switching combustion from stratified combustion to uniform combustion in a low load rotational region when a combustion temperature is low. CONSTITUTION:An operative condition of an internal combustion engine M1 is detected by an operative condition detecting means M2, and a fuel amount of the internal combustion engine M1 is calculated in accordance with a detection result of the operative condition detecting means M2 by an arithmetic means M3 to determine whether a combustion mode is stratified or uniform combustion. In a fuel injection means M4, fuel is injected directly into a combustion chamber. In a fuel switching correction means M5, when the combustion chamber is at a low temperature, the lower decreased is the temperature the lower in a load rotational region combustion is switched from the stratified combustion to the uniform combustion. When the combustion chamber is at a low temperature, the uniform combustion is performed in a low load rotational region as compared with at the time of high temperature, and in the uniform combustion, injection timing of fuel is advanced earlier than the stratified combustion, so that atomization of combustion is sufficiently performed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection internal combustion engine.

0002

2. Description of the Related Art Japanese Patent Application Laid-Open No. 60-30420 discloses an in-cylinder direct injection type spark ignition engine in which the fuel injection timing is advanced as the load increases. In this engine, during low load operation, fuel is injected near the spark plug in the latter half of the compression stroke to form a combustible air-fuel mixture near the spark plug to ensure good ignition and combustion. During operation, fuel is injected during the first half of the intake stroke, allowing the fuel to diffuse sufficiently into the cylinder to increase air utilization and improve output.

[0003] In this engine, during medium load operation, fuel is injected from the latter half of the intake stroke to the vicinity of the first half of the compression stroke, and this injected fuel is diffused throughout the cylinder. However, the amount of fuel injected during medium-load operation is not as large as during high-load operation, so the mixture formed by the fuel diffused throughout the cylinder becomes too lean, making ignition and combustion difficult. There is.

[0004] To solve this problem, Japanese Patent Application Laid-Open No. 2-16
Publication No. 9834 discloses that when the load is light, fuel is injected into a cavity provided on the top surface of the piston, and the fuel distribution changes from a rich mixture layer to an air layer due to the air flow inside the cavity. An internal combustion engine that generates an air-fuel mixture to achieve stratified combustion is disclosed.

[0005]

[Problems to be Solved by the Invention] However, at low temperatures, the temperature of the piston and the walls of the combustion chamber is low, so the generation of air-fuel mixture is slow, and a sufficient stratified air-fuel mixture is not formed, resulting in poor emissions and the generation of smoke. There was a problem.

[0006] The present invention has been made in view of the above points.
An object of the present invention is to provide a direct injection internal combustion engine that improves emissions and prevents the generation of smoke by switching from stratified combustion to uniform combustion in a low load rotation range when the combustion chamber temperature is low.

[0007]

Means for Solving the Problems FIG. 1 shows a principle diagram of the apparatus of the present invention.

In the figure, the operating state of the internal combustion engine M1 is detected by the operating state detecting means M2, and the calculating means M3 calculates the amount of fuel for the internal combustion engine M1 according to the detection result of the operating state detecting means M2, and performs stratified combustion. Determine the combustion mode: homogeneous combustion.

The fuel injection means M4 injects fuel directly into the combustion chamber. When the temperature of the combustion chamber is low, the combustion switching correction means M5 switches from stratified combustion to uniform combustion in a lower load rotation range as the temperature decreases.

0010

[Operation] In the present invention, when the combustion chamber is low temperature, uniform combustion is performed in a lower load rotation range than when it is high temperature, and in uniform combustion, the fuel injection timing is earlier than in stratified combustion, so that the combustion is sufficiently atomized. It will be held in

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows a sectional view of an embodiment of an internal combustion engine according to the present invention.

In the figure, 1 is a cylinder block, 2 is a piston, 3 is a cylinder head fixed on the cylinder block 1, 4 is a combustion chamber, 5 is an air intake valve, 6 is an exhaust valve, and 7 is an air intake port. , 8 is an exhaust port, 9 is a spark plug, and 10 is a fuel injection valve.

A cavity 15 is formed on the top surface of the piston 2 and extends from below the spark plug 9 to below the tip of the fuel injection valve 10.

Fuel injection control of the above-mentioned internal combustion engine is performed by an electronic control unit 20 shown in FIG.

The electronic control unit 20 has a bidirectional bus 2
ROM (read only memory) 22, RAM (random access memory) 23, C interconnected by 1
PU (microprocessor) 24, backup RAM
25, an input port 26, and an output port 27. A throttle sensor 30 installed in the throttle valve generates an output voltage proportional to the throttle valve opening, a water temperature sensor 31 generates an output voltage proportional to the cooling water temperature, and an intake air temperature sensor 32 generates an output voltage proportional to the temperature of the intake air. Generates a proportional output voltage. The throttle sensor 30, water temperature sensor 31,
The output voltage of each of the intake temperature sensors 32 is determined by the A/D converter 34,
It is supplied to the input port 26 via 35 and 36, respectively.

Furthermore, the input port 26 includes a rotation speed sensor 40 that generates an output signal representing the engine rotation speed NE, and a crank angle sensor 41 that generates an output pulse every time the crankshaft (not shown) rotates by a certain angle. Connected. On the other hand, the output port 27 is connected to the fuel injection valve 10 via a drive circuit 45.

FIGS. 4 and 5 show flowcharts of one embodiment of fuel injection timing control processing. This process is part of the main routine and is executed every few milliseconds.

In the figure, in step 50, the rotational speed NE and throttle opening TA are read, in step 51, the injection timing map shown in FIG. 5 is referred to using the rotational speed NE and throttle opening TA, and in step 52, Injection timings IFTHOTH and IFTHOTS for uniform combustion and stratified combustion are determined from the injection timing map. In the map of FIG. 5, the injection timing IF increases as the rotational speed NE increases.
THOTH, IFTHOTS (unit: angle BT before top dead center)
DC) is large.

Further, the maximum throttle opening value ta2 for performing stratified combustion is larger than the minimum throttle opening value ta1 for uniform combustion, and the throttle opening value ta1 is larger than the minimum value ta1 for performing uniform combustion.
In the range from ta2 to ta2, the injection timing can be determined for both stratified combustion and uniform combustion. In addition, the injection timings IFTHOTH and IFTHOTS are all values in a state where the engine has been warmed up. In step 53, the engine coolant temperature THW is read, in step 54, the injection timing water temperature correction map shown in FIG. 7 is referred to, and in step 55, the injection timing water temperature correction value C
Find IFTTHW (unit: angle before top dead center). The injection timing water temperature correction value CIFTTHW increases in value when the cooling water temperature is low and the temperatures of the piston 2 and the combustion chamber 4 are low.

Thereafter, in step 56, the injection execution timings IFTEXECH and IFTEXECS are determined using the following equations.

[0021]IFTEXECH=IFTHOTHIFT
EXECS=IFTHOTS+CIFTTHW2 in Figure 8
Injection execution timing IFTE in cycle engine
Indicates XECS.

Next, in step 57 of FIG. 5, the combustion switching map shown in FIG. A threshold curve LSHHOT for switching to stratified combustion is determined from . threshold curve H
Hysteresis characteristics are provided by setting two types, SHHOT and LSHHOT.

In step 59, using the water temperature THW,
0 is read, and in step 60, the threshold water temperature correction coefficient CSH for stratified combustion and uniform combustion is read.
Find THWH and CSHTHWL. Step 61
Then, by the following formula, the stratified combustion/uniform combustion correction threshold curve HSH
, LSH, respectively.

[0024]HSH=HSHHOT×CSHTHWHL
SH = LSHHOT x CSHTHWL The threshold water temperature correction coefficient CSHTHWL has a smaller value than the correction coefficient CSHTHWH at low and high temperatures, so the above correction will change the switching from stratified combustion to uniform combustion and change from uniform combustion to stratified combustion as the temperature becomes lower and there are more disturbances. The difference in hysteresis between the switching and the switching becomes wider, and the switching is restricted.

Next, in step 62, it is determined whether or not stratified combustion is currently being performed. If stratified combustion is being performed, step 63 is performed.
Correct the throttle opening TA and rotational speed NE, respectively, by adjusting the throttle opening TAHSH and rotational speed NEHS on the threshold curve HSH.
If the throttle opening TA and rotation speed NE are both large compared to H and are located above the correction threshold curve HSH in FIG. If both numbers NE are small, that is, if the load rotation range is located below the correction threshold curve HSH, the stratified combustion mode is set in step 66. Next, if it is determined in step 62 that stratified combustion is not occurring, that is, uniform combustion is occurring, then in step 64 the throttle opening TA and rotational speed NE are compared with the throttle opening TALSH and rotational speed NELSH on the correction threshold curve LSH. However, if both the throttle opening TA and the rotation speed NE are small and are located below the correction threshold curve LSH in FIG.
In Step 6, the stratified combustion mode is set, and if both the throttle opening degree TA and the rotational speed NE are large and located above the correction threshold curve LSH, the uniform combustion mode is set in Step 65. In step 67, the injection execution timing IFTEXECH or I of the mode set in step 65 or 66 is determined.
Actual injection is started using FTEXECS and the process ends.

[0026] In this way, when the combustion chamber is low temperature, uniform combustion occurs in a low load rotation range compared to when it is high temperature, and in uniform combustion, the fuel injection timing is earlier than in stratified combustion, so that the combustion is sufficiently atomized. It is done. Therefore, emissions are improved and smoke generation can be prevented.

In the above embodiment, the cooling water temperature THW is used to determine the temperature of the combustion chamber 4 to determine the threshold water temperature correction coefficients CSHTHWH, CSHTHWL, but instead of this, the intake air temperature THA is used to determine the correction coefficient CSHTHW.
A threshold intake temperature correction coefficient similar to H, CSHTHWL may be obtained, and the present invention is not limited to the above embodiment.

[0028]

Effects of the Invention As described above, the direct injection internal combustion engine of the present invention can improve the formation of air-fuel mixture, improve emissions, and prevent the generation of smoke, and is extremely useful in practice. be.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is a cross-sectional structural diagram of the internal combustion engine of the present invention.

FIG. 3 is a block diagram of an electronic control unit.

FIG. 4 is a flowchart of fuel injection timing control processing.

FIG. 5 is a flowchart of fuel injection timing control processing.

FIG. 6 is a diagram showing an injection timing map.

FIG. 7 is a diagram showing an injection timing water temperature correction map.

FIG. 8 is a diagram showing IFTEXECS.

FIG. 9 is a diagram showing a combustion switching map.

FIG. 10 is a diagram showing a threshold water temperature correction map.

[Explanation of symbols]

2 Piston 4 Combustion chamber 10 Fuel injection valve 15 Cavity 30 Throttle sensor 31 Water temperature sensor 32 Intake temperature sensor M1 Internal combustion engine M2 Operating state detection means M3 calculation means M4 Fuel injection means M5 Combustion switching correction means

Claims (1)

[Claims] Claim 1: Fuel is directly injected into the combustion chamber, and during small fuel injection, a mixture with uneven fuel distribution is generated in which the air-fuel ratio changes from a rich mixture layer to an air layer in a cavity provided in a piston. In a direct-injection internal combustion engine that performs stratified combustion and produces a mixture with uniform fuel distribution in the piston cavity and combustion chamber during large fuel injection to perform uniform combustion, when the temperature of the combustion chamber is low, A direct injection internal combustion engine characterized by having a combustion switching correction means for switching from stratified combustion to uniform combustion in a load rotation range where the temperature is lower.