Abstract:
An adjustment system for a carburetor of an engine places a housing structure around the head of an adjustment screw to inhibit access to the head of the idle fuel adjustment screw except by properly trained technicians who possess an appropriately shaped tool which allows this access. In this way, the housing can function as intended, to limit access by untrained personnel to the idle fuel adjustment screw, while not requiring that it be completely removed or destroyed in order to allow appropriate access by trained personnel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is generally related to an adjustment system for an engine and, more particularly, to an adjustment system which limits access to an idle fuel mixture screw. 
     2. Description of the Related Art 
     U.S. Pat. No. 5,603,869, which issued to McNew et al. on Feb. 18, 1997, describes a fuel mixture limitation device. The device limits post-adjustment rotation of an adjustment screw on single adjustment screw carburetors. On one embodiment, the limitation device uses a limiter cap removably attached to the adjustment screw which works in conjunction with a limiter stop attached to the carburetor. 
     U.S. Pat. No. 5,635,113, which issued to Walsh et al. on Jun. 3, 1997, describes a carburetor adjustment screw apparatus. The apparatus is intended for use with a diaphragm-type carburetor and it comprises a screw member having a shaft and a head by which the shaft may be rotated, with a generally tubular open-ended housing surrounding the head of the screw member. A cap member is mounted in the housing and is movable axially of the screw member between a first position and a second position. 
     U.S. Pat. No. 5,753,148, which issued to King et al. on May 19, 1998, describes a carburetor needle valve adjustment limiter cap apparatus. The limiter cap has a hollow cylindrical outer body of rigid material. It carries a limiter arm. A spring steel hollow retainer clip sleeve is telescopically received in the body and has inwardly and outwardly protruding resilient barbs reversely oriented relative to one another to respectively engage the cap body and the needle valve shank to respectively prevent retrograde relative telescopic motion between the clip and the body and between the clip and the valve shank. 
     U.S. Pat. No. 5,984,281, which issued to Hacker et al. on Nov. 16, 1999, describes a carburetor needle valve and limiter cap installation and adjustment apparatus. It describes an improvement in a limiter cap holder wherein the clip spring legs are interconnected by a spring web that flexes to accommodate flexing of the clip legs free ends during insertion of the associated limiter caps into the retaining clip and prolongs the effective friction grip service life of the clip. 
     U.S. Pat. No. 6,691,988, which issued to Warfel et al. on Feb. 17, 2004, describes a tamper resistant carburetor mixture needle. The adjustment screw arrangement is intended for use with a carburetor. The arrangement includes a carburetor body having at least one air/fuel adjustment screw threaded therein. The adjustment screw has a threaded shank and a head portion. The head portion is defined by a smooth top surface and an undulant, uneven side surface capable of being engaged and mated by an adjusting tool having a complementary undulant, uneven side surface capable of being engaged and mated by an adjusting tool having a complementary undulant, uneven surface for initial adjustment of the air/fuel mixture in the carburetor. 
     U.S. Pat. No. 6,708,959, which issued to Dow on Mar. 23, 2004, describes a carburetor valve assembly. It has a plastic cam body connected to a plastic shaft which extends into the carburetor body and valve head press-fit into a slot formed through the plastic shaft. 
     The patents described above are hereby expressly incorporated by reference in the description of the present invention. 
     Environmental restrictions require that threaded adjustment needles of carburetors be protected from improper manipulation. These regulations are intended to prevent the users of engines from improperly calibrating the idle fuel mixture ratio and, as a result, causing an engine to emit excessive pollutants. Most of these protective devices also inhibit the proper adjustment of the idle fuel mixture screw by a trained technician, such as the personnel of an engine repair facility. As a result, the adjustment of the idle fuel device requires excessive effort on the part of the skilled technician. 
     It would therefore be significantly beneficial if a device could be developed which inhibits the adjustment of the idle fuel screw by unqualified personnel while allowing the proper adjustment of that idle fuel screw by trained personnel whose responsibility it is to properly calibrate the engine and appropriately set the idle fuel adjustment screw. 
     SUMMARY OF THE INVENTION 
     An adjustment system for an engine, made in accordance with a preferred embodiment of the present invention, comprises an engine component, such as a carburetor, a rotatable adjustment member, such as an idle fuel mixture screw, and a housing. The rotatable adjustment member is shaped to be supported by the engine component for rotation about a rotational axis. It has a first end which is insertable into a retention opening formed in the engine component in a preferred embodiment of the present invention. The rotatable adjustment member has a second end extending away from the engine component. A head is formed at the second end of the rotatable adjustment member. The housing is shaped to at least partially surround the head. The rotational axis of the rotatable adjustment member extends through a first surface of the housing. An access opening is formed in the first surface. The rotational axis of the rotatable adjustment member extends through the access opening. 
     The rotatable adjustment member is threaded into the retention opening in a preferred embodiment of the present invention. This preferred embodiment can further comprise an adjustment tool which is shaped to pass at least partially through the access opening. The adjustment tool has an operative end which is shaped to engage the head in torque transmitting relation. The operative end can have a pair of inwardly facing surfaces which are shaped to receive a pair of outwardly facing surfaces of the head therebetween. The access opening can be a round hole which extends through the first surface. The round hole can have a diameter which is greater than a maximum thickness dimension of the operative end of the tool. The diameter is greater than a maximum thickness dimension of the head in a preferred embodiment of the present invention. 
     The rotational axis of the rotatable adjustment member is generally perpendicular to the first surface in a preferred embodiment of the present invention and an internal surface of the housing defines a cavity, with the head being spaced apart from the internal surface of the housing. The area of the access opening is less than twenty five percent of the area of the first surface in a preferred embodiment of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more fully and completely understood from a reading of the description of the preferred embodiment in conjunction with the drawings, in which: 
         FIG. 1  is an illustration of a carburetor with the adjustment system of the present invention shown attached thereto; 
         FIG. 2  is a sectioned isometric view of the present invention in association with its adjustment tool; 
         FIG. 3  is similar to  FIG. 2 , but not sectioned; 
         FIG. 4  is a side sectioned view of the present invention in association with its adjustment tool; 
         FIG. 5  is an isometric view of the rotatable adjustment member or idle fuel adjustment screw; and 
         FIG. 6  is an isometric view of the adjustment tool of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Throughout the description of the preferred embodiment of the present invention, like components will be identified by like reference numerals. 
       FIG. 1  is a side view of a carburetor  10  with which the adjustment system of the present invention can be used. Reference numeral  14  identifies a housing, shown as a section view in  FIG. 1 , which is shaped to at least partially surround a head  18  of a rotatable adjustment member  20 . An access opening  26  is formed in a first surface  28  of the housing  14 . The other portions of the carburetor  10  are generally well known to those skilled in the art and will not be described in detail herein. The rotatable adjustment member  20  is shaped to be supported by the carburetor  10  for rotation about a rotational axis  30 . 
       FIG. 2  is an isometric section view of the adjustment system, shown removed from the carburetor  10  for purposes of clarity and to facilitate the explanation of its various components. The rotatable adjustment member  20  has a first end  40  which is insertable into a retention opening formed in the carburetor. The rotatable adjustment member  20  has a second end  44  which extends away from the engine component. The head  18  is formed at the second end  44  of the rotatable adjustment member  20 . The housing  14  is shaped to at least partially surround the head  18 , as illustrated in the section view of  FIG. 2 . The rotational axis  30  of the rotatable adjustment member  20  extends through the first surface  28  of the housing  14 . The access opening  26  is formed in the first surface  28 . The rotational axis  30  of the rotatable adjustment member  20  extends through the access opening  26  as illustrated in  FIG. 2 . 
     As described above, in a preferred embodiment of the present invention, the rotatable adjustment member  20  is an idle fuel mixture screw and the engine component is a carburetor  10 . The rotatable adjustment member  20  is threaded into the retention opening of the carburetor  10 , with threads that are provided on the barrel-shaped portion  50  identified in  FIG. 2 . Although the threads are not illustrated in  FIG. 2  at the portion  50 , it should be understood that machine threads are provided on this outer cylindrical surface so that the rotatable adjustment member  20  can be threaded into the retention opening of the carburetor  10  which is similarly threaded. 
     With continued reference to  FIG. 2 , an adjustment tool  60  is shaped to pass at least partially through the access opening  26  and into the cavity  64  defined by the housing structure  14 . The adjustment tool  60  has an operative end  68  which is shaped to engage the head  18  in torque transmitting relation. The operative end  68  has a pair of inwardly facing surfaces,  71  and  72 , which are shaped to receive a pair of outwardly facing surfaces,  81  and  82 , of the head  18 . Although outwardly facing surface  82  and inwardly facing surface  71  are not clearly visible in  FIG. 2 , they will be described in greater detail below. 
     With continued reference to  FIG. 2 , it can be seen that in a preferred embodiment of the present invention, the access opening  26  is a round hole which extends through the first surface  28 . The round hole, which is shown in section view in  FIG. 2 , has a diameter which is greater than a maximum thickness dimension of the operative end  68  of the tool  60 . The diameter of the access hole  26  is also greater than a maximum thickness dimension of the head  18  in a preferred embodiment of the present invention. The rotational axis  30  of the rotatable adjustment member  20  is generally perpendicular to the first surface  28  in a preferred embodiment. An internal surface  80  of the housing  14  defines the cavity  64  and the head  18  is spaced apart from the internal surface  80  of the housing  14 . In other words, the head  18  is supported in non-contact association with the internal surface  80  of the housing  14  and is generally surrounded by the walls of the housing  14 . The cross-sectional area of the access opening  26 , in a particularly preferred embodiment of the present invention, is less than twenty five percent of the total cross-sectional area of the first surface  28 . In a particularly preferred embodiment of the present invention, the diameter of the access opening  26  is approximately 6.5 millimeters. The effective diameter of the first surface  28 , in that same preferred embodiment, is approximately 17.0 millimeters. As a result, the cross-sectional area of the access opening  26  is less than twenty five percent of the area of the first surface  28 . Minimizing the relative area of the access opening  26 , in this way, helps to inhibit inappropriate access to the head  18  by personnel who are not properly qualified to make the associated adjustments in the operation of the carburetor  10 . That is the purpose of providing the protective housing  14  around the head  18  of the idle fuel mixture screw  20 . However, the operative end  68  of the tool  60  is shaped and sized to pass through the access opening  26  to allow a trained technician to rotate the rotatable adjustment member  20  as needed to make a proper adjustment of the operation of the carburetor  10 . 
     With continued reference to  FIG. 2 , it can be seen that the first end  40  of the rotatable adjustment member  20  extends through a rear surface  90  of the housing  14  to allow the threaded portion  50  to engage threads of the retention opening of the carburetor  10 . In addition, a spring  92  is located between the rear surface  90  and an enlarged collar  94  formed on the rotatable adjustment member  20 . This spring  92  exerts a force which retains the housing  14  in position as shown in  FIG. 1 . 
       FIG. 3  is an isometric representation of the adjustment system of a preferred embodiment of the present invention, without the sectioning of the housing  14 . The generally round shape of the access opening  26  is shown aligned, by dashed lines, with the operative end  68  of the tool  60  for the purpose of illustrating how the tool  60  can allow access to the head  18  for purposes of permitting a skilled technician to properly adjust the idle fuel mixture of the carburetor. 
       FIG. 4  is a side section view of the components illustrated in  FIGS. 2 and 3 . In the section view of  FIG. 4 , the relative size of the access opening  26  and the operative end  68  of the tool  60  can be compared by observing the dashed lines which align the operative end  68  of the tool  60  with the access opening  26 . The operative end  68  can be inserted through the first surface  28  and into contact with the head  18 . The inwardly facing surfaces,  71  and  72 , of the tool  60  can then engage the outwardly facing surfaces,  81  and  82 , of the head  18  to allow torque to be applied to the rotatable adjustment member  20  to cause it to rotate about its rotational axis  30 . This allows an expert technician to make adjustments in the idle fuel mixture even though access to the head  18  is denied to unauthorized personnel who are not in possession of a tool such as the adjustment tool  60 . A conventional screw driver will not be able to cause the rotatable adjustment member  20  to rotate about axis  30 . 
     With continued reference to  FIG. 4 , it can be seen that the housing structure  14  is a combination of a first generally tubular member  100  and a second generally tubular member  102  which are assembled together to form the housing structure  14 . Although the relative sizes of the access opening  26  and the first surface  28  have been described above as having the access opening being less than twenty five percent of the area of the first surface  28 , it should be understood that alternative embodiments of the present invention could function as intended if the access opening is less than thirty percent of the area of the first surface  28  or, alternatively, if the access opening  26  is less than fifty percent of the area of the first surface  28 . The important characteristic of this relationship is that the access opening  26  be sufficiently small, in relation to the first surface  28  and the head  18  of the idle fuel mixture screw  20 , to inhibit easy access to the head  18  by those who are not properly trained to perform the adjustment or calibration of the idle fuel mixture screw. Ideally, a particularly preferred embodiment of the present invention would incorporate an access opening  26  that is at a minimum possible diameter which is sufficient to allow the operative end  68  of the tool  60  to pass therethrough to engage the head  18 , but not large enough to allow easy access to an untrained person using conventional tools, such as needle-nose pliers or screw drivers. 
       FIG. 5  is an enlarged isometric view of the rotatable adjustment member  20  and  FIG. 6  is an enlarged isometric view of the adjustment tool  60 . The collar  94  on the rotatable adjustment member  20  is sized, in a particularly preferred embodiment of the present invention, to prevent the rotatable adjustment member  20  from passing completely through the access opening  26  in a direction out of the cavity  64 . In other words, the head  18  is shaped to pass into the access opening  26  under certain conditions, but the collar  94  limits the total movement of the rotatable adjustment member  20  in a direction through the access opening  26  in the first surface  28 . As is generally known to those skilled in the art, the first end  40  of the rotatable adjustment member is shaped to allow adjustment of fuel passing through a conduit. This is accomplished through the use of the tapered tip at the first end  40 . The tool  60  is provided with a hex-shaped portion  110  at the end which is opposite from the operative end  68 . This facilitates the use of a wrench or similar tool to exert torque on the tool  60  which, in turn, is transmitted through the inwardly and outwardly directed surfaces,  71 ,  72 ,  81 , and  82 , to the rotatable adjustment member  20 . 
     With reference to  FIGS. 1–6 , a particularly preferred embodiment of the present invention provides a carburetor  10  and an idle fuel mixture screw  20  which is shaped to be supported by the carburetor  10  for rotation about a rotational axis  30 . The idle fuel mixture screw  20  has a first end  40  which is insertable into a retention opening formed in the carburetor  10 . The idle fuel mixture screw  20  has a second end which extends away from the carburetor  10 . A head  18  is formed at the second end of the idle fuel mixture screw  20 . A housing  14  is shaped to at least partially surround the head  18 . The rotational axis  30  of the idle fuel mixture screw  20  extends through a first surface  28  of the housing  14 . An access opening  26  is formed in the first surface  28  and the rotational axis  30  of the idle fuel mixture screw  20  extends through the access opening  26 . An adjustment tool  60  is shaped to pass at least partially through the access opening  26 . The adjustment tool  60  has an operative end  68  which is shaped to engage the head  18  in torque transmitting relation. The operative end  68  has a pair of inwardly facing surfaces,  71  and  72 , which are shaped to receive a pair of outwardly facing surfaces,  81  and  82 , of the head  18  therebetween. An internal surface  80  of the housing  14  defines a cavity  64  and the head  18  is spaced apart from the internal surface  80  of the housing  14 . The area of the access opening  26 , in one embodiment of the present invention, is less than fifty percent of the area of the first surface  28 . The access opening  26  is a hole which extends through the first surface  28  and the hole is shaped to permit a maximum thickness dimension of the operative end  68  to pass therethrough. The rotational axis  30  of the idle fuel mixture screw  20  is generally perpendicular to the first surface  28 . 
     Although the present invention has been described in particular detail and illustrated to show a preferred embodiment, it should be understood that alternative embodiments are also within its scope.