Background Art It is known to provide fuel injection for two stroke engines and one form of this injection is air assist injection directly into the cylinder of the two stroke engine.

One reason for such injection is to attempt to reduce the emissions of two stroke engines in order to comply with future regulatory standards. One such injection system is that patented, manufactured and licenced by the Orbital Engine Company of Perth Australia.

Whilst such injection systems provide improved emission performances relative to conventional loop scavenged two stroke motors, the cost of the injector unit with its electronic control, an electric fuel pump, air compressor and injector constitutes a substantial cost and thereby overcomes the inherent simplicity of a two stroke engine. As a consequence, an overhead valve four stroke engine of substantially conventional construction becomes economically competitive. This has lead many current two stroke engine manufacturers to contemplate cessation of manufacture of two strokes and commencement of manufacture of four stroke internal combustion engines.

A fundamental problem with fuel injection is that in order to decrease emissions it is necessary for the particle size of the injected fuel droplets (known as atomised fuel) to be decreased and this has required increasing pressures. For example, a fuel injector operating a pressure of approximately 20 bar (2 MPa or 300 psi) will produce a particle size of approximately 40 microns and current automotive equipment operating at a pressure of 150 bar (15MPa or 2,250 psi) manages to

produce a particle size of approximately 10 microns. This fuel particle size is highly desirable in order to achieve low emissions but is extremely difficult to create for an engine intended to be used in low cost consumer applications such as lawn mowers, brush cutters, and similar small powered appliances.

As will be explained hereafter, in a particularly advantageous preferred form of the present invention, an auxiliary cylinder and auxiliary piston are located within the interior of the main piston and atomised fuel is introduced into an auxiliary chamber formed between the auxiliary piston and the auxiliary cylinder. Since the piston is hot, as the atomised fuel evaporates it effectively cools the main piston while the particle size of the atomised fuel particles is simultaneously rapidly reduced.

Preferably an injector mechanism in the form of a one way valve centrally located in the main piston enables the pressurised substantially evaporated fuel to be injected directly into the combustion chamber, preferably centrally and immediately below the spark plug. This preferably rich fuel mixture is surrounded by pure air which has been introduced into the crankcase and used to scavenge the combustion chamber via a substantially conventional transfer port. Thus the abovementioned preferred arrangement enables a stratified charge to be created within the combustion chamber.

Prior art searches conducted after the priority date have disclosed various auxiliary cylinder arrangements, none of which it is believed have entered into commercial production. In addition, it is believed that none of these arrangements have been positioned to substantially evaporate atomised fuel in order to reduce the size of the remaining particles of unevaporated fuel.

US Patent No. 792,119 (Clifton 1905) discloses an internal combustion engine with a main piston defining a combustion chamber and an auxiliary piston which pre- compresses the fuel air mixture prior to its being transferred to the combustion chamber.

US Patent No. 2,545, 999 (Hirschberg) discloses a two stroke powered percussive tool in which a main piston and an auxiliary piston interior thereof are

provided, the purpose of the auxiliary piston being to supply a source of compressed air for scavenging and charging purposes.

US Patent No. 2,586, 621 (De Laage) discloses a two stroke engine having a moveable sleeve between the piston and crankcase so that the volume of scavenging air is larger than the volume of the combustion chamber thereby ensuring a complete replenishment of the fuel air mixture within the combustion chamber at the beginning of each cycle.

US Patent No. 3,177, 853 (Hendershot) discloses a four stroke engine in which an auxiliary piston is provided with air from the crankcase so as to ensure a continuous stream of air into the crankcase from the atmosphere, this air being injected into the combustion chamber and ultimately expelled via the exhaust. The purpose of this arrangement is to prevent"blow by"of combustion products from the combustion chamber into the crankcase thereby leading to pollution via the crankcase breather tube. Because of the flow of air into the crankcase, any"blow by"gases are automatically recycled back into the combustion chamber to be exhausted in the normal fashion.

US Patent No. 3,996, 903 (Cseh) discloses a secondary piston within the primary piston to provide a pump which increases crankcase suction and therefore increased pressure in the transfer port.

German Published Application No. 199 06 456 (Geyer) discloses an engine block 1 in which a main piston 2 reciprocates. An inner piston 3 is located within the main piston 2 and is provided with two inlet valves 6 which communicate with an inlet port 17. Fuel air mixture is drawn through the inlet port 17 via the valves 6 into a pre-compression chamber 7 where the mixture is compressed prior to being introduced into the combustion chamber via an inlet valve 4. Exhaust gases are exhausted via an exhaust valve 5 operated by a rocker arm 10. The arrangement of the valves 4,5 is intended to replace the traditional transfer port and exhaust port and

thus enable two stroke operation with the convenience of conventional four stroke valving for the inlet and exhaust.

Object of the Invention The task of the present invention is to provide both a method of operating an internal combustion engine, and an internal combustion engine, in which emissions are reduced by the drawing of substantially pure air (rather than a fuel air mixture) into the crankcase, for ultimate transfer to the combustion chamber, and injection of substantially evaporated fuel directly into the combustion chamber.

Summary of the Invention In accordance with the first aspect of the present invention there is disclosed a method of operating an internal combustion engine having a combustion chamber formed by a piston mounted for reciprocating motion within a cylinder and also having a crankcase, an exhaust outlet in said cylinder, and a transfer port interconnecting said crankcase and combustion chamber, said method comprising the steps of : 1. moving said piston towards top dead centre to expand said crankcase volume and draw substantially pure air into said crankcase, 2. moving said piston away from top dead centre to open said exhaust outlet and contract said crankcase volume thereby introducing said substantially pure air into said combustion chamber via said transfer port to sequentially scavenge and charge said combustion chamber, 3. substantially atomising a liquid fuel and permitting same to substantially evaporate, 4. moving said piston towards top dead centre to substantially close said exhaust outlet and then injecting said evaporated fuel into said combustion chamber, 5. igniting said evaporated fuel within said combustion chamber as said piston approaches top dead centre, and 6. moving said piston away from top dead centre to open said exhaust outlet and thereby exhaust said combustion chamber.

In accordance with the second aspect of the present invention there is disclosed an internal combustion engine having a combustion chamber formed by a piston mounted for reciprocating motion within a cylinder and having a crankcase, an exhaust outlet in said cylinder opened and closed by movement of said piston, and a transfer port interconnecting said crankcase and combustion chamber and opened and closed by movement of said piston, wherein said crankcase is directly connected to the atmosphere to draw substantially pure air into said crankcase as said piston moves to expand said crankcase, and transfer same to said combustion chamber as said piston moves to open said transfer passage, atomising means to atomise a liquid fuel and supply said atomised fuel to an evaporator means in thermal communication with said combustion chamber to thereby evaporate said atomised fuel, an injector means supplied by said evaporator means and arranged to inject said evaporated fuel into said combustion chamber, and ignition means associated with said combustion chamber and arranged to ignite said evaporated fuel in said combustion chamber as said piston moves towards top dead centre.

Brief Description of the Drawings Preferred embodiments of the present invention will now be described with reference to the drawings in which: Fig. 1 is a stylised longitudinal cross-section through a single cylinder two stroke internal combustion engine in accordance with the preferred embodiment incorporating a modified piston arrangement and illustrating the piston during the compression stroke, Fig. 2 is a view similar to Fig. 1 but illustrating the piston at top dead centre, Fig. 3 is a view similar to Fig. 1 but illustrating the power stroke, Fig. 4 is a view similar to Fig. 1 but illustrating the exhaust and scavenging procedures, Fig. 5 is a longitudinal cross sectional view through the main piston, Fig. 6 is a plan view of the arrangement, Fig. 7 is a view similar to Fig. 1 and illustrating a lubrication arrangement, and Fig. 8 is a view similar to Fig. 1 but illustrating another embodiment of auxiliary piston.

Detailed Description It will be apparent from Figs. 1-4 that most of the two stroke engine is substantially conventional, the engine 1 having a crankcase 2 and main cylinder 3 within which a main piston 4 is reciprocally mounted. The main cylinder or combustion chamber 3 has a cylinder head 5 incorporating a centrally located spark plug 6.

Within the crankcase 2 is a crankshaft 8 having a sealed bearing and which supports a connecting rod 9. The connecting rod 9 extends between the crankshaft 8 and a substantially conventional gudgeon pin 10 mounted in the main piston 4.

In addition, the preferred engine has a substantially conventional carburettor 12, an exhaust port 13 in the side wall of the main cylinder 3, a substantially conventional transfer passage (not illustrated in Figs. 1-4 but illustrated at 107 in Fig.

8) interconnecting the crankcase 2 and a transfer port 7 (Fig. 4) located in the side wall of the main cylinder 3 at right angles to, and spaced just below, the exhaust port 13. The arrangement of the transfer port and exhaust port is substantially conventional save that the spacing of the transfer port 7 preferably just below the exhaust port 13 increases turbulence in the air introduced via the transfer passage into the combustion chamber 3. In addition, the crankcase 2 has an air inlet 15.

It will be appreciated that with the exception of the air inlet 15 thus far the main components of the engine 1 are substantially conventional and thus need not be changed from a manufacturer's existing model when introducing a new low emissions model incorporating the present invention.

Reciprocally mounted within the interior of the main piston 4 is an auxiliary piston 24 which is coaxial with the main piston 4. A cylindrical housing 25 is mounted on the gudgeon pin 10 and has a side wall 26 against which the auxiliary piston 24 seals. An inlet tube 28 interconnects the cylindrical housing 25 and an inlet port 29 in the side wall of the main piston 4 and positioned opposite the carburettor 12.

The auxiliary piston 24 is connected to the connecting rod 9 by means of a mechanical linkage comprising a spur arm 31 on the connecting rod 9 and a kinked link member 32 which is pivoted at one end on the spur arm and at the other end on the auxiliary piston 24. It will be seen by inspection of Figs. 1-4 that as the connecting rod 9 moves in synchronism with the main piston 4, so the spur arm 31 and link member 32 contrive to move the axial piston 24 so as to adjust the volume of a space which is conveniently termed an auxiliary chamber 30 formed between the upper surface of the auxiliary piston 24, the lower surface of the crown 34 of the main piston 4 and the interior of the side walls of the main piston 34.

In addition, preferably centrally mounted in the top 34 of the main piston 4 is an injector valve 36 which is normally closed and is spring loaded (as illustrated in Fig 5) so as to open when the pressure difference between the combustion chamber 3 and the auxiliary chamber 30 exceeds a predetermined pressure difference.

The operation of the auxiliary piston 24 and auxiliary chamber 30 is as follows. As seen in Fig. 2, with the main piston 4 at top dead centre, the injector valve 36 is closed and the auxiliary piston 24 is moving downwardly relative to the main piston 4, thereby expanding the auxiliary chamber 30 and drawing in fuel air mixture from the carburettor 12 via the inlet port 29 and inlet tube 28. As the rotation of the engine continues, the inlet port 29 is closed and the volume of the auxiliary chamber 30 reaches a maximum as illustrated in Fig. 3.

As illustrated in Fig. 4, by bottom dead centre the spur arm 31 and link member 32 have begun to move the auxiliary piston 24 towards the crown 34 of the main piston 4 thereby decreasing the volume of the auxiliary chamber 30 and pressurising the air fuel mixture. As the rotation of the engine continues, as seen in Fig. 1 the volume of the auxiliary chamber 30 reaches a minimum. Since the pressure within the auxiliary chamber 30 exceeds that of the main cylinder 3 by a substantial margin (in the preferred embodiment up to approximately four bar relative to two bar in the combustion chamber 3) so the injector valve 36 opens. This injects the fuel air

mixture into the main cylinder 3 directly towards the spark plug 6 and away from the edges of the main piston 4. The result is a highly stratified charge in which a rich mixture is located immediately adjacent the spark plug, but a very lean mixture is located elsewhere in the main cylinder 3. Furthermore, the fuel air mixture from the carburettor 12 which is relatively cold (having undergone an expansion as a result of passing through the jet of the carburettor), has been pre-warmed by being held adjacent the crown 34 of the main piston 4. In this way not only is the air fuel mixture warmed, but the main piston 4 is cooled simultaneously. The warming of the air fuel mixture prior to its injection ensures that substantially all the fuel (gasoline or petrol) is fully evaporated and thus the particle size of the fuel is extremely small (typically five microns or less). This makes a substantial contribution to the reduction of emissions.

Bearing in mind the operation of the auxiliary piston 24 as explained above, it will be seen that in relation to the overall operation of the engine, in Fig. 1 the air fuel mixture is injected into the combustion chamber 3. At Fig. 2 the main piston 4 is at top dead centre and the spark plug 6 has fired. At Fig. 3 the power stroke is under way. At Fig. 4, firstly, the exhaust port and secondly the transfer port have opened thereby allowing the exhaust gases to be swept from the combustion chamber 3 by substantially pure air which has entered the crankcase 2 via the air inlet 15 as seen in Fig. 2. This has the consequence that no unburnt hydrocarbons are included in the scavenging air, thereby still further reducing emissions. Further, by the time the compression stroke is underway as illustrated in Fig. 1, the combustion chamber 3 contains substantially entirely pure air since no fuel is introduced into the combustion chamber 3 via the crankcase 2.

Turning now to Fig. 7, a lubrication arrangement is illustrated in schematic form. An oil reservoir 40 containing enough oil to substantially last the operating life of the small engine, is connected to a two part block 41 which houses two reed valves 42 and 43. A push rod 45 is mounted on a rotary cam 46 which is rotated via a gear wheel 47. Rotary motion of the gear wheel 47 is induced by a diaphragm 48 which senses the pressure in the crankcase 2 via a tube 49.

As the push rod 45 rises and falls once for every say, 1,000, cycles of the engine, so a small amount of oil is drawn through the reed valve 42 and pushed through the reed valve 43 in turn and into an oil supply pipe 51. The pipe 51 directs oil to an oil supply duct 52 which passes through the side wall of the main cylinder 3.

The oil supply duct 52 lubricates between the cylinder 3 and main piston 4 directly.

In addition, within the main piston 4 is a oil branch line 53 which, when the piston 4 is in the position illustrated in Fig. 7, is immediately opposite the oil supply duct 52.

Thus negative pressure within the crankcase 2 enables oil from the oil supply duct 52 to enter the oil branch line 53. Similarly, the negative pressure within the crankcase 2 permits an oil mist to be supplied in minute quantities directly to the gudgeon pin 10, spur arm 31, and auxiliary cylinder 30.

In addition, the piston 4 is fabricated in two parts, the upper part including the piston rings and the lower part the oil branch line 53. Where these two parts mate, a circumferential groove 55 is formed in the upper part facing the lower part. This groove 55 forms a tunnel when the two parts of the piston 4 are mated together. Oil is able to flow into this tunnel from the oil supply duct 52 and thus travel (in two opposite directions) right around the piston 4 where it is able to exit the tunnel formed by groove 55 at one or more nozzles 56. The mist of oil supplied by the oil branch line 53 and nozzle (s) 56 typically has an air to oil ratio of the order of 800: 1 so that a single oil reservoir 40 having a volume of typically 200ml can last for the entire expected operating life of the engine.

An alternative embodiment of the present invention is illustrated in Fig. 8 and like parts will be indicated with a designation number increased by 100 relative to that used in relation to Figs. 1-7. Thus the engine 101 has a crankcase 102 and a main cylinder 103 within which the main piston 104 is mounted. A connecting rod 109 connects the piston 104 to a crankcase 108 as before. A transfer passage 107 interconnects the crankcase 2 and the combustion chamber 103.

Unlike the arrangements of Figs. 1-7, in Fig. 8 an auxiliary cylinder 130 is formed in the cylinder head 105 and is provided with an injector valve 136 which

interconnects the auxiliary cylinder or chamber 130 with the combustion chamber 103.

Located within the auxiliary chamber 130 is an auxiliary piston 124 which is biased by means of a spring 155 into the position illustrated in Fig. 8. A rocker arm 156 transmits the motion of a plunger 157 driven by a cam 158 on the engine shaft 159 so as to reciprocate the auxiliary piston 124 in synchronism with the rotation of the engine shaft 159. In this way the auxiliary chamber 130 is cyclically compressed and expanded as before. A carburettor (not illustrated but conventional) provides air and atomised fuel at an air/fuel ratio of approximately 3: 1 to the auxiliary chamber 130 where the atomised fuel is able to evaporate thereby substantially reducing the particle size. The pure air introduced into the combustion chamber 103 via the transfer passage 107 together with the fuel introduced into the combustion chamber via the injector valve 136 results in an overall air/fuel ratio of approximately 15: 1.

The foregoing describes only one embodiment of the present invention and modifications, obvious to those skilled in the art can be made thereto without departing form the scope of the present invention. For example, the auxiliary piston 24 need not be co-axial with the main piston 4. Also, the spur on the connecting rod can be replaced with a secondary connecting rod with the auxiliary chamber taking the form illustrated in Fig. 8. The reed valves in the lubricating arrangement can be replaced with rotary or sleeve valves. Finally, the present invention can also be adapted for four-stroke operation.

The term"comprising" (and its grammatical variations) as used herein is used in the inclusive sense of"having"or"including"and not in the exclusive sense of "consisting only of.