JP2005344535A - Secondary air supply device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently perform exhaust emission control and catalyst activation by secondary air supply without requiring a heating means. <P>SOLUTION: In a V-type internal combustion engine provided with an exhaust system having independent banks and having a catalytic converter installed in an exhaust duct after merge of the exhaust system, secondary air is supplied to the exhaust system of one bank and fuel increase is performed for all cylinder at a time of secondary air supply. Consequently, after-burn of HC occurs in the independent exhaust system in which secondary air is supplied, and after-burn of HC occurs in a part where exhaust systems of each bank merge to promote purification of HC and activation of the catalytic converter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a secondary air supply device for an internal combustion engine that aims at early activation of a catalyst device after starting the engine by supplying secondary air to an exhaust system.

In Patent Document 1, secondary air introduced into an exhaust pipe is heated by a heating means to raise the temperature, thereby reacting with harmful components in the exhaust efficiently and purifying the exhaust efficiently. There is a disclosure of a supply device.
JP 05-312034 A

However, in the configuration using the heating means as in the above prior art, the system cost increases by providing the heating means, and the exhaust gas purification performance changes due to the abnormal function of the heating means. There was a problem that the control system became complicated because it was necessary to add.
The present invention has been made in view of the above problems, and provides a secondary air supply device for an internal combustion engine capable of efficiently purifying exhaust gas and catalytic activity by supplying secondary air without requiring a heating means. The purpose is to do.

  Therefore, according to the first aspect of the present invention, in an internal combustion engine in which a plurality of exhaust systems directly below the internal combustion engine are provided independently, and a catalyst device is installed downstream of a collection portion of the plurality of exhaust systems, the plurality of exhaust systems A cylinder corresponding to an exhaust system to which secondary air is supplied and a cylinder corresponding to an exhaust system to which secondary air is not supplied when supplying the secondary air to a part of the secondary air. In contrast, the fuel supply amount is increased and corrected.

According to such a configuration, HC afterburning (oxidation) occurs in the exhaust system in which the secondary air is supplied due to the increase in fuel in the cylinder corresponding to the exhaust system in which the secondary air is supplied. Due to the increase in fuel in the cylinder corresponding to the exhaust system to which no fuel is supplied, the afterburning of HC further occurs at the collecting part of the exhaust system.
Therefore, even when the distance from the internal combustion engine to the catalyst device is long, the exhaust temperature can be kept high, and both effects of reducing HC due to early activation of the catalyst device and reducing HC due to afterburning of HC are achieved. Can be obtained without using heating means.

According to the second aspect of the present invention, the fuel supply amount increase correction is performed so that the total fuel amount matches the sum of the intake air amount and the secondary air supply amount of the internal combustion engine.
According to such a configuration, the air fuel ratio of the cylinder combustion mixture is corrected to be rich by dividing the plurality of independent exhaust systems into an increase corresponding to the amount of air that increases by the amount of secondary air. It is possible to generate afterburning of HC in the exhaust system to which HC is supplied and afterburning of HC at the junction of the exhaust system.

According to a third aspect of the present invention, the internal combustion engine has a plurality of banks, and has an independent exhaust system for each of the plurality of banks.
According to this configuration, in an internal combustion engine having a plurality of banks such as a V-type engine and a horizontally opposed engine, the secondary air is supplied to the exhaust system of some banks, while the fuel increase is made to the cylinders of all banks. I do.

Therefore, in an internal combustion engine having a plurality of banks such as a V-type engine and a horizontally opposed engine, the heating means is used for both the effects of reducing the HC due to the early activation of the catalytic device and reducing the HC due to the afterburning of the HC. It is obtained without.
The invention according to claim 4 is configured such that the increase in the fuel supply amount accompanying the supply of the secondary air is changed according to the increase in the fuel supply amount according to other conditions.

According to this configuration, when an increase is made in response to the supply of secondary air, if there is an increase request according to other conditions, the final increase level is set according to the increase according to the other conditions. By changing, the amount of increase appropriate to the supply state of secondary air is aimed at.
In the invention according to claim 5, the larger one of the increase correction request value corresponding to the supply of the secondary air and the increase correction request value according to other conditions is set as the increase target when the secondary air is supplied. It was set as the structure to do.

According to such a configuration, for example, when an increase correction is performed to ensure the operational stability after the engine is started, the increase request for ensuring the engine stability and the increase for responding to the supply of secondary air are performed. Since the larger one with the demand is selected, the necessary increase can be secured while avoiding the excessive correction.
It should be noted that the time when the increase correction request value corresponding to the supply of the secondary air is selected after the engine is started can be set as the supply start timing of the secondary air.

According to a sixth aspect of the invention, the ignition timing is retarded while the secondary air is being supplied.
According to such a configuration, the ignition timing is retarded during the supply of the secondary air, so that the temperature of the exhaust gas discharged from the engine is increased, thereby further increasing the temperature of the catalyst device.

Embodiments of the present invention will be described below.
FIG. 1 is a system configuration diagram of an internal combustion engine in the embodiment.
In FIG. 1, an internal combustion engine 1 is an engine used as a drive source for a vehicle, and is a V-type engine including left and right banks.
Exhaust gas from the cylinders of the right bank 1A and the left bank 1B is led out by exhaust manifolds 2A and 2B provided independently of each other.

Exhaust ducts 3A and 3B are connected to the collective portions of the exhaust manifolds 2A and 2B, and downstream ends of the exhaust ducts 3A and 3B are collected and connected to the collective duct 4.
The exhaust system composed of the exhaust manifold 2A and the exhaust duct 3A and the exhaust system composed of the exhaust manifold 2B and the exhaust duct 3B correspond to a plurality of independent exhaust systems provided immediately below the internal combustion engine 1.

The collective duct 4 is provided with a catalytic converter 5 having a three-way catalyst as a catalytic device.
On the other hand, the air that has passed through the air cleaner 6 is distributed and supplied to the cylinders of each bank through the intake pipe 7 to the internal combustion engine 1, and the intake air amount of the engine 1 is adjusted by the throttle valve 8.

Each cylinder is provided with a fuel injection valve 9 for supplying fuel to the intake port or cylinder of each cylinder.
Here, an air-fuel mixture is generated in the combustion chamber by the fuel injected from the fuel injection valve 9 to each cylinder and the air distributed to each cylinder, and the air-fuel mixture is ignited and burned by spark ignition by the spark plug 10. , Work to push down the piston.

The work of pushing down the piston in each cylinder is converted into the rotation of the crankshaft, and the rotation of the crankshaft is taken out and used for driving the vehicle.
Further, a secondary air supply device for supplying secondary air into the exhaust manifold 2B on the left bank 1B side is provided.
The secondary air supply device includes an air pump 11, a secondary air suction pipe 12, a secondary air supply pipe 13, and a 2 air control valve 14.

The air pump 11 is a device that forcibly feeds secondary air into the exhaust system by a pump unit driven by a motor (or engine).
The secondary air suction pipe 12 is a pipe that communicates the suction port of the air pump 11 with the intake pipe 7 between the air cleaner 6 and the throttle valve 8.
The secondary air supply pipe 13 is a pipe that communicates the discharge port of the air pump 11 and each branch portion of the exhaust manifold 2B.

The secondary air control valve 14 is interposed in the middle of the secondary air supply pipe 13 and is an electromagnetic valve that opens and closes the secondary air supply pipe 13 and is closed when the secondary air is not supplied. Thus, the backflow of the exhaust gas to the air pump 11 side is prevented.
The engine control unit (ECU) 20 includes a microcomputer, receives detection signals from various sensors, detects operating conditions of the internal combustion engine 1, and determines a fuel injection control signal and ignition according to the detection results. While outputting a signal, the air pump 11 and the 2 air control valve 14 are controlled to control the supply of secondary air.

  As the various sensors, an air flow meter 21 that detects an intake air amount of the engine 1 and a crank angle provided in the intake pipe 7 downstream of the connecting portion of the secondary air suction pipe 12 and upstream of the throttle valve 8. A crank angle sensor 22 for detecting the position, a water temperature sensor 23 for detecting the coolant temperature of the engine 1, and an air-fuel ratio sensor 24 for detecting the exhaust air-fuel ratio based on the oxygen concentration in the exhaust gas just before the catalytic converter 5 are provided. ing.

The engine control unit 20 calculates a basic fuel injection amount Tp from the intake air amount detected by the air flow meter 21 and the engine rotational speed calculated based on the signal from the crank angle sensor 22.
Further, various correction coefficients CO including at least a post-start-up increase coefficient Kas that is set according to the water temperature at the time of start-up and gradually subtracted after the start-up are calculated so that the air-fuel ratio detected by the air-fuel ratio sensor 24 matches the target air-fuel ratio. The air-fuel ratio feedback correction coefficient LMD to be performed and the correction amount Ts based on the battery voltage are obtained.

Then, a final fuel injection amount Ti is calculated based on the basic fuel injection amount Tp, various correction values CO, and air-fuel ratio feedback correction coefficient LMD, and the valve opening time of the fuel injection valve 9 is calculated based on the fuel injection amount Ti. To control.
Ti = Tp × CO × LMD + Ts
Here, referring to the time chart of FIG. 3, the secondary air supply control will be described according to the flowchart of FIG.

When the engine is started in step S1, it is determined in step S2 whether a secondary air supply start condition is satisfied.
As the supply start condition, it is determined that the water temperature at the start is equal to or lower than a predetermined temperature, and that the post-start-up increase coefficient Kas is lowered to the same level as a predetermined increase correction request at the time of supplying secondary air.

If the supply start condition is not satisfied, the process proceeds to step S3, the air pump 11 is kept OFF, and the secondary air is not supplied.
On the other hand, when the water temperature at the start is equal to or lower than the predetermined temperature and the post-startup increase coefficient Kas is reduced to the same level as the increase correction request at the time of supplying the secondary air, the process proceeds to step S4 and subsequent steps to supply the secondary air.

In step S4, the driving of the air pump 11 is started and the secondary air control valve 14 is controlled to open.
In step S5, the post-startup increase coefficient Kas is clamped to the increase correction request level at the time of secondary air supply, and the fuel injection amounts of all cylinders are increased and corrected in response to the increase correction request at the time of secondary air supply. .

That is, the post-start-up increase coefficient Kas after clamping is used as a value corresponding to an increase correction request at the time of secondary air supply, not a post-start-up increase request.
However, the correction level based on the increase coefficient Kas after starting may be reset to 0, and a correction coefficient that satisfies the increase correction request at the time of secondary air supply may be started instead.
Further, as the post-startup increase coefficient Kas decreases from the increase correction request at the time of secondary air supply, the increase correction coefficient at the time of secondary air supply is increased so that the post-startup increase coefficient Kas and the increase at the time of secondary air supply are increased. It is good also as a structure which aims at fuel amount increase from both of a correction coefficient.

According to the above configuration, during the period from the start to the end of the secondary air supply, the larger one of the request for the increase after starting and the increase request for supplying the secondary air is selected, and the increase correction of the fuel injection amount is performed. (See FIG. 3).
Accordingly, it is avoided that the increase request due to the condition other than the secondary air overlaps with the increase request for responding to the supply of the secondary air, and the excessive increase correction is avoided. As a result, the supply of the secondary air and the increase corresponding to the supply of the secondary air can be started at an early stage, while the activation timing of the catalytic converter 5 can be advanced.

Further, when the correction request due to the increase after start is greater than the increase correction request during the secondary air supply, the increase correction is performed according to the correction request due to the increase after start to ensure the operational stability immediately after the start. The purpose of increasing the weight can be achieved.
The increase correction request level at the time of supplying the secondary air is set to a value that can substantially obtain the total fuel amount corresponding to the theoretical air-fuel ratio with respect to the sum of the intake air amount of the internal combustion engine and the supply amount of the secondary air. The air-fuel ratio of the cylinder combustion mixture becomes richer than the stoichiometric air-fuel ratio, and the HC discharged to the exhaust system by the rich combustion is burned after in a lean atmosphere due to the supply of secondary air.

In addition, in synchronization with the start of the increase accompanying the supply of secondary air (0 reset of the increase after start-up), the air-fuel ratio feedback control for setting the target air-fuel ratio to the theoretical air-fuel ratio (excess air ratio λ = 1) is started.
When the secondary air is supplied and the fuel increase correction is performed as described above, afterburning of HC occurs in the exhaust system on the left bank 1B side to which the secondary air is supplied, and the exhaust temperature rises. It is done.
On the other hand, since secondary air is not supplied to the exhaust system on the right bank 1A side, there is almost no HC afterburning in the exhaust system on the right bank 1A side, but oxygen remaining from the afterburning on the left bank 1B side is included. When the exhaust gas having a relatively high temperature and the exhaust gas containing a lot of HC on the right bank 1A side merge, HC afterburning occurs again at the junction.

Accordingly, the exhaust gas whose temperature is increased by the afterburning is introduced into the catalytic converter 5 and the catalytic activity is promoted. On the other hand, the HC in the exhaust gas is converted into a harmless component by the afterburning, and the secondary air is heated. Without providing any means, early activation of the catalyst and reduction of HC emissions immediately after startup can be achieved.
When secondary air is supplied to the exhaust manifolds of the left and right banks, afterburning of HC occurs. In this case, if the exhaust pipe length to the catalytic converter 5 is long, the exhaust temperature decreases during that time, and the catalytic converter 5 cannot be sufficiently promoted.

On the other hand, if the HC afterburning occurs in two stages along the exhaust flow method, the exhaust temperature can be kept high and introduced into the catalytic converter 5. Even if the pipe length is long, the temperature rise of the catalytic converter 5 can be sufficiently promoted.
By the way, if the increase is excessive with respect to the supply amount of the secondary air, the exhaust air-fuel ratio at the inlet of the catalytic converter 5 becomes rich. Conversely, if the increase is too small with respect to the supply amount of the secondary air, the catalyst The exhaust air-fuel ratio at the inlet of the converter 5 becomes lean.

However, the exhaust air-fuel ratio at the inlet of the catalytic converter 5 is detected by the air-fuel ratio sensor 24, and the fuel injection amount is feedback controlled. As a result, the increase level during the supply of secondary air is the exhaust level at the inlet of the catalytic converter 5. The air-fuel ratio is corrected to the stoichiometric air-fuel ratio.
Therefore, even if there is an error in the preset increase correction request level when supplying secondary air, it is corrected to an increase level suitable for the supply amount of secondary air and the state of afterburning, and the catalyst activity is stably promoted. In addition, HC emissions can be stably suppressed.

In step S6, it is determined whether or not the ignition timing retard start condition is satisfied.
As the ignition timing retard start condition, for example, it is determined that a predetermined time has elapsed since the start of the secondary air supply, and the engine 1 is stably operated in a state where the supply of the secondary air and the increase correction are performed. After that, it is preferable to retard the ignition timing.
However, the ignition timing may be retarded simultaneously with the start of the supply of secondary air.

When the ignition timing retard start condition is satisfied, the routine proceeds to step S7, where the ignition timing is retarded from the normal value.
The retard amount at the ignition timing is set to a value that is within the stability limit in the combustion state of the rich air-fuel mixture due to the increase accompanying the supply of secondary air.
That is, the retard limit is increased by the amount that the fuel is increased and the air-fuel ratio of the combustion mixture is enriched, so that the ignition timing is retarded accordingly.

By retarding the ignition timing, the exhaust temperature discharged from the engine 1 can be raised, and the activation of the catalytic converter 5 can be further promoted in combination with the effects of the supply of secondary air and the increase in fuel. .
In step S8, it is determined whether or not a predetermined time has elapsed since the supply of secondary air by the air pump 11 was started.

When the secondary air is supplied for the predetermined time, the process proceeds to step S9, the air pump 11 is stopped, and the secondary air control valve 14 is closed.
In the next step S10, clamping of the post-startup increase coefficient Kas is stopped, and the increase level based on the post-startup increase coefficient Kas is reset to 0, thereby stopping the increase correction of all cylinders corresponding to the supply of secondary air.

In step S11, the ignition timing retard is stopped and returned to the normal ignition timing according to the engine load and the engine speed.
In the above embodiment, the internal combustion engine is a V-type engine. However, other than this, a W-type engine, a horizontally opposed engine, or the like may be used. The structure provided may be sufficient.

Furthermore, the increase to the cylinder corresponding to the exhaust system to which the secondary air is supplied differs from the increase to the cylinder corresponding to the exhaust system to which the secondary air is not supplied according to the afterburning state of the HC in the exhaust system. It can be set as the structure to make.
For example, the exhaust temperature at the downstream side of the secondary air supply unit in the exhaust system to which the secondary air is supplied is detected, while the exhaust temperature in the vicinity of the collecting part of the exhaust system is detected, and the HC is detected from these temperatures. It is possible to detect the burning state and increase or decrease the increase level between the left and right banks based on the detection result.

Furthermore, the fuel supply amount can be increased by, for example, injecting the fuel supply amount in the exhaust stroke and more actively supplying HC to the exhaust system.
Here, technical ideas other than the claims that can be grasped from the above embodiment will be described together with the effects thereof.
(A) In the secondary air supply device for an internal combustion engine according to any one of claims 1 to 6,
An air-fuel ratio sensor for detecting an exhaust air-fuel ratio at the inlet of the catalyst device;
A secondary air supply for an internal combustion engine, wherein the fuel supply amount is feedback-controlled so that the air-fuel ratio detected by the air-fuel ratio sensor becomes a stoichiometric air-fuel ratio when at least secondary air is supplied. apparatus.

According to such a configuration, by performing feedback control of the air-fuel ratio at the catalyst inlet to the stoichiometric air-fuel ratio, it is possible to supply fuel that is sufficient for afterburning with the supply of secondary air without excess or deficiency. The occurrence of catalyst activity failure due to increase or insufficient increase is avoided.
(B) In the secondary air supply device for an internal combustion engine according to claim 5,
The other increase correction is a post-start-up increase correction that is gradually changed from the start of the engine, and the required value in the post-start-up increase correction is the same as the increase correction required value when the secondary air is supplied. A secondary air supply device for an internal combustion engine, wherein supply of secondary air is started when the level drops to a level.

According to such a configuration, when the increase after starting is gradually subtracted and becomes small until it matches the increase correction request value when supplying the secondary air, the supply of the secondary air is started from that point. An increase correction corresponding to the supply of secondary air is performed.
Therefore, it is possible to start the supply of secondary air at an early stage while satisfying the request for an increase after start-up, and it is possible to avoid an excessive increase in the fuel supply amount after the start of the supply of secondary air.
(C) The secondary air supply device for an internal combustion engine according to claim 6,
A secondary air supply device for an internal combustion engine, wherein the ignition timing is retarded after a predetermined time has elapsed from the start of supply of the secondary air.

  According to this configuration, the ignition timing can be retarded after the operation in a state where the secondary intake air is supplied and the fuel supply amount is increased, and the operation stability is greatly reduced by the retard of the ignition timing. You can avoid that.

1 is a system configuration diagram of an internal combustion engine in an embodiment. The flowchart which shows the secondary air supply control in embodiment. The time chart which shows the change characteristic of the secondary air supply amount in the embodiment, the fuel amount increase, the air-fuel ratio, the exhaust temperature, and the ignition timing.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 1A ... Right bank, 1B ... Left bank, 2A, 2B ... Exhaust manifold, 3A, 3B ... Exhaust duct, 4 ... Collecting duct, 5 ... Catalytic converter, 6 ... Air cleaner, 7 ... Intake pipe, 8 ... Throttle valve, 9 ... Fuel injection valve, 10 ... Spark plug, 11 ... Air pump, 12 ... Secondary air suction pipe, 13 ... Secondary air supply pipe, 14 ... Two air control valve, 20 ... Engine control unit (ECU), 21 ... Air flow meter, 22 ... Crank angle sensor, 23 ... Water temperature sensor, 24 ... Air-fuel ratio sensor

Claims (6)

A secondary air supply device for an internal combustion engine, wherein a plurality of exhaust systems directly below the internal combustion engine are provided independently, and a catalyst device is installed downstream of a collection portion of the plurality of exhaust systems,
A cylinder corresponding to an exhaust system to which secondary air is supplied when supplying secondary air to a part of the plurality of exhaust systems, and an exhaust system to which secondary air is not supplied A secondary air supply device for an internal combustion engine, wherein an increase correction of the fuel supply amount is performed for the cylinders corresponding to.   2. The secondary of the internal combustion engine according to claim 1, wherein an increase correction of the fuel supply amount is performed so that the total fuel amount matches the sum of the intake air amount and the secondary air supply amount of the internal combustion engine. Air supply device.   The secondary air supply device for an internal combustion engine according to claim 1 or 2, wherein the internal combustion engine includes a plurality of banks and has an independent exhaust system for each of the plurality of banks.   The internal combustion engine according to any one of claims 1 to 3, wherein the increase in the fuel supply amount accompanying the supply of the secondary air is changed according to the increase in the fuel supply amount according to other conditions. Engine secondary air supply device.   The larger one of the increase correction request value corresponding to the supply of secondary air and the increase correction request value according to other conditions is set as an increase target when supplying the secondary air. The secondary air supply device for an internal combustion engine according to claim 4.   The secondary air supply device for an internal combustion engine according to any one of claims 1 to 5, wherein the ignition timing is retarded during the supply of the secondary air.

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