Abstract:
In at least some embodiments, the present invention relates to an automatic choke system for use in an engine having a muffler and a choking mechanism that are located remotely apart from one another. The system includes a thermally responsive device, at least one component that serves to connect, at least in part, the device to the choking mechanism, and a further mechanism for conveying heat from the muffler to the device. Additionally, the system in at least one embodiment includes at least one of: (a) a pipe for conveying a fluid from a first location proximate the muffler to a second location proximate the device, the pipe being comprised within the further mechanism; and (b) a rotatable axle that spans a majority of a distance between the first location and a third location that is proximate the choking mechanism, the axle being comprised within the at least one component.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional patent application No. 61/059,239 entitled “Automatic Choke System” filed on Jun. 5, 2008, which is hereby incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to internal combustion engines and, more particularly, to choke systems employed in internal combustion engines. 
       BACKGROUND OF THE INVENTION 
       [0003]    Engine start and run quality at various temperatures is typically dependent on fuel enrichment. A proper variation of fuel enrichment for a naturally aspirated gasoline engine can be achieved by way of a carburetor and a choke plate used in conjunction with one another. Generally speaking, the choke plate is capable of operating to constrict the flow of air into the carburetor inlet, such that the air passing through the constricted inlet passes through a smaller opening resulting in an increased velocity and decreased pressure within the body (venturi) of the carburetor downstream of the inlet. Reducing the pressure through the body (venturi) of the carburetor increases the pressure differential at the fuel source, thereby increasing the amount of fuel flowing into and through the venturi section of the carburetor body. 
         [0004]    Typically it is desirable to vary the positioning of a choke plate in an engine depending upon engine operational circumstances. In particular, it typically is desirable to have more fuel entering the engine relative to the amount of air entering the engine when the engine is cold and/or first starting, and so it is commonly the case that a choke plate will be positioned so as to block more air flow at the carburetor inlet under these circumstances (moved to its “closed” position), while positioned so as not to block as much air flow or any air flow at other times (moved to its “open” position). To avoid having to manually adjust the position of the choke plate during start-up and at other running conditions of the engine, automatic choking control systems (also referred to as auto-choke systems or automatic choke systems) are often employed. 
         [0005]    Although automatic choke systems are widely employed in the automotive industry, cable controlled choke systems are more common in the small engine industry, particularly small engines employed in consumer applications (e.g., engines for use in lawnmowers, snow throwers, snow blowers, etc.), due largely to the complexity and high cost of existing automatic choke systems. Further, the automatic choke systems that do exist for application in the small engine consumer market are nevertheless inadequate in at least some respects. For example, many conventional automatic choke systems for use in small engines are inadequately designed, such that during operation the systems can result in undesirable engine performance including, for example, generation of black smoke during start-up or during warm-up conditions, contamination of engine oil with fuel, and engine spark plug fouling. Also, many conventional automatic choke systems for small engines do not account for variations in engine and carburetor design that necessitate varying degrees of choking during the restarting of an engine, after the engine has been running, during cool-down of the engine, and under other application load conditions. 
         [0006]    It would therefore be advantageous if an improved automatic choke system was designed that could serve to properly choke (or avoid choking) the engine carburetor to achieve or enhance one or more desired types of operational behavior of the engine (e.g., quick start-up) under one or more operational circumstances. In at least some embodiments, it would be advantageous if such an improved automatic choke system was capable of manipulating the choke plate in response to engine temperature and/or engine load demand, was capable of fully opening the choke plate once the engine was fully warm (or at a temperature at which choke is not desired), and/or was capable of adjusting choke operation for start-up, warm-up, restart, cool-down, application load conditions, and/or other conditions. In at least some further embodiments, it would be advantageous if such an automatic choke system was simpler and/or less costly than conventional automatic choke systems. 
       SUMMARY OF THE INVENTION 
       [0007]    In at least some embodiments, the present invention relates to an automatic choke system for use in an internal combustion engine having a muffler and a choking mechanism that are located remotely apart from one another on the engine. The choke system includes a thermally responsive device, at least one component that serves to connect, at least in part, the thermally responsive device to the choking mechanism, and a further mechanism for conveying heat from the muffler to the thermally responsive device. Additionally, the choke system further comprises at least one of: (a) at least one pipe for conveying at least one fluid from a first location that is at least proximate the muffler to a second location that is at least proximate the thermally responsive device, the at least one pipe being comprised within the further mechanism; and (b) at least one physically rotatable axle that spans a majority of a distance between the first location and a third location that is at least proximate the choking mechanism, the at least one physically rotatable axle being comprised within the at least one component. 
         [0008]    Further, in at least some embodiments, the present invention relates to an automatic choke system for use in an internal combustion engine having a heat source and a choking mechanism including a choke plate. The choke system includes a first structure that is the thermally responsive, and a second structure connected at least indirectly at a first end to the first structure and at a second end to the choking mechanism. Additionally, the choke system also includes a heat transfer channel at least indirectly linking the heat source to the first structure. The heat transfer channel enables heated air to proceed from the heat source to the first structure and additionally allows for conduction of heat from the heat source to the first structure, whereby heat received at the first structure causes a response at the first structure, which in turn causes the second structure to operate so as to effect a movement of the choking mechanism. 
         [0009]    Also, in at least some embodiments, the present invention relates to a heat activated choke system for use in an internal combustion engine having a heat source and a choking mechanism. The choke system includes a module including a thermally responsive first structure, the module being mounted directly upon the heat source such that heat from the heat source is conducted to the thermally responsive first structure. Further, the choke system also includes at least one linking component coupled to the choking mechanism, where actuation of the at least one linking component cause actuation of the choking mechanism. Additionally, the choke system also includes an additional component linking the first structure to the at least one linking component, the additional component spanning a majority of a distance separating the heat source and the choking mechanism, where additional component experiences rotational motion upon actuation of the first structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective, cutaway view of an internal combustion engine employing an automatic choke system in accordance with at least some embodiments of the present invention; 
           [0011]      FIG. 2A  is a front perspective view of the carburetor and the automatic choke system of  FIG. 1  shown in more detail; 
           [0012]      FIG. 2B  is a rear perspective view of the carburetor and automatic choke system of  FIG. 1  shown in more detail; 
           [0013]      FIG. 3A  is an exploded view of certain portions of the thermal control system of the automatic choke system along with the carburetor of  FIGS. 2A-2B ; 
           [0014]      FIG. 3B  is an additional exploded view showing additional components of the thermal control system of the automatic choke system and the carburetor of  FIGS. 2A-3A ; 
           [0015]      FIG. 4A  is an exploded view, from the carburetor end, of an alternate embodiment of a thermal control system of an automatic choke system that can be employed in an engine such as that shown in  FIG. 1 , in accordance with at least some other embodiments of present invention; 
           [0016]      FIG. 4B  is an additional exploded view of the thermal control system of the automatic choke system of  FIG. 4A  as viewed from a heat source end; 
           [0017]      FIG. 5A  is an exploded view of another alternate embodiment of a thermal control system of an automatic choke system that can be employed in an engine such as that shown in  FIG. 1 , in accordance with at least some additional embodiments of the present invention; 
           [0018]      FIG. 5B  shows a cross-sectional view, taken along line  5 B- 5 B of  FIG. 5A , of portions of the thermal control system of  FIG. 5A ; and 
           [0019]      FIG. 6  is an exploded view of the vacuum control system of the automatic choke system of  FIG. 1 , in accordance with at least some embodiments of the present embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    Referring first to  FIG. 1 , a perspective, cutaway view of an internal combustion engine  1  is shown in accordance with at least some embodiments of the present invention. As shown in  FIG. 1 , among other components, the internal combustion engine  1  includes a carburetor  2  on which is mounted an automatic choke system  4 . The internal combustion engine  1  can be any of a wide variety of engines. Particularly, the automatic choke system  4  is contemplated for use in, as part of, or in conjunction or combination with a wide variety of engines (not shown) that can employ a carburetor such as the carburetor  2 . In other embodiments, the automatic choke system  4  can be employed in other types of engines as well. 
         [0021]    Further as shown in  FIG. 1  (which shows the engine  1  with a cover removed), the automatic choke system  4  includes a thermal control system  6  and a vacuum control system  8 , which are described in greater detail below. Specifically, the thermal and the vacuum control systems  6  and  8 , respectively, are employed for the automatic control and adjustment of a rotatable choke plate shaft and arm assembly  14  (see  FIGS. 2A and 2B ) for achieving proper (or at least enhanced) control over a choke plate of the carburetor  2 , thus allowing for proper (or enhanced) engine choking operation over a wide range of temperature and operational conditions and enhancing overall engine performance. 
         [0022]    Referring now to  FIGS. 2A and 2B , a front perspective view and a rear perspective view, respectively, are provided showing the automatic choke system  4  of  FIG. 1  having the thermal control system  6  and the vacuum control system  8  mounted on the carburetor  2 , in accordance with a first embodiment of the present invention. The automatic choke system  4  and carburetor  2 , and particularly the thermal control system  6 , are shown in greater detail in  FIGS. 3A and 3B , described below. 
         [0023]    Turning now to  FIG. 3A , an exploded view of the automatic choke system  4  of  FIGS. 1-2B  is provided, which particularly shows in more detail components of the thermal control system  6 . As should be evident from  FIG. 3A , when the automatic choke system  4  is fully assembled, the rotatable choke plate shaft and arm assembly  14  is attached to a first end of a corrosion resistant (e.g., zinc-plated) steel link  20 . As shown, the link  20  can in particular be attached to an orifice  27  on the choke plate shaft and arm assembly  14 . The choke plate shaft and arm assembly  14  rotates to and from a closed choke position (and, correspondingly, from and to an open choke position) with a linear-planar motion of the link  20 . The link  20  at its second end (opposite its first end) is also tangentially connected to a thermally responsive bimetallic coil spring  22 , which is in constant communication with a heat source (e.g., a muffler  24 , as will be described with respect to  FIG. 3B ). More particularly, the link  20  is attached to a formed eyelet  23  of the coil spring  22 . As the coil spring  22  expands and contracts in response to heat (or the absence of heat) from the heat source, it unwinds (or winds) resulting in actuation of the link  20  and the linear-planar motion that causes movement of the choke plate shaft and arm assembly  14  and this movement of the choke plate. 
         [0024]    Typically, the time it takes to fully actuate (e.g., expand/unwind or contract/wind) the coil spring  22  is a direct function of the engine&#39;s ability to reject heat to the environment. Experiments of this effect have proven that the operational time for full actuation of the coil spring  22  is about  2 - 3  minutes. However, many physical factors have an influence on the time rate of complete actuation, which can result in greater than 2-3 minutes (or in some cases potentially lesser amounts) of time being required for actuation of the coil spring. 
         [0025]    The attachment of the link  20  to the coil spring  22  is constrained with the exception to rotate about the formed eyelet  23 . The coil spring  22  resides within an enclosure including a corrosion resistant (e.g., zinc-plated) formed steel lower bracket  26  and an upper housing  28  constructed of die-cast aluminum, die-cast zinc or plastic (thermoset or thermoplastic). The lower bracket  26  includes an arc-shaped slot  25  through which the link  20  proceeds so as to reach the formed eyelet  23 . The lower bracket  26  additionally includes a raised feature at its central location to support the coil spring  22 , which restricts most of the coils of the coil spring from contacting the lower bracket, thereby reducing debris obstruction or undesirable heat transfer. An aluminum dust shield  30  is also employed in the present embodiment to separate the coil spring  22  and link  20  from binding. 
         [0026]    With respect to the upper housing  28 , depending upon the embodiment it can take various forms and, more particularly, can include various features that serve to retain the coil spring  22 . For example, in one exemplary embodiment (not shown), the upper housing  28  is cast to include a slot by which a central tab of the coil spring  22  is captured. Such a cast feature with the slot for engaging the coil spring  22  can be integral to the upper housing  28 . While not allowing for any (or at least not much) adjustment to the angular position of the coil spring  22 , such a cast feature can be desirable from the standpoints of lowering cost and manufacturing process control. Also, in such an embodiment, the dust shield  30  in addition to restricting binding as described above also can serve to constrain the coil spring  22  from expanding in the radial direction, such that the link  20  maintains proper clearance to a slot in the bracket from which the links extends. 
         [0027]    In another exemplary embodiment, which is shown in  FIG. 3A , the upper housing  28  can take a different form. More particularly, in this embodiment a corrosion resistant (e.g., zinc-plated steel, stainless steel, or bronze) actuator or rotatable post  32  with a locking nut  34  is employed to allow angular adjustment of the coil spring  22  within the upper housing  28 . In alternate embodiments, other variations and mechanisms for holding the coil spring  22  in position within the upper housing  28  can be employed as well. 
         [0028]    Regardless of whether the coil spring  22  is retained within the upper housing  28  in either of the above-described exemplary manners or in another manner, the upper housing is fastened to the lower bracket  26 . For this purpose, as shown in  FIG. 3A , a pair of screws  36  can be used. Depending upon the embodiment, additional screws  36  or other fastening and/or engaging mechanisms can also or instead be employed to connect the upper housing  28  to the lower bracket  26 . Additionally mounted upon and supported by the lower bracket  26  are the coil spring  22  (particularly insofar as it is retained by the upper housing  28 ), the link  20 , the dust shield  30 , and the actuator and the locking nut  32  and  34 , respectively. The lower bracket  26  in turn is attached to the body of the carburetor  2  by way of a screw  38 , with the link  20  being coupled to the choke plate shaft and arm assembly  14 . In other embodiments, a plurality of the screws and/or other fastening/engaging mechanisms can be employed also or in addition to the screw  38  for the purpose of attaching the lower bracket  26  (and thus all of the other components attached thereto) to the carburetor  2 . 
         [0029]    In order for the coil spring  22  to vary in length/position so as to actuate the choke plate shaft and arm assembly  14 , heat (or lack thereof) must be communicated to the coil spring from a heat source. Referring now to  FIG. 3B , an additional exploded view  18  is provided showing heat transfer system components by which heat from a heat source is conveyed to the coil spring  22 . As shown, in the present embodiment the heat source is the muffler  24  (including certain associated components as discussed further below), and heat is transferred from the muffler  24  to the upper housing  28  by way of a cross-over tube  40 . The cross-over tube  40  in particular is a hollow tube that allows air flow to occur therethrough. As will be described further below, by virtue of its design the cross-over tube  40  allows for convective heat transfer (e.g., due to air flow within the tube) and conductive heat transfer to occur between the muffler  24  and the coil spring  22  within the upper housing  28 . 
         [0030]    The cross-over tube  40  is typically insulated to restrict heat from being radiated away from the tube as it is conveyed by convection and conduction to the coil spring  22  via the upper housing  28 . Such insulation of the cross-over tube  40 , to achieve a low rate of heat transfer away from the tube, can be provided in several manners. More particularly, as illustrated in  FIG. 3B , in at least some embodiments the cross-over tube  40  is a formed corrosion resistant (e.g., zinc-plated) steel tube  42  that is covered with braided fiberglass sleeving  44  and wrapped with fiberglass tape  46  to restrict fraying of the sleeving. Alternatively, although the cross-over tube  40  serves to transfer heat by way of convection (e.g., due to the air flowing therethrough) as well as conduction, in other embodiments conduction by the cross-over tube need not always occur (with convection instead being sufficient) and so the cross-over tube need not always be made out of conductive type materials. Rather, as also illustrated in  FIG. 3B , a cross-over tube  48  (which would be a replacement for, rather than be implemented in addition to, the cross-over tube  40 ) can be instead manufactured from a plastic-type material  50 , which can be, for example, thermoplastic (e.g., glass-filled PPA or PA-66) or thermoset plastics. Using the cross-over tube  48 , heat loss from inside the tube to the outside environment would be restricted, albeit conduction of heat down the tube would also be restricted. In still alternate embodiments (not shown), other types of tubes constructed from other types of materials for reducing (or possibly eliminating) heat loss can be employed as well. 
         [0031]    Further as shown in  FIG. 3B , the cross-over tube  40  (or, alternatively, the cross-over tube  48  or another type of tube) connects to an outlet  52  of a heat transfer tube  54 , which in the present embodiment is made from a copper or aluminum material having a high coefficient of heat conduction and is capable of being mechanically formed easily. The heat transfer tube  54 , although mounted along the exterior surface of the muffler  24 , does not conduct exhaust gases or otherwise assist with operation of the muffler. Rather, the heat transfer tube  54  (particularly the walls of the heat transfer tube) serves to receive heat from the muffler  24  (heat source) by conduction. This heat is in turn conducted to the cross-over tube  40  by way of the interfacing between that tube and the outlet  52 . Thus, regardless of whether the cross-over tube allows for conduction down its length, conduction at least occurs from the muffler  24  to the air traveling within the heat transfer tube  54  and cross-over tube, via the wall the heat transfer tube. 
         [0032]    Additionally, an inlet  56  of the heat transfer tube  54  is positioned to collect (“scoop up”) or otherwise receive spent air from the engine&#39;s cooling fan (not shown). The inlet  56  of the heat transfer tube  54  in particular is placed downstream not only of the cooling fan but also downstream of the engine cylinder(s) (not shown) over which the fan is blowing air, such that the air received by the inlet of the heat transfer tube is heated due to the heat given off by the cylinder(s), and such that the heated air serves to communicate heat through the heat transfer tube  54  by convection. Thus, the heat transfer tube  54  transfers heat to the cross-over tube  40  by both conduction (e.g., from the muffler  24  through its walls) and convection (e.g., due to the air flowing therethrough). 
         [0033]    Also as shown in  FIG. 3B , the inlet  56  of the heat transfer tube  54  includes a screen assembly that is intended to protect the heat transport system (e.g., the heat transfer tube  54  and the cross-over tube  40 ) from dust and small debris, by restricting much (if not all) of such material from entering the inlet; Additionally, to promote the retention of heat within the heat transfer tube  54 , an insulating gasket enclosure  58  made of graphite and coated with steel sheet metal (e.g., a composite) can be formed around the top and sides of the heat transfer tube along the muffler  24 , such that most if not all of the heat transfer tube is contained within the space formed between the insulating gasket enclosure and the muffler. A corrosion-resistant (e.g., zinc-plated) cover  60  further is provided to protect the insulating gasket enclosure  58 . The heat transfer tube  54 , insulating gasket enclosure  58  and cover  60  all fit over weld studs  62  extending from the muffler  24 , to which those components are fastened securely with nuts  64  and flat washers  66 , such that all of those components are fastened securely to the muffler. An additional wall structure  70  can also be employed as an interface between the heat transfer and cross-over tubes  54 ,  40 . 
         [0034]    Given the above-described arrangement of  FIG. 3B , heat from the muffler  24  is transferred to the coil spring  22  in two manners. First, heat is transferred conductively, from the heat transfer tube  54  to the cross-over tube  40  and then down that tube to the upper housing  28  and the coil spring  22 . Additionally, heat is transferred convectively. More particularly, due to the action of the fan, warm air is pushed into the inlet  56  of the heat transfer tube  54 . The warm air then proceeds through the heat transfer tube  54 , out of the outlet  52 , and into the cross-over tube  40  (or other tube). The warm air, which is warmed further by the heat being conducted by the heat transfer tube  54  and the cross-over tube  40 , further then proceeds down the cross-over tube  40  to the coil spring  22 . The flow of air toward the coil spring  22  not only helps directly to heat the coil spring, but also increases the rate at which the cross-over tube  40  conveys heat to the coil spring by way of conduction. As already discussed, heating (or cooling) of the coil spring  22  causes the coil spring to contract (or expand) in response to the heat transfer, thereby resulting in winding (or unwinding) of the coils of the coil spring. This in turn causes the link  20  to experience the linear-planar motion, which results in movement of the choke plate shaft and arm assembly  14 , so as to vary the opening and/or closing of the choke plate. 
         [0035]    Notwithstanding the aforementioned description of the thermal control system  6  for conveying heat from the muffler  24  to the coil spring  22  via the cross-over and the heat transfer tubes  40  (or  48 ) and  54 , respectively, the thermal control system need not always employ those tubes for actuation of the choke plate. Rather, in at least some alternate embodiments, various other types of thermal control systems, as will be described in  FIGS. 4A to 5B , can be used to vary the position of the choke plate. 
         [0036]    Turning specifically to  FIGS. 4A and 4B , exploded views showing components of an alternate thermal control system  72  that can be employed with respect to the automatic choke system  4  of  FIG. 1  are shown, in accordance with some other embodiments of the present invention. In contrast to the thermal control system  6  described with respect to  FIGS. 2A-3B , the thermal control system  72  of  FIGS. 4A-4B  does not employ any cross-over tube  40  or other mechanism for conveying heat from a muffler to a coil spring. Rather, the thermal control system  72  employs a mechanically actuatable shaft assembly and a bimetallic coil spring  74  that is mounted directly to a muffler  76  (which in alternate embodiments could be another heat source). Additionally, as discussed further below, that shaft assembly in combination with additional components are then employed to mechanically link the coil spring  74  to the engine choke. 
         [0037]    More particularly as shown, a corrosion resistant (e.g., zinc-plated or stainless) steel link  78  is attached to a choke plate shaft lever assembly  80  at one end, and to an actuation shaft lever arm  82  at the other end. More particularly, the link  78  is attached to an orifice  83  of the lever arm  82  and to an orifice  85  of the choke plate shaft lever assembly  80 . The actuation shaft lever arm  82  is rotationally supported on an aluminum or steel bracket  81 . The actuation shaft lever arm  82  can be constructed from die-cast aluminum or plastic and can be affixed or locked to the link  78  in any of a variety of manners including, for example, by way of an interference press fit, by way of a keyed formation that is locked into location with a threaded set-screw, or by being molded directly onto the link. Although not shown, a bushing or bearing made of plastic or other suitable material can be additionally present to facilitate low-friction rotational movement of the arm relative to the bracket (similarly, although not specifically mentioned above or below, other bushings or bearings can also be present at other locations in various embodiments of the present invention to facilitate rotational movement between components). The actuation shaft lever arm  82  in turn is connected (at an end opposite the link  78 ) to an actuation shaft  84 , which itself is constructed from corrosion resistant (e.g., zinc-plated or stainless) steel. The connection between the actuation shaft  84  and the actuation shaft lever arm  82  again can be achieved in any of a variety of manners including, for example, an interference press fit, a keyed formation locked by way of set screws, and molding. Other attaching and/or engaging mechanisms can be employed as well for connecting the actuation shaft lever arm  82  to the actuation shaft  84  and the link  78 . 
         [0038]    At the other end of the actuation shaft  84  is located a bimetallic spring cover housing  86  for retaining the coil spring  74 . The cover housing  86  additionally includes an actuator  87  (see  FIG. 4B ) located on the inboard side of the coil spring  74 , which is machined from corrosion resistant (e.g., zinc-plated or stainless) steel or bronze alloy. Depending upon the embodiment, the actuator  87  is connected to the actuation shaft  84  (and indirectly to the actuation shaft lever arm  82 ) at a specific orientation with respect to actuation shaft lever arm axis to facilitate proper movement of the coil spring  74 . The bimetallic spring cover housing  86  is formed by stamping and is made from sheet metal such as galvanized, zinc-plated or stainless steels or aluminum. 
         [0039]    Fixed to the cover housing  86  is a bimetallic spring locating pin  88  made from corrosion resistant (e.g., zinc-plated or stainless) steel. The pin  88  is machined from a material that is sufficiently soft that the pin can be riveted to the cover housing  86 . The coil spring  74  has an eyelet  90  at its outermost coil, which fits over the spring locating pin  88  fixing the location of the coil spring relative to the central tab of the spring coil where it is captured by a slot in the actuator  87 . The actuation shaft assembly (e.g., the actuation shaft  84  and the actuation shaft lever arm  82 ) is constrained from translating on the plane parallel to the face of the cover housing  86  by a bearing surface  91  formed at the center of the cover housing, into and through which the actuation shaft fits. Thus, by virtue of connecting the coil spring  74  to the actuator  87  and thereby to the actuation shaft  84 , the coil spring is capable of rotating independently for facilitating adjustment of the choke plate. 
         [0040]    The coil spring  74  is contained within the cover housing  86  by way of a mounting plate  92 , which together with the cover housing forms an enclosure relative to the outside environment and additionally serves to contain heat within the cover housing. In the present embodiment, the mounting plate  92  is formed from corrosion resistant sheet metal such as galvanized, zinc-plated or stainless steel, or aluminum. The mounting plate  92  is additionally affixed to an exterior surface of the muffler  76  by way of hex nuts  94  and washers  96 , which are affixed to studs  98  welded to that exterior surface. By virtue of connecting the coil spring  74  (via the mounting plate  92 ) to the muffler  76 , heat conducted from the muffler is able to activate the coil spring  74 . 
         [0041]    More particularly, heat from the muffler  76  is transferred to the coil spring  74  through the mounting plate  92 , thereby resulting in expansion (or contraction) of the coil spring, which in turn leads to unwinding (or winding) of the coils of the coil spring. Since the actuation shaft assembly is free to rotate only (rather than translating across the surface of the cover housing  86 ), the actuation shaft assembly responds accordingly to the unwinding (or winding) of the coil spring  74 , which again is based on temperature changes occurring within the cover housing  86  due to temperature changes experienced by the muffler  76  on which the cover housing is mounted. Thus, due to the unwinding (or winding) of the coil spring  74 , the link  78  is moved in a linear plane resulting in movement of the choke plate shaft lever assembly  80  and, consequently, corresponding movement of the choke plate. 
         [0042]    Given the above-described design, the thermal control system  72  is a conductive heat transfer system employing a closed system environment design, in contrast to the open system environment design represented by the thermal control system  6  described above in relation to  FIGS. 2A-3B . In at least some respects, this closed system environment design is advantageous relative to the open system environment design. In particular, by connecting the coil spring  74  directly to the muffler  76  (directly by way of merely the mounting plate  92 ), a mechanism for transferring heat from the muffler to the coil spring such as the cross-over tube  40  of the thermal control system  6  is not needed. Thus, the thermal control system  72  offers a lower part count and lower cost with a lower risk of failures associated with the interaction of environmental conditions (e.g., interaction with dust and debris) than does the first embodiment shown in the exploded view. 
         [0043]    Turning now to  FIGS. 5A and 5B , another thermal control system  100  capable of being employed with respect to the automatic choke system  4  of  FIG. 1  is shown in accordance with some alternate embodiments of the present invention. The thermal control system  100  can be considered a modified version of the thermal control system  6  insofar as a coil spring is positioned at the location of the carburetor  2  (also see  FIG. 3A ) rather than at the location of the muffler  24  (see  FIG. 3B ) and consequently heat from the muffler must be conveyed to the coil spring. However, while the thermal control system  6  is an open system environment design, the thermal control system  100  is a closed system environment design since, rather than employing the cross-over tube  40  and heat transfer tube  54  allowing for air from the outside environment to be heated (or further heated, assuming that the received air is already somewhat heated due to passage by one or more engine cylinder(s)) and directed toward the coil spring, instead a heat pipe  102  and associated components are employed for this purpose. 
         [0044]    More particularly as shown in  FIG. 5A , an exploded view of the thermal control system  100  is provided showing how the heat pipe  102  links a heat transfer block  104  at one of its ends to the muffler  24  (not shown in  FIG. 5A , but shown in  FIG. 3B ) at its opposite end. Mounted upon the heat transfer block  104  additionally are a cover housing  106 , a bimetallic coil spring  108  and a dust plate  110 , with the dust plate generally being positioned between the coil spring and the heat transfer block. The cover housing  106 , which extends over and around the coil spring  108  and dust plate  110  so as to enclose those components in relation to the heat transfer block  104 , among other things serves to protect the coil spring  108  from direct communication with the environment. The cover housing  106  (which retains the coil spring  108 ) and the dust plate  110  are connected to the heat transfer block  104  by way of a pair of fasteners  112 . Additionally, the heat transfer block  104  is mounted upon (or even possibly integral with) a lower bracket  114  that in turn is mounted upon the carburetor  2  (again as shown, for example, in  FIG. 3A ). The coil spring  108  is housed, retained, free to un-coil (or coil) and thus actuate the choke plate shaft and arm assembly  14  (again see  FIG. 3A ), in a manner similar or identical to that described with respect to the first embodiment shown in the exploded view of  FIG. 3A . 
         [0045]    Referring further to  FIG. 5B , a cross-sectional view of the heat pipe  102  and heat transfer block  104  taken along line  5 B- 5 B of  FIG. 5A  is additionally provided. Typically, the heat pipe  102  is a sealed tube with liquid inside that can conduct heat better than can a hollow tube such as the cross-over tube  40  of  FIG. 3B . Upon being heated (e.g., by the muffler  24 ), the liquid in the tube evaporates and travels along the tube length. Eventually the liquid gives up the absorbed heat, however, and condenses back into liquid, typically within the heat transfer block  104  such that the released heat can heat up (by conduction and/or radiation) the coil spring  108 . Subsequently the condensed liquid is returned back to the muffler, where it can be evaporated again. Still referring to  FIGS. 5A and 5B , the heat transfer block  104 , which connects to the end of the heat pipe  102  opposite the muffler  24 , serves to transfer and/or radiate heat into the coil spring  108 . 
         [0046]    In operating the heat pipe  102  and heat transfer block  104 , gravity can be a factor. In particular, if the muffler  24  is physically lower than the heat transfer block  104 , condensation of the liquid inside the heat pipe  102  at the opposite or cool end of the heat pipe (that is, proximate the heat transfer block) can easily find its way back to the muffler (e.g., aided by gravity). Nevertheless, if the muffler  24  is physically higher than the heat transfer block  104 , the flow of condensed liquid from the cool end back to the muffler is not aided by gravity and another mechanism of returning the condensate to the muffler can be desirable. In at least some embodiments, metallic wicks (e.g., thin bits of metal pieces) are provided, which reside inside the tubing to promote the condensate to flow against gravity back to the muffler, for example, by a capillary or a capillary-like action. In other embodiments, other mechanism(s) for facilitating the flow of condensate from the cool end (the heat transfer block end) to the hot end (muffler end) can be employed as well. 
         [0047]    During operation, the heat pipe  102  can have a heat conduction rate that is up to several hundred times the conductive rate of a hollow tube such as the cross-over tube  40 . Consequently, the overall diameter and length of the heat pipe  102  can be smaller than those of a cross-over tube while still achieving greater heat conduction. Thus, the use of the heat pipe  102  can provide a smaller and lighter packaging arrangement than is achieved using a comparable cross-over tube. Generally, any of a wide variety of heat pipes that are commonly available or frequently used can be employed. Additionally, due to the higher conduction associated with the heat pipe  102 , actuation of the coil spring  108  can proceed at a higher speed. 
         [0048]    Turning now to  FIG. 6 , an exploded view is provided showing exemplary components  116  of the vacuum control system  8  of the automatic choke system  4 . The vacuum control system  8  works independently of the various thermal control systems described in  FIGS. 2A-5B  resulting in immediate actuation of the choke plate to a desired angular position. More specifically, the vacuum control system  8  is a mechanical mechanism that serves to open the choke plate using engine vacuum (a vacuum pull-off assembly), which works independently of any thermally activated bi-metallic control mechanism. 
         [0049]    Typically, the function of the vacuum control system is to instantly, but not fully, open the choke plate upon start-up of the engine and the resulting vacuum. The purpose of this operation is to provide enhanced run quality, since the engine&#39;s demand for added fuel is the highest at the onset of cranking, just prior to start-up. This is even more evident with colder temperatures. Ideally, after start-up a reduction of fuel enrichment can be tolerated but not completely eliminated until the engine has reached a higher operating temperature or stable speed or combination of both, which allows for less choke. The rotation angle to which the vacuum assembly opens the choke plate is generally predetermined, but can also be varied. In any event, typically the partial opening of the choke plate by the vacuum control system  8  is later superceded with further (full) opening of the choke plate by a thermal control system once sufficient engine heating has occurred. 
         [0050]    As shown, the components  116  of the vacuum control system  8  includes a gasoline impervious rubber (Nitrile, fluorinated silicone and other similar materials) diaphragm  118 . Further as shown, a boss structure  120  is positioned adjacent to the diaphragm  118 , on a front side (particularly the left side as shown in  FIG. 6 ) of the diaphragm. The boss structure  120  is in fixed contact with the diaphragm and, in one embodiment, is sealed to the diaphragm using an epoxy or by way of another manner of fastening. Positioned up against the center of the diaphragm  118 , on a rear side (particularly the right side as shown in  FIG. 6 ) of the diaphragm, is additionally a spring  122 . The spring  122  can be kept in place relative to the diaphragm  120  (e.g., kept from moving radially outward away from a center of the diaphragm) by forming a pocket or circular ridge along the side of the diaphragm into which an end of the spring fits. 
         [0051]    Notwithstanding the above description, in another embodiment an additional spring cup can be positioned along the rear side (i.e., the right side as shown in  FIG. 6 ) of the diaphragm for receiving the spring  122  and holding it in place relative to the diaphragm. In such embodiment, the spring cup can be coupled to the boss structure  120  by way of a rivet extending through a hole in the diaphragm itself. By tightly coupling the boss structure  120  and the spring cup toward one another and up against the sides of the diaphragm, a seal can be maintained between the two sides of the diaphragm notwithstanding the hole in the diaphragm. It should be noted that each of the boss structure  120  and the spring  122  (as well as any spring cup in embodiments where such structure is present) can be made from corrosion resistant steel (e.g., zinc-plated or stainless steel), among other materials. 
         [0052]    Further as illustrated by  FIG. 6 , when the components  116  are assembled, the rubber diaphragm  118  is additionally sandwiched between a rear cover housing  124  and a front cover housing  126 . The rear cover housing  124  includes a formed pocket on its interior (not shown) for receiving the end of the spring  122  that is opposite the end of the spring that is proximate the diaphragm  118 . The front cover housing  126  serves to seal the rear cover housing  124  from the atmosphere. By virtue of the front cover housing  126 , the rear cover housing  124  and the rubber diaphragm  118 , a vacuum chamber is formed within a rear cavity or hemisphere formed by the rear cover housing and the diaphragm (within which is situated the spring  122 ), while an atmospheric-pressure chamber is formed within a front cavity or hemisphere formed by the front cover housing and the diaphragm. The front cover housing  126  additionally includes mounting feet  128  formed integrally therewith for attaching to the carburetor body via screws  130  (see  FIG. 3A ). 
         [0053]    Both of the front and rear cover housings,  126  and  124 , respectively, can be made from injection molded plastics such as glass-filled PPA, PA-66, or from die-cast aluminum or die-cast zinc or formed from corrosion resistant (e.g., zinc plated or stainless) steel plate. An adjustable link  132  threads into the central section of the boss structure  120  (which can be considered a diaphragm actuator). The complete vacuum control system  8  is held together with screws  134  and the rear hemisphere (e.g., the cavity formed by the rear cover housing  124 ) is sealed by the diaphragm bead about its perimeter. A hose  136  (see  FIG. 3A ) connects between the rear hemisphere and a vacuum port at the carburetor body to communicate with the engine air pressure stream. The link  132  (see  FIG. 3A ) attaches into the slot of the choke plate shaft and arm assembly  14  (again see  FIG. 3A ). 
         [0054]    Given this design, upon engine start-up, a vacuum pressure within the carburetor  2  is communicated to the sealed-off chamber formed between the diaphragm  118  and the rear cover housing  124  by way of the hose  136 . This in turn causes movement of the diaphragm away from a normal position as biased by the spring  122 . Movement of the diaphragm in turn causes movement of the link  132 , which in turn causes movement of the choke plate shaft and arm assembly  14  and thus the choke plate. 
         [0055]    Notwithstanding the embodiments of the automatic choke system described above with respect to  FIGS. 1-6 , it is an intention of this invention to encompass a variety of arrangements including a variety of refinements and/or additional features to the embodiments described above. Additionally, the exact shapes, sizes and materials of the various components described above can vary depending upon the embodiment and the application employing the automatic choke system. For example, although the various components of  FIGS. 1-6  have been described as being constructed of specific materials, it should be understood that in other embodiments, other types of materials can be employed as well. Although the above description primarily focuses upon embodiments in which the heat source providing heat for actuating the coil spring is the muffler (and/or the heat transfer tube associated therewith), in other embodiments one or more other engine components can be used to provide heat instead of, or in addition to, the muffler (e.g., an exhaust manifold). Further, while a coil spring is discussed above as being a thermally responsive device, in other embodiments other thermally responsive components can be used instead of, or in addition to, such a coil spring. Although some embodiments of the present inventive automatic choke system have both a thermal control system and a vacuum control system, other embodiments need only have one of these systems. 
         [0056]    Further, as already noted, the automatic choke system can be employed in a variety of types of engines. For example, in at least some embodiments, the automatic choke system  4  can be used in the Courage family of vertical and/or horizontal crankshaft engines available from the Kohler Company of Kohler, Wis. Also, in at least some embodiments, the automatic choke system can be employed in conjunction with SORE engines including Class 1 and Class 2 small off-road engines such as those implemented in various machinery and vehicles, including, for example, lawnmowers, air compressors, and the like. Indeed, in at least some such embodiments, the present invention is intended to be applicable to “non-road engines” as defined in 40 C.F.R. §90.3, which states in pertinent part as follows: “Non-road engine means . . . any internal combustion engine: (i) in or on a piece of equipment that is self-propelled or serves a dual purpose by both propelling itself and performing another function (such as garden tractors, off-highway mobile cranes, and bulldozers); or (ii) in or on a piece of equipment that is intended to be propelled while performing its function (such as lawnmowers and string trimmers); or (iii) that, by itself or in or on a piece of equipment, is portable or transportable, meaning designed to be and capable of being carried or moved from one location to another. Indicia of transportability include, but are not limited to, wheels, skids, carrying handles, dolly, trailer, or platform.” 
         [0057]    Also, it is contemplated that embodiments of the present invention are applicable to engines that have less than one liter in displacement, or engines that both have less than one liter in displacement and fit within the guidelines specified by the above-mentioned regulations. In still further embodiments, the present invention is intended to encompass other small engines large spark ignition (LSI) engines, and/or other larger (mid-size or even large) engines. 
         [0058]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.