JP2010127175A - Combustion control device of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion control device of a diesel engine capable of improving exhaust gas performance, by performing combustion control based on a proper combustion rate corresponding to an operation state. <P>SOLUTION: When the operation state of an engine is transitional operation or a combustion state is ordinary diesel combustion and an after-burning determining period is larger than an after-burning allowable threshold value, reference MFB is set to the reference MFB latter period (S4), and when the combustion state is premixed combustion or the ordinary diesel combustion and the after-burning determining period is the after-burning allowable threshold value or less, the reference MFB is set to the reference MFB first period (S6), and the combustion control is performed based on an MFB angle. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a combustion control device for a diesel engine, and more particularly to a technique for controlling combustion based on a combustion ratio.

In recent years, a method is known in which an in-cylinder pressure sensor is provided in a combustion chamber of an engine to detect the in-cylinder pressure, and an engine operating state is controlled based on a combustion state calculated from the in-cylinder pressure.
For example, based on the in-cylinder pressure detected by the in-cylinder pressure sensor, the heat generation rate in the cylinder corresponding to the crank angle is obtained, and the combustion rate (MFB: Mass Fraction of Burnt Fuel) is calculated from the integration of the heat generation rate. There is a control device for an engine (internal combustion engine) that controls ignition timing so that a predetermined crank angle is obtained at a predetermined combustion rate (see Patent Document 1).
JP 2006-220139 A

The technique disclosed in Patent Document 1 controls the ignition timing with a predetermined combustion rate of 50% in the embodiment and a crank angle at the combustion rate of 50% as a reference crank angle (CA50).
In Patent Document 1 and an engine that performs combustion control based on a combustion ratio, a predetermined combustion ratio is generally set to 50%. If the gasoline engine can freely control the combustion start timing by ignition with the spark plug, the intended combustion can be caused by setting the ignition timing at a combustion ratio of 50%.

However, in a diesel engine that does not have a spark plug or the like and combustion is started by spontaneous ignition, the combustion start timing cannot be controlled, and the intended combustion cannot necessarily occur.
In general diesel combustion, combustion is a combination of a premixed combustion period in which fuel and air are mixed in advance from fuel injection to spontaneous ignition and a diffusion combustion period in which combustion occurs immediately after fuel injection. . Diesel engines also have a premixed combustion mode in which the exhaust gas performance is improved in a low-load and low-speed range, and the engine is operated only by premixed combustion.

Thus, in a diesel engine, combustion differs depending on the operating state of the engine. For example, even at the same combustion rate of 50%, the crank angle (actual MFB angle) at that time varies greatly.
If the combustion control is performed based on the MFB angle having a large variation in this way, the combustion becomes unstable, and there is a problem that the exhaust performance deteriorates due to the generation of smoke or the like.

  The present invention has been made to solve such problems, and the object of the present invention is to improve the exhaust gas performance by performing combustion control based on an appropriate combustion ratio according to the operation state. It is to provide a combustion control device for a diesel engine.

  In order to achieve the above object, in the combustion control apparatus for a diesel engine according to claim 1, combustion is performed based on in-cylinder pressure detecting means for detecting the in-cylinder pressure of the diesel engine, and in-cylinder pressure detected by the in-cylinder pressure detecting means. Combustion ratio calculating means for calculating a ratio, and combustion control for adjusting the fuel injection timing so that a predetermined target crank angle is obtained at a predetermined reference combustion ratio based on the combustion ratio calculated by the combustion ratio calculating means A combustion control apparatus for a diesel engine comprising: a predetermined target crank corresponding to the combustion ratio after the switching; It is characterized in that the fuel injection timing is adjusted so as to be an angle.

  According to a combustion control apparatus for a diesel engine according to claim 2, in the combustion control means according to claim 1, the combustion control means is a normal diesel combustion in which combustion is combustion only by premixed combustion or diffusion combustion is generated not only by premixed combustion. A combustion state determination means for determining whether the combustion ratio is equal to the first target crank angle corresponding to the first combustion ratio and the second combustion ratio that is a combustion ratio higher than the first combustion ratio A second target crank angle is set, and when the combustion state determining means determines that the combustion is only premixed combustion, the predetermined combustion ratio to be referred to is switched to the first combustion ratio, When the fuel injection timing is adjusted so as to be the first target crank angle at the first combustion ratio, and the combustion state determining means determines that the combustion is normal diesel combustion, Switching a predetermined combustion ratio to irradiation in the second combustion rate, it is characterized in that adjusting the fuel injection timing so as to be the second target crank angle when the combustion rate of the second.

  According to a third aspect of the present invention, there is provided a combustion control apparatus for a diesel engine according to the second aspect, wherein the combustion control means includes a post-burn determination period calculating means for calculating a post-burn determination period corresponding to a post-burn period of the normal diesel combustion. When the combustion state determining means determines that the combustion is normal diesel combustion, and when the afterburn determination period is equal to or less than a predetermined threshold, the predetermined combustion ratio to be referred to is set as the first combustion ratio. The fuel injection timing is adjusted so as to be the first target crank angle at the first combustion ratio by switching to the combustion ratio.

According to a fourth aspect of the present invention, there is provided the diesel engine combustion control apparatus according to the third aspect, wherein the afterburn determination period is a period from the end of fuel injection to the end of combustion.
6. The diesel engine combustion control apparatus according to claim 5, wherein, in any one of claims 1 to 4, the combustion control means is configured to perform the predetermined combustion as the reference when the operation state of the diesel engine is a transient operation state. The ratio is switched to the second combustion ratio, and the fuel injection timing is adjusted so as to be the second target crank angle at the second combustion ratio.

  According to the diesel engine combustion control apparatus of the present invention using the above means, in the diesel engine that controls the fuel injection timing according to the combustion ratio calculated from the in-cylinder pressure, the predetermined combustion ratio to be referred to is set. The fuel injection timing is adjusted so that a predetermined target crank angle corresponding to the combustion ratio is obtained when the combustion ratio is switched after the switching.

In this way, by switching the combustion ratio to be referenced according to the combustion state, even in a diesel engine whose combustion start time cannot be controlled and the combustion state varies greatly depending on the operating state of the engine, combustion control suitable for the combustion state is performed. It can be carried out.
Thereby, the stable combustion can be caused with respect to various operation states, and the exhaust gas performance can be improved.

  According to the combustion control apparatus for a diesel engine according to claim 2, the fuel injection is performed based on the first target crank angle corresponding to the first combustion ratio which is a relatively low combustion ratio when the combustion is only premixed combustion. The fuel injection timing is adjusted based on the second target crank angle corresponding to the second combustion ratio, which is a relatively high combustion ratio, when the timing is adjusted and the combustion is normal diesel combustion other than premixed combustion.

Thus, in the case of pre-mixed combustion in which combustion is comparatively short without post-combustion, the time of ignition can be appropriately controlled by controlling fuel injection based on a relatively low combustion rate. Thereby, the improvement of the exhaust gas performance by the premixed combustion can be further promoted and the output can be improved.
On the other hand, in the case of normal diesel combustion where afterburning occurs, the afterburning period can be increased by controlling fuel injection based on a relatively high combustion rate so as to refer to the later stage of combustion that has a large effect on afterburning. This can prevent the delay of combustion. Thereby, generation | occurrence | production of the smoke by normal diesel combustion can be suppressed.

According to the combustion control apparatus for a diesel engine according to claim 3, when it is normal diesel combustion and the afterburn period is short, fuel injection is controlled based on a relatively low first combustion ratio.
That is, even in the case of normal diesel combustion, when the afterburning period is short and there is little risk of occurrence of smoke, the output can be optimized by controlling fuel injection based on the initial stage of combustion.

According to the combustion control apparatus for a diesel engine according to claim 4, the afterburn determination period is a period from the end of fuel injection to the end of combustion.
Thus, the end point of fuel injection can be easily detected from the instruction signal to the fuel injection valve, and the end point of combustion can be easily detected from the combustion ratio calculating means, and the afterburning period determination period can be easily calculated.

  According to the combustion control apparatus for a diesel engine according to claim 5, when the engine operating state is a transient operation, the predetermined combustion ratio to be referred to is switched to the second combustion ratio which is a relatively high combustion ratio. Then, the fuel injection timing is adjusted so that the second target crank angle corresponding to the second combustion ratio is obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of a combustion control apparatus for a diesel engine according to the present invention, and FIG. 2 is a control block diagram of the combustion control apparatus for a diesel engine according to the present invention. Hereinafter, a description will be given based on FIG.
An engine 1 shown in FIG. 1 is a four-cylinder common rail diesel engine that directly injects high-pressure fuel accumulated in a common rail (not shown) into each cylinder 2. FIG. 1 shows a cross section of one of the four cylinders.

The engine 1 is configured such that a cylinder head 6 is mounted on an upper portion of a cylinder block 4 in which a plurality of cylinders 2 are formed.
Each cylinder 2 is provided with a piston 8 that can slide up and down, and a combustion chamber 10 is formed surrounded by the top surface of the piston 8, the inner wall of the cylinder 2, and the lower surface of the cylinder head 6.
In the cylinder head 6, a fuel injection valve 12 that directly injects fuel into the combustion chamber 10, and an in-cylinder pressure sensor 14 (in-cylinder pressure detecting means) that detects the pressure in the combustion chamber 10, that is, the in-cylinder pressure, are burned. It is provided so as to face the room 10.

  The cylinder head 6 is formed with an intake port 16 that communicates with the combustion chamber 10 and extends on one side in the width direction of the engine 1 and an exhaust port 18 that communicates with the combustion chamber 10 and extends on the other side in the width direction of the engine 1. ing. Further, the cylinder head 6 is provided with an intake valve 20 and an exhaust valve 22 corresponding to the intake port 16 and the exhaust port 18, respectively, for communicating and blocking the ports 16 and 18 and the combustion chamber 10. Yes. Two intake ports 16 and two exhaust ports 18 are provided for each cylinder, and two intake valves 20 and two exhaust valves 22 are provided correspondingly.

An intake pipe 24 communicating with the intake port 16 is connected to one side in the width direction of the engine 1.
The intake pipe 24 is provided with an air cleaner (not shown) on the intake upstream side, and an air flow sensor 26 for detecting the intake air amount in the engine 1 is provided on the intake downstream side. The intake pipe 24 includes a compressor 28a of a turbocharger 28 that supercharges intake air, an intercooler 30 that cools the supercharged intake air, and a throttle valve 32 that adjusts the intake air amount. Are provided in order.

On the other hand, an exhaust pipe 34 communicating with the exhaust port 18 is connected to the other side in the width direction of the engine 1.
The exhaust pipe 34 is provided with a turbine 28b that is connected to the compressor 28a of the turbocharger 28 and a rotating shaft and rotates by an exhaust flow.
Further, the exhaust upstream side portion of the exhaust pipe 34 and the intake downstream side portion of the intake pipe 24 communicate with each other via an EGR passage 36 so that the exhaust gas can be recirculated to the intake system. The EGR passage 36 is provided with an EGR cooler 38 that cools the EGR gas and an EGR valve 40 that adjusts the amount of EGR gas returned to the intake system.

Further, a vehicle equipped with the engine 1 is provided with an ECU 42 (combustion control means) as a control device for performing comprehensive control including operation control of the engine 1 and the like. The ECU 42 is composed of a CPU, a memory, a timer counter, and the like, and calculates various control amounts and controls various devices based on the control amounts.
For example, various sensors such as the in-cylinder pressure sensor 14, the airflow sensor 26, the crank angle sensor 44 that detects the crank angle of the engine 1, and the accelerator opening sensor 46 are connected to the input side of the ECU 42. From the detected value, the load acting on the engine 1, the engine rotational speed, the intake O ₂ concentration, and the like can be calculated. Various devices such as the fuel injection valve 12, the throttle valve 32, and the EGR valve 40 of each cylinder are connected to the output side of the ECU.

The ECU 42 performs switching control of the operating state of the engine 1 and combustion control in each cylinder based on information acquired from the various sensors.
Specifically, in the switching control of the operating state of the engine 1 by the ECU 42, the ECU 42 switches a preset operation mode according to the load acting on the engine 1 and the engine speed.

  For example, when the operation state is in the low load low rotation speed region, the fuel injection timing is set relatively on the advance side, and the operation is performed only by premixed combustion in which air and fuel are mixed in advance and then spontaneously ignited. The premixed combustion mode is performed. In the premixed combustion mode, the temperature of the EGR gas is increased by increasing the recirculation amount of the EGR gas with respect to the premixed combustion at a high temperature, and the generation of NOx is suppressed.

  On the other hand, when the operation state is outside the low-load low-speed region where the premixed combustion mode is established, the fuel injection timing is set on the relatively retarded side, and combustion is mainly generated during fuel injection. The normal combustion mode for diesel combustion is used. In the normal combustion mode, premixed combustion is performed in the first half of the combustion due to a delay in ignition of the fuel and the like, and then diffusion combustion in which combustion occurs immediately after injection is performed.

  In the combustion control by the ECU 42, the heat generation rate is calculated from the in-cylinder pressure information detected by the in-cylinder pressure sensor 14, and the heat generation amount obtained by integrating the heat generation rate is calculated. Further, a combustion ratio (hereinafter also referred to as MFB) is calculated from the heat generation amount, and the fuel injection timing is controlled so that the predetermined combustion ratio becomes a predetermined crank angle (hereinafter also referred to as MFB angle). (Combustion rate calculation means).

Specifically, in the combustion cycle of the engine 1, the product of the in-cylinder pressure P and the value obtained by raising the in-cylinder volume V to the power of the polytropic index n is constant from the polytropic equation shown in the following equation (1). Further, when the combustion cycle of the engine 1 is regarded as an adiabatic change, the polytropic index n is replaced with the specific heat ratio κ in the cylinder.
PV ⁿ = PV ^κ = constant (1)
The heat generation rate dQ / dθ, which is the heat generation amount per unit crank angle of the heat generation amount Q generated in the combustion chamber 10, is expressed by the in-cylinder pressure P, the in-cylinder volume V, It is calculated from the specific heat ratio κ.

That is, the amount of heat generation is calculated by integrating (integrating) the heat generation rate dQ / dθ.
Then, assuming that the heat generation amount at the end of combustion, that is, the maximum value of the heat generation amount is 100%, the ratio of the heat generation amount according to the crank angle is obtained as the combustion ratio. The specific heat ratio κ used in the above formulas (1) and (2) varies depending on the change in gas accompanying combustion, but for the sake of simplification of calculations, etc. It will be handled as a constant value.

  The ECU 42 stores information such as the heat generation amount and the combustion ratio as a combustion history, and advances or delays the fuel injection timing so that the predetermined target crank angle is reached at a predetermined combustion ratio that is referred to in the next combustion. Performs feedback control to make the angle. Hereinafter, the predetermined combustion ratio to be referred to is referred to as a reference MFB (%), the predetermined target crank angle corresponding to the reference MFB is referred to as a target MFB angle, and the crank angle corresponding to the reference MFB actually calculated from the combustion history. Is called the actual MFB angle, and the crank angle will be described assuming that the retard direction is large.

Further, the ECU 42 stores in advance two reference MFBs corresponding to the combustion state, and performs combustion control by switching the two reference MFBs according to changes in the combustion state.
Hereinafter, the combustion control executed in the ECU 42 will be described in more detail.
First, as shown in FIG. 2, regarding the combustion control, the ECU 42 includes a premixed combustion determination unit 50 (combustion state determination unit), a post-burn period determination unit 52 (post-burn determination period calculation unit), and a reference MFB switching unit. 54, a PID control unit 56 is formed.

  The premix combustion determination unit 50 receives a fuel injection end timing and an ignition timing, and also receives a premix determination offset value set according to the operating state. The fuel injection end time is the drive signal end time to the fuel injection valve 12, and the ignition time is the MFB 0% time corresponding to the start of combustion in the combustion history. The premix determination offset value corresponds to the determination of premix combustion, and is a correction value for calculating the timing when fuel injection from the fuel injection valve 12 is actually finished in consideration of response delay and the like. This is the mixing period of fuel and air necessary for combustion.

  Further, the premix combustion determination unit 50 compares the ignition timing with a value obtained by adding the premix determination offset value to the fuel injection end timing, and determines whether the previous combustion was combustion of only premix combustion or diffusion combustion. It has the function to determine whether it was normal diesel combustion including. Then, the premixed combustion determination unit 50 determines that the determination result is 1 when the fuel injection end timing is retarded from the ignition timing, and the fuel injection end timing advances from the ignition timing. In the case of only premixed combustion on the corner side, a judgment value 0 is output.

  The afterburning period determination unit 52 receives the fuel injection end timing, the afterburn determination offset value, the combustion end timing, and the afterburning allowable threshold. The afterburn determination offset value corresponds to the determination of the afterburn period, and is a correction value for calculating the timing when the fuel injection from the fuel injection valve 12 has actually ended in consideration of a response delay or the like. The combustion end time is a time when the MFB becomes 100% in the combustion history. From the relationship between the occurrence of smoke and the afterburning period, the afterburning allowable threshold is a threshold at which the amount of smoke generated increases when the afterburning determination period becomes longer than the above afterburning allowable threshold. The afterburn determination period is a value corresponding to the afterburn period of combustion.

  Further, the afterburning period determination unit 52 calculates the afterburning determination period by subtracting the value obtained by adding the afterburning determination offset value to the fuel injection end timing from the end of combustion timing. Furthermore, the post-burn determination period and the post-burn allowance threshold are compared, and when the post-burn determination period is greater than the post-burn allowance threshold, the determination value is 1, and when the post-burn determination period is less than the post-burn allowance threshold, The judgment value 0 is output.

The reference MFB switching unit 54 obtains a logical product of the determination value output from the premixed combustion determination unit 50 and the determination value output from the post-burn period determination unit 52, and according to the result of the logical product. And a function of switching the target MFB angle switch 54a and the actual MFB angle switch 54b.
Specifically, the reference MFB switching unit 54 determines that the target MFB angle switch 54a is obtained when the result of the logical product is true, that is, in the case of normal diesel combustion and the afterburn determination period is greater than the afterburn allowable threshold. The actual MFB angle switch 54b is referred to as a switch 1. On the other hand, when the result of the logical product is false, that is, when only the premixed combustion is performed or when the afterburn determination period is equal to or less than the afterburning allowable threshold, both the switches 54a and 54b are switched to the switch 0.

  In the reference MFB switching unit 54, a reference MFB late period (for example, MFB 50%) (second combustion ratio) and a reference MFB early period (for example, MFB 20%) (first combustion ratio) are set in advance as the reference MFB. When the target MFB angle switch 54a is the switch 1, the target MFB late angle corresponding to the reference MFB late period is output, and when the target MFB angle switch 54a is the switch 0, the target MFB early angle corresponding to the reference MFB previous period is output. The actual MFB angle switch 54b outputs the actual MFB late angle corresponding to the late reference MFB when the switch is 1, and the actual MFB early angle corresponding to the early reference MFB when the switch is 0.

Further, although not shown, the reference MFB switching unit 54 sets the target MFB angle switch 54a and the actual MFB angle switch 54b regardless of the result of the logical product when the operation state of the engine 1 is a transient operation. The switch 1 outputs the target MFB late angle and the actual MFB late angle.
Then, the reference MFB switching unit 54 outputs the target MFB angle and the actual MFB angle set as described above.

The PID control unit 56 performs feedback control of the fuel injection timing by PID control including proportional operation, integration operation, and differentiation operation based on the difference between the target MFB angle output from the reference MFB switching unit 54 and the actual MFB angle, and instructs It has a function to output the injection timing.
Next, the flow of combustion control by the combustion control apparatus for a diesel engine according to the present invention will be described.

FIGS. 3 and 4 show a combustion control routine by the combustion control apparatus for a diesel engine according to the present invention in a flowchart, which will be described with reference to FIG. In the following description, the crank angle is set larger on the retard side.
As shown in FIG. 3, the ECU 42 detects the in-cylinder pressure from the in-cylinder pressure sensor 14 as step S1.

In step S2, the combustion ratio is calculated based on the in-cylinder pressure detected in step S1 and stored as a combustion history. Based on the combustion history, the target MFB late angle corresponding to the reference MFB late stage and the target corresponding to the reference MFB early stage are calculated. The MFB previous-term angle is calculated and stored in the reference MFB switching unit 54.
In step S3, it is determined whether or not the engine operating state is a transient operation. This is determined from, for example, the rate of change in the accelerator opening. If the determination result is true (Yes), the process proceeds to step S4.

In step S4, the reference MFB is set to the reference MFB late period. That is, the reference MFB switching unit 54 outputs the target MFB late angle and the actual MFB late angle by using the target MFB angle switch 54a and the actual MFB angle switch 54b as the switch 1, respectively.
On the other hand, if the determination result in step S3 is false (No), the process proceeds to step S5.
In step S5, the premix combustion determination unit 50 determines whether or not the combustion state of the engine 1 is normal diesel combustion including diffusion combustion. When the determination result is false (No), that is, when the combustion is only premixed combustion and the determination value 0 is output from the premixed combustion determination unit 50, the process proceeds to step S6.

In step S6, the reference MFB is set to the previous period of the reference MFB. That is, the reference MFB switching unit 54 outputs the target MFB previous angle and the actual MFB previous angle by setting the target MFB angle switch 54a and the actual MFB angle switch 54b to switch 0, respectively.
On the other hand, when the determination result of step S5 is true (Yes), that is, when normal diesel combustion is performed and the determination value 1 is output from the premix combustion determination unit 50, the process proceeds to step S7.

In step S7, the afterburning period determination unit 52 calculates a afterburning determination period that is a period from the fuel injection timing to the combustion end timing.
In step S8, it is determined whether or not the afterburn determination period is greater than the afterburn tolerance threshold.
If the determination result is false (No), that is, if the afterburn determination period is equal to or less than the afterburning allowable threshold value and within the allowable range regarding smoke generation, the process proceeds to step S6, and the reference MFB is set to the reference MFB late period. To do.

When the determination result is true (Yes), that is, when the afterburn determination period is larger than the afterburn allowable threshold and the afterburn determination period exceeds the allowable range with respect to the occurrence of smoke, the process proceeds to step S4, The reference MFB is set to the previous period of the reference MFB.
After step S4 or step S6, the process proceeds to step S9 in FIG. The steps after step S9 are executed by the PID control unit 56.

  In step S9, the difference between the target MFB angle corresponding to the reference MFB set in step S4 or step S6 and the actual MFB angle is 0 or more, that is, the actual MFB angle coincides with the target MFB angle or the target MFB angle. It is determined whether or not it is on the more advanced side. If the determination result is false (No), that is, if the actual MFB angle is more retarded than the target MFB angle, the process proceeds to step S10.

In step S10, the command injection timing is advanced to control the actual MFB angle, and the routine returns.
On the other hand, if the determination result of step S9 is true (Yes), the process proceeds to step S11.
In step S11, it is determined whether or not the difference between the target MFB angle and the actual MFB angle is 0, that is, whether the target MFB angle and the actual MFB angle coincide with each other.

When the determination result is true (Yes), the routine is returned with the same command injection timing as the previous time.
If the determination result is false (No), that is, if the actual MFB angle is more advanced than the target MFB angle, the process proceeds to step S12.
In step S12, in order to retard the actual MFB angle, the command injection timing is retarded and the routine returns.

Here, FIG. 5 shows a time chart showing the fuel injection rate, the heat generation rate, and the combustion rate of the premixed combustion and the normal diesel combustion, and the operation when the combustion control is performed based on the time chart. The effect will be described.
As shown by a broken line in FIG. 5, in the premixed combustion in which the ignition timing Tbs0 is retarded from the fuel injection end timing Tie0, the heat generation rate only rises once, the combustion period is short, and the combustion rate rises rapidly. It becomes.

In the premixed combustion showing such a combustion state, the reference MFB is switched to the first reference MFB (MFB 20%) which is a relatively low combustion rate. Then, the fuel injection timing is feedback-controlled so that the actual MFB previous angle corresponding to the reference MFB previous time becomes the target MFB previous angle.
In this way, in the case of premixed combustion with short after-burning and short combustion, it is possible to appropriately control the ignition timing by controlling the fuel injection based on the early stage of combustion. Thereby, the improvement of the exhaust gas performance by the premixed combustion can be further promoted and the output can be improved.

  On the other hand, as shown by the solid line in FIG. 5, in the normal diesel combustion in which the ignition timing Tbs1 is advanced from the fuel injection end timing Tie1, referring to the heat generation rate, immediately after the combustion, the amount of premixed combustion, The combustion of the diffusion combustion starts up. Further, after the diffusion combustion, that is, after the fuel injection end timing Tie1, the heat generation rate gradually decreases as the afterburning period. Thus, normal diesel combustion has premixed combustion, diffusion combustion, and afterburning period, and the combustion period is relatively long, and the combustion rate rises more slowly than premixed combustion.

In the normal diesel combustion, when the afterburn determination period, which is the period from the fuel injection end timing Tie1 to the combustion end timing Tbe1, is equal to or less than the afterburning allowable threshold, the reference MFB is relatively low as in the above premixed combustion. By switching to the first period of reference MFB, which is the combustion ratio (MFB 20%), combustion control is performed that can appropriately control the time of ignition.
On the other hand, in the normal diesel combustion, when the afterburn determination period is longer than the afterburning allowable threshold, the reference MFB is switched to the reference MFB late period (MFB 50%) which is a relatively high combustion ratio. Then, the fuel injection timing is feedback controlled so that the actual MFB late angle corresponding to the reference MFB late phase becomes the target MFB late angle.

Also, when the engine operating state is a transient operation, the reference MFB is switched to the reference MFB late phase, and the fuel injection timing is feedback-controlled so that the target MFB late angle is obtained.
In this way, when the post-combustion period in normal diesel combustion is long and combustion is delayed, or during transient operation where combustion tends to be unstable, fuel injection is performed with reference to the late stage of combustion that has a large effect on post-combustion. By controlling, it is possible to prevent an increase in the afterburning period and suppress a combustion delay. Thereby, generation | occurrence | production of the smoke at the time of normal diesel combustion and a transient operation can be suppressed.

From these things, in the diesel engine combustion control device according to the present invention, it is possible to perform combustion control based on an appropriate combustion ratio according to the operating state, and to improve exhaust gas performance.
Although the description about the embodiment of the combustion control device of the diesel engine according to the present invention is finished above, the embodiment is not limited to the above embodiment.
For example, in the above embodiment, the engine 1 is a four-cylinder common rail type diesel engine, but is not limited to the engine having the configuration, and may be a diesel engine having another configuration.

  In the above embodiment, the reference MFB late period and the reference MFB early period are set as the reference MFB, and the two reference MFBs are switched. However, three or more reference MFBs are set and selected from them. It is also possible to adopt such a configuration.

It is a schematic block diagram of the combustion control apparatus of the diesel engine which concerns on this invention. It is a control block diagram of the combustion control apparatus of the diesel engine which concerns on this invention. It is a flowchart which shows the combustion control routine by the combustion control apparatus of the diesel engine which concerns on this invention. FIG. 4 is a continuation of the flowchart of FIG. 3. It is the time chart which showed the fuel injection rate, heat release rate, and combustion rate of premix combustion and normal diesel combustion.

Explanation of symbols

1 Engine 2 Cylinder 12 Fuel Injection Valve 14 Cylinder Pressure Sensor (Cylinder Pressure Detection Means)
42 ECU (combustion control means)
44 Crank angle sensor 50 Premixed combustion determination unit (combustion state determination means)
52 Afterburning period determination unit (Afterburning period calculation means)
54 Reference MFB switching unit 54a Target MFB angle switch 54b Actual MFB angle switch 56 PID control unit

Claims (5)

In-cylinder pressure detecting means for detecting the in-cylinder pressure of the diesel engine,
Combustion rate calculation means for calculating a combustion rate based on the in-cylinder pressure detected by the in-cylinder pressure detection means;
Combustion control of a diesel engine comprising combustion control means for adjusting a fuel injection timing so that a predetermined target crank angle is obtained at a predetermined reference combustion ratio based on the combustion ratio calculated by the combustion ratio calculation means A device,
The combustion control means switches the predetermined combustion ratio to be referred to according to the combustion state, and adjusts the fuel injection timing so as to obtain a predetermined target crank angle corresponding to the combustion ratio after the switching. Diesel engine combustion control device. The combustion control means has combustion state determination means for determining whether the combustion is combustion only by premixed combustion or normal diesel combustion in which not only premixed combustion but also diffusion combustion occurs,
A first target crank angle corresponding to the first combustion ratio and a second target crank angle corresponding to a second combustion ratio that is a combustion ratio higher than the first combustion ratio are set;
When the combustion state determining means determines that the combustion is only premixed combustion, the predetermined combustion ratio to be referred to is switched to the first combustion ratio, and the first combustion ratio at the first combustion ratio is changed. Adjust the fuel injection timing to achieve the target crank angle,
When it is determined by the combustion state determining means that the combustion is normal diesel combustion, the predetermined combustion ratio to be referred to is switched to the second combustion ratio, and the second combustion ratio is the second combustion ratio. 2. The combustion control apparatus for a diesel engine according to claim 1, wherein the fuel injection timing is adjusted so as to achieve a target crank angle. The combustion control means has a post-burn determination period calculation means for calculating a post-burn determination period corresponding to the post-burn period of the normal diesel combustion,
When the combustion state determining means determines that the combustion is normal diesel combustion, and when the afterburn determination period is equal to or less than a predetermined threshold value, the predetermined combustion ratio as the reference is set to the first combustion. 3. The diesel engine combustion control apparatus according to claim 2, wherein the fuel injection timing is adjusted so as to be the first target crank angle at the first combustion ratio.   4. The diesel engine combustion control apparatus according to claim 3, wherein the afterburn determination period is a period from the end of fuel injection to the end of combustion.   When the operation state of the diesel engine is in a transient operation state, the combustion control means switches the predetermined combustion ratio to be referred to the second combustion ratio, and the first combustion ratio at the second combustion ratio is changed. 5. The diesel engine combustion control device according to claim 1, wherein the fuel injection timing is adjusted so that a target crank angle of 2 is obtained.

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