Piston engines

Details Piston engines Piston engines

1986-10-14

1988-10-11

Myhre, Charles J.

Internal-combustion engines

Particular piston and enclosing cylinder construction

Cylinder detail

F02F 300

Patent

active

047763086

DESCRIPTION:

BRIEF SUMMARY
This invention concerns piston engines.
In piston engines, particularly 4-stroke petrol engines, the exhaust residue is hot and it preheats the fresh fuel/air mixture. This preheating causes the mixture in the cylinder to be relatively hot at the start of combustion. However, because the mixture is relatively hot, the heat added by the combustions of the fuel produces a smaller increase in pressure and less power.
If the amount of the exhaust residue could be reduced than the temperature of the fuel/air mixture in the cylinder would be reduced. That would mean that the same heat and fuel would produce a greater pressure and more power. As the amount of the exhaust residue was reduced so the proportion of fresh fuel/air mixture would be increased, which would further increase the combustion pressure and power output for a given quantity of fuel.
Furthermore it would be desirable to have a clearance at the end of the compression that was related to the desired pressure of fuel mixture in the cylinder for optimum economy.
The object of this invention is to provide a four stroke engine powered by a fuel/air mixture wherein piston clearances in its cyclinders can vary according to the pressure within the cylinder.
According to this invention there is provided a four-stroke engine wherein piston clearance is dependent on the pressure within the cylinder.
Preferably the pistons have a smaller clearance from the cylinder head at the end of their exhaust stroke than at the end of the compression stroke. In this way virtually all of the hot exhaust residues will be expelled from the cylinder so that the temperature of the next fuel/air mixture input will be lower. Thus less heat and fuel will be required for a desired power output.
At the end of the compression stroke the clearance of the piston from the cylinder head will be greater than at the end of the exhaust stroke. That is because of the pressure of the fuel/air mixture in the cylinder but as the clearance is dependent on the pressure within the cylinder the compression ratio will be favourable.
The above applies not only to an engine under normal load conditions but also under light or heavy load conditions because the engine has the ability to vary its piston clearances in accordance with the pressure within the cylinder whether as a reduced pressure at light load or higher pressure at heavy load.
In a preferred embodiment the pistons of the engine each have a secondary piston reciprocally movable in a chamber in the main piston. The connection of each main piston to its connecting rod is via its secondary piston. For retention of the secondary piston in the main piston, the secondary piston may have a lateral extension or flange retained in a wider part of the chamber.
The secondary piston preferably provides two substantially sealed spaces above and below the lateral extension or flange. Sealing is preferably by way of piston rings. At the end of the exhaust stroke there is no significant pressure in the cylinder so that the inertia of the main piston causes it to move close to the cylinder head relatively unhindered by the weight or movement of the connecting rod. This is because said lower space volume is compressed whilst the upper space volume expands. The movement of the main piston close to the cylinder head expels virtually all of the hot exhaust gases from the cylinder so reducing the temperature therein for the next input of fuel/air mixture, which as mentioned above is desirable.
On the compression stroke the fuel/air mixture in the cylinder opposes the movement of the main piston towards the cylinder head. This means that the upper space volume is compressed as the secondary piston tries to assist movement of the main piston towards the cylinder head. At the same time, of course, the lower space volume increases.
During sustained heavy load, low speed, conditions, which might normally cause detonation or knock, the piston system of the invention can provide more clearance volume (less inertia--more compression). A higher nominal compression rat

REFERENCES:
patent: 1305567 (1919-06-01), Ritter
patent: 2686512 (1954-08-01), Beam
patent: 2791991 (1957-05-01), Ickes
patent: 4359976 (1982-11-01), Steele

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