JP3500938B2 - Combustion control device for diesel engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control device for a diesel engine that reduces NOx (nitrogen oxide) and PM (particulate matter).

[0002]

NO emitted from a diesel engine
An exhaust gas recirculation system in which a part of the exhaust gas is recirculated into the intake air is effective for reducing the amount of x, but on the other hand, if the exhaust gas recirculation rate is increased, PM tends to increase accordingly. Therefore, the exhaust gas recirculation rate could not be increased so much to suppress the PM.

On the other hand, low temperature premixed combustion of a diesel engine has been attracting attention as a method for simultaneously reducing NOx and PM, which are in a trade-off relationship ("New combustion concept of small DI diesel engine" automobile). Technical Papers Vol.28 No.1 P.41 19
97).

This is to simultaneously realize reduction of NOx by low temperature combustion and reduction of PM by premixed combustion.
By recirculating part of the exhaust gas into the intake air, the maximum combustion temperature is suppressed and NOx generation is suppressed, while increasing the chances of contact between fuel spray and air (oxygen) as much as possible before ignition. In order to lengthen the contact time and realize gentle premixed combustion, the gas flow in the combustion chamber is increased, and the fuel injection timing is delayed to extend the ignition delay period until the fuel is ignited.

In this low-temperature premixed combustion, since a large amount of exhaust gas recirculates the premixed combustion at a low oxygen concentration, the combustion speed is lowered, and gentle combustion with less combustion noise can be realized.

[0006]

However, when low temperature premixed combustion is realized in this way, when the engine load increases and the fuel injection amount becomes relatively large, the oxygen amount necessary for combustion is secured. Therefore, it becomes necessary to reduce the exhaust gas recirculation rate. If this is not done, a large increase in HC, CO, PM due to incomplete combustion and deterioration of fuel efficiency cannot be avoided due to insufficient oxygen.

As a result, when the oxygen concentration in the working gas is increased and the effect of suppressing the premixed combustion speed is diminished, rapid premixed combustion occurs, which sometimes causes combustion noise called diesel knock.

As can be seen from FIG. 14, diesel combustion is composed of premixed combustion and diffusion combustion, which are shown separately, but when the pressure rise in the combined combustion rate waveform becomes steep, the diesel knock occurs. Cause

FIG. 15 shows the load and the exhaust gas recirculation rate (EGR rate).
The combustion rate waveforms are shown in order as the value is changed.

As can be seen from the figure, in A and B in the figure where the load is small and the fuel injection amount is small, the EGR rate is high and the oxygen concentration is low, so the premixed combustion period is long and the combustion is gentle. On the other hand, when the EGR is sharply reduced and the amount of fuel is not so much yet, but the oxygen concentration is high, the premixed combustion period is short and the combustion rate is steep. For this reason, the diesel knock increases rapidly in this region.

On the other hand, the load is further increased,
In E and F, which are regions where the fuel injection amount increases, the required oxygen concentration relatively decreases due to the increase in fuel even though the EGR is stopped, so the premixed combustion period increases and the comparison is made. The combustion will be milder and diesel knock will be reduced.

FIG. 16 shows a driving range during acceleration of the vehicle, and it can be seen that the vehicle passes through the knocking range during acceleration from a low load. This is because the EGR rate sharply decreases with acceleration,
On the other hand, diesel knock occurs in a region where the fuel injection amount is not so large yet. Further, even in a region where the premixed combustion speed due to EGR should originally be suppressed, when there is a response delay in the supply of EGR gas, such as during slow acceleration from deceleration of the vehicle (EGR is cut), Diesel knock may occur.

As described above, even in the case of low-temperature premixed combustion, a diesel knock is temporarily generated when the EGR sharply decreases during transient operation or when oxygen is excessively present in the fuel. There was an unavoidable problem.

The present invention has been proposed to solve such a problem. Focusing on the oxygen concentration in the working gas and the fuel injection period as control factors for determining the premixed combustion, the fuel is adjusted according to the oxygen concentration. By controlling the injection period, the purpose is to avoid diesel knock during transient operation.

[0015]

A first aspect of the present invention is directed to a fuel injection valve for injecting fuel into a combustion chamber, means for controlling the fuel injection timing and injection period, and a portion of exhaust gas recirculated into intake air. And a means for calculating the oxygen concentration in the working gas, a means for calculating the fuel injection period, and a premixed combustion period for diesel combustion from the oxygen concentration and the fuel injection period. Means, means for setting a target premixed combustion period according to the operating state, means for comparing the calculated premixed combustion period with the target premixed combustion period, and by this comparison the premixed combustion period is the target premixed combustion period. When the combustion period is shorter than the combustion period, there is provided combustion correction means for extending the fuel injection period with the same fuel injection amount.

A second aspect of the invention is a fuel pressure accumulating chamber for accumulating high pressure fuel pumped from a fuel pump, a means for controlling the fuel pressure in the fuel accumulating chamber to a target value, and the pressure controlled high pressure fuel for the combustion chamber. Fuel injection valve for injecting fuel into the fuel injection unit, means for variably controlling the injection period of the fuel injection valve, and control means for driving the fuel injection control unit so that the fuel injection amount and the injection timing correspond to the operating state. And a means for calculating a concentration of oxygen in the working gas, a means for calculating an injection period of fuel, and a means for calculating an oxygen concentration in the working gas, the oxygen concentration and the fuel injection period. Means for calculating the premixed combustion period of diesel combustion from, and means for setting the target premixed combustion period according to the operating state, and means for comparing the calculated premixed combustion period with the target premixed combustion period. And by this comparison, when the premixed combustion period is shorter than the target premixed combustion period, combustion correction means for decompressing and correcting the fuel pressure in the fuel accumulating chamber so as to extend the fuel injection period with the same fuel injection amount. Is equipped with.

In a third aspect of the present invention, the combustion correction means corrects the fuel pressure when the premixed combustion period is shorter than the target premixed combustion period, and when the premixed combustion period is longer than the target premixed combustion period, it depends on the operating condition. Is configured to maintain a basic fuel pressure of.

In a fourth aspect of the present invention, the means for calculating the oxygen concentration in the working gas is based on a fuel injection amount signal, an intake air amount signal, and an oxygen concentration signal from an exhaust sensor installed in the exhaust system. It is configured to calculate the oxygen concentration in the working gas.

In a fifth aspect, the means for calculating the oxygen concentration in the working gas calculates the oxygen concentration in the working gas based on the fuel injection amount signal, the intake air amount signal, and the exhaust gas recirculation amount signal. To be configured.

According to a sixth aspect of the present invention, the premixed combustion period calculating means calculates the premixed combustion period obtained from the fuel injection period when the exhaust gas recirculation is not performed in the operating state, and the exhaust gas recirculation is performed. It is configured so that the actual premixed combustion period is obtained by adding the delay period obtained according to the oxygen concentration during the combustion.

In a seventh aspect of the invention, the means for setting the target premixed combustion period has a diesel knock in each operating state,
The target premixed combustion period is set so that the unburned emission and the unburned emission are the minimum period within the allowable range.

[0022]

In the first and second aspects of the invention, the oxygen concentration in the working gas increases as the exhaust gas recirculation gas suddenly decreases in the process of increasing the amount of fuel, such as during engine acceleration, and the effect of suppressing premixed combustion is achieved. And the combustion pressure rises sharply after ignition, and diesel knock is likely to occur. However, the actual premixed combustion state is always detected, and the premixed combustion is performed rapidly so that the premixed combustion period becomes shorter than the target premixed combustion period set according to the operating state at that time. If so, a correction is made to extend the fuel injection period.

In the second aspect of the invention, this is performed by substantially lowering the fuel injection pressure, and if the fuel injection pressure is lowered, the fuel injection period required to maintain the same fuel injection amount becomes longer.

By extending the fuel injection period in this way, the premixed combustion period is correspondingly lengthened and the combustion is moderated. As a result, diesel knock that is likely to occur during transient operation is avoided, and combustion Noise is also reduced.

In the third aspect of the invention, the fuel injection pressure is decompressed and corrected only when the actual premixed combustion period is shorter than the target premixed combustion period, and when it is long, the basic fuel injection pressure is maintained and excessive. It is possible to avoid the adverse effect caused by the excessive pressure increase without increasing the fuel injection pressure.

According to the fourth and fifth aspects, the oxygen concentration in the working gas can be calculated easily and accurately.

In the sixth aspect of the invention, the premixed combustion period is calculated based on the fuel injection period, so that the actual premixed combustion period can be estimated easily and accurately.

In the seventh invention, the target premix combustion period is set not only for reducing diesel knock but also for H
The reduction of unburned emissions such as C and PM is set to fall within the allowable range, so that not only operability such as during transient operation but also exhaust performance can be favorably maintained.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall structure. 51 is a diesel engine main body, 52 is an exhaust passage, 53 is an intake passage, and a part of exhaust gas is returned to the intake passage 53 (EG
An exhaust gas recirculation passage 54 for performing the R) is provided, and an exhaust gas recirculation control valve 55 for controlling the exhaust gas recirculation amount is provided in the middle thereof. The opening degree of the exhaust gas recirculation control valve 55 is feedback-controlled based on a signal from the controller 60 so as to match the target exhaust gas recirculation amount according to the operating state.

A fuel injection valve 1 for injecting fuel directly into the engine combustion chamber 56 is provided, and the fuel injection valve 1 includes:
As will be described later, the common rail (high pressure fuel pressure accumulator) 26
High pressure fuel is supplied to the high pressure fuel. Then, the fuel injection amount and the injection timing are set according to the operating state, and the fuel injection valve 1 is controlled to be opened / closed by a signal from the controller 60 so as to have respective set values.

In order to realize the low temperature premixed combustion while recirculating a part of the exhaust gas into the intake air, although not shown, a swirl for producing a gas flow for promoting the mixing of the fuel and the air in the combustion chamber 56. Control means and the like are provided.

In order to maintain this low-temperature premixed combustion in good condition, the premixed combustion period of the fuel is calculated, and this premixed combustion period is longer than the target premixed combustion period set according to the operating state. The fuel injection period is feedback-controlled so that it will not be shortened.

In order to suppress the diesel knock to an allowable range, a gentle premixed combustion, in other words, the premixed combustion period has an appropriate length, but if it is too long, HC and PM will be reduced. Getting worse.

According to the experiments conducted by the present inventors, the premixed combustion period substantially coincides with the fuel injection period when EGR is not performed, and even when EGR is performed, the fuel injection period,
It has been found that it changes corresponding to the oxygen concentration in the working gas.

Therefore, the actual premixed combustion period is compared with the target premixed combustion period which is appropriately set according to the operating state, and the fuel injection period is set so as not to become shorter than the target premixed combustion period. The premix combustion period is controlled by adjusting
When 0 is set, for example, the common rail pressure (fuel injection pressure) is reduced and corrected.

The fuel injection period required to inject the same amount of fuel becomes longer as the fuel injection pressure becomes lower. Therefore, the fuel injection period can be lengthened by adjusting the fuel injection pressure.

As will be described later, the premixed combustion period changes depending on the state of EGR at that time, the oxygen concentration in the working gas, the fuel injection period, etc. Therefore, the controller 6
0 is a signal from the lift sensor 61 for detecting the fuel injection start timing and the fuel injection end timing of the fuel injection valve 1, and the lift sensor 62 serving as the opening signal of the exhaust gas recirculation control valve 55.
Detection signals from an exhaust sensor 63 (wide-range λ sensor) that detects the oxygen concentration in the exhaust, an intake air amount sensor 64 that detects the amount of intake air, and the like represent engine speed, accelerator opening, cooling that represent other operating conditions. It is input together with a detection signal such as water temperature, and the fuel injection pressure is feedback-controlled as described later.

FIG. 2 shows details of the fuel injection valve 1 and FIG. 3 shows details of the fuel injection system.

In FIG. 2, the fuel injection valve 1 is composed of an injection nozzle holder 2, an injection nozzle 3 and an injection valve drive section 4, and a retaining nut 5 integrates the injection nozzle holder 2 and the injection nozzle 3. Has been done. A needle valve sliding hole 6 and a fuel storage chamber 7 are formed in the injection nozzle 3, and a nozzle hole 8 communicating with the fuel storage chamber 7 is formed at the tip.

The large diameter portion 10 of the needle valve 9 is slidably fitted in the needle valve sliding hole 6. A connecting portion 11 is formed on the large diameter portion 10 of the needle valve 9, and a small diameter portion 12 and a valve body portion 13 are integrally formed on the lower tip end portion. Then, the valve body portion 13 opens and closes the seat portion X to turn on / off the fuel injection from the nozzle hole 8.

The push rod 14 abuts on the tip of the connecting portion 11 of the needle valve 9, and is further urged by the spring 16 in the valve closing direction. Further, the pin 17 positions the ejection nozzle 3 and the ejection nozzle holder 2. The push rod 14 is slidably fitted in a cylinder 15 formed in the injection nozzle holder 2.

An injection valve drive unit 4 for driving the needle valve 9 and the push rod 14 is arranged above the injection nozzle holder 2, and an electromagnetic valve 22 is arranged in the injection valve drive unit 4 and a connector unit. A control current is supplied via 23.

The solenoid valve 22 has a valve body 22a depending on the energized state.
Is displaced, and the communication passage 39 that communicates the back pressure chamber 38 of the push rod 14 with the low pressure chamber 20 on the fuel outlet 24 side is opened and closed.
When the solenoid valve 22 is de-energized, the return spring 21 pulls up the valve body 22a and opens the communication passage 39. Thereby, the back pressure chamber 38 of the push rod 14
Pressure is released.

A fuel supply passage 19 for high pressure fuel is formed in the injection nozzle holder 2, and one end of the fuel supply passage 19 is formed in the injection nozzle holder 2.
Connected to the inlet 18 and the other end of the fuel storage chamber 7
And also to the back pressure chamber 38. The high-pressure fuel in the common rail 26 is supplied to the fuel reservoir chamber 7 and the back pressure chamber 38 via the inlet 18 and the fuel supply passage 19. The leaked fuel in the fuel injection valve 1 is the fuel outlet 2
4, the leak fuel in the fuel injection valve 1 is returned to the fuel tank from the fuel outlet 24. Normally, the needle valve 9 is closed by the push rod 14 which receives the pressure of the back pressure chamber 38. Solenoid valve 2
When the power supply to the fuel cell 2 is released, the communication passage 39 is opened and the pressure in the back pressure chamber 38 is lowered, and the pushing force from the back portion of the push rod 14 is reduced. The needle valve 9 lifts and opens, and fuel is injected.

When the solenoid valve 22 is de-energized, the valve body 2
2a closes the communication passage 39, the pressure in the back pressure chamber 38 rises,
At this time, since the pressure receiving area in the direction of pushing down the push rod 14 is large, the needle valve 9 is pushed down against the spring 16 to close the valve, and the fuel injection is stopped.

Therefore, the fuel injection amount and the injection timing can be freely controlled by controlling the energization interval and timing of the solenoid valve 22. In addition to the main injection, the pilot injection has a plurality of energization times per cycle. You can control it freely.

Next, referring to FIG. 3, the fuel injection valve 1 for each cylinder is connected via an injection pipe 27 to a so-called common rail 26, which is a high pressure accumulating pipe common to each cylinder. A high-pressure supply pump 30 is connected to the common rail 26 via a supply pipe 28 and a check valve 29. This high-pressure supply pump 3
0 controls the pressure of the fuel sucked from the fuel tank 31 through the fuel filter 32 through the fuel feed pump 33 to a predetermined high pressure. In this case, the drive shaft 34 having a cam rotates in synchronization with the engine rotation, the piston in the high pressure supply pump 30 reciprocates, the fuel from the fuel feed pump 33 is pressurized, and the common rail 26
Is supplied to. Further, the high-pressure supply pump 30 is always provided with a discharge amount control solenoid valve 35 for controlling the common rail pressure to a desired pressure.

Further, a pressure sensor 37 for detecting the fuel pressure in the common rail (common rail pressure = fuel injection pressure) is arranged on the common rail 26, and the controller 60 is, in principle, provided with this detected pressure in advance in advance of load or engine rotation. Feedback control is performed by adjusting the discharge amount via the solenoid valve 35 so that the basic common rail pressure set according to the number or the corrected common rail pressure set in relation to the premix combustion period is obtained.

The above control contents executed by the controller 60 will be described in more detail below with reference to the flowchart shown in FIG.

This flowchart is repeated in synchronization with the engine rotation, and the engine speed Ne, the engine load Q, and the cooling water temperature Tw are read in step S1.

In step S2, the basic fuel injection amount, the basic injection timing (advance value), the basic exhaust gas recirculation rate (EGR rate), and the basic common rail pressure, which are determined based on the above, are set as shown in FIG. ) To (D).

In step S3, the target premixed combustion period during which diesel knock can be avoided is read from the map set as shown in FIG. 6, for example.

In this case, the target premixed combustion period becomes longer as the fuel injection amount increases, and also relatively increases as the engine speed becomes higher.
And PM are also set to appropriate values that can be suppressed within the allowable range. It should be noted that a constant premixed combustion period that can avoid rapid premixed combustion (diesel knock) can be given as a constant.

In step S4, the injection period of the fuel injected from the fuel injection valve is calculated. This can be calculated as the period from the rise to the fall of the output of the needle valve lift sensor of the fuel injection valve described above.

However, in addition to this, it is read from a map of the fuel injection amount using the engine speed, the fuel injection amount, and the common rail pressure as parameters, and is calculated from the opening / closing signal period of the solenoid valve of the fuel injection valve for controlling the fuel injection timing. You can also

In step S5, the oxygen concentration in the working gas is calculated. It measures the residual oxygen concentration in the exhaust from the output of the exhaust sensor, and estimates the oxygen concentration contained in the working gas based on this, the fuel injection amount at that time, and the fresh air amount measured by the intake air amount sensor. To do. Alternatively, for example, the oxygen concentration can be calculated from the intake air amount, the EGR amount obtained from the intake manifold negative pressure and the exhaust gas recirculation control valve opening, and the fuel injection amount.

In order to accurately estimate the oxygen concentration in the working gas at the time of a transition or the like, advance processing is performed on the calculated oxygen concentration by approximating the dynamic response delays of the intake system and the EGR system by linear delays. .

Next, at step S6, the premixed combustion period is calculated from the fuel injection period obtained as described above and the oxygen concentration in the working gas.

As shown in FIG. 7, this is based on the fact that the premixed combustion period when EGR is not carried out coincides with the fuel injection period, based on the detected fuel injection period.
The premixed combustion period THp at R is calculated.

Next, the increase margin ΔTHp of the premixed combustion period when the oxygen concentration in the working gas decreases due to EGR
Is calculated based on the calculated oxygen concentration based on the characteristics shown in FIG. This increase amount increases as the oxygen concentration decreases, that is, the EGR rate increases, and the increase amount becomes zero when the oxygen concentration is normal in the atmosphere.

However, in this example, in order to reduce the calculation load on the computer, the correction based on the oxygen concentration is made only when the oxygen concentration is 17.5% or less. Note that FIG.
Is converted to a common rail pressure, that is, a constant fuel injection pressure.

Then, the premixed combustion period THp during EGR
1 is calculated as THp + ΔTHp.

In step S7, the target premixed combustion period is compared with the calculated actual premixed combustion period. If the target premixed combustion period is longer than the target premixed combustion period, the premixed combustion is considered to be mild and the process proceeds to step S9. The common rail pressure is used as the basic set pressure as it is, but when it is shorter than the target premixed combustion period, the routine proceeds to step S8, where the correction amount of the common rail pressure is calculated.

That is, when the actual premixed combustion period is shorter than the target value, the premixed combustion is too rapid. Therefore, in order to moderate the premixed combustion, the fuel injection period is made longer than the fuel injection period at that time. For this purpose, the common rail pressure, that is, the fuel injection pressure is reduced, and thereby the fuel injection period required to maintain the same fuel injection amount is extended.

In step S9, the corrected common rail pressure signal is output, and the pressure is reduced so as to match the common rail pressure.

For correction of the common rail pressure, for example, as shown in FIG. 9, the relationship between the fuel injection amount and the injection period is stored in advance in a map by using the common rail pressure as a parameter for each engine speed, and at that time. Based on the fuel injection amount, the common rail pressure is calculated so that the fuel injection period is required to eliminate the deviation between the target premixed combustion period and the actual premixed combustion period.

Alternatively, the common rail pressure is reduced by a predetermined step value Δp, and feedback control is performed so as to match the corrected target value from the relationship with the actual injection period obtained from the output of the needle valve lift sensor of the fuel injection valve. You can also do it.

In this way, the target premixed combustion period is compared with the actual premixed combustion period, and when the actual premixed combustion period is shorter than the target premixed combustion period, the common rail pressure is reduced. The optimum fuel injection period is controlled to obtain the target premixed combustion period.

Next, the overall operation will be described.

In the operating region where the engine load is small, the exhaust gas recirculation control valve 55 is opened to perform EGR, thereby realizing low temperature premixed combustion and reducing NOx while reducing NOx.
And reduce PM emissions.

While the fuel injection amount increases as the accelerator opening increases when the engine is in a transient state, the opening of the exhaust gas recirculation control valve 55 sharply decreases to reduce EGR, and the EGR decreases.
Plummets and stops.

In this fuel increase process, the oxygen concentration in the working gas increases as the EGR gas decreases sharply, the effect of suppressing premixed combustion diminishes, and the rise in combustion pressure after ignition becomes sharp, which causes diesel knock. Easier to do.

However, in the present invention, the premixed combustion state is always detected, that is, the premixed combustion period is calculated, and this premixed combustion period is calculated from the target premixed combustion period set according to the operating state at that time. When the premixed combustion is performed more rapidly than the target state, that is, when the premixed combustion is performed more rapidly than the target state, the common rail pressure is reduced to perform a correction to extend the fuel injection period.

When the common rail pressure is lowered, the fuel injection period required to maintain the same fuel injection amount becomes longer, and by extending this injection period, the premixed combustion period is correspondingly lengthened and the combustion is gentle. become. As a result, diesel knock is avoided and combustion noise is reduced.

FIG. 15 shows the characteristics of the C dotted line showing how the premixed combustion is moderated.

FIG. 10 and FIG. 11 show such control. In the region where diesel knock is generated, the fuel injection period is longer and the common rail pressure is lower than in the conventional premixed combustion. is doing.

In FIG. 12, as the fuel injection amount increases due to acceleration, the premixed combustion period shortens before the EGR is cut, and in the conventional case, the engine enters the knocking region as it is. In the present invention, it is possible to extend the premixed combustion period by increasing the fuel injection period and control so as not to enter the knocking region.

In the operating range in which the fuel injection amount becomes larger than a certain amount even when the EGR is stopped, the diesel knock is suppressed even if the fuel injection pressure is not reduced. This is an increase in the fuel injection amount. It can be presumed that the proportion of oxygen required for combustion relatively decreases with this, and the premixed combustion period becomes longer.

Further, FIG. 13 shows the behavior of the EGR characteristic during transient operation, but fuel cut during deceleration (EGR also cut)
In the re-acceleration from the region, there is a time delay depending on the volume of the intake pipe, the EGR pipe, and the like until the EGR returns to the normal state, and the EGR rate tends to relatively decrease. In such a state, the oxygen concentration in the working gas increased compared to the fuel amount, and diesel knock was likely to occur during acceleration, but by controlling the common rail pressure with less response delay than EGR, premixing It became possible to reliably avoid diesel knocks by lengthening the combustion period.

It should be noted that when the common rail pressure is lowered and the fuel injection period is extended, HC and PM tend to increase accordingly, but in the present invention, the target premixed combustion is estimated while estimating the actual premixed combustion period. As the common rail pressure is corrected by feedback control so that it falls within a certain period, the common rail pressure will not be reduced more than necessary and can be suppressed to the minimum necessary pressure reduction, so rebounding to the exhaust characteristics is avoided as much as possible. It is possible. When the premixed combustion period is longer than the target value, the common rail pressure is maintained as it is at the optimum value according to the operating state, so that there is no adverse effect on combustion due to the common rail pressure being increased more than necessary.

Therefore, deterioration of exhaust characteristics such as HC and PM or deterioration of fuel consumption can be prevented as much as possible while avoiding diesel knock and increase in combustion noise during transient operation.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view of the fuel injection valve.

FIG. 3 is a configuration diagram of a fuel supply system.

FIG. 4 is a flowchart showing a control operation.

FIG. 5 is an explanatory diagram showing characteristics of an operating state, where A is a fuel injection amount characteristic, B is a fuel injection timing characteristic, C is an exhaust gas recirculation characteristic, and D is a common rail pressure characteristic.

FIG. 6 is an explanatory diagram showing characteristics of a target premixed combustion period.

FIG. 7 is a characteristic diagram showing a relationship between a premixed combustion period and a fuel injection amount.

FIG. 8 is an explanatory view showing an increase margin of a fuel injection period.

FIG. 9 is an explanatory diagram showing a correction characteristic of common rail pressure.

FIG. 10 is an explanatory view showing how the fuel injection period is changed in comparison with the related art.

FIG. 11 is an explanatory view showing how the common rail pressure is changed in comparison with the related art.

FIG. 12 is an explanatory diagram showing characteristics of a premixed combustion period during transient operation.

FIG. 13 is an explanatory diagram showing EGR characteristics during transient operation.

FIG. 14 is an explanatory diagram showing a combustion state with a combustion rate waveform.

FIG. 15 is an explanatory diagram showing a combustion state when the load and the EGR state are sequentially changed by a combustion rate waveform.

FIG. 16 is a transient operation characteristic diagram showing the relationship between EGR and knocking.

[Explanation of symbols]

1 fuel injection valve 22 Solenoid valve 26 Common Rail 51 diesel engine 55 Exhaust gas recirculation control valve 60 controller 61 Lift sensor

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Claims (7)

(57) [Claims] 1. A diesel engine equipped with a fuel injection valve for injecting fuel into a combustion chamber, means for controlling the fuel injection timing and injection period, and means for recirculating a part of exhaust gas into intake air. A means for calculating the oxygen concentration in the gas, a means for calculating the fuel injection period, a means for calculating the premixed combustion period of diesel combustion from the oxygen concentration and the fuel injection period, and a target depending on the operating state Means for setting the premixed combustion period, means for comparing the calculated premixed combustion period with the target premixed combustion period, and by this comparison, if the premixed combustion period is shorter than the target premixed combustion period, the same fuel is used. A combustion control device for a diesel engine, comprising: a combustion correction unit that extends a fuel injection period at an injection amount. 2. A fuel pressure chamber for storing high-pressure fuel pumped from a fuel pump, means for controlling the fuel pressure in the fuel pressure chamber to a target value, and fuel for injecting the pressure-controlled high-pressure fuel into the combustion chamber. An injection valve, means for variably controlling the injection period of the fuel injection valve, control means for driving the fuel injection control means so that the fuel injection amount and the injection timing are in accordance with the operating state, and exhaust gas In a diesel engine equipped with a part of which recirculates into intake air, a means for calculating the oxygen concentration in the working gas, a means for calculating a fuel injection period, and a diesel combustion based on the oxygen concentration and the fuel injection period. Means for calculating the premixed combustion period, means for setting the target premixed combustion period according to the operating state, means for comparing the calculated premixed combustion period with the target premixed combustion period, When the premixed combustion period is shorter than the target premixed combustion period by comparison of the above, combustion correction means for reducing the fuel pressure in the fuel pressure accumulating chamber so as to extend the fuel injection period with the same fuel injection amount, A combustion control device for a diesel engine, comprising: 3. The combustion correction means decompresses and corrects the fuel pressure when the premixed combustion period is shorter than the target premixed combustion period, and when the premixed combustion period is longer than the target premixed combustion period, the basic fuel according to the operating state. The combustion control device for a diesel engine according to claim 2, which maintains a pressure. 4. The means for calculating the oxygen concentration in the working gas is based on a fuel injection amount signal, an intake air amount signal, and an oxygen concentration signal from an exhaust sensor installed in the exhaust system. The combustion control device for a diesel engine according to any one of claims 1 to 3, wherein the oxygen concentration is calculated. 5. The means for calculating the oxygen concentration in the working gas calculates the oxygen concentration in the working gas based on a fuel injection amount signal, an intake air amount signal, and an exhaust gas recirculation amount signal. A combustion control device for a diesel engine according to any one of 3 to 3. 6. The premixed combustion period calculation means is a premixed combustion period obtained from a fuel injection period when exhaust gas recirculation is not performed in the operating state, and oxygen when exhaust gas recirculation is performed. The combustion control device for a diesel engine according to claim 1, wherein the combustion delay period obtained according to the concentration is added to obtain an actual premixed combustion period. 7. The target premixed combustion period setting means sets the target premixed combustion period such that the diesel knock and the unburned emissions are in a minimum period within an allowable range in each operating state. A combustion control device for a diesel engine according to any one of claims 1 to 6.