Abstract:
The present invention facilitates proper control of the scavenging air and fuel-air mixture for a stratified scavenging two-cycle engine that is based on a crankcase compression/scavenging method, using any carburetor. The present invention includes a drive member, which rotates based on an accelerator operation, installed on the air valve of the air passage, wherein the drive member is movable through angular reciprocal movements. A slave member, which constantly contacts a cam provided on the drive member is installed on the throttle valve of the carburetor, and wherein the slave member is movable through linear reciprocal movements. A fuel flow-rate controlling mechanism works in cooperation with these linear reciprocal movements. The carburetor can be freely designed without regard to the orientation of the air passage and a looseness- and play-free interlocking mechanism having a cam and a spring can maintain the air valve and the throttle valve in a proper opening relationship, thereby stably operating the engine without upsetting the air/fuel ratio.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of co-pending application Ser. No. 10/193,741 filed Jul. 9, 2002, which application is fully incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a crankcase compression/scavenging method and, more particularly, to a scavenging air/fuel-air mixture control device for a stratified scavenging two-cycle engine that is designed to first sweep out the combustion gas by introducing air into the combustion chamber during scavenging and then to introduce a fuel-air mixture.  
         BACKGROUND OF THE INVENTION  
         [0003]    For a two-cycle engine in which a fuel-air mixture inside a combustion chamber ignites and explodes, pushing down the piston, the exhaust port first opens to begin exhausting the combustion gas, and then the scavenging port opens, introducing the fuel-air mixture supplied to the crankcase into the combustion chamber to exhaust the remaining combustion gas, a known alternative includes an air passage that is connected to the scavenging passage linking the crankcase and the combustion chamber. When the scavenging port opens, the scavenging air in the air passage is first introduced into the combustion chamber to exhaust the combustion gas, and then the fuel-air mixture in the crankcase is introduced into the combustion chamber via the scavenging passage.  
           [0004]    The air valve for controlling the scavenging air flow rate, provided in the air passage, and the throttle valve for controlling the output of the carburetor, which is a fuel-air mixture formation means provided in the fuel-air mixture passage connected to the crankcase, must be coordinated with each other in order to prevent incomplete combustion and to stabilize engine operation. To achieve such an objective, the air passage and the fuel-air mixture passage are positioned adjacent to each other vertically, and then the air valve and the throttle valve are integrated to make them work together as described in JP H10-252565; or in configurations in which the air passage and the fuel-air mixture passage are positioned in other ways, the air valve and the throttle valve work together via a linking mechanism as described in JP H9-125966 and JP H9-287521.  
           [0005]    In the aforementioned configuration in which the air passage and the fuel-air mixture passage are positioned adjacent to each other vertically and are integrated, the interlocking mechanism for the air valve and the throttle valve is either unnecessary or can be extremely simple. Thus, it is easy to keep these two valves coordinated at proper degrees of opening. However, such a configuration places significant restrictions on the carburetor structure and on the positioning of various mechanisms, significantly reducing the degree of design freedom and making it impossible to incorporate it into an existing carburetor as is, thereby resulting in inconvenience.  
           [0006]    On the other hand, the configuration in which the air valve and the throttle valve work together via a linking mechanism can accept either an existing or a freely-designed carburetor. However, manufacturing variations in the linking mechanism and the required clearance in the link junction make it difficult to maintain a proper opening relationship between the air valve and the throttle valve. A particular concern exists in that such a configuration may upset the air/fuel ratio in that partial load region, thereby lowering engine performance. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a vertical cross-sectional diagram illustrating the first embodiment of the present invention.  
         [0008]    [0008]FIG. 2 is a cross-sectional diagram along line A-A in FIG. 1.  
         [0009]    [0009]FIG. 3 is a cross-sectional diagram along line B-B in FIG. 1.  
         [0010]    [0010]FIG. 3 is a cross-sectional diagram along line B-B in FIG. 1.  
         [0011]    [0011]FIG. 4 is a vertical cross-sectional diagram illustrating the second embodiment of the present invention.  
         [0012]    [0012]FIG. 5 is a cross-sectional diagram along line A-A in FIG. 4.  
         [0013]    [0013]FIG. 6 is a cross-sectional diagram along line B-B in FIG. 4.  
     
    
     SUMMARY OF THE INVENTION  
       [0014]    The present invention has been developed in order to solve the aforementioned problems, and its objective is to provide a scavenging air/fuel-air mixture control device that can incorporate freely-designed carburetors into the fuel-air mixture passages, and that can also maintain the opening relationship between the mutually separate air valve and throttle valve by linking them via an interlocking mechanism that is free from looseness or play.  
         [0015]    In order to solve the aforementioned problems, the scavenging air/fuel-air mixture control device of present invention is provided with an air valve for controlling the scavenging air flow rate that is installed in the air passage connected to the scavenging passage for linking the crankcase with the combustion chamber. The air valve opens and closes the air passage through angular reciprocal movements of its valve body. A throttle valve for controlling the output is provided on the carburetor incorporated in the fuel-air mixture passage connected to the crankcase. The throttle valve opens and closes the fuel-air mixture passage through linear reciprocal movements of its valve body. An interlocking mechanism provided for the air valve and the throttle valve includes a flow rate-controlling mechanism for the fuel to be sent into the fuel-air mixture passage.  
         [0016]    The interlocking mechanism has a drive member that is fixed to the valve shaft of the air valve and rotates based on accelerator operation, and a slave member that linearly reciprocates by following a cam provided on the drive member. The cam is fixed onto the valve shaft of the throttle valve. The interlocking mechanism opens and closes the air valve and the throttle valve in relation with each other in response to accelerator operation. The fuel flow rate-controlling mechanism has a metering needle provided on the throttle valve and a metering window provided in the fuel passage leading from the constant fuel chamber to the fuel-air mixture passage. The flow rate of the fuel to be sent into the fuel-air mixture passage is controlled by having the metering needle vary the open area of the metering window according to the degree of opening of the throttle valve.  
         [0017]    According to the present invention, by having the air valve and the throttle valve as separate members that are linked through an interlocking mechanism, the carburetor structure and various mechanisms can be freely designed to achieve superior function, without being subjected to the restrictions of the air passage. Moreover, fixing the drive member, which is equivalent to the throttle valve lever in an ordinary carburetor, to the valve shaft of the air valve and having its cam make the slave member on the throttle valve side linearly reciprocate, tends to eliminate looseness or play between the air valve and the throttle valve, thereby properly maintaining their opening relationship. Additionally, by utilizing the linear reciprocal movements of the throttle valve to control the fuel flow rate, the flow rates between the scavenging air and fuel-air mixture as well as the air/fuel ratio can be properly maintained over the entire engine operation range.  
         [0018]    Further, objects and advantages of the invention will become apparent from the following detailed description and accompanying drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    Before explaining the embodiments of the present invention with reference to the drawings, an engine overview is provided based on FIGS. 3 and 6. An engine  1  has a cylinder  2 , a crankcase  3 , and a piston  4 . An exhaust port  6   a , which is the inlet of an exhaust passage  6 , and a scavenging port  7   a , which is the outlet of a scavenging passage  7  linking the crankcase  3  and a combustion chamber  5  located above the piston  4 , open into the cylinder  2 . In addition, an air passage  14  is connected to a location near scavenging port  7   a  of the scavenging passage  7  and a fuel-air mixture passage  20  is connected to the crankcase  3 .  
         [0020]    When the piston  4  begins to ascend from the bottom dead center, the capacity of the crankcase  3  increases, and at the same time, the piston  4  closes the exhaust port  6   a  and the scavenging exhaust port  7   a . As a result, the pressure inside the crankcase  3  and the scavenging passage  7  declines, drawing fuel-air mixture from the fuel-air mixture passage  20  into the crankcase  3 , and drawing air from the air passage  14  into the scavenging passage  7  and then into the crankcase  3 . When the piston  4  nears the top dead center, the fuel-air mixture that was supplied to the combustion chamber  5  in the previous stroke ignites and explodes, and when the piston  4  begins to descend, the pressure inside the crankcase  3  rises. Meanwhile, opening the exhaust port  6   a  and the scavenging port  7   a  exhausts the combustion gas inside the combustion chamber  5  to the exhaust passage  6 ; at the same time, the air inside the scavenging passage  7  jets into the combustion chamber  5 , exhausting the remaining combustion gas. The fuel-air mixture that was drawn into the crankcase  3  is supplied into the combustion chamber  5  via the scavenging passage  7  following the air. The piston  4  then reaches the bottom dead center.  
         [0021]    A crank shaft  10 , which is connected via a connecting rod  8  and a crank arm  9  to the piston  4 , which linearly reciprocates based on the repetition of the aforementioned strokes, rotates as in a conventional two-cycle engine.  
         [0022]    [0022]FIGS. 1, 2, and  3  illustrate the first embodiment of the present invention. The area where an air valve  15 A of the air passage  14  is provided is positioned alongside and near the fuel-air mixture passage  20  in a main body  19 A of a carburetor  18 A in which a throttle valve  22 A of fuel-air mixture passage  20  is provided. Air that enters an air supply passage  13  via an air cleaner, not shown in the figure but connected to the air supply passage  13  provided with a choke valve  12 , is branched into the two passages  14  and  20 .  
         [0023]    The air valve  15 A is a conventional butterfly valve in which a disc-shaped valve body  17 A is fixed onto a valve shaft  16 A rotatably supported in the main body  19 A.  
         [0024]    A valve body  23 A of the throttle valve  22 A has a bottom, is cylindrical in shape, and is fitted into a valve hole  21 A formed in the main body  19 A perpendicularly to the fuel-air mixture passage  20 . The tip on the open end of the valve body  23 A protrudes outside the main body  19 A and functions as a valve shaft  24 A. A ring-shaped groove passage  25  is provided on the peripheral surface of the valve body  23 A, and a guiding groove  26 , which goes through in the direction of the fuel-air mixture passage  20 , is provided on the bottom of the valve body  23 A.  
         [0025]    A plate-shaped drive member  32 A is secured onto the valve shaft  16 A of the air valve  15 A. The drive member  32 A, which is provided with a post  33 A to which an accelerator cable is to be connected, rotates the air valve  15 A in the opening direction as the driver operates the accelerator, and rotates the air valve  15 A in the closing direction based on a return spring  34 A, which consists of a helical coil spring installed surrounding the valve shaft  16 A in the space between the drive member  32 A and the main body  19 A. That is, the drive member  32 A is equivalent to a throttle valve lever that is fastened to the throttle valve shaft of the carburetor to open/close the throttle valve.  
         [0026]    A cam  35 A, whose cam surface  36 A is oriented to the side opposite the air valve  15 A, i.e., to the side opposite the main body  19 A, is provided along an arc that is centered around the valve shaft  16 A. A contact  39 A, consisting of a ball rotatably held at the tip of an adjustment screw  38 A screwed into one horizontal arm  37 Aa of a c-shaped slave member  37 A, contacts the cam surface  36 A. The valve shaft  24 A of the throttle valve  22 A is secured onto the other horizontal arm  37 Ab of the slave member  37 A. A vertical arm  37 Ac has a guiding protrusion  42 A, which is fitted into a guiding groove  41 A that extends in the vertical direction of a bracket  40 A provided in the main body  19 A.  
         [0027]    A spring  44 A, which works to keep the contact  39 A in constant contact with the cam surface  36 A, is installed between the top area of the bracket  40 A, which extends in the horizontal direction, and the horizontal arm  37 Aa, which supports the contact  39 A. The spring  44 A is a helical coil spring, and is engaged with the horizontal arm  37 Aa so as to constantly press the valve body  23 A of the throttle valve  22 A, to which the slave member  37 A is secured, to one side of the valve hole  21 A.  
         [0028]    The aforementioned drive member  32 A, cam  35 A, slave member  37 A, and spring  44 A comprise an interlocking mechanism  31 A for the air valve  15 A and the throttle valve  22 A. The guiding groove  41 A and the guiding protrusion  42 A comprise a rotation-prevention mechanism  43 A for the slave member  37 A and the throttle valve  22 A.  
         [0029]    Next, a known diaphragm-based constant fuel chamber  51 A is provided on the side opposite the aforementioned various mechanisms of the main body  19 A. A main jet  53 A is installed on top of the constant fuel chamber  51 A, and a metering cylinder  54  is positioned on top of the main jet  53 A. The metering cylinder  54  goes through a supply chamber  56  formed by an installation opening into which the main jet  53 A and the metering cylinder  54  are fitted, with its tip protruding into the bottom of the valve hole  21 A. The metering cylinder  54  has a vertically elongated triangular metering window  55 A on the side that faces the supply chamber  56 .  
         [0030]    The supply chamber  56  and the downstream side of the throttle valve  22 A of the fuel-air mixture passage  20  are connected via the supply passage  57 ; and the aforementioned main jet  53 A, metering cylinder  54 , supply chamber  56 , and supply passage  57  comprise a fuel passage  52 A, which extends from the constant fuel chamber  51 A to the fuel-air mixture passage  20 . An air bleed passage  58 , which extends from the air supply passage  13 , is connected to the supply chamber  56 .  
         [0031]    The base end of a metering needle  62 A is inserted into the valve body  23 A of the throttle valve  22 A. The metering needle  62 A is held by the valve body  23 A by being pressed by a pressing spring  64  onto a plug  63 , which plugs the opening of the valve body  23 A. The tip of the metering needle  62 A is inserted into the metering cylinder  54  without any gaps to speak of. The aforementioned metering window  55 A and the metering needle  62 A comprise a fuel flow-rate controlling mechanism  61 A, and the idling fuel flow rate can be adjusted by changing how deeply the plug  63  is screwed in.  
         [0032]    The air valve  15 A and the throttle valve  22 A related to the present embodiment having the aforementioned configuration are placed in positions that close the air passage  14  and the fuel-air mixture passage  20 , respectively, when the engine is being idled. The groove passage  25  and the guiding groove  26  of the throttle valve  22 A are positioned in the maximum width area and bottom area, respectively, of the fuel-air mixture passage  20 , allowing the air to pass at the flow rate required for idling. During idling, the metering needle  62 A is placed in a position that slightly opens the metering window  55 A, allowing the fuel to pass at the flow rate required for idling.  
         [0033]    When the driver operates the accelerator, thereby rotating the drive member  32 A, the air valve  15 A opens, gradually increasing the flow rate of the scavenging the air flowing through the air passage  14 . Simultaneously, the cam surface  36 A pushes up the contact  39 A, moving the valve body  23 A of the throttle valve  22 A secured to the slave member  37 A in the direction out of the valve hole  21 A. The valve-opening action increases the opening area of the fuel-air mixture passage  20 , and at the same time, the metering needle  62 A moves with the valve body  23 A to increase the opening area of the metering window  55 A, increasing the flow rate of the fuel-air mixture while maintaining a predetermined air/fuel ratio.  
         [0034]    According to the present embodiment, by turning the adjustment screw  38 A, which holds the contact  39 A, the heights of the slave member  37 A and the throttle valve  22 A can be changed, thus adjusting the idle opening of the throttle valve  22 A. Having the spring  44 A make the contact  39 A of the slave member  37 A constantly contact the cam surface  36 A, and having the drive member  32 A and the slave member  37 A secured onto the valve shafts  16 A and  24 A, respectively, tends to eliminate looseness or play in the interlocking mechanism  31 A for the air valve  15 A and the throttle valve  22 A, thus properly maintaining their opening relationship.  
         [0035]    Furthermore, according to the present embodiment, the use of a helical coil spring for the spring  44 A can press the valve body  23 A of the throttle valve  22 A to one side of the valve hole  21 A, and can keep the guiding protrusion  42 A of the rotation-prevention mechanism  43 A pressed against one side of the guiding groove  41 A, ensuring stable linear reciprocal movements without looseness. Moreover, since the contact  39 A and the spring  44 A are positioned on the central axis of the throttle valve  22 A, even more stable linear reciprocal movements of the cam  35 A can be achieved.  
         [0036]    Additionally, the present embodiment provides an advantage in the ring-shaped groove passage  25  and the guiding groove  26 , which is in the direction of the fuel-air mixture passage  20 , provided on the valve body  23 A of the throttle valve  22 A, can make the air flow during idling uniform and can prevent fuel clogging by discharging any fuel that might enter the valve hole  21 A by traveling around the metering needle  62 A. Furthermore, the entire fuel-air mixture passage  20  or the front and back of the throttle valve  22 A, i.e., nearly the entire area spanning from the entrance area to the exit area, has an elliptical shape whose minor axis is in the direction of the linear reciprocal movements of the throttle valve  22 A and whose major axis is in the direction perpendicular to the minor axis. This flattened shape can increase the cross-sectional area of the fuel-air mixture passage  20  or reduce the overall height of the device by decreasing the strokes of the linear reciprocal movements.  
         [0037]    [0037]FIGS. 4, 5, and  6  illustrate a second embodiment of the present invention, in which the air passage  14  and the fuel-air mixture passage  20  are separate and independent from each other without having a common body. The air cleaners for the entrances of these passages may be either independent or shared.  
         [0038]    An air valve  15 B provided in the air passage  14  is a widely-known rotary valve, which consists of a cylindrical valve body  17 B, in which a throughhole  27  having the same diameter as the air passage  14  is provided in the diameter direction, and a valve shaft  16 B; which is rotatably supported by a body  28  by fitting the valve body  17 B in a valve hole  29  provided by placing the air passage  14  orthogonally relative to the body  28 .  
         [0039]    A valve body  23 B of a throttle valve  22 B, which is one of the components of a carburetor  18 B, is a rectangular flat plate which is fitted into a flat valve hole  21 B formed in a main body  19 B orthogonally to the fuel-air mixture passage  20 . A valve shaft  24 B, which extends from the center of the valve body  23 B, protrudes to the outside of the main body  19 B. The valve body  23  has a notch-shaped opening  30  in the middle of the opposite side.  
         [0040]    A flat plate-shaped drive member  32 B provided with a post  33 B for connecting the accelerator cable is secured to the valve shaft  16 B of the air valve  15 B, and rotates the air valve  15 B in the opening direction as the driver operates the accelerator. A return spring  34 B, which consists of a helical coil spring installed surrounding the valve shaft  16 B in the space between the drive member  32 B and the body  28 , rotates the air valve  15 B in the closing direction.  
         [0041]    A cam  35 B, whose cam surface  36 B is oriented toward the air valve  15 B, i.e., toward the body  28 , is provided along an arc that is centered around the valve shaft  16 B. Meanwhile, a flat plate-shaped slave member  37 B is secured to the valve shaft  24 B of the throttle valve  22 B, and a contact  39 B consisting of a ball rotatably held at the tip of an adjustment screw  38 B screwed into the slave member  37 B contacts the cam surface  36 B.  
         [0042]    A guiding protrusion  42 B is provided on the tip opposite from the adjustment screw  38 B across the valve shaft  24 B of the slave member  37 B, and is fitted into a guiding groove  41 B of a bracket  40 B provided on the main body  19 B. Furthermore, a spring  44 B, which works to keep the contact  39 B in constant contact with the cam surface  36 B, is installed between the main body  19 B and the slave member  37 B, surrounding the valve shaft  24 B. The spring  44 B is a helical coil spring, and is engaged with the slave member  37 B so as to constantly press the valve body  23 B and guiding the protrusion  42 B to one side of a valve hole  21 B and of the guiding groove  41 B, respectively.  
         [0043]    The aforementioned drive member  32 B, cam  35 B, slave member  37 B, and spring  44 B comprise an interlocking mechanism  31 B for the air valve  15 B and the throttle valve  22 B. The guiding groove  41 B and the guiding protrusion  42 B comprise a rotation-prevention mechanism  43 B for the slave member  37 B and the throttle valve  22 B. Of course, in the present embodiment, the valve body  23 B of the throttle valve  22 B is a flat plate and is fitted into a flat valve hole  21 B, which functions as a rotation-prevention mechanism, and therefore the aforementioned rotation-prevention mechanism  43 B may be omitted. However, providing the rotation-prevention mechanism  43 B can ensure smooth linear reciprocal movements without applying a twisting force to the valve body  23 B or valve shaft  24 B.  
         [0044]    Next, a known diaphragm-based constant fuel chamber  51 B is provided on the side opposite the aforementioned various mechanisms of the main body  19 B, and a fuel nozzle  66  is positioned on top of a main jet  53 B provided on top of this constant fuel chamber  51 B. The fuel nozzle  66  protrudes from the bottom of the valve hole  21 B into the fuel-air mixture passage  20 , and a metering window  55 B, which extends in the vertical direction, is provided on the side of the area facing the fuel-air mixture passage  20 . The aforementioned main jet  53 B and the fuel nozzle  66  comprise a fuel passage  52 B, which extends from the constant fuel chamber  51 B to the fuel-air mixture passage  20 .  
         [0045]    An opening  30  provided in the valve body  23 B of the throttle valve  22 B is designed to surround the part of the fuel nozzle  66  protruding into the fuel-air mixture passage  20  with a gap in the idling position, allowing the air to pass through this gap at the flow rate required for idling. Moreover, a metering needle  62 B goes through the valve shaft  24 B on its central axis, and the metering needle  62 B is held by valve shaft  24 B having its tip inserted into the fuel nozzle  66  and a screw  65  at its base screwed into the valve shaft  24 B such that it can adjust the idling fuel flow rate. The aforementioned metering window  55 B and the metering needle  62 B comprise a fuel flow-rate controlling mechanism  61 B.  
         [0046]    The air valve  15 B and the throttle valve  22 B related to the present embodiment having the aforementioned configuration are placed in positions that close the air passage  14  and the fuel-air mixture passage  20 , respectively, when the engine is being idled. Air at the flow rate required for idling flows through the gap formed between the opening  30  of the throttle valve  22 B and the fuel nozzle  66 . During this step, the metering needle  62 B is placed in a position that slightly opens the metering window  55 B, allowing the fuel to pass at the flow rate required for idling.  
         [0047]    When the driver operates the accelerator, thereby rotating the drive member  32 A, the air valve  15 B opens, gradually increasing the flow rate of the scavenging air flowing through the air passage  14 . At the same time, the slave member  37 B is pushed up along the cam surface  36 B by the spring  44 B, pulling up the valve body  23 B of the throttle valve  22 B. The valve-opening action increases the opening area of the fuel-air mixture passage  20 , and at the same time, the metering needle  62 B moves with the valve body  23 B to increase the opening area of the metering window  55 B, increasing the flow rate of the fuel-air mixture while maintaining a predetermined air/fuel ratio.  
         [0048]    The present embodiment can also provide the same effects as the first embodiment, i.e., the adjustment screw  38 B can be used to adjust the idling opening of the throttle valve  22 B, the opening relationship between the air valve  15 B and the throttle valve  22 B can be properly maintained without looseness or play in the interlocking mechanism  31 B, and the flattened shape of the fuel-air mixture passage  20  can increase its cross-sectional area or reduce the overall height of the device.  
         [0049]    Additionally, the present embodiment provides the advantage of a simpler overall structure because of the fact that the shape of the slave member  37 B is simple and the rotation-prevention mechanism  43 B may be omitted. Furthermore, as shown in FIG. 4, since the air passage  14  can be positioned at a higher location than the fuel-air mixture passage  20 , the passage leading to the scavenging passage of the engine can be shortened and the shape of the passage can be simplified, which constitute additional advantages.  
         [0050]    As explained above, according to the present invention, there are no restrictions on the carburetors that can be used, and any freely-designed carburetor can be incorporated into the fuel-air mixture passage; and the air valve and the throttle valve can be maintained at a proper opening relationship by linking them through an interlocking mechanism that is free of looseness or play, thereby ensuring optimum engine performance over the entire operation range.  
         [0051]    While various preferred embodiments of the invention have been shown for purposes of illustration, it will be understood that those skilled in the art may make modifications thereof without departing from the true scope of the invention as set forth in the appended claims including equivalents thereof.