JP3726580B2 - Control device for direct-injection spark-ignition internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a direct injection spark ignition internal combustion engine.
[0002]
[Prior art]
In recent years, fuel has been configured to be directly injected into the combustion chamber of an engine. For example, fuel is usually injected during the intake stroke and burned in a homogeneous mixture (a state where fuel is evenly distributed throughout the combustion chamber) (homogeneous). In a predetermined operating state (low rotation, low load state, etc.), fuel is injected during the compression stroke to form a stratified stratified mixture consisting of an flammable mixture that can be ignited around the spark plug An internal combustion engine (direct injection spark ignition type internal combustion engine) that performs combustion (stratified lean combustion) at an extremely lean air-fuel ratio (an air-fuel ratio in the vicinity of the lean limit) is known (JP-A-62). No. 191622 and Japanese Patent Laid-Open No. 2-169834).
[0003]
In addition, regarding the direct-injection spark-ignition internal combustion engine as described above, the local air-fuel ratio around the spark plug is made rich in the process from cold start to warm-up, thereby creating a local air shortage state and combustion. The exhaust combustion catalyst (CO) and a part of the unburned fuel react with the excess oxygen in the cylinder after the main combustion to increase the exhaust temperature, thereby promoting the activation of the exhaust purification catalyst. (See JP-A-10-169488).
[0004]
Furthermore, the applicant of the present application forms a stratified mixture with a rich air-fuel ratio around the spark plug in view of the problem that ignition is unstable in the above-described technique, which in turn increases unburned fuel (HC) emissions. However, by nebulizing the atomized fuel sufficiently, for example by delaying the ignition timing from the normal stratified lean combustion, the combustion is stabilized and the activation of the exhaust purification catalyst due to the rise in the exhaust temperature is promoted. A technology for suppressing fuel (HC) emissions has been proposed (Japanese Patent Application No. 11-46612).
[0005]
[Problems to be solved by the invention]
By the way, in order to increase the exhaust gas temperature and promote the activation of the exhaust gas purification catalyst as described above, a stratified mixture having a rich air-fuel ratio is locally formed around the spark plug to perform stratified combustion. In this case, at the time of cold start, first, in order to ensure stable combustibility, homogeneous combustion is performed in which a homogeneous mixture is formed in the entire combustion chamber and then combustion is performed. After the exhaust purification catalyst is activated, it is switched to homogeneous lean combustion, and further switched to stratified lean combustion and homogeneous stoichiometric combustion according to operation requirements.
[0006]
However, since stratified combustion has lower thermal efficiency than homogeneous combustion in which fuel and air are sufficiently mixed, a torque step occurs when switching between stratified combustion for raising the exhaust temperature and homogeneous combustion before and after that. This causes a problem that drivability is impaired.
[0007]
The present invention has been made paying attention to such a conventional problem, and suppresses generation of a torque step at the time of switching between stratified combustion for raising the exhaust gas temperature and homogeneous combustion, and stable operability can be obtained. An object of the present invention is to provide a control apparatus for a direct injection spark ignition internal combustion engine.
[0008]
[Means for Solving the Problems]
For this reason, the invention according to claim 1
When switching combustion from homogeneous combustion in which a homogeneous air-fuel mixture is formed and burned to the entire combustion chamber when ignition is performed to stratified combustion in which an air-fuel ratio is richer than the stoichiometric air-fuel ratio around the spark plug and burned. While performing homogeneous combustion, gradually retard the ignition timing until the ignition timing that makes it possible to eliminate the torque step at the time of combustion switching, and simultaneously advance the retard correction amount at the same time as switching of combustion, and the stratified combustion The ignition timing is gradually retarded until the ignition timing reaches the maximum retardation within the engine stability limit. It is characterized by correcting.
[0009]
Moreover, as shown in FIG.
A fuel injection valve that directly injects fuel into the combustion chamber of the engine;
A spark plug for spark ignition of the air-fuel mixture in the combustion chamber,
Stratified combustion control means for controlling the fuel injection amount, fuel injection timing, and ignition timing so that a stratified mixture whose air-fuel ratio is richer than stoichiometry is formed around the spark plug and burned;
Homogeneous combustion control means for controlling the fuel injection amount, fuel injection timing, and ignition timing so as to form a homogeneous air-fuel mixture in the entire combustion chamber and burn it,
Combustion switching means for switching between stratified combustion by the stratified combustion control means and homogeneous combustion by the homogeneous combustion control means according to the engine operation request;
At the time of switching from homogeneous combustion to stratified combustion, the ignition timing is gradually corrected until the ignition timing at which the torque difference at the time of switching the combustion can be eliminated while performing the homogeneous combustion, and at the same time as the switching of the combustion, The angle correction is advanced at once, and the ignition timing is gradually retarded to the ignition timing that reaches the maximum retardation within the engine stability limit while performing the stratified combustion. It is characterized by including a combustion switching ignition timing correcting means for correcting.
[0010]
According to the invention according to claim 1 or claim 2,
When there is a request to raise the exhaust gas temperature, the stratified charge combustion control means controls the fuel injection amount of the fuel injection valve, the fuel injection timing, and the ignition timing of the ignition plug). A rich stratified mixture is formed and burned. In this way, since the stratified mixture has an air-fuel ratio richer than stoichiometric, incomplete combustion products (CO) are generated by main combustion, and the incomplete combustion products are recombusted in the combustion chamber and exhaust passage after main combustion. As a result, the exhaust temperature rises and the exhaust purification catalyst is activated.
[0011]
In addition, homogeneous combustion is required at low temperature starting or after the activation of the exhaust purification catalyst. (The homogeneous combustion control means controls the fuel injection amount, fuel injection timing, and ignition timing to produce a homogeneous mixture in the entire combustion chamber. To form and burn.
[0014]
And from homogeneous combustion When switching to stratified combustion for increasing the exhaust gas temperature, it is necessary to compensate for an increase in torque in order to eliminate a decrease in torque when switching to stratified combustion with low thermal efficiency. However, in homogeneous combustion, since the normal ignition timing is controlled by MBT (maximum torque generation ignition timing), it is not possible to perform ignition timing correction control for correcting torque increase (no advance angle allowance). ).
[0016]
So when switching Gradually increase the ignition timing until you can secure an advance angle that allows torque increase correction Retard the torque step When the ignition timing correction that can be eliminated becomes possible, the ignition timing correction corresponding to the torque step elimination is performed at once. Furthermore, after switching to combustion, change the ignition timing. While performing stratified combustion after switching, until the ignition timing reaches the maximum retarded angle within the engine stability limit Gradually correct the ignition timing.
[0017]
In this way, the torque step at the time of switching the combustion can be reliably eliminated, and the ignition timing can be gradually changed in each combustion before and after the switching, so that the torque can be prevented from changing suddenly during this time.
[0018]
Also, Claim 3 The invention according to
The intake air amount is corrected so as to eliminate the torque change accompanying the ignition timing change in each combustion state.
[0019]
Claim 3 According to the invention according to
When the ignition timing is gradually changed in each combustion state, when the ignition timing is changed in the retarded direction, the torque tends to decrease due to the retarded angle, so that the intake air is eliminated so as to eliminate the decrease in the torque. When the amount is corrected to increase and the ignition timing is changed in the advance direction, the torque tends to increase due to the advance, so the intake air amount is corrected to decrease so as to eliminate the increase in torque.
[0020]
As a result, the torque change can be suppressed as much as possible from the time when the combustion switching request is generated until the target ignition timing in the steady state after the combustion switching is reached.
Also, Claim 4 The invention according to
The stratified combustion is performed by dividing fuel injection into an intake stroke and a compression stroke, and a fuel mixture in which the air-fuel ratio is leaner than stoichiometric is formed in the entire combustion chamber by fuel injection in the intake stroke, and fuel in the compression stroke is formed. It is characterized in that an air-fuel mixture having a richer air-fuel ratio than stoichiometric is formed around the spark plug by injection, and the air-fuel mixture is combusted.
[0021]
Claim 4 According to the invention according to
A homogeneous mixture is formed in the entire combustion chamber by the fuel injected in the intake stroke, and then a stratified mixture whose air-fuel ratio is richer than stoichiometric is formed around the spark plug by the fuel injected in the compression stroke.
[0022]
As a result, the rich stratified mixture around the spark plug is mainly burned, and the incompletely combusted product (CO) generated by the main combustion is reburned together with the lean mixture, and flames reach the corners of the combustion chamber. Can be propagated well, so that the low temperature region (quenching area) in the combustion chamber can be a small region that is the same as that in the homogeneous combustion. Furthermore, since the excess oxygen in the region where the lean air-fuel mixture burns remains after the main combustion, the temperature of the remaining oxygen at the end of the main combustion is also relatively high, and the CO re-combustion is more Proceed quickly.
[0023]
Also, Claim 5 The invention according to
In the stratified combustion, the ratio of fuel injection in the intake stroke in the vicinity of the switching region to homogeneous combustion is increased.
[0024]
Claim 5 According to the invention according to
When stratified combustion for increasing the exhaust gas temperature is performed in the vicinity of the switching region for homogeneous combustion, the ratio of fuel injection in the intake stroke is set to be larger than that in the case where the fuel is separated from the switching region.
[0025]
As a result, the ratio of the homogeneous air-fuel mixture formed in the entire combustion chamber is increased by the fuel injection in the intake stroke, and the state close to the homogeneous combustion is switched to the homogeneous combustion. Can be reduced. Therefore, it becomes easy to perform the combustion switching control by the ignition timing control, and even when the ignition timing is gradually changed as described above, the change period can be shortened to quickly switch the combustion.
[0026]
Also, Claim 6 The invention according to
In the stratified combustion, the air-fuel ratio of the air-fuel mixture that is unevenly distributed around the spark plug at the time of ignition is richer than the stoichiometric air-fuel ratio that can be ignited, and the air-fuel ratio is in an atomized state that can be ignited The fuel injection amount and the fuel injection timing are controlled by controlling the ignition timing of the spark plug.
[0027]
Claim 6 According to the invention according to
The fuel injection amount and fuel injection timing that are injected from the fuel injection valve into the combustion chamber during the compression stroke are controlled, and the state of the air-fuel mixture formed thereby is unevenly distributed around the spark plug when ignition is performed. The ignition timing is controlled so that the air-fuel ratio of the air is richer than the stoichiometric air-fuel ratio and can be ignited.
[0028]
As a result, the air-fuel ratio of the air-fuel mixture that is unevenly distributed around the spark plug becomes a rich air-fuel ratio with good ignitability, and a sufficient atomization time of the injected fuel is ensured, so that stable ignition is always obtained, CO can be generated stably.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
In FIG. 2 showing the system configuration of the first embodiment of the present invention, an air flow meter 3 for detecting the intake air flow rate Qa and a throttle valve 4 for controlling the intake air flow rate Qa are provided in the intake passage 2 of the engine 1. A fuel injection valve 5 is provided facing the combustion chamber of each cylinder.
[0030]
The fuel injection valve 5 is driven to open by a drive pulse signal set in a control unit 50, which will be described later, and burns fuel that is pumped from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator (not shown). It can be directly injected into the room.
[0031]
A spark plug 6 that is mounted facing the combustion chamber and ignites the intake air-fuel mixture based on an ignition signal from the control unit 50 is provided in each cylinder.
[0032]
On the other hand, in the exhaust passage 7, an air-fuel ratio sensor 8 (an oxygen sensor that performs rich / lean output) detects the air-fuel ratio of the exhaust gas mixture by detecting the concentration of a specific component (for example, oxygen) in the exhaust gas. Or a wide area air-fuel ratio sensor that linearly detects the air-fuel ratio over a wide area), and an exhaust purification catalyst 9 for purifying exhaust gas is provided downstream thereof. Has been. The exhaust purification catalyst 9 performs oxidation of CO, HC and reduction of NOx in the exhaust in the vicinity of stoichiometric, that is, the theoretical air-fuel ratio {λ = 1, A / F (air weight / fuel weight) · 14.7}. A three-way catalyst that can purify the exhaust gas or an oxidation catalyst that oxidizes CO and HC in the exhaust gas can be used.
[0033]
Further, a downstream oxygen sensor 10 that detects the concentration of a specific component (for example, oxygen) in the exhaust and outputs a rich lean gas is provided on the exhaust downstream side of the exhaust purification catalyst 9.
[0034]
Here, in order to suppress a control error associated with deterioration of the air-fuel ratio sensor 8 or the like by correcting the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 8 based on the detection value of the downstream oxygen sensor 10. Although the downstream oxygen sensor 10 is provided (for the so-called double air-fuel ratio sensor system), it is necessary to perform the air-fuel ratio feedback control based on the detected value of the air-fuel ratio sensor 8. The downstream oxygen sensor 10 can be omitted. When air-fuel ratio feedback control is not performed, both the air-fuel ratio sensor 8 and the downstream oxygen sensor 10 can be omitted.
[0035]
In the present embodiment, the 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 predetermined time, or The engine rotational speed Ne can be detected by measuring the cycle of the crank reference angle signal.
[0036]
A water temperature sensor 12 that is provided facing the cooling jacket of the engine 1 and detects the cooling water temperature Tw in the cooling jacket is provided.
Further, a throttle sensor 13 (which can also function as an idle switch) for detecting the opening degree of the throttle valve 4 is provided.
[0037]
By the way, in this embodiment, the throttle valve control apparatus 14 which can control the opening degree of the said throttle valve 4 with actuators, such as a DC motor, is provided.
[0038]
The throttle valve control device 14 electronically controls the opening degree of the throttle valve 4 based on the drive signal from the control unit 50 so that the required torque calculated based on the driver's accelerator pedal operation amount and the like can be achieved. Can be configured.
[0039]
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 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 drive the fuel injection amount (fuel The amount of supply) is controlled, the ignition timing is set, and the ignition plug 6 is ignited at the ignition timing.
[0040]
Note that, for example, stratified combustion is performed by injecting fuel into the combustion chamber in a compression stroke in a predetermined operation state (low / medium load region, etc.) and forming a combustible air-fuel mixture in the vicinity of the spark plug 6 in the combustion chamber. On the other hand, in other operating conditions (high load region, etc.), fuel can be injected into the combustion chamber during the intake stroke, so that an air-fuel mixture with a substantially uniform mixing ratio can be formed in the entire cylinder so that homogeneous combustion can be performed. The fuel injection timing (injection timing) can also be changed according to the operating state.
[0041]
By the way, in the control unit 50 according to the present embodiment, the exhaust purification catalyst 9 is activated early while suppressing the discharge of HC into the atmosphere from the start to the activation of the exhaust purification catalyst 9. In order to achieve this, input signals from various sensors such as the key switch 16 are received and, for example, the following control is performed. In the embodiment illustrated in the present specification, the average air-fuel ratio in the combustion chamber is substantially stoichiometric when performing the second stratified combustion for increasing the exhaust gas temperature according to the present invention, so this combustion form is stratified stoichiometric combustion. It expresses.
[0042]
Specifically, for example, a flowchart as shown in FIG. 3 is executed.
In step (denoted as S in the figure, hereinafter the same) 1, it is determined whether the ignition signal of the key switch 16 is turned ON (the key position is set to the ignition ON position) by a method similar to the prior art. To do. If YES, the process proceeds to Step 2, and if NO, this flow ends.
[0043]
In step 2, it is determined whether or not the start signal of the key switch 16 is turned on (whether the key position is set to the start position) by a method similar to the prior art. That is, it is determined whether or not there is a cranking request by a starter motor (not shown).
[0044]
If YES, it is determined that there is a start 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 starter motor is started and the engine 1 is cranked as in the prior art.
[0045]
In step 4, as in the prior art, fuel injection for start-up (direct fuel injection in the intake stroke, see FIG. 5B) is performed, and the engine 1 is operated (direct injection homogeneous combustion).
[0046]
In the next step 5, it is determined whether or not the exhaust purification catalyst 9 is not activated. The determination can be replaced by, for example, determining whether the downstream oxygen sensor 10 provided facing the exhaust passage 7 is not activated. That is, whether or not the exhaust purification catalyst 9 is activated can be determined based on the state of change in the detection value number of the downstream oxygen sensor 10.
[0047]
Further, the engine water temperature Tw or the oil temperature or the like is detected to estimate the temperature (or the outlet temperature) of the exhaust purification catalyst 9, and activation of the exhaust purification catalyst 9 can be determined based on the result, or directly. Further, it can also be determined by detecting the temperature (or outlet temperature) of the exhaust purification catalyst 9.
[0048]
If the catalyst is not activated (if YES), go to step 6.
On the other hand, if the catalyst is activated (if NO), it is determined that there is no need for control for promoting the catalyst activation, and the process proceeds to step 10, and in order to improve fuel consumption, etc. Combustion is performed in the combustion mode, and this flow is finished.
[0049]
In Step 6, it is determined whether or not the temperature of the piston 15 (particularly the surface temperature of the crown recess) is equal to or higher than a predetermined temperature (stratified stoichiometric combustion transition allowable temperature). Such a determination can be made by directly detecting with a thermocouple or the like embedded in the piston 15 (especially the crown), or by detecting the engine water temperature Tw or the oil temperature, the piston (especially the crown) temperature is determined. It is also possible to perform estimation and perform based on the result.
[0050]
Specifically, for example, the simulation can be performed based on the pseudo water temperature TWF correlated with the piston crown surface temperature, the pseudo water temperature TWF correlated with the piston crown surface temperature is estimated, and the result is a predetermined value. This can be done depending on whether TWF1 (stratified stoichiometric combustion transition permission temperature) has been reached or not (see FIGS. 6 and 7 of Japanese Patent Application No. 11-46612).
[0051]
In the case of YES, it is assumed that even if stratified stoichiometric combustion for promoting catalyst activation, which will be described later, is performed, good ignitability, combustibility, and engine stability (engine operability) are obtained. Proceed to
[0052]
On the other hand, in the case of NO, if the stratified stoichiometric combustion for promoting the activation of the catalyst described later is performed, the piston crown surface temperature is lower than a predetermined value, so the mist of the stratified mixture using the piston crown surface The transition to stratified stoichiometric combustion is prohibited as there is a possibility that ignition and vaporization promotion will not be carried out well, and there is a possibility that the ignitability, combustion stability and engine stability (engine driveability) will decrease. Then, the routine returns to step 4 in order to continue the direct fuel injection (direct injection homogeneous combustion) in the intake stroke.
[0053]
In Step 7, when the catalyst is not activated, it is necessary to promote the activation of the catalyst, and the piston crown surface temperature is equal to or higher than the predetermined temperature so that the stratified mixture can be generated satisfactorily. In order to prioritize the driving performance under the driving conditions where high output is required, homogeneous combustion is performed, so that it is set according to the operating region determined by the engine speed and load as shown in FIG. A combustion method is determined according to a combustion switching map or the like. And if it is the operation range which performs stratified stoichiometric combustion in this map, it will progress to Step 8, and will shift to stratified stoichiometric combustion for catalyst activation promotion, and will perform stratified stoichiometric combustion. If homogeneous combustion is set in the operation region, the process proceeds to step 4 and homogeneous combustion is selected even after stratified stoichiometric combustion is once started.
[0054]
In step 8, stratified stoichiometric combustion is performed after control for eliminating a torque step, which will be described later, is performed. Specifically, for example, about 50 of the total fuel amount {fuel weight necessary to achieve a substantially stoichiometric (theoretical air-fuel ratio)} that can be almost completely burned with the amount of intake air per combustion cycle, for example, about 50 % To approximately 90% of the fuel weight is injected and supplied into the combustion chamber in the intake stroke to form a homogeneous mixture that is relatively leaner than the stoichiometric air in the entire combustion chamber {the fuel shown in FIG. 5B The remaining fuel weight of about 50% to about 10% is injected and supplied into the combustion chamber in the compression stroke, and the air-fuel mixture is relatively richer (higher fuel concentration) than the stoichiometry around the spark plug 6. Are formed in layers {see FIG. 5 (A)} and burned (see FIG. 6).
[0055]
The stratified stoichiometric combustion mode is such that the air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel ratio formed in the combustion chamber during the intake stroke (by the intake stroke injection in this embodiment) is 16 to 28, and the fuel during the compression stroke The share ratio between the fuel injection amount during the intake stroke and the fuel injection amount during the compression stroke is set so that the air-fuel ratio of the air-fuel mixture richer than the stoichiometry formed around the spark plug by injection becomes 9-13. You may make it set.
[0056]
Further, if the air-fuel ratio of each air-fuel mixture is set in the above range, the average air-fuel ratio in the combustion chamber is set to an air-fuel ratio (for example, a range of 13.8 to 18) slightly deviated from the stoichiometric air-fuel ratio. Also good.
[0057]
According to the stratified stoichiometric combustion as described above, it is possible not only to raise the exhaust temperature as compared with the conventional homogeneous stoichiometric combustion, but also to reduce the amount of unburned HC discharged from the combustion chamber to the exhaust passage. .
[0058]
That is, according to the stratified stoichiometric combustion, the conventional combustion mode {combustion mode in which only homogeneous combustion, only stratified combustion, or additional fuel is injected after the later stage of combustion (after the expansion stroke or during the exhaust stroke)} Compared with the case where the engine is warmed up, the early activation of the exhaust purification catalyst 9 is greatly promoted while suppressing the emission of HC into the atmosphere between the start of start and the exhaust purification catalyst 9 being activated. It will be possible.
[0059]
Next, in step 9, as in step 5, it is determined whether or not the exhaust purification catalyst 9 has been activated (whether the warm-up has been completed). If yes, go to step 10. If NO, the routine returns to step 8 where stratified stoichiometric combustion is continued until the exhaust purification catalyst 9 is activated.
[0060]
In step 10, a combustion mode (homogeneous stoichiometric combustion, homogeneous lean combustion, stratified lean combustion, etc.) that can achieve desired exhaust performance, fuel efficiency performance, driving performance (output performance, stability, etc.), etc., depending on the operating conditions After shifting to, this flow ends. However, immediately after it is determined that the exhaust purification catalyst 9 has been activated, switching to homogeneous stoichiometric combustion is performed so that the torque step between homogeneous combustion, particularly stratified stoichiometric combustion, can be reduced.
[0061]
In the present embodiment, the transition to the stratified stoichiometric combustion is prohibited in an operating state that may adversely affect the flammability of the stratified stoichiometric combustion (for example, when the piston crown surface temperature is lower than a predetermined temperature). However, when it is desired to give the highest priority to the early activation of the exhaust purification catalyst 9, such a configuration may not be adopted (that is, step 6 in the flowchart of FIG. 3 is omitted). Can also be done).
[0062]
Next, the control according to the present invention for suppressing the torque step at the time of switching between the stratified stoichiometric combustion and the homogeneous combustion before and after that will be described.
First, ignition timing correction control at the time of switching from homogeneous combustion to stratified stoichiometric combustion will be described with reference to the flowchart shown in FIG.
[0063]
In step 11, it is determined whether or not stratified stoichiometric combustion is permitted (when stratified stoichiometric combustion is selected in step 7 of FIG. 3).
When stratified stoichiometric combustion is permitted, that is, when there is a request for switching from the current homogeneous combustion to stratified stoichiometric combustion for increasing the exhaust gas temperature, the routine proceeds to step 12 where the torque step at the time of combustion switching is set. Ignition timing retardation correction control necessary for suppression is started, and the initial value of the retardation ratio is set to 0%.
[0064]
That is, when switching from homogeneous combustion to stratified stoichiometric combustion, it is necessary to compensate for an increase in torque in order to eliminate the torque drop when switching to stratified stoichiometric combustion with low thermal efficiency. Since it is controlled to MBT (maximum torque generation ignition timing) so as to achieve a predetermined fuel consumption (or engine stability), there is no ignition timing advance correction allowance for increasing the torque. Therefore, correction is performed to gradually retard the ignition timing until an advance angle that can correct torque increase at the time of combustion switching can be secured.
[0065]
In step 13, in order to perform the retardation correction gradually, the retardation ratio is incremented by a predetermined amount. Specifically, the retardation rate is increased by a% (for example, 1%) every unit time (for example, 10 ms).
[0066]
In step 14, a retardation amount is calculated. Specifically, first, based on the engine rotational speed and the load (basic fuel injection amount Tp, etc.), an advance angle correction allowance that enables torque increase correction that can eliminate a torque step at the time of combustion switching can be secured. The target retard ignition timing is calculated by searching from a map or the like, and the successive retard amount is calculated by the following equation.
[0067]
Retard amount = (MBT−target retard ignition timing) × retard rate
In step 15, the ignition timing is finally calculated by the following equation.
Ignition timing = MBT-retard amount
In this way, after the combustion switching request is generated, the ignition timing is gradually retarded to approach the target retard ignition timing (FIG. 8 [A] → [B]).
[0068]
In step 16, it is determined whether or not the target retard ignition timing has been reached based on whether the retard ratio has reached 100% or the like, and the process returns to step 13 until the target retard ignition timing is reached, and gradually. Delay angle correction.
[0069]
When it is determined that the target retarded ignition timing has been reached, the routine proceeds to step 17 where the combustion is switched from homogeneous combustion to stratified stoichiometric combustion. Specifically, as shown in step 7 of FIG. 3, the fuel injection from the fuel injection valve 5 is switched from intake stroke injection to intake stroke injection and compression stroke injection (split injection) to switch to stratified stoichiometric combustion.
[0070]
Further, the routine proceeds to step 18, and the ignition timing is returned to the MBT before the start of the retardation correction by setting the retardation ratio to 0 simultaneously with the combustion switching (FIG. 8 [B] → [C]). That is, by correcting the total retardation correction amount in the advance direction at once, occurrence of a torque step (a in FIG. 8) at the time of combustion switching is eliminated. Thereby, stable drivability can be ensured.
[0071]
In step 19 and subsequent steps, control is performed to gradually approach the optimum target ignition timing in the stratified stoichiometric combustion after the switching.
First, in step 19, the retardation ratio is incremented by a predetermined amount. Specifically, similarly to the step 13, the retardation rate is increased by a% (for example, 1%) every unit time (for example, 10 ms).
[0072]
Then, in step 20, a sequential retardation amount is calculated. That is, based on the engine speed and load (basic fuel injection amount Tp, etc.), the target retarded ignition timing in stratified stoichiometric combustion is calculated by searching from a map, etc. Is calculated.
[0073]
Retard amount = (MBT−target retard ignition timing) × retard rate
Here, the target retarded ignition timing in the stratified stoichiometric combustion is, for example, retarded to the maximum (retard) within the engine stability limit (operability). In this way, the exhaust temperature can be raised to the maximum. However, the ignition timing may be retarded to such an extent that engine stability equivalent to that of the conventional combustion mode is achieved. Even in this case, the ignition timing can be significantly retarded with respect to the conventional case by stratified stoichiometric combustion. Therefore, the effect of increasing the exhaust temperature can be greater than that of the conventional one.
[0074]
In step 21, the ignition timing is finally calculated by the following equation.
Ignition timing = MBT-retard amount
In this way, after switching to combustion, the ignition timing is gradually retarded to approach the target retarded ignition timing in stratified stoichiometric combustion (FIG. 8 [C] → [D]).
[0075]
In step 22, it is determined whether or not the target retard ignition timing has been reached based on whether or not the retard ratio has reached 100%, etc., and the process returns to step 19 until the target retard ignition timing is reached, and gradually retards. Let the angle be corrected.
[0076]
In this way, it is possible to eliminate the torque step at the time of switching from the homogeneous combustion for starting to the stratified stoichiometric combustion for increasing the exhaust temperature.
Next, ignition timing correction control at the time of switching from the stratified stoichiometric combustion to the homogeneous combustion will be described with reference to the flowchart shown in FIG.
[0077]
In step 31, it is determined whether or not homogeneous (stoichiometric) combustion is permitted (when homogeneous combustion is selected in step 7 or step 10 of FIG. 3).
When homogeneous combustion is permitted, that is, when the warm-up is completed from the current stratified stoichiometric combustion and the exhaust purification catalyst 9 is activated, or a request for switching to homogeneous combustion is generated due to an operation region change due to acceleration or the like. When it is, the routine proceeds to step 32, where ignition timing advance correction control necessary to suppress the torque step during combustion switching is started. At this time, the initial value of the retardation ratio is set to 100%.
[0078]
That is, when switching from stratified stoichiometric combustion to homogeneous combustion, it is necessary to compensate for a decrease in torque in order to eliminate an increase in torque when switching to homogeneous combustion with high thermal efficiency. However, as described above, in this embodiment, stratified stoichiometric combustion is performed. Since the ignition timing in combustion is retarded as much as possible within the engine stability limit, if retarding beyond this, the operation becomes unstable, so that it is practically impossible to perform retard correction. Therefore, correction is performed to gradually advance the ignition timing until a retard angle that allows torque reduction correction at the time of combustion switching is secured.
[0079]
In step 33, the retard ratio is decremented by a predetermined amount in order to gradually perform the advance correction. Specifically, the retardation rate is decreased by a% (for example, 1%) every unit time (for example, 10 ms).
[0080]
In step 34, the retardation amount is calculated. Specifically, first, based on the engine speed and load (basic fuel injection amount Tp, etc.), the MBT of the ignition timing in the homogeneous combustion after the combustion switching is calculated by searching from a map, etc. Based on the ignition timing in the stratified stoichiometric combustion, that is, the target retarded ignition timing, the successive retard amount is calculated by the following equation.
[0081]
Retard amount = (MBT−target retard ignition timing) × retard rate
In step 35, the ignition timing is finally calculated by the following equation.
Ignition timing = MBT-retard amount
In this way, after the combustion switching request is generated, the ignition timing is gradually advanced to approach the MBT during the homogeneous combustion (FIG. 8 [D] → [C]).
[0082]
In step 36, it is determined whether or not the MBT has been reached based on whether or not the retardation ratio has reached 100%. The process returns to step 33 until the MBT is reached, and the lead angle is gradually corrected.
[0083]
When it is determined that the MBT has been reached, the routine proceeds to step 37 where the combustion is switched from stratified stoichiometric combustion to homogeneous combustion. Specifically, the fuel injection from the fuel injection valve 5 is switched to the injection of only the intake stroke, and the combustion is switched to homogeneous combustion.
[0084]
Further, the routine proceeds to step 38, and simultaneously with the combustion switching, the ignition timing is corrected by a predetermined amount corresponding to the torque increase cancellation at the time of combustion switching at once, so that the target for eliminating the torque step in the homogeneous combustion is corrected. Switching to the retarded ignition timing (FIG. 8 [C] → [B]). Thereby, generation | occurrence | production of the torque level difference (a of FIG. 8) at the time of combustion switching can be eliminated, and the stable operativity can be ensured.
[0085]
In step 39 and subsequent steps, control is performed to gradually approach MBT in the homogeneous combustion after the switching.
First, in step 39, the retardation ratio is decremented by a predetermined amount. Specifically, similarly to the step 33, the retardation ratio is decreased by a% (for example, 1%) every unit time (for example, 10 ms).
[0086]
Then, in step 40, the sequential retardation amount is calculated. That is, based on the MBT in the homogeneous combustion and the target retarded ignition timing immediately after the combustion is switched to eliminate the torque step, the successive retard amount is calculated by the following equation.
[0087]
Retard amount = (MBT−target retard ignition timing) × retard rate
In step 41, the ignition timing is finally calculated by the following equation.
Ignition timing = MBT-retard amount
In this way, after switching to combustion, the ignition timing is gradually retarded to approach MBT in homogeneous combustion (FIG. 8 [B] → [A]).
[0088]
In step 42, it is determined whether or not the MBT has been reached based on whether or not the retardation ratio has become 0%, etc., and the process returns to step 39 until the target retard ignition timing is reached, and the advance angle is gradually corrected.
[0089]
In this way, it is possible to eliminate a torque step at the time of switching from stratified stoichiometric combustion for increasing the exhaust gas temperature to homogeneous combustion after completion of warm-up.
Further, as described above, the delay correction in the homogeneous combustion and the stratified stoichiometric combustion during the period from when the request for the combustion switching occurs until the actual combustion is switched and during the transition to the target ignition timing after the combustion switching. Since the advance angle correction is performed gradually, the torque change due to the retard angle correction or the advance angle correction can be made gradual. However, in order to eliminate the torque change, the intake air amount correction is performed. The intake air amount correction control at the time of the combustion switching will be described with reference to the time chart of FIG. 11 according to the flowchart of FIG. It should be noted that when the advance of the ignition timing is corrected, the intake air amount is corrected in a decreasing direction so as to suppress an increase in torque. However, in this embodiment, the MBT during homogeneous combustion including the advance correction is used. Is set as an increase correction amount of the intake air amount, and at the time of advance correction, the intake air amount is corrected to decrease by decreasing the increase correction amount.
[0090]
In FIG. 10, in step 51, it is determined whether the combustion is homogeneous combustion or stratified stoichiometric combustion.
When it is determined that the combustion is homogeneous, the routine proceeds to step 52, where the amount of retardation at the time of homogeneous combustion, that is, the amount of retardation set for the MBT at the time of homogeneous combustion before switching to the stratified stoichiometric combustion (see FIG. 7) or the retard amount set for the MBT after switching to the homogeneous combustion (step 39 in FIG. 9) so as to correct the torque decrease due to the retard amount with respect to the MBT. The amount of increase correction of the air amount is calculated.
[0091]
For simplicity, the increase correction amount of the intake air amount is proportionally calculated with respect to the retard amount as in the following equation (the same applies hereinafter).
Increase correction amount [L / min] = retard amount [deg] x air amount [L / min / deg]
Further, when it is determined in step 51 that the stratified stoichiometric combustion is performed, the routine proceeds to step 53, where the intake air amount increase correction control based on the MBT at the time of homogeneous combustion is performed. An increase correction amount for the intake air amount is calculated for the retard amount obtained by adding the retard amount calculated for MBT in the stratified stoichiometric combustion to the retard amount. That is, after switching to stratified stoichiometric combustion in FIG. 7, the intake air amount for the retard amount obtained by adding the retard amount at the retard rate of 100% set in step 14 and the retard amount calculated in step 20. 9 is calculated, and the stratified stoichiometric combustion before switching to the homogeneous combustion in FIG. 9 is performed at the retardation ratio 100% calculated in step 14 of FIG. 7 before switching to the stratified stoichiometric combustion. An increase correction amount for the intake air amount is calculated for the retard amount obtained by adding the retard amount and the retard amount calculated in step 34 of FIG. Or it is calculated similarly even if the increase correction amount for the retard amount in the stratified stoichiometric combustion is added to the increase correction amount at the time of combustion switching.
[0092]
In step 54, the opening degree of the throttle valve 4 is corrected and controlled based on the increase correction amount of the intake air amount calculated for each combustion.
In this way, the torque change can be suppressed until the target ignition timing in the steady state after the combustion switching occurs after the combustion switching request is generated, and the drivability at the time of combustion switching is as stable as possible. Can be made.
[0093]
Further, as described above, in the present embodiment, fuel injection is performed by dividing into the intake stroke and the compression stroke at the time of stratified stoichiometric combustion. In this case, in the vicinity of the switching region from stratified stoichiometric combustion to homogeneous combustion, FIG. As shown, the injection ratio in the intake stroke is increased (in the figure, the injection ratio in the compression stroke is shown).
[0094]
However, the present invention can also be applied to stratified stoichiometric combustion in which injection is performed only in the compression stroke, an air-fuel mixture layer richer than stoichiometric is formed around the spark plug, and the outer combustion chamber space is an air layer. In this case as well, the average air-fuel ratio in the combustion chamber is preferably in the vicinity of the stoichiometric range.
[0095]
In addition, it is preferable to retard the ignition timing in the steady state during the stratified stoichiometric combustion as compared with the stratified lean combustion as in this embodiment or the like. However, according to the stratified stoichiometric combustion, even if the ignition timing is set to MBT, Since the ignition timing can be retarded with respect to the MBT in the combustion mode and the engine stability can be improved, both the engine stability and the exhaust gas temperature rise can be achieved at a high level. Applicable to the present invention.
[0096]
That is, the present invention is a stratified combustion capable of generating an incomplete combustion gas and raising an exhaust gas temperature by forming a stratified mixture rich in air-fuel ratio around the spark plug and richer in stoichiometry, Any engine that switches between homogeneous combustion is applicable.
[0097]
Further, in the present embodiment, since the intake stroke injection is also performed by the fuel injection valve 5 that directly injects into the combustion chamber, the layout is easy with the cost reduction, but the fuel injection valve that performs the intake stroke injection is used as the intake port. The arrangement may be sufficient, and there is a merit that the injection amount accuracy can be improved by using a low flow rate fuel injection valve.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of the present invention.
FIG. 2 is a system configuration diagram according to the embodiment of the present invention.
FIG. 3 is a flowchart for explaining control in the embodiment.
FIG. 4 is a combustion switching map used for switching combustion according to an operation region in the embodiment.
FIG. 5A is a schematic diagram for explaining direct injection compression stroke injection. (B) is a schematic diagram for explaining direct injection intake stroke injection. (C) is a top view at the time of fuel injection.
FIG. 6 is a view for explaining the state of air-fuel mixture formation in the combustion chamber of the stratified stoichiometric combustion mode according to the present invention.
FIG. 7 is a flowchart for explaining control at the time of switching combustion when switching from homogeneous combustion to stratified stoichiometric combustion in the embodiment.
FIG. 8 is a diagram showing a state of ignition timing control when switching between homogeneous combustion and stratified stoichiometric combustion.
FIG. 9 is a flowchart for explaining control during combustion switching when switching from stratified stoichiometric combustion to homogeneous combustion in the same embodiment;
FIG. 10 is a flowchart for explaining intake air amount correction control for correcting a torque change associated with ignition timing control in the embodiment;
FIG. 11 is a diagram showing the intake air amount correction control.
FIG. 12 is a diagram showing a division ratio between intake stroke injection and compression stroke injection in a region in the vicinity of switching from stratified stoichiometric combustion to homogeneous combustion in the embodiment;
[Explanation of symbols]
1 Internal combustion engine
4 Throttle valve
5 Fuel injection valve
6 Spark plug
7 Exhaust passage
8 Air-fuel ratio sensor
9 Exhaust gas purification catalyst
10 Downstream oxygen sensor
11 Crank angle sensor
13 Throttle sensor
14 Throttle valve control device
15 piston
50 Control unit

Claims (6)

When switching combustion from homogeneous combustion in which a homogeneous air-fuel mixture is formed and combusted throughout the combustion chamber during ignition to stratified combustion in which the air-fuel ratio is richer than the stoichiometric air-fuel ratio around the spark plug and burned. While performing homogeneous combustion, gradually retard the ignition timing until the ignition timing that makes it possible to eliminate the torque level difference at the time of combustion switching. A control device for a direct-injection spark ignition internal combustion engine, wherein the ignition timing is gradually corrected to an ignition timing that is at the most retarded angle within the engine stability limit . A fuel injection valve that directly injects fuel into the combustion chamber of the engine;
A spark plug for spark ignition of the air-fuel mixture in the combustion chamber,
Stratified combustion control means for controlling the fuel injection amount, fuel injection timing, and ignition timing so that a stratified mixture whose air-fuel ratio is richer than stoichiometry is formed around the spark plug and burned;
Homogeneous combustion control means for controlling the fuel injection amount, fuel injection timing, and ignition timing so as to form a homogeneous air-fuel mixture in the entire combustion chamber and burn it,
Combustion switching means for switching between stratified combustion by the stratified combustion control means and homogeneous combustion by the homogeneous combustion control means according to the engine operation request;
At the time of switching from homogeneous combustion to stratified combustion, the ignition timing is gradually corrected until the ignition timing at which the torque step at the time of combustion switching can be eliminated while performing the homogeneous combustion. Combustion switching ignition timing correction means for advancing the angle correction at a stretch and gradually correcting the ignition timing to the ignition timing that is at the most retarded angle within the engine stability limit while performing the stratified combustion A control device for a direct-injection spark-ignition internal combustion engine. 3. The control device for a direct injection spark ignition type internal combustion engine according to claim 2 , wherein the intake air amount is corrected so as to eliminate the torque change accompanying the ignition timing change in each combustion state. The stratified combustion is performed by dividing fuel injection into an intake stroke and a compression stroke, and a fuel mixture in which the air-fuel ratio is leaner than stoichiometric is formed in the entire combustion chamber by fuel injection in the intake stroke and fuel in the compression stroke 4. The direct eruption according to any one of claims 1 to 3 , wherein an air-fuel ratio is formed around the spark plug by injection and the air-fuel ratio is richer than stoichiometric, and the air-fuel mixture is combusted. Control device for a flower ignition type internal combustion engine. 5. The control device for a direct injection spark ignition type internal combustion engine according to claim 4 , wherein in the stratified combustion, a ratio of fuel injection is increased in an intake stroke in the vicinity of a switching region to homogeneous combustion. In the stratified combustion, the air-fuel ratio of the air-fuel mixture that is unevenly distributed around the spark plug at the time of ignition is richer than the stoichiometric air-fuel ratio that can be ignited, and the air-fuel ratio is in an atomized state that can be ignited. 6. The control apparatus for a direct injection spark ignition type internal combustion engine according to claim 1 , wherein the control is performed by controlling a fuel injection amount and a fuel injection timing in the engine and an ignition timing of the spark plug. .

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