JP2751626B2 - In-cylinder direct injection spark ignition engine - Google Patents

Description

The present invention relates to a direct injection type spark ignition engine.

[Conventional technology]

A fuel injection valve for injecting fuel directly into the cylinder is provided.At low load, the ignition plug is directed in the second half of the compression stroke to inject fuel to perform stratified combustion, and at medium / high load, the intake stroke and the second half of the compression stroke. An in-cylinder direct injection spark ignition engine in which fuel is injected to perform weak stratified combustion is disclosed in Japanese Patent Application Laid-Open No. 2-169834.

[Problems to be solved by the invention]

However, in this internal combustion engine, when the engine is cold, the temperature in the cylinder, for example, the wall temperature of the combustion chamber is low, so that the evaporation of the fuel injected into the cylinder is deteriorated, so that it is necessary for ignition and flame propagation. However, there is a problem that the formation of a suitable air-fuel mixture is insufficient and good combustion cannot be obtained.

Also, for example, during acceleration from low load operation,
A similar problem arises due to the relatively low temperature in the cylinder.

[Means for solving the problem]

According to the present invention, in order to solve the above problems, in an internal combustion engine in which fuel is directly injected into a cylinder during a compression stroke so as to be ignited by an ignition plug, fuel injection of a compression stroke injection is performed at a low temperature in the cylinder. The timing is advanced and the ignition timing is advanced.

(Operation)

When the temperature in the cylinder is low, the fuel injection timing of the compression stroke injection is advanced and the ignition timing is advanced. As a result, a flame nucleus is formed at an early stage, and as a result, the temperature in the cylinder becomes higher, so that the evaporation of the fuel is promoted and a good air-fuel mixture can be formed.

〔Example〕

Referring to FIG. 1, 1 is a cylinder block, 2 is a cylinder head, 3 is a piston, 4 is a cylinder chamber, 5 is an intake pipe, and 6 is an exhaust pipe. A linkless throttle valve 7 is arranged in the intake pipe 5. The throttle valve 7 is controlled to be opened and closed by a step motor 8, and is almost fully opened except during idle operation and during deceleration operation. The tip of the fuel injection valve 9 extends to the cylinder chamber 4 and can directly inject fuel into the cylinder chamber.
The fuel injection valve 9 of each cylinder is a common pressure chamber for each fuel injection valve 9.
The pressure storage chamber 10 is connected to a fuel pump 11 and is filled with high-pressure fuel having a substantially constant pressure. The ignition plug 12 is connected to an igniter 14 via a distributor 13.

The electronic control unit 30 is composed of a digital computer, and is connected to a ROM (read only memory) 32 and a RAM (random access memory) by a bidirectional bus 31.
33, a CPU (microprocessor) 34, an input port 35 and an output port 36 are provided. The crank angle sensor 25 for detecting the engine speed is built in the distributor 13, and the output signal of the crank angle sensor 25 is input to the input port 35. Water temperature sensor 26 for detecting engine cooling water temperature
Is connected to the input port 35 via the AD converter 37. An accelerator opening sensor 27 for detecting the depression amount of an accelerator pedal (not shown) is connected to an input port 35 via an AD converter 38.

On the other hand, the output port 36 is connected to the fuel injection valve 9, the igniter 14, and the step motor 8 via the automatic circuits 39, 40, 41, respectively.

FIG. 2 is an enlarged sectional view of the engine body of FIG. Referring to FIG. 2, the concave combustion chamber 20 formed at the top of the piston includes a large-diameter shallow dish 21 on the upper side, and a lower deep dish 22 formed at the center of the shallow dish 21. The deep plate portion 22 is formed to have a smaller diameter than the shallow plate portion 21.

The intake port (not shown) is a swirl port, and the fuel injection valve 9 has a multi-hole hole nozzle. Therefore, the fuel injection valve 9 injects rod-shaped fuel having a relatively strong penetration force and a small spread angle. The fuel injection valve 9 is disposed at the top of the cylinder chamber 4 so as to face diagonally downward. The fuel injection direction and fuel injection timing of the fuel injection valve 9 are determined so that the injected fuel is directed into the combustion chamber 20.
The ignition plug 12 is disposed so as to be located in the concave combustion chamber 20 at the time of the top dead center of the piston 3.

FIG. 3 shows a control pattern of the compression stroke injection and the intake stroke injection. Referring to FIG. 3, the horizontal axis represents the engine load. In FIG. 3, the fuel injection amount Q is taken as the load.
The vertical axis represents the fuel injection amount Q. Until the load region corresponding to the fuel injection amount Q _S, the fuel only during the compression stroke is injected. Compression stroke fuel injection amount is made to gradually increase up to Q _S. In the fuel injection amount Q _S, the compression stroke fuel injection amount is
Intake stroke fuel injection amount with used to lower rapidly to Q _D is caused to abruptly increase to Q _P. Q _S is the fuel injection amount near the medium load, as the sum of the Q _D and Q _P shown by the following equation.

Here _{Q S = Q D + Q P} , Q D is the least compression stroke fuel injection amount capable of forming a ignitable mixture by the spark plugs 12, Q _P is fuel cylinder chamber which is injected in the intake stroke This is the minimum intake stroke fuel injection amount that allows the ignition fire by the spark plug 12 to propagate when it is homogeneously diffused into the inside 4.

In a load region in which the fuel injection amount is larger than Q _S and smaller than Q _H , the entire fuel injection amount Q is divided into a compression stroke and an intake stroke, and the fuel is injected. The stroke fuel injection amount is increased as the load increases.

In the fuel injection amount Q _H greater load range, because the concentration of the premixed gas in the cylinder chamber formed by the intake stroke injection for the fuel injection amount is large deep enough to ignition, the compression stroke injection for the ignition And the entire required fuel injection amount is injected in the intake stroke.
Q _H is minimal intake stroke fuel injection amount that can form a uniform mixture which can be ignited by a spark plug even when the fuel is homogeneously diffused in the cylinder chamber.

FIG. 4 is a diagram showing the fuel injection control pattern of FIG. 3 in the relationship between load and crank angle.

Referring to FIG. 2 again, in the lower load range than the near medium load Q _S, the total amount of the required injection quantity toward the combustion chamber 20 from the fuel injection valve 9 is injected in the compression stroke later. The fuel injection timing is delayed so that most of the fuel is injected into the deep dish 22. The fuel adhering to the inner wall surface of the deep dish portion 22 evaporates and atomizes, and forms a dense and mixed gas layer including a combustible region in the combustion chamber 20. A part of the air-fuel mixture layer is ignited by the ignition plug 12, and good combustion is completed mainly in the deep dish portion 22.

In a load region higher than Q _{S and} lower than Q _H near the middle load, as shown in FIG. 5, the intake stroke injection is executed at the beginning of the intake stroke (FIG. 5 (a)), Fuel is injected toward the chamber 20. The injected fuel F collides downwardly with the shallow plate portion 21, a part of which is reflected into the cylinder chamber 4, and another portion adheres to the wall surface of the shallow plate portion 21 and is evaporated and atomized by heating from the wall surface. In these fuels, a premixed gas P is formed during the period from the intake stroke to the compression stroke due to the intake vortex SW and the turbulence R of the intake flow. (FIG. 5 (b)). The air-fuel ratio of the premixed air P is set to such an extent that the ignition flame can propagate. When the suction vortex SW is strong, a premixed gas is formed such that the area around the outer periphery of the cylinder chamber 4 is dense and the area near the center is thin.

If the fuel is injected when the piston 3 is located closer to the top dead center when the intake stroke injection timing is advanced, most of the fuel is injected into the deep dish portion 22, and most of the fuel is injected into the deep dish portion 22. It is premixed and vaporized in the section 22.

Subsequently, compression stroke injection is performed in the latter half of the compression stroke (FIG. 5 (c)), and most of the fuel is injected into the deep dish portion 22.
The fuel adhering to the inner wall surface of the deep dish portion 22 is vaporized by pressurization from the wall surface and the compressed air, and is diffused and mixed by the vortex SW, thereby forming a heterogeneous mixed gas layer including a combustible region. A part of the air-fuel mixture layer is ignited by the ignition plug 12, and the combustion of the heterogeneous air-fuel mixture proceeds (FIG. 5 (d)). In the process of developing the flame B formed by this combustion in the deep dish portion 22,
Propagation to the surrounding premixed gas, and furthermore, the combustion proceeds to the outside of the deep dish portion 22 by the reverse squish flow S.

When the compression stroke injection timing is advanced and fuel is injected into both the shallow plate portion 21 and the deep plate portion 22, the flame is widely distributed in the shallow plate portion 21 and the deep plate portion 22, and the flame is diffused into the premixed gas. Flame propagation can be made easier.

By the way, in such an internal combustion engine, when the engine is cold, the temperature in the cylinder, for example, the wall temperature of the combustion chamber 20 is low, so that the evaporation of the fuel injected into the cylinder is deteriorated. However, the formation of an air-fuel mixture required for the combustion becomes insufficient, so that good combustion cannot be obtained.

Further, since the temperature in the cylinder decreases as the fuel injection amount decreases, the temperature in the cylinder relatively decreases during acceleration after a low-load operation, causing the same problem as described above.

Therefore, in this embodiment, when the temperature in the cylinder is low, the fuel injection timing of the compression stroke injection is advanced and the ignition timing is advanced. That is, as shown in FIG. 4, when the temperature in the cylinder is low, the compression stroke injection timing and the ignition timing are advanced as shown by the solid line, when the temperature in the cylinder is not low (indicated by the dotted line). Have been.

As a result, the flame nucleus is formed early, and the temperature in the cylinder becomes higher in combination with the heat generated by the gas compression in the compression stroke, so that the evaporation of fuel can be promoted. As a result, a good air-fuel mixture can be formed, and thus good combustion can be obtained.

FIG. 6 shows a routine for executing this embodiment. This routine is executed by interruption every fixed crank angle. Referring to FIG. 6, first, in step 60, the total fuel injection amount gain Q is calculated from a map of the accelerator depression amount and the engine speed. Then the compression stroke fuel injection amount Q _C from the map of the total fuel injection amount Q and the engine speed at step 61 is calculated. Next, at step 62 stroke compression from the compression stroke fuel injection amount Q _C and the engine speed of the map fuel injection timing A _C is calculated. Next, at step 63, the ignition timing _Ig is calculated from the map of the total fuel injection amount Q and the engine speed. In step 64, it is determined whether or not the engine cooling water temperature TW is 70 ° C. or higher, that is, whether or not the engine is cold. If TW <of 70 ° C., i.e. at the time of engine cold flow proceeds to step 67, the compression stroke fuel injection amount Q _C is determined whether 0 or not. Q _C ≠
0, that is, when the compression stroke injection is performed, advance amount X of the compression stroke fuel injection timing A _C is calculated proceeds to step 68. Next, at step _S , X is added to the compression stroke fuel injection timing AC, and the fuel injection timing is advanced by the advance amount X. Here, the compression stroke fuel injection timing _AC is an angle measured from the compression top dead center to the intake bottom dead center. Then advance amount Y of step 70 the ignition timing I _g is calculated. Then Y is added to the ignition timing I _g In step 71, it is caused to only advance amount Y advance.

On the other hand, if it is determined that Q _C = 0 in step 67,
That is, when the compression stroke injection is not executed, the ignition timing I _g is made to advance in step 70 and step 71.

On the other hand, if it is determined in step 64 that TW ≧ 70 ° C.,
The process proceeds to step 65, the average fuel injection quantity Q _A is calculated by the following equation.

Q _A = [sum] Q _n / n [sum] Q _n, where denotes the nearest sum of total fuel injection quantity Q of past n times the current, thus calculating the average fuel injection quantity of the past n times by [sum] Q _n / n Can be. Cylinder temperature is higher the larger the fuel injection amount, thus Q _A is indirectly indicates cylinder temperature. That means that Q _A is low indicates that the cylinder temperature is low. Then calculating the difference in step 66 and this total fuel injection amount Q and the average fuel injection quantity Q _A. When Q-Q _A exceeds a predetermined value, for example, 15 mm ³ or more, it indicates that the temperature in the cylinder is relatively low. For example, when the acceleration operation is performed from the low load operation, Q−Q _A > 15. Also in this case, there is a problem that good ignition and combustion cannot be obtained as in the case of cold engine. Therefore, when Q−Q _A > 15, the routine proceeds to step 67 and below, and when the compression stroke injection is executed, the compression stroke fuel injection timing _AC and the ignition timing I _g
If the compression stroke injection is not executed, only the ignition timing is advanced.

On the other hand, if it is determined that Q−Q _A ≦ 15, the present routine ends. That compression stroke fuel injection timing A _C and the ignition timing I _g if the cylinder is not at a low temperature is not allowed to advance.

In the present embodiment, the intake stroke injection and the compression stroke injection are executed by one fuel injection valve 9, but two fuel injection valves are provided, and one of the fuel injection valves executes the intake stroke injection. At the same time, the compression stroke injection may be executed by the other fuel injection valve.

〔The invention's effect〕

Since a good air-fuel mixture can be formed even at a low temperature in the cylinder, a good fuel can be obtained.

[Brief description of the drawings]

1 is an overall view of an internal combustion engine, FIG. 2 is a longitudinal sectional view of an engine body, FIG. 3 is a diagram showing an example of a control pattern of compression stroke injection and intake stroke injection, and FIG. FIG. 5 is a diagram showing a control pattern as a relationship between load and crank angle, FIG. 5 is an explanatory diagram showing a state of fuel injection, and FIG. 6 is a flowchart for calculating a compression stroke fuel injection timing and an ignition timing. 4 ... cylinder chamber, 9 ... fuel injection valve, 12 ... spark plug, 26 ... water temperature sensor.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 43/00 301 F02D 43/00 301B F02P 5/15 F02P 5/15 B

Claims (1)

(57) [Claims] In an internal combustion engine in which fuel is directly injected into a cylinder during a compression stroke to be ignited by an ignition plug, when the temperature in the cylinder is low, the fuel injection timing of the compression stroke injection is advanced and the ignition timing is adjusted. In-cylinder direct injection spark ignition engine with advanced timing.