Abstract:
To provide a two-cycle internal combustion engine capable of preventing the blow-by phenomenon to improve fuel economy and attain a high exhaust gas purifying performance, and increasing the responsiveness of fuel injection volume. In a two-cycle internal combustion engine, a chamber is disposed in scavenging passages for communicating a crank chamber to a combustion chamber, sealable control valves are respectively disposed in an inlet and an outlet of the chamber, and a fuel feeding system for the supply of fuel into the chamber is provided. The chamber is communicated to one scavenging passage out of a plurality of parallel scavenging passages. The combustion chamber side control valve disposed at an outlet of the chamber on the downstream side of the crank case side control valve provided at an inlet of the chamber, is positioned at the bottom portion of a scavenging passage communicated to the chamber.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a two-cycle internal combustion engine capable of preventing a blow-by phenomenon of a mixture in a combustion chamber thereby improving fuel economy and attaining better exhaust gas purifying performance. 
     2. Description of Background Art 
     In a related art, fuel supplied by a carburetor to a two-cycle internal combustion engine is mixed with intake air and the resulting mixture is sucked into a crank chamber and is then supplied into a combustion chamber through a scavenging port. In this case, since the timing of the opening an exhaust port is set earlier than that of the scavenging port (an upper edge of the exhaust port is higher than that of the scavenging port), the mixture fed into the combustion chamber is discharged into an exhaust passage, thus easily causing a so-called blow-by phenomenon. 
     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 the 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 is connected to the combustion chamber through an air passage, a solenoid valve is disposed in the lower end of the air passage, and a fuel injection valve capable of injecting fuel towards 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 the crankcase and the cylinder block, an intake control valve is interposed between a crank chamber and said chamber, a scavenging control valve is interposed between said chamber and a combustion chamber in a cylinder, and a fuel injection valve is provided for injection of fuel toward said chamber. 
     In the two-cycle internal combustion engine described in Japanese Patent Laid-open No. Hei 3-100318, with respect to the fuel injected from the fuel injection valve, part of the fuel deposited in the air passage falls by gravity, entering the crank chamber through a check valve disposed at the bottom of the air passage, and flows in a state wherein the fuel is atomized into the combustion chamber from the crank chamber through another scavenging port. As a result, it is difficult to sufficiently prevent the blow-by phenomenon and to obtain a stable combustion. Further, it is difficult to suitably control the amount of fuel fed into the combustion chamber, resulting in degraded responsiveness. 
     In the two-cycle internal combustion engine described in Japanese Patent Laid-open No. Hei 5-302521, all of the intake air in the crank chamber is introduced through the intake control valve and is mixed with the fuel introduced into the chamber through the fuel injection valve. The resulting mixture flows into the combustion chamber through the scavenging control valve. Accordingly, the two-cycle internal combustion engine is not configured so as to permit only air to flow from the crank chamber 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 opened to the lower portion of said chamber, the opening position thereof is not the lowest, so that the fuel injected into said chamber remains at the bottom of said chamber, thus giving rise to a problem that the amount of fuel fed into the combustion chamber cannot be accurately proportional to the amount of fuel injected from the fuel injection valve, resulting in degraded responsiveness. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     To provide an improved two-cycle internal combustion engine capable of solving the above-described problems, the present invention has been made wherein a two-cycle internal combustion engine is provided in which a control valve for operably controlling a communication passage which communicates a combustion chamber to a chamber contiguous to a fuel injection device is disposed in the communication passage and fuel is fed into said combustion chamber via said communication passage. The chamber contiguous to said fuel injection device is juxtaposed on a side of said combustion chamber and at least a control portion of said control valve is positioned lower than a communicating portion through which said communication passage is communicated to said chamber contiguous to said fuel injection device. 
     In the present invention, fuel is supplied into the combustion chamber through the communication passage, so that at the scavenging stroke, a burned gas in the combustion chamber can be positively discharged from the exhaust port by introducing air not mixed with fuel into the combustion chamber through the scavenging passage. As a result, it is possible to prevent blow-by of the mixture in the combustion chamber and to improve a scavenging efficiency due to air scavenging upon low load running. 
     Since at least the control portion of the control valve is positioned lower than the communicating portion at which the communication passage is communicated to the chamber contiguous to the fuel injection device, even if the fuel supplied from the fuel injection device into said chamber remains at a bottom portion of said chamber and/or at lower portions of both the communication passage communicated to said chamber and the control valve, the remaining fuel can be almost positively discharged into the combustion chamber. As a result, it is possible to suitably, responsively control the amount of the fuel supplied into the combustion chamber and hence to obtain a stable combustion state. 
     Further, since the chamber contiguous to the fuel injection device is juxtaposed on a side of the combustion chamber, the entire engine can be compactly formed into a substantially square shape in a side view, and thereby the vertical length of the entire engine can be shortened as compared with the case where said chamber is disposed over the combustion chamber. As a result, in the case of mounting the engine on a vehicle, it is possible to increase the degree of freedom in layout, and particularly, in the case of mounting the engine on a motorcycle, it is possible to eliminate an inconvenience in which the vehicular height and the minimum ground clearance become higher. 
     According to the present invention, the fuel supplied into the combustion chamber scavenges the remaining burned gas without occurrence of the blow-by thereof, with a result that the fuel can be positively fed into the combustion chamber. 
     According to the present invention, it is possible to easily control opening/closing of the control valve in synchronization with rotation of the crank shaft of the engine. 
     According to the present invention, a relatively small amount of air to be mixed with fuel supplied to the combustion chamber through the communication passage between the combustion chamber and the chamber contiguous to the fuel injection device can be positively sucked in said chamber, and also a pressure sufficient to feed the mixture into the combustion chamber through the communication passage can be obtained. 
     Further, the mixture becomes rich and the resulting rich mixture flows into the combustion chamber which has been sufficiently scavenged by the air (not mixed with fuel) passing another scavenging passage, so that it is possible to suitably adjust the concentration of the mixture in the combustion chamber and hence to obtain a desirable combustion state. This makes it possible to improve fuel economy and attain a high exhaust gas purifying performance. 
     In addition, at the beginning of scavenging, the valves (gate valve and control valve) at the outlet and the inlet of the chamber are closed and air not mixed with fuel is introduced from another scavenging port into the combustion chamber, to positively discharge the burned gas in the combustion chamber from the exhaust port. This is effective to prevent blow-by of the mixture introduced in the combustion chamber through the communication passage upon completion of scavenging (upon closing of the scavenging port). 
     According to the present invention, the filling of the chamber with air can be performed by making use of a high pressure in the combustion chamber, so that it is possible to obtain a positive, stable and high chamber pressure as compared with the filling using pressure in the crank chamber. 
     The mixture obtained by filling said chamber with air becomes rich, and the resulting rich mixture flows in the combustion chamber which has been sufficiently scavenged by the air (not mixed with fuel) passing through another scavenging passage, so that it is possible to suitably adjust the concentration of the mixture in the combustion chamber and hence to obtain a desirable combustion state. This makes it possible to improve fuel economy and attain a high exhaust gas purifying performance. 
     Since highly compressed air for forming the rich mixture is obtained from the combustion chamber, the control valve in the communication passage between the chamber and the combustion chamber can be provided in a cylinder wall near the combustion chamber. As a result, it is possible to shorten a length of a portion of the communication passage extending between the control valve and the mixture injection port, and hence to reduce the amount of a carrier gas (air) required to allow the fuel to pass through the communication passage. 
     In addition, the timing of the opening of the control valve must be set in consideration with respect to the time required for the fuel to pass through the communication passage and hence it must be set to be earlier for a higher rotational speed. However, according to the present invention, since the length of the portion of the communication passage between the control valve and the mixture injection port can be shortened as described above, a time required for the fuel to pass through the communication passage can be shortened and thereby an effect of the time factor on the setting of the timing of opening the control valve is reduced. As a result, it is possible to easily set the timing of the opening of the control valve, and hence to improve the suitability of the set-up timing of the opening of the control valve to rotational speeds over a wide range. 
     According to the present invention, it is possible to simplify the communication passage and hence to facilitate the manufacture thereof. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 illustrates a vertical sectional view of a first embodiment of the present invention; 
     FIG. 2 illustrates a vertical sectional view taken on line II—II in FIG. 1; 
     FIG. 3 illustrates a vertical sectional view taken on line III—III in FIG. 1; 
     FIG. 4 is an enlarged vertical sectional side view of a principal portion of FIG. 1; 
     FIG. 5 is a transverse sectional plan view taken on line V—V in FIG. 4; 
     FIG. 6 is a transverse sectional plan view taken on line VI—VI in FIG. 1; 
     FIG. 7 is a view as seen in the direction of arrows VII—VII in FIG. 1, wherein dotted portions indicate 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 vertical sectional front view of a cylinder block; 
     FIG. 10 is a transverse sectional plan view taken on 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 illustrates 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 illustrates a diagram showing a state of 90° before arrival at the top dead center (TDC); 
     FIG. 16 is a view illustrating an operational cycle of the embodiment; 
     FIG. 17 is a vertical sectional view of a second embodiment of the present invention; 
     FIG. 18 is a transverse sectional view taken on line XVIII—XVIII of FIG. 17; 
     FIG. 19 is an enlarged view of a principal portion of FIG. 17; 
     FIG. 20 is a vertical sectional side view showing a schematic configuration of a mechanism of transmitting power between a crank shaft and a rotary valve in the embodiment shown in FIG. 17; 
     FIG. 21 is a partial vertical sectional view of the rotary valve in the embodiment shown in FIG. 17; 
     FIG. 22 is a vertical sectional view taken on line XXII—XXII of FIG. 21; 
     FIG. 23 is a vertically sectional side view taken on line XXIII—XXIII of FIG. 21; 
     FIG. 24 is a view illustrating an operational cycle of the embodiment shown in FIG. 17; 
     FIG. 25 is a plan view of a cylinder block in a third embodiment of the present invention; 
     FIG. 26 is a vertical sectional side view taken on line XXVI—XXVI of FIG. 25, showing a state in which a cover is mounted; 
     FIG. 27 is a transverse sectional plan view taken on line XXVII—XXVII of FIG. 26, showing a state in which the cover is removed; 
     FIG. 28 is a vertical sectional side view taken on line XXVIII—XXVIII of FIG. 26; 
     FIG. 29 is a partly vertical sectional view of a rotary valve in the embodiment shown in FIG. 28; 
     FIG. 30 is a diagram showing a state at the time of compression/filling of air chamber/suction in the embodiment shown in FIG. 25; 
     FIG. 31 is a diagram, similar to FIG. 30, showing a state at the time of expansion; 
     FIG. 32 is a diagram, similar to FIG. 30, showing a state a t the time of fuel injection/exhaust/scavenging; 
     FIG. 33 is a diagram, similar to FIG. 30, showing a state at the time of exhaust/supply of mixture/suction; and 
     FIG. 34 is a view illustrating an operational cycle of the embodiment shown in FIG.  25 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will be described with reference to FIGS. 1 to  16 . 
     In a spark ignition type two-cycle internal combustion engine  1  of the present invention which is mounted on a motorcycle (not shown), a cylinder block  3  and a cylinder head  4  are sequentially stacked above a crank case  2  and integrally combined with each other. 
     A piston  6  is vertically slidably inserted into a cylinder bore  5  formed in the cylinder block  3 . The piston  6  and a crank shaft  8  are connected to each other by a connecting rod  7  in such a manner 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 the crank case  2 , with a throttle valve  11  and a reed valve  12  interposed in series in the intake passage  10 . The throttle valve  11  is connected to a throttle grip (not shown) through a connecting 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. 
     A total of four air supply scavenging passages  14  and  15 , two each on the right and left sides, are provided for communicating an upper portion of the cylinder bore  5  to a crank chamber  9  are formed in the crank case  2  and the cylinder block  3 . A rich mixture supply scavenging passage  18  is formed in a position closer to the rear portion of the vehicle body. A scavenging port  19  of the rich mixture supply scavenging passage  18  is located higher than scavenging ports  16  and  17  of the air supply scavenging passages  14  and  15 . The rich mixture supply scavenging passage  18  extends downwardly from the scavenging port  19  towards the intake passage  10  and is opened to a valve receiving hole  20  formed in the crank case  2  in parallel with the crank shaft  8 . A cylinder bore  5  side exhaust port  22 , formed in an exhaust passage  21 , is located opposite to the scavenging port  19 . 
     A generally hemispherical combustion chamber  13 , formed above the cylinder bore  5 , is offset towards the exhaust port  22 , and an ignition plug  23  is disposed in the combustion chamber  13 . 
     An air passage  24  is formed in the cylinder block  3  at a position directly above the intake passage  10 . Air introducing grooves  25  are formed in an underside of the cylinder block  3  which are brought in contact with the crank case  2 . The air introducing grooves  25  extend around an outer periphery of the cylinder bore  5  to communicate the air supply scavenging passages  14  positioned closer to the intake passage  10  to the air passage  24 . A reed valve  26  as a crank chamber side control valve is provided above the air passage  24 , and a partition wall  27  is formed in the cylinder block  3  on a side of the combustion chamber  13  so as to surround the reed valve  26 , with a cover  28  which is removably attached to an open edge of the partition wall  27 . The partition wall  27  and the cover  28  constitute a chamber  29 . 
     Air passages  30  extending in the vertical direction are formed in the cylinder block  3  on right and left sides of the air passage  24 , while a mixing chamber  31  is formed in the crank case  2 . The mixing chamber  31  is communicated to the air passages  30  through communication passages  32  provided at both right and left ends communicated to lower ends of the air passages  30 . A rotary valve  33  as a combustion chamber side control valve is rotatably inserted in the valve receiving hole  20 . The rotary valve  33  has a valve chamber  34  circumferentially opened at its longitudinal central portion and a fuel introducing passage  35  extending from the left end of the rotary valve  33  in such a manner so as to be in communication with the valve chamber  34 . The rotary valve  33  is, as will be described later, rotated in the same direction as that of the crank shaft (counterclockwise in FIGS.  1  and  4 ). 
     A fuel injection valve mounting hole  36  is formed in the crank case  2  and extends from the rear portion of the vehicle body towards the mixing chamber  31 . A fuel injection valve  37  is mounted in the fuel injection valve mounting hole  36 ; while a fuel injection valve mounting hole  38  extends from the left surface of the crank case  2  towards the fuel introducing passage  35  and communicates with the fuel introducing passage  35  formed in the crank case  2 . A fuel injection valve  39  is mounted in the fuel injection valve mounting hole  38 . 
     As shown in FIGS. 1 and 6, an exhaust control valve  40  is disposed near the exhaust port  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  into an arcuate shape in vertical cross-section and an exhaust passage member  42  is formed substantially into the same shape as that of the recess  41 . The exhaust control valve  40  is fitted in the gap  43 . A base portion of the exhaust control valve  40  is integrally mounted on rotating shafts  45  which 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 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 rotational speed of the spark ignition type two-cycle internal combustion engine  1  as independent variables, whereby the exhaust control valve  40  is rocked for selecting an optimal exhaust opening matched with the operating condition. 
     As shown in FIGS. 2,  3  and  11 , the crank case  2  is split into a left crank case  21  and a right crank case  2   r  with respect to split faces  46 . A main shaft  47  and a counter shaft  48 , positioned behind the crank shaft  8 , are rotatably supported by the left crank case  21  and the right crank case  2   r . A clutch  49  is mounted on the main shaft  47  and a train of speed change gears  50  are mounted on the main shaft  47  and counter shaft  48 . A driven gear  52  of the clutch  49  meshes with a drive gear  51  mounted at the right end of the crank shaft  8 . A chain sprocket  53  is integrally mounted at the left end of the counter shaft  48 , and an endless chain is provided between 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 operated and the clutch  49  is in an engaged state, a rotating force of the crank shaft  8  is transmitted to the chain sprocket  53  through the driving gear  51 , driven gear  52 , clutch  49 , speed change gears  50 , and counter shaft  48 . The rear wheel is thus rotated. 
     A balancer weight  54  for canceling a primary force of inertia of the crank shaft  8 , which is located at an obliquely upward position behind the crank shaft  8 , is rotatably supported by both the left and right crank cases  2   l ,  2   r . A balanced gear  55  is integrally mounted at the right end (in the figure) of the balancer weight  54 , and a driven gear  56  is integrally mounted on the right side of the rotary valve  33 . A drive gear  57  is provided on the crank shaft  8 , the balancer gear  55 , and the driven gear  56 , successively mesh with each other. Upon rotation of the crank shaft  8 , the balancer weight  54  is rotated in the direction opposed to the crank shaft  8  and the rotary valve  33  is rotated in the same direction as that of the crank shaft, each at the same speed as the rotational speed of the crank shaft  8 . 
     A drive gear  58  is fitted at the right end of the rotary valve  33  and a plunger type oil pump  59  is disposed adjacent to the right side of the rotary valve  33 . An intermediate gear  62  meshes with both the driving gear  58  and a driven gear  61  integrated with a drive shaft  60  of the oil pump  59 . The oil pump  59  is operated when the rotary valve  33  is rotated with rotation of the crank shaft  8 . 
     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 a 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  meshes with the drive 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 cooling water in the engine  1  is fed to a radiator (not shown) for cooling and is returned again into a cooling water passage  68  in the engine  1 . 
     In the illustrated spark ignition type two-cycle internal combustion engine  1  having the above configuration, when the crank shaft  8  is rotated counterclockwise in FIGS. 12 to  15  by means of a starter motor (not shown), the scavenging port  19  of the rich mixture supply scavenging passage  18  is closed by 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 ignition plug  23  is ignited at a predetermined timing before the top dead center. Further, with the 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  reaches the top dead center (TDC), the mixture in the combustion chamber  13  burns and expands and the crank chamber  9  is compressed with the descent of the piston  6  to compress the air present in the crank chamber  9 , as shown in FIG.  13 . 
     At a point in time after an elapse of 90° from the top dead center (TDC), which varies depending on a vertical position of the exhaust control valve  40 , the exhaust port  22  is opened to discharge the burned gas from the exhaust passage  21 . At almost the same time, the air compressed in the crank chamber  9  flows from the air supply scavenging passage  14  located near the intake passage  10  into the air passage  24  through the air introducing grooves  25  and is then introduced from the air passage  24  into the chamber  29  through the reed valve  26 . 
     At a point in time after an elapse of about 122° from the top dead center (TDC), the scavenging ports  16  and  17  are opened with the descent of the piston  6 , resulting in the air (not containing fuel) present in the crank chamber  9  flows from the ports  16  and  17  into the combustion chamber  13  through the air supply scavenging passages  14  and  15  to force out the burned gas present in the combustion chamber  13  toward the exhaust port  22 . In other words, the scavenging is effected with the 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 ). 
     At a time point after an elapse of about 58° from the bottom dead center (BDC), the scavenging ports  16  and  17  are closed with the ascent of the piston  6  to stop the scavenging performed by the inflow of the air from both the ports. At almost the same time, the valve chamber  34  of the rotary valve  33  is opened to both the mixing chamber  31  and the rich mixture supply scavenging passage  18 , so that the rich mixture present in the mixing chamber  31  passes through the rich mixture supply scavenging passage  18  and is supplied into the combustion chamber  13  through the scavenging port  19  to scavenge the remaining burned gas. Since the crank chamber  9  expands with the ascent of the piston  6 , air is introduced into the crank chamber  9  from the intake passage  10  through the reed valve  12 . In addition, the blow-by phenomenon of the mixture upon scavenging of the remaining burned gas only occurs to a small extent. 
     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 through the combustion chamber  13  and is discharged to the exhaust passage  21 , is prevented. This makes it possible to improve fuel economy and prevent air pollution caused by the unburned gas. 
     Since only air is supplied in the crank chamber  9 , 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, the oil is supplied from the oil pump  59  to the bearing portion of the crank shaft  8  and the sliding portion between the cylinder bore  5  and the piston  6  through the oil feed paths  63  and  64 . Accordingly, the two-cycle internal combustion engine  1  can be operated in a state with a reduction in frictional loss, while preventing white-smoking caused by the oil mixed in the fuel. 
     Since the rotary valve  33  is provided at a point lower than the communication passage  32  which is in communication with the chamber  29  and the mixing chamber  31 , even if the fuel supplied from the fuel injection valves  37 ,  39  into the mixing chamber  31  is stuck on an inner wall of the mixing chamber  31  and remains on a bottom portion of the mixing chamber  31  and in the valve chamber  34 , the remaining fuel can be almost positively discharged into the combustion chamber  13 . This makes it possible to, responsively control the supplied amount of the fuel into the combustion chamber  13  and hence to realize a stable combustion state. 
     Since the two fuel injection valves  37  and  39  are provided, not only a large amount of fuel can be injected but also a fine flow control of the fuel can be easily performed while maintaining the metering accuracy of the fuel at a high level. 
     Since the fuel injection valve  37  is disposed in a radial direction of the rotary valve  33  and the fuel injection valve  39  is disposed in the direction of the rotational axis of the rotary valve  33 , both the valves  37  and  39  can be disposed near the rotary valve  33  without interference therebetween and thereby the fuel can be positively injected into the valve chamber  34  of the rotary valve  33 . Further, the fuel can be prevented from remaining in the mixing chamber  31  by suppressing the amount of fuel injected from the fuel injection valve  37  and the sizes of the particles of the fuel injected from the fuel injection valves  37  and  39  can be made further reduced in size by collision of the particles of the fuel injected from the fuel injection valves  37 ,  39 . 
     Since the fuel injection valve  39  is disposed on the rotational axis of the rotary valve  33 , the fuel can be injected into the valve chamber  34  irrespective of the opening position of the valve chamber  34  in the rotary valve  33 . The fuel injected from the fuel injection valve  39  can be sufficiently mixed with the sucked air by allowing the fuel to intersect a radial air current passing through the valve chamber  34  in the rotary valve  33 , to thereby accelerate the atomization of the fuel. 
     Additionally, since the valve chamber  34  in the rotary valve  33  is in communication with the rich mixture supply scavenging passage  18  in a state after being previously in communication with the mixing chamber  31 , even if the fuel in a liquid state remains in the vicinity of the rotary valve  33 , such liquid fuel adheres on the rotary valve on the valve chamber  34  side and can be atomized by a current of air from the beginning of the next opening period. 
     Next, a second embodiment for carrying out the present invention will be described with reference to FIGS. 17 to  24 . 
     In this embodiment, the air passage  24  which was provided in the first embodiment is omitted. Air is compressed to a high pressure at the compression stroke and is sucked from the combustion chamber  13  into the chamber  29  through a pair of air communication passages  70 . In the chamber  29 , the air sucked in is mixed with fuel which is injected from fuel injection valves  83 ,  84  in the same manner as in the first embodiment, to form a rich mixture. The resulting rich mixture is supplied into the combustion chamber  13  through a rich mixture supply scavenging passage  73  upon completion of the scavenging stroke (see FIG.  24 ). 
     The filling of the chamber  29  with the high pressure air supplied from the combustion chamber  13  starts simultaneously with the compression stroke after completion of the exhaust stroke as shown in FIG. 24, and stops after stopping of the supply of the rich mixture into the combustion chamber  13 . The other operations are the same as those in the first embodiment, and therefore, the explanation thereof is omitted. 
     Next, there will be described a means of realizing, according to this embodiment, the timing of the filling of the chamber  29  with highly compressed air supplied from the combustion chamber  13  and of stopping the filling and the timing of the supply of a rich mixture from the chamber  29  into the combustion chamber  13  and stopping the supply of the rich mixture. 
     A control valve capable of commonly opening/closing the pair of the air passages  70  and the rich mixture supply scavenging passage  73  is interposed therein. Such a control valve is a rotary valve as in the first embodiment. 
     The rotary valve  76  is fitted in a valve receiving hole  82 , and the pair of the air passages  70  and the rich mixture gas supply scavenging passage  72  are opened in the valve receiving hole  81 . 
     As shown in FIGS. 21 to  23 , a cutout  77  having a specific length in the peripheral direction and a cutout  78  formed in a substantially crescent in cross-section for opening the pair of the air passages  70  and the rich mixture supply scavenging passage  73  are formed around an outer periphery of the rotary valve  76  at positions corresponding to the pair of the air passages  70  and the rich mixture supply scavenging passage  73 . These cutouts can realize the timing of the filling the chamber  29  with highly compressed air supplied from the combustion chamber  13  and of stopping the filling and the timing of the supply of a rich mixture from the chamber  29  into the combustion chamber  13  and stopping the supply of the rich mixture as shown in FIG.  24 . 
     A pulley  79  is integrally mounted at an axial end of the rotary valve  76 . As shown in FIG. 20, a cog belt  81  is provided between the pulley  79  and a pulley  80  integrally mounted on a balancer shaft  69 . When the spark ignition type two-cycle internal combustion engine  1  is operated, the crank shaft  8  is rotated and thereby the drive gear  57  integrally mounted on the crank shaft  8  meshes with the balanced gear  55 , so that the balancer weight  54  integrally mounted on the balancer shaft  69  is rotated in the reversed direction to the crank shaft  8  and the rotary valve  76  is also rotated in the reversed direction of the crank shaft  8 , each at the same rotational speed as that of the crank shaft  8 . 
     The cutout  77  as a fuel control portion of the rotary valve  76  is, as fully shown in FIG. 19, set to be positioned lower than a mixture suction port  75  as a communication portion of the rich mixture supply scavenging passage  73  to the chamber  29  when the cutout  77  controls the flow of the rich mixture passing through the rich mixture supply scavenging passage  73 . In addition, a mixture injection port  74  is provided as a communication portion of the rich mixture supply scavenging passage  73  to the combustion chamber  13 . Further, a highly compressed air suction port  71  is provided as a communication portion of the air passage  70  to the combustion chamber  13 . A highly compressed air injection port  72  is a communication portion for the air passage  70  and the chamber  29 . 
     In this embodiment, since the chamber  29  is filled with the air supplied from the combustion chamber  13  under the compression stroke through the pair of the air passages  70  as described above, a higher and nearly constant pressure in the combustion chamber  13  can be used for the filling the chamber  29  with the air. Accordingly, as compared with the filling of the chamber  29  with air using a pressure in the crank chamber  9  in the first embodiment, it is possible to obtain a positive, stable and high chamber pressure without being affected by a reduction in pressure due to a full-opening of a throttle valve accompanied by the increased engine speed. 
     Since the rich mixture obtained by filling the chamber  29  with air flows in the combustion chamber  13  which has been sufficiently scavenged with the air (not mixed with fuel) passing through the air supply scavenging passages  14 ,  15 , it is possible to fill the combustion chamber  13  with a mixture at a suitable concentration, and hence to realize a desirable combustion state. This is effective to improve fuel economy and attain a high exhaust gas purifying performance. Since highly compressed air for forming a rich mixture is obtained from the combustion engine  13 , the rotary valve  76  in the communication passage for communicating the chamber  29  to the combustion chamber  13  can be provided on a cylinder wall near the combustion chamber  13 , so that the length of the communication passage between the rotary valve  76  and the mixture injection port  74  can be shortened, thereby reducing an amount of the air required to allow the fuel to pass through the communication passage. 
     In addition, a time required for the fuel to pass through the communication passage can be shortened, to reduce the effect of the time factor on the setting of the timing for the opening of the rotary valve  76 . This makes it possible to easily set the timing of the opening of the rotary valve  76  and to improve the suitability of the set-up timing of the opening of the rotary valve  76  to rotational speeds over a wide range. 
     Since the cutout  77  of the rotary valve  76  opens and closes the rich mixture supply scavenging passage  79  and the portion of actually controlling the flow of the rich mixture (control portion of the rotary valve  76 ) is positioned lower than the mixture suction port  75 , even if the fuel injected from the fuel injection valves  83 ,  84  adheres on an inner wall of the chamber  29  and remains on a bottom portion of the chamber and the lowermost portion of the rich mixture supply scavenging passage  73  communicated with the chamber  29  and in the rotary valve  76 , the remaining fuel can be almost positively discharged into the combustion chamber  13 , with the result that the amount of the fuel supplied into the combustion chamber  13  can be suitably, responsively performed to result in a stable combustion state. 
     Next, a third embodiment for carrying out the present invention will be described with reference to FIGS. 25 to  34 . In this embodiment, a common communication  86  is provided in place of the pair of the air passages  70  and the rich mixture supply scavenging passage  73  in the second embodiment, and correspondingly, only one cutout  90  of a rotary valve  89  is provided as shown in FIG.  29 . 
     Accordingly, the filling of the chamber  29  with highly compressed air supplied from the combustion chamber  13  and the supply of a rich mixture from the chamber  29  into the combustion chamber  13  are both performed through the common communication passage  86  when the communication passage  86  is opened through the cutout  90  of the rotary valve  89 . The pressure for the filling of the highly compressed air and the supply of the rich mixture into respective chambers are based on a pressure balance between both the chambers. 
     As shown in FIG. 34, the timing of the stopping and the filling of the chamber  29  with highly compressed air supplied from the combustion chamber  13  and the timing of the supply of the rich mixture from the chamber  29  into the combustion chamber  13  and of the stopping of the supply of the rich mixture are the same as those in the second embodiment. 
     On the contrary, the timing of the starting of the filling of the chamber  29  with the highly compressed air supplied from the combustion chamber  13  is different from that in the second embodiment in that it corresponds to the time when the pressure balance in the combustion chamber  13  is equalized to that of the chamber  29  and the supply of the rich mixture from the chamber  29  to the combustion chamber  13  is stopped due to the fact that the communication passage  86  is continuously in communication from the starting of the supply of the rich mixture from the chamber  29  into the combustion chamber  13  to the stopping of the filling of the chamber  29  with the highly compressed air supplied by the combustion chamber  13  by the action of the cutout  90  having the specific length in the circumferential direction of the rotary valve  89 . 
     Since the port  87 , as the communication portion of the communication passage  86  to the combustion chamber  13 , is enlarged in its longitudinal length and also has a cross-section with both sides thereof largely expanded towards the combustion chamber  13  in order to facilitate the suction of a sufficient amount of the highly compressed air into the chamber  29  (see FIGS. 26,  28 ). 
     In this embodiment, the communication passage  86  includes a communication passage  86   a , an obliquely, upwardly extending communication passage  86   b , and an obliquely, upwardly extending communication passage  86   c  bend perpendicularly from the communication passage  86   b . The communication passages  86   a ,  86   b  are respectively disposed on the combustion chamber  13  side and the chamber  29  side with respect to the control portion of the rotary valve  89 . An end portion of the communication passage  86   c  is in communication with the chamber  29  through an opening  88 . 
     The fuel injected from two fuel injection valves (not shown) passes through the right and left portions of the communication passage  86   b  and is mixed with highly compressed air sucked from the chamber  29  through the communication passage  86   c , to form a rich mixture. The resulting rich mixture is injected into the combustion chamber  13  through the control portion of the rotary valve  89 . 
     Accordingly, since the control portion of the rotary valve  89  is positioned lower than the portion of the communication passage  86   c  bend perpendicularly to the communication passage  86   b  (the portion at which the air sucked from the chamber  29  collides with the injected fuel) as well as the opening  88 , even if the fuel remains in the communication passage  86   b  and in the control portion of the rotary valve  89 , the remaining fuel is almost positively discharged into the combustion chamber  13  by the strong mixed air flow moved by an intermittent opening/closing of the rotary valve  89 . As a result, it is possible to suitably, responsively control the amount of the fuel supplied into the combustion chamber  13 , and hence to obtain a stable combustion state. 
     The detailed explanation of the various states of the engine at points of compression/filling of the air chamber/suction, expansion, fuel injection/exhaust/scavenging, and exhaust/supply of mixture/suction shown in FIGS. 30 to  33  is omitted. 
     In addition, an opening  88  is provided as a communicating portion of the communication passage  86  to the chamber  29 . A receiving hole  91  is provided for the rotary valve  89 , and  92  is a fuel injection valve mounting hole. 
     According to the embodiment having the above configuration, it is possible to simplify the structure of the highly compressed air passage and the rich mixture supply scavenging passage as well as the structure of the control valve, and hence to facilitate the manufacture thereof. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.