STRATIFIED SCAVENGING TWO-CYCLE ENGINE

Abstract: A stratified scavenging two-cycle engine is capable of doing away with emission of a mixture into the atmosphere and reducing intake resistance of air. For this purpose, an air intake port (11) is provided in a position a predetermined distance away from scavenging ports (51) toward a crank chamber (20) in an axial direction of a cylinder (1), and the scavenging ports (51) are connected to the air intake port (11) through a piston (3) to thereby supply air to scavenging flow passages (50) from the air intake port (11) through the scavenging ports (51) at the time of intake stroke.

Description: Technical Field The present invention relates to a stratified scavenging two-cycle engine, and particularly relates to a stratified scavenging two-cycle engine which is configured to take in a mixture and air for scavenging separately. Background Art This type of stratified scavenging two-cycle engine conventionally has a scavenging flow passage for connecting a cylinder chamber to a crank chamber, with a mixture flow passage for supplying a mixture being connected to the crank chamber, and with an air flow passage for supplying air being connected to the scavenging flow passage. A scavenging port of the scavenging flow passage, and an exhaust port of an exhaust pipe are opened to the cylinder chamber. The aforesaid air flow passage is provided with a lead valve (a check valve) 80 shown in FIG. 12 for only allowing the air to flow toward the scavenging flow passage. In the stratified scavenging two-cycle engine configured as above, a piston 3 ascends, thereby starting to reduce the pressure inside a crank chamber 20 and increase the pressure inside the cylinder chamber 10, and as the piston 3 ascends, a scavenging port 81 and an exhaust port are sequentially closed. In this situation, a mixture flows into the crank chamber 20 with the pressure therein being reduced, and air from an air flow passage 83 pushes the lead valve 80 open to flow therein through a scavenging flow passage 85. When the piston 3 reaches the vicinity of the top dead center, the mixture in the cylinder chamber 10 is ignited, and thereafter the piston 3 descends. The piston 3 descends, thereby starting to increase the pressure inside the crank chamber 20, and while the piston 3 is descending, the exhaust port and the scavenging port 81 are sequentially opened, and combustion gas is exhausted from the exhaust port. Subsequently, when the scavenging port 81 is opened, the air staying in the scavenging flow passage 85 bursts out into the cylinder chamber 10 by the pressure inside the crank chamber 20. As a result, the combustion gas remaining in the cylinder chamber 10 is expelled. Subsequently, the mixture in the crank chamber 20 is charged into the cylinder chamber 10 through the scavenging flow passage 85. Again, when the piston 3 starts to ascend from the bottom dead center, the pressure inside the crank chamber 20 starts to reduce, and the cycle as described above is repeated once again. According to the stratified scavenging two-cycle engine configured as above, the inside of the cylinder chamber 10 can be initially scavenged by air, therefore making it possible to prevent the combustible gas from being discharged by the blow-by of the mixture, which provides the advantage that the exhaust gas becomes clean. However, in the aforesaid stratified scavenging two-cycle engine, as shown in FIG. 12, the air flowing into the scavenging flow passage 85 from the lead valve 80 does not flow in a position 81A in the vicinity of the scavenging port 81, and therefore the mixture remains in this area. There exists a disadvantage that the mixture, together with the air staying in the scavenging flow passage 85, is discharged from the exhaust port into the atmosphere with the combustion gas via the cylinder chamber 10, when the scavenging port 81 opens in the exhaust stroke in which the piston 3 descends. In addition, the lead valve 80 is provided in the air flow passage 83, therefore causing the disadvantage that the lead valve 80 becomes intake resistance when air is taken into the scavenging flow passage 85. Further, the number of components increases due to the lead valve 80, and the structure is complicated, thus causing the disadvantage of the cost increasing. GB 07926 A A.D. 1913 and US-A-5,425,346, each disclose a stratified scavenging two-cycle engine including an air intake port, a scavenging port, and an exhaust port which are connected to the cylinder chamber of the engine, a mixture intake port connected to the crank chamber, and a scavenging flow passage for connecting the cylinder chamber to the crank chamber. The air intake port is axially displaced from the scavenging port toward the crank chamber and circumferentially displaced from the scavenging port by a predetermined angle in the circumferential direction of the cylinder. At the intake stroke, air is supplied to the scavenging flow passage from the air intake port through a channel which is formed at least partially in the piston and connected to the scavenging flow passage at a position between the scavenging port and the crank case. GB 08385 A A.D. 1915 discloses a stratified scavenging two-cycle engine including an air intake port, a scavenging port, and an exhaust port which are connected to the cylinder chamber of an engine, a mixture intake port connected to the crank chamber, and a scavenging flow passage for connecting the cylinder chamber to the crank chamber, wherein the air intake port is provided immediately below the scavenging port toward the crank chamber, and the scavenging port is connected to the air intake port through a recess-shaped passage formed in the outer perimeter of the piston to thereby supply air to the scavenging flow passage from the air intake port through the scavenging port at the time of the intake stroke. Disclosure of the Invention The present invention is made in view of the aforesaid disadvantages, and its object is to provide a stratified scavenging two-cycle engine, which takes in a mixture, and air for scavenging separately, is capable of doing away with emission of the mixture into the atmosphere by filling a scavenging flow passage with air and reducing intake resistance of air, and is less expensive with the number of components being reduced. In order to attain the above object, a stratified scavenging two-cycle engine according to claim is provided. According to the above configuration, the air intake port and the mixture intake port are separately connected to the cylinder chamber and the crank chamber respectively, and air is supplied to the scavenging flow passages for connecting the cylinder chamber to the crank chamber via the piston, therefore making it possible to fill at least the cylinder chamber side of the scavenging flow passage with air at the time of intake stroke. In addition, since the air intake port is opened at the lower position the predetermined distance away from the scavenging ports toward the crank chamber, when the top portion of the piston opens the scavenging ports at the time of scavenging stroke, the air intake port is already closed, and therefore air or the mixture does not flow back to the air flow passage, thus making a lead valve needless. Accordingly, in the scavenging stroke, the combustion gas can be initially scavenged from the cylinder chamber by means of the air in the scavenging flow passage, and thus the mixture does not flow into the atmosphere. Further, the reed valve for taking air into the scavenging flow passage is not needed, thereby making it possible to reduce the intake resistance of air and the number of components. Further, the stratified scavenging two-cycle engine is characterized in that the piston has a channel on the outer perimeter thereof, and the channel connects the scavenging ports to the air intake port and disconnects the mixture intake port from the scavenging ports, at the time of intake stroke. According to the above configuration, in the intake stroke, since the mixture intake port is disconnected from the scavenging ports, the mixture does not stay in the scavenging flow passages, thus making it possible to fill the scavenging flow passages with air. Accordingly, in the intake stroke, the combustion gas in the cylinder chamber can be scavenged by means of the air in the scavenging flow passages, and thus the mixture does not leak into the atmosphere. Furthermore, the stratified scavenging two-cycle engine is characterized in that the mixture intake port is opened and closed by the piston. According to the above configuration, in the scavenging stroke, when the top portion of the piston opens the scavenging ports, the mixture intake port is already closed, whereby the mixture does not flow back to the mixture flow passage, and thus the lead valve can be made needless. In addition, since the reed valve for supplying the mixture to the crank chamber is not needed, the number of components can be reduced. Brief Description of the Drawings FIG. 1 is a partially cutaway perspective view of a stratified scavenging two-cycle engine of a first embodiment according to the present invention; FIG. 2 is a sectional view of the stratified scavenging two-cycle engine of the first embodiment according to the present invention, showing a sectional view taken along the 2-2 line in FIG. 1; FIG. 3 is a sectional view of the stratified scavenging two-cycle engine of the first embodiment according to the present invention, showing a sectional view taken along the 3-3 line in FIG. 1; FIG. 4 is a sectional plane view of the stratified scavenging two-cycle engine of the first embodiment according to the present invention, showing a sectional view taken along the 4-4 line in FIG. 5; FIG. 5 is a sectional side view of the stratified scavenging two-cycle engine, which is near the top dead center, of the first embodiment according to the present invention, showing a sectional view taken along the 5-5 line in FIG. 4; FIG. 6 is a sectional side view of the stratified scavenging two-cycle engine in FIG. 5 in a state in which it is near the bottom dead center; FIG. 7 is a partially cutaway perspective view of a stratified scavenging two-cycle engine of a second embodiment according to the present invention; FIG. 8 is a sectional plane view of the stratified scavenging two-cycle engine of the second embodiment according to the present invention, showing a sectional view taken along the 8-8 line in FIG. 9; FIG. 9 is a sectional side view of the stratified scavenging two-cycle engine, which is near the top dead center, of the second embodiment according to the present invention, showing a sectional view taken along the 9-9 line in FIG. 8; FIG. 10 is a partially cutaway perspective view of a ' stratified scavenging two-cycle engine of a third embodiment according to the present invention; FIG. 11 is a partially cutaway perspective view of a stratified scavenging two-cycle engine of a fourth embodiment according to the present invention; and FIG. 12 is a partial sectional view of a conventional stratified scavenging two-cycle engine, showing a sectional view of a lead valve element provided at an air flow passage and a scavenging flow passage. Best Mode for Carrying out the Invention Preferred embodiments of the present invention will be explained with reference to FIG. 1 to FIG. 11 below. A stratified scavenging two-cycle engine represented by a first embodiment will be initially shown in FIG. 1 to FIG. 6. In FIG. 1 to FIG. 6, a crankcase 2 is provided at the bottom side of a cylinder 1. A piston 3 is provided at the cylinder 1 to be slidably and closely inserted therein, and the piston 3 is connected to a crank 42 in the crankcase 2 via a connecting rod 41. A space with variable volumetric capacity, which is on the top of the piston 3 in the cylinder 1, is a cylinder chamber 10, and a space, which is under the piston 3 and surrounded by the cylinder 1 and the crankcase 2, is a crank chamber 20. It should be noted that regarding the aforesaid "closely inserted", a clearance is provided in the illustrations in FIG. 4 to FIG. 6 to facilitate the explanation. Two scavenging flow passages 50 for connecting the cylinder chamber 10 and the crank chamber 20 are provided in the cylinder 1 and the crankcase 2 as shown in FIG. 3. The scavenging flow passages 50 are opened at the cylinder chamber 10 (the inner perimeter surface of the cylinder 1) as scavenging ports 51. An air intake port 11 and a mixture intake port 12 are provided in the inner perimeter surface of the cylinder 1. The air intake port 11 and the mixture intake port 12 are vertically arranged to be away from each other by a predetermined distance La along the axial direction of the cylinder 1. A position at which the air intake port 11 is opened is lower than a position at which scavenging ports 51 are opened by a predetermined distance Lb in the axial direction of the cylinder 1. As for the positions at which the scavenging ports 51 are opened, the two scavenging ports 51 are provided at the positions each displaced 90 degrees in a direction of the perimeter of the circle as shown in FIG. 4. The positions of the scavenging port 51, however, are not necessarily limited to the angle of 90 degrees, but can be appropriately selected according to the positional relationship between the air intake port 11 and the exhaust port 13, and asymmetry positions may be selected. Further, the number of the scavenging ports 51 is not limited to two, and only one may be suitable. A width Ba of the opening of the scavenging port 51 along the axial direction is formed to be opened less than the predetermined distance La by which the air intake port 11 is separated from the mixture intake port 12 (the width Ba < the predetermined distance La). The air intake port 11 is opened and closed by the movement of the piston 3, thereby making it possible to connect to and cut off from a channel (passage) 30 formed on the outer perimeter of the piston 3. The channel 30 is formed on the outer perimeter of the piston 3 in a L-shaped form in side view, and in a plane view, it is formed in the semi-circle of the outer perimeter of the piston 3 with a predetermined depth in plane view, as shown in a plane view in FIG. 4 and a side view in FIG. 5. The T-shaped channel 30 formed on the outer perimeter of the piston 3 connects with the air intake port 11 opened at the position lower than the scavenging ports 51 by the predetermined distance Lb, and connects the air intake port 11 and the two scavenging ports 51 at the time of air intake stroke, thereby allowing air to be taken into the crank chamber 20 through the air intake port 11, the channel 30, and the two scavenging flow passages 50 (shown by the solid line arrow Y). At the time of scavenging stroke, when the top portion of the piston 3 opens the scavenging port 51, the air intake port 11 is already closed, because the air intake port 11 is opened at the position lower than the scavenging ports 51 by the predetermined distance Lb toward the crankcase 20. For this reason, in the prior art, a back-flow is prevented by means of a lead valve 80, but in the present invention, the piston 3 closes the air intake port 11 to thereby prevent air or a mixture from flowing back to an air flow passage, thus making the lead valve 80 unnecessary. Further, since the width Ba of the opening of the scavenging port 51 is smaller than the predetermined distance La by which the air intake port 11 and the mixture intake port 12 are separated, when the L-shaped channel 30 is opened to the mixture intake port 12 at the lower position, an end portion 30a of the channel 30 does not connect with the scavenging port 51, whereby the scavenging port 51 is closed by the piston 3 as shown in FIG. 6. Accordingly, at the time of intake stroke, a mixture does not flow into the scavenging flow passage 50 through the channel 30. As described above, the channel 30 is in a state in which the air intake port 11 is disconnected from the two scavenging ports 51 at the time of the above scavenging stroke (a state in which the piston 3 is in a position lowered a little in FIG. 6). Thereby air is prevented from flowing back to the air intake port 11, and the mixture intake port 12 is in a state in which it is disconnected from the scavenging ports 51. In the above, the aforesaid air intake port 11 and the channel 30 compose the air flow passage for supplying air into the scavenging flow passages 50. The mixture intake port 12 is formed almost in a rectangular form in the inner perimeter surface of the cylinder 1, and is opened and closed by a skirt portion of the piston 3. The mixture intake port 12 opens at the time of intake stroke in which the piston 3 ascends and the pressure inside the crank chamber 20 reduces, thereby allowing the mixture to be taken into the crank chamber 20 (shown by the dotted line arrow W), and the mixture intake port 12 closes at the time of scavenging stroke in which the piston 3 descends and the pressure inside the crank chamber 20 increases, thereby preventing the mixture from being blown back to a carburetor side. As a result, a reed valve for preventing the back-flow is not required when a mixture is supplied into the crank chamber 20. Further, the cylinder 1 is provided with an exhaust port 13 opened to the cylinder chamber 10 at a position higher than the scavenging ports 51 in the axial direction of the cylinder 1, as shown in FIG. 2 and FIG. 6. In the stratified scavenging two-cycle engine configured as above, as a result that the piston 3 ascends from the bottom dead center (the position near that shown in FIG. 6), the pressure in the crank chamber 20 starts to reduce while the pressure in the cylinder chamber 10 starts to rise, and the scavenging ports 51 and the exhaust port 13 close in order. In this situation, as shown in FIG. 5, in the position near the lower position of the top dead center, the air intake port 11 is in a state in which it is connected to the scavenging flow passages 50 via the channel 30 and the scavenging ports 51, and the mixture intake port 12 opens to be connected to the crank chamber 20. As a result, air is absorbed into the crank chamber 20 from the air intake port 11 through the channel 30 and the scavenging flow passages 50. In this situation, the mixture staying in the scavenging flow passages 50 is swept into the crank chamber 20 by air, and thus the scavenging flow passages 50 are filled with air. When the piston 3 further ascends and reaches the vicinity of the top dead center, the mixture in the cylinder 10 is ignited to explode, whereby the piston 3 starts to descend. The pressure in the crank chamber 20 then starts to rise, with the channel 30 being shut to the air intake port 11 and the scavenging port 51, and with the mixture intake port 12 being closed by the piston 3, the piston 3 descends, thereby increasing the pressure in the crank chamber 20. In this situation, even if the pressure in the crank chamber 20 rises, the air in the scavenging flow passages 50 is not blown back to the air intake port 11 side, or the mixture in the crank chamber 20 is not blown back to the carburetor side. Further, during the descent of the piston 3, the exhaust port 13 and the scavenging ports 51 are opened to the cylinder chamber 10 in order, and initially, combustion gas is discharged from the exhaust port 13. Subsequently, when the scavenging ports 51 are opened to the cylinder chamber 10, the air staying in the scavenging flow passages 50 bursts out into the cylinder 10 by the increased pressure in the crank chamber 20. Thereby, the residual combustion gas in the cylinder 10 is expelled into the atmosphere from the exhaust port 13 via a silencer. Subsequently, the mixture in the crank chamber 20 is charged into the cylinder chamber 10 through the scavenging flow passages 50. Again, the piston 3 starts to ascend from the bottom dead center to thereby start to reduce the pressure in the crank chamber 20 to close the scavenging ports 51 and the exhaust port 13 in order, thus repeating the above cycle once again. Accordingly, the reed valve conventionally used for taking air into the scavenging flow passages 50 is not required, therefore making it possible to reduce intake resistance of air and the number of components. Since the channel 30 is connected to the scavenging ports 51 when air is taken in, the mixture is prevented from remaining in the scavenging flow passages 50. Consequently, in the exhaust stroke, unlike the situation in which the lead valve is used as in the prior art, the combustion gas remaining in the cylinder chamber 10 can be expelled into the atmosphere by the air filling the scavenging flow passages 50, thus preventing the mixture from emitting into the atmosphere. Further, the channel 30 can be simultaneously formed when the piston 3 is manufactured by casting, and therefore providing the channel 30 does not increase a burden, for example, in the manufacturing thereof. In addition, since the reed valve is not used, failures relating to the reed valve are eliminated, thus making it possible to increase reliability. Further, the space for placing the lead valve is not needed, therefore making it easy to reduce the size. Furthermore, timing for introducing air can be controlled by means of the channel 30 provided at the piston 3, therefore making it possible to facilitate the optimization of the quantity of air and mixture. Next, a second embodiment of the present invention will be explained with reference to FIG. 7, FIG. 8, and FIG. 9. It should be noted that the elements common to those in the above first embodiment will be given the same numerals and symbols, and the explanation thereof will be omitted. A point in which the second embodiment differs from the first embodiment is that in the first embodiment, the air intake port 11 and the mixture intake port 12 are vertically arranged, but in the second embodiment, two of air intake ports 11A and 11B are laterally provided with the mixture intake port 12 between them. As in the first embodiment, the positions at which the air intake ports 11A and 11B are opened are provided at the positions lower than the positions at which the scavenging ports 51 are opened by the predetermined distance Lb in the axial direction of the cylinder 1 as shown in FIG. 9. The positions at which the scavenging ports 51 are opened are provided at the positions displaced by the angle of 90 degrees respectively in the circumferential direction as shown in FIG. 8, as in the first embodiment. A through-hole 31 for the mixture is formed in the piston 3, and two L-shaped channels 30A and 30B for air are also formed therein at the symmetric positions with the through-hole 31 between them. The mixture intake port 12 is connected to the crank chamber 20 via the through-hole 31 provided in the piston 3 in the intake stroke. The two left and right air intake ports 11A and 11B are connected to the L-shaped channels 30A and 30B respectively extending to the left and right along the outer perimeter of the piston 3 in the intake stroke. In the stratified scavenging two-cycle engine configured as above, the same operational effects as in the aforesaid first embodiment are provided. Next, a third embodiment of the present invention will be explained with reference to FIG. 10. It should be noted that the elements common to those in the aforesaid first embodiment will be given the same numerals and symbols, and the explanation thereof will be omitted. A point in which the third embodiment differs from the first embodiment is that in the first embodiment, the air intake port 11 and the mixture intake port 12 are vertically arranged, but in the third embodiment, the air intake port 11 is constructed by piping. The air intake port 11 is placed at the position lower than the positions, at which the scavenging ports 51 are opened, by the predetermined distance Lb, and is connected to the channel 30 extending laterally along the outer perimeter of the piston 3. Accordingly, the air intake port 11 can be provided at any position in the circumferential direction. In the stratified scavenging two-cycle engine configured as above, the same operational effects as in the aforesaid first embodiment are provided. Next, a fourth embodiment of the present invention will be explained with reference to FIG. 11. It should be noted that the elements common to the aforesaid third embodiment will be given the same numerals and symbols, and the explanation thereof will be omitted. A point in which the fourth embodiment differs from the first embodiment is that in the first embodiment, the air intake port 11 and the mixture intake port 12 are vertically arranged, and the mixture intake port 12 is opened and closed by the piston 3, but in the fourth embodiment, a mixture intake port 12A is directly connected to the crank chamber 20, and the back-flow of the supplied mixture is controlled by the known lead valve (the check valve) not illustrated. In the stratified scavenging two-cycle engine configured as above, the same operational effects as in the aforesaid first embodiment are also provided. In the stratified scavenging two-cycle engine configured as above, air can be supplied into the scavenging ports 51 via the channel 30 of the piston 3, therefore making it possible to fill at least the cylinder chamber 10 side of the scavenging flow passage 51 with air. It is preferable to push_the combustion gas out by filling the scavenging flow passages 50 or part of the cylinder chamber 10 connecting to the scavenging flow passages 50. Consequently, in the scavenging stroke, the combustion gas in the cylinder chamber 10 can be initially scavenged by air, thus making it possible to prevent the mixture staying in the scavenging flow passages 50 from discharging therefrom as in the case in which the conventional lead valve 80 is used. In each of the above embodiments, the passage connecting the air intake port 11 and the scavenging ports 51 is composed of the channel 30, but this passage may be, for example, in the form of a hole which is constructed to penetrate the piston 3 to connect the air intake port 11 and the scavenging ports 51. Further, the passage (the channel 30) is constructed to connect to with the scavenging flow passages 50 via the scavenging ports 51, but the passage (the channel 30) may be constructed to connect with some midpoint in the scavenging flow passages 50. Industrial Availability The present invention is useful as a stratified scavenging two-cycle engine, which takes in a mixture, and air for scavenging separately, is capable of doing away with emission of the mixture into the atmosphere and reducing intake resistance of air, and is less expensive with the number of components being reduced.

Claims: A stratified scavenging two-cycle engine including an air intake port (11), at least one scavenging port (51), and an exhaust port (13) which are connected to a cylinder chamber (10) of an engine, a mixture intake port (12) connected to a crank chamber (20), and at least one scavenging flow passage (50) for connecting the cylinder chamber (10) to the crank chamber (20), wherein the air intake port (11) is provided in a position a predetermined distance away from each scavenging port (51) toward the crank chamber (20) in an axial direction of the cylinder (1), each scavenging port (51) is displaced from the intake port (11) by a predetermined angle in the circumferential direction of the cylinder (1), and each scavenging port (51) is connected to the air intake port (11) through an L-shaped channel (30) formed on the outer perimeter of the piston (3) with a predetermined depth to thereby supply air to each scavenging flow passage (50) from the air intake port (11) through each scavenging port (51) at the time of intake stroke. The stratified scavenging two-cycle engine in accordance with claim 1, wherein a position of the piston (3) at which the air intake port (11) is opened by movement of the piston (3) is lower than a position of the piston (3) at which each scavenging port (51) is opened by movement of the piston (3) and at a time of scavenging stroke, when a top portion of the piston (3) opens the scavenging port (51), the air intake port (11) is already closed. The stratified scavenging two-cycle engine in accordance with Claim 1 or Claim 2, wherein the channel (30) connects each scavenging port (51) to the air intake port (11) and disconnects the mixture intake port (12) from each scavenging port (51), at the time of intake stroke. The stratified scavenging two-cycle engine in accordance with Claim 1 or Claim 2 or Claim 3, wherein the mixture intake port (12) is opened and closed by the piston (3).

Inventors: NOGUCHI MASANORI, NOGUCHI, MASANORI
Applicants: KOMATSU ZENOA KK, PETROLEUM ENERGY CENTER FOUND, KOMATSU ZENOAH CO., PETROLEUM ENERGY CENTER
Application year: 1998
Main classification: F02B25
IPC codes: F02F3, F02B25, F02F1, F02B75