Abstract:
A carbureted two-cycle engine including an intake channel, a choke valve in the intake channel fixed to a pivotable choke valve shaft and lever, and a throttle valve in the intake channel fixed to a pivotable throttle valve shaft and lever. The engine includes an air channel in communication with fresh air, and an air valve fixed to a pivotable air valve shaft and lever. A piston within a cylinder of the engine includes a transfer port for intermittently connecting the intake channel and the air channel with a combustion chamber. An activating lever pivotably mounted to the air valve shaft transmits movement of the throttle lever to the air valve lever after a predetermined angle of rotation of the throttle lever. A fast idle latch is engagable by the choke lever to hold the throttle lever in a fast idle position until the throttle lever is separately moved.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to carburetors for two cycle engines, and more particularly to a carburetor and air-valve assembly and linkage.  
           [0002]    Two-cycle engines are desirable for handheld tools where weight is critical because of their high power to weight ratio as compared to four-cycle engines. However, trapping efficiency of conventional two-cycle engines will not meet the low emissions requirements set forth by government regulations in the future because the fundamental design of the two-cycle engine results in too much unburned fuel being discharged into the atmosphere.  
           [0003]    The discharge of raw, unburned fuel into the atmosphere is substantially caused by the exhaust and transfer ports being opened and closed by the piston, and for a small period both are open simultaneously during the piston travel. During that small duration of time, when both the intake and exhaust ports are open, the unburned fuel can exit the engine, which increases the measured emissions output of the engine while decreasing the engine&#39;s efficiency. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0004]    [0004]FIG. 1 is a front view of a carburetor and air-valve assembly according to a first embodiment of the present invention;  
         [0005]    [0005]FIG. 2 is a cross-sectional view of the carburetor and air-valve assembly of FIG. 1 in which the valve positions are shown in an idle mode of operation;  
         [0006]    [0006]FIG. 3 is a cross-sectional view of a second embodiment of a carburetor and air-valve assembly according to the present invention;  
         [0007]    [0007]FIG. 4 is a cross-sectional view of a third embodiment of a carburetor and air-valve assembly according to the present invention;  
         [0008]    [0008]FIG. 6 is a left side view of the carburetor and air-valve assembly of FIG. 1;  
         [0009]    [0009]FIG. 7 is a rear view of the carburetor and air-valve assembly of FIG. 1 showing a throttle trigger attached thereto;  
         [0010]    [0010]FIG. 8 is a right side view of the carburetor and air-valve assembly of FIG. 1;  
         [0011]    [0011]FIG. 9 is a cross-sectional view of the carburetor and air-valve assembly of FIG. 1 taken along of section line  9 - 9 ;  
         [0012]    [0012]FIG. 10 is a view of the carburetor and air-valve assembly of FIG. 1 taken in the direction of line B-B in FIG. 6, including a choke knob attached thereto;  
         [0013]    [0013]FIG. 11 is the same view as FIG. 10 but showing the throttle lever rotated until it first starts to open the air valve;  
         [0014]    [0014]FIG. 12 is the same view as FIG. 10 but showing the throttle lever at full open position and the air valve also is rotated to its full open position;  
         [0015]    [0015]FIG. 13 is the same view as FIG. 10 but showing the throttle lever in a fast idle position, and the choke knob pulled out to a full choke position;  
         [0016]    [0016]FIG. 14 is the same view as FIG. 13 but showing the choke pushed in to it&#39;s normally open position, and the fast idle still activated;  
         [0017]    [0017]FIG. 15 is a view of the carburetor and air-valve assembly according to a third embodiment of the invention, corresponding to the view of FIG. 10, including an adjustment screw;  
         [0018]    [0018]FIG. 16 is a view of the carburetor and air-valve assembly according to a fourth embodiment of the invention, corresponding to the view of FIG. 10;  
         [0019]    [0019]FIG. 17 is a view of the embodiment of FIG. 17 with the levers rotated to a full throttle position;  
         [0020]    [0020]FIG. 18 is a chart depicting the relationship between the air and throttle valve progression from fully closed through fully open according to the present invention;  
         [0021]    [0021]FIG. 19 is a cross sectional view of the carburetor and air valve assembly of FIG. 1 taken along section line  19 - 19 , including an engine cylinder; and  
         [0022]    [0022]FIG. 20 is a cross sectional of a carburetor and air valve assembly, corresponding to FIG. 110, according to a sixth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    According to the present invention, a first embodiment of a carburetor and air valve assembly  10  is shown in FIGS. 1, 2,  6 - 15 ,  18  and  19 . Referring to FIG. 2, a carburetor  12  serves for supplying fuel and air mixture to an internal combustion engine  14 . The carburetor  12  is a diaphragm-type carburetor  12  for an internal combustion engine  14  that operates with stratified air scavenging, specifically but not limited to hand held power equipment, such as chain saws, string trimmers, brush cutters, pole saws, or the like. The carburetor  12  comprises a carburetor housing  16  in which is formed a continuous intake channel portion  18  having a venturi section  20 . The carburetor has two independent butterfly valves within the intake channel  18 . The first valve is called the choke valve  22 , and when closed it restricts the air opening to enrich the fuel-air ratio for improved cold starting performance. The second valve inside the carburetor  12  is the throttle valve  24 , which varies the amount and flow of the fuel-air mixture, which in turn controls the engine speed.  
         [0024]    The throttle valve  24  is located down stream from the venturi section  20 . The throttle valve  24  is pivotally held via a shaft  26  that is mounted in the carburetor housing  16 . A main fuel-delivery duct  28  opens into the venturi section  20 . Fuel-delivery idle ducts (not shown) open into the intake channel portion  18  in the vicinity of the throttle valve  24 . The channels and ducts are supplied fuel from the fuel-filled control chamber (not shown) from within the carburetor housing  16 , which are in turn supplied via fuel line from a fuel tank (not shown). The fuel is pumped to the carburetor  12  via a fuel pump powered by fluctuating crankcase pressure from the two-cycle engine  14 .  
         [0025]    In addition to the intake channel portion  18 , by means of which a fuel/air mixture is supplied to the internal combustion engine  14 , an air channel  30  is provided and has an air butterfly valve  32  mounted on a pivotable shaft  34 . The air channel  30  acts as a bypass to the intake channel portion  18  and connects a clean air side of an air filter housing  36  with an airport  38  in the cylinder  40 . By way of the linkage described below, the two separate valves  24 ,  32  are timed and orientated specifically to obtain peak performance of the engine in the forms of horsepower and emissions.  
         [0026]    As best seem from FIG. 9, the shaft  26  of the throttle valve  24  and the shaft  34  of the air valve  32  are disposed approximately parallel to one another. Alternatively, the throttle valve shaft  26  may be disposed at an angle relative to the air valve shaft  34  according to the present invention.  
         [0027]    The carburetor  12  is responsible for delivering a blend of fuel and air to the engine  14 , which is drawn into the crankcase through a fuel port  42  on the side of the cylinder  40 . This cylinder fuel port  42  is opened and closed by the piston  44  pivotally connected to the crankshaft that rotates horizontally in the crankcase and is supported by bearings. The carburetor  12  is constructed similarly to that of a conventional two-cycle engine, but with a slightly smaller venturi  20  size to compensate for the air channel  30 . The combined cross-sectional areas of the air channel  30  and intake channel  18  of the carburetor  12  are similar to that of a standard two-cycle engine. Once the fuel/air enters the crankcase it is fed to the combustion chamber by transfer ports  46 ,  48 , which are also opened and closed by the piston&#39;s  44  travel up and down the cylinder bore. These ports  46 ,  48  opening and closing are timed to achieve maximum performance.  
         [0028]    The air channel  30  and air valve  32  are responsible for delivering fresh air to the top of the transfer ports  46 ,  48  in order to help improve the emissions characteristic of the two-cycle engine  14 . This stratified air scavenging engine concept is designed to reduce the amount of unburned fuel that leaves the combustion chamber when the exhaust port is open. This is achieved by dispersing the fresh air from the air channel  30  into the combustion chamber first when the exhaust port is open, and scavenging the exhausted fuel with the fresh air. Immediately following the fresh air charge is the fuel-air mixture that is delivered from the crankcase through the transfer ports  46 ,  48  into the combustion chamber. By separating the fresh air and the fuel-air mixture in such a stratified fashion to reduce the unburnt fuel discharged from the exhaust port, engine emissions are reduced and engine efficiency is increased.  
         [0029]    In the first embodiment, shown in FIG. 2, the air channel  30  is formed by a separate air valve housing  50 , which is trapped between the carburetor housing  16  and the air filter housing  36 . Carburetor mounting screws  52  are used to secure the air valve housing  32  and the air filter housing  36  to an intake adaptor  54 . The air channel  30  is transversely connected to the intake adaptor  54  by a flexible rubber tube  56 . The rubber tube  56  forms an airtight seal at its ends  58 ,  60  on each of the air valve housing  32  and intake adaptor  54 , respectively. Alternately the air channel  30  could be formed by a rigid material instead of the rubber tube  56  described.  
         [0030]    The intake adaptor  54  provides heat insulation between the engine  14  and the carburetor  12  and the air inlet  30 . Excessive heat on the carburetor  12  from the engine  14  will vaporize the gasoline prematurely and cause what is commonly known as “vapor lock.” If this occurs, not enough fuel enters the engine  14  and the engine  14  will not function.  
         [0031]    Both the air channel  30  and the intake channel  18  are connected to the air filter housing  36  which contains a filter element. The filter element traps and prevents dirt, dust and other particles from entering the engine  14 , which would cause internal damage to the engine components. The air channel  30  is connected to a clean air chamber  62  of the air filter housing  36  to the intake adaptor  54 , which feeds the cylinder air port  38 . The clean air chamber  62  inside the air filter housing  36  may be a single chamber or may alternately be separated into individual and separate areas by a divider wall  64  formed in the air filter housing  36 .  
         [0032]    According to a second embodiment, as shown in FIG. 3, the air valve  32  and a pivotable air valve shaft  34  are secured within an alternative air filter housing  36 ′ which would eliminate the air valve housing  50  of the first embodiment.  
         [0033]    According to a third embodiment, as shown in FIG. 4, similar to that in FIG. 3, a straight tube  56 ′ could be used by extending a second alternative filter housing  36 ″ out and downward.  
         [0034]    According to a fourth embodiment, as shown in FIG. 5, the intake adapter  54 ′ is formed of two pieces, a first intake adapter portion  54   a ′ and a second intake adapter portion  54   b ′. The second intake adapter portion  54   b ′ has an angular offset which allows the use of a straight tube  56 ″ to connect to the filter housing  36 ′, rather than the curved tube  56  of the first and second embodiments. Further, the two piece intake adapter  54 ′ may be formed through conventional casting methods since each portion  54   a ′,  54   b ′ does not contain any compound curves.  
         [0035]    Referring again to the first embodiment shown in FIGS. 1, 2,  6 - 15 ,  18  and  19 , a linkage mechanism described hereinafter functionally connects the throttle valve  24  and air valve  32 . Additional linkage also allows for a choke operation during cold starting, and a fast idle setting for starting. This is achieved with several levers that all work together to rotate the butterfly valves into ideal positions for different modes of operation.  
         [0036]    The air valve  32  must cooperate with the throttle valve  24  in the carburetor  12  since both valve  24 ,  32  are responsible for governing the amount of fuel-air mixture that is delivered to the engine  14 . The air valve  32  must also remain closed during slow engine speeds, like starting and idling, or the engine  14  will stall because the mixture goes too lean (not enough fuel to produce combustion). The linkage mechanism describe hereinafter is designed to not open the air valve  32  until the throttle valve  24  has rotated approximately 30 degrees from its normally closed position. This angle can be adjusted as appropriate for a particular application. Referring to FIG. 18, once the air valve  32  starts to open, its progression to a fully open position is non-linear, and does not have the same opening rate as the throttle valve  24 . The different slopes between the throttle valve  24  and air valve  32  allow for optimization of performance for mid-range power and acceleration. This progression can be modified by use of cam shapes on the lever or lobe-shaped slider pin. The opening of the air valve  32  is opened slowly, so to not drown the engine with too much fresh air. Once the throttle valve  24  has achieved approximately 86% full open, the air valve  32  has less affect, and therefore can complete it&#39;s progression to full open at an accelerated rate.  
         [0037]    As best shown in FIGS. 7 and 9, a first end  66  of the throttle valve shaft  26  carries a throttle valve actuating lever  68  that is connected with a throttle trigger  70  by means of a wire or cable  72  for adjusting the throttle valve  24 . In particular, the actuating lever  68  is fixedly disposed at the first end  66  of the butterfly valve shaft  26  and is spring loaded in the closing direction of the throttle valve  24  by means of a return spring  74 .  
         [0038]    A second end  76  of the throttle valve shaft  26  projects out of the carburetor housing  16  and fixedly carries a throttle lever  78 . On opposite ends of the throttle valve shaft  26 , the actuating lever  68  and the throttle lever  78  both being fixedly fastened to the throttle valve shaft  26  rotate together. The air valve shaft  34  carries an air valve lever  80 , which is fixedly disposed at an end  82  of the air valve shaft  34 , and is spring loaded in the closing direction of the air valve  32  by means of an air valve return spring  84 . An activating lever  86  is pivotally mounted on the air valve shaft  34 , but is not fixed to the air valve shaft  34 , and therefore is free to rotate about the air valve shaft  34 . The activating lever  86  is spring loaded in the closing direction of the air valve  32  by means of a return spring  88 . The activating lever  86  has a protruding member  90  that will contact the air valve lever  80  on the air valve shaft  34  at a specific point during it&#39;s rotation, at an angle of engagement  92  as shown in FIG. 12. This angle of engagement  92  corresponds to the angle that the throttle valve  24  must rotate before the air valve  32  starts to move and is a functional aspect of the two-stroke engine&#39;s acceleration performance. The nominal measure of the angle of engagement  92  is approximately 30 degrees, but can be varied to obtain different acceleration properties.  
         [0039]    An alternative design according to a third embodiment of the present invention is shown in FIG. 15 which includes an adjustment screw  94  is shown fastened into the activating lever  86  and the end of the adjustment screw  94  contacts the air valve lever  80 . By turning the adjustment screw  94  in and out it will effectively change the angle of engagement  92  from the nominal 30-degree angle. This adjustment will allow for manufacturing to accommodate for variances that occur because of normal manufacturing tolerances.  
         [0040]    As shown in FIG. 10, the activating lever  86  has a protruding boss  96 , which intersects the path of the throttle lever  78  and forms a transmission connection between the throttle valve  24  and air valve  32  (see FIG. 9). The boss  96  slides along the throttle lever  78  for the entire range of angular rotation  98  of the throttle valve shaft  26  to fully open the throttle valve  24  as shown in FIG. 12. During the angle of rotation  98  of the throttle valve  24  the activating lever  86  will progress through its angular range of rotation  100  until the air valve shaft  34  has also achieve full open position for the air valve  32 . The progression of the throttle valve  24  opening in respect to the air valve  32  will have an affect on the acceleration of the two-stroke engine&#39;s performance. Both the throttle valve  24  and the air valve  32  by design will open fully at the end of the rotational travel  98  and  100 , but the rate of opening maybe different. FIG. 18 shows an example of the rate of opening of the throttle valve  24  and the air valve  32 .  
         [0041]    An alternate design according to a fourth embodiment of the present invention is shown in FIG. 16 &amp; FIG. 17. The pivotally mounted activating lever  86  is replaced with a fixed activating lever  102 . The fixed activating lever  102  is positively connected to the end of the air valve shaft  34  and the air valve lever  80  so that they rotate together. There is an intentional clearance  104  between the throttle lever  78  and a protruding boss  106  on the activating lever  102 . The clearance  104  allows for the throttle valve  24  to open 30 degrees of rotation while the air valve  32  remains closed. After the initial 30 degrees of travel of the throttle lever  86 , the throttle lever  86  will contact the protruding boss  106  on the activating lever  102  and start rotating the air valve  32  in the opening direction. Both the throttle valve  24  and the air valve  32  will reach full open position at the same time, but not at the same rate, similar to FIG. 18. The throttle valve  24  and air valve  32  are shown in FIG. 17 at their respective full open positions with the levers  78 ,  80  at their full limits of travel  108  and  110 .  
         [0042]    As shown in FIG. 18 the slope and intersection points of the curves can be arranged and changed with change in pivot positions of the two butterfly valve shafts  34 ,  26  in respect to each other, and in respect to the contact point of the protruding boss  96  or  106 , along with the angle of engagement  92  of first contact between the activating lever  86  and air valve lever  80 . Even the physical shape of the contact boss  96  can be changed from a true circle cross section to one of an elliptical shape, cam profile, or other shape. A contact surface  112  of the throttle lever  78  can also be formed with a curved profile to achieve a similar change in the curves shown in FIG. 18.  
         [0043]    Starting from idle position shown in FIG. 10 and FIG. 2, the throttle valve  24  is opened by pivoting the throttle valve shaft  26  in an opening direction  114 , so that greater quantity of fuel-air mixture is conveyed to the internal combustion engine  14  so that the speed of the internal combustion engine increases. As soon as the throttle valve  24 , i.e. the throttle valve shaft  26 , in the opening direction  114  has transmittally rotated the activating lever  86  through a free play extent to the angle of engagement  92  that is determined by the spacing between the protruding member  90  on the activating lever  86  and the air valve lever  80 , then by means of rotational force i.e. torque, the air valve lever  80  is also pivoted in an opening direction  116 , as a result of which by means of the shaft  34  the air valve  32  in the air channel  30  is carried along in the opening direction  116 . In addition to the fuel-air mixture, air for combustion by itself, which is expediently collected previously in the transfer ports  46 ,  48  from the crankcase to the combustion chamber, is conveyed to the internal combustion engine via the air channel  30 . For this purpose, as shown in FIG. 19, a branch element  118  is formed by the piston casting  44 ; the branching air supply channels  120  and  122  formed in the piston casting  44  open into the corresponding transfer ports  46  and  48 .  
         [0044]    An alternate design according to a sixth embodiment of the present invention is shown in FIG. 20, where an alternative air channel  30 ′ branch element  142  is located upstream from the piston  44 , which has separate air channels  120  and  122  formed in an alternative piston casting  44 ′. The branch element can be formed within the casting of the cylinder  40 , or within the intake adaptor  54 , or within the air tube  56 , or any combination thereof.  
         [0045]    Along with the mechanical transmission between the air valve and the throttle valve there is another mechanism that allows for easier starting of the two-cycle engine. A “fast idle” portion of the linkage mechanism mounted on the carburetor  12  is designed to manually advance the throttle valve  24  position approximately 20 degrees for starting of the engine  14 . Of course, this angle can be adjusted as appropriate for a particular application. This throttle advance allows for easier starting of the engine  14  since there will be more fuel allowed to enter the engine than would be allowed at the normally closed or idle position. A fast idle lever  124  is rotated when a choke knob  126  is pulled by the operator, which in turn rotates the choke valve  22 . The fast idle lever  124  is pivoted to a choke valve shaft  128  such that it is free to rotate about the choke valve shaft  128 . When the choke knob  126  is pulled, a choke valve lever  130  catches the fast idle lever  124  and rotates it which in turn lifts the throttle valve lever  78  into the “fast idle position.” The two levers  78 ,  124  are held in place by a small catch or notch  138  formed into the throttle lever  78 . The choke knob  126  can be pushed back in to open the choke valve  22  without affecting the fast idle advance because the fast idle lever  124  turns freely on the choke valve shaft  128 . Small torsion springs are located on both valve shafts  26 , choke valve shaft  128  to provide positive return force to their normal positions.  
         [0046]    As shown in FIG. 13 pulling the choke knob  126  out to a limit of linear travel  134 , which is nominally 10 mm, will transversely rotate the choke valve shaft  128  for an angle of rotation  132 . The end of the choke knob  126  is pivotally connected to the choke lever  130 . The choke lever  130  is fixed to the end of the choke valve shaft  128  and has a butterfly valve  22  affixed to the choke valve shaft  128 . The choke valve shaft  128  is pivotally mounted in the carburetor housing  16  and when closed will enrich the fuel to air ratio for easier cold starting of the two-cycle engine  14 . The choke lever  130  when rotated will contact a fast idle latch or lever  124 . The fast idle lever  124  is pivotally mounted on the choke valve shaft  128  and is free to rotate about that axis. When the fast idle lever  124  is rotated by the choke lever  130  through it angle of rotation  132  it contacts the throttle lever  78  and rotates the throttle lever  78  for an angle of rotation  136  to a fast idle position. In this embodiment, the angle of rotation  136  is approximately 20 degrees open from its at rest, closed position and allows the throttle valve  24  to be positioned for optimum starting of the two-cycle engine. The throttle lever  78  is held in the starting position by a small notch  138  (FIG. 12) formed in the throttle lever  78  which the fast idle lever  124  engages.  
         [0047]    Often when starting a two-cycle engine it is necessary to repeatedly open and close the choke valve. During this process, the throttle lever  78  it is kept in the fast idle position by the fast idle lever  124  as shown in FIG. 14. The choke knob  126  can be pushed back-in the limit of travel  134  to open the choke butterfly valve  22  by means of the transmission connection. The fast idle lever  124  will remain engaged in the notch  138  in the throttle lever  78 , and the throttle lever  78  will stay at the rotated angle  136  or the fast idle position. This is achieved because the fast idle lever  124  is freely pivot about the choke valve shaft  128 . A return spring  140  as shown in FIG. 6 is connected to the fast idle lever  124  and the carburetor housing  16 . The return spring  140  acts upon the fast idle lever  124  in a counterclockwise direction (opposite direction  114 ), which will disengage the fast idle lever  124  from the throttle lever  78 . Thus, the fast idle lever  124  can be returned to the normal at-rest position by activating the throttle trigger  70  which is connected to the throttle lever  78 . When the throttle lever  78  is rotated open, the fast idle lever  124  is released by the notch  138  in the throttle lever  78  allowing the return spring  140  to rotate the fast idle lever  124  back to the normal at-rest position.  
         [0048]    Although the described embodiments related to a piston ported two-cycle engine with stratified air scavenging, meaning the piston  44  opened and closed the air port  38  during the normal piston stroke in the cylinder  40 , the present invention can be equally utilized on a two-cycle engine with stratified air scavenging with a reed style check valve mounted in the transfer ports  46 ,  48 .  
         [0049]    It should be evident that this disclosure is by way of example and that various changes maybe made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.