JP4239584B2 - Ignition timing control device for in-cylinder direct injection spark ignition engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in ignition timing control of an in-cylinder direct injection spark ignition engine.
[0002]
[Prior art]
There is a type in which an operation region is divided into a stratified combustion region and a homogeneous combustion region, and ignition is performed once in the homogeneous combustion region, and continuous ignition is performed twice in the stratified combustion region (see Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-2173
[0004]
[Problems to be solved by the invention]
By the way, in a cylinder direct injection type spark ignition engine, stratified combustion is performed at a lean air-fuel ratio in a predetermined operation range. However, the setting conditions for stratified combustion are different in adjacent operation regions of the predetermined operation region in which stratified combustion is performed. That has been proposed.
[0005]
When the air-fuel type formation method in the stratified combustion zone in this type will be described with respect to the air guide type, the adjacent operating zones in the stratified combustion zone are classified 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 air-fuel mixture formation method in each of the regions R1 and R2 is as follows.
[0006]
Air-fuel mixture formation method in region R1: In order to form a stable stratified air-fuel mixture in this region where the fuel injection amount is small, a compact spray is applied to the space surrounded by the cylinder head and the cavity of the rising piston crown surface. (See the left side of FIG. 12). In addition, the gas flow field is originally weak, and this force is not used to form the air-fuel mixture, but the air-fuel mixture 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 fuel injection amount is large, so the injection period is set longer. At that time, in order to prevent the generation of smoke and unburned fuel, it is necessary to make the injection start time 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. In this state, the air-fuel mixture is formed (see the right side of FIG. 12). At that time, the gas flow is utilized instead of forming the air-fuel mixture only by the injection period and the penetration force of the spray. That is, by closing the 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 igniting the plug. The mixture is formed into a stable mixture.
[0008]
As described above, since the formation method of the air-fuel mixture is different between the two regions R1 and R2, the setting conditions for the stratified charge combustion (the operating state of the gas flow valve, the air-fuel ratio, the EGR rate, the injection timing, the ignition, etc.) are in the adjacent operation region Time) is very different. Therefore, when the operating condition crosses the boundary between the adjacent operating regions, it is necessary to switch the stratified combustion setting condition from a value suitable for the region R1 to a value suitable for the region R2, or vice versa. is there. Specifically, when moving from the region R1 to the region R2, the gas flow valve is moved from the open state to the closed state, and when moving from the region R2 to the region R1, the gas flow valve is opened from the closed state. You must switch to
[0009]
However, since the combustion state changes transiently during the closing operation or opening operation of the gas flow valve, there is a possibility that the stable combustion region determined by the injection timing and the ignition timing may be excluded. This will be described with reference to FIG. 6. FIG. 6 shows the difference in the stable combustion region due to the difference in the operating state of the gas flow control valve (TCV). Here, the horizontal axis is the injection timing (the 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 shown, only the double circle is the combustion stable region, and the outside 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 for improving fuel efficiency, and the EGR rate is increased in order to reduce NOx that is often generated in the lean state. For this reason, the combustion stable region is narrow in both regions R1 and R2, and the combustion stable region in region R1 is shown in the upper right, whereas the combustion stable region in region R2 is shown in the upper left. Comparing the two, the upper left corner has a slightly larger double circle region, so the combustion stable region is wider. It can also be seen that the ignition timing is biased toward the advance side in the upper right combustion stable region than in the upper left combustion stable region.
[0011]
The two parallel lines shown in the figure are drawn 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. If it is on the advance side (upper side), it enters the combustion stable region in the region R1, and if it is on the retard side (lower side) from the lower line, it enters the combustion stable region on the region R2. That is, there is no ignition timing in which the two regions R1 and R2 can be in the combustion stable region. Therefore, the state shown in the upper right (stratified combustion state in the region R1) is changed to the state shown in the upper left (stratified combustion state in the region R2) or vice versa without maintaining the combustion timing and changing the ignition timing. It cannot be transferred. Therefore, when the stratified combustion is to be maintained during the transition from the region R1 to the region R2 or vice versa, the set value of the stratified combustion must be set sweetly in order to ensure the combustion stability. That is, in the case of FIG. 6 again, if the air-fuel ratio is enriched with respect to the upper right and upper left and the EGR rate is decreased, the combustion stable region is expanded as shown in the lower right and lower left. In these two states, lower right and lower left, in order to investigate whether there is an ignition timing that can be in the combustion stable region without changing the ignition timing, when drawing the two parallel lines shown in the figure, this time If the ignition timing is between the upper straight line and the lower straight line, both 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 relaxed so that the lower right and lower left states can be obtained, the ignition timing (and the injection timing) is kept constant between the lower right and lower left. Therefore, even if the TCV is switched from the open state to the closed state or vice versa, it means that the combustion stable region is not deviated.
[0012]
However, the reason why the combustion stable region becomes larger in the lower right and lower left states is that the combustion gas is heated to a high temperature by enriching the air-fuel ratio and decreasing the EGR rate. As a result, NOx emissions increase. In the drawing, an equal NOx emission amount line is written, and the NOx emission amount increases as the line width increases. In the lower right and lower left states, it can be seen that the line width of the equal NOx emission amount line crosses the combustion stable region more than the upper right and upper left states, and the NOx emission amount increases.
[0013]
In this way, if the stratified combustion setting is set sweetly in order to maintain the stratified combustion even when crossing the boundary between adjacent operating regions having different stratified combustion setting conditions in the stratified combustion region, the NOx emission amount is reduced. Will increase the exhaust.
[0014]
Therefore, the present invention performs igniting at the ignition timing required for either of the stratified combustion by crossing the boundary between adjacent operating regions where the ignition timing, which is the setting condition for stratified combustion, is different. The purpose is to stably maintain stratified combustion even when crossing the boundary between adjacent operating regions with 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 apparatus is to increase the chance of ignition in the operation region where the set conditions of the stratified combustion are the same. In other words, in stratified combustion, the spray injected into the combustion chamber space is brought together into a gas mixture while being transported to the spark plug using the gas flow, so that the ignition is performed when the gas mixture exists near the spark plug. In order not to miss the ignition opportunity, multiple multiple ignitions are performed. On the other hand, the present invention provides an ignition timing optimally set in one operating region and an ignition timing optimally set in the other operating region when crossing the boundary between adjacent operating regions having different stratified combustion setting conditions. These two continuous ignitions are performed, and the technical idea is different from that of the conventional device.
[0016]
[Means for solving problems]
The present invention relates to an in-cylinder direct injection spark ignition engine that performs stratified combustion at a lean air-fuel ratio in a predetermined operating region, and an ignition timing that is a setting condition for stratified combustion in an adjacent operating region of the predetermined operating region in which stratified combustion is performed. Is required at the time of crossing the boundary of the adjacent operation region when the gas flow state and the ignition timing, which are the setting conditions for stratified combustion, are at least different in the adjacent operation region. Two-ignition execution means for igniting the ignition timing is provided.
[0017]
【The invention's effect】
When the setting conditions for stratified combustion are different in the adjacent operating regions in the stratified combustion region, the combustion state changes transiently when crossing the boundary between the adjacent operating regions. However, in the present invention, when crossing the boundary between the adjacent operating regions, ignition is performed at the ignition timing required for either, so that any ignition timing is It becomes the most suitable for the combustion form at the time, and it becomes possible to connect the adjacent operation areas with different combustion forms. Thereby, the combustion state of low fuel consumption and low exhaust (NOx) can be maintained while ensuring continuity of operation.
[0018]
Further, even if a means for increasing the ignition energy by using a longer discharge or the like is not used, the continuous operation can be performed with the minimum required amount of ignition energy, so that the cost is not increased.
[0019]
DETAILED DESCRIPTION OF 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 an in-cylinder direct injection 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 the cylinder block 3, and a piston 5 that slides on the cylinder 4. The spark plug 7 faces the center of the combustion chamber, and two intake ports 8a and 8b and two exhaust ports 9a and 9b face each other with the spark plug 7 sandwiched between the combustion chamber ceiling wall inclined in a pent roof shape. Provided. 10a and 10b are intake valves for opening and closing the openings to the combustion chamber 6 of the intake ports 8a and 8b, 11a and 11b are exhaust valves for opening and closing the openings to the combustion chamber 6 of the exhaust ports 9a and 9b, Reference numeral 13 denotes a tumble control valve (hereinafter simply referred to as “TCV”) as a gas flow control valve that throttles the intake air when it is closed in the middle of the intake ports 8a and 8b.
[0022]
A fuel injection valve 12 facing the combustion chamber 6 from its side is provided on the ceiling wall of the combustion chamber 6. The fuel injection valve 12 is located on the side of each intake valve 10a, 10b and between each intake port 8a, 8b and faces the combustion chamber 6.
[0023]
In the engine, stratified combustion operation is performed in the regions R1 and R2 which are the low and medium rotation speed regions and the low load region shown in FIG. 3, and in this stratified combustion region (R1, R2), the gas flow in the combustion chamber 6 is flown. The fuel spray directly injected from the fuel injection valve 12 into the combustion chamber 6 is guided to the vicinity of the spark plug 7 while being collected, and the mixture that has become a mass of the air-fuel mixture in this process is ignited. A method of guiding the fuel injected from the fuel injection valve 12 to the spark plug 7 in the form of an air-fuel mixture is called an air guide type.
[0024]
The method for forming the air-fuel mixture by the air guide method will be described in detail with reference to FIG. 2. The figure shows the time course from the left side to the right side.
[0025]
When TCV is open:
In the region R1 shown in FIG. 3, the gas flow field is originally weak, and it is difficult to form an air-fuel mixture using this gas flow. Therefore, 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 as it approaches 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 spark 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, gas flow can be used. That is, when the TCV 13 is closed, the intake air flows only from the upper half of each intake port 8a, 8b, and the flow velocity of the intake air is increased. The piston 5 turns on the axis perpendicular to the center line of the cylinder 4 on the crown. The tumble to occur occurs with sufficient strength (see the arrow at the left end of the lower stage in FIG. 2). The cavity 5a is formed in a shallow dish shape to promote this tumble. For this reason, the fuel spray injected from the fuel injection valve 12 spreads in a conical shape centering on 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 direction in which the spark plug 7 is located, and forms an air-fuel mixture mass that can be ignited in the process. And, by igniting the air-fuel mixture reaching the vicinity of the spark plug 7, a stable stratified combustion operation becomes possible.
[0027]
In this case, the fuel injection amount in the region R2 is larger than that in the region R1, and the injection period is increased accordingly. At that time, if the fuel adheres to the crown surface, it may cause smoke and unburned fuel. To prevent this, the injection start timing is set to the advance side from the region R1 (compression stroke injection), and the position of the piston crown surface However, the mixture is formed in a lower state. Similarly, the ignition timing is set to the advance side from the region R1.
[0028]
As described above, the two regions R1 and R2 adjacent to each other in the stratified combustion region have different formation methods of the air-fuel mixture, so that the stratified combustion setting conditions (TCV13 operating state, 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, strong tumbling occurs in the combustion chamber 6 even when the TCV 13 is open. 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 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 when the air-fuel mixture near the stoichiometric air-fuel ratio is combusted. It is.
[0031]
On the other hand, the target air-fuel ratio in the stratified combustion zone is a value larger than 14.7, and EGR (exhaust gas recirculation) is performed in order to reduce NOx that is exhausted a lot at this lean air-fuel ratio. In FIG. 3, EGR is also performed in the region R3. Whereas EGR in the stratified combustion region is mainly aimed at reducing NOx, EGR in region R3 is mainly aimed at improving fuel efficiency.
[0032]
In FIG. 3, “λ” represents the excess air ratio. There is the following relationship between the excess air ratio λ and the air-fuel ratio.
[0033]
Excess air ratio λ = air / fuel ratio / theoretical air / fuel ratio (1)
For example, in the region R3, the target air-fuel ratio is the stoichiometric air-fuel ratio, so if this is substituted into the equation (1), λ = 1. In the region R4, the target air-fuel ratio is the stoichiometric air-fuel ratio or a value on the richer side than the stoichiometric air-fuel ratio, that is, a value equal to or less than 14.7. Therefore, if this is substituted into the equation (1), λ ≦ 1.
[0034]
FIG. 4 is a control system diagram of the in-cylinder direct injection spark ignition engine.
[0035]
The engine includes an ignition device capable of performing ignition twice (multiple ignition). The ignition device includes an ignition coil 22 that stores electric energy from the battery, a power transistor, and an ignition plug 7 provided on the ceiling of the combustion chamber 6. The ignition signal that commands ignition once from the engine controller 41 is a power. When the primary current of the ignition coil 22 is cut off (ignition timing) when it is sent to the transistor, a high voltage is generated on the secondary side of the ignition coil 22, and the spark plug 7 performs spark discharge in response to this high voltage. . When an ignition signal for commanding ignition twice is sent from the engine controller 41 to the power transistor, the spark plug 7 performs spark discharge twice.
[0036]
In FIG. 4, the ignition device for only the cylinder located at the lowermost stage is described, but the description is omitted because the remaining cylinders are the same. Further, since a specific configuration of an ignition device capable of performing ignition twice is known, a description thereof will be 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 with 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 Is introduced into the intake passage 24 as an inert gas, and the inert gas suppresses the generation of NOx by lowering the combustion gas temperature in the stratified combustion region (regions R1, R2). In (region R3), the pumping loss is reduced and the fuel efficiency is improved.
[0038]
A NOx trap catalyst 31 is provided in the exhaust passage 23 downstream of the branch port of the EGR passage 25. The NOx trap catalyst 31 traps NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and removes the trapped NOx when the air-fuel ratio of the inflowing exhaust is the stoichiometric or rich air-fuel ratio. At the same time, the desorbed NOx is reduced and purified using HC and CO in the exhaust 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 (the amount of depression of the accelerator pedal), and to prevent a torque step from occurring when switching between the stratified combustion region and the 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 the accelerator opening (corresponding to the engine load) from the accelerator sensor 42, a signal of the reference position from the crank angle sensor 43 (a signal for controlling the ignition timing and the fuel injection timing), and a signal for each crank angle of 1 °. In the engine controller 41 to which a signal from the air flow meter 44 is input, depending on the operating conditions
(1) Control of fuel injection amount and fuel injection timing through the fuel injection valve 12,
(2) Control of ignition timing via the spark plug 7,
(3) Control of the EGR valve opening (EGR rate) via the EGR valve 26;
(4) Control of the throttle valve opening through the throttle valve 28,
(5) Regeneration treatment of NOx trap catalyst 31
And controlling the opening and closing of the TCV 13.
[0041]
The fuel injection control (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 set so that this target equivalence ratio Tfbya is obtained. The fuel injection amount is calculated and 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. Along with this, 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 is lifted to open the injection hole. The longer the fuel injection pulse width, the longer the valve opening period of the fuel injection valve 12, and the fuel injection amount increases. Thus, in actual control, the equivalence ratio is used instead of the air-fuel ratio. There is a relationship of equation (2) described later between the equivalence 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 zone, and the fuel injection timing is set in the intake stroke in which the piston 5 falls in the homogeneous combustion zone.
[0043]
The controls (2), (3), and (4) are 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 that the target EGR rate is obtained. 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 this target air amount.
[0044]
The reproduction process (5) is as follows. Even when the NOx amount trapped in the NOx and the lap catalyst 31 is accumulated to some extent, the air-fuel ratio is temporarily switched to the theoretical air-fuel ratio or the rich air-fuel ratio even in the stratified combustion region. Play.
[0045]
Assuming that the above controls (1) to (5) are performed as described above, in this embodiment, when crossing the boundary between the adjacent operation zones R1 and R2 in the stratified combustion zone shown in FIG. Two ignitions, the ignition timing optimally set in one operating region R1 and the ignition timing optimally set in the other operating region R2, are performed.
[0046]
This will be described with reference to FIG. 5. In FIG. 5, the left half is the operating state of the TCV 13, the air-fuel ratio A / F, and the EGR rate when the region R1 is shifted from the region R1 to the region R2, and the right half is the reverse. FIG. 5 is a waveform diagram showing how injection timing IT and ignition timing Adv change. The injection timing IT and the ignition timing Adv are on the advance side.
[0047]
In this case, the series of operations shown in the right half of FIG. 5 is just 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]
As shown in the left half of FIG. 5, t1 and t2 are allocated to each timing, the driving condition is shifted from the region R1 to the region R2 at the timing t1, and the control at the time of shifting the region is finished at the timing t2. .
[0049]
<1> Air-fuel ratio: The air-fuel ratio A / F is gradually decreased from the appropriate value in the region R1 to the appropriate value in the region R2 from the timing t1 when the region R1 shifts to the region R2. The reason why the air-fuel ratio A / F is changed with a predetermined inclination is to prevent torque fluctuation at the time of shifting to the region.
[0050]
<2> Operating state of TCV 13 and EGR rate: The TCV 13 is closed at the timing of t1, and the EGR rate is switched to a conforming value in the region R2. The TCV 13 is closed with a predetermined inclination with respect to energization to the TCV actuator. This inclination is determined by the changing speed of the TCV actuator. In addition, the target EGR rate changes stepwise from the conforming value in the region R1 to the conforming value in the region R2 at the timing of t1, whereas the actual EGR rate (shown in the third stage in the left half of FIG. 5) The solid line is the actual movement of the EGR rate), which decreases with a predetermined inclination. This inclination is also determined by the changing speed of the EGR valve actuator 27.
[0051]
In this case, since the closing speed of the TCV 13 and the actual EGR rate changing speed are not 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 matching value in the region R2 are not the same. These timings are also different from the timing at which the air-fuel ratio reaches a conforming value in the region R2. However, in FIG. 5, for the sake of simplicity, the three timings are matched, that is, the TCV 13 settles to the fully closed position at the timing t2, the air-fuel ratio A / F reaches the conforming value in the region R2, and the actual EGR rate is It is assumed that the matching value in the region R2 is reached.
[0052]
<3> Injection timing: From the timing t1, the injection timing is gradually advanced 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 conforming value in the region R2 is also shown to match the other three timings for the sake of simplicity.
[0053]
<4> Ignition timing: Between t1 and t2, that is, during the transition to the region, two ignition timings, that is, the conforming value in the region R1 and the conforming value in the region R2.
[0054]
Thus, in the present embodiment, when shifting from the region R1 to the region R2, during the region transition, the two ignition timings of the ignition timing adaptive value in the region R1 and the ignition timing adaptive value in the region R2 are used. Although the ignition is performed, a method different from the present embodiment will be described with reference to FIG. 6 for comparison.
[0055]
FIG. 6 shows the difference in the combustion stable region due to the difference in the operating state of the TCV 13. Here, the horizontal axis is the injection timing IT (the right side is the retarded angle side), and the vertical axis is the ignition timing Adv (the upper side is the advanced angle side), and the combustion stable region is determined on the basis of these balances. Of the quadruple shown, only the double circle is the combustion stable region, and the outside is the combustion unstable region.
[0056]
In the regions R1 and R2, the air-fuel ratio is in a lean state for improving fuel efficiency, and the EGR rate is increased in order to reduce NOx that frequently occurs in the lean state. For this reason, the combustion stable region is narrow in both regions R1 and R2, and the combustion stable region in region R1 is shown in the upper right, whereas the combustion stable region in region R2 is shown in the upper left. Comparing the two, the upper left corner shows that the double circle region is slightly larger, and therefore the combustion stable region is wider. It can also be seen that the ignition timing is biased toward the advance side in the upper right combustion stable region than in the upper left combustion stable region.
[0057]
The ignition timing required in the adjacent operation regions (regions R1 and R2) is different because the strength of the gas flow varies greatly between the open state and the closed state of the TCV 13, thereby transferring the stratified mixture. This is because the force changes and the timing at which the stratified mixture reaches the spark plug 7 is different.
[0058]
The two parallel lines shown in the drawing are drawn to check whether 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 on the advance side from the upper line, it enters the combustion stable region in the region R1, and if it is on the retard side from the lower line, it enters the combustion stable region in the region R2. This means that there is no ignition timing that can be in the stable combustion region without changing the ignition timing in the two regions R1 and R2, so that the combustion can be kept stable and the state shown in the upper right without changing the ignition timing. On the contrary, it is not possible to shift from the upper left state to the upper right state to the upper left state. In other words, if the ignition timing and the injection timing are kept the same and a part of the combustion stable region is overlapped, the combustion will remain stable without changing the ignition timing and the injection timing and from the upper right to the upper left. Conversely, the state can be shifted from the upper left to the upper right.
[0059]
For this reason, the state shown in the lower right and the state shown in the lower left are added. In the lower right, the air-fuel ratio is enriched and the EGR rate is reduced with respect to the state shown in the upper right, and the lower left in 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. Accordingly, in order to investigate 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, the two parallel lines shown in the drawing are now drawn. If the ignition timing is between the upper straight line and the lower straight line, the combustion stable region can be entered in both the lower right and lower left states. This means that between the lower right and the lower left, combustion stability is maintained even when 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, or vice versa. It means not to go out of the area.
[0060]
Thus, in order to move from the upper right state in which the TCV 13 is in the open state to the upper left state in which the TCV 13 is in the closed state, or vice versa, the lower right and lower left states are in the middle. I understand that I should add. That is, the TCV 13 is opened from the upper right state where the TCV 13 is in the open state, and the air-fuel ratio is enriched and the EGR rate is decreased to move to the lower right state. In this state, the TCV 13 is closed from the open state. If the air-fuel ratio is made lean again to the conforming value in the region 2 and the EGR rate is increased to the conforming value in the region 2, the state is shifted to the upper left state. In addition, the TCV 13 is closed from the upper left state where the TCV 13 is in the closed state, and the air-fuel ratio is enriched and the EGR rate is decreased to move to the lower left state. In this state, the TCV 13 is switched from closed to open. If the air-fuel ratio is made lean again to the appropriate value in the region R1 and the EGR rate is increased to the appropriate value in the region R1, the state moves to the upper right.
[0061]
However, in the method of sandwiching the operation of enriching the air-fuel ratio and decreasing the EGR rate during the region transition in this way, the combustion stable region becomes large in the lower right and lower left states because the combustion gas becomes hot. This is because NOx emissions increase due to the high temperature of the combustion gas. In the drawing, an equal NOx emission amount line is written, and the NOx emission amount increases as the line width increases. In the lower right and lower left states, it can be seen that the line width of the equal NOx emission amount line crosses the combustion stable region more than the upper right and upper left states, and the NOx emission amount increases.
[0062]
On the other hand, according to the region transition method according to the present embodiment, the ignition is performed at two timings, i.e., the ignition timing suitable for the open state of the TCV13 and the ignition timing suitable for the closed state of the TCV13, regardless of the operating state of the TCV13. Thus, regardless of whether the combustion stable region is in the upper right or upper left state shown in FIG. 6, stratified combustion can be stably maintained.
[0063]
The control at the time of area shift executed by the engine controller 41 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, and is executed at regular intervals (for example, every 10 msec).
[0065]
In Step 1, it is checked whether or not the operating condition (determined from the engine speed and load) is in the stratified combustion region (regions R1 and R2 shown in FIG. 3). If it is not in the stratified charge combustion zone, the current process is terminated.
[0066]
When in the stratified charge combustion zone, the routine proceeds to step 2 where the zone transition switching flag (initially set to zero) is checked. Here, if the region transition flag = 0 is described, 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. When the operating condition is in the region R2 this time and the operating 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 to set the region transition flag = 1. This in-region transition flag is a flag that becomes 1 when transitioning from the region R1 to the region R2, and becomes zero when the region transition control is terminated, as will be described later.
[0067]
If the operating condition is not in the region R2 this time or if it is in the region R2 both this time and the previous time, the current process is terminated.
[0068]
FIG. 8 is for calculating the target equivalent ratio Tfbya, and is executed at regular time intervals (for example, every 10 msec).
[0069]
Although the air-fuel ratio is described in FIG. 6, the equivalence ratio is used in actual control. There is the following relationship 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 a value on the rich side of the stoichiometric air-fuel ratio, the equivalent ratio exceeds 1.0. Conversely, when the air-fuel ratio is a value on the lean side of the stoichiometric air-fuel ratio, the equivalent ratio is less than 1.0. Value.
[0071]
In step 11, the basic value Tfbya0 of the target equivalence ratio is calculated based on the operating conditions. For example, the target equivalence ratio basic value map is prepared separately for the homogeneous combustion zone and the stratified combustion zone, and after determining which combustion zone the operating conditions are in, the engine speed and load at that time The target equivalence ratio basic value Tfbya0 may be obtained by searching a map of the determined combustion range from the above.
[0072]
In Steps 12 and 13, it is checked whether or not the region transition flag is 1 at this time, and whether or not the region transition flag is 0 last time. If the region transition flag = 0 at this time, the process proceeds to step 14 where the basic value Tfbya0 is directly input to the target equivalent ratio Tfbya.
[0073]
If the region transition flag is 1 and the region transition flag is 0 last time, that is, immediately after the region transition flag is switched from zero to 1, the operating condition is shifted from the region R1 to the region R2. Immediately after the operation), the process proceeds to step 15 and the basic value Tfbya0 is put into “TfbyaTR (previous)” representing the previous value of the target equivalence ratio during the region shift.
TfbyaTR = TfbyaTR (previous) + Δ1 (3)
Where Δ1: a predetermined positive value (for example, a constant value),
The target equivalence ratio TfbyaTR during the region transition is calculated by the following equation.
[0074]
In step 17, the target equivalent ratio TfbyTR during this region transition 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 is shifted from the area R1 to the area R2, the current target equivalence ratio basic value Tfbya0 is a conforming value in the area R2. Since Tfbya0 is a matching value in the region R1, this time Tfbya0 is increased stepwise to a matching value in the region R2. On the other hand, the target equivalent ratio TfbyaTR during the region transition is a value that gradually increases from the conforming value in the region R1 toward the conforming value in the region R2, so the operating condition has shifted from the region R1 to the region R2. Immediately after that, the target equivalent ratio TfbyaTR during the region transition is smaller than Tfbya0 that changes in a stepwise manner. Therefore, the process proceeds to step 18 and the value of the target equivalent ratio TfbyaTR during the region transition is set as the target equivalent ratio Tfbya.
[0075]
On the other hand, when the region transition flag = 1 at this time, step 15 is skipped from steps 12 and 13, and the operation of step 16 is executed. If the target equivalent ratio TfbyTR during the region transition is smaller than the basic value Tfbya0, step 18 is performed. Perform the operation.
[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 when the operating condition shifts to the region R2, and the target equivalent ratio TfbyaTR during the region shift is calculated by Δ1 per calculation cycle. It is an equation that gradually increases. This is an operation from the second stage t1 in the left half of FIG. 5 to just before t2. As a result, the air-fuel ratio moves toward a conforming value in the region R2.
[0077]
When the target equivalent ratio TfbyaTR during the region transition eventually becomes equal to or greater than the basic value Tfbya0 due to the gradual increase of the target equivalent ratio TfbyaTR during the region transition, the process proceeds from step 17 to step 19 to end the control during the region transition, and the region transition flag = In addition to preparing for the next region transition as 0, the basic value Tfbya0 is set as the target equivalent ratio Tfbya in step 20.
[0078]
The target equivalent ratio TFBYA calculated in this way is used in a calculation flow of a fuel injection pulse width Ti (not shown).
Ti = Tp × Tfbya × (α + αm−1) × 2 + Ts (4)
Where 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 formula.
[0079]
FIG. 9 is for driving the TCV 13 to open and close, and is executed at regular intervals (for example, every 10 msec).
[0080]
In step 31, it is checked whether or not the operating condition is in the stratified combustion zone. If the operating condition is in the stratified combustion zone, the process proceeds to step 32 to see whether the operating condition is in the zone R1 or R2. When the operating condition is in the region R1, the routine proceeds to step 33 and the TCV 13 is opened, and when the operating condition is in the region R2, the routine proceeds to step 34 and the TCV 13 is closed. Further, even when not in the stratified charge combustion zone, the routine proceeds from step 31 to step 33 and the TCV 13 is opened.
[0081]
FIG. 10 is for setting the injection timing, and is executed at regular intervals (for example, every 10 msec).
[0082]
In step 41, the injection timing basic value IT0 is calculated. In the stratified combustion zone, 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 is 1 at this time, and whether or not the area transition flag is 0 at the previous time. If the region transition flag is 0 at this time, the routine proceeds to step 44, where the basic value IT0 is directly input to the injection timing IT.
[0084]
If the region transition flag is 1 and the region transition flag is 0 last time, that is, immediately after the region transition flag is switched from zero to 1, the operating condition is shifted from the region R1 to the region R2. Immediately after the operation), the routine proceeds to step 45, where the basic value IT0 is entered in “IT (previous)” representing the previous value of the injection timing during the region shift, and in step 46,
ITTR = ITTR (previous) + Δ2 (5)
However, Δ2: a predetermined positive value (for example, a constant value),
The injection timing ITTR during the region shift is calculated by the following equation, and this is shifted to the injection timing IT in step 47.
[0085]
On the other hand, when the region transition flag = 1 at this time, step 45 is skipped from steps 42 and 43 and the operations of 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 when the operating condition shifts to the region R2, and the injection timing ITTR during the region shift is set by Δ2 per calculation cycle. It is a formula that gradually increases. This is an operation from the fourth stage t1 in the left half of FIG. 5 to just before t2. As a result, the injection timing IT moves toward a conforming value in the region R2.
[0087]
FIG. 11 is for calculating the ignition timing, and is executed at regular intervals (for example, every 10 msec).
[0088]
In step 41, it is checked 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, the ignition timing basic value ADV0 may be obtained by providing the ignition timing basic value map and 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 region, the routine proceeds from step 41 to step 44 to check whether or not the region is in the region R2. If it is area | region R1, it will progress to step 45 and will calculate the ignition timing A with which stable combustion is obtained in area | region R1 based on the driving | running condition 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, the ignition timing map 1 is provided, and the ignition timing map 1 is determined from the rotational speed and load of the engine 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 set to the second ignition timing ADV2. In step 47, the ignition timing A in the region R1 obtained in step 45 is transferred to the memory and stored.
[0093]
While in the region R1, the operations in steps 45 to 47 are repeated, 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 where the current operating condition is present is stored in the memory.
[0094]
When the operating condition is 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 in the combustion stable region in the region R2 as shown in the upper left of FIG.
[0095]
If the operating condition changes in the region R2, the combustion stable region in the region R2 also moves accordingly. Therefore, for example, the ignition timing map 2 is provided, and the ignition timing map 2 is determined 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. When the region transition flag = 0, the routine proceeds to step 50 where the ignition timing B obtained at 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, when the region transition flag = 1, the routine proceeds from step 49 to step 51, where the memory value stored in step 47 (ignition timing A in the region R1 immediately before transitioning to the region R2) is used as the first ignition timing ADV1. At the same time, 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 way are used in an ignition timing control flow (not shown), and the actual crank angle is set to the ignition timing ADV1, ADV2. The primary side circuit of the ignition coil 22 is cut off at a timing coincident with the above, whereby a spark is blown to the spark plug 7.
[0099]
Here, the operation of the present embodiment will be described.
[0100]
The setting conditions for stratified combustion may be different in adjacent operating regions in the stratified combustion region. For example, in the regions R1 and R2 shown in FIG. 3, the operating state of the TCV 13, the EGR rate, the air-fuel ratio, the injection timing, and the ignition timing are different. In this case, both the region R1 in which the TCV 13 is open and the region R2 in which the TCV 13 is closed have the maximum EGR rate leaving a certain range of the combustion stable region, and thus the combustion stable regions overlap in the regions R1 and R2. No (see upper right and upper left in FIG. 6).
[0101]
In this case, for example, to shift from the region R1 to R2, it is necessary not only to switch the operation of the TCV 13 from the open state to the closed state, but at the same time, at least change the ignition timing to a conforming value in the region R2.
[0102]
However, if the TCV 13 operating state and ignition timing that greatly affect the combustion state are changed at the same time, it is conceivable that the combustion state changes greatly in a transient manner, and the stable combustion region determined by the injection timing and the ignition timing is deviated. there is a possibility.
[0103]
On the other hand, in the present embodiment (the invention described in claim 2), when the TCV 13 is shifted from the region R1 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. Region R2 in which ignition is performed at two timings, i.e., an ignition timing A that is optimal for obtaining a stable combustion and an ignition timing B that is optimal for obtaining stable stratified combustion after the transition to the region, and TCV 13 is in a closed state When the transition to the region R1 in which the TCV 13 is in the open state is made, the ignition timing B that was optimal for obtaining stable stratified combustion before the region transition and the optimum for obtaining stable stratified combustion after the region transition Are ignited at two timings, i.e., ignition timing A. That is, regardless of the operating state of the TCV 13, the combustion stable region is shown in FIG. 6 by igniting at the ignition timing A suitable for the open state of the TCV 13 and the ignition timing B suitable for the closed state of the TCV 13. Regardless of which state is the upper right or upper left, stratified combustion can be performed stably.
[0104]
Thus, according to the present embodiment (the invention described in claim 2), adjacent operating regions R1, R2 in which the operating state and ignition timing of the TCV 13, which is a setting condition for stratified combustion, of the stratified combustion region differ at least. Even when crossing the boundary, it is possible to connect adjacent operation areas with different combustion modes, thereby maintaining a low fuel consumption and low exhaust (NOx) combustion state while ensuring continuity of operation. Can do.
[0105]
Further, even if no means for increasing the ignition energy by using a long discharge or the like is used, continuous operation can be performed with the minimum required amount of ignition energy input, so that the cost is not increased.
[0106]
In the embodiment, the case where the two-time 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. A multi-point ignition device may be provided.
[0107]
The method of performing the ignition twice is not limited to that of the embodiment. For example, a map in which the engine rotation speed and load are used as parameters and the ignition timings A and B are assigned as a couple is created, and the ignition timings A and B are obtained by searching this map during the region transition. 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 two-time ignition execution means described in claim 1 is performed 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 of forming an air-fuel mixture by an air guide method.
FIG. 3 is an operation region diagram.
FIG. 4 is a control system diagram of an in-cylinder direct injection spark ignition engine.
FIG. 5 is a waveform diagram for explaining the operation at the time of area transition according to the present embodiment.
FIG. 6 is a characteristic diagram showing the difference in the stable combustion region due to the difference in the operating state of the TCV.
FIG. 7 is a flowchart for explaining setting of a region transition 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 injection timing setting.
FIG. 11 is a flowchart for explaining calculation of ignition timing.
FIG. 12 is an explanatory view showing a method of forming an air-fuel mixture by an air guide method.
[Explanation of symbols]
7 Spark plug
11 Ignition system
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, which is the setting condition for stratified combustion, differs at least between the adjacent operating regions in the predetermined operating region where stratified combustion is performed, the ignition timing required for either of them when crossing the boundary of the adjacent operating regions An ignition timing control device for an in-cylinder direct injection spark ignition engine, characterized by 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, which is the setting condition for stratified combustion, and the ignition timing are at least different in the adjacent operating regions of the predetermined operating region where stratified combustion is performed, which is required when crossing the boundary between the adjacent operating regions. An ignition timing control device for an in-cylinder direct injection spark ignition engine, characterized in that it comprises a two-time ignition execution means for igniting 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. Ignition timing control device for 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 regions. 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 operating ranges is limited to both the advance side and the retard side. Ignition timing control device.

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