Abstract:
A carburetor for an internal combustion engine has a carburetor housing and a mixture forming passage provided in the carburetor housing. A throttle and a choke valve are rotatably arranged in the mixture forming passage on a throttle shaft and a choke shaft, respectively. A lever arrangement has a throttle adjusting lever mounted on the throttle shaft and a choke adjusting lever mounted on the choke shaft. The throttle valve and the choke valve are adjustable in several operating positions and the lever arrangement assumes appropriate positions corresponding to the operational positions, respectively. A release device for releasing a locking action between the throttle adjusting lever and the choke adjusting lever when an emergency stop is actuated is provided. A spring forcing the choke adjusting lever in a direction toward an engagement plane with the throttle adjusting lever.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a carburetor for an internal combustion engine comprising a mixture forming passage formed in a carburetor housing in which passage a throttle valve and a choke valve are rotatably supported. A lever arrangement is provided that comprises a throttle adjusting lever attached to the throttle shaft and a choke adjusting lever attached to the choke shaft, wherein the throttle valve and the choke valve are adjustable in several operating positions and the lever arrangement assumes corresponding positions. 
         [0002]    U.S. Pat. No. 6,550,749 discloses a carburetor for an internal combustion engine of a motor-operated hand-held power tool. The carburetor comprises a throttle valve and a choke valve. For adjusting the throttle valve and the choke valve in interdependent positions as a function of several operating positions such as idle position, cold start position, and warm start position, a switch is provided that is arranged directly on the carburetor and is connected to the choke valve. In this connection, the choke valve and the throttle valve are mechanically coupled with another in such a way that the switch in each of the operating positions assumes a different position. Upon rotation of the switch, an intermediate plate that is supported on the choke shaft is rotated and locks in a predetermined position at the throttle lever. 
         [0003]    U.S. Pat. No. 6,000,683 discloses a carburetor for small internal combustion engines that comprises a throttle valve and a choke valve wherein pretensioning means are provided that tension the throttle valve and the choke valve in the direction toward defined positions. A locking device between both valves is provided that secures the two flaps in their starting positions against the action of the pretensioning means. The locking device is releasable by a movement of the throttle valve away from its starting position and comprises a choke lever and a correlated intermediate lever that can be brought into locking engagement with one another. The locking action is released when an operator actuates an accelerator in order to accelerate the engine because the throttle lever is pivoted and releases the intermediate lever. 
         [0004]    In the known arrangements release of the locking device is possible only upon actuation of the accelerator while in all other adjusted positions of the operating elements the locking action between throttle valve and intermediate lever remains intact. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the present invention to provide a carburetor of the aforementioned kind in which an operating switch for different operating positions also includes an emergency stop position in which, upon emergency release, the locking action between the throttle adjusting lever and the choke adjusting lever is released. 
         [0006]    In accordance with the present invention, this is achieved in that a release device for releasing engagement between the throttle adjusting lever and the choke adjusting lever in case of emergency stop activation is provided and a spring is present that forces the choke adjusting lever in the direction of an engagement plane with the throttle adjusting lever. 
         [0007]    By means of the present invention, it is provided that the lever provided on the carburetor and correlated with the choke valve and also the choke valve itself are moved into a basic position from which position a new actuating process can be realized. When the emergency stop is not actuated, the release kinematics has no effect on the lever kinematics of throttle valve and choke valve. 
         [0008]    According to a preferred embodiment of the invention, the choke adjusting lever is connected fixedly to the choke shaft and the spring loads the choke valve additionally in the direction of an open position. In this way, the number of components can be reduced. The release device on the choke shaft is preferably supported so as to be moveable to a limited extent relative to the choke adjusting lever. In this way, the choke valve can be moved into its open position even though the actuator switch is still in its emergency stop position. According to a first embodiment it is advantageous that the release device for releasing the choke adjusting lever is slidable axially on the choke shaft against the force of a spring. By this movement, the choke adjusting lever is moved into another plane relative to the throttle adjusting lever so that the locking action is released. 
         [0009]    According to a second embodiment, the choke adjusting lever is pivotably supported on the choke shaft and the device is formed by an actuating rod that generates the tilting movement. For this purpose, the choke adjusting lever is supported advantageously on a transverse pin that projects through the choke shaft. In the choke adjusting lever there is expediently an elongate opening into which one end of the choke shaft projects; between the contour of the opening and the end of the choke shaft a spacing is provided that enables a defined tilting angle. 
         [0010]    According to an expedient embodiment, a coil spring is provided that is concentrically arranged relative to the choke shaft and loads the choke adjusting lever in the rotary direction and in the axial direction. In this way, the coil spring fulfills two functions, i.e., restoring the choke valve into its open position and restoring the choke adjusting lever into the plane for interaction with the throttle adjusting lever. In the first embodiment, the release device comprises in an expedient way a choke control lever that may be coupled mechanically with the choke adjusting lever. The choke control lever is secured on the choke shaft but is freely rotatable relative thereto at least in one direction. This choke control lever comprises at least one follower that engages a cutout in the choke adjusting lever. In this connection, the follower is designed such that the choke control lever acts on the choke adjusting lever when the choke valve is to be closed. 
         [0011]    For producing the axial movement of the choke adjusting lever it is expedient that the choke control lever comprises at least one ramp that interacts with the choke adjusting lever in the axial direction. It is moreover advantageous that two followers are arranged on the choke control lever, preferably diametrically opposed relative to the choke shaft, and on each one of the followers a ramp is provided. In this way, the forces can be uniformly distributed and jamming of the choke control lever is prevented. In order to reduce the actuating forces, it is expedient that on the choke adjusting lever slanted surfaces are formed that have the same slant angle as the ramps. It is moreover expedient that on the choke adjusting lever a projection is provided that serves as a stop for the follower in the closing direction of the choke valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0012]      FIG. 1  is a perspective view of a first embodiment of the carburetor. 
           [0013]      FIG. 2  is a view of the carburetor in the direction of a lever arrangement for a throttle valve and a choke valve in a stop opposition. 
           [0014]      FIG. 3  is a detail illustration of a portion of the carburetor substantially in the direction of arrow III in  FIG. 2 . 
           [0015]      FIG. 4  is a view according to  FIG. 2  with the lever arrangement in idle position. 
           [0016]      FIG. 5  is a view in a similar perspective as in  FIG. 3  showing the idle position. 
           [0017]      FIG. 6  is a view according to  FIG. 2  showing the starting position of the lever arrangement. 
           [0018]      FIG. 7  is a forwardly tilted perspective view of the portion of the carburetor according to  FIG. 3  in the starting position. 
           [0019]      FIG. 8  is a view according to  FIG. 2  showing a choke position. 
           [0020]      FIG. 9  is a perspective view similar to  FIG. 7 , but rotated somewhat about the vertical axis of the carburetor, in the choke position. 
           [0021]      FIG. 10  is a view according to  FIG. 2  in an intermediate position of the movement of the levers after activation of the operating switch into an emergency stop position. 
           [0022]      FIG. 11  is a detail of the carburetor in perspective illustration with the lever arrangement in the intermediate position according to  FIG. 10 . 
           [0023]      FIG. 12  is a perspective view of a second embodiment of the carburetor. 
           [0024]      FIG. 13  is another view of the carburetor of  FIG. 12  with an operating switch and an operating rod. 
           [0025]      FIG. 14  is an illustration according to  FIG. 13  during the triggering movement. 
           [0026]      FIG. 15  is a modified view of the carburetor according to  FIG. 12  showing the levers in the released position. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]      FIG. 1  shows a carburetor  1  for an internal combustion engine, for example, in a power tool. The carburetor  1  comprises a carburetor housing  2  with a mixture forming passage  3  extending therein as well as a throttle valve  4  and a choke valve, not shown in  FIG. 1 . The throttle valve  4  is attached to a rotatably supported throttle shaft  5  that is provided, at an end that projects from the housing  2 , with an actuator lever  6  and, at the other end projecting from the housing  2 , is provided with a throttle adjusting lever  7 . To the actuator lever  6  a throttle linkage or a throttle cable is connected in order to adjust the throttle valve  4  by rotating the throttle shaft  5 . This rotary movement is also performed by the throttle adjusting lever  7  that is connected to the throttle shaft  5 . 
         [0028]    Transversely to the mixture forming passage  3  in the carburetor housing  2  a choke shaft  8  is arranged on which the choke valve, not shown in  FIG. 1 , is mounted. On the end of the choke shaft  8  which projects from the carburetor housing  2 , a choke adjusting lever  9  is arranged that is connected to the choke shaft  8  such that it rotates with it but is axially slidable on it. Moreover, on this end of the choke shaft  8  a choke control lever  10  is arranged which is rotatable relative to the choke shaft  8  and the choke adjusting lever  9 . The choke control lever  10  has an opening  11  that is engaged by a control rod that is actuatable by an operating switch. The choke control lever  10  has two followers  12  extending parallel to the choke shaft  8  that engage recesses  13  of the choke adjusting lever  9 . 
         [0029]    In  FIG. 2  the carburetor  1  is shown in a view onto the lever arrangement for the throttle valve and the choke valve in a stop position.  FIG. 2  shows the actuator lever  6  projecting on the left side from behind the carburetor housing  2 . On the end of the throttle shaft  5  the throttle adjusting lever  7  is positioned and comprises an arm  14  that extends parallel to a tangent of the throttle shaft  5  and comprises a leg  15  that is bent at a right angle toward the choke adjusting lever  9 . In this stop position the leg  15  engages a cutout  16  at the edge of the choke adjusting lever  9 . In this position of the choke adjusting lever  9 , the choke valve  22  that projects on the right side of the carburetor housing  2  from the mixture forming passage is in completely open position. The choke control lever  10  engages with its followers  12  the recesses  13  of the choke adjusting lever  9 ; in this position, the followers  12  engage edges  28  of the choke adjusting lever  9 . The positions of the throttle adjusting lever  7  and of the choke adjusting lever  9  in  FIG. 2  are assumed as a result of the restoring springs acting on these levers. The position of the choke control lever  10  is determined by the afore mentioned control rod and the operating switch of the power tool. 
         [0030]      FIG. 3  shows a detail illustration of a portion of the carburetor  1  substantially in the direction of arrow III of  FIG. 2 . The throttle shaft  5  projects from the carburetor housing  2  and on its end the throttle adjusting lever  7  is attached. Moreover, the choke shaft  8  projecting from the carburetor housing  2  can be seen on which the choke control lever  10  and the choke adjusting lever  9  are mounted. Concentrically to the choke shaft  8  a coil spring  17  is arranged whose one end has a leg  18  which engages behind the throttle shaft  5  and whose other end is bent to a hook  19  that is hooked onto a projection  9 ′ of the choke adjusting lever  9 . The coil spring  17  thus has the function to return the choke adjusting lever  9  and thus also the choke valve into the position in which the mixture forming passage is completely open. In addition, the coil spring  17  acts as pressure spring because it is supported with one end on the carburetor housing  2  and with the other end on the choke adjusting lever  9  and therefore forces the choke adjusting lever  9  against the choke control lever  10 . 
         [0031]    The followers  12  on the choke control lever  10  project into the recesses  13  of the choke adjusting lever  9 ;  FIG. 3  shows that the followers  12  have on one side a ramp  20  that rests against a slanted surface  27  of the edge  28 . On the other side the follower  12  has a contour  26  that extends at a right angle relative to the choke adjusting lever  9 . With this configuration it is possible that in the clockwise rotary direction of the choke control lever  10  the ramp  20  glides on slanted surface  27  and when doing so pushes the choke adjusting lever  9  against the force of the coil spring  17  downwardly, i.e., in axial direction of the choke shaft  8 . 
         [0032]    In the counterclockwise rotary direction of the choke control lever  10 , the follower  12  with its contour  26  rests against the projection  9 ′ and entrains in this way the choke adjusting lever  9  so that the choke valve is adjusted in the direction of closing of the mixture forming passage. The other follower of the choke control lever  10  that is not visible in  FIG. 3  is designed in the same way; this holds true also for the other slanted surface  27  on the choke adjusting lever  9 . 
         [0033]      FIG. 4  shows a view of the carburetor  1  according to  FIG. 2 ;  FIG. 5  shows a view according to  FIG. 3 , each Figure showing the lever arrangement in idle position. This idle position differs from the starting position illustrated in  FIGS. 2 and 3  by the changed position of the choke control lever  10  because lever  10  is now positioned with contour  26  of its followers  12  on corresponding radial projections  9 ′,  9 ″ of the choke adjusting lever  9 . In idle position, in contrast to the stop position, the ignition of the internal combustion engine is switched on.  FIG. 5  illustrates that the throttle adjusting lever  7  and the choke adjusting lever  9  are in a common engagement plane.  FIG. 4  shows that on the choke adjusting lever  9  two slanted surfaces  27  are provided diametrically opposed to one another relative the axis of rotation of the choke shaft  8 . In other respects, the reference numerals in  FIGS. 4 and 5  for same parts are the same as those of  FIGS. 2 and 3 . 
         [0034]      FIG. 6  shows a view of the carburetor  1  in a starting position of the lever arrangement. In order to reach this starting position, by means of the already mentioned operating switch the throttle cable that is connected to the actuator lever  6  and the control rod that is attached to the choke control lever  10  are moved such that the actuator lever  6  together with the throttle valve is rotated about an angle in the clockwise direction and the choke control lever  10  with the choke adjusting lever  9  are pivoted about an angle in counterclockwise direction. The movement of the throttle adjusting lever  7  causes the arm  14  to be moved by the choke adjusting lever  9  and the leg  15  is pivoted far enough away from the cutout  16  in order to enable rotation of the choke adjusting lever  9 . The control rod moves the choke control lever  10  in counterclockwise direction so that the choke adjusting lever  9  is entrained wherein the rotary angle is sufficient in order for the leg  15  to catch behind the locking nose  21  provided on the circumference of the choke adjusting lever  9  and to rest against the choke adjusting lever  9 . In this way, the choke valve is now in the starting position, i.e., it releases partially the cross-section of the mixture forming passage. 
         [0035]      FIG. 7  shows a detail of the carburetor  1  similar to the view of  FIG. 3 . This illustration also shows the choke valve  22  projecting from the carburetor housing  2 . The leg  15  of the throttle adjusting lever  7  catches behind the locking nose  21  so that the choke adjusting lever  9  and the choke control lever  10  are prevented from returning into the rest position as a result of the action of the coil spring  17 . In other respects, for same parts the same reference numerals as in  FIG. 6  are used. 
         [0036]      FIG. 8  shows a view of the carburetor  1  in a choke position of the lever arrangement. In this position, the choke control lever  10  and the choke adjusting lever  9  are farther rotated in counterclockwise direction so that the choke valve is moved into its closed position. The throttle adjusting lever  7  remains unchanged because the leg  15  is supported on an arched edge  23  ( FIG. 9 ) that is curved about the axis of rotation of the choke adjusting lever  9 . The reference numerals in  FIGS. 8 and 9  are the same for same parts as in the preceding Figures. 
         [0037]    In  FIG. 9 , a detail of the carburetor in the choke position of the lever arrangement is illustrated wherein the arched edge  23  on which the leg  15  is supported is visible. In this position of the valves in the carburetor  1  the internal combustion engine can be started wherein, after the engine has started, upon first actuation of the accelerator by the operator the throttle adjusting lever  7  is pivoted in the clockwise direction and in this way the choke adjusting lever  9  and the choke valve are returned by the coil spring in clockwise direction into the initial position. 
         [0038]      FIG. 10  shows the carburetor  1  in a view onto the lever arrangement in an intermediate position of the levers during their movement after actuation of the operating switch into the emergency stop position. When for the operating switch of the power tool the emergency stop position is selected while the lever arrangement on the carburetor  1  is still in the starting position, the actuating rod moves the choke control lever  10  in clockwise direction. By doing so, the ramps  20  of the followers  12  slide along the slanted surfaces  27  of the choke adjusting lever  9  (compare  FIG. 3 ) which causes the choke adjusting lever  9  to move in axial direction of the choke shaft  8  against the force of the coil spring  17 . The followers  12  are then supported on the surface of the choke adjusting lever  9  as shown in  FIG. 11 . This axial displacement of the choke adjusting lever  9  is sufficient in order to move the choke adjusting lever  9  into a plane below the throttle adjusting lever  7  and to thus cancel or release the locking action of the leg  15  on the locking nose  21 , as shown in  FIG. 11 . The coil spring  17  ensures that the choke adjusting lever  9  and the choke valve are returned into the basic position. Since the leg  15  is now again in the area of the cutout  16  and the followers  12  in the area of the recesses  13 , the choke adjusting lever  9  is forced by the coil spring  17  in the axial action of the choke shaft  8  against the choke control lever  10 . 
         [0039]      FIG. 12  shows a second embodiment of a carburetor  31  that comprises a housing  32  with a mixture forming passage  33  arranged therein as well as a throttle valve  34  and choke valve (not visible in  FIG. 12 ). The throttle valve is attached on a rotatably supported throttle shaft  35  which is provided on an end that is projecting from the housing  32  with a throttle adjusting lever  36 . Transversely to the mixture forming passage  33  in the carburetor housing  32  a choke shaft is arranged of which only one end  37  is visible in  FIG. 12 . A choke adjusting lever  38  is arranged on the choke shaft which in the illustration according to  FIG. 12  is located in a common engagement plane with the throttle adjusting lever  36 . For attaching the choke adjusting lever  38  on the choke shaft a transverse pin  45  is provided on which the choke adjusting lever  38  is pivotably supported about the axis of the transverse pin  45 . 
         [0040]    Between the housing  32  and the choke adjusting lever  38  concentrically on the choke shaft a coil spring  39  is provided that serves for returning the choke valve into its completely open position as well as for loading the choke adjusting lever in the direction toward the engagement plane. In the choke adjusting lever  38  an elongate opening  40  is provided into which the end  37  of the choke shaft projects. The end  37  is designed with respect to its cross-section such that only in longitudinal direction of the opening  40  and thus at a right angle to the longitudinal axis of the transverse pin  45  a relative movement is possible. The positions of the throttle adjusting lever  36  and the choke adjusting lever  38  in  FIG. 12  corresponds to the starting position illustrated in  FIG. 6 . 
         [0041]    In  FIG. 13  the carburetor  31  according to  FIG. 12  is shown in a different view wherein in addition also an actuating switch  41  and actuating rod  42  are illustrated. The actuating rod  42  is connected with one end  42 ′ to the actuating switch  41  and the end  42 ″ is hooked into an appropriate receptacle  43  on the choke adjusting lever  38 . As a function of the position that is adjusted by means of the operating switch  41 , the choke adjusting lever  38  is adjusted also, for example, into the starting position illustrated in  FIG. 12 . The throttle adjusting lever  36  mounted on the throttle shaft  35  and the choke adjusting lever  38  mounted on choke shaft  44  are in the common engagement plane in which an interaction of the levers is enabled. The choke adjusting lever  38  is attached by means of transverse pin  45  on the choke shaft  44  wherein the coil spring  39  forces the choke adjusting lever  38  into the engagement plane.  FIG. 13  also shows a choke valve  46  located within the mixture forming passage  33 . 
         [0042]    Moving the operating switch  41  into the emergency stop position causes the movement of the actuating rod such that the end  42 ″ presses against the choke adjusting lever  38 . Since the point of force introduction is outside of the axis of the transverse pin  45 , the choke adjusting lever  38  is pivoted about this axis and the end  38 ′ of the choke adjusting lever  38  facing the throttle adjusting lever  36  is lowered against the force of the coil spring  39 . In  FIG. 14  a position during the described release procedure is illustrated. In other respects, for same parts the same reference numerals as in  FIGS. 12 and 13  are used. 
         [0043]      FIG. 15  shows a modified view of the carburetor  31  according to  FIG. 12  in the released state of throttle adjusting lever  36  and choke adjusting lever  38 . In this connection, the choke adjusting lever  38  is pivoted about the axis of the transverse pin  45  so that the end  38 ′ of the choke adjusting lever  38  is lowered to a position below the lower edge of the throttle adjusting lever  36  and the mutual engagement is thus canceled. The coil spring  39  then returns the choke adjusting lever  38  and the choke valve  46  into the initial position in which the choke valve  46  completely opens the mixture forming passage  33 . Moreover, the coil spring  39  pushes the side of the choke adjusting lever  38  where the end  38 ′ is located upwardly so that the choke adjusting lever  38  is positioned again in the engagement plane. In other respects, for same parts the same reference numerals as those in  FIGS. 12 to 14  are used. 
         [0044]    The specification incorporates by reference the entire disclosure of German priority document 10 2009 014 362.9 having a filing date of Mar. 21, 2009. 
         [0045]    While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.