GB2101209A - Four stroke I.C. engine with air transfer porting - Google Patents

Abstract

A four-stroke internal combustion engine has a transfer port remote from its cylinder head and connected to a source of air under pressure, the arrangement being such that the piston uncovers the port to allow air inflow at the beginning of both the compression and exhaust strokes. <IMAGE>

Description

SPECIFICATION Improvements to the internal combustion engine There are basically two types of internal combustion engine. The four-stroke Otto Cycle and the two-stroke cycle.

The four-stroke engine uses valves at the top of the cylinder which open and close in a set sequence. The inlet valve opens to allow air to be drawn in on the suction stroke. The valve closes and the air or gas is compressed on the compression stroke. The mixture is then ignited and the expanding gas pushes the piston down on the power stroke. The exhaust valve opens and the returning piston expels burnt gas.

The two-stroke engine works on the same principal but it is a much more simple design.

Instead of valves, ports in the cylinder wall are opened and closed by the reciprocating piston.

The top side of the cylinder is used for compression and power and the rear side of the piston (crank case) is used as a compressor to suck in air or gas to re-charge the top cylinder.

When the piston rises in a two-stroke engine, the air or gas in the top of the cylinder is compressed. At the same time a port in the underside is uncovered, allowing air to be sucked in. The compressed mixture in the top of the cylinder is ignited and the expanding gas pushes the piston down. This closes the inlet port in the cylinder wall and this causes pressure to be built up on the under side of the piston. On approaching the bottom of its stroke, the trapped air or gas under the piston is rapidly discharged into the top cylinder, when a connecting air transfer passage is uncovered by the descending piston. This rush of air removes the burnt gas and replenishes the cylinder, ready for the next stroke.

There are disadvantages and limitation to both types of engine and it is the purpose of this invention to overcome most of these problems.

The problems are: Four-stroke engine, removal of heat from cylinder between cycles. Limitation by the overheating of exhaust valve. Limitation on the amount of air available in the cylinder at speed.

Residue of burnt gas left in cylinder after exhaust stroke.

Two-stroke engine, excess of burnt gas trapped in top of cylinder after each cycle. Problem of recharging cylinder and expelling exhaust gas at speed. Removing excess heat after each cycle.

The present invention provides a four-stroke internal combustion engine having an inlet valve for a combustible mixture and an exhaust valve for spent gases, a transfer port being provided into the cylinder at a position remote from the cylinder head and being connected to a source of air under pressure, the piston uncovering the port to allow air inflow at the beginning of the compression stroke to increase the amount of oxygen available for combustion and at the beginning of the exhaust stroke to encourage scavenging of exhaust gases, there being a cooling effect at each air inflow.

The air can be supplied to the port from a pressurised crankcase via a transfer duct.

Alternatively, the air can be supplied to the port from a duct connected to a supercharger driven by the exhaust gases.

The invention will be described further, by way of example with reference to the accompanying drawings, wherein:- Fig. 1 shows, in cross-section, a first preferred engine of the invention, the four views being sequential and showing engine operation; and Fig. 2 shows a second embodiment.

The present invention combines the best features of both two and four stroke engines. The topside of a first embodiment of engine is a fourstroke engine, using valves in the top of the cylinder and a piston in the conventional way. The underside of the piston is used as a compression chamber, as in the two-stroke engine. When the piston rises on the compression stroke on this engine, a port is uncovered by the rising piston and air is sucked into the underside of the piston.

When the piston descends on the power stroke, the port is closed by the descending piston and the air trapped under the piston is compressed.

Near the bottom of the stroke, the exhaust valve in the top cylinder opens. Simultaneously the piston uncovers the port of the transfer passage between the bottom and top cylinder, causing a rush of compressed air to be discharged into the top cylinder. This accelerates the removal of exhaust gases through the exhaust valve and at the same time removing excess heat from the cylinder wall and exhaust valve.

As the piston rises on the exhaust stroke, the connecting passage between the top and bottom cylinder is closed by the rising piston. The port on the underside of the piston is opened and air is again sucked into the underside of the cylinder.

When the piston reaches the top of its stroke, the exhaust valve closes and the inlet valve opens. The returning piston sucks in air or gas on the inlet stroke. As the piston descends, the port on the underside of the piston is again closed, causing the new charge of air under the piston to be compressed. Near the bottom of the stroke the inlet valve begins to close. The piston again uncovers the transfer passage port between the bottom and top cylinders and compressed air, at high velocity, is discharged into the top cylinder, causing more air to be available for the compression stroke.

When looked at in more detail, the advantage of this arrangement in re-charging the engine with compressed air, at the completion of each stroke, becomes more evident.

In conventional engines there is always excess in the fuel to air ratio, drawn in through the inlet valve on the suction stroke. By introducing more air at the completion of the inlet stroke, this is rectified and more efficient combustion takes place. As the speed of the engine increases, the inlet suction time decreases, thus making the engine less efficient. By introducing more air at this stage, the performance of the engine is greatly improved.

When the excess air is mixed with the exhaust gases, the temperature and toxic content is greatly reduced. This, combined with the more efficient means of combustion, significantly reduces atmospheric pollution.

In an alternative embodiment, the transfer port is connected by a duct to a supercharger driven by the exhaust gases. The function in the second embodiment is exactly the same as in the first embodiment, but the use of a supercharger is probably more practicable than the use of crankcase compression to supply the air.

Claims (4)

1. A four-stroke internal combustion engine having an inlet valve for a combustible mixture, and an exhaust valve for spent gases, a transfer port being provided into the cylinder at a position remote from the cylinder head and being connected to a source of air under pressure, the piston uncovering the port to allow air inflow at the beginning of the compression stroke to increase the amount of oxygen available for combustion and at the beginning of the exhaust stroke to encourage scavenging of exhaust gases, there being a cooling effect at each air inflow.

2. An engine as claimed in claim 1, wherein the source of air under pressure is a sealed crankcase of the engine, an inlet port to the crankcase being provided and arranged so that reciprocation of the piston pumps air into the crankcase to supply the transfer port via a transfer passage between the transfer port and the crankcase.

3. An engine as claimed in claim 1, wherein the source of air under pressure is a supercharger connected by a duct to the transfer port.

4. A four-stroke internal combustion engine substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.