JP2004204704A - Ignition timing control device for direct cylinder injection type spark ignition engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably keep stratified charge combustion, even in crossing a boundary of neighboring operating areas as different in set condition of the stratified charge combustion. <P>SOLUTION: In a direct cylinder injection type spark ignition engine performing the stratified charge combustion at a lean air-fuel ratio in predetermined operating areas, the engine has twice ignition execution means 41, 7, 22 performing ignition at the ignition timing requested from the neighboring operating areas, in coming across the boundary of the neighboring operating areas when at least the ignition timing as a set condition of the stratified charge combustion is different, in the neighboring operating areas out of the predetermined areas where the stratified combustion is performed. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in ignition timing control of a direct injection type spark ignition engine.
[0002]
[Prior art]
There is one in which an operating region is divided into a stratified combustion region and a homogeneous combustion region, and ignition is performed once in the homogeneous combustion region, and two continuous ignitions are performed in the stratified combustion region (see Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. H11-2173
[Problems to be solved by the invention]
By the way, in a direct injection type spark ignition engine, stratified combustion at a lean air-fuel ratio is performed in a predetermined operation range. However, if the setting conditions of stratified combustion are different in an adjacent operation range in the predetermined operation range in which stratified combustion is performed. Some suggestions have been made.
[0005]
The method of forming the air-fuel mixture in the stratified combustion region will be described with reference to an air guide system. In the stratified combustion region, adjacent operation regions are distinguished into a region R1 and a region R2. For example, as shown in FIG. 3, the low rotation speed side of the stratified combustion region is defined as a region R1, and the high rotation speed side is defined as a region R2. The method of forming an air-fuel mixture in each of the regions R1 and R2 is as follows.
[0006]
Method of forming air-fuel mixture in region R1: In order to form a stable stratified air-fuel mixture in this region where the fuel injection amount is small, the air is compactly sprayed into the space surrounded by the cylinder head and the cavity of the rising piston crown. (See the left side of FIG. 12). Also, the gas flow field is originally weak, and the mixture is not formed by using this force, but is formed by the injection period and the penetration force of the spray.
[0007]
Air-fuel mixture formation method in region R2: In this region, the injection period is set long because the fuel injection amount is large. At that time, from the viewpoint of suppressing the generation of smoke and unburned fuel, it is necessary to make the injection start timing earlier than in the case of the region R1 in order to prevent the fuel from adhering to the crown surface, and the position of the piston crown surface is further lowered. An air-fuel mixture is formed in the closed state (see the right side of FIG. 12). At that time, the gas flow is used instead of forming the air-fuel mixture only by the injection period and the penetration force of the spray. That is, by closing a gas flow control valve provided in the intake port, a gas flow (tumble flow) is generated in the cylinder, and the spray injected into the combustion chamber space is collected using the generated gas flow while the ignition plug is being used. To form a stable mixture.
[0008]
As described above, since the method of forming the air-fuel mixture is different between the two regions R1 and R2, the setting conditions of the stratified combustion (the operation state of the gas flow valve, the air-fuel ratio, the EGR rate, the injection timing, the ignition Timing, etc.) are significantly different. For this reason, when the operating condition crosses the boundary of the adjacent operating range, it is necessary to switch the setting condition of the stratified combustion from a value suitable for the region R1 to a value suitable for the region R2 or vice versa. is there. Specifically, the gas flow valve is shifted from the open state to the closed state when shifting from the area R1 to the area R2, and the gas flow valve is shifted from the closed state to the open state when shifting from the area R2 to the area R1. Have to switch to
[0009]
However, since the combustion state changes transiently during the closing operation and the opening operation of the gas flow valve, there is a possibility that the combustion state is out of the stable combustion region determined by the injection timing and the ignition timing. This will be described with reference to FIG. 6. FIG. 6 shows a difference in the combustion stable region due to a difference in the operation state of the gas flow control valve (TCV). Here, the horizontal axis is the injection timing (right side is the retard side), and the vertical axis is the ignition timing (the upper side is the advance side), and the combustion stable region is determined on the basis of these balances. Of the quadruple circles shown, only the double circle portion is the combustion stable region, and the outside thereof is the combustion unstable region.
[0010]
In the regions R1 and R2, which are stratified combustion regions, the air-fuel ratio is in a lean state in order to improve fuel efficiency, and the EGR rate is increased in order to reduce NOx generated in this lean state. Therefore, the stable combustion region is narrow in both the regions R1 and R2, and the stable combustion region in the region R1 is shown on the upper right, while the stable combustion region in the region R2 is shown on the upper left. Comparing the two, the area of the double circle is slightly larger in the upper left, so the combustion stable area is wider accordingly. Further, it can be seen that the ignition timing is more deviated toward the advance side in the upper right combustion stable region than in the upper left combustion stable region.
[0011]
Now, in order to check whether there is an ignition timing that can be in the combustion stable region in the two regions R1 and R2 without changing the ignition timing, the two parallel lines shown are drawn. If it is on the advanced angle side (upper side), it enters the combustion stable area in the region R1. That is, there is no ignition timing in both the combustion stability regions in the two regions R1 and R2. Accordingly, the state shown at the upper right (the stratified combustion state in the region R1) changes from the state shown at the upper right (the stratified combustion state in the region R1) to the state shown at the upper left (the stratified combustion state in the region R2) without changing the ignition timing while maintaining combustion stability, or vice versa. It cannot be moved. Therefore, when the stratified combustion is to be continued during the transition from the region R1 to the region R2 or vice versa, the set value of the stratified combustion must be set loosely in order to secure the combustion stability. That is, referring again to the case of FIG. 6, if the air-fuel ratio is made richer with respect to the upper right and upper left and the EGR rate is made smaller, the combustion stable region is expanded as shown in the lower right and lower left. In these lower right and lower left states, two parallel lines are drawn to check whether there is an ignition timing that can be kept in the combustion stable region without changing the ignition timing. If the ignition timing is between the upper straight line and the lower straight line, both of the lower right and lower left states can be in the combustion stable region. This means that if the setting conditions for stratified combustion are reduced so that the lower right and lower left states are obtained, the ignition timing (and also the injection timing) is kept constant between the lower right and lower left. Means that even if the TCV is switched from the open state to the closed state, or vice versa, from the closed state to the open state, the TCV does not deviate from the combustion stable region.
[0012]
However, the reason why the combustion stable region is large in the lower right and lower left states is that the combustion gas is heated by enriching the air-fuel ratio and decreasing the EGR rate. NOx emissions increase due to gasification. In the figure, an equal NOx emission amount line is drawn, and it indicates that the NOx emission amount increases as the line width increases. In the lower right and lower left states, the line width of the NOx emission line crossing the combustion stable region is larger than that in the upper right and upper left states, indicating that the NOx emission increases.
[0013]
As described above, if the stratified combustion set value is set to be low in order to maintain the stratified combustion even when crossing the boundary between adjacent operating regions in which the stratified combustion setting conditions are different in the stratified combustion region, the NOx emission amount Increases, and the exhaust gas deteriorates.
[0014]
Accordingly, the present invention provides a method for stratified combustion by igniting any required ignition timing when the ignition timing, which is a setting condition of the stratified combustion, crosses the boundary of at least different adjacent operating ranges. It is another object of the present invention to stably maintain stratified combustion even when crossing the boundary between adjacent operation regions having different setting conditions.
[0015]
On the other hand, the reason why the multiple ignition is performed twice in the stratified combustion region in the above-described conventional device is to increase the chance of ignition in the operation region in which the set conditions of the stratified combustion are the same. That is, in the stratified combustion, since the spray injected into the combustion chamber space is combined using the gas flow and transported to the ignition plug as a mixture, the ignition is performed when the mixture exists near the ignition plug. And two multiple ignitions are performed so as not to miss an opportunity for ignition. On the other hand, according to the present invention, when the setting conditions of the stratified combustion cross different boundaries of adjacent operation regions, the ignition timing optimally set in one operation region and the ignition timing optimally set in the other operation region Is performed twice, and the technical idea is different from that of the above-described conventional apparatus.
[0016]
[Means for solving the problem]
The present invention provides an in-cylinder direct injection type spark ignition engine that performs stratified combustion at a lean air-fuel ratio in a predetermined operation range. Which is required when crossing the boundary of the adjacent operation range when the gas flow state and the ignition timing, which are the setting conditions of the stratified combustion, are at least different in the adjacent operation range. There is provided a double ignition execution means for performing ignition also at the ignition timing.
[0017]
【The invention's effect】
If the setting conditions for stratified combustion differ between adjacent operating regions in the stratified combustion region, the combustion state changes transiently when crossing the boundary of the adjacent operating region. Although there is a possibility that the ignition timing may deviate from the determined stable combustion region, in the present invention, when crossing the boundary of the adjacent operation range, ignition is performed at either required ignition timing, so that either ignition timing is It is optimal for the combustion mode at the time, and it is possible to connect adjacent operating regions having different combustion modes. This makes it possible to maintain a low fuel consumption and low exhaust (NOx) combustion state while ensuring the continuity of operation.
[0018]
Further, even if a means for increasing the ignition energy by prolonging the discharge is not used, the continuous operation can be performed by inputting the necessary minimum ignition energy, so that the cost is not increased.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0020]
FIG. 1 is a schematic configuration diagram of a direct injection type spark ignition engine.
[0021]
As shown in FIG. 1, a combustion chamber 6 is defined between a cylinder head 2, a cylinder 4 formed in a cylinder block 3, and a piston 5 sliding on the cylinder 4. The ignition plug 7 faces the center of the combustion chamber, and two intake ports 8a and 8b and two exhaust ports 9a and 9b are opposed to each other on the ceiling wall of the combustion chamber which is inclined in a pent roof shape so as to sandwich the ignition plug 7 therebetween. Provided. 10a and 10b are intake valves for opening and closing openings of the intake ports 8a and 8b to the combustion chamber 6, 11a and 11b are exhaust valves for opening and closing openings of the exhaust ports 9a and 9b to the combustion chamber 6, Reference numeral 13 denotes a tumble control valve (hereinafter simply referred to as "TCV") as a gas flow control valve which is located in the middle of the intake ports 8a and 8b and throttles intake when closed.
[0022]
A fuel injection valve 12 is provided on the ceiling wall of the combustion chamber 6 so as to face the combustion chamber 6 from its side. The fuel injection valve 12 faces the combustion chamber 6 at a position beside the intake valves 10a and 10b and between the intake ports 8a and 8b.
[0023]
In the engine, the stratified combustion operation is performed in regions R1 and R2 which are a low-medium rotation speed region and a low load region shown in FIG. 3. In this stratified combustion region (R1, R2), the gas flow in the combustion chamber 6 is reduced. The fuel spray directly injected into the combustion chamber 6 from the fuel injection valve 12 is led to the vicinity of the ignition plug 7 by using the fuel injection valve 12 to ignite the mixture formed in this process. A method of bringing the fuel injected from the fuel injection valve 12 into a mass of air-fuel mixture and guiding the mixture to the ignition plug 7 is called an air guide type.
[0024]
The method of forming the air-fuel mixture by the air guide method will be described in detail with reference to FIG. 2. FIG. 2 shows the time course from the left side to the right side.
[0025]
When TCV is open:
Since the gas flow field is originally weak in the region R1 shown in FIG. 3 and it is difficult to form the air-fuel mixture using this gas flow, the air-fuel mixture is formed by the penetration force of the spray. That is, in order to inject fuel into the space formed between the cylinder head 2 and the piston cavity 5a, which is formed as approaching the top dead center, the injection timing is set to the retard side (compression stroke injection). The spray injected into this narrow space reaches the ignition plug 7 while forming an air-fuel mixture only by the penetration force of the spray (see the upper part of FIG. 2).
[0026]
When TCV is closed:
In the region R2 shown in FIG. 3, the gas flow can be used. That is, when the TCV 13 is closed, the intake air flows only from the upper half of each of the intake ports 8a and 8b, so that the flow velocity of the intake air increases, and the piston 5 turns on the crown of the piston 5 about the axis perpendicular to the cylinder 4 center line. Tumble occurs with sufficient strength (see the leftmost arrow at the bottom of FIG. 2). The cavity 5a is formed in a shallow dish shape to promote the tumble. Therefore, the fuel spray injected from the fuel injection valve 12 spreads conically around the center line of the fuel injection valve 12. The fuel spray injected from the fuel injection valve 21 by the above-described tumble is guided in a certain direction of the ignition plug 7, and forms an ignitable mixture in the process. Then, by igniting the mixed gas mass that has reached the vicinity of the ignition plug 7, a stable stratified combustion operation can be performed.
[0027]
In this case, the fuel injection amount is larger in the region R2 than in the region R1, and the injection period is correspondingly longer. At this time, if the fuel adheres to the crown surface, it causes smoke and unburned fuel to be generated. To prevent this, the injection start timing is set to be advanced from the region R1 (compression stroke injection), and the position of the piston crown surface is set. However, the mixture is formed in a lower state. Similarly, the ignition timing is set to be more advanced than the region R1.
[0028]
As described above, since the method of forming the air-fuel mixture is different between the two adjacent regions R1 and R2 in the stratified combustion region, the stratified combustion setting conditions (the operation state of the TCV 13, the air-fuel ratio, EGR rate, injection timing, ignition timing, etc.) are greatly different.
[0029]
On the other hand, in the regions R3 and R4 (homogeneous combustion regions) shown in FIG. 3, since a strong tumble is generated in the combustion chamber 6 even when the TCV 13 is open, the TCV 13 is opened and the combustion chamber 6 By injecting fuel in the intake stroke while making a tumble, a homogeneous air-fuel mixture near the stoichiometric air-fuel ratio is generated in the entire combustion chamber 6, thereby performing a homogeneous combustion operation.
[0030]
Here, the target air-fuel ratio in the homogeneous combustion region is basically the stoichiometric air-fuel ratio (14.7). This is because when the air-fuel mixture near the stoichiometric air-fuel ratio is burned, NOx, HC, and CO in the exhaust gas can be simultaneously purified by a three-way catalyst (added to a NOx trap catalyst 31 described later) provided in the exhaust passage 21. It is.
[0031]
On the other hand, the target air-fuel ratio in the stratified combustion region is a value larger than 14.7, and EGR (exhaust gas recirculation) is performed in order to reduce NOx that is frequently emitted at a lean air-fuel ratio. In FIG. 3, EGR is performed also in the region R3. While the EGR in the stratified combustion region is mainly for reducing NOx, the EGR in the region R3 is mainly for improving fuel efficiency.
[0032]
In FIG. 3, “λ” indicates an excess air ratio. The following relationship exists between the excess air ratio λ and the air-fuel ratio.
[0033]
Excess air ratio λ = air-fuel ratio / stoichiometric air-fuel ratio (1)
For example, since the target air-fuel ratio is the stoichiometric air-fuel ratio in the region R3, when this is substituted into the equation (1), λ = 1. In the region R4, the target air-fuel ratio is a stoichiometric air-fuel ratio or a value richer than the stoichiometric air-fuel ratio, that is, a value of 14.7 or less. Therefore, when this is substituted into the equation (1), λ ≦ 1.
[0034]
FIG. 4 is a control system diagram of the direct injection type spark ignition engine.
[0035]
The engine includes an ignition device capable of performing two ignitions (multiple ignitions). The ignition device includes an ignition coil 22 for storing electric energy from a battery, a power transistor, and an ignition plug 7 provided on the ceiling of the combustion chamber 6. An ignition signal for instructing ignition once by the engine controller 41 is a power signal. When the primary current is sent to the transistor and the primary current of the ignition coil 22 is cut off (ignition timing), a high voltage is generated on the secondary side of the ignition coil 22 and the spark plug 7 receives the high voltage and performs spark discharge. . When an ignition signal for instructing ignition twice is sent from the engine controller 41 to the power transistor, the spark plug 7 performs two spark discharges.
[0036]
Although FIG. 4 shows the ignition device of only the cylinder located at the lowermost stage, the description is omitted because the same applies to the remaining cylinders. Further, the specific configuration of the ignition device capable of performing two ignitions is known, so that the description thereof is omitted (see Japanese Patent Application Laid-Open No. 11-2173).
[0037]
The engine also includes an EGR valve 26 as an EGR device. The EGR valve 26 is interposed in an EGR passage 25 communicating the exhaust passage 23 and the intake passage 24, and is driven by an EGR valve actuator 27. When the EGR valve 26 is opened in a predetermined EGR region, a part of the exhaust gas is exhausted. Is introduced into the intake passage 24 as an inert gas. The inert gas lowers the temperature of the combustion gas in the stratified combustion region (regions R1 and R2) to suppress the generation of NOx. In (region R3), the pumping loss is reduced and the fuel efficiency is improved accordingly.
[0038]
The exhaust passage 23 downstream of the branch port of the EGR passage 25 is provided with a NOx trap catalyst 31. The NOx trap catalyst 31 traps NOx in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and removes the trapped NOx when the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio or the rich air-fuel ratio. At the same time, the desorbed NOx is reduced and purified using HC and CO in the exhaust gas as reducing agents. The NOx trap catalyst 31 has a three-way catalyst function. A three-way catalyst may be provided separately from the NOx trap catalyst 31.
[0039]
In order to generate an engine torque corresponding to the accelerator opening (depression amount of an accelerator pedal) and to prevent a torque step from being generated when switching between a stratified combustion region and a homogeneous combustion region, a throttle is provided in the intake passage 24. An electronically controlled throttle device comprising a valve 28 and a throttle actuator 29 for driving the valve 28 is provided.
[0040]
A signal of an accelerator opening (corresponding to an engine load) from an accelerator sensor 42, a signal of a reference position from the crank angle sensor 43 (a signal for controlling ignition timing and fuel injection timing), and a signal for every 1 ° of crank angle The engine controller 41 to which a signal from the air flow meter 44 is input receives control of the fuel injection amount and the fuel injection timing via the fuel injection valve 12 in accordance with the operating conditions.
(2) control of the ignition timing via the ignition plug 7,
(3) control of the EGR valve opening (EGR rate) via the EGR valve 26,
(4) Throttle valve opening control via the throttle valve 28;
(5) The regeneration process of the NOx trap catalyst 31 is performed, and the opening and closing of the TCV 13 is controlled.
[0041]
The fuel injection control of the above (1) is as follows. The optimum target equivalence ratio Tfbya is calculated for each of the stratified combustion region (R1 and R2) and the homogeneous combustion region (R3 and R4) shown in FIG. 3, and the fuel injection amount is adjusted so as to obtain the target equivalence ratio Tfbya. The fuel injection amount is converted into a valve opening period of the fuel injection valve 12 and a pulse signal including the valve opening period is output to a drive circuit (not shown) of the fuel injection valve 12. Accordingly, a drive current corresponding to the pulse signal is sent from the drive circuit to the actuator of the fuel injection valve 12, and the needle of the fuel injection valve 12 lifts to open the injection hole. The longer the fuel injection pulse width is, the longer the valve opening period of the fuel injection valve 12 is, so that the fuel injection amount is increased. Thus, in the actual control, the equivalent ratio is used instead of the air-fuel ratio. There is a relationship of the following equation (2) between the equivalent ratio and the air-fuel ratio.
[0042]
Further, the fuel injection timing is set in the latter half of the compression stroke in which the piston 5 rises in the stratified combustion region, and the fuel injection timing is set in the intake stroke in which the piston 5 descends in the homogeneous combustion region.
[0043]
The control of the above (2), (3) and (4) is as follows. The ignition timing is calculated based on the accelerator opening and the engine speed. A target EGR rate is calculated based on the accelerator opening and the engine speed, and the EGR valve opening is calculated so as to obtain the target EGR rate. A target torque is calculated based on the accelerator opening and the engine speed, a target air amount is calculated based on the target torque, and a throttle valve opening is calculated so as to obtain the target air amount.
[0044]
The reproduction process of the above (5) is as follows. The air-fuel ratio is temporarily switched to the stoichiometric air-fuel ratio or the rich air-fuel ratio even in the stratified combustion region at the timing when a certain amount of the NOx and the NOx trapped in the lap catalyst 31 accumulate, thereby periodically switching the NOx trap catalyst 31. To play.
[0045]
Assuming that the controls (1) to (5) are performed as described above, in the present embodiment, when the vehicle crosses the boundary between the adjacent operation regions R1 and R2 in the stratified combustion region shown in FIG. Two ignitions are performed: an ignition timing optimally set in one operation range R1 and an ignition timing optimally set in the other operation range R2.
[0046]
This will be described with reference to FIG. 5. In FIG. 5, the left half in the transition from the region R1 to the region R2, and the right half in the transition from the region R1 to the reverse, the operation state of the TCV 13, the air-fuel ratio A / F, and the EGR rate. FIG. 4 is a waveform diagram showing how the injection timing IT and the ignition timing Adv change. The upper side of the injection timing IT and the ignition timing Adv is the advanced side.
[0047]
In this case, the series of operations shown in the right half of FIG. 5 is the reverse of the series of operations shown in the left half of FIG. 5, and therefore, only the series of operations in the left half of FIG. 5 will be described.
[0048]
In the left half of FIG. 5, t1 and t2 are allocated to each timing as shown in the figure, and the operating condition shifts from the region R1 to the region R2 at the timing of t1, and the control at the time of shifting to the region ends at the timing of t2. .
[0049]
<1> Air-fuel ratio: The air-fuel ratio A / F is gradually reduced from the value suitable for the region R1 to the value suitable for the region R2 from the timing of t1 when the region R1 shifts to the region R2. The reason why the air-fuel ratio A / F is changed at a predetermined inclination is to prevent torque fluctuation at the time of shifting to the region.
[0050]
<2> TCV 13 operating state and EGR rate: The TCV 13 is closed at the timing of t1, and the EGR rate is switched to a suitable value in the region R2. The TCV 13 is closed with a predetermined inclination with respect to energization of the TCV actuator. This inclination is determined by the change speed of the TCV actuator. Also, while the target EGR rate changes stepwise from the adaptation value in the area R1 to the adaptation value in the area R2 at the timing of t1, the actual EGR rate (shown in the third half of the left half of FIG. 5) The solid line represents the actual movement of the EGR rate), which decreases with a predetermined slope, which is also determined by the change speed of the EGR valve actuator 27.
[0051]
In this case, since the closing speed of the TCV 13 and the changing speed of the actual EGR rate are not actually the same, the timing at which the TCV 13 settles to the fully closed position and the timing at which the actual EGR rate reaches the appropriate value in the region R2 are not the same. Further, these timings are also different from the timings at which the air-fuel ratio reaches the appropriate value in the region R2. However, in FIG. 5, for simplicity, the three timings are matched, that is, at the timing of t2, the TCV 13 settles to the fully closed position, the air-fuel ratio A / F reaches the appropriate value in the region R2, and the actual EGR rate is reduced. It is assumed that the matching value in the region R2 is reached.
[0052]
<3> Injection timing: The injection timing is gradually advanced from the timing of t1 until the injection timing changes from the appropriate value in the region R1 to the appropriate value in the region R2. The timing at which the injection timing reaches the appropriate value in the region R2 is also shown in agreement with the other three timings for simplicity.
[0053]
<4> Ignition timing: Two ignition timings, from t1 to t2, that is, during the transition to the region, a suitable value in the region R1 and a suitable value in the region R2.
[0054]
As described above, in the present embodiment, when shifting from the area R1 to the area R2, during the area shift, two ignition timings, that is, the appropriate value of the ignition timing in the area R1 and the appropriate value of the ignition timing in the area R2, are used. A method of igniting, which is different from the present embodiment for comparison, will be described with reference to FIG.
[0055]
FIG. 6 shows the difference in the stable combustion region due to the difference in the operation state of the TCV 13. Here, the horizontal axis is the injection timing IT (the right side is the retard side), and the vertical axis is the ignition timing Adv (the upper side is the advance side), and the combustion stable region is determined on the balance between these. Of the quadruple circles shown, only the double circle portion is the combustion stable region, and the outside thereof is the combustion unstable region.
[0056]
In the regions R1 and R2, the air-fuel ratio is in a lean state in order to improve fuel efficiency, and the EGR rate is increased in order to reduce NOx generated in this lean state. Therefore, the stable combustion region is narrow in both the regions R1 and R2, and the stable combustion region in the region R1 is shown on the upper right, while the stable combustion region in the region R2 is shown on the upper left. Comparing the two, the upper left area is slightly larger in the double circle area, indicating that the combustion stable area is wider accordingly. Further, it can be seen that the ignition timing is more deviated toward the advance side in the upper right combustion stable region than in the upper left combustion stable region.
[0057]
The difference between the ignition timings required in the adjacent operation regions (regions R1 and R2) is that the strength of the gas flow greatly changes between the open state and the closed state of the TCV 13 to transfer the stratified mixture. This is because the force changes and the timing at which the stratified mixture reaches the spark plug 7 differs.
[0058]
Now, the two parallel lines shown are drawn in order to check whether or not there is an ignition timing that can be in the combustion stable region without changing the ignition timing in the two regions R1 and R2. If it is more advanced than the upper line, it enters the combustion stable region in the region R1, and if it is more retarded than the lower line, it enters the combustion stable region in the region R2. This means that there is no ignition timing in the combustion stable region without changing the ignition timing in both the regions R1 and R2, and therefore, the state shown in the upper right without changing the ignition timing while keeping the combustion stable. On the contrary, it is not possible to move from the upper left state to the upper right state to the upper left state. Conversely, if the ignition timing and the injection timing are kept the same and a part of the combustion stable region overlaps, the combustion will be stable from the upper right to the upper left without changing the ignition timing and the injection timing, without changing the ignition timing and the injection timing. On the contrary, the state can be shifted from the upper left to the upper right.
[0059]
For this reason, a state shown at the lower right and a state shown at the lower left are added. The lower right shows the state shown in the upper right and the lower left shows the state in which the air-fuel ratio is made richer and the EGR rate is made smaller than the state shown in the upper left. As a result of these operations, the combustion stable region is increased in both the lower right and lower left states. Therefore, in order to check whether or not there is an ignition timing that can be in the combustion stable region without changing the ignition timing in both the lower right and lower left states, two parallel lines shown in the drawing are drawn. If the ignition timing is between the upper straight line and the lower straight line, both can be in the combustion stable region in the lower right and lower left states. This means that even if the TCV 13 is switched from the open state to the closed state with the ignition timing Adv and the injection timing IT kept constant between the lower right and the lower left, or vice versa, the combustion is stable. It means that it will not go out of the area.
[0060]
Thus, in order to shift from the upper right state where the TCV 13 is in the open state to the upper left state where the TCV 13 is in the closed state or vice versa without deviating from the combustion stable region, the lower right state and the lower left state must be interposed. You can see that it should be added. That is, while the TCV 13 is in the open state from the upper right state in which the TCV 13 is in the open state, the air-fuel ratio is enriched and the EGR rate is reduced, and the TCV 13 is shifted to the lower right state. The state is shifted to the lower left state, and the air-fuel ratio is again made lean to the appropriate value in the area 2 and the EGR rate is increased to the appropriate value in the area 2 to shift to the upper left state. From the upper left state where the TCV 13 is closed, the TCV 13 is enriched and the EGR rate is decreased while the TCV 13 is closed, and the state is shifted to the lower left state. In this state, the TCV 13 is switched from closed to open. The state shifts to the lower right state, the air-fuel ratio is again made lean to the appropriate value in the region R1, and the EGR rate is increased to the appropriate value in the region R1.
[0061]
However, in the method in which the operation for enriching the air-fuel ratio and decreasing the EGR rate in the middle of the region transition as described above, the reason why the combustion stable region is large in the lower right and lower left states is that the combustion gas is heated to a high temperature. The NOx emission increases due to the high temperature of the combustion gas. In the figure, an equal NOx emission amount line is drawn, and it indicates that the NOx emission amount increases as the line width increases. In the lower right and lower left states, the line width of the NOx emission line crossing the combustion stable region is larger than that in the upper right and upper left states, indicating that the NOx emission increases.
[0062]
On the other hand, according to the region shifting method according to the present embodiment, regardless of the operation state of the TCV 13, the ignition is performed at two ignition timings suitable for the open state of the TCV 13 and the ignition timing suitable for the closed state of the TCV 13. Thus, stratified combustion can be stably maintained regardless of whether the combustion stable region is in the upper right or upper left state shown in FIG.
[0063]
The control performed by the engine controller 41 at the time of shifting to the region will be described in detail based on a flowchart. However, only the transition from the region R1 to the region R2 will be described.
[0064]
FIG. 7 is for setting the area transition flag, which is executed at regular time intervals (for example, every 10 msec).
[0065]
In step 1, it is determined whether or not the operating conditions (determined from the engine speed and load) are in the stratified combustion region (regions R1 and R2 shown in FIG. 3). If it is not in the stratified combustion region, the current process is terminated.
[0066]
When the engine is in the stratified combustion zone, the process proceeds to step 2 and a zone shift switching flag (initial setting to zero) is checked. Here, assuming that the in-region shift flag = 0, at this time, the process proceeds to steps 3 and 4 to determine whether or not the operating condition is in the region R2 this time and whether or not the operating condition was in the region R1 last time. View. If the operation condition is in the region R2 this time and the operation condition was in the region R1 last time, that is, immediately after the transition from the region R1 to the region R2, the process proceeds to step 5 and the region transition flag = 1 is set. The area transition flag is set to 1 when transitioning from the area R1 to the area R2, and becomes zero when terminating the area transition control as described later.
[0067]
When the operation condition is not in the region R2 this time, or when the operation condition is in the region R2 both this time and the previous time, the current process is terminated as it is.
[0068]
FIG. 8 is for calculating the target equivalent ratio Tfbya, and is executed at regular time intervals (for example, at every 10 msec).
[0069]
Although FIG. 6 illustrates the air-fuel ratio, the equivalent ratio is used in actual control. The following relationship exists between the equivalence ratio and the air-fuel ratio.
[0070]
Equivalent ratio = 14.7 / air-fuel ratio ... (2)
From equation (2), when the air-fuel ratio is the stoichiometric air-fuel ratio (14.7), the equivalent ratio is 1.0. When the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the equivalent ratio exceeds 1.0. Conversely, when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the equivalent ratio is less than 1.0. Value.
[0071]
In step 11, a basic value Tfbya0 of the target equivalent ratio is calculated based on the operating conditions. For example, a map of the basic value of the target equivalence ratio is separately provided for the homogeneous combustion region and the stratified combustion region, and after determining which combustion region the operating condition is in, the engine speed and load at that time are determined. Then, the target equivalent ratio basic value Tfbya0 may be obtained by searching a map of the determined combustion region from the above.
[0072]
In steps 12 and 13, it is checked whether or not the area transition flag = 1 this time and whether the area transition flag = 0 last time. If the flag is “0”, the routine proceeds to step 14, where the basic value Tfbya0 is directly used as the target equivalent ratio Tfbya.
[0073]
This time when the area transition flag is 1 and the previous area transition flag is 0, that is, immediately after the area transition flag is switched from zero to 1 (the operation condition is shifted from the area R1 to the area R2). If it is (immediately after), the routine proceeds to step 15 where the basic value Tfbya0 is entered into “TfbyaTR (previous)” representing the previous value of the target equivalent ratio during the transition to the region, and at step 16,
TfbyaTR = TfbyaTR (previous) + Δ1 (3)
Here, Δ1: a positive predetermined value (for example, a constant value),
The target equivalent ratio TfbyaTR during the transition to the region is calculated by the following equation.
[0074]
In step 17, the target equivalent ratio TfbyaTR during the shift to the region is compared with the target equivalent ratio basic value Tfbya0. Immediately after the area transition flag is switched from zero to 1, that is, immediately after the operating condition shifts from the area R1 to the area R2, the current target equivalent ratio basic value Tfbya0 is an appropriate value in the area R2, and Since Tfbya is a suitable value in the region R1, Tfbya is increased stepwise to a suitable value in the region R2 this time. On the other hand, since the target equivalent ratio TfbyaTR during the transition to the region is a value that gradually increases from the conformance value in the region R1 toward the conformance value in the region R2, the operating condition transitions from the region R1 to the region R2. Immediately thereafter, the target equivalence ratio TfbyaTR during the transition to the area is smaller than Tfbya0 that changes stepwise, and therefore, the process proceeds to step 18 and the value of the target equivalence ratio TfbyaTR during the transition to the area is set as the target equivalence ratio Tfbya.
[0075]
On the other hand, when the flag during the transition to the area is 1, the step 15 is skipped from the steps 12 and 13 and the operation of the step 16 is executed. When the target equivalence ratio TfbyaTR during the transition to the area is smaller than the basic value Tfbya0, the step 18 is executed. Perform the above operations.
[0076]
The above equation (3) is repeated not only at the timing when the operating condition shifts from the region R1 to R2 but also after the shift to the region R2, and the target equivalent ratio TfbyaTR during the shift to the region is calculated by Δ1 per calculation cycle. It is a formula that increases gradually. This is for performing the operation from t1 to immediately before t2 in the second half of the left half of FIG. As a result, the air-fuel ratio moves toward the appropriate value in the region R2.
[0077]
If the target equivalence ratio TfbyaTR during the transition to the area eventually becomes equal to or more than the basic value Tfbya0 due to the gradual increase of the target equivalent ratio TfbyaTR during the transition to the area, the process proceeds from step 17 to step 19 to end the control at the time of the area transition and the area transition flag = In step 20, the basic value Tfbya is set to the target equivalence ratio Tfbya at step 20 in preparation for the next area transition.
[0078]
The target equivalence ratio TFBYA calculated in this manner is used in a calculation flow of a fuel injection pulse width Ti (not shown). For example, Ti = Tp × Tfbya × (α + αm−1) × 2 + Ts (4)
Here, Tp: basic injection pulse width,
α: air-fuel ratio feedback correction coefficient,
αm: Air-fuel ratio learning value,
Ts: invalid pulse width,
The fuel injection pulse width Ti at the time of sequential injection is calculated by the following equation.
[0079]
FIG. 9 is for opening and closing the TCV 13 and is executed at regular intervals (for example, every 10 msec).
[0080]
In step 31, it is determined whether the operating condition is in the stratified combustion region. If the operating condition is in the stratified combustion region, the process proceeds to step 32, and it is determined whether the operating condition is in the region R1 or R2. When the operating condition is in the region R1, the routine proceeds to step 33, in which the TCV 13 is opened. When the operating condition is in the region R2, the routine proceeds to step 34, in which the TCV 13 is closed. Further, even when the vehicle is not in the stratified combustion region, the process proceeds from step 31 to step 33 to open the TCV 13.
[0081]
FIG. 10 is for setting the injection timing, and is executed every fixed time (for example, every 10 msec).
[0082]
In step 41, an injection timing basic value IT0 is calculated. In the stratified combustion region, IT0 is a predetermined crank angle position in the compression stroke. IT0 may simply be a constant value.
[0083]
In steps 42 and 43, it is checked whether or not the area transition flag = 1 this time, and whether the area transition flag = 0 last time. In this case, when the area transition flag is 0, the routine proceeds to step 44, where the basic value IT0 is directly entered into the injection timing IT.
[0084]
This time when the area transition flag is 1 and the previous area transition flag is 0, that is, immediately after the area transition flag is switched from zero to 1 (the operation condition is shifted from the area R1 to the area R2). If it is (immediately after), the routine proceeds to step 45, where the basic value IT0 is set to “IT (previous)” representing the previous value of the injection timing during the transition to the region.
ITTR = ITTR (previous) + Δ2 (5)
Here, Δ2: a positive predetermined value (for example, a constant value),
The injection timing ITTR during the transition to the region is calculated by the following formula, and this is shifted to the injection timing IT in step 47.
[0085]
On the other hand, this time, when the flag during the area transition is 1 in the previous time, the steps 45 and 45 are skipped from the steps 42 and 43 and the operations in steps 46 and 47 are executed.
[0086]
The above equation (5) is repeated not only at the timing when the operating condition shifts from the region R1 to R2 but also after the shift to the region R2 in this manner. It is a formula to increase gradually. This is for performing the operation from t1 in the fourth half of the left half of FIG. 5 to just before t2. As a result, the injection timing IT moves toward the appropriate value in the region R2.
[0087]
FIG. 11 is for calculating the ignition timing, and is executed every fixed time (for example, every 10 msec).
[0088]
In step 41, it is determined whether or not the operating condition at that time is in the stratified combustion region. If it is not the stratified combustion region, the routine proceeds to step 42, where the basic value ADV0 of the ignition timing is calculated based on the operating conditions at that time. For example, an ignition timing basic value map may be provided, and the ignition timing basic value ADV0 may be obtained by searching the ignition timing basic value map from the engine speed and load at that time.
[0089]
In step 43, the basic value ADV0 is shifted to the first ignition timing ADV1 [° BTDC], and zero is set to the second ignition timing ADV2 [° BTDC]. ADV2 = 0 indicates that the second ignition is not performed.
[0090]
When the operating condition is in the stratified combustion range, the process proceeds from step 41 to step 44, and it is determined whether or not it is in the region R2. If it is in the region R1, the process proceeds to step 45, and the ignition timing A at which stable combustion is obtained in the region R1 is calculated based on the operating conditions at that time. That is, the ignition timing A is an ignition timing set in the combustion stable region in the region R1 as shown in the upper right of FIG.
[0091]
If the operating conditions change in the region R1, the combustion stable region in the region R1 also moves accordingly. For example, an ignition timing map 1 is provided, and the ignition timing map 1 is obtained from the engine speed and load at that time. The ignition timing A may be obtained by searching.
[0092]
In step 46, the ignition timing A thus obtained is shifted to the first ignition timing ADV1, and zero is inserted into the second ignition timing ADV2. In step 47, the ignition timing A in the region R1 obtained in step 45 is moved to a memory and stored.
[0093]
The operations of steps 45 to 47 are repeated while in the region R1, and only the latest value of the ignition timing A is stored in the memory. For this reason, when the operating condition shifts from the region R1 to the region R2, the ignition timing in the region R1 close to the region R2 having the current operating condition is stored in the memory.
[0094]
When the operating condition is in the region R2, the process proceeds from step 44 to step 48, and the ignition timing B at which stable combustion is obtained in the region R2 is calculated based on the operating condition at that time. That is, the ignition timing B is an ignition timing set within the combustion stable region in the region R2 as shown in the upper left of FIG.
[0095]
If the operating conditions change in the region R2, the combustion stable region in the region R2 also moves accordingly. For example, the ignition timing map 2 is provided, and the ignition timing map 2 is obtained from the engine speed and load at that time. The ignition timing B may be obtained by searching.
[0096]
In step 49, the area transition flag is checked. If the flag is "0", the routine proceeds to step 50, in which the ignition timing B obtained in step 48 is shifted to the first ignition timing ADV1, and zero is set to the second ignition timing ADV2.
[0097]
On the other hand, if the flag is "1", the process proceeds from step 49 to step 51, and the memory value stored in step 47 (the ignition timing A in the region R1 immediately before the transition to the region R2) is set to the first ignition timing ADV1. And the ignition timing B obtained in step 48 is shifted to the second ignition timing ADV2.
[0098]
The two ignition timings of the first ignition timing ADV1 and the second ignition timing ADV2 calculated in this manner are used in an unillustrated ignition timing control flow, and the actual crank angles are determined by the ignition timings ADV1 and ADV2. The primary circuit of the ignition coil 22 is cut off at the timing coincident with the above, whereby a spark is blown to the ignition plug 7.
[0099]
Here, the operation of the present embodiment will be described.
[0100]
The setting conditions for stratified combustion may differ between adjacent operation regions in the stratified combustion region. For example, the operating state of the TCV 13, the EGR rate, the air-fuel ratio, the injection timing, and the ignition timing are different between the regions R1 and R2 shown in FIG. In this case, both the region R1 where the TCV 13 is open and the region R2 where the TCV 13 is closed have the maximum EGR rate while leaving a certain range of the combustion stable region. Therefore, the combustion stable region overlaps between the regions R1 and R2. No (see upper right and upper left in FIG. 6).
[0101]
In this case, for example, in order to shift from the region R1 to the region R2, it is necessary not only to switch the operation of the TCV 13 from the open state to the closed state, but also to change at least the ignition timing to an appropriate value in the region R2.
[0102]
However, if the operating state of the TCV 13 and the ignition timing, which greatly affect the combustion state, are simultaneously changed, the combustion state may be significantly changed transiently, and the stable combustion area determined by the injection timing and the ignition timing is out of the range. there is a possibility.
[0103]
On the other hand, in the present embodiment (the invention described in claim 2), when the TCV 13 shifts from the region R1 in which the TCV 13 is in the open state to the region R2 in which the TCV 13 is in the closed state, stable stratified combustion is performed before the region shift. And ignition timing B, which are optimal for obtaining stable stratified combustion after the transition to the region, respectively, and in the region R2 where the TCV 13 is in the closed state. When the TCV 13 shifts to the region R1 where the TCV 13 is in the open state, the ignition timing B which is optimal for obtaining stable stratified combustion before the region shift and the optimal ignition timing B for obtaining stable stratified combustion after the region shift are determined. The ignition is performed at two timings with the ignition timing A. That is, regardless of the operation state of the TCV 13, the ignition is performed at two ignition timings A suitable for the open state of the TCV 13 and an ignition timing B suitable for the closed state of the TCV 13, so that the combustion stable region is shown in FIG. In either of the upper right and upper left states, stratified combustion can be stably performed.
[0104]
As described above, according to the present embodiment (the invention according to claim 2), the adjacent operating regions R1 and R2 in which the operating state of the TCV 13 and the ignition timing which are the setting conditions of the stratified combustion are at least different from each other in the stratified combustion region. It is possible to connect adjacent operating regions having different combustion modes even when crossing the boundary of the above, thereby maintaining low fuel consumption and low exhaust (NOx) combustion while ensuring continuity of operation. Can be.
[0105]
Further, even if a means for increasing the ignition energy by elongating the discharge or the like is not used, the continuous operation can be performed with the minimum necessary input of the ignition energy, so that the cost is not increased.
[0106]
In the embodiment, the case where the double ignition execution means is configured by the engine controller 41 and the multiple ignition device 11 has been described. However, instead of the multiple ignition device, two ignition plugs are provided with slightly shifted positions. Alternatively, a multi-point ignition device may be provided.
[0107]
The method of performing the two ignitions is not limited to the embodiment. For example, a map is created in which the ignition timings A and B are assigned by using the engine speed and load as parameters, and the ignition timings A and B are obtained by searching this map during the transition to the region to determine the ignition timings A and B. The ignition timing A may be inserted into the ignition timing ADV1 and the ignition timing B may be inserted into the second ignition timing ADV2.
[0108]
The function of the double ignition execution means according to claim 1 is fulfilled by steps 41, 44 to 51 and the ignition device 11 in the flow of FIG.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an in-cylinder direct injection spark ignition engine according to an embodiment.
FIG. 2 is an explanatory view showing a method for forming an air-fuel mixture by an air guide system.
FIG. 3 is an operation area diagram.
FIG. 4 is a control system diagram of a direct injection type spark ignition engine.
FIG. 5 is a waveform chart for explaining the operation of the present embodiment when shifting to a region.
FIG. 6 is a characteristic diagram showing a difference in a stable combustion region due to a difference in an operation state of the TCV.
FIG. 7 is a flowchart for explaining setting of an area shift flag.
FIG. 8 is a flowchart for explaining calculation of a target equivalent ratio.
FIG. 9 is a flowchart for explaining TCV opening / closing control.
FIG. 10 is a flowchart for explaining the setting of the injection timing.
FIG. 11 is a flowchart for explaining the calculation of the ignition timing.
FIG. 12 is an explanatory view showing a method of forming an air-fuel mixture by an air guide system.
[Explanation of symbols]
7 spark plug 11 ignition device 12 fuel injection valve 13 TCV (gas flow control valve)
22 ignition coil 41 engine controller

Claims (5)

In a direct injection type spark ignition engine that performs stratified combustion at a lean air-fuel ratio in a predetermined operating range,
When the ignition timing that is the setting condition of the stratified combustion is at least different in the adjacent operation range of the predetermined operation range in which the stratified combustion is performed, when crossing the boundary of the adjacent operation range, the ignition timing required for either An ignition timing control device for a direct injection type spark ignition engine, comprising a double ignition execution means for performing ignition. In a direct injection type spark ignition engine that performs stratified combustion at a lean air-fuel ratio in a predetermined operating range,
When the gas flow state and the ignition timing, which are the setting conditions of the stratified combustion, are at least different in the adjacent operation range of the predetermined operation range in which the stratified combustion is performed, which is required when crossing the boundary of the adjacent operation range. An ignition timing control device for a direct injection type spark ignition engine, comprising a double ignition execution means for performing ignition even at an ignition timing which is different from the ignition timing. The cylinder according to claim 2, further comprising a gas flow control valve, wherein the gas flow control valve is opened in one of the adjacent operation regions, and the gas flow control valve is closed in the other of the adjacent operation regions. An ignition timing control device for an internal direct injection spark ignition engine. The ignition timing control device for a direct injection type spark ignition engine according to claim 2, further comprising an EGR device, wherein the EGR rate is increased in each of the adjacent operation ranges. The in-cylinder direct injection spark ignition engine according to claim 4, wherein the timing at which the stratified mixture can be ignited in any of the adjacent operation ranges is restricted to the advance side and the retard side. Ignition timing control device.

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