JP2513004B2 - In-cylinder direct injection spark ignition engine - Google Patents

Description

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

[Conventional technology]

In JP-A-62-191622, a concave combustion chamber is formed at the top of the piston, and this combustion chamber is provided with a shallow dish and a deep dish having a diameter smaller than that of the shallow dish formed near the center of the shallow dish. It has a two-layer structure with the first part, the first fuel injection that is injected by penetration force toward the upper part of the shallow plate part of the combustion chamber from the intake stroke to the first half of the compression stroke, and the deep plate of the combustion chamber near the compression top dead center. It is possible to perform a second fuel injection with a high penetration force to the engine portion, and to execute the first and second fuel injections during engine high load operation, and to perform only the second fuel injection during low and medium load operation. A direct injection type spark ignition engine is disclosed.

[Problems to be Solved by the Invention]

However, this engine has a problem that the transient performance is not good because the in-cylinder temperature does not follow the change of the load during the transient operation of changing the load. That is, during steady engine operation, the in-cylinder temperature is a substantially constant temperature determined by the fuel injection amount. During steady-state operation, the steady-state in-cylinder temperature rises as the fuel injection amount increases. From steady operation, for example, when the load decreases and the fuel injection amount decreases, the in-cylinder temperature cannot follow the decrease in the fuel injection amount, so the in-cylinder temperature corresponds to the decreased fuel injection amount. Constantly higher than the in-cylinder temperature. As a result, the temperature of the combustion chamber wall becomes high, the evaporation of the fuel adhering to the wall surface of the combustion chamber is promoted, and the mixture formation is accelerated. Therefore, the time from when the air-fuel mixture is formed to when it is ignited becomes long, the air-fuel mixture is caused to flow into the air flow, and a thin region is generated, which makes combustion unstable. In particular, when the load is reduced from the steady operation at the output air-fuel ratio to reduce the injection amount and the amount becomes close to the stoichiometric air-fuel ratio, the air-fuel mixture that is easy to ignite is formed early and knocking occurs. On the other hand, for example, when the load increases and the fuel injection amount increases, the in-cylinder injection temperature transiently becomes lower than the steady-state in-cylinder temperature corresponding to the increased fuel injection amount. For this reason, the temperature of the combustion chamber wall becomes low, the evaporation of the fuel adhering to the wall surface of the combustion chamber becomes insufficient, and a rich region is generated, which causes smoke and a reduction in output.

[Means for solving the problem]

According to the present invention to solve the above problems, in a direct injection type spark ignition engine for a cylinder, which directly injects a required fuel injection amount according to an engine operating state into an intake stroke and a compression stroke,
During the decrease transient operation where the load decreases, the fuel injection ratio, which is the ratio of the intake stroke fuel injection amount to the compression stroke fuel injection amount, is made smaller than the fuel injection ratio during the steady operation at the same load as the decrease transient operation, or the load The fuel injection ratio is made to be larger than the fuel injection ratio at the time of steady operation with the same load as at the time of increasing transient operation during the increasing transient operation.

[Action]

During the reduced transient operation in which the load decreases, the fuel injection ratio (= intake stroke fuel injection amount / compression stroke fuel injection amount) is made smaller than the fuel injection ratio in the steady operation with the same load as during the reduced transient operation, that is, The ratio of the intake stroke fuel injection amount is reduced. As a result, the mixture formation is suppressed.

On the other hand, during the increased transient operation where the load increases, the fuel injection ratio is made larger than the fuel injection ratio during the steady operation of the same load as during the increased transient operation, that is, the ratio of the intake stroke fuel injection amount is increased. As a result, the mixture formation is promoted.

〔Example〕

FIG. 1 is a block diagram of a four-cylinder gasoline engine that employs an embodiment of the present invention. In the figure, 1 is the engine body, 2
Is a surge tank, 3 is an air cleaner, 4 is an intake pipe connecting the surge tank 2 and the air cleaner 3, 5 is an electrostrictive fuel injection valve for injecting fuel into each cylinder, 6 is a high pressure reservoir tank, and 7 is high pressure. Discharge pressure controllable high-pressure fuel pump for pumping high-pressure fuel to reservoir tank 6 via conduit 8, 9 is a fuel tank, 10 is fuel from fuel tank 9 to high-pressure fuel pump 7 via conduit 11. Each low pressure fuel pump is shown. The discharge side of the low-pressure fuel pump 10 is connected to a piezoelectric element cooling introduction pipe 12 for cooling the piezoelectric element of each fuel injection valve 5. The piezoelectric element cooling return pipe 13 is connected to the fuel tank 9, and the fuel flowing through the piezoelectric element cooling introduction pipe 12 is collected in the fuel tank 9 through the return pipe 13. Each branch pipe 14 connects each fuel injection valve 5 to the high pressure reservoir tank 6.

The electronic control unit 20 is composed of a digital computer, and has a ROM (Read Only Memory) 22, a RAM (Random Access Memory) 23, a CPU (Microprocessor) 24, an input port 25, which are mutually connected by a bidirectional bus 21.
And an output port 26. The pressure sensor 27 attached to the high pressure reservoir tank 6 detects the pressure P in the high pressure reservoir tank 6, and the detection signal is input to the input port 25 via the A / D converter 28. Engine speed Ne
The output pulse of the crank angle sensor 29 that generates an output pulse proportional to is input to the input port 25. An output voltage of an accelerator opening sensor 30 that generates an output voltage according to an opening θA of an accelerator pedal (not shown) is input to an input port 25 via an A / D converter 31. On the other hand, each fuel injection valve 5 is connected to the output port 26 via each drive circuit 34 to 37. Further, the high-pressure fuel pump 7 is connected to the output port 26 via the drive circuit 38.

FIG. 2 shows a side sectional view of the fuel injection valve 5. Referring to FIG. 2, reference numeral 40 denotes a needle inserted into a nozzle 50;
Is a pressure rod, 42 is a movable plunger, 43 is a spring chamber 44
A compression spring, which is arranged inside and presses the needle 40 downward, 45 is a pressure piston, 46 is a piezoelectric element, 47 is formed between the top of the movable plunger 42 and the piston 45 and is filled with fuel. The pressure chamber and 48 are needle pressurizing chambers, respectively. The needle pressurizing chamber 48 is connected to the high pressure reservoir tank 6 (FIG. 1) via the fuel passage 49 and the branch pipe 14, so that the high pressure fuel in the high pressure reservoir tank 6 passes through the branch pipe 14 and the fuel passage 49. Are supplied into the needle pressurizing chamber 48.
When the piezoelectric element 46 is charged, the piezoelectric element 46 expands, thereby increasing the fuel pressure in the pressurizing chamber 47. As a result, the movable plunger 42 is pressed downward, and the nozzle opening 53 is kept closed by the needle 40. On the other hand, when the electric charge charged in the piezoelectric element 46 is discharged, the piezoelectric element 46 contracts,
The fuel pressure in the pressurizing chamber 47 decreases. As a result, the movable plunger 42 rises, the needle 40 rises, and the nozzle opening
Fuel is injected from 53.

Referring to FIG. 3, 60 is a cylinder block, 61 is a cylinder head, 62 is a piston, 63 is a concave combustion chamber formed on the top surface of the piston 62, and 64 is between the top surface of the piston 62 and the inner wall surface of the cylinder head 61. The formed cylinder chambers and 65 are spark plugs arranged so as to be located in the concave combustion chamber 63 at the top dead center of the piston 62, respectively. The fuel injection valve 5 is arranged in the concave combustion chamber 63 so as to be capable of injecting fuel and directed obliquely downward to the cylinder chamber 64.

The combustion chamber 63 has a double structure of a large-diameter shallow dish portion 66 on the upper side and a deep dish portion 67 on the lower side formed in the central portion of the shallow dish portion 66, and the deep dish portion 67 is shallow. The diameter is smaller than that of the dish 66. A groove that guides the fuel injected from the fuel injection valve 5 to a gap position with the spark plug 65 is provided on the inner peripheral surface of the deep plate portion 67.

Required fuel injection amount Q calculated according to the operating state of the engine
Is injected separately into the intake stroke injection and the compression stroke injection (see FIG. 4). In the intake stroke, the fuel injected toward the inside of the combustion chamber 63 once adheres to the inner wall surface of the combustion chamber 63 and then evaporates to form a premixture. The fuel injected in the intake stroke can take a long time from fuel injection to ignition. Therefore, the fuel injected in the intake stroke sufficiently evaporates to form a premixed gas and diffuses into the combustion chamber 63 and the cylinder chamber 64.

In the compression stroke injection, the fuel injection valve 5 allows the injected fuel to be injected into the shallow dish portion 66 when the injection timing is early, while on the other hand, when the injection timing is late and the piston 62 further rises. It is arranged so that it can be injected into the deep plate portion 67. In the high-load operation region in the compression stroke injection, among the fuel injected from the fuel injection valve 5, the initially injected fuel adheres to the upper combustion chamber, that is, the wall surface of the shallow dish portion 66, and then swirl flow or squish flow. At the same time, they are evaporated, diffused, and mixed while flowing in the shallow dish 66.

On the other hand, the injected fuel injected in the latter period, after adhering to the wall surface of the lower combustion chamber, that is, the basin portion 67, flows in the outer basin portion 67 together with the squish flow and swirl flow, and a part of it flows into the combustion chamber 63. It is guided to the gap position of the spark plug 65 along the groove provided on the inner wall. When ignited by the spark plug 65, the fire generated by the ignition rides on the swirl and diffuses in the deep dish part 67, and part of it is generated by the reverse squish flow generated by the movement of the piston 62. Guided to section 66 side. As a result, the fuel that was initially injected and stayed in the shallow dish portion 66 and the premixed gas formed by the intake stroke injection start combustion, and the shallow dish portion 66 has the same air flow as the deep dish portion 67. Along with the spread of the fire, a part of the fire goes out of the combustion chamber 63, and the combustion is completed while using the premixed gas in the dead volume.

Further, in the light load operation range in the compression stroke injection, fuel is injected into the deep plate portion 67, a small amount of the injection material is evaporated in a small volume, and the air-fuel ratio is locally set to an appropriate level so as not to become thin. It is kept and ignited, and this fire propagates to the premixed gas to obtain good combustion.

Next, the operation of this embodiment will be described with reference to FIG.
The routine shown in FIG. 5 is executed by interruption every constant crank angle.

Referring to FIG. 5, first, at step 70, the engine speed NE and the accelerator opening degree θA are read. Subsequently, at step 71, the required fuel injection amount Q is calculated from the map 1 shown in FIG. 6 based on the accelerator opening degree θA and the engine speed NE. As shown in FIG. 6, Q increases as θA and NE increase. In step 72, the average fuel injection amount Q _AV for the past n injections (for example, about 1 minute) from the present time is calculated by the following equation.

Here, Ti is the fuel injection time of the i-th fuel injection, P is the fuel pressure (constant), and k is a coefficient for converting T · P into the fuel injection amount. Q _AV is assumed to be the fuel injection amount (load) during engine steady operation. In step 73, it is determined whether the required fuel injection amount Q is Q _AV + E or more, and in step 74 it is determined whether Q is Q _AV −E or less. Here, E is a constant, and hunting is prevented by making Q _AV have a predetermined range. Also, since the in-cylinder temperature has a relatively good followability in slow deceleration and slow acceleration, it is determined that the steady state is assumed for changes in the injection amount below a predetermined value corresponding to slow acceleration and slow deceleration, and overcompensation is prevented. are doing. Also, even if E is set to a size that is equivalent to hunting prevention, the values of C in maps 3 and 4 are corrected according to the deviation between Q and Q _AV , and the larger the deviation, the larger the amount of change in C. The same effect can be obtained. When a negative determination is made in step 73 and step 74, that is, when the fuel injection amount Q is within the range of Q _AV −E and Q _AV + E, the current required fuel injection is higher than the fuel injection amount Q _AV during steady operation. The quantity Q hardly changes, so that it is judged that it is not in a transient operating state, and the routine proceeds to step 75. In step 75, the fuel injection ratio C is calculated from the map 2 (FIG. 7) based on the required fuel injection amount Q. The fuel injection ratio C is
It shows the ratio of the intake stroke fuel injection quantity Q _{I to} the compression stroke fuel injection quantity Q _C, and is calculated by the following equation.

FIG. 7 shows the relationship between the required fuel injection amount Q and the fuel injection ratio C at the time of steady engine operation without large load fluctuation, and C increases linearly as Q increases.

If an affirmative decision is made in step 73, that is, during transient operation in which the load increases (during increasing transient operation), the routine proceeds to step 76, where the fuel injection ratio C is determined from map 3 (Fig. 8).
Is calculated based on the required fuel injection amount Q. FIG. 8 shows the relationship between Q and C during transient engine operation in which the load increases, and C increases along an upwardly convex curve as Q increases. Comparing the C value of Map 3 and the C value of Map 2 (FIG. 7) corresponding to the same Q value, the C value of Map 3 is always greater than the C value of Map 2.

Even if the load increases from the steady operation state and the fuel injection amount increases, the in-cylinder temperature cannot follow the increase in the fuel injection amount, so the in-cylinder temperature corresponds to the increased fuel injection amount. The temperature inside the cylinder will be transiently lower than the temperature. Even in such an operating state, if the fuel is injected at the same fuel injection ratio C as that in the steady operation, the evaporation of the fuel becomes insufficient, and the smoke is generated and the output is lowered.

Therefore, in a transient operating state in which the load increases, the fuel injection ratio C is made to be larger than C in the steady operation, and the ratio of the intake stroke injection that can take a longer time to evaporate the fuel is increased. As a result, a sufficient evaporative atomization time can be secured and a good mixture can be formed, and thus good combustion can be obtained.

On the other hand, if the affirmative determination is made in step 74, that is, during the transient operation in which the load decreases (during transient operation), the process proceeds to step 77, and the fuel injection ratio C is requested from the map 4 (FIG. 9). It is calculated based on the fuel injection amount Q. FIG. 9 shows the relationship between Q and C during transient engine operation in which the load decreases, and as Q increases, C increases along a downwardly convex curve. The value of C in map 4 is always smaller than the value of C in map 2 (FIG. 7) corresponding to the same value of Q.

Even if the load decreases from the steady operation state and the fuel injection amount decreases, the in-cylinder temperature cannot follow the decrease in the fuel injection amount, so the in-cylinder temperature corresponds to the decreased fuel injection amount. It becomes higher than the steady-state in-cylinder temperature transiently. Even in such an operating state, when the fuel is injected at the same fuel injection ratio C as that in the steady operation, the mixture formation is accelerated, so that the time from the formation of the mixture to the ignition becomes longer, and the mixture becomes longer. Are made to flow into the air flow, and a thin region is generated, making combustion unstable.

Therefore, in such a transient operation state in which the load is reduced, the fuel injection ratio C is made smaller than C in the steady operation, and the ratio of intake stroke injection is made smaller. This can prevent combustion instability and knocking due to premature mixture formation.

In step 78, the intake stroke fuel injection amount Q _I is
Then, the compression stroke fuel injection amount Q _C is calculated by the following equation, respectively.

In step 80, the intake stroke fuel injection time T _I and the compression stroke fuel injection time T _C are calculated from Map 5 (FIG. 10) based on Q _I and Q _C. As shown in Figure 10, T _I
And T _C increase linearly as Q _I and Q _C increase. In step 81, map 6 (Fig. 11) shows Q _I and
Based on the Q _C, the intake stroke fuel injection start timing TS _I and the compression stroke fuel injection start timing TS _C is calculated. FIG.
The relationships between the intake stroke and compression stroke fuel injection amounts Q _I and Q _C and the intake stroke and compression stroke fuel injection start timings TS _I and TS _C indicated by the injection advance angle from the compression top dead center are shown, respectively. In the intake stroke injection, the fuel atomization time can be set sufficiently long, so TS
_I is a constant crank angle regardless of Q _I. On the other hand, in compression stroke injection, TS _C increases as Q _C increases, and injection is started earlier. This is because the fuel injection time T _C is longer as Q _C is larger. After the above steps, this routine is ended, and fuel injection is executed by another routine not shown.

It should be noted that the control may be such that the change of the predetermined period C is continued after it is determined in Steps 73 and 74 that the vehicle is in excessive operation.

Further, in the present embodiment, the determination of the steady operation, the decrease operation and the increase transient operation is performed based on the fuel injection amount, but the determination may be performed based on the accelerator opening degree θA.

Further, in this embodiment, the fuel injection ratio is changed during both the decrease and increase transient operation, but there is little problem in either transient condition due to control of the engine cooling system, the fuel injection itself, or the intake system. In this case, the fuel injection ratio may be changed as in this embodiment only when either the decrease or the increase transient operation is performed.

〔The invention's effect〕

As described above, according to the present invention, the mixture formation is suppressed during the decreasing transient operation, and the combustion instability and knocking due to the mixture formation being too early can be prevented.

On the other hand, during the increasing transient operation, the air-fuel mixture formation is promoted, and it is possible to prevent the generation of smoke and the decrease in the output due to the delay in the air-fuel mixture formation, and to obtain good combustion.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a 4-cylinder in-cylinder direct injection spark ignition engine adopting an embodiment of the present invention, FIG. 2 is a vertical sectional view of a fuel injection valve, and FIG. 3 is a vertical sectional view of an engine body. FIG. 4 is a diagram showing fuel injection timing, FIG. 5 is a flow chart for carrying out the embodiment of the present invention, and FIG. 6 shows the relationship between the accelerator opening and the required fuel injection amount with the engine speed as a parameter. FIG. 7 to FIG. 9 are diagrams showing the relationship between the required fuel injection charge Q and the fuel injection ratio C, and FIG. 7 is a diagram showing the relationship between Q and C during steady operation. Figure 8 shows Q and C during increasing transient operation.
FIG. 9 is a graph showing the relationship between Q and C during a decreasing transient operation, and FIG. 10 is a graph showing the relationship between the intake stroke and compression stroke fuel injection amount and the intake stroke and compression stroke fuel injection time. FIG. 11 is a diagram showing the relationship between the intake stroke and compression stroke fuel injection amount and the intake stroke and compression stroke fuel injection start timing. 1 ... Engine body, 5 ... Fuel injection valve, 20 ... Electronic control unit, 63 ... Combustion chamber.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display F02D 41/34 9523-3G F02D 41/34 H

Claims (1)

(57) [Claims] 1. A required fuel injection amount according to an engine operating state,
In a direct injection spark ignition engine for direct injection that performs split injection into an intake stroke and a compression stroke, during a decrease transient operation in which the load decreases, the fuel injection ratio, which is the ratio of the intake stroke fuel injection amount to the compression stroke fuel injection amount, is reduced as described above. The fuel injection ratio can be made smaller than the fuel injection ratio during steady operation under the same load as during transient operation, or during increased transient operation where the load increases In-cylinder direct injection spark ignition engine with a large size.