A two-stroke internal combustion engine includes at least one gaseous communication charge passage between a crankcase chamber and a combustion chamber of the engine and a piston to open and close the top end of the passage and a rotary valve to open and close the lower end of the transfer passage. The air inlet port to the transfer passage for stratified scavenging is opened and closed by the crank-web that has passages and cutouts. The rotary valve replaces the one-way reed valve used in stratified scavenged and charged two-stroke engines. The air passes from the lower end of transfer passage to the top end and into the crankcase through the piston passage, alternatively air may also pass through the adjacent transfer passage directly or through a passage in the piston into the crankcase. A two-stroke engine also consists of a charge injection system controlled by the crank web eliminating the one-way valve.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to two stroke internal combustion engines and, particularly, to such engines with stratified scavenging.

A particular field of application of the invention is a two-stroke internal combustion engine. One application of the invention is to a small high speed two stroke engine, such as utilized in hand-held power equipment such as leaf blowers, string trimmers, hedge trimmers, also in wheeled vehicle applications such as mopeds, motorcycles, scooters, and in small outboard boat engines. The small two stroke engine has many desirable characteristics, including simplicity of construction, low cost of manufacturing, high power-to-weight ratios, high speed operational capability and, in many parts of the world, ease of maintenance.

Inherent drawbacks of two stroke engines are high emission levels and poor fuel economy due to short-circuit loss of fuel and air charge during the scavenging process. One drawback of the simple two-stroke engine is a loss of a portion of the fresh unburned fuel charge from the cylinder during the scavenging process. In the two-stroke engine, the homogeneous charge enters the cylinder through transfer ports during the scavenging process, when the exhaust port is also open. As such, some of the charge escapes through the exhaust port leading to high levels of hydrocarbons (HC) in the tailpipe. This leads to the poor fuel economy and high emission of unburned hydrocarbon, thus, rendering the simple two stroke engine difficult to comply with increasingly stringent governmental pollution restrictions. This drawback can be relieved by separating the scavenging of the cylinder, with fresh air, from the charging of the cylinder, with fuel. This separation can be achieved by having a buffer medium of air between the fresh charge and the burnt gas, during the scavenging process.

Several concepts and technologies have been proposed or tried to circumvent the short-circuit loss of fresh charge. Among these techniques are direct or indirect fuel injections, stratified scavenging, air-head, air assisted fuel injection, and compressed wave injection. Most of these technologies are either complex, expensive or need more parts. The fuel injection technology is not economical for small engines but air-head scavenging and stratified scavenging are promising.

An air-head scavenging system disclosed in U.S. Pat. No. 6,513,466 consists of an air channel leading into the storage space in the crankcase and has a reed valve. The filling time is very dependent on the pressure difference across the reed valve and is more likely dependent on engine speed and load. This may lead to an optimum performance only at a certain operating range of speed and load. The storage space may become a dead space when charge bypasses the storage space. U.S. Pat. Nos. 4,821,787, 6,112,708, and 6,367,432 describe reed valve controlled air passage in air-head scavenged two-stroke engines. The use of reed valves increases the cost and complexity and the performance is subject to quality of the reed valves. John Deere has used Reed valve controlled charge injection called compressed wave injection in the hand held application two-stroke engines. Again the use of reed in the engine can add cost and complexity to the engine.

It is desirable to have a simple two-stroke engine with fewer parts and that is easy to manufacture and assemble. It is also desirable to have an air volume high enough to improve the delivery ratio and scavenging and have asymmetric air inlet timing.

SUMMARY OF THE INVENTION

A two stroke internal combustion engine includes at least one transfer passage in gaseous communication between a crankcase chamber and a combustion chamber of the engine, an air passage through the crankcase to the crankcase chamber and in gaseous communication with a carburetor of the engine, and a rotatable circular disk rotatably connected to a crankshaft of the engine. At least one first rotary shut-off valve is located in a radially outermost section of the circular disk bordered by a periphery of the circular disk and operatively disposed between the transfer passage and the crankcase chamber for opening and closing gaseous communication between the transfer passage and the crankcase chamber. At least one second rotary shut-off valve is located on the circular disk bordered by a periphery of the circular disk and operatively disposed between the air passage and the transfer passage for opening and closing gaseous communication between the air passage and the transfer passage.

In the exemplary embodiment of the two stroke internal combustion engine the first and second rotary shut-off valves are operably located on the on the circular disk to close the air passage to the transfer passage when the transfer passage is open between the combustion chamber and the crankcase chamber and to close off the transfer passage between the combustion chamber and the crankcase chamber when the air passage is opened to the transfer passage. In a more particular exemplary embodiment of the two stroke internal combustion engine the rotatable circular disk is a crank web, the first rotary shut-off valve is a conical cut out sector in a periphery of the crank web, and the second rotary shut-off valve is a notched cut out in the periphery of the crank web. An engine incudes a cylinder having at least one transfer passage that is a channel in a cylinder bore. A top end of the channel opens into a combustion chamber of the cylinder and the lower end opens into a crankcase chamber of the engine. The top end is opened and closed by a piston operably disposed in the cyliner bore, where as the lower end is alternatively opened and closed into the ambient air by a rotary valve, which in one embodiment of the engine is a crank web. When the rotary valve opens the air inlet to the lower end of transfer passage, as the piston is moving upward, a piston passage in a piston skirt of the piston opens a transfer port into the crankcase. The piston passage may be a window in the piston or a special passage with a fluid diode type that will be described later. The crank web also alternatively opens the lower end of the transfer passage into the crankcase. Connection of transfer passage to air and crankcase is alternative and is accomplished by a groove and cut out in the crank web. A main charge is injected into the crankcase in a usual manner either through a piston-controlled inlet, rotary valve, or a reed valve system.

One embodiment of the engine includes quadruplet transfer passage having a lower end of a first transfer passages closest to an exhaust port is alternatively connected to the ambient air by the rotary valve. The top end of the first transfer passage is connected to an adjacent second transfer passage either through a cut out in the piston or directly through a connecting passage at the top between the first and second transfer passages. The quadruplet passage increases the total volume of air and air acts as a buffer medium in both the transfer passages. It also helps clear the fresh charge in the transfer passages from the previous cycle.

By controlling the lower of transfer passage during scavenging asymmetric timing may be accomplished by the use of rotary valve. Thus the lower end of the transfer passage closest to the exhaust port may be shut off early during the end of scavenging process and may also have delayed opening.

A total length of the transfer passage may be increased by having the transfer passage continue into the crankcase as a grove on the crankcase wall. By using the crank web as a rotary valve to open and close the air inlet to lower end of transfer passage and a window or passage in the piston to open and close the top end of transfer passage into the crankcase, asymmetric air inlet timing is achieved. Thus there is no need for reed valves in the engine disclosed herein.

In one embodiment of the engine, the crank web and passage in the piston has been used to effect three-way scavenging in which air enters the combustion chamber ahead of lean air-fuel charge followed by the rich air-fuel charge. In another embodiments of the engine the crank web and the passage in the piston control a rich charge, thus eliminating a reed valve used in John Deere's compressed wave injection engine and completely replacing it with the rotary valve.

DETAILED DESCRIPTION OF THE INVENTION

Air-head scavenged engines provide a buffer medium of air between the fresh charge and the burned gas during the scavenging process. When the transfer ports open, the air enters the combustion chamber first and is most likely to be short-circuited, in the sense a small fraction of air is lost into the exhaust. The air is inducted into the transfer passage during the intake process, when the piston is ascending. Typically, a reed valve is provided at the top of the transfer passages for inducting only air into top of the transfer passages that stays in the transfer passages to act as a buffer medium. In some instances, piston ports are also provided in place of reed valves. The disadvantage with the reed valves is that it adds parts and are speed sensitive and the performance is subject to quality of the assembly of reeds and reed themselves.

In the exemplary embodiment the rotary valve, which can be a crank web as described in this case, replaces the reed valves. The two-stroke engine described in this embodiment consists of air inlet ports, opened and closed by the crank web cut out in the crank web for gaseous communication between the air inlet ports and the crankcase port at the bottom end of the transfer passages and the transfer ports at the top end of the transfer passages, which are opened and closed by the top of the piston and also by either cut out in the piston or by the passages in the piston. The cut out in the crank web acts as a rotary valve that periodically establishes gaseous communication between the ambient air and the transfer passages. The second cut out provides gaseous communication between the crankcase and the transfer passage. Thus the crank web alternatively communicates bottom end of the transfer passage with the ambient air and crankcase. The two-stroke engine cycle processes determine which way the bottom of transfer passage opens into.

The air inlet port is in gaseous communication with lower end of the transfer passage at appropriate time only. The timing of the gaseous communication between the air inlet port and the transfer passage is controlled by the passage in the crank web (could be groove or counter sunk). The crank web during the scavenging and expansion process shuts off the air inlet port. The lower end of the transfer passage is open and closed to the crankcase at appropriate time by the cutout on the crank web. Thus the crank web acts as a rotary valve to time the flow air into transfer passage from ambient during intake process and opens the transfer passage to crank case during scavenging process. The air in the transfer passage acts as a buffer medium between the charge and the burnt gas to minimize the loss of charge into exhaust and hence lowers the exhaust emission.

FIGS. 1 through 11illustrate a dual transfer passage two-stroke engine10, wherein there are two transfer passages11(and ports) one on each side of the exhaust port50. A piston16is connected to the crankshaft22having a crankshaft axis19by a connecting rod18. As the piston16moves upward after the exhaust port50is closed, the counter sunk passage751on the outer face550of the crank web21establishes a gaseous communication between the air inlet port650and the crankcase port111at the lower end of transfer passage11. Around the same time the transfer port33is open into the crankcase26by the passage613in the piston16. Thus the differential pressure between the crankcase and the ambient lets the air to flow into the transfer passage11through the carburetor34, air control valve94, passage817in the heat dam134and into the air passage88in the crankcase28. Air continues to flow into the transfer passage as long as there is pressure difference across ambient and crankcase26and until the air inlet port650is shut off by the crank web21. The gaseous communication between the crankcase port111and air inlet port650may be cut off either before the piston reaches TDC or slightly past TDC. The asymmetric timing of the air inlet port650is achievable by the location of trailing edge687and angular length B of the countersunk passage751on the crank web21. By closing the crankcase port111during the down ward stroke of the piston, the reverse flow of air into the countersunk passage in the crank web and hence back into ambient is prevented. By virtue of long passage102in the piston, the entry of live charge from crankcase26into the transfer passage11may be prevented. Also, the inertia of the air flowing into the crankcase through the passage past TDC helps prevent reverse flow of air and or charge into the transfer passage.

As the piston descends, and before the top of the piston opens transfer port33, the crankcase port111at the lower end of the transfer passage11is opened by the cut out244on the periphery43of the crank web21. The location of leading edge179with respect to TDC position determines the start of scavenging process. The opening of the crankcase port111can be leading ahead or trailing behind the opening of the transfer port33by the piston. The angular length ‘A’ between the leading edge179and the trailing edge178determines the duration of the crankcase port111opened into the crankcase26. The intake of main air-fuel charge occurs though the inlet port84and through the carburetor control valve585in a normal way. The opening of the intake port84may be delayed with respect to the air inlet port650. A typical port timing for the exemplary air-head scavenged two-stroke engine is shown in Table 1.

As the piston descends down, it opens the exhaust port50first and then the transfer ports33. When the transfer ports33are opened, the air in the transfer passage11enters the combustion chamber30first ahead of the charge. Thus pure air acts as a buffer medium between the burnt gas and the fresh charge during the scavenging process. Since air enters the combustion chamber first and has the longest path to travel in the combustion chamber, it is the one that is most likely to be lost into the exhaust port50. Thus air-head scavenging minimizes the loss of fresh charge into the tail pipe and hence lowers the unburned hydrocarbon emission into the ambient. The scavenging duration by the charge may be delayed by delaying the opening of the crankcase port111. Thus the duration of time for which charge is likely to escape into the exhaust port may be shortened as determined by the angular length ‘A’ of the cut out244in the crank web21. Also, after discharging trapped air into the combustion chamber, the discharge of charge following the air may be momentarily interrupted by shutting off the crankcase port111by the crank web. In that case the cut out244is made of two segments; a first cut out244afor the discharge of air through the port33. After momentarily shutting the crankcase port111the second cut out751opens the crankcase port111for discharge of charge. Descending of piston toward BDC helps build up crankcase pressure when the crankcase port111is momentarily shut off. Increased crankcase pressure around BDC position of the piston helps the delayed discharge of charge into the combustion chamber.

The proper functioning of the rotary valve depends on the good clearance between the port and the rotary valve. If the clearance between the two is excessive it may lead to poor sealing. In order to ensure proper seal between the face550of the crank web21and the crankcase wall, unique inserts619and652have been used.FIGS. 7 and 8ashow the air inlet port650and the crankcase port111with inserts652and619respectively in the corresponding ports. The insert is a small piece of tube inserted into the crankcase port111and the air inlet port650. The front face of the insert always keeps pressed against the face of the rotary valve, ensuring a proper seal between the insert and the rotary valve. At the back of the insert is a spring614that presses the insert away from the crankcase. The outer face of the insert pressed against the crank web always rests on the uncut face of the crank web and as such it does not get caught in the cut out. The insert652may be made of a non-metallic material and the spring614may either be a separate piece or an integral of the insert652. The inserts may be of soft material in comparison to the crank web. A high temperature plastic reinforced with glass fiber may be used.

FIGS. 8 and 9show where the crank web21has a through passage245for uncovering the crankcase port111during the scavenging process. When the piston is ascending, the counter sunk passage751on the outer surface550of the crank web21, establishes gaseous communication between the air inlet port650and the crankcase port111for filling the transfer passage11with air during intake process. InFIG. 8,8a, and9, the crankcase port111is at a lower position and the transfer passage11is longer than it is illustrated inFIGS. 1 through 4. The air inlet passage818in the heat dam638is a single through passage.

FIGS. 8 through 10show the air passage861splitting into left and right passages950on the cylinder flange430and then there is a air passage851in the crankcase28going down and opening into air inlet port650, through a passage960(shown inFIGS. 6 and 7). The advantage is that the carburetor34containing control valves585for air-fuel and94for pure air is more compact. The adapter638between the carburetor34and the cylinder12is also small.

FIG. 11shows where the air inlet passage860is in the crankcase splitting into left and right passages850in crankcase flange428. The air passage850opens into the passage851going down into the crankcase passage960(shown inFIGS. 6 and 7) that runs along the crankshaft axis19, and into the air inlet port650.

FIGS. 12 through 16illustrate quadruplet transfer passage system in a two-stroke engine. In the quadruplet transfer passages, there are four transfer passages one pair on each side of the exhaust port50. The air is inlet into the crankcase port650at lower end100of the transfer passage11, which is closest to the exhaust port50. However, the air instead of flowing out of transfer port33into the crankcase26, it flows into the adjacent transfer passage211. The transfer ports33and233are in gaseous communication with each other through passage101in the piston16.FIG. 17(e) illustrates the passage in the piston. Where as inFIG. 16, the gaseous communication between the transfer passages11and211is through a direct passage543between the two passages. As the piston ascends the passage101in the piston16establishes at an appropriate time the communication between the adjacent transfer passages11and211through transfer ports33and233. Thus the air entering from port619at the bottom of the transfer passage11flows into the transfer passage211clearing the passage11of the fresh charge from the previous cycle. The charge and air in the transfer passage211flows into the crankcase26through the crankcase port222at the lower end of the transfer passage211. It may be observed that the location of the ports619and222at are a different heights, While619is opened closed by the crank web21, the port222may be either fully open all the time or may be closed by the piston as the piston descends toward BDC. Depending on the air inlet timing, the air may partially fill the transfer passage211after completely filling the transfer passage11or fill it completely. The intake of air-fuel mixture occurs in a normal way through the carburetor34, charge control valve80, inlet passage107and the inlet port84. The inlet port84opens later during the intake process after the start of induction of air into the transfer passage. The delay in charge inlet timing ensures filling of transfer passage11and at least partially the transfer passage211with pure air for an effective air-head scavenging. The carburetor may be a double barrel carburetor having a air-fuel butterfly valve to control air-fuel mixture to the inlet port to the cylinder and an air only butterfly valve to control pure air to the crankcase chamber through the air passage, and a link interconnecting the butterfly valves as illustrated inFIGS. 12 and 13.

During the scavenging process, the transfer ports33and233open simultaneously or may have staggered timing, where port233farthest from exhaust port50, opens a few degrees ahead of port33. The air flowing from the transfer port33acts as a buffer medium between the charge and the burnt gas, thus minimizing the loss of charge into the exhaust. By virtue of crank web being able to provide asymmetric crankcase port timing, the opening of the crankcase port619may be delayed while opening the transfer port33ahead of233to have a blow down of exhaust gas into the transfer passage11without adversely effecting the crankcase pressure. When the air is discharged later during the scavenging process, it may trap a layer of burnt gas between the fresh charge and the air, which ensures better trapping of the charge. This minimizes the loss of charge into the exhaust, which lowers the engine out emission of unburned fuel.

It is also possible in a quadruplet transfer passage system for only the transfer passage11closest to the exhaust port to receive air while the transfer passage211is not in communication with passage11. In that case the piston may have a window for gaseous communication between transfer passage11and the crankcase26during intake of air into the transfer passage11. The piston with a window is shown inFIG. 17(f).

FIGS. 17(a) through17(f) illustrate different piston configurations usable with the exemplary embodiment, described above. In the case of a quadruplet transfer passages the piston17(e) provides communication between the transfer ports33and233through an annular piston passage103illustrated as an annular groove in the piston. The height of the passage103determines the duration of the communication between the ports33and233. Similarly a window104illustrated inFIG. 17(f) provides passage between the transfer port33and the crankcase26for filling the transfer passage11with pure air during air intake timing.FIG. 17(b) andFIG. 17(c) illustrates a long passage on the piston skirt17. The length of the piston passage102(612) may help prevent reverse flow of charge into the transfer passage when the piston is descending.

FIG. 17(c) illustrates a piston passage612with a fluid diode615which offers resistance for reverse flow of charge into the transfer passage11while offering no resistance or minimum resistance for the flow in one direction (toward crankcase). In a quadruplet transfer passage, any combination of the piston configurations may be used. In the sense that the piston may provide gaseous communication during early or late phase of air intake into transfer passages while providing a window or direct passage into crankcase during early or late intake phase of air into transfer passage.

FIG. 16shows where there is no valve to regulate the inlet of pure air into transfer passages. The air inlet has just an air cleaner95. The inertia of air may keep most of air in the transfer passage11and566at high speeds, while expelling back some of the air into ambient at idle and low speeds. The air inlet timing may be such that the mass of air trapped in the passage may be proportional to engine speed and or load. Thus it may eliminate the need for expensive double barrel or butterfly valve type carburetor in an air-head scavenged engine.

The air and air-fuel control valves can either be a barrel valve type shown inFIGS. 1,8, and21or a butter fly valve type shown inFIGS. 12 through 15.

InFIG. 16, the passage543between the transfer passage11and211is of unique shape. The top face547of the passage543and the lower face551are at an angle to the horizontal plane. The angles are such that when the transfer port233opens first it may provide a stratified charge discharge through the port233where some of the air in the transfer passage11is also discharged through the port233while maintaining a stratified layer of air and charge. Also, after the port33is open, the discharge in the ports33and233are such that the charge do not flow into the transfer port33, while flow of charge through233may draw some air from the passage11. Thus a layer of air may be provided between the charge flowing into chamber30and the burnt gas escaping into the exhaust port50. The same objective may also be achieved by the passage illustrated inFIGS. 23 and 24.

InFIGS. 14 through 16, the lower end of the transfer passage11has a crankcase port41. A passage around the crankshaft axis in the side walls of the crankcase28in the form of a channel566enclosed by the side face550of the crank web21. The intent of the long channel on the side walls of the crankcase28is to provide a compact but long transfer passage that holds a larger mass of pure air. One end of the channel566communicates with the crankcase port41and the other end has a ‘L’ shaped tip and an outlet554for gaseous communication with the air inlet port650through a cut out (recess)751on the outer face550of the crank web21. The functioning of the air intake and scavenging is identical to the description provided earlier forFIGS. 1 through 11. However, the crankcase port41remains closed all the time by the crank web. During the intake of air, the ambient air is in gaseous communication with the transfer passage11for induction of air through the air inlet port650, cut out751in the crank web, and the channel566at the midsection of the ‘L’ shaped tip, as shown inFIGS. 14 and 16. During the scavenging process, the cut out244opens the tip of ‘L’ section at the port554, as shown inFIG. 15.

FIGS. 18–23illustrate an exemplary embodiment of a two-stroke engines with an alternative rotary valve design, where in the transfer passage port620is opened and closed to the crankcase by a conical cut out sector755in a periphery753of the crank web21while the air inlet port650is opened and closed by the outside surface and a notched cut out680on the crank web21. The crankcase port619is at an angle to the side wall of the crankcase. In the sense that the port620is directly at the lower end of the transfer passage11. Where as inFIGS. 1 through 16ports111and619are on the sidewall of the crankcase.

The lower end of the transfer passage11has a crankcase port620that is alternatively in gaseous communication with the ambient air through the cutout680on the outside face550of the crank web21and an air inlet port650. The crankcase port620is also alternatively in gaseous communication with the crankcase26. The crankcase port620is opened into the crankcase26by the cutout753on the periphery43of the crank web21. The lower end of the second transfer passage211is in gaseous communication with the crankcase26through a crankcase port222(shown inFIGS. 12 through 16andFIGS. 21 and 22). Crankcase port222may or may not be controlled by the piston skirt, particularly as the piston approaches BDC.

As the piston16moves upward, the top edge of the piston skirt17closes the transfer port33first,233next and then the exhaust port50. Both the transfer ports33and233may be closed simultaneously if the transfer port timing is not staggered (in the sense one port opens earlier than the second). After the exhaust port50is closed the crank web shuts off the communication between crankcase port620and the crankcase26. As the piston continues to move upward the air inlet port650is opened by the cutout680and a little later the cutout680opens the crankcase port620, while the section of the crank web has shuts off direct flow of gas between crankcase port620and the crankcase26. However, the top of the transfer passage11can be in gaseous communication with the crankcase26either 1) directly through passage102in the piston (shown inFIGS. 2 and 18), 2) through closed passage103in the piston into the adjacent transfer passage211(shown inFIG. 20), 3) through a passage542between the transfer passages11and211(shown inFIGS. 23 and 24, or 4) a open passage543(shown inFIG. 16or a combination of any of the above.

As the piston continues to move upward, the sub-atmospheric pressure in the crankcase26draws air from ambient (outside the crankcase) into the transfer passage11through the air inlet passage88, air inlet port650, and into the crankcase port620shown inFIG. 21 through 23. The air then passes through the transfer passage11and into the crankcase26either directly through piston passage102or into the adjacent transfer passage211. As the crankshaft continues to rotate and the piston moves past TDC, the air inlet port650is closed by the crank web outer face550. And a little later the crank web also closes the crankcase port620inFIG. 21 through 23. The intake of air-fuel mixture called the charge occurs in a usual manner through the charge intake port84. The timing of the charge inlet may occur later than a conventional engine. Delayed intake opening for charge helps fill the transfer passage11with pure air. As the air is filled into the transfer passage, the passage11(and211in a quadruplet transfer passage system) is cleared of the charge from the previous cycle.

As the piston starts to move downward the charge in the crankcase26is pressurized. If the crankcase port620is not closed, then the fresh charge may enter the transfer passage11. However, since the crank web closes the crankcase port, the charge does not enter the transfer passage from the lower end. In a quadruplet type transfer passage and when the air is contained in both the transfer passages11and211, closing the crankcase port620prevents the reverse flow of air into the crankcase26. However, charge may enter the transfer passage211through the crankcase port222. The volume and length of the transfer passage11and211may be such that even when the charge enters the transfer passage211, it may not reach the transfer passage11as the crankcase port620is closed.

In order to completely eliminate the entry of charge into the transfer passage211, the crankcase port222may also be either closed by the crank web or by the piston port, where the piston skirt closes the port222until the transfer port233is open. The opening and closing of the transfer port in the crankcase (or in the cylinder) has been disclosed in patent application Ser. No. 10/446,393, filing date May 28, 2003 by the same Inventors.

As the piston descends the exhaust port50is open first. The transfer port is open next. Since it is the air that is entering the combustion chamber first and has the longest residential time, it is more likely that it is the air that gets short circuited into the exhaust port. Thus the air-head scavenging system minimizes the loss of charge into the exhaust and thus lowers the unburned hydrocarbons in the tail pipe exhaust.

When quadruplet transfer ports are used, most of the air is retained in the transfer passage11, which is closest to the exhaust port50. The transfer port233farthest from the exhaust port50may open first in the case of a staggered transfer ports. In that case, as the top of the transfer port211also has some air and it enters the combustion chamber first followed by the charge. The second transfer port33may open a few degrees later discharging pure air in front of charge and acts as a buffer medium between the fresh charge and the burnt exhaust gas.

It is possible to open the crankcase port111(620) later after the transfer port33is open, since the crankcase port is opened and closed by the crank web. Thus an asymmetric timing is possible with the crank web controlled crankcase port system.

InFIGS. 23 and 24, the cap539is a plug used after machining the transfer ports33and233and the connecting passage542. The included angles between faces508&512and511&504are important and they may converge close to the cylinder wall opposite the exhaust port. The included angle between the face512and the imaginary plane passing through cylinder axis517and the center of exhaust port50is such that the flow forces the charge flowing through transfer port233to be as close to the cylinder wall opposite the exhaust port as possible. The included angle between face504and the similar imaginary plane passing through517and center of exhaust port50is smaller than the angle formed by the face512.

FIG. 24illustrates a cross sectional view of a quadruplet port type transfer passage arrangement. In that, there are pair of transfer passages11and211on each side of the exhaust port50. And there is a pair of transfer ports33and233associated with each pair of transfer passages respectively. In the exemplary embodiment the transfer passages11and211are interconnected at the top by a passage542and has a bridge546between the two ports33and233that separates the two transfer ports33and233. The interconnecting passage542has a diverging shape with a face513diverging toward the port233so as to prevent reverse low from passage211into11during scavenging. The passage542may be of different shape also so as to prevent or minimize the flow of media from passage211into11. The passage542may also be an insert with a fluid diode that allows a free flow of air from passage11to passage211, while resisting the reverse flow of charge from passage211into11. It may also have a one way valve between the passage11and211.

InFIG. 25the function of the air inlet is similar to the description for the operation of engine shown inFIG. 1. However, in addition to the air, a rich charge system is added where a very rich air-fuel charge is inducted and injected into the combustion chamber30through a separate charge passage39. The engine consists of a three-way carburetor547and a three-way scavenging system. The charge passage39consists of segments545,552,555and548. Segment545has a charge injection port40at the top end open into the combustion chamber30. The port40is opened and closed by the piston. The segment545runs down in the cylinder14into the segment552, which is a channel on the cylinder flange430. The channel552runs around the cylinder14and opens into the lower end of the segment555. The charge passage555connects into the segment548, which has a port549in the cylinder12that opens into the crankcase. The port549is opened and closed by the piston16. The piston skirt17has a port557to time the start of injection when the piston is descending.

As the piston16ascends the piston skirt17opens the port549and thus establishing gaseous communication between the crankcase26and the ambient through the carburetor547. The rich charge now flows into the charge passage39through a one-way valve36. As the piston continues to ascend the air inlet into the transfer passage11and the lean air-fuel charge into the crankcase26occurs in a manner described earlier for the engine shown inFIG. 1.

The induction of rich charge into the charge passage39ends as the pistons begins to descend. The increase in crankcase pressure forces the one-way valve39to close. After the blow down of exhaust gas through the exhaust port50, the scavenging occurs first through the transfer port33where air enters the combustion chamber first followed by lean charge. As the piston continues to descend the crankcase port111may be closed and about the same time or before, the window557on the piston skirt17opens port549for injection of charge into the combustion chamber30. Thus the scavenging process occurs in three phases; first the air enters, followed by the lean charge through the transfer port33and then the rich charge is injected through the injection port40. The transfer passage system may be of quadruplet type described earlier and shown inFIGS. 12,15, and21. Also, the air inlet and crank web design may be of any type described in this invention.

FIGS. 29 through 35illustrate charge injection system where the lower end of the rich charge passage39is controlled by the crank web21and the top end by the piston16for start and end of charge induction into the charge passage. The start and end of charge injection into the combustion chamber may also be controlled by the crank web and have an asymmetric timing.

The carburetor551consists of two passages300for rich charge and310for either only air or very lean charge. The passage310opens into the passage312in the adapter plate, which communicates into the crankcase through the main inlet port84. The rich charge passage300opens into a charge inlet passage302, which has a charge inlet port60in the crankcase.

One end of the charge passage39has a charge injection port40opening into the combustion chamber where it is opened by the top of the piston16during scavenging and injection process. The charge passage39has a section545running down into the channel552in the cylinder flange430that runs around the cylinder14and opens into the passage544in the crankcase. The passage544in the crankcase opens into the crankcase26through a crankcase port41which is opened and closed by the cut outs in the crank web21. The rich charge passage302that is in communication with the carburetor551has a charge inlet port60in the crank case. The cut out45(556inFIG. 33) on the outside face550of the crank web21establishes gaseous communication between charge inlet port60and the crankcase port41when the piston is ascending. The rich charge flows into the charge passage39from the lower end of the charge passage and into the crankcase26through the charge injection port40and through the piston passage603(shown inFIG. 32). Thus as the rich charge fills the charge passage39it clears the passage39of the residual lean charge from the previous cycle. Induction of rich charge ends when the crank web21closes the charge inlet port60as the piston reaches TDC or past TDC. In the case where the piston has a window similar to the one shown inFIG. 17(f), then the height of the piston window determines the duration of induction. The induction of main lean charge or just air into the crankcase26occurs in a usual manner through the inlet port84. The main inlet84may be off set from the induction passage39as shown inFIGS. 31,33,34, and36or the inlet passage84may be split around the passage39as shown inFIGS. 26,27, and28.

As the piston descends the piston opens the exhaust port50first and the scavenging occurs as the transfer ports33and233are opened. As the piston descends the crankcase port41is opened again by the cut out44(558inFIG. 33) in the crank web for injection. The lower ends514and2514of the transfer passages11and211shown inFIGS. 29 and 30may be shut off by the piston skirt16at the piston edge520thus forcing the charge and the crankcase content through the charge passage39through the charge injection port40into the combustion chamber. Thus the control of charge inlet by the crank web eliminates the need for one-way valve39(shown inFIG. 25). Also, an asymmetric timing is achieved by the use of crank web for timing the charge induction and injection.

The segment552of the charge passage39may be on the cylinder flange430as shown inFIG. 34with the charge passage544in the crankcase26shown inFIG. 35. The segment552shown as553inFIG. 37may be on the crankcase flange428as shown in the Figure and the cylinder that matches this arrangement is shown inFIG. 36.

The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. While there have been described herein, what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein and, it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention.