JP2002235592A - Cylinder injection internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylinder injection internal combustion engine allowing catalysts to be heated efficiently. SOLUTION: When a rise in temperature of catalysts 18A to 18C is requested, a fuel injection means 9 is driven to inject fuel directly into a combustion chamber 3 during compression stroke so that an air/fuel ratio becomes near a stoichiometric air/fuel ratio or an air/fuel ratio slightly leaner than the stoichiometric air/fuel ratio, a valve timing adjusting means 10 is driven to set the closing timing of an exhaust valve 7 to before an exhaust top dead center, and an ignition timing by an ignition means 8 is delayed more than that in normal operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for raising the temperature of a catalyst in a direct injection type internal combustion engine, in particular, a direct injection type internal combustion engine capable of adjusting the opening / closing timing of an exhaust valve and / or an intake valve.

[0002]

2. Description of the Related Art A catalyst provided in an internal combustion engine of a vehicle has an effect of purifying harmful components (HC, CO, NOx, etc.) in exhaust gas. However, in order to obtain this exhaust gas purifying effect, it is necessary that the catalyst has reached a predetermined activation temperature, and a sufficient effect cannot be obtained when the catalyst temperature is low, such as at the time of a cold start. This point is the same in a cylinder injection type internal combustion engine that has been put into practical use in recent years.However, in a cylinder injection type internal combustion engine, various catalyst temperature increasing technologies that take advantage of the characteristic that the fuel injection timing can be arbitrarily controlled are used. Proposed.

For example, Japanese Patent Application Laid-Open No. 2000-240485 discloses that when the temperature of a catalyst is required, stratified combustion is performed by injecting fuel during a compression stroke so that the air-fuel ratio becomes close to the stoichiometric air-fuel ratio. Techniques are disclosed. This technology locally generates a region where the air-fuel ratio is rich and a region where the air-fuel ratio is lean by stratified combustion, generates a large amount of CO and H ₂ by incomplete combustion in the rich air-fuel ratio region, and generates a large amount of CO and H2 in the lean air-fuel ratio region. it is the excess O ₂ which was to generate.
That is, according to this technique, a large amount of CO, H ₂ and O ₂ can be simultaneously supplied to the catalyst, and CO, H ₂ on the catalyst can be supplied.
_The temperature of the catalyst can be efficiently increased by the heat of reaction caused by the oxidation reaction between ₂ and O ₂ .

[0004] In the cylinder injection type internal combustion engine, there is also known a technique in which the temperature of a catalyst is raised by injecting additional fuel during an expansion stroke after injection of main fuel. The additional fuel injected during the expansion stroke does not contribute to the output of the internal combustion engine, and much of its energy becomes heat, raising the exhaust temperature. To increase the temperature of the catalyst efficiently.

[0005]

In each of the above prior arts, the combustion state of the internal combustion engine is controlled by the fuel injection timing, taking advantage of the characteristic of the direct injection type internal combustion engine that the fuel injection timing can be arbitrarily controlled. To raise the temperature of the catalyst. However, parameters for controlling the combustion state of the internal combustion engine include, in addition to the above-described fuel injection timing, ignition timing, opening and closing timing of exhaust valves and intake valves, and the like. Therefore, if the combustion state of the internal combustion engine is controlled using not only the fuel injection timing but also control parameters other than the fuel injection timing, it is considered that more efficient control of the catalyst temperature rise is possible.

The present invention has been made in view of the above problems, and has as its object to provide an in-cylinder injection type internal combustion engine capable of efficiently raising the temperature of a catalyst.

[0007]

In order to achieve the above object, a direct injection internal combustion engine of the present invention is provided with a control means for controlling the temperature of a catalyst provided in an exhaust passage for purifying exhaust gas. , The following temperature raising control is executed. That is, when the temperature of the catalyst is required to be raised, the fuel is injected into the combustion chamber during the compression stroke by driving the fuel injection means so that the air-fuel ratio becomes close to or slightly leaner than the stoichiometric air-fuel ratio. In addition to direct injection, the valve timing adjusting means is driven to set the closing timing of the exhaust valve before the top dead center of the exhaust gas, and the ignition timing by the ignition means is retarded from that in the normal operation.

Normally, when the ignition timing is retarded, an increase in the exhaust gas temperature due to afterburning combustion can be expected. However, when the ignition timing is late, combustion becomes unstable and drivability such as torque fluctuation may be deteriorated. There is. However, in the direct injection internal combustion engine of the present invention, stratified combustion with a high combustion speed is realized by injecting fuel during the compression stroke, thereby improving combustion stability. Further, by setting the closing timing of the exhaust valve before the exhaust top dead center, the overlap (valve overlap) between the opening periods of the intake valve and the exhaust valve is reduced, so that the internal EG of the internal combustion engine is reduced.
R is reduced, which also enhances combustion stability.
Therefore, even when the ignition timing is retarded as described above, the exhaust gas temperature is reliably increased by securing stable after-burning combustion, and CO, H ₂ and excess O ₂ generated by the compression stroke injection on the catalyst. The temperature of the catalyst can be efficiently raised in combination with the above reaction.

Further, unburned fuel (unburned HC) generated in a quenching zone (extinguishable region) in a cylinder wall, a piston wall, or a piston top land portion in an internal combustion engine is:
Normally, the exhaust passage (exhaust port) is raised by raising the piston.
However, by setting the closing timing of the exhaust valve before the exhaust top dead center as described above, the unburned HC is trapped in the combustion chamber without being pushed out into the exhaust passage. Therefore, the unburned HC is reburned in the combustion chamber, and even when the temperature of the catalyst is not sufficiently raised immediately after the start of the control, the unburned HC is discharged to the outside.
C emission can be suppressed.

[0010] When the temperature of the catalyst is required to be raised, the temperature of the catalyst is not activated when the idling or lean operation is continued for a certain period of time in addition to the cold start of the internal combustion engine. For example, when the temperature is lowered to a temperature lower than or is likely to be lowered. The determination of the presence / absence of the temperature increase request is made, for example, by directly detecting the catalyst temperature or estimating the catalyst temperature from the exhaust gas temperature that can be detected by the high-temperature sensor. It may be determined that there is a temperature raising request. When the cooling water temperature (or oil temperature) of the internal combustion engine drops to a predetermined temperature, it may be determined that there is a temperature increase request. The type of the catalyst is not limited, and a storage NOx catalyst, a selective reduction NOx catalyst, or the like can be applied in addition to the three-way catalyst. Further, there is no limitation on the position of the catalyst, and the catalyst may be an underfloor catalyst or a proximity catalyst.

When the air-fuel ratio (A / F) at the time of the temperature rise control is too rich, the degree of incomplete combustion is too high, so that a large amount of unburned fuel is generated. This may cause smoldering and cause smoke. On the other hand, if it is too lean, the amount of generated CO will be insufficient, and the fuel efficiency will deteriorate and the drivability will decrease. Therefore, the air-fuel ratio (A / F) at the time of the temperature rise control is preferably set in the range of 14 to 18, and more preferably, in the range of 14.5 to 16. Similarly, the air-fuel ratio of the rich region locally generated around the ignition means is preferably in the range of 8 to 10. Further, control of the air-fuel ratio may be an open-loop control but, more preferably, O ₂ sensor installed upstream of the catalyst to perform the feedback control of the air-fuel ratio at the time of activation.

In the compression stroke injection in the temperature raising control, preferably, the injection timing is within the compression stroke range more than the injection timing in the compression stroke injection during the normal operation when compared at the same load and the same rotation speed. Is advanced. By advancing the injection timing in this way, fuel can be injected when the combustion chamber space is relatively large, and the diffusion of fuel can be promoted to further improve combustion stability. Further, the generation of smoke can be suppressed by sufficiently securing the atomization time of the injected fuel.

The ignition timing after the lapse of the predetermined time may be at least retarded from that in the normal operation, and is preferably set after the top dead center. Specifically, it is preferable to set the range from top dead center to 30 degrees after top dead center,
More preferably, it is set in the range of 5 to 20 degrees after the top dead center. By setting the ignition timing within such a range, the exhaust gas temperature can be increased without deteriorating fuel efficiency or drivability.

In the above-described in-cylinder injection type internal combustion engine, more preferably, at a predetermined time after the start of the temperature raising control, the closing timing of the exhaust valve is changed from before exhaust top dead center to the closing timing of the normal control ( The control means is configured to maintain the setting of the temperature increase control for the air-fuel ratio, the fuel injection timing, and the ignition timing. When the closing timing of the exhaust valve is changed before the exhaust top dead center as described above, unburned HC can be trapped in the combustion chamber, but the output of the internal combustion engine decreases. Further, as the catalyst temperature rises, the ability of the catalyst to purify unburned HC gradually increases. Thus, at a predetermined time when it can be determined that the catalyst has been activated to some extent, the closing timing of the exhaust valve is changed from before exhaust top dead center to the closing timing during normal control to prevent a decrease in the output of the internal combustion engine. In addition to this, unburned HC is supplied to the catalyst together with CO and excess O ₂ to promote the oxidation reaction on the catalyst, so that the temperature of the catalyst can be raised more efficiently.

It is preferable that the predetermined period during which the setting of the closing timing of the exhaust valve is switched is a period until the catalyst temperature reaches the predetermined temperature. The catalyst temperature may be detected directly from the catalyst, or may be estimated from the exhaust gas temperature detected by the high temperature sensor. Furthermore, the water temperature (or oil temperature) of the internal combustion engine
May be used to estimate the catalyst temperature. In addition, the relationship between the time elapsed from the start of the temperature increase control and the catalyst temperature is determined in advance by an experiment or the like, and the time elapsed from the start of the temperature increase control is measured by a timer. , The setting of the valve overlap or the ignition timing may be switched.

The valve timing adjusting mechanism of the valve timing adjusting means may be a switching type, a phase switching type, an eccentric type, an electromagnetic valve type, or the like, which can be changed to at least two valve timings. Preferably, the mechanism is such that the valve timing can be continuously changed, such as a vane type variable timing mechanism. In this case, the closing timing of the exhaust valve is set before the exhaust top dead center in accordance with the degree of increase in the catalyst temperature (or the exhaust temperature, the water temperature, the oil temperature, or the like) or in accordance with the elapsed time from the start of the temperature increase control. It is preferable to gradually retard the closing timing during the normal control.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. First, an outline of a direct injection internal combustion engine according to an embodiment of the present invention will be described.
The in-cylinder injection type internal combustion engine is a four-stroke engine provided with intake, compression, expansion and exhaust strokes in one operation cycle, and is of a spark ignition type and capable of directly injecting fuel into a combustion chamber. Have been. More specifically, the direct injection internal combustion engine is configured as shown in the schematic configuration diagram of FIG.

As shown in FIG. 1, a cylinder head 2 of an in-cylinder injection type internal combustion engine (hereinafter referred to as an engine) 1 has
The intake passage 4 and the exhaust passage 5 are connected so that they can communicate with the combustion chamber 3. The communication between the intake passage 4 and the combustion chamber 3 is controlled by an intake valve 6, and the communication between the exhaust passage 5 and the combustion chamber 3 is controlled by an exhaust valve 7. Among them, the exhaust valve 7 is provided with a valve timing adjusting device 10 for variably adjusting the opening / closing timing of the exhaust valve 7. The mechanism of the valve timing adjusting device (valve timing adjusting means) 10 is publicly known, and therefore detailed description is omitted here. For example, the vane rotor is rotated in a housing of a timing pulley connected to a crankshaft via a timing belt. The vane rotor is connected to an exhaust camshaft. By controlling the hydraulic pressure applied to the vane rotor, the phase of the exhaust camshaft with respect to the timing pulley is adjusted, and the opening / closing timing of the exhaust valve 7 can be continuously adjusted.

The cylinder head 2 is provided with a fuel injection valve (fuel injection means) 9 for each cylinder. The fuel injection valve 9 is configured to directly inject fuel into the combustion chamber 3.
The opening is arranged so as to face the combustion chamber 3.
This fuel injection valve 9 is supplied with fuel pressurized by a low-pressure fuel pump and a high-pressure fuel pump (not shown). Further, an ignition plug (ignition means) 8 is provided at the center of the top of the combustion chamber 3 of each cylinder of the cylinder head 2.

The intake passage 4 is provided with an intake manifold 11 for introducing intake air into the combustion chamber 3 of each cylinder. In the cylinder head 2, an intake port is provided relatively upright with respect to the combustion chamber 3 for each cylinder, and the intake manifold 11 is connected to the cylinder head 2 so as to communicate with each intake port. Intake manifold 1
A throttle valve 12 for adjusting the amount of intake air is provided upstream of 1.

On the other hand, in the exhaust passage 5, the combustion chamber 3 of each cylinder is provided.
An exhaust manifold 17 that collects exhaust gas discharged from the exhaust gas into one is provided. The cylinder head 2 is provided with an exhaust port in a relatively horizontal direction for each cylinder.
The exhaust manifold 17 is connected to the cylinder head 2 so as to communicate with each exhaust port. As the exhaust manifold 17, a dual type exhaust manifold is employed to prevent interference of exhaust gas discharged from the combustion chamber 3 of each cylinder and improve engine output. A catalyst device 18 and a muffler (muffler) (not shown) are provided below the vehicle floor on the downstream side of the exhaust manifold 17. The catalyst device 18 is provided with a harmful component (C
This is a device for purifying O, unburned HC, and NOx, and has a structure in which three-way catalysts 18B and 18C are arranged upstream and downstream of a storage NOx catalyst 18A.

Further, an electronic control unit (ECU) 30 as control means for controlling the engine 1 is provided in the vehicle interior. The ECU 30 includes an input / output device, a ROM,
It comprises a RAM, a CPU, a timer counter and the like, and performs comprehensive control of the engine 1 based on detection information from various sensors connected to the input side. ECU3
As the sensor connected to the input side of
Is provided with a throttle position sensor (TPS) 20 for detecting an opening degree θth of the throttle valve 12 at a portion where the throttle valve 12 is provided. In the exhaust passage 5, an O ₂ sensor 21 and a high-temperature sensor 22 are provided at an upstream portion of the catalyst device 18. The O ₂ sensor 21 is a sensor for detecting the oxygen concentration in the exhaust gas, and has a characteristic that its output greatly changes at a stoichiometric air-fuel ratio. High temperature sensor 2
Reference numeral 2 denotes a sensor for detecting the temperature of the exhaust gas. further,
As another sensor, the water temperature WT of the cooling water of the engine 1
, A crank angle sensor 24 that outputs a signal in synchronization with the rotation of the crankshaft, an accelerator opening sensor, an air flow sensor, and the like (not shown). The signal from the crank angle sensor 24 is used for calculating the engine speed Ne.

On the other hand, on the output side of the ECU 30, a spark plug 8, a fuel injection valve 9, and a valve timing adjusting device 10
Etc. are connected. The ECU 30 controls the ignition timing of the ignition plug 8, the fuel injection timing and fuel injection amount from the fuel injection valve 9, the exhaust valve 7 by the valve timing adjustment device 10, based on the detection information from the various sensors 20 to 24. The opening / closing timing of is controlled.

The fuel injection mode (fuel injection mode) of the engine 1 according to the present embodiment includes an intake stroke injection mode in which fuel is injected during an intake stroke to perform premix combustion, and a fuel injection mode during a compression stroke. And a compression stroke injection mode in which stratified combustion is performed by injecting fuel into two different fuel injection timings. More specifically, as the intake stroke injection mode, intake O ₂ -F that performs feedback control using the signal from the O ₂ sensor 21 so that the air-fuel ratio becomes stoichiometric.
/ B mode, intake lean mode in which open-loop control is performed so as to have a leaner air-fuel ratio (lean air-fuel ratio) than in stoichio, and intake air in which open-loop control is performed so as to have an air-fuel ratio richer than stoichio (rich air-fuel ratio) An O / L mode is provided. On the other hand, the compression stroke injection mode includes a compression lean mode in which open-loop control is performed so as to provide a leaner air-fuel ratio than the intake lean mode, and a slightly lean air-fuel ratio (A / A) that is slightly leaner than stoichiometric.
A compression bright lean mode (compression S / L mode) for performing open loop control so that F = 15 to 16) is provided.

Of the above injection modes, each of the intake stroke injection mode and the compression lean mode is used for normal fuel injection control, and the ECU 30 operates the engine 1 determined by the accelerator opening and the engine speed Ne. An appropriate fuel injection mode is selected according to the state. On the other hand, the compression S / L mode is used for fuel injection control at the time of temperature increase control described later. The temperature increase control is a control method of the engine 1 selected when the temperature increase of the catalyst device 18 is required, that is, in a situation where the temperatures of the catalysts 18A to 18C are decreasing. In 1, E
The CU 30 is realized by comprehensively controlling the ignition timing of the spark plug 8 and the opening / closing timing of the exhaust valve 7 by the valve timing adjusting device 10 in addition to the fuel injection mode described above.

Hereinafter, the temperature raising control according to one embodiment of the present invention will be described with reference to the flowchart of FIG. 2 and the time chart of FIG. When the temperature of the catalyst device 18 is required to be raised, in addition to the cold start of the engine 1, idling and lean operation (particularly, compression lean operation in which the degree of leaning is large) continue for a relatively long time. The activated catalyst device 18 (catalysts 18A-18)
When the temperature of (C) falls below the activation temperature or when it is likely to fall, the present embodiment will be described with reference to the temperature rise control when the engine 1 is started cold.

First, in step S10, the ECU 30
When a start switch (for example, an ignition key) is operated and turned on, that is, when it is determined that the engine 1 has started, the timer T used in this control routine is reset to 0 and the count is counted. Start (ie, timer on, see FIG. 3 (d)). Then, in step S20, the engine rotation speed Ne becomes the predetermined value Ne0.
It is determined that (Ne0> idling rotational speed) has been reached, and when the start determination is completed, the process proceeds to the next step S30. As shown in FIG. 3A, after the engine 1 is started, the intake O / L mode is set as the fuel injection mode until the engine speed Ne reaches the predetermined value Ne0 in order to supply sufficient fuel for the start. Selected.

In step S30, the ECU 30 determines whether the temperature raising control can be executed. In particular,
Water temperature (cooling water temperature) WT, engine rotation speed Ne, target average effective pressure Pe (estimated from accelerator opening and engine rotation speed Ne), and vehicle speed V correspond to predetermined values WT1, Ne, respectively.
1, Pe1 and V1 are determined (see FIG. 3E).
To FIG. 3 (h)]. Under the condition that any one of the engine rotation speed Ne, the target average effective pressure Pe, and the vehicle speed V is high, the operating state of the engine 1 is out of the compression stroke injection region and can be regarded as a normal running state in which the exhaust gas temperature is high. The temperature of the catalyst device 18 can be increased without using the temperature increase control. Conversely, if the temperature increase control is performed, the exhaust purification catalyst device 18 may be excessively heated. The cooling water temperature WT detected by the water temperature sensor 23 is a predetermined value, that is, the engine 1
Is determined to be equal to or lower than the warm-up temperature WT1 at which the exhaust purifying catalyst device 18 can be regarded as warm-up.

Therefore, when any one of the water temperature WT, the engine speed Ne, the target average effective pressure Pe, and the vehicle speed V is larger than the corresponding predetermined value WT1, Ne1, Pe1, V1 (No)
(Route), the ECU 30 executes the normal control in step S40 without executing the temperature increase control. That is, the fuel injection mode, the ignition timing, and the opening / closing timing of the exhaust valve 7 according to the operating state of the engine 1 are selected. On the other hand, when the water temperature WT, the engine speed Ne, the target average effective pressure Pe, and the vehicle speed V are all less than or equal to the corresponding predetermined values WT1, Ne1, Pe1, V1 (Yes route), the process proceeds to the next step S50. First of step S50
A stage temperature increase control (first temperature increase control) is executed.

The temperature increase control is realized by comprehensive control of the fuel injection mode, the ignition timing, and the opening / closing timing of the exhaust valve 7 as described above. Specifically, step S5
In the first temperature increase control of 0, the ECU 30 selects the compression S / L mode as the fuel injection mode, sets the ignition timing after the compression top dead center, and sets the opening and closing timing of the exhaust valve 7 as shown in FIG. The closing timing of the valve 7 is set before the top dead center of the exhaust gas (see FIGS. 3A to 3C).

When the catalyst temperature is low and the purifying ability of the catalyst device 18 is low as in the case of a cold start, it is more effective to reduce the unburned HC by making the air-fuel ratio as lean as possible within a range in which combustion does not deteriorate. At this time, the compression stroke injection burns faster because of stratified combustion than the intake stroke injection, and has excellent combustion stability and good drivability. In addition, when the compression stroke injection is performed by controlling the air-fuel ratio to a stoichiometric vicinity or a slightly lean air-fuel ratio slightly leaner than the stoichiometric ratio, the rich region where the fuel concentration is extremely high and the lean region where the fuel concentration is low are locally controlled. A region is formed in the combustion chamber 3. In the rich region, incomplete combustion occurs due to the local lack of oxygen, and a relatively large amount of CO, H
₂ is generated, O ₂ is not contributing to the combustion will be present many as excess O ₂ in the lean region.

Therefore, by selecting the compression S / L mode as the fuel injection mode as described above, the highly reactive CO, H ₂ and excess O ₂ are simultaneously supplied to the catalyst device 18 via the exhaust passage 5. The temperature of the catalyst device 18 is increased by the heat of reaction between CO, H ₂ and O ₂ by the oxidation reaction in the exhaust passage 5 and the catalyst device 18. If the air-fuel ratio is too rich, the degree of incomplete combustion is too high, and a large amount of unburned HC is generated.
This may cause smoldering of the spark plug 8 and generate smoke. Conversely, if the air-fuel ratio is too lean, C
In addition to the shortage of O and H ₂ generation, this leads to deterioration of fuel efficiency and drivability. Therefore, the air-fuel ratio in the temperature raising control is preferably set in the range of 14 to 18, and more preferably in the range of 14.5 to 16. The air-fuel ratio of the rich region locally generated around the ignition plug 8 is preferably in the range of 8 to 10.

The ECU 30 selects the compression S / L mode as the fuel injection mode and, at the same time, retards the ignition timing until after the compression top dead center. By retarding the ignition timing in this manner, sufficient afterburning in the expansion stroke is possible, and the temperature of the catalyst device 18 is more quickly increased by the increase in the exhaust gas temperature due to the afterburning. In particular, CO, with only the heat of reaction of H ₂ and O _2, the catalyst 18A~
When the catalyst 18C is not activated at all or its activation degree is low, it takes time until the catalysts 18A to 18C are activated. However, as described above, the ignition timing is retarded to increase the exhaust gas temperature. Yes, catalysts 18A-18C
(Especially 18B) can be activated by heating it sufficiently. As a result, CO supplied by the fuel injection in the compression S / L mode, the H ₂ and O ₂ can be effectively reacted on the catalyst 18A to 18C (particularly 18B), the catalyst 18A to 18C by the heat of reaction (Especially 18B) will be activated even earlier.

In the case where the ignition timing is greatly retarded as described above, the combustion is normally unstable and the drivability such as torque fluctuation is deteriorated. In addition to retarding the ignition timing, compression stroke injection with high combustion stability is performed. Further, as described above, the closing timing of the exhaust valve 7 is set before the top dead center of the exhaust to reduce the overlap of the valve opening period between the exhaust valve 7 and the intake valve 6 from that in the normal operation. The combustion stability is also improved by reducing the internal EGR of the engine 1. Therefore, even when the ignition timing is greatly retarded, drivability does not deteriorate due to a decrease in combustion stability. In addition, the improvement of the combustion stability by reducing the overlap of the valve opening period compensates for the deterioration of the combustion stability due to the leaning, so that the leaning can be achieved more easily.

Further, when setting the opening / closing timing of the normal exhaust valve 7, a piston (not shown) as shown in FIG.
The exhaust valve 7 closes after reaching the top dead center, so that unburned HC generated in the quenching zone of the cylinder wall, the piston wall, or the piston top land portion, causes the exhaust passage (exhaust port) 5 to rise due to the rise of the piston. Will be pushed out. Immediately after the start of the engine 1, the degree of activation of the catalyst device 18 is low, so that the unburned HC discharged into the exhaust passage 5 is discharged to the outside without being purified by the catalyst device 18. However, in this embodiment, since the closing timing of the exhaust valve 7 is set before the exhaust top dead center as described above, the unburned H
C is confined in the combustion chamber 3 without being pushed out into the exhaust passage 5 and recombusted in the combustion chamber 3.

That is, according to the first temperature raising control in step S50, the fuel is injected during the compression stroke so that the air-fuel ratio becomes close to stoichiometric or a slightly lean air-fuel ratio, the ignition timing is retarded, The synergistic effect of setting the closing timing of the exhaust valve 7 before the top dead center of the exhaust gas has an effect that the temperature of the catalyst device 18 can be efficiently raised while suppressing the emission of unburned HC to the outside. Can be

Next, in step S60, the ECU 30 determines whether or not the timer has counted a predetermined timer time T1. The predetermined timer time T1 is a time that is preliminarily determined by an experiment or the like, for example, after the cold start, it is estimated that the catalyst temperature has risen to the extent that the unburned HC is purified to some extent by executing the first temperature raising control in step S50. Is set to If the timer has not reached the predetermined timer time T1 (No route), the ECU 30 proceeds to step S
After the processing of 30, the first temperature raising control of step S50 is continued, and when the timer has counted the predetermined timer time T1 (Yes route), the processing of the next step S70 is performed.

In step S70, the ECU 30 executes the second
It is determined whether or not the step-wise temperature increase control (second temperature increase control) may be executed. Specifically, similarly to step S30,
Water temperature WT, engine speed Ne, target average effective pressure Pe,
The vehicle speeds V correspond to respective predetermined values WT1, Ne1, and Pe.
1, V1 or less is determined [FIG. 3 (e) to FIG.
(See (h)). The water temperature WT and the engine speed N
If any of e, the target average effective pressure Pe, and the vehicle speed V is larger than the corresponding predetermined value WT1, Ne1, Pe1, V1 (No route), the ECU 30 does not execute the second temperature increase control. In step S80, normal control is executed. On the other hand, a predetermined value WT1, which corresponds to any of the water temperature WT, the engine speed Ne, the target average effective pressure Pe, and the vehicle speed V,
If Ne1, Pe1, V1 or less (Yes route), the process proceeds to the next step S90, and the second temperature raising control is executed. Here, the predetermined value W used in the start determination of the first temperature raising control is used.
Although T1, Ne1, Pe1, and V1 are also used in the start determination of the second temperature raising control, the predetermined values WT2, Ne different from the first temperature raising control are used.
2, Pe2 and V2 may be used.

In the second temperature raising control in step S90, EC
U30 selects the compression S / L mode as the fuel injection mode and delays the closing timing of the exhaust valve 7 to the closing timing during normal operation as shown in FIG. 4 while the ignition timing is delayed [FIG. (A) to FIG. 3 (c)]. By changing the closing timing of the exhaust valve 7 from before the exhaust top dead center to the closing timing of the normal control, a decrease in the engine output is prevented, and CO and excess O generated by the compression stroke injection are prevented.
_The unburned HC is also supplied to the catalyst device 18 together with ₂ etc., and the oxidation reaction on the catalyst device 18 is promoted.
8 will be activated even earlier.

That is, according to the second temperature raising control in step S90, the fuel is injected during the compression stroke so that the air-fuel ratio becomes close to stoichiometric or a slightly lean air-fuel ratio, the ignition timing is retarded, The synergistic effect of changing the closing timing of the exhaust valve 7 to the closing timing during normal operation provides an effect that the temperature of the catalyst device 18 can be more efficiently raised. In particular, the catalyst device 18 disposed under the floor according to the present embodiment is far from the main body of the engine 1, so that the exhaust gas temperature tends to decrease before the exhaust gas reaches the catalyst device 18, and the dual-type exhaust manifold 17 has less exhaust interference. Since the reaction in the exhaust manifold 17 is small, the heat capacity is large, and at the same time, the surface area (radiation area) is large, so that the exhaust temperature is easily lowered. However, even with such a structure that is disadvantageous for maintaining the exhaust gas temperature, it is possible to quickly raise the catalyst device 18 to the activation temperature and quickly increase the purification efficiency of harmful substances (HC, CO and NOx). it can.

After the temperature increase control is executed to increase the temperature of the catalyst device 18 as described above, the ECU 30 then performs the process of step S100. In step S100, the ECU
30 determines whether or not the timer has counted a predetermined timer time T2, that is, whether or not the total continuation time of the first and second temperature raising controls has exceeded the predetermined timer time T2. The predetermined timer time T2 is set in advance by an experiment or the like, for example, to a time after it is estimated that the temperature of the catalyst device 18 has risen to a predetermined temperature close to the activation temperature by executing the temperature raising control after the cold start. ing. Then, the timer is set to a predetermined timer time T2.
If it has not reached (No route), the ECU 30
After the processing in step S70, the second temperature raising control is continued in step S90 again. On the other hand, when the timer has counted the predetermined timer time T2 (Yes route), the process of the next step S110 is performed. That is, in step S110, the ECU 30 ends the temperature raising control (see FIGS. 3A to 3C), and sets the fuel injection mode, ignition timing, and exhaust valve 7 according to the operating state of the engine 1. Normal control is performed again by selecting the opening / closing timing.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the spirit of the present invention. . For example, in the above-described embodiment, the ignition timing is retarded until after the compression top dead center. However, if the ignition timing is retarded at least from the ignition timing at the time of the normal control, the catalyst device 18 is increased due to the increase in the exhaust gas temperature due to afterburning. The temperature can be raised, and the desired effect of the present invention can be achieved.

[0043] After the O ₂ sensor 21 in the Atsushi Nobori control of the reaches the activation state, the feedback so that the air-fuel ratio becomes the stoichiometric near or slight lean air-fuel ratio by using a signal from the O ₂ sensor 21 Control may be performed. By performing the compression stroke injection while performing the feedback control so that the air-fuel ratio becomes close to stoichiometric or a slightly lean air-fuel ratio, the compression S
As in the case where the / L mode is selected, a relatively large amount of CO, H ₂ and excess O ₂ can be generated by stratified combustion. Further, since the feedback control is performed, the air-fuel ratio can be set more accurately than in the open loop control in the compression S / L mode, and control accuracy can be improved. Further, in the compression stroke injection, a relatively large amount of H ₂ is generated by local incomplete combustion due to the stratified charge combustion in the exhaust gas, O ₂ sensor 21 than the H ₂ is O ₂
Because the diffusion speed of the coat layer covering the Pt electrode is high,
Since the O ₂ concentration is detected to be smaller than the actual value, the output of the O ₂ sensor 21 becomes slightly rich. Therefore, even when feedback control is performed using stoichiometric as the target air-fuel ratio, the actual air-fuel ratio is naturally controlled to a slightly leaner air-fuel ratio slightly leaner than stoichiometric.

In FIG. 1, the O ₂ sensor 21 is arranged on the upstream side of the catalyst device 18. However, the O ₂ sensor 21 may be arranged on the downstream side of the catalyst device 18, and furthermore, on both upper and downstream sides. May be. Further, a linear air-fuel ratio sensor can be used as the O ₂ sensor 21. In this case, feedback control can be performed using an arbitrary air-fuel ratio as a target air-fuel ratio.

The injection timing of the compression stroke injection (compression S / L mode) in the temperature raising control may be advanced from the injection timing of the compression stroke injection during the normal operation. By advancing the injection timing in this manner, fuel can be injected when the space of the combustion chamber 3 is relatively large, and there is an advantage that the diffusion of fuel can be promoted and the combustion stability can be further improved. . In addition, there is an advantage that generation of smoke can be suppressed by sufficiently securing the atomization time of the injected fuel.

When the throttle valve 12 is of an electronic control type, the throttle valve 12 may be opened in accordance with the ignition timing retard angle to increase the intake air amount. Since the output decreases when the ignition timing is retarded, there is an advantage that controlling the throttle valve 12 in this manner can compensate for the decrease in output due to the retardation of the ignition timing. Also,
Although the engine 1 of the above-described embodiment includes the dual-type exhaust manifold 17 with less exhaust interference in order to improve the output, the engine 1 has a small heat radiation area and heat capacity, which is advantageous for preventing the exhaust temperature from lowering, and low in cost. A single type exhaust manifold 17 may be provided. Further, a clamshell type exhaust manifold (reactive exhaust manifold) having a volume for positively causing exhaust interference may be provided. According to this type of exhaust manifold, the exhaust temperature can be further increased by the reaction of unburned components accompanying exhaust interference inside the exhaust manifold.

In the above-described embodiment, the timing of switching from the first temperature raising control to the second temperature raising control is measured using a timer.
The control may be switched when the catalyst temperature Tex is estimated from the exhaust gas temperature immediately upstream of the fuel cell 8 and the estimated catalyst temperature Tex reaches a predetermined temperature (a temperature at which the catalyst can be determined to be activated to some extent) Tex1. Similarly, regarding the end time of the temperature increase control, the temperature increase control may be ended when the estimated catalyst temperature Tex reaches a predetermined temperature (a temperature at which the catalyst can be determined to be sufficiently activated) Tex2. The catalyst temperature Tex is estimated by, for example, referring to a map that stores the relationship between the exhaust temperature and the catalyst temperature Tex, using a predetermined calculation formula that uses the exhaust temperature as a parameter, and calculating the engine load, The estimation may be made based on the engine speed, vehicle speed, air-fuel ratio, and the like. Further, instead of estimating the catalyst temperature Tex from the exhaust gas temperature, the coolant temperature WT (or oil temperature) detected by the coolant temperature sensor 23 may be used.

Further, in the above-described embodiment, the closing timing of the exhaust valve 7 is switched in a step-like manner when the predetermined timer time T1 has elapsed, but the catalyst temperature (or exhaust temperature, water temperature, oil temperature, etc.) is changed. The timing may be gradually retarded from before the exhaust top dead center to the closing timing during normal control according to the degree of rise.

[0049]

As described above in detail, according to the in-cylinder injection type internal combustion engine of the present invention, the reburning of unburned HC in the combustion chamber by setting the closing timing of the exhaust valve before the top dead center is performed. , The emission of unburned HC to the outside can be suppressed, the stratified combustion is achieved by the compression stroke injection, and the internal EGR is reduced by reducing the overlap between the opening periods of the exhaust valve and the intake valve. The increase in the exhaust gas temperature by retarding the ignition timing from that in the normal operation and the reaction of CO, H ₂ and excess O ₂ generated by the compression stroke injection on the catalyst while increasing the combustion timing while improving the combustion stability. There is an effect that the temperature of the catalyst can be efficiently raised by the synergistic effect.

Also, by changing the closing timing of the exhaust valve from before the exhaust top dead center to the closing timing during the normal control at a predetermined time after the start of the temperature increase control, CO generated by the compression stroke injection and excess O _Since unburned HC can be supplied to the catalyst along with ₂ etc., the oxidation reaction on the catalyst is promoted, and the temperature of the catalyst is raised more efficiently in combination with the rise in exhaust gas temperature due to the retardation of the ignition timing. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a direct injection internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a control routine of a temperature rise control at the time of a cold start according to an embodiment of the present invention.

FIG. 3 is a time chart showing control contents of the temperature raising control shown in FIG. 2, and includes a timer value (d), a water temperature (e), an engine rotation speed (f), a target effective pressure (g), and a vehicle speed (h). And the respective settings of the corresponding fuel injection mode (a), ignition timing (b), and exhaust valve closing timing (c).

FIG. 4 is a diagram illustrating setting of a closing timing of an exhaust valve during a valve opening period according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine (in-cylinder injection type internal combustion engine) 2 Cylinder head 4 Intake passage 5 Exhaust passage 6 Intake valve 7 Exhaust valve 8 Spark plug (ignition means) 9 Fuel injection valve (fuel injection means) 10 Valve timing adjustment device (valve timing adjustment) Means) 12 Throttle valve 18 Catalyst device 18A Storage NOx catalyst 18B, 18C Three-way catalyst 20 Throttle position sensor 21 O ₂ sensor 22 High temperature sensor 23 Water temperature sensor 24 Crank angle sensor 30 ECU (control means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) F02D 13/02 F02D 13/02 J 3G301 H 41/02 301 41/02 301A 41/04 330 41/04 330M 41/34 41/34 H F02P 5/15 F02P 5/15 E (72) Inventor Yuki Tamura 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Inventor Yasuyuki Yamaguchi Minato, Tokyo 5-33-8 Shiba-ku, Mitsubishi Motors Corporation (72) Inventor Shigeo Yamamoto 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Inventor Hideo Nakai Shiba, Minato-ku, Tokyo 5-33-8, Mitsubishi Motors Corporation (72) Inventor Fumiaki Hiraishi 5-33-8, Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation F-term (reference) 3G018 BA 33 CA12 DA74 EA17 EA21 FA01 FA07 FA16 GA09 GA24 3G022 AA06 CA01 CA02 DA02 GA01 GA05 GA06 GA08 GA09 GA10 3G084 AA04 BA13 BA15 BA17 BA23 BA24 BA28 CA01 CA02 DA10 EA11 EB12 FA07 FA10 FA13 FA20 FA27 FA29 FA33 FA35 FA03 A03 ABA3A09 CB03 CB05 CB07 DA02 DB11 DC01 EA01 EA05 EA07 EA10 EA16 EA18 EA33 FA01 FA04 FB02 FB10 FB11 FC07 3G092 AA06 AA09 AA11 AB02 BB01 BB06 BB11 DA03 DE03Y EA01 EC01 FA03 FA15 GA01 GA02 H01Z03 HC06 JA25 JA26 KA01 KA05 LB04 LC01 MA11 MA26 NA08 ND01 NE01 NE11 NE12 PA01Z PA11Z PB03Z PD02Z PD12Z PE01Z PE03Z PE08Z PE09Z PE10Z

Claims (2)

[Claims] 1. A catalyst provided in an exhaust passage for purifying exhaust gas, fuel injection means for directly injecting fuel into a combustion chamber, valve timing adjustment means for adjusting opening / closing timing of an exhaust valve, and the combustion chamber An ignition means capable of igniting the air-fuel mixture and, when a temperature rise of the catalyst is required, the fuel injection means is driven so that the air-fuel ratio becomes close to the stoichiometric air-fuel ratio or becomes slightly leaner than the stoichiometric air-fuel ratio. While injecting fuel during the compression stroke, the valve timing adjusting means is driven to set the closing timing of the exhaust valve to before exhaust top dead center,
A direct injection internal combustion engine, further comprising control means for executing a temperature raising control for retarding the ignition timing of the ignition means from that during normal operation. 2. The method according to claim 1, wherein the control means changes the closing timing of the exhaust valve at a predetermined time after the start of the temperature raising control to a closing timing of the normal control from before exhaust top dead center. Item 6. An in-cylinder injection internal combustion engine according to item 1.