Abstract:
A carburetor, especially for the internal combustion engine in a motor-driven implement, is provided. Formed in the carburetor is an intake channel that has at least one partition extending in the direction of the longitudinal axis of the intake channel. The partition divides the intake channel into at least one air channel and at least one mixture channel. At least one fuel nozzle opens into the mixture channel. Pivotably mounted in the intake channel is a butterfly valve. To obtain a favorable starting and acceleration condition, with reduced exhaust gas values in the full throttle range, the butterfly valve is provided with at least two sections that are moveable relative to one another.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a carburetor, especially for the internal combustion engine in a motor-driven implement.  
           [0002]    U.S. Pat. No. 6,101,991 discloses a two-cycle engine having a partition formed in the intake channel thereof. The partition divides the intake channel into an air channel that conveys substantially fuel-free air, as well as into a mixture channel that conveys fuel/air mixture. In the carburetor, a butterfly valve is disposed in the partition. Due to the common butterfly valve, the air channel and the mixture channel are opened or closed together. When the two-cycle engine is started, a sufficient supply of fuel is necessary. In contrast, the amount of fuel-free air that is supplied should be relatively low. In order with a two-cycle engine according to U.S. Pat. No. 6,101,991 to achieve an adequate supply of fuel during the starting process or in the lower partial load range and during acceleration, the carburetor must be appropriately adjusted. This means that even in the full throttle range a correspondingly large amount of fuel is supplied. Consequently, the exhaust gas values of such an engine are impaired.  
           [0003]    It is therefore an object of the present invention to provide a carburetor, especially for the internal combustion engine in a motor-driven implement, that enables a control of the fuel and air supply that is adapted to the operating range or condition of the engine. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    This object, and other objects and advantages of the present invention, will appear more clearly from the following specification in conjunction with the accompanying schematic drawings, in which:  
         [0005]    [0005]FIG. 1 shows a two-cycle engine having one exemplary embodiment of an inventive single-flow carburetor;  
         [0006]    [0006]FIG. 2. is a side view of a carburetor taken in the direction of the arrow II in FIG. 1;  
         [0007]    [0007]FIG. 3 shows the carburetor of FIG. 2 with the butterfly valve in the open position;  
         [0008]    [0008]FIG. 4. is a view of the carburetor taken in the direction of the arrow IV in FIG. 2;  
         [0009]    [0009]FIG. 5 is a cross-sectional view through the carburetor taken along the line V-V in FIG. 2. 
     
    
     SUMMARY OF THE INVENTION  
       [0010]    The carburetor of the present invention includes an intake channel formed in the carburetor, wherein at least one partition is disposed in the intake channel, extends in the direction of the longitudinal axis thereof, and divides the intake channel into at least one air channel and at least one mixture channel, wherein at least one fuel nozzle opens out into the mixture channel, wherein a butterfly valve is pivotably mounted in the intake channel, and wherein the butterfly valve is provided with at least two sections that are moveable relative to one another.  
         [0011]    Forming the butterfly valve with at least two sections that are moveable relative to one another makes it possible to already open a channel formed in the intake channel, while another channel remains closed. Especially during start-up, in the lower partial throttle range, and during acceleration, it is thereby possible to control the supply of air in such a way that the supply of fuel/air mixture is increased and the mixture thus become richer.  
         [0012]    In particular, it is provided that one section of the butterfly valve form an air valve section that in the closing position substantially closes at least one air channel, and that the other section of the butterfly valve form a mixture valve section that in the closing position, in other words in the idling position, substantially closes at least one mixture channel. Thus, for idling the mixture channel can already be slightly opened, while the air valve section still substantially closes off the air channel. This prevents the underpressure in the mixture channel, which brings about the fuel supply, from being reduced by in-flowing air and thereby reducing the supply of fuel. The carburetor can be set lean, so that good exhaust gas values result in the full throttle range. A good starting condition results if the sections, starting from the closing position of the butterfly valve, are moveable relative to one another by about 5 to 25°, especially by 10 to 20°.  
         [0013]    A favorable structural embodiment results if one section is fixedly connected with a shaft, and another section is fixedly connected with a hollow shaft, whereby at least a portion of the length of the first shaft is surrounded by the hollow shaft. This results in a space-saving arrangement. As a consequence, it is also possible to centrally mount both of the valve sections. One section is advantageously connected with a cross member that is disposed on the hollow shaft. The hollow shaft thus does not extend over the entire width of the intake channel. Furthermore, the hollow shaft thereby does not obstruct the relative movement of the valve sections. At the same time, sufficient installation space is provided for fixing the section on the shaft, for example via a screw.  
         [0014]    The air valve section is advantageously spring-loaded in the direction toward its closing position. This spring ensures that the air valve section substantially closes off the air channel while the mixture valve section is already opening. Due to the spring-loading, the relative position of the sections to one another can be maintained up to complete opening of the butterfly valve. Thus, in the opening position the air valve section is not completely open, but rather is opened by an angle that corresponds to the rotational moveability of these sections relative to one another and remains inclined relative to the longitudinal axis of the intake channel. A first end of the spring is expediently fixed in position on the carburetor housing, and a second end of the spring is fixed in position on an air valve shaft that is fixedly connected with the air valve section. To fix the rotational moveability, it is provided that an engagement member is connected with an air valve shaft, with a further engagement member, which is connected with a butterfly valve shaft, being associated with the first engagement member, whereby the air valve shaft is fixedly connected with the air valve section, and the butterfly valve shaft is fixedly connected with the mixture valve section. In the closing position of the air valve section and the mixture valve section of the butterfly valve, the two engagement members have an angular spacing from one another in the circumferential direction that corresponds to the maximum rotational moveability of the butterfly valve sections relative to one another. When the mixture valve section opens, the angular spacing of the engagement members is reduced in conformity with the opening angle of the mixture valve section. When the maximum rotational moveability is reached, the engagement members rest against one another so that upon a further opening movement of the mixture valve section, the air valve section is correspondingly also opened.  
         [0015]    The air valve shaft and the butterfly valve shaft advantageously extend at least from the intake channel to the outer side of the carburetor housing. The engagement members can thus be disposed on the outer side of the housing. However, it is also possible to provide the engagement members on the butterfly valve shaft and the air valve shaft in the interior of the intake channel or in the interior of the housing. A disk is expediently fixedly connected with the butterfly valve shaft on the outer side of the housing, whereby the engagement member is disposed on the disk. In particular, the air valve shaft extends from the disk that is connected with the butterfly valve shaft into the intake channel. An easy to manufacture embodiment of the engagement members results if a disk is fixedly disposed on the air valve shaft, and the engagement member is disposed on this disk. The engagement members are, in this connection, advantageously embodied as dogs or pawls that, on the disks that are disposed next to one another, come into engagement with one another.  
         [0016]    Further specific features of the present invention will be described in detail subsequently.  
       DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]    Referring now to the drawings in detail, the two-cycle engine  1  schematically illustrated in FIG. 1 is, in particular, disposed in a manually-guided implement, such as a power chain saw, a cut-off machine, or the like. The two-cycle engine  1  has a cylinder  2  in which is formed a combustion chamber  3 . The combustion chamber  3  is delimited by a reciprocating piston  5  that, via a connecting rod  6 , drives a crankshaft  7  that is rotatably mounted in a crankcase  4 . The two-cycle engine  1  has an inlet  20  for fuel/air mixture into the crankcase  4 , as well as an outlet  10  for the withdrawal of exhaust gases from the combustion chamber  3 . In prescribed positions of the piston  5 , the crankcase  4  is connected with the combustion chamber  3  via two symmetrically arranged transfer channels  12  that are remote from the outlet  10 , as well as two symmetrically arranged transfer channels  15  that are near the outlet  10 . The transfer channels  12  and  15  open into the combustion chamber  3  via transfer windows  13  and  16  respectively. Other arrangements of the transfer channels, as well as a different number of transfer channels, can also be expedient. Disposed in the piston  5  are two symmetrically formed piston windows  14  that in prescribed positions of the piston, especially in the region of the upper dead center position, fluidically connect an air channel  8 , which conveys substantially fuel-free air and opens into the cylinder  2  via an air channel window  9 , with the transfer windows  13  and  16  of the transfer channels  12  and  15 .  
         [0018]    During operation of the two-cycle engine  1 , in the region of the upper dead center position of the piston  5 , fuel/air mixture is supplied to the crankcase  4  from the mixture channel  21  via the inlet  20 . At the same time, substantially fuel-free air is supplied to the transfer channels  12  and  15  via the piston window  14 . The supply of fuel/air mixture and substantially fuel-free air can also be effected in a time-delayed manner. The fuel/air mixture is compressed in the crankcase  4  during the downward stroke of the piston  5 . In the region of the upper dead center position of the piston  5 , the transfer windows  13  and  16  open to the combustion chamber  3 . First, substantially fuel-free air flows out of the transfer channels  12  and  15 , and subsequently fuel/air mixture flows out of the crankcase  4  into the combustion chamber  3 . The substantially fuel-free air displaces the exhaust gases that are still in the combustion chamber  3  through the outlet  10 . During the upward stroke of the piston  5 , the fuel/air mixture in the combustion chamber  3  is compressed, and is ignited in the region of the upper dead center position of the piston  5  by the spark plug  11 . Due to the combustion, the piston  5  is forced in the direction toward the lower dead center position. The exhaust gases in the combustion chamber  3  flow through the outlet  10  as soon as this outlet is released by the piston  5 . The exhaust gases that still remain in the combustion chamber  3  are displaced toward the outlet  10  by the substantially fuel-free air that flows in through the transfer channels, as well as by the subsequently flowing-in fuel/air mixture.  
         [0019]    For the preparation of the fuel/air mixture, a carburetor  25  is provided that in particular is embodied as a diaphragm carburetor. Formed in the carburetor  25  is an intake channel  22 . In the carburetor  25 , a rotatably mounted butterfly valve  26  is disposed in the region of the idling nozzles  27 . A venturi section  45  is formed in the intake channel  22  upstream of the butterfly valve  26 . In the region of the venturi section  45 , a main nozzle  28  is provided for the supply of fuel into the intake channel  22 . A partition  31  is disposed in the intake channel  22  and extends in the direction of the longitudinal axis  24  of the intake channel. This partition  31  expediently extends over the entire length of the carburetor  25 . The partition  31  divides the intake channel  22  into the air channel  8  and the mixture channel  21 . The air channel  8  and the mixture channel  21  are also separately embodied downstream of the carburetor  25  up to the two-cycle engine. The idling nozzles  27 , as well as the main nozzle  28 , open out into the mixture channel  21 , whereas substantially fuel-free air is supplied to the air channel  8 .  
         [0020]    In the region of the butterfly valve  26 , the partition  31  has a connection opening  32 , the cross-sectional area of which in particular corresponds approximately to the cross-section area of the butterfly valve  26 . The butterfly valve  26  has two sections that are moveable relative to one another, namely an air valve section  29  and a mixture valve section  30 . In the closing position, the mixture valve section  30  closes off the mixture channel  21  in a substantially airtight manner, while the air valve section  29  is disposed in the region of the air channel  8  and in the closing position substantially closes off the air channel in an airtight manner. When the butterfly valve  26  is not completely opened, the air channel  8  is connected with the mixture channel  21  via the connection opening  32 . Thus, a portion of the fuel can flow through the connection opening  32  into the air channel  8 . In the full throttle range, the mixture valve section  30  rests against an abutment surface  50  formed on the partition  31 . In the full throttle range, the abutment surface  50  expediently adjoins the mixture valve section  30  in a sealing manner.  
         [0021]    Due to the relative moveability of the butterfly valve sections relative to one another, in the full throttle range the air valve section  29  can be inclined relative to the longitudinal axis  24  of the intake channel  22 . In this range, the partition  31  can be embodied in such a way that also in the region of the air valve section  29 , the air channel  8  and the mixture channel  21  are fluidically separated from one another. In so doing, a storage of air is achieved in the transfer channels  12  and  15  with substantially fuel-free air, so that the fuel portion that escapes through the outlet  10  is low. However, a gap can also remain between the partition  31  and the air valve section  29 .  
         [0022]    Disposed upstream of the carburetor  25  is an air filter  17 , which has a dirty chamber  19  and a clean chamber  23  that is separated from the clean  19  chamber by filter material  18 . The intake channel  22  opens out at the clean chamber  23  of the air filter  17 . This prevents dirt particles from being conveyed to the internal combustion engine  1 . The partition  31  can advantageously extend into the air filter  17  up to the filter material  18 .  
         [0023]    In FIG. 2, the carburetor  25  is illustrated in a side view. The carburetor  25  is provided with a carburetor housing  33 , in which the intake channel  22  is formed. The carburetor housing  33  has two mounting openings  34  via which the carburetor  25  can, for example, be fixed in position on the air filter  17 . In FIG. 2, the butterfly valve  26 , which includes the air valve section  29  and the mixture valve section  30 , is illustrated in the closed position, i.e. in the idling position. In this connection, the idling is established only by an adjustment, in other words by a slight opening, of the mixture valve section  30 . The air valve section  29  thus substantially closes the air channel  8 , while the mixture valve section  30  substantially closes the mixture channel  21 , in other words in conformity with the idling position. The mixture valve section  30  is fixed via a screw  37  on a throttle or butterfly valve shaft  35  that extends through the carburetor housing  33 . The air valve section  29  is fixed on a cross member  44  that extends in the intake channel  22  in the direction of the longitudinal axis  51  of the butterfly valve shaft  35 . The cross member  44  is fixedly connected with a hollow shaft  38 . In particular, the cross member  44  is monolithically formed with the hollow shaft  38  as a portion thereof. The hollow shaft  38  extends from the intake channel  22  up to the outer side of the carburetor housing  33 . The hollow shaft  38  is disposed concentrically relative to the butterfly valve  35  and surrounds the same. The butterfly valve shaft  35  is thus mounted on one side of the intake channel  22  in the hollow shaft  38 , and on the opposite side in a bearing means  36  formed in the housing  33 . In this connection, the bearing means  36  is in particular embodied as a bore in the housing  33 . The hollow shaft  38  is similarly mounted in a bearing means  36  that is embodied as a bore in the housing  33 .  
         [0024]    The air valve section  29  is spring-loaded in a closing direction. For this purpose, a helical spring  39  is provided, a first end  46  of which is fixed in position on a pin  40  that extends into the carburetor housing  33 . The helical spring  39  is disposed coaxially relative to the longitudinal axis  51  of the butterfly valve shaft  35 . The second end  47  of the helical spring  39  is fixedly connected with the hollow shaft  38 . For this purpose, a disk  41  is disposed on that end of the hollow shaft  38  that extends out of the housing  33 ; the second end  47  of the helical spring  39  is fixed in position on a finger  52  of the disk  41 . Disposed on that side of the disk  41  that faces away from the housing  33  is a further disk  42  that is fixedly connected with the butterfly valve shaft  35 . The disks  41 ,  42  can, for example, be axially fixed by a screw  53 .  
         [0025]    In FIG. 3, the butterfly valve  26  is illustrated in the open position. In this connection, the air valve section  29  is shown in the plane of the partition  31 . However, the air valve section  29  could also be inclined relative to this plane. The air valve section  29  is fixed in position on the cross member  44  that is connected with the hollow shaft  38 . Formed in the intake channel  22  is the venturi section  45 , in the region of which the main nozzle  28  opens into the mixture channel  21 . In the air channel  8 , the venturi section  45  has a less pronounced configuration.  
         [0026]    The air valve section  29  and the mixture valve section  30  are coupled with one another via engagement members  48 ,  49 . As illustrated in FIG. 4, one engagement member  48  is disposed on the disk  42  that is fixedly connected with the butterfly valve shaft  35 . The other engagement member  49  is disposed on the disk  41  that is fixedly connected with the hollow shaft  38 . In the closing position of the butterfly valve  26 , the engagement members  48 ,  49  have an angular spacing δ relative to one another. This angular spacing is from 5 to 25°, especially from 10 to 20°. An angular spacing δ of about 15° is seen as being advantageous. In the closing position of the butterfly valve  26 , the engagement member  48  rests against an abutment  54  that is advantageously formed on the disk  41 . If the mixture valve section  30  opens, the engagement member  48  moves in a direction toward the engagement member  49 . As soon as the mixture valve section  30  has moved by the maximum rotational moveability α, the engagement member  48  rests against the engagement member  49 . Upon further opening of the mixture valve section  30 , the air valve section  29  is taken along by the engagement members  48 ,  49 , so that the air valve section  29  also opens. With a significant underpressure in the air channel  8 , the air valve section  29  can open against the force of the spring  39  until the engagement member  48  comes to rest against the abutment  54 . Thus, too great of an enrichment of the fuel/air mixture due to the underpressure can be prevented.  
         [0027]    [0027]FIG. 5 makes clear the angular positions of the air valve section  29  and of the mixture valve section  30 . The mixture valve section  30  can move about an opening angle γ up to the completely open position. The opening angle γ is advantageously approximately 75°. Until the mixture valve section  30  has opened about the rotational movement α, the air valve section  29  remains closed. Only thereafter is the air valve section  29  opened. The air valve section  29  thus has an opening angle β that corresponds to the difference of the opening angle γ of the mixture valve section  30  and the maximum rotational movement α. In the opening position, the air valve section  29  is thus inclined by the maximum rotational movement α relative to the longitudinal axis  24  of the intake channel  22 . In this inclined position, however, the air valve section  29  is disposed in the shadow of the butterfly valve shaft  35 , thus avoiding an influencing of the flow in the intake channel  22 . The air valve section  29  can, however, also be disposed in the plane of the partition  31 .  
         [0028]    For assembly, a slot  43  is provided in the carburetor housing  33  through which can be inserted first the mixture valve section  30  with the fixed butterfly valve shaft  35  and subsequently the air valve section  29  with the hollow shaft  38  fixed thereon. An assembly through the intake channel  22  is not readily possible due to the partition  31 .  
         [0029]    [0029]FIG. 4 clearly shows the arrangement of the helical spring  39  having the second end  47  on the finger  52  as well as the first end  46  on the pin  40 . FIG. 5 illustrates the arrangement of the cross member  44  on the periphery of the butterfly valve shaft  35 ,  
         [0030]    It can be expedient to provide further partitions for dividing the intake channel  22  into a number of sections. It can also be expedient to divide the butterfly valve  26  into a plurality of sections. It can furthermore be advantageous to fixedly connect the mixture valve section with a hollow shaft, and to fixedly connect the air valve section with a solid shaft.  
         [0031]    The specification incorporates by reference the disclosure of priority document DE 102 32 341 of Jul. 17, 2002.  
         [0032]    The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.