GB2232718A

GB2232718A - Two-stroke engine exhaust control

Info

Publication number: GB2232718A
Application number: GB8913906A
Authority: GB
Inventors: Gianuario Sergio Demontis
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-06-16
Filing date: 1989-06-16
Publication date: 1990-12-19
Anticipated expiration: 2009-06-16
Also published as: GB2232718B; GB8913906D0

Abstract

A fuel-injected crankcase compression two-stroke engine has a cylinder head 2 provided with a through-going passage leading to an exhaust port 5 and the crown of the piston has a hollow stem 7 projecting from the piston crown and extending into the passage in the cylinder head 2. Sealing rings 4 are provided between the wall of the stem 7 and the wall of the cylinder head passage to prevent the escape of gases between these walls and a series of apertures 9 are provided in the wall of the piston stem 6 to permit the escape of exhaust gases from the combustion chamber to the exhaust port. Pairs of diametrically opposed fuel injectors (14, Fig. 3) and spark plugs (15) may be provided in the head 2. <IMAGE>

Description

Title: IMPROVEMENTS IN INTERNAL COMBUSTION ENGINES This invention relates to internal combustion engines and is particularly concerned with fuel-injected twostroke combustion engines.

Conventional two-stroke internal combustion engines suffer from the disadvantages of high hydrocarbon exhaust emissions and high fuel consumption primarily as a result of the scavenging process which allows the fuel/air mixture to escape directly to the exhaust system and residual exhaust gases to dilute the inlet charge causing misfiring under throttled conditions.

It has previously been proposed to overcome these disadvantages by utilising a fuel injection system in which the fuel is injected directly into the combustion chamber. One such system has been produced by Orbital Walbro Corporation which is based on a pneumatic principle of operation and provides excellent fuel atomization and high operating speed. This system allows the precise injection of highly atomized particles of petrol into the combustion chamber after the fresh charge has been trapped and displays greatly reduced exhaust emissions while giving up to a 30% improvement in fuel consumption.

The present invention aims to provide a still further improvement in the performance of a fuel-injected twostroke internal combustion engine.

According to the invention, there is provided a fuelinjected two-stroke internal combustion engine comprising a cylinder, a piston reciprocally mounted in the cylinder, an inlet leading into the crankcase of the engine and at least one transfer passage leading from the crankcase to the cylinder, the or each transfer passage terminating in a or a respective transfer port in the wall of the cylinder and arranged to be covered and uncovered by the piston during its reciprocating movement, wherein the cylinder has a head provided with a through-going passage leading to an exhaust port and wherein the crown of the piston is provided with a hollow stem projecting from said piston crown and extending into the passage in the cylinder head, sealing rings being provided between the wall of the stem and the wall of the cylinder head passage to prevent the escape of gases between said walls and at least one aperture being provided in the wall of the piston stem to permit the escape of exhaust gases from the combustion chamber to the exhaust port.

The engine is preferably provided with at least one fuel injector located in the cylinder head and ignition means may take the form of one or more spark plugs.

The invention will now be described in detail, by way of example, with reference to the drawings, in which: Fig. 1 is a vertical section through one embodiment of an engine according to the invention showing the piston at the bottom dead centre (BDC) position; Fig. 2 is a vertical section, on a different plane, of the engine shown in Fig. 1 but showing the piston in the top dead centre (TDC) position; and Fig. 3 is an underneath view of a cylinder head for the engine according to the invention.

Referring to the drawings, the engine comprises a cylinder 1 which is mounted on a crankcase (not shown).

A cylinder head 2 is mounted on the cylinder 1 and has a through-going stepped bore in which a stepped collar 3 having a stepped bore is fitted. A piston 6 is reciprocally mounted in the cylinder and has a hollow stem 7 extending upwardly from its crown, the stem extending through the bore in the collar 3 into an exhaust port 5 which is formed integrally with or secured to the cylinder head 2. An enlarged diameter portion 8 is provided on the end of the piston stem 7 and sealing rings 4 are provided in the wall of the bore of the collar 3 to ensure a gas-tight seal between the wall of said bore and the wall of the piston stem 7.

Said piston stem 7 is further provided, adjacent its end, with a series of apertures 9 in its wall.

Transfer passages 11 extend in the material of the cylinder 1 from the crankcase to transfer ports 12 in the wall of the cylinder. The transfer ports 12 are so located that, when the piston 6 is at BDC as shown in Fig. 1, the ports are above the crown of the piston and are uncovered. An inlet port 13 leads into the crankcase and is so arranged that, when the piston 6 is at TDC as shown in Fig. 2, the lower end of the piston skirt is above the inlet port 13 so that this port is uncovered.

A pair of fuel injectors 14 and a pair of spark plugs 15 are provided in the cylinder head 2.

The operation of the engine illustrated in the drawings will now be described. Starting with the piston at TDC as shown in Fig. 2, the combustible mixture in the combustion chamber has been fired by the spark plugs 15 and air has been sucked into the crankcase through the inlet port 13 which has been uncovered by the piston skirt. The ignited gases expand and, as a result, drive the piston 6 down. At this stage, the apertures 9 in the piston stem 7 are located in the exhaust port 5 and the sealing rings 4 prevent the escape of the burning gases from the combustion chamber. As the piston 6 descends, the inlet port 13 is first covered by the piston skirt and the air in the crankcase is progressively compressed.Further downwards movement of the piston 6 results in the apertures 9 in the piston stem 7 entering the combustion chamber so that the exhaust gases can now enter the exhaust port 5 as indicated by the arrows 16 in Fig. 1.

As the piston 6 continues its descent, the transfer ports 12 are uncovered and the air in the crankcase is forced by the descending movement of the piston along the transfer passages 11 to enter the cylinder, as indicated by the arrows 17 in Fig. 1, and forces the exhaust gases out of the combustion chamber. The air also has a cooling effect on the piston crown, the piston stem, the cylinder and the cylinder head.

When the piston 6 reaches BDC, the transfer ports 12 are fully uncovered and the piston now commences its ascent stroke. The transfer ports 12 are first covered by the piston and shortly afterwards the apertures 9 in the piston stem 7 pass through the sealing rings 4 in the collar 3 to seal the combustion chamber. Fuel is injected into the combustion chamber by the fuel injectors 14 at a convenient point during the ascending stroke of the piston and the fuel/air mixture is ignited by the spark plugs shortly before TDC. At the same time during the ascent of the piston 6, the inlet port 13 is uncovered by the piston skirt and a fresh charge of air is sucked into the crankcase as indicated by the arrow 18 in Fig. 2. The cycle is then repeated.

The engine is desirably so arranged that the volume of air sucked into the crankcase through the inlet port 13 is equal to the total capacity of the cylinder plus 20-30%. The volume occupied by the piston stem 7 desirably represents 20-30% of the cylinder volume so that, when the air in the crankcase is transferred to the cylinder, its volume will exceed the cubic capacity of the cylinder by some 20-30%.

While Fig. 2 shows a fuel injector 14 and a spark plug 15 in the same plane, this is not the preferred arrangement and has been shown in this manner purely to explain the operation of the engine according to the invention. The preferred arrangement is shown in Fig. 3 in which two fuel injectors 14 and two spark plugs 15 are provided, the fuel injectors and spark plugs being located diametrically opposite to each other, respectively, and orthogonally with respect to the adjacent spark plugs or fuel injectors.

While the timing of the fuel injection and ignition may be adjusted to suit the desired characteristics and performance of the engine, it is suggested that fuel injection should take place from the two diametrically opposed injectors 14 at about 900 before TDC followed by ignition from the two orthogonally arranged and diametrically opposed spark plugs 15 some 100-150 later.

Although the invention has been described with reference to a single cylinder engine, it will be appreciated by those skilled in the art that the invention is not restricted to such engines and is equally applicable to twin, three, four, five, six, eight cylinder engines or indeed to engines having any number of cylinders.

Further, the cylinder head of the or each cylinder may be provided with any suitable number of fuel injectors and/or spark plugs and, thus, one, three or four of each may be provided as alternatives if desired. Moreover, ignition need not necessarily be by way of spark plugs and other suitable ignition means may be utilised if desired.

The engine according to the present invention provides improvements in exhaust emissions as well as cooling by the utilisation of uni-directional scavenging with clean air which will normally be filtered before being allowed to enter the crankcase. While such an engine made from conventional materials such as aluminium alloys will normally require additional air or water cooling, it is possible that with the continued development of new materials such as ceramics or carbon fibres, the cooling effect of the sucked-in air will be sufficient and additional cooling means may not be necessary with engines made from such materials.

The invention is not restricted to the above-described embodiment but modifications and variations may be made without departing from the scope of the invention. For example, instead of providing sealing rings 4 in the collar 3, or as an addition to these sealing rings, the piston stem 7 may be provided with sealing rings in the nature of conventional piston rings.

Claims

1. A fuel-injected two-stroke internal combustion engine comprising a cylinder, a piston reciprocally mounted in the cylinder, an inlet leading into the crankcase of the engine and at least one transfer passage leading from the crankcase to the cylinder, the or each transfer passage terminating in a or a respective transfer port in the wall of the cylinder and arranged to be covered and uncovered by the piston during its reciprocating movement, wherein the cylinder has a head provided with a through-going passage leading to an exhaust port and wherein the crown of the piston is provided with a hollow stem projecting from said piston crown and extending into the passage in the cylinder head, sealing rings being provided between the wall of the stem and the wall of the cylinder head passage to prevent the escape of gases between said walls and at least one aperture being provided in the wall of the piston stem to permit the escape of exhaust gases from the combustion chamber to the exhaust port.

2. An engine according to claim 1, wherein the engine is provided with at least one fuel injector in the cylinder head.

3. An engine according to claim 1 or claim 2, wherein the engine is provided with an ignition means in the form of a pair of diametrically-opposed spark plugs.

4. An engine according to claims 2 and 3, wherein a pair of diametrically-opposed fuel injectors are provided in the cylinder head, said fuel injectors being orthogonally disposed with respect to the spark plugs.

5. An engine according to any preceding claim, wherein a collar is provided in the passage in the cylinder head and wherein the piston stem extends through said collar.

6. A fuel-injected two-stroke internal combustion engine substantially as described herein with reference to the drawings.

6. An engine according to claim 5, wherein the sealing rings are provided in said collar.

7. An engine according to any preceding claim, wherein the exhaust port is formed integrally with the cylinder head.

8. A fuel-injected two-stroke internal combustion engine substantially as described herein with refs nice to the drawings.

Amendments to the claims have been filed as follows 1. A fuel-injected two-stroke internal combustion engine comprising a cylinder, a piston reciprocally mounted in the cylinder, an inlet leading into the crankcase of the engine and at least one transfer passage leading from the crankcase to the cylinder, the or each transfer passage terminating in a or a respective transfer port in the wall of the cylinder and arranged to be covered and uncovered by the piston during its reciprocating movement, the cylinder having a head provided with a through-going passage leading to an exhaust port, the crown of the piston being provided with a hollow stem projecting from said piston crown and extending into the passage in the cylinder head, sealing rings being provided between the wall of the stem and the wall of the cylinder head passage to prevent the escape of gases between said walls, at least one aperture being provided in the wall of the piston stem to permit the escape of exhaust gases from the combustion chamber to the exhaust port, wherein a collar is provided in the passage in the cylinder head, wherein the piston stem extends through said collar and the sealing rings are provided in the collar.

5. An engine according to any preceding claim, wherein the exhaust port is formed integrally with the cylinder head.