Internal-combustion engines – Particular piston and enclosing cylinder construction – Cylinder detail
Patent
1993-07-14
1994-10-25
Kamen, Noah P.
Internal-combustion engines
Particular piston and enclosing cylinder construction
Cylinder detail
123568, F02F 314
Patent
active
053579194
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to the reduction of the hydrocarbon content of the exhaust gas emissions of a spark ignited four-stroke internal combustion engine.
BACKGROUND OF THE INVENTION
When the cyclic variation of the hydrocarbon content of exhaust gases is studied in detail, it is noted that there are peaks of high hydrocarbon concentration immediately when an exhaust valve opens and just before the exhaust valve closes. In a well tuned engine, the hydrocarbon concentration between these two peaks is significantly lower and within the range expected from complete combustion. The two peaks are not therefore caused by an incorrect fueling map and other reasons must be the cause of the presence of unburnt fuel in the exhaust.
The present invention is concerned with the cause of the second peak which occurs at the end of the exhaust event rather than the first peak. It is generally believed that a major cause of this problem is the presence in the combustion chamber of small crevices into which fuel can be compressed but into which the combustion flame cannot penetrate. One such crevice is that surrounding the piston top land that is to say the small space between the piston and the cylinder above the top piston ring. During the compression stroke, fuel and air are compressed into this space. During combustion, the expanding flame front pushes mixture ahead of it into this crevice tending to increase the amount of fuel stored even further. However, the flame cannot enter this crevice because it is bound by two cold walls and the flame is quenched during its attempt to penetrate into this gap. Consequently, a quantity of fuel remains trapped in the crevice throughout the power stroke until the pressure in the combustion chamber during the exhaust stroke drops to allow the unburnt charge to escape from the crevice. The unburnt charge will then reside near the top of the piston and will be discharged towards the end of the exhaust stroke.
Attempts have been made in the prior art to reduce the crevice volume by reducing the distance between the piston crown and the top ring but this causes problems because the top ring then runs hotter and reduces engine life.
OBJECTS OF THE INVENTION
The invention therefore seeks to provide a four-stroke engine in which the hydrocarbon content of the exhaust gases is reduced, especially near the end of the exhaust stroke.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a four-stroke spark ignited internal combustion engine which comprises a variable volume working chamber defined between a reciprocating piston, which has at least one sealing piston ring, and a cylinder, characterised by an auxiliary chamber having a fixed volume significantly smaller than the maximum volume of the working chamber and communicating with the working chamber by a passage disposed in the cylinder wall at a position above the top piston ring when the piston is near the bottom of its stroke so that end gases at the end of the power stroke are stored in the auxiliary chamber, the auxiliary chamber communicating with the crankcase when the piston is near the top of its exhaust stroke so that the stored end gases are discharged into the crankcase.
Preferably, the auxiliary chamber is an annular chamber surrounding the cylinder and connected to the combustion chamber by a plurality of passages distributed about the circumference of the piston.
It should be mentioned that there are described in the prior art two-stroke engines which have an auxiliary chamber which is at times connected to the working chamber and at times to the crankcase. Examples of such engines are to be found in GB 2 223 802 and GB 2 083 550. Because of the fundamental differences between two-stroke and four stroke engines, these auxiliary chambers serve totally different functions and their dimensions and geometries are different from those of the auxiliary chamber required in the present invention.
In a two stroke engine, the crankcase serves to compress the charge supplied
REFERENCES:
patent: 1530864 (1925-03-01), Vaughan
patent: 4060059 (1977-04-01), Blaser
patent: 4191150 (1980-03-01), Siewert
patent: 4466409 (1984-08-01), Asaka
patent: 4475510 (1984-10-01), Asaka
Drouillard Jerome R.
Ford Motor Company
Kamen Noah P.
May Roger L.
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