Two-stroke engine and components thereof

A piston arrangement for an engine is provided and includes a crankshaft located within a crank case and a primary piston located within a first cylinder and interconnected to the crankshaft by a first drive rod for converting reciprocating motion of the primary piston within the first cylinder driven by combustion occurring within the first cylinder into rotational motion of the crankshaft. The arrangement also includes a pumping piston located within a second cylinder and interconnected to the crankshaft by a second drive rod for converting the rotational motion of the crankshaft into reciprocating motion of the pumping piston within the second cylinder. The pumping piston is located between the primary piston and the crank case and seals the first and second cylinders from the crankcase. A stepped-piston and a two-stroke engine are also disclosed.

BACKGROUND

The present invention relates in general to two-stroke combustion engines and components thereof.

SUMMARY

A piston arrangement for an engine is provided and includes a crankshaft located within a crank case and a primary piston located within a first cylinder and interconnected to the crankshaft by a first drive rod for converting reciprocating motion of the primary piston within the first cylinder driven by combustion occurring within the first cylinder into rotational motion of the crankshaft. The arrangement also includes a pumping piston located within a second cylinder and interconnected to the crankshaft by a second drive rod for converting the rotational motion of the crankshaft into reciprocating motion of the pumping piston within the second cylinder. The pumping piston is located between the primary piston and the crank case and seals the first and second cylinders from the crankcase. The reciprocating motion of the pumping piston within the second cylinder aids in drawing fresh air or air-fuel mixture into the first and second cylinders for a new cycle and aids in pushing exhausted gas-charge of a previous cycle out through an exhaust port.

According to another aspect, an engine or two-stroke engine is provided.

According to a further aspect, a stepped piston arrangement is provided.

DETAILED DESCRIPTION

According to an embodiment as shown inFIGS. 1-9, a two-stroke engine10is provided in which a crank case12of the engine10does not form part of a scavenging process. In automotive usage, scavenging is the process of pushing exhausted gas-charge out of the cylinder and drawing in a fresh draught of air or fuel/air mixture for the next cycle.

As shown inFIGS. 1-9, a main piston14is located in a first cylinder16and a pumping piston18is located within a secondary cylinder20located below the first cylinder16and above the crank case12. The pumping piston18slides along the length of the main piston14to seal off the first and secondary cylinders,16and20, from the crank case12. The pumping piston18essentially functions as a variable volume crank case, as well as a “phased” scavenging system.

For example, as best shown inFIG. 2, the drive rod22of the main piston14extends through the pumping piston18and is connected to the crankshaft24for rotation thereabout. The drive rod26of the pumping piston18is also connected to the crankshaft24approximately 90° ahead of the main piston14. Thus, inFIG. 2, when the main piston14is at a 90° ATDC (after top dead center) position, the pumping piston18is at a BDC (bottom dead center) position and remains 90° ahead of the main piston14throughout the rotation of the crankshaft24. The benefits of the above described arrangement are more efficient use of transfer port timing and the ability to create a positive push to the transfer flow, which make the transfer process less dependent on an expansion chamber pipe.

The engine10can also include a sliding gate valve (not shown) that is extendable over the exhaust port28. The sliding gate valve may project upwardly from the pumping piston18as the reciprocating motion of the pumping piston is already in time with the exhaust valve. Thus, no other external valving system would be needed to position the sliding gate valve over the exhaust port28to close the exhaust port28or to remove the gate valve from the exhaust port28to open the exhaust port28.

Turning toFIGS. 1-9, inFIG. 1, combustion30has just occurred and the main piston14is traveling downward powered by the combustion. InFIG. 1, the main piston14is at a 45° ATDC position with the pumping piston at a 135° ATDC position. Thus, the pumping piston18is moving in its downward stroke ingesting fresh intake charge32.

InFIG. 2, the main piston14has reached about a 90° ATDC position and the exhaust port28has just been cracked open and the exhaust gases34from the combustion30are starting to exit through the exhaust port28. The intake charge32under the primary piston14has stopped filling because the pumping piston18has reached its BDC position and will thereafter start heading upward to compress the fresh intake mixture32.

InFIG. 3, the exhaust gases34have all but escaped the combustion chamber and the fresh intake charge mixture32is starting to fill the first cylinder16due to the position of the main piston14opening the transfer ports36. The pumping piston18has started to move up in its stroke and is helping to push the fresh intake mixture32through the transfer ports36up into the first cylinder16. InFIG. 3, the main piston14is at the 135° ATDC position.

InFIG. 4, the main piston14has almost reached the BDC position and a conventional intake transfer phase will have typically started to slow down at this point. However, this is not true in the illustrated embodiment because the pumping piston18is still traveling up its bore in the secondary cylinder20and thereby is continuing to compress and push the fresh intake charge32through the transfer ports36. At this point, the sliding gate valve which may extend from the pumping piston will be in position to close the exhaust port28.

InFIG. 5, the main piston14is at a BDC position and the pumping piston18is at about a 90° BTDC (before top dead center) position with 90° of rotation remaining for further transfer pumping as described above.

InFIG. 6, the main piston14is at a 135° BTDC position on its way up to start compressing the fresh intake mixture32in the first cylinder16. In a typical two-stroke engine, the charge might start to travel back down the transfers because of lack of positive pressure in the crank case; however, because the pumping piston18is there aiding in the pumping of the transfers, the transfer flow will keep on flowing out the transfer ports36into the first cylinder16helping to charge the first cylinder16thereby aiding in power and efficiency.

InFIG. 7, the main piston14has closed off the transfer ports36and is starting to compress the mixture in the top part of the first cylinder16. At this time, the pumping piston18is at its TDC (top dead center) position and is about to start moving downward to thereby start ingesting the next new intake charge.

InFIG. 8, the main piston14is at a 45° BTDC position getting ready to ignite the fuel/air mixture. The pumping piston18is at about a 45° ATDC and has already created a good low pressure below the main piston14for the next new intake charge to start filling the space under the main piston14.

InFIG. 9, combustion has occurred and the main piston14is at a TDC position and the inlet expansion phase will be at its greatest at this crank angle. The pumping piston18is at a 45° ATDC traveling downward in its stroke helping to create a negative pressure ratio to aid the next new intake charge coming through the intake tract into the secondary cylinder20. This means that the pumping piston18helps the engine ingest more intake charge than it would without it.

At this point, the pistons are as shown inFIG. 1to start the phase over again.

The above description illustrates an embodiment of how aspects of the present invention may be implemented and should not be deemed to be the only embodiment. One of ordinary skill in the art will appreciate that based on the above disclosure, other arrangements, embodiments, implementations and equivalents may be employed without departing from the scope hereof.

By way of example, while the discussion above may be directed to a conventional non-stepped piston design, embodiments may also be utilized with stepped piston arrangements. For instance, an alternate embodiment is shown inFIGS. 10-12having a stepped-piston40and a pumping piston and exhaust valve42. This alternate embodiment is similar in most ways to the embodiment illustrated inFIGS. 1-9discussed above. For instance, the pumping piston42is located below the stepped-piston40and above a crank case44.

In this embodiment, the pumping piston42slides along a length of the stepped-piston40and has a sliding gate valve46that is extendable over an exhaust port48. The sliding gate valve46projects upwardly from the pumping piston42and the reciprocating motion of the pumping piston42positions the sliding gate valve46over the exhaust port48to close the exhaust port48or to remove the gate valve46from the exhaust port48to open the exhaust port48.

A drive rod50of the stepped piston40extends through the pumping piston42and is connected to a crankshaft52for rotation thereabout. For instance,FIG. 10illustrates the TDC (top dead center) position of the stepped piston40,FIG. 11illustrates the 135° ATDC (after top dead center) position of the stepped piston40, andFIG. 12illustrates the 90° BTDC (before top dead center) position of the stepped piston40.

A drive rod54of the pumping piston42is also connected to the crankshaft52approximately 90° ahead of the stepped piston40. Thus, for instance, when the stepped piston40is at a 90° BTDC (below top dead center) position (see FIG.12), the pumping piston42is at a TDC (top dead center) position and remains 90° ahead of the stepped piston40throughout the rotation of the crankshaft24.

As the pumping piston40is moved from the TDC position (seeFIG. 10) to the 135 ATDC position (FIG. 11), the exhaust port48opens and gases are permitted to flow therethrough. However, on the upstroke of the pumping piston42, see the movement fromFIGS. 11 to 12, the sliding gate valve46moves into a position to seal the exhaust port48.

Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention.