Field of Invention:

The invention is related to two stroke engines and two stroke engines with crank case scavenging in particular.

Background of the Invention:

It is well known that in the two stroke engines the fuel/air mixture or the air alone gets compressed in the crank case and then the compressed mixture enters the cylinder. These engines need lubrication. The lubrication is achieved by either mixing the lubricant in the fuel or having a separate lubrication system. Mixing the lubricant in the fuel has advantage that this doe not need dedicated lubrication system, but has the disadvantage that the lubrication may not be proper. The disadvantage being that the amount of lubrication can not be controlled depending upon different engine operating conditions during running of the engine. Having a dedicated lubrication system has an advantage that the amount of lubrication can be controlled depending upon different engine operating conditions during running of the engine, but the disadvantage is that it involves additional cost.

The US patent 4414929 discloses a lubricant system for the two stroke engines. The prior art discloses a lubricant system which provides fuel/lubricant mixture from carburetor directly to certain components of the engine such as rod bearings.

Advantages of the invention:

The advantage of the invention is that the engine does not need any lubrication in the crank case. This is due to the material used in the construction of the engine.

Objective of the invention:

The objective of the invention is to provide an engine which does not need lubrication for the piston and the connecting rod bearings.

Brief description of the drawings:

Figure 1: Shows the schematic of the engine according to the invention

Description of the invention:

Shown in figure 1 is a schematic of the engine 10 according to the invention. The engine comprises a cylinder pressure bore 11, a cylinder block disposed in a crankcase 12, a cylinder 14 in which a piston 16 moves reciprocally. The piston 16 is connected to a crankshaft 18 by means of a connecting rod 20. A set of bearings 21 support the coupling of the piston 16, the connecting rod 18 and the crankshaft 18. The crankshaft 18 is connected to a flywheel 22 and to a driveshaft which is not shown in fig. An intake port provides air to the engine and an exhaust port disposes the exhaust gases away from the engine. These ports are not shown in the fig.

A Set of rolling bearings 26 support he crank shaft.

The parts of the engine which are relevant for describing the invention are disclosed in this document. Some parts of the engine which are commonly known are neither explained nor shown in the figures.

The engine operates in a two stroke crankcase compression cycle. The engine shown in fig. may have more than one cylinder 14; only one cylinder is shown as an example. The crankshaft rotates when the pistons move reciprocally. The piston moves in the cylinder and a combustion chamber is formed at the top of the cylinder.

The intake port delivers air to each of the crankcases. The air is finally delivered to the combustion chamber after compression in the crank case 12 and the cylinder 14.

The air coming into the crankcase 12 is compressed by the piston 16 when the piston 16 is moving towards the crankshaft 18. The compressed air then moves towards the combustion chamber through a scavenge system.

A fuel supply system which is not shown completely in the fig. supplies the fuel to the engine. The fuel supply system comprises a fuel tank, fuel filters, fuel pump etc. In one embodiment, part of the fuel supply system may be a carburetor. In another embodiment, the fuel supply system may comprise fuel injectors.

The engine shown in fig. 1 has fuel injector 24. Each of the cylinders is provided with a fuel injector. The injectors are disposed in the combustion chamber. An electronic control unit which is not shown in fig. controls the injectors.

The engine may also be provided with an ignition system, which is not shown in fig. 1.

The spark plug is part of the ignition system. The ECU controls the spark plugs for igniting the air fuel mixture in the combustion chamber.

Each combustion chamber is provided with an exhaust port and all the exhaust ports normally get connected through a set of pipes forming an exhaust channel. The exhaust channel guides the exhaust gases outside of the combustion chambers and into the atmosphere. The exhaust ports are either opened or closed with the reciprocal movement of each piston.

The fuel injector injects fuel into the combustion chamber. The injected fuel is mixed with the air in the combustion chamber to ignite the air/fuel mixture. The ECU controls the injection timing and the amount of fuel injected into the chamber. Once the air/fuel mixture burns in each combustion chamber, the pressure produced in the combustion chamber moves each piston. At this time, exhaust ports are uncovered. The exhaust gases are discharged through the exhaust ports and then through the exhaust channel.

As part of the operation of the engine, the air is sucked into the crank case through the intake ports, the air undergoes preliminary compression in the crank case when the pistons are moving towards the crankshaft, the air gets further compressed when the pistons move towards the combustion chamber, the ECU commands the injectors to inject the fuel and if required also commands the spark plug to ignite the fuel. When the pistons are moving towards the combustion chamber, the exhaust gases are pushed out of the cylinder through the exhaust ports.

In the prior arts the engine needs lubrication to lubricate the piston, the connecting rod and the bearings used in the engine. These kinds of engines are lubricated with fresh-oil total-loss lubrication or mixture lubrication. This Kind of lubrication leads during the scavenging process to transport of oil particle into the exhaust system as well as into the combustion chamber. This leads to higher HC-Emissions and the unburned oil particles in the exhaust-system are damaging any kind of exhaust gas after treatment systems.

The invention proposes to focus on new materials for the piston 16 as well as for the bearings 21 used in the crankcase areas. These materials can be composite material or fibre reinforced composite material. For this especially composite from aluminium and carbon are of interest. With this material it is possible to design an engine which runs without any lubricant in the crankcase. Due to this fact there is an improvement in raw-emission of the engine and it is possible to use exhaust gas after treatment systems on a
two stroke engine. With this feature especially in combination of direct injecting engines (diesel as well as petrol) it should be possible to fulfil further emission norms.

The invention proposes a design of a two stroke engine with a crankcase free of lubrication oil. For this purpose a special material has to be use for the components Piston and con-rod bearings. The design is optimized in regards of minimum crankcase volume to increase the efficiency of the scavenging process. With this design it is possible to reduce exhaust gas emissions and improve the efficiency of the engine.

For plain bearings with solid state friction, materials having low friction co-efficient are considered.

Often one of the part has a "self-lubrication-property" and the other with radial bearing as steel. Carbon is suitable as a bearing material, because its wear works as a lubricant (self-lubrication-property). The carbon modification graphite possesses crystal planes which can lightly glide on each other. It is to be noted that, with higher load, the friction coefficient rises and with it the temperature. Nevertheless, they are suitable for higher temperatures where lubricated bearings fail.

WE CLAIM:

1. A two stroke crank case scavenged internal combustion engine (10) comprising :

- a crankcase (12)

- a crank shaft (18) partly enclosed in the crankcase (12)

- a cylinder (14)

- a piston (16) reciprocally moving in the said cylinder (14), the said piston (16) connected to the said crankshaft (18) through a connecting rod 20 and a set of bearings (21)

- a combustion chamber formed at one end of the cylinder (14)

- an intake passage to provide air to the said engine

- an exhaust passage to guide the exhaust gases away from the combustion chamber

Wherein the said piston 16 and the said bearings (21) are made of a composite material which does not need any lubrication

2. A two stroke crank case scavenged internal combustion engine (10) according to claim 1 wherein the piston (16) is made of fibre reinforced composite material

3. A two stroke crank case scavenged internal combustion engine (10) according to claim 1 wherein the bearings (21) are made of fibre reinforced composite material

4. A two stroke crank case scavenged internal combustion engine (10) according to claim 1 wherein the piston (16) is made of composite material from aluminium and carbon

5. A two stroke crank case scavenged internal combustion engine (10) according to claim 1 wherein the bearings (21) are made of aluminium and carbon.