JP2002266668A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for internal combustion engine for ensuring the stability of combustion in a SOCH engine equipped with a cam phase changing mechanism by setting a cam phase to a neutral position when performing a control for reducing unburned HC in exhaust gas in cold starting. SOLUTION: In the SOCH engine 1 equipped with the cam phase changing mechanism 8, when the control for reducing unburned HC in exhaust gas in cold starting is performed in order to reconcile a combustion control for reducing the unburned HC in exhaust gas in cold starting and combustion stability, the cam phase changing mechanism 8 is driven by a control means 31 to control the cam phase to the neutral position, and the internal EGR is reduced to ensure the stability of combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine having a cam phase changing mechanism, which ensures the stability of combustion at the time of a cold start of an SOHC internal combustion engine.

[0002]

2. Description of the Related Art In a gasoline internal combustion engine (hereinafter referred to as "engine"), further reduction of exhaust gas, particularly unburned hydrocarbons (hereinafter referred to as "unburned HC") is required. Therefore, lean-burn (lean combustion) during cold start of the engine
A method has been proposed in which the unburned HC is reduced by sufficiently operating the fuel injected into the cylinder to reduce unburned HC, and the catalyst is activated by delaying the ignition timing (retard) to increase the exhaust gas temperature. I have.

There is also a control device that employs a cam phase changing mechanism separately from the above-described method to improve engine performance and fuel efficiency. Particularly, in the DOHC engine, a cam phase variable mechanism is provided on the intake valve side to control the cam phase angle to the most retarded angle even at the time of engine start and idle operation, thereby narrowing the overlap of the supply and exhaust valves. Control is performed to reduce the amount of internal EGR (blow back to the intake pipe).

[0004]

However, in order to reduce the unburned HC in the exhaust gas at the time of a cold start, the ignition timing is retarded (retard), the air-fuel ratio is made lean, the exhaust pressure is increased, and EG is increased.
Various combustion controls such as an increase in R and two-stage combustion are performed. However, these controls often make the combustion state unstable.

On the other hand, an SOHC equipped with a cam phase changing mechanism
In the engine, the cam phase at the time of stop is set to the most retarded angle due to problems such as driving oil pressure, and at the most retarded cam phase,
Internal EGR increases. Therefore, in a SOHC engine equipped with a cam phase change mechanism, when performing combustion control such as leaning or retarding to reduce unburned HC in exhaust at the time of a cold start, the internal EGR becomes more unstable when the internal EGR is large. Combustion state is added, combustion is not stable, and unburned HC
In addition to the effect of reducing the temperature, there is a risk of misfiring in the worst case.

For this reason, according to the present invention, in a SOHC engine equipped with a cam phase changing mechanism, when the control for reducing the unburned HC in the exhaust gas at the time of a cold start is performed, the cam phase is set to the neutral position and the combustion stability is set. It is an object of the present invention to provide a control device for an internal combustion engine which ensures the above.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, an S-type motor having a cam phase changing mechanism is provided.
Unburned H in exhaust gas at the time of cold start in the OHC engine
When performing control for reducing unburned HC in exhaust gas at the time of a cold start in order to achieve both combustion control for reducing C and combustion stability, the internal EGR is reduced by setting the cam phase to a neutral position to reduce combustion. Ensure stability.

According to the second aspect of the invention, the internal EGR is reduced by setting the neutral position of the cam phase to a valve overlap period in which the compression top dead center overlaps the intake stroke range and the exhaust stroke range. . Preferably, the neutral position of the cam phase is set near the center of the valve overlap period in which the compression top dead center overlaps the intake stroke range and the exhaust stroke range.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. FIG. 1 is an overall configuration diagram of an SOHC internal combustion engine including a cam phase changing mechanism according to the present invention. As shown in FIG. 1, the engine 1 is configured as an intake pipe injection type engine, and a SOHC 4-valve type is employed as a valve operating mechanism thereof. A timing pulley 4 is fixed to the front end of the camshaft 3 on the cylinder head 2.
Is connected to the crankshaft 6. Crankshaft 6
The camshaft 3 is rotated together with the timing pulley 4 with the rotation of the camshaft 3, and the intake cams 3a,
The intake cam 7b and the exhaust valve 7b are opened and closed by the exhaust cam 3b via the rocker arms Ra and Rb.

A vane type variable timing mechanism (VVT) 8 is provided between the camshaft 3 and the timing pulley 4.
Is provided. The configuration of the variable timing mechanism 8 as the cam phase changing mechanism is described in, for example, Japanese Patent Application Laid-Open No. 2000-2760.
Although not described in detail in Japanese Patent Application Laid-Open No. 9-1997, the details thereof will not be described, but a vane rotor is rotatably provided in a housing provided on the timing pulley 4, and the cam shaft 3 is connected to the vane rotor. An oil control valve (hereinafter, referred to as OCV) 9 is connected to the variable timing mechanism 8, and uses hydraulic oil supplied from an oil pump 10 of the engine 1 to apply hydraulic pressure to the vane rotor according to switching of the OCV 9. As a result, the phase of the camshaft 3 with respect to the timing pulley 4, that is, the opening / closing timing of the intake valve 7a and the exhaust valve 7b is adjusted.

The variable timing mechanism 8 is locked with the cam phase controlled to the most retarded position when the engine 1 is stopped for the following reason. In other words, the phase variable type (vane type, helical type) variable timing mechanism that varies according to the engine oil pressure makes it difficult to secure a sufficient oil pressure in the low rotation speed range where the engine is hot, so the control phase is likely to fluctuate. At the most retarded position, a stable phase can be maintained by cam friction. Further, at the most retarded position, the phase of the variable timing mechanism is mechanically locked so that the phase is maintained even when the engine is stopped, and is fixed at the most retarded angle even when there is no oil pressure at the next start. Therefore, there is no generation of abnormal noise due to vane flapping (helical type backlash flapping).

On the other hand, the intake port 11 of the cylinder head 2
The intake passage 12 is connected to the intake passage 12. The intake air introduced into the intake passage 12 from the air cleaner 13 as the piston 16 descends is adjusted from the fuel injection valve 15 after the flow rate is adjusted according to the opening of the throttle valve 14. And flows into the cylinder via the intake port 11 when the intake valve 7a is opened.

The exhaust port 17 of the cylinder head 2
The exhaust gas is ignited by the ignition plug 19, and the exhaust gas after combustion is guided from the exhaust port 17 to the exhaust passage 18 with the rise of the piston 16 when the exhaust valve 7b is opened. It is discharged outside through a silencer (not shown). An ECU (engine) including an input / output device (not shown), a storage device (ROM, RAM, BURAM, etc.) for storing a control program, a control map, and the like, a central processing unit (CPU), a timer counter, etc. Control unit) 31 is installed, and the engine 1
Performs comprehensive control of Various sensors such as a rotation speed sensor 32 for detecting the engine rotation speed Ne, a throttle sensor 33 for detecting the opening degree TPS of the throttle valve 14, and a water temperature sensor 34 for detecting the cooling water temperature Tw are connected to the input side of the ECU 31. I have. The output side of the ECU 31 is connected to the OCV 9, the fuel injection valve 15, the spark plug 19, and the like.

The ECU 31 determines an ignition timing, a fuel injection amount, and the like based on detection information from each sensor, and controls driving of the ignition plug 19 and the fuel injection valve 15. Further, the target phase angle of the timing variable mechanism 8 is calculated from the engine speed Ne and the throttle opening TPS according to a preset map, and the OCV 9 is driven to control the actual phase angle to the target phase angle. Further, at the time of the cold start of the engine 1, in order to suppress the discharge of unburned HC, a dedicated phase angle control different from that at the time of the warm start is executed.

Next, the phase angle control executed by the ECU 31 during a cold start will be described with reference to the time charts of FIGS. In order to reduce unburned HC by leaning during idle operation immediately after the cold start of the engine and sufficiently burning the injected fuel into the cylinder, there is a lean limit air-fuel ratio (A / F). The air-fuel ratio is considered to be maximum when the cam phase is at a certain value. FIG.
In the SOHC engine 1 having the variable timing mechanism 8 shown in FIG. 1, the valve overlap (VOL) between the intake valve 7a and the exhaust valve 7b is set to a predetermined angle (for example, 16).
°) and the cam phase and lean air-fuel ratio (A /
F) shows an example of a relationship between the lean limit air-fuel ratio and approximately 1;
It is about 6. Therefore, if it is possible to make the engine lean, the amount of unburned HC discharged is reduced by that amount. That is, the lean limit at the time of starting increases, and the unburned HC can be reduced because the lean limit is increased accordingly.

However, in the SOHC engine, the overlap range between the intake cam and the exhaust cam does not change.
Since the exhaust gas enters the front side (exhaust stroke range) of C, the exhaust gas pushed out from the cylinder by the piston enters the intake side as it is, is re-inhaled, and the internal EGR increases. Further, when the retard is retarded, the overlap enters the rear side of the compression top dead center TDC (intake stroke range), so that the exhaust valve is opened despite the piston being lowered, so that the exhaust gas is re-inhaled. , The internal EGR increases. For this reason, if the cam phase is shifted too much on either the advance side or the retard side, the internal EGR increases and combustion deteriorates. Therefore, it is necessary to set the intake cam phase to an optimum cam phase position.

Therefore, in FIG. 2, the cam phase when the lean limit air-fuel ratio (A / F) reaches the maximum value is defined as a neutral position (cam phase 0 °). (TDC) is preferably controlled to be in an intermediate phase of the valve overlap during the valve overlap period. By setting the compression top dead center TDC to the intermediate phase of the valve overlap, the internal EGR
Can be suppressed.

When the engine 1 is stopped, the intake valve 7
The cam phase a is held at the most retarded position shown in FIG. 4 by the timing variable mechanism 8 so that the intake valve 7a starts opening after the intake top dead center TDC (referred to as “intake stroke range”). Has become. When the ignition switch is operated to start, the cranking of the engine 1 is started at the cam phase position, the ignition timing control and the fuel injection control are executed by the ECU 31, and the engine 1 is cranked to reach the first explosion ( (Fig. 3).

At the time of this start, since the evaporation of the fuel injected into the intake port 11 is not promoted, the fuel adheres to the back side of the intake valve 7a or the inner wall of the intake port 11, and own weight during the valve closing period. As a result, liquid is accumulated near the lower valve seat. When the intake valve 7a is opened in the intake stroke range, the fuel is kept in a liquid state and the piston 1
6, the gas flows into the cylinder with the downward movement, burns in the fuel stroke through the compression stroke, and is discharged to the exhaust side in the exhaust stroke. That is, a situation in which the liquid fuel flowing into the cylinder is directly discharged to the exhaust side is prevented.

When it is determined by the ECU 31 that the engine is to be started cold based on the coolant temperature Tw or the like, as shown in FIG. That is, the opening / closing timing of the intake valve 7a is controlled to be advanced, and the position shown in FIG. 4, that is, the top dead center TDC is shifted to the intermediate position of the overlap between the intake valve 7a and the exhaust valve 7b. By controlling the cam phase angle to the advanced side, the intake valve 7a starts opening before the top dead center TDC. Incidentally, in the time chart of the intake cam phase in FIG.
It corresponds to.

Since the opening of the intake valve 7a precedes the top dead center TDC, a valve overlap period also exists before the top dead center TDC (hereinafter referred to as "exhaust stroke range"). Even if the fuel passes through to the exhaust side, it is drawn back into the cylinder in the subsequent intake stroke range, and is reliably vaporized and burned. By setting the compression top dead center TDC to the intermediate phase of the valve overlap, the internal EGR
(Exhaust gas that once flows to the exhaust side and then flows back into the cylinder)
Can be suppressed, and stable combustion can be obtained even when lean or retard is performed (FIG. 3), so that emission of unburned HC immediately after starting is reduced.

At this time, the exhaust valve 7b closes after the top dead center TDC, and at this point after a few strokes from the initial explosion, the exhaust valve 7b moves to the intake port 11 side as the engine speed Ne increases. Since a sufficient negative pressure is generated, exhaust gas once discharged to the exhaust side (exhaust gas containing a large amount of unburned HC discharged at the end of the exhaust stroke) is supplied to the intake port 1.
Backflow into 1. The exhaust gas that has flowed back is burned in the next combustion stroke, and the exhaust port 1
Since the temperature of 1 is raised to promote the evaporation of the next injected fuel, the discharge of the liquid fuel to the exhaust side is prevented.

Thereafter, when the ECU 31 determines that the engine 1 has shifted to the warm-up operation based on the cooling water temperature Tw or the like, the opening / closing timing of the intake valve 7a is retarded,
It is returned to the state at the start of the start shown in FIG. 4, that is, the most retarded angle. In this manner, the cam phase is set to the neutral position control when the engine is started cold and lean or retarded during idling operation.

When the ECU 31 determines that the engine is warm starting based on the cooling water temperature Tw or the like, the cam phase is set to the most retarded position, so that the internal EGR slightly increases. Improved combustion provides stable combustion. Further, since the closing of the intake valve 7a is delayed, the pump loss is reduced, and the opening of the exhaust valve 7b is delayed, so that the expansion stroke is lengthened and fuel efficiency is improved.

The opening / closing timing of the intake valve 7a is maintained at the most retarded position as long as the idle operation is continued even after the start is completed.
When e and the throttle opening TPS increase, the advance is controlled accordingly. Further, performance and fuel efficiency can be improved in the entire operation range of the engine 1 by changing the cam phase.

Although the embodiment has been described above, aspects of the present invention are not limited to the above embodiment. For example, in the above embodiment, the vane-type variable timing mechanism 8 is provided. However, the configuration of the variable-timing mechanism is not limited to this. For example, the variable-timing mechanism may be replaced with a helical-type variable mechanism. Eccentric timing variable mechanism that changes the amount of eccentricity, switching type variable timing mechanism that selectively operates cams with different characteristics, electromagnetic timing variable mechanism that opens and closes valves directly with an electromagnetic actuator, etc. It may be replaced.

In the above embodiment, the intake pipe injection type S
Although applied to the OHC engine, the invention can also be applied to, for example, an in-cylinder injection type SOHC engine that injects fuel directly into a cylinder. In this case as well, the cam phase is set to the neutral position control during the idling operation by performing the cold start similarly to the above-described embodiment,
Stable combustion can be obtained even when lean or retard is performed, and the emission of unburned HC immediately after starting can be suppressed.

Further, since the vane type variable timing mechanism 8 locks at the intermediate phase, it may be operated at the intermediate phase from the start of cooling to perform lean or retard.

[0029]

As described above, according to the engine control apparatus of the present invention, in the SOHC engine equipped with the cam phase changing mechanism, the combustion control and the combustion for reducing the unburned HC in the exhaust during the cold start are performed. In order to balance with stability,
When performing control to reduce unburned HC in exhaust during cold start, stable combustion can be obtained even when lean or retard is performed by setting the cam phase to the neutral position and reducing the internal EGR. Thus, the emission of unburned HC immediately after the start can be reduced.

The internal EGR can be reduced by setting the neutral position of the cam phase to a valve overlap period in which the compression top dead center overlaps the intake stroke range and the exhaust stroke range.

[Brief description of the drawings]

FIG. 1 shows an SOH having a variable cam phase mechanism according to the present invention.
1 is an overall configuration diagram illustrating an embodiment of a control device for a C engine.

FIG. 2 is a characteristic diagram showing an example of a relationship between a cam phase and a lean limit air-fuel ratio (A / F) when a valve overlap between an intake valve and an exhaust valve is set to a predetermined angle in the engine shown in FIG. .

FIG. 3 is a time chart showing an example of a rotational speed characteristic and an intake cam phase control after the engine shown in FIG. 1 is started.

FIG. 4 is a time chart showing cam phase angle control by the variable timing mechanism of the engine shown in FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 SOHC engine 3 Camshaft 3a Intake cam 3b Exhaust cam 7a Intake valve 7b Exhaust valve 8 Variable timing mechanism (cam phase changing mechanism) 31 ECU (valve timing control means)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G018 AB05 AB18 BA33 CA20 EA02 EA11 EA17 EA21 EA31 FA07 FA26 GA07 GA08 GA09 3G092 AA01 AA05 AA11 AB02 DA01 DA02 DA09 DA10 DA12 DG05 EA01 EA16 EC09 FA18 GA01 GA02 GA04 HA06Z 3G301 HA19 JA02 JA26 KA01 KA05 KA07 LA07 LC01 NE01 NE12 NE22 PA11Z PE01Z PE08Z PF16Z

Claims (2)

[Claims] In a control device for an SOHC internal combustion engine equipped with a cam phase changing mechanism, when performing combustion control to reduce unburned hydrocarbons in exhaust gas during cold start, the cam phase changing mechanism is moved to a neutral position. A control device for an internal combustion engine, comprising: control means for controlling the internal combustion engine. 2. The control device for an internal combustion engine according to claim 1, wherein the neutral position is set such that the compression top dead center is during a valve overlap period.