Abstract:
The present application is directed to a drive system. The drive system comprises a drive shaft and a driven wheel assembly. The wheel assembly includes a split axle coupled perpendicular to the drive shaft. An overrunning clutch is coupled between each section of the split axle and the drive shaft. A wheel is coupled to spin with each axle section. The wheels receive power from the drive shaft and are driven so that when power is applied from the drive shaft to the driven wheel assembly, whichever wheel that is spinning the slowest receives the power. The drive system may be incorporated into any number of vehicles to improve traction around turns, improve wheel slippage on uneven terrain and generates new options for how and where vehicles may be ridden.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Patent Application No. 61/520,783, filed Jun. 15, 2011 entitled “Drive System for Vehicles”, which is incorporated herein by reference. 
    
    
     FIELD 
     This patent application generally relates to a drive system for vehicles. More specifically it relates to a drive system including a split axle, each section of the split axle coupled to a single drive shaft by overrunning clutches. 
     BACKGROUND 
     Two, three and four wheeled vehicles have been around for hundreds of years. Various types of drive systems have been developed to help facilitate their movement. Traditional bicycles have a back, powered wheel on a single axle and a front non-powered wheel on a single axle. If the back wheel loses traction, the bicycle may slow down and even stop. Adding a second wheel to an axle can increase both traction and stability for a vehicle. However, when going around turns the inner and outer wheels follow paths of different lengths and need to spin at different rates. The wheel on the outer part of the turn travels further and therefore needs to spin faster to keep up with the wheel on the inner part of the turn. This difference in spin rates can create traction problems for the vehicle when going around turns. The current patent application provides a new type of drive system for vehicles that improves traction around turns, improves wheel slippage on uneven terrain and generates new options for how and where vehicles can be ridden. 
     SUMMARY 
     One aspect of the present patent application is directed to a drive system. The drive system comprises a drive shaft and a driven wheel assembly. The driven wheel assembly includes a split axle coupled perpendicular to the drive shaft. The split axle has two axle sections. An overrunning clutch is coupled between each axle section and the drive shaft. A wheel is coupled to spin with each axle section. The wheels receive power from the drive shaft and are driven so that when power is applied from the drive shaft to the driven wheel assembly, whichever wheel that is spinning the slowest receives the power. 
     Another aspect of the present application is directed to vehicle. The vehicle comprises a frame assembly with a steering assembly. The frame assembly defines a front end, rear end and lean plane for the vehicle. The vehicle further comprises a front wheel assembly coupled to the front end and a drive shaft assembly mounted to the frame assembly. The drive shaft assembly has a drive shaft lying along the lean plane. A rear driven wheel assembly is coupled to the rear end. The rear driven wheel assembly has a rear split axle including two rear axle sections that are coupled perpendicular to the drive shaft, an overrunning clutch coupled between each rear axle section and the drive shaft, a rear wheel coupled to spin with each rear axle section, the rear wheels receiving power from the drive shaft assembly through the drive shaft. When power is applied from the drive shaft to the rear driven wheel assembly, whichever rear wheel is spinning the slowest receives the power. 
     Still another aspect of the present application is directed to a kit for converting a bike with front and rear wheel dropouts into a four-wheel vehicle. The kit comprises a front wheel assembly including a front wheel dropout connector. The kit further comprises a rear driven wheel assembly. The rear driven wheel assembly includes i) a rear wheel dropout connector, ii) a drive shaft assembly mounted to the dropout connector and operable to receive power from the bike, and iii) the rear driven wheel assembly has a rear split axle including two rear axle sections that are coupled perpendicular to the drive shaft, an overrunning clutch coupled between each rear axle section and the drive shaft, a rear wheel coupled to spin with each rear axle section, the rear wheels operable to receive power from the drive shaft assembly through the drive shaft. When power is applied from the drive shaft to the rear driven wheel assembly, whichever rear wheel that is spinning the slowest receives the power. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The foregoing and other aspects and advantages presented in this patent application will be apparent from the following detailed description, as illustrated in the accompanying drawings, in which: 
         FIG. 1  is a perspective view of one embodiment of a vehicle incorporating the drive system according to the present patent application; 
         FIG. 2  is a perspective view of the drive shaft assembly integrated with the rear driven wheel assembly for the vehicle illustrated in  FIG. 1 ; 
         FIG. 3  is a partial cut away, perspective view of the drive shaft assembly integrated with the rear driven wheel assembly for the vehicle illustrated in  FIG. 1 ; 
         FIG. 4  is a partial cut away, topside view of the drive shaft assembly integrated with the rear driven wheel assembly for the vehicle illustrated in  FIG. 1 ; 
         FIG. 5  is an exploded view of the drive shaft assembly integrated with the rear driven wheel assembly for the vehicle illustrated in  FIG. 1 ; 
         FIG. 6  is a sectional, schematic view of an overrunning clutch along lines  6 - 6  in  FIG. 5 , but in the unexploded configuration; 
         FIG. 7  is a perspective view of the drive shaft assembly integrated with the rear driven wheel assembly for the vehicle illustrated in  FIG. 1  when the rear driven wheel assembly moves over uneven terrain; 
         FIG. 8 a    is a rear view of the drive shaft assembly integrated with the rear driven wheel assembly for the vehicle illustrated in  FIG. 1  when the rear driven wheel assembly moves over flat terrain; 
         FIG. 8 b    is a rear view of the drive shaft assembly integrated with the rear driven wheel assembly for the vehicle illustrated in  FIG. 1  when the rear driven wheel assembly moves over uneven terrain; 
         FIG. 8 c    is a rear view of the drive shaft assembly integrated with the rear driven wheel assembly for the vehicle illustrated in  FIG. 1  when the rear driven wheel assembly moves over uneven terrain; 
     
    
    
     DETAILED DESCRIPTION 
     Drive system  18  is shown in  FIGS. 1-8   c . For illustrative purposes drive system  18  is shown integrated to form one possible variation of a vehicle  20  where the vehicle has four wheels and other specific elements. However, it is understood that drive system  18  could be integrated to drive a wide variety of other vehicles that incorporate alternative elements. The variations of elements that may be associated with vehicle  20  will be presented throughout this patent application. 
     One embodiment of vehicle  20 , as shown in  FIG. 1 , comprises a frame assembly  22  and a steering assembly  24 . Frame assembly  22  defines a front end, a rear end and lean plane  25  for vehicle  20 . Vehicle  20  additionally comprises a front wheel assembly  26  coupled to the front end of frame assembly  22 . Vehicle  20  also comprises drive system  18  mounted to frame assembly  22 . Drive system  18  comprises drive shaft assembly  28 , driven wheel assembly  30  and power assembly  32 . For the particular embodiment of vehicle  20  shown in  FIG. 1 , driven wheel assembly  30  is a rear driven wheel assembly and coupled to the back end of vehicle  20 . In other embodiments, the driven wheel assembly  30  may be located at other positions along frame assembly  22 . Wheels  68   a  and  68   b  are engaged to receive power from drive shaft assembly  28 . Power is generated by power assembly  32  and this input power transferred to drive shaft assembly  28 . Seat  31  may or may not be included as a component of vehicle  20  depending on how the vehicle is intended to be used. 
     Drive shaft assembly  28  and driven wheel assembly  30  are integrally connected as shown in  FIGS. 1-4 . The individual components of which are shown in  FIG. 5 . Drive shaft assembly  28  includes a drive shaft  34  lying along lean plane  25  of frame assembly  22 . Drive shaft  34  lies alone drive axis (axis B). Drive shaft  34  resides at least partially within drive case  36 . Drive case  36  may be constructed from several drive case plates or other alternative support structures. Drive shaft  34  is supported by two bearings  38   c  and  38   d . Drive case  36  is anchored to frame assembly  22  by drive case mounting plate  40  that has two extensions from the drive case and interlocks with rear wheel dropouts  42  of the frame assembly. Although mounting plate  40  is a convenient way to mount drive case  36  to a standard bike frame, a wide range of other structures exist to mount the drive case to frame assembly  22 . For example, drive case  36  could be constructed as an integral part of frame assembly  22  instead of an attachment. 
     A variety of power assemblies  32  can be used to rotate drive shaft  34 . For example, a conventional pedal and chain power assembly  32  may be used as shown in  FIG. 1 . Similarly, drive shaft  34  may be directly rotated by a motor. Further, pedals or a motor may be combined with a belt to form a power assembly. Still further, drive shaft assembly  28  may be directly driven by power assembly  32 , the power assembly including only peddles, a power shaft and with or without gears or sprockets. It is therefore possible to have a variety of power transmission components coupled to transfer input power from a variety of power assemblies  32  to drive shaft  34 . 
     In the case of the conventional pedal and chain power assembly  32 , a power input shaft  44  is further coupled at a right angle to drive shaft  34  by a set of bevel gears  46   a  and  46   b ,  FIG. 4 . Input shaft  44  is journaled through the wall of drive case  36  and supported by two bearings  38   a  and  38   b . The end of input shaft  44  that extends outside drive case  36  is coupled to a driven sprocket  48  having teeth that engage a drive chain  50 . Drive chain  50  wraps around pedal sprocket  52 , which also has teeth that engage the chain. Drive chain  50  provides a continuous loop around pedal sprocket  52  and driven sprocket  48 . Pedal sprocket  52  is mounted to a pedal shaft  53  journaled through frame assembly  22 . Pedals  54  extend from the pedal shaft. Operation of the pedal and chain power assembly  32  is such that when a force is applied to pedals  54 , the force will cause drive chain  50  to rotate input shaft  44  around axis A, which then rotates drive shaft  34 . In one embodiment,  FIGS. 4 and 5 , a power input overrunning clutch  56  is provided between driven sprocket  48  and input shaft  44  to allow for power to be applied in one direction to the input shaft. The power input overrunning clutch  56  is not necessary in other embodiments. Power input overrunning clutch  56  includes an inner race, an outer race and roller elements. Driven sprocket  48  is mounted to outer race and inner race is mounted to input shaft  44 . 
     Coupling of drive shaft assembly  28  to driven wheel assembly  30  occurs along drive shaft  34 . Drive case  36  has a U-shaped element  62  having u-ends  63  that extends from the rear end of the drive case. U-shaped element  62  provides support to that portion of drive shaft  34  that resides outside the drive case and passes through wheel case  64 . Drive shaft  34  is supported by a bearing  38   e  where the drive shaft exits the rear of drive case  36 . U-shaped element  62  also provides support to the rear end of wheel case  64  by support shaft  66  and bearing  38   f.    
     Wheel case  64  pivots around drive shaft  34  and support shaft  66  along axis B, within U-shaped element  62 . Support shaft  66  is located inline and concentric to drive shaft  34 . Wheel case  64  contains those elements that control how power is distributed to each of the wheels  68   a  and  68   b . For the particular embodiment of the vehicle in  FIG. 1 , the wheels  68   a  and  68   b  are rear wheels, but it is understood that the rear wheels could be driven wheels associated with different vehicles and not necessarily in the rear position relative to those specific different vehicle configurations. Wheel case  64  is constructed from several wheel case plates or other structure sufficient to support the associated components such as a casting or a welded frame structure. The rear end of drive shaft  34  is supported by bearing  38   e  where the drive shaft enters the front end of wheel case  64 . Drive shaft  34  is terminated with a bevel gear  46   c . Bevel gear  46   c  engages at a right angle another bevel gear  46   d . Bevel gear  46   d  is integrated with the two sections of a split axle  70 . Bevel gear  46   d  is positioned such that the bevel gear can engage the two sections of the split axle  70 . Axle sections  70   a  and  70   b  are coupled to bevel gear  46   d  by two overrunning clutches  72   a  and  72   b.    
     Overrunning clutch  72   a  and  72   b , schematically illustrated in  FIG. 6 , may be any one from the group including a roller clutch, a sprag clutch, a freewheel clutch or ratchet mechanism. Overrunning clutch  72   a  is made up of an inner race  74   a  and an outer race  76   a . Overrunning clutch  72   b  is made up of an inner race  74   b  and an outer race  76   b . Roller elements  75  are contained between inner race  74   a  and outer race  76   a  and also between inner race  74   b  and outer race  76   b . Roller elements  75  may be cylinders, cylinders with bias elements, pawls, etc. Cylinders may have a circular or elliptical cross-section. Roller elements  75  engage their respective inner race in the drive direction to impart power to the inner race, but the roller elements disengage to allow the inner race to turn freely when it is turning faster than the outer races. Axle section  70   a  is mounted to inner race  74   a . Axle section  70   b  is mounted to inner race  74   b . Axle section  70   a  is supported by two bearings  38   g  and  38   h  as it passes through a first side of wheel case  64 . Axle sections  70   a  and  70   b  divide the applied force between wheels  68   a  and  68   b . Overrunning clutches  72   a  and  72   b  determine which wheel  68   a  or  68   b  the force is applied to. Wheel  68   a  is concentrically mounted to axle section  70   a . Axle section  70   b  is also supported by two bearings,  38   i  and  38   j , as the axle section passes through the opposite side of case  64 . Wheel  68   b  is concentrically mounted to rear axle section 70   b . Wheels  68   a  and  68   b  rotate around axis C. 
     Over running clutches  72   a  and  72   b  are structured so that the outer race has a direction of engagement  77  with inner race,  FIG. 6 . The two overrunning clutches are mounted to spin along an axis with their direction of engagement in the same direction around that axis. However, because the overrunning clutches are mounted to two separate sections of a split axle  70 , each associated wheel may spin independently of the other wheel. For each wheel if the outer race turns in the direction of engagement, the inner race turns with the outer race as long as the inner race is not already turning faster than the outer race. If the inner race is turning faster than the outer race, then the inner race continues to turn freely. If the outer race turns opposite the direction of engagement, the inner race turns freely and independent of the rotation of the outer race. The inner race may also turn freely in the driven direction if the outer race is not turning at all. This feature of the overrunning clutches working together with the drive shaft and the rear wheels is key to the improved operation of vehicle  20 . The two overrunning clutches  72   a  and  72   b  allow for the varying speed of the two wheels  68   a  and  68   b  when making turns with vehicle  20 . This allows the outside wheel (wheel following longer arc of a turn) to freely rotate at a faster rate than the inside wheel (wheel following shorter arc of a turn) when vehicle  20  is moving through a turn, while still maintaining a driving force on the inside wheel. This same concept also applies for the varying speed of the two wheels  68   a  and  68   b  when one is going over uneven terrain. For example, if one of the wheels needs to go up and over something, that wheel will have a longer travel path. Overrunning clutches  72   a  and  72   b  allow the wheel taking the longer path to freely rotate at a faster rate than the wheel taking the shorter path, but still maintain a driving force on the wheel taking the shorter path. Furthermore, on terrain with differing levels of traction (e.g., ice or mud), power is delivered to the wheel with the most traction. This is because a wheel with no friction will spin freely as the overrunning clutch is disengaged and the wheel with friction will have that overrunning clutch engage. Since there are two wheels in the rear wheel assembly, the traction capability is double that of a two-wheeled bike where only a single back-powered wheel exists and if that single powered wheel slips there is no traction. 
     For the particular embodiment of vehicle  20  shown in  FIG. 1 , by having drive shaft  34  supported on bearings ( 38   c ,  38   d ,  38   e ,  38   f ), frame assembly  22  with associated lean plane  25  is free to rotate in either direction relative to the ground around lean axis (axis B) and have axle sections  70   a  and  70   b  still apply a rotational force to drive either or both of wheels  68   a  and  68   b . Lean axis and drive axis are co-linear, they both coincide with axis B. This allows the rider to shift their body weight along with the lean plane to compensate for centripetal forces when going around turns. Also, by having the wheels tilt independently of the lean plane, more direct contact of the wheels occurs with any uneven terrain allowing more traction, a smoother ride and a more controlled ride. This feature is demonstrated in  FIGS. 7-8   c  that show wheels  68   a  and  68   b  riding over uneven terrain while keeping lean plane  25  and the rider in an optimum position for riding. However, it is also possible to have drive system  18  incorporated with a vehicle so that there is no lean plane and just provide the benefits of the wheels rotating at different speeds for improved handling around turns. 
     For the embodiment shown in  FIG. 1 , steering assembly  24  may include the steering elements of a conventional bike, namely a steering shaft  80  journaled within a steering column  82  at the front end of frame assembly  22 . The lower end of steering shaft  80  may split into a fork structure  86  where each fork has a brake tab  88  and ends in a front wheel dropout  90 . Handlebars  92  extend from the upper end of steering shaft  80 . In other embodiments of vehicle  20 , a steering wheel may replace the handle bars of steering assembly  24 . Also, steering assembly  24  does not have to be split, but may take the form of a single shaft. Furthermore, steering assembly  24  may incorporate a tie rod steering linkage assembly. 
     Front wheel assembly  26  may include two front wheels  94 . Each front wheel  94  may be coupled to spin on a single front axle or coupled to spin on one of two front axle sections. Front axle  96  lies along a front spin axis  98 . In the embodiment shown in  FIG. 1 , front wheel assembly further includes a front wheel mount  100  that extends upward from front axle  96  to engage front wheel dropouts  90  and brake tabs  88 . Front axle  96  is mounted to the lower end of front wheel mount  100 . Front wheel mount  100  has two locking plates  102  that extend from the upper end. Each locking plate  102  has brake tab holes  104  for mounting to brake tabs  88  and a wheel dropout hole for mounting to wheel dropouts  90 . Front wheel mount  100  can be rotated through a range of angles around an axis extending through wheel dropouts  90  and locked in place. The locking mechanism may include bolts, a quick release mechanism or any number of alternative fastening structures. Alternatively, vehicle  20  may deviate from the structure of  FIG. 1  and have only one front wheel or no front wheel assembly at all and be ridden similar to a unicycle. 
     In other embodiments of vehicle  20 , front wheel assembly  26  and rear wheel assembly  30  can be fitted with an independent suspension system or truck assemblies to further improve handling and comfort of the vehicle across uneven terrain. In other embodiments, vehicle  20  may have independent steering of each of the front wheels. In other embodiments, multiple gears  110  and a gear shifter  112  may be incorporated with the drive and power assemblies. In yet another embodiment of vehicle  20 , front wheel assembly  26  may be replaced with a powered drive system similar to drive system  18  having a split driven wheel assembly including the overrunning clutches and connected to a drive shaft. In this embodiment, vehicle  20  would have four independently powered wheels. In still another embodiment the front wheel assembly, rear driven wheel assembly and drive shaft assembly may be supplied as an attachment for a standard bike. The front wheel assembly would mount to the front wheel dropouts, and the drive shaft assembly coupled with the rear driven wheel assembly would mount to the back wheel dropouts and pedal power assembly of the standard bike. And in still yet another embodiment, frame assembly  22  can be custom designed to take advantage of potential aesthetic, ergonomic and functional advantages of the drive system. 
     While several embodiments of the invention, together with modifications thereof, have been described in detail herein and illustrated in the accompanying drawings, it will be evident that various further modifications are possible without departing from the scope of the invention. Nothing in the above specification is intended to limit the invention more narrowly than the appended claims. The examples given are intended only to be illustrative rather than exclusive.