JP4883319B2 - Exhaust gas purification device for in-cylinder internal combustion engine - Google Patents

Description

  The present invention relates to an in-cylinder injection internal combustion engine, and more particularly to an exhaust purification technology at the time of starting.

In a multi-cylinder in-cylinder injection internal combustion engine, in order to activate an exhaust purification catalyst at the time of cold start, one that performs a compression sleek lean operation after engine startup is known.
In the compression-slight lean operation, stratified combustion is formed in the cylinder by injecting fuel so that the combustion air-fuel ratio is slightly leaner than the stoichiometric air-fuel ratio in the compression stroke. Then, by appropriately controlling the fuel injection timing and the ignition timing, the injected fuel is concentrated in the vicinity of the electrode of the spark plug to locally enrich the air-fuel ratio. While thereby generating much is occurring incomplete combustion of carbon monoxide (CO), locally will exist many excess oxygen (O ₂₎ in a region other than the region to be rich, and the CO and O ₂ Are simultaneously discharged to the exhaust passage. When both CO and O ₂ reach the exhaust purification catalyst through the exhaust passage, an oxidation reaction is caused by the action of the catalyst, and the temperature of the exhaust purification catalyst is raised by the reaction heat.

Further, rich lean operation is known as a method for increasing the catalyst temperature. The rich lean operation is applicable to a multi-cylinder internal combustion engine, and increases the exhaust temperature by exhausting excess fuel (HC) to the exhaust passage by making the air-fuel ratio of some cylinders rich, while others By making the cylinder of the cylinder lean, a large amount of O ₂ is discharged into the exhaust passage. When HC and O ₂ reach the exhaust purification catalyst, an oxidation reaction is caused by the action of the catalyst, and the temperature of the exhaust purification catalyst is raised by the reaction heat (Patent Document 1).
Japanese Patent No. 3627561

However, in the above-described compression-slight lean operation, although the combustion air-fuel ratio is set to lean, the HC emission is suppressed, but the increase in the fuel injection amount is restricted, so that the temperature rise effect is limited.
On the other hand, in the rich lean operation described above, when the temperature of the exhaust purification catalyst has dropped significantly immediately after the cold start, even if HC is supplied, the exhaust purification catalyst is rather cooled by the HC, There is a possibility that the oxidation reaction is not sufficiently performed and HC flows out downstream of the exhaust purification catalyst.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an in-cylinder injection type internal combustion engine that can quickly activate an exhaust purification catalyst while suppressing the outflow of HC during cold start. An object of the present invention is to provide an exhaust emission control device for an engine.

In order to achieve the above object, an invention of claim 1 is provided in an exhaust passage of a multi-cylinder in-cylinder injection internal combustion engine, and purifies harmful components in exhaust under an atmosphere near the stoichiometric air-fuel ratio. In a predetermined period immediately after the start of the engine and the engine, a compression light lean operation is performed in which fuel is injected into the cylinder so that the combustion air-fuel ratio becomes lean in the vicinity of the theoretical air-fuel ratio in the compression stroke. The cylinders of the engine perform a rich operation in which fuel is injected into the cylinder so that the combustion air-fuel ratio becomes rich in the intake stroke, while the other cylinders continue the compression slur lean operation, and the operation control means for performing the rich lean operation And.

According to a second aspect of the present invention, in the first aspect of the invention, there is further provided an ignition timing control means for retarding the ignition timing of a part of the cylinders that makes the combustion air-fuel ratio rich during the rich lean operation in the operation control means. To do.
According to a third aspect of the present invention, in the second aspect, the operation control means further injects fuel into the cylinder of each cylinder so that the overall air-fuel ratio of all the cylinders is close to the theoretical air-fuel ratio in the rich lean operation. It is characterized by controlling the amount.

  According to the exhaust gas purification apparatus for a direct injection internal combustion engine according to claim 1 of the present invention, the compression light lean operation is performed for a predetermined time immediately after the engine is started. The catalyst temperature can be raised by supplying carbon oxide and performing an oxidation reaction there. Further, in the compression slur lean operation, since the combustion air-fuel ratio is lean near the stoichiometric air-fuel ratio, generation of HC can be suppressed. Then, after a predetermined time has elapsed from the start of the engine, a rich operation is performed in some of the cylinders, so that excess fuel HC is supplied to the exhaust purification catalyst. At this point in time, the temperature of the exhaust purification catalyst has slightly increased due to the compression-slight lean operation, and therefore, by supplying HC, the oxidation reaction is reliably performed and the catalyst temperature can be significantly increased. Therefore, even at the time of cold start, the exhaust purification catalyst can be activated quickly while suppressing the outflow of HC.

According to the exhaust gas purification apparatus for a cylinder injection internal combustion engine according to claim 2 of the present invention, the ignition timing of the cylinder that makes the combustion air-fuel ratio rich at the time of rich lean operation is retarded, so that air stability is ensured while ensuring combustion stability. The amount can be increased and therefore the exhaust flow rate can be increased to raise the catalyst temperature more quickly.
According to the exhaust gas purification apparatus for a cylinder injection internal combustion engine according to claim 3 of the present invention, the exhaust air purifying efficiency of the exhaust gas purifying catalyst is increased because the overall air fuel ratio of all the cylinders is close to the theoretical air fuel ratio during the rich lean operation. It can be secured sufficiently.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a multi-cylinder engine (in-cylinder injection internal combustion engine) 1 according to the present invention.
As shown in FIG. 1, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, so that fuel can be directly injected into the combustion chamber 8. It is said that.

A fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe. Specifically, the fuel supply device includes a fuel pump. The fuel pump pressurizes the fuel in the fuel tank and supplies the pressurized fuel to the fuel injection valve 6.
An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected so as to communicate with each intake port. A throttle valve 11 is connected to the other end of the intake manifold 10, and the throttle valve 11 is provided with a throttle sensor 11a for detecting the throttle opening.

Further, an exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of the exhaust manifold 12 is connected so as to communicate with each exhaust port. An exhaust pipe 20 is connected to the other end of the exhaust manifold 12, and a muffler (not shown) is connected to the exhaust pipe 20 via an exhaust purification catalyst 30.
The exhaust purification catalyst 30 is a selective reduction type NOx catalyst (hereinafter referred to as NOx catalyst) 30a that selectively purifies NOx in exhaust in the presence of HC, and oxidizes NOx, HC, and CO in exhaust under a stoichiometric air-fuel ratio. The three-way catalyst 30b, which is reduced to a harmless substance and purified to be harmless, is provided, and the three-way catalyst 30b is disposed downstream of the NOx catalyst 30a.

An exhaust temperature sensor 32 that detects the temperature of the exhaust gas that has passed through the exhaust purification catalyst 30 as the catalyst temperature of the exhaust purification catalyst device 30 is provided on the downstream side of the exhaust purification catalyst 30.
The engine 1 is provided with a crank angle sensor 13 for detecting a crank angle and a water temperature sensor 14 for detecting the temperature of engine cooling water.
The ECU (electronic control unit) 40 includes an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), and the like. Further, the ECU 40 is provided with a timer counter and has a function of measuring an elapsed time after starting.

In addition to the throttle sensor 11a, the crank angle sensor 13, the water temperature sensor 14, and the exhaust temperature sensor 32 described above, various sensors such as an air-fuel ratio sensor (not shown) are connected to the input side of the ECU 40. Detection information is input.
On the other hand, various output devices such as a spark plug 4 are connected to the output side of the ECU 40 via a fuel injection valve 6 and an ignition coil 9. Based on detection information from various sensors such as the throttle sensor 11a, the ECU 40 calculates a fuel injection amount, a fuel injection timing, an ignition timing, and the like that realize the target combustion air-fuel ratio from, for example, a map and outputs various output devices. To control.
Further, the ECU 40 (operation control means) is not only a normal operation that operates based on the fuel injection amount, fuel injection timing, and ignition timing set based on detection information from various sensors such as the throttle sensor 11a, but also a compression slightly. Operation and rich lean operation are possible.

In the compression-slight lean operation, the fuel injection amount is set so that the combustion air-fuel ratio is slightly leaner than the stoichiometric air-fuel ratio, and then fuel is injected in the compression stroke.
In the rich lean operation, some cylinders (for example, the second and third cylinders in the case of a four-cylinder engine) are set to other cylinders (for example, 1 to 1) so that the combustion air-fuel ratio becomes rich (for example, air-fuel ratio 13.5). The fuel injection amount is set so that the combustion air-fuel ratio of the second and fourth cylinders becomes lean (for example, air-fuel ratio 15.5). Further, the cylinder set to the lean employs the above-described compression / slight lean operation. Further, in the present embodiment, during the compression / slight lean operation, the overall air-fuel ratio of all the cylinders (the air-fuel ratio at the collecting portion of the exhaust manifold 12) is set to the stoichiometric air-fuel ratio, and the ignition timing is retarded (ignition timing control means). ). In the present embodiment, the same number of rich cylinders and lean cylinders are used in the rich lean operation. However, the present invention is not limited to this, and at least one each is sufficient.

FIG. 2 is a flowchart showing how to select an operation mode at the time of starting.
This routine is repeated during engine operation.
In step S10, an elapsed time T after starting is input from the timer counter, and it is determined whether or not this is within a predetermined time B. If the elapsed time T after the start is within the predetermined time B (T ≦ B), the process proceeds to step S20. The predetermined time B is a setting execution time for both the compression-slight lean operation and the rich-lean operation, and is set to a time necessary for sufficiently ensuring the purification efficiency in the exhaust purification catalyst 30 at the time of cold start. That's fine.

  In step S20, it is determined whether or not the elapsed time T after start input from the timer counter in step S10 is within a predetermined time A (predetermined period) (T ≦ A). When the elapsed time T after the start is within the predetermined time B (T ≦ B), the process proceeds to step S30. The predetermined time A is a set execution time of the compression sleek lean operation, and is necessary for raising the HC supplied by the rich lean operation at the cold start to a temperature at which the exhaust purification catalyst 30 is efficiently oxidized. Set to time.

In step S30, the compression sleek lean operation is selected. Then, this control is returned.
If it is determined in step S20 that the elapsed time T after start has exceeded the predetermined time A (T> A), the process proceeds to step S40.
In step S40, rich lean operation is selected.

If it is determined in step S10 that the elapsed time T after start has passed the predetermined time B (T> B), the process proceeds to step S50.
In step S50, normal operation is selected. Then, this routine is returned.
Next, operations and effects of the present embodiment will be described with reference to FIGS. 3 and 4.
FIG. 3 is a time chart showing changes in operation mode, fuel injection (end) timing, catalyst temperature, HC concentration and CO concentration in exhaust gas at the time of start. In the figure, the solid line indicates the present embodiment, and the broken line indicates the case of only the compressed slline operation.

  As shown in FIG. 3, until the predetermined time A elapses from the start, the compression slick lean operation is performed, and thereafter, until the predetermined time B elapses, the rich operation and the compression slight lean operation are performed. The fuel injection (end) timing is retarded because fuel is injected during the compression stroke during the compression lean operation. When the rich lean operation is started, fuel is injected during the intake stroke in the rich operation cylinder. Advances ahead of the injection timing at the time. The CO concentration in the exhaust gas gradually rises from the start of the compression lean lean operation and rapidly increases from the start of the rich lean operation.

Accordingly, the catalyst temperature of the exhaust purification catalyst 30 gradually increases from the start of the compression slur lean operation and rapidly increases from the start of the rich lean operation, similarly to the increase in the CO concentration in the exhaust. Although the HC concentration in the exhaust gas temporarily increases immediately after the start, it is kept low during the subsequent compression slur lean operation and rich lean operation.
FIG. 4 is a graph showing changes in catalyst inlet temperature and catalyst temperature with rich lean operation time. As shown in FIG. 4, the catalyst inlet temperature rises as the rich lean operation time elapses. The catalyst temperature further rises due to the oxidation reaction at the exhaust purification catalyst 30 as the catalyst inlet temperature rises.

As described above, in this embodiment, since the compression light lean operation is performed at the time of starting, the exhaust gas temperature is increased, and CO is supplied to the catalyst, and the CO is oxidized there, whereby the catalyst temperature can be increased. . Further, in the compression slur lean operation, since the air-fuel ratio in the cylinder is lean near the stoichiometric air-fuel ratio, generation of HC can be suppressed.
When the elapsed time A elapses and the HC oxidation capability of the catalyst is ensured, the rich operation is performed in some cylinders. Accordingly, HC is supplied to the catalyst, and a higher temperature raising effect is obtained by oxidation of HC. During the rich lean operation, the entire air-fuel ratio of all cylinders is set to the stoichiometric air-fuel ratio, so that the exhaust purification efficiency of the exhaust purification catalyst 30 (three-way catalyst 30b) can be maximized, and NOx, HC And other harmful substances can be efficiently removed. In addition, since the ignition is retarded in the rich cylinder during the rich lean operation, the amount of air is increased and the catalyst temperature can be further increased.

  Further, in the present embodiment, the lean cylinder during the rich lean operation does not perform the simple lean operation but continues the compression sleek lean operation. Even if HC is supplied from the rich cylinder quickly without reaching the appropriate temperature, the effect of increasing the temperature of the exhaust purification catalyst 30 is continuously obtained by the compression light lean operation, and the HC in the exhaust purification catalyst 30 is obtained. The oxidation reaction of can be promoted. Therefore, it is not necessary to make the switching timing from the compression lean lean operation to the rich lean operation accurate, and the switching control can be facilitated.

In addition, when the present invention is adopted in an engine capable of controlling the valve timing, in addition to the above control, it is preferable to perform control so as to further increase the valve overlap during the compression / slight lean operation. By increasing the valve overlap in this manner, the volumetric efficiency is increased, so that the exhaust gas temperature rises and the exhaust purification catalyst 30 can be activated more rapidly.
Further, since the internal EGR is increased by increasing the valve overlap, it is possible to reduce the discharge of HC even when the catalyst temperature is still lowered. In addition, if the valve overlap is excessively enlarged, the combustion deteriorates and conversely causes an increase in HC. Further, when expanding the valve overlap, it is preferable to enlarge the exhaust side (slow the closing timing of the exhaust valve). Compared with the case where the valve overlap is increased by increasing the valve opening timing on the intake side, the exhaust temperature can be further increased while suppressing the HC emission amount.

  In the above embodiment, the operation mode is switched based on the elapsed time T after starting, but may be switched based on the temperature of the exhaust purification catalyst 30 (for example, the exhaust temperature input from the exhaust temperature sensor 32).

1 is a schematic configuration diagram of an in-cylinder fuel injection type engine according to the present invention. It is a flowchart which shows the selection point of the operation mode in ECU which concerns on embodiment of this invention. 6 is a time chart showing changes in operation mode, fuel injection timing, catalyst temperature, HC concentration in exhaust, and CO concentration at start-up. It is a graph which shows transition of the catalyst entrance temperature and catalyst temperature accompanying progress of rich lean operation time.

Explanation of symbols

1 Engine 4 Three-way catalyst 6 Fuel injection valve 14 Spark plug 40 ECU

Claims (3)

An exhaust purification catalyst that is provided in an exhaust passage of a multi-cylinder in-cylinder internal combustion engine and purifies harmful components in exhaust under an atmosphere near the theoretical air-fuel ratio;
In a predetermined period immediately after the engine is started, a compression light lean operation is performed in which fuel is injected into the cylinder so that the combustion air-fuel ratio becomes lean in the vicinity of the theoretical air-fuel ratio in the compression stroke. A rich operation in which fuel is injected into the cylinder so that the combustion air-fuel ratio becomes rich in the intake stroke, while the other cylinders continue the compression-slight lean operation, and operation control means for performing the rich lean operation ; An exhaust emission control device for a cylinder injection internal combustion engine.   The exhaust emission control device for a direct injection internal combustion engine according to claim 1, further comprising ignition timing control means for retarding the ignition timing of the some cylinders during rich lean operation in the operation control means.   The operation control means further controls the amount of fuel injected into the cylinder of each cylinder so that the overall air-fuel ratio of all the cylinders is close to the theoretical air-fuel ratio in the rich-lean operation. 2. An exhaust emission control device for a cylinder injection internal combustion engine according to 2.

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