Patent Publication Number: US-11384714-B2

Title: Auto-choke device of carburetor

Description:
CROSS REFERENCE TO PRIOR APPLICATION 
     This application is a National Stage patent application of PCT International Patent Application No. PCT/JP2018/013859 (filed on Mar. 30, 2018) under 35 U.S.C. § 371, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to an automatic choke device of a carburetor provided in an engine. 
     BACKGROUND ART 
     There has been known an automatic choke device that automatically opens and closes a choke valve of a carburetor in accordance with a temperature of an engine main body, thereby facilitating starting of an engine, particularly, starting at a low temperature. For example, an automatic choke device described in Patent Document 1 includes a wax that is attached to an engine main body, a rod that performs a linear motion in conjunction with thermal expansion of the wax, a choke lever that rotates in conjunction with the linear motion of the rod, and a choke shaft that is arranged so as to be able to abut against the choke lever and connected to a choke valve of a carburetor. In this type of automatic choke device, since the wax continues to be thermally expanded (hereinafter, referred to as “overstroke of wax” as appropriate) even after the choke valve is fully opened, it is necessary to absorb the overstroke of the wax. 
     RELATED ART REFERENCE 
     Patent Document 
     Patent Document 1: JP-A-2006-037804 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the automatic choke device described in Patent Document 1, since the choke lever includes two lever members that can be individually rotated, and a connecting spring that connects the two lever members, and the overstroke of the wax is absorbed by expansion of the connecting spring, the number of components increases, and an excessive stress acts on a support portion of the connecting spring, so that it is necessary to increase rigidity of the lever member or the like. 
     The present invention provides an automatic choke device of a carburetor that can suppress the number of components and appropriately absorb overstroke of a wax. 
     Solution to Problem 
     According to the present invention, there is provided an automatic choke device of a carburetor including: 
     a wax attached to an engine main body; 
     a rod configured to perform a linear motion in conjunction with expansion of the wax; 
     a choke lever configured to rotate in conjunction with the linear motion of the rod; and 
     a choke shaft arranged so as to be able to abut against the choke lever and connected to a choke valve of the carburetor, 
     wherein the choke lever includes a flat portion that engages with an engaging portion of the choke shaft, and a circular arc portion that is formed in a circular arc shape so as to be continuous from the flat portion and is brought into sliding contact with the engaging portion of the choke shaft. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide the automatic choke device for a carburetor that can suppress the number of components and appropriately absorb the overstroke of the wax. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view of an engine according to an embodiment of the present invention. 
         FIG. 2  is a perspective view of the engine with a top cover removed, as viewed from an obliquely front and upper side. 
         FIG. 3  is an exploded perspective view of the engine as viewed from the oblique front and upper side. 
         FIG. 4  is a perspective view of the engine with a crankcase cover or the like removed, as viewed from an obliquely rear and upper side. 
         FIG. 5  is a plan view of the engine with the crankcase cover or the like removed. 
         FIG. 6  is an exploded perspective view of an automatic choke device. 
         FIG. 7  is a side view of the automatic choke device. 
         FIG. 8  is a sectional view taken along a line A-A in  FIG. 7 . 
         FIGS. 9A, 9B, 9C, 9D, and 9E  are explanatory views showing an operation of the automatic choke device, in which  FIG. 9A  is an explanatory view showing a state when the engine is stopped (cold state),  FIG. 9B  is an explanatory view showing a state immediately after the engine is started,  FIG. 9C  is an explanatory view showing a state when the engine is warming up,  FIG. 9D  is an explanatory view showing a state in which a choke valve is fully opened, and  FIG. 9E  is an explanatory view showing an overstroke state of a wax. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to  FIGS. 1 to 9E . An engine E of the present embodiment is a small-sized general-purpose engine mounted on a walk-behind lawn mower or the like, and includes an OHV vertical engine as an engine main body  1 . In the present specification or the like, in order to simplify and clarify the description, an axial center direction of a crankshaft  11  is defined as an upper-lower direction, a direction in which a piston  13  slides back and forth is defined as a front-rear direction, which is orthogonal to the upper-lower direction, and a direction orthogonal to the upper-lower direction and the front-rear direction is defined as a left-right direction. In the drawings, a front side of the engine E is shown as Fr, a rear side thereof is shown as Rr, a left side thereof is shown as L, a right side thereof is shown as R, an upper side thereof is shown as U, and a lower side thereof is shown as D. 
     [Engine] 
     As shown in  FIGS. 1 to 5 , the engine E of the present embodiment includes the engine main body  1 , a fan  2  for cooling that is arranged above the engine main body  1  and also functions as a flywheel, a fan cover  3  that accommodates the fan  2 , a recoil starter  4  that is arranged above the fan  2  and performs a starting operation of the engine main body  1 , a top cover  5  that covers at least upper portions of the engine main body  1 , the fan  2 , the fan cover  3 , and the recoil starter  4 , a fuel tank  6  that stores fuel in the engine main body  1 , an air cleaner  7  that purifies intake air from the engine main body  1 , and a muffler  8  that exhausts exhaust gas of the engine main body  1  while muffling the exhaust gas. 
     [Engine Main Body] 
     The engine main body  1  includes an engine block  10  having a crankcase portion  10   a  and a cylinder portion  10   b , the crankshaft  11  that is rotatably supported by the crankcase portion  10   a  in an upper-lower direction, the piston  13  that is slidably fitted in the cylinder portion  10   b  and connected to the crankshaft  11  via a connecting rod  12 , an intake valve  14  that is provided on a head portion  10   c  of the cylinder portion  10   b , an exhaust valve  15 , a spark plug  16 , a head cover  17  that covers the head portion  10   c  of the cylinder portion  10   b , a valve-operating mechanism  18  that operates the intake valve  14  and the exhaust valve  15  in accordance with a rotation of the crankshaft  11 , a carburetor  22  that generates an air-fuel mixture of fuel and air and supplies the air-fuel mixture into the cylinder portion  10   b , a governor device  23  that automatically opens and closes a throttle valve (not shown) of the carburetor  22  in accordance with a rotational speed (the number of rotations) of the crankshaft  11 , and an automatic choke device  25  that automatically opens and closes a choke valve  24  of the carburetor  22  in accordance with a change in the temperature of the engine main body  1 . 
     The engine block  10  of the present embodiment is divided into three parts including a crankcase main body  19  that includes a bottom portion  19   b  having a first crankshaft insertion hole  19   a , and a tubular portion  19   d  in which the bottom portion  19   b  is integrally formed at a lower end portion thereof and a case opening portion  19   c  is provided at an upper end portion thereof, a crankcase cover  20  that has a second crankshaft insertion hole  20   a , and covers the case opening portion  19   c  of the crankcase main body  19 , and a cylinder unit  21  that extends forward from the tubular portion  19   d  of the crankcase main body  19 . In addition, the crankcase main body  19  and the crankcase cover  20  configure the crankcase portion  10   a , and the cylinder unit  21  configures the cylinder portion  10   b , but a configuration of the engine block  10  is not limited to that of the present embodiment, and can be changed as appropriate. 
     [Carburetor] 
     As shown in  FIGS. 4 and 6 , the carburetor  22  includes a carburetor main body  26  having an intake passage  26   a  penetrating in the left-right direction, the choke valve  24  arranged on an upstream side of the intake passage  26   a , and the throttle valve (not shown) arranged on a downstream side of the intake passage  26   a.    
     The carburetor main body  26  is attached to the cylinder portion  10   b  of the engine main body  1  such that a downstream side opening portion of the intake passage  26   a  communicates with an intake port  10   d  of the engine main body  1  (see  FIG. 3 ), and an upstream side opening portion of the intake passage  26   a  is connected to the air cleaner  7 . In addition, the carburetor main body  26  includes a fuel supply portion  26   b  to which fuel is supplied from the fuel tank  6  via a fuel tube  27 , and the fuel supply portion  26   b  communicates with a fuel nozzle (not shown) that opens into the intake passage  26   a  between the choke valve  24  and the throttle valve. That is, in an intake stroke of the engine main body  1 , the outside air is sucked into the intake passage  26   a  of the carburetor main body  26  through the air cleaner  7 , the sucked air sucks out the fuel from the fuel nozzle to become the air-fuel mixture of air and fuel, and the air-fuel mixture is supplied to the cylinder portion  10   b  of the engine main body  1 . 
     The choke valve  24  and the throttle valve are butterfly type valve bodies that are rotatably supported by the carburetor main body  26  via valve shafts  28 ,  29  extending in the upper-lower direction. The throttle valve is a valve for adjusting an amount of the air-fuel mixture to be supplied to the engine main body  1 , is kept in a fully open position before the engine main body  1  is started, and is controlled to a closing side so as to maintain a predetermined engine speed by the governor device  23  when the engine main body  1  is started. 
     The choke valve  24  is a valve for adjusting a ratio of air and fuel in the air-fuel mixture. When the choke valve  24  is controlled to a closing side, the ratio of the fuel in the air-fuel mixture increases, and starting of the engine main body  1 , particularly, starting at low temperature is facilitated. The choke valve  24  is connected to the automatic choke device  25  via the valve shaft  28 , and an opening degree thereof is automatically controlled in accordance with the change in the temperature of the engine main body  1 . 
     [Governor Device] 
     As shown in  FIGS. 4 and 5 , the governor device  23  includes a rotational speed detection unit  30  that is arranged in the crankcase portion  10   a  of the engine main body  1  and detects the rotational speed (the number of rotations) of the crankshaft  11 , a governor lever  31  that is integrally provided on an upper end portion of the valve shaft  29  of the throttle valve, and a rotational speed transmission portion  32  that takes out the rotational speed of the crankshaft  11  detected by the rotational speed detection portion  30  as a rotation change of an arm member  32   a  and transmits the rotational speed to the governor lever  31  via a rod member  32   b.    
     The rod member  32   b  is connected to one end portion of the arm member  32   a , is pulled rearward by an urging force of an arm return spring  32   c  connected to the other end portion of the arm member  32   a  when the engine is stopped, and is pushed forward in accordance with an increase in the rotational speed of the crankshaft  11  after the engine is started. 
     The rod member  32   b  is connected to one end portion  31   a  of the governor lever  31 , and when the engine is stopped, the one end portion  31   a  is pulled rearward by the rod member  32   b  to rotate the valve shaft  29  in a direction in which the throttle valve opens. A governor stopper  26   c  for regulating a rotation of the governor lever  31  in an opening direction is provided in a protruding manner on an upper portion of the carburetor main body  26 , and when the engine is stopped, a stopper engaging portion  31   b  of the governor lever  31  is engaged with the governor stopper  26   c  to keep the throttle valve in a fully open state. In addition, after the engine is started, the governor lever  31  pushes the one end portion  31   a  forward by the rod member  32   b  in accordance with the rotational speed of the crankshaft  11  to rotate the valve shaft  29  in a direction of closing the throttle valve, thereby maintaining a predetermined engine speed. 
     [Automatic Choke Device] 
     As shown in  FIGS. 6 to 8 , the automatic choke device  25  includes a wax  41  that is attached to the engine main body  1 , a rod  43  that is connected to the wax  41  via a retainer  42  and performs a linear motion (jumping operation) in conjunction with thermal expansion of the wax  41 , a rod return spring  44  that pushes back the retainer  42  and the rod  43  in conjunction with thermal contraction of the wax  41 , a choke lever  45  that rotates in conjunction with the linear motion of the rod  43 , a holding member  46  that supports the rod  43  and the choke lever  45 , a choke shaft  47  that is arranged so as to be able to abut against the choke lever  45  and connected to the choke valve  24  of the carburetor  22 , and a shaft return spring  48  that urges the choke shaft  47  in the direction of closing the choke valve  24 . 
     That is, the automatic choke device  25  of the present embodiment includes the wax  41  that thermally expands in accordance with temperature rise of the engine main body  1 . When the engine is stopped (when the engine temperature is low), the choke valve  24  of the carburetor  22  is maintained on the closing side to facilitate the starting of the engine main body  1 , while after the engine is started, the choke valve  24  of the carburetor  22  is controlled to an opening side by the thermal expansion of the wax  41  in accordance with the temperature rise of the engine main body  1 . However, in the automatic choke device  25 , since overstroke occurs in which the wax  41  continues the thermal expansion even after the choke valve  24  is fully opened, it is necessary to absorb the overstroke of the wax  41 . Hereinafter, a configuration of each portion of the automatic choke device  25  will be described with reference to  FIGS. 6 to 8 . 
     (Wax) 
     The wax  41  is a heat-sensitive actuator that encloses a heat-sensitive material whose volume changes in accordance with a change in the temperature, expands and contracts in accordance with a change in the volume of the heat-sensitive material, and is configured to thermally expand in a length direction as the temperature rises and thermally contract in the length direction as the temperature falls. The wax  41  of the present embodiment is arranged at a side surface of the cylinder portion  10   b  of the engine main body  1 , that is, closer the crankcase portion  10   a  side than the intake port  10   d , avoiding a position in the vicinity of the intake port  10   d  (see  FIG. 3 ). Specifically, a tubular portion  10   e  is provided in a protruding manner on a side surface of the cylinder portion  10   b  of the engine main body  1 , and the wax  41  is accommodated in the tubular portion  10   e.    
     That is, in the vicinity of the intake port  10   d , due to latent heat of vaporization of the fuel, the temperature of the wax  41  may deviate from a temperature in a combustion chamber at the time of soaking after the engine is stopped, but a temperature rise characteristic of the wax  41  can be made close to a temperature characteristic of the combustion chamber by arranging the wax  41  on the side surface of the cylinder portion  10   b  of the engine main body  1 , that is, at a position separated from the intake port  10   d.    
     (Holding Member) 
     The holding member  46  integrally includes an attachment portion  46   a  that is attached to the engine main body  1 , a tubular rod support portion  46   b  that supports the rod  43  so as to be movable in the left-right direction, and a choke lever support portion  46   c  that rotatably supports the choke lever  45  via a pin  49 . According to such a holding member  46 , the number of components can be reduced as compared with a case where a holding member for supporting the rod  43  that performs a linear motion and a holding member for supporting the choke lever  45  that performs a rotating motion are separately provided. 
     When the carburetor  22  is attached to the engine main body  1 , the attachment portion  46   a  of the holding member  46  is sandwiched between the carburetor  22  and the engine main body  1 , and is fixed and fastened together with the carburetor  22  and the engine main body  1  by a bolt (not shown) that fastens the carburetor  22  to the engine main body  1 . According to the attachment portion  46   a  of the holding member  46 , the number of components can be reduced as compared with a case of being fixed to the engine main body  1  with a dedicated bolt. 
     (Rod) 
     The rod  43  integrally includes a rod main body  43   a  that is supported by the rod support portion  46   h  of the holding member  46  so as to be movable in the left-right direction, a retainer connecting portion  43   b  that is provided at a base end portion of the rod main body  43   a  and is connected to the retainer  42 , and a choke lever connecting portion  43   c  that is provided at a distal end portion of the rod main body  43   a  and connected to the choke lever  45 . 
     The choke lever connecting portion  43   c  includes an upward extending portion  43   d  that extends upward from a distal end of the rod main body  43   a  and is inserted into a rod connecting hole  45   b  of the choke lever  45  to interlock the choke lever  45  with a linear motion of the rod  43  in a pushing direction and a pulling direction, and a coming-off prevention portion  43   e  that extends outward from an upper end of the upward extending portion  43   d  and prevents the upward extending portion  43   d  from coming off. 
     (Choke Lever) 
     The choke lever  45  includes a choke lever main body  45   a  that is rotatably supported by the choke lever support portion  46   c  of the holding member  46  via the pin  49 , a rod connecting hole  45   b  that is formed in the vicinity of a rotation center (pin  49 ) of the choke lever main body  45   a  and is connected to the rod  43 , a flat portion  45   c  that engages with a choke lever engaging portion  47   d  of the choke shaft  47 , and a circular arc portion  45   d  that is formed in a circular arc shape so as to be continuous (a circular arc shape with a rotation center of the choke lever  45  as a circular arc center) from the flat portion  45   c  and is brought into sliding contact with the choke lever engaging portion  47   d  of the choke shaft  47 . 
     According to such a choke lever  45 , one choke lever  45  can be substituted for an automatic choke operation performed by two lever members and one connecting spring in an automatic choke device in the related art, so that the number of components can be reduced. 
     That is, during warming up of the engine main body  1 , the flat portion  45   c  of the choke lever  45  engages with the choke lever engaging portion  47   d  of the choke shaft  47  to rotate the choke shaft  47 , so that the choke valve  24  can be opened in conjunction with the expansion of the wax  41 . On the other hand, after the choke valve  24  is fully opened, the circular arc portion  45   d  of the choke lever  45  is brought into sliding contact with the choke lever engaging portion  47   d  of the choke shaft  47 , so that the overstroke of the wax  41  can be absorbed without rotating the choke shaft  47 . 
     Since the circular arc portion  45   d  of the choke lever  45  is brought into sliding contact with the choke lever engaging portion  47   d  of the choke shaft  47  and absorbs the overstroke of the wax  41 , rigidity of each member can be reduced as compared with a case where the overstroke of the wax  41  is received by a connecting spring as in the related art. 
     The choke lever  45  of the present embodiment is a plate-shaped member, and the flat portion  45   c  and the circular arc portion  45   d  are provided on a side surface of the plate-shaped member. According to such a choke lever  45 , the choke lever  45  can be reduced in a size by setting the flat portion  45   c  and the circular arc portion  45   d  of the choke lever  45  on the side surface of the plate-shaped member having high rigidity. 
     (Choke Shaft) 
     The choke shaft  47  includes a choke shaft main body  47   a  that is integrally provided on an upper end portion of the valve shaft  28  of the choke valve  24  and is urged by the shaft return spring  48  in a direction of closing the choke valve  24 , a first stopper engaging portion  47   b  and a second stopper engaging portion  47   c  that extend in an outer diameter direction from the choke shaft main body  47   a  and engages with a choke stopper  26   d  provided in a protruding manner on the upper portion of the carburetor main body  26  to regulate a rotation range of the choke shaft  47 , a choke lever engaging portion  47   d  that extends in the outer diameter direction from the choke shaft main body  47   a  and engages or is brought into sliding contact with the choke lever  45 , and a governor lever engaging portion  47   e  that extends in the outer diameter direction from the choke shaft main body  47   a  and engages with the governor lever  31 . 
     The first stopper engaging portion  47   b  engages with the choke stopper  26   d  at a position at which the choke valve  24  is in a fully closed state so as to regulate the rotation of the choke shaft  47  in the direction of closing the choke valve  24 . In addition, the second stopper engaging portion  47   c  engages with the choke stopper  26   d  at a position at which the choke valve  24  is in the fully open state so as to regulate the rotation of the choke shaft  47  in a direction of opening the choke valve  24 . 
     During warming up of the engine main body  1 , the choke lever engaging portion  47   d  is pushed by the flat portion  45   c  of the choke lever  45  to rotate the choke shaft  47 , thereby opening the choke valve  24  in conjunction with the expansion of the wax  41 . On the other hand, after the choke valve  24  is fully opened, the choke lever engaging portion  47   d  is brought into sliding contact with the circular arc portion  45   d  of the choke lever  45 , so that the overstroke of the wax  41  is absorbed without rotating the choke shaft  47 . 
     Immediately after starting the engine main body  1  and during warming up, the governor lever engaging portion  47   e  is pushed by the other end portion  31   c  of the governor lever  31  that controls a slot valve of the carburetor  22  in the closing direction in accordance with the rotation of the crankshaft  11  to rotate the choke shaft  47 , so that the choke valve  24  is slightly opened, and appropriate intake air can be taken even before the wax  41  expands. Incidentally, the governor lever  31  includes a circular arc portion  31   d  that is formed in a circular arc shape so as to be continuous from the other end portion  31   c  that pushes the governor lever engaging portion  47   e  (a circular arc shape with a rotation center of the governor lever  31  as a circular arc center), and is brought into sliding contact with the governor lever engaging portion  47   e  of the Choke shaft  47 . After the other end portion  31   c  of the governor lever  31  pushes the governor lever engaging portion  47   e  to open the choke valve  24  by a predetermined amount, the circular arc portion  31   d  is brought into sliding contact with the governor lever engaging portion  47   e  to maintain the opening degree of the choke valve  24 . 
     In the present embodiment, when arranging the governor lever  31  and the choke lever  45  on the upper surface portion of the carburetor  22 , the governor lever  31  and the choke lever  45  are arranged at positions different in a distance from the upper surface of the carburetor  22 , and a rotation area of the governor lever  31  and a rotation area of the choke lever  45  overlap each other. According to this arrangement, the automatic choke device  25  can be reduced in the size. 
     [Operation of Automatic Choke Device] 
     Next, the operation of the automatic choke device  25  will be described with reference to  FIGS. 9A, 9B, 9C, 9D, and 9E . 
     As shown in  FIG. 9A , since the wax  41  is in a contracted state when the engine is stopped (cold state), the choke lever  45  is maintained at an initial position where the choke lever  45  does not engage with the choke lever engaging portion  47   d  of the choke shaft  47  due to an urging force of the rod return spring  44 . In addition, the choke shaft  47  is maintained at an initial position where the choke valve  24  is in the fully closed state by the urging force of the shaft return spring  48 . The governor lever  31  is maintained at an initial position where the throttle valve is in the fully open state by the urging force of the arm return spring  32   c.    
     As shown in  FIG. 9B , since the wax  41  is in the contracted state immediately after the engine is started, the choke lever  45  maintains the initial position, but the governor lever  31  is rotated in accordance with the rotation of the crankshaft  11  so as to rotate the choke shaft  47 , so that the choke valve  24  is slightly opened, the appropriate intake air can be taken even before the wax  41  expands. Further, in this state, the ratio of the fuel in the air-fuel mixture sucked from the carburetor  22  to the cylinder portion  10   b  of the engine main body  1  is increased, so that the starting of engine main body  1  is facilitated. 
     As shown in  FIG. 9C , since the wax  41  thermally expands when the engine is warming up, the choke lever  45  advances from the initial position in accordance with the temperature rise of the engine main body  1 , and the flat portion  45   c  of the choke lever  45  engages with the choke lever engaging portion  47   d  of the choke shaft  47  to rotate the choke shaft  47 . As a result, the choke valve  24  is opened in conjunction with the expansion of the wax  41 , and the ratio of the fuel in the air-fuel mixture sucked from the carburetor  22  to the cylinder portion  10   b  of the engine main body  1  is gradually lowered. 
     As shown in  FIG. 9D , when the choke valve  24  is fully opened, an engaging position between the flat portion  45   c  of the choke lever  45  and the choke lever engaging portion  47   d  of the choke shaft  47  reaches an engaging range end position of the flat portion  45   c , that is, a sliding contact range start position of the circular arc portion  45   d.    
     As shown in  FIG. 9E , in the overstroke state of the wax  41 , the circular arc portion  45   d  of the choke lever  45  is brought into sliding contact with the choke lever engaging portion  47   d  of the choke shaft  47 , so that the overstroke of the wax  41  can be absorbed without rotating the choke shaft  47 . 
     The above embodiment may be appropriately modified, improved, or the like. For example, in the embodiment described above, the automatic choke device of a carburetor applied to the OHV vertical engine has been described, but the automatic choke device of a carburetor of the present invention can also be applied to engines other than the OHV vertical engine. 
     At least the following matters are described in the present specification. Components corresponding to the above-described embodiment are shown in parentheses, but the present invention is not limited thereto. 
     (1) An automatic choke device of a carburetor including: 
     a wax (wax  41 ) attached to an engine main body (engine main body  1 ); 
     a rod (rod  43 ) configured to perform a linear motion in conjunction with expansion of the wax; 
     a choke lever (choke lever  45 ) configured to rotate in conjunction with the linear motion of the rod; and 
     a choke shaft (choke shaft  47 ) arranged so as to be able to abut against the choke lever and connected to a choke valve (choke valve  24 ) of the carburetor (carburetor  22 ), 
     wherein the choke lever includes a flat portion (flat portion  45   c ) that engages with an engaging portion (choke lever engaging portion  47   d ) of the choke shaft, and a circular arc portion (circular arc portion  45   d ) that is formed in a circular arc shape so as to be continuous from the flat portion and is brought into sliding contact with the engaging portion of the choke shaft. 
     According to (1), since one choke lever can be substituted for an automatic choke operation performed by two lever members and one connecting spring in an automatic choke device in the related art, the number of components can be reduced. 
     That is, during warming up of an engine, the choke valve can be opened in conjunction with expansion of the wax by engaging the flat portion of the choke lever with the engaging portion of the choke shaft. On the other hand, after the choke valve is fully opened, the circular arc portion of the choke lever is brought into sliding contact with the engaging portion of the choke shaft, so that the overstroke of the wax can be absorbed. 
     In addition, since the circular arc portion of the choke lever is brought into sliding contact with the engaging portion of the choke shaft and absorbs the overstroke of the wax, rigidity of each member can be reduced as compared with the case where the overstroke of the wax is received by a connecting spring as in the related art. 
     (2) The automatic choke device of a carburetor according to (1), 
     wherein the choke lever is a plate-shaped member, and 
     wherein the flat portion and the circular arc portion are provided on a side surface of the plate-shaped member. 
     According to (2), the choke lever can be reduced in a size by setting the flat portion and the circular arc portion of the choke lever on the side surface of the plate-shaped member having high rigidity. 
     (3) The automatic choke device of a carburetor according to (1) or (2), 
     wherein the rod and the choke lever are supported by a holding member (holding member  46 ) attached to the engine main body. 
     According to (3), the number of components can be reduced by supporting the rod that performs a linear motion and the choke lever that performs a rotating motion by the holding member attached to the engine main body. 
     (4) The automatic choke device of a carburetor according to any one of (1) to (3), 
     wherein the choke shaft is capable of abutting against a governor lever (governor lever  31 ) connected to a throttle valve of the carburetor. 
     According to (4), the choke shaft is slightly opened in conjunction with a governor immediately after the engine is started, so that appropriate intake air can be taken before the wax expands. 
     (5) The automatic choke device of a carburetor according to (4), 
     wherein the governor lever and the choke lever are arranged at positions different in a distance from a wall surface of the carburetor, and 
     wherein a rotation area of the governor lever and a rotation area of the choke lever overlap each other. 
     According to (5), the governor lever and the choke lever are arranged at the positions different in the distance from the wall surface of the carburetor, and the rotation area of the governor lever and the rotation area of the choke lever overlap each other, so that the automatic choke device can be reduced in the size. 
     (6) The automatic choke device of a carburetor according to any one of (1) to (5), 
     wherein the wax is arranged on a side surface of a cylinder portion (cylinder portion  10   b ) of the engine main body. 
     According to (6), in the vicinity of the intake port, due to the latent heat of vaporization of fuel, a temperature of the wax may deviate from a temperature in a combustion chamber at the time of soaking after the engine is stopped, but a temperature rise characteristic of the wax can be made close to a temperature characteristic of the combustion chamber by arranging the wax on a side surface of the cylinder portion of the engine main body. 
     REFERENCE SIGNS LIST 
       1  engine main body 
       10   b  cylinder portion 
       22  carburetor 
       24  choke valve 
       25  automatic choke device 
       31  governor lever 
       41  wax 
       43  rod 
       45  choke lever 
       45   c  flat portion 
       45   d  circular arc portion 
       46  holding member 
       47  choke shaft 
       47   d  choke lever engaging portion (engaging portion)