JPS6139065Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an exhaust gas purification device for an internal combustion engine that includes a three-way catalyst device in the exhaust system.

A three-way catalyst device, which simultaneously oxidizes HC and CO contained in exhaust gas and reduces NOx, works effectively only when the air-fuel ratio of the mixture is within an extremely narrow range around the stoichiometric air-fuel ratio.

Therefore, in an internal combustion engine equipped with a three-way catalyst device, the amount of fuel supplied is often feedback-controlled so that the air-fuel mixture reaches the stoichiometric air-fuel ratio while detecting the oxygen concentration in the exhaust gas.

However, when warming up the engine, a rich air-fuel mixture is required to ensure smooth operation, so during such operations, feedback control is temporarily stopped and a rich air-fuel mixture is supplied to warm up the engine. We are trying to promote this.

However, when supplying a rich mixture like this,
HC and CO, which are unburned components contained in the exhaust gas, increase, and the three-way catalytic converter is unable to absorb these components due to lack of oxygen.
A phenomenon occurred in which HC and CO could not be fully oxidized.

Conventionally, as a measure against this problem, a device as shown in FIG. 1 has been proposed (Utility Model Application No. 160010/1983).

1 is the engine body, 2 is an air cleaner, 3 is an intake manifold, 4 is an intake throttle valve, and 5 is an exhaust manifold. A three-way catalyst device 6 is installed in the exhaust pipe 7, and an oxygen sensor 12 is installed upstream thereof. It will be done.

A fuel injection valve 13 is attached to each intake port of the intake manifold 3, and opens and closes in response to a drive pulse signal from a control circuit (microcomputer) 14 to direct fuel sent from the fuel tank (pump) 11 to the intake port. Supply injection.

The control circuit 14 includes an air flow meter 15 that measures the amount of intake air, an ignition coil 19 that outputs a signal corresponding to the engine speed, a cooling water temperature sensor 16 that detects the warm-up state of the engine, and the oxygen sensor 12 mentioned above. Output is input respectively.

While the engine is warming up, the control circuit 14 calculates the fuel injection amount based on the output of the air flow meter 15 and the ignition coil 19 so as to obtain a rich mixture, and opens and closes the fuel injection valve 13 in synchronization with the engine rotation. Activate.

On the other hand, after the engine warms up, the fuel injection amount calculated to obtain the stoichiometric air-fuel ratio is
The corrected pulse signal is used to open and close the fuel injection valve 13 to accurately feedback control the air-fuel mixture to the stoichiometric air-fuel ratio, thereby maintaining the three-way catalytic converter 6 at its best.

In order to deal with the increase in HC and CO in the exhaust gas due to the rich mixture during warm-up, the secondary air introduction passage 8
is installed in the exhaust system, and secondary air is introduced upstream of the three-way catalyst device 6 using the exhaust pulsation using the reed valve 10.

A cutoff valve 9 is interposed at the entrance of the secondary air introduction path 8, and is opened by a signal from the control circuit 14 only during warm-up when the cooling water temperature is below a predetermined value.

In this way, during warm-up when feedback control is stopped and a rich mixture is supplied, secondary air is simultaneously introduced upstream of the three-way catalyst device 6, so that the three-way catalyst device 6 can be efficiently used as an oxidation catalyst device. HC and CO can be effectively oxidized and removed.

After warming up, the shutoff valve 9 closes, so the supply of secondary air is stopped, and at the same time, the air-fuel mixture is feedback-controlled to the stoichiometric air-fuel ratio, and the three-way catalyst device 6 oxidizes HC and CO and reduces NOx.

However, when a rich air-fuel mixture is supplied during warm-up and secondary air is sent into the exhaust gas as described above, a new problem arises in that afterburn is more likely to occur during deceleration. This was particularly likely to occur when decelerating from high to medium speeds or when the throttle valve was fully closed after revving.

It is common for a car to be started before the engine has warmed up sufficiently, but if the vehicle enters a deceleration state while driving before the engine has finished warming up, the amount of fuel adhering to the inner walls of the intake manifold will increase rapidly, especially in the early stages of deceleration. The resulting negative pressure may cause the mixture to be sucked into the cylinder all at once, making the originally rich air-fuel mixture even richer, and the rich air-fuel mixture is not completely combusted and is emitted as exhaust gas.

When secondary air is supplied here, explosive combustion occurs. If such afterburn occurs repeatedly, the three-way catalyst device 6 may burn out, etc.
This may shorten the life of the catalyst.

In order to solve this problem, the present invention is designed to stop the supply of secondary air at the beginning of deceleration from a predetermined rotation speed until the end of warm-up. The purpose is to prevent afterburn and improve the durability of the catalyst.

Hereinafter, an embodiment of the present invention will be described based on FIG. 2, and the same reference numerals will be used for substantially the same parts as in FIG. 1.

In this embodiment, a carburetor 20 is used as a fuel supply device.
Therefore, the control circuit 14 normally controls the air-fuel ratio of the air-fuel mixture produced by the carburetor 20 to the stoichiometric air-fuel ratio by feedback control.

Specifically, the amount of air introduced from an air bleed connected to the fuel passage is controlled by an on/off type solenoid valve 21.

During warm-up, the air-fuel ratio of the air-fuel mixture is enriched to a predetermined state by, for example, fully closing the air bleed.

In order to detect the deceleration state, a throttle switch 22 is provided to detect when the intake throttle valve 4 is fully closed.
The control circuit 14 receives the signal from this switch 22,
The deceleration state is determined from the engine rotational speed signal (signal from the ignition coil 19) at that time.

During deceleration, the three-way solenoid valve 24 is switched to cut off the suction negative pressure via the negative pressure introduction path 25 and introduce atmospheric air into the diaphragm chamber 23 of the cutoff valve 9.

When atmospheric air is introduced into the diaphragm chamber 23, the diaphragm 27 is pushed by the spring 26, and the shutoff valve 9 is closed to stop introducing secondary air.

Note that the shutoff valve 9 and the reed valve 10 are provided inside the air cleaner 2.

The rest of the configuration is the same as that shown in FIG. 1. Next, the operation will be explained. As mentioned above, when the engine is warmed up, the air-fuel ratio feedback control is stopped, a rich mixture is supplied, and the shutoff valve 9 is opened to introduce secondary air into the exhaust.

As a result, unburned HC and CO are removed using the three-way catalyst device 6 as an oxidation catalyst device.

On the other hand, when the system shifts to a deceleration state during this warm-up period, that is, while the throttle valve 4 is fully closed and the rotation speed is above a predetermined value, the control circuit 14 switches the three-way solenoid valve 24 to release it to the atmosphere, and the shutoff valve 9 is fully closed. Hold.

Therefore, during this period, no secondary air is introduced into the exhaust gas, and even if exhaust gas containing unburned fuel is discharged,
Since there is no oxygen in the exhaust gas, explosive combustion will not occur all at once.

On the other hand, even if the throttle valve 4 is closed, there is no risk of afterburn during idling, where the engine speed is low, so the control circuit 14 switches the three-way solenoid valve 24 to guide the intake negative pressure to the diaphragm chamber 23. Open the shutoff valve 9 to introduce secondary air.

When air-fuel ratio feedback control is started after warm-up, the control circuit 14 outputs a signal to close the cutoff valve 9. In this state, the air-fuel mixture is at the stoichiometric air-fuel ratio, so the air-fuel mixture does not become very rich even in the early stages of deceleration, and there is almost no excess oxygen in the exhaust gas, so afterburn does not occur. In this embodiment, a carburetor is used as the fuel supply device, but the same effect can be obtained by using a fuel injection valve.

In addition, the suction negative pressure entering the diaphragm chamber 23 of the shutoff valve 9 is controlled by the three-way solenoid valve 24, but the on-off type solenoid valve 24 does not use suction negative pressure and operates the shutoff valve 9 with a signal from the control circuit 14. Needless to say, it may be opened and closed directly with a valve.

As described above, according to the present invention, when the air-fuel ratio feedback control is stopped and a rich mixture is being supplied during warm-up and a deceleration state is entered, the supply of secondary air is cut off. It is possible to prevent afterburn, which tends to occur at the beginning of deceleration or immediately after idling, and improve the durability of exhaust systems such as three-way catalytic converters.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a conventional device, and FIG. 2 is a schematic configuration diagram of the present invention. 1...Engine body, 3...Intake manifold, 4
...Intake throttle valve, 5...Exhaust manifold, 6...
Three-way catalyst device, 7...Exhaust pipe, 8...Secondary air introduction path, 9...Shutoff valve, 10...Reed valve, 1
2... Oxygen sensor, 14... Control circuit, 16...
Cooling water temperature sensor, 19...Ignition coil, 22...
Throttle switch, 24...3-way solenoid valve. 27
...Diaphragm.

Claims (1)

[Scope of utility model registration request] A three-way catalyst device installed in the exhaust passage of an internal combustion engine,
A secondary air introduction device that introduces secondary air into the upstream exhaust passage of this three-way catalyst device, an oxygen sensor that also detects the oxygen concentration of the upstream exhaust, and a cooling water temperature sensor that detects the warm-up state of the engine are installed. After warming up the engine, the operation of the secondary air introduction device is stopped and the air-fuel mixture supplied to the engine is feedback-controlled to the stoichiometric air-fuel ratio based on the output of the oxygen sensor. A device for detecting the deceleration state of an engine in an exhaust gas purification device for an internal combustion engine that controls the air-fuel ratio to be richer than the fuel ratio, operates a secondary air introduction device, and uses a three-way catalyst device as an oxidation catalyst device. 1. An exhaust gas purification device for an internal combustion engine, comprising: a control device that stops the operation of the secondary air introduction device even before warming up at an initial stage of deceleration from a predetermined rotation speed or higher.