Abstract:
A carburetor arrangement for an internal combustion engine in a manually guided implement, such as a power chainsaw, a cut-off machine, etc. is provided. A regulating chamber delimited by a regulating diaphragm is provided. Upon deflection of the diaphragm due to underpressure in the regulating chamber, the latter is connected with a fuel tank. Via at least one nozzle, the regulating chamber opens into an air channel that supplies fuel/air mixture to the engine. The carburetor arrangement includes a scavenging pump that is disposed in a return line from the regulating chamber to the fuel tank, and in which is formed a pump chamber. The scavenging pump serves to completely fill the regulating chamber with fuel before start-up of the engine. To prevent the fuel/air mixture from becoming too lean after start-up, especially upon opening of the choke valve, a supply line is provided from the pump chamber into the air channel and supplies additional fuel to the air channel during the run-up phase.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a carburetor arrangement for an internal combustion engine in a manually guided implement, such as a power chainsaw, a cut-off machine, or the like.  
           [0002]    EP 0 786 591 discloses a carburetor arrangement that includes a scavenging pump and an injection pump as the actual starting aid. By actuating the injection pump, fuel can be introduced into the intake channel prior to starting the engine. As a result, an adequate supply of fuel to the internal combustion engine is intended to be achieved already for the first ignitions without a choke. The injected quantity of fuel is, however, consumed as the engine starts.  
           [0003]    An internal combustion engine is generally started with the choke valve closed. If, after start-up of the engine, the choke valve is opened too rapidly, the mixture can become too lean, especially with a cold engine. As a consequence, the engine stalls. A renewed starting with the choke closed can lead to the supply of too much fuel to the combustion chamber. Numerous further attempts are then necessary in order to start the engine.  
           [0004]    It is therefore an object of the present invention to provide a carburetor arrangement of the aforementioned general type that provides an adequate amount of fuel to an internal combustion engine during the starting and run-up phases. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    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:  
         [0006]    [0006]FIG. 1 is a cross-sectional view through one exemplary embodiment of an inventive diaphragm carburetor, with the third and fourth valves open;  
         [0007]    [0007]FIG. 2 shows the carburetor of FIG. 1 with the first and second valves open;  
         [0008]    [0008]FIG. 3 shows the carburetor arrangement in the start-up phase with the choke valve coupled to the valve position; and  
         [0009]    [0009]FIG. 4 shows the carburetor arrangement of FIG. 3 in the run-up phase. 
     
    
     SUMMARY OF THE INVENTION  
       [0010]    The carburetor arrangement of the present invention comprises: a regulating chamber that is delimited by a regulating diaphragm and that, upon deflection of the diaphragm, is connected with a fuel tank, wherein the regulating chamber, via at least one nozzle, opens into an air channel that conveys fuel/air mixture to the internal combustion engine; a scavenging pump that is disposed in a return line that leads from the regulating chamber to the fuel tank, wherein a pump chamber is formed in the scavenging pump; and an intake mechanism that is provided with a supply line that is adapted to establish communication from the pump chamber into the air channel.  
         [0011]    Due to the presence of the supply line from the pump chamber of the scavenging pump into the air channel, additional fuel can be supplied to the air channel. Due to the enrichment of the mixture from the pump chamber in the start-up and run-up phases of the engine, in the operating state the carburetor can be set to a lesser supply of fuel. In the full throttle range, the fuel consumption is thus reduced, whereupon the emissions are also reduced. The additional supply of fuel in the run-up phase causes the engine to already have a high output in this phase. Thus, the full output is not available only after run-up of the engine. The fuel is taken from the pump chamber of the scavenging pump. The pump chamber is thus nearly entirely emptied, so that the operator is forced to actuate the scavenging pump prior to the next start-up. This ensures that the regulating chamber is again completely filled with fuel. A filled pump chamber, which leads to the operator not actuating the scavenging pump, accompanied by simultaneous emptying of the regulating chamber, is thereby avoided.  
         [0012]    It is provided that a first valve is disposed in the supply line that in particular in the run-up phase of the internal combustion engine is open. Thus, fuel can be supplied to the engine in this phase of operation in a precisely controlled manner. In particular, a second valve is disposed in a pressure line that opens into the pump chamber. The pressure line expediently connects the crankcase of the internal combustion engine with the pump chamber. By means of the pressure conveyed via the pressure line into the pump chamber, the discharge of fuel into the air channel is ensured. The valve permits the precise switching on and off of the pressure charge. To avoid a fuel supply from the pump chamber, via the pressure line, into the crankcase of the internal combustion engine, a check valve, especially a diaphragm check valve, is disposed in the pressure line. The first and second valves are expediently coupled in such a way that both valves are either opened or closed. By charging the scavenging pump with pressure via the pressure line, there is ensured that fuel can flow out of the pump chamber to the air channel.  
         [0013]    A third valve is expediently disposed in the return line downstream of the pump chamber. In particular, a fourth valve is disposed in the return line upstream of the pump chamber. The third and fourth valves are in particular coupled in such a way that both valves are either opened or closed. When the third and fourth valves are opened, the scavenging pump can be used to purge the regulating chamber. In particular, the first valve is coupled with the third valve in such a way that one of the two valves is opened and the other is closed. When the third valve is opened, the scavenging pump is in pump operation. Upon actuation of the scavenging pump, fuel is drawn out of the fuel tank into the regulating chamber. Air that has accumulated in the regulating chamber is withdrawn from the regulating chamber with the fuel. Fuel and possibly air pass out of the regulating chamber into the pump chamber. When the pump chamber is nearly filled with fuel, the latter is conveyed into the fuel tank upon further actuation of the scavenging pump. In this phase, the first valve is closed, so that no fuel can pass out of the pump chamber into the air channel. With the first valve opened and the third valve closed, a flow of fuel out of the pump chamber into the fuel tank is prevented. The entire amount of fuel present in the pump chamber flows into the air channel. The second valve is expediently also coupled with the fourth valve in such a way that one of the valves is opened and the other is closed.  
         [0014]    It is provided that a throttle valve is disposed in the supply line. As a result, it is possible to regulate the amount of fuel additionally introduced into the air channel via the supply line. In particular, a check valve is disposed in the supply line, with the opening pressure of the check valve being greater than the pressure that during idling of the internal combustion engine prevails in the pressure line. The check valve can, for example, have an opening pressure of 100 to 600 mbar, especially 200 to 400 mbar. Due to the check valve, a supply of fuel via the supply line is prevented during idling of the internal combustion engine.  
         [0015]    The first, second, third and fourth valves are advantageously formed in a common valve slide. In this way, the valves are reliably coupled with one another. An appropriate valve slide or rotary valve can be produced in a straightforward manner. It is robust and can be easily operated. The diaphragm carburetor is provided with a pivotably mounted butterfly valve in the air channel, and upstream of the butterfly valve has a pivotably mounted choke valve. The position of at least one valve is advantageously coupled with the position of the choke valve. In particular, with choke valve open, the first valve is opened and the third valve is closed. During start-up of the engine, the regulating chamber can thus first be flooded with fuel. The choke valve is already closed for the start-up of the engine. The engine is then started. During opening of the choke valve, the first valve is opened, so that additional fuel is conveyed to the air channel in the run-up phase.  
         [0016]    To prevent actuation of the scavenging pump in the run-up phase and in the operating phase, a cover element is provided, the position of which is coupled to the position of the third valve, and which cover element releases the scavenging pump when the third valve is opened. This ensures that the scavenging pump can only be used to draw fuel into the regulating chamber, and a pumping of fuel into the air channel via the first valve and the supply line is prevented.  
         [0017]    Further specific features of the present invention will be described in detail subsequently.  
       DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]    Referring now to the drawings in detail, illustrated in FIG. 1 is a carburetor arrangement that comprises a diaphragm carburetor  1  into which is integrated a scavenging pump module  33 . The scavenging pump module  33  can, however, also be embodied separately. Formed in the diaphragm carburetor  1  is an air channel  2  in which are disposed a rotatably or slidably mounted choke valve  20  and, downstream of the choke valve, a butterfly valve  21 . The air channel  2  is provided in particular in the region between the choke valve  20  and the butterfly valve  21  with a venturi section  45 . A primary idling nozzle opens out in the region of the butterfly valve  21 , and upstream of the primary idling nozzle  16  a secondary idling nozzle  17  opens out into the air channel  2 . With the butterfly valve  21  closed, the primary idling nozzle  16  is disposed downstream of the butterfly valve  21  and the secondary idling nozzle  17  is disposed upstream of the butterfly valve  21 .  
         [0019]    A main nozzle  30  opens out into the air channel  2  in the region of the venturi section  45 . The fuel supply of the idling nozzles  16 ,  17  can be adjusted via an idling set screw  18 . The fuel supply of the main nozzle  30  is adjustable via a main set screw  19 . The nozzles  16 ,  17 ,  30  are supplied from a regulating chamber  11 , which is in turn supplied with fuel from the fuel tank  22 . A regulating diaphragm  12  is disposed in a wall that delimits the regulating chamber  11 . That side of the regulating diaphragm  12  that faces away from the regulating chamber  11  is acted upon by pressure, for example by the pressure that prevails downstream of the air filter, or by ambient pressure. If there is an underpressure in the regulating chamber  11 , the regulating diaphragm  12  is deflected in a direction toward the regulating chamber  11 . The inlet control lever  13 , which is mounted on a pin  46  and is supported against one wall of the regulating chamber  11  via the inlet spring  14 , actuates the inlet needle  15 , which thereby releases the opening  48 . The regulating chamber  11  is thus supplied with fuel via the fuel line  47 .  
         [0020]    A fuel filter  10  is disposed in the fuel line  47 . Disposed upstream of the fuel filter  10  is the diaphragm pump  3 , which serves for conveying the fuel. The fuel line  47  is connected with the fuel tank  22  via the fuel intake connector  4 . The diaphragm pump  3  is provided with a pump diaphragm  7 , one side of which delimits the fuel line  47 , and the other side of which is in contact with a pulse chamber  8  that communicates with a pulsating pressure via a pulse fitting  9 . As a consequence of the pulsating pressure, the pump diaphragm  7  is deflected, especially toward both sides. Disposed upstream of the pump diaphragm  7  is an inlet valve  5 , and disposed downstream of the pump diaphragm is an outlet valve  6 . The inlet valve  5  and the outlet valve  6  are embodied as check valves and prevent a return flow of the fuel. When the inlet valve  5  is opened, fuel flows into the diaphragm pump  3 . As the pressure in the diaphragm pump  3  increases, the outlet valve  6  opens, while the inlet valve  5  closes. The fuel flows out of the diaphragm pump  3 .  
         [0021]    The scavenging pump module  33  includes a scavenging pump  23  having a pump bellows  24 , which is in particular made of an elastic polymeric material. The scavenging pump  23  also has a pump chamber  25  that is formed in the pump bellows  24 . In this connection, the pump chamber  25  designates the chamber into which fuel is drawn during operation of the pump, and out of which the fuel is pressed. From the regulating chamber  11 , a return line  35  leads through the scavenging pump  23  to the fuel tank  22 . Disposed upstream of the scavenging pump  23 , in the return line  35 , is a check valve  27 , and disposed downstream of the scavenging pump  23  is a check valve  28 . The check valves  27 ,  28  are in particular disposed directly at the inlet and the outlet into and out of the pump chamber  25  respectively. The check valves ensure that the scavenging pump  23  can convey fuel only in the conveying direction  26 . A flowing of the fuel in the opposite direction is prevented by the check valves  27 ,  28 . Formed in the return line  35 , between the regulating chamber  11  and the scavenging pump  23 , is a fourth valve  44 . Downstream of the scavenging pump  23  the return line  35  is provided with a third valve  43 . The valves  43  and  44  are formed in a common valve slide  31 . Thus, the third valve  43  and the fourth valve  44  are opened and closed in common. Also disposed in the valve slide  31  are a first valve  41  and a second valve  42 , which are both closed in the position of the valve slide  31  shown in FIG. 1.  
         [0022]    In the position of the valve slide  31  shown in FIG. 1, by pressing the pump bellows  24  in, the fuel present in the pump chamber  25  is partially pressed out of the pump chamber through the check valve  28 . When the shape of the pump bellows  24  returns due to its elasticity, an underpressure is produced in the pump chamber  25  that effects a flowing of fuel from the regulating chamber  11  into the pump chamber  25 . In this way, fuel is drawn in from the fuel tank  22  via the regulating chamber  11 . The underpressure in the pump chamber  25  produces in the regulating chamber  11  an underpressure that effects the opening of the opening  48 . As a result, fuel is drawn into the regulating chamber  11  from the fuel tank  22 . From the regulating chamber  11 , fuel and air that has accumulated in the regulating chamber  11  are drawn into the pump chamber  25 . When the pump chamber  25  is nearly full of fuel, upon further actuation of the scavenging pump the fuel is pressed via the return line  35  into the fuel tank  22 . This ensures that even after the internal combustion engine has not been running, the regulating chamber  11  can be completely filled with fuel prior to starting the engine.  
         [0023]    In FIG. 2, the diaphragm carburetor  1  is shown with the valve slide  31  in a position in which the first valve  41  and the second valve  42  are opened, and the third valve  43  and the fourth valve  44  are closed. The second valve  42  is disposed in a pressure line  37  that connects the pump chamber  25  with the crankcase  39  of an internal combustion engine  38 . The section of line between the second valve  42  and the scavenging pump  23  is thereby at the same time a portion of the return line  35  when the second valve  42  is closed and the fourth valve  44  is opened. The check valve  27  thus also acts in the pressure line  37 . Disposed in the pressure line  37  is a diaphragm check valve  29  that rectifies the pulse from the crankcase, which has an approximately sinusoidal shape. Thus, only the high pressure sides of the pulse can reach the pump chamber  25 . As a result, there is largely prevented a drawing-in of fuel from the pump chamber  25  and the pressure line  37  into the crankcase  39 .  
         [0024]    Downstream of the pump chamber  25 , a supply line  36  leads from the pump chamber into the air channel  2 . The supply line  36  opens into the air channel  2  via a bore  32 . Disposed in the supply line  36  is the first valve  41 , which is formed in the valve slide  31  and is thus coupled with the second, third and fourth valves. The portion of the line formed between the first valve  41  and the pump chamber  25  is a portion of the return line  35  when the third valve  43  is opened and the first valve  41  is closed. Disposed downstream of the first valve  41 , in the supply line  36 , is a throttle valve  34  that serves to regulate the quantity of fuel that is to be injected.  
         [0025]    Prior to starting the engine, and during the first combustions, in particular as long as the choke valve  20  is closed, the valve slide  31  is expediently in the position illustrated in FIG. 1, where the third valve  43  and the fourth valve  44  are open. After the engine has started, especially during the run-up phase after the first combustions, i.e. with the choke valve  20  open, the valve slide  31  is expediently in the position illustrated in FIG. 2, where the first valve  41  and the second valve  42  are open, and the third valve  43  and the fourth valve  44  are closed.  
         [0026]    In the position of the valve slide  31  illustrated in FIG. 2, the fuel is conveyed out of the pump chamber  25  into the air channel  2  via the supply line  36  as a consequence of the pressure that is produced in the crankcase  39  and that is conveyed via the pressure line  37  into the pump chamber  25 . As a result, the fuel/air mixture in the air channel is enriched with additional fuel. This prevents the fuel/air mixture from becoming lean. At the same time, the pump chamber  25  is thereby in particular completely emptied. The quantity of fuel present in the pump chamber  25  is expediently such that after injection of the fuel quantity into the air channel  2 , the internal combustion engine  38  has run up, and an enrichment of the fuel/air mixture is no longer necessary.  
         [0027]    To couple the position of the valves  41 ,  42 ,  43 ,  44  to the position of the choke valve  20 , a coupling mechanism  49 , such as that illustrated in FIGS. 3 and 4, can be provided. The control lever  40  of the choke valve  20  is coupled via the coupling mechanism  49 , which can, for example, be embodied as a lever, to a lever  50  that is fixedly connected with the choke valve  20 . Actuation of the control lever  40  thus effects, via the coupling mechanism  49  and the lever  50 , an opening or closing of the choke valve  20 . The control lever  40  at the same time actuates the slide valve  31 , in which the valves  41 ,  42 ,  43 ,  44  are formed.  
         [0028]    In FIG. 3, the system is illustrated in the starting position. The choke valve  20  is closed. The butterfly valve  21  is slightly opened. By means of the lever  50  and the coupling mechanism  49 , the control lever  40  is coupled with the position of the choke valve  20 . The control lever  40 , which is embodied as a tilt lever, simultaneously actuates the valve slide  31 . The pivot point  51  of the control lever  40  is fixed in position on the scavenging pump module  33 . When the choke valve  20  is closed, the third valve  43  and the fourth valve  44  in the valve slide  31  are open, as illustrated in FIG. 3. By actuating the scavenging pump  23 , fuel can thus be drawn out of the fuel tank  22  and into the regulating chamber  11 . After the regulating chamber  11  is completely filled with fuel, the engine is started. Due to the closed choke valve  20 , air can flow in the direction of the internal combustion engine only through a bypass formed in the choke valve  20 . By means of the idling nozzles  16  and  17 , fuel is supplied to the combustion air. The fuel/air mixture, which has a relatively high proportion of fuel, is supplied to the internal combustion engine  38 .  
         [0029]    After the first few combustions, the choke valve  20  is opened by the operator. This can be effected, for example, by actuating the control lever  40 . The opened choke valve  20  is illustrated in FIG. 4. The control lever  40  has a portion  52  that in the position of the control lever  40  illustrated in FIG. 4 covers the pump bellows  24  of the scavenging pump  23 . The pump bellows  24  is not accessible for the operator, so that an actuation of the scavenging pump  23  is prevented. The control lever  40  simultaneously actuates the valve side  31 , as a result of which the third valve  43  and the fourth valve  44  are closed, and the first valve  41  and the second valve  42  are opened. The pump chamber  25  is connected via the pressure line  37  with the crankcase  39  of the internal combustion engine  38 . The overpressure that is rectified by the diaphragm check valve  29  presses the fuel out of the pump chamber  25  into the supply line  36 . By means of the bore  32 , the fuel is supplied to the air channel  2 . As a result of the opened choke valve  20 , a large portion of combustion air can flow through the air channel  2  in the direction of the internal combustion engine  38 . An adequate fuel supply is ensured in the run-up phase by the fuel from the pump chamber  25  that is additionally supplied to the air channel  2 . As soon as the pump chamber  25  is emptied, no additional fuel can any longer be supplied to the air channel  2 . Since to this point in time the engine has warmed up, additional supply of fuel is no longer necessary.  
         [0030]    Instead of the valves formed in the valve slide, individual valves can also be provided that can be coupled in any desired manner. The opening pressure of the check valve  27  or  28  can expediently have an opening pressure of 100 to 600 mbar, especially 200 to 400 mbar. At a pressure in the pressure line  37  during idling of the internal combustion engine  38  of about 50 mbar, an opening pressure of the check valve  28  of about 250 mbar is advantageous. Instead of the portion  52  of the control lever  40  that covers the pump bellows  24  of the scavenging pump  23 , and thus forms a cover element, and which is monolithically formed with the control lever  40 , it can be advantageous to provide for this purpose a separate cover element, the position of which is coupled to the position of the valves, i.e. of the valve slide. To make the scavenging pump  23  inaccessible, the cover element expediently covers the scavenging pump  23  at least partially; however, it can also be advantageous for the cover element to make the scavenging pump  23  inaccessible or to expose it in some other manner.  
         [0031]    The specification incorporates by reference the disclosure of German priority document 102 33 282.7 filed 23 Jul. 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.