Two-cycle internal combustion engine

Abstract: It is intended to provide a two-cycle internal combustion engine capable of preventing the blow-by phenomenon, thereby improving both fuel economy and exhaust purifying performance, and superior in the responsivity of fuel injection volume. [Means for Attaining the Subject] In a two-cycle internal combustion engine wherein a chamber (29) is disposed in a scavenging passages which provide communication between a crank chamber (9) and a combustion chamber (6), sealable control valves (26) and (33) are disposed in an inlet and an outlet, respectively, of the chamber (29), and a fuel feeding system (37) for the supply of fuel into the chamber (29) is provided, the present invention is characterized in that the chamber (29) is brought into communication with one scavenging passage (18) out of a plurality of parallel scavenging passages, and the control valve (33) disposed in the chamber outlet, which is on the combustion chamber side and on a scavenging downstream side, is positioned at the bottom part of the scavenging passage (18) communicating with the chamber (31) with respect to the control valve (26) disposed in the chamber inlet which is on the crank chamber side.

Description: The present invention relates to a two-cycle internal combustion engine capable of preventing a blow-by phenomenon of an air-fuel mixture in a combustion chamber to improve fuel economy and attain a high exhaust gas purifying performance. In a conventional two-cycle internal combustion engine, fuel supplied by a carburetor, etc. is mixed with intake air and the resulting mixture is introduced into a crank chamber, then is supplied into a combustion chamber through a scavenging port. Since the timing of opening of an exhaust port is set earlier than that of the scavenging portion (the upper edge of the exhaust port is higher than that of the scavenging port), the mixture fed into the cumbustion chamber is discharged to an exhaust passage, thus causing what is called a blow-by phenomenon easily. Although the blow-by phenomenon is suppressed by an exhaust pulsating effect in an exhaust chamber, it is difficult for the suppression to cover the whole operation range, resulting in that both fuel economy and exhaust purifying performance are affected. In an effort to solve the above-mentioned problem, two-cycle internal combustion engines have been proposed in Japanese Patent Laid-open Nos.Hei 3-100318 and Hei 5-302521. In the two-cycle internal combustion engine disclosed in Japanese Patent Laid-open No. Hei 3-100318, a high pressure chamber is connected to a crank chamber through a check valve, the high pressure chamber and a combustion chamber are interconnected through an air passage, a solenoid valve is disposed in the lower end of the air passage, and a fuel injection valve capable of ejecting fuel toward the combustion chamber is provided at the upper end of the air passage. In the two-cycle internal combustion engine disclosed in Japanese Patent Laid-open No. Hei 5-302521, a chamber is formed in a position adjacent to both crank case and cylinder block, an intake control valve is interposed between a crank chamber and the said chamber, a scavenging control valve is interposed between the said chamber and a combustion chamber in a cylinder, and a fuel injection valve is provided for the ejection of fuel toward the said chamber. In the two-cycle internal combustion engine described in Japanese Patent Laid-open No. Hei 3-100318, of the fuel ejected from the fuel injection valve, the portion deposited on the air passage falls by gravity, then enters the crank chamber through a check valve disposed at the bottom of the air passage, and flows without being atomized into the combustion chamber from the interior of the crank chamber through another scavenging port. Therefore, the blow-by phenomenon is not prevented to a satisfactory extent and it is difficult to effect stable combustion; besides, the amount of fuel fed into the combustion chamber is not appropriately controlled and thus the responsivity is poor. WO-A-9504212 discloses a two-cycle internal combustion engine according to the preamble of claim 1. The present invention relates to an improvement of a two-cycle internal combustion engine which has overcome the above-mentioned problem. In a two-cycle internal combustion engine wherein a chamber is formed within a scavenging passage communicating between a crank chamber and an upper portion of a cylinder bore, sealable control valves are disposed in an inlet and an outlet, respectively, of said chamber, wherein fuel feed system is provided for the supply of fuel into said chamber, and wherein said chamber is communicated with one of a plurality of parallel scavenging passages, the invention is characterized in that the control valve disposed in the chamber outlet, which is on the combustion chamber side and on a scavenging downstream side, is positioned on the bottom part of a section of the scavenging passage including said chamber with respect to the control valve disposed in the chamber inlet. In the present invention, as mentioned above, a chamber is included in one of a plurality of parallel scavenging passages, sealable control valves are disposed in an inlet and an outlet, respectively, of said chamber, and a fuel feed system is provided for the supply of fuel into said chamber. Therefore, in the initial stage of scavenging, the inlet and outlet control valves in said chamber are closed, allowing fresh air not containing fuel to be introduced into the combustion chamber through another scavenging passage, whereby the gas after combustion in the combustion chamber can be discharged positively from an exhaust port and hence it is possible to prevent the blow-by phenomenon of the air-fuel mixture in the combustion chamber. Besides, when the engine is operating at a low load, the scavenging efficiency can be improved by air scavenging. In the two-cycle internal combustion engine described in Japanese Patent Laid-open No. Hei 5-302521, the whole of the intake air in the crank chamber is introduced into through the intake control valve into the chamber adjacent to both crank chamber and cylinder block, then is mixed therein with the fuel which has been introduced into the said chamber through the fuel injection valve, and the whole of the resulting mixture flows into the combustion chamber through the scavenging control valve. Thus, the two-cycle internal combustion engine in question is not constructed so as to permit only air to flow from the interior of the crank case into the combustion chamber through a scavenging port, and hence the blow-by phenomenon is unavoidable. Further, although an upstream side of the scavenging control valve is open to the lower portion of the said chamber, the opening position is not the lowest position, so that the fuel injected into the said chamber stays at the bottom of the chamber, thus giving rise to the problem that the amount of fuel fed into the combustion chamber cannot accurately be proportional to the amount of fuel injection and thus the responsivity is low. In the present invention, the combustion chamber-side control valve disposed in the chamber outlet, which is on the scavenging downstream side, is positioned at the lowest part of the scavenging passage with both control valves interposed therein, with respect to the crank chamber-side control valve, so even if the fuel fed into the said chamber from the fuel feed system is deposited on the inner wall of the chamber and stays at the lowest part of the scavenging passage including the chamber, substantially the whold of the stagnant fuel can be discharged positively into the combustion chamber by a violent scavenging stream induced by intermittent opening and closing motions of the combustion chamber-side control valve located at the bottom of the scavenging passage, whereby it is possible to ensure a stable combustion state. In the present invention, moreover, the fuel fed into the said chamber from the fuel feed system is mixed with a relatively small amount of fresh air which has been supplied into the said chamber, to form a rich mixture, and this mixture flows into the combustion chamber which has been scavenged thoroughly with fuel-free air after passage through another scavenging passage. Therefore, the mixture thus introduced into the combustion chamber has an appropriate concentration and assures a satisfactory combustion, whereby there are attained both high level of fuel economy and high exhaust purifying performance. An embodiment of the present invention illustrated in the drawings will be described hereinunder. Fig. 1 is a longitudinal sectional view of an embodiment of the present invention; Fig. 2 is a longitudinal sectional view taken along line II-II in Fig. 1; Fig. 3 is a longitudinal sectional view taken along line III-III in Fig. 1; Fig. 4 is an enlarged longitudinal sectional view of a principal portion of Fig. 1; Fig. 5 is a plan view in transverse section taken along line V-V in Fig. 4; Fig. 6 is a plan view in transverse section taken along line VI-VI in Fig. 1; Fig. 7 is a view as seen in the direction of arrows VII-VII in Fig. 1, the dotted portions indicating faces of abutment with the crank case; Fig. 8 is a view as seen in the direction of arrows VIII-VIII in Fig. 1; Fig. 9 is a front view in longitudinal section of a cylinder block; Fig. 10 is a plan view in transverse section taken along line X-X in Fig. 9; Fig. 11 is a view as seen in the direction of arrows XI-XI in Fig. 1; Fig. 12 is a diagram showing a state of 45° before arrival at the top dead center (TDC); Fig. 13 is a diagram showing a state of 45° after passing the top dead center (TDC); Fig. 14 is a diagram showing a state of arrival at the bottom dead center (BDC); Fig. 15 is a diagram showing a state of 90° before arrival at the top dead center (TDC); and Fig. 16 is an explanatory view illustrating an operation cycle of this embodiment. In a spark ignition type two-cycle internal combustion engine 1 embodying the present invention, which is mounted on a two-wheeled motor vehicle (not shown), a cylinder block 3 and a cylinder head 4 are successively stacked above a crank case 2 and combined together integrally. A piston 6 is inserted vertically slidably into a cylinder bore 5 formed in the cylinder block 3. The piston 6 and a crank shaft 8 are interconnected through a connecting rod 7 so that the crank shaft 8 is rotated with ascent and descent of the piston 6. An intake passage 10 extending from the back to the front of the vehicle body is connected to an intake passage 10 in the crank case 2, with a throttle valve 11 and a reed valve 12 being disposed within the intake passage 10. The throttle valve is connected to a throttle grip (not shown) through a connection means (not shown) in such a manner that the opening of the throttle valve 11 is increased by twisting the throttle grip in one direction. Further, a total of four, two each on the right and left sides, of scavenging passages 14 and 15 which provide communication between the upper portion of the cylinder bore 5 and a crank chamber 9 are formed in the crank case 2 and the cylinder block 3. A scavenging passage section 18 for the supply of rich mixture is formed in a position closer to the rear portion of the vehicle body and in which position a scavenging opening 19 thereof is located higher than scavenging openings 16 and 17 of the scavenging passages 14 and 15 for the supply of air. The scavenging passage section 18 for the supply of rich mixture extends downward from the scavenging opening 19 toward the intake passage 10 and is opened to a valve receiving hole 20 formed in the cylinder block 3 in parallel with the crank shaft 8. A cylinder bore 5-side exhaust opening 22 formed in the exhaust passage 21 is located in a position opposed to the scavenging opening 19. Besides, a generally semispherical combustion chamber 13 formed above the cylinder bore 5 is offset toward the exhaust opening 22, and a sparking plug 23 is disposed in the combustion chamber 13. In the cylinder block 3, an air passage 24 is formed in a position just above the intake passage 10. In the underside of the cylinder block 3 which is in abutment with the crank case 2 there are formed air introducing slots 25 extending around the outer periphery of the cylinder bore 5 to provide communication between the scavenging passage 14 for the supply of air positioned closer to the intake passage 10 and the air passage 24. Above the air passage 24 is disposed a reed valve 26 as a crank chamber-side control valve, and a partition wall 27 is formed on the cylinder block 3 so as to enclose the reed valve 26, with a cover 28 being attached removably to an opening edge of the partition wall 27. The partition wall 27 and the cover 28 constitute a chamber 29. In the cylinder block 3, moreover, vertically directed air passages 30 are formed on both right and left sides of the air passage 24, while in the crank case 2 is formed a mixing chamber 31 which is in communication at both right and left ends thereof with the lower ends of the air passages 30 and centrally communicated through communication holes 32. In the valve receiving hole 20 is rotatably disposed a rotary valve 33 as a combustion chamber-side control valve. In the rotary valve 33 are formed a valve chamber 34 which is circumferentially open centrally in the longitudinal direction and a fuel introducing passage 35 extending from the left end of the rotary valve 33 and communicating with the valve chamber 34. The rotary valve 33 is rotated in the same rotating direction (counterclockwise in Figs.1 and 4). In the crank case 2, moreover, is formed a fuel injection valve mounting hole 36 from the rear portion of the vehicle body toward the mixing chamber 31, into which hole 36 is mounted a fuel injection valve 37. Further, from the left side face of the crank case 2 toward the fuel introducing passage 35 is formed a fuel injection valve mounting hole 38 which is in communication with the fuel introducing passage 35, with a fuel injection valve 39 being fitted in the hole 38. As shown in Fig. 6, an exhaust control valve 40 is disposed near the exhaust opening 22 of the exhaust passage 21. A gap 43 having a substantially uniform width is formed between a recess 41 formed in the cylinder block 3 and having an arcuate longitudinal section and an exhaust passage member 42 formed substantially in the same longitudinal sectional shape, and the exhaust control vale 40 is fitted in the gap 43. A base portion of the exhaust control valve 40 is integrally mounted to rotating shafts 45 are rotatably supported by both the exhaust passage member 42 and an exhaust pipe mounting member 44 integrally combined with the exhaust passage member 42. The rotating shafts 45 are each connected to an exhaust control servo-motor (not shown). The exhaust control servo-motor operates in accordance with a control signal outputted from a CPU (not shown) on the basis of an exhaust opening map using the degree of opening of the throttle valve 11 and the number of revolutions of the spark ignition type two-cycle internal combustion engine 1 as independent variables, whereby the exhaust control valve 40 is rocked so as to give an optimal exhaust opening conforming to the operating condition. As shown in Figs.3 and 11, the crank case 2 is split right and left into a left crank case 2l and a right crank case 2r with split faces 46 as a boundary. In positions behind the crank shaft 8 a main shaft 47 and a counter shaft 48 are supported rotatably by the left crank case 2l and the right crank case 2r. A clutch 49 is mounted on the main shaft 47 and a group of speed change gears 50 are mounted on the main shaft 47 and counter shaft 48. A driven gear 52 of the clutch 49 is brought into mesh with a driving gear 51 mounted on the right end of the crank shaft 8. A chain sprocket 53 is integrally mounted on the left end of the counter shaft 48, and an endless chain is entrained on both the chain sprocket 53 and a chain sprocket mounted to a rear wheel (not shown). When the spark ignition type two-cycle internal combustion engine 1 is started and the clutch 49 is set to an engaged state, the rotating force of the crank shaft 8 is transmitted via driving gear 51, driven gear 52, clutch 49, speed change gears 50 and counter shaft 48 to the chain sprocket 53, whereby the rear wheel is rotated. In an obliquely upward position behind the crank shaft 8, a balancer weight 54 for cancelling a primary force of inertia of the crank shaft 8 is supported rotatably by both left and right crank cases 2l,2r. A balancer weight 55 is integrally mounted at the right end of the balancer weight 54, and a driven gear 56 is integrally mounted on the right-hand portion of the rotary valve 33. A driving gear 57 on the crank shaft 8, as well as the balancer gear 55 and driven gear 56, are successively brought into mesh with one another. Upon rotation of the crank shaft 8 the balancer weight 54 is rotated in the direction opposite to the crank shaft 8 and the rotary valve 33 is rotated in the same direction as the crank shaft, each at the same speed as the rotational speed of the crank shaft. Further, a driving gear 58 is fitted on the right end of the rotary valve 33, a plunger type oil pump 59 is disposed adjacent the right-hand side of the rotary valve 33, and an intermediate gear 62 is in mesh with both the driving gear 58 and a driven gear 61 which is integrated with a drive shaft 60 of the oil pump 59. When the rotary valve 33 is rotated with rotation of the crank shaft 8, the oil pump 59 is operated. Oil from the oil pump 59 is supplied to a bearing portion of the crank shaft 8 through an oil feed path 63 (see Fig. 2) and is also supplied through an oil feed path 64 (see Fig. 10) to the sliding portion between the cylinder bore 5 and the piston 6. As shown in Fig. 2, a driven gear 67 integrated with a rotating shaft 66 of a water pump 65 is in mesh with the driving gear 51 mounted at the right end of the crank shaft 8. Upon start-up of the spark ignition type two-cycle internal combustion engine 1, the water pump 65 is rotated, so that the cooling water in the engine 1 is fed to a radiator (not shown) for cooling and again returns into a cooling water passage 68 in the engine 1. The illustrated spark ignition type two-cycle internal combustion engine 1 is constructed as above, so when the crank shaft 8 is rotated counterclockwise in Figs.12 to 15 by means of a starter motor (not shown), the scavenging opening 19 of the scavenging passage section 18 for the supply of a rich mixture is closed with the piston 6 at a time point of 75° ahead of the top dead center (TDC), so that the combustion chamber 13 is compressed, and the sparking plut 23 is ignited at a predetermined timing ahead of the top dead center. Further, with ascent of the piston 6, the crank chamber 9 continues to expand and the intake of air is continued (see Fig. 12). After the piston 6 has reached the top dead center (TDC), as shown in Fig. 13, the mixture in the combustion chamber 13 burns and expands, and as the piston descends, the crank chamber 9 is compressed to compress the air present therein. The thus-compressed air flows from the scavenging passage 14 for the supply of air located near the intake passage 10 into the air passage 24 through the air introducing slots 25 and then from the interior of the air passage 24 into the chamber 29 through the reed valve 26. Further, at a time point elapsed 90° from the top dead center (TDC), which time point varies depending on a vertical position of the exhaust control valve 40, the exhaust opening 22 is opened and the gas after combustion is discharged from the exhaust passage 21. Then, at a time point of about 122° from the top dead center (TDC) the scavenging openings 16 and 17 are opened with descent of the piston 6, resulting in that the air (free of fuel) present in the crank chamber 9 flows from the openings 16 and 17 into the combustion chamber 13 through the scavenging passages 14 and 15 for the supply of air, whereby the gas after combustion present in the combustion chamber 13 is forced out toward the exhaust opening 22, allowing scavenging to be effected with air alone. At the same time, fuel is injected into the mixing chamber 31 from the fuel injection valves 37 and 39 to produce a rich mixture (see Fig. 14). Next, at a time point of about 58° elapsed from the bottom dead center (BDC) the scavenging openings 16 and 17 are closed with ascent of the piston 6 to stop the scavenging performed by the inflow of air from both openings. At the same time, the valve chamber 34 in the rotary valve 33 is opened to both mixing chamber 31 and scavenging passage section 18 for the supply of a rich mixture, so that the rich mixture presenting the mixing chamber 31 passes through the interior of the scavenging passage section 18 and is supplied into the combustion chamber 13 through the scavenging opening 19. Besides, since the crank chamber 9 expands with ascent of the piston 6, air is introduced into the crank chamber from the intake passage 10 through the reed valve 12. Thus, in the spark ignition type two-cycle internal combustion engine 1, since scavenging with only air is performed in the initial stage of scavenging, the blow-by phenomenon that the mixture passes as it is through the combustion chamber 13 and is discharged to the exhaust passage 21, is prevented and it is thereby possible to improve fuel economy and prevent air pollution caused by the gas not having subjected to combustion. Even if the bearing portion of the crank shaft 8 and the sliding portion between the cylinder bore 5 and the piston 6 are not lubricated with the oil mixed in the fuel, which is ascribable to the supply of only air into the crank chamber 9, oil is supplied from the oil pump 59 to the crank shaft bearing portion and the cylinder-piston sliding portion through the oil feed paths 63 and 64, the two-cycle internal combustion engine 1 can perform operation in a diminished state of frictional loss and it is also possible to prevent white-smoking caused by the oil mixed in the fuel. Moreover, since two fuel injection valves 37 and 39 are provided, not only it is possible to eject a large amount of fuel but also it is possible to easily make a fine flow control while maintaining the metering accuracy at a high level. Further, since the fuel injection valve 37 is disposed in the radial direction of the rotary valve 33 and the fueld injection valve 39 disposed in the direction of the rotational axis of the rotary valve, both valves 37 and 39 can be disposed near the rotary valve 33 without mutual interference and therefore the fuel injection into the valve chamber 34 of the rotary valve 33 can be ensured. Moreover, it is possible to suppress the amount of fuel ejected from the fuel injection valve 37 and thereby prevent the fuel from remaining in themixing chamber 31. Besides, it is possible to let the particles of fuel ejected from the fuel injection valves 37 and 39 collide with one another and thereby attain a further atomization of the fuel. Additionally, since the fuel injection valve 39 is disposed on the rotational axis of the rotary valve 33, fuel can be injected into the valve chamber 34 irrespective of the opening position of the valve chamber 34 in the rotary valve 33, and fuel can be ejected from the fuel injection valve 39 so as to intersect a radial air current passing through the valve chamber 34 in the rotary valve 33, thereby permitting the fuel to be mixed with the intake air to a sufficient extent. Consequently, it is possible to accelerate the atomization. Further, in a precommunicated state with the interior of the mixing chamber 31 the valve chamber 34 in the rotary valve 33 comes into communication with the scavenging passage section 18 for the supply of a rich mixture, so even if fuel in a liquid state remains in the vicinity of the rotary valve 33, such liquid fuel adheres to the valve chamber 34 side in the rotary valve 33 and can be atomized by a current of air from the beginning of the next opening period. It is intended to provide a two-cycle internal combustion engine capable of preventing the blow-by phenomenon, thereby improving both fuel economy and exhaust purifying performance, and superior in the responsivity of fuel injection volume. In a two-cycle internal combustion engine wherein a chamber 29 is formed within a scavenging passage 14,25,24,18 which provides communication between a crank chamber 9 and an upper portion of a cylinder bore 5, sealable control valves 26 and 33 are disposed in an inlet and an outlet, respectively, of the chamber 29, wherein a fuel feeding system 37 for the supply of fuel into the chamber 29 is provided and wherein the chamber 29 is brought into communication with one scaventing passage 14, 25, 24, 18 out of a plurality of parallel scavenging passages 14; 15; 14,25, 24,18, the invention is characterized in that the control valve 33 disposed in the chamber outlet, which is on the combustion chamber side and on a scaventing downstream side, is positioned at the bottom part of a section 18 of the scavenging passage 14,25,24,18 including the chamber 29 with respect to the control valve 26 disposed in the chamber inlet which is on the crank chamber side.

Claims: A two-cycle internal combustion engine wherein a chamber (29) is formed within a scavenging passage (14,25,24,18) communicating between a crank chamber (9) and an upper portion of a cylinder bore (5), with a sealable control valve (26,33) being disposed in an inlet and an outlet, respectively, of said chamber (29), wherein a fuel feed system (37) is provided for the supply of fuel into said chamber (29) and wherein said chamber (29) is communicated with one (14,25,24,18) of a plurality of parallel scavenging passages (14;15; 14,25,24,18), characterized in that the control valve (33) disposed in the chamber outlet is positioned on the bottom part of a section (18) of the scavenging passage (14,25,24,18) including said chamber (29) with respect to the control valve disposed in the chamber inlet. A two-cycle internal combustion engine according to claim 1, wherein a fuel feed system for the supply, of atomized fuel is disposed in the vicinity of the combustion chamber-side control valve (33).

Inventors: ASAI MASAHIRO, ISHIBASHI YOICHI, ASAI, MASAHIRO, ISHIBASHI, YOICHI, Asai, Masahiro, Honda Gijutsu Kenkyusho, Ishibashi, Yoichi, Honda Gijutsu Kenkyusho
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1996
Main classification: F02B25
IPC codes: F02B75, F02B25, F02M69, F02M67, F02F1, F02B61