Patent Publication Number: US-6901892-B2

Title: Two stroke engine with rotatably modulated gas passage

Description:
This application claims the benefit of U.S. Provisional Application No. 60/400,916, filed on Aug. 3, 2002 and Provisional Application No. 60/400,968, filed on Aug. 3, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The present invention relates to two stroke internal combustion engines and, particularly, to such engines with a rotatable disk valve in the engine for modulating gas passages. 
     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 injecting the liquid fuel into the cylinder or, more preferably, by injecting the fuel charge by utilizing a pressurized air or lean charge source, separate from the fresh air scavenge, to spray the fuel into the cylinder. 
     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 injection, stratified scavenging, air head, air assisted fuel injection, and compressed wave injection. Most of these technologies are either complex, expensive or have limitations as to the benefits throughout the operating range of an engine. The fuel injection technology is not economical for small engines but air head scavenging and stratified scavenging are promising. 
     An air assisted fuel injection system using compressed wave injection is disclosed in U.S. Pat. No. 6,273,037. The compressed wave injection system engine uses the piston to control the charge induction and, thus, the opening and closing time of induction is symmetrical about the TDC. Also, the charge depends on the wave dynamics for injection. This may lead to an optimum performance only at a certain operating range of speed and load. 
     U.S. Pat. No. 4,253,433, March 1981, by G. P. Blair, discloses a stratified scavenging system in which the retention of charge in the injection tube during induction depends on the length of the tube and has no timing system to start and end induction and injection of the charge. As such, the system may perform best in a narrow range of engine speed and load. 
     It is desirable to have a two stroke engine with flexibility to vary the injection passage volume and timing during operation of the engine. It is also desirable to have a two stroke engine with ability to optimize engine variables for a variety and range of engine operating condition from idle through full load and speed. It is also desirable to have a two stroke engine with a charge induction and injection timing in a stratified scavenging system that can be varied continuously and, in real time and, the volume of the charge inducted that can also be changed. The design is also applicable to inlet timing, in a rotary valve system, where charge inlet and closing timing can be varied. Also, the same system can be used to vary the transfer port timing. Further, the system can be used to vary the transfer or boost port timing and passage volume. It is also desirable to have fixed unsymmetrical timing for charge induction and injection, and/or for scavenging process. 
     SUMMARY OF THE INVENTION 
     A two stroke internal combustion engine includes at least one gaseous communication passage between a crankcase chamber and a combustion chamber of the engine and a rotatable circular disk rotatably connected to a crankshaft of the engine. At least one 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 passage and the crankcase chamber for opening and closing gaseous communication between the passage and the crankcase chamber. One embodiment of the rotary shut-off valve includes at least one circumferentially extending pathway that extends axially at least partially through the disk. The pathway is rotatably disposed between the passage and the crankcase chamber for opening and closing gaseous communication between the passage and the crankcase chamber. In the exemplary embodiment, the pathway extends circumferentially less than 180 degrees. One embodiment of the pathway is a circumferentially extending annular slot that extends axially at least partially through the periphery of the circular disk. The disk may be disposed within the crankcase chamber and also may be a crank web of the engine. 
     Some embodiments of the rotary shut-off valve include at least two circumferentially spaced apart and circumferentially extending pathways extending axially at least partially through the disk. The pathways extend circumferentially less than 180 degrees and the pathways are rotatably disposed between the passage and the crankcase chamber for opening and closing gaseous communication between the passage and the crankcase chamber. 
     Other embodiments of the engine include an angularly adjustable ring having an annular channel disposed between the circumferentially extending pathway and the passage and a ring port through the ring leading to the annular channel. More particular embodiments of the engine include a rotary shut-off valve with at least two circumferentially spaced apart and circumferentially extending pathways extending axially at least partially through the disk and extending circumferentially less than 180 degrees. The pathways are rotatably disposed between the passage and the crankcase chamber for opening and closing gaseous communication between the passage and the crankcase chamber. A fixed lip extending into the annular channel may be incorporated to vary the volume of channel by rotating the ring and the channel. 
     One embodiment of the pathway is a circumferentially extending annular rectangular cross-sectional slot that extends axially at least partially through the periphery of the circular disk. Another embodiment of the pathway is an annular L-shaped pathway having a radially inwardly extending annular slot intersecting an axially extending annular slot. The radially inwardly extending annular slot includes a radially outwardly facing radial inlet in the periphery. The axially extending annular slot includes an axially facing axial outlet located radially inwardly of the periphery. 
     Other embodiments of the engine include an angularly adjustable ring concentrically disposed around the periphery of the circular disk, an annular ring channel extending circumferentially partway through the angularly adjustable ring and disposed between the crankcase chamber and the passage, and a ring port in the adjustable ring that is rotatably open to the radially inwardly extending annular slot through the radially outwardly facing radial inlet. 
     Another embodiment of the engine includes the circumferentially extending annular rectangular cross-sectional slot axially adjacent to the L-shaped pathway, both of which extend axially at least partially through the periphery of the circular disk. Axially adjacent first and second angularly adjustable rings concentrically surrounding the circular disk and first and second annular ring channels extending circumferentially partway through the first and second angularly adjustable rings, respectively. The first annular ring channel is disposed between the crankcase chamber and the one gaseous communication passage and the second annular ring channel is disposed between the crankcase chamber and a second gaseous communication passage. The first and second annular ring channels include first and second ring ports, respectively, with the first ring port being rotatably open to the radially inwardly extending annular slot through the radially outwardly facing radial inlet in the periphery and the second ring port being rotatably open to the annular rectangular cross-sectional slot. 
     A more particular embodiment of the two stroke internal combustion engine includes a carburetor including first and second barrels in gaseous flow communication with a charge injection port and a main inlet port, respectively. The charge injection port and the main inlet port lead into a combustion chamber of a cylinder bore of the engine. A first flow passage extends between the first barrel and the charge injection port. An injection passage extends between the first flow passage and the crankcase chamber. At least one rotary shut-off valve located in a radially outermost section of the circular disk bordered by a periphery of the circular disk is operatively disposed between the injection passage and the crankcase chamber for opening and closing gaseous communication between the injection passage and the crankcase chamber. At least one transfer passage connects in gaseous communication the crankcase chamber and the combustion chamber in the cylinder bore of the engine. 
     Another more particular embodiment of the two stroke internal combustion engine includes a cylinder block housing a cylinder bore and a piston disposed within the cylinder bore connected by means of a connecting rod to a crank throw on a circular crank web of a crankshaft. The crankshaft is journaled for rotation about a crankshaft axis within a crankcase chamber of a crankcase affixed to a lower end of the cylinder block. A combustion chamber is defined within the cylinder bore above the piston and at least one transfer passage connects in gaseous communication to the crankcase chamber and the combustion chamber in the cylinder bore of the engine. First and second piston ports are disposed in a skirt of the piston and connected in gaseous communication by an air channel. The first piston port is translatably alignable with an air inlet port disposed through the cylinder block to the cylinder bore. The second piston port is translatably alignable with a transfer port leading to the transfer passage. A rotatable circular disk is rotatably connected to a crankshaft of the engine and at least one rotary shut-off valve 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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and other features of the invention are explained in the following description, taken in connection with the accompanying drawings where: 
         FIG. 1  is a longitudinal sectional view illustration of an exemplary embodiment of a two stroke engine with a stratified scavenging system controlled by a rotatable disk and having a fixed volume injection tube. 
         FIG. 2  is a sectional view illustration of the engine through  2 — 2  in FIG.  1 . 
         FIG. 2A  is a perspective view illustration of a crank web with rotary shut-off valves in the engine illustrated in FIG.  1 . 
         FIG. 3  is a longitudinal sectional view illustration of the engine through  3 — 3  in FIG.  1 . 
         FIG. 4  is a longitudinal sectional side view illustration of an exemplary embodiment of a two stroke engine with a stratified scavenging system controlled by a rotatable disk and having a fixed volume injection tube with a reed valve controlled inlet system engine illustrated in FIG.  2 . 
         FIGS. 5A-5G  are sectional view illustrations of a sequence of cycle events for the stratified scavenging system illustrated in FIG.  1 . 
         FIG. 6  is a first sectional view illustration of a disk controlled stratified scavenging system with variable volume injection and a variable timing ring system with timing ring adjacent to a disk. 
         FIG. 7  is a second sectional view illustration of the stratified scavenging system illustrated in  FIG. 6  with the disk more particularly illustrated. 
         FIG. 8  is side view illustration of  FIG. 7  with the ring adjacent to disk/crank web. 
         FIG. 9  is an exploded view illustration of the variable volume injection and timing ring system illustrated in FIG.  6 . 
         FIG. 10  is a cross-sectional view illustration of the ring with a channel on a periphery within the ring through  10 — 10  in FIG.  9 . 
         FIG. 11  is a side view illustration of the ring illustrated in FIG.  10 . 
         FIG. 12  is a side view illustration of an alternative ring with the channel on a side of the ring. 
         FIG. 13  is sectional view illustration of the alternative ring illustrated in FIG.  12 . 
         FIG. 14  is a vertical view illustration of a disk controlled stratified scavenging system with a ring on a periphery of the disk. 
         FIG. 15  is a side view illustration of the disk controlled stratified scavenging system illustrated in FIG.  14 . 
         FIG. 16  is a side view illustration of an injection passage having a lip in the disk controlled stratified scavenging system illustrated in FIG.  14 . 
         FIG. 17  is vertical view illustration of a piston controlled transfer port at the lower end of a transfer passage in the disk controlled stratified scavenging system illustrated in FIG.  14 . 
         FIG. 17A  is vertical view illustration of a piston having a piston skirt window for the controlled transfer port illustrated in FIG.  17 . 
         FIG. 18  is a sectional view illustration of a control lever for the ring illustrated in  FIGS. 17 and 18 . 
         FIG. 19  is vertical side view illustration of a fixed timing variable length injection tube system for compressed wave injection system. 
         FIG. 20  is a sectional view illustration of the ring through  20 — 20  in FIG.  19 . 
         FIG. 21  is a sectional view illustration of the ring illustrated in FIG.  20 . 
         FIG. 22  is a vertical sectional view illustration of an exemplary embodiment of a two stroke engine having a variable intake timing system. 
         FIG. 22A  is a sectional view illustration through  22 A— 22 A in FIG.  22 . 
         FIG. 22B  is an exploded view illustration of the variable inlet timing system shown in FIG.  22 A. 
         FIG. 23  is a vertical sectional view illustration of a variable transfer passage volume and timing system controlled by a rotatable disk for a two stroke engine. 
         FIG. 24  is a sectional view illustration of the engine through a crankshaft axis in  FIG. 23  with two rings around the crank webs. 
         FIG. 25  is a sectional view illustration of one of the rings and the crank web for the variable volume and timing transfer passage system illustrated in FIG.  24 . 
         FIG. 26  is a sectional view illustration of the crank web illustrated in FIG.  25 . 
         FIG. 27  is a sectional view illustration of the ring illustrated in FIG.  25 . 
         FIG. 28  is a second sectional view illustration of the ring illustrated in FIG.  25 . 
         FIG. 29  is a vertical sectional view illustration of a two stroke engine with a variable transfer passage volume and timing controlled by rings adjacent to the disks. 
         FIG. 30  is a vertical sectional view illustration of a two stroke engine with crank web controlled transfer port scavenging system with fixed timing. 
         FIG. 31  is a vertical sectional view illustration of a two stroke engine with a variable transfer passage volume and timing system with an air head scavenging system. 
         FIG. 32  is a sectional view illustration through  32 — 32  in FIG.  31 . 
         FIG. 33  is the vertical view illustration of air head scavenged engine with fixed crankcase port timing. 
         FIG. 34  is a vertical sectional view illustration of a two stroke engine with an air head scavenging system and fixed unsymmetrical transfer port timing of the air head scavenging system and open channels in the piston. 
         FIG. 35  is a sectional view illustration of the engine through a crankshaft axis in FIG.  34 . 
         FIG. 36  is a vertical sectional view illustration of a two stroke reed valve controlled engine with an air head scavenging system with open channels in the piston. 
         FIG. 37  is a vertical sectional view illustration of a two stroke engine with variable transfer passage volume and timing and with a selective exhaust gas recirculation system and an open channel on the piston. 
         FIG. 38  is a vertical sectional view illustration of a two stroke engine with fixed transfer passage volume and timing and with a selective exhaust gas recirculation system and an open channel on the piston. 
         FIG. 39  is a sectional view illustration of the engine through a crankshaft axis in FIG.  38 . 
         FIG. 40  a vertical sectional view illustration of a two stroke engine with dual rings to control variable transfer port and charge timing and volume. 
         FIG. 41  is a sectional view illustration of the dual rings and crank web illustrated in FIG.  40 . 
         FIG. 42  is a sectional view illustration of the crank web illustrated in FIG.  41 . 
         FIG. 43  is a sectional view illustration of the dual rings illustrated in FIG.  40 . 
         FIG. 44  is a vertical sectional view illustration of a two stroke engine with a multi-ring system for variable transfer passage volume and timing, stratified charge injection system with variable volume injection passage and timing, and variable inlet timing system, where the crank web is stepped. 
         FIG. 45  a vertical sectional view illustration of a two stroke engine with a multi-ring system for variable transfer passage volume and timing, stratified charge injection system with variable volume injection passage and timing, and a reed valve inlet system. 
         FIG. 46  is the vertical side view illustration of a multi-ring system for variable transfer passage volume and timing, stratified charge injection system with variable volume injection passage and timing and variable inlet timing with air head scavenging system. 
         FIG. 47  is the side view illustration of an exemplary embodiment of a two stroke engine with a stratified scavenging system controlled by a rotatable disk and having a fixed timing for charge injection tube and transfer passage crankcase port timing. 
         FIG. 48  is a sectional view illustration of the stratified scavenging engine through a crankshaft axis in FIG.  47 . 
         FIG. 49  is a top looking down cross-sectional view illustration of the stratified scavenging engine through  49 — 49  in FIG.  48 . 
         FIG. 49A  is a perspective view illustration of a crank web with rotary shut-off valves in the engine illustrated in FIG.  48 . 
         FIG. 50  is the side view illustration of a two stroke engine with a three-way scavenging system. 
         FIG. 51  is the vertical side view illustration of the engine through  51 — 51  in FIG.  50 . 
         FIG. 52  is the vertical side view illustration of the engine through  52 — 52  in FIG.  50 . 
         FIG. 53  is a top looking down cross-sectional view illustration of the engine through  53 — 53  in FIG.  52 . 
         FIG. 54  is a perspective view illustration of a crank web with rotary shut-off valves in the engine illustrated in  FIGS. 52-53 . 
         FIG. 56  is a diagrammatic illustration of a three-way carburetor illustrated in FIG.  51  and in a wide open throttle position. 
         FIG. 57  is a diagrammatic illustration of a three-way carburetor illustrated in FIG.  51  and in a partially closed throttle position. 
         FIG. 58  is a diagrammatic illustration of a fuel jet assembly in the three-way carburetor illustrated in FIG.  56 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Illustrated in  FIGS. 1-4  is an exemplary two stroke engine  10  having a cylinder block  12  that houses a cylinder bore  14 . A piston  16  reciprocates within the cylinder bore  14  and is connected by means of a connecting rod  18  to a crank throw  20  on a circular crank web  21  of a crankshaft  22 . The crankshaft  22  is journaled for rotation about a crankshaft axis  19  within a crankcase chamber  26  of a crankcase  28  that is affixed to the lower end of the cylinder block  12  in a suitable manner. A combustion chamber  30  is defined as a region within the cylinder bore  14  above the piston  16 . The engine includes a two-way scavenging system including two transfer passages  11  between the crankcase chamber  26  and the combustion chamber  30 . The transfer passages  11  are used for scavenging and allowing a fresh fuel/air charge to be drawn from the crankcase chamber  26  into the combustion chamber  30  through a transfer port  33  in the cylinder block  12  at the completion of a power stroke. 
     A rich fuel/air mixture is inducted into the combustion chamber  30  of the cylinder bore  14  by a charge induction system  32  which includes a carburetor  34 , a one-way non-return valve  36 , an injection tube  38 , and a charge injection port  40  extending through the cylinder block  12  into the cylinder bore  14  to point below the combustion chamber  30 . The injection tube  38  provides an injection passage  39  for gaseous communication between the combustion chamber  30  and the crankcase chamber  26 . The charge injection port  40  is used for injection of the rich charge contained in the injection tube  38  which occurs only during an injection portion of a scavenging process that is during the descending of piston or early compression process. An injection insert  303  having a curved passage is disposed between the injection passage  39  and the charge injection port  40 . The curved passage is aimed upward into the combustion chamber  30  to direct the charge toward the top of the combustion chamber away from the exhaust port  50  thus keeping the flow of charge closer to the cylinder wall  14  opposite to the exhaust port  50 . The injector insert may be made of two pieces for ease of manufacturing. 
     The injection passage  39  leads to and is in fluid communication with a crankcase port  41  in the crankcase  28  which is open to a rotary shut-off valve  48 . The timing of the induction of the fuel/air mixture and injection of fuel is controlled by the rotary shut-off valve  48  mounted on the circular disk which, in this embodiment, is a crank web  21  that is rotatably connected to the crankshaft  22 . Circumferentially extending first and second axial gas pathways, illustrated as rectangular cross-sectional annular slots  44  and  45 , extend axially at least partially through a radially outermost section  52  of the circular disk or crank web  21  bordered by a periphery  43  of the circular disk or crank web  21  and are alignable with a crankcase port  41  open to the passage or injection tube  38 . 
     The annular slots  44  and  45  of the engine  10  engine illustrated in  FIG. 2  extend radially outwardly through the periphery of the disk and axially at least partially through the radially outermost section  52  of the circular disk in the engine illustrated in FIG.  2 . The circumferentially extending first and second axial gas pathways, the annular slots  44  and  45 , are generally arcuate about the crankshaft axis  19  having vertex angles A less than 180 degrees with a vertex at the axis. The circumferentially extending axial gas pathways may also be annular slots that are located radially inwardly of the periphery of the disk and exend axially completely through the the circular disk in the engine. 
     The start of injection occurs when the crankcase port  41  is opened by the slots  44  and  45  in the crank web  21 . Induction of rich charge into the injection tube  38  occurs during ascending of piston when the crankcase port  41  is opened again by the slot  44  in the crank web. The rich charge is regulated by a barrel regulating valve  81  in a first barrel  300  of the carburetor  34  illustrated in  FIGS. 1 and 4 . A first flow passage  302  extends between the first barrel  300  and the charge injection port  40 . The injection tube  38  and the injection passage  39  connects to the first flow passage  302  between the barrel regulating valve  81  in a first barrel  300  and the charge injection port  40  and provides gaseous communication between the combustion chamber  30  and the crankcase chamber  26 . The crank web  21  closes off the crankcase port  41  and the injection passage  39  in the injection tube  38  until the crankcase port  41  is circumferentially aligned with the first or second slots  44  and  45  thus allowing gaseous communication between the crankcase chamber  26  and the injection passage  39 . The circumferentially extending first and second axial gas pathways such as the annular slots  44  and  45  provide a valve flowpath between the crankcase port  41  and the crankcase chamber  26 . 
     A main inlet port  84  in the cylinder block  12  through to the cylinder bore  14  allows a lean charge to flow directly into the crankcase chamber  26  below the charge injection port  40 . The lean charge flow flows though and is controlled by a lean charge barrel regulating valve  79  in a second barrel  310  of the carburetor  34 , as illustrated in  FIG. 1  when the piston is ascending. A second flow passage  312  extends between the second barrel  310  and the main inlet port  84 . A butterfly valve  80  may be used to regulate flow though the main inlet port  84  as illustrated in FIG.  4 . The main inlet port  84  is closed during scavenging process by the piston or a reed valve  36  as the case may be. Note that reed valves are one-way valves. In  FIGS. 1 and 51  the reed valve  36  is illustrated in the open position when charge port  40  is open as during the charge injection process. The reed valve  36  should be closed during injection process and it is shown open for clarity and illustrative purposes only. 
     The first and second slots  44  and  45  are cut through the crank web  21  though other types of disks attached to the crankshaft  22  may be used. The first and second slots  44  and  45  are cut-away sections of the crank web  21 . The first and second slots  44  and  45  open and close fluid communication between the injection tube  38  and the crankcase chamber  26  as the crank web  21  rotates with the crankshaft  22 , thus, providing the valving function of the rotary shut-off valve  48 . Opening and closing each of the first and second slots  44  and  45  between the injection tube  38  and the crankcase chamber  26  induces a fuel/air mixture charge through one of the slots into the injection passage  39  on one cycle of the engine, or a first half rotation of the crank web  21 . The fuel/air mixture is discharged through the injection tube  38  into the combustion chamber  30  during the next cycle of the engine  10 . 
     Timing of the opening and closing of the slots  44  and  45  and, thus, the rotary shut-off valve  48  is asymmetric. By not having the second slot  45 , the injection tube  38  will be closed by the crank web at the crankcase end of the injection tube  38 . In that case, the injection of charge is achieved by the compressed air assisted injection principle as described in U.S. Pat. No. 6,273,037. However, the advantage with this embodiment is that the crank web offers unsymmetrical timing for start and end of charge induction into the injection tube  38 . 
     The engine&#39;s operation is illustrated in  FIGS. 5A-5G . As the piston moves upward toward top dead center (TDC), illustrated in  FIG. 5A , the transfer port  33 , the charge injection port  40 , and exhaust port  50  are closed by the piston  16 . During the upward stroke, crankcase pressure in the crankcase chamber  26  drops below ambient pressure creating a pressure difference between ambient and crankcase chamber. Illustrated in  FIG. 5B  is continued rotation of the crank web  21  aligning one of the slots in the periphery of the crank web  21  with the crankcase port  41  allowing the fuel and air charge to flow into the injection tube  38  through the carburetor  34  and the one-way non-return valve  36  (illustrated as a reed valve) and a regulating fuel/air mixture valve  81 . The charge continues to flow until the crank web closes the port as illustrated in  FIGS. 5C and 5D . As the piston continues to ascend at about 40 to 50 degrees before the piston reaches top dead center, the main inlet port  84  is opened by the piston (illustrated in FIG.  5 C.). The lean charge is then inducted into the crankcase chamber  26  through a regulating valve  79  leading to the main inlet port  84 . The induction of lean charge through the main inlet port  84  may start slightly before the end of induction of rich charge into the injection tube  38 , that is slightly before the crankcase port  41  is closed by the crank web  21 . 
     Referring back to  FIG. 4 , a circumferentially extending slot length LS (an arc) of the slots in the crank web determines the crank angle duration and amount of charge that is inducted into the injection tube  38 . A tube length LT of the injection tube  38  is set so that no charge will flow into the crankcase during wide open throttle conditions. Alternatively, the volume and timing may be determined such that only a fraction of the full charge, an amount sufficient to lubricate the crankcase, is allowed to enter the crankcase, in which case only air may enter the crankcase chamber through the through the main inlet port  84 . 
     After or during closing of the charge induction, the main intake system is carried out in a usual manner and is regulated by a butterfly valve  80  illustrated in  FIG. 4  or a barrel valve  79  as illustrated in FIG.  1 . The main intake system may be piston port controlled as illustrated in  FIG. 1 , reed valve controlled as illustrated in  FIG. 4 , or disk valve controlled as illustrated in  FIGS. 22 and 44 . The embodiment of the engine in  FIG. 4  illustrates a reed valve type and  FIGS. 1-3  illustrate a piston port type main air intake system as examples. In the case of reed valve type main inlet system, the start and end of induction of lean charge through the air control butterfly valve  80 , one-way reed valve  82  and main inlet port  84  is dependent on the pressure difference across the reed valve  82  and the pressure required to open the reed valve  82 . The air control butterfly valve  80  controls only air and the fuel/air mixture valve  81  controls fuel/air mixture. 
     Rotary intake type may also be used. As the piston moves downwardly during the expansion stroke, the crankcase pressure rises, during which time the crankcase port  41  is closed as illustrated in  FIGS. 5D and 5E . The main inlet port  84  is closed by the piston when piston port is used or the reed valve when reed valve inlet system is used. If the rotary valve is used for main inlet then the crank web closes the main inlet port. Blow down and exhaust occurs as usual except that the medium that enters the cylinder first when transfer port  33  opens is either an air charge or a lean charge. The charge injection occurs later during the scavenging process. The charge injection time is controlled by the crank web.  FIG. 5F  illustrates the injection time beginning with the second slot  45  opening the crankcase chamber  26  to the injection passage  39  and  FIG. 5G  illustrates the injection time ending with the second slot  45  closing the crankcase chamber  26  to the injection passage  39 . 
     A three-way scavenging system illustrated in  FIGS. 50-54  operates in a similar way described above. However, as the piston ascends, the induction of rich charge into the injection tube  38  starts 5 to 25 degrees ABDC and ends 20 degrees BTDC to 10 degrees ATDC. There is a overlap of air induction into transfer passage  11  during the induction of rich charge into the injection passage  39 . The induction of air into transfer passage  11  starts 10 to 20 degrees ABDC to 80 to 50 degrees BTDC. Induction of air into transfer passage  11  is for a smaller crank angle duration just enough to fill the transfer passage volume. The main inlet of lean charge into the crankcase chamber  26  occurs through the main inlet port  84  in a usual manner, where the main inlet port  84  is opened by the piston 60 to 40 degrees BTDC. 
       FIGS. 6 through 17  illustrate a variable volume charge induction and injection timing stratified scavenging system. The crank web  21  (or a disk on the crankshaft) times a fuel rich charge inducted through the carburetor  34 . An angularly adjustable ring  56 , concentric to and stationary with respect to the crankshaft  22 , is adjacent to or housed within the crankcase  28  and is disposed between the crankcase chamber  26  and the injection passage  39 . An annular channel  58  extending circumferentially partway through the ring  56  is disposed between the crankcase chamber  26  and the injection passage  39 . The annular channel  58  is disposed between the periphery  43  of the circular disk or crank web  21  and the injection tube  38  and the injection passage  39 . 
     The annular channel  58  is in fluid communication with the injection passage  39  through a ring port  60  in the ring  56  leading to one end of the annular channel  58 . The annular channel  58  is designed to hold a fraction of the total volume of charge or volume of the injection tube  38  and, thus, operates as an extension of the injection passage  39  leading from the charge injection port  40  to the crankcase port  41  in the crankcase  28 . A segment of a ring may be used instead of a full ring. The ring is a stationary angularly adjustable component, meaning that it does not rotate with the crankshaft but can be angularly adjusted or rotated in order that it can be phase shifted with respect to the crankshaft. The ring can be in a fixed position to provide a fixed volume and fixed asymmetric timing. The ring can be adjacent to the crank web outside the crankcase as illustrated in  FIGS. 8-13  or enclosed in the crankcase as illustrated in  FIGS. 14-16 . 
     Referring to  FIGS. 6-17 , the ring port  60  is opened and closed by the slots  44  and  45  in the crank web  21  and are alignable with a crankcase port  41  open to the injection passage  39  in the injection tube  38 . A lower end  37  of the injection passage  39  opens in to the channel  58  in the ring  56 . An upper end  35  of the injection passage  39  terminates at the charge injection port  40  into the cylinder. 
       FIGS. 15 and 16  illustrate a controllable variable volume channel  58  with a fixed lip  70  extending into the channel  58  at the lower end  37  of the injection passage  39 . The volume of channel  58  can be varied by rotating the ring  56  and the channel  58 . The volume of the channel between the lip and a closed end  78  of the channel  58  is a dead volume, which is passive. Therefore, the total volume for the charge includes the injection passage  39  and the effective volume of the channel  58  not including the dead volume between lip  70  and the closed end  78  of the channel  58 . The ring  56  is rotated by means of a timing lever  74  attached to the ring illustrated in  FIG. 18  or some other actuation apparatus such as gears or a cable. A pinion gear actuation apparatus is another option. 
     In operation, as the piston  16  moves upward, the first injection port  40  is closed by the piston (which also closes exhaust and transfer ports  50  and  33 ), and the pressure in the crankcase  28  drops. At an appropriate time, the ring port  60  is opened by the crank web  21  by aligning one of the slots  44  with the ring port, thus, allowing the fuel/air charge to flow into the injection passage  39  through the carburetor  34 . The charge continues to fill the injection passage  39  and the channel  58  in the ring until the crank web  21  closes the ring port  60 . The timing of the opening of the ring port and the total volume of the injection passage  39  are fixed for a given angular position of the ring  56 . The main intake occurs in a usual manner through an air lean charge regulating butterfly valve  80  into the crankcase. A reed valve  82  type inlet with the regulating butterfly valve  80  is illustrated in FIG.  4 . Alternatively, the main air/lean charge intake may occur in a usual manner through an air/lean charge butterfly type regulating valve  80  into the crankcase through a piston controlled main inlet port  84  of a piston port type inlet engine as illustrated in  FIGS. 1 ,  2 ,  8 ,  14 , and  15 . The main inlet port serves as the charge inlet port. 
     As the piston  16  moves down during the expansion process, the crankcase pressure rises compressing the crankcase charge. Depending on the ring port  60  timing, the charge may or may not be subject to this crankcase compression. The piston  16  opens the exhaust port  50  causing blow down. The transfer ports  33  are open after a few crank degrees later, leading to scavenging process. The ring port  60  is later opened by the crank web  21  injecting the rich charge into the combustion chamber  30  through charge injection port  40 . Thus, with the appropriate angle of one of the slots on the crank web  21 , the start of injection can be optimized and continuously be varied by rotating the ring  56 . 
     Referring to in  FIG. 17 , the transfer ports  33  are located below the combustion chamber and extend through the cylinder block  12  to the cylinder bore  14 . Cylinder ports  111  are located below transfer ports  33  and extend through the cylinder block to the cylinder bore. The transfer passage  11  connect in gaseous communication the transfer and cylinder ports  33  and  111  respectively. For an effective injection, the cylinder ports  111  at lower ends  100  of the transfer passages  11  may be cut-off from the crankshaft chamber  26  forcing the crankcase gases to flow through the injection passage  39 . The cylinder ports  111  extend through the cylinder block  12  to the cylinder bore  14 . The cylinder ports  111  at the lower ends  100  of transfer passages  11  or elsewhere along the transfer passages are closed off from the crankcase chamber by the piston  16 . More particularly the cylinder ports  111  at the lower ends  100  of transfer passages  11  are closed off from the crankcase chamber by a piston skirt  113  of the piston  16 . One particular timing setting for closing off the transfer passage  11  from the crankcase chamber is at about 20 degrees BDC. Thus opening and closing of the injection passage  39  (or passages) to the crankcase chamber is controlled by the crank web  21  and the opening and closing of the transfer passages  11  to the crankcase chamber is controlled by the piston. 
       FIG. 17A  illustrates windows  111   a  that may be incorporated into the piston skirt  113  as an alternative for closing the cylinder ports  111  with a lower edge of piston skirt. The windows  111   a  are translatably alignable with the cylinder ports  111 . The windows  111   a  allow the cylinder ports  111  to be closed during compression when the piston is ascending, which lowers the effective crankcase chamber volume by cutting off the transfer passage volume. The windows  111   a  are translatably alignable with the cylinder ports  111 . This should be timed to occur early during the scavenging process, between about 100 degrees ATDC and 170 degrees ATDC. The piston skirt shuts off the cylinder ports late during the scavenging process as the piston approaches BDC position, about 30 degrees BBDC to 5 degrees BBDC. The cylinder ports  111  (may also be viewed as crankcase ports) at the lower end  100  of transfer passages  11  may alternatively be closed off from the crankcase chamber by the crank web  21  as illustrated in  FIG. 48  which has fixed timing and engine casing port timing illustrated in  FIGS. 44-46  that have variable timing ring systems. 
     It is also possible with the crank web timing system to have a delayed charge injection, where the injection of charge may be started when the piston begins to move upward after BDC. This is accomplished by closing the scavenging and injection a few degrees before the piston reached BDC during the expansion cycle. Thus, a crankcase pressure may be built for later utilization for injection through the charge injection port  40 . Thus, only air/lean mixture is injected into the combustion chamber  30  during early part of the scavenging process. The rich charge injected later is most likely to be trapped. Therefore, it is the air/lean charge that gets short-circuited and this lowers the HC emission and improves trapping of fuel. 
     By rotating the timing ring  56 , the timing of the ring port  60  can be advanced or retarded. The ring port timing affects the charge induction and injection timing which also affects the charge volume. For example, at higher speeds the timing can be advanced while the charge volume is increased. The volume can be made to decrease which depends on the angular location of the ring port  60  with respect to direction of crankshaft rotation. 
       FIGS. 19-21  illustrates a variable length compressed air assisted injection tube engine which is designed for varying the length of the injection passage  39  without varying the timing for a compressed air assisted injection system (CWI). A compressed air assisted injection system engine is disclosed in U.S. Pat. No. 6,273,037. The engine disclosed in U.S. Pat. No. 6,273,037 uses the piston to control the charge induction and, thus, the opening and closing time of induction is symmetrical about the TDC. Also, the charge depends on the wave dynamics for injection. This may lead to an optimum performance only at a certain operating range of speed and load. In a CWI, the injection of charge is accomplished by the reflection of a pressure wave and, thus, the length of the tube is important for optimum performance. 
     A CWI with a fixed length tube may have optimum performance in narrow ranges of speed and loads. The variable length compressed wave injection tube engine illustrated in  FIG. 19  incorporates the rotatable ring  56  illustrated in  FIGS. 20 and 21 . The channel  58  is formed by an annular notch  59  in the periphery of the ring  56  and the crankcase housing  61 . A crankcase housing port  64  replaces the ring port  60  in the ring and, thus, has a fixed timing. Both ends of the channel  58  are closed. By rotating the ring, the effective tube length LT of the injection tube  38  is varied without altering the induction timing. This embodiment of the engine allows the fixed timing to be unsymmetrical and controlled by the crank web. Thus, the effective length can be varied to optimize the performance and can be tuned to acoustic characteristics at different speeds. By rotating the ring, the effective length of the injection tube  38  is varied, while beginning and end of charge induction into the tube is fixed. Thus, the acoustic characteristics of CWI may be optimized at every operating condition of the engine, from idle to wide open throttle condition by varying the rotational position of the ring. 
     Illustrated in  FIGS. 22 ,  22 A, and  22 B is a variable inlet port timing rotary disk valve system. An intake passage  92  from the carburetor  34  opens into the channel  58  in the ring  56  at an intake passage port  90 . The channel  58  operates as a part of the intake passage  92  and has a crankcase port  41  which is open to the crankshaft chamber  26  at one end and is closed at the opposite end. The opening and closing of the ring port is controlled by the crank web  21 . The ring can be rotated to control and vary the opening and closing time of the charge inlet timing. The timing can be optimized for a wide range of speeds to improve the breathing efficiency of the engine. 
     A two stroke engine  10  illustrated in  FIGS. 23-28  is used to vary timing of the transfer port  33  to optimize the scavenging process. The lower end  100  of the transfer passage  11  opens into the channel  58  in the ring  56 . A ring port  60  at one end of the ring opens into the crankcase  28 . The ring port  60  is opened and closed by the crank web  21 . Thus, rotating the ring  56  can vary opening and closing of the ring port  60  at the lower end  100  of the transfer passage  11  and alter the scavenging timing which can be used to provide asymmetric ring port timing. The channel  58  on the ring  56  effectively operates as an extension of the transfer passage  11  and, thus, the effective volume and length of the transfer passage  11  is varied as the ring  56  is rotated. In a conventional system, the transfer port timing is fixed and is controlled by the piston and, thus, the timing is symmetrical. The inherent problem of such conventional systems is loss of charge and transfer of blow down pressure into the crankcase at certain operating conditions during scavenging. The variable rotatable ring in the system disclosed herein may reduce or eliminate this problem. 
     In some conventional engine designs, each transfer duct is provided with a cut-off valve (typically a reed valve) at its junction with the crankcase, the transfer passage having a length selected for best pressure wave effect to fulfill the requirements. In the present invention, the timing may be controlled by the crank web, in which the timing is variable and the transfer passage length also can be varied to optimize the performance at wider ranges of speeds. The added advantage is that the exhaust port lead is very much reduced in comparison with that normally employed. Consequently, when exhaust port opens a high pressure plug of exhaust gas enters the transfer port. By this time, however, the crankcase port at the other end of the duct is closed and the gas in the duct is thus compressed under a positive pressure. The explosion end pressure (cylinder pressure) is dropping all the time as exhaust port opens and, concurrently with this, a reverse low pressure wave is initiated in the transfer duct, following the original positive wave. This not only evacuates the plug of exhaust gas from the transfer duct to follow the residuals out of the exhaust port but, by causing a depression at the lower end of the duct, it assists the flow from crankcase to cylinder through the crankcase port which is now open. 
     The variable ring  56  in the scavenging system can reduce exhaust port lead which increases effective expansion ratio of the engine. It can reduce the probability of exhaust gas entering the crankcase in any circumstances and regardless of the pressure value at any particular instant. It can improve scavenge pressure resulting from the reverse wave action in the transfer duct and the fact that because the crank port can be closed as soon as the crankcase content is discharged. The variable ring scavenging system can reduce any tendency for a reversal of flow in the transfer duct when the piston is rising after BDC. The effective length of the duct can be varied for effective pressure wave effect at all the speeds. When the piston is rising after BDC, the effective crankcase volume is lower in the variable ring scavenging system than in a conventional system because the transfer duct volume is removed from the total volume which helps breathing characteristics. 
     In some conventional engines disclosed in U.S. Pat. No. 6,491,006, the blow down of exhaust into the transfer duct is intentional. This is believed to delay the discharge of fresh charge into the cylinder and hence lower the scavenging loss of charge. The variable ring scavenging system provides a variable length transfer duct and adjustable ring port timing which enhance the benefits of blow down of exhaust into transfer duct. Blow down into long transfer ducts are used as a means of delaying the discharge of fresh charge into the cylinder and the exhaust blown down into the transfer duct also acts as a buffer medium. The rotatable ring provides a means for changing the duct length and, thus, the buffer medium volume. The ring port is open to crankcase and is not timed by the crank web for start of the scavenging process. 
     The engine  10  illustrated in  FIG. 30  provides fixed timing of the transfer port  33  controlled by the crank web  21 . The lower end  100  of the transfer passage opens directly into the crankshaft chamber  26  through a crankcase port  41 . The opening and closing of the crankcase port  41  is controlled by the crank web  21 . 
       FIGS. 31 and 32  illustrate a two stroke engine  10  having a air head scavenging system with the variable volume and timing transfer passage ring  56  which improves the performance of an air head scavenging system wherein the lower end  100  of transfer passage  11  is controlled by the crank web  21 . After the transfer passage is filled with air, the ring port  60  at the lower end  100  of the transfer passage  11  can be closed to prevent flow of air into the crankshaft chamber  26  in the crankcase  28 . This is accomplished by closing the ring port  60  using the crank web  21  and rotary shut-off valve  48  illustrated in FIG.  31 . The rotatable ring  56 , illustrated in  FIGS. 24 and 29 , may be used to provide a variable volume transfer passage for varying and optimizing the volume of air inducted into the transfer passage according to speed and load conditions. Closing the ring port  60  after the transfer passage is filled with air enhances the charge induction into the crankcase through the piston controlled, reed valve or rotary valve main intake system. 
     As the piston moves upward, the drop in pressure in the crankshaft chamber  26  causes the ambient air to flow into the transfer passage  11  through an air passage  88  and reed valve  89  as illustrated in FIG.  31 . The quantity of air is regulated by an air control barrel valve  94 . And air control valve  94  is linked to an air/fuel mixture regulating valve  80 . The ring port  60  and the crank web  21  mounted rotary shut-off valve  48  control the timing of flow of air. The variable ring  56  position alters the total transfer passage volume and timing. Thus, the trapped air in the transfer passage is more controllable in this design. Using the rotatable variable ring  56  and the crank web  21  controlled scavenging system, the start of injection of air ahead of fresh charge can be varied. Thus, the air entering the cylinder bore  14  ahead of the charge acts as a buffer medium between the burnt gas and the fresh charge. It is the air that is likely to be short-circuited that minimizes the loss of fuel and hence lowers the unburned hydrocarbon emission. 
       FIG. 33  illustrates an air head scavenging system with a fixed transfer port timing. The crankcase ports  41 , which are in fluid communication with the transfer passages  11 , are opened and closed by the crank web  21  to start and end induction of air into the transfer passage  11  through the one-way reed valve  89 . Once the induction of air into the transfer passage  11  is shut-off by the crank web, the induction of main charge into the crankcase chamber  26  is more effective, as the crankcase chamber volume is now cut-off from the transfer passage volume. 
     A conventional single barrel carburetor such as a single butterfly valve type carburetor may be used to operate the air head scavenged engine. This is accomplished because the volume of air trapped in the transfer passage  11  is constant at all speeds and may be used to lower the hydrocarbon emission even at idle. Thus, only the main charge going into the crankcase chamber may be regulated for load and speed control while full air is supplied into the transfer passage without having to dilute the crankcase chamber charge with the air. The excess air is shut-off from getting into the crankcase during the idling and wide open throttle. During the scavenging process, the start of injection of air into the combustion chamber  30  may be delayed by the crank web. An air filter may be provided right at the air reed valve  89  and, thus, eliminating the need for any air pipe or passage  88 . This means the air is supplied to top of transfer passage during intake process at all operating conditions, and there is no need for the regulating air control barrel valve  94  illustrated in  FIGS. 31 and 32 . In which case, a conventional carburetor may be used for air head scavenging where the transfer passage crankcase port  41  is open and shut-off by the crank web  21 , as illustrated in FIG.  33 . 
     There can be more than two transfer passages in the engine. In U.S. Pat. No. 6,491,004, for example, the engine has two pairs of transfer passages. One transfer passage of the first pair in on each side of the exhaust port and is used for air head scavenging as described above and the second pair is located for use as in a conventional engine. The rotary shut-off valve  48 , as described above, may be used as shut-off valve either for both the pair of transfer passages or for just one pair of transfer passages that handle air. When two pairs of transfer passages are used, the disk valve may delay one pair of transfer passage opening into crankcase to delay discharge of charge into the combustion chamber  30  while providing the other pair that handle air with advanced passage opening timing for air head scavenging. For example, this embodiment would add a rotary shut-off valve to the lower end of transfer passages in the engine disclosed in U.S. Pat. Nos. 6,289,856, 6,112,708, 6,240,886, and 5,425,346. 
     The engines disclosed in U.S. Pat. Nos. 6,289,856, 5,425,346, and 5,379,732 are examples of engines having air head scavenging controlled by piston ports and channels in piston skirts. The lower ends of the transfer passages are constantly open into the crankcase chamber, thus, making it possible for air to flow into the crankcase chamber during wide open or full throttle running condition. At idle, the air flow into the transfer passages is either completely shut-off or partial. In such engines, as the piston travels downward the crankcase pressure builds up which may lead to reverse flow of air back into the ambient. 
       FIGS. 34-36  illustrates an example of piston controlled air head scavenging system controlled by the rotary shut-off valve which is illustrated as the crank web  21 . The engine operates like a conventional two stroke engine. First and second piston ports  99  and  101  are disposed on the skirt  113  of the piston  16  and are connected to each other in gaseous communication by an air channel  96 . The transfer port  33  and exhaust port  50  are closed by the piston  16  as it ascends. During the upward stroke, pressure in the crankshaft chamber  26  drops below ambient creating a pressure difference between ambient and crankcase chamber  26 . At this time, the rotation of the crank web aligns first annular slots  44  with the crankcase port  41  at the lower end  100  of the transfer passage  11 . As the piston travels upward, the first piston port  99  aligns with an air inlet port  98  disposed through the cylinder block  12  and which leads to an air cleaner  95  associated with the carburetor  34  (another example of which is further illustrated in FIG.  51 ). At about the same time, the second piston port  101  aligns with the transfer port  33  connected to the transfer passage  11 . Thus, the air channel  96  provides fluid communication between the crankcase chamber  26  and the ambient air. 
     The pressure difference between the crankcase chamber  26  and ambient allows the air to flow into the transfer passage  11  through air control barrel valve  94 , air inlet port  98 , air channel  96 , and the second piston port  101 , transfer port  33  on the cylinder bore  14  and into the transfer passage  11  until such time the piston closes the air inlet port  98  in the cylinder bore  14 . Just about the same time, the crank web  21  closes the lower end  100  of the transfer passage  11  at the crankcase port  41 . This cuts off the gaseous flow communication between the crankcase and the transfer passage. 
     In a piston ported induction system, as illustrated in  FIG. 34 , further upward movement of the piston uncovers the main inlet port  84  (for charge induction) in the cylinder block  12  through to the cylinder bore  14  for induction of air fuel charge into the crankcase chamber  26 . The main inlet port  84  is angularly offset from the air inlet port  98  and allows charge to flow into the crankcase chamber  26  through a second flow passage  312  leading from the carburetor  34 . A butterfly valve  80  may be used to regulate flow through the main inlet port  84 . In a reed valve system, illustrated in  FIG. 36 , the main charge induction begins as soon as the pressure difference across the crankcase chamber  26  and the ambient opens the reed valve  82 . A rotary inlet may also be used in conjunction with the piston controlled air head scavenging. As the piston  16  moves downward during the expansion stroke, the crankcase pressure rises. 
     At a certain position, the piston will again uncover the air inlet port. At this time, a rise in crankcase pressure may cause the charge to flow into the transfer passage and, thus, force the air and charge to flow out back through the air channel  96  into the atmosphere. However, since the crank web can have asymmetrical timing, the web keeps the lower end of transfer passage closed at the crankcase port  41 . Thus, the loss of air or charge is prevented by using a web as a shut-off valve in a controlled transfer passage system, which is novel as described here. The crank web opens the transfer passage  11  for regular scavenging just before the piston  16  opens the transfer port  33 . During the scavenging process, it is the air that enters the combustion chamber first and is most likely to be short-circuited into the exhaust port. Thus, air acts as a buffer medium between the burnt gas and the fresh charge, which minimizes the emission and improves fuel economy. The design of the crank web controlling the transfer passage for improved sealing between the crankcase chamber  26  and the transfer passage (and ambient), particularly as the piston descends, may be used with any of the piston channel systems described in the U.S. Pat. Nos. 6,289,856 and 5,425,346. 
     In a scavenging process similar to that of the air head scavenging system explained above, the exhaust gas can be used as a buffer medium during an early part of the scavenging process. The exhaust gas is brought in to the top of the transfer passage  11  through piston channels in the piston as described in U.S. Pat. No. 5,425,341. In U.S. Pat. No. 5,425,341, the piston channels are inside the piston. Piston channels  97  outside the piston  16  are illustrated in  FIGS. 37-39 .  FIG. 37  illustrates the exhaust gas recirculation into the transfer passages  11  where the lower port is opened and closed by the crank web  21  and has a variable volume and timing ring  56 .  FIGS. 38 and 39  have fixed transfer passage  11  volume and fixed timing. As the piston  16  moves upward and at a particular crank angle, the piston channel  97  in the piston aligns with the exhaust port  50  and the transfer port  33  allowing the exhaust gas to flow into the transfer passage  11  due to a pressure differential. The amount of exhaust gas flowing into the transfer passage  11  can be controlled by the position of the ring port  60  and the crank web  21 , which controls the timing. When the transfer ports  33  open, recirculated exhaust gas enters the combustion chamber  30  first and is likely to be short-circuited. Thus, the escape of fresh air fuel charge into the exhaust is minimized. 
     A multiple ring scavenging system, illustrated in  FIGS. 40-46 , provides variable transfer port timing, variable charge injection timing, and variable inlet timing with and without air head systems in a manner as explained above. Axially adjacent first and second angularly adjustable rings  109  and  110  concentrically surround the circular disk or crank web  21 . The first and second angularly adjustable rings  109  and  110  have first and second annular ring channels  180  and  182  extending circumferentially partway through the first and second angularly adjustable rings  109  and  110 , respectively. The first and second annular ring channels  180  and  182  have first and second ring ports  186  and  188 . The transfer passage  11  culminates at the first annular ring channel  180  in the ring  109  at the crankcase  28  of the engine illustrated in FIG.  40 . The injection passage  39  of the injection tube  38  culminates at the second annular ring channel  182  of the second ring  110  in crankcase  28  of the engine illustrated in FIG.  40 . The first ring  109  and its first annular ring channel  180  are behind the second ring  110  in the view so only the second ring  110  is illustrated in  FIG. 40. A  single lever (not shown in  FIGS. 40-43 ) may control and rotate angularly adjustable rings in the multiple ring systems. 
       FIGS. 40-43  illustrate the multiple ring scavenging system with variable volume and timing for charge and variable volume and timing for transfer passage.  FIG. 42  illustrates one of the many ways possible for the crank web  21  to have multiple circumferentially extending axial gas pathways to control timings of the different ring ports.  FIGS. 41 and 42  illustrate an example of multiple circumferentially extending axial gas pathways through the crank web  21 . First and second axial gas pathways illustrated as first and second annular slots  144  and  145  are cut through or extend axially partially through the radially outermost section  52  bordered by the periphery  43  of the circular disk or crank web  21 . Third and fourth annular L-shaped pathways  154  and  156  have third and fourth radially inwardly extending annular slots  158  and  160  that intersect third and fourth axially extending annular slots  162  and  164  respectively. The third and fourth radially inwardly extending annular slots  158  and  160  have radially outwardly facing third and fourth radial inlets  170  and  172 , respectively, in the periphery  43 . The third and fourth axially extending annular slots  162  and  164  have axially facing third and fourth axial outlets  174  and  176 , respectively, that are located radially inwardly of the crank web&#39;s  21  periphery  43 . 
     The first and second angularly adjustable rings  109  and  110  are disposed between the crankcase chamber  26  and the injection passages  39  and between the crankcase chamber  26  and the transfer passage  11  respectively. The first annular ring channel  180  is rotatably alignable with the lower end  37  of the charge passage  39 . The second annular ring channel  182  is rotatably alignable with the lower end  100  of the transfer passage  11 . The first ring port  188  in the angularly adjustable ring  109  is rotatably open to the third and fourth radially inwardly extending annular slots  158  and  160  through the radially outwardly facing third and fourth radial inlets  170  and  172  respectively in the periphery  43 . The second ring port  186  in the angularly adjustable ring  110  is rotatably open to the first and second annular slots  144  and  145 . The first annular ring channel  180  controls transfer passage volume and timing, while the second annular ring channel  182  controls charge induction volume and timing through the injection passage  39 . 
     One embodiment of the crank web  21  is a step type where a larger diameter disk section controls the transfer port timing either of fixed or variable timing type illustrated in FIG.  44 . The main intake system is a rotary valve type with variable inlet timing, as illustrated in FIG.  44 . Angularly adjustable rings to control intake and charge induction could be mounted concentrically to the web and adjacent to each other. The main intake system illustrated in  FIG. 45  is a reed valve type with multiple ring system for charge and transfer passage volume and timing.  FIG. 46  illustrates an air head scavenging system with charge injection and multiple ring system. 
       FIGS. 47 ,  48 ,  49  and  49 A illustrate a web controlled fixed timing for transfer ports and charge system. The main inlet is a piston ported system. In this embodiment, the construction of the engine becomes easier. The functioning of the charge and main intake is identical to the two-way scavenging system illustrated in FIG.  1 . However, in addition to using web as a shut-off valve for charge, the transfer passage lower port is also opened and closed to the crankcase chamber  26  by the rotary shut-off valve. Engine ports  111  at lower ends  100  of the transfer passages  11  are opened and closed by rectangular cross-sectional annular slots  318 , further illustrated in  FIG. 49A , to open and close the transfer passages  11  between the crankcase chamber  26  and the combustion chamber  30  to effect scavenging. 
     Illustrated in  FIGS. 50-54  is an exemplary two stroke engine  20  having a cylinder block  12  that houses a cylinder bore  14 . A piston  16  reciprocates within the cylinder bore  14  and is connected by means of a connecting rod  18  to a crank throw  20  between first and second crank webs of a crankshaft  22 . The crankshaft  22  is journaled for rotation within a crankcase chamber  26  of a crankcase  28  that is affixed to the lower end of the cylinder block  12  in a suitable manner. A combustion chamber  30  is defined with a region within the cylinder bore  14  above the piston  16 . Transfer passages  11  between the crankcase chamber  26  and the combustion chamber  30  are used for scavenging and allow fresh air initially followed by fresh lean fuel/air charge to be drawn from the crankcase chamber  26  through crankcase transfer ports into the combustion chamber  30  through transfer ports  33  in the cylinder block  12  at the completion of a power stroke. 
     A rich fuel/air mixture is inducted into the combustion chamber  30  of the cylinder bore  14  by a charge induction system which includes a three-way carburetor  132 , an air filter  95 , a one-way non-return valve  36 , a tube  38 , and a charge injection port  40  to the cylinder bore  14  in the cylinder block  12 . The tube  38  provides a passage  39  for gaseous communication between the combustion chamber  30  and the crankcase chamber  26 . The passage  39  leads to and is in fluid communication with a crankcase charge port  46  in the crankcase  28  which is controlled by and open to a first rotary shut-off valve  148 . The timing of the induction of the rich fuel/air mixture and injection of fuel is controlled by the first rotary shut-off valve  148  mounted on a disk which, in this embodiment, is the second crank web  142  that is rotatably connected to the crankshaft  22 . 
     The first rotary shut-off valve  148  includes circumferentially extending first and second gaseous pathways illustrated as slots  44  and  45  formed in the second crank web  142 . The slots  44  and  45  are alignable with the crankcase charge port  46  open to the injection passage  39 . The second crank web  142  closes off the crankcase charge port  46  and the injection passage  39  in the injection tube  38  until the crankcase charge port  46  is circumferentially aligned with the first or second slots  44  and  45 , thus, allowing gaseous communication between the crankcase chamber  26  and the passage  39 . 
     The first and second slots  44  and  45  are cut in the second crank web  142 , though other types of disks attached to the crankshaft  22  may be used. The first and second slots  44  and  45  are cut-away sections of the second crank web  142 . The first and second slots  44  and  45  open fluid communication between the tube  38  and the crankcase chamber  26  as the second crank web  142  rotates with the crankshaft  22 . The first rotary valve  148  formed in the second crank web opens and closes off the crankcase charge port  46 , thus, providing the valving function of the first rotary shut-off valve  148  as the second crank web  142  rotates with the crankshaft  22 . 
     Opening and closing each of the first and second slots  44  and  45  between the tube  38  and the crankcase chamber  26  induces a fuel/air mixture charge into the passage  39  during fraction of one cycle of the engine, or a fraction of a first half rotation of the second crank web  142 , and a discharge of the fuel/air mixture through the tube  38  into the combustion chamber  30  during the next cycle of the engine  20 . Timing of the opening and closing of the slots  44  and  45  by the first rotary shut-off valve  148  is asymmetric. 
     In a variation to the opening of the crankcase charge port  46  by the slot  45  for injection of charge in the charge passage into combustion chamber  30 , the crankcase charge port  46  may be kept closed by the first rotary valve  148  for the blow down pressure into the passage  39  to reflect off of the first rotary valve  148  to perform like a compressed air assisted wave injection engine such as the one disclosed in U.S. Pat. No. 6,273,037. 
     Transfer passages  11  provide fluid communication between the combustion chamber  30  at the transfer ports  33  and crankcase chamber  26  at crankcase transfer ports. The crankcase transfer ports are controlled by second rotary shut-off valves  149  on the first and second crank webs  121  and  142 . Each of the second rotary shut-off valves  149  includes first and second tabs  190  and  191  on each of the first and second crank webs  121  and  142 . The first and second tabs  190  and  191  are alignable with crankcase transfer ports  111 . 
     During the first half rotation of the crankshaft, when the piston is ascending, the crankcase transfer ports  111  are opened by the second rotary shut-off valves  149  and the crankcase is in fluid communication with the ambient air. As the crankcase pressure is lower than the ambient, air fills the transfer passage  11 . The air flow is supplied to the transfer passages  11  through one-way reed valves  89  at the end of air passages  88  as illustrated in FIG.  52 . The air flow is supplied to the transfer passages  11  by an air intake system including an air control valve  94  of a three-way carburetor  132  leading to air passages  88  illustrated in FIG.  51 . The air control valve  94  controls only the air, a fuel/air mixture valve  81  is used for controlling fuel/air mixture, and the two valves are linked to each other. 
     At an appropriate time, the engine ports  111  are closed by the first tabs  191  to prevent the flow of air into the crankcase. Closing off of the transfer passages  11  from the crankshaft chamber  26  lowers the effective crankshaft chamber volume for further induction of lean charge during ascending of the piston  16 . This allows the lean charge to flow into the crankshaft chamber  26  from the carburetor  132  through the lean passage  107  and through the main inlet port  84 . As the piston  16  descends, the crankshaft chamber  26  pressure is increased. While air is retained in the transfer passages  11 , the rich charge is retained in the passage  39 . During a fraction of the ascending stroke and during the fraction of the descending stroke, the air is trapped between the transfer ports  33  and the engine ports  111 . 
     The transfer ports  33  are shut-off by the piston and the engine ports  111  are shut-off by the first and second tabs  190  and  191  of the second rotary shut-off valves  149 . Similarly, the rich charge in the tube  38  is trapped between the injection port  40  and the crankcase port  46 . The piston shuts off the injection port  40  in the cylinder and the first rotary shut-off valve  148  cuts off the crankcase port  46 . Control of engine ports  111  for the transfer passages  11  and control of the crankcase port  46  allows the engine to have unsymmetrical induction and injection timing for both the charge and air to achieve stratified scavenging and charging. During the scavenging process, the engine ports  111  are opened first to allow the air to lead the lean charge into the combustion chamber  30  and allow the air to act as a buffer medium between the fresh charge and the burnt gas. Rich charge injected later through the charge injection port  40  is timed by the first rotary shut-off valve  148  for low emission. 
     Piston channel controlled air head system may also be used for induction of air into transfer passages as illustrated in  FIGS. 34-36 . When the piston channel system is used in engine  20 , it eliminates the need for reed valves  80  in engine  20 . 
     An example of port timings for a piston ported two stroke engine is illustrated in the chart below. The timings can be optimized depending on intake system, application, and engine size.
     Typical port timings for a charge injected stratified charge scavenging system piston ported engine.   Charge crankcase port  41  (and where used ring port  60 ), open for charge induction about 20 to 10 degrees ABDC and close 20 degrees BTDC to 10 degrees ATDC.   Intake port  84 , open 60 to 40 degrees BTDC and close 60 to 40 degrees ATDC.   Exhaust port  50 , open 100 to 125 degrees ATDC and close 100 to 125 degrees BTDC.   Transfer port  33 , open 110 to 135 degrees ATDC and close 110 to 135 degrees BTDC.   Charge injection port  40 , open 105 to 120 degrees ATDC and close 105 to 120 degrees BTDC.   Charge crankcase port  41  (and when used ring port  60 ), open for injection 100 to 120 degrees ATDC and close 10 degrees BBDC to 10 degrees ABDC.   Transfer passage  11  and crankcase transfer port  111 , open 10 to 20 degrees ABDC for air induction through air passage  88 .   Transfer passage  11  and crankcase port  111 , close 80 to 50 degrees BTDC for ending induction of air.   Transfer passage  11  and crankcase port  111 , open 100 to 125 degrees ATDC for start of scavenging and close 25 degrees BBDC to 5 degrees ABDC to cut off port  111 .
 
Wherein:
   ATDC=After top dead center   BTDC=Before top dead center   ABDC=After bottom dead center   BBDC=Before bottom dead center.   

     The three-way carburetor  132  is illustrated in more detail in  FIGS. 56-58 . As the piston  16  ascends in the cylinder bore  14  of the engine, the pressure in the crankcase chamber drops below ambient. The differential pressure between the crankcase chamber and the ambient (outside of the carburetor) causes air to flow into the crankcase chamber through the appropriate passages (transfer passages or charge passages). There are three flow transversely extending venturi passages in a longitudinally extending barrel  403  of a three-way carburetor. An air venturi passage  404  allows only air, which is regulated by the air control barrel valve  94 , to flow into the transfer passage  11 . A rich charge venturi passage  405  flows a rich charge regulated by a rich charge barrel valve  81  into the charge passage  39 . A lean charge venturi passage  406  flows a lean charge regulated by a lean charge barrel valve  80  directly into the crankcase chamber  26 . The air control, rich charge, and lean charge barrel valves are mounted on a rotatable barrel valve body  479 . 
     Fuel is mixed with the air in the rich and lean charge venturi passages  405  and  406 . As air passes through the rich and lean charge venturi passages  405  and  406 , the pressures in the venturi passages drop. The differential pressure between a fuel metering chamber  412  and the rich and lean charge venturi passages  405  and  506  causes the fuel to be discharged into air streams in the venturi passages through respective lean and rich jets  410  and  411 . 
     A pulse line  426  is in communication with the crankcase chamber  26  and the pulse chamber  427 . Positive and negative pressures in the crankcase chamber  26  causes the pump diaphragm  418  to pulsate drawing fuel from the fuel tank  421  through the fuel supply line  420  and the second flapper valve  419  into the pump chamber  417 . As crankcase chamber pressure rises, the pulse chamber  427  exerts pressure on the pump diaphragm  418  which causes the fuel in the pump chamber  417  to flow into the metering chamber  412  through the first flapper valve  416  and first fuel line  415 . The diaphragm needle valve assembly  413  controls the flow of fuel into the metering chamber. The metering diaphragm  414  activates the needle valve assembly  413 . As the fuel flows into the venturi passages the pressure drops in the metering chamber which causes the needle valve to allow the fuel to flow from the pump chamber. 
     The fuel jet assembly  409  consists of a combination of lean jet  410  and a rich jet  411 .  FIG. 58  shows an enlarged illustration of the jets assembly and the main needle. The lower end of the jet assembly  409  opens into the metering chamber  412  and may have more than one fuel spray hole  410  in the lean venturi passage. The upper end of the jet has a V shaped slot  430  through which the fuel flows into the rich venturi passage. The amount of fuel that flows into the rich charge venturi passage  405  is controlled by the main needle  407  which moves up and down as the barrel valve body  479  is rotated by a throttle for load and speed regulation. As the barrel valve body  479  is rotated for speed and load, it regulates the flow of charge and air into the engine. 
     The rotation of barrel valve body  479  causes a throttle cam  408  to ride on a cam pin  425  which causes the barrel  403  to rise. The main needle  407  attached to the barrel  403  also rises which increases the fuel flow area in the V shaped slot  430 . The flow of fuel increases in proportion to the flow of air through the rich charge venturi passage  405 . As the throttle is opened more and more, a larger fraction of the total fuel (fuel through lean jet  410  plus fuel through rich jet  411 ) flows through the rich jet  411 . As a result the ratio of fuel through rich jet to the fuel through lean jet depends on the throttle position. It may therefore be fair to assume that the richness of air-fuel ratio flowing through the lean venturi passage directly into the crankcase chamber  26  decreases with increase in throttle opening. Thus a rich charge is supplied to the crankcase chamber during idle and part throttle and a very lean charge during 30% and higher speed and load conditions. This helps to lower the emissions, particularly at wide open throttle condition and helps a stable idle running and fast throttle response. 
     The carburetor also includes a primer bulb  423  which has one way valves built into it. It is a manual pump used to prime the metering chamber to remove the air or fuel vapor trapped in the metering chamber. As the prime bulb is depressed manually, the fuel is pumped back into the fuel tank  421  through the return line  424 . As the bulb is released the fuel (or air or vapor during initial period) is drawn into the bulb from the metering chamber. During this time, the diaphragm needle valve is lowered allowing the fuel to be drawn from the fuel tank through the flapper valves and pump chamber. The third flapper valve  428  at the entrance to the main jet  409  prevents the air from venturi passage to get into the metering chamber during priming. 
     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. 
     Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims: