JP2004028031A - Control device and method of direct injection spark ignition-type engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize the control of high quality by totally taking into consideration the exhaust temperature rise effect, the combustion stability, the HC performance and the smoke performance, in a case of the stratification stoichiometric combustion by performing the initial injection in an intake stroke and a later injection in a later half of compression stroke by dividing the fuel injection by a fuel injection valve 8, when the warming-up of an exhaust clarifying catalyst 16 is requested immediately after the starting. <P>SOLUTION: An injection period of the later injection by the fuel injection valve 8 is advanced, and simultaneously an ignition period by an ignition plug 9 is retarded, in accordance with the indication of higher engine temperature by a parameter correlated with the engine temperature. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device and a control method for a direct injection spark ignition engine.
[0002]
[Prior art]
As a conventional technique, there is one described in Japanese Patent Application Laid-Open No. 2000-73820.
This is because, in a direct injection spark ignition engine, when the exhaust gas purification catalyst is not warmed up, the fuel injection is divided into two times to perform early injection in the intake stroke and late injection in the compression stroke. On the other hand, when the engine temperature is higher than the predetermined temperature in the catalyst unwarmed state, the late injection (compression stroke injection) is retarded as compared with the case where the engine temperature is equal to or lower than the predetermined temperature.
[0003]
This reduces the amount of HC and other emissions from the engine when the catalyst is not warmed up, and increases the exhaust temperature to promote warming up of the catalyst. By adjusting the combustion state accordingly, the effects of improving emissions and promoting warm-up are enhanced while ensuring combustion stability.
[0004]
[Problems to be solved by the invention]
However, in the above-described conventional technology, the late injection (compression stroke injection) is retarded with an increase in the engine temperature when the catalyst is not warmed up, in order to obtain an effect of increasing the exhaust gas temperature while ensuring combustion stability. However, the smoke is not focused on, and the smoke increases when retarded in this way.
[0005]
It is an object of the present invention to realize better control when a warm-up request of an exhaust purification catalyst is taken into consideration in consideration of an exhaust gas temperature increasing effect, combustion stability, HC performance, and smoke performance.
[0006]
[Means for Solving the Problems]
For this reason, in the present invention, at the time of a warm-up request of the exhaust purification catalyst, the fuel injection is divided, the early injection and the late injection are performed by the ignition timing, and a parameter correlated with the engine temperature indicates that the engine temperature is high. The later the injection timing of the late injection is advanced.
[0007]
【The invention's effect】
According to the present invention, by setting the injection timing with the maximum effect by the engine temperature, it is possible to enhance the effects of improving emissions and promoting warm-up while ensuring combustion stability, and in particular, to significantly improve smoke performance.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a system configuration of an embodiment of the present invention, which will be described first.
A throttle valve 3 for controlling an intake air amount is provided in an intake passage 2 of the engine 1. The throttle valve 3 is an electronically controlled throttle valve driven by a throttle actuator 4 such as a DC motor, and the throttle opening is controlled based on a drive signal from the control unit 20.
[0009]
A fuel injection valve 8 faces a combustion chamber 7 of each cylinder defined by a cylinder head 5 and a piston 6 of the engine 1. A bowl (recess) 6a is formed on the crown of the piston 6 at a position eccentric to the intake side, and the fuel injection valve 8 is directed obliquely downward from the intake side.
At a predetermined time during the intake stroke or the compression stroke, the fuel injection valve 8 is energized by a solenoid in response to an injection pulse signal from the control unit 20 to open the valve, and directly injects fuel controlled to a predetermined pressure into the combustion chamber 7. I do.
[0010]
An ignition plug 9 is provided in the combustion chamber 7 of each cylinder so as to face from substantially the center of the cylinder head 5. The ignition plug 9 spark-ignites the air-fuel mixture based on an ignition signal from the control unit 20. I do.
When fuel is injected from the fuel injection valve 8 in the intake stroke, the injected fuel diffuses into the combustion chamber 7 to form a homogeneous mixture, and is ignited by the ignition plug 9 and burns. Such combustion is called homogeneous combustion, and is classified into homogeneous stoichiometric combustion, homogeneous lean combustion, and the like in combination with air-fuel ratio control.
[0011]
When fuel is injected from the fuel injection valve 8 in the compression stroke (particularly in the latter half), the injected fuel concentrates around the ignition plug 9 by riding on a tumble flow utilizing the bowl portion 6a on the piston crown. A stratified mixture is formed, and is ignited by the ignition plug 9 and burned. Such combustion is called stratified combustion, and usually has an extremely lean air-fuel ratio and is called stratified lean combustion.
[0012]
The fuel supply system to the fuel injection valve 8 will be described. The fuel in the fuel tank 10 is sucked by an electric low-pressure fuel pump 11, and the low-pressure fuel discharged from the low-pressure fuel pump 11 is a high-pressure fuel pump driven by an engine. 12 is supplied.
The pressure of the fuel discharged from the low-pressure fuel pump 11 and supplied to the high-pressure fuel pump 12 is adjusted to a predetermined low pressure by a low-pressure pressure regulator 13 provided in a return passage returning to the fuel tank 10.
[0013]
The high-pressure fuel discharged from the high-pressure fuel pump 12 is supplied to the fuel injection valve 8, and the fuel pressure is adjusted to a predetermined high pressure by a high-pressure pressure regulator 14 provided in a return passage returning to the suction side of the high-pressure fuel pump 12. Adjusted.
The high-pressure regulator 14 can continuously change the opening area of the return passage based on a control signal from the control unit 20, and thereby can control the fuel pressure to the fuel injection valve 8 arbitrarily.
[0014]
On the other hand, an exhaust purification catalyst 16 is disposed in the exhaust passage 15. As the exhaust purification catalyst 16, a three-way catalyst for oxidizing CO and HC in the exhaust gas and reducing NOx in the vicinity of the stoichiometric gas, or an oxidation catalyst for oxidizing CO and HC in the exhaust gas, or a three-way catalyst in the vicinity of the stoichiometric gas And a NOx trap catalyst or the like that traps NOx in the exhaust gas in the lean state and reduces and purifies the trapped NOx in the stoichiometric to rich state can be used.
[0015]
Signals from various sensors are input to the control unit 20 for controlling the engine.
The crank angle sensor 21 generates a crank reference angle signal and a crank unit angle signal in synchronization with engine rotation. The control unit 20 can detect the engine speed Ne by measuring the cycle of the crank reference angle signal from the crank angle sensor 21 or counting the crank unit angle signal for a certain period of time.
[0016]
The accelerator pedal sensor 22 detects a driver's accelerator pedal operation amount (accelerator opening) APO.
The air flow meter 23 is disposed upstream of the throttle valve 3 in the intake passage 2 and detects an intake air amount Qa.
The throttle sensor 24 detects the opening TVO of the throttle valve 3. Further, an idle switch which is turned ON when the throttle valve 3 is fully closed is also built in.
[0017]
The water temperature sensor 25 faces the water jacket of the engine 1 and detects a cooling water temperature (water temperature) Tw.
The fuel pressure sensor 26 is disposed in a fuel supply passage from the high-pressure fuel pump 12 to the fuel injection valve 8, and detects a fuel pressure (fuel pressure) Pf to the fuel injection valve 8.
The air-fuel ratio sensor 27 is disposed upstream of the exhaust gas purification catalyst 16 in the exhaust passage 15 and 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 the intake air-fuel mixture. And is used for air-fuel ratio feedback control.
[0018]
Further, an air-fuel ratio sensor 28 is disposed downstream of the exhaust purification catalyst 16. The downstream air-fuel ratio sensor 28 corrects the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 27 based on the detection value, thereby suppressing a control error due to the deterioration of the air-fuel ratio sensor 27 and the like. Used for
The control unit 20 includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like, and according to an operation state detected based on signals from the various sensors, The opening degree of the throttle valve 3 is controlled via the throttle actuator 4, the high pressure regulator 14 is controlled to control the fuel pressure to the fuel injection valve 8, the fuel injection timing and the fuel injection amount are set, and the fuel injection valve is controlled. 8, the fuel injection is controlled, the ignition timing is set, and the ignition plug 9 is ignited at the ignition timing.
[0019]
Then, the combustion mode is controlled according to the operating state. That is, during normal operation (after completion of warm-up of the exhaust purification catalyst 16), stratified lean combustion by compression stroke injection is performed, for example, in a low load region, while homogeneous stoichiometric combustion by intake stroke injection is performed, for example, in a high load region. Alternatively, a homogeneous lean combustion is performed.
Here, in the present invention, when a warm-up request of the exhaust purification catalyst 16 is made immediately after the start, the fuel injection is divided and the intake stroke injection and the compression stroke injection are performed, so that a relatively rich stratified shape around the ignition plug 9 is obtained. And a relatively lean air-fuel mixture is formed in the entire combustion chamber 7 surrounding the air-fuel mixture, and the overall air-fuel ratio is controlled to be substantially stoichiometric. Such a combustion mode is herein referred to as stratified stoichiometric combustion (stratified stoichiometric combustion by split injection).
[0020]
In the stratified combustion, for example, approximately 50 to 90% of the total fuel amount (fuel weight required to achieve a stoichiometric air-fuel ratio) that can be substantially completely burned with the intake air amount per combustion cycle As shown in FIG. 2 (A), the weight is injected in the intake stroke, and a leaner air-fuel mixture than the stoichiometric mixture is formed in the entire combustion chamber. Then, as shown in FIG. 2 (B), the remaining approximately 50 to 10% of the fuel weight is injected in the latter half of the compression stroke, and a mixture richer than the stoichiometric mixture is formed around the ignition plug 9 to form a layer. Burn.
[0021]
The concept of stratified stoichiometric combustion is as follows.
(1) A lean air-fuel mixture is formed in the vicinity of the combustion chamber wall surface by the intake stroke injection to secure O2 necessary for afterburning.
(2) A rich air-fuel mixture is formed around the spark plug by the compression stroke injection to improve the initial ignition performance, thereby improving the combustion stability.
(3) CO is generated by combustion of the rich air-fuel mixture to promote after-burning with O2 in the lean air-fuel mixture near the combustion chamber wall surface, thereby reducing HC and increasing exhaust gas temperature.
(4) The ignition timing can be retarded by improving the initial ignition performance, and the ignition timing is retarded to further increase the exhaust gas temperature due to the afterburning effect.
[0022]
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 amounts of HC and NOx discharged from the combustion chamber 7 to the exhaust passage 10 are reduced. be able to. Accordingly, the early activation of the exhaust purification catalyst 16 can be promoted while suppressing the emission of HC and NOx into the atmosphere from the start of the start until the exhaust purification catalyst 16 is activated.
[0023]
For this reason, the control unit 20 receives the input signals from the key switch 30 and the various sensors in addition to the key switch 30 during the period from the start of the start to the activation of the exhaust gas purification catalyst 16 (when the catalyst needs to be warmed up). The control as shown in the flowchart of FIG. 4 is performed.
FIG. 3 is a flowchart of the startup combustion control.
[0024]
In S1, it is determined whether or not the ignition signal of the key switch 30 is turned on (whether the key position is set to the ignition ON position). If YES, proceed to S2; if NO, end this flow.
In S2, it is determined whether or not the start signal of the key switch 30 has been turned on (the key position has been set to the START position). If YES, it is determined that there is a cranking request for starting, and the process proceeds to S3. If NO, it is determined that there is no cranking request yet, and the process returns to S1.
[0025]
In S3, the starter motor is started to drive and the engine is cranked in the same manner as in the prior art for starting.
In S4, for the start, homogeneous combustion (homogeneous stoichiometric combustion) by intake stroke injection is performed as in the conventional case.
In S5, it is determined whether the exhaust purification catalyst 16 is activated. This determination can be made based on whether or not the air-fuel ratio sensor 28 disposed downstream of the exhaust purification catalyst 16 in the exhaust passage 15 is activated (whether the rich / lean output is inverted). Of course, the temperature of the exhaust gas purification catalyst 16 may be detected directly or indirectly from the exhaust gas temperature, and the determination may be made based on the detected temperature. Alternatively, the temperature of the exhaust gas purification catalyst 16 may be estimated from the water temperature Tw, and the determination may be made based on the estimated temperature.
[0026]
If the exhaust purification catalyst 16 has not been activated (if NO), the process proceeds to S6. On the other hand, if the exhaust purification catalyst 16 has been activated (if YES), it is determined that there is no need to perform control for promoting catalyst activation, and the process proceeds to S8, in which a conventional normal combustion is performed to improve fuel efficiency. By the control, combustion is performed in a combustion mode (homogeneous stoichiometric combustion, homogeneous lean combustion, stratified lean combustion, etc.) according to the operation state, and the present flow ends.
[0027]
In S6, it is determined whether or not a condition for permitting stratified stoichiometric combustion by split injection for promoting catalyst activation is satisfied. Specifically, for example, when all of the following conditions (1) to (3) are satisfied, stratified stoichiometric combustion is permitted.
(1) The air-fuel ratio sensor 27 is activated (alternatively, a predetermined time has elapsed since the complete explosion). This is necessary when performing air-fuel ratio feedback control during stratified stoichiometric combustion. Since the air-fuel ratio sensor 27 is provided on the upstream side of the catalyst 16 and has a small heat capacity, the activation speed is extremely high as compared with the catalyst 16. In addition, since the air-fuel ratio sensor 27 can be forcibly heated (activated) by an electric heater or the like, the detection result of the air-fuel ratio sensor 27 during the stratified stoichiometric combustion (during the warm-up process of the catalyst 16) can be obtained. It is possible to perform air-fuel ratio feedback control based on the above.
[0028]
(2) Being idle. Specifically, it is confirmed that the idle switch is ON and that the engine speed Ne and the intake air amount Qa are within predetermined upper limit values to lower limit values, respectively.
(3) The water temperature Tw is equal to or higher than a predetermined value. This is because, when the water temperature Tw is lower than the predetermined value, the piston crown surface temperature is low, and the atomization and vaporization promotion of the stratified mixture using the piston crown surface are not performed well.
[0029]
If the conditions for permitting stratified stoichiometric combustion are not satisfied, the shift to stratified stoichiometric combustion by split injection is prohibited, and the process returns to S4 in order to continue homogeneous combustion by intake stroke injection.
If the conditions for permitting stratified stoichiometric combustion are satisfied, the process proceeds to S7.
In S7, stratified stoichiometric combustion by split injection is performed to promote early activation of the exhaust purification catalyst 16. Detailed control here is performed in accordance with the flowchart of FIG. 4 described later, including control at the time of switching from homogeneous combustion to stratified stoichiometric combustion and control at the time of switching from stratified stoichiometric combustion to homogeneous combustion after completion of warm-up.
[0030]
During such stratified stoichiometric combustion, it is determined whether or not the exhaust purification catalyst 16 has been activated (S22 in the flow of FIG. 4). If not activated, stratified stoichiometric combustion is continued but activated. If so, the stratified stoichiometric combustion is terminated, and the routine proceeds to S8.
In S8, as a normal combustion control, the mode is shifted to a combustion mode (homogeneous stoichiometric combustion, homogeneous lean combustion, stratified lean combustion, etc.) according to the operating state, and then this flow is finished.
[0031]
FIG. 4 is a flowchart of stratified stoichiometric combustion control, which is executed in S7 of the flow of FIG.
In S11, prior to switching from homogeneous combustion to stratified stoichiometric combustion, control is performed to switch the fuel pressure (fuel pressure) to the fuel injection valve 8 to the fuel pressure required to perform stratified stoichiometric combustion (see FIG. 11A). . In stratified stoichiometric combustion, fuel is divided into an intake stroke and a compression stroke, and fuel injection is performed. Therefore, when performing single injection so that the pulse width of each injection is greater than or equal to a value that can ensure linearity with respect to the fuel injection amount, Switching control is performed so as to lower the fuel pressure in comparison.
[0032]
More specifically, since the actual fuel pressure detected by the fuel pressure sensor 26 is compared with the target fuel pressure and the valve opening duty to the high pressure regulator 14 is feedback-controlled, the target fuel pressure is set to a predetermined low pressure side. , The valve opening duty is increased, the return flow rate is increased, and the fuel pressure is reduced. Then, after the actual fuel pressure reaches the target fuel pressure and stabilizes, the process proceeds to S12.
[0033]
In S12, the ignition timing is gradually retarded (see FIG. 11B).
When switching from the homogeneous combustion to the stratified stoichiometric combustion, it is necessary to increase and correct the torque in order to eliminate the torque decrease at the time of switching to the stratified stoichiometric combustion with low thermal efficiency. Since it is controlled to the MBT (maximum torque generation ignition timing) so as to achieve fuel efficiency (or engine stability), there is no advance correction of the ignition timing for increasing the torque as it is.
[0034]
Therefore, first, in S12, the ignition timing is gradually retarded until an advance correction allowance capable of correcting a torque increase at the time of combustion switching can be secured. More specifically, a target retard ignition timing that can secure the advance correction allowance is calculated from a map or the like based on the engine speed, load, and the like, and a predetermined retard ratio is calculated until the target retard ignition timing is reached. And gradually retard.
[0035]
In S13, it is determined whether or not the ignition timing has reached the target retarded ignition timing. If not, the process returns to S12 to further retard the ignition timing. As a result, when the target retard ignition timing has been reached, the process proceeds from S13 to S14 in order to switch from homogeneous combustion to stratified stoichiometric combustion.
In S14, the compression stroke injection timing in the stratified stoichiometric combustion is set to be advanced as the water temperature Tw is higher (for example, in the range of 60 ° BTDC to 70 ° BTDC) according to the water temperature Tw which is a parameter correlated to the engine temperature. . Note that the intake stroke injection timing is constant (for example, 50 ° ATDC).
[0036]
Specifically, as shown in the flowchart of FIG. 5, referring to the map of FIG. 6 in S101, the basic compression stroke injection timing for stratified stoichiometric combustion (basic IT; In step S102, a correction value (ΔIT) from the water temperature Tw on the advance side with respect to the basic IT is set with reference to the table of FIG. 7, and in step S103, ΔIT is added to the basic IT. The compression stroke injection timing for stratified stoichiometric combustion (IT = basic IT + ΔIT) is calculated.
[0037]
In S15, the normal fuel injection (only the intake stroke injection) is switched to the split injection of the intake stroke injection and the compression stroke injection, and the stratified stoichiometric combustion is started by performing the compression stroke injection at the timing set in S14. (See FIG. 11c).
In S16, at the same time as the switching to the stratified stoichiometric combustion, the ignition timing is advanced at a stretch (the amount of the retard correction is set to 0), and the ignition timing is returned to the MBT before the start of the retard correction (see c in FIG. 11). This eliminates the occurrence of a torque step at the time of combustion switching, and ensures stable operability.
[0038]
In S17, the optimum ignition timing (target value) in the stratified stoichiometric combustion is set so as to be retarded as the water temperature Tw is higher according to the water temperature Tw which is a parameter correlated with the engine temperature (for example, 7 ° BTDC to 0 °). BTDC range).
Specifically, as shown in the flowchart of FIG. 8, the basic ignition timing for stratified stoichiometric combustion (basic ADV; advanced angle value from compression TDC) is determined from the engine speed and the load in S201 with reference to the map of FIG. ), And in S202, a correction value (ΔADV) for retarding the basic ADV from the water temperature Tw with reference to the table of FIG. 10 is set. In S203, ΔADV is subtracted from the basic ADV to obtain a stratified stoichiometric combustion. Is calculated (ADV = basic ADV−ΔADV).
[0039]
In S18, the ignition timing is gradually retarded (see d in FIG. 11). That is, control is performed to gradually retard the ignition timing (target value) for the stratified stoichiometric combustion set in S17. The optimal ignition timing in stratified stoichiometric combustion is retarded as much as possible within the limits of combustion stability, HC performance, smoke performance, etc., so that the exhaust gas temperature can be raised as much as possible. .
[0040]
In this way, the torque step at the time of switching from the homogeneous combustion for starting to the stratified stoichiometric combustion for raising the exhaust gas temperature is eliminated, and after the switching, the activation of the exhaust purification catalyst 16 by the stratified stoichiometric combustion is maximized. can do.
In S19, it is determined whether or not the ignition timing has reached an optimal ignition timing (target value) in stratified stoichiometric combustion. If not, the process returns to S18 and further retards the ignition timing. As a result, if the target retard ignition timing has been reached, the process proceeds from S19 to S20.
[0041]
In S20, similarly to S14, the compression stroke injection timing in stratified stoichiometric combustion is reset according to the water temperature Tw that gradually rises with the promotion of warm-up according to the flowchart of FIG. 11e).
In step S21, similarly to step S17, the ignition timing in the stratified stoichiometric combustion is reset according to the water temperature Tw that gradually rises with the promotion of warm-up according to the flowchart of FIG. 8 so as to be retarded as the water temperature Tw increases (FIG. 11). F)).
[0042]
In S22, it is determined whether or not the exhaust purification catalyst 16 has been activated (warm-up has been completed). This determination is performed in the same manner as in S5 of the flow in FIG.
If the exhaust purification catalyst 16 has not been activated (if NO), the process returns to S20 and S21. Therefore, stratified stoichiometric combustion is continued while resetting the compression stroke injection timing and the ignition timing from the water temperature Tw.
[0043]
On the other hand, if the exhaust purification catalyst 16 is activated (if YES), the process proceeds to S23 and thereafter, and control at the time of switching from stratified stoichiometric combustion to homogeneous combustion is started to end stratified stoichiometric combustion (FIG. 11). g).
In S23, the ignition timing is gradually advanced. That is, in contrast to the control at the time of switching from homogeneous combustion to stratified stoichiometric combustion, in order to suppress a torque increase at the time of combustion switching, a delay correction allowance for retarding the ignition timing at the time of combustion switching is secured. Therefore, the angle is gradually advanced (see h in FIG. 11).
[0044]
In S24, it is determined whether or not the ignition timing has reached the target advance ignition timing. If not, the process returns to S23 to further advance the ignition timing. As a result, when the target advance ignition timing has been reached, the process proceeds from S24 to S25.
In S25, in order to correspond to normal fuel injection, switching control is performed so as to increase the fuel pressure (fuel pressure) to the fuel injection valve 8 (see i in FIG. 11). Specifically, the actual fuel pressure detected by the fuel pressure sensor 26 is compared with the target fuel pressure, and the valve opening duty to the high-pressure pressure regulator 14 is feedback-controlled. By returning to the value, the valve opening duty is reduced, the return flow rate is reduced, and the fuel pressure is increased.
[0045]
In S26, by switching to the normal homogeneous combustion by terminating the split injection (see i in FIG. 11).
In S27, at the same time as switching to homogeneous combustion, the ignition timing is immediately retarded (see i in FIG. 11). This eliminates the occurrence of a torque step at the time of combustion switching, and ensures stable operability.
[0046]
In S28, the ignition timing is gradually advanced (see j in FIG. 11). That is, the angle is gradually advanced to the MBT suitable for the combustion after the switching.
In S29, it is determined whether or not the ignition timing has reached the MBT. If not, the flow returns to S28 to further advance the ignition timing. As a result, if the MBT has been reached, the process returns from S29.
[0047]
FIG. 11 shows a series of controls at the time of switching from the homogeneous combustion to the stratified stoichiometric combustion and from the stratified stoichiometric combustion to the homogeneous combustion.
Next, the control of the fuel injection timing (particularly the compression stroke injection timing) and the ignition timing in the stratified stoichiometric combustion in the present invention will be described in more detail.
Since the compression stroke injection timing IT during stratified stoichiometric combustion affects the combustion performance, conventionally, the operability and combustion stability are secured based on the injection timing in stratified lean combustion after warm-up. It is set to be the maximum.
[0048]
However, as shown in FIG. 12, the range of the compression stroke injection timing IT in which stratified stoichiometric combustion can be achieved changes depending on the engine temperature (water temperature) (A1 to A3). Therefore, if the water temperature is neglected, the IT must be set within an extremely narrow region so that stratified stoichiometric combustion is realized in all temperature ranges, and the exhaust temperature increase effect due to the IT delay is sufficiently achieved. Can not.
[0049]
Therefore, it is desirable to determine the compression stroke injection timing IT according to the engine temperature (water temperature).
In addition, when the fuel pressure is reduced in order to secure the injection time of the fuel injection valve in the divided injection during stratified stoichiometric combustion, as shown by EX in FIG. The force is reduced, the fuel spray is spread, and the fuel spray reaching around the spark plug 9 via the bowl portion 6a on the piston crown surface is reduced.
[0050]
Therefore, as the engine temperature (water temperature) becomes lower, it is necessary to delay the compression stroke injection timing to secure the fuel amount around the spark plug.
On the other hand, as the engine temperature (water temperature) increases, the atomization of fuel improves, so that the air-fuel ratio around the spark plug becomes over-rich, and smoke is generated as unburned.
[0051]
Therefore, the over-rich is prevented by advancing the compression stroke injection timing with an increase in the engine temperature (water temperature).
Therefore, in stratified stoichiometric combustion at the time of catalyst warm-up request, the compression stroke injection timing IT is advanced as the engine temperature (water temperature) increases.
Further, not only the compression stroke injection timing IT during stratified stoichiometric combustion but also the ignition timing ADV is similarly controlled so as to be optimal according to the engine temperature (water temperature).
[0052]
FIG. 13 shows the combustion stability limit, the smoke limit, and the HC limit during stratified stoichiometric combustion with the ignition timing ADV on the horizontal axis and the compression stroke injection timing IT on the vertical axis, when the water temperature Tw = 20 ° C. (at the time of cooling). The bold line shows a thin line when the water temperature Tw = 40 ° C. (warm-up process).
According to this, it is understood that the substantially triangular settable region surrounded by the three limit lines changes according to the water temperature Tw.
[0053]
In addition, in the substantially triangular shape (within the settable area) surrounded by the three limit lines, the top of the injection timing IT retard side and the ignition timing ADV retard side where the exhaust gas temperature increasing effect is maximum is the best effect point. In contrast to the effect vest at the water temperature Tw = 20 ° C., the effect vest point at the water temperature Tw = 40 ° C. moves to the lower left (injection timing IT advance direction and ignition timing ADV retard direction).
[0054]
Therefore, as the engine temperature (water temperature) rises, the compression stroke injection timing IT is advanced and the ignition timing ADV is retarded, so that the effect is set to its maximum.
Next, the setting of the compression stroke injection timing during stratified stoichiometric combustion will be described in more detail.
FIG. 14A shows changes in combustion stability, smoke, HC, and exhaust temperature with respect to the compression stroke injection timing IT during stratified stoichiometric combustion at a water temperature Tw = 20 ° C.
[0055]
When the compression stroke injection timing IT is retarded, the surroundings of the ignition plug become rich, resulting in a large CO, and the after-burning of O2 in the lean mixture formed by injection in the intake stroke can be promoted, thereby reducing HC. An increase in exhaust temperature is obtained.
However, if the compression stroke injection timing IT is too retarded, the air-fuel ratio around the ignition plug exceeds the rich limit (approximately A / F <9), and the combustion becomes unstable, and at the same time, the fuel remains unburned. As a result, smoke is generated.
[0056]
Therefore, it is necessary to set the compression stroke injection timing IT at which combustion stability is established and no smoke is generated. In the case of FIG. 14A, the compression stroke injection timing IT is determined by the combustion stability limit.
FIG. 14B shows changes in combustion stability, smoke, HC, and exhaust temperature with respect to the compression stroke injection timing IT during stratified stoichiometric combustion at a water temperature Tw = 40 ° C.
[0057]
Even when the water temperature Tw = 40 ° C., although the absolute values of the HC and the exhaust temperature change, the tendency is the same as when the water temperature Tw = 20 ° C. As for the combustion stability and smoke, the smoke limit shifts to the advanced side, and is reversed from the combustion stability limit. Therefore, in the case of FIG. 14B, the compression stroke injection timing IT is determined by the smoke limit.
Therefore, as is clear from the comparison between the best effect point (flammability limit) in FIG. 14A and the best effect point (smoke limit) in FIG. 14B, the engine temperature (water temperature) increases. In addition, it is understood that it is better to advance the compression stroke injection timing IT.
[0058]
Next, the setting of the ignition timing at the time of stratified stoichiometric combustion will be described in more detail.
FIG. 15 shows changes in combustion stability, smoke, HC, and exhaust temperature with respect to the ignition timing ADV during stratified stoichiometric combustion at a water temperature Tw = 20 ° C., for example.
When the ignition timing ADV is retarded, afterburning can be promoted, and HC reduction and exhaust temperature rise can be obtained. Also, smoke is reduced. However, if the ignition timing ADV is too retarded, the combustion becomes unstable. Therefore, the ignition timing ADV to be set is determined by the combustion stability limit.
[0059]
The combustion stability limit becomes more retarded as the engine temperature (water temperature) rises. This is because, as the engine temperature (water temperature) rises, fuel atomization is promoted, and a good air-fuel mixture is secured around the ignition plug and the wall of the combustion chamber. This is because there is room.
Therefore, it can be seen that it is better to retard the ignition timing ADV along with the shift of the combustion stability limit to the retard side due to an increase in the engine temperature (water temperature).
[0060]
As described above, according to the present embodiment, at the time of a warm-up request of the exhaust purification catalyst, fuel injection is divided, and early injection in the intake stroke and late injection in the second half of the compression stroke are performed by the ignition timing, By advancing the injection timing of the late injection as the parameter correlating to the engine temperature indicates that the engine temperature is higher, it is possible to enhance the effects of improving emissions and promoting warm-up while ensuring combustion stability. Performance can be greatly improved.
[0061]
Further, according to the present embodiment, at the time of a warm-up request for the exhaust gas purification catalyst, the ignition timing is retarded so that a parameter correlated to the engine temperature indicates that the engine temperature is high. Control can be performed in which the exhaust temperature increase effect, combustion stability, HC performance, and smoke performance are more comprehensively considered.
Further, according to this embodiment, when performing the split injection at the time of the warm-up request of the exhaust purification catalyst, the injection pressure in each injection in the split injection is made longer by lowering the fuel pressure than in the normal single injection. Thus, each injection can be performed in a linear region of the injection pulse width-fuel injection amount characteristic, and control accuracy can be improved.
[0062]
Further, according to the present embodiment, by using the engine water temperature as a parameter correlated to the engine temperature, it can be easily implemented without adding a special sensor.
In the above embodiment, the engine water temperature is used as a parameter correlated to the engine temperature. However, the piston crown surface temperature directly related to the combustion performance (particularly, the surface temperature of the bowl 6a recessed in the crown surface of the piston 6). May be used.
[0063]
The piston crown surface temperature may be directly detected by a thermocouple or the like embedded in the piston 6 (particularly, the crown surface), or may be estimated as a pseudo coolant temperature based on the engine coolant temperature Tw.
The pseudo water temperature corresponding to the piston crown surface temperature has a delay with respect to a change in the engine water temperature based on an initial value corresponding to the cooling water temperature at the time of starting and a delay correction coefficient corresponding to the intake air amount for each predetermined cycle. It can be calculated by having it.
[0064]
A specific estimation method will be described with reference to FIG.
The pseudo water temperature TWF [t] (t is the elapsed time after the ignition signal is turned on), which is correlated with the piston crown surface temperature, starts from the pseudo water temperature initial value TWF0 according to the starting water temperature TWe0, and the intake air amount per unit time. It converges toward the engine coolant temperature Twe with a first-order delay by a delay correction coefficient Ktwf determined by Qa.
[0065]
TWF [t] = TWe [t] − (TWe [t] −TWF [t−1]) × (1−Ktwf) where TWF [0] = TWe [0], and t is IGN / SW-ON. This is the elapsed time. The pseudo water temperature initial value TWF0 can be obtained by referring to a table or the like shown in FIG. 16 based on the starting water temperature TWe0, and the delay correction coefficient Ktwf is referred to a table or the like shown in FIG. 16 based on the intake air amount Qa. You can ask for it.
[0066]
As described above, by using the piston crown surface temperature as a parameter correlated to the engine temperature, when a rich air-fuel mixture is formed around the ignition plug using the piston crown surface, the temperature directly related to the success or failure of stratified stoichiometric combustion. Can be detected.
[Brief description of the drawings]
FIG. 1 is a system diagram of an engine showing an embodiment of the present invention.
FIG. 2 is an explanatory diagram of stratified stoichiometric combustion.
FIG. 3 is a flowchart of start-time combustion control.
FIG. 4 is a flowchart of stratified stoichiometric combustion control.
FIG. 5 is a flowchart for setting a compression stroke injection timing for stratified stoichiometric combustion;
FIG. 6 is a basic value map of a compression stroke injection timing for stratified stoichiometric combustion.
FIG. 7 is a correction value table for a compression stroke injection timing for stratified stoichiometric combustion.
FIG. 8 is a flowchart of setting an ignition timing for stratified stoichiometric combustion.
FIG. 9 is a basic value map of ignition timing for stratified stoichiometric combustion.
FIG. 10 is a correction value table for stratified stoichiometric combustion ignition timing.
FIG. 11 is a timing chart of switching from a start to a stratified stoichiometric combustion.
FIG. 12 is a diagram showing an IT establishment region according to water temperature.
FIG. 13 is a diagram showing an area where IT and ADV can be set;
FIG. 14 is a diagram showing a change in performance due to IT;
FIG. 15 is a diagram showing a change in performance due to ADV.
FIG. 16 is an explanatory diagram of a piston crown surface temperature estimation method.
[Explanation of symbols]
1 engine
2 Intake passage
3 Throttle valve
6 piston
6a bowl
7 Combustion chamber
8 Fuel injection valve
9 Spark plug
12 High pressure fuel pump
14 High pressure regulator
15 Exhaust passage
16 Exhaust gas purification catalyst
20 control unit
25 Water temperature sensor

Claims (11)

In a direct-injection spark-ignition engine in which a fuel injection valve is arranged directly in the cylinder, fuel injection is divided when warm-up of the exhaust purification catalyst is required, and early injection and late injection are performed by the ignition timing. A control device for a direct injection spark ignition engine, wherein the injection timing of late injection is advanced as a parameter correlated with the engine temperature indicates that the engine temperature is higher. 2. The control device for a direct injection spark ignition engine according to claim 1, wherein the early injection is performed in an intake stroke and the latter injection is performed in a compression stroke. 3. The control device for a direct-injection spark ignition engine according to claim 2, wherein the late injection is performed in the latter half of the compression stroke. The engine according to any one of claims 1 to 3, wherein the ignition timing is retarded as the parameter correlated to the engine temperature indicates that the engine temperature is higher when the exhaust purification catalyst is required to warm up. Control device for direct injection spark ignition type engine. A bowl portion is formed on the piston crown surface, and the fuel injection valve injects fuel in a direction toward the bowl portion. In the latter half of the compression stroke, a parameter correlated with the engine temperature indicates that the engine temperature is higher. 2. The control device for a direct-injection spark ignition engine according to claim 1, wherein the engine is advanced. 6. The control device for a direct-injection spark ignition engine according to claim 5, wherein, when a warm-up of the exhaust purification catalyst is requested, the ignition timing is retarded as a parameter correlated to the engine temperature indicates that the engine temperature is higher. The direct injection spark according to any one of claims 1 to 6, wherein when performing the split injection at the time of a warm-up request of the exhaust purification catalyst, the fuel pressure is made lower than in a normal single injection. Control device for ignition engine. The control device for a direct injection spark ignition engine according to any one of claims 1 to 7, wherein the parameter correlated with the engine temperature is an engine coolant temperature. The control device for a direct injection spark ignition engine according to any one of claims 1 to 7, wherein the parameter correlated with the engine temperature is a piston crown surface temperature. At the time of requesting warm-up of the exhaust purification catalyst, the fuel injection is divided into early injection during the intake stroke and late injection during the compression stroke, and the later injection indicates that the parameter correlated to the engine temperature indicates that the engine temperature is higher. A method for controlling a direct-injection spark ignition engine, wherein the injection timing of the engine is advanced. 11. The control method for a direct-injection spark ignition engine according to claim 10, wherein the ignition timing is retarded as the parameter correlated to the engine temperature indicates that the engine temperature is higher when the exhaust purification catalyst is required to warm up.

Images