JPH1193642A - Exhaust emission control device for multi-cylinder internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the introduction of the exhaust gas including the predetermined quantity or more of hydrocarbon into the intake air through an exhaust circulating pipe by closing the exhaust circulating pipe, and thereafter, injecting the predetermined quantity or more of hydrocarbon when judged that the predetermined quantity or more of hydrocarbon should be injected to the catalyst connected to the exhaust pipe. SOLUTION: In case of supplying the fuel of HC to the NOx catalyst 12 in an internal combustion engine, quantity of fuel to be supplied to the NOx catalyst 12 is decided on the basis of the NOx discharged amount, which is estimated on the basis of the output of an intake pressure sensor 5 and a crank angle sensor 6, and the output of an upstream side temperature sensor 13 and a downstream side temperature sensor 14. In the case where the quantity of fuel to be supplied exceeds the predetermined quantity, an exhaust circulating valve 16 is closed, and thereafter, main injection is performed, and continuously auxiliary injection is performed in an expanding stroke or an exhausting stroke separately from the main injection. Introduction of the exhaust gas including the predetermined quantity or more of fuel into the intake air is thereby prevented, and while NOx included in the exhausted gas is purified by the NOx catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust purification system for a multi-cylinder internal combustion engine.

[0002]

2. Description of the Related Art Nitrogen oxides emitted from an internal combustion engine (hereinafter referred to as nitrogen oxides)
Bottom, NO_XExhaust gas purification devices for purifying
You. For example, JP-A-6-74022 discloses NO_XTo
If the oxygen concentration in the exhaust gas is very high,
In the state, hydrocarbon (hereinafter, HC) is adsorbed on the catalyst surface
To form active species of HC, and the active species of HC and NO
_XNO by reacting with_XNO to purify_XSelection
Selective reduction catalyst (hereinafter referred to as NO _XExhaust purifier equipped with a catalyst)
An arrangement is disclosed. In this exhaust gas purification device, HC is converted to NO.
_XOne cylinder provided with HC supply means for supplying to the catalyst
Attached to the exhaust branch pipe connected to the Also on
In the exhaust purification device disclosed in the above publication,
NO_XExhaust gas into the intake air to reduce the volume
Exhaust circulation pipe for introduction is attached to the above HC supply means
It is connected to an unbranched exhaust branch.

[0003]

[SUMMARY OF THE INVENTION Incidentally, HC amount to be supplied to the NO _X catalyst is determined by the engine operating condition.
At this time, when the amount of HC to be supplied to the NO _X catalyst is equal to or more than a predetermined amount, there is a problem that exhaust gas containing a large amount of hydrocarbons is introduced into intake air through an exhaust circulation pipe. is there. Accordingly, an object of the present invention is to provide a method in which, when the amount of hydrocarbons supplied to the catalyst is equal to or greater than a predetermined amount, exhaust gas containing the predetermined amount or more of hydrocarbons is introduced into intake air through an exhaust circulation pipe. It is to prevent that.

[0004]

According to a first aspect of the present invention, an exhaust branch pipe connected to each cylinder is assembled and connected to a common exhaust pipe to form a common exhaust pipe. And an exhaust branch pipe for introducing exhaust gas into the intake air is connected to at least one of the exhaust branch pipes, and another exhaust branch pipe is connected to the exhaust branch pipe to which the exhaust circulation pipe is connected. Alternatively, in the exhaust purification device for a multi-cylinder internal combustion engine that injects hydrocarbons to be supplied to the catalyst in a cylinder to which the another exhaust branch pipe is connected, the carbonization for determining the amount of hydrocarbons to be supplied to the catalyst is performed. When the hydrogen amount determining means determines that a predetermined amount or more of hydrocarbons should be injected, the hydrogen amount determining means injects a predetermined amount or more of hydrocarbons after closing the exhaust circulation pipe. Thus, the exhaust circulation pipe is always closed when a predetermined amount or more of the hydrocarbon is injected into the exhaust gas.

According to a second aspect of the present invention, in the first aspect, the hydrocarbon amount determining means is configured such that the catalyst temperature is higher than a predetermined temperature and the catalyst is poisoned by the hydrocarbon. It is determined that more than a predetermined amount of hydrocarbons should be injected.

[0006]

FIG. 1 is a diagram showing the configuration of an exhaust gas purifying apparatus for an internal combustion engine according to an embodiment of the present invention. In FIG. 1, 1 is an engine main body, # 1, # 2, # 3, and # 4 are first cylinders, second cylinders, third cylinders, and fourth cylinders 2a, 2b, Reference numerals 2c and 2d denote a first fuel injection valve, a second fuel injection valve, a third fuel injection valve, and a fourth fuel injection valve for supplying engine driving fuel and exhaust gas purification fuel into the corresponding cylinders # 1 to # 4, respectively. The fuel injection valve 3 is an intake passage connected to the engine body 1, and 4 is an intake manifold connected to the intake passage 3. An intake pressure sensor 5 for detecting an intake air pressure for calculating an intake air amount is attached to the intake manifold 4.
Further, the internal combustion engine of the present invention includes a crank angle sensor 6 for detecting a crank angle. Each of the fuel injection valves 2a to 2d is connected to a fuel distribution means common to the fuel injection valves 2a to 2d, that is, a common rail 30. Common rail 30
Is connected to the fuel tank 31 via the pump P. Fuel pressurized by the fuel tank 31 to a predetermined pressure is stored in the common rail 30. Further, a fuel pressure sensor 32 is attached to the common rail 30 as pressure detecting means for detecting the pressure of the fuel in the common rail 30.

The first cylinder # 1, the second cylinder # 2, the third cylinder #
A first exhaust branch pipe 7a, a second exhaust branch pipe 7b, a third exhaust branch pipe 7c, and a fourth exhaust branch pipe 7d are respectively connected to the third and fourth cylinders # 4. The first exhaust branch pipe 7a, the second exhaust branch pipe 7b, and the fourth exhaust branch pipe 7d are joined at an upstream junction 8 on the downstream side of the engine body 1, and the collecting pipe 9
Connected to. The collecting pipe 9 and the third exhaust branch pipe 7c are joined at a downstream junction 10 further downstream of the upstream junction 8. In this specification, “upstream” and “downstream” are terms used in a direction along the flow of exhaust gas.

The internal combustion engine of the present invention includes a supercharger 11 for supercharging intake air to increase an amount of air to be taken. The supercharger 11 includes an intake-side turbine wheel 11 a disposed in the intake passage 3 on the upstream side of the intake manifold 4.
And an exhaust-side turbine wheel 11b disposed in the exhaust passage 20 on the downstream side of the downstream-side merging section 10. In the present invention, since the exhaust-side turbine wheel 11b is disposed at a position where the exhaust gas discharged from each cylinder merges, the amount of exhaust gas passing through the exhaust-side turbine wheel 11b is large, and the supercharging effect of the supercharger 11 is obtained. Can be maintained to the maximum.

The intake side turbine wheel 11a and the exhaust side turbine wheel 11b are connected to each other by one shaft 11c. The exhaust-side turbine wheel 11b receives and rotates the exhaust gas from a direction parallel to the rotation surface of the exhaust-side turbine wheel 11b, and discharges the exhaust gas in a direction perpendicular to the rotation surface. On the other hand, the intake-side turbine wheel 11a is
b, the air is drawn from a direction perpendicular to the rotation surface of the intake-side turbine wheel 11a, and the intake air is sent out in a direction parallel to the rotation surface.

An exhaust gas purifying catalyst 12 for purifying nitrogen oxides (hereinafter, NO _x ) discharged from the internal combustion engine is disposed in an exhaust passage 20 downstream of the exhaust turbine wheel 11b. The exhaust gas purifying catalyst 12 of the present invention can be used in a state where the air-fuel ratio of the air-fuel mixture burned in the engine is much higher than the stoichiometric air-fuel ratio, so that when the oxygen concentration in the exhaust gas is very high, the hydrocarbon (hereinafter referred to as HC) is used. the adsorbed on the catalyst surface to produce an active species HC, which is _the NO _X selective reducing catalyst for purifying NO _X by reacting an active species and NO _X in the HC (hereinafter, NO _X catalyst). The upstream end portion of the NO _X catalyst 12 is arranged upstream temperature sensor 13 for detecting a temperature of said upstream end portion, the downstream end portion of the NO _X catalyst 12 downstream temperature for detecting the temperature of the downstream portion Sensor 1
4 are arranged.

An exhaust circulation pipe 15 for introducing exhaust gas into the intake air is connected to the fourth exhaust branch pipe 7d. The other end of the exhaust circulation pipe 15 is connected to the intake manifold 4. The exhaust circulation pipe 15 is provided with an exhaust circulation valve 16 for controlling whether or not exhaust gas is introduced into the intake air.
The exhaust circulation valve 16 is connected to a suction pump 18 and the atmosphere via a three-way valve 17. The exhaust circulation valve 16 is controlled to open and close according to the operating state of the engine. When the three-way valve 17 allows the exhaust circulation valve 16 to communicate with the atmosphere, atmospheric pressure is applied to the interior of the exhaust circulation valve 16 and the exhaust circulation valve 16 is closed. On the other hand, the exhaust circulation valve 16 and the suction pump 18 are controlled by the three-way valve 17.
Are communicated with each other, a negative pressure is applied to the exhaust circulation valve 16 and the exhaust circulation valve 16 is opened. As a result, exhaust gas is introduced into the intake air. The NO _X amount generated in the internal combustion engine increases as the flame propagation speed during combustion increases. Further, the NO _X generation amount increases as the combustion temperature during combustion increases. On the other hand, since the inert gas slows down the flame propagation during combustion, the flame propagation speed during combustion decreases as the amount of inert gas in the intake air increases. Further, since the inert gas absorbs heat during combustion, the combustion temperature during combustion decreases as the amount of inert gas in the intake air increases. Therefore, when exhaust gas containing CO ₂ and H ₂ O, which are inert gases, is introduced into the intake air, the flame propagation speed during combustion decreases and the combustion temperature during combustion is suppressed to a low level. The accompanying generation of NO _X is suppressed.

In FIG. 1, a control unit (ECU) 40 is composed of a digital computer, and is connected to a CPU (microprocessor) 4 via a bidirectional bus 41.
2, a ROM (read only memory) 43, a RAM (random access memory) 44, a B-RAM (backup RAM) 45, an input port 46, an output port 47, and a clock generator 48. The output voltages of the intake pressure sensor 5, the upstream temperature sensor 13, the downstream temperature sensor 14, and the fuel pressure sensor 32 correspond to the corresponding AD converter 4.
9 to the input port 46. The output voltage of the crank angle sensor 6 is directly input to the input port 46. On the other hand, the output port 47 is connected to each of the fuel injection valves 2a to 2d and the three-way valve 1 via the corresponding drive circuit 50.
7 is connected.

Next, the operation of the internal combustion engine of this embodiment will be described. First, the fuel pressure in the common rail 30 is detected by the fuel pressure sensor 32 at a predetermined crank angle in the compression stroke of each of the cylinders # 1 to # 4. Next, each cylinder # 1
The pre-injection is executed immediately before the compression top dead center of ~ ♯4,
A predetermined amount of fuel is injected from each of the fuel injection valves 2a to 2d. NO _X pre injection generated in the cylinder
This is an injection performed to reduce the volume and noise generated in the cylinder. Next, main injection is performed at a predetermined crank angle near the compression top dead center after the fuel supplied by pre-injection ignites in the cylinder. The main injection is an injection executed for driving the engine. The main injection fuel amount to be injected from each of the fuel injection valves 2a to 2d by the main injection is determined based on the depression amount of an accelerator pedal (not shown).

A valve opening time for opening the fuel injection valves 2a to 2d in order to supply the pre-injection fuel amount and the main injection fuel amount to be injected from the fuel injection valves 2a to 2d by the pre-injection and the main injection. Is determined based on the fuel pressure in the common rail 30. The pre-injection and main injection in each cylinder are executed in the order of the first cylinder # 1, the third cylinder # 3, the fourth cylinder # 4, and the second cylinder # 2.

Furthermore HC for purifying NO _X in NO _X catalyst 12 in the present embodiment, i.e. supplied to the NO _X catalyst 12 fuel as follows. First, NO _X
NO _X from the engine to the fuel quantity to be supplied to the catalyst 12 is estimated from the output of the intake air pressure sensor 5 and the crank angle sensor 6
It is determined based on the discharge amount and the outputs of the upstream temperature sensor 13 and the downstream temperature sensor 14. Here, when NO _X catalyst 12 fuel amount to be supplied to less than a predetermined amount in a state where the exhaust recirculation valve 16 is opened, the main injection after the main injection is executed in the third cylinder ♯3 Separately, the sub-injection is performed in the expansion stroke or the exhaust stroke of the third cylinder # 3. Third fuel injection valve 2c by sub-injection
HC for purifying exhaust gas supplied from the
C) is caused to reach the NO _X catalyst 12 by the exhaust gas. NO _X in the exhaust gas is purified by the NO _X catalyst 12 by the reducing action of the purifying HC.

The predetermined amount is set to an amount that does not cause a problem in engine operation even if fuel is introduced into the intake air via the exhaust circulation pipe. The execution timing of the sub-injection is determined based on the temperature in the third cylinder # 3 estimated from the output of the upstream temperature sensor 13 and the fuel pressure in the common rail 30. Further, the valve opening time during which the third fuel injection valve 2c is opened to supply the amount of sub injection fuel to be injected from the third fuel injection valve 2c by the sub injection is determined based on the fuel pressure in the common rail 30.

On the other hand, when the amount of fuel to be supplied to the NO _X catalyst 12 is equal to or greater than a predetermined amount, the exhaust gas circulation valve 1
6 is closed, and thereafter, after the main injection is performed in the third cylinder # 3, the third cylinder # 3 is executed separately from the main injection.
The sub-injection is executed in the expansion stroke or the exhaust stroke of. Thus it is possible to prevent the exhaust gas containing a predetermined amount or more of the fuel is introduced into the intake air, and the NO _X in the exhaust gas can be purified in the NO _X catalyst.

Also, NO_XHC adheres to the catalyst 12 and N
O_XWhen the catalyst 12 is poisoned, that is, deteriorated, NO
_XNO in catalyst 12_XBecause there is no purification action,
HC supplied by sub-injection is NO_XIn catalyst 12
NO without being consumed_XIt passes through the catalyst 12. Therefore
In this embodiment, NO_XWhen the catalyst 12 has deteriorated,
Stop firing. This allows it to be supplied by sub-injection
HC is NO_XCan be discharged outside through the catalyst
Is prevented. Furthermore, NO_XWith the catalyst 12 degraded
NO emitted from the engine when there is_XOutside without being purified
Will be discharged. Therefore, in this embodiment, NO_XCatalyst 1
2 is performed as follows.
You. First, the exhaust circulation valve 16 is closed and the exhaust circulation pipe 15 is closed.
Close, then NO_XThe temperature of the catalyst 12 is a predetermined temperature
When the temperature exceeds the predetermined amount,
Is supplied into the third cylinder # 3 by sub-injection. The above
The predetermined temperature is such that the HC supplied by the sub-injection is N
O_XThe temperature is set so as to be burned in the catalyst 12. I
Therefore, in the present embodiment, the predetermined amount
The exhaust circulation pipe is closed before injecting the above fuel.
Exhaust gas containing more than a predetermined amount of fuel
It is prevented from being introduced into the air. Furthermore, exhaust gas
Is not introduced into the intake air, so combustion in the cylinder
The temperature rises. Therefore NO _XEarly temperature of catalyst 12
Or higher than a predetermined temperature. NO_Xcatalyst
HC supplied to NO. 12 is NO_XFuel attached to catalyst 12
With NO_XIt is burned in the catalyst 12.
No_XThe deterioration of the catalyst 12 is recovered.

Next, the pre-injection / main injection execution control of this embodiment will be described with reference to the flowchart of FIG. In the flowchart of FIG. 2, n indicates a cylinder number,
It changes in the order of 3, 4, and 2. First, in step S110, the current crank angle CA is set to a predetermined pre-injection crank angle PC at which pre-injection is to be performed in the n-th cylinder.
It is determined whether or not Apn (CA = PCApn). If it is determined in step S110 that CA = PCApn, the process proceeds to step S112, in which the fuel injection valve of the n-th cylinder is opened for a predetermined pre-injection opening time tpn to execute pre-injection, and step S114 is performed. Proceed to. On the other hand, if it is determined in step S110 that CA ≠ PCApn, step S110 is repeated until it is determined that CA = PCApn.

In step S114, the current crank angle CA is a predetermined main injection crank angle PCAmn at which the main injection is to be performed in the n-th cylinder (CA = PC
Amn). If it is determined in step S114 that CA = PCAmn, the process proceeds to step S1.
Proceeding to 16, the fuel injection valve of the n-th cylinder is opened for the predetermined main injection valve opening time tmn, the main injection is executed, and the process ends. On the other hand, in step S114, CA ≠
If it is determined that PCAmn, step S114 is repeated until it is determined that CA = PCAmn.

Next, the main injection fuel amount calculation control of this embodiment will be described with reference to the flowchart of FIG. Note that FIG.
In the flowchart, n indicates a cylinder number,
It changes in the order of 3, 4, and 2. First, the depression amount Da of the accelerator pedal is read in step S210. Next, proceeding to step S212, the fuel injection required to inject the main injection fuel amount to be supplied into the n-th cylinder by the main injection from the fuel injection valve based on the accelerator pedal depression amount Da read in step S210. Valve opening time t
Calculate mpn. Next, proceeding to step S214, the valve opening time tmpn calculated in step S212 is set to the main injection valve opening time tmn, and the process ends.

Next, the sub-injection execution control of this embodiment will be described with reference to the flowchart of FIG. First, step S
At 310, it is determined whether or not the current crank angle CA is a predetermined sub-injection crank angle CAs3 at which the sub-injection is to be performed in the third cylinder (CA = CAs3). If it is determined in step S310 that CA = CAs3, the flow advances to step S312 to open the third fuel injection valve 2c in the third cylinder for a predetermined sub-injection opening time ts3 to execute sub-injection. , And the process ends. On the other hand, if it is determined in step S310 that CA ≠ CAs3, step S310 is repeated until it is determined that CA = CAs3.

Next, the sub-injection fuel amount calculation control of this embodiment will be described with reference to the flowchart of FIG. First, in step S410, the catalyst upstream temperature Tu detected by the upstream temperature sensor 13, the catalyst downstream temperature Td detected by the downstream temperature sensor 14, the intake air pressure Pi detected by the intake pressure sensor 5, the crank angle sensor Angle CA and Fuel Pressure Sensor 32 Detected by Sensor 6
The fuel pressure Pc in the common rail 30 detected by the above is read. Next, the process proceeds to step S412 and proceeds to step S410.
The fuel injection valve opening time tsp required to inject the sub-injection fuel amount to be supplied into the third cylinder by the sub-injection from the third fuel injection valve 2c on the basis of the data read in at the time tsp
3 and the sub-injection execution timing PCAs3 at which the sub-injection is to be executed, and then proceeds to step S414.

Next, in step S414, NO_XCatalyst 12
It is determined whether or not is poisoned by HC. Stay
NO in step S414_XCatalyst 12 poisoned by HC
When it is determined that the
HC is NO_XWhen it is determined that the catalyst has passed through the catalyst 12,
Proceeding to step S416, the sub-injection execution control of FIG.
Next, proceeding to step S418, the exhaust circulation valve 16 is closed.
And prepare for the catalyst deterioration recovery process to be executed later.
Proceeding to step S420, the control proceeds to a predetermined time Ptsp3.
A value obtained by multiplying the number α is set as the sub-injection valve opening time ts3,
Proceed to step S422. Note that the coefficient α is larger than 1.
No. On the other hand, if NO in step S414 _XCatalyst 12
If it is determined that HC has not been poisoned,
Proceed to S426.

In step S422, the catalyst upstream side temperature Tu
Is equal to or higher than a predetermined catalyst upstream-side temperature PTu (T
u ≧ PTu) is determined. Incidentally, the catalyst upstream temperature Tu predetermined supplied to the NO _X catalyst 12 H
This is the temperature at which C is burned. If it is determined in step S422 that Tu ≧ PTu, the process proceeds to step S422.
Proceeding to 424, the crank angle CAsp3 calculated in step S412 is set to the predetermined crank angle CAs3 at which the sub-injection is to be executed, and then proceeding to step S424 to start the sub-injection execution control of FIG. finish. When the sub-injection is performed in this manner, the deterioration of the NO _X catalyst 12 is recovered. On the other hand, in step S422, Tu
If it is determined that <PTu, Step S420 is repeated until it is determined that Tu ≧ PTu. Step S
At 426, the valve opening time ts calculated at step S412
p3 is smaller than a predetermined time Ptsp3 (ts
It is determined whether or not p3 <Ptsp3). Step S4
If it is determined in step 26 that tsp3 <Ptsp3, the process proceeds to step S428 to open the exhaust gas circulation valve 16, and then in step S430, the valve opening time tsp3 calculated in step S412 is replaced with the sub-injection opening time ts3. Then, the process proceeds to step S424, in which the crank angle CAsp3 calculated in step S412 is set to the predetermined crank angle CAs3 at which the sub-injection is to be executed, and then proceeds to step S424 to execute the sub-injection execution control of FIG. Is started, and the process ends. On the other hand, step S426
When it is determined that tsp3 ≧ Ptsp3,
Proceeding to step S432, the exhaust gas circulation valve 16 is closed, and then proceeding to step S424, the crank angle CAsp3 calculated in step S412 is set to a predetermined crank angle CAs3 at which sub-injection is to be executed. Proceeding to S424, the sub-injection execution control of FIG. 4 is started, and the process ends. In the above embodiment, the sub-injection is executed from the same fuel injection valve as the main injection to supply the HC for purification. However, HC supply means is separately provided in the exhaust branch pipe to which the exhaust circulation pipe is not connected. Purification HC may be supplied from a supply unit. Further, in a state where the oxygen concentration in the exhaust gas is very high, NO _X is absorbed and stored, and HC is stored.
The it is also possible to apply the present invention on the catalyst by releasing NO _X is reacted with HC when supplied.

[0026]

According to the first and second aspects of the invention, the exhaust circulation pipe is always closed when a predetermined amount or more of hydrocarbon is injected into the exhaust gas. Therefore, exhaust gas containing a predetermined amount or more of hydrocarbons is prevented from being introduced into the intake air through the exhaust circulation pipe.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a flowchart showing pre-injection / main injection execution control according to the embodiment of the present invention.

FIG. 3 is a flowchart illustrating main injection fuel amount calculation control according to the embodiment of the present invention.

FIG. 4 is a flowchart showing sub-injection execution control according to the embodiment of the present invention.

FIG. 5 is a flowchart showing a sub injection fuel amount calculation control according to the embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 engine body 7a first exhaust branch pipe 7b second exhaust branch pipe 7c third exhaust branch pipe 7d fourth exhaust branch pipe 9 collecting pipe 11 turbocharger 11a intake turbine wheel 11b exhaust side turbine wheel 12 ... NO _X catalyst 15 ... exhaust circulation pipe 16 ... exhaust recirculation valve 17 ... three-way valve 20 ... exhaust passage 30 ... common rail 32 ... pressure sensor

Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02M 25/07 580 F02M 25/07 580A

Claims (2)

[Claims] An exhaust circulation pipe for collecting exhaust branch pipes connected to respective cylinders, connecting them to a common exhaust pipe, arranging a catalyst in the common exhaust pipe, and introducing exhaust gas into intake air. Is connected to at least one of the exhaust branch pipes, and the catalyst should be supplied to the catalyst in an exhaust branch pipe different from the exhaust branch pipe to which the exhaust circulation pipe is connected or in a cylinder to which the other exhaust branch pipe is connected. In the exhaust gas purifying apparatus for a multi-cylinder internal combustion engine that injects hydrocarbons, the hydrocarbon amount determining means for determining the amount of hydrocarbons to be supplied to the catalyst should inject a predetermined amount or more of hydrocarbons. An exhaust purification device for a multi-cylinder internal combustion engine, characterized in that when it is determined, a predetermined amount or more of hydrocarbon is injected after closing the exhaust circulation pipe. 2. The hydrocarbon amount determination means determines that a predetermined amount or more of hydrocarbons should be injected when the catalyst temperature is higher than a predetermined temperature and the catalyst is poisoned by hydrocarbons. 2. The exhaust gas purifying apparatus for a multi-cylinder internal combustion engine according to claim 1, wherein: