JP2008240554A - Fuel injection control device of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control device of a diesel engine capable of restraining generation of NOx and smoke, while reducing combustion noise, in the diesel engine for performing pilot injection. <P>SOLUTION: The pilot injection timing is controlled so that a time interval τep-cp up to the pilot combustion starting timing θcp from the pilot injection finishing timing θep, becomes target time τreq set by a map based on an engine speed Ne and the total injection quantity Qall. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel injection control device for a diesel engine, and more particularly to a technique for controlling an injection timing and an injection amount of pilot injection injected before main injection.

  Engines that inject fuel directly into the cylinder, such as common rail diesel engines, can perform fuel injection multiple times at any time during a single combustion cycle consisting of an intake stroke, compression stroke, expansion stroke, and exhaust stroke It is. Therefore, the number and timing of fuel injections are changed according to the operating state of the engine.For example, by performing pilot injection that precedes main injection, rapid increase in combustion pressure is suppressed, and combustion noise is reduced. Can be planned.

As specific fuel injection control in a diesel engine that performs pilot injection in this manner, the time interval between pilot injection and main injection and the amount of fuel injected by pilot injection are controlled within an appropriate range to stabilize combustion. A configuration for reducing the noise and combustion noise is disclosed (see Patent Document 1).
JP 2006-2760 A

However, in the above-mentioned Patent Document 1, the time interval between the two injections is controlled based on the combustion center of gravity between the pilot combustion caused by the pilot injection and the main combustion caused by the main injection. Not done.
In the pilot injection, when the injection timing is in the vicinity of the top dead center, steep combustion occurs immediately after the fuel injection, the NOx emission amount increases, and there is a tendency that the smoke increases as the injection amount increases. With such a configuration, there is a problem that the exhaust gas performance deteriorates.

Further, in the above-mentioned Patent Document 1, the configuration is such that the parameters in the fuel injection are gradually adjusted by closed loop control so as to keep the combustion center of gravity and the like within an appropriate range, but in such a configuration, until reaching the target state. Several cycles are required, and there is a problem that responsiveness is poor.
The present invention has been made to solve such problems, and the object of the present invention is to reduce combustion noise and suppress the generation of NOx and smoke in a diesel engine that performs pilot injection. An object of the present invention is to provide a fuel injection control device for a diesel engine.

  In order to achieve the above-described object, the fuel injection control device for a diesel engine according to claim 1 is a fuel injection control device for a diesel engine provided with fuel injection means capable of injecting fuel into the combustion chamber a plurality of times. Fuel injection control means for controlling main injection executed by the fuel injection means and pilot injection injected prior to the main injection; pilot combustion detection means for detecting start timing of pilot combustion caused by the pilot injection; The fuel injection control means includes a pilot so that a time interval from a pilot injection end time to a pilot combustion start time detected by the pilot combustion detection means becomes a target time set according to an operating state of the engine. It is characterized by controlling the injection timing.

The fuel injection control device for a diesel engine according to claim 2, wherein the fuel injection control means controls the fuel injection amount of the pilot injection in accordance with a time interval from the pilot injection start timing to the main injection start timing. It is a feature.
The fuel injection control device for a diesel engine according to claim 3 is characterized in that the target time is set according to at least the fuel injection pressure.

  According to the fuel injection control apparatus for a diesel engine of the first aspect of the present invention using the above means, the pilot injection is performed so that the time interval from the pilot injection end timing to the pilot combustion start timing becomes the target time according to the operating state of the engine. By controlling the timing, the interval from pilot injection to pilot combustion can be made appropriate, and steep pilot combustion can be prevented from occurring. In other words, pilot combustion can be made gentle, thereby reducing combustion noise and suppressing generation of NOx and smoke.

According to the fuel injection control device for a diesel engine of claim 2, the pilot injection timing and the main injection are controlled by controlling the fuel injection amount of the pilot injection according to the time interval from the pilot injection start timing to the main injection start timing. The ignition delay of the main injection due to the expansion of the time interval can be prevented.
According to the fuel injection control device for a diesel engine according to claim 3, the target time is set easily and accurately according to the operating state by setting the target time according to the fuel injection pressure that strongly influences the pilot combustion. can do.

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 fuel injection control device for a diesel engine according to the present invention. With reference to FIG. 2, fuel injection control by the fuel injection control device for a diesel engine according to the present invention is executed. The time chart which showed the combustion state of this in time series is shown. Hereinafter, description will be made based on these drawings.

An engine 1 shown in FIG. 1 is a four-cylinder common rail type diesel engine in which high-pressure fuel accumulated in a common rail 2 is supplied into a combustion chamber of each cylinder 4 by a fuel injection valve 6 (fuel injection means).
An intake manifold 8 is connected to the intake side of the engine 1, and an intake pipe 10 extends from the intake manifold 8. The intake pipe 10 is provided with an air cleaner 12 at the intake upstream end, and a compressor 14a of the turbocharger 14 is provided in the middle. Further, an intercooler 16 is provided on the intake downstream side of the compressor 14a, and an intake control valve 18 is provided on the intake downstream side.

On the other hand, an exhaust manifold 20 is connected to the exhaust side of the engine 1, and an exhaust pipe 22 extends from the exhaust manifold 20. An EGR passage 24 is connected to the exhaust manifold 20 and the intake manifold 8, and an EGR valve 26 that adjusts the recirculation amount of EGR gas is provided in the EGR passage 24.
In the middle of the exhaust pipe 22, a turbine 14b connected coaxially with the compressor 14a is provided.

Further, an exhaust aftertreatment device 28 is provided on the exhaust downstream side of the exhaust pipe 22. Although not shown, for example, a NOx storage catalyst is accommodated in the exhaust aftertreatment device 28, and a particulate filter (DPF) that collects particulates in the exhaust is accommodated downstream of the NOx storage catalyst. Yes.
Further, the vehicle equipped with the engine 1 is provided with an ECU 30 (fuel injection control means) as a control device for performing comprehensive control including operation control of the engine 1 and the like. It is composed of a memory, a timer counter, and the like, performs various control amount calculations, and controls various devices based on the control amounts.

  For example, on the input side of the ECU 30, a crank angle sensor 32 that detects a crank angle of the engine 1, an intake air temperature sensor 34 that is provided in the intake manifold 8 and detects an intake air temperature, and a supercharging pressure sensor 36 that detects a supercharging pressure, Various sensors such as an in-cylinder pressure sensor 38 (pilot combustion detecting means) provided in each cylinder 4 for detecting the in-cylinder pressure and an accelerator opening sensor 40 for detecting the depression amount of the accelerator pedal are connected. Various devices such as the fuel injection valve 6, the intake control valve 18, and the EGR valve 26 for each cylinder are connected to the output side of the ECU 30.

Then, the ECU 30 sets the fuel injection amount and the fuel injection timing to each cylinder 4 based on the information acquired from the various sensors, and controls the fuel injection valve 6 according to the fuel injection amount and the fuel injection timing.
Specifically, in the fuel injection of the engine 1, main injection and pilot injection that is performed prior to the main injection are performed. The ECU 30 independently performs the fuel injection amount and the fuel for the main injection and the pilot injection. Set the injection timing.

Specifically, for the main injection, the ECU 30 is based on the engine speed Ne calculated from the crank angle detected by the crank angle sensor 32 and the accelerator pedal depression amount detected by the accelerator opening sensor 40. A main injection amount Qm and a main injection start timing θim necessary for the operation of the engine 1 are set and executed from a map stored in advance.
On the other hand, for pilot injection, the ECU 30 starts pilot injection from a time interval τep-cp from the pilot injection end timing θep in the previous combustion cycle as shown in FIG. 2 to the pilot combustion start timing θcp caused by the pilot injection. The timing θip is set, and the pilot injection amount Qp is set from the time interval τip-im between the pilot injection start timing θip and the main injection start timing θim. In the present embodiment, as shown in FIG. 2, the main injection start timing θim is set near the top dead center (TDC), and the pilot injection is so-called early pilot injection, which is advanced by a predetermined crank angle or more than the main injection. It is set at the time.

Here, the pilot injection timing and injection amount setting control will be described in more detail.
Referring to FIG. 3, FIG. 3 is a flowchart showing a pilot injection control routine executed by the fuel injection control device for a diesel engine according to the present invention, and FIG. 4 to FIG. 9 show the pilot injection control routine. The various maps used are shown. Hereinafter, description will be made along the flowchart of FIG. 3 with reference to FIG. 2 and FIGS.

First, in step S1, the in-cylinder pressure Pc from each of the in-cylinder pressure sensors 38, the engine speed Ne from the crank angle sensor 32, the intake air temperature Tin from the intake air temperature sensor 34, and the supercharging pressure Pb from the supercharging pressure sensor 36 are obtained. Get each.
In step S2, the heat generation rate is calculated from the in-cylinder pressure Pc acquired in step S1, and the pilot combustion start timing θcp is detected.

Specifically, the pilot combustion start timing θcp is detected from the heat generation rate calculated from the in-cylinder pressure Pc as shown in FIG. 2, and the heat rise start timing after pilot injection (around −15 degrees in FIG. 2). Is the pilot combustion start timing θcp.
In step S3, the target time τreq of the time interval τep-cp from the pilot injection end timing θep to the pilot combustion start timing θcp is set from the map based on the engine speed Ne and the total injection amount Qall. The total injection amount Qall is the sum of the fuel injection amounts Qp and Qm of the pilot injection and the main injection. Here, the total injection amount Qall is obtained from the fuel injection information executed in the previous combustion cycle stored in the ECU 30. And

  Specifically, since the time interval τep-cp tends to shorten the interval as the injection pressure Pf increases, the atomization of the fuel tends to become shorter. Therefore, the target time τreq is equal to the injection pressure Pf as shown in the map of FIG. Set to be shorter as the value increases. The injection pressure Pf is set higher as the engine speed Ne and the total injection amount Qall are higher as shown in FIG. 5 and lower as the engine speed Ne is lower. Therefore, the target time τreq corresponding to the injection pressure Pf can be set by a map based on the engine speed Ne and the total injection amount Qall as shown in FIG. 6, and the engine speed Ne and the total injection amount Qall are high in the map. The shorter the area, the longer the lower area.

  The interval from fuel injection to combustion is affected by the strength of in-cylinder flow, the in-cylinder pressure, the in-cylinder temperature, etc. in addition to the injection pressure Pf. These factors are also affected by the engine speed Ne and the total injection amount. Since it changes according to Qall, the above-mentioned elements can be obtained by setting in advance a map showing the optimum value of the target time τreq according to the engine speed Ne and the total injection amount Qall as shown in FIG. It is possible to set the target time τreq in consideration.

In the following step S4, the target time τreq set in step S3 is corrected by the correction amount Δτ set based on the intake air temperature Tin and the boost pressure Pb acquired in step S1.
Specifically, as shown in FIG. 7, the correction amount Δτ is set on the increasing side as the intake air temperature Tin becomes lower than the predetermined intake air temperature Tin1, and is set on the decreasing side as it increases. Further, with respect to the supercharging pressure Pb, the correction amount Δτ is set on the increasing side as the supercharging pressure Pb becomes lower than the predetermined supercharging pressure Pb1, as shown in FIG.

In the correction, the in-cylinder pressure and the in-cylinder temperature affected by the history of the operating state of the engine 1 are replaced with the intake air temperature and the boost pressure that can be easily detected, and according to the intake air temperature Tin and the boost pressure Pb. As a result of the correction, the target time τreq becomes a value according to the actual operation state.
In the next step S5, the pilot injection ends at a timing advanced by the target time τreq from the pilot combustion start timing θcp of the previous combustion cycle so that the time interval τep-cp becomes the target time τreq corrected in step S4. The pilot injection start timing θip that becomes the timing θep is calculated and set.

  Further, in step S6, based on the pilot injection start timing θip set in step 5 and the main injection start timing θim set by the main injection control, the pilot injection amount Qp is set by a map as shown in FIG. Specifically, the pilot injection amount Qp is set so as to increase as the time interval τip-im between the main injection start timing θim and the pilot injection start timing θip becomes longer, as shown in the map of FIG. That is, as the pilot injection timing is advanced and the interval with the main injection is increased, the injection amount Qp of the pilot injection is increased to ensure the in-cylinder temperature before the main injection.

In step S7, the fuel injection valve 6 executes pilot injection at the pilot injection start timing θip set in step S5 and the pilot injection amount Qp set in step S6, and the routine returns.
As described above, the pilot is set so that the time interval τep-cp from the pilot injection end timing θep to the pilot combustion start timing θcp becomes the target time τreq corresponding to the operating state of the engine 1 based on the engine speed Ne and the total injection amount Qall. By controlling the injection timing, the interval from pilot injection to pilot combustion can be made appropriate, and steep pilot combustion can be prevented from occurring. That is, pilot combustion can be made gentle, thereby reducing combustion noise and suppressing generation of NOx and smoke.

Further, by setting the fuel injection amount Qp in the pilot injection in accordance with the time interval τip-im from the pilot injection start timing θip to the main injection start timing θim, the ignition delay of the main injection due to the interval increase with the pilot injection timing Can be prevented.
Although the description of the embodiment of the fuel injection control device for a 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 heat generation rate is calculated from the in-cylinder pressure Pc detected by the in-cylinder pressure sensor 38 to detect the pilot combustion start timing θcp, but the means for detecting the pilot combustion start timing is not limited to this. However, it may be detected by a sensor capable of directly detecting the combustion start timing or other elements.
In the above embodiment, a map corresponding to the fuel injection pressure Pf is set from the engine speed Ne and the total injection amount Qall, and the target time τreq is set based on the map. For example, the fuel injection pressure may be directly detected, and the target time may be set according to the fuel injection pressure.

  In the above embodiment, the target time τreq set in step S3 is corrected according to the intake air temperature Tin and the supercharging pressure Pb. However, the correction factor is not limited to this. If the flow and the in-cylinder temperature can be directly detected, it is more preferable to perform correction according to the in-cylinder flow and the in-cylinder temperature.

It is a schematic block diagram of the fuel-injection control apparatus of the diesel engine which concerns on this invention. It is the time chart which showed the combustion state at the time of performing the fuel-injection control by the fuel-injection control apparatus of the diesel engine which concerns on this invention in time series. It is a flowchart which shows the pilot injection control routine performed by the fuel injection control apparatus of the diesel engine which concerns on this invention. It is a map which shows the target time with respect to injection pressure. It is a map which shows the injection pressure with respect to engine speed and total injection quantity. It is a map which shows the target time with respect to an engine speed and total injection quantity. It is a map which shows the corrected amount with respect to intake air temperature. It is a map which shows the correction amount with respect to a supercharging pressure. It is a map which shows the pilot injection quantity with respect to the time interval of pilot injection and main injection.

Explanation of symbols

1 engine 2 common rail 4 cylinder 6 fuel injection valve (fuel injection means)
30 ECU (fuel injection control means)
32 Crank angle sensor 34 Intake air temperature sensor 36 Supercharging pressure sensor 38 In-cylinder pressure sensor (pilot combustion detection means)

Claims (3)

A fuel injection control device for a diesel engine provided with fuel injection means capable of injecting fuel into a combustion chamber a plurality of times,
Fuel injection control means for controlling main injection executed by the fuel injection means and pilot injection injected prior to the main injection;
Pilot combustion detection means for detecting the start timing of pilot combustion caused by the pilot injection,
The fuel injection control means sets the pilot injection timing so that the time interval from the pilot injection end timing to the pilot combustion start timing detected by the pilot combustion detection means becomes a target time set according to the operating state of the engine. A fuel injection control device for a diesel engine, characterized by being controlled.   2. The fuel injection of a diesel engine according to claim 1, wherein the fuel injection control means controls a fuel injection amount of the pilot injection according to a time interval from the pilot injection start timing to the main injection start timing. Control device.   The fuel injection control device for a diesel engine according to claim 1 or 2, wherein the target time is set according to at least a fuel injection pressure.

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