JP4135233B2 - Internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine having a two-stage combustion mode in which fuel is combusted by a main injection in a compression stroke or an intake stroke and a sub-injection in an expansion stroke to raise the temperature of an exhaust gas purification catalyst.
[0002]
[Prior art]
In recent years, in order to reduce harmful exhaust gas components and improve fuel efficiency, a multi-cylinder in-cylinder injection engine (in-cylinder) that injects fuel directly into a combustion chamber instead of an intake pipe injection engine that injects fuel into the intake pipe. Various injection engines have been proposed. In the multi-cylinder in-cylinder injection engine, an intake stroke injection mode in which fuel injection is mainly performed in an intake stroke and a compression stroke injection mode in which fuel injection is mainly performed in a compression stroke are switched according to an operation state. Yes. Even in a multi-cylinder in-cylinder injection engine, a lean combustion operation (lean operation) is possible with a lean air-fuel ratio according to the operating state.
[0003]
Incidentally, an exhaust gas purification catalyst (catalyst) is provided in the exhaust passage of the internal combustion engine, and the exhaust gas is purified by the catalyst. This catalyst needs to be activated by raising the temperature to a certain temperature in order to exhibit the exhaust gas purification ability. In recent years, exhaust gas purification has been demanded immediately after the start of an internal combustion engine due to stricter regulations on exhaust gas, etc., and it is desired to raise the temperature of the catalyst early for early activation of the catalyst.
[0004]
Therefore, in the above-described in-cylinder injection engine, instead of the normal combustion mode in which fuel is injected and burned only in the compression stroke injection mode or the intake stroke injection mode, the compression stroke injection mode or the intake stroke injection is performed immediately after starting. It has been proposed to inject and burn fuel in the mode and to inject additional fuel in the expansion stroke to burn (two-stage combustion mode) and to raise the temperature of the catalyst at an early stage (see JP-A-8-296485) ) By implementing the two-stage combustion mode with the in-cylinder injection engine, it is possible to quickly raise the catalyst temperature while suppressing an increase in cost without adding a hardware configuration such as a heater for heating the catalyst.
[0005]
[Problems to be solved by the invention]
When the two-stage combustion mode is performed, the target air-fuel ratio is set by the total amount of the fuel injected in the compression stroke injection mode or the intake stroke injection mode and the additional fuel injected in the two-stage combustion mode. When switching between the two-stage combustion mode and the normal combustion mode, the target air-fuel ratio is gradually changed in order to reduce torque shock. For this reason, when the early activation of the catalyst is realized by the two-stage combustion mode, how to carry out the air-fuel ratio control at the time of switching between the two-stage combustion mode and the normal combustion mode makes the exhaust gas performance good or bad. It has a big impact.
[0006]
The present invention has been made in view of the above circumstances, and provides an internal combustion engine capable of performing accurate air-fuel ratio control when switching between a two-stage combustion mode and an ordinary combustion mode for rapid temperature rise of a catalyst. Objective.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention achieves the target non-lean air by the two-stage combustion mode in which the fuel is burned at the lean air-fuel ratio by the main injection in the compression stroke or the intake stroke and the sub-injection in the expansion stroke, and the injection of only the main injection. A non-lean combustion mode in which fuel is burned at a fuel ratio,
At the time of transition from the non-lean combustion mode to the two-stage combustion mode, the amount of fuel by the main injection is gradually reduced and the execution of the sub-injection is switched instantaneously,
By providing control means for gradually increasing the amount of fuel by the main injection and gradually decreasing the amount of fuel by the sub-injection at the time of transition from the two-stage combustion mode to the non-lean combustion mode. It prevents an over-lean state during transition between the combustion mode and the non-lean combustion mode, and prevents deterioration of exhaust gas performance.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. 1 is a schematic configuration of a direct injection internal combustion engine according to an embodiment of the present invention, FIG. 2 is a fuel injection control map, FIG. 3 is a time chart of a two-stage combustion mode, and FIGS. A flowchart of the two-stage combustion mode is shown.
[0009]
The configuration of a multi-cylinder in-cylinder injection internal combustion engine will be described with reference to FIG. As the multi-cylinder in-cylinder internal combustion engine, for example, an in-cylinder in-line four-cylinder gasoline engine (in-cylinder injection engine) 1 that directly injects fuel into a combustion chamber is applied. The in-cylinder injection engine 1 has a combustion chamber, an intake device, an exhaust gas recirculation device (EGR device) and the like designed exclusively for in-cylinder injection.
[0010]
A spark plug 3 is attached to each cylinder of the cylinder head 2 of the in-cylinder injection engine 1 and an electromagnetic fuel injection valve 4 is attached to each cylinder. An injection port of the fuel injection valve 4 is opened in the combustion chamber 5 so that the fuel injected from the fuel injection valve 4 is directly injected into the combustion chamber 5. A piston 7 is supported on the cylinder 6 of the direct injection engine 1 so as to be slidable in the vertical direction, and a hemispherical cavity 8 is formed on the top surface of the piston 7. The cavity 8 generates a reverse tumble flow opposite to the normal tumble flow in the intake air flow.
[0011]
An intake port 9 and an exhaust port 10 facing the combustion chamber 5 are formed in the cylinder head 2. The intake port 9 is opened and closed by driving the intake valve 11, and the exhaust port 10 is opened and closed by driving the exhaust valve 12. A large-diameter exhaust gas recirculation port (EGR port) 15 branches obliquely downward from the exhaust port 10.
[0012]
A water temperature sensor 16 for detecting the cooling water temperature is provided in the vicinity of the cylinder 6 of the direct injection engine 1. Further, a crank angle sensor 17 that outputs a crank angle signal at a predetermined crank position of each cylinder is provided, and the crank angle sensor 17 can detect the engine rotation speed.
[0013]
An intake pipe 40 is connected to the intake port 9 via an intake manifold 21, and the intake manifold 21 is provided with a surge tank 22. The intake pipe 40 is provided with an air cleaner 23, an air flow sensor 26 for detecting the intake air amount, and a throttle body 24. The intake pipe 40 is provided with an air bypass pipe (not shown) that bypasses the throttle body 24 and intakes the intake manifold 21.
[0014]
The throttle body 24 is provided with a butterfly throttle valve 29 that opens and closes the flow path, and a throttle position sensor 30 that detects the opening of the throttle valve 29. The throttle position sensor 30 outputs a throttle voltage corresponding to the opening degree of the throttle valve 29, and the opening degree of the throttle valve 29 is recognized based on the throttle voltage.
[0015]
On the other hand, an exhaust pipe 33 is connected to the exhaust port 10 via an exhaust manifold 32, and an O ₂ sensor 34 is attached to the exhaust manifold 32. Further, the exhaust pipe 33 is provided with an exhaust gas purification catalyst (catalyst) 35 and a muffler (not shown). The EGR port 15 is connected to the upstream side of the intake manifold 21 via the EGR pipe 36, and an EGR valve 37 is provided in the EGR pipe 36.
[0016]
The vehicle is provided with an electronic control unit (ECU) 61 as a control device. The ECU 61 includes an input / output device, a storage device for storing a control program, a control map, and the like, a central processing unit, timers and counters. It has been. The ECU 61 performs comprehensive control of the cylinder injection engine 1. Detection information of various sensors and switches (for example, an air conditioner switch, a power steering switch, an inhibitor switch, etc.) for detecting the operating status of an air conditioner device, a power steering device, an automatic transmission device, etc. is input to the ECU 61. Based on the detection information of the engine and the switches, the fuel injection mode and the fuel injection amount as well as the ignition timing and the EGR gas introduction amount are determined, and the fuel injection valve 4, the ignition plug 3, the EGR valve 37, etc. are driven and controlled. To do.
[0017]
In the in-cylinder injection engine 1 described above, the intake flow that flows into the combustion chamber 5 from the intake port 9 forms a reverse tumble flow, and fuel is injected from the fuel injection valve 4 after the middle of the compression stroke to use the reverse tumble flow. On the other hand, a small amount of fuel is collected only in the vicinity of the spark plug 3 disposed at the center of the top of the combustion chamber 5, and an extremely lean air-fuel ratio is obtained at a portion separated from the spark plug 3. By setting only the vicinity of the spark plug 3 to the stoichiometric air-fuel ratio or a rich air-fuel ratio, fuel consumption is suppressed while realizing stable stratified combustion (stratified super lean combustion).
[0018]
When high output is obtained from the in-cylinder injection engine 1, the fuel from the fuel injection valve 4 is injected into the intake stroke to homogenize the entire combustion chamber 5 and perform premix combustion. Of course, since the theoretical air-fuel ratio or the rich air-fuel ratio can provide a higher output than the lean air-fuel ratio, fuel injection is performed at a timing at which fuel atomization and vaporization are sufficiently performed, High output is obtained efficiently.
[0019]
The ECU 61 determines the fuel injection mode by searching the current fuel injection region from the fuel injection map of FIG. 2 based on the operating load Pe and the engine speed Ne according to the opening of the throttle valve 29. Thus, the fuel injection amount corresponding to the target air-fuel ratio in each fuel injection mode is determined, and the fuel injection valve 4 is drive-controlled according to this fuel injection amount, and the spark plug 3 is drive-controlled. At the same time, opening / closing control of the EGR valve 37 is also performed.
[0020]
In the low load region such as during idling or low speed running, the late injection lean mode (compression lean mode) in FIG. 2 is selected as the fuel injection region. In the compression lean mode, fuel injection is performed during the compression stroke (particularly in the latter half of the compression stroke) in order to achieve lean operation by stratified super-lean combustion and improve fuel efficiency.
[0021]
In a medium load region such as during high-speed traveling, the fuel injection region is selected from the first-term injection lean mode (intake lean mode) or stoichiometric feedback mode in FIG. In the intake lean mode, fuel injection is performed during the intake stroke (particularly in the first half of the intake stroke) in order to achieve lean operation by premixed combustion and obtain output by slow acceleration. In the stoichiometric feedback mode, fuel injection is performed during the intake stroke in order to achieve stoichiometric operation (theoretical air-fuel ratio operation) by premixed combustion and to improve the output from the intake lean mode.
[0022]
In the high load region such as during rapid acceleration, the open loop mode in FIG. 2 is selected as the fuel injection region. In the open loop mode, rich operation by premixed combustion is realized and the output is improved compared to the stoichiometric feedback mode. Further, in the region where the throttle valve is substantially fully closed due to inertial traveling or traveling to stop, the fuel injection region becomes the fuel cut mode in FIG. 2, and the supply of fuel into the combustion chamber 5 is stopped. .
[0023]
In the in-cylinder injection engine 1 described above, in addition to the combustion mode of only the main injection in which fuel is injected in the compression stroke or the intake stroke described above, in order to activate the catalyst 35, the sub-injection in which additional fuel is injected during the expansion stroke Is equipped with a two-stage combustion mode implemented together with the main injection. In the main injection and the sub-injection in the two-stage combustion mode, the fuel is burned with the total air-fuel ratio being a lean air-fuel ratio.
[0024]
The two-stage combustion mode is implemented at the time of cold start, for example, where the catalyst temperature is considered not to reach the activation temperature, and the two-stage combustion mode is a sub-combustion mode in which fuel is injected and burned in the compression stroke by the main injection. By additionally injecting fuel in the expansion stroke and burning it by injection, the catalyst 35 is heated quickly and activated early. The main injection in the two-stage combustion mode may be performed during the intake stroke.
[0025]
For example, when the conditions for permitting the compression lean mode and the two-stage combustion mode (details will be described later) are satisfied and the rotational speed Ne of the engine 1 does not reach a predetermined rotational speed (when the vehicle is stopped), as shown in FIG. In addition, the combustion mode is switched from the open-loop mode of the intake stroke injection to the two-stage combustion mode (t1). At the same time, as shown in FIG. 3 (d), the expansion pulse rises (t1) and the expansion stroke injection is performed. Thus, the catalyst 35 is activated early. Then, as shown in FIG. 3 (c), in order to reduce torque shock at the time of mode switching, when the target air-fuel ratio is gradually leaned and the target air-fuel ratio becomes a predetermined air-fuel ratio, the injection end timing is compressed. The compression stroke injection in the compression lean mode that becomes the stroke is performed. Thereafter, when the permission condition for the compression lean mode or the two-stage combustion mode is not satisfied, as shown in FIG. 3A, the combustion mode is switched from the two-stage combustion mode to the non-lean combustion mode, for example, the open loop mode. (t2) The fuel is injected only by the main injection of the intake stroke injection.
[0026]
When the combustion mode is switched from the two-stage combustion mode to the open-loop mode, the target air-fuel ratio is gradually changed from the lean air-fuel ratio in the two-stage combustion mode to the non-lean air-fuel ratio in the open-loop mode in order to reduce torque shock. (FIG. 3 (b) t2 to t3), the air-fuel ratio is controlled by controlling the fuel amount in the open loop mode (fuel control by main injection). At this time, if the sub-injection is eliminated simultaneously with the end of the two-stage combustion mode (shown by a two-dot chain line from t2 to t3 in FIG. 3 (d)), the fuel instantaneously becomes insufficient with respect to the target air-fuel ratio. It will be in a lean state.
[0027]
For this reason, in the present embodiment, at the time of transition of the combustion mode from the two-stage combustion mode to the open loop mode, the fuel amount by the main injection by the intake stroke injection is gradually increased (from t2 to t3 in FIG. 3 (b)). The target air-fuel ratio is gradually changed to the non-lean side as shown in FIG. 5), and the fuel amount by the sub-injection in which fuel is additionally injected during the expansion stroke is gradually reduced. That is, as shown by the solid line from t2 to t3 in FIG. 3 (d), the expansion pulse is gradually lowered (tailed). As a result, it is possible to prevent an over-lean state at the time of transition of the combustion mode switching from the two-stage combustion mode to the open loop mode, and to prevent deterioration of the exhaust gas performance.
[0028]
The situation in the two-stage combustion mode in which fuel injection is performed in the compression stroke and the expansion stroke will be specifically described as an example based on FIGS.
[0029]
As shown in FIG. 4, at the time of the cold start, which is the start in the state where the catalyst 35 is not activated, it is determined in step S1 whether or not the conditions for permitting the compression lean mode are satisfied. The permission condition for the compression lean mode is whether the fuel injection mode is in the compression lean mode region by searching the current fuel injection region from the fuel injection map of FIG. 2 based on the operating load Pe and the engine speed Ne. Judged by no. However, at the time of cold start, the permitted water temperature in the two-stage combustion mode in which fuel injection is performed in the compression stroke and the expansion stroke is the determination value of the permitted water temperature in the compression lean mode. It is set to a low value compared to. It should be noted that other parameters may be added to allow the compression lean mode.
[0030]
If it is determined in step S1 that the permission condition for the compression lean mode is satisfied, it is determined in step S2 whether the permission condition for the two-stage combustion mode is satisfied. In the two-stage combustion mode, for example, the water temperature when the key is in an off state or during cranking is within a predetermined range, the engine rotational speed Ne is equal to or lower than the predetermined rotational speed, the idle condition is established, and the vehicle is stopped. Is permitted when all of the above conditions are satisfied. The permission conditions for the two-stage combustion mode can be variously changed depending on the vehicle type, the usage environment, etc., in addition to the above embodiment examples, such as appropriately combining the above conditions or adding other parameters.
[0031]
If it is determined in step S2 that the permission condition for the two-stage combustion mode is satisfied, it is determined in step S3 whether or not the engine rotational speed Ne has exceeded the specified rotational speed NeA, that is, the engine rotational speed Ne is too high. It is determined whether or not there is. When it is determined in step S3 that the engine rotational speed Ne does not exceed the specified rotational speed NeA, the process proceeds to step S4, and the combustion mode is switched from the open loop mode to the two-stage combustion mode (t1 in FIG. 3). Then, the process proceeds to step S5, where the compression stroke injection and the expansion stroke injection in the compression lean mode are performed, the two-stage combustion mode is performed, the temperature of the catalyst 35 is raised, and the catalyst 35 is activated (t1 in FIG. 3). To t2).
[0032]
If it is determined in step S1 that the permission condition for the compression lean mode is not satisfied, if it is determined in step S2 that the permission condition for the two-stage combustion mode is not satisfied, and the engine speed Ne is defined in step S3. If it is determined that the rotational speed is NeA or higher, the process returns and the two-stage combustion mode is not performed.
[0033]
After the two-stage combustion is executed in step S5, it is determined in step S6 whether the permit condition for the compression lean mode is not satisfied or whether the permit condition for the two-stage combustion mode is not satisfied. If it is determined that the permit condition for the compression lean mode and the permit condition for the two-stage combustion mode are not satisfied, the execution of the two-stage combustion is continued in step S5. If it is determined in step S6 that the permit condition for the compression lean mode is not satisfied or the permit condition for the two-stage combustion mode is not satisfied, that is, the permit condition for the compression lean mode and the permit condition for the two-stage combustion mode are If it is determined that even one has not been established, the process proceeds to step S7 shown in FIG.
[0034]
As shown in FIG. 5, in step S7, the combustion mode is switched from the two-stage combustion mode to the open loop mode (t2 in FIG. 3). That is, in step S8, the target air-fuel ratio in the compression stroke injection in the compression lean mode is gradually tailed in the non-lean direction from lean to gradually increase the fuel amount (FIG. 3 (b) solid line from t2 to t3). When the fuel ratio reaches a predetermined air-fuel ratio, the compression lean mode is switched to the open-loop mode intake stroke injection in step S9 (solid line from t2 to t3 in FIG. 3 (c)). At the same time, in step S10, the target air-fuel ratio in the expansion stroke injection is gradually decreased from the non-lean direction to the lean direction to gradually reduce the fuel amount, and in step S11, the fuel injection in the expansion stroke injection is terminated (FIG. 3 (d)). Solid line from t2 to t3). And it transfers to step S12 and implements the intake stroke injection of an open loop mode.
[0035]
In step S7, the combustion mode is switched from the two-stage combustion mode to the open loop mode. However, when the water temperature is high by judging the water temperature or the like, or when the torque required by the driver is relatively small, the stoichiometric mode is changed. You may make it switch to a mode.
[0036]
It is desirable to set the tailing end timing when the fuel amount injected in the expansion stroke is gradually decreased to the tailing end timing when the fuel amount is gradually increased. In this case, settings such as setting tailing gain individually based on experimental values, or changing the target air-fuel ratio to gradually decrease the fuel amount so as to be linked to the tailing situation of gradually increasing the fuel amount, etc. Is possible. Since the expansion stroke injection does not contribute to torque fluctuation, the tailing situation in which the fuel amount in the expansion stroke injection is gradually decreased may not be completely matched with the tailing situation in which the fuel amount in the intake stroke injection is gradually increased. This is possible, and no torque shock or the like occurs.
[0037]
The in-cylinder injection engine 1 described above performs the two-stage combustion mode for early activation of the cold start catalyst 35 and then changes the combustion mode from the two-stage combustion mode to the open-loop mode at the transition time. Since the fuel amount in the main injection injected in the stage combustion mode is gradually increased and the fuel amount in the expansion stroke injection in the two-stage combustion is gradually decreased, the fuel instantaneously becomes less than the target air-fuel ratio. No longer becomes an overlean state. For this reason, it is possible to prevent an overlean state at the time of transition of switching of the combustion mode from the two-stage combustion mode to the open loop mode and to prevent deterioration of the exhaust gas performance.
[0038]
In the present embodiment, the case where the two-stage combustion mode is applied to the temperature increase control for the early activation of the catalyst at the cold start has been described, but the present invention is not limited to this, For example, it can also be used when the two-stage combustion mode is applied to the temperature rise control for sulfur purge of the storage NOx catalyst.
[0039]
Further, in the present embodiment example, the fuel amount tailing for preventing overleaning at the time of transition from the two-stage combustion mode to the open loop mode has been described, but conversely, the transition transient from the open loop mode to the two-stage combustion mode is described. If the expansion stroke injection has a characteristic as indicated by a one-dot chain line in FIG. 3D, the same fuel amount tailing can be applied to prevent over-rich. It should be noted that tailing of the fuel amount in the expansion stroke at this time can be set to be completely inconsistent with the tailing situation in which the fuel amount in the compression stroke injection is gradually decreased, and the tailing of the expansion stroke prior to the tailing of the compression stroke injection is possible. If the operation is terminated, the effect of the two-stage combustion mode can be obtained more quickly.
[0040]
【The invention's effect】
The internal combustion engine of the present invention includes a two-stage combustion mode in which fuel is burned at a lean air-fuel ratio by main injection in a compression stroke or an intake stroke and a sub-injection in an expansion stroke, and fuel at a target non-lean air-fuel ratio by injection of only main injection. A non-lean combustion mode for burning, and at the time of transition from the non-lean combustion mode to the two-stage combustion mode, the amount of fuel by the main injection is gradually decreased and the execution of the sub-injection is instantaneously switched, By providing control means for gradually increasing the amount of fuel by the main injection and gradually decreasing the amount of fuel by the sub-injection at the time of transition from the two-stage combustion mode to the non-lean combustion mode. It is possible to prevent an overlean state at the time of transition between the combustion mode and the non-lean combustion mode. As a result, accurate air-fuel ratio control can be performed at the time of switching between the two-stage combustion mode for early activation of the catalyst and the normal combustion mode, and deterioration of exhaust gas performance can be prevented.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a direct injection internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a fuel injection control map.
FIG. 3 is a time chart of a two-stage combustion mode.
FIG. 4 is a flowchart of a two-stage combustion mode.
FIG. 5 is a flowchart of a two-stage combustion mode.
[Explanation of symbols]
1 Multi-cylinder in-cylinder injection internal combustion engine (in-cylinder injection engine)
2 Cylinder head 4 Fuel injection valve 5 Combustion chamber 35 Exhaust gas purification catalyst (catalyst)
61 ECU

Claims (1)

A two-stage combustion mode in which fuel is burned at a lean air-fuel ratio by a main injection in a compression stroke or an intake stroke and a sub-injection in an expansion stroke;
A non-lean combustion mode in which fuel is burned at a target non-lean air-fuel ratio by injection of only the main injection,
At the time of transition from the non-lean combustion mode to the two-stage combustion mode, the amount of fuel by the main injection is gradually reduced and the execution of the sub-injection is switched instantaneously,
And wherein during transient switching of the two-stage combustion mode to the non-lean combustion mode in which a gradual control means for reducing the amount of fuel by the auxiliary injection with gradually increasing the amount of fuel by the main injection An internal combustion engine.

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