JPH0586848A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide a means which efficiently supplies secondary air to exhaust systems of an internal combustion engine having independent exhaust systems in every one of two cylinder groups, such as a V-engine. CONSTITUTION:Secondary air is intaken from an intake pipe 3 through an air inlet pipe 21, and supplied to exhaust manifolds 4a, 4b of both banks of a V-engine 1 by means of an air pump 9. Control valves 10a, 10b are provided respectively on branch pipes 23a, 23b for supplying secondary air to each bank. The secondary air is alternately supplied to the banks by opening and closing the valves alternately with specified intervals. Exhaust secondary air-fuel ratios at respective banks are periodically changed to lean and rich sides, so that a supplying amount of the secondary air is reduced. As for the catalyst atmosphere, it is keeps a value of approximate a theoretical air-fuel ratio due to oxygen storage effect of catalysts 5a, 5b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more specifically to a means for supplying secondary air to each of the exhaust systems provided for every two cylinder groups, such as a V-type engine. The present invention relates to an exhaust emission control device.

[0002]

2. Description of the Related Art A catalytic converter using a three-way catalyst or the like is provided in an exhaust passage of an internal combustion engine to discharge HC, CO, NO _{x in} exhaust gas.
Exhaust gas purification devices that purify harmful components such as the above are generally used. As is known, HC and C in the catalyst
The oxidation reaction of the O component rapidly decreases when the air-fuel ratio becomes rich (fuel excess). On the other hand, during cold operation of the internal combustion engine, the amount of fuel is increased for the purpose of stabilizing the engine performance, and the air-fuel ratio becomes rich. Therefore, in order to prevent an increase in the amount of HC and CO components discharged from the catalyst and to accelerate the catalyst temperature rise by promoting the oxidation reaction of HC and CO, secondary air is introduced into the exhaust passage on the upstream side to make the exhaust air-fuel ratio lean. Measures to shift to the side are taken.

An example of an exhaust gas purifying device that supplies secondary air to each exhaust system of an internal combustion engine having independent exhaust systems in two cylinder groups such as a V-type engine There is one described in Japanese Patent Laid-Open No. 61-113913. In the device of the publication, air suction valves are provided on the exhaust manifolds of the left and right banks of a horizontally opposed engine, and the exhaust manifolds and the engine intake system are connected by secondary air supply pipes via the air suction valves. There is. When it is necessary to supply the secondary air when the engine is cold, both air suction valves are opened, and the secondary air is simultaneously supplied to the exhaust manifolds of both banks.

[0004]

[Problems to be Solved by the Invention] However, the above-mentioned actual exploitation 6
In the device of JP-A 1-113913, secondary air is supplied to both banks at the same time, and the exhaust gas of both banks is always kept lean (air excess). Therefore, a large amount of secondary air is supplied to the secondary air supply pipe. It is necessary to let air flow. For this reason, it is necessary to increase the diameter of the connection port and connection pipe for intake of secondary air from the intake system, making it difficult to secure the installation position of the connection port. There was a problem of worsening sex. Further, since the exhaust gases of both banks are always held to the lean side, the HC and CO components are sufficiently purified, but on the contrary, there is a problem that the purification capability of NO _X components is lowered. Furthermore, when the catalyst temperature is low at engine startup and the oxidation reaction on the catalyst is not sufficiently performed, the catalyst is cooled by the introduction of a large amount of secondary air and the catalyst activation temperature is reached (catalyst warm-up). ) Was delayed.

In view of the above problems, the present invention provides a secondary air supply pipe connection port to the intake system, piping, parts, etc. when supplying secondary air to two mutually independent exhaust systems such as a V-type engine. It is an object of the present invention to provide an exhaust gas purification device that can be simplified in size to improve the mountability, and can reduce the NO _x purification capacity and the delay in catalyst warm-up due to the supply of secondary air.

[0006]

According to the present invention, a plurality of cylinders are divided into two groups, and an exhaust system is provided for each cylinder group.
In an exhaust gas purification device that supplies secondary air, an air intake pipe that takes in secondary air from an intake system of the internal combustion engine, and a branch from the intake pipe to supply secondary air to each of the cylinder group exhaust systems. A secondary air supply pipe and a control valve arranged on the secondary air supply pipe branch portion or on each secondary air supply pipe on the downstream side of the branch portion, and alternately at predetermined intervals in each of the cylinder group exhaust systems. An exhaust gas purification apparatus for an internal combustion engine, characterized in that the control valve is operated to supply secondary air.

[0007]

The secondary air taken in from the intake system is supplied to the exhaust manifolds of both banks via the secondary air supply pipe and the control valve. Since the control valve operates to alternately supply the secondary air to both banks, the air-fuel ratio becomes lean in the exhaust system of each bank while the secondary air is being supplied, and the secondary air is Rich when not supplied.

Thus, by varying the exhaust air-fuel ratio between the rich side and the lean side at a predetermined interval, the oxygen storage effect of the catalyst is exerted, and the catalyst always operates near the stoichiometric air-fuel ratio. Good purification is performed for all three NO _x components. Further, by periodically varying the exhaust air-fuel ratio between the rich side and the lean side, it becomes possible to reduce the amount of secondary air by about half compared to the case where the lean side is always held as in the conventional case. It is possible to reduce the size and simplification of the connection port and the piping parts, and promote the catalyst warm-up.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of the exhaust gas purification device of the present invention. In FIG. 1, reference numeral 1 denotes an engine, and in this embodiment, a V type engine having a V type cylinder arrangement is used. Reference numeral 3 is an intake pipe for supplying intake air to the cylinders of both the left and right banks of the engine 1, 2 is an air cleaner provided at the inlet of the intake pipe 3, and 3a is a throttle valve.

The cylinders of the left and right banks of the engine 1 are connected to the exhaust pipe 7 via independent exhaust manifolds 4a and 4b.
a, 7b. Further, the exhaust pipes 7a and 7b are respectively provided with catalytic converters 5a and 5b using a three-way catalyst.
Is arranged to purify HC, CO, and NO _x components in the exhaust gas. Exhaust pipes 7a, 7b catalytic converter 5a,
Secondary air supply ports 8a and 8b are provided on the upstream side of 5b, and the secondary air is supplied to the catalyst upstream side via the two branch pipes 23a and 23b.

In this embodiment, an electric air pump 9 is provided for supplying secondary air. Air is sucked into the secondary air supply pipe 22 from the air cleaner 2 downstream side of the intake pipe 3 through the air intake pipe 21. Sending out. The secondary air supply pipe 22 is connected to the exhaust pipes 7a and 7a by the branch pipes 23a and 23b.
It is connected to the secondary air supply ports 8a and 8b. The branch pipes 23a and 23b are provided with check valves 12a and 12b for preventing backflow of exhaust gas into the branch pipes, as well as the secondary air supply ports 8.
control valves 10a, 1 for controlling the secondary air supply to a, 8b
0b is provided. The control valves 10a and 10b are solenoid valves, and open / close in accordance with the output of the control device 11 to open the branch pipe 23.
Control the flow of secondary air in a and 23b.

As will be described later, in this embodiment, the control device 11
Alternately opens and closes the control valves 10a and 10b at predetermined intervals to alternately supply the secondary air to the secondary air supply ports 8a and 8b. Therefore, the control valves 10 are
Instead of providing a and 10b, one electromagnetic three-way valve is provided at the branch portion of the branch pipes 23a and 23b from the secondary air supply pipe 22, and the branch pipes 23a and 23b are alternately arranged.
The electromagnetic three-way valve may be switch-controlled so as to communicate with the.

Further, an electronic control unit (ECU) shown by reference numeral 25 in the drawing comprises a known digital computer for performing basic control such as fuel injection control and ignition timing control of the engine.
Is. The ECU 25 controls the operation of the air pump 9 and the control device 11 by determining whether or not the secondary air needs to be supplied based on the engine cooling water temperature and the like other than the above. In this embodiment, the temperature of the engine cooling water in the secondary air supply is a predetermined value (for example, 40 ° C to 60 ° C).
It is performed when the engine warm-up is not completed. After the engine warm-up is completed, the ECU 25 controls the exhaust O ₂ sensors 6a, 6 provided on the exhaust manifolds 4a, 4b.
Since the fuel injection amount is feedback-controlled so that the exhaust gas has the stoichiometric air-fuel ratio based on the output of b, the secondary air supply is not required. When the engine is cold, in order to stabilize the operating condition of the engine, the fuel injection amount is increased without performing feedback control, so the exhaust air-fuel ratio is shifting to the rich side, and the secondary air is purified for purification of HC and CO components. Air supply is required. As described above, conventionally, the secondary air is supplied so that the exhaust air-fuel ratio (hereinafter referred to as "secondary air-fuel ratio") at the catalytic converter inlet is always kept leaner than the stoichiometric air-fuel ratio. Therefore, a large amount of secondary air is required to continuously supply the secondary air to the exhaust systems of both banks, which deteriorates the mountability of the device, reduces the NO _x purification capacity, and increases the warm-up time. It was

In the present invention, the control device 11 includes the control valve 10
By alternately opening and closing a and 10b and utilizing the oxygen storage effect of the catalyst, the amount of secondary air is reduced to solve the above problem. An oxygen storage component such as a rare earth oxide or a transition metal oxide is added to the catalyst. This oxygen storage component is
It absorbs oxygen in the exhaust under lean air-fuel ratio conditions and releases the absorbed oxygen under lean conditions under rich air-fuel ratio conditions to mitigate fluctuations in the exhaust air-fuel ratio and make the exhaust air-fuel ratio near the catalyst stoichiometric. Performs the action of approaching the fuel ratio. Therefore, the catalyst can always be maintained in the atmosphere near the stoichiometric air-fuel ratio by periodically interrupting the supply of the secondary air and changing the exhaust air-fuel ratio to the rich side and the lean side. However, since the oxygen storage capacity of the catalyst is limited, it is necessary to appropriately set the fluctuation cycle of the secondary air-fuel ratio in order to effectively use the oxygen storage effect. If the air-fuel ratio fluctuates to the lean side even after the fluctuation cycle is too long and the catalyst absorbs oxygen to the maximum oxygen storage capacity, the oxygen in the exhaust gas is no longer stored in the catalyst and is wasted from the exhaust pipe. Because it will be discharged.

As a result of the experiment, the fluctuation cycle of the air-fuel ratio is set to 0.
It has been found that the oxygen storage effect can be used most effectively when set to about 5 to 2 Hz. Therefore, in this embodiment, the control device 11 alternately opens and closes the control valves 10a and 10b in a cycle in the range of 0.5 to 2 Hz, and sets the exhaust secondary air-fuel ratios of both banks to the rich side and the lean side at the above cycle. It is fluctuating.

FIG. 2 shows the exhaust air-fuel ratio at the catalyst inlet and the exhaust air-fuel ratio at the catalyst outlet when the secondary air is continuously supplied as in the prior art and when the secondary air is periodically supplied as in this embodiment. It is a figure showing a change of exhaust air-fuel ratio. FIG. 2 (a) shows the exhaust air-fuel ratio at the catalyst inlet, the dotted line shows the case where secondary air is continuously supplied to always keep the exhaust air-fuel ratio on the lean side, and the solid line intermittently shows a constant cycle. The case where secondary air is supplied is shown. When the secondary air is supplied intermittently, the air-fuel ratio fluctuates between the lean side and the rich side according to ON / OFF of the secondary air.

FIG. 2B shows the exhaust air-fuel ratio at the catalyst outlet. When secondary air is continuously supplied (dotted line), the oxygen storage capacity of the catalyst is maintained in a saturated state, so oxygen is not absorbed or released by the catalyst and the air-fuel ratio at the catalyst outlet is The same change as the dotted line in FIG. On the other hand, when the secondary air is supplied intermittently (solid line), the absorption and release of oxygen are repeated according to the air-fuel ratio fluctuations on the catalyst inlet side, so the air-fuel ratio fluctuations on the inlet side are averaged and the catalyst is The air-fuel ratio at the outlet is close to the stoichiometric air-fuel ratio.

As can be seen from FIG. 2, when secondary air is continuously supplied to keep the air-fuel ratio lean as in the conventional case, it corresponds to the difference from the theoretical air-fuel ratio (FIG. 2 (b), A). It can be seen that the amount of air does not contribute to the oxidation reaction of the HC and CO components and is simply discharged through the catalyst. For this reason, there arises a problem that the amount of secondary air unnecessarily increases and that the NO _x purification capability of the catalyst is lowered in a lean atmosphere.
On the other hand, when the secondary air is supplied intermittently, the oxygen absorbed when the air-fuel ratio becomes lean at the catalyst inlet side is released at the rich air-fuel ratio, so the oxygen in the secondary air is effectively oxidized. It contributes to the reaction, and the HC and CO components can be satisfactorily purified with about half the amount of air that is supplied continuously from the secondary air. Moreover, since the catalyst is always kept near the stoichiometric air-fuel ratio, the NO _X purification capacity does not decrease.

Next, FIG. 3 shows a flowchart of the secondary air supply control operation. This routine is executed by the ECU 25 at regular intervals. When the routine starts in the figure, it is determined in step 110 whether the engine cooling water temperature is equal to or higher than a predetermined value T (for example, T = 60 ° C.), and if the water temperature is equal to or lower than the predetermined value, the cold fuel increase is performed in step 120. It is determined whether or not it has been broken. If the cooling water temperature is equal to or higher than the predetermined value in step 110, or if the amount of fuel is not increased in step 120 even if the water temperature is equal to or lower than the predetermined value, feedback control of the air-fuel ratio is performed and the exhaust gas is theoretically discharged. Since the air-fuel ratio is maintained, the secondary air is not supplied and the operation of the control device 11 is stopped (step 150) and the electric air pump 9 is stopped (step 160), and the routine is ended. On the other hand, if the fuel amount has been increased in step 120, the control valves 10a, 10
The controller 11 of b is operated, and then the electric air pump 9 is operated in step 140. Thereby, the control device 1
1 is for controlling the control valves 10a and 10b in a predetermined cycle (0.5 to 2H).
z) to open and close alternately, and the secondary air supply ports 8a of both banks,
Secondary air is intermittently supplied to each of 8b.

In the present embodiment, the discharge flow rate of the air pump is set to a flow rate at which the maximum required secondary air amount can be supplied and the discharge flow rate is not particularly controlled. It is also possible to calculate the exhaust air-fuel ratio from the amount and change the rotation speed of the electric air pump 9 to control the secondary air amount according to the operating conditions so that the secondary air-fuel ratio has an appropriate fluctuation range. Is.

Although the above embodiment has been described only for the case of supplying the secondary air by using the air pump, the present invention is similarly applicable to the case of introducing the secondary air by using the conventional air suction valve. Is.

[0022]

The exhaust gas purifying apparatus of the present invention is configured to alternately supply the secondary air to the exhaust systems of both banks of a V-type engine or the like, thereby reducing the overall secondary air supply amount and piping. The components can be downsized and simplified, and the mountability of the device can be improved. Further, according to the present invention, since the oxygen storage effect of the catalyst can be effectively utilized, HC, CO,
It becomes possible to maintain the purification ability of the NO _x 3 component high and prevent the catalyst warm-up time from increasing due to excessive secondary air supply.

[Brief description of drawings]

FIG. 1 is a schematic view showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram for explaining changes in the exhaust air-fuel ratio on the catalyst inlet side and the catalyst outlet side.

FIG. 3 is a flowchart showing a secondary air supply control operation.

[Explanation of symbols]

 1 ... V type engine 4a, 4b ... Exhaust manifold 5a, 5b ... Catalytic converter 8a, 8b ... Secondary air supply port 9 ... Air pump 10a, 10b ... Control valve 11 ... Control valve control device 21 ... Air intake pipe 22 ... Secondary Air supply pipes 23a, 23b ... Branch pipe 25 ... Electronic control device

Claims (1)

[Claims] 1. An exhaust gas purification apparatus for dividing a plurality of cylinders into two groups and supplying secondary air to each exhaust system of an internal combustion engine having an exhaust system for each cylinder group. An air intake pipe for taking in secondary air from the system, a secondary air supply pipe branched from the intake pipe for supplying secondary air to each of the cylinder group exhaust systems, and the secondary air supply pipe branching portion Or with a control valve arranged on each secondary air supply pipe on the downstream side of the branch portion,
An exhaust emission control device for an internal combustion engine, wherein the control valve is operated so as to alternately supply the secondary air to each of the cylinder group exhaust systems at predetermined intervals.