Abstract:
An adjustable cam shaft sprocket for allowing small adjustments to a cam shaft. The adjustable cam shaft sprocket comprises an inner member and an outer member, the inner member being placed concentrically within the first circular member and held in place by a fastener. A series of openings located at the perimeter of the inner member and outer member are arranged such that only one pair of openings between the inner member and the outer member are aligned for each hole alignment. A shear pin is inserted through the aligned pair of openings to prevent the inner member from rotating with respect to the outer member. A small adjustment to the cam shaft is achieved by removing the shear pin, rotating the inner member with respect to the outer member so that a second pair of openings is aligned, and re-inserting the shear pin.

Description:
SCOPE 
     The present invention relates to internal combustion engines. More specifically, the present invention relates to an adjustable cam shaft sprocket for allowing small adjustments to a camshaft. 
     BACKGROUND 
     As is well known, for a four-cycle internal combustion engine to run smoothly, the rotation of the crankshaft and the camshaft must remain in synchronization. Should they fall out of synchronization, serious damage can occur to the engine. Furthermore, it is well known that the maximum horsepower from an engine can be achieved by adjusting the camshaft so that the cams open and close the various engine valves at precisely the right times, thereby improving pumping efficiency. 
     Generally, in internal combustion engines, a timing chain, belt, or gear is installed around a crank shaft gear, or cam shaft sprocket, mounted on one end of the crank shaft. The timing chain is also installed around a crank shaft gear, which is mounted on one end of a crank shaft. The timing chain thus transfers rotational energy from the crank shaft to the cam shaft sprocket and, hence, the cam shaft. This serves the purpose of not only causing the cam shaft to rotate, but it also maintains the rotational synchronization of these two shafts. 
     Generally, an engine will operate efficiently within given operating tolerances when the timing chain is installed so that a proper relationship to the drive shaft is achieved. A course adjustment of the cam shaft, and thus, the cams themselves, can be achieved by adjusting the timing chain on the cam shaft gear plus or minus one link in the timing chain. However, this allows only a course adjustment to the cam shaft. 
     To achieve maximum engine performance, the cam shaft may be further adjusted with respect to the crank shaft by using an adjustable cam shaft sprocket. As shown in FIG. 1 a , an adjustable cam shaft sprocket comprises an inner member and an outer member. The inner member is installed concentrically within the outer member, the outer member being toothed for engaging the timing chain. The inner member and the outer member are fastened together using one or more bolts. A fine adjustment of the cam shaft sprocket can be achieved by loosening the bolts, thereby allowing the outer member to be adjusted by any amount with respect to the inner member. When the desired amount of adjustment is achieved, the bolts are tightened so that the inner member and the outer member do not rotate with respect to each other. 
     One problem with using an adjustable cam shaft sprocket as described above is that over time, the inner member can rotate with respect to the outer member, either by a small amount or a large amount. If the members rotate a small amount with respect to each other, engine performance will suffer. If the members rotate a large amount with respect to each other, a gross misalignment of the cam shaft with respect to the crank shaft will occur, and severe engine damage may result. Rotation between the members occurs because the bolts do not prevent the members from moving with respect to each other. The members are held together by the frictional force between the members that result when the bolts are tightened. 
     Another method of adjusting a cam shaft is by using a device as shown in FIG. 1 b . This device is bolted directly onto the end of a cam shaft and a timing belt or chain is installed around the teeth on the perimeter of the device. The cam shaft has openings which align with one or more holes in the device. When the cam shaft is in the desired position, it is hoped that one of the holes on the device will be aligned with one of the cam shaft openings. If so, then a shear pin is inserted through the aligned openings, and a bolt is tightened to keep the device secured to the end of the cam shaft. If a pair of openings does not align, the belt or chain must be removed and the device repositioned and the hole alignment must be performed again. Even when an initial alignment between openings is achieved, the relative position of the cam shaft with respect to the drive shaft may change slightly due to various factors, such as stretching in the timing belt or chain, and the alignment procedure must be done again. Thus, achieving the desired cam shaft alignment becomes a long, repetitive task. 
     What is needed is an adjustable cam shaft sprocket that will allow fine adjustments to the cam shaft while preventing rotation between the members with respect to each other during normal engine operation. Ideally, the adjustment would not require removal of the timing belt or timing chain, and would be accomplished in a relatively short period of time. 
     SUMMARY 
     The present invention is directed to an apparatus for allowing small adjustments to a cam shaft. In one embodiment, the present invention comprises a shear pin and a first circular member having a toothed outer surface for receiving a timing chain or belt, a first cam shaft opening, and a recessed planar surface having a first number of openings located proximate to a perimeter of the recessed planar surface. The present invention further includes a second circular member having a second planar surface and a cylindrical portion extending perpendicularly from the second planar surface, the second planar surface having a cam shaft opening extending through the cylindrical portion and a second number of openings located proximate to a perimeter of the second planar surface, the second circular member for being placed concentrically within said first circular member wherein the second circular member is prevented from rotating with respect to said first circular member by inserting the shear pin through one of the second number of openings and through one of the first number of openings, wherein the second circular member may be adjusted incrementally with respect to the first circular member by removing the shear pin and rotating the second circular member with respect to the first circular member such that a second one of the second number of openings is aligned with a second one of the first number of openings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects presented are best understood when viewed in accordance with the following description of the drawings: 
     FIGS. 1 a  and  1   b  illustrate prior art adjustable cam shaft sprockets; 
     FIG. 2 illustrates an adjustable cam shaft sprocket in accordance with one embodiment; 
     FIG. 3 illustrates a shear pin of FIG. 2 in accordance with one embodiment; 
     FIGS. 4 a  and  4   b  illustrate an outer member of FIG. 2 in accordance with one embodiment, wherein FIG. 4 a  shows the outer member in a plan view and FIG. 4 b  shows the outer member in a side view; 
     FIGS. 5 a  and  5   b  illustrate an inner member of FIG. 2 in accordance with one embodiment, wherein FIG. 5 a  shows the inner member in a plan view and FIG. 5 b  shows the inner member in a side view; 
     FIG. 6 illustrates a side view of the adjustable cam shaft sprocket of FIG. 2 in an assembled state, showing hidden surfaces which would normally not be seen; 
     FIG. 7 illustrates a close-up view of one section of the inner member of FIGS. 5 a  and  5   b  assembled with the outer member of FIGS. 4 a  and  4   b;    
     FIG. 8 illustrates another close-up view of the section shown in FIG. 7, showing a small clockwise adjustment of the inner member of FIGS. 5 a  and  5   b  with respect to the outer member of FIGS. 4 a  and  4   b  from the alignment shown in FIG. 7; and 
     FIGS. 9 a  and  9   b  illustrate the relationship between openings in the outer member of FIGS. 4 a  and  4   b  and openings in the inner member of FIGS. 5 a  and  5   b , wherein FIG. 9 a  shows openings located on the outer member and FIG. 9 b  shows openings located on the inner member. 
    
    
     DETAILED DESCRIPTION 
     FIG. 2 illustrates an adjustable cam shaft sprocket  200  in accordance with one embodiment. Adjustable cam shaft sprocket  200  comprises a shear pin  202 , an outer member  204 , and inner member  206 . Inner member  206  is seating concentrically within outer member  204  and held in place by bolts  212 . Although FIG. 2 shows four bolts  212 , it should be understood that any number of bolts may be used to hold inner member  206  against outer member  204 . 
     Shear pin  202 , otherwise known as a shoulder bolt, is used to maintain alignment between inner member  206  and outer member  204 . Shear pin  202  is placed through one of a number of openings  208  located on a planer surface of inner member  206  and also through one of a number of openings located on a planer surface of outer member  204 . The relationship between the holes located on inner member  206  and outer member  204  determines the amount of adjustment between the members, and thus, the amount of adjustment which is applied to a cam shaft which is installed through cam shaft opening  210 . 
     In one embodiment, inner member  206  measures approximately 3⅜ inches in diameter and is approximately {fraction (3/16)} inches thick. Outer member  204  measures approximately 4 inches in diameter and is 1⅛ inches thick in the area of teeth  214 . Outer member  204  comprises a planar surface which is recessed from teeth  214  by approximately ⅜ inches. A wall formed by the recessed planar surface of outer member  204  forms a diameter which is slightly larger than the diameter of inner member  206  so that inner member  206  may be placed concentrically within outer member  204 . Both inner member  206  and outer member  204  comprise a rigid material, such as aluminum, steel, or any other material known by those skilled in the art for generally constructing such an adjustable cam shaft sprocket. Both inner member  206  and outer member  204  are manufactured by methods well known in the art. 
     FIG. 3 illustrates shear pin  202  in accordance with one embodiment. Shear pin  202  comprises a head  300 , a shaft  302 , and a threaded end  304 . In operation, threaded end  304  is inserted through one of a number of openings located on a planar surface of inner member  206  and screwed into one of a number of threaded openings located on a planar surface of outer member  204 . Shear pin  202  is tightened into place generally by applying torque to head  300  using any number of devices, such as a socket wrench, Allen wrench, screwdriver, etc. Of course, for each of the just-named embodiments, head  300  is fashioned accordingly. For example, head  300  comprises a hexagonal shape for receiving a socket wrench or head  300  comprises a pan head with a slotted cutout for receiving a screwdriver. Head  300  also limits the amount of distance shear pin  202  will travel into the threaded opening of the outer member, as the undersurface  306  of head  300  rests directly on the planar surface of inner member  206  upon installation. Of course, a washer could be used in another embodiment in which case the washer would be situated between undersurface  306  and the planar surface of inner member  206 . 
     When shear pin  202  is installed through the two members as explained above, shaft  302  prevents the members from rotating with respect to each other. If one member tries to rotate with respect to the other, a shear force is exerted on the surface of shaft  302 , but as long as shear pin  202  is resilient enough to withstand such force, the members will not rotate with respect to one another. As such, shear pin  202  generally comprises some sort of metal or alloy, such as stainless steel, aluminum, etc., and is appropriately thick enough to withstand such force. 
     Shear pin  202  can alternatively comprise other shapes and features without departing from its use with adjustable cam shaft sprocket  200 , i.e., aligning the two members to each other and preventing rotation therebetween. For example, as discussed above, head  300  might comprise different shapes to afford various types of tools, or, in another embodiment, head  300  may not be present at all. In this case, head  300  is simply an extension of shaft  302 . 
     FIGS. 4 a  and  4   b  illustrate outer member  204  in accordance with one embodiment. FIG. 4 a  shows outer member  204  in a plan view while FIG. 4 b  shows outer member  204  in a side view. In FIG. 4 a , outer member  204  comprises a circularly-shaped object having teeth  400  located on its perimeter. Teeth  400  are used to engage a timing chain (not shown) which is used to rotate the assembled adjustable cam sprocket  200 . In one embodiment, outer member  204  comprises a diameter of six inches, however outer member  204  may alternatively be larger or smaller in diameter. Teeth  400  generally span the entire height of outer member  204 , as shown in FIG. 4 b , although in other embodiments, this may not be the case. 
     Outer member  204  also comprises a planar surface  402 . Planar surface  402  comprises a number of openings  404  for receiving shear pin  202 . In one embodiment, each of openings  404  comprises a threaded recess for securing shear pin  202  in place. The threaded recesses also serve to remove shear pin  202  when desired. In other embodiments, openings  404  may comprise through holes or recesses having fastening means inserted therein for securing shear pin  202  in place. The openings  404  are generally located near the periphery of planar surface  402 , although in other embodiments, they may be located anywhere and, in general, maintain a circular shape with respect to one another. Outer member  204  as shown in FIG. 4 a  comprises twenty openings  404 , however in other embodiments, a greater or fewer number of openings could be used. Planar surface  402  additionally comprises opening  406  for allowing a center portion of inner member  206  to pass upon assembly. Opening  406  may be of any desired shape, however it is generally circular in shape. Bolt openings  408  allow bolts  212  (shown in FIG. 2) to pass. Bolt openings  408 , in one embodiment, are threaded. In another embodiment, oblong openings  408  are not threaded, allowing bolts  212  to pass, while a nut secures bolts  212  in place. Although FIG. 4 a  shows 4 bolt openings  408 , it should be understood that a greater or fewer number of bolt openings may be used in other embodiments. 
     FIGS. 5 a  and  5   b  illustrate inner member  206  in accordance with one embodiment. FIG. 5 a  shows inner member  206  in a plan view while FIG. 5 b  shows inner member  206  in a side view. Inner member  206  is circular when viewed in plan view as shown. The diameter of inner member  206  is such that inner member  206  will fit within wall  410  of outer member  204 . Inner member  206  additionally comprises oblong openings  502  for allowing bolts  212  to pass. The oblong openings  502  are generally oblong in nature to allow rotational, or angular, adjustment of inner member  206  within outer member  204  during use. 
     Inner member  206  additionally comprises a cam shaft opening  504 , for allowing one end of a cam shaft to pass. Cam shaft opening  504  generally comprises a notch  506  which operates as a key for mounting the cam shaft through cam shaft opening  504  (the cam shaft generally comprises a raised extrusion which fits into cam shaft notch  506 ). The notch  506  also acts to connect the cam shaft to inner member  206  so that, during operation, as the timing chain turns outer member  204  and thus inner member  206 , the cam shaft is rotated as the timing chain is moved by the crank shaft. 
     Inner member  206  additionally comprises a portion  508  which extends perpendicularly away from an under surface  512 , located opposite to planar surface  510 . As such, inner member  206  resembles a “T”, as shown in FIG. 5 b . The portion  508  is cylindrical in nature, and comprises a diameter which fits within a channel  412  of outer member  204 . Portion  508  is not used in other embodiments. 
     Inner member  206  additionally comprises openings  208 , as shown in FIG. 5 a . Openings  208  each allow shear pin  202  to be inserted therethrough. In one embodiment, inner member  206  comprises twenty-one openings  208  located near an outer circumference of planar surface  510 . It should be understood that any number of openings  208  could be used in an alternative embodiment. It should also be understood that the location of openings  208  may be located in another area of planar surface  510 , although they will generally retain a circular relationship with each other. 
     FIG. 6 illustrates a side view of adjustable cam shaft sprocket  200  in an assembled state, showing hidden surfaces which would normally not be seen. Inner member  206  is positioned into outer member  204  by inserting portion  508  of inner member  206  through opening  406  of outer member  204 . The diameter of wall  410  is slightly larger in diameter than the diameter of planar surface  510  of inner member  206 , so that inner member  206  is free to rotate when it is inserted into outer member  204 . One of the openings  208  of inner member  206  is aligned with one of the openings  404  of outer member  204 , then shear pin  202  is inserted through both openings and secured in place. In one embodiment, shear pin  202  comprises a threaded end  304  which is screwed into opening  404 , as described above. 
     Once shear pin  202  has been secured through the one of the openings  208  and  404 , inner member  206  and outer member  204  are secured together using one or more bolts  212  (only one bolt  206  is shown if FIG. 6 for clarity). The assembly of adjustable cam shaft sprocket  200  is then complete. After assembly, adjustable cam shaft sprocket  200  is then installed onto one end of a cam shaft, then a timing belt or timing chain is used to engage teeth  400  with a gear mounted to a crank shaft. Of course, the cam shaft must be aligned with the crank shaft, and generally known techniques are used to ensure that this is so. 
     Once the cam shaft has been properly aligned with the crank shaft, a further refinement of this relationship can be achieved using adjustable cam shaft sprocket  200 . 
     Inner member  206  can be rotationally adjusted in very small amounts with respect to outer member  204  as follows. The bolts  212  are loosened and shear pin  202  is removed so that inner member  206  and installed cam shaft can rotate with respect to outer member  204 . Inner member  206  may then be rotated in very small increments in either a clockwise or counter-clockwise direction. As inner member  206  is rotated with respect to outer member  204 , only one set of openings  208  and  404  will align, allowing shear pin  202  to be inserted therethrough. This concept is best illustrated in FIGS. 7 and 8 as follows. 
     FIG. 7 illustrates a close-up view of one section of inner member  206  assembled with outer member  204 . Various details of both inner member  206  and outer member  204  have been omitted so that the relationship between openings  208  and  404  can be shown. 
     As shown in FIG. 7, opening  208   a  is aligned with opening  404   a  such that shear pin  202  can be inserted through both openings without obstruction (opening  404   a  is not shown in FIG. 7 because of the alignment with opening  208   a ). When openings  208   a  and  404   a  are aligned, general no other openings will be aligned, although in other embodiments, it may be possible that more than one pair of openings may be aligned. This concept is illustrated in FIG. 7, with opening  208   b  having a small misalignment between it and opening  404   b . Opening  208   c  is slightly more misaligned with opening  404   c  than opening  208   b  is with respect to opening  404   b . Successive pairs of openings become more and more misaligned as one views the pairs in a clockwise direction from openings  208   a  and  404   a.    
     FIG. 8 illustrates another close-up view of the same section of inner member  206  and outer member  204 . Again, various details of both inner member  206  and outer member  204  have been omitted so that the relationship between openings  208  and  404  can be shown. 
     FIG. 8 illustrates a small clockwise adjustment of inner member  206  with respect to outer member  204  from the alignment shown in FIG.  7 . In this illustration, opening  208   b  is aligned with opening  404   b  such that shear pin  202  can be inserted through both openings without obstruction (opening  404   b  is not shown in FIG. 8 because of the alignment with opening  208   b ). When openings  208   b  and  404   b  are aligned, generally no other openings will be aligned. Again, this concept illustrates that opening  208   c  is slightly misaligned with opening  404   c , while opening  208   a  is slightly misaligned with opening  404   a.    
     The smallest amount of adjustment that can be achieved is generally related to the relative offset between openings  208  and  404  located on their respective members and the number of openings formed in outer member  204  with respect to inner member  206 . FIGS.  9   a  and  9   b  illustrates this concept. 
     In FIG. 9 a , outer member  204  is shown, having 20 openings spaced equally apart near the perimeter of planar surface  510 . Thus, each opening  404  is 360/20 or 18 degrees apart from one another. FIG. 9 b  shows inner member  206 , having 21 openings. The number of openings on inner member  206  and their location dictate the number of discrete adjustments, and the amount of angular adjustment, the members may have with one another. In the embodiment shown in FIGS. 9 a  and  9   b , a total of 21 possible angular relationships between members is possible, that is, there may be zero degrees, and plus or minus 10 degrees of angular adjustment, in one degree increments, between members. The location of the openings in inner member  206  is calculated as follows. 
     In FIG. 9 b , a reference opening  900  is used as a reference point and references zero degrees when aligned with outer member  204 . Thus, in the “zero degree” position, reference opening  900  of inner member aligns with opening  902  of outer member  204 . To determine the number of openings in inner member  206 , the total amount of adjustment desired in one direction is divided by the incremental adjustment desired. Thus, in this embodiment, the total amount of adjustment desired in either direction is 10 degrees and the desired incremental adjustment is 1 degree. 10 divided by 1 is equal to 10, therefore 10 openings are needed in a clockwise direction from reference opening  900 , and 10 openings are needed in a counter-clockwise direction from reference opening  900 . 
     The placement of the openings in inner member  206  with respect to reference opening  900  are calculated by the following formula:            (       360                 degrees     -     total                 adjustment                 desired                 in                 both                 directions       )       (       total                 #                 of                 openings     -   1     )       =     degrees                 between                 openings                            
     In this embodiment then, the distance between openings on inner member  206  is 17.0 degrees ((360−20)/(20−1)). The openings are formed on inner member  206  in both the clockwise and the counter-clockwise direction and are 17.0 degrees apart from each other beginning at reference opening  900 . 
     In should be understood that, in another embodiment, the openings on inner member  206  may be spaced equally from each other and the openings on outer member  204  may be spaced in accordance with the above formula. 
     The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.