Abstract:
A chain and sprocket transmission system for small all-terrain vehicles couples a high-speed, low-horsepower motor to a small diameter ground-engaging vehicle driving wheel. The chain and sprocket transmission system includes a small driving sprocket directly driven by the high-speed, low-horsepower motor. A large driven sprocket coaxially rotates with the small-diameter ground-engaging wheel. An endless chain has links for encircling in a loop the small driving sprocket and the large driven sprocket for powering the small-diameter ground-engaging wheel. A chain keeper pivots over the small driving sprocket. This chain keeper has a chain-contacting tongue elastically biased with respect to the keeper toward the inside of the chain loop. The chain-contacting tongue contacts and tensions the chain at the idle chain linkage between the small driving sprocket and the large driven sprocket.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
         [0001]    NOT APPLICABLE  
         STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    NOT APPLICABLE  
         REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK.  
         [0003]    NOT APPLICABLE  
           [0004]    This invention relates to a chain drive and a chain transmission system for small all-terrain vehicles, such as motorized scooters or motorized carts. More particularly, a chain drive which effects high reduction between a high-speed, low-horsepower motor and a slower speed, driven small-diameter ground-engaging wheel is disclosed. A unique chain keeper acts as a tensioner, lubricator, guard and guide, enabling the system use of a small-size chain and sprocket drive having low inertia and high speed reduction between the motor and driven wheel.  
         BACKGROUND OF THE INVENTION  
         [0005]    Chain drives for small all-terrain vehicles, such as scooters and go carts, are replete with problems. First, such vehicles operate in a dirt and mud environment. The resultant ambient grit produces high chain wear with resultant chain lengthening.  
           [0006]    Chain lengthening due to chain wear can be easily understood. In the case of a chain having 94 links, chain wear for each link will occur at three separate places. First, each link is held together by a link pin. As the pin diameter decreases due to wear, the overall length of the link will increase in each chain direction by the amount of the wear. Second, each chain link includes forward-extending links and rearward-extending links. Each of these respective forward-extending and rearward-extending links fastens to the link pin at an aperture. Each of these apertures is subject to wear, especially in the grit environment. Each aperture as it is subject to wear becomes an individual contributor to chain lengthening.  
           [0007]    Because there are two apertures for each pin at each link, the chain wear at each aperture will contribute to chain lengthening. Thus, in the chain having 94 links, there are additively 94 pins and 188 apertures all subject to wear. Each wear point, being a pin or an aperture, lengthens the chain. Presuming that the small all-terrain vehicles are continually operated in a grit environment, adjustment for chain length change becomes an ongoing proposition.  
           [0008]    A rapidly lengthening chain on a small all-terrain vehicle increases the probability of chain and sprocket derailment. Generally speaking, the smaller the chain, the more rapid the wear.  
           [0009]    It is known to use mechanical tensioning devices in such environments. However, such conventional mechanical tensioners require pivot points, spring bias, and chain idlers. They impose a considerable complication on a chain and sprocket drive. In the case of a small all-terrain vehicle, further complication of mechanical tensioning devices is disadvantageous, especially in the limited space available between the driving low-horsepower, high-speed motor and the sprocket-driven small-diameter ground-engaging wheel.  
           [0010]    Small all-terrain vehicles typically use low-horsepower, high-speed motors. For example, in the scooter which forms a preferred example of this invention, a 2-½ horsepower 8000 rpm motor is used. This motor is used to drive wheels in the order of eight to nine inches. Rotation reduction is a key transmission system issue.  
           [0011]    At the same time, small all-terrain vehicles place high dynamic loading on their transmissions. For example, where the wheels of such vehicles temporarily leave the ground and become airborne, return of the powered wheel to the ground normally produces high dynamic shock loads on the transmission system. As a result, many chain transmission systems have tried using chain sizes that can withstand the high dynamic shock loads. Unfortunately, with increased chain size, sprocket size and sprocket inertia increases. Increased sprocket size necessitates the use of a larger transmission system, requires the use of intermediate so-called idler or “jack” shafts, and increases transmission inertia, inhibiting acceleration and deceleration.  
           [0012]    Intermediate idler or “jack” shafts present an especially undesired complication to chain and sprocket transmission systems for small all-terrain vehicles. In such idler or jack shafts systems, a first chain loops the high-speed drive sprocket at the low-horsepower motor to a second driven sprocket on the idler or jack shaft. A second chain loops the third drive sprocket on the idler or jack shaft and extends to a fourth driven sprocket at the small ground-engaging wheel. The additional mechanical parts of the idler or jack shaft and two sprockets, the additional second chain, the complexity of mounting the idler or jack shaft and the two sprockets, and the space required for such idler or jack shaft and two sprockets are generally unsuitable for small all-terrain vehicle chain transmissions.  
           [0013]    Presuming that one wishes to use a small-size chain and sprocket drive for an all-terrain vehicle, the load limits of such small chains also become a problem. For example, a No. 25 chain has a tensile load limit in the order of 900 pounds (compared to the 2500-pound tensile load limit of the No. 35 chain). With normally available chain and sprocket transmissions, a lighter chain realizes greater probability of chain failure.  
           [0014]    Finally, and presuming that one is going to use small chain for such an all-terrain vehicle high-reduction chain and sprocket transmission, the transmission of power from a small high-speed sprocket to the small chain presents a power transmission issue. By definition, a small-diameter sprocket contacts the chain at a small number of lugs. Where the total power of the engine is delivered to a small chain at a reduced number of lugs, the probability of load failure and chain failure increases directly proportional to the increased power transfer at each sprocket lug to each chain link.  
         BRIEF SUMMARY OF THE INVENTION  
         [0015]    A chain and sprocket transmission system for small all-terrain vehicles couples a high-speed, low-horsepower motor to a small diameter ground-engaging vehicle driving wheel. The chain and sprocket transmission system includes a small driving sprocket directly driven by the high-speed, low-horsepower motor. A large driven sprocket coaxially rotates with the small-diameter ground-engaging wheel. An endless chain has links for encircling in a loop the small driving sprocket and the large driven sprocket for powering the small-diameter ground-engaging wheel. A chain keeper pivots over the small driving sprocket. This chain keeper has a chain-contacting tongue elastically biased with respect to the keeper toward the inside of the chain loop. The chain-contacting tongue contacts and tensions the chain at the idle chain linkage between the small driving sprocket and the large driven sprocket. In the case of the small driving sprocket, chain contact with the small driving sprocket is increased to enable power transmission and distribution over an increased number of sprocket lugs and chain links. Preferably, the chain keeper is a one-piece construction, preferably molded from a high-impact, wear-resistant, low-chain-slide-friction plastic material. This molded chain keeper has a rigid section along the tension side of the chain, the pivot mounting to the small driven sprocket, and the chain-contacting tongue elastically biased with respect to the rigid section of the keeper across the pivot mounting. The one-piece chain keeper defines a groove for maintaining chain and sprocket alignment. The molded chain keeper acts as a chain guard protecting both the chain and the vehicle operator. Further, the one-piece chain keeper has an aperture through which lubricant can flow to the chain during power transmission. There results the chain and sprocket transmission system with a one-piece chain keeper that provides a chain tensioner, a chain lubricator, a chain guide, and a chain guard. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a perspective view of a rider on a scooter having the chain transmission system of this invention;  
         [0017]    [0017]FIG. 2 is an enlarged side perspective view taken above and to the side of the small-diameter, high-speed-motor-driven sprocket and the large-diameter, ground-engaging wheel driving sprocket illustrating the placement of the chain keeper of this disclosure;  
         [0018]    [0018]FIG. 3 is a side elevation of the one-piece integrally molded chain keeper of this transmission system illustrating in phantom the lubrication aperture and lubrication pouch;  
         [0019]    [0019]FIG. 4 is a side elevation of the keeper pivoted in a first position about the small high-speed driving sprocket to supply tension to the idle section of the chain when the chain is of a first length; and  
         [0020]    [0020]FIG. 5 is a side elevation of the keeper pivoted in a second position about the small high-speed driving sprocket to supply tension to the idle section of the chain when the chain is of a second and longer length. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    Referring to FIG. 1, rider R (shown in broken lines) stands upon scooter platform P steering scooter  10  at steering handle  12  to direct steered front wheel  11 . Engine  15  powers rear driven wheel  14  to propel scooter  10  as directed by rider R.  
         [0022]    Referring to FIGS. 3 and 4, chain keeper  20  is illustrated in side elevation. Engine driven sprocket cavity  21  is the point of rotation for mounting rotating chain keeper  20  about engine driven sprocket  31 . Chain keeper  20  is mounted at over center lock  40  at over center lock slot  26 . Between mounting at the engine driven sprocket cavity  21  and the over center lock slot  26 , chain keeper  20  is maintained in fixed relation about engine driven chain sprocket  31  and chain  30 .  
         [0023]    Typically, engine driven sprocket  31  has eight or nine lugs and is designed to fit to a No. 25 chain. Engine driven sprocket  31  turns at relatively high speed. It is common for the sprocket to rotate at 8000 rpm. Thus, it will be understood the chain  30  in its interaction with driven sprocket  31  passing around the wheel driving sprocket  32  is in effect a speed reduction system.  
         [0024]    Continuing on with FIG. 3, an elastic bridge section  22  enables tongue  24  to be biased at chain depressing surface  25  against chain  30 . It will be understood that once chain keeper  20  is angularly adjusted about engine driven sprocket  31 , tongue  24  at chain depressing surface  25  will cause chain  30  to maintain a substantially constant tension.  
         [0025]    Over center lock slot  26  enables keeper  20  to pivot about engine driving sprocket cavity  21 . As will hereinafter be set forth, this pivot allows tongue  24  to be biased at chain contacting surface  25  to maintain chain  30  under proper tension at all times.  
         [0026]    It will be remembered that scooter  10  operates in what is essentially a gritty environment. This being the case, constant lubrication is desirable. To this end, a lubricant pouch  29  is placed within a pouch-receiving cavity  28  and discharges lubricating fluid for chain  30  through aperture  27  on to the underlying chain. Since the chain is gathered from underlying aperture  27  to and toward engine driving sprocket cavity  21 , keeper  20  serves to lubricate chain  30 .  
         [0027]    Additionally, it will be noted that pouch  29  protrudes above keeper  20 . In such protrusion, pouch  29  is in a position where it may be readily activated by the foot of rider R. Accordingly, lubrication can be placed upon chain  30  even while scooter  10  is being operated (or even raced).  
         [0028]    Finally, keeper  20  has handholds  23 , which enabled the keeper to be pivoted about engine driving sprocket cavity  21 . As will hereinafter become more apparent, when chain  30  undergoes wears and elongates, over center lock  40  is released (see FIG. 2). Thereafter, keeper  20  is grasped at one of the handholds  23  and pivoted upwardly about engine driven sprocket  31  to cause tongue  24  to exert pressure on chain  30 . This enables constant tension to be maintained on chain  30  even though the chain substantially and rapidly elongates during use.  
         [0029]    The action of keeper  20  in maintaining proper tension on chain  30  can be best understood with respect to the cartoon series of FIGS. 4 and 5.  
         [0030]    Referring first to FIG. 4, a No. 25 chain is shown disposed around wheel driving sprocket  32  and engine driven sprocket  31 . It will be seen that keeper  20  is parallel to chain along its major surface to and until chain  30  reaches engine driven sprocket cavity  21 . Upon reaching engine driven sprocket cavity  21 , chain  30  passes over chain depressing tongue  24  at chain contacting surface  25 .  
         [0031]    It will be understood that chain  30  is under tension between wheel driving chain sprocket  32  and engine driven chain sprocket  31 . At engine driven chain sprocket  31 , power from engine E will be transmitted from sprocket teeth on engine driven chain sprocket  31  to chain  30 . This power will supply the tension at chain  30 .  
         [0032]    At the same time, when chain  30  leaves engine driven sprocket  31  and returns to wheel driving sprocket  32 , tension on chain  30  will be practically nonexistent. Consequently, there is a need to apply tension to the chain  30 . This function is served by chain depressing tongue  24  at chain contacting surface  25 . It will be understood that without tension, chain  30  could well derail from wheel driving sprocket  32  as chain  30  is gathered to that sprocket.  
         [0033]    Referring to FIG. 5, chain  30  has been subject to elongation. Most probably, such elongation will occur from operation of the chain in a gritty environment. It will be seen that chain keeper  20  has been rotated about engine driven sprocket  31  in an upwards direction. This has caused chain-depressing tongue  24  to contact chain  30  at chain contacting surface  25 . In such contact, chain  30  has been disposed or wrapped around engine driven sprocket  31  along an extended periphery of the sprocket  31 .  
         [0034]    The individual functions of the chain  30  and chain keeper  20  will now be set forth.  
         [0035]    First, chain  30  is maintained under tension. As chain  30  is gathered from the wheel driving sprocket  32  to and towards engine driven sprocket  31 , this section of chain immediately underlying lubricating aperture  27  is linearly disposed because of the ambient tension upon the chain. At engine driven sprocket  31 , the power of the engine is transmitted to the links of the chain  30 . Typically, there is a total of eight or nine chain engaging lugs at engine driven sprocket  31 . As the total power of the engine is delivered to chain  30  by this relatively small engine driven sprocket  31 , a correspondingly small number of lugs on the sprocket transmits power to the links of the chain. By ensuring that the chain contacts a maximum number of lugs on the relatively small sprocket  31 , the danger of breaking the chain at any one of the links or damaging the sprocket at any one of the lugs is vastly reduced. As can be seen in the view of FIG. 5, as compared to the view of FIG. 4, adjustment of the chain keeper  20  causes chain  30  to wrap about engine driven sprocket  31  at greater angularity as chain  30  wears and elongates.  
         [0036]    Second, keeper  20  functions as a chain lubricator. It will be seen in the views of FIG. 4 and FIG. 5, chain  30  proceeds from under lubricant channel  27  to and toward engine driven sprocket cavity  21 . Any oil deposited on chain  30  will be impelled upon engine driven sprocket cavity  21  and chain-depressing tongue  24  at chain depressing tongue surface  25 . Consequently, lubrication will be ensured.  
         [0037]    Third, chain keeper  20  functions as a chain guard. Should chain  30  part, the presence of guard  20  will prevent the bitter end of the chain from whipping or otherwise injuring the driver.  
         [0038]    Forth, chain keeper  20  will wear at its points of contact with chain  30 . Typically, chain keeper  20  is made from a hard plastic, such as nylon or UHMW, to enable sliding of the chain with respect to chain keeper  20 . Such sliding will cause the hard plastic of the chain keeper  20  to be worn with a chain-guiding groove. Such a groove, especially at chain depressing tongue  24  in the vicinity of chain depressing tongue surface  25  will guide chain  30  to and toward wheel driving sprocket  32 , preventing derailment of chain  30  as it is fed towards wheel driving sprocket  32 . This groove, at depressing tongue  24 , is highly desirable; accordingly chain keeper  20  may be manufactured with the groove preformed in the chain keeper.  
         [0039]    Fifth, it will be understood that chain  30  and its respective sprockets  31 , and  32  are all essentially light and relatively inexpensive. They can be replaced at minimal cost at relatively frequent intervals. For example, where the scooter  10  is raced, engine driven sprocket  31  and chain  30  can be replaced at the beginning of each race.  
         [0040]    Typically, the No. 25 chain utilized with this invention has a maximum tensile force in the range of 900 pounds. Engine E is typically coupled to engine driven sprocket  31  by a conventional centrifugal clutch. As the speed of engine E increases, the conventional centrifugal clutch engages. At the same time, when driven wheel R momentarily leaves the ground and then suddenly re-engages with the ground, the conventional centrifugal clutch will slip and serve to absorb any shock, which might exceed the tensile limit of chain  30 .  
         [0041]    Some specifics about chain  30 , engine driven sprocket  31 , and wheel driving sprocket  32  can be instructive. The chain  30 , being a No. 25 chain, has approximately 94 separate links with approximately 188 apertures. Thus, there are 248 possible points in chain  30  where elongation of the chain can and does occur.  
         [0042]    Second, engine driven sprocket  31  has only six to nine lugs with about five of these respective lugs being in contact with the links of chain  30  at any given time. Total power transmission will occur between those lugs and chain links that are in contact with one another around engine driven sprocket  31 . Thus, to avoid total power transmission between less than five of these respective lugs and a less than five of these respective links, tongue  24  at chain contacting tongue surface  25  is needed.  
         [0043]    Third, wheel-driving sprocket  32  at the point where it gathers chain  30 , is an ideal place for chain derailment to occur. Thus the guiding function of any grooves formed within chain keeper  20  can be critical, especially as chain  30  elongates.