JPH0327750B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an internal combustion engine that sets the air-fuel ratio during idling to the lean side.

Some internal combustion engines set the air-fuel ratio to a value on the lean side when idling, but in this case, when accelerating from idling, the air-fuel ratio is changed to the rich side. In order to improve the acceleration response, it is necessary to quickly switch the air-fuel ratio. However, in conventional carburetors, this switching cannot be performed quickly, resulting in delayed response and poor acceleration.

JP-A No. 53-31034 proposes an air introduction passage connecting the carburetor body passage downstream of the throttle valve with an atmospheric source, and a diaphragm type on-off valve provided in this air introduction passage. . This prior art describes that the on-off valve may be opened to introduce air when the vehicle is idling. However, in the case of the prior art, when air is introduced during idle, a large amount of air is sucked in through the air introduction passage that bypasses the throttle valve during idle.
There is a problem that the engine speed during idling fluctuates because the amount of intake air increases.

The present invention aims to solve this problem and reduce the change in air flow rate when the engine is lean during idle. In order to achieve this object, the air-fuel ratio control device for an internal combustion engine according to the present invention has the following features:
A valve that is open when the engine is idling and is closed at other times, having an air introduction passageway with one end open to the slow system fuel passageway that connects the slow port opening in the main body to the fuel supply source and the other end connected to the atmosphere. Means is provided in the air introduction passage.

Referring to the drawings, in FIG. 1, reference numeral 10 denotes a carburetor main body, within which a small bench lily 14 is located inside a large bench lily 12, and a throttle valve 16 is located downstream of the small bench lily 14.

A slow port 18 is provided near the throttle valve 16 in the idle position, and an idle port 20 is located downstream thereof, and the idle port 20 communicates with the slow port 20 via an idle adjustment screw 22. The slow port 20 communicates with a float chamber (not shown) via a slow fuel passage 24.

According to the present invention, the union 26 is installed so that one end thereof opens in the slow fuel passage 24 near the slow port 18, and the other end of the union 26 is connected to the pipe 28, the check valve 30 as valve means, and the pipe 32.
It is connected to an atmospheric air outlet port 34 formed slightly upstream of the idle position of the throttle valve 16 through the throttle valve 16. The check valve 30 is arranged to allow atmospheric air to flow from the atmospheric air outlet port 32 to the slow port 18.

Next, to describe the operation shown in FIG. 1, at idle, the throttle valve 16 is connected to the atmospheric pressure outlet port 34.
, so port 34 is at atmospheric pressure, while slow port 18 is at negative pressure. This creates a flow of air from the atmosphere outlet port 34 through the pipe 32, check valve 30, pipe 28, and union 26 into the slow port 18. Therefore, the pressure in the slow passage 24 approaches atmospheric pressure, and the slow passage 24
4, the amount of fuel sucked in decreases, and as a result, the air-fuel ratio at idle is set higher by this amount.
The value is on the lean side as shown in A in the figure.

In the region B of FIG. 2 where the throttle valve 16 is rotated from the idle state and the amount of intake air is increased, the throttle valve 16 is located upstream of the port 34, so the port 34 becomes a negative pressure and the check valve 30 is closed. . Therefore, air cannot flow from the atmosphere intake port 34 to the slow port 18 as it does during idling, and as a result, the air-fuel ratio becomes a rich value as shown in FIG. 2B. By setting the air-fuel ratio to the rich side, acceleration operation from idling can be performed well. Furthermore, since the air-fuel ratio is switched by intermittent introduction of air into the slow port 18, the switching can be done more quickly and stepwise than in the past, and followability is improved.

In a second embodiment of the present invention shown in FIG. 3, a negative pressure on/off valve 50 is used as the valve means in place of the check valve 30 of FIG. The on-off valve 50 has a diaphragm 501 and a valve body 502 attached to the diaphragm 501. A negative pressure chamber 503 is formed below the diaphragm 501 and communicates with an idle sensing port 54 provided slightly downstream of the idle position of the throttle valve 16 via a negative pressure passage 52. A spring 504 acts on the diaphragm 501 to normally urge the valve body 502 to seat on the valve seat 505. Note that the valve seat 505 communicates with the pipe 28 on the slow port side. Further, an atmospheric chamber 506 is formed above the diaphragm 501 and communicates with the atmosphere upstream from the carburetor bench lily portion via the pipe 32.

In the operation of this second embodiment, since the idle sensing port 54 is under negative pressure during idle, this negative pressure communicates with the negative pressure chamber 503 and suctions the diaphragm 501 against the spring 504.
02 from the valve seat 505. In this way, the atmosphere is introduced into the slow port 18 through the pipe 32, the atmospheric chamber 506, the pipe 28, and the union, resulting in a lean air-fuel ratio as shown in FIG. 2A. Further, during acceleration from idle, the idle sensing port 54 is located upstream of the throttle valve 16, so the pressure in the chamber 503 becomes atmospheric pressure, and the action of the spring 504 causes the valve body 50 to
2 sits on the valve seat 505 and disconnects the pipes 32 and 28. Therefore, the introduction of air into the slow port 18 is stopped, and the air-fuel ratio becomes rich as shown in FIG. 2B.

The embodiment shown in FIG. 3 also has the advantage of being able to quickly switch the air-fuel ratio in a stepwise manner when transitioning from idling to acceleration.

According to this invention, the amount of fuel sucked out from the slow system is reduced by introducing air into the slow passage during idling, and the air-fuel ratio is set lean during idling, so if the intake air amount during idling is large, First, since there is little variation in engine speed, the driving feeling can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a carburetor according to the present invention, FIG. 2 is an air-fuel ratio characteristic diagram according to the present invention, and FIG. 3 is a second embodiment. 16... Throttle valve, 18... Slow port, 24... Slow fuel passage, 28, 32... Air introduction pipe, 30... Check valve, 50... Open/close valve.

Claims (1)

[Claims] 1. It has an air introduction passage whose one end is open to the slow system fuel passage that connects the slow port opening in the main body of the carburetor to the fuel supply source, and whose other end is connected to the atmosphere,
An air-fuel ratio control device for an internal combustion engine, wherein a valve means that is opened when the engine is idling and closed at other times is provided in the air introduction passage.