JPH1122535A - Compression ignition internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of NOx and soot at the time of a low-load operation. SOLUTION: In a compression ignition internal combustion engine, the operating region of the engine is split into a low-load side operating region X and a high-load side operating region Y across a predetermined boundary Z. When the operating state of the engine lies in the low-load side operating region X, an early injection I1 of fuel is made at about 60 deg. before the compression top dead center. When the operating state of the engine lies on the high-load side than the boundary Z of the operating region, the injection is switched to the compression top dead center injection I2 injecting fuel near the compression top dead center.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compression ignition type internal combustion engine.

[0002]

2. Description of the Related Art In a compression ignition type internal combustion engine, the degree of dispersion of fuel injected into a combustion chamber has a great influence on combustion. That is, the combustion temperature in order to heat value of the per unit volume fuel is dispersed throughout the combustion chamber is lowered is lowered, gentle combustion is performed does not occur of the NO _x and thus. In addition, soot is not generated because sufficient air exists around the fuel particles. Therefore, there is known a compression ignition type internal combustion engine in which fuel is injected during a compression step before 60 degrees before a compression top dead center in order to disperse the injected fuel throughout the combustion chamber (Japanese Patent Application Laid-Open No. 7-317588). Gazette).

That is, when the pressure in the combustion chamber increases, the air resistance increases, so that the injected fuel hardly spreads throughout the combustion chamber. Therefore, in this compression ignition type internal combustion engine, the pressure in the combustion chamber is low and the compression top dead center is low. The fuel is injected before 60 degrees before.

[0004]

If the way the injected fuel throughout the combustion chamber in this way [0005] to disperse, when the fuel injection amount is small is gentle combustion NO _x and HC is not generated is performed. However, when the fuel injection amount increases, the fuel starts to ignite early, and once the fuel ignites early, the temperature in the combustion chamber increases, so that the fuel ignites earlier. As a result, the combustion gradually intensified, a large amount of the NO _x and soot as well knocking will occur.

[0005]

According to a first aspect of the present invention, there is provided a compression ignition type internal combustion engine in which fuel is injected into a combustion chamber. Is divided into a low load side operation region and a high load side operation region at the boundary, and when the operation state of the engine is on the low load side beyond the boundary of this operation region, the operation state is almost 60 degrees before the compression top dead center. Fuel is injected at an early stage, and when the operating state of the engine becomes higher than the boundary of the operating range, switching is made to compression top dead center injection in which fuel is injected near the compression top dead center.

In the second invention, in the first invention,
The boundary of the operation region is moved according to the operation state of the engine. In a third aspect based on the second aspect, the boundary of the operation region is shifted to a lower load side as the temperature of the intake air supplied into the combustion chamber increases. In a fourth aspect based on the second aspect, the boundary of the operation region is moved according to the state of combustion when the early injection is performed.

[0007] In the fifth invention, in the fourth invention,
A determination means for determining whether or not a predetermined normal combustion is performed when the early injection is performed; and a predetermined normal combustion is performed when the early injection is performed. When it is determined that there is no such condition, the boundary of the operation region is moved to the low load side. In a sixth aspect based on the fifth aspect, the determination means determines that predetermined normal combustion is not being performed when the knocking intensity generated by the engine exceeds a predetermined value.

[0008] In the seventh invention, in the fourth invention,
The boundaries of the operating range are determined for each predetermined engine speed range. In an eighth aspect based on the second aspect, in the second aspect, the boundary of the operating region comprises a first boundary and a second boundary on a lower load side than the first boundary. The injection is switched to, and at the second boundary, the compression top dead center injection is switched to the early injection.

In the ninth invention, in the eighth invention,
The first boundary is moved according to the state of combustion at the time of the early injection, and the second boundary is moved to the low load side when the first boundary is moved to the low load side.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7
Represents an intake valve, 8 represents an intake port, 9 represents an exhaust valve, and 10 represents an exhaust port. The intake port 8 is connected to the corresponding intake branch 11
Connected to the surge tank 12 via the
2 is an exhaust turbocharger 14 via an intake duct 13
Of the compressor 15. On the other hand, exhaust port 1
0 is connected to an exhaust turbine 18 of an exhaust turbocharger 14 via an exhaust manifold 16 and an exhaust pipe 17.

The exhaust manifold 16 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter, referred to as EGR) passage 19, and an electrically controlled EGR control valve 20 is disposed in the EGR passage 19. Each fuel injection valve 6 is connected via a fuel supply pipe 21 to a fuel reservoir, a so-called common rail 22. Fuel is supplied into the common rail 22 from an electric control type variable discharge fuel pump 23, and the fuel supplied into the common rail 22 is supplied to the fuel injection valve 6 through each fuel supply pipe 21. A fuel pressure sensor 24 for detecting the fuel pressure in the common rail 22 is attached to the common rail 22. Based on an output signal of the fuel pressure sensor 24, a fuel pump 23 is provided so that the fuel pressure in the common rail 22 becomes a target fuel pressure. Is controlled.

The electronic control unit 30 is composed of a digital computer, and a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a backup RAM 33a always connected to a power source, and a CPU ( Microprocessor)
34, an input port 35 and an output port 36. The output signal of the fuel pressure sensor 22 is input to the input port 35 via the corresponding AD converter 37. An intake temperature sensor 25 that generates an output voltage proportional to the intake air temperature is attached to the surge tank 12, and the output voltage of the intake temperature sensor 25 is input to an input port 35 via a corresponding AD converter 37. A knocking sensor 26 is attached to the cylinder head 3, and the knocking sensor 26 is connected to a peak hold circuit 28 through a low-pass filter 27.
Is connected to the input terminal. The output terminal of the peak hold circuit 28 is connected to the input port 3 via the corresponding AD converter 37.
5 is connected.

A load sensor 41 for generating an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is supplied to an input port via a corresponding AD converter 37. 35 is input. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. On the other hand, the output port 36 is connected to the fuel injection valve 6, the EGR control valve 20, the fuel pump 23 and the peak hold circuit 28 via the corresponding drive circuit 38.
Is connected to the reset input terminal.

FIG. 2 shows the output voltage V of the knocking sensor 26.
_SAnd the output voltage V of the peak hold circuit 28_PStrange
Shows that When knocking occurs, the engine body 1
At this time, the knocking sensor 26
Output voltage V relative to vibration intensity _SOccurs. Peak Ho
Output voltage V_PIs the knocking that has occurred so far
Output voltage V of the sensing sensor 26_SIs held at the peak value of
You. The output voltage V of the peak hold circuit 28_PIs like
If a reset signal is generated every fixed crank angle
Reset.

As described at the beginning, when the fuel injection amount is small, if the injected fuel is dispersed throughout the combustion chamber 5, NO _x
Mild combustion without soot generation is performed. That is, when fuel is injected and the piston 4 rises and the temperature in the combustion chamber 5 becomes equal to or higher than a certain temperature, the fuel vapor around the fuel particles is combined with oxygen. At this time, if the fuel particles are gathered, that is, if the density of the fuel particles is high, the fuel particles receive a heat of oxidation reaction of the evaporated fuel of the surrounding fuel particles and become high temperature. As a result, the hydrocarbons in the fuel particles become hydrogen molecules H ₂ and carbon C
Pyrolyzed into Hydrogen molecules H generated by this thermal decomposition
₂ hot generated by burning explosively, NO _x will occur to thus. On the other hand, when carbon C is generated by thermal decomposition, these carbons are bonded to each other, and a part thereof is discharged as soot. If the density of the fuel particles is high, NO due to the thermal decomposition of hydrocarbons in the fuel particles
_x Yeast soot occurs. Such NO _x in order to prevent the occurrence of Yasusu may be Shiteyare increase the spacing between the fuel particles will be do it by widely dispersing the fuel particles for that.

The curve in FIG. 3 shows only the compression action of the piston 4.
This shows the change in the pressure P in the combustion chamber 5 due to the change. From FIG.
As can be seen, the pressure P in the combustion chamber 5 is almost equal to B before the compression top dead center.
It rises rapidly above TDC 60 degrees. This is the intake valve
No reciprocating internal combustion regardless of the valve opening timing of 7
Even in an engine, the pressure P in the combustion chamber 5 is shown in FIG.
Changes. As the pressure P in the combustion chamber 5 increases, the air resistance increases
Fuel is not dispersed over a wide area because
To disperse the fuel over a wide range, the pressure P in the combustion chamber 5
It is necessary to perform fuel injection when the pressure is low. Therefore
In the embodiment according to the present invention, the compression in which the pressure P in the combustion chamber 5 is low is low.
Fuel injection I 60 degrees before BTDC before top dead center ₁, That is, early injection
I am trying to shoot. In fact, BTDC before compression top dead center
Early injection I before 60 degrees₁NO_xAnd soot
Almost no longer occurs.

The operating range of NO _x and soot performed early injection I ₁ in such BTDC BTDC60 degrees earlier in hardly occurs is shown in the operating region X in FIG.
In FIG. 4, the vertical axis Q indicates the fuel injection amount.
The horizontal axis N indicates the engine speed. As can be seen from FIG. 4, this operation region X is an operation region where the fuel injection amount Q is small, that is, an operation region on the low load side.

On the other hand, as the fuel injection amount Q increases, the density of the fuel particles increases. Therefore, even when the fuel injection amount Q is increased, that is, when the operating state of the engine is in the operating region Y of FIG. 4, early injection is performed before BTDC 60 degrees before the compression top dead center. fuel ignited prematurely by pyrolysis, resulting NO _x and soot as well knocking will occur. Therefore, in the embodiment according to the present invention, the operating state of the engine is shifted from the operating region X to the boundary Z.
, The operation is switched to the compression top dead center injection in which fuel injection is performed substantially near the compression top dead center as in a normal compression ignition type internal combustion engine.

FIG. 5 shows the fuel injection timing. In FIG. 5, the vertical axis indicates the crank angle, and the horizontal axis indicates the fuel injection amount Q. As shown in FIG. 5, in the operation region X, the fuel injection I ₁ occurs 60 degrees before the compression top dead center (BTDC).
Is performed. Operation θS1 and θE1 in the region X shows the injection start timing and injection completion timing of each fuel injection I _1, timing completed injection in the embodiment shown in FIG. 5 theta
E1 is fixed at approximately 80 ° before compression top dead center (BTDC).

On the other hand, as shown in FIG. 5, in the operating region Y, the fuel injection I near the compression top dead center (TDC) is performed.
₂ is done. ΘS2 and θE2 in operation region Y
Shows the injection start timing and injection completion timing of each fuel injection I _2, the injection start timing θS2 in the embodiment shown in FIG. 5 is fixed to approximately the compression top dead center (BTDC) 5 degrees.

In FIG. 5, the fuel injection amount Q is a function of the depression amount L of the accelerator pedal 40 and the engine speed N. The fuel injection amount Q is stored in advance in the ROM 32 in the form of a map as shown in FIG. Is stored in On the other hand, the injection start timing of the fuel injection I ₁ in the operating region X in FIG. 5? S1
Is also a function of the depression amount L of the accelerator pedal 40 and the engine speed N, and the injection start timing θS1 is also stored in the ROM 32 in advance in the form of a map as shown in FIG. In addition, in FIG.
₂ is also a function of the amount of depression L of the accelerator pedal 40 and the engine speed N.
E2 is also stored in the form of a map as shown in FIG.
32.

As described above, the early injection I₁NO
_xLittle soot and therefore as early as possible
Injection I₁Is preferably performed. Therefore shown in FIG.
The boundary Z between the operating area X and the operating area Y is NO_xAnd soot
It is set to the limit at which it begins to grow. This limit is used in experiments
The limit value can be obtained from the
The boundary Z of the driving area is
It would be preferable to control it. Also, early injection
I₁And compression top dead center injection I_TwoTo prevent frequent repetition
It is preferable to stop it,₁And pressure
Top dead center injection I _TwoHysteresis for the switching action of
Preferably, it is provided.

FIG. 7 shows an embodiment according to the present invention.
As shown in FIG.
Engine speed range n₁, N_Two, ... n_TenDivided into each institution
Turn range n₁, N_Two, ... n_TenFor the first boundary M
₁, M_Two, ... M_TenAnd a second, lower load side than the first boundary
Boundary L₁, L_Two, ... L_TenAnd the first boundary M₁,
M_Two, ... M_TenIs early injection I₁NO when performing_xand
To the limit value where regular combustion with little soot is generated
The first boundary M to be maintained₁, M_Two, ... M _TenLearning
I try to control. Note that in FIG.
I₁From top dead center injection I_TwoTo the first boundary M₁,
M_Two, ... M_TenAnd the compression top dead center injection I_Two
Early injection I₁To the second boundary L₁, L_Two, ... L_TenTo
Is switched.

More specifically, the first boundary M
_1, M _2, ... M ₁₀ and the second boundary _{L 1, L 2, ... L} 10
Are represented by the engine load, and in the embodiment shown in FIG. 7, the values of the first boundaries M ₁ , M ₂ ,... M ₁₀ are represented by the fuel injection amount Q. Thus the fuel injection amount Q in the embodiment shown in FIG. 7 is a first boundary M _1, M _2, ... is switched to the compression top dead center injection I ₂ early injection I ₁ exceeds M _10, the fuel injection amount Q Is smaller than the second boundaries L ₁ , L ₂ ,..., L ₁₀ from the compression top dead center injection I ₂ to the early injection I ₁
Will be switched to

As described above, the limit value of the operating region X where NO _x and soot start to be generated, that is, the first boundary can be obtained by experiments. In the embodiment according to the present invention, as shown in FIG. 8, the values of the first boundary determined by the experiment are set as reference boundary values m ₁ , m ₂ ,..., M ₁₀ and the respective engine speed ranges n ₁ , n ₂ ,. ₁₀ are stored for each. Also,
As shown in FIG. 8, each engine speed range n ₁ , n ₂ ,.
learning value of each first boundary relative to _{n 10 G 1, G 2,} ... G
_Ten are provided.

Next, a first boundary Mi (i = 1, 2,... 1)
0) and the learning control of the second boundary Li (i = 1, 2,..., 10) will be described. As described above, the early injection I ₁
When the fuel injection amount increases, the fuel starts to ignite early, and once the fuel ignites early, the temperature in the combustion chamber increases, so that the fuel ignites earlier. As a result, knocking occurs because the combustion becomes gradually intense, and the engine speed starts to increase. This time is the limit of the operation region X, and therefore, since the knocking has occurred, it can be determined that it is the limit of the operation region X. When in this embodiment of the present invention the output voltage V _P of the peak hold circuit 28 in FIG. 2 exceeds a set value V _o is therefore determined to be the limit of the operating range X, the first boundary in this case to the low load side I try to move it.

That is, in the embodiment according to the present invention, the learning value Gi of the first boundary is calculated gradually. Gi = mi + Δmi where mi is the reference boundary value shown in FIG.
Is a correction value. When the fuel injection amount Q is between the first boundary value Mi and the second boundary value Li, that is, Mi>Q> Li
Output voltage V _P of the peak hold circuit 28 exceeds the set value V _O correction value Δmi is provided to gradually decrease when, as a result learned value Gi is is gradually decreased. When the learning value Gi decreases, the first boundary value Mi also decreases.

On the other hand, when Mi>Q> Li, V _p ≦ V _O
If so, the correction value Δmi is gradually increased, and as a result, the learning value Gi is also gradually increased. At this time the first
Is gradually increased. Thereafter, if V _P > V _O again when Mi>Q> Li, the learning value Gi is obtained.
Is decreased, and the first boundary value Mi is also decreased. Thus, the first boundary value Mi is maintained at the limit where knocking occurs.

Further, if the temperature of the intake air supplied into the combustion chamber 5 increases during the early injection I ₁ , early ignition tends to occur. Therefore, in the embodiment according to the present invention, the first boundary value Mi is moved to the lower load side as the temperature of the intake air supplied into the combustion chamber 5 increases. That is, specifically, the first boundary value Mi is obtained based on the gradually increasing value.

Mi = K · Gi where K is a correction coefficient and Gi is the above-mentioned learning value. FIG. 9 shows the relationship between the correction coefficient K and the temperature T of the intake air. When the temperature T of the intake air exceeds a certain temperature, the value of the correction coefficient K is decreased as the intake air temperature T increases, and thus the first boundary value Mi is decreased.

The second boundary value Li is calculated based on the following equation. Li = Mi−ΔQ Here, ΔQ is a constant value. That is, the second boundary value Li is obtained by subtracting the constant value ΔQ from the first boundary value Mi. Next, the interrupt routine shown in FIG. 10 will be described. This routine is executed by interruption every fixed crank angle. When this interruption routine is executed, a reset signal shown in FIG. 2 is generated.

Referring to FIG. 10, first, the current engine speed range ni is determined based on the engine speed N.
Next, at step 51, the fuel injection amount Q is set to the first boundary value M.
It is determined whether it is between i and the second boundary value Li. If Q ≦ Li or Q ≧ Mi, the process jumps to step 58. On the other hand, when Li <Q <Mi, the routine proceeds to step 52.

In step 52, the peak hold circuit 28
Is determined whether or not the output voltage _VP is higher than the set value V _O. When V _P > V _O , that is, when the knocking intensity is equal to or more than a predetermined value, the routine proceeds to step 53, where the correction value Δm
A constant value α is subtracted from i. Next, at step 55, an addition result obtained by adding the correction value Δmi to the reference boundary value mi is set as a learning value Gi. Therefore, the learning value Gi is gradually reduced as long as V _P > V _O. On the other hand, step 52
If it is determined that V _P ≦ V _O , the routine proceeds to step 54, where a fixed value β (β <α) is added to the correction value Δmi, and then the routine proceeds to step 55. Therefore, V _P ≦ V _O
In the case of, the learning value Gi is gradually increased. The learning value Gi is stored in the backup RAM 33a.

Next, at step 56, it is determined whether or not the learning value Gi has become larger than the reference boundary value mi. G
When i ≦ mi, the process proceeds to step 58. On the other hand, when Gi> mi, the routine proceeds to step 57, where Gi is set to mi.
Then, the process proceeds to step 58. Therefore, the learning value Gi
Is controlled so as not to exceed the reference boundary value mi. In step 58, a correction coefficient K is calculated from the relationship shown in FIG. 9 based on the intake air temperature T detected by the intake air temperature sensor 25. Next, at step 59, the learning value Gi is multiplied by the correction coefficient K to obtain the first boundary value Mi (= K ·
Gi) is calculated. Next, at step 60, the second boundary value Li (= Mi−ΔQ) is calculated by subtracting the constant value ΔQ from the first boundary value Mi. Then a reset signal is fed to the reset input terminal of the step 61 in the peak hold circuit 28, whereby the output voltage V _P of the peak hold circuit 28 is made zero.

FIG. 11 shows an injection control routine.
Referring to FIG. 11, first, at step 70, the fuel injection amount Q is calculated from the map shown in FIG.
Next, at step 71, the current engine speed region ni is determined. Next, at step 72, it is determined whether or not a flag X indicating that the operating state of the engine is in the operating region X (FIG. 4) is set. When the flag X is set, that is, when the operating state of the engine is in the operating region X, the routine proceeds to step 73.

In step 73, it is determined whether or not the fuel injection amount Q has become larger than the first boundary value Mi. Q ≦
In the case of Mi, the routine proceeds to step 74, where the injection start timing θS1 is calculated from the map shown in FIG. Next, at step 75 the early injection I ₁ is performed. On the other hand, when it is determined in step 73 that Q> Mi, the routine proceeds to step 76, where the flag X is reset. Next, in step 78, the injection completion timing θE2 is calculated from the map shown in FIG. Next, at step 79 the compression top dead center injection I ₂ is performed. That is switched early injection I ₁ becomes a Q> Mi compression top dead center injection I _2.

On the other hand, when it is determined in step 72 that the flag X has not been set, the routine proceeds to step 77, where it is determined whether the fuel injection amount Q has become smaller than the second boundary value Li. When Q ≧ Li, the routine proceeds to step 78, where the injection completion timing θE2 is calculated from the map shown in FIG. Next, at step 79 the compression top dead center injection I ₂ is performed. On the other hand, when it is determined in step 77 that Q <Li, step 8
Going to 0, the flag X is set, then step 74
At the injection start timing θE from the map shown in FIG.
1 is calculated. Next, at step 75, the early injection I ₁
Is performed. That is, when Q <Li, the compression top dead center injection I
₂ is switched to the early injection I ₁ from.

[0038]

NO _x and soot can be prevented from occurring at the time of engine low load operation, according to the present invention.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing an output voltage V _{s of a} knocking sensor and an output voltage V _p of a peak hold circuit.

FIG. 3 is a diagram showing a change in pressure P in a combustion chamber.

FIG. 4 is a diagram showing operation regions X and Y.

FIG. 5 is a diagram showing an injection timing.

FIG. 6 is a diagram showing a map of a fuel injection amount Q and the like.

FIG. 7 is a diagram showing a first boundary value Mi and a second boundary value Li.

FIG. 8 is a diagram showing a reference boundary value mi and a learning value Gi.

FIG. 9 is a diagram showing a correction coefficient K;

FIG. 10 is a flowchart of an interrupt routine.

FIG. 11 is a flowchart for performing injection control.

[Explanation of symbols]

 5 combustion chamber 6 fuel injection valve 26 knocking sensor

Claims (9)

[Claims] In a compression ignition type internal combustion engine in which fuel is injected into a combustion chamber, an operation region of the engine is divided into a low load side operation region and a high load side operation region with a predetermined boundary as a boundary. When the operating state of the engine is lower than the boundary of the operating range, the engine is divided into about 60% before the compression top dead center.
Compression ignition in which fuel is injected early before the start of operation and the engine is switched to compression top dead center injection in which fuel is injected near the compression top dead center when the operating state of the engine is higher than the boundary of the operating region. Type internal combustion engine. 2. The compression ignition type internal combustion engine according to claim 1, wherein a boundary of the operation region is moved according to an operation state of the engine. 3. The compression ignition type internal combustion engine according to claim 2, wherein the boundary of the operation region is shifted to a lower load side as the temperature of the intake air supplied into the combustion chamber becomes higher. 4. The compression ignition type internal combustion engine according to claim 2, wherein the boundary of the operating region is moved in accordance with a state of combustion when the early injection is performed. 5. A control device for determining whether or not a predetermined normal combustion is being performed when the early injection is performed, wherein a predetermined value is determined when the early injection is performed. The compression ignition type internal combustion engine according to claim 4, wherein when it is determined that normal combustion is not being performed, the boundary of the operation region is moved to a low load side. 6. A compression ignition type engine according to claim 5, wherein said judging means judges that predetermined normal combustion is not being performed when the knocking intensity generated by the engine exceeds a predetermined value. Internal combustion engine. 7. The compression ignition type internal combustion engine according to claim 4, wherein a boundary of the operating region is determined for each predetermined engine speed range. 8. A boundary between the operating region and a first boundary.
The first boundary is switched from the early injection to the compression top dead center injection at the first boundary, and the second boundary is switched from the compression top dead center injection to the early injection at the second boundary. The compression ignition type internal combustion engine according to claim 2, which is switched. 9. The first boundary is moved according to the state of combustion when the early injection is performed, and the second boundary is low when the first boundary is moved to a low load side. The compression ignition type internal combustion engine according to claim 8, wherein the compression ignition type internal combustion engine is moved to a load side.