WO1990008884A1

WO1990008884A1 - An improved cylinder and piston assembly for a two-stroke cycle internal combustion engine

Info

Publication number: WO1990008884A1
Application number: PCT/EP1990/000107
Authority: WO
Inventors: Renzo Dellarosa
Original assignee: Renzo Dellarosa
Priority date: 1989-01-24
Filing date: 1990-01-19
Publication date: 1990-08-09
Also published as: IT8912001A0

Abstract

A cylinder (10) and piston (5) assembly for a two-stroke cycle internal combustion engine has a passageway (2) the opening of which is controlled by suitable valve means (1, 9) to communicate a pump casing (3) with an exhaust zone (4) of cylinder (10) at least in vicinity of the B.D.C. and/or the T.D.C. of piston (5). Opening of passageway (2) in the vicinity of the B.D.C. causes a flow of fresh pressurized gases to pass from pump casing (3) to exhaust zone (4) in a direction towards the inside of cylinder (10), thereby to prevent by a 'wall effect' escaping of fresh gases from the cylinder. The following results are obtained: improved filling of cylinder chamber which results in higher power and gradual supply thereof; lower fuel consumption and reduced air pollution.

Description

AN IMPROVED CYLINDER AND PISTON ASSEMBLY FOR A TWO-STROKE CYCLE INTERNAL COMBUSTION ENGINE.

This invention relates to an improved cylinder and piston assembly for a two-stroke cycle internal combustion engine which is in particular effective to prevent escaping of scavenging mixture from cylinder. As is known, two-stroke cycle engines have a disadvantage in that they do not attain sufficient volumetric efficiency at all rpm; this results from a bad filling of the cylinder which is especially due to escaping (and, thus, to loss) of fresh gases from exhaust.

Adequate overcoming of this problem would result in: improved turbulence in cylinder improved efficiency reduced fuel consumption curtailed polluting unburnt gases.

Technical measures taken hitherto have involved use of valve means at the exhaust, expansion muffles, etc., but results attained thereby still leave large margins to improvements.

If technological progess has, in fact, enabled very high power levels to be attained at high rpm, this has been to the detriment of power at low and medium rpm, which resulted in uneven power curves and high consumptions (losses) in fresh gases (air-fuel).

It is an object of this invention to provide means for improving power of a two-stroke cycle engine at all rpm thereof, in particular at low and medium rpm. The above object is attained according to the invention by providing pressure equalizing means between the pump casing and the exhaust zone of each cylinder.

In particular, these pressure equalizing means comprise a passageway by which the pump casing and the exhaust zone are caused to communicate with each other, through operation of appropriate valve means, at least in the vicinity of B.D.C. (bottom dead center) and/or T.D.C. (top dead center) of the piston. The valve means which open and close the passageway communicating the pump casing wiht the exhaust zone are preferably formed by the piston skirt and ports provided in the piston skirt, which ports are arranged in such positions as to momentarily interfere with opening of the passageway into the cylinder chamber during a working cycle.

When the piston, working in expansion and compression, pumps towards B.D.C. to open the discharge port of the corresponding cylinder, burnt gases will rush y their own pressure towards the exhaust wone. Before the piston reaches the B.D.C, a flow of fresh gases due to pressure difference between exhaust zone and pump casing will pass from pump casing through the passageway to exhaust zone fo form a barrier against flow of fresh gases from outlets (which the piston has opened meanwhile) thereby to prevent these fresh gases from going out, and also to assist in improving filling of cylinder to provide turbulence inside this latter which will make for more complete burning.

When the piston moves up to T.D.C. (top dead center) after having closed the connecting passageway, during compression and induction stroke, at the time of maximum vacuum, said passageway will again open into pump casing (for a fraction astride of T.D.C), whereby vacuum existing in pump casing permits fresh residual gases from previous stroke to be recovered and added to those sucked-in from carburetor and, at the same time, it limits vacuum peaks on the same intake.

The pressure equalizing system according to the invention finds application to any type of two-stroke cycle engine; successful results are particularly evidenced in connection with high performance engines, even in the case of such propulsors as used for racing purposes. Power curves become more linear, fuel consumptions are reduced, emission of polluting (unburnt) gases from exhaust are curtailed.

A turbulence effect is created in cylinder which improves combustion.

In substance, by this system it is obtained that the air-fuel mixture (fresh gases) passes from outlets to cylinder without subsequently escaping, except for a negligible amount, from exhaust thereby to limit such phenomena as high fuel comsumption, unburnt gas emission and, as a result, power loss.

Finally, this system enables a greater amount of fresh gases to enter the cylinder and, above all, it permits an as great as possible part thereof to be utilized.

The invention will now be described in connection with a preferred embodiment shown by way of a non resctrictive example with reference to the accompanying drawings, in whic : figure 1 is a side elevational view of a piston as modified according to the invention, figures 2 to 6 show a cylinder and piston assembly in accordance with the invention, with the cylinder being shown in cross-section in several successive working positions, from T.D.C. to B.D.C.

Referring now to the above figures, reference numerals 5 and 10 show a piston and a cylinder, respectively. 3 is a pump casing and 2 a passageway formed in the wall of cylinder 10 to permit communication of pump casing 3 with an exhaust zone 4 which is arranged downstream of cylinder discharge port 8. Suitable ports 1 and 9 are provided on skirt 11 of piston 5 to open the connecting passageway 2.

Designated by 6 and 7 are outlet ports for admitting fresh gases to the chamber of cylinder 10, and an intake zone, respectively. The above mentioned elements are thought to be sufficient matter for an understanding of operation of the cylinder and piston assembly according to the invention, which is describe below.

During a working cycle, starting from T.D.C (figure 2), the piston 5 moves down to comraence opening " of discharge port 8, as shown figure 3 (expansion and exhaust stroke). Upon opening of discharge port 8, the burnt gases will (by their own pressure) make their way towards the exhaust zone 4 to be then released to atmosphere. In going on with its stroke towards B.D.C, the piston 5 continues to open discharge port 8 and it also opens, through its port 1, the passageway 2 communicating the pump casing 3 and the exhaust zone 4 with each other (figure 4) .

Now, since (at high rpm) the pressure in exhaust zone 5 becomes higher, for a small fraction of time, then that in pump casing 3, there will be created a pressure equalizing flow between these two zones in a direction towards the pump ^" casing, through passageway 2. The exhaust hot gases that are, for said fraction of time, contacted with fresh gases in pump casing 3, give up their own heat thereto which results in an increase in volume. Thus, an increased compression is obtained in pump casing and, therefore, a faster discharge of fresh gases is produced from outlet 6 which is contributive to improved scavenging or filling at high rpm.

A short time before B.D.C is attained (figure 5), pressure will drop downstream of discharge port 8, so that a reverse flow to the preceding one is created, i.e. from pump casing 3 towards discharge port 8, still through passageway 2.

This flow creates a barrier against escaping of fresh gases from outlets 6 which tend to flow out of discharge port 8. In the period when fresh gases from pump casing are entrained also towards discharge port 8 through passageway 2, this passageway 2 also functions as an outlet of the discharge port.

On subsequent up-stroke of the piston (figure 6), a short time prior to T.D.C. , the passageway 2 is opened by port 9 to again communicate the pump casing 3 (now in vacuum state) with exhaust zone 4.

Fresh gases issued from previous filling period of cylinder and stagnating downstream of discharge port 8, are recovered and readmitted to pump casing 3 along with those entered during the suction stroke.

Thus, a decrease in vacuum is obtained in pump casing 3, and a more constant velocity of fresh gas admission is maintained from the induction pipe, whereby filling of pump casing is improved too.

To sum up, the following results are obtained less fresh gases lost from exhaust; higher power at all rpm; less unburnt gas at exhaust, i.e. less air pollution. In carrying out the invention, the passageway 2 and the ports 1 and 9 may be provided in any number and be shaped, sized and positioned in any way according to specific requirements; in particular, the passageway 2 can be either cast integral with cylinder 10 or provided as a pipe fitting external thereto.

Claims

1. A cylinder and piston assembly for a two-stroke internal combustion engine, characterized in that pressure equalizing means are provided between a pump casing (3) and an exhaust zone (4).

2. The cylinder and piston assembly according to claim

1, wherein said pressure equalizing means comprise at least one passageway (2) for selectively putting the pump casing (3) in communication with the exhaust zone (4).

3. The cylinder and piston assembly according to claim

2, wherein suitable valve means are arranged along said passageway (2) for opening or closing thereof.

4. The cylinder and piston assembly according to any of claims 1 to 3, wherein the passageway (2) is provided by pipe fittings external to pump casing (3) and exhaust zone (4) .

5. The cylinder and piston assembly according to any of claims 1 to 3, wherein the passageway (2) is formed in the wall of cylinder (10).

6. The cylinder and piston assembly according to claim 5, wherein the passageway (3) is cast integral with cylinder (10) .

7. The cylinder and piston assembly according to claim 5 or 6 , wherein the valve means for opening and closing the passageway (2) are provided by the skirt (11) of piston (5) and by ports (1,9) in said piston skirt, said ports (1,9) being arranged in such positions as to be able, during a working cycle, to momentarily interfere with opening of passageway (2) into the chamber of cylinder ( 10 ) .

8. The cylinder and piston assembly according to any of claims 1 to 7, wherein the passageway (2) for communicating the pump casing (3) and the exhaust zone (4) with one another, is opened in the vicinity of B.D.C (bottom dead center) and/or T.D.C. (top dead center) of piston (5) .

9. The cylinder and piston assembly according to claim 8, wherein opening of passageway (2) in proximity to B.D.C creates, at high rpm, first a flow towards pump casing (3) and subsequently a flow in a reverse direction.

10. The cylinder and piston assembly according to claim 8, wherein opening of passageway (2) in the vicinity of T.D.C. caused a decrease in vacuum in pump casing (3).

11. A two-stroke cycle internal combustion engine, characterized in that the engine includes pressure equalizing means according to any of claims 1 to 10 provided between the pump casing (3) and the associated exhaust zone (4) of each cylinder and piston assembly in the engine.

12. A method of equalizing pressure between a pump casing (3) and an exhaust zone (4) of a cylinder and piston asssembly for a two-stroke cycle internal combustion engine, characterized in that the method comprises causing the pump casing (3) and the exhaust zone (4) to communicate with one another at least in vicinity to the B.D.C. and/or the T.D.C. of a piston (5).