Abstract:
A self-compensating tire compression device is provided for use with a trainer. The device attaches to a frame, such as a bicycle, that holds the axis of a driving wheel fixed. The device has a pivoting portion that presses a driven portion of a resistance device against the driving wheel. The pivoting point of the pivoting portion is located on the trainer to provide a static contact pressure between the driving wheel and the driven wheel, and when the driving wheel begins to rotate and the resistance device begins to resist the rotation, the contact pressure between the driving wheel and the driven wheel increases to prevent slippage between the two wheels.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    FOR NON-PROVISIONAL OF PROVISIONAL—This application claims the benefit of U.S. Provisional Application No. 62/040,682, filed Aug. 22, 2014, the disclosures of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Stationary bicycle trainers have been popular in the last few decades as a means to use an existing bicycle on a stationary device that provides resistance to pedaling without the need to also balance, as is required with a bicycle roller. 
         [0003]    In the current art, most bicycle trainers and a variety of resistance mechanisms, that rely on the bicycle&#39;s own tire to drive a resistance device, use a framework to rigidly mount the rear wheel while holding the bicycle upright. In all of these applications, the resistance mechanism is located behind the rear wheel and pivotally attached to the framework below the resistance device, or “upstream” of the tire&#39;s direction of rotation. This is a convenient place to locate a pivot, and allows the driven cylinder of the resistance mechanism to be adjusted into the tire to a degree that reduces or eliminates slippage at the highest torque the cyclist can put out. This method of compressing a driven cylinder into the bicycle tire will be referred to as “Fixed Compression” herein. 
         [0004]    For example; for a cyclist to put out a maximum of 700 watts the resistance device must compress the rear tire sufficiently to prevent slipping. Realistically, however, most of the time a user will spend on a trainer is at much lower wattage, such as 150 to 200. Therefore, most of the time the tire is compressed and distressed unnecessarily. 
         [0005]    This causes three problems; A) the tire will wear quickly if it is highly distressed. In fact, many manufacturers make a special “trainer tire” that is a harder rubber compound capable of lasting longer in trainers. These tires cannot be used on the road because their hard composition causes reduced coefficient of friction to a road surface and is relatively easy for a cyclist to lose control. B) high distress at low power consumes power that limits the minimum effort for the cyclist and C) high distress with no power input consumes inertia from relatively light bicycle wheels, requiring heavier flywheels to compensate for the loss. Bicycle trainer manufacturers typically design for a certain degree of inertia to provide for a smooth stroke since it is nearly impossible to power through a 360 degree pedal rotation with constant power. Uneven power application will cause exaggerated changes in wheel speed, especially with lightweight bicycle wheels unless a heavier flywheel (integral to the bicycle trainer) is employed to better control wheel speed, acceleration, and deceleration. An improved tire compression device is needed. 
       SUMMARY OF THE INVENTION 
       [0006]    The resistance mechanism is mounted to the framework, allowing it to pivot “downstream” of the tire&#39;s rotation. By doing this, the tangential force on the resistance mechanism (caused by the frictional interface between the tire and the driven cylinder) translates to a rotational force about the pivot of the resistance mechanism pivot arm which drives the driven cylinder harder against the tire. The intent of the design is that the pivot point will be strategically positioned so that the ratio of normal force to tangential force matches or exceeds the coefficient of friction between the tire and the driven cylinder, in which case the tire will never slip and a minimal amount of normal force is necessary by the application of a spring to maintain contact with the tire with little to no power load from the cyclist. This will be referred to as “Automatic Compression” herein. 
         [0007]    An alternative embodiment is also proposed which has several advantages: A) a smaller flywheel can be used because the speed of the flywheel can be increased as compared to the speed of the driven cylinder by using different pulley or sprocket diameters between the driven cylinder and the resistance mechanism. A smaller flywheel may be desired to reduce the overall weight and cost of the device. B) Moving the mass to the pivot center of the pivot arm reduces the overall moment of inertia of the pivot arm assembly, comprising the pivot arm, driven cylinder, resistance mechanism, and associated components. Reducing the moment of inertia makes the pivot arm more responsive to sudden changes in speed of the bicycle wheel, further avoiding any potential for slippage between the bicycle tire and the driven cylinder. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    A preferred embodiment of this invention has been chosen wherein: 
           [0009]      FIG. 1  is an isometric side view of the system as mounted to a bicycle; 
           [0010]      FIG. 2  is a side view section  2 - 2  of the system in  FIG. 1 ; 
           [0011]      FIG. 3  is a top view of partial section  3  of the system in  FIG. 1 ; 
           [0012]      FIG. 4  is a simplified side view showing the forces and mounting points of the system; 
           [0013]      FIG. 5  is a graph showing the power vs speed for fixed and automatic compression; 
           [0014]      FIG. 6  is a side view of an alternate embodiment of the system; and 
           [0015]      FIG. 7  is a side view of an alternate embodiment of the system. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    An automatic tire compression bicycle trainer system  10  as shown in  FIG. 1  is designed to be attached to the rear axle of a typical bicycle  12 . As is commonly known in the art, a rear wheel  14  is driven by a crank  16  through a chain  20  and series of sprockets. As the user rotates the crank  16 , the driving gear  18  pulls on the chain  20 . Movement of the chain  20  causes the rear sprocket  22  to begin turning. The rear sprocket  22  drives the rear wheel  14  about the driving axis  26 . Attached to the rear wheel  14  and forming the outermost diameter is a rear tire  24 ,  FIG. 2 . Tires on most bicycles are pneumatic, meaning that air pressure internal to the tire causes the tire to maintain its shape. The air also acts as a cushion to absorb surface irregularities and allows the user to adjust ride quality by increasing or decreasing the pressure. 
         [0017]    The system  10 , as shown in  FIG. 1 , is made up of a frame  28  with a front stabilizing portion  30 , a rear portion  32  with a bridge portion  38 , and an axle mounting portion  34 . The front stabilizing portion  30  and the bridge portion  38  have a lower surface  36  which is designed to rest on the ground. Since gyroscopic forces on both wheels assist the user in maintaining balance on the bike, a trainer where one wheel is stationary requires the bicycle  12  be held upright and fixed from movement to the frame  28  as is shown in  FIG. 1 . The portions  30  and  32  connect at the mounting portion  34 . As shown in  FIG. 1 , the bridge portion  38  has a resistance mounting portion  39  that holds a resistance device  60 . The mounting portion  34  is adapted to attach to the rear axle of the bicycle  12 . The frame  28  is shown attaching directly to the rear axle but it is contemplated that the device could attach to any portion of the frame of the bicycle. As shown in  FIG. 2 , the resistance mounting portion  39  has a pivot point  40  where a pivot arm  42  rotates. The pivot arm  42  includes a driven cylinder  44  that rotates about a driven axis  46 . The driven cylinder  44  has an outside diameter  48  where it contacts the outside surface of the rear tire  24  at a contact point  50 . As shown in  FIG. 4 , the contact point  50  is tangent to both the rear tire  24  and the driven cylinder  44 . 
         [0018]    In one embodiment, the driven cylinder  44  is a resistance device  52  as is shown in  FIGS. 4 ,  6 , and  7 . The resistance device  52  rotates about the driven axis  46  and resists rotation. The resistance device  52  can use different methods to resist rotation. It is desired that the resistance device  52  increases resistance as the rotational speed increases. One style involves eddy currents (shown in  FIG. 3 ), which use magnets  51  in proximity to a metal (usually aluminum) drum. Another option uses viscous fluid, friction material  53 , or other mechanical means. Other options involve fans or a combination of the previously mentioned styles. In the eddy current drive, magnets  51  ride on a carrier that may be eccentric to the driven axis  46 . As the outside cylinder rotates, magnets that ride on the internal carrier generate eddy currents in the outside cylinder. In this embodiment, a progressive resistance device is used where the outside cylinder is typically the outside diameter  48  of the resistance device  52 . As the eddy currents increase in the cylinder, the drag force created pulls the magnets about the offset axis, causing them to become closer to the drum, and therefore further increasing the drag. The offset axis is spring loaded to allow the offset axis to return the magnets back to a nominal position inside the drum. The eddy current resistance mechanism is known in the art and the subject of other utility patents. It is contemplated that the resistance is located on the driven axis  46  but offset to the side to allow for clearance or increased size without requiring a taller frame  28 . 
         [0019]    In another embodiment, the driven cylinder  44  contains no resistance device but contains a pulley or sprocket  54 ,  FIGS. 2 and 3  that drives a belt or chain  56 , which in turn drives another pulley or sprocket  58  which is attached to the resistance device  60 . As stated previously, resistance devices are well known in the art of bicycle trainers. The driven cylinder  44  typically would have a lower mass or rotational inertia than a normal resistance device. The driven cylinder  44  drives a chain or belt  56  to the resistance device mounted at or close to the pivot point of the pivot arm. Using different sized pulleys or sprockets, as is shown in  FIGS. 2-3 , the ratio between the driven cylinder and the resistance device can be multiplied or divided. The separate resistance device allows the system to be more responsive to sudden changes in the rotational speed of the wheel  24 . 
         [0020]    The outside diameter  48  is held in biased contact with the outside surface of the tire  24  via a spring  41 . The spring  41  holds the pivot arm  42  with enough static force (shown as normal force  76  in  FIG. 4 ) for the tire  24  to begin rotating against the driven cylinder  44  without slippage. The spring  41  is shown in  FIG. 1  and removed in other FIGS. for simplicity. As shown, the spring  41  applies tension to a portion of the pivot arm  42  to bias the outside diameter  48  wheel  14 . It is contemplated that the spring  41  is implemented in compression to accomplish the same task. It is further contemplated that a balancing mechanism is implemented instead of a spring in order to maintain biased contact at contact point  50 . 
         [0021]    As shown in  FIG. 4 , the tire  24  increasing in speed causes the driven cylinder  44  to create drag by resisting rotation. It either creates drag directly or has drag created by another driven device. This drag creates a line of applied force  62  that travels from the contact point  50  to the pivot point  40 . This is shown in  FIG. 4  as applied force  62 . Because the pivot point  40  is not located on the tangent line or the normal force line, the applied force  62  is split into a tangent force  70  and a normal force  76 . The normal force  76  is increased as a proportion of the force  62 . If the pivot point  40  was intersected by the tangent force  70 , the normal force  76  would remain the same regardless of the drag in the system. If the pivot point  40  was intersected by the normal force  76 , the driven cylinder  44  would be simply pushed out of the way as the tire  24  rotates. 
         [0022]    As is shown in  FIG. 5 , drag and torque are directly related. The tangential force  70  creates a moment about the pivot point  40  of the pivot arm  42  calculated as tangential force*dimension  74 . This moment is reacted by the normal force*dimension  72 . These two forces are constrained to be equal, so tangential force*dimension  74 =normal force*dimension  72 . This can be rewritten as dimension  72 /dimension  74 =Tangential force/Normal force. The coefficient of friction is the force required to move the two sliding surfaces over each other (tangential force), divided by the force holding them together, (normal force). So long as the ratio of tangential force to normal force remains lower than the coefficient of friction between the tire and the driven cylinder  44 , the tire will not slip. This relationship also defines the relationship of dimension  72  to dimension  74 . This is all visible in  FIG. 4 . 
         [0023]    At rest, the normal force  76  from the driven cylinder  44  is from the spring  41 . Once the driven cylinder  44  begins moving, the resistance device  52 ,  60  begins to cause drag in the system. The drag creates a force  62  that is a line that intersects the contact point  50  and the pivot point  40 . Because the force  62  is at an angle to the tangential force  70  and the normal force  76 , the force  62  resists the tangential force  70  created by the tire  24 . The force is a compressive force between the pivot point and the point of contact between the outside surface  50  and the outside diameter  48  of the driven cylinder  44 . The reaction force is split into two components, one of those components adds into the normal force  76 . The moment as shown in  FIG. 6  is counterclockwise when the wheel  14  is rotating clockwise. The moment as shown in  FIG. 7  is counterclockwise when the wheel  14  is rotating clockwise. 
         [0024]    The calculated effect of automatic compression versus fixed compression can be seen in the graphs shown in  FIG. 5 . With fixed compression  33 , there is a predetermined amount of drag on the tread surface of the tire regardless of speed. At higher speeds it becomes irrelevant and matches the drag caused by automatic compression  35 . At lower speeds, the automatic compression drag force is significantly reduced. The drag vs. speed graph is shown in  FIG. 5 . 
         [0025]    One of the effects, as mentioned earlier, is to simulate the effect of a flywheel, where on the sudden application of high power the additional resistance caused by higher tire distress provides the same net effect as pushing against a flywheel. Likewise, the sudden removal of power decreases tire distress and allows the wheel to spin more freely, also providing the same net effect as a flywheel. 
         [0026]    The chart in  FIG. 5  is drag vs. speed, assuming a resistance device is employed that provides non-linear power vs speed such as a typical fluid mechanism, or the progressive resistance device. The upper curve  33  is the drag that would be represented by a fixed compression device. The lower curve  35  represents the drag present by the automatic compression device. It allows for a more highly non-linear relationship of power and speed, which provides the designer of a training system more flexibility in tuning a power curve to suit the needs of the consumer. 
         [0027]    As shown in  FIGS. 1-4  and  6 , the driven cylinder  44  or resistance device  60  is shown with the rotating tire causing a compressive force on the pivot arm  42 . It is possible to accomplish the same tire compression compensation by relocating the pivot point  40  on the opposite side of the tangent line. This setup is shown in  FIG. 7 . In this embodiment, the pivot point  40  is located closer to the rotating axis of the rear tire  24 . As the resistance device  52  begins to generate drag, the applied force  62  translates to a tangent force  70  and a normal force  76 . 
         [0028]    It is understood that while certain aspects of the disclosed subject matter have been shown and described, the disclosed subject matter is not limited thereto and encompasses various other embodiments and aspects. No specific limitation with respect to the specific embodiments disclosed herein is intended or should be inferred. Modifications may be made to the disclosed subject matter as set forth in the following claims.