JP2003120370A - Control device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a stable combustion state of low-temperature premixed combustion in a transient state in a diesel engine. SOLUTION: In low-temperature premixed combustion, the stability of a combustion state (combustion stability) is detected, and if it is low, a fuel injection for an engine output consists of a main injection Pm and a sub injection Ps. The main injection injects at least a part of a demand fuel quantity, and the sub injection injects the shortage in the demand fuel quantity within an ignition delay period from the main injection. The combustion stability is predictively detected according to a rate of change in accelerator travel, an estimate of compression end temperature and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine control device, and more particularly, to a technique for maintaining a stable combustion state of low temperature premixed combustion in a transient state in a case of operation by low temperature premixed combustion. Regarding

[0002]

2. Description of the Related Art In general combustion in a diesel engine, first, a combustible mixture is formed by the vaporization of injected fuel, and when a cylinder reaches a predetermined temperature and pressure range, it is ignited and initially combusted. (Premixed combustion) occurs. Then, due to this combustion, the temperature and pressure inside the cylinder become even higher, and thereafter, the fuel burns (diffuse combustion) while evaporating simultaneously with the injection. In such a conventional combustion method, since the period from the start of injection to the ignition (the ignition delay period) is shorter than the entire combustion period, the latter diffusion combustion is the main.

By the way, Japanese Patent No. 2864 relating to the present applicant
No. 896 discloses that the ratio of premixed combustion to the entire combustion period is positively made higher than that of diffusion combustion.
A technique is disclosed in which premixed combustion is mainly performed to reduce nitrogen oxides (NOx) and smoke (particulate matter; PM) emitted from a diesel engine.

In this technique, the oxygen concentration in intake air is reduced by exhaust gas recirculation (EGR) or the like to lower the combustion temperature, and the fuel injection timing is retarded to a greater degree than usual so that the heat generation pattern becomes a single stage. The ignition delay period is lengthened so that the combustion takes a form. As a result, the PM emission amount is reduced by premixing the combustion in a state where the generation of NOx is suppressed by the low temperature combustion. Actually, the above-mentioned combustion mainly composed of diffusion combustion (hereinafter, also simply referred to as “diffusion combustion”) and the combustion mainly composed of premixed combustion (hereinafter, referred to as “diffusion combustion”) The term "low-temperature premixed combustion") is generally switched according to the operating state, as shown in FIG.

[0005]

[Problems to be Solved by the Invention] As described above,
According to the technique disclosed in Japanese Patent No. 2864896, while the combustion state of the low temperature premixed combustion is stable,
Both NOx and PM emissions are reduced. However, when the low temperature premixed combustion is performed, if the fuel injection is simply ended within the ignition delay period, the ignitability may deteriorate in a specific operating state and the combustion state may become unstable. .

Here, as a concrete example, consider a case where the operating state changes from a low load region to a high load side in response to an acceleration request from the driver. At this time, if the operation is performed by the low temperature premixed combustion after the change, the fuel injection amount is increased and the fuel injection timing is retarded in response to the increase in the required load, but at the same time, the EGR rate ((EGR (Amount / fresh air amount) × 100 [%]) is reduced and the boost pressure is increased. Among these, the fuel injection amount and the fuel injection timing can be controlled without delay by electronic control or the like. However, it is inevitable that the control of the EGR rate and the supercharging pressure is delayed. And for the acceleration request,
Oxygen concentration becomes insufficient due to delayed response of EGR rate,
Alternatively, if a sufficiently high in-cylinder temperature (compression end temperature) cannot be obtained due to a delay in supercharging pressure response, the ignition delay period becomes too long, which may cause misfire and discharge unburned fuel (HC). .

The present invention has been made in view of the above circumstances, and an object thereof is to detect combustion stability when performing low temperature premixed combustion, and determine whether the combustion state is unstable or When there is a risk of becoming unstable, the fuel injection is specially controlled to recover or maintain the fuel injection. The present invention particularly aims to maintain a stable combustion state of low temperature premixed combustion in a transient state.

[0008]

Therefore, according to the invention described in claim 1, (A) combustion temperature control means for lowering the oxygen concentration of intake air to lower the combustion temperature, and (B) diffusion combustion as the main constituent. The first combustion method described above and the second combustion method mainly including premixed combustion, in which the fuel injection is ended within the ignition delay period when the combustion temperature is lowered by the combustion temperature control means and the fuel injection is performed. A combustion method switching means for switching in accordance with the operating state, (C) fuel injection control means for controlling the injection operation of the fuel injection valve in accordance with the switching result by the combustion method switching means, and (D) in the case of the second combustion method Combustion stability detection means for detecting the stability of the combustion state (combustion stability) of the diesel engine control device is configured to detect combustion stability when the fuel injection control means is based on the second combustion method. Detected by means The main injection for injecting at least a part of the required fuel amount for the engine output, and the auxiliary injection for injecting the fuel as an additional amount or a deficiency amount with respect to the required fuel amount after the main injection. The auxiliary injection is controlled based on the combustion stability, and is terminated within the ignition delay period of the main injection.

That is, according to the present invention, if necessary depending on the detected combustion stability, auxiliary injection is performed while the fuel injected by the main injection is forming an ignition atmosphere, and the ignition source is set. The point is to form. At this time, since the auxiliary injection is ended within the ignition delay period from the main injection, the establishment itself of the second combustion method is not impaired. When the shortage of the required fuel amount is injected by the auxiliary injection, the total injection amount with the main injection matches the required fuel amount.

According to the second aspect of the invention, the auxiliary injection is performed when the combustion stability is lower than the predetermined value as the lower limit value of the normal range. In the invention according to claim 3, the injection amount by the auxiliary injection is increased as the combustion stability is lower. In the invention described in claim 4, the number of injections of the auxiliary injection is increased as the combustion stability is lower.

According to the fifth aspect of the invention, the combustion stability is detected as a lower value as the rate of change of the operating state is larger. Further, in the invention of the sixth aspect, the accelerator opening as the operating state is opened. The combustion stability is detected as a lower value when the change rate of the engine speed, the required torque, or the engine speed is larger. In the invention according to claim 7, in the combustion stability detecting means, the target compression end temperature calculating means for calculating the target compression end temperature as the target value of the compression end temperature or its equivalent amount based on the operating state, and the actual The actual compression end temperature detecting means for detecting the actual compression end temperature as an estimated value of the compression end temperature or its equivalent amount, and the target compression end temperature calculated by the target compression end temperature calculating means and the actual compression end temperature The combustion stability is detected as a lower value as the difference from the actual compression end temperature detected by the detection means is larger. In the invention according to claim 8,
The actual compression end temperature is detected based on at least one of the EGR rate and the supercharging pressure.

[0012] In the invention described in claim 9, the compression ratio is set to a predetermined low compression ratio, and the operating region by the first combustion system is set on the lower load side than the operating region by the second combustion system. I decided to provide it. By setting the compression ratio to a low value by retarding the intake valve closing timing than usual, it is possible to perform the operation by the second combustion method in the operation region on the higher load side. On the other hand, in response to the decrease in the compression end temperature due to the decrease in the compression ratio, the operating region for the first combustion method is provided on the low load side. Here, based on the acceleration request from the driver,
When the operating range of the first combustion system is changed to the operating range of the second combustion system, the EGR rate is reduced in the one having the EGR device and the supercharging pressure is reduced in the one having the supercharger. Since it is increased, there is a high possibility that a response delay occurs and the combustion state becomes unstable. According to the present invention, the auxiliary injection is performed according to the combustion stability even during such a transition of the operating region.

In a tenth aspect of the invention, (A) a combustion temperature control means for lowering the oxygen concentration of intake air to lower the combustion temperature, (B) a first combustion system mainly composed of diffusion combustion, and combustion A combustion method that switches between a second combustion method mainly for premixed combustion, in which fuel injection is ended within the ignition delay period when the combustion temperature is lowered by the temperature control means, and is performed according to the operating state Switching means, and (C)
A diesel engine controller is provided with fuel injection control means for controlling the injection operation of the fuel injection valve according to the switching result by the combustion method switching means, and the compression ratio in the case of the second combustion method is set to a predetermined low compression. In addition to setting the ratio, the combustion mode switching means provides the operating range for the first combustion method on the lower load side than the operating range for the second combustion method, and further, the fuel injection control means controls the low load. From the operating range that should be provided by the first combustion method on the side
The main injection that injects at least a part of the required fuel amount for the engine output and the main injection of fuel that is an addition or shortage of the required fuel amount during the predetermined period immediately after the transition to the power operating range by the combustion method The auxiliary injection to be injected later is performed, and this auxiliary injection is ended within the ignition delay period of the main injection.

[0014]

According to the invention of claim 1, in the case of the second combustion system, the main injection and the auxiliary injection are performed according to the combustion stability, and the auxiliary injection is performed based on the combustion stability. By controlling, even if the ignition delay period becomes too long in the conventional fuel injection due to the transient state and the combustion state becomes unstable, the ignitability is improved and the ignition delay period is appropriately controlled and stabilized. The combustion state can be maintained. here,
If the total injection amount of the main injection and the auxiliary injection is made equal to the required fuel amount, this effect can be obtained without deteriorating the fuel consumption.

According to the second aspect of the present invention, when the combustion stability is within the normal range, it is possible to perform normal fuel injection for the second combustion method, so the operation of the fuel injection valve is performed. Needlessly be complicated. According to the third aspect of the present invention, by increasing the injection amount of the auxiliary injection as the combustion stability is lower, the combustion state can be maintained stable even if there is a possibility that the combustion state will be significantly destabilized. Alternatively, if the combustion condition is currently unstable, this can be recovered early.

According to the invention of claim 4, by increasing the number of injections of the auxiliary injection as the combustion stability is lower, it is possible to form an optimum ignition source for maintaining the stable combustion state. The combustion state can be further stabilized.
According to the invention of claim 5, by detecting the combustion stability based on the change rate of the operating state, the combustion state becomes unstable due to a response delay or the like caused by a change in the EGR rate or the supercharging pressure. This can be predicted and reflected in the control of the auxiliary injection. Therefore, it is possible to prevent the combustion state from becoming unstable. Especially, if the accelerator opening degree, the required torque, or the engine rotation speed is adopted as the operating state according to the invention of claim 6, the prediction can be facilitated.

According to the seventh aspect of the present invention, the compression end temperature which has a dominant influence on the ignitability or its equivalent amount (for example, the compression end pressure which can be substituted as a parameter equivalent to the compression end temperature) is adopted, By detecting the combustion stability based on the difference between the target value and the actual value, it can be estimated that the combustion state becomes unstable. In particular, according to the invention of claim 8, since the actual compression end temperature or its equivalent amount can be accurately detected based on at least one of the EGR rate and the supercharging pressure, the reliability of this estimation result is improved. It

According to the invention of claim 9, not only it is possible to perform the operation by the second combustion system in the operation region on the higher load side, but also the first combustion method is performed in response to the acceleration request.
It is possible to maintain a stable combustion state when the operation of the second combustion method is changed to the operation of the second combustion method. Claim 1
According to the invention of No. 0, since the auxiliary injection is performed when the operation by the first combustion method is changed to the operation by the second combustion method, the stable combustion state is maintained in the transient state generated based on the acceleration request. it can. Here, if the total injection amount of the main injection and the auxiliary injection is made to match the required fuel amount, this effect can be obtained without deteriorating the fuel consumption.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a diesel engine (engine) 1 according to an embodiment of the present invention. An air filter (not shown) is attached to the introduction portion of the intake passage 3 connected to the engine body 2, where dust and the like floating in the intake air are removed. Then, a detection signal corresponding to the intake air amount is output from the air flow meter 31 installed immediately downstream of the air filter, and is input to the electronic control unit (ECU) 41.

A variable nozzle turbocharger 4 is interposed in the intake passage 3, and intake air that has passed through the air flow meter 31 is compressed by the compressor section 4a and sent out. Further, an intercooler 5 is installed along with the turbocharger 4 in the intake passage 3, and the intake air pressure-fed from the compressor portion 4a is cooled here and then distributed to each cylinder in the manifold portion.

An injector 6 is installed in the engine body 2 so as to face the upper center of the combustion chamber of each cylinder.
The fuel compressed to a predetermined pressure by the fuel pump 7 is introduced into the common rail 8 through the fuel supply pipe, and is supplied to each injector 6 from there. Injector 6 is E
It operates according to a control signal from the CU 41, is driven to open at a predetermined time, and directly injects a predetermined amount of fuel into the cylinder.

A turbine portion 4b of the turbocharger 4 is installed in the exhaust passage 9. The nozzle opening of the variable nozzle of the turbocharger 4 is detected by a sensor (not shown), and the detection signal is input to the ECU 41. The ECU 41 controls the nozzle opening according to the operating state. Exhaust gas passing through the turbine section 4b is
After being purified by an exhaust aftertreatment device (not shown) such as a filter, it is released into the atmosphere.

The exhaust passage 9 and the surge tank 10 communicate with each other through an EGR passage 11, and a control valve (EGR valve) 12 is installed in this passage. The EGR valve 12 is
The exhaust gas is driven by a drive device 13 such as a step motor that receives a control signal from the ECU 41, and when the valve is opened, the exhaust gas whose flow rate is controlled to an appropriate amount according to the opening degree is returned to the intake system.

In addition to the above, the sensors provided in the engine 1 include a crank angle sensor 32 for detecting a unit crank angle or a reference crank angle used when calculating the engine speed Ne, and a driver's crank angle sensor 32. An accelerator sensor 33 that detects an accelerator opening APO corresponding to an accelerator operation amount, a water temperature sensor 34 that detects a temperature (water temperature) Tw of engine cooling water, and the like are provided. All of these detection signals are input to the ECU 41.

Next, of the controls executed by the ECU 41, the control routine for controlling the fuel injection by the injector 6 will be described with reference to the flowchart shown in FIG. In S (step) 1, the engine speed Ne, the accelerator opening APO, and the water temperature Tw as operating conditions are read.

In S2, the basic injection timing Ti and the basic injection amount Qi for fuel injection control are calculated based on the engine speed Ne and the accelerator opening APO. Where Ti
Is a fuel injection timing for achieving a predetermined combustion method that should be switched according to the operating region as shown in FIG.
It is set by reading from the map allocated in correspondence with Ne and APO. Here, the water temperature T is added to the read Ti
It is also possible to make a correction according to w or the like and advance the angle when the temperature is low. The fuel injection timing Ti in the case of the low temperature premixed combustion is retarded compared to that in the case of the diffusion combustion, and is set so that the fuel injection is started within a predetermined range after the compression top dead center at the crank angle. On the other hand, the basic injection amount Qi is read from the map allocated corresponding to Ne and APO,
The larger the APO, the larger the dose.

In S3, it is determined which operating region of the map shown in FIG. 3 the current operating state is based on the engine speed Ne and the accelerator opening APO. Operating area A
If it is determined that the other operating area B
Alternatively, if it is determined to be in C, the process proceeds to S7. In the present embodiment, in which the combustion method is switched between the diffusion combustion and the low temperature premixed combustion according to the operating state to control the engine 1, the compression ratio is made lower than that of a normal engine and a predetermined low compression ratio is set. By setting to, the operating region A is expanded to the higher load side (to the operating region B side). On the other hand, the compression end temperature (in-cylinder temperature when the piston is at the compression top dead center) decreases due to the low compression ratio, and low-temperature premixed combustion is stably performed in the operation region C on the low load side. Has become difficult. Therefore, in the operating region C, the operation is performed by diffusion combustion, and the pilot injection is performed to further improve the ignitability. Therefore, when it is determined in S3 that the current operating state is in the operating region C and the process proceeds to S7, a drive pulse for performing pilot injection is formed in S7 and is output to the injector 6.

At S4, the rate of change of the accelerator opening APO
(Rate of accelerator opening change) Rapo is calculated. Rapo
Is the accelerator opening APO saved just before this routine.
The bef is subtracted from the APO read this time, and the difference is controlled
It is calculated by gradually decreasing at the cycle T (Rapo = (AP
O-APObef) / T). At S5, the accelerator opening is changed.
It is determined whether the conversion rate Rapo is a predetermined value A or more.
Predetermined value A maintains stable combustion state in low temperature premix combustion
Set according to the limit of change in operating condition within the range
As long as Rapo falls below this, stable combustion condition
Indicates that can be maintained. In this step, Rap
When it is determined that o is less than the predetermined value A, the process proceeds to S7.
Drive pulse is generated and output as usual.
When o is a predetermined value A or more and the combustion state becomes unstable
If determined, proceed to S6 to read auxiliary injection conditions
After that, proceed to S7.

Here, the auxiliary injection according to the present invention is a main injection for injecting at least a part of the required fuel amount for engine output (here, the basic injection amount Qi corresponds to this). Next, the fuel is injected as an additional amount or a deficient amount with respect to the required fuel amount. The auxiliary injection condition according to the present embodiment is the ratio r of the injection amount of the auxiliary injection to the basic injection amount Qi. The auxiliary injection fuel ratio r (where 0 ≦ r <1) is increased stepwise according to the accelerator opening change rate Rapo, for example, as shown in FIG. ) Continuously increase as shown in FIG.

In FIG. 4A, the auxiliary injection fuel ratio r is
The accelerator opening degree Rapo is set to 0 in a range that is less than a predetermined value A1 (= A), and Rapo is set to r1 in a range that is A1 or more and less than A2 (where A1 <A2). In addition, Rapo is A2 or more, and A3
(Provided that r2 (provided that r2 is less than A2 <A3)
1 <r2) is set. Such judgments are A1 to An.
And read the optimum r for the current situation.

On the other hand, in FIG. 4B, the auxiliary injection fuel ratio r is set to 0 within a range in which the accelerator opening Rapo is less than the predetermined value A1 (= A), but if A1 or more,
It is increased with the increase of Rapo. If the stable combustion state cannot be maintained in S5 and the auxiliary injection condition is read in S6, in the subsequent S7, a drive pulse is formed according to the auxiliary injection condition. Here, in the present embodiment, an amount obtained by multiplying the basic injection amount Qi by the auxiliary injection fuel ratio r is set as the fuel amount Qs (= Qi × r) to be injected by the auxiliary injection, and this Qs is subtracted from the amount Qi. Is the fuel amount Qm (= Qi−Qi × r) to be injected by the main injection. In addition, S
The amount of fuel injected when the process proceeds to S7 on the assumption that the stable combustion state can be maintained at 5 is the basic injection amount Qi.

Next, the effects obtained by the above control will be described. In this embodiment, the EGR device and the turbocharger are provided, but the target EGR rate and the target supercharging pressure in the steady state are set with reference to the maps shown in FIGS. To briefly describe the tendency of each map,
In FIG. 5, the target E increases as the load increases or the rotation speed increases.
The GR rate is set low, while on the other hand, in FIG.
The higher the load or the higher the rotational speed, the higher the target boost pressure is set.

Here, consider a case where the driver suddenly depresses the accelerator to request an acceleration from the driving state indicated by the point c1 to the driving state indicated by the point a1 in the map shown in FIG. At this time, the fuel injection amount Qi and the fuel injection timing Ti are controlled without a response delay with respect to the change in the operating state. However, a change in the actual EGR rate with respect to the change in the target EGR rate and a change in the actual supercharging pressure with respect to the change in the target supercharging pressure each cause a response delay as shown in FIG. 7.

As shown in FIG. 7 (a), when the target EGR rate is decreased in response to the acceleration request, the actual change in the EGR rate is delayed, and the exhaust gas is recirculated in excess of the set amount. Then, the oxygen concentration becomes insufficient in the cylinder. Further, as shown in FIG. 7B, when the target supercharging pressure is increased and the actual change of the supercharging pressure is delayed and falls below the set value, the compression end temperature cannot be sufficiently obtained. In the required operating region A, the basic injection timing Ti is delayed in order to perform the low temperature premixed combustion as compared with the case of the normal diffusion combustion, and when the oxygen concentration and the compression end temperature become insufficient,
The ignition delay period becomes longer and the combustion state becomes unstable, which may lead to misfire.

In the present embodiment, the change of the accelerator opening APO (accelerator opening change rate Rap
Focusing on (o), when Rapo is equal to or greater than the predetermined value A, auxiliary injection is performed. FIG. 8 conceptually shows the period Δt in which the auxiliary injection is performed, where the horizontal axis represents the time t and the vertical axis represents the accelerator opening change rate Rapo. Acceleration starts at time t0, and at time t1 a predetermined value A
When the acceleration request exceeds, the auxiliary injection is performed. After the auxiliary injection, at time t2, Rapo has a predetermined value A.
Continue until less than.

FIG. 9 illustrates changes in the heat generation rate from the operating states c1 to a as an explanation of the effect obtained in this embodiment.
A comparison is made between the case where the auxiliary injection is performed under the acceleration request to 1 (a) and the case where the normal fuel injection is performed under the same acceleration request (b). The horizontal axis represents the crank angle and the vertical axis represents the heat release rate. In FIG. 9 (b), there is a possibility that combustion may become slow and misfire may occur as a result of a delay in response to changes in the EGR rate and the supercharging pressure in response to an acceleration request and a prolonged ignition delay period. I understand.

On the other hand, in FIG. 9A, the ignition delay period is shorter than that in FIG. 9B because the auxiliary injection (driving pulse Ps) is performed, and combustion is excellent. You can see that it is progressing. Here, the injection timing of the auxiliary injection is set so that the ignition delay period at that time is substantially the same as that in the case of performing the low temperature premixed combustion in the steady state (without the auxiliary injection). That is, it is preferable that the auxiliary injection causes combustion in the transient state with the same ignition delay as in the steady state. However, in order to establish the low temperature premixed combustion, the auxiliary injection is ended within the ignition delay period of the main injection (before the crank angle Cb in the figure).

Further, in the present embodiment, when performing the auxiliary injection, the basic injection amount Qi corresponding to the changed operating state (point a1 in FIG. 3) is not corrected, and the auxiliary injection is performed according to the change of the operating state. The ratio r of the amount of fuel to be injected to Qi is controlled by the injection. For this reason, the total injection amount becomes constant, so that the fuel efficiency is not deteriorated. In the above description, the change of the accelerator opening APO is adopted as the change of the operating state, but the present invention is not limited to this, and the required torque or the engine speed may be adopted as an alternative parameter. . Then, in the same manner as described above, the required torque change rate and the engine speed change rate are calculated, and when the auxiliary injection is performed when these values correspond to values that show a sudden change in the operating state such that a stable combustion state cannot be maintained. Good.

Next, another embodiment of the present invention will be described. In the present embodiment, of the fuel injection control executed by the ECU 41, only the process relating to divided injection is different. Below, only this different part is demonstrated. In the first embodiment described above, in order to detect the combustion stability of low temperature premixed combustion (the stability of the combustion state predicted when low temperature premixed combustion is performed), the operating state (accelerator opening, required torque) is detected. Alternatively, the change in the engine speed) is focused on, but here, the compression end temperature that dominantly affects the ignitability is adopted. Then, when the current compression end temperature is much lower than the target temperature for performing favorable low temperature premixed combustion, the ignition injection is performed because the ignition delay period becomes too long.

FIG. 10 is a flow chart of a fuel injection control routine according to this embodiment. In the same chart, steps that perform the same processing as in the flowchart shown in FIG. 2 above are assigned the same reference numerals as in FIG. 2, and description thereof is omitted here. If it is determined in S3 that the current operating state is in the low temperature premixed combustion zone A, S14
Then, the target compression end temperature tTc which is the target value of the compression end temperature in the steady state is set.

At S15, the actual EGR rate Regr is calculated. In calculating Regr, first, the intake air amount Qa0 when the EGR rate is 0% is read from the map. Then, based on this and the value detected by the air flow meter 31, it is calculated by the following equation. Regr = ((Qa0-intake air amount Qa) / Qa0) ×
In step S16, the estimated value (actual compression end temperature) Tc of the actual compression end temperature is calculated based on the EGR rate Regr. Specifically, the specific heat ratio κ corresponding to the gas composition of the intake air is estimated based on the Regr and the operating state, and the estimated κ is substituted into the following equation to calculate Tc. In the equation, ε is a compression ratio.

Tc = intake air temperature in intake manifold × ε ^ (κ−1) In S17, target compression end temperature tTc and actual compression end temperature Tc
It is determined whether the difference ΔTc (= tTc−Tc) from the difference is greater than or equal to a predetermined value B. The predetermined value B is set in correspondence with the limit (lower limit) value of the compression end temperature at which good ignitability can be obtained. Here, when it is determined that ΔTc is less than B, the actual compression end temperature Tc is close to the target compression end temperature tTc, and good ignitability is obtained.
Go to. On the other hand, when it is determined that ΔTc is B or more, Tc is far below tTc, and the ignition performance is considered to be poor, and the process proceeds to S18.

In S18, the auxiliary injection fuel ratio r as the auxiliary injection condition according to this embodiment is read. Where r
(However, 0 ≦ r <1), as in the case shown in FIG.
It may be increased stepwise as shown in FIG. 11 (a) or may be increased continuously as shown in FIG. 11 (b).
In FIG. 11A, in the auxiliary injection fuel ratio r, the difference ΔTc between the target compression end temperature tTc and the actual compression end temperature Tc is a predetermined value B.
It is set to 0 within the range of less than 1 (= B), and ΔTc is B
It is set to r1 in the range of 1 or more and less than B2 (B1 <B2). Then, ΔTc is set to r2 (however, r1 <r2) within a range where it is not less than B2 and less than B3 (however, B2 <B3), and the same judgment is repeated thereafter.

On the other hand, in FIG. 11 (b), the auxiliary injection fuel ratio r is set to 0 in the range where ΔTc is less than the predetermined value B1 (= B), but if it is B1 or more, ΔTc increases. It is increased accordingly. Then, in S7, auxiliary injection is performed in the same manner as described above according to the read auxiliary injection conditions.

FIG. 12 conceptually shows the time Δt for performing the auxiliary injection in this embodiment, in which the horizontal axis represents the time t and the vertical axis represents the actual compression end temperature Tc. When the target compression end temperature tTc is switched at time t0 in response to the acceleration request, the difference ΔTc between tTc and Tc becomes equal to or larger than the predetermined value B, so that the auxiliary injection is started. Then T
The auxiliary injection is continued until c increases and ΔTc becomes less than the predetermined value B at time t1.

The compression end temperature adopted in this embodiment is a parameter equivalent to the compression end pressure. Therefore, the compression end pressure may be used instead of the compression end temperature for performing the auxiliary injection in the above description. That is, FIG.
In the flowchart of step S14, the target compression end pressure tPc is set as a target value of the compression end pressure in the steady state, and the actual compression end pressure Pc, which is the actual compression end pressure, is calculated based on the EGR rate Regr in S16. At tPc
When the difference ΔPc (= tPc-Pc) between the Pc and Pc is greater than or equal to the predetermined value B ′, the auxiliary injection condition is read in S18.

In a diesel engine equipped with a supercharger, in order to calculate the compression end temperature (or the compression end pressure), the supercharging pressure may be adopted instead of the EGR rate Regr. When the boost pressure is insufficient, the target compression end temperature t
This is because it is considered that the actual compression end temperature Tc is lower than Tc and the ignitability is deteriorated. In the above, as a description of the effect, the case where the operating region is switched from the diffusion combustion region C to the low temperature premixed combustion region A has been described. However, according to the present invention, even when the operating state is changed in the same operating region A, if the stable combustion state cannot be maintained, it is possible to maintain it by performing the auxiliary injection. Is.

Next, another embodiment of the present invention will be described. The example in which the auxiliary injection is performed once by one drive pulse has been described above, but in the present embodiment, the auxiliary injection is divided into a plurality of times. Therefore, the auxiliary injection that is performed separately will be described. The auxiliary injection division number N is read as an auxiliary injection condition together with the auxiliary injection fuel ratio r in S6 and the like of the flowchart shown in FIG. 2, and is shown in FIG. 13 in consideration of the control capability of the injector 6. Thus, the higher the auxiliary injection fuel ratio r is, the larger the number is set. Here, since r is set based on the accelerator opening change rate Rapo, Rapo can be substituted, and the required torque change rate and the engine speed change rate can be substituted.

FIG. 14 shows changes in the drive pulse waveform of the injector 6 depending on the auxiliary injection fuel ratio r. Here, an increase in r corresponds to a decrease in combustion stability. Therefore, the auxiliary injection is divided into a large number of times when the combustion state is likely to become unstable.
However, in order not to impair the establishment of the low temperature premixed combustion itself, regardless of the number of divisions N, the main injection (pulse Pm)
Of all auxiliary injections (pulse Ps1) divided within the ignition delay period of
~ Psn) is completed. In order to prevent the fuel consumption from deteriorating, the total amount of fuel injected by the main injection and all the auxiliary injections should match the basic injection amount Qi.

Thus, the lower the combustion stability, the more
Combustion state can be improved by dividing auxiliary injection into many times.
No matter how unstable it becomes,
It can form a suitable ignition source and maintain a stable combustion state.
Thus, the low temperature premixed combustion can be stably performed.
In the above explanation, changes in operating conditions such as accelerator
Stability of low-temperature premixed combustion by focusing on compression and compression end temperature
Auxiliary injection is performed when the value is low. But
However, the present invention is not limited to this, and the operation of FIG.
When the operating state has changed from the area C to the operating area A
It is considered that the combustion state of low temperature premixed combustion becomes unstable.
Then, the auxiliary injection will be performed for a predetermined period immediately after such transition.
You may ask.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a diesel engine according to an embodiment of the present invention.

FIG. 2 is a flowchart of fuel injection control according to the embodiment.

FIG. 3 is a combustion mode switching map according to the embodiment.

FIG. 4 is a conceptual diagram showing setting of an auxiliary injection fuel ratio r according to changes in operating conditions.

FIG. 5 is a setting map of a target EGR rate in the diesel engine according to the embodiment of the present invention.

[Fig. 6] Same as above, setting map of target supercharging pressure in diesel engine

FIG. 7 is a time chart showing transient changes in EGR rate and supercharging pressure under acceleration demand.

FIG. 8 is a conceptual diagram showing an execution period of auxiliary injection according to a change in operating state.

FIG. 9 is a time chart of the heat release rate showing the effect of the present invention.

FIG. 10 is a flowchart of fuel injection control according to another embodiment of the present invention.

FIG. 11 is a conceptual diagram showing setting of the auxiliary injection fuel ratio r based on the compression end temperature.

FIG. 12 is a conceptual diagram showing an execution period of auxiliary injection focusing on a compression end temperature.

FIG. 13 is a conceptual diagram showing setting of the number of divisions of auxiliary injection.

FIG. 14 is a conceptual diagram showing the setting of the drive pulse of the injector when the auxiliary injection is divided and performed.

FIG. 15 is a general example of a combustion mode switching map.

[Explanation of symbols]

1 ... engine 2 ... Engine body 3 ... Intake pipe 4 ... Turbocharger 6 ... Injector 10 ... EGR passage 11 ... EGR control valve 31 ... Air flow meter 32 ... Crank angle sensor 33 ... Accelerator sensor 34 ... Water temperature sensor

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Claims (10)

[Claims] 1. A combustion temperature control means for lowering the oxygen concentration of intake air to lower the combustion temperature, a first combustion system mainly composed of diffusion combustion, and the combustion temperature control means for lowering the combustion temperature. A combustion system switching means for switching between a second combustion system mainly composed of premixed combustion, which is sometimes performed after the fuel injection is completed within the ignition delay period, in accordance with the operating state, and a combustion system switching device depending on the switching result by the device. The fuel injection control means for controlling the injection operation of the fuel injection valve, and the combustion stability detection means for detecting the stability of the combustion state in the case of the second combustion method. In the case of the second combustion method, a main injection for injecting at least a part of the required fuel amount for engine output according to the combustion stability detected by the combustion stability detection means, and the required fuel amount Against A supplementary injection for injecting additional or insufficient fuel after the main injection is performed, the supplementary injection is controlled based on the combustion stability, and is ended within the ignition delay period of the main injection. Diesel engine control device. 2. The control device for a diesel engine according to claim 1, wherein the fuel injection control means causes the auxiliary injection to be performed when the combustion stability is lower than a predetermined value as a lower limit value of the normal range. 3. The control device for a diesel engine according to claim 1, wherein the fuel injection control means increases the injection amount by the auxiliary injection as the combustion stability is lower. 4. The control device for a diesel engine according to claim 1, wherein the fuel injection control means increases the number of injections of the auxiliary injection as the combustion stability is lower. 5. The control device for a diesel engine according to claim 1, wherein the combustion stability detecting means detects the combustion stability as a lower value as the rate of change of the operating state is larger. . 6. The combustion stability detecting means detects the combustion stability as a lower value as the rate of change of the accelerator opening, the required torque or the engine speed as the operating state is larger. Diesel engine controller. 7. The target compression end temperature calculating means for calculating the target compression end temperature as a target value of the compression end temperature or its equivalent amount based on the operating state, the combustion stability detecting means,
And a target compression end temperature calculated by the target compression end temperature calculating means, and an actual compression end temperature detecting unit for detecting an actual compression end temperature as an estimated value of an actual compression end temperature or its equivalent amount, The diesel engine control device according to claim 1, wherein the combustion stability is detected as a lower value as the difference from the actual compression end temperature detected by the actual compression end temperature detection means is larger. 8. The control device for a diesel engine according to claim 7, wherein the actual compression end temperature detecting means detects the actual compression end temperature based on at least one of the exhaust gas recirculation rate and the boost pressure. 9. A compression ratio is set to a predetermined low compression ratio, and in the combustion mode switching means, the first combustion system should be used on a lower load side than an operating region in which the second combustion system should be used. The control device for a diesel engine according to claim 1, wherein an operating region is provided. 10. A combustion temperature control means for lowering the oxygen concentration of intake air to lower the combustion temperature, a first combustion method mainly composed of diffusion combustion, and the combustion temperature control means for lowering the combustion temperature. A combustion system switching means for switching between a second combustion system mainly composed of premixed combustion, which is sometimes performed after the fuel injection is completed within the ignition delay period, in accordance with the operating state, and a combustion system switching device depending on the switching result by the device. And a fuel injection control means for controlling the injection operation of the fuel injection valve, the compression ratio in the case of the second combustion method is set to a predetermined low compression ratio, and the combustion method switching means includes: The operating region according to the first combustion method is provided on the lower load side than the operating region according to the second combustion method, and the fuel injection control means further includes the first fuel provided on the low load side. Main injection for injecting at least a part of the required fuel amount for engine output in a predetermined period immediately after the transition from the power operating region according to the system to the power operating region according to the second combustion system, and addition to the required fuel amount A control device for a diesel engine, characterized in that auxiliary injection for injecting fuel as a minute or shortage after the main injection is performed and the auxiliary injection is ended within an ignition delay period of the main injection.