Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
1999-02-16
2001-10-09
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
C123S0730CA, C123S0730PP
Reexamination Certificate
active
06298811
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a stratified scavenging two-cycle engine and, more particularly, to a stratified scavenging two-cycle engine which includes an air supply flow passage, for supplying air, and a mixture supply flow passage, for supplying mixture separately, and which conducts the purification of exhaust gas by setting the ratio of the flow rates through the two flow passages at a predetermined valve.
BACKGROUND ART
As for a two-cycle internal combustion engine, it is generally known that in an exhaust stroke a part of the fuel mixture, which is fed into a cylinder chamber, flows out of an exhaust port to an exhaust flow passage along with combustion gas and is exhausted to the outside, thus causing air pollution.
The engine of Japanese Utility Model Publication No. 55-4518 is proposed as an example of a solution to the aforesaid problem. According to the above, a variable valve is provided in an air supply flow passage, which introduces air into a scavenging flow passage, connected to a scavenging port, owing to the negative pressure in the crank chamber before starting a scavenging stroke, the variable valve passing an extremely small quantity of air, including a zero flow, in an operation state of low rotation and low load operation of the engine, and increasing the flow rate of air in states other than the aforesaid operation state. Thus, in a scavenging stroke in which the scavenging port is opened, air is fed into a fuel flow passage from the crank chamber to form a layer of air between the combustion gas and a scavenging flow in the cylinder chamber, thereby preventing blow-by of the fuel mixture. In addition, the aforesaid air supply quantity is zero or very small at the time of low rotation and low load operation of the engine, thus preventing an excessive rarefaction of the fuel mixture, eliminating poor ignition, and stabilizing the combustion operation. Moreover, it is described that the aforesaid air supply quantity into the cylinder chamber increases at the time of low rotation and low load operation of the engine, thus effectively fulfilling the aforesaid operation of preventing blow-by of mixture.
The engine of Japanese Laid-open Patent No. 58-5423 is proposed as another example. According to that document, a crank chamber compression two-cycle internal combustion engine has an exhaust port and a scavenging port in the sidewall of a cylinder chamber, and the exhaust port and the scavenging port are opened and closed by a sidewall of the piston. Air is sucked into a scavenging flow passage, connected to the scavenging port through an air supply flow passage, due to negative pressure in the crank chamber, and sucked air is fed into the cylinder chamber prior to the fuel mixture which is sent from the crank chamber at beginning of a scavenging stroke in which the scavenging port is opened. At this time, it is intended that the scavenging port is not opened to the crank chamber due to the sidewall of the piston even at a lower dead center, and that the scavenging flow passage, connected to the scavenging port, is at least more than twice as long as that of the conventional crank chamber compression two-cycle internal combustion engine. Moreover, the total volume of the scavenging port and the scavenging flow passage is designed to be 20% or more of the stroke volume. Thus, an initial part of the scavenge, which is blown to exhaust, can be almost entirely an air component with an extremely low fuel content. Accordingly, the quantity of an initial scavenge, which is not mixed with the fuel mixture in the crankcase, can be selected so as to be an optimum value according to the volume of the scavenging flow passage. When a liquid fuel, such as gasoline or the like, is used, a large quantity of liquid fuel, adhering to the wall surface of the scavenging flow passage, evaporates, due to the high speed flow of sucked air accompanied by pulsation, and is mixed in the initial part of scavenge and blown to exhaust with the scavenge, thereby significantly reducing the stratified scavenging effect of this system. It is described, however, that the use of fuel gas almost prevents the mixing of the fuel into the sucked air in the scavenging flow passage.
In the aforesaid Japanese Utility Model Publication No. 55-4518, the quantity of air supplied is zero or very small at the time of low rotation and low load operation of the engine, thus preventing excessive rarefaction of the fuel mixture, eliminating poor ignition, and stabilizing the combustion operation. Moreover, the aforesaid quantity of air supplied into the cylinder chamber increases at the time of low rotation and low load operation of the engine, thus effectively fulfilling the aforesaid operation of preventing blow-by of mixture. However, in recent years, a demand for purification of the exhaust has increased more and more, the emission regulation has tightened up, and the purification of the exhaust gas at the time of the whole range of rotation of the engine, as well as at the time of low rotation and low load operation of the engine, is desired. For instance, in California 1999 Regulation as an example, it is demanded that the emission rate of total hydrocarbon (hereinafter referred to as “THC”) be not more than 50 [g/HP*h]. Therefore, there is a disadvantage in that it is difficult for the above regulation to be only satisfied with the engine of Japanese Utility Model Publication No. 55-4518.
According to the aforesaid Japanese Laid-open Patent No. 58-5423, the scavenging flow passage is designed to be at least more than twice as long as that of the conventional crank chamber compression two-cycle internal combustion engine, and the total volume of the scavenging port and the scavenging flow passage is designed to be 20% or more of the stroke volume. However, this is an art applied only to fuel gas. With the use of fuel gas, blow-by is prevented. On the contrary, with the use of a liquid fuel, such as gasoline or the like, a large quantity of liquid fuel adhering to the wall surface of the scavenging flow passage evaporates, due to the high speed flow of sucked air accompanied by pulsation, and is mixed in the initial part of the scavenge and blown to exhaust with the scavenge. In addition, since the scavenging flow passage is provided outside of the crankcase, there arise disadvantages in that the crankcase is increased in size and the production becomes difficult.
SUMMARY
In view of the aforesaid disadvantages of the conventional engines, an object of the present invention is to provide a stratified scavenging two-cycle engine which includes an air supply flow passage for supplying air and a mixture supply flow passage for supplying mixture separately and whose simple configuration can satisfy the regulation of the emission rate of THC in the exhaust gas by setting the ratio of the flow rates through the two flow passages at a predetermined value.
In a first aspect of a stratified scavenging two-cycle engine according to the present invention for attaining the aforesaid object, the stratified scavenging two-cycle engine is characterized in that it includes: a piston; a cylinder block, for housing the piston was to be vertically slidable and having an exhaust port and a scavenging port in a sidewall; a crankcase, connected to the cylinder block; a scavenging flow passage for connection between a crank chamber, provided in the crankcase, and the scavenging port; an air supply flow passage, connected to the scavenging flow passage, for supplying air through a check valve; and a mixture supply flow passage, for supplying to the crank chamber a mixture to which fuel from a fuel supply means is supplied, wherein the supply quantity ratio R=qa/Qf, which is the ratio of a supply quantity qa of air flowing through the air supply flow passage to a supply quantity Qf of mixture flowing through the mixture supply flow passage during a suction stroke in which the pressure in the crank chamber is negative, is in the range of 0.7≦R≦1.4. Moreover, the supply quantity ratio R
Kobayashi Buhei
Noguchi Masanori
Sawada Toshiharu
Huynh Hai
Kamen Noah P.
Komatsu Zenoah & Co.
Sidley Austin Brown & Wood
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