JP2002188550A - Control device for direct-injection spark-ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve responsiveness when shifting from stratified stoichiometric combustion to uniform combustion by acceleration in a direct-injection spark- ignition engine. SOLUTION: Combustion is performed in a stratified stoichiometric combustion form by divided fuel injection until an exhaust emission catalyst is activated. When accelerated in this state, the larger the throttle valve opening TVO and its change speed ΔTVO are, the larger the spark advance correction rate at which the advance correction is made, and when reaching the target ignition timing MBT in uniform combustion, the fuel injection is changed to one injection in an intake stroke, and a swirl control valve is opened to change to uniform combustion. A shift to the uniform combustion is thereby made at the torque rise rate and changeover time corresponding to the degree of acceleration, and a good engine response is obtained while absorbing torque level difference.

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 a direct-injection spark ignition engine, and more particularly to an ignition timing control at the time of switching the combustion system in an engine that switches the combustion system in accordance with an operation state.

[0002]

2. Description of the Related Art In recent years, a direct-injection spark ignition type engine has been employed in which stratified combustion is performed by directly injecting and supplying fuel into a combustion chamber of an engine for the purpose of improving fuel efficiency and exhaust gas purification performance. In the direct-injection spark ignition engine, the fuel is divided and injected into the intake stroke and the compression stroke in order to promote the activation and activation of the exhaust purification catalyst, so that the air-fuel ratio around the spark plug is richer than stoichiometric. There is one in which a stratified mixture having an air-fuel ratio is formed, and a mixture having an air-fuel ratio leaner than the stoichiometric mixture is formed outside the stoichiometric mixture and burned (see Japanese Patent Application Laid-Open No. 10-212987).

[0003] That is, by shifting to the main combustion by the lean mixture while increasing the combustion speed in the initial combustion of the relatively rich mixture around the spark plug, the ignition timing can be retarded. Thus, the after-burning of excess fuel is performed to increase the exhaust gas temperature while suppressing the emission of HC, NOx and the like, thereby promoting the activation of the exhaust purification catalyst. The air-fuel ratio of the air-fuel mixture around the ignition plug may be stoichiometric. Hereinafter, the combustion of the air-fuel mixture thus formed is referred to as stratified stoichiometric combustion.

By the way, for example, even when stratified stoichiometric combustion is performed due to a request for a rise in exhaust gas temperature as described above,
When the engine is accelerated, the combustion mode is switched to homogeneous combustion, in which a homogeneous mixture is formed in the entire combustion chamber to secure the output, and combustion is switched at the same time when the combustion operation is requested by the acceleration operation. A step is generated.

For this reason, there has been proposed an apparatus in which ignition timing correction for suppressing a torque step is performed at the time of combustion switching as described above. Specifically, at the time of switching from stratified stoichiometric combustion (homogeneous combustion) to homogeneous combustion (stratified stoichiometric combustion), the ignition timing is corrected to an ignition timing suitable for the combustion after switching after the switching request is issued. By switching the combustion from, the occurrence of a torque step is suppressed.

[0006]

However, for example, in the case of the above-described ignition timing correction at the time of rapid acceleration, it takes too much time to complete the correction, so that the switching of combustion is delayed, and the engine response is deteriorated to ensure good operability. Sometimes I couldn't do it. Specifically, stratified stoichiometric combustion is semi-stratified combustion, in which a swirl control valve (flow control valve) mounted in an intake passage or the like is closed to increase the gas flow in the combustion chamber, and combustible mixing around the ignition plug is performed. It forms air and secures stable combustion.

On the other hand, when a rapid acceleration is required, while the stratified stoichiometric combustion is maintained, the swirl control valve and the like for enhancing the gas flow are closed, and the intake air is throttled. , The engine response may be deteriorated, and the drivability may be deteriorated. The present invention has been made in view of such a conventional problem, and provides a control device for a direct-injection spark ignition type engine capable of obtaining a good transient operation performance while suppressing the occurrence of a torque step. The purpose is to:

[0008]

According to the operating condition of the engine, homogeneous combustion is performed by forming a homogeneous mixture in the entire combustion chamber and burning the mixture, and the air-fuel ratio around the ignition plug is stoichiometric or richer than stoichiometric. After the generation of the combustion switching request, the ignition timing is corrected to a target ignition timing suitable for the combustion switching. After that, the combustion is switched, and the correction ratio of the ignition timing is variably controlled according to the accelerator opening.

According to the first aspect of the invention, when the combustion switching request is generated, the correction ratio to the target ignition timing is set in accordance with the accelerator opening indicating the driver's request. The switching of the combustion is executed in an appropriate time so as to satisfy the condition, and it is possible to achieve both the absorption of the torque step and the transient operability.

The invention according to claim 2 provides homogeneous combustion in which a homogeneous air-fuel mixture is formed and burned in the entire combustion chamber according to the engine operating state, and the air-fuel ratio around the spark plug is stoichiometric or richer than stoichiometric. An engine that switches between stratified stoichiometric combustion, which forms an air-fuel mixture and forms a leaner air-fuel mixture on the outside, and burns the mixture.
After the combustion switching request is generated, the ignition timing is corrected to a target ignition timing suitable for the combustion switching, and then the combustion switching is performed, and the correction ratio of the ignition timing is variably controlled according to the speed of change of the accelerator opening. It is characterized by doing.

According to the second aspect of the present invention, when a combustion switching request is generated, the correction ratio to the target ignition timing is set according to the speed of change of the accelerator opening indicating the driver's request. The switching of the combustion is executed in an appropriate time so as to satisfy the drivability, and both the absorption of the torque step and the transient drivability can be achieved.

According to the third aspect of the present invention, there is provided homogeneous combustion in which a homogeneous air-fuel mixture is formed and burned in the entire combustion chamber in accordance with the engine operating state, and an air-fuel ratio around the spark plug is stoichiometric or richer than stoichiometric. An engine that switches between stratified stoichiometric combustion, which forms a lean air-fuel mixture and forms a leaner air-fuel mixture on the outside, and burns the mixture.
After the generation of the combustion switching request, the ignition timing is corrected to a target ignition timing suitable for the combustion switching, and then the combustion switching is performed, and the correction ratio of the ignition timing is changed to the accelerator opening and the changing speed of the accelerator opening. It is characterized in that it is variably controlled in response.

According to a third aspect of the present invention, when a combustion switching request is generated, the target ignition timing is corrected in accordance with both the accelerator opening indicating the driver's request and the changing speed of the accelerator opening. Since the ratio is set, the switching of the combustion is executed in an appropriate time so as to satisfy the required driving performance more accurately grasped, and it is possible to achieve both the absorption of the torque step and the transient driving performance.

Further, the invention according to claim 4 is characterized in that when switching from the stratified stoichiometric combustion to the homogeneous combustion, the correction ratio in the advance direction for bringing the ignition timing closer to the target ignition timing is increased when the accelerator opening is large. It is characterized by doing.
According to the fourth aspect of the invention, when the accelerator opening is increased, such as during rapid acceleration, the correction ratio in the advance direction to the target ignition timing (MBT) suitable for homogeneous combustion is set to a large value. Is promptly corrected to the target ignition timing, and is switched to homogeneous combustion in a short time.

On the other hand, at the time of gentle acceleration where the accelerator opening remains small, the correction ratio in the advance direction is set to a relatively small value, so that the combustion is switched to homogeneous combustion while the torque is increased relatively slowly. Therefore, the combustion shifts to the homogeneous combustion with the torque increasing speed and the switching time according to the required acceleration, and the acceleration response (engine response) can be satisfied while absorbing the torque step.

Further, the invention according to claim 5 is characterized in that, when switching from the stratified stoichiometric combustion to the homogeneous combustion, the switching to the target ignition timing is completed when the accelerator opening is equal to or greater than a predetermined opening. The correction ratio is set. According to the fifth aspect of the invention, when the accelerator opening is equal to or larger than the predetermined opening, the switching to the target ignition timing is completed and the combustion is switched to the homogeneous combustion. Acceleration responsiveness can be ensured.

In the invention according to claim 6, when switching from the stratified stoichiometric combustion to the homogeneous combustion, the correction ratio in the advance angle per unit time for bringing the ignition timing closer to the target ignition timing is determined by the accelerator opening degree. It is characterized in that it is increased when the increasing speed is high. According to the sixth aspect of the present invention, at the time of rapid acceleration in which the speed of change of the accelerator opening is large, the advance correction ratio per unit time to the target ignition timing (MBT) suitable for homogeneous combustion, that is, the value at which the advance correction speed is large Therefore, the ignition timing is advanced to the target ignition timing in a short time, and is switched to the homogeneous combustion in a short time.

On the other hand, at the time of gentle acceleration in which the speed of change of the accelerator opening is small, the advance correction speed is set to a relatively small value, so that the combustion is switched to homogeneous combustion while increasing the torque relatively slowly. Therefore, the combustion shifts to the homogeneous combustion with the torque increasing speed and the switching time according to the required acceleration, and the acceleration response (engine response) can be satisfied while absorbing the torque step.

Further, the invention according to claim 7 is provided with an intake flow control valve for promoting formation of the mixture for the stratified stoichiometric combustion, and closes the flow control valve at the same time as switching from the stratified stoichiometric combustion to the homogeneous combustion. From open to open. According to the seventh aspect of the present invention, as described above, by providing the intake flow control valve, an appropriate intake flow is generated in the combustion chamber, and the formation of a fuel-air mixture for stratified stoichiometric combustion is promoted. Although the stoichiometric combustion can be performed, the stratified stoichiometric combustion in which the intake flow control valve is operated cannot cover the required intake air amount at the time of rapid acceleration.

Therefore, by applying the present invention and quickly switching from stratified stoichiometric combustion to homogeneous combustion, there is a great effect that the demand for rapid acceleration can be satisfied. Further, in the invention according to claim 8, during the stratified stoichiometric combustion, a lean air-fuel mixture is formed in the entire combustion chamber by the combustion injection during the intake stroke, and the air-fuel ratio around the ignition plug is formed by the fuel injection during the compression stroke. It is characterized by forming a stoichiometric mixture or a richer mixture than a stoichiometric mixture.

According to the eighth aspect of the invention, the fuel mixture is divided into the intake stroke and the compression stroke and the fuel is injected, so that the mixture for stratified stoichiometric combustion can be formed easily and in a favorable state. The invention according to claim 9 is characterized in that the accelerator opening is detected by a throttle opening.

According to the ninth aspect of the present invention, the same function can be obtained by using the detected value of the throttle opening in accordance with the accelerator opening, and the ignition timing can be controlled at the time of combustion switching according to the actual intake characteristic.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
Description will be given based on the attached drawings. In FIG. 1 showing a system configuration of an embodiment of the present invention, an air flow meter 3 for detecting an intake air flow rate Qa and a throttle valve 4 for controlling the intake air flow rate Qa are provided in an intake passage 2 of an engine (internal combustion engine) 1. In addition, a swirl control valve 21 as an intake flow control valve for stratified stoichiometric combustion is attached to the intake port of each cylinder. The swirl control valve 21 is throttle-controlled at the time of stratified stoichiometric combustion by an actuator 22 controlled by the control unit 50, so that the gas flow in the combustion chamber is strengthened to form a mixture suitable for stratified stoichiometric combustion.

A fuel injection valve 5 is provided so as to face the combustion chamber of each cylinder. The fuel injection valve 5 is driven to open by a drive pulse signal set by the control unit 50, and is supplied with a pressure from a fuel pump (not shown) to be controlled to a predetermined pressure by a pressure regulator (not shown). It can be supplied directly to the jet.

Each cylinder is provided with an ignition plug 6 mounted facing the combustion chamber and igniting the intake air-fuel mixture based on an ignition signal from the control unit 50. On the other hand, an exhaust passage 7 is provided with an air-fuel ratio sensor 8 (rich / rich) that detects the concentration of a specific component (for example, oxygen) in the exhaust gas to detect the air-fuel ratio of the exhaust gas and thus the intake air-fuel mixture.
It may be an oxygen sensor that performs a lean output, or may be a wide-range air-fuel ratio sensor that linearly detects the air-fuel ratio over a wide range.) An exhaust gas for purifying exhaust gas is provided downstream of the sensor. A purification catalyst 9 is provided. The exhaust purification catalyst 9 has a stoichiometric condition, that is, a stoichiometric air-fuel ratio ｛λ =
1. A three-way catalyst capable of purifying exhaust gas by oxidizing CO and HC in the exhaust gas and reducing NOx in the vicinity of A / F (air weight / fuel weight) · 14.7１４, or CO in the exhaust gas , An oxidation catalyst for oxidizing HC, or a ternary function near the stoichiometric air-fuel ratio, traps NOx in the exhaust at a lean air-fuel ratio, and reduces and releases the trapped NOx at a stoichiometric or rich air-fuel ratio. NOx trap catalyst or the like can be used.

Further, a specific component (for example, oxygen) concentration in the exhaust gas is detected downstream of the exhaust gas purifying catalyst 9 in the exhaust gas.
A downstream oxygen sensor 10 that outputs rich / lean is provided. Here, the downstream oxygen sensor 1
By correcting the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 8 with the detection value of 0 to suppress a control error due to deterioration of the air-fuel ratio sensor 8 or the like (a so-called double air-fuel ratio sensor system). Although the downstream oxygen sensor 10 is provided, the downstream oxygen sensor 10 is omitted when it is sufficient to perform the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 8. Is what you can do. When the air-fuel ratio feedback control is not performed, both the air-fuel ratio sensor 8 and the downstream oxygen sensor 10 can be omitted.

Since the air-fuel ratio sensor 8 is provided on the exhaust gas upstream side of the exhaust gas purification catalyst 9 and has a small heat capacity, the activation speed is extremely higher than that of the exhaust gas purification catalyst 9. Further, since the temperature of the air-fuel ratio sensor 8 can be forcibly raised (activated) by an electric heater or the like, the detection of the air-fuel ratio sensor 8 during the stratified stoichiometric combustion (during the warm-up process of the exhaust purification catalyst 9) is performed. It is possible to perform air-fuel ratio feedback control based on the result.

Therefore, in the present embodiment, the air-fuel ratio sensor 8 is activated immediately after the start, and the detection of the air-fuel ratio sensor 8 is performed so that the air-fuel ratio of the entire combustion chamber becomes stoichiometric during stratified stoichiometric combustion described later. Feedback control is performed based on the value. Further, a crank angle sensor 11 is provided, and the control unit 50 counts a crank unit angle signal output from the crank angle sensor 11 in synchronization with the engine rotation for a certain period of time, or The engine rotation speed Ne can be detected by measuring the period.

A water temperature sensor 12 is provided facing the cooling jacket of the engine 1 and detects a cooling water temperature Tw in the cooling jacket. Further, a throttle sensor 13 for detecting the opening of the throttle valve 4 is provided.
(Can also function as an idle switch)
Is provided. By the way, in the present embodiment,
A throttle valve control device 14 that can control the opening of the throttle valve 4 by an actuator such as a DC motor is provided.

The throttle valve controller 14 electronically controls the opening of the throttle valve 4 based on a drive signal from the control unit 50 so as to achieve the required torque calculated based on the accelerator opening and the like. Can be configured. Detection signals from the various sensors are input to a control unit 50 including a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like. The opening degree of the throttle valve 4 is controlled via the throttle valve control device 14 in accordance with the operating state detected based on the signals from the sensors, and the fuel injection valve 5 is driven to control the fuel injection amount (fuel (Supply amount), the ignition timing is set, and the ignition plug 6 is ignited at the ignition timing.

For example, fuel is injected into the combustion chamber in a compression stroke in a predetermined operation state (low / medium load region, etc.), and a combustible air-fuel mixture is formed in a stratified form around the ignition plug 6 in the combustion chamber to perform stratified combustion. On the other hand, in other operation states (such as a high-load region), fuel can be injected into the combustion chamber during the intake stroke to form a mixture having a substantially uniform mixture ratio over the entire cylinder and perform homogeneous combustion. As described above, the fuel injection timing (injection timing) is also configured to be changeable according to the operating state and the like.

Further, the control unit 50 controls the exhaust purification catalyst 9 while suppressing the emission of HC into the atmosphere from the start to the time when the exhaust purification catalyst 9 is activated.
Key switch 1 to enable early activation of
6, and receives the input signals from various sensors and performs, for example, the following control. Specifically, for example, a flowchart as shown in FIG. 2 is executed.

In step (denoted by S in the figure, hereinafter the same), in step 1, whether the ignition signal of the key switch 16 has been turned ON (whether the key position has been set to the ignition ON position) is determined by the same method as in the past. Judge. If YES, proceed to Step 2; if NO, end this flow. In step 2, it is determined whether or not the start signal of the key switch 16 has been turned ON (whether or not the key position has been set to the start position) by a method similar to the related art. That is, it is determined whether or not there is a cranking request by a starter motor (not shown).

If YES, it is determined that there is a starting cranking request, and the process proceeds to step 3. If NO, it is determined that there is no cranking request yet, and the process returns to step 1. In step 3, the driving of the starter motor is started and the engine 1 is cranked as in the conventional case. In step 4, the fuel injection for starting (direct fuel injection in the intake stroke, see FIG. 3B) is performed as in the related art.
The engine 1 is operated (direct injection homogeneous combustion).

In the next step 5, it is determined whether or not the exhaust purification catalyst 9 has been activated. The determination can be made by detecting the temperature of the catalyst 9 by providing a sensor or estimating the temperature of the catalyst 9 from the operation history of the engine. If the catalyst has not been activated (YES), proceed to step 6. On the other hand, if the catalyst is activated (if NO), it is determined that there is no need to perform control for promoting catalyst activation, and the process proceeds to step 13, where switching to homogeneous combustion is performed while performing ignition timing switching control.

In step 6, it is determined whether the conditions for permitting the stratified stoichiometric combustion are satisfied. Specifically, when both of the following conditions are satisfied, stratified stoichiometric combustion is permitted. The air-fuel ratio sensor 8 is activated (alternatively, a predetermined time has elapsed since the complete explosion).

The idle switch is ON. If it is determined that the conditions for permitting the stratified stoichiometric combustion are satisfied, good ignitability and flammability even if stratified stoichiometric combustion for promoting catalyst activation described below is performed, and furthermore, engine stability. It is determined that (engine drivability) and the like are obtained, and the process proceeds to step 7.

On the other hand, in the case of NO, if stratified stoichiometric combustion is performed to promote the activation of the catalyst, which will be described later, the combustion stability and the engine stability (engine operability) may be reduced. Then, the process returns to step 4 in order to prohibit the shift to the stratified stoichiometric combustion and continue the direct fuel injection (direct injection homogeneous combustion) in the intake stroke. In step 7, switching to stratified stoichiometric combustion is performed while performing ignition timing control in accordance with switching from the homogeneous combustion to stratified stoichiometric combustion.

An outline of the ignition timing control will be described. First, the ignition timing [MBT (maximum torque generation ignition timing)] in the homogeneous combustion is gradually retarded to gradually reduce the generated torque in the homogeneous combustion. After retarding to the target retarded ignition timing suitable for stoichiometric combustion, switching to stratified stoichiometric combustion is performed, and at the same time, the ignition timing is advanced by the retard correction at a stretch to eliminate a torque step at the time of combustion switching. Thereafter, the retard is gradually retarded until the target retard ignition timing.

When the transition to stratified stoichiometric combustion is completed, stratified stoichiometric combustion is continued at step 8. Specifically, in the stratified stoichiometric combustion, for example, the total amount of fuel that can be substantially completely burned with the intake air amount per combustion cycle {the fuel weight required to achieve a substantially stoichiometric (stoichiometric air-fuel ratio)} Among them, for example, a fuel weight of about 50% to about 90% is injected and supplied into the combustion chamber during the intake stroke to form a homogeneous mixture which is relatively leaner than the stoichiometric mixture throughout the combustion chamber. B) formed by the fuel injection shown in FIG.
% Of fuel weight is injected and supplied into the combustion chamber in the compression stroke, and a mixture richer (higher in fuel concentration) than the stoichiometric mixture is formed around the ignition plug 6 (see FIG. 3 (A)). ,
Burn (see FIG. 4). However, the mixture around the ignition plug 6 may be stoichiometric.

In the stratified stoichiometric combustion mode, the air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel mixture formed in the combustion chamber (in this embodiment, by the intake stroke injection) during the intake stroke is 16 to 28, and the compression stroke The fuel injection amount during the intake stroke and the fuel injection amount during the compression stroke are adjusted so that the air-fuel ratio of the mixture richer than the stoichiometric mixture formed around the spark plug by the fuel injection during the fuel injection is 9 to 13. The share ratio may be set.

If the air-fuel ratio of each air-fuel mixture layer is set in the above range, the average air-fuel ratio in the combustion chamber is set to an air-fuel ratio slightly deviated from the stoichiometric air-fuel ratio (for example, in the range of 13.8 to 18). May be set. According to the above-described stratified stoichiometric combustion, not only can the exhaust gas temperature be raised as compared with the conventional homogeneous stoichiometric combustion, but also the amount of unburned HC discharged from the combustion chamber to the exhaust passage can be reduced. .

That is, according to the stratified stoichiometric combustion, the conventional combustion mode: only homogeneous combustion, only stratified combustion, or combustion in which additional fuel is injected after the latter stage of combustion (after the expansion stroke or during the exhaust stroke). As compared with the case where the warm-up is performed in the form (1), the early activation of the exhaust purification catalyst 9 is suppressed while suppressing the discharge of HC into the atmosphere from the start of the start until the exhaust purification catalyst 9 is activated. This can be greatly promoted.

Returning to FIG. 2, after switching to stratified stoichiometric combustion as described above, it is determined in step 9 whether or not acceleration has occurred. If it is determined that the vehicle has accelerated, step 1
After 0, the ignition timing switching control is performed, and then, in step 11, the combustion is switched to homogeneous combustion. Further, when it is determined in step 9 that the exhaust gas has not been accelerated, it is determined in step 12 whether or not the exhaust purification catalyst 9 has been activated. When it has not been activated, the process returns to step 8 to continue stratified stoichiometric combustion. If it is determined that the combustion has been activated, the routine proceeds to step 13, where switching to homogeneous combustion is performed while performing ignition timing switching control.

The ignition timing switching control according to the present invention, which is performed at the time of transition to homogeneous combustion in step 10 when it is determined in step 9 that acceleration has occurred, will be described with reference to the flowchart shown in FIG. FIG. 5 is a flowchart of the ignition timing switching control routine. In step 21, it is determined whether or not homogeneous (stoichiometric) combustion is permitted (acceleration is determined in step 9 in FIG. 2 and a request for switching to homogeneous combustion is generated).

Then, when homogeneous combustion is permitted,
That is, when the request for switching from the stratified stoichiometric combustion to the homogeneous combustion by the accelerating operation is generated, the process proceeds to step 22.
Then, the ignition timing advance correction control commensurate with the switching to the homogeneous combustion is started. At this time, the initial value of the retardation ratio is
It is set to 100%. That is, when switching from stratified stoichiometric combustion to homogeneous combustion, the ignition timing in stratified stoichiometric combustion is retarded to the maximum within the engine stability limit.
From the retarded ignition timing in stratified stoichiometric combustion to MBT (maximum torque generation ignition timing) which is an ignition timing suitable for homogeneous combustion, advance correction is performed to suppress the generation of a torque step due to combustion switching.

In step 23, the retard amount is calculated. That is, since the ignition timing control is controlled by the retard amount from the MBT which is the target ignition timing at the time of the final combustion switching, the retard amount is calculated. The calculation of the retard amount will be described with reference to the flowchart of the subroutine shown in FIG.

In step 31, the throttle valve opening TV
Calculate the retardation correction rate p by O. This retardation correction rate p
Is set as a correction coefficient to be multiplied by the amount of retardation of the ignition timing at the time of the occurrence of the combustion switching request for the MBT. MBT by increasing the amount
Is set to be close to Specifically, as shown in FIG. 7, when the throttle valve opening TVO is equal to or smaller than the first predetermined opening A, p = 1 is constant, and the second predetermined opening is larger than the first predetermined opening A. If it is less than B, p is set to gradually decrease from 1 to 0 in accordance with an increase in TVO, and the second predetermined opening B
As described above, p is set to be constant at 0.

In step 32, the throttle valve opening TV
The decrement amount q of the retardation ratio by the change rate ΔTVO of O is calculated. The decrement amount q is set as a lead angle correction ratio per unit time from the present ignition timing to the MBT in homogeneous combustion, and the larger the change speed ΔTVO, the larger the value, that is, the shorter the time. M
It is set to reach BT. Specifically, as shown in FIG. 8, when the change speed ΔTVO is equal to or lower than the first predetermined speed C, q is constant at the minimum value, and when the change speed ΔTVO is higher than the first predetermined speed C and lower than the second predetermined speed D, Is set such that q gradually increases from a minimum value to a maximum value in accordance with an increase in ΔTVO, and is set to be constant at q = maximum value at a second speed D or higher.

In step 33, the calculated decrement amount q is decremented from the current retardation ratio to update the retardation ratio. As a result, the retardation rate decreases by q every execution cycle of this routine. Step 34
Then, the retard amount for MBT is calculated by the following equation. Retard amount = (MBT-target retard ignition timing) × p × retard ratio Here, the target retard ignition timing is the ignition timing in the stratified stoichiometric combustion at the time of a request to switch to homogeneous combustion, and The amount of retardation of the retarded ignition timing with respect to MBT (MBT-target retarded ignition timing) is multiplied by a retardation correction rate p corresponding to the sequential throttle valve opening TVO, and
Each time the execution cycle of this routine is performed, the decrement amount q is multiplied by a retardation ratio that is subtracted.

After calculating the amount of retardation in this way, FIG.
Returning to step 24, the ignition timing before the combustion switching is calculated as in the following equation. Ignition timing = MBT-retard amount In step 25, it is determined whether the ignition timing calculated in step 24 has advanced to MBT (retard amount = 0).

Until the MBT is reached, the process returns to step 23 to control the ignition timing set in step 24 while calculating and updating the retard amount. Thus, the MBT
When it is determined that the ignition timing has reached the MBT, while performing the advance correction of the ignition timing approaching to, the routine proceeds to step 26 where the combustion is switched. Specifically, the fuel injection is switched to a single injection in the intake stroke, and the swirl control valve 21 is fully opened to secure a sufficient amount of intake air to form a homogeneous mixture in the entire combustion chamber to perform homogeneous combustion. .

Thereafter, the routine proceeds to step 27, where the ignition timing referred to from the map is set based on the operating state such as the engine speed and the load, and the ignition timing is controlled to the set ignition timing. The state of the above control is shown in FIG. The accelerator operation during acceleration causes the throttle valve opening TVO to change from a low opening to full opening at a predetermined change rate ΔTVO as shown by the solid line in the figure.
If it increases by 1, until the TVO reaches the first predetermined opening degree A (Y in the figure), the decrement amount of the retardation ratio set by ΔTVO1 from the ignition timing at the time of the combustion switching request during stratified stoichiometric combustion The angle is advanced at a predetermined rate per time by q.

After the TVO becomes equal to or greater than the first predetermined opening degree A, the advance correction is performed by decreasing the retard correction rate p in accordance with the increasing TVO, so that the advance correction ratio increases. When the TVO reaches the second predetermined opening degree B (Z in the drawing), the retardation correction rate p = 0 and reaches the MBT. Further, as shown by the dashed line in the drawing, during rapid acceleration at a larger change speed ΔTVO2, the decrement amount q of the retardation ratio is set to a large value in accordance with the increase of ΔTVO, and TVO is set to a second predetermined value. Since the time required to reach the opening degree B is short, the ignition timing is advanced at a large rate immediately after the start-up, and the characteristics reach the MBT in a shorter time.

The dotted line shows the case where the conventional decrement q of the retardation ratio is fixed and the correction by the retardation correction rate p is not performed (p = 1), and the ignition timing is independent of TVO and ΔTVO. Takes a long time to reach MBT at Y ′ and switch to homogeneous combustion, and cannot satisfy the acceleration response. On the other hand, in the present embodiment, it is possible to reach the required ignition timing of homogeneous combustion at MBT at a correction ratio commensurate with the request for acceleration in accordance with TVO and ΔTVO. In addition, the swirl control valve can be switched to homogeneous combustion together with the opening operation, so that the engine response and thus the operability are improved.

Conventionally, even when switching from stratified stoichiometric combustion to homogeneous combustion by acceleration, at the same time as combustion switching, the torque is once stepwise retarded by a predetermined amount so as to completely eliminate the torque step at the time of switching, and then the MBT again. Since the ignition timing control is gradually approached, reaching the MBT by homogeneous combustion is further delayed (Z ′ in the figure). However, during acceleration, even if torque increases due to combustion switching, it is hard to feel as a torque step because it meets the acceleration request, and the required ignition timing (MBT) is promptly increased.
Therefore, it is considered that it is more suitable to meet the demand by switching to the maximum output. Therefore, even after the combustion is switched, the required ignition timing MBT in the homogeneous combustion is immediately controlled without performing the retard correction. However, in step 12 of FIG.
When switching from stratified stoichiometric combustion to homogeneous combustion is performed in step 13 when it is determined that the combustion has been activated, the torque is temporarily retarded by a predetermined amount at the same time as switching to homogeneous combustion to completely reduce the torque shock at the time of combustion switching. After the cancellation, the ignition timing is controlled to gradually approach the MBT again.

Further, in the present embodiment, when sudden acceleration occurs, Δ
When the decrement amount q of the retard amount with respect to TVO is sufficiently increased, the retard ratio reaches 0 so that the throttle valve opening TVO reaches the second predetermined opening B earlier. It is also possible to use ΔTVO
, The switching of combustion is performed more quickly. Further, the calculation of the retardation ratio in step 23 may be performed by the following equation.

In this equation, the advance correction amount per unit time according to ΔTVO is not affected by the magnitude of the retard correction rate p. The properties to be achieved. Which formula is selected may be appropriately determined in consideration of engine characteristics. Further, in the present embodiment, an example in which the advance correction ratio is variably controlled for both TVO and ΔTVO has been described.
The advance angle correction ratio may be variably controlled with respect to only one of TVO and ΔTVO. That is, the retardation correction rate p is configured to be variably controlled according to TVO,
Alternatively, the configuration may be such that the decrement amount of the retardation ratio is variably controlled according to ΔTVO.

In this embodiment, since the throttle valve opening is detected as an amount corresponding to the accelerator opening, the ignition timing can be controlled in accordance with the actual intake characteristics. May be used.

[Brief description of the drawings]

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

FIG. 2 is a flowchart of overall control in the embodiment.

FIG. 3A is a schematic view for explaining direct injection compression stroke injection. (B) is a schematic diagram for explaining direct injection intake stroke injection. (C) is a plan view at the time of fuel injection.

FIG. 4 is a view for explaining a state of formation of an air-fuel mixture in a combustion chamber in a stratified stoichiometric combustion mode.

FIG. 5 is a flowchart for explaining control at the time of combustion switching when switching from stratified stoichiometric combustion to homogeneous combustion in the embodiment.

FIG. 6 is a flowchart showing a subroutine for calculating a retard amount in the above control.

FIG. 7 is a diagram showing characteristics of a retard correction rate p with respect to a throttle valve opening TVO in the above control.

FIG. 8 is a throttle valve opening change rate Δ in the above control.
The figure which shows the characteristic of the decrement amount q of the retardation ratio with respect to TVO.

FIG. 9 is a time chart showing a state at the time of the control.

[Explanation of symbols]

 Reference Signs List 1 engine 4 throttle valve 5 fuel injection valve 6 spark plug 7 exhaust passage 8 air-fuel ratio sensor 9 exhaust purification catalyst 21 swirl control valve 50 control unit

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F02D 41/04 305 F02D 41/04 330B 330 330C 41/10 305 41/10 305 330B 330 43/00 301B 43/00 301 301H F02P 5/15 FF term (reference) 3G022 AA07 CA04 DA01 EA07 FA06 GA08 3G084 BA09 BA13 BA17 DA11 DA15 FA10 3G301 HA01 HA04 HA16 HA17 JA03 JA04 KA06 KA12 LA05 LB04 MA01 MA11 ND01 NE01 NE11 NE12 NE13 NE14 NE14 NE15 NE14 NE13 NE14 NE15 PD09Z PE01Z PE03Z PE08Z PE09Z PF04Z

Claims (9)

[Claims] According to an engine operating condition, homogeneous combustion is performed in which a homogeneous mixture is formed in the entire combustion chamber and burned, and an air-fuel ratio is formed around the spark plug with a stoichiometric or richer mixture than the stoichiometric mixture. An engine that switches between stratified stoichiometric combustion in which an air-fuel mixture leaner than the stoichiometric mixture is formed and burns, wherein after the combustion switching request is issued, the ignition timing is corrected to a target ignition timing suitable for the combustion switching, and then the combustion switching is performed. And controlling the correction ratio of the ignition timing variably in accordance with the accelerator opening. 2. A homogeneous combustion in which a homogeneous air-fuel mixture is formed and burned in the entire combustion chamber in accordance with an operation state of the engine, and an air-fuel ratio is formed around the ignition plug to have a stoichiometric or richer air-fuel ratio. An engine that switches between stratified stoichiometric combustion in which an air-fuel mixture leaner than the stoichiometric mixture is formed and burns, wherein after the combustion switching request is issued, the ignition timing is corrected to a target ignition timing suitable for the combustion switching, and then the combustion switching is performed. And controlling the correction ratio of the ignition timing variably in accordance with the rate of change of the accelerator opening. 3. A homogeneous combustion in which a homogeneous air-fuel mixture is formed and burned in the entire combustion chamber in accordance with an engine operating state, and an air-fuel ratio is formed around the spark plug to form a stoichiometric or richer air-fuel mixture. An engine that switches between stratified stoichiometric combustion in which an air-fuel mixture leaner than the stoichiometric mixture is formed and burns, wherein after the combustion switching request is issued, the ignition timing is corrected to a target ignition timing suitable for the combustion switching, and then the combustion switching is performed. And controlling the correction ratio of the ignition timing variably in accordance with the accelerator opening and the rate of change of the accelerator opening. 4. The method according to claim 1, wherein, when switching from the stratified stoichiometric combustion to the homogeneous combustion, the correction ratio in the advance direction for bringing the ignition timing closer to the target ignition timing is increased when the accelerator opening is large. The control device for a direct injection spark ignition engine according to claim 1 or 3. 5. The correction ratio in the advance direction is set such that when switching from stratified stoichiometric combustion to homogeneous combustion, switching to the target ignition timing is completed when the accelerator opening is equal to or greater than a predetermined opening. The control device for a direct-injection spark ignition engine according to claim 4. 6. When switching from the stratified stoichiometric combustion to the homogeneous combustion, the correction ratio in the advance direction per unit time for bringing the ignition timing close to the target ignition timing is increased when the rate of increase of the accelerator opening is large. The control device for a direct-injection spark ignition engine according to claim 2 or 3, wherein: 7. An intake flow control valve for promoting formation of an air-fuel mixture for stratified stoichiometric combustion, wherein the flow control valve is switched from closed to open simultaneously with switching from stratified stoichiometric combustion to homogeneous combustion. Claim 1 to Claim 6
The control device for a direct injection spark ignition engine according to any one of the above. 8. During the stratified stoichiometric combustion, a lean air-fuel mixture is formed in the entire combustion chamber by combustion injection during an intake stroke.
The direct-injection spark ignition method according to any one of claims 1 to 7, wherein the fuel injection during the compression stroke forms a stoichiometric air-fuel ratio or a mixture richer than the stoichiometric air-fuel ratio around the ignition plug. Control device for internal combustion engine. 9. The control device for a direct injection spark ignition engine according to claim 1, wherein the accelerator opening is detected by a throttle opening.