JP4868168B2 - Combustion control device for in-cylinder internal combustion engine - Google Patents

Description

  The present invention relates to an in-cylinder injection internal combustion engine, and more particularly, to a technique for suppressing blow-up during start-up.

2. Description of the Related Art In a cylinder injection type internal combustion engine (hereinafter referred to as an engine), there is known a combustion control device capable of switching between intake stroke injection for injecting fuel in an intake stroke and compression stroke injection for injecting fuel in a compression stroke.
In the intake stroke injection, the fuel is sufficiently diffused from the end of fuel injection to ignition to make the air-fuel ratio uniform in the cylinder, so that the amount of fuel injection into the cylinder can be increased and the engine torque can be increased. Can be secured. On the other hand, in the compression stroke injection, the diffusion of fuel in the cylinder is relatively small at the time of ignition, and stratified combustion is possible. Therefore, the air-fuel ratio in the entire cylinder can be suppressed and the fuel consumption can be reduced. Therefore, in general, intake stroke injection is selected at high rotation or high load, and compression stroke injection is selected at low load and low rotation.

By the way, when the engine is started, volumetric efficiency is increased due to a delay in lowering of the manifold pressure due to the capacity of the intake system of the engine, and the engine speed is temporarily increased excessively. Such a large blow-up at the start causes problems such as making the driver feel uncomfortable and increasing HC (unburned fuel) emissions.
In view of this, a technique has been developed that suppresses the blow-up by retarding the ignition timing in response to an excessive increase in the engine speed at the start (Patent Document 1).
Japanese Patent Laid-Open No. 2005-214072

  However, in an engine that performs intake stroke injection at the time of start-up, although combustion stability is secured to some extent even if the ignition timing is retarded in order to suppress blow-up, in an internal combustion engine that can perform compression stroke injection as described above When performing the compression stroke injection at the start, if the ignition timing is retarded, the combustion may become unstable. This is because in the compression stroke injection, it is necessary to accurately control the timing of the fuel injection timing and the ignition timing in order to achieve stratified combustion, and when the ignition timing is retarded, a mixture with a sufficient concentration is formed near the electrode of the spark plug. This is because there is a risk of misfire without being present.

Further, at the time of start-up, there is a possibility that the rotational speed of the fuel pump is not sufficiently increased and the fuel injection pressure is not sufficiently ensured, which is also a factor of unstable combustion.
The present invention has been made to solve such a problem, and an object of the present invention is to provide a cylinder injection type internal combustion engine that performs compression stroke injection at the time of start-up, while ensuring combustion stability and at the time of start-up. An object of the present invention is to provide a combustion control device that can sufficiently suppress blow-up.

In order to achieve the above object, a first aspect of the present invention provides a combustion control device for a cylinder injection type internal combustion engine capable of starting a compression injection that starts by injecting fuel in a compression stroke. Blow-up that retards the ignition timing according to the difference between the engine speed detected by the rotation speed detection means and the predetermined rotation speed so that the engine rotation speed that blows up at the start time converges to the predetermined rotation speed. The retard amount by the blow-up restraining means and the retarding means so that the ignition timing does not exceed the retard limit set based on the fuel injection timing into the cylinder and the fuel injection pressure into the cylinder at the start of the compression injection. And a retard limiting means for limiting the above.

Further, in the invention of claim 2, in claim 1, blow-out up suppressing unit, that converge by further reducing the amount of fuel injected into the cylinder, a blown-up engine rotational speed at the time of starting the predetermined rotational speed Features.

According to a third aspect of the present invention, in the second aspect of the present invention, the blow-up suppressing means changes a reduction amount of the fuel injection amount into the cylinder based on the fuel injection pressure into the cylinder.

  According to the combustion control apparatus for a direct injection internal combustion engine according to claim 1 of the present invention, at the start of compression injection, the retard amount for suppressing the blow-up is limited so as not to exceed the retard limit. Retard is prevented and combustion stability at the start of compression injection can be ensured. In particular, since the retard limit is set based on the timing of fuel injection into the cylinder, it is possible to sufficiently suppress the blow-up by increasing the retard amount while ensuring the combustion stability.

Furthermore, since the retard limit is set based also on the fuel injection pressure, the retard limit can be set in consideration of changes in combustibility due to fluctuations in the fuel injection pressure. Therefore, at the time of starting, for example, even when the pressurizing capacity of the fuel pump is not yet fully exhibited, the retard limit corresponding to the fuel injection pressure is set and the combustion stability can be ensured.

According to the combustion control apparatus for a cylinder injection type internal combustion engine according to claim 2 of the present invention, since the blow-up at the start is converged by reducing not only the retard but also the fuel injection amount, the blow-up is suppressed only by the retard. Even when it is not possible, the blow-up can be more sufficiently suppressed.
According to the combustion control apparatus for a cylinder injection internal combustion engine according to claim 3 of the present invention, the reduction amount of the fuel injection amount is changed based on the fuel injection pressure, so that the change in combustibility due to the fluctuation of the fuel injection pressure is taken into consideration. The fuel injection amount thus set can be set, and the combustion stability can be sufficiently ensured.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an engine (cylinder injection type internal combustion engine) 1 according to the present invention.
As shown in FIG. 1, an electromagnetic fuel injection valve 6 is attached to the cylinder head 2 of the engine 1 together with a spark plug 4 for each cylinder, so that fuel can be directly injected into the combustion chamber 8. Has been.

A fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe. Specifically, the fuel supply device includes a fuel pump. The fuel pump pressurizes the fuel in the fuel tank and supplies the pressurized fuel to the fuel injection valve 6.
An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected so as to communicate with each intake port. A throttle valve 11 is connected to the other end of the intake manifold 10, and the throttle valve 11 is provided with a throttle sensor 11a for detecting the throttle opening.

The cylinder head 2 has an exhaust port formed in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 12 is connected to communicate with each exhaust port. An exhaust pipe 20 is connected to the other end of the exhaust manifold 12, and a muffler (not shown) is connected to the exhaust pipe 20 via an exhaust purification catalyst 30.
The exhaust purification catalyst 30 includes two catalysts, a selective reduction type NOx catalyst (hereinafter referred to as NOx catalyst) 30a that selectively purifies NOx in exhaust gas in the presence of HC, and a three-way catalyst 30b. The three-way catalyst 30b is disposed downstream of the NOx catalyst 30a.

The engine 1 includes a crank angle sensor (rotational speed detecting means) 13 that detects a crank angle and detects an engine rotational speed Ne from the transition of the crank angle, a water temperature sensor 14 that detects a water temperature of engine cooling water, and fuel injection. A fuel pressure sensor 16 for detecting the pressure (fuel pressure) PFL of the fuel supplied to the valve 6 is provided.
The ECU (Electronic Control Unit) 40 includes an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like. The timer counter particularly has a function of measuring an operation time after the engine is started.

In addition to the throttle sensor 11a, the crank angle sensor 13, the water temperature sensor 14, and the fuel pressure sensor 16 described above, various sensors such as an air-fuel ratio sensor (not shown) are connected to the input side of the ECU 40. Detection information is input.
On the other hand, various output devices such as a spark plug 4 are connected to the output side of the ECU 40 via a fuel injection valve 6 and an ignition coil 9. The ECU 40 calculates the fuel injection amount, the fuel injection timing, the ignition timing, etc. for realizing the target air-fuel ratio such as the theoretical air-fuel ratio and the lean air-fuel ratio based on detection information from various sensors, for example, by reading from the map. Control various output devices.

Further, by controlling the fuel injection timing, the ECU 40 can selectively implement, as the fuel injection mode, an intake stroke injection mode in which fuel injection is performed in the intake stroke and a compression stroke injection mode in which fuel injection is performed in the compression stroke. It has become.
In the intake stroke injection mode, the time from the end of fuel injection to ignition is relatively long, and uniform premixed combustion is possible. Therefore, the air-fuel ratio in the entire cylinder can be increased to ensure a large engine torque. On the other hand, in the compression stroke injection mode, since the time from the end of fuel injection to ignition is relatively short and stratified combustion is possible, the air-fuel ratio in the entire cylinder can be suppressed and fuel consumption can be reduced. The ECU 40 selects the compression stroke injection mode at the time of low rotation and low load, and the intake stroke injection mode at the time of high rotation or high load. Further, the ECU 40 inputs the cooling water temperature from the water temperature sensor 14 as the engine temperature at the start, determines whether or not it is in a cold state, and at the cold state, that is, at the cold start, the purification efficiency of the exhaust purification catalyst 30 is determined. Therefore, the compression stroke injection mode is selected so that the HC is not supplied excessively, and the compression injection start is executed.

In the present embodiment, the ECU 40 further retards the ignition timing (basic ignition timing) calculated based on the detection information from the various sensors and starts the air-fuel ratio (basic A / F) at the start. The injection amount is controlled to suppress the blow-up of the rotational speed Ne (blow-up suppressing means).
FIG. 2 is a flowchart showing the control procedure of the ignition timing and the air-fuel ratio in the ECU 40 according to the embodiment of the present invention.

This flowchart is repeatedly executed during engine operation.
First, in step S10, it is determined whether or not the operation time after startup measured by the timer counter is within a predetermined time (predetermined time after startup). The predetermined time after the start may be set to a time at which the rising of the engine rotational speed Ne surely converges to the predetermined rotational speed Ne1 (for example, the idling set speed) after the engine is started. If it is within the predetermined time after startup, the process proceeds to step S20.

In step S20, it is determined whether or not the engine rotational speed Ne input from the crank angle sensor 13 is greater than a predetermined rotational speed Ne1. If the engine speed Ne is greater than the predetermined speed Ne1, the process proceeds to step S30.
In step S30, the blow-up rotational speed ΔNe is obtained. Specifically, ΔNe = Ne−Ne1 is calculated. Then, the process proceeds to step S40.

In step S40, it is determined whether or not it is a compression injection start, that is, whether or not the compression stroke injection mode is set at the current engine start. If it is the compression injection start, the process proceeds to step S50.
In step S50, it is determined whether or not the control ignition timing TESIT is a retard lower limit ignition timing TRDKAGENIT described later. Specifically, it is determined whether or not the currently set ignition timing has reached the ignition timing (retard limit) retarded to the maximum within a range where combustion is established. When the control ignition timing TESIT is not (has not reached) the retard lower limit ignition timing TRDKAGENIT, the process proceeds to step S60.

  In step S60, the fuel pressure PFL is input from the fuel pressure sensor 16 as information related to the fuel injection pressure, and the fuel injection end timing TFL (fuel injection timing) is input to calculate the retard lower limit ignition timing TRDKAGENIT. The retard lower limit ignition timing TRDKAGENIT is calculated using, for example, FIG. FIG. 3 is a graph showing the range of fuel injection end timing TFL and ignition timing (combustion establishment range) in which combustion is established. (A) is when fuel pressure PFL is equal to or higher than specified fuel pressure PFL1, and (B) is fuel pressure PFL. Shows a case where is lower than the specified fuel pressure PFL1. In this figure, as an example, the retard lower limit ignition timing TRDKAGENIT when the fuel injection end timing TFL is a and the basic ignition timing before retarding are shown as a reference. In this step, (A) or (B) in FIG. 3 is selected according to the fuel pressure PFL, and the lower limit value (the most retarded angle) of the ignition timing within the combustion establishment range according to the fuel injection end timing TFL from the selected diagram. Is read out as the retard lower limit ignition timing TRDKAGENIT. Then, the process proceeds to step S70.

In step S70, the ΔNe retard amount TRDΔNe is calculated based on the blow-up rotational speed ΔNe calculated in step S30. The ΔNe retard amount TRDΔNe may be obtained by reading from a map that has been confirmed and set in advance so that the blowing rotational speed ΔNe converges to the predetermined rotational speed Ne1. Then, the process proceeds to step S80.
In step S80, the control ignition timing TESIT is calculated. The control ignition timing TESIT is obtained by calculating the ΔNe retard amount TRDΔNe calculated in step S70 from the basic ignition timing TBSIT which is the ignition timing before retarding calculated based on the detection information input from various sensors such as the throttle sensor 11a. Find by subtraction. Then, the process proceeds to step S90.

  In step S90, it is determined whether or not the control ignition timing TESIT calculated in step S80 is less than the retard lower limit ignition timing TRDKAGENIT (retarded side) calculated in step S60. If it is determined that the control ignition timing TESIT is less than the retard lower limit ignition timing TRDKAGENIT, the process proceeds to step S100. If it is determined that the control ignition timing TESIT is equal to or greater than the retard lower limit ignition timing TRDKAGENIT (advance side), this routine is returned.

In step S100, the control ignition timing TESIT is rewritten to the retard lower limit ignition timing TRDKAGENIT calculated in step S60 (retard limiting means). Then, this routine is returned.
On the other hand, if it is determined in step S50 that the control ignition timing TESIT is the retard lower limit ignition timing TRDKAGENIT, the process proceeds to step S110.

  In step S110, ΔNe air-fuel ratio leaning amount A / FLEANΔNe is calculated based on the blow-up rotational speed ΔNe calculated in step S30. The ΔNe air-fuel ratio leaning amount A / FLEANΔNe can be obtained by reading from a map that has been confirmed in advance and set the leaning amount of the air-fuel ratio such that the blow-up rotational speed ΔNe converges to the predetermined rotational speed Ne1. Good. Then, the process proceeds to step S120.

In step S120, the control air-fuel ratio A / FES is calculated. The control air-fuel ratio A / FES is calculated from the basic air-fuel ratio A / FBS, which is the target air-fuel ratio calculated based on detection information input from various sensors such as the throttle sensor 11a described above, to the ΔNe air-fuel ratio calculated in step S110. Calculate by adding the leaning amount A / FLEANΔNe. Then, the process proceeds to step S130.
In step S130, the fuel pressure PFL is input from the fuel pressure sensor 16, and the leaning limit value A / FLEANGEN is calculated according to the fuel pressure PFL. Specifically, it is determined whether or not the fuel pressure PFL is equal to or higher than the specified fuel pressure PFL1, and if it is equal to or higher than the specified fuel pressure PFL1, the lean limit value A / FLEANGEN1 is selected as the lean limit value A / FLEANGEN. If the fuel pressure is lower than PFL1, select the lean limit A / FLEANGEN2. Then, the process proceeds to step S140. The leaning limit value A / FLEANGEN1 and the leaning limit value A / FLEANGEN2 are numerical values obtained after confirmation in advance, and these numerical values will be described below with reference to FIG. FIG. 4 is a graph showing the relationship between the air-fuel ratio A / F and the engine torque. (A) shows the case where the fuel pressure PFL is equal to or higher than the specified fuel pressure PFL1, and (B) shows the case where the fuel pressure PFL is lower than the specified fuel pressure PFL1. . When the fuel pressure PFL is equal to or higher than the specified fuel pressure PFL1, the air-fuel ratio at which the engine torque at which the engine can be stably operated in FIG. 1A corresponds to the leaning limit value A / FLEANGEN1. On the other hand, when the fuel pressure PFL is lower than the specified fuel pressure PFL1, the air-fuel ratio that is the lowest value of the engine torque in FIG. 5B corresponds to the leaning limit value AFLEANGEN2.

In step S140, it is determined whether or not the control air-fuel ratio A / FES calculated in step S120 is larger than the leaning limit value AFLEANGEN set in step S130. If it is larger than the lean limit value AFLEANGEN, the process proceeds to step S150.
In step S150, the control air-fuel ratio A / FES is rewritten to the lean limit value AFLEANGEN set in step S130. Then, this routine ends.

If it is determined in step S140 that the control air-fuel ratio A / FES is equal to or less than the lean limit value AFLEANGEN, or if it is determined in step S10 that a predetermined time or more has elapsed after starting, or in step S20, the engine speed Ne is When it is determined that the rotation speed is equal to or lower than the predetermined rotation speed Ne1, this routine is returned.
On the other hand, if it is determined in step S40 that the compression injection start has not occurred, the process proceeds to step S160.

In step S160, a ΔNe retard amount TRDΔNe is calculated based on the blow-up rotational speed ΔNe calculated in step S30. Then, the process proceeds to step S170.
In step S170, the control ignition timing TESIT is calculated. The control ignition timing TESIT is obtained by subtracting the ΔNe retard amount TRDΔNe calculated in step S160 from the basic ignition timing TBSIT. Then, this routine ends.

  With the above configuration, in the present embodiment, retarding of the ignition timing is started when the engine rotational speed Ne becomes equal to or higher than the predetermined rotational speed Ne1 at the start of compression injection. At that time, the retard lower limit ignition timing TRDKAGENIT is set to The lower limit is set within the combustion establishment range that changes according to the fuel injection timing TFL. Thus, the retard limit is set according to the fuel injection timing TFL, so that the retard amount can be set large. Therefore, at the start of compression injection, while ensuring combustion stability, the blow-up is sufficiently suppressed, and the amount of HC in the exhaust can be sufficiently reduced.

Further, in the present embodiment, when the control ignition timing TESIT has already reached the retard lower limit ignition timing TRDKAGENIT, the fuel injection amount is reduced, so that the blow-up can be further suppressed.
Further, in the present embodiment, the retard lower limit ignition timing TRDKAGENIT and the leaning limit value AFLEANGEN are changed according to the fuel pressure PFL. Therefore, for example, after the fuel pressure PFL is reduced at the time of starting the engine, the combustion is reliably established. A large reduction amount of the retard amount and the fuel injection amount can be secured.

FIG. 5 is a time chart showing changes in the engine rotational speed Ne, the control ignition timing TESIT, the control air-fuel ratio A / FES, and the HC emission amount at the start of the compression injection in the present embodiment. In the figure, the solid line indicates the case where the retard and lean control is performed by the combustion control apparatus of the present embodiment, and the dotted line indicates the case where the retard and lean control is not performed.
As shown in FIG. 5, in the present embodiment, retarding of the ignition timing is started when the engine rotational speed Ne becomes equal to or higher than the predetermined rotational speed Ne1 due to the blow-up at the start of the compression injection, and accordingly, the engine rotational speed Ne is started. Rise is suppressed. When the engine speed Ne continues to increase as the retard alone is not sufficient, lean control is also performed, so that further increase in the engine speed Ne is suppressed, and the blow-up at the start of compression injection is suppressed. More suppressed.

  This is the end of the description of the embodiment. However, the embodiment of the present invention is not limited to this embodiment. For example, in this embodiment, the retard lower limit ignition timing TRDKAGENIT and the leaning limit value AFLEANGEN are changed in two stages depending on whether or not the fuel pressure PFL is equal to or higher than the specified fuel pressure PFL1, but these are continuously changed according to the fuel pressure PFL. May be changed. In this way, the retard lower limit ignition timing TRDKAGENIT and the leaning limit value AFLEANGEN can be set more accurately, and the blow-up can be more sufficiently suppressed.

In the present invention, it is not necessary to change any one of the retard lower limit ignition timing TRDKAGENIT and the leaning limit value AFLEANGEN according to the fuel pressure PFL , and at least the retard lower limit ignition timing TRDKAGENIT according to the fuel injection timing TFL and the fuel pressure PFL. If the retard amount is set by limiting the combustion amount, it is possible to suppress the blow-up while ensuring the combustion stability.

1 is a schematic configuration diagram of an in-cylinder fuel injection type engine according to the present invention. It is a flowchart which shows the control point of the ignition timing and fuel injection amount in ECU which concerns on embodiment of this invention. It is a graph which shows the range of the fuel injection completion timing and ignition timing in which combustion is materialized, (A) shows the case where a fuel pressure is more than a regulation fuel pressure, (B) shows the case where a fuel pressure is lower than a regulation fuel pressure. It is a graph which shows the relationship between an air fuel ratio and an engine torque, (A) shows the case where a fuel pressure is more than a regulation fuel pressure, (B) shows the case where a fuel pressure is lower than a regulation fuel pressure. 6 is a time chart showing changes in engine rotation speed, control ignition timing, control air-fuel ratio, and HC emission amount at the start of compression injection in the present embodiment.

Explanation of symbols

1 Engine 4 Spark Plug 6 Fuel Injection Valve 13 Crank Angle Sensor 16 Fuel Pressure Sensor 40 ECU

Claims (3)

In a combustion control device for a direct injection internal combustion engine capable of starting compression injection by injecting fuel in a compression stroke,
A rotational speed detecting means for detecting the engine rotational speed;
Blow-up suppression means for retarding the ignition timing according to the difference between the engine rotation speed detected by the rotation speed detection means and the predetermined rotation speed so that the engine rotation speed blowing up at the start time converges to the predetermined rotation speed; ,
At the start of the compression injection, the retard amount by the blow-up suppressing means is limited so that the ignition timing does not exceed the retard limit set based on the fuel injection timing into the cylinder and the fuel injection pressure into the cylinder. Retard retard means to
A combustion control apparatus for a cylinder injection internal combustion engine, comprising: The in-cylinder injection internal combustion engine according to claim 1 , wherein the blow-up suppressing means further reduces the amount of fuel injected into the cylinder so as to converge the engine rotation speed blowing up at the start to a predetermined rotation speed. Engine combustion control device. The combustion of the direct injection internal combustion engine according to claim 2 , wherein the blow-up suppressing means changes a reduction amount of the fuel injection amount into the cylinder based on a fuel injection pressure into the cylinder. Control device.

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