Abstract:
The present invention is a piston-actuated bicycle pedal assist system mounted to a bicycle for intermittent assistance with pedaling. This system includes a pedal rotatably attached to a pedal arm. The pedal arm fixedly attaches to a crankshaft such that rotation of the pedal arm and continuous movement of a piston head actuate the crankshaft. A propellant bottle provides propellant flow through propellant tubing. A propellant actuator controls propellant flow into at least one manifold connected to at least one propellant motor cylinder. This manifold includes a check valve that permits one-way propellant flow into the propellant motor cylinder. The check valve alternately opens by the piston head and seals automatically. The piston head includes a piston flap seal reversibly forming a seal that creates a pressure differential within a propellant motor cylinder chamber. This pressure differential controls downward movement of the piston head and an attached piston shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/907,089 filed on Nov. 21, 2013. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates to the field of self-propelled vehicles and more specifically to a system for intermittently assisting propulsion. 
       BACKGROUND 
       [0003]    Many individuals like to use bicycles with battery or electric power sources incorporated in order to reduce effort and fatigue while increasing potential speeds. However, these bicycles may break down if the battery dies, the system malfunctions or for other related reasons. Additionally, many people prefer the physical exertion associated with a traditional bicycle, but may sometimes wish for a degree of assistance when they become overly fatigued or reach an especially steep or rough area. 
         [0004]    Devices are known in the prior art that relate to power-assisted bicycles. Some devices provide a power-assisted bicycle with a regenerative brake system that uses an electric motor. Other devices provide a power-assisted bicycle that has a microprocessor for determining the amount of power output necessary to keep the user pedaling at a constant rate. These devices are primarily designed to automatically supplement the energy supplied by the rider, without requiring the rider to act. 
         [0005]    For example, a pedelec (from pedal electric cycle) is a bicycle where a small electric motor assists pedaling. Pedelecs include an electronic controller, which stops the motor producing power when the rider is not pedaling or when the rider reaches a certain speed—usually 25 km/h. Pedelecs are useful for people who have to ride in hilly areas or where there are often strong headwinds. Users can convert ordinary conventional bicycles to pedelecs with the addition of the necessary parts, i.e. motor, battery etc. 
         [0006]    Several problems are known in the art with respect to electric bicycles. These bicycles are costly to design and difficult to repair. Electric bicycles require mechanical configuration with either sensors or an electronic function that does not require precise speed control. Electric bicycles are bulky and can weigh in excess of forty pounds, making them difficult to carry or store. When the battery drains, then not only is pedaling assistance terminated, but the rider must pedal with significant extra weight on the bicycle. 
         [0007]    Accordingly, there have been attempts in the art to replace electric with pneumatic ones. For example, U.S. Pat. No. 4,568,097 teaches a centrifugal air pump in combination with a turbine to pedal a bicycle for a rider. This system does not allow for stored gas or intermittent activation of pedaling assistance. WIPO publication 2006/122333 teaches a bicycle powered by a pneumatic motor, but does not specify a structure for the motor. 
         [0008]    There are significant obstacles to creating a pneumatic motor for a bicycle. Pneumatic motors, in particular those on small vehicles such as bicycles, must be capable of providing sufficient propulsion with minimal use of propellant. One problem known in the art is that conventional pneumatic motors waste a significant portion of propellant due to inadequate metal-on-metal piston-chamber seals. Furthermore, because these seals have a high level of friction, motors lose part of the energy provided by propellant. Because small vehicles such as bicycles can only carry a limited amount of propellant, they must be more efficient in propellant use. 
         [0009]    It is desirable to develop a bicycle motor system that is simple and lightweight, but also highly efficient. 
         [0010]    It is further desirable to develop a bicycle motor system that can provide intermittent pedaling assistance to increase the length of time that it may be used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIGS. 1   a  and  1   b  illustrate a partial back view and a right side view, respectively of an exemplary pedal assist system. 
           [0012]      FIGS. 2   a  and  2   b  illustrate a magnified partial right side view of an exemplary pedal assist system at different points in a pedaling cycle. 
       
    
    
     TERMS OF ART 
       [0013]    As used herein, the term “reference axis” means an axis drawn along a frame bracket from the horizontal axis of a crankshaft to the top surface of a bicycle saddle. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention is a piston-actuated bicycle pedal assist system mounted to a bicycle for intermittent assistance with pedaling. This system includes at least one pedal rotatably attached to at least one pedal arm. The pedal arm fixedly attaches to at least one crankshaft such that rotation of the pedal arm and continuous movement of a piston head actuate the crankshaft. A propellant bottle provides propellant flow through propellant tubing. A propellant actuator controls propellant flow into at least one manifold connected to at least one propellant motor cylinder. This manifold includes a check valve that permits one-way movement of the propellant flow into the propellant motor cylinder. The check valve alternately opens by the piston head and seals automatically. The piston head includes a piston flap seal reversibly forming a seal. The seal creates a pressure differential within a chamber in the propellant motor cylinder. This pressure differential controls downward movement of the piston head and a piston shaft attached to the piston head. This system may use expansion of compressed gas or combustion to move the piston head and shaft. 
       DETAILED DESCRIPTION OF INVENTION 
       [0015]    For the purpose of promoting an understanding of the present invention, references are made in the text to exemplary embodiments of a pedal assist system, only some of which are described herein. It should be understood that no limitations on the scope of the invention are intended by describing these exemplary embodiments. One of ordinary skill in the art will readily appreciate that alternate but functionally equivalent components may be used. The inclusion of additional elements may be deemed readily apparent and obvious to one of ordinary skill in the art. Specific elements disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to employ the present invention. 
         [0016]    It should be understood that the drawings are not necessarily to scale. Instead, emphasis has been placed upon illustrating the principles of the invention. Like reference numerals in the various drawings refer to identical or nearly identical structural elements. 
         [0017]    Moreover, the terms “about,” “substantially” or “approximately” as used herein may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. 
         [0018]      FIGS. 1   a  and  1   b  illustrate a partial back view and a right side view, respectively of an exemplary pedal assist system  100 . For clarity,  FIG. 1   a  only shows the right side of pedal assist system  100 . Pedal assist system  100  includes a bicycle frame assembly  10 , a propellant assembly  30 , two manifolds  40   a  and  40   b , two propellant motor cylinders  50   a  and  50   b , and an optional regenerative braking system  60 . Elements of pedal assist system  100  are constructed from metals such as steel, titanium or aluminum, carbon fiber, polymers, composites, a combination of two or more materials or any other suitable material. 
         [0019]    Bicycle frame assembly  10  includes frame bracket  11 , a bracket shaft  12 , a plurality of rotational fittings  13 , two pedals  14   a  and  14   b , two pedal arms  15   a  and  15   b , two crankshafts  16   a  and  16   b , two pedal linkages  17   a  and  17   b , two cylinder shafts  18   a  and  18   b , a shaft linkage  19 , a chainring  20 , a chain  21 , a cassette  22  and a rear wheel  23 . 
         [0020]    Frame bracket  11  connects bicycle frame assembly  10  to a bicycle B. Frame bracket  11  has an upside-down U-shape and is located between bicycle B and crankshafts  16   a  and  16   b . To optimize hip and knee flexion, most bicycles include a horizontal offset between a location where a rider seats and the locations of crankshafts  16   a  and  16   b . Angling frame bracket  11  at a non-zero angle from vertical accommodates such a horizontal offset. This non-zero angle may range from approximately 1 degree to approximately 25 degrees. 
         [0021]    At a first end, frame bracket  11  also supports a bracket shaft  12 , which connects to manifolds  40  of propellant motor cylinders  50  via rotational fittings  13 . Each rotation fitting  13  rotatably connects bracket shaft  12  at one end and fixedly connects to a manifolds  40  at a second end. Rotation fittings  13  allow manifolds  40  and the connected propellant motor cylinders  50  to pivot about bracket shaft  12 . Rotation fittings  13  may be, but are not limited to, rod end bearings, swivel bearings or a clevis fastener. 
         [0022]    Two pedals  14   a  and  14   b  provide means for motive force input from a rider. Pedals  14   a  and  14   b  may be any type of bicycle pedal known in the art. Pedals  14   a  and  14   b  rotatably connect to two pedal arms  15   a  and  15   b , respectively. In turn, pedal arms  15   a  and  15   b  fixedly connect to the outer ends of two crankshafts  16   a  and  16   b , respectively. Crankshafts  16   a  and  16   b  pass through a second end of frame bracket  11 , to which crankshafts  16   a  and  16   b  rotatably connect. In order to accommodate most riders comfortably, the smallest dimension between pedal arms  15   a  and  15   b  can measure no more than 4.8 inches. 
         [0023]    The inner ends of crankshafts  16   a  and  16   b  fixedly connect to center points of two pedal linkages  17   a  and  17   b , respectively. Each of pedal linkages  17   a  and  17   b  rotatably connects to an outer end of cylinder shafts  18   a  and  18   b , respectively. Each of cylinder shafts  18   a  and  18   b  connects to one of propellant motor cylinders  50  via rotational fittings  13 . Each rotation fitting  13  rotatably connects one of cylinder shafts  18   a  and  18   b  at one end and fixedly connects to one of propellant motor cylinders  50  at a second end. Rotation fittings  13  allow propellant motor cylinders  50  to pivot about cylinder shafts  18   a  and  18   b . Shaft linkage  19  fixedly connects the inner ends of cylinder shafts  18   a  and  18   b.    
         [0024]    As is common in the art, one of crankshafts  16   a  and  16   b  fixedly connects to a chainring  20 . In use without activation of pedal assist system  100 , a bicycle rider alternately presses down on each pedal  14   a  or  14   b , thereby applying a rotational force to chainring  20 . Rotation of chainring  20  moves chain  21  forward, causing cassette  22  to rotate. Because cassette  22  fixes to rear wheel  23 , rotation of cassette  22  likewise causes rear wheel  23  to rotate, thereby propelling bicycle B. 
         [0025]    Propellant assembly  30  includes a propellant bottle  31 , a release valve  32 , propellant tubing  33  and a propellant actuator  34 . Elements of propellant assembly  30  are constructed from steel, aluminum, carbon fiber, polymers, composites or any other suitable material. 
         [0026]    Propellant bottle  31  includes a release valve  32  and holds a volume of propellant under pressure. This propellant serves as a power source. Propellant bottle  31  may hold propellants such as, but not limited to, air, carbon dioxide, nitrogen, methane or any liquefied petroleum propellant. When pedal assist system  100  utilizes combustible propellants, combustion is an option. Propellant bottle  31  may be similar or identical to compressed gas cylinders used for paintball or other recreational sports. Propellant bottle  31  may be refillable or single-use. 
         [0027]    Release valve  32  connects to propellant tubing  33 . Release valve  32  regulates propellant flow and steps down propellant pressure, reducing propellant pressure to a level that will not damage pedal assist system  100 . Actuating release valve  32  allows propellant to travel from propellant bottle  31  along propellant tubing  33  until the propellant reaches propellant actuator  34 . Because propellant bottle  31  typically mounts to a lower portion of bicycle B, a rider would find difficulty triggering release valve  32  while riding. When not actuated, propellant actuator  34  interrupts the flow of propellant from propellant bottle  31  to manifolds  40 . Because propellant actuator  34  typically mounts to an upper portion of bicycle B, such as the handlebars, a user may more easily actuate propellant actuator  34  to permit flow of propellant from propellant bottle  31  to manifolds  40   a  and  40   b.    
         [0028]    Each manifold  40   a  or  40   b  includes a propellant inlet  41 , a manifold passage  42 , a propellant outlet  43 , a fitting connection  44  and a check valve  45 . Each manifold  40   a  or  40   b  mounts to and seals a first end of one of propellant motor cylinders  50   a  or  50   b , respectively. Portions of manifolds  40   a  and  40   b  are constructed from steel, aluminum, carbon fiber, polymers, composites or any other suitable material. Portions of manifolds  40   a  and  40   b  may be integrally constructed or assembled from multiple discrete components. Manifolds  40   a  and  40   b  must be capable of receiving propellant while rotating. 
         [0029]    Propellant inlet  41  connects to propellant tubing  33 , enabling delivery of propellant through manifold passage  42 , out propellant outlet  43  and into one of propellant motor cylinders  50   a  or  50   b . Fitting connection  44  provides a connection between manifolds  40   a  and  40   b  and a second end of one of rotational fittings  13 . In the exemplary embodiment, this connection is a threaded connection. In other embodiments, the connection may be a welded, soldered, adhesive, snap-fit, press-fit, interlocking or integral connection. 
         [0030]    Check valve  45  resides within manifold passage  42 . When actuated, check valve  45  allows passage of propellant from manifold passage  42 , out propellant outlet  43  and into one of propellant motor cylinders  50   a  or  50   b . In the exemplary embodiment, check valve  45  is a ball-and-spring valve. In this embodiment, the spring has a spring constant between approximately 23 g/mm to approximately 133 g/mm. In this embodiment, the spring is a helical spring, sized so that the ratio between spring and ball diameter ranges from approximately 0.40 to approximately 0.85. In other embodiments, check valve  45  may be a diaphragm, a swing check valve or a rocker valve similar to an overhead valve used in an internal combustion engine. 
         [0031]    Each of propellant motor cylinders  50   a  and  50   b  includes a chamber  51 , a piston head  52 , a piston spring  53 , a piston flap seal  54 , at least one optional vent opening  55 , a piston shaft  56  and an exhaust port  57 . Propellant motor cylinders  50   a  and  50   b  are single-acting cylinders when pedal assist system  100  is a pneumatic-based system. When pedal assist system  100  is a combustion-based system, then propellant motor cylinders  50   a  and  50   b  may be double-acting cylinders. Manifold  40   a  or  40   b  fixedly seals chamber  51  at a first end. Piston head  52  and piston flap seal  54  seal chamber  51  at a variable second end. The inner walls of chamber  51  have a low surface texture to reduce friction caused by the movement of piston flap seal  54  along chamber  51 . 
         [0032]    The size of piston head  52  at least partially closes chamber  51 . The ratio between the diameters of piston head  42  and chamber  51  ranges from approximately 0.94469 to approximately 0.99911. Piston spring  53  and piston flap seal  54  attach to a first side of piston head  52 . The size of piston spring  53  actuates check valve  45  at a certain point in an up stroke of piston head  52 , thereby allowing a bolus of pressurized propellant to enter chamber  51 . 
         [0033]    This bolus causes piston flap seal  54  to expand on a down stroke of piston head  52 . In embodiments that do not include a vent opening  55 , piston flap seal  54  creates a seal between the inner wall of chamber  51  and the outer periphery of piston head  52 . In embodiments that do include at least one vent opening  55 , piston flap seal  54  creates a seal chamber  51  and piston head  52 , as well as a seal over vent opening  55 . 
         [0034]    In an unexpanded shape, piston flap seal  54  resembles a cup having a rim thickness that is thinner than a center point thickness, when measured in cross section. The cup shape forms an angle of between approximately 20 degrees and 40 degrees when measured in cross-section from one side to another. The ratio of overall thickness of piston flap seal  54  to center point thickness ranges from approximately 1.5 to approximately 3.7. 
         [0035]    The thinner rim allows piston flap seal  54  to flatten and expand when actuated by propellant pressure. The propellant pressure used to actuate piston flap seal  54  ranges from approximately 30 psi to approximately 120 psi. Piston flap seal  54  is constructed from a non-metallic polymer such as silicone. Any material used to construct piston flap seal  54  must be sufficiently stiff to spring back to its unexpanded state after pressure relief, while also pliable enough to conform to and seal chamber  51  and piston head  52 . These materials typically have a Shore A durometer between approximately 20 and approximately 65. 
         [0036]    A first end of piston shaft  56  rotatably attaches to a second side of piston head  52 . A second end of piston shaft  56  rotatably attaches to a rotational fitting  13 , itself attached to a one of cylinder shafts  18   a  or  18   b . Exhaust port  57  lies towards a bottom end of chamber  51 . At the end of the down stroke, piston head  52  clears exhaust port  57  and allows exhaustion of propellants. 
         [0037]    In certain embodiments, a user may remove and replace manifolds  40   a  and  40   b , and propellant motor cylinders  50   a  and  50   b . This allows a user to replace broken or worn-out parts, or exchange parts adapted for a particular use or tolerance with others adapted to different conditions. A user may remove bracket shaft  12  from frame bracket  11  to free manifolds  40   a  and  40   b , and remove piston shaft  56  from linkage with respective crankshaft  16   a  or  16   b  to free propellant motor cylinders  50   a  and  50   b . In additional embodiments using a threaded fitting connection  44 , a user can free one of manifolds  40   a  or  40   b  from its rotational fitting  13  by rotating manifold  40   a  or  40   b , and its respective propellant motor cylinder  50   a  or  50   b    
         [0038]    Certain embodiments also include an optional regenerative braking system  60 . This allows pedal assist system  100  to harvest previously wasted energy from bicycle B brakes. 
         [0039]      FIGS. 2   a  and  2   b  illustrate magnified partial right side views of an exemplary pedal assist system at different points in an exemplary pedaling cycle. In the exemplary pedaling cycle, when piston head  52  comes up to the top of the up stroke, piston spring  53  actuates check valve  45 , thereby opening manifold passage  42 . The opening of manifold passage  42  forces high pressure propellants into chamber  51 , where the propellant pressure expands piston flap seal  54  to seal any vent openings  55  in piston head  52 . Once the pressure within chamber  51  equalizes, check valve  45  remains open until the propellant pressure on piston head  52  forces piston head  52  down, removing piston spring  52  from check valve  45  and closing check valve  45 . When piston head  52  reaches the bottom of the down stroke, the reduced propellant pressure allows piston flap seal  54  to retract to reduce friction on the next up stroke. Retraction of piston flap seal  54  also allows propellant to escape from propellant vent openings  55  when piston head  52  begins the next up stroke. 
         [0040]    One of the key concepts of pedal assist system  100  is the angle of applied power when in use. When the rider is not applying a significant amount of torque, i.e. when each pedal arm  15   a  and  15   b  approaches an angle of approximately 70 degrees to approximately 110 degrees with respect to the reference axis, each respective propellant motor cylinder  50   a  and  50   b  is at the top of the up stroke, and capable of supplying maximum torque. Likewise, when propellant motor cylinders  50   a  and  50   b  are not applying a high amount of torque, the rider is in a position to supply torque. This ensures that torque remains high throughout the pedaling cycle. 
         [0041]    Specifically, the particular angle of applied power results from angularly offsetting cylinder shafts  18   a  and  18   b  from pedal arms  15   a  and  15   b , respectively, with regard to a central point found at crankshafts  16   a  and  16   b , again respectively. As pedal arms  15   a  and  15   b  rotate about the horizontal axes of crankshafts  16   a  and  16   b , respectively, the horizontal axes of cylinder shafts  18   a  and  18   b , also rotate about the horizontal axes of crankshafts  16   a  and  16   b , respectively. However, because pedal arms  15   a  and  15   b  have an angular offset of approximately 90 degrees from cylinder shafts  18   a  and  18   b , respectively, pedal assist system  100  applies torque at a point in the pedaling cycle when the rider is not applying a significant amount of torque.