JP2003148222A - Compression ignition type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress instable combustion in a low load area, when low heat rate pilot/main combustion is implemented. SOLUTION: In a compression ignition type internal combustion engine, the amount and timing of fuel jetted from a fuel injection valve is controlled based on an engine operational state. The engine comprises: a first injection mode to perform pilot injection in the amount and timing where a maximum heat rate is not more than 60 kJ/s by the pilot injection, and then to perform main injection at the timing succeeding to a compression top dead center; and a second injection mode to perform the pilot/main injection based on a condition not satisfying the condition of the first injection mode. The second injection mode is performed in an engine low load area II, and the first injection mode is performed in an engine high load area I. In the low load area, normal pilot/ main injection is performed to suppress instable combustion.

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, and more particularly to a compression ignition type internal combustion engine in which exhaust gas is cleaned by improving a combustion mode.

[0002]

2. Description of the Related Art Environmental demands for internal combustion engines, especially diesel engines, have been increasing more and more in recent years, and there is an urgent need to improve the exhaust gas. Therefore, a diesel particulate filter (DP) that collects soot such as black smoke
Although various post-treatment technologies such as F) and NOx catalysts for reducing and purifying NOx have made remarkable progress, it is still desirable to improve the combustion form itself because it leads to drastic measures.

In ordinary diesel combustion, near compression top dead center (generally 10
° BTDC to 10 ° ATDC)), single-stage (one-time) fuel injection is performed, the fuel is partially ignited after a predetermined ignition delay period, and then the fuel evaporates according to diffusion of the fuel.
It takes the form of diffusion combustion in which mixing with air and combustion proceed to perform combustion while sequentially diffusing the flame in a turbulent state.

On the other hand, smoke and N
Various improvements have been made to meet the increasing demand for Ox reduction. To reduce NOx, EGR (Exhausus
tGas Recirculation: Exhaust gas recirculation)
Has been conventionally known to be effective and has been widely realized. However, since the EGR recirculates the exhaust gas, it is impossible to avoid the deterioration of smoke.

Further, in the normal combustion, the in-cylinder pressure may be rapidly increased due to the rapid initial combustion, and a large combustion noise may be generated. Therefore, in order to prevent this, a two-stage injection may be performed in which a small amount of pilot injection is executed before the main injection (main injection) that is performed at normal timing.
In this case, after the fuel injected by the pilot injection is ignited and the fire is created, the fuel injected by the main injection is burned based on this fire, so that the rapid initial combustion and the rapid increase in the cylinder pressure are suppressed, and the combustion noise is reduced. To be prevented. The combustion mode at this time is basically the same as that of diffusion combustion.

However, in such a normal pilot-main injection, there is a problem that smoke is deteriorated by performing the pilot injection.

[0007]

By the way, in recent years, new combustion systems have been proposed for these technologies.
One is M for the purpose of simultaneous reduction of NOx and smoke.
This is referred to as K (Modulated Kinetics) combustion. This can also be expressed as low temperature premixed combustion, and its outline is as follows. That is, since reduction of the combustion temperature is effective for reducing NOx, this is performed by a relatively large amount of EGR. There is concern that smoke will increase, but this will be addressed by premixing the fuel. There are two methods for premixing: early injection, in which fuel is injected earlier than usual, and retard injection, in which fuel is injected later than usual. Retard injection is adopted because it is held. In summary, MK combustion aims to reduce NOx and smoke simultaneously by combining a large amount of EGR and retard injection. In addition, as a reference document, “Vehicle Engineering Society Papers Vol. 28, No. 1, 1997-1, p. 41”,
"Vol. 28, No. 2, 1997-4, p. 2
9 ”etc.

However, in MK combustion, single-stage injection is performed after the compression top dead center, and the ignition and combustion are performed slowly after a relatively long premixing period. Is low, combustion is unstable, and misfires and white smoke are likely to occur. Further, since it is premised that a large amount of EGR is executed, a large smoke reducing effect cannot be expected.

On the other hand, as disclosed in Japanese Unexamined Patent Publication No. 2000-310150, there is one in which pilot injection is performed at an earlier timing than usual, and main injection is performed at a timing at which misfire occurs without pilot injection. This aims at further reduction of NOx.

However, although this is effective in reducing NOx, continuous combustion by pilot injection still occurs before the main injection, and smoke is generated by combustion by pilot injection, which is a cause of worsening smoke. .

Therefore, it is difficult to improve smoke with these techniques, and it is not always sufficient to cope with strict exhaust gas regulations in the future.

Therefore, as a solution to this problem, the present inventors have
We newly invented a combustion (injection) mode with low heat generation rate pilot main combustion (injection) and filed an application for it before (Japanese Patent Application No. 20).
01-315289). The low heat generation rate pilot injection reduces the soot generation due to the pilot injection by controlling the amount and timing of the pilot injection so that the maximum heat generation rate due to the pilot injection is suppressed to 60 kJ / s or less.

However, according to this low heat release rate pilot injection, there is a problem that combustion becomes unstable due to deterioration of fuel ignitability when the engine is operating in a low load region.

Therefore, the present invention was devised in view of the above problems, and its purpose is to provide a low heat generation rate pilot injection,
It is to suppress the instability of combustion in the low load region of the engine.

[0015]

SUMMARY OF THE INVENTION The present invention comprises a fuel injection valve for injecting fuel into a combustion chamber in a cylinder, and controls the amount and timing of fuel injected from the fuel injection valve based on engine operating conditions. In the compression ignition type internal combustion engine thus configured, the pilot injection is performed from the fuel injection valve in the fuel injection control mode with the fuel injection amount and the fuel injection timing such that the maximum heat generation rate by the pilot injection becomes 60 kJ / s or less. The first injection mode in which the main injection is performed from the fuel injection valve at a timing after compression top dead center, and the pilot injection from the fuel injection valve is performed based on a condition that does not satisfy the conditions of the first injection mode. The second injection mode for executing the main injection is provided, and the fuel injection control is executed in the second injection mode in the low load region of the engine, and In a high load region of the emission to perform the fuel injection control by the first injection mode, in which switching the fuel injection control mode.

According to this, in the low load region, the normal pilot main injection is performed without performing the low heat generation rate pilot main injection. As a result, instability of combustion in the low load region can be suppressed.

Here, in the low load region of the engine,
It is preferable to switch the fuel injection control mode so that the fuel injection control is executed in the second injection mode in the low speed region of the engine and the fuel injection control is executed in the first injection mode in the high speed region of the engine.

It is preferable that a hysteresis is provided at the switching point of the fuel injection control mode.

It is preferable that a predetermined moderation control is executed when the fuel injection control mode is switched.

In the above compression ignition type internal combustion engine mounted on a vehicle, a damper control for preventing a coupled vibration between the engine and the vehicle is executed when the fuel injection amount changes abruptly. When the switching of the fuel injection control mode occurs during execution, it is preferable that the switching of the fuel injection control mode is executed after a lapse of a predetermined time from the start of execution of the damper control.

[0021] In the first injection mode, it is preferable that the EGR device performs EGR.

The compression ignition type internal combustion engine may be a common rail type diesel engine.

Further, according to the present invention, a fuel injection valve for injecting fuel into a combustion chamber in a cylinder, a common rail for constantly supplying high pressure fuel to the fuel injection valve, and an amount of fuel actually injected from the fuel injection valve are provided. In a common rail type diesel engine provided with a control unit that controls the injector so that the timing becomes a target fuel injection amount and a target fuel injection timing that are predetermined based on the engine operating state,
In the fuel injection control mode, the control means causes the fuel injection valve to execute the pilot injection with the fuel injection amount and the fuel injection timing such that the maximum heat generation rate by the pilot injection becomes 60 kJ / s or less, and then the compression is performed. A first injection mode in which the main injection is executed from the fuel injection valve at a timing after dead center, and a pilot injection and a main injection are executed from the fuel injection valve based on a condition that does not satisfy the conditions of the first injection mode. The fuel injection control mode is provided so that the fuel injection control is executed in the second injection mode in the low load region of the engine and the fuel injection control is executed in the first injection mode in the high load region of the engine. It is to switch.

Further, the present invention provides a method for controlling a compression ignition type internal combustion engine in which the amount and timing of fuel injected from a fuel injection valve into a combustion chamber in a cylinder are controlled based on an engine operating state. As a control mode, pilot injection is executed from the fuel injection valve with a fuel injection amount and fuel injection timing such that the maximum heat generation rate due to pilot injection is 60 kJ / s or less, and then the above-mentioned timing is applied after compression top dead center. A first injection mode for executing main injection from the fuel injection valve and a second injection mode for executing pilot injection and main injection from the fuel injection valve based on conditions that do not satisfy the conditions of the first injection mode are set. , In the low load region of the engine, the fuel injection control is executed in the second injection mode, and in the high load region of the engine, the first injection mode is set. Ri to perform fuel injection control, a control method for switching the fuel injection control mode.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a compression ignition type internal combustion engine according to this embodiment. The compression ignition type internal combustion engine referred to here is an engine of a type in which fuel injected into a combustion chamber in a cylinder is self-ignited by compression in the cylinder, typically a diesel engine, particularly a common rail type in this embodiment. It is a common rail diesel engine equipped with a fuel injection device. Although the figure shows a single cylinder for convenience, it is of course possible to have multiple cylinders.
This engine is mounted on the vehicle.

Reference numeral 1 denotes an engine body, which is composed of a cylinder (cylinder) 2, a cylinder head 3, a piston 4, an intake port 5, an exhaust port 6, an intake valve 7, an exhaust valve 8, an injector 9 as a fuel injection valve, and the like. To be done. A combustion chamber 10 is formed in the cylinder 2, and fuel is injected from the injector 9 into the combustion chamber 10. A cavity 11 is formed at the top of the piston 4, and the cavity 11 forms a part of the combustion chamber 10. The cavity 11 is in the form of a reentrant type combustion chamber with a raised bottom center. The fuel injected from the injector 9 always reaches the inside of the cavity 11. This is because if fuel adheres to the side wall of the cylinder 2 or the like, problems such as unburned HC discharge occur.

The intake port 5 is connected to the intake pipe 12, and the exhaust port 6 is connected to the exhaust pipe 13. In addition, a turbocharger 14 is provided in this engine to supercharge intake air by utilizing exhaust energy. Reference numeral 15 is a turbine, and 16 is a compressor. Compressor 16
An intake air amount sensor 17 for detecting the intake air amount is provided on the upstream side, and an intercooler 18 for cooling the intake air is provided on the downstream side of the compressor 16. However, it goes without saying that the present invention is also effective for a naturally aspirated engine without a turbocharger.

Further, this engine is also equipped with an EGR device 19. The EGR device 19 includes an intake pipe 12 and an exhaust pipe 1.
An EGR pipe 20 that connects the EGR valve 3 and the EGR pipe 21, an EGR valve 21 for adjusting the EGR amount, and an EGR cooler 22 that cools the EGR gas upstream of the EGR valve 21. The intake pipe 12 is provided with an intake throttle valve 23 for appropriately restricting intake air on the upstream side of the connection portion with the EGR pipe 20.

The injector 9 is connected to the common rail 24, and high-pressure fuel (20 to 200 MPa) corresponding to the injection pressure stored in the common rail 24 is constantly supplied to the injector 9. The fuel pressurized and fed by the high-pressure pump 25 is supplied to the common rail 24 at any time.

An electronic control unit (hereinafter referred to as ECU) 26 is provided for electronically controlling this engine. EC
U26 detects the actual engine operating state from various sensors, and based on this engine operating state, the injector 9,
The EGR valve 21, the intake throttle valve 23, and a metering valve (not shown) for adjusting the fuel pressure feed amount from the high pressure pump 25 are controlled. In addition to the intake air amount sensor 17, the sensors include an accelerator opening sensor, an engine rotation sensor, a common rail pressure sensor (none of which is shown), and the like. The actual intake air amount, accelerator opening, engine rotation speed ( EC) such as engine speed, crank angle of engine, common rail pressure, etc.
It is designed to be detected by U26.

The injector 9 is turned on by the ECU 26.
It has an electromagnetic solenoid that is turned on / off, and opens the fuel when the electromagnetic solenoid is on to inject fuel, and closes the electromagnetic solenoid when it is off to stop fuel injection. The ECU 26 mainly determines the target fuel injection amount and the target fuel injection timing (timing) from the engine rotation speed and the accelerator opening degree, and at the same time when the timing actually arrives, only for a time corresponding to the target fuel injection amount. Turn on the electromagnetic solenoid. The larger the target fuel injection amount, the longer the ON time.

More specifically, the ECU 26 executes the two-stage injection by the relatively small amount of pilot injection and the relatively large amount of main injection. Specifically, the ECU 26 determines the target fuel injection timing and the target fuel injection amount based on the engine operating state for each of the pilot injection and the main injection according to a predetermined map or the like,
When each target fuel injection timing arrives, the injector 9 is operated for a time corresponding to each target fuel injection amount.
Is turned on, and the pilot injection and the main injection corresponding to each target fuel injection timing and target fuel injection amount are executed.

Further, the ECU 26 determines the target common rail pressure according to the operating state of the engine, and feedback-controls the common rail pressure so that the actual common rail pressure approaches the target common rail pressure.

The injector 9 is located substantially coaxially with the cylinder 2 and injects fuel radially from a plurality of injection holes at the same time. The angle between the axis L of each fuel spray and the cylinder center C is always constant.

Next, the contents of fuel injection control in this engine will be described.

This engine or ECU 26 has two fuel injection control modes. One is called a low heat generation rate pilot main injection mode (corresponding to the first injection mode of the present invention), and one is called a normal injection mode (corresponding to the second injection mode of the present invention).

The normal injection mode is a mode in which normal pilot injection and main injection are executed, and their fuel injection timing and fuel injection amount are usually the same. Regarding the fuel injection timing, the main injection is usually set near the same compression top dead center, that is, about 10 ° BTDC to 10 ° ATDC, and the pilot injection is 15 to 20 ° before the main injection.
The time interval (pilot interval) between the pilot injection and the main injection is set to be about BTDC and is relatively short. Regarding this combustion mode, as described above, the fuel injected by the main injection is ignited and burned based on the ignition type created by the pilot injection, and basically the diffusion combustion mode is adopted. By such two-stage injection, abrupt initial combustion and abrupt increase of in-cylinder pressure are prevented, and combustion noise is suppressed.

Next, the low heat generation rate pilot / main injection mode will be described.

In this mode, in order to suppress the generation of soot, the maximum heat generation rate by pilot injection is 60 kJ / s.
It is characterized in that the amount and timing of pilot injection are controlled so as to be suppressed below. By suppressing the maximum heat generation rate due to pilot injection, the fuel injected into the cylinder due to pilot injection does not continue to burn until the main injection is performed, and soot generation due to pilot injection is suppressed. Can reduce the amount of soot discharged from the engine. This combustion (injection) form is called low heat release rate pilot main combustion (injection),
The fuel injection control mode that realizes this combustion (injection) form is the low heat generation rate pilot main injection mode.

FIG. 2 shows the results of an actual machine test in which the state of heat generation in the cylinder with respect to changes in pilot injection timing was investigated. The horizontal axis is the crank angle. On the vertical axis, (a) at the bottom is the solenoid current flowing through the electromagnetic solenoid of the injector 9, and (b) is the heat generation rate (heat generation amount per second; kJ / s). Note that the heat release rate in FIG. 7B is a calculation result obtained from the actually measured value of the cylinder internal pressure.

The figure shows the timing and amount of main injection,
The four injection forms (1), in which the amount of pilot injection is constant and only the timing of pilot injection is changed, are also shown. Pilot injection timings of 48 ° BTDC (-48 ° ATDC, the same applies below), 38 ° BTDC, 28 ° BTDC, and 18 ° BTD, respectively.
It is C. The main injection timing is 5 ° ATDC. Note that all of these timings are when the injector 9 is ON.
It is specified by the start time.

The general pilot injection timing is set so as to approach the main injection as much as possible. 2500 rpm under the constraints of the currently widely used hardware
Since it is about 15 to 20 ° BTDC in the following medium and low speed rotations, can be said to be a general pilot injection timing. On the other hand, the pilot injection timing is advanced earlier or advanced in the order of
Has been done.

On the other hand, the main injection timing of this embodiment is set after the compression top dead center TDC, and is set on the retard side as compared with the general main injection timing under the same operating conditions. That is, the main retard injection is executed. This is to promote the lean dilution and premixing of the fuel in the region where the in-cylinder temperature is lowered to reduce smoke.

As can be seen from FIG. 7B, in the case of, a remarkable peak of the heat generation rate by the pilot injection is observed, and in the case of, such a remarkable peak is not observed. The peak value (maximum value) of the heat release rate tends to increase as the pilot injection timing is retarded. In the case of, the fuel (light oil) by the pilot injection is continuously ignited or burned at the peak generation timing, and it is therefore predicted that soot is generated. Therefore, the pilot injection timing of is not so preferable.

On the contrary, as in the case of and, as the pilot injection timing is earlier, the fuel is injected in a state where the in-cylinder pressure and the in-cylinder temperature are lower, so that the in-cylinder pressure and the in-cylinder temperature at which ignition is possible are reached. By this time, sufficient premixing is possible, no remarkable peak of heat generation rate occurs, and no soot is generated.

From these results, the inventors of the present invention paid attention to the heat release rate by pilot injection and conducted a test described later. As a result, the heat release rate peak by pilot injection and the soot when the main injection was performed together were carried out. It was newly found that there is a strong correlation with the occurrence of. Therefore, the fuel injection amount and the fuel injection timing in the pilot injection are determined to be optimum as described later.

By the way, as shown in the figure, compared with, there was no peak of the heat release rate,
The pilot injected fuel tends to burn with the main injected fuel executed after the top dead center, and the peak value of the heat release rate tends to increase when the main injected fuel burns. The peak value of the heat release rate generated after the main injection is highest at, and becomes lower as follows. That is, the earlier pilot injection is performed, the longer the ignition delay becomes, and the stronger the tendency is to burn the fuel together with the main injection fuel at a stretch.

As described above, in the early pilot injection, a higher peak value of the heat release rate is obtained after the main injection executed after the top dead center, as compared with the normal pilot injection, so that the combustion is performed relatively rapidly and the output is increased. And improved fuel economy are expected.

As described above, it can be said that the pilot injection timing should be earlier, but if it is too early, the fuel injected from the injector will not enter the cavity because the piston is located considerably below. If this happens, the injected fuel will adhere to the side walls of the cylinder,
This causes problems such as oil dilution and increase in unburned HC.
Therefore, the limit of the pilot injection timing on the advance side is
The timing is preferably such that the fuel injected from the injector just barely enters the cavity. In other words, as shown in FIG. 1, it is when the crank angle is such that the fuel L injected from the injector 9 passes through the inlet end edge 27 of the cavity 11. This crank angle is usually about 50 ° BTDC.

On the other hand, the retard side limit of the pilot injection timing and the pilot injection amount should be optimally determined in consideration of the above-described heat release rate and soot correlation. That is, if the pilot injection timing is retarded too much or the pilot injection amount is set too large, a remarkable heat generation rate peak occurs and soot occurs.

The results of the tests conducted to determine these are shown in FIGS. 5 and 6.

FIG. 5 shows the relationship between the pilot injection timing and the maximum heat generation rate due to the pilot injection. The horizontal axis indicates the pilot injection timing (° ATDC),
The vertical axis is the maximum heat generation rate (kJ / s; kilojoule per second). Further, FIG. 6 shows the relationship between the maximum heat release rate due to pilot injection and the soot (soot). The horizontal axis is the soot (g / kWh) and the vertical axis is the maximum heat release rate (kJ / s). . The maximum heat release rate referred to here is the peak value (maximum value) of the heat release rate due to pilot injection that occurs before top dead center in the heat release rate diagram of FIG.

The test shows that the displacement per cylinder is about 800 cc.
Of two types of pilot injections (A; 3 mm ³ / st, B; 6 mm ³ / st) in the multi-cylinder engine of No. 1 and in the multi-cylinder engine of the displacement per cylinder of about 400 cc
It carried out with respect to the kind of pilot injection amount (C; 1.2 mm ³ / st). For each of A to C, the pilot injection timing is changed in the range of −10 to −50 ° ATDC, and three diagrams A, B, and C in the graph are obtained.
As a common test condition, the output torque of the engine is from A to
C. The total fuel injection amount is set so as to be constant under each condition, the total injection amount is set to about a medium load, and the main injection timing is set after the compression top dead center. Here, the main injection is performed after the compression top dead center at a timing at which combustion gradually progresses even without pilot injection, and at a timing and amount at which ignition does not occur until the main injection is completed. Be seen. By the way, if the main injection is performed before and near the top dead center, ignition will start immediately and smoke and NOx cannot be reduced.

The graphs in FIGS. 2, 3 and 4 correspond to A, B and C, respectively. In other words, the graphs of FIG. 2, FIG. 3, and FIG. 4 are created based on the results of the tests under the respective conditions of A, B, and C.
Graph is created.

As can be seen from FIG. 5, the maximum heat generation rate tends to decrease as the pilot injection timing is advanced (advanced). Further, the smaller the pilot injection amount, the smaller the maximum heat generation rate, and the increase rate of the maximum heat generation rate with respect to the retardation of the timing (that is, the inclination of the diagram) tends to decrease.

Next, in FIG. 6, the pilot injection timing is advanced, the maximum heat generation rate is decreased, and the soot is also decreased as the diagram moves toward the left side. If the maximum heat generation rate is 60 kJ / s or less, a good soot level can be obtained under any of A, B, and C conditions.

From this result, therefore, the fuel injection amount and the fuel injection timing in the pilot injection are set so that the maximum heat release rate in the combustion chamber is 60 kJ / s or less. And The pilot injection performed with such a fuel injection amount and fuel injection timing is referred to as a low heat generation rate pilot injection. In other words, the pilot injection amount and timing at which the maximum heat generation rate is 60 kJ / s are the upper limit value of the injection amount and the retard side limit value of the timing. As a result, the combustion of the pilot injection fuel alone is prevented, and as a result, the smoke can be suppressed together with the main injection performed after the top dead center.

Returning to FIG. 5, the maximum heat release rate is 60 kJ /
Condition A (3 mm ³/ St) is about −
Before 39 ° ATDC (39 ° BTDC), Condition B (6m
m³/ St) about -40 ° ATDC (40 ° BTD
Before C), condition C (1.2 mm³/ St) is about -27
Before ° ATDC (27 ° BTDC). So this
The pilot injection corresponding to each of A, B, and C conditions
The timing shall be set.

As described above, the maximum heat release rate is 60 kJ /
The combustion (injection) mode of the present embodiment accompanied by the pilot injection that is s or less is referred to as low heat generation rate pilot main combustion (injection). The combustion modes are summarized below. First, when pilot injection is performed with the optimum amount and timing as described above, this injected fuel is sufficiently diffused in the combustion chamber to be diluted and premixed, and the fuel in the cylinder is continuously ignited and burned. Is suppressed. This state is maintained beyond the compression top dead center TDC until the combustion timing of the main injection. When the main injection is executed at the main injection timing set after the top dead center, the cylinder pressure and temperature are lower than usual, so after a longer ignition delay period than usual, the main injection fuel is diluted with the pilot injection. Ignite and burn with the mixture. At this time, the premixing of the main injected fuel has already progressed sufficiently, so that the generation of soot due to combustion is suppressed.

According to the low heat generation rate pilot main combustion (hereinafter also referred to as "main combustion method"), since the low heat generation rate pilot injection is performed together with the retard domain injection, after the main injection as compared with the single stage injection retarded combustion. The premixing period can be shortened, and combustion after the main injection can be rapidly performed in a state where the temperature in the cylinder is low as shown in FIG. This can prevent deterioration of fuel efficiency. Further, by premixing the pilot injected fuel, the in-cylinder temperature at the time of combustion of the main injected fuel can be increased, and the combustion can be stabilized.

On the other hand, the main combustion system has the above optimum amount,
Since the pilot injection is performed at the optimum timing, the combustion of the pilot injection fuel does not occur before the main injection, and the smoke can be improved as compared with the technique of JP 2000-310150 A.

As described above, in the compression ignition type internal combustion engine in which the pilot injection is performed and the retarder domain injection is performed after the compression top dead center, the amount and timing of the pilot injection can be optimized, and the smoke caused by the pilot injection can be suppressed. Can be suppressed.

In the low heating rate pilot main injection mode (first injection mode), the EGR device 19 executes EGR to suppress NOx.

Although the main combustion system has the above-mentioned advantages, there is a problem that combustion becomes unstable due to deterioration of fuel ignitability when the engine is operating in a low load region.

Therefore, the engine of the present embodiment executes the fuel injection control by switching the fuel injection control mode to the normal injection mode (second injection mode) in the low load region. This will be described in detail below.

FIG. 7 is a fuel injection control mode switching map stored in advance in the ECU 26. The ECU 26 compares this map with the actual engine speed and load to determine whether the fuel injection control mode is the first injection mode or the second injection mode. Either one of them is selected to execute the fuel injection control. As can be seen from this map, in the region II on the low load and low rotation side, the fuel injection control by the second injection mode is executed, and in the region I on the high load (exceeds the low load) or the high rotation side, The fuel injection control in the single injection mode is executed. Here, the second injection mode may be uniformly set in the low load region, but even if the load is low, the problem of deterioration of fuel ignitability does not occur in the region on the high rotation side. In the region, the fuel injection control in the first injection mode is executed to obtain the benefit of this combustion method. Since the region I in which the first injection mode is used in the entire operation region is significantly wider than the region II in which the second injection mode is used, the benefits of the main combustion system can be obtained in a wide operation region.

As described above, the fuel injection control mode is switched to the second injection mode in the low load region, though only on the low rotation side, so that the instability of combustion can be suppressed.

In the simplest case, the mode switching is performed when the actual operating state exceeds the switching point H. However, this method has a disadvantage that hunting occurs because frequent switching is performed when the operating state is maintained near the switching point H.

To prevent this, it is preferable to provide a hysteresis at the switching point as shown in FIG. That is, although FIG. 8 shows the hysteresis with respect to the engine load, the switching load from the second injection mode to the first injection mode is set to a value H1 on the high load side, and the switching load from the first injection mode to the second injection mode is set. Is a value H2 on the low load side. By providing such hysteresis, hunting can be prevented and control can be stabilized. It should be noted that such hysteresis is also preferably provided at the engine speed switching point.

On the other hand, this mode switching has the following problems. That is, different maps of the target fuel injection timing and the target fuel injection amount are prepared in advance for the first injection mode and the second injection mode, and are stored in the ECU 26. When the switching is performed, the fuel injection timing and amount may change, and in the case of the engine mounted on the vehicle, the occupant may recognize the switching shock based on the change.

Therefore, in order to prevent this switching shock, it is preferable to execute the following smoothing control.

FIG. 9 shows the contents of the smoothing control, the upper part shows the fuel injection control mode, and the lower part shows the main injection timing. As shown in the lower part, the value of the main injection timing near the mode switching point (more specifically, the value of the target fuel injection timing of the main injection) is different in both modes. The value of the second injection mode is t2, and the value of the first injection mode is t1.

First, when the fuel injection control mode is switched from the second injection mode to the first injection mode based on the change in the engine operating state (a1), the main injection timing immediately changes from the value t2 of the second injection mode to the second injection mode. The value t1 of the second injection mode is gradually changed to the value t1 of the first injection mode without switching to the value t1 of the first injection mode (b1). In the illustrated example, a ramp function for transition is set, and the ramp constant is set to a value in a range where switching shock does not occur.

Next, even when the fuel injection control mode is switched from the first injection mode to the second injection mode based on the change in the engine operating state (a2), the main injection timing immediately changes to the value of the first injection mode. Without changing from t1 to the value t2 of the second injection mode, the value t1 of the first injection mode is gradually changed to the value t2 of the second injection mode (b
2). The transition at this time is also performed according to the ramp function as described above.

By executing such smoothing control, a sudden change in the main injection timing can be prevented, and a switching shock at the time of switching the fuel injection control mode can be prevented.

Although the illustrated example is for the main injection timing, such smoothing control is preferably performed for the main injection amount, pilot injection timing and pilot injection amount as necessary.

Further, in the engine of the present embodiment, the variable vanes provided in the turbine 15 of the turbocharger 14 are controlled according to the engine operating state, and the intake throttle valve 23 is controlled according to the engine operating state, so that the intake The amount can be controlled. With regard to the variable vane opening, the intake throttle valve opening, and the intake amount, the target values according to the engine operating state are stored in advance in the ECU 26 in a map format for each fuel injection control mode, and the actual engine operating state and Each target value is decided by comparing with the map.

In this case, when the variable vane opening, the intake throttle valve opening, or the target value of the intake amount changes between the modes when the fuel injection control mode is switched, these are also annealed as described above. It is preferable to exercise control.

Next, in the engine of this embodiment, damper control is executed to prevent the coupled vibration between the engine and the vehicle when the fuel injection amount changes relatively rapidly.

FIG. 10 schematically shows the control contents.
Is. For example, as shown in the figure, it is assumed that the actual engine operating state suddenly changes due to the driver suddenly stepping on the accelerator and the target fuel injection amount Qt rapidly increases. Normally, a fuel injection amount equal to this target fuel injection amount Qt is actually injected, so that the engine torque sharply increases,
The vehicle is about to accelerate. However, since the engine mount can be regarded as an elastic body, the engine vibrates as the engine torque rapidly increases, and this vibration is coupled with the vibration of the vehicle, and a large coupled vibration R is generated in the vehicle as illustrated. There are cases. Therefore, damper control is to automatically control the fuel injection amount of the engine so as to suppress the coupled vibration R by giving a vibration (indicated by a broken line) of an opposite phase to the coupled vibration R. The damper control is performed when the differential value ΔQt (= dQt / dt) of the target fuel injection amount Qt exceeds a preset threshold value S.

By the way, when the damper control and the fuel injection control mode switching interfere with each other and are executed at the same time, the fuel injection amount change by the damper control and the fuel injection amount and the fuel injection timing change by the mode switching cooperate with each other. On the contrary, the vibration of the vehicle may be amplified. This may cause the occupant to recognize the fact of mode switching.

Therefore, in order to prevent this, when they interfere with each other, the fuel injection control mode switching is temporarily stopped and delayed.

FIG. 11 shows the contents of this control.
(A) is the target fuel injection amount Qt, (b) is the differential value ΔQt (= dQt / dt) of the target fuel injection amount Qt, and (c) is the fuel injection control mode. Here, the damper control is executed only when the differential value ΔQt exceeds the positive threshold value S, and the damper control is not executed when the differential value ΔQt is a negative value. It is optional to execute even the most negative value.

The sudden increase in the target fuel injection amount Qt that appears first c
With respect to 1, since the differential value ΔQt does not exceed the positive threshold value S, the damper control is not executed. Therefore, at this time, if the engine operating state approaches the switching point of the fuel injection control mode, the mode is switched immediately as indicated by d1.

On the other hand, for the sudden increase c2 of the target fuel injection amount Qt that appears next, the differential value ΔQt exceeds the positive threshold value S. Therefore, the damper control is executed. At this time, even if the engine operating state approaches the switching point of the fuel injection control mode, the mode switching is not executed immediately as indicated by d2, and the mode is changed after a predetermined delay time td has elapsed from the start of the damper control execution. To switch. The delay time td is set to a time at which the damper control is completely completed or almost converges, and is, for example, 0.6.
s.

As described above, when the fuel injection control mode is switched during the execution of the damper control, the fuel injection control mode is switched after a lapse of a predetermined time from the start of the execution of the damper control, so that the vibration of the vehicle is amplified. Can be prevented.

As described above, when switching the fuel injection control mode,
By executing each switching control (hysteresis control, smoothing control and delay control) as described above, it becomes possible to suppress the influence on drivability due to mode switching.
It is possible to suppress the occurrence of switching shock and the like. Further, it is possible to prevent the occupant from recognizing the fact of the changeover, and it becomes possible to perform the changeover in terms of product performance, so that the exhaust gas can be improved over the entire operating region of the engine. The above switching controls can be combined appropriately.

Various other embodiments can be adopted as the embodiment of the present invention. For example, it is possible to correct the switching point H in the switching map of FIG. 7 according to the warm-up state of the engine. That is, the map is basically determined after the engine is warmed up.On the other hand, when the temperature inside the cylinder is low, such as when the engine is cold, heat generation due to pilot injection is reduced and combustion becomes unstable. There is a risk of becoming. Therefore, in such a case, the above correction is effective. For example, it is preferable to correct (move) the switching point H to the high load side and / or the high rotation side as the water temperature is lower.

In this embodiment, the normal injection mode is given as an example of the second injection mode according to the present invention, but the present invention is not limited to this, and the point is that the pilot is based on the condition that the condition of the first injection mode is not satisfied. All the injection modes that execute the injection and the main injection can be set to the second injection mode.

[0091]

In summary, according to the present invention, when the low heat release rate pilot / main combustion is realized, it is possible to suppress the instability of combustion in the low load region, which is an excellent effect.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a compression ignition type internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between pilot injection timing and heat release rate.

FIG. 3 is a graph showing the relationship between pilot injection timing and heat release rate.

FIG. 4 is a graph showing the relationship between pilot injection timing and heat release rate.

FIG. 5 is a graph showing the relationship between pilot injection timing and maximum heat release rate.

FIG. 6 is a graph showing the relationship between soot and maximum heat release rate.

FIG. 7 is a fuel injection control mode switching map.

FIG. 8 shows a hysteresis at a mode switching point.

FIG. 9 is a time chart showing the content of smoothing control.

FIG. 10 is a time chart schematically showing the contents of damper control.

FIG. 11 is a time chart showing the contents of delay control for mode switching.

[Explanation of symbols]

1 engine body 2 cylinders 4 pistons 9 injectors 10 Combustion chamber 11 cavities 19 EGR device 24 common rail 26 Electronic control unit (control means) 27 Entrance edge H, H1, H2 Fuel injection control mode switching point L Injection fuel axis R coupled vibration

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02M 25/07 570 F02M 25/07 570J 45/02 45/02 47/00 47/00 EF term (reference) ) 3G062 AA01 AA03 AA05 BA04 BA05 BA06 CA06 EA10 ED01 ED04 ED08 ED10 FA02 FA03 FA23 GA01 GA04 GA06 GA15 3G066 AA07 AA11 AA13 AB02 AC09 AD12 BA14 BA24 BA25 CB01 DC18 DC01 DC08 DC08 DC08 DC08 DC08 DB08 DC18 DA08 DA08 DA01 DA04 DA04 DA09 BA20 CA03 DA10 DA39 EA13 EB08 EB09 EB25 FA00 FA07 FA10 FA33 FA38 3G092 AA02 AA13 AA17 AA18 BB01 BB06 BB08 BB13 DB03 DC03 DC08 DE03S DE06S DG07 EA01 EA02 EB05 EC09 FA15 GA03 GA16 HA01Z HB03Z HE01Z HF08Z 3G301 HA02 HA11 HA13 JA23 JA24 JA25 JA37 KA07 KA08 LC01 MA11 MA18 MA23 NA01 NA08 NC02 NC04 NE11 NE12 NE21 NE26 PA01Z PB08A PB08Z PE01Z PE03Z PF03Z

Claims (9)

[Claims] 1. A compression ignition internal combustion engine comprising a fuel injection valve for injecting fuel into a combustion chamber in a cylinder, and controlling the amount and timing of fuel injected from the fuel injection valve based on an engine operating state. In the engine, as a fuel injection control mode, pilot injection is executed from the fuel injection valve at a fuel injection amount and fuel injection timing such that the maximum heat release rate by pilot injection is 60 kJ / s or less, and then compression top dead center. The first injection mode in which the main injection is executed from the fuel injection valve at the following timing, and the second injection in which the pilot injection and the main injection are executed from the fuel injection valve based on the condition that does not satisfy the conditions of the first injection mode. Mode, the fuel injection control is executed by the second injection mode in the low load region of the engine, and in the high load region of the engine. So that the serial first injection mode executing the fuel injection control, a compression ignition internal combustion engine, characterized in that switching the fuel injection control mode. 2. In the low load region of the engine, the fuel injection control is executed in the second injection mode in the low speed region of the engine, and the fuel injection control is executed in the first injection mode in the high speed region of the engine. The compression ignition type internal combustion engine according to claim 1, wherein the fuel injection control mode is switched. 3. The compression ignition type internal combustion engine according to claim 1, wherein a hysteresis is provided at a switching point of the fuel injection control mode. 4. The compression ignition type internal combustion engine according to claim 1, wherein a predetermined moderation control is executed when the fuel injection control mode is switched. 5. The compression ignition internal combustion engine according to claim 1, which is mounted on a vehicle, for preventing a coupled vibration between the engine and the vehicle when the fuel injection amount changes abruptly. When the damper control is executed and the switching of the fuel injection control mode occurs during the execution of the damper control,
5. The compression ignition internal combustion engine according to claim 1, wherein switching of the fuel injection control mode is executed after a lapse of a predetermined time from the start of execution of the damper control. 6. The compression ignition type internal combustion engine according to claim 1, wherein EGR is performed by an EGR device in the first injection mode. 7. The compression ignition type internal combustion engine according to claim 1, wherein the compression ignition type internal combustion engine is a common rail type diesel engine. 8. A fuel injection valve for injecting fuel into a combustion chamber in a cylinder, a common rail for constantly supplying high-pressure fuel to the fuel injection valve, and an amount and timing of fuel actually injected from the fuel injection valve. In a common rail type diesel engine including a control unit that controls an injector so that a target fuel injection amount and a target fuel injection timing that are predetermined based on an engine operating state are achieved, the control unit sets the fuel injection control mode as a fuel injection control mode. Pilot injection is performed from the fuel injection valve at a fuel injection amount and fuel injection timing such that the maximum heat generation rate by pilot injection is 60 kJ / s or less, and then the fuel injection valve is performed at a timing after compression top dead center. From the first injection mode for executing the main injection from A second injection mode for executing pilot injection and main injection from the fuel injection valve, the fuel injection control is executed in the second injection mode in the low load region of the engine, and the first injection mode in the high load region of the engine. A common rail type diesel engine, characterized in that the fuel injection control mode is switched so as to execute fuel injection control by means of. 9. A control method for a compression ignition type internal combustion engine, wherein an amount and timing of fuel injected from a fuel injection valve into a combustion chamber in a cylinder are controlled based on an engine operating state, wherein a fuel injection control mode is set. Pilot injection is performed from the fuel injection valve at a fuel injection amount and fuel injection timing such that the maximum heat generation rate by pilot injection is 60 kJ / s or less, and then the fuel injection valve is performed at a timing after compression top dead center. The first injection mode for executing the main injection from the fuel injection valve and the second injection mode for executing the pilot injection and the main injection from the fuel injection valve are set based on the conditions that do not satisfy the conditions of the first injection mode. The fuel injection control is executed in the second injection mode in the low load region, and in the first injection mode in the high load region of the engine. To perform the fuel injection control, a control method of a compression ignition type internal combustion engine, characterized in that switching the fuel injection control mode.