Patent Publication Number: US-2006011155-A1

Title: Carburetor for two-stroke engine

Description:
CROSS REFERENCE OF RELATED APPLICATION  
      This application is a continuation of application Ser. No. 10/834,315 filed Apr. 27, 2004, which application is fully incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to a carburetor for supplying fuel to a two-stroke engine in which scavenging air is introduced to the fuel chamber prior to an air/fuel mixture.  
     BACKGROUND OF THE INVENTION  
      There are two-stroke engines in which scavenging air is introduced to the combustion chamber during the downward stroke of the piston, and an air/fuel mixture is introduced to the combustion chamber after exhausting combustion gas. Known examples of these methods of introduction include feeding scavenging air to a scavenging channel connected to the crankcase and the fuel chamber, feeding an air/fuel mixture to the crankcase, and sequentially introducing these to the fuel chamber; directly introducing scavenging air to the fuel chamber, feeding an air/fuel mixture to the crankcase, and introducing the air/fuel mixture to the combustion chamber after the scavenging air; or directly introducing scavenging air and an air/fuel mixture in sequential fashion to the combustion chamber.  
      The flow rate of scavenging air and the air/fuel mixture must be made substantially proportional in order to prevent incomplete combustion, stabilize engine operation, and so forth; an air valve is therefore provided to the air channel for supplying scavenging air to the engine; and the air valve is operated in coordination with the throttle valve of the carburetor, which is a means for forming an air/fuel mixture.  
      This type of two-stroke engine is used as a power source for portable machinery and other small machines and, as a result, carburetors or air channels, air valves/throttle valve interlocking mechanisms, and other components must be installed in narrow locations requiring these components to be kept as small as possible.  
      Described in Japanese Patent Application Laid-open No. 10-252565 (&#39;565 application) as a proposal for satisfying the above-described requirements is a configuration in which a carburetor with an air intake passage for forming a portion of the air/fuel mixture channel is provided with an air passage that forms a portion of the air channel and diverges from the air intake passage inlet portion. A throttle valve in the air intake passage and an air valve in the air passage are integrated in rotary configuration. The air intake passage is connected to the engine by way of a through hole provided to an adiabatic wall, and the air passage is connected to the engine by way of a conduit pipe.  
      Described in Japanese Patent Application Laid-open Nos. 11-336613 and 2000-73869 (&#39;869 application) is a configuration in which the rotary air valve in the &#39;565 application is substituted with a butterfly air valve that is integrated with the rotary throttle valve, and a conduit pipe forming a portion of the air channel is substituted with a through hole provided in the adiabatic wall.  
      Furthermore, described in Japanese Patent Application Laid-open No. 2002-227653 (&#39;653 application) is a configuration in which a carburetor with an air intake passage for forming a portion of the air/fuel mixture channel is provided with a separate air passage for forming a portion of the air channel. Both the throttle valve in the air intake passage and the air valve in the air passage are fashioned as butterfly valves and are interlocked with each other by means of a linking mechanism. The air intake passage and the air passage are connected to the engine by way of a through hole and a conduit pipe that is provided to the adiabatic wall.  
      The carburetors in each of the applications described above are advantageous in that they are compact. The carburetors are compact because the air passage for forming a portion of the air intake channel is provided in parallel fashion to the air intake passage for forming a portion of the air/fuel mixture channel in the carburetor main body and because an air valve is disposed in the air passage. The carburetors are made further compact because the air valve and the throttle valve are integrated with each other and do not have interlocking mechanisms.  
      However, as noted in each of the above described applications, the carburetors are mounted in a predetermined location on the side face of the engine with an adiabatic wall interposed therebetween. For this reason, in a configuration in which the air passage, which is made to substantially the same length as the air intake passage, is connected from the back end thereof to a predetermined location in the engine by way of an external conduit pipe as in conventional systems, positioning the conduit pipe tends to be extremely difficult depending on the location for feeding scavenging air because the space between the carburetor main body and the engine is narrow. Described in Japanese Patent Application Laid-open No. 9-268917 (&#39;917 application) is a configuration in which the air channel is made to diverge from the carburetor inlet portion from the air intake passage, and is connected to a predetermined position on the side face of the engine by way of an external conduit pipe. This configuration easily conforms to a variety of positional relationships between the location for feeding scavenging air and the location for feeding the air/fuel mixture in the engine because of the considerable freedom to place the conduit pipe. However, the carburetor of the &#39;917 application is configured such that the throttle valve and the air valve are disposed at a right angle to each other, which complicates the interlocking mechanism and raises concerns that excessive force may be applied.  
      In the carburetors described in the &#39;869 and &#39;653 applications, the air passage and the air intake passage are connected to the engine by way of a conduit hole and a through hole formed in an adiabatic wall. Such carburetors can be used with only one type of engine, that is to say, with an engine in which a mutual match is established between the location for feeding the air/fuel mixture and the location for feeding scavenging air, and between the conduit hole and the through hole. Such carburetors are inapplicable to a large number of engines with differing positional relationships between the location for feeding the air/fuel mixture and the location for feeding scavenging air.  
     SUMMARY OF THE INVENTION  
      The present invention is directed to solving the above-stated problems. An object thereof is to provide a universal carburetor which can be used with a variety of engines, in which the interlocking mechanism for the throttle valve and the air valve is simple, and which can be easily mounted in narrow places.  
      The present invention provides a first device for solving the above-described drawbacks, wherein a carburetor main body with an air intake passage for forming a portion of an air/fuel mixture channel for feeding an air/fuel mixture to the engine is provided with an air passage for forming a portion of an air channel for feeding scavenging air to the engine. The air passage is mutually parallel with the air intake passage and comprises an air valve, and the front end thereof is positioned closer to the base end side than to the engine-side front end face of the carburetor main body. The air valve and a throttle valve disposed in the air intake passage are both butterfly valves, the valve stems thereof are mutually parallel, and the valves are operated in coordination with each other with the help of an interlocking mechanism to perform opening and closing action.  
      The present invention also provides a second device for solving the above-described drawbacks, comprising through holes in an adiabatic wall disposed between a carburetor main body and an air intake passage in the carburetor main body provided with an air/fuel mixture channel for feeding an air/fuel mixture to the engine. The device also comprising an air passage in the carburetor main body, which is also provided with an air channel for feeding scavenging air to the engine. The device further comprising a conduit pipe for connecting the air passage to the engine. The air passage is parallel with the air intake passage and comprises an air valve, and the front end thereof is positioned closer to the base end side than to the engine-side front end face of the carburetor main body. The air valve and a throttle valve disposed in the air intake passage are both butterfly valves, the valve stems thereof are mutually parallel, and the valves are operated in coordination with each other with the help of an interlocking mechanism to perform opening and closing action.  
      When the carburetor of the present invention is mounted on an engine with the location for feeding the air/fuel mixture connected to the air/fuel mixture channel, the space between the engine can be expanded because the front end of the air passage is positioned further to the base end side than to the engine-side front end face of the carburetor main body. As a result, the freedom in placing the conduit pipe for connecting the air passage to the location for feeding scavenging air is increased, and the arrangement can be adapted to a variety of engines with different positional relationships between the location for feeding the air/fuel mixture and the location for feeding scavenging air. Also, the throttle valve and the air valve are butterfly valves and the valve stems are parallel, so the interlocking mechanism is simple, the freedom in placing the conduit pipe is considerable, and placement in narrow places is facilitated.  
      Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a longitudinal section of the carburetor related to the first embodiment of the present invention mounted on an engine.  
       FIG. 2  is a view of the left-hand side of the carburetor of  FIG. 1 .  
       FIG. 3  includes views of a second embodiment of the present invention, wherein (A) is a view of the left-hand side, and (B) is a longitudinal section.  
       FIG. 4  includes views of a third embodiment of the present invention, wherein (A) is a view of the left-hand side, and (B) is a longitudinal section. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Describing the embodiments of the present invention with reference to the diagrams,  FIG. 1  is a longitudinal section in which the carburetor  21  related to the first embodiment of the present invention is mounted on a stratified scavenging two-stroke engine  1 . The engine  1  has a cylinder  2 , a crankcase  3 , and a piston  4 . A scavenging port  7   a , which is the outlet of a scavenging channel  7 , which links the crankcase  3 , an exhaust port  6   a  as an inlet of an exhaust channel  6 , and a combustion chamber  5  above the piston  4 , opens to the cylinder  2 . Also, an air/fuel mixture feed port  8  with a check valve  8   a  opens to the crankcase  3 , and a scavenging air feed port  9  with a check valve  9   a  opens to a location near the scavenging port  7   a  in the scavenging air channel  7 .  
      When the piston  4  begins to ascend from the bottom dead center, the crankcase  3  increases in capacity and the piston  4  closes the exhaust port  6   a  and the scavenging port  7   a . The pressure in the crankcase  3  and the scavenging channel  7  consequently decreases, an air/fuel mixture is fed from the air/fuel mixture feed port  8  to the crankcase  3 , and scavenging air is fed from the scavenging air feed port  9  to the scavenging channel  7  and the crankcase  3 .  
      When the piston  4  nearly reaches the top dead center, the air/fuel mixture introduced to the combustion chamber  5  in a prior step ignites and combusts, and when the piston  4  then begins to descend, the pressure in the crankcase  3  increases. At the same time, the exhaust port  6   a  and the scavenging port  7   a  open to expel the exhaust gas in the combustion chamber  5  into the exhaust channel  6 . The scavenging air in the scavenging channel  7  is introduced to the combustion chamber  5  from the scavenging port  7   a  to expel the remaining combustion gas. The air/fuel mixture in the crankcase  3  subsequently passes through the scavenging air channel  7  and into the combustion chamber  5 , and the piston  4  reaches the bottom dead center.  
      Due to the above-described repetition, the crankshaft  12  coupled to the linearly reciprocating piston  4  by way of a connecting rod  10  and a crank arm  11  rotates in the same manner as a conventional two-stroke engine.  
      Next, the carburetor  21  related to the first embodiment of the present invention shown in  FIGS. 1 and 2  comprises mutually overlapping manual start pump  27  on the lower surface of the carburetor main body  22  with a horizontally extending air intake passage  24 , pulsating diaphragm fuel pump  28  operated as a result of the pulsating pressure of the crankcase  3 , and diaphragm fuel metering mechanism  29  that acts so as to continuously ensure that a constant quantity of fuel is delivered to the air intake passage  24 .  
      A rod-shaped or plate-shaped arm  30  that extends upward is coupled to the upper surface of the base end portion of the carburetor main body  22  and a tubular piece  31  is coupled to the upper end of the arm  30 . The arm  30  and tubular piece  31  are fashioned into an integrally molded component.  
      The carburetor  21  of the present embodiment is mounted on the engine  1  via an interposed adiabatic wall  36  that is overlaid on the front end face of the carburetor main body  22 . The air intake passage  24  and a through hole  25  provided in the adiabatic wall  36  are positioned on the same center axis line to form an air/fuel mixture channel  23 . The air/fuel mixture channel  23  is linked to the air/fuel mixture feed port  8 , and the front end of the adiabatic wall  36  is fitted into the entrance end of the air/fuel mixture feed port  8 .  
      The base end of the tubular piece  31  is positioned further rearward from the base end face of the carburetor main body  22 , the front end thereof is positioned further to the base end side than to the front end face of the carburetor main body  22 , and the inside thereof forms an air passage  33  that extends parallel to the air intake passage  24 . A tubular joint  37  is mounted on the entrance end of the scavenging air feed port  9 . The front end of the tubular piece  31  and the tubular joint  37  are conjoined by a flexible conduit pipe  34 . The tubular joint  37 , feed port  9 , and tubular piece  31  form a scavenging channel  32  for feeding scavenging air to the engine  1 .  
      The output-controlling throttle valve  26  provided to the air intake passage  24 , and the air valve  35  designed for controlling the flow rate of scavenging air and provided to the air passage  33  are both butterfly valves. The valve stems  26   a  and  35   a  of these valves  26  and  35  extend parallel to each other in the horizontal direction; and open and close in coordination with the help of an interlocking mechanism  38 . The interlocking mechanism  38  comprises levers  38   a  and  38   b  mounted on the stem ends thereof and a linking rod  38   c  by which the levers  38   a  and  38   b  are linked.  
      An air cleaner  39  is overlaid on the base end face of the carburetor main body  22 , the base end of the tubular piece  31  protrudes into the interior thereof, and the air/fuel mixture channel  23  and the air channel  32  are individually linked to the air cleaner  39  and are supplied with air.  
      According to the present embodiment, the carburetor main body  22  is mounted close to the engine  1  on the other side of the adiabatic wall  36 . The space formed by the scavenging air feed port  9  of the engine  1  is considerable because the front end of the air passage  33  is positioned substantially in the center above the carburetor main body  22 . Hence, the flexible conduit pipe  34  can be coupled with these without excessive bending even if the scavenging air feed port  9  is positioned above the extended center shaft line of the air passage  33 .  
      According to the present embodiment, the interlocking mechanism  38  is a simple structure, can be disposed in narrow places, and can be smoothly linked without concern of causing damage or malfunctioning due to the application of excessive force because the throttle valve  26  and the air valve  35  are both butterfly valves, the valve stems  26   a  and  35   a  thereof rotate without moving in the direction of the center shaft line, and the valve stems  26   a  and  35   a  are parallel to each other.  
      FIGS.  4 (A) and (B) depict a second embodiment of the carburetor of the present invention. The carburetor  41  comprises a manual starter pump  47  on one side of the carburetor main body  42  with a horizontally extending air intake passage  44 , a pulsating diaphragm fuel pump  48  disposed on the upper face and operated as a result of the pulsating pressure of the crankcase, and a diaphragm fuel metering mechanism  49  on the lower face that acts so as to ensure that a constant quantity of fuel is continuously delivered to the air intake passage  44 .  
      A wall piece  50  in the form of a flat plate protruding upward above the base end portion of the carburetor main body  42  is aligned and integrally molded with the same surface as the base end face.  
      The carburetor  41  of the present embodiment is also mounted on the engine  1  with an interposed adiabatic wall  56  that is overlaid on the front end face of the carburetor main body  42 . The air intake passage  44  and a through hole  45  provided in the adiabatic wall  56  are positioned on the same center axis line to form an air/fuel mixture channel  43 , and are connected to the air/fuel mixture feed port of the engine.  
      Here, the carburetor  41  of the present embodiment is coupled to an engine comprising two scavenging air channels individually fed with scavenging air. Two inlets  53   a  are disposed adjacent to each other and parallel to the air intake passage  44 , tubular joints  51  comprising short pipes are mounted on the front ends of the inlets  53   a  and made to protrude forward from the wall piece  50 , and the inlets  53   a  and tubular joints  51  form air passages  53 . The tubular joints  51  couple with a flexible conduit pipe  54  connected to the scavenging air feed port of the engine, and the inlets  53   a , tubular joints  51 , and conduit pipe  54  form an air channel  52  for feeding scavenging air to the engine.  
      The output-controlling throttle valve  46  provided to the air intake passage  44 , and the air valves  55  designed for controlling the flow rate of scavenging air and provided to the inlets  53   a  of the air passages  53  are each butterfly valves. The valve stems  46   a  and  55   a  of the throttle valve  46  and air valve  55  are mutually parallel and extend in the horizontal direction. The valves operate in coordination with each other with the help of the same interlocking mechanism  58  as the embodiment depicted in  FIGS. 1 and 2  to perform opening and closing action. The two air valves  55  have the same valve stem  55   a . The air cleaner  59  is overlaid on the base end faces of the carburetor main body  42  and the wall piece  50 , and the interior thereof is linked individually to the air/fuel mixture channel  43  and the air channel  52 .  
      In the present embodiment, the front ends of the tubular joints  51  are positioned substantially in the center above the carburetor main body  42 , so an interlocking mechanism such as a fuel pump  48  can be mounted without any trouble on the upper face toward the front of the wall piece  50  of the carburetor main body  42 , and the space formed by the scavenging air feed port is considerable in the same manner as in the embodiment depicted in  FIGS. 1 and 2 , so the conduit pipe  54  can be coupled without excessive bending. Furthermore, the same effects as in  FIGS. 1 and 2  can be obtained in that the interlocking mechanism  58  is also a simple structure, can be disposed in narrow places, and can be smoothly linked without application of excessive force.  
      FIGS.  3 (A) and (B) show a third embodiment of the carburetor of the present invention. The carburetor  61  is obtained as a result of the mutual overlapping of a manual starter pump  67 , a fuel pump  68 , and a diaphragm fuel metering mechanism  69  in the same manner as in the first working embodiment on the lower face of the carburetor main body  62  with a horizontally extending air intake passage  64 . A wall piece  70  in the form of a flat plate protruding upward above the base end portion of the carburetor main body  62  is aligned and integrally molded with the same surface as the base end face.  
      The carburetor  61  of the present embodiment is also mounted on the engine with an interposed adiabatic wall  76  that is overlaid on the front end face of the carburetor main body  62 . An air intake passage  64  and a through hole  65  provided in the adiabatic wall  76  are positioned on the same center axis line to form an air/fuel mixture channel  63 , and are connected to the air/fuel mixture feed port of the engine.  
      The wall piece  70  has a single inlet  73   a  in parallel with the air intake passage  64 . A tubular joint  71  comprising a short pipe is fixedly inserted into the front end of the inlet  73   a  and made to protrude forward from the wall piece  70 . The inlet  73   a  and the tubular joint  71  form an air passage  73 . The tubular joint  71  couples with a flexible conduit pipe  74  connected to the scavenging air feed port of the engine. The inlet  73   a , tubular joint  71 , and conduit pipe  74  form an air channel  72  for feeding scavenging air to the engine.  
      The output-controlling throttle valve  66  provided to the air intake passage  64 , and the air valve  75  designed for controlling the flow rate of scavenging air and provided in the tubular joint  71  are both butterfly valves. The valve stems  66   a  and  75   a  of the throttle valve  66  and air valve  75  are mutually parallel and extend in the horizontal direction. The valves are operated in coordination with each other with the help of the same interlocking mechanism  78  as in the first and second embodiments to perform opening and closing action. The air cleaner  79  is overlaid on the base end face of the carburetor main body  62  and the wall piece  70 , and the interior thereof is linked individually to the air/fuel mixture channel  63  and the air channel  72 .  
      In the present embodiment as well, the front end of the tubular joint  71  is positioned substantially in the center above the carburetor main body  62 , so the space formed by the scavenging air feed port is considerable in the same manner as in the first and second embodiments, and the conduit pipe  74  can be coupled without excessive bending. Furthermore, the same effects as in the first and second embodiments can be obtained in that the interlocking mechanism  78  also has a simple structure, can be disposed in narrow places, and can be smoothly linked without application of excessive force.  
      The present invention may also be adapted to situations in which the air intake passages  24 ,  44 , and  64  and the air passages  32 ,  52 , and  72  have a horizontal relationship rather than a vertical relationship, or to situations in which the valve stems  26   a ,  35   a ,  46   a ,  55   a ,  66   a , and  75   a  are disposed in a diagonal direction rather than a horizontal direction. Also, the arm  30 , the short tubular piece  31 , and the wall pieces  50  and  70  may be separately fabricated and fixed together rather than integrally molded with the carburetor main bodies  22 ,  42 , and  62 .  
      As described above, the carburetor of the present invention allows an air passage for feeding scavenging air, and an interlocking mechanism between the throttle valve and air valve to be easily mounted in narrow locations in a variety of engines with different positional relationships between the location for feeding the air/fuel mixture and the location for feeding scavenging air.  
      In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, each feature of one embodiment can be mixed and matched with other features shown in other embodiments. Features and processes known to those of ordinary skill may similarly be incorporated as desired. Additionally and obviously, features may be added or subtracted as desired. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.