Internal-combustion engines – Two-cycle – Combined pump and motor cylinder
Reexamination Certificate
2001-12-21
2004-06-15
Gimie, Mahmoud (Department: 3747)
Internal-combustion engines
Two-cycle
Combined pump and motor cylinder
C123S197300, C123S072000
Reexamination Certificate
active
06748909
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a supercharged two-stroke or four-stroke internal combustion engine having one or more cylinders, and operating by admitting a carburated mixture or by admitting fresh air with the direct or indirect injection of fuel. The invention is just as applicable to petrol engines equipped with spark plugs as it is to diesel engines which use compression ignition.
Although the invention is described hereinafter with more particular reference to a single-cylinder engine in the case of a two-stroke engine, which is well suited to all applications of small industrial engines intended for motorized cultivation, garden tools, lawn mowers, cutters, scrub clearers or the like, the invention is not in any way restricted thereto and is also applicable to two-stroke or four-stroke multi-cylinder in-line or V engines.
BACKGROUND OF THE INVENTION
A two-stroke single-cylinder engine which operates with natural aspiration into the cylinder of a carburated mixture which passes through the crankcase is already known. This engine has a pipe for admitting the air/fuel mixture and a pipe for exhausting the burnt gases, both of which pipes open in the form of ports toward the bottom of the cylinder, near bottom dead center (BDC). The carburated mixture from the carburetor is drawn into the crankcase through a valve, during the upstroke of the piston which causes a depression in the crankcase, and is then delivered to the cylinder, during the downstroke of the piston, causing a raised pressure in the crankcase. During the downstroke of the piston, the mixture inlet ports are open at practically the same time as the exhaust ports, which means that about 20% of the mixture is discharged directly to the exhaust, leading to a high fuel consumption and a great deal of atmospheric pollution. The main advantage of this engine is its low cost, but new antipollution standards will ultimately spell the end for this type of engine.
Another known engine is of the loop scavenging type, which operates with a positive-displacement compressor, for example of the Roots type, making it easier to introduce the carburated mixture into the cylinder and to generate low-pressure supercharging. This engine also has a mixture inlet pipe and an exhaust pipe, the pipes both opening via ports toward the bottom of the cylinder. In this engine, the carburated mixture is admitted into the cylinder from the compressor, with an orientation such that the mixture experiences a loop-like upward rotating movement after the manner of a “loop-the-loop” in the cylinder, while the burnt gases from the previous cycle are discharged to the exhaust ports. The particular arrangement of the inlet and exhaust ports makes it possible for part of the admitted mixture not to be exhausted directly, and this reduces both fuel consumption and environmental pollution.
Yet another known engine is of the uniflow type, which also operates using a positive-displacement compressor. This engine has an inlet pipe connected at its upstream end to the compressor and at its downstream end to an inlet ring which opens via a number of ports toward the bottom of the cylinder, with an orientation such that the mixture is introduced with a great deal of rotational movement. The burnt gases are discharged at the top of the cylinder through one or more exhaust valves. This type of engine allows control over the filling of the cylinder and the possible recirculation of burnt gases, so as to obtain combustion which causes less pollution. Furthermore, when this type of engine is operating on the diesel cycle, introducing the air near the bottom of the cylinder makes it possible to obtain a great deal of air rotation, which is needed for obtaining good efficiency. This engine makes it possible to consume even less fuel than the loop-scavenging engine, and also makes it possible to reduce polluting emissions.
However, these last two types of engine cost far more than engines with transfer via the crankcase, because they contain more parts, particularly the compressor, and furthermore, in the case of the uniflow engine, valve control means. Furthermore, compressors of the Roots type are of low efficiency; for example, a two-stroke single-cylinder engine with a one-liter cylinder capacity and a power of 55 kW will consume 17 kW for driving the compressor. What is more, a Roots compressor does not operate beyond a pressure higher than 1.2 bar.
Finally, engines with exhaust and inlet valves are known and these are able to obtain the lowest consumptions and the lowest emissions, but this type of engine is also the most expensive because both the exhaust valves and the inlet valves have to be controlled. The efficiency of this engine is better because the control of the opening and closing of the valves using parts external to the cylinder means that the entire piston stroke can be used whereas with the previous engines in which admission was via ports, part of the compression stroke and of the expansion stroke was lost.
SUMMARY OF THE INVENTION
The object of the invention is to provide a supercharged two-stroke or four-stroke internal combustion engine, for example of the loop scavenging, uniflow or valve type, or of the four-stroke valves type, which allows the efficiency to be improved and the emissions to be reduced.
To this end, the subject of the invention is a two-stroke or four-stroke internal combustion engine, operating by admitting a carburated mixture or by admitting fresh air with the direct or indirect injection of fuel, the engine having at least one engine cylinder, an engine piston which executes a reciprocating movement in said engine cylinder, said engine piston coupled by a connecting rod to the wrist pin of a crankshaft so as to drive said crankshaft in rotation, and at least one compressor having a compressor cylinder and a compressor piston engaged in said compressor cylinder so as to define at least one variable-volume compression chamber, wherein said compression chamber is connected to said engine cylinder by an inlet pipe in order to supercharge the engine cylinder with carburated mixture or with fresh air, said inlet pipe ending at an inlet member of the engine cylinder, wherein said engine comprises a coupling means for coupling said compressor piston to said crankshaft, said coupling means arranged to drive said compressor piston in a reciprocating movement in said compressor cylinder as said crankshaft rotates so that, at least at a predetermined operating speed, a supercharging pressure generated by said compressor piston in the compression chamber and propagated through said inlet pipe, reaches a maximum value in said engine cylinder at substantially the same time as the inlet member of said engine cylinder is shut off.
This feature makes it possible to obtain a supercharged engine in which combustion is more complete, thus increasing efficiency and reducing exhaust pollution. The choice of producing the maximum pressure in the combustion chamber of the engine cylinder at substantially the same time as the inlet member is shut off makes it possible, for the desired operating speed, to optimize the amount of fresh air or carbureted mixture introduced into the engine cylinder in each cycle, while at the same time controlling the richness of the mixture, thus increasing the torque and mechanical power. It should be noted that a phase shift between the top dead center of the compression piston and the top dead center of the engine piston is chosen so as to obtain a maximum pressure in the engine cylinder at the time that the inlet member is shut off so that the geometric value of this phase shift can vary to a large extent as a function of numerous constructional and operational parameters of the engine and of the compressor.
According to a particular embodiment of the invention, the coupling means comprises a cam follower member connected to said compressor piston to drive said compressor piston, said cam follower member being kept in contact with a cam profile carried by said crankshaft during at lea
Gimie Mahmoud
Young & Thompson
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