Single-cylinder 4-cycle engine

Details Single-cylinder 4-cycle engine Single-cylinder 4-cycle engine

1999-12-16

2001-09-04

Yuen, Henry C. (Department: 3747)

Internal-combustion engines

Charge forming device

Including exhaust gas condition responsive means

C123S478000

Reexamination Certificate

active

06283105

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a single-cylinder 4-cycle engine including a control means for feedback-controlling the amount of fuel supplied, based on a signal from an oxygen concentration sensor for detecting a concentration of oxygen in an exhaust gas. The concentration sensor is provided between an exhaust port and an exhaust emission control catalyst.
2. Description of the Prior Art
In an engine including an exhaust emission control catalyst of a noble metal such as platinum-rhodium and the like, disposed in an exhaust passage, to convert harmful components in an exhaust gas, it is a conventional practice to detect the concentration of oxygen in the exhaust gas with an oxygen concentration sensor provided in the exhaust passage at a location upstream of the exhaust emission control catalyst, to maximize the performance of the exhaust emission control catalyst, and to control the air-fuel ratio of an air-fuel mixture supplied to the engine in a range near a theoretical air-fuel ratio, based on the detected concentration of oxygen.
In a multi-cylinder engine in which the exhaust gas is discharged in sequence from a plurality of cylinders at every predetermined crank angle, the pulsation of the flow of exhaust gas in an exhaust passage is suppressed to a relatively small level. However, in a single-cylinder 4-cycle engine in which the exhaust stroke occurs only one time per two rotations of a crankshaft, a large pulsation may be produced in the flow of exhaust gas in the exhaust passage, and the exhaust gas passing through the exhaust emission control catalyst, may flow backwards in the exhaust passage due to the pulsation in some cases. The exhaust emission control catalyst has the effect of oxidizing the exhaust gas and for this reason, the concentration of oxygen in the exhaust gas flowing backwards from the exhaust emission control catalyst is deviated from an intrinsic value. If the false concentration of oxygen is detected for feedback-control of the amount of fuel supplied, there is a possibility that proper control cannot be carried out. Particularly, it is a recent tendency to position the exhaust port and the exhaust emission control catalyst at a smaller distance spaced apart from each other, in order to activate the exhaust emission control catalyst and provide compactness of the engine. Therefore, the distance between the exhaust emission control catalyst and the oxygen concentration sensor is also smaller, wherein the pulsation of the exhaust gas is liable to exert an influence.
SUMMARY OF THE INVENTION
The present invention has been accomplished with the above circumstance in view, and it is an object of the present invention to ensure that the concentration of oxygen in the exhaust gas can be detected without being influenced by the pulsation of the exhaust gas.
To achieve the above object, there is provided a single-cylinder 4-cycle engine comprising a control means for feedback-controlling the amount of fuel supplied, based on a signal from an oxygen concentration sensor for detecting the concentration of oxygen in an exhaust gas, which is provided between an exhaust port and an exhaust emission control catalyst, wherein the control means controls the amount of fuel supplied in a feedback manner based on the concentration of oxygen detected during an exhaust stroke.
With the above arrangement, when the exhaust gas is discharged during the exhaust stroke of the engine, the concentration of oxygen in the exhaust gas is detected by the oxygen concentration sensor. Therefore, it is possible to prevent the mis-detection of the concentration of oxygen in the oxidized exhaust gas flowing backwards from the exhaust emission control catalyst due to the pulsation of the exhaust gas, and to accurately feedback-control the amount of fuel supplied, based on the properly detected concentration of oxygen in the exhaust gas. Moreover, it is difficult to receive the influence of the pulsation of the exhaust gas and hence, the exhaust emission control catalyst can be disposed at a location near the exhaust port, whereby the exhaust gas having a high temperature can be supplied to the exhaust emission control catalyst, leading to an enhanced effect of purifying the exhaust gas, and the compactness of the engine can be achieved.
In addition, the control means includes a stroke discriminating means for discriminating an exhaust stroke and a compression stroke, and controls the amount of fuel supplied in a feedback manner based on the concentration of oxygen during the exhaust stroke determined by the stroke discriminating means.
With the above arrangement, the exhaust and compression strokes are discriminated by the stroke discriminating means provided in the control means. Therefore, it is possible to reliably discriminate the exhaust and compression strokes in which the crankshaft assumes the same phase.
Further, the stroke discriminating means detects the angular speed of a crankshaft of the engine and determines the exhaust stroke, when the detected angular speed is larger.
With the above arrangement, it is possible to reliably discriminate the exhaust stroke from the compression stroke because the angular speed of the crankshaft is larger during the exhaust stroke and smaller during the compression stroke.
Further, the time required for one rotation of the crankshaft is detected, and the stroke discriminating means determines the exhaust stroke when the detected time is shorter.
With the above arrangement, it is possible to reliably discriminate the exhaust stroke from the compression stroke considering that the time required for one rotation of the crankshaft is smaller for one rotation of the crankshaft including the exhaust stroke and larger for one rotation of the crankshaft including the compression stroke.
In addition, the stroke discriminating means determines the exhaust stroke, based on the phase of a cam shaft which drives one of an intake valve and an exhaust valve of the engine.
With the above arrangement, the exhaust stroke occurs only one time per one rotation of the cam shaft and hence, it is possible to reliably determine the exhaust stroke, based on the phase of the cam shaft.


REFERENCES:
patent: 4401079 (1983-08-01), Aoki et al.
patent: 4515131 (1985-05-01), Suzuki et al.
patent: 5148369 (1992-09-01), Uchinami et al.
patent: 5566663 (1996-10-01), Hamburg et al.
patent: 5628299 (1997-05-01), Marzonia et al.
patent: 5722372 (1998-03-01), Hosoe et al.

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