Saving Oil

Just How Different (and how much better) is LIM?
Minimizing Oil Consumption

Each cylinder in a four-stroke engine has two kinds of valves, intake valves and exhaust valves. LIM engines have only intake valves. Most conventional two-stroke cylinders are said to have no valves, but there is a valve in the crank case allowing air to enter, which then closes to retain it. In two-stroke engines, exhaust is through the exhaust port, which is just a hole in the lower third (or less) on one side of the cylinder. The exhaust port in a LIM cylinder is smaller in height, but much wider.

The valve in the crank case in a typical two-stroke engine is a piece of springy material inside the intake port. It leans inwards when the piston is rising, allowing air to enter the crank case, and leans against the port, sealing it, when the piston, on its power stroke, is compressing the contents of the crank case. There can be no oil bath in such a crank case, but there is in a LIM type engine.

If such a piece of springy material could withstand the heat of the combustion chamber, something like the LIM type system would probably have been devised in the nineteenth century. This would have caused two-stroke engines to dominate the market, since the LIM system is more power efficient and less expensive than four-stroke engines.

LIM's enabling breakthrough is the hard metal valve used in the LIM cylinder head. This valve is held against its seat, to seal the cylinder, by a light spring. The spring has only enough tension to keep the valve seated when the pressure differential is insignificant, with only a slightly higher pressure above the head, on the outside of the cylinder.

Like most springs, its force increases as it is distorted from its initial shape. It is probable that at certain rotational speeds the spring contributes to perfect timing, by starting to close the valve and accelerating it to its seated position in such a way that the valve will seal the cylinder, trapping the air, just at the best possible moment.

With this in mind, our newest designs feature adjustable spring tension. In production units, a micro processor will probably adjust spring tension to the speed of the engine, providing variable valve timing which will be nearly perfect at all working ranges of RPM.

The valve and guide materials are dissimilar. They are selected for their ability to work together with minimal friction and abrasion. It is helpful that the head is used only for intake, which is a far cooler process than exhaust. No liquid lubrication is therefore necessary. Oil is therefore not needed in the head area, and all the oil is kept in the crank case.

In all internal combustion engines, some of the combustion product squeezes past the piston and around the compression rings, providing no power. In typical four-stroke and most two-stroke engines, these "blow-by" gases go directly to the crank case, and in four-stroke engines, the combustion by products in the blow by gases thus pollute the oil. This provides the ingredients for organic acids, which cause harm to the metal parts which must be lubricated.

The blow-by gases in a LIM engine leave through the exhaust ports and cannot pas the piston to pollute the oil. An absence, therefore, of organic acid in the oil is one of the reasons oil in a LIM engine will seldom need changing.

Learn more about the Advantages

Learn more about the Simple Cycle Engine

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