Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
1999-04-14
2001-04-17
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
C123S0730CA, C123S0730PP
Reexamination Certificate
active
06216650
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a stratified scavenging two-cycle engine, and more particularly to a stratified scavenging two-cycle engine, in which control of an air flow rate provides favorable acceleration performance and can prevent deterioration of exhaust gas.
BACKGROUND ART
As a conventional stratified scavenging two-cycle engine of this kind, a stratified scavenging two-cycle engine that includes a scavenging flow passage for connection between a cylinder chamber and a crank chamber and an air flow passage connected to the scavenging flow passage and that is structured in such a manner that pressure reduction in the crank chamber, with upward movement of a piston, permits a fuel mixture to be drawn into the crank chamber and permits air to be drawn into the crank chamber, through the scavenging flow passage from the air flow passage, is known. In the stratified scavenging two-cycle engine structured as described above, there is an advantage that combustion gas can be pushed out by air from the scavenging flow passage, thus making exhaust gas cleaner by greatly reducing an introduction of a fuel mixture during combustion gas expulsion.
In the aforesaid stratified scavenging two-cycle engine, however, there is a disadvantage that the fuel mixture is rarefied by air, whereby an air-fuel ratio (weight of air/weight of fuel) having a substantial ratio of air to fuel becomes thinner (increases), thus deteriorating acceleration performance. As a measure to improve acceleration performance, it is required that the air-fuel ratio is thickened (decreases) by increasing the supply amount of fuel also at a time of stationary engine speed in accordance with acceleration performance to draw an enriched fuel mixture into the crank chamber. In that case, however, an exhaust gas quality at the time of a stationary engine speed (i.e., other than a time of acceleration) deteriorates.
SUMMARY OF THE INVENTION
In view of the aforesaid disadvantages, an object of the present invention is to provide a stratified scavenging two-cycle engine, in which a fuel mixture and air are separately drawn and that controls a supplied flow rate of air to improve acceleration performance and to prevent deterioration of exhaust gas at a time of stationary engine speed and a time of acceleration.
To attain the aforesaid object, a stratified scavenging two-cycle engine according to the present invention is characterized by including a scavenging flow passage for connection between a cylinder chamber and a crank chamber, an air flow passage connected to the scavenging flow passage, an air flow rate controller for controlling a flow rate of air fed to the scavenging flow passage from the air flow passage, and a fuel mixture flow rate controller for controlling a flow rate of a fuel mixture drawn into the crank chamber from a fuel mixture flow passage, the aforesaid air flow rate controller throttling an air flow rate at the time of acceleration.
According to the aforesaid configuration, when a piston ascends, pressure in the crank chamber lowers so that a fuel mixture flows into the crank chamber, and air flows into the crank chamber through the scavenging flow passage from the air flow passage. Namely, the scavenging flow passage is filled with air, and inside the crank chamber, the fuel mixture is rarefied by air from the scavenging flow passage. Therefore, in the stratified scavenging two-cycle engine, an air-fuel ratio of a fuel mixture drawn from the fuel mixture flow passage is set in a higher range so as to make the air-fuel ratio optimum in combustion after the fuel mixture is rarefied by air.
Subsequently, when pressure in the cylinder chamber sharply rises by ignition of the fuel mixture in the cylinder chamber and the piston descends, pressure in the crank chamber rises. When the piston descends to a predetermined position, an exhaust port opens, for example, and combustion gas flows out of the exhaust port so that pressure in the cylinder chamber sharply drops, and a scavenging port which is an end portion on the side of the cylinder chamber of the scavenging flow passage opens. Then, air in the scavenging flow passage flows into the cylinder chamber, and subsequently the fuel mixture in the crank chamber flows into the cylinder chamber through the scavenging flow passage.
Specifically, combustion gas can be pushed out of the exhaust port by only air at a point in time when scavenge starts, thus preventing deterioration of exhaust gas due to an introduction of a fuel mixture. Moreover, a proper air-fuel ratio mixture fills the cylinder chamber, thereby also preventing deterioration of exhaust gas. Accordingly, exhaust gas can be cleaned at the time of stationary engine speeds.
Meanwhile, when the flow rate of a fuel mixture fed to the crank chamber is increased by the fuel mixture flow rate controller, engine speed increases. At the time of such engine acceleration, an air flow rate is throttled by the air flow rate controller. Hence, the flow rate of air flowing into the crank chamber is relatively lower than the flow rate of a fuel mixture flowing into the same crank chamber, as compared with stationary engine speeds.
Namely, a thicker air-fuel ratio fuel mixture fills the cylinder chamber, thus improving acceleration performance of the engine. At this time, since the supply amount of fuel is not increased at the time of acceleration as in the prior art, the supply amount of fuel is small even at the time of acceleration, thus preventing deterioration of exhaust gas more than in the prior art. In addition, in the stratified two-cycle engine of the present invention, the supply amount of fuel is not increased at the time of acceleration, whereby deterioration of exhaust gas can be prevented more than in the prior art even at the time of a stationary engine speed.
A stratified scavenging two-cycle engine according to the present invention is characterized by including a scavenging flow passage for connection between a cylinder chamber and a crank chamber, an air flow passage connected to the scavenging flow passage, an air flow rate controller for controlling a flow rate of air fed to the scavenging flow passage from the air flow passage, and a mixture flow rate controller for controlling a flow rate of a fuel mixture drawn into the crank chamber from a fuel mixture flow passage, the aforesaid air flow rate controller being opened later than the mixture flow rate controller at the time of acceleration.
According to the aforesaid configuration, the same effect as that of the aforesaid embodiment can be obtained. In this embodiment, the same effect that is described above is obtained at the time of acceleration, and moreover an air-fuel ratio becomes the same as that at stationary engine speed by eliminating delay when predetermined acceleration is obtained, whereby accelerating performance can be improved and exhaust gas after acceleration can be made cleaner than in the prior art.
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Huynh Hai
Komatsu Zenoah & Co.
Sidley & Austin
Wolfe Willis R.
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