Abstract:
A carburetor fuel valve adjustment and limiter assembly for a combustion engine limits the maximum and minimum fuel amounts delivered through the valve of the carburetor. A needle valve of the adjustment and limiter assembly cooperates with a collar and pin generally located axially inward of an enlarged valve head. The collar of the limiter assembly is arranged telescopically with a valve shaft and yieldably biased to lock to the head when moved in an axially outward direction. When locked, and upon rotation of the valve, first and second stops carried by the collar are arranged to bear on a stationary pin carried by a carburetor body. During manufacture, the collar can be pushed axially inward against the bias of a spring to disengage the collar from the head to permit rotation of the needle valve while the collar remains stationary for unlimited adjustment of the needle valve.

Description:
FIELD OF THE INVENTION 
     This invention relates to a carburetor fuel adjustment assembly, and more particularly to a fuel adjustment and limiter assembly of a fuel needle valve of a carburetor for an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     Government agencies of an increasing number of countries are applying exhaust emission control regulations to protect the environment. These regulations are being applied to all combustion engines including engines used in marine, lawn and garden equipment such as outboard motors, garden tractors, chain saws, lawn mowers and hedge trimmers. One means of limiting excessive exhaust emissions in a small engine is to restrict the maximum amount of fuel delivered to the combustion chamber. This maximum fuel amount is pre-set on each individual engine by the engine manufacturer with the understanding that the end user requires some adjustment capability to meet changing work conditions and environmental factors such as altitude and ambient temperature. The higher the altitude and temperature, the lower the air density, and thus the amount of fuel mixed with the air must be decreased to maintain the proper oxygen to fuel ratio necessary to efficiently operate the engine. The user of the engine must therefore be able to adjust the fuel to air mixture ratios and may do so via low and high speed needle valves protruding from the carburetor. 
     Not only is it desirable to limit the richness of the fuel-to-air mixture because of exhaust emission regulatory concerns, but the engine manufacturer of a two cycle engine product also wants to restrict minimum amounts of fuel, or the leanness of the fuel to air mixture. Often a user will desire more power from a two cycle engine and will attempt to operate the engine in an ultra-lean state. This will cause a two cycle engine to operate at a temperature higher than its design temperature and may decrease its useful life and lead to service and warranty concerns. Therefore, known limiter caps are designed not only to restrict the carburetor to a maximum amount of fuel, but also to restrict the carburetor to a minimum amount of fuel. 
     Limiter caps secured to the projecting ends of the low and high speed needle valves are commonly used to restrict the end user from demanding too much fuel from a carburetor which could exceed regulatory emission limits. The user purchases the engine already factory set to a desired fuel amount, adequate for efficient operation in low lying areas. Should the engine be utilized in a high altitude area, the user can still decrease the amount of fuel supplied to compensate for the low air density and/or ambient temperature. 
     In a conventional needle valve, the valve has an enlarged metallic head having an outward end face that defines a diametric recess or slot for receipt of a tool or blade of a screwdriver to rotate the valve to adjust fuel flow. The limiter cap has a similar diametric recess or hole in an end wall for access of the screwdriver, and a continuous inner surface defining a bore for receipt of the head. The inner surface may have serrations which axially mate with serrations on the head so the limiter cap when in a user assembled state rotates in unison with the head. Typically, a peripheral side or outer surface of the limiter cap has at least one radially projecting tab which engages at least one stop of the carburetor body in both the fuel rich and fuel lean directions and thereby limits fuel adjustment capability by the end user. 
     Due to carburetor and engine design and manufacturing tolerances, a manufacturer&#39;s setting of a specific carburetor to an optimum fuel amount prior to use on a specific engine, or within a specific environment such as altitude, is not practical. The limiter cap assembly is therefore supplied in a non-engaged mode in which the cap is not mated to the needle valve head and is often separate from the carburetor itself. Unfortunately, supplying a carburetor with un-assembled parts contributes to manufacturing or assembly inefficiencies and possible regulatory violations if the caps are never actually fully engaged to the valves. 
     Other needle valve assemblies, such as that disclosed in U.S. Pat. No. 6,467,757, to Douyama, and incorporated herein by reference, have a limiter cap which is pre-engaged to the carburetor body by the carburetor manufacturer for delivery to the engine manufacturer who then engages and locks the limiter cap to the valve head after final adjustments are made during operation on a specific engine. Three axially spaced projections disposed on the outer surface of the limiter cap are required to press-fit and hold the cap in the pre-engaged position and then to press-fit and lock the cap in the engaged position. When pre-engaged, the limiter cap projects outward from the carburetor body and the valve head, and the un-mated serrations of the valve head are spaced axially away from the serrations of the limiter cap. When the limiter cap is pre-engaged, a screwdriver blade is inserted through the cap hole for factory rotational adjustment of the needle valve while the limiter cap is un-mated from the needle valve. Upon adjustment completion, the caps are press fitted directly over the needle valve head, mating the serrations and received in the carburetor body. Once engaged to the valve head, the end user has restricted adjustment of the needle valve by rotating the limiter cap which, in-turn, rotates the needle valve. 
     Unfortunately, during factory adjustment, if a worker employee misses the elongated hole with the screwdriver, the limiter cap may inadvertently be pushed-in axially into engagement with the needle valve head and thereby prevent factory adjustment without destroying the cap by forcibly removing it. Furthermore, the press-fit between the cap projections and the carburetor body requires that the cap be made of a resilient synthetic resin material such as nylon or other resilient thermoplastic material. 
     Yet further, government agencies are beginning to disapprove limiter caps made of plastic material for fear they are not completely tamper proof and ultimately can be forcibly removed by the end user. Simply switching known plastic limiter caps to a metal material is not workable because they require a degree of resiliency and pliability to be press fitted over the needle head. 
     SUMMARY OF THE INVENTION 
     A fuel adjustment and limiter assembly for a carburetor of a combustion engine limits the maximum and minimum fuel amounts delivered adjustably through the carburetor, by preferably at least one fuel needle valve. A shaft of the needle valve engages threadably to the carburetor body in the cavity for axial movement of a needle or distal end of the shaft into the fuel passage for adjustably obstructing fuel flow through the passage. The limiter assembly has a collar arranged telescopically with the enlarged head and orientated circumferentially with a pin disposed in the bore and engaged generally to the body. The collar, shaft and enlarged head are preferably sheltered completely within the carburetor body for tamper-proof protection. 
     Normally, the collar is biased into a locked position with the head by a compression spring which generally pushes the collar axially outward against the enlarged head causing mating indices of the collar to mate with mating features of the enlarged head. When locked, rotation of the head by an end user causes the collar to rotate with the head. An axially inward projecting canopy of the collar carries circumferentially opposing first and second stops which when in contact with the pin limit the rotation in either direction and thus set an adjustment range. During manufacture, this adjustment range is set either in a fuel rich or opposite fuel lean direction by first rotating the needle valve and locked collar until the pin circumferentially align to an axially extending slot in the collar, then moving the collar axially inward against the bias of the spring placing the pin in the slot. With the pin in the slot, the collar is spaced axially inward from the enlarged head and the previously mated features and indices are un-mated designating an unlocked position of the collar. When the collar is in the unlocked position, the pin prevents rotation of the collar with respect to the enlarged head. The head can then be rotated and the mating indices and features repositioned. Once the range is adjusted, release of the collar causes the force of the spring to shift the collar axially outward, re-engaging the collar with the head and causing the pin to slip out of the slot and re-align axially with the first and second stops. 
     Objects, features and advantages of this invention include a tamper-proof fuel mixture adjustment assembly which is completely pre-assembled to the carburetor prior to delivery to an engine manufacture, has an adjustment range which can easily be reset during manufacture, and yet is tamper-proof by the end user. Further advantages include improved emissions, longer engine life, a simple, robust and inexpensive design, and has a long, useful and maintenance-free life. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiments and best mode, appended claims and accompanying drawings in which: 
         FIG. 1  is a side view of a carburetor body capable of utilizing a fuel adjustment and limiter assembly of the present invention; 
         FIG. 2  is a cross section of the carburetor body taken along line  2 — 2  of  FIG. 1 ; 
         FIG. 3  is a perspective view of the fuel adjustment and limiter assembly in the carburetor body; 
         FIG. 4  is a perspective view of the fuel adjustment assembly in a locked position with portions of the carburetor body in section to show internal detail; 
         FIG. 5  is a perspective view of the fuel adjustment and limiter assembly similar to  FIG. 4  except illustrating a low speed needle valve in an un-locked position; 
         FIG. 6  is a perspective view of the fuel mixture adjustment valves illustrating the low speed needle valve in a locked position and a high speed needle valve in an unlocked position; 
         FIG. 7  is a perspective view of the fuel mixture adjustment valves similar to  FIG. 6  except illustrating the low speed needle valve in an unlocked position and the high speed needle valve in a locked position; 
         FIG. 8  is a side view of a collar of the fuel mixture adjustment assembly; 
         FIG. 9  is an end view of the collar; 
         FIG. 10  is a cross section of the collar taken along line  10 — 10  of  FIG. 9 ; 
         FIG. 11  is a perspective view of a modified form of a fuel mixture adjustment and limiter assembly; 
         FIG. 12  is a end view of a grommet of the fuel adjustment and limiter assembly of  FIG. 11 ; 
         FIG. 13  is a top view of the grommet; 
         FIG. 14  is a cross section of the grommet taken along line  14 — 14  of  FIG. 12 ; 
         FIG. 15  is an end view of a collar of the modified version of the fuel adjustment and limiter assembly; 
         FIG. 16  is a side view of the collar of  FIG. 15 ; 
         FIG. 17  is a perspective view of a special tool  90  utilized for adjustment by a manufacturer; and 
         FIG. 18  is a cross section of a socket of a modification of the tool. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring in more detail to the drawings,  FIG. 1–7  illustrate a fuel flow rate adjustment and limiter assembly  20  in a carburetor body  22 , embodying the present invention. The fuel adjustment and limiter assembly  20  has a low speed needle valve  24  and preferably a high speed needle valve  26 , as is well known in the art, for adjusting fuel flow through the carburetor body  22 . First and second collars  28 ,  30  carried by the respective first and second needle valves  24 ,  26  cooperate with respective first and second stop pins  32 ,  34  to limit the end user&#39;s ability to adjust the fuel flow. When the collars  28 ,  30  are in an extended releasable locked position  36  (as best shown in  FIGS. 3 and 4 ), an end user can rotate the first and/or second needle valve  24 ,  26  to adjust fuel flow. The locked collars  28 ,  30  rotate in unison with the respective valves  24 ,  26  until they abut the respective pins  32 ,  34  in either circumferential direction, at which point further rotation of the respective needle valves  24 ,  26  by the end user is prevented, thus limiting the extent of fuel flow adjustment by the end user  22 . 
     The first and second pins  32 ,  34  are rigid and fixed to the carburetor body  22 , and the respective first and second collars  28 ,  30  are slidably received axially and engaged releasably to the respective needle valves  24 ,  26  when in the locked position  36 . On some carburetor applications only one of the needle valves  24 ,  26  and associated collar and pin may be used. In either case, the collars  28 ,  30  are tamper proof and protectively sheltered by the carburetor body  22  whether in an unlocked position  38  for unlimited manufacture adjustment or in the lock position  36  for limited end user adjustment. 
     The low and high speed needle valves  24 ,  26  are generally parallel, disposed side-by-side, and rotate about a respective first rotation axis  40  and second rotation axis  42 . Each valve  24 ,  26  has an axially extending shank or shaft  44  with a threaded central portion  44 ′ threadably engaging a complementary threaded portion of the carburetor body  22  within the respective bores  45 ,  47 . Rotation of the shafts  44  within the bores  45 ,  47  of the body  22  adjusts and controls the fuel flow within the carburetor by axial movement of its preferably tapered tip or distal end  46  in and out of a fuel feed channel or passage  48  and relative to the carburetor body  22  as is well known in the art. 
     Preferably, the bores  45 ,  47  generally communicate outward with a common cavity  49  defined by a shroud  51  of the carburetor body  22 . The valves  24 ,  26  are generally positioned, preferably concentrically, between the body  22  and the rotating shafts  44  by a common bushing or grommet  53  disposed in the body  22  at the bottom of the cavity  49 , acting primarily as a friction inducing retainer with preferably some degree of sealing characteristics. The shafts project axially outward through the bushing  53  and have a concentric cylindrical portion  50  and an enlarged head  52  disposed in the cavity  49 . For end user adjustment of each valve  24 ,  26 , it has a diametric recess or slot  54  in an end face  56  of its head  52 . The recess  54  is generally perpendicular to the longitude or rotation axis  40  or  42  of the shaft  44  and receives a tool, such as a blade of a screwdriver (not shown), for rotation of the valve shaft  44 . 
     As best shown in  FIGS. 6–10 , an outer circumferential surface  58  of the enlarged head  52  is generally perpendicular to the end surface  56  and carries at least one mating feature  60  which mates with at least one mating indicia  62  carried by a circumferential and radially inner face  64  of a sleeve  66  of each collar  28  and  30 . Preferably, the mating features  60  and the mating indices  62  are a plurality of axially extending serrations or ribs but can also be any type of releasable mating engagement which when engaged inhibits relative rotation between the collar and head and when unlocked permits rotational adjustment between the enlarged head  52  and the respective collar  28  or  30 . 
     The collars  28 ,  30  generally function independently of one-another. Each collar has a through-bore  63  substantially defined by the inner face  64  of the sleeve  66 . The through-bore  63  communicates axially between and through an annular outward face  68  of the sleeve  66  and through a circumferential shoulder  70  disposed directly axially inward from face  68  of the sleeve  66  and extending radially inward of the bore  63 . When the collars  28 ,  30  are in the locked position  36 , the annular outward face  68  of the collars  28 ,  30  is substantially flush with the leading surface  56  of the head  52  and an inward annular surface  72  of the enlarged head  52  is preferably in axial contact with a radially inward annular face  73  of the shoulder  70  of the collars  28 ,  30 . Preferably, the shroud  51  of the carburetor body  22  circumferentially encloses and extends axially over, and outboard of, the end faces of the locked collars  28 ,  30  and the valve heads  52 . Preferably each collar  28 ,  30  is received with a slight clearance in the counter bore or common cavity  49  in the shroud  51  which is coaxial with the collar received therein. With the shroud  51  sheltering the collars  28 ,  30 , the end user&#39;s only access for valve adjustment is from the exposed end surface  56  with the diametric recess  54  for receipt of a blade of a screw driver. Exposure of the locked collars  28 ,  30  to the end user is limited generally to the annular outward end face  68  thereof. With such limited exposure, tools generally available to the end user are not capable of unlocking the collars  28 ,  30  from the respective heads  52 . During normal operation of the needle valves  24 ,  26 , the end user can rotate the valves  24 ,  26  through a limited range of about one hundred and twenty degrees before the pins  32 ,  34 , which preferably project radially inward from the shroud  51 , abut either one of opposite circumferentially facing first and second stops  76 ,  78  carried by a circumferential canopy or finger  80  projecting axially inward from the shoulders  70  of the collars  28 ,  30 . This limited range, however, may vary with any specific application or characteristics of the carburetor. 
     With final adjustments made by the end user, any tendency to fall out of adjustment, possibly due to external forces such as vibration, is minimized by the grommet  53  disposed generally about the shaft  44 . A compression spring  82  is compressed axially between the grommet  53  and a radially inward annular face  83  of the shoulder  70  of the respective collars  28 ,  30  for biasing the collars into the locked position  36  and preferably are aligned coaxially with the collars by being received in an annular pocket  81  generally defined circumferentially between the stops  76 ,  78  and axially inward of a circumferential guide or end face  84 . Preferably, when the collars  28 ,  30  are in the locked position  36 , the respective pins  32 ,  34  are spaced axially only slightly inward from the guiding end face  84  and are radially and axially overlapped with the finger  80  since the pins  32 ,  34  must be engagable by the stops  76 ,  78  of the fingers or canopies  80 . 
     To permit the collars  28 ,  30  to unlock from the valve heads  52 , each collar has a blind slot  86  which extends axially through the guide  84  and into the sleeve  66 , radially and has one edge or side co-planar with the face of the stop  76  of the finger or canopy  80 . When the collar  28 ,  30  is rotated so that the stop  76  bears on the pin  32 ,  34 , the pin is aligned with the slot  86  so that the collar can be depressed or moved axially inward to disengage from or unlock its associated valve head  52 , so that its associated valve  24 ,  26  can be freely rotated relative to the carburetor body to adjust fuel flow. When the collar  28 ,  30  is in its extended or locked position  36  and its associated valve  24 ,  26  is rotated so that its guide  84  overlies its associated pin  32 ,  34 , the collar cannot be axially depressed sufficiently to move to its disengaged or unlocked position  38  because its guide  84  will bear on its associated pin  32 ,  34 . 
     Often the carburetor manufacturer will make an initial adjustment of the low and high speed needle valves  24 ,  26  after they are assembled to the carburetor body  22  along with the collars  28 ,  30 , stop pins  32 ,  34 , springs  82  and bushing  53 . Subsequently, after a carburetor is assembled on a specific engine and while the engine is operating, the high and low speed valves  24 ,  26  are adjusted typically by the engine manufacturer to establish the desired low and high speed fuel flow rates for a balance of the optimum engine efficiency, performance and compliance with engine exhaust gas emission regulations. These adjustments or settings of the needle valve  24 ,  26  can be made by the carburetor and engine manufactures by rotating each collar  28 ,  30  so that its stop surface  76  engages the pin  32 ,  34  thereby aligning the pin with the slot  86 , depressing or displacing axially inward the collar to its unlocked position  36  shown in  FIG. 5 , rotating the needle valve  24 ,  26  to provide the desired adjustment or setting of the fuel flow rate controlled by the valve, and then releasing the depressed collar  28 ,  30  so that it will be returned by the bias of the spring  82  to the locked position  36  shown in  FIG. 4  with the serrations  60 ,  62  on the collar and the valve head interengaged so that the collar rotates in unison with the valve to limit the extent to which the valve can be adjusted by an end user. The setting of the valve by the carburetor and engine manufacturers can be made utilizing a special tool  90  not available to an end user. As shown in  FIG. 17 , tool  90  has a socket  92  co-axially slidably receivable over the valve head  52  and with an annular face  94  on a free end which can bear on the collar to depress or axially move it to its unlocked position  38 . Preferably, for rotating the valve, the socket  92  also has therein an array of circumferentially spaced and axially extending ribs or serrations  96  which are complementary to and engagable with the serrations  60  of the head for rotating the valve in response to rotation of the socket. To adjust the needle valves  24 ,  26 , the socket can be disposed on the head  52 , advanced to depress the collar, rotated it clockwise or counterclockwise as needed to adjust or set the valve and retracted to remove the socket and release the collar. The socket may be manipulated manually or advanced, rotated and retracted by an automated driver. As shown in  FIG. 17 , for manual manipulation of the socket  90 , it may be either removably or permanently attached to one end of a shank  98  with a handle  100  fixed to the shank adjacent its other end. As shown in  FIG. 18 , in another form of a suitable socket  92 ′, it may have a smooth internal bore  102  with a diameter slightly larger than the maximum diameter of the valve head  56  and a blade  104  disposed therein which can be received in the slot  54  when the collar  28 ,  30  is depressed or axially displaced to its unlocked position so that rotation of the blade  104  rotates the valve to adjust or set it to its desired position. 
     The greater the number of serrations  60 ,  62  the more refined can be the manufacturing adjustment of the valves  24 ,  26 . Preferably, the collars  28 ,  30 , pins  32 ,  34  and needle valves  24 ,  26  are made of a non-pliable metallic material to prevent unintentional distortion which may impact the adjustment range and further guard against tampering. 
     Referring to  FIGS. 11–16 , a modification of the fuel mixture adjustment assembly  20 ′ is illustrated wherein the radially projecting pins  32 ,  34  fixed to the shroud  51  are replaced with a single block or pin  32 ′ extending radially between and interconnected with the grommets  53 ′. Preferably the pin  32 ′ and both grommets  53 ′ are integral and made in one piece. In this application, the design of the grommets  53 ′ is somewhat more complex, however, machining of the carburetor body  22 ′ is simplified and the number of overall parts is reduced. Unlike assembly  20 , the pin  32 ′ can be molded as a unitary piece with the grommet  53 ′. As illustrated, the pin  32 ′ and grommets  53 ′ are preferably an injected molded plastic part having friction inducing and preferably sealing characteristics. Pin  32 ′ is thus generally larger than the metallic pins  32 ,  34  to enhance strength. Likewise, as shown in  FIGS. 15 ,  16 , the slot  86 ′ of a collar  28 ′ is also larger to receive the pin  32 ′. 
     While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. For instance, the mating features  60  and indices  62  can be generally carried by the shoulder  70  of the collar  28 ,  30  and the inward annular surface  72  of the enlarged head  52  to accomplish a similar locking axial engagement. It is not intended herein to mention all the possible equivalent forms or ramifications of the invention. It is understood that the terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention.