Abstract:
This invention discloses a lever operated vehicle propulsion system wherein the levers move substantially horizontally and couplers are adjusted along each lever to control the mechanical advantage available to the vehicle operator. Drive chains that are attached to each coupler and engage a pair of freewheel sprockets that, in turn, engage an axle or hub that is attached to a drive wheel. The free ends of the drive chains are connected together by a tensioning device to maintain tension in the drive chains. Also disclosed is a power transmission device that may be used to engage or disengage a drive wheel of a three or four wheeled vehicle from the drive axle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       SEQUENCE LISTING OR PROGRAM  
       [0003]    Not Applicable. 
       BACKGROUND  
       [0004]    This invention relates to human-powered vehicle propulsion systems, such as those used on bicycles and three and four wheeled human-powered vehicle designs. 
         [0005]    Most contemporary bicycle (and other pedal-driven vehicle) designs employ a drive sprocket that is coupled to a vehicle frame in such a way that the sprocket&#39;s axis is fixed relative to the frame. Two cranks are coupled to the sprocket; one on each side. The cranks extend radially in opposite directions away from the axis of the sprocket. A pedal is pivotally attached to the opposite end of each crank. The operator is located over the pedals and exerts alternating input forces downward against each pedal using the operators&#39; feet. When the sprocket is positioned so that a pedal is forward of the axis of the sprocket, then the component of the downward input force that is perpendicular to the crank acts to develop torque around the sprocket. This torque rotates the sprocket. Usable power is developed by the speed of rotation of the sprocket and this torque. Therefore, one of the efficiencies of the system may be judged by determining the percentage of the operator&#39;s input force that is used to develop this torque. 
         [0006]    The pedal moves in a circular pattern with respect to the vehicle frame. Only that component of the input force that is perpendicular to the crank acts to develop the torque that drives the wheel. Viewing the traditional bicycle from the operator&#39;s right side and starting with the right pedal at the top of its revolution, the input force is parallel to the crank. Though the operator is exerting force, there is no the torque developed. During typical operation, the momentum of the elements in the propulsion system will move the pedal through this position. As the pedal moves forward, the component of the input force that is perpendicular to the crank increases. It is not until the pedal and crank are about 40° from the starting position that more than a significant amount of the input force, about 75 percent, acts to develop torque. The pedal is forced downward through a point where the input force is perpendicular to the crank the maximum amount of input force acts to develop torque. As the pedal continues to rotate clockwise, the amount of the input force used to develop torque decreases. At about 140° from the starting position, this efficiency decreases below about 75 percent. When the pedal is at the bottom of its circular pattern, the input force is again parallel with the crank and no torque is created. Little, if any, force is applied on the return stroke to develop torque. Any force exerted upwardly by the operator is countered by the weights of the pedal assembly and the operator&#39;s body. 
         [0007]    Therefore, a significant amount of the input force exerted by the operator acts to develop useable torque for only about 100° of the 360° of a pedal&#39;s rotation. One series of attempts to develop a more efficient transfer of the force exerted by the operator has incorporated the use of levers. The levers typically isolate a portion of the power stroke wherein the input force is substantially perpendicular to the lever. Examples of lever-operated designs may be found in U.S. Pat. No. 6,554,309 to Thir, U.S. Pat. No. 7,011,376 to Sepulveda, U.S. Pat. No. 5,785,337 to Ming, and U.S. Pat. No. 4,574,649 to Seol. However, each of these references suffers from one or more of the following disadvantages: 
         [0008]    a. additional weight created by additional components, 
         [0009]    b. lack of adequate shifting mechanisms, 
         [0010]    c. failure to truly maximize the transmission of force, 
         [0011]    d. significant energy is lost to the extension of tensioner springs, 
         [0012]    e. lack of ability to maximize the force developed, and 
         [0013]    f. greater manufacturing and maintenance costs created by additional components. 
         [0014]    For the foregoing reasons, there is a need for a robust, efficient, lever-operated propulsion system that may be manufactured and maintained cost effectively. 
       SUMMARY  
       [0015]    I claim a vehicle propulsion system having two pedal arm assemblies, each connected pivotally to a vehicle frame so that the force generated by the operator is substantially perpendicular to each pedal arm assembly during the power stroke. Each pedal arm assembly includes a coupler. The position of each drive coupler may be adjusted along the pedal arm to change the mechanical advantage used by the vehicle operator. Each coupler is connected to a drive chain and each drive chain engages the teeth of each of two drive sprockets, respectively. A tensioner cable is connected to the free end of each drive chain and travels around an idler pulley to maintain tension in the drive chains. The system requires few sprockets and idler pulleys, thus decreasing the manufacturing and maintenance costs and increasing system reliability. The system may be used on bicycles or vehicles with more than two wheels. These vehicles may include a seat with a seat back that allows the operator to develop greater forces against the pedals than achievable with contemporary designs. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a bicycle with the propulsion system claimed. 
           [0017]      FIG. 2  is a detailed view of the elements of the claimed propulsion system. 
           [0018]      FIG. 3  shows a bicycle with the propulsion system claimed, including the drive chain housing. 
           [0019]      FIG. 4  shows a three wheeled vehicle with the propulsion system claimed. 
           [0020]      FIG. 5  shows a claimed power transmission system that may be used on vehicles with a drive axle to allow the vehicle to be moved backward without binding the drive chains of the propulsion system. 
       
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
       [0021]      1  First Pedal 
         [0022]      2  Second Pedal 
         [0023]      3  First Pedal Arm 
         [0024]      4  Second Pedal Arm 
         [0025]      5  Pivot 
         [0026]      6  Crank 
         [0027]      7  Second Drive Chain 
         [0028]      8  First Drive Chain 
         [0029]      9  Idler Pulley 
         [0030]      10  Second Drive Sprocket 
         [0031]      11  First Drive Sprocket 
         [0032]      12  Hub 
         [0033]      13  Second Drive Chain Connector 
         [0034]      14  First Drive Chain Connector 
         [0035]      15  Tensioner Cable 
         [0036]      16  Drive Wheel 
         [0037]      17  First Drive Coupler 
         [0038]      18  Second Drive Coupler 
         [0039]      19  Shifting Chain 
         [0040]      20  Seat 
         [0041]      21  Seat Back 
         [0042]      22  Vehicle Frame 
         [0043]      23  Drive Chain Housing 
         [0044]      101  Drive Axle 
         [0045]      102  Engaging Shaft 
         [0046]      103  Engaging Arm 
         [0047]      104  Engaging Arm Slot 
         [0048]      105  Engaging Plate Channel 
         [0049]      106  Engaging Plate 
         [0050]      107  Engaging Dowel 
         [0051]      108  Axle Flange 
         [0052]      109  Dowel Guide Sleeve 
         [0053]      110  Drive Wheel Hub Flange 
         [0054]      111  Engagement Holes in Drive Wheel Hub Flange 
         [0055]      112  Drive Wheel Hub 
       DETAILED DESCRIPTION  
       [0056]    This invention is intended to be used to propel human-powered vehicles, such as bicycles. The vehicle frame  22  is part of the vehicle and is not claimed. The vehicle may include two or more wheels. There are several conventional designs available to the public for three and four wheeled human-powered vehicles. As shown in  FIGS. 1 and 2 , the propulsion system includes a first pedal arm  3  on the left side of the vehicle frame  22  and a second pedal arm  4  on the opposite side of the vehicle frame  22 . At one end, the pedal arms  3 ,  4  are pivotally attached to the frame of the vehicle. This pivot  5  may be facilitated by any of several various available bearing and bushing designs. Pedals  1 ,  2  are attached to the other end of each pedal arm  3 ,  4 , providing the operator interface. Drive couplers  17 ,  18  are attached to each pedal arm  3 ,  4  in such a way that the position of each drive coupler  17 ,  18  may be adjusted along a substantial portion of the length of the respective pedal arm  3 ,  4 . Each drive coupler  17 ,  18  is attached to a first and a second drive chain  7 ,  8 , respectively. The first drive chain  8  engages the first drive sprocket  11 . The second drive chain  7  engages the second drive sprocket  10 . Each drive sprocket  10 ,  11  incorporates conventional freewheel hub technology and freely rotates in one direction without engaging the hub  12  or axle  101  and engages the hub  12  or axle  101  when rotated in the opposite direction. Drive chain connectors  13 ,  14  are used at the free ends of the drive chains  7 ,  8  to attach the drive chains to a tensioner cable  15 . As each pedal  1 ,  2  is depressed in turn, the tensioner cable  15  rides back and forth across an idler pulley  9  that is coupled to the vehicle frame. The idler pulley  9  is attached to the vehicle frame  22  and is free to rotate about its axis as the tensioner cable  15  moves. 
         [0057]    The pedal arms  3 ,  4  pivot around a common axis. The connection between the pedal arms  3 ,  4  and the vehicle frame  22  is facilitated by use of commercially available means such as roller or ball bearings or solid bushings (not shown). The bearings are held in a pivot housing  5  that is attached to the top rail of the vehicle frame by means such as weldment or clamp. The pivot housing  5  is positioned parallel to the axis of the drive wheel  16  or axle (not shown). The pivot housing  5  may be affixed to or incorporated into any point on the vehicle frame that allows the pedal arm to remain substantially perpendicular to the force developed by the operator. Therefore, the pivot may alternatively be located substantially below the pedals  1 ,  2 . This orientation may be preferable in a 3 or 4-wheeled vehicle due to the absence of a top rail in most contemporary vehicle designs. Any method of attachment that allows the pedal arms to pivot around an axis that is fixed with respect to the vehicle frame will meet the inventive concept. 
         [0058]    A shaft (not shown) is located along the pivotal axis in the pivot  5  and positioned coaxially with the bearings. A crank  6  is coupled to one end of the shaft allowing the operator to rotate the shaft to a desired position. Two small sprockets (not shown) are attached to the shaft, one over the center of each pedal arm  3 ,  4 . Another small sprocket (not shown), coplanar to the first, is located at the other end of each pedal arm  3 ,  4 . The pedal arms  3 ,  4  may be manufactured from a square tube, though many shapes could be used, of constant cross-sectional dimension over a significant portion of its length. The drive couplers  17 ,  18  are short sections of tubing that are only slightly larger than and whose internal cross-sections are similar in shape to the external cross-sections of the respective pedal arms  3 ,  4 . The drive couplers  17 ,  18  are located on the pedal arms  3 ,  4  and slide back and forth along the pedal arms  3 ,  4 . A small shifting chain  19  is wrapped around the two sprockets of each pedal arm  3 ,  4 . Each end of the shifting chain  19  is coupled to one side of the respective drive coupler  17 ,  18  so that the rotation of the crank  6  will slide the drive couplers  17 ,  18  along the pedal arms  3 ,  4  and fixing the position of the crank  6  will substantially fix the position of the drive couplers  17 ,  18  along the pedal arms  3 ,  4 . Incorporating slides of nylon or brass or other suitable material between the coupler and the pedal arm will facilitate the motion of the coupler. U.S. Pat. No. 6,554,309 to Thir discloses a shifting mechanism employing the same theory of operation. There are many shifting methods, however, that will meet the objects of the invention. For instance, threaded couplers could be coupled to threaded rods placed along the center of each pedal arm or couplers could be attached to control rod and cable assemblies. This invention is intended to incorporate any such method of positioning the drive couplers  17 ,  18  along the length of the pedal arms  3 ,  4 . It is advantageous, but not necessary that the shifting mechanism create the same change in position of both drive couplers  17 ,  18 . For instance, the rotation of the crank  6  moves both drive couplers  17 ,  18  the same distance along the pedal arms  3 ,  4 . Independent movement of the drive couplers does not make the system unusable and may be provide certain advantages. For instance, if one of the operator&#39;s legs is stronger than the other (which is typically the case) the couplers could be adjusted to accommodate. Removing the shifting method from the traditional sprocket cluster has an additional advantage of allowing the operator to change the “gearing” of the vehicle while the vehicle is stopped. On a traditional bicycle, the operator must often make rapid stops in traffic that do not allow sufficient time to change the gearing of the vehicle to a gear ratio appropriate for starting movement again. The operator must then start the movement of the vehicle with a higher than desired gear ratio. The present invention allows the operator to focus on operating the vehicle until the stop is made and then adjust the gear ratio after the vehicle has stopped. 
         [0059]    Each drive coupler  17 ,  18  includes a yoke that is designed to accept the ends of the drive chains  7 ,  8 . The last link of each drive chain  7 ,  8  is attached to the yoke of the respective drive coupler  17 ,  18 . The drive chains  7 ,  8  themselves are similar to those used on contemporary bicycle designs. 
         [0060]    Each drive chain  7 ,  8  engages one of two drive sprockets  10 ,  11 . The drive sprockets  10 ,  11  are located on each side of the hub  12  of the drive wheel  16 . Contemporary freewheel and cassette hubs have a freewheel mechanism incorporated into the hub. These hubs incorporate pawls that engage the hub when rotated in one direction and either brake or freewheel in the other direction. The present invention employs this readily available technology. When viewing the vehicle from the operators left side, both drive sprockets  10 ,  11  engage the hub  12  when the sprocket is rotated in a counterclockwise direction. This allows each drive sprocket  10 ,  11  to be engaged to the hub  12  when force is exerted on the respective pedal  4 ,  3 . 
         [0061]    The paragraph above describes the engagement of a drive wheel hub in a two wheeled design. This propulsion system is especially applicable to three and four-wheeled vehicle designs in which the seating positions are often more conventional than a bicycle and the operator is in a more horizontal position. The design requirement to allow the operator maximum control over his body&#39;s center of gravity is significantly reduced by the more stable platform. Also, in a seated position, the lever operation is more comfortable that the circular motion required by contemporary designs.  FIG. 4  shows a three wheeled design. The drive sprockets  10 ,  11  engage an axle  101  instead of engaging the hub  12  of the drive wheel  16 . 
         [0062]    Each drive chain  7 ,  8  travels around the respective drive sprocket and continues toward the front of the vehicle. Many types of connections may be used to attach the tensioner cable  15  to the ends of each drive chain  7 ,  8  at the drive chain connectors  13 ,  14 . The preferred embodiment employs a crimped fitting on each end of the tensioner cable  15  that mates with the last link in the end of each drive chain  7 ,  8 . The preferred tensioner cable  15  is constructed of continuous rubber strands with an outer Nylon sheath, like a bungee cord, though other substances may be used. 
         [0063]    In the preferred embodiment, two cylindrical plastic drive chain housings  23  are fixedly attached to the vehicle frame  22  and act as guides for the drive chains  7 ,  8  and tensioner cable  15 . The drive chain housings  23  enclose a portion of each drive chain  7 ,  8 , the drive chain connectors  13 ,  14 , and a portion of the tensioner cable  15  between the respective drive sprocket  10 ,  11  and the idler pulley  9 . The drive chain housings  23  allow for minimal tension to be placed on the tensioner cable  15  and prevent the drive chains  7 ,  8  from accidentally disengaging from the drive sprockets  10 ,  11 . These drive chain housings  23  may be composed of multiple pieces to allow for more efficient maintenance access and housing removal. 
         [0064]    In the preferred embodiment, the seat of the vehicle is fixed to the vehicle frame and positioned substantially rearward of the pedal arms  3 ,  4 . The seat  20  has a seat back  21 . The operator sits in the seat  20  and places one foot against each pedal  3 ,  4 . The operator presses against the seat back  21  to develop force against each pedal  3 ,  4  and alternately depresses each pedal  3 ,  4 . The depression of each pedal  3 ,  4  will cause the other pedal to return to its disengaged position. However, minimal energy is lost to deformation of the tensioner cable  15  because the tensioner cable  15  maintains a substantially constant length during normal operation. The elastic characteristic of the tensioner cable  15  prevents the tensioner cable  15  or the drive chains  7 ,  8  from accidentally becoming disengaged from the idle pulley  9  or drive sprockets  10 ,  11  and thus requiring the operator to stop the vehicle and correct the failure. 
         [0065]    While doing so increases the energy lost to deformation of the tensioner cable, this design exhibits the additional benefit of decoupling the dependency of the motion of each of the operator&#39;s legs. An operator may depress both pedals simultaneously or only use one leg to propel the vehicle. 
         [0066]    Mechanical advantage is adjusted by rotating the crank  6 . This moves the drive couplers  17 ,  18  along the respective pedal arms  3 ,  4 . Moving the drive couplers  17 ,  18  away from pivot  5  will decrease the mechanical advantage of the operator, but move the drive wheel  16  through a greater number or revolutions with each stroke of a pedal arm  3 ,  4 . This setting would be used at higher speeds. Conversely, moving the drive couplers  17 ,  18  closer to the pivot housing  5  will increase the mechanical advantage. This would be used when starting movement of the vehicle or climbing. 
         [0067]    One potential shortcoming of this propulsion system is that some existing freewheeling sprocket designs will not allow the sprocket to disengage from the hub when there is pressure on the sprocket and the vehicle is moved backward. In the present design, rolling the vehicle backwards may pull both drive chains until the pedal arms reached the limit of there travel. Two wheeled designs may easily be picked up or turned around in a small space. Three and four wheeled designs are typically heavier and more difficult to negotiate.  FIG. 5  shows a device that may be incorporated to address this concern on three and four wheeled vehicles with a drive axle  101 . Operating the device disengages the drive axle  101  from a drive wheel  16 . The vehicle may have two drive wheel  16   s,  one at each end of the drive axle  101 , whereby two identical devices would be required. Alternatively, the vehicle may have one drive wheel  16  on one end of the drive axle  101  and a freewheeling wheel on the other end. 
         [0068]    The engaging shaft  102  is pivotally attached to the vehicle frame  12 . The operator rotates the engaging shaft  102  to operate the device. Two engaging arms  103  are fixedly attached to the engaging shaft  102  so that they swing in an arc when the engaging shaft  102  is rotated. Each engaging arm  103  comprises an elongated engaging arm slot  104 . A boss on each of two engaging plate channels  105  rides within each elongated slot  104 , respectively. Thus, the engaging plate channels  105  are moved back and forth by the rotation of the engaging shaft  102 . The engaging plate channels  105  loosely capture the engaging plate  106 . The engaging plate  106  is a rotating disk positioned so that its rotational axis is collinear with the axis of the drive axle  101 . A number of engaging dowels  107  project from the outbound face of the engaging plate  106 . Fewer dowels may be used, but three is a good balance between manufacturing costs and strength. These dowels  107  ride inside of the corresponding dowel guide sleeves  109  on the axle flange  108 . The axle flange  108  is a disk that is welded or otherwise permanently attached to the drive axle  101 . Though shown is an exploded view, the dowels  107  are located within the dowel guide sleeves  109  even when the device is in the disengaged configuration. When engaged, the engaging plate  106  is forced toward the drive wheel  16  and the dowels  107  protrude from the outbound side of the axle flange  108  and into engagement holes  111  in the drive wheel hub flange  110 . This flange is part of or fixedly attached to the drive wheel hub  112 . Only a small space, preferably less than 0.25 inch, separates the drive wheel hub flange  110  from the axle flange  108 . The drive wheel hub  112  rides on bearings and is otherwise free to rotate about the drive axle  101 . The components are dimensioned such that, when disengaged, the ends of the dowels  107  clear the inbound face of the drive wheel hub flange  110  by less than 0.25 inch. The tolerances between the dowels  107  and the dowel guide sleeves  109  and the engaging holes  111  in the drive wheel hub flange  110  are sufficiently tight to minimize play between the motion of the drive axle  101  and that of the drive wheel  16 . Aluminum or steel are the preferred materials to be used in the construction of this device. Though other materials could be used, these materials may be dimensioned to withstand the stresses developed. A friction clutch would be an obvious variation on this design. 
         [0069]    Although the description above contains many specificities, these should not be construed as limiting the scope of the invention. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.