JPH0599021A - Internal combustion engine - Google Patents

Abstract

PURPOSE:To ignite with good condition so as to enable stable combustion by increasing a ratio between a fuel injection amount during compressive stroke and a fuel injection amount during intake stroke in response to increase of voltage detected by a discharge start voltage detecting means. CONSTITUTION:Resistances 18, 19 for partial pressure are connected to an ignition plug 6 in parallel. A peak voltage hold circuit 39 is connected to a point between the resistances 18 and 19, and it is also connected to an input port 25 through an AD converter 31. It is thus possible to detect discharge starting voltage of the ignition plug 6. When mixture gas is ignited by the ignition plug 6, the ratio between a fuel injection amount under compressive stroke and a fuel injection amount under intake stroke is increased in response to an increase of voltage detected by the discharge starting voltage detecting means 39. It is thus possible to form mixture gas having good ignition property around the ignition plug 6 at the time of ignition, and also obtain good ignition so as to achieve stable combustion.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to internal combustion engines.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication (Kokai) No. 2-169834 discloses that when a low load operation is performed, all of the required fuel injection amount is injected in a compression stroke to form an air-fuel mixture around an ignition plug, and when a medium and high load operation is performed, an intake stroke is performed. Disclosed is an internal combustion engine configured to inject fuel into an engine cylinder to form a premixed air-fuel mixture and to inject fuel into the engine cylinder in a compression stroke to form an ignition air-fuel mixture in the vicinity of a spark plug. There is.

[0003]

However, in this internal combustion engine, in the region on the low load side of the region where the required fuel injection amount is divided into the intake stroke and the compression stroke and injected, the spark plug surroundings at the time of ignition. It is difficult to reliably form an air-fuel mixture with good ignition, which causes a problem that combustion becomes unstable.

[0004]

In order to solve the above problems, according to the present invention, fuel is injected in the intake stroke to form a premixed gas in the engine cylinder, and fuel is injected into the engine cylinder in the compression stroke. In an internal combustion engine configured to inject an air-fuel mixture in the vicinity of a spark plug, discharge start voltage detection means for detecting a voltage at which discharge is started when the air-fuel mixture is ignited by the spark plug is provided. In response to the increase in the voltage detected by the starting voltage detecting means,
The ratio of the compression stroke fuel injection amount to the intake stroke fuel injection amount is increased.

[0005]

The discharge start voltage of the spark plug increases as the air-fuel ratio of the air-fuel mixture around the spark plug increases during ignition. Therefore, the discharge start voltage of the spark plug indirectly represents the air-fuel ratio of the air-fuel mixture around the spark plug at the time of ignition. For this reason,
As the discharge start voltage increases, that is, when the air-fuel mixture around the spark plug becomes lean during ignition, the ratio of the compression stroke fuel injection amount to the intake stroke fuel injection amount is increased to increase the spark plug during ignition. I try to enrich the surrounding air-fuel mixture.

[0006]

1 is a general view of a four-cylinder gasoline engine which is an embodiment of the present invention. In the figure, 1 is an engine body, 2 is a surge tank, 3 is an intake pipe extending from the surge tank 2, 4 is a throttle valve provided in the middle of the intake pipe 3, and 5 is fuel for directly injecting fuel into each cylinder. Injection valve, 6
Is a spark plug, 7 is a high pressure reservoir tank, 8 is a high pressure conduit 9
A high-pressure fuel pump capable of controlling the discharge pressure for pumping high-pressure fuel into the reservoir tank 7 via the fuel tank 10, 10 is a fuel tank, and 11 is a conduit 12 for supplying fuel from the fuel tank 10 to the high-pressure fuel pump 8. Low pressure fuel pumps are shown respectively. The discharge side of the low-pressure fuel pump 11 is connected to a piezoelectric element cooling introduction pipe 13 for cooling the piezoelectric element of each fuel injection valve 5. The return pipe 14 for cooling the piezoelectric element is connected to the fuel tank 10, and the fuel flowing through the introduction pipe 13 for cooling the piezoelectric element is collected in the fuel tank 10 via the return pipe 14. Each branch pipe 15 connects each high-pressure fuel injection valve 5 to the high-pressure reservoir tank 7.

A pressure sensor 3 is provided in the high pressure reservoir tank 7.
6 is attached, and this pressure sensor 36 detects the fuel pressure in the high pressure reservoir tank 7. Based on the detection value of the pressure sensor 36, the high pressure fuel pump 8 is controlled so that the fuel pressure in the high pressure reservoir tank 7 becomes the target fuel pressure. An air flow meter 37 for detecting the intake air amount QA is arranged at the inlet of the intake pipe 3.

FIG. 2 is a block diagram showing the configuration of the electronic control unit 20. Referring to FIG. 2, the electronic control unit 20 is composed of a digital computer, and has a ROM (Read Only Memory) 22 and a RAM (Random Access Memory) 2 which are mutually connected by a bidirectional bus 21.
3, CPU (microprocessor) 24, input port 2
5 and output port 26.

The pressure sensor 36 is connected to the input port 25 via the AD converter 30. A crank angle sensor 38 that generates an output pulse proportional to the engine speed Ne is connected to the input port 25. Further, the air flow meter 37 is connected to the input port 25 via the AD converter 32.
On the other hand, the output port 26 has the corresponding drive circuits 33 and 34.
Are connected to the high-pressure fuel pump 7 and the fuel injection valve 5, respectively. Further, the output port 26 is connected to the igniter 16 via the drive circuit 35. The igniter 16 is connected to the spark plug 6 via an ignition coil 17.

Resistors 18 and 19 for voltage division are provided in parallel with the spark plug 6.
Are connected. The peak voltage hold circuit 39 is connected between the resistors 18 and 19, and the peak voltage hold circuit 3 is connected.
9 is connected to the input port 25 via the AD converter 31. As a result, the discharge start voltage VSP of the spark plug 6 can be detected. FIG. 3 shows a side sectional view of the fuel injection valve 5. Referring to FIG. 3, 40 is a needle inserted into the nozzle 50, 41 is a pressure rod, 42 is a movable plunger, 43 is a spring accommodating chamber 44, and the needle 4 is
A compression spring that presses 0 downward, 45 a pressure piston, 46 a piezoelectric element, and 47 a movable plunger 42.
And a fuel-filled pressure chamber formed between the top of the cylinder and the piston 45, and 48 a needle pressure chamber. The needle pressurizing chamber 48 is connected to the high-pressure reservoir tank 7 (FIG. 1) via the fuel passage 49 and the branch pipe 14, so that the high-pressure fuel in the high-pressure reservoir tank 7 passes through the branch pipe 14 and the fuel passage 49. It is 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 and the fuel pressure in the pressurizing chamber 47 decreases. As a result, the movable plunger 42 rises and the needle 4
0 rises, and fuel is injected from the nozzle port 53.

FIG. 4 is a vertical sectional view of the engine shown in FIG. Referring to FIG. 4, 60 is a cylinder block, 61
Is a cylinder head, 62 is a piston, 63 is a piston 6
2 is a substantially cylindrical recess formed on the top surface of the piston 2, 64 is the piston 6
2 shows cylinder chambers formed between the top surface and the inner wall surface of the cylinder head 61, respectively. The spark plug 6 faces the cylinder chamber 64 and is attached to a substantially central portion of the cylinder head 61. Although not shown in the drawing, an intake port and an exhaust port are formed in the cylinder head 61, and intake valves 66 (see FIG. 7A) are provided at the openings of the intake port and the exhaust port into the cylinder chamber 64, respectively. And an exhaust valve is arranged.
The fuel injection valve 5 is a swirl type fuel injection valve, and injects a fuel atomized fuel having a wide spread angle and a weak penetration force. The fuel injection valve 5 is arranged diagonally downward, is arranged at the top of the cylinder chamber 64, and is arranged so as to inject fuel toward the vicinity of the spark plug 6. Further, the fuel injection direction and the fuel injection timing of the fuel injection valve 5 are determined so that the injected fuel is directed to the recess 63 formed at the top of the piston 62.

The internal combustion engine of the present embodiment is a cylinder injection type internal combustion engine capable of split injection of a fuel injection amount according to the engine operating state into an intake stroke and a compression stroke, and in FIG. Shows the ratio of the intake stroke fuel injection amount and the compression stroke fuel injection amount in. Referring to FIG. 5, the horizontal axis represents the load of the engine. In FIG. 5, the fuel injection amount Q is taken as the load, and the vertical axis also shows the fuel injection amount Q.

From the fuel injection amount Q _I when the fuel injection amount indicating the engine load is idling to the fuel injection amount Q _M when the medium load is
The fuel is injected only in the compression stroke, and the fuel injection amount Q _C in the compression stroke is gradually increased from the idle fuel injection amount Q _I to the medium load fuel injection amount Q _M. When the fuel injection amount indicating the engine load exceeds Q _M , the compression stroke fuel injection amount is sharply reduced from Q _M to Q _D , and the fuel injection amount Q _S in the intake stroke is sharply increased to Q _P. Q _M is the fuel injection amount near the middle load, and Q _D
Is expressed by the following formula as the sum of Q _p and Q _p .

Q _M = Q _D + Q _P Here, Q _D is the minimum compression stroke fuel injection amount that can form an air-fuel mixture that can be ignited by the spark plug 6, and is smaller than the idle fuel injection amount Q _I. Further, the Q _P is the minimum intake stroke fuel injection amount capable ignition flame propagation due to spark plug 6 when the injected fuel homogeneously diffused in the cylinder chamber 64 during the intake stroke. From the fuel injection amount Q _M at medium load to the fuel injection amount Q _H at high load, the fuel injection amount is divided into a compression stroke and an intake stroke for injection, and the compression stroke fuel injection amount is Q regardless of the engine load. _The intake stroke fuel injection amount is made to increase as the engine load increases, with _D being constant.

When the engine load exceeds the maximum fuel injection amount Q _W beyond the high load fuel injection amount Q _H ,
Since the amount of fuel injection is large, the concentration of the pre-mixture formed in the intake stroke injection is sufficiently high for ignition, so the compression stroke injection for ignition is stopped and the total amount of fuel injection required in the intake stroke It is supposed to be jetted. The high-load fuel injection amount Q _H is the minimum intake stroke fuel injection amount that can form a homogeneous mixture that can be ignited by the spark plug even when the fuel is uniformly diffused in the cylinder chamber.

As shown in FIG. 6, the intake stroke means the period from the top dead center of the exhaust process to the bottom dead center of the intake process, and the compression stroke means the bottom dead center of the intake process to the top dead center of the compression process. It means the period to the dead point. The intake stroke injection is executed within the period indicated by D _I. This period D _I corresponds to almost the first half of the intake stroke. The compression stroke injection is performed within the period indicated by D _C. This period D _C corresponds to almost the latter half of the compression stroke. Since the fuel is injected within the period D _I or D _C , the injected fuel does not directly impinge on the cylinder block 60, so that the injected fuel hardly adheres to the inner surface of the cylinder block 60.

In the load region lower than near the middle load (fuel injection amount Q _M ), as shown in FIG. 4, only the compression stroke injection is executed in the latter half of the compression stroke, and the fuel injection valve 5 to the spark plug 6 and the piston are discharged. The fuel is injected toward the concave portion 63 on the top surface 62. This injected fuel has a weak penetration force, and since the pressure in the cylinder chamber 64 is high and the air flow is weak,
The injected fuel is unevenly distributed in the region K near the spark plug 6. Since the fuel distribution in this region K is non-uniform and changes from the rich air-fuel mixture layer to the air layer, in the region K there is a combustible air-fuel mixture layer near the stoichiometric air-fuel ratio where combustion is most likely to occur. Therefore, the combustible air-fuel mixture layer near the spark plug 6 is easily ignited, and this ignition flame propagates to the entire heterogeneous air-fuel mixture layer to complete combustion. As described above, in the low load region lower than the medium load, the fuel is injected near the spark plug 6 in the latter stage of the compression stroke, thereby forming a combustible mixture layer near the spark plug 6, and thus achieving good ignition and Combustion will be obtained.

On the other hand, in the load region higher than near the middle load (fuel injection amount Q _M ), as shown in FIG. 7, the intake stroke injection is executed in the early stage of the intake stroke (FIG. 7A), and the fuel injection is performed. Fuel is injected from the valve 5 toward the spark plug 6 and the recess 63 on the top surface of the piston 62. This injected fuel is a spray-like fuel having a large divergence angle and a weak penetrating force. A part of the injected fuel floats in the cylinder chamber 64, and the other is a recess 63.
Clash with. These injected fuels are diffused in the cylinder chamber 64 by the turbulence T in the cylinder chamber 64 caused by the intake air flow flowing into the cylinder chamber 64 from the intake port, and the premixed air mixture P during the intake stroke to the compression stroke. Are formed (FIG. 7B). The air-fuel ratio of this premixed gas P is
The air-fuel ratio is such that ignition flame can propagate. Incidentally, FIG.
In the state of (b), since the extension of the central axis of the injected fuel is directed to the cylinder wall, when the penetrating force of the injected fuel is strong, a part of the spray may directly adhere to the cylinder wall. In this embodiment, there is no particular problem because the injection with relatively weak penetration is performed, but in the embodiment of the present invention, the effect of preventing fuel from adhering to the cylinder wall surface is enhanced by setting the injection-free period in this period. ing. Then, the latter half of the compression stroke (Fig. 7
The compression stroke injection is executed in (c), and the fuel is injected from the fuel injection valve 5 toward the vicinity of the spark plug 6 and the recess 63 on the top surface of the piston 62. Since the injected fuel is originally directed to the spark plug 6, the penetration force is weak, and the pressure in the cylinder chamber 64 is large, the injected fuel is in the region K near the spark plug 6.
Unevenly distributed. The fuel distribution in this region K is also non-uniform,
Since the rich air-fuel mixture layer changes to the air layer, a combustible air-fuel mixture layer near the stoichiometric air-fuel ratio where combustion is most likely to exist in this region K. Therefore, when the combustible air-fuel mixture layer is ignited by the spark plug 6, combustion proceeds around the non-uniform air-fuel mixture region K (FIG. 7 (d)). In this combustion process, the flame propagates to the premixed gas P sequentially from the periphery of the combustion gas B whose volume has expanded, and the combustion is completed. As described above, in the medium load and high load regions, by injecting the fuel in the early stage of the intake stroke to form the air-fuel mixture for flame propagation in the entire cylinder chamber 64 and injecting the fuel in the latter stage of the compression stroke. A relatively rich air-fuel mixture is formed in the vicinity of the ignition plug 6 to form an air-fuel mixture for ignition and flame kernel formation.

In particular, during medium load operation, when the entire required injection amount is injected in the intake stroke or the first half of the compression stroke as in the conventional engine, the injected fuel diffuses into the entire cylinder chamber 64, so There is a problem in that the air-fuel mixture formed in the chamber 64 becomes too thin, which makes ignition and combustion difficult. On the other hand, when the entire required injection amount is injected in the latter half of the compression stroke during medium load operation, a large amount of smoke is generated, and there is a problem that the air utilization ratio cannot be increased and a sufficiently high output cannot be obtained. is there.

Therefore, as described above, during the medium load operation, the divided injection is performed in the intake stroke and the compression stroke,
They are trying to obtain high output by good ignition and combustion with high air utilization. In addition, in the vicinity of medium load, the homogeneous mixture formed by the fuel injected in the intake stroke may have an air-fuel ratio that allows flame propagation that is thinner than the air-fuel ratio that can be ignited, and fuel consumption can be improved by lean combustion. You can

By the way, in FIG. 5, the fuel injection amount is Q _M
Between Q _H and Q _{H, and in} the region where the required fuel injection amount is divided into the intake stroke and the compression stroke and injected, the low load side region, that is, the region close to Q _M , around the spark plug during ignition. It is difficult to reliably form an air-fuel mixture with good ignition, which causes a problem of unstable combustion.

Therefore, in this embodiment, as shown in FIG.
Since the discharge start voltage VSP of the spark plug increases as the air-fuel ratio of the air-fuel mixture around the spark plug increases during ignition,
By detecting the discharge start voltage VSP, the air-fuel ratio of the air-fuel mixture around the spark plug at the time of ignition is indirectly detected. The discharge start voltage VSP is, for example, an air-fuel ratio of 1
When it becomes lower than the discharge starting voltage VB corresponding to 3, it is determined that rich misfire has occurred, and the ratio of the compression stroke fuel injection amount is decreased to make the air-fuel mixture around the ignition plug lean at the time of ignition. ing. This is to prevent rich misfire.

On the other hand, when the discharge start voltage VSP becomes lower than the discharge start voltage VA corresponding to, for example, the air-fuel ratio of 25, it is determined that a lean misfire has occurred, and the ratio of the fuel injection amount in the compression stroke is increased. At the time of ignition, the air-fuel mixture around the spark plug is made rich. This is to prevent lean misfire. FIG. 9 shows a routine for calculating the intake stroke and the compression stroke fuel injection amount. This routine is executed by interruption every constant crank angle.

Referring to FIG. 9, first, at step 70, the required fuel injection amount Q is the engine speed Ne and QA.
/ Ne based map (see FIG. 10).
Here, QA / Ne is the intake air amount per one revolution of the engine and represents the engine load. Next, at step 71, the division ratio QR is calculated based on the required fuel injection amount Q. Here, the division ratio QR is the ratio of the intake stroke fuel injection amount Q _{S to} the required fuel injection amount Q.

Map of required fuel injection amount Q and division ratio QR
Is as shown in FIG. FIG. 11 corresponds to FIG.
And the required fuel injection amount Q is Q_ITo Q_MUntil the QR is 0
Therefore, all of the required fuel injection amount Q is in the compression stroke.
Is jetted. Q_MTo Q _HUp to the intake stroke and
The compression stroke injection is executed, and the intake stroke is increased as the load increases.
The ratio of fuel injection amount increases. Q_HTo Q_WUp to QR
Becomes 1.0, and all of the required fuel injection amount Q is in the intake stroke.
It is jetted at.

Referring again to FIG. 9, at step 72 it is determined whether QR is 0 or equal to 1. Step 7 if the split ratio QR is not equal to 0 and 1
In step 3, the correction value KQR is added to QR. Correction value K
QR is calculated in the routine shown in FIG. 12 described later. In step 74, it is determined whether QR is 0 or more, and Q
If R <0, the routine proceeds to step 75, where QR is set to 0.
On the other hand, if QR ≧ 0, the routine proceeds to step 76, where it is judged whether or not QR ≦ 1. If QR> 1, the process proceeds to step 77 and QR is set to 1. If QR ≦ 1, the value of QR is maintained as it is.

In step 78, the intake stroke fuel injection amount Q _S is calculated based on the following equation. Q _S = Q · QR Next, at step 79, the compression stroke fuel injection amount Q _C is calculated by subtracting the intake stroke fuel injection amount from Q. When it is determined in step 72 that QR is 0 or 1, steps 73 to 77 are skipped and QR is not corrected and is maintained at 0 or 1.

FIG. 12 shows a routine for calculating the correction value KQR. This routine is executed by interruption every constant crank angle. Referring to FIG. 12, first, at step 90, the discharge start voltage VSP is read.
Next, at step 91, it is judged if VSP> VA. As described above, VA is a discharge start voltage corresponding to, for example, the air-fuel ratio 25 (see FIG. 8). VSP> VA
In this case, it is assumed that lean misfiring occurs because the air-fuel mixture in the vicinity of the ignition plug is too thin at the time of ignition, and the correction value KQR is decreased by α in step 92. As a result, the split ratio QR decreases, and thus the ratio of the compression stroke fuel injection amount increases, so that the air-fuel mixture near the spark plug at the time of ignition can be enriched. As a result, lean misfire can be prevented and thus stable combustion can be obtained.

On the other hand, if VSP = VA, step 9
In step 3, it is determined whether VSP <VB. As described above, VB is the discharge start voltage corresponding to the air-fuel ratio 13 (see FIG. 8). If VSP <VB, it is determined that rich misfiring occurs because the air-fuel mixture near the spark plug is excessively rich at the time of ignition, and the routine proceeds to step 94, where the correction value KQR is increased by α. As a result, the split ratio QR increases, and thus the ratio of the compression stroke fuel injection amount decreases,
It is possible to make the air-fuel mixture near the spark plug lean at the time of ignition. As a result, rich misfiring can be prevented and thus stable combustion can be obtained.

As in this embodiment, the discharge start voltage VS
Instead of using the value of P as it is to judge the misfire, for example, the discharge start voltage at the time of fuel cut (when the air-fuel mixture is not formed) is set as the reference discharge start voltage VSP ₀ ,
By determining the misfire based on the ratio of VSP to VSP _0, it is possible to remove factors such as changes with time and perform more accurate control.

In this embodiment, one fuel injection valve is used to execute the intake stroke injection and the compression stroke injection. However, a port fuel injection valve is added to each intake port of each cylinder to perform the intake stroke injection. The port fuel injection valve may be used for this purpose.

[0032]

EFFECTS OF THE INVENTION At the time of ignition, an air-fuel mixture with good ignition can be formed around the spark plug, and therefore, good ignition can be obtained, and thus stable combustion can be obtained.

[Brief description of drawings]

FIG. 1 is an overall view of an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a block diagram of an electronic control unit.

FIG. 3 is a vertical sectional view of a fuel injection valve.

4 is a longitudinal sectional view of the engine of FIG.

FIG. 5 is a diagram showing an example of a control pattern for compression stroke injection and intake stroke injection.

FIG. 6 is a diagram showing a fuel injection timing.

FIG. 7 is an operation explanatory diagram when executing intake stroke and compression stroke injection.

FIG. 8 is a diagram showing the relationship between the air-fuel ratio near the spark plug and the discharge start voltage VSP of the spark plug immediately before ignition.

FIG. 9 is a flowchart for calculating an intake stroke and a compression stroke fuel injection amount.

FIG. 10 is a map of the fuel injection amount Q based on the engine speed Ne and QA / Ne.

FIG. 11 is a map of a division ratio QR based on a fuel injection amount Q.

FIG. 12 is a flowchart for calculating a correction amount KQR.

[Explanation of symbols]

 5 ... Fuel injection valve 6 ... Spark plug

Claims (1)

[Claims] 1. A fuel mixture is injected in an intake stroke to form a premixed mixture in an engine cylinder, and a fuel mixture is injected in an engine cylinder in a compression stroke to form an ignition mixture near an ignition plug. In the internal combustion engine, the discharge start voltage detecting means for detecting the voltage at which the discharge is started when the mixture is ignited by the spark plug is provided, and the intake air is increased in accordance with the increase in the voltage detected by the discharge start voltage detecting means. An internal combustion engine in which a ratio of a compression stroke fuel injection amount to a stroke fuel injection amount is increased.