JPH059484Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an exhaust gas purification device that is installed in the exhaust system of an internal combustion engine and that simultaneously purifies HC, CO, and NO _x in exhaust gas.

[Conventional technology and problems]

Conventionally, HC, CO and
An exhaust purification system using a three-way catalyst to simultaneously purify three components of NO _x is known. However, as shown in Figure 3, the range of air-fuel ratios that can simultaneously purify these three components is narrow, so in exhaust purification systems for engines with electronically controlled fuel injection devices, O ₂ sensors used for air-fuel ratio control are used. If the air-fuel ratio leans towards the rich or lean side due to deterioration of the
The amount of NO _x or HC released will increase.

Therefore, a sweeper system that includes an oxidation catalyst in addition to the three-way catalyst has been proposed. In other words, this sweeper system has a three-way catalyst in the upstream part of the container into which exhaust gas is introduced, and an oxidation catalyst in the downstream part, and the three-way catalyst purifies NO _x .
It purifies HC and CO using an oxidation catalyst, and in order to make the oxidation catalyst work, 2
Air is now being supplied. In order to introduce secondary air in this way, the applicant has already proposed the following in Utility Application No. 103723/1983 (Kokai No. 19618/1983).
We proposed a configuration in which one cylinder is deactivated during low-load operation and used as an air pump.

However, such a configuration in which one cylinder is used as an air pump requires a valve device to switch between stopping and returning the cylinder, and the durability of the movable part of this valve device poses a problem. In addition, with this configuration, the amount of secondary air supplied is too large, which causes the oxidation catalyst to be cooled and its temperature to drop, preventing sufficient reaction and increasing the amount of HC and CO released. occurs. Furthermore, when one cylinder is deactivated, the vibration of the entire engine increases, which is undesirable in terms of noise, and conversely, when that cylinder is restarted, there is a problem that a shock occurs because that cylinder has been cooled. .

On the other hand, in order to reduce NO _x in exhaust gas,
Exhaust gas recirculation (EGR) systems are known that guide exhaust gas to the intake passage to suppress the generation of NO _x in the combustion chamber.

However, if exhaust gas recirculation is performed while the engine is running with the air-fuel mixture in a lean state, combustion becomes unstable and fluctuations in the combustion state increase, resulting in a problem that good drivability cannot be obtained.

The present invention was made with the aim of solving the above problems all at once.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention aims to provide more than half of the first cylinders, which are always supplied with an air-fuel mixture near the stoichiometric air-fuel ratio during engine operation; A second cylinder, which is smaller in number than the number of cylinders, is supplied with a lean air-fuel mixture only when the engine is operating at low load, and operates with an air-fuel mixture near the stoichiometric air-fuel ratio when operating other than at low-load operation. a catalyst device provided in an exhaust passage connected to each of the cylinders and having a three-way catalyst and an oxidation catalyst; and an exhaust gas recirculation mechanism that recirculates only the exhaust gas of the first cylinder to the intake passage of the cylinder. In the catalyst device, the three-way catalyst is disposed upstream of the oxidation catalyst, and the exhaust gas from the first cylinder passes through the three-way catalyst and then flows into the oxidation catalyst. An exhaust gas purification device for an engine is provided, characterized in that exhaust gas from a second cylinder is configured to flow into a position downstream of a three-way catalyst and upstream of an oxidation catalyst.

[Operation] Normally, the operation is performed with an air-fuel mixture near the stoichiometric air-fuel ratio, but in low-load operating conditions, lean air-fuel mixture is supplied only to a relatively small number of second cylinders, so the second cylinder While the engine continues to operate and generates torque through low _NOx combustion using a lean mixture, a significant proportion of excess oxygen remaining in the exhaust gas flows into the oxidation catalyst along with the exhaust gas.

Apart from that, a relatively large number of primary
The cylinder first causes the exhaust gas to flow into the three-way catalyst. Therefore, the exhaust gas of the first cylinder, which has been purified mainly of NO _x , further flows into the oxidation catalyst and mixes with the exhaust gas of the second cylinder mentioned above. HC and CO are also purified by oxidation by the remaining oxygen. Therefore, even without providing a special air pump for the oxidation catalyst, excess oxygen in the exhaust gas of the second cylinder is supplied to the exhaust gas of a larger number of other cylinders at the oxidation catalyst. Also, at that time, the second
Since the cylinders are in operation and generate torque, there is no risk of vibrations in the entire engine due to torque fluctuations or shocks when switching, unlike when some cylinders are stopped and used as an air pump.

Exhaust gas recirculation is performed only for a relatively large number of first cylinders and not for a relatively small number of second cylinders. Therefore, there is no fear that the lean mixture will be supplied to the second cylinder and the combustion state of the second cylinder will become unstable. During low-load operation, the second cylinder uses a lean mixture to achieve low _NOx combustion, and in other operating conditions, as with the first cylinder, it basically supplies a mixture at a stoichiometric air-fuel ratio. However, since the number of cylinders is relatively small, there is no problem overall even if exhaust gas recirculation is not performed. In this way, in operating conditions other than low-load operation,
Since the air-fuel mixture near the stoichiometric air-fuel ratio is supplied not only to the first cylinder but also to the second cylinder, sufficient engine output is ensured.

〔Example〕

The present invention will be explained below with reference to illustrated embodiments.

FIG. 1 shows an engine to which an embodiment of the present invention is applied. The engine body 10 includes #1, #2,
#3, #4 cylinders 11, 12, 13, 14 are provided, among which #1, #2, #3 cylinders 11, 1
Numbers 2 and 13 are first cylinders to which the exhaust manifold 25 is connected, and cylinder #4 is a second cylinder to which an exhaust pipe 36 independent of the exhaust manifold 25 is connected.

#1, #1, #3, #4 cylinders 11, 12, 1
Intake manifold 1 connected to 3 and 14
Each of the branch pipes 5 is provided with fuel injection valves 21, 22, 23, and 24 corresponding to each cylinder. Intake ports 31, 3 that communicate these branch pipes with each cylinder
Among the cylinders 2, 33, and 34, the first cylinders 11, 12,
The intake ports 31, 32, and 33 communicating with the second cylinder 13 have a straight shape, and the intake port 34 communicating with the second cylinder 14 is a swirl port such as a helical port to generate an intake swirl. A throttle valve 17 is provided in the intake pipe 16 connected to the base of the intake manifold 15, and an air flow meter 1 is provided on the upstream side of the throttle valve 17.
8 is arranged, and an air cleaner 19 is installed on the most upstream side.
will be provided. After passing through the air cleaner 19, the air flow is measured by the air flow meter 18, and the air is measured by the air intake pipe 16.
The air introduced into the interior is regulated by the throttle valve 17, and then distributed to each branch pipe in the intake manifold 15, and is then distributed to the intake ports 31, 32, 3.
Each cylinder 11, 12, 13, 14 through 3, 34
is supplied to

An exhaust manifold 25 is connected to the exhaust ports of the first cylinders 11, 12, and 13, and an O ₂ sensor 26 is provided at the base of the exhaust manifold 25. The downstream opening of the front exhaust pipe 27 connected to this base is connected to the inlet part 41 of the catalyst device 40, and the catalyst device 4
The outlet portion 42 of the rear exhaust pipe 29 is connected to the upstream opening of the rear exhaust pipe 29 having the muffler 28 .
The catalyst device 40 has a three-way catalyst 43 and an oxidation catalyst 44, with the three-way catalyst 43 disposed near the inlet section 41 and the oxidation catalyst 44 disposed near the outlet section 42. Thus, a space 45 is formed between these catalysts 43 and 44. On the other hand, an exhaust pipe 36 is connected to the exhaust port 35 of the second cylinder 14 , and the downstream opening of the exhaust pipe 36 faces the space 45 of the catalyst device 40 .

Therefore, the exhaust gas from the first cylinders 11, 12, 13 passes through the three-way catalyst 43, and then passes through the oxidation catalyst 44 and is discharged to the rear exhaust pipe 29. On the other hand, exhaust gas from the second cylinder 14 is introduced into the space 45, passes through the oxidation catalyst 44, and is discharged to the rear exhaust pipe 29.

EGR pipe 60 is #1, #2, #3 cylinder 1
The exhaust manifold 25 connected to cylinders 1, 12, and 13 is connected to each branch pipe of the intake manifold 15 connected to these cylinders 11, 12, and 13. The EGR valve 61 is provided in the middle of the EGR pipe 60 and is driven by an actuator 62 to open and close the EGR pipe 60. The actuator 62 has a shell 63 partitioned by a diaphragm 64 to form a variable pressure chamber 65, and an EGR valve 61 connected to the diaphragm 64.
It is constructed by accommodating a spring 66 therein and connecting a negative pressure pipe 67 that opens near the throttle valve 17 of the intake pipe 16. When the throttle valve 17 is opened to a predetermined degree, the negative pressure in the intake pipe 16 is guided to the variable pressure chamber 65 via the negative pressure pipe 67, and the diaphragm 64 is thereby displaced toward the variable pressure chamber 65 against the spring 66. Then, the EGR valve 61 releases the EGR pipe 60.

The amount of fuel injected from the fuel injection valves 21, 22, 23, 24 is determined by the engine load (= intake air amount/
determined by the engine speed) and the oxygen concentration in the exhaust gas. Therefore, the electronic control unit (ECU) 50 equipped with a microcomputer receives a signal indicating the intake air amount from the air flow meter 18, a signal indicating the engine rotation speed from the rotation speed detector 51, and a signal indicating the engine rotation speed from the rotation speed detector 51.
Further, a signal indicating the oxygen concentration in the exhaust gas is inputted from the O ₂ sensor 26, respectively. ECU50 is
The fuel injection amount for each cylinder 11, 12, 13, 14 is set by a program according to the flowchart shown in FIG.

The control routine shown in Figure 2 is, for example, 200 msec.
Interrupts are processed every time. In this control routine, in step 101, the intake air amount and engine rotational speed are read, and in step 102, it is determined whether the engine is being operated at a high load. Engine load is expressed as intake air amount/engine speed,
If not operating under high load, step 103, 104
Execute. That is, #1, #2, #3 cylinder 1
Feedback control is performed so that the air-fuel ratios of Nos. 1, 12, and 13 are approximately the stoichiometric air-fuel ratio (slightly rich, air-fuel ratio≈14.5). This feedback control, as is conventionally known, is to control the fuel injection amount so that the value of the detection signal from the O ₂ sensor 26 becomes a predetermined value. On the other hand, the air-fuel ratio of #4 cylinder 14 is set to a super lean state (air-fuel ratio≈20).

Therefore, #1, #2, #3 cylinders 11, 1
The exhaust gases No. 2 and 13 are discharged into the exhaust manifold 25 as shown in FIG. However, #1, #2,
The exhaust gas of #3 cylinder is a little rich,
First, by passing through the three-way catalyst 43
_NOx is purified. Also, at this low load, the negative pressure introduced to the actuator 62 causes the EGR valve 6 to
1 opens, and a portion of the exhaust gas from the #1, #2, and #3 cylinders is thereby recirculated to the intake passages of these cylinders through the EGR pipe 60. Therefore,
_NOx in the exhaust gas from the #1, #2, and #3 cylinders is also reduced by this exhaust gas recirculation. On the other hand, HC contained in the exhaust gas passing through the three-way catalyst 43 and
Although CO is not sufficiently purified by the three-way catalyst 43, this exhaust gas is diluted by the exhaust gas from the #4 cylinder 14 in the space 45 and is led to the oxidation catalyst 44 in a lean state. HC and CO in this exhaust gas are sufficiently purified by this oxidation catalyst 44.

The #4 cylinder 14 operates in a super lean state, but at this time, the intake air introduced into the combustion chamber of the #4 cylinder 14 is generating a swirl flow through the intake port 34, so that the fuel injection valve 24 does not inject the fuel. Coupled with the fact that the timing is set to coincide with the intake stroke of the cylinder 14, the air-fuel mixture in the combustion chamber is stratified and stable combustion is performed. Exhaust gas from this #4 cylinder 14 is transferred to exhaust pipe 3.
6 to the space of the catalyst device 40 , where the HC and CO are purified by the oxidation catalyst 44 and discharged to the rear exhaust pipe 29 . In addition,
NO _x in the exhaust gas from the #4 cylinder 14 is present in a small amount because the air-fuel ratio is ultra-lean, so there is no problem even if it is not purified by the catalyst.

If it is determined in step 102 that the engine is being operated under high load, the process proceeds to step 105.
The control to make the air-fuel ratio of the #4 cylinder 14 lean is canceled, and fuel is supplied to all cylinders 11, 12, 13, and 14, and the amount of fuel is increased. Therefore, all cylinders are in a rich state (air fuel ratio =
12~13), and sufficient output can be obtained.

As described above, according to this embodiment, the #4 cylinder 14 operates in a lean state during low-load operation, so unlike the configuration in which some cylinders are deactivated,
The torque difference between each cylinder is small, engine vibration is reduced, and noise is reduced. Like this #4
Since the cylinder 14 operates even during low-load operation, the #4 cylinder 14 is not cooled, and when returning to normal operating conditions, there is less shock and the drivability is stable. Since the oxidation catalyst is not cooled by secondary air from the idle cylinders, the purification reaction of the catalyst is prevented from deteriorating. During this low-load operation, NO _x generated from the #1, #2, and #3 cylinders 11, 12, and 13 is recirculated to the intake passage side via the EGR pipe 60, and further purified by the three-way catalyst 43. #1, #2, #3, #4 cylinder 11, 1
HC and CO generated from 2, 13, and 14 are purified by the oxidation catalyst 44. Therefore, the exhaust gas is effectively purified. At this time again, #4
Since the exhaust gas of the cylinder 14 is not recirculated to the intake passage side, there is no risk of deterioration of combustion in the #4 cylinder 14, and engine stability is not impaired due to misfires or torque reduction, resulting in good drivability. Become. On the other hand, when the load increases to a certain extent, the amount of fuel is increased for all cylinders, and sufficient output is obtained.

Furthermore, this embodiment does not require a special secondary air supply device such as a pump, so it is inexpensive, and it also has excellent durability because it does not have moving parts such as a valve device as in the conventional case. There is.

Note that the number of first cylinders is not limited to three, and a plurality of second cylinders may be provided similarly.

[Effect of idea]

According to the present invention, a lean mixture is supplied to a relatively small number of second cylinders only during low-load operation, and the oxygen remaining in the exhaust gas is used to process the exhaust gas from the first cylinder in the oxidation catalyst. There is no need to install a special air pump for the oxidation catalyst, and since the second cylinder is always running and generating torque without stopping, some cylinders can be stopped and Unlike those used as air pumps, there is no vibration caused by torque fluctuations or shock during switching. Even though NO _x , HC, and CO in the exhaust gas are all effectively removed, the operating conditions at low loads do not become unstable, and the operation is sufficient at times other than low loads. Large output can be obtained.

[Brief explanation of drawings]

Figure 1 is a sectional view showing an engine to which an embodiment of the present invention is applied, Figure 2 is a flowchart of the control routine, and Figure 3 is a graph showing the purification rates of NO _x , HC, and CO with respect to the air-fuel ratio. be. 11, 12, 13...first cylinder, 14...second cylinder, 43...three-way catalyst, 44...oxidation catalyst, 60...EGR pipe, 62...EGR valve.

Claims (1)

[Scope of utility model registration request] When the engine is running, the first cylinder is always supplied with an air-fuel mixture near the stoichiometric air-fuel ratio and operates, and the number of cylinders is smaller than the number of first cylinders, and the engine is operated at low load. A second cylinder is provided with a lean air-fuel mixture only at times, and is operated with an air-fuel mixture near the stoichiometric air-fuel ratio during operation other than during low-load operation, and an exhaust passage connected to each of the above cylinders. , a catalyst device having a three-way catalyst and an oxidation catalyst, and an exhaust gas recirculation mechanism that recirculates only the exhaust gas of the first cylinder to the intake passage of the cylinder. It is arranged upstream of the oxidation catalyst so that the exhaust gas of the first cylinder passes through the three-way catalyst and then flows into the oxidation catalyst, and the exhaust gas of the second cylinder is arranged downstream of the three-way catalyst. 1. An engine exhaust purification device, characterized in that the exhaust gas is configured to flow into a position upstream of an oxidation catalyst.