Abstract:
A unique structure for an indoor exercise bike that provides strength in its design, as well as the flexibility to create an aesthetically appealing frame structure. The monocoque frame design, including two symmetrical halves joined together, forms a very strong, light shell that can take on a variety of shapes and sizes. The seat structure, handlebar structure, drive train and support platforms are all able to be readily attached to the primary frame structure to provide an exercise bicycle that is sturdy, easy to manufacture, and light enough to easily move when necessary.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 10/051,602, filed on Jan. 17, 2002, which is a non-provisional application claiming priority to U.S. Provisional Patent Application No. 60/262,768 entitled “Exercise Bicycle Frame” filed on Jan. 19, 2001, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention involves an exercise bicycle and various aspects of the exercise bicycle. 
     BACKGROUND 
     One of the most enduring types of exercise equipment is the exercise bicycle. As with other exercise equipment, the exercise bicycle and its use are continually evolving. Early exercise bicycles were primarily designed for daily in home use and adapted to provide the user with a riding experience similar to riding a bicycle in a seated position. These early exercise bicycles extensively used cyclindrical tubing for nearly all components of the frame. In many examples, early exercise bicycles include a pair of pedals to drive a single front wheel. To provide resistance, early exercise bicycles and some modern exercise bicycles were equipped with a brake pad assembly operably connected with a bicycle type front wheel so that a rider can increase or decrease the pedaling resistance by tightening or loosening the brake pad engagement with the rim of the front wheel. 
     As exercise bicycles became increasingly popular in health clubs, the need for greater durability than is provided by cylindrical tubing emerged as many riders used the exercise bicycle throughout the day and night. Moreover, whether in health clubs or at home, the use and features provided by exercise bicycles evolved as many riders sought to achieve an exercise bicycle riding experience more similar to actual riding, which often includes pedaling up-hill, standing to pedal, and the like. One point in the evolution of the exercise bicycle is the replacement or substitution of the standard bicycle front wheel with a flywheel. The addition of the flywheel, which is oftentimes quite heavy, provides the rider with a riding experience more similar to riding a bicycle because a spinning flywheel has inertia similar to the inertia of a rolling bicycle tire. 
     Another point in the evolution of the use of the exercise bicycle is in group riding programs at health clubs, where transition between various different types of riding is popular, such as riding at high revolutions per minute (RPM), low RPM, changing the resistance of the flywheel, standing up to pedal, leaning forward, and various combinations of these types of riding. This evolution of the use of the exercise bicycle also brought about more demand for sturdy and durable exercise bicycles. 
     To meet the need for sturdier exercise bicycles that would stand up to continuous use throughout the day, that would support a heavy rapidly rotating flywheel, and that would stand up to group type exercise programs, exercise bicycles began being designed with square or box-beam type tubing, which in some instances is more durable and sturdy than cylindrical tubing. One drawback of box-beam type tubing is that it provides little flexibility in designing an aesthetically pleasing exercise bicycle. 
     Another drawback of exercise bicycles made with box-beam type tubing is that they are heavy and difficult to move. In some health clubs and in many homes, space is limited and is oftentimes used for many different purposes. For example, a room in a health club may be used for aerobics one hour and then used by a group of people all riding exercise bicycles the next hour, which requires that the exercise bicycles be moved around within or in and out of the room. 
     In addition to demand for durable sturdy exercise bicycles, riders desire exercise bicycles that can be adapted to fit a particular riders size. To meet this need, exercise bicycles with adjustable seats, adjustable handlebars, and the like have been designed. In some conventional exercise bicycles, box beam type posts and tubes are used for the seat and the handlebar in adjustable configurations. Typically, box beam tubing has as a square or rectangular cross section and therefore has four walls, with about 90 degree angles between the walls. For example, a square seat tube will receive a square seat post with a seat in an adjustable configuration which allows the seat post to be set within the seat tube at a variety of different heights. 
     One drawback of using box beam tubing in adjustable handlebar assemblies and seat assemblies is that oftentimes no walls are positively engaged or only one wall of the tube will engage one wall of the post. To move within the tube, the post must fit within the tube relatively loosely. To fix the post within the tube at a particular position, such as adjusting the height of the seat post or the height of the handlebar stem, oftentimes a pin will be inserted through an aperture in the tube to engage a corresponding aperture in the post. In such an arrangement, the seat, the handlebar, or both will oftentimes have a fairly loose feeling and might wobble noticeably during riding. In some instances, an additional device might force the rear wall of the post against the rear wall of the tube resulting in one wall of the post engaging one wall of the tube. In such an arrangement, wobbling and the feeling of unsteadiness might be reduced, but oftentimes is not eliminated. Besides having a feeling of unsteadiness, such movement between the post and the tube can result in metal on metal squeaking and can also cause wear and tear on the components. 
     It is with this background in mind that the present invention was developed. 
     SUMMARY OF THE INVENTION 
     The present invention includes a unique structure for an indoor exercise bike that provides strength in its design, as well as the flexibility to create an aesthetically appealing frame structure. The monocoque frame design, including two symmetrical halves joined together, forms a very strong, light shell that can take on a variety of shapes and sizes. The seat structure, handlebar structure, drive train and support platforms are all able to be readily attached to the primary frame structure to provide an exercise bicycle that is sturdy, easy to manufacture, and light enough to easily move when necessary. 
     According to one present aspect of the invention, the instant invention includes a frame for an exercise bicycle for supporting a flywheel, a seat assembly, and a handlebar assembly, the frame including a monoframe having an upper front end, a lower front end, and a rear end, and a set of forks, wherein the upper front end is attached to the forks and the lower front end is in a fixed position relative to the forks to make a rigid structure. 
     According to a further aspect of the present invention, the monoframe is a hollow body defined by two panels rigidly attached together and defining a space therebetween. 
     According to another aspect of the present invention, the exercise bicycle frame includes a monocoque frame member defining a rear support, a top support extending generally forwardly and upwardly from the rear support, and a seat support extending generally upwardly from the rear support, the seat support between the rear support and the top support. 
     According to another aspect of the present invention, the seat assembly and the handlebar assembly both utilize nested trapezoidal tubing to provide secure adjustment of the handlebar assembly or the seat assembly with respect to the frame. 
     Other features, utilities, and advantages of various embodiments of the invention will be apparent from the following, more particular description of embodiments of the invention as illustrated in the accompanying drawings and set forth in the appended claims. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The detailed description will refer to the following drawings, wherein like numerals refer to like elements, and wherein: 
         FIG. 1  is a perspective view of an exercise bicycle according to one embodiment of the invention; 
         FIG. 2  is a side view of an exercise bicycle according to one embodiment of the invention; 
         FIG. 3  is an exploded perspective view of the exercise bicycle illustrated in  FIG. 2 ; 
         FIG. 4  is a perspective view of an exercise bicycle frame according to one embodiment of the invention; 
         FIG. 5A  is an exploded left-side perspective view of a monocoque frame member illustrating a left monocoque panel and a right monocoque panel according to one embodiment of the invention; 
         FIG. 5B  is an exploded right-side perspective view of the monocoque frame member illustrated in  FIG. 5A ; 
         FIG. 6A  is a perspective view of a brake assembly according to one embodiment of the invention; 
         FIG. 6B  is a view of the rear of the brake assembly taken along line  6 B— 6 B of  FIG. 2 ; 
         FIG. 6C  is a section view taken along line  6 C— 6 C of  FIG. 6B  illustrating a vibration dampening device according to one embodiment of the invention; 
         FIG. 7A  is a section view taken along line  7 — 7  of  FIG. 2  illustrating a pop pin in engagement with a head tube and a handlebar stem according to one embodiment of the invention; 
         FIG. 7B  is a section view taken along line  7 — 7  of  FIG. 2  illustrating the pop pin disengaged from the handlebar stem according to one embodiment of the invention; 
         FIG. 8A  is a section view taken along line  8 A— 8 A of  FIG. 7A ; 
         FIG. 8B  is a section view taken along line  8 B— 8 B of  FIG. 7B ; 
         FIG. 9  is an exploded perspective view of a seat assembly according to one embodiment of the invention; and 
         FIG. 10  is a perspective view of an alternative embodiment of the exercise bicycle according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of one embodiment of an exercise bicycle  20  according to the invention. The exercise bicycle includes a frame  22  with a monoframe structure  23  supporting a pedal assembly  24  ( FIGS. 1 ,  2 ), a front fork  26  connected with the monoframe structure for supporting a flywheel  28 , a head tube  30  projecting upwardly from the front fork  26  and adjustably supporting a handlebar assembly  32 , and a seat tube  34  projecting upwardly from the monoframe structure and adjustably supporting a seat assembly  36  having a seat  38 . For convenience, the terms “rear,” “front,” “right,” and “left” will refer to the perspective of a user sitting on the seat  38  of the exercise bicycle and facing toward the handlebar assembly  32 .  FIG. 2  is a side view of another embodiment of an exercise bicycle according to the invention. The exercise bicycle illustrated in  FIG. 1  has a bottom tube  40  that is an integral extension of the central monoframe structure while the exercise bicycle illustrated in  FIG. 2  has a separate square bottom tube  42  that is secured to the monoframe structure. The bottom tube  42  structure is discussed in more detail below. The exercise bicycles illustrated in  FIG. 1  and  FIG. 2  are similar in all other respects.  FIG. 3  is an exploded perspective view of the exercise bicycle illustrated in  FIG. 2 . 
     Generally speaking, a user operating the exercise bicycle will oftentimes first adjust the seat assembly  36  and the handlebar assembly  32 . The seat  38  may be adjusted both vertically and horizontally and the handlebars may be adjusted vertically. Once the exercise bicycle is properly adjusted, the user will sit on the seat  38  and begin pedaling. Pedaling will cause the flywheel  28  to begin to rotate, and the harder the user pedals the faster the flywheel will rotate. The flywheel is fairly heavy, which makes it fairly strenuous to start the flywheel rotating, but once it is rotating it has inertia which helps keep the flywheel rotating. 
       FIG. 4  is a perspective view of one embodiment of the frame of the exercise bicycle illustrated in  FIGS. 2 and 3 . In  FIG. 4 , the frame is shown by itself, with various components of the exercise bicycle removed, such as the handlebar assembly, the pedal assembly, the seat assembly, and the flywheel. Referring to  FIGS. 1–4 , the frame  20  is supported on the floor or any other suitable surface at a rear base  43  and a front base  44 . The rear base  43  and the front base  44  extend laterally with respect to the length of the exercise bicycle  20  to provide lateral support when side-to-side forces are applied to the exercise bicycle, such as when standing on the pedals and pedaling vigorously and when mounting or dismounting the exercise bicycle. In one example, a rear laterally extending partially curved plate  46  is connected with the rear portion of the monoframe structure  23  and is secured with the rear base  43 , and a front laterally extending partially curved plate  48  is connected with the bottom of the front forks  26  and the front of the bottom tube  42  and is secured to the front base  44 . 
     As best shown in  FIG. 3 , adjustable floor stands  50  extend downwardly from the bottom outside portions of the rear base  43  and the front base  44  to level the exercise bicycle  20  in the event the exercise bicycle is used on a sloped or uneven surface. In addition, one or more wheels  52  are connected with the front of the front base  44  to allow a user to conveniently move the exercise bicycle. In one example, a left and a right wheel are each rotabably supported on a corresponding left and right brackets that are connected proximate the left and right side of the base, respectively, and extend forwardly and somewhat upwardly from the front base. The bracket is oriented somewhat upwardly so that the exercise bicycle may be pivoted from the rear upwardly and forwardly to cause the wheels to move downwardly and engage the floor, from which position the exercise bicycle may be rolled along the floor to a different location. Alternatively, one wheel may be rotabably supported at the front of the front base rather than two wheels. 
     The central monoframe portion  23  of the frame  22 , in one example, is made from a left side panel  54  and a right side panel  56  seam welded together. The monoframe structure provides a central support structure for the frame  22  that is sturdy and durable to withstand the rigors of use by many riders and yet also fairly light weight to provide easy maneuverability about a health club or a home. In addition, the shape of the monoframe structure may be configured into any number of aesthetically pleasing shapes, the frame examples illustrated herein being only discrete examples of such aesthetically pleasing shapes. 
       FIG. 5A  is an exploded left-side perspective view of the monoframe structure illustrating the inner portion of the right side panel  56  and the outer portion of the left side panel  54 .  FIG. 5A  also illustrates the welded connection between the bottom tube  42  and a seat post  34  within the monoframe structure according to one embodiment of the invention, which is discussed below.  FIG. 5B  is an exploded right-side perspective view of the monoframe structure illustrating the outside of the right side panel  56  and the inside of the left side panel  54 . The seat tube  34  and the bottom tube  42  can be welded to the side panels along their length, or can just be attached to the side panels where the tubes extend out of the monoframe structure (such as by welding around the perimeter of the respective tube). 
     The two side panels  54  and  56  of the monoframe structure  23  are substantially mirror images of each other. The panels define corresponding peripheral edges  58  that mate together when the two panels  54  and  56  are engaged. In one example, the two side panels define a hollow space between the side panels. In one example, the mating peripheral edges  58  align with each other and can overlap or butt together as necessary to allow for a seam weld between the peripheral edges  58  to secure the panels  54  and  56  together. The seam weld extends along the entire length of the abutting peripheral edges and thus provides very high strength in the connection between the two side panels. The side panels may be secured together through other means besides a seam weld, such as a series of spot welds, a series of rivets, interlocking releasable tabs, and the like. In one embodiment, the side panels are made of stamped steal and are between 2.0 mm and 2.5 mm thick. The stamped steel, however, can be any suitable thickness depending on the loads that the exercise bicycle needs to withstand. In addition, the side panels may be made from any suitable material besides steel, such as an alloy, aluminum or plastic. If plastic or other polymer side panels are used, the side panels may be secured by a suitable adhesive, interlocking releasable tabs, sonic welding, and the like. 
     A forwardly widening rear support  60  is defined at the lower rear of the monoframe structure  23 . In one example, the rear support  60  defines an upper curved (convex) wall  62 , which is connected with the rear plate  46  and a lower curved (concave) wall  64 , which is also connected with the rear plate  46 . The rear support portion  60  of the monoframe  23  is defined entirely by corresponding portions of the left  54  and right  56  side panels. 
     From the rear support  60 , the monoframe structure defines a forwardly sweeping aesthetically pleasing shape that widens into a central monoframe portion  66 . The monoframe has a generally curved (convex) top surface and a generally curved (concave) bottom surface. An upper or top support structure  68  extends forwardly and upwardly from the upper forward portion of the central monoframe portion  66 , a lower or bottom support structure  70  extends forwardly and downwardly from the lower front portion of the central monoframe portion  66 , and a seat support structure  72  extends upwardly from the upper portion of the central monoframe  66  between the rear support  60  and the top support  68 . In the embodiments of the invention discussed herein, the arcuate surfaces of the monoframe provide aesthetically pleasing lines of the frame generally. In addition, the smooth sweeping curves of the monoframe reduce stress risers and can be adjusted to provide any number of aesthetically pleasing shapes without impacting the strength of the monoframe structure. 
     The front of the top support structure  68  of the monoframe  23  is connected to the head tube  30  adjacent the top of the front forks  26 . In the embodiment illustrated in  FIGS. 1–4 , the vertical dimension of the top support structure  68  generally narrows as it sweeps forwardly and upwardly from the central monoframe portion  66  to the head tube  30 . The top support structure  68  defines an upper surface and a lower surface. The upper surface of the top support is generally curved (convex) along its length from rear to front between the central monoframe portion  66  and the front forks  26 , while the lower surface of the top support is generally curved (concave) along its length from rear to front. The upper surface of the top support  68  maintains the continuity of the forwardly sweeping shape of the monoframe that begins at the rear support  60 . 
     The top support  68 , as best shown in  FIGS. 5A and 5B , is defined by the attached side panels  54  and  56  of the monoframe  23  and requires no box-beam, cylindrical, or other type of tubing. The forward end of the top support  68  defines an aperture including a rim  74  defined by the combined side panels. The rim  74  at the front end of the top support  68  is attached with the rear wall of the head tube  30  by a seam weld between the rim  74  and the top support  78 . This weld is a long “butt” joint and thus provides significant strength between the top tube and the front forks  26 . 
     The bottom support structure  70  defines a narrowing or tapering shape extending forwardly and downwardly from the central monoframe structure  66 . In one example, the bottom support structure  70  defines a top curved (convex) surface and a bottom curved (concave) surface. The top surface of the bottom support intersects with the lower surface of the top support in a continuous sweep that defines a forwardly extending concave front surface (C-shaped) of the central monoframe portion  66  adapted to cooperate with the flywheel  28  as discussed below. The bottom curved surface of the bottom support structure  70  maintains the continuity of the curved sweep of the monoframe that begins at the rear support  60 . The curve along the top of the monoframe is convex upwardly. The curve along the bottom is concave downwardly, and the curve along the front is concave forwardly, thereby forming a general triangular body structure that provides excellent strength characteristics. 
     As shown in  FIGS. 2–4 ,  5 A and  5 B, the upper surface and the lower surface of the bottom tube portion  70  of the monoframe converge to define a bottom tube aperture  76  having a rectangular shape. A bottom tube  42  defining a rectangular cross section extends forwardly and downwardly from the bottom tube opening  76  and is connected at its forward end with the front laterally extending plate  48 , which is secured with the front base  44 . The bottom tube  42  extends through the bottom tube aperture  76  and into the hollow space defined by the two side panels  54  and  56 , in one example. If desired, the bottom tube  42  can be welded around its perimeter to the outside rim of the bottom tube aperture  76  to add further strength to the frame. In addition, the bottom tube  42  can be welded along its length to the inside of one of the side panels of the monoframe  23 , such as the left panel or the right panel, to provide further support between the seat tube and monoframe. Besides complementing the appealing aesthetic quality of the flowing lines of the monoframe, the tapering shape of the bottom tube structure also facilitates welding the rim of the bottom tube opening  76  to the bottom tube  42  such as when automated welding equipment is used. The end of the bottom tube  42  inside the monoframe is attached to the bottom portion of the seat tube  34 , such as by welding. 
     The bottom tube  42  is shown in  FIGS. 2–5B  as a separate tube extending from the bottom tube opening  76 . The monoframe, however, may be configured to define an integrated bottom tube support that is part of the bottom tube structure and extends downwardly and forwardly from the bottom tube support structure  70 , such as is shown in  FIG. 1 . In the embodiment of the invention with an integrated bottom tube  78 , the bottom tube  78  is made entirely from the monoframe side panels  54  and  56 , and does not include any square tubing, cylindrical tubing, or the like. 
     The seat support portion  72  of the monoframe structure  23  extends generally upwardly from the central monoframe structure  66 . The seat support  72  is part of the monoframe structure and, in one example, is defined by two mating mirror image side portions of the monoframe structure, which are seam welded together. The seat tube portion includes a curved front wall and a curved rear wall. The front wall and the rear wall converge together to define a rectangular seat tube aperture  80  through which the seat tube  34  extends upwardly and somewhat rearwardly. In one example, the seat tube aperture  80  is trapezoidal and is adapted to cooperate with the seat tube  34 , which is also trapezoidal. The trapezoidal nature of the seat tube  34  and other tubing is discussed in more detail below. 
     The seat tube  34  extends through the seat tube aperture  80  in the upper central portion of the monoframe  23  and into the hollow space defined by the two side panels  54  and  56 , in one example. If desired, the seat tube  34  can be welded around its perimeter to the outside rim of the seat tube aperture  80  to add further strength to the frame. The seat support  72  defines flowing sweeping lines complementary to the other lines of the monoframe. The shape of the seat support  72  also facilitates seam welding the seat tube  34  to the rim of the seat tube opening  80 . As with the bottom tube  42 , the seat tube is illustrated herein as a separate tube extending upwardly from the central portion of the monoframe  66 . The monoframe, however, may be configured to define an integrated seat tube that is part of the seat tube portion of the monoframe and that extends upwardly and somewhat rearwardly from the area of the seat support adjacent the seat tube aperture. The integrated seat tube is made from mirror image portion of the side panels, as shown in  FIG. 1 . As an integrated seat tube, no additional tubing is needed. 
     Referring to  FIG. 5 , an embodiment of the invention with the seat tube  34  connected to the bottom tube  42  within the hollow space defined by the two side panels  54  and  56  is shown. The bottom tube  42  is welded to the lower portion of the seat tube  34  to impart additional strength and rigidity to the frame  20 . Alternatively or additionally, the seat tube  34  and bottom tube  42  may be welded to the inside of one of the side panels  54  and  56  of the monoframe, welded to the rim of the seat tube aperture  80  or the bottom tube aperture  76  respectively, or some combination of welds to secure the seat tube  34  and bottom tube  42  to the monoframe. 
     Typically, the bottom tube  42  and seat tube  34  are chromed or stainless steel and are dimensioned in any reasonable size to withstand the intended use of the exercise bicycle. The tubes can be rectangular, square, oval, cylindrical, and solid or hollow. In one example, the bottom tube  42  and the seat tube  34  are hollow, which makes the tubes lighter than a solid tube. In the event a polymer monoframe is used, then polymer tubing may also be used, which may be glued, sonic welded, or otherwise connected with the monoframe. 
     As best shown in  FIGS. 2 and 4 , at the front of the frame, the front fork  26  extends between the front support plate  48  and the forward portion of the top support  68 . The front fork  26  includes a left fork leg and a right fork leg, each extending upwardly from the front support and defining a space in which the flywheel is located as shown in  FIGS. 1 and 2 . A left receiving bracket  82  and a right receiving bracket  84  are positioned on the inside surface of each of the fork legs for securing opposing ends of an axle of the flywheel  28 . When positioned in the receiving brackets the flywheel  28  is located between the front fork legs. The portion of the flywheel  28  generally rearward of the axle occupies the space defined by the rearwardly extending curved face of the central monoframe  66  bordered by the lower surface of the top portion  68  and the upper surface of the bottom support  70 . The flywheel  28  includes a flywheel sprocket circumferentially disposed about the axle on the right side of the flywheel and configured to receive a chain. In addition, the flywheel may include a freewheel clutch mechanism, such as is shown in U.S. Pat. No. 5,961,424 entitled “Free Wheel Clutch Mechanism for Bicycle Drive Train” and related patent application Ser. No. 09/803,630, filed Mar. 9, 2001 entitled “Free Wheel Clutch Mechanism for Bicycle Drive Train” which are both hereby incorporated by reference in their entirety. The freewheel clutch mechanism disengages the rotation of the flywheel from the rotation of the pedal assembly and drive train when the user impacts a force on the pedals contrary to the rotation of the flywheel, and that force is sufficient to overcome a break-free force of the free wheel clutch mechanism. 
     The drive train  86  includes an axle  88  having crank arms  90  extending transversely from each end of the axle, and a drive sprocket  92  circumferentially disposed about the right side of the drive axle. See  FIGS. 1 and 2 . The chain  94  is operably connected between the drive sprocket  92  and the flywheel sprocket  96 . Referring to  FIGS. 4 and 5A  and  5 B, a crank set bearing bracket  98  or bottom bracket is attached to a forward wall of the seat tube  34  just above the bottom tube  42 . The bearing bracket  98  rotatably supports the drive train  86 . The crank set bearing bracket  98  is positioned in the central monoframe portion  66  and extends between the two side panels  54  and  56  that make up the monoframe. Each panel of the monoframe defines an aperture  100  through which the opposing ends of the bearing bracket  98  extend and through which the drive train axle extends. The portion of the bottom bracket extending through the side panel apertures may be welded to the side panels to provide further structural support and rigidity to the frame. The crank arms  90  and the drive sprocket  92  are mounted on the portions of the drive axle that extend out of the monoframe structure. 
     Referring to  FIGS. 1 and 3 , the drive sprocket  92  is located on the right side of the monoframe and supports the chain  94  operably connected with the flywheel sprocket  96 . In the embodiment shown herein, the drive sprocket  92  is larger than the flywheel sprocket  96  to allow the rider to develop a high revolution per minute (RPM) rate of the flywheel and thus create a high momentum while at the same time having less RPMs at the crank arms. In such a configuration, the rider is able to achieve an exceptionally vigorous workout similar to riding a bicycle at a fairly high rate of speed. The size of the drive sprocket and flywheel sprocket, however, may be configured in any way required to achieve a desired RPM rate at the flywheel or at the crank arms. In addition, a gearing structure with a plurality of sprockets of differing size may be connected with the drive axle or with the flywheel axle to achieve a desired work out. As shown in  FIG. 1 , a drive train shroud  102  may be provided to cover the drive sprocket, the chain, the flywheel sprocket and other drive train components so that unintentional contact with the drive train is reduced. 
     The top of each fork leg defines an inwardly extending curve  104  that abuts the side wall of the head tube  30 . In the embodiment shown herein, the top support  68  is welded to the rear wall of the head tube  30 , the left fork leg is welded to a left side wall of the head tube, and the right fork leg is welded to a right side wall of the head tube. The head tube  30  extends downwardly past the attachment with the fork legs and defines a dampening aperture  106  extending between the front wall and the rear wall for supporting a brake assembly. 
       FIG. 6A  is a perspective view of a brake assembly  108  according to one embodiment of the invention.  FIG. 6B  is a rear view of the brake assembly  108  connected to the rear wall of the head tube taken along line  6 B— 6 B of  FIG. 2 . Referring to  FIGS. 3 ,  6 A, and  6 B, the brake assembly includes a left  110  and a right brake arm  112 , each having a generally inverted L-shape with a downwardly extending arm  114  and  116 , respectively, adapted to adjustably receive a brake pad  118  and a generally horizontal arm  120  and  122 , respectively, adapted to receive a brake cable  123 . The brake arms are configured so that the brake pads may engage the rim  124  of the flywheel  28 . Adjacent the intersection of the downwardly extending arm and the generally horizontal arm, each brake arm is pivotally connected to a mounting bracket  126  that positions the pivots above and to either side of the flywheel. 
     Referring to  FIG. 6B , an adjustment knob  128  is rotabably supported on a mounting bracket  130  connected with the head tube  30 . The adjustment knob  128  includes a downwardly extending threaded post  132  adapted to engage a plate  134  supporting the brake cable  123  and defining a threaded aperture adapted to cooperate with the threaded post  132 . Rotation of the knob  128  in a clockwise direction draws the plate  134  upwardly and accordingly draws the brake cable  123  upwardly, and rotating the knob  128  in a counter clockwise direction moves the plate  134  downwardly and hence relaxes the brake cable  123 . Drawing the brake cable  123  upwardly causes the ends of the generally horizontal arms  120  and  122  connected with the brake cable  123  to move upwardly and thereby brings the brake pads  118  into engagement with the flywheel  28 . The brake assembly also includes one or more springs biased so that relaxing of the brake cables causes the brake arms to move away from engagement with the flywheel  28 . 
       FIG. 6C  is a section view taken along line  6 C— 6 C of  FIG. 6B  illustrating a vibration dampening device used to connect the brake assembly with the frame. The vibration dampening device includes a rod  136  and a front grommet  138  and a rear grommet  140  for supporting the rod. The front and rear grommets are supported in the aperture  106  defined in the lower portion of the head tube  30 . The rod  136  extends through both grommets and fixes the mounting bracket  126  to the head tube  30 . The grommets are made of a resilient, rubber-like material. The vibration dampening device reduces translation of any vibrations from the flywheel to the frame of the exercise bicycle. 
     A lever  133  attaches to the rod  132  just below the knob and above the mounting bracket  130 . The lever extends forwardly of the rod and forms a fulcrum (pivot point) at which point the lever is pivoted to lift the knob and apply the brake without having to turn the knob. This thus acts as a quick-stop brake. 
     Referring to  FIG. 3 , an exploded perspective view of a handlebar assembly  32  is shown according to one embodiment of the invention. The handlebar assembly includes a handlebar adjustably supported in the head tube  30  by a handlebar stem  142 . The handlebar includes a ring  144  connected to a transverse bar  146 . The handlebar also includes left  147  and right  148  prong grips extending forwardly from the transverse bar  146 . The handlebars provide a variety of gripping positions for the user. 
     In one example, the handlebar stem  142  defines a trapezoidal cross section adapted to fit within a corresponding trapezoidal aperture defined by the head tube  30 . The front of the handlebar stem defines a plurality of apertures  150  adapted to receive a pop pin  152 , which is discussed in more detail below. An insert  154  may be fitted between the stem  142  and head tube  30  to reduce friction between the head tube  30  and the stem  142  when adjusting the handlebars  32  and to reduce any squeaking caused by metal on metal contact between the head tube  30  and handlebar stem  142  (without the insert) that might be caused when the stem is moved relative to the head tube. The insert  154  defines an upper flange  156  that engages the upper rim of the head tube. The insert  154  also defines a plurality of apertures slightly larger than the apertures in the handlebar stem, which apertures align with the apertures in the stem. 
       FIGS. 7A and 7B  are cross sections of the head tube  30  and handlebar stem  142  taken along line  7 — 7  of  FIG. 2 .  FIGS. 8A and 8B  are cross section of the head tube  30  and handlebar stem taken along line  8 A— 8 A of  FIG. 7A  and along line  8 B— 8 B of  FIG. 7B , respectively. Referring particularly to  FIGS. 4 ,  8 A and  8 B, in one embodiment, a front wall  158  of the head tube  30  is wider than a rear wall  160  of the head tube, and side walls  162  taper inwardly from the outside edges of the front wall  158  to the outside edges of the rear wall  160  to define a trapezoidal aperture adapted to receive the handlebar stem  142 . The handlebar stem  142  or post is also trapezoidal and configured to be received by the head tube  30 . In one embodiment, the stem  142  also includes a front wall  164  that is wider than a rear wall  166 , and side walls  168  that taper inwardly from the outside edges of the front wall  164  to the outside edges of the rear wall  166 . The width of the front  164  and rear  166  walls of the stem  142  are less than the width of the front  158  and rear  160  walls of the head tube  30 , and the length of side walls  168  of the stem  142  are less than the length of the side walls of the head tube  30  so that the stem  142  will fit in the head tube  30 . The front walls are generally parallel with the rear walls and the angles between the front walls and the side walls of each of the head and stem are nearly equal. Configured as interengaging trapezoids, the handlebar stem can positively engage at least two walls, and preferably three, of the head tube  30  for a secure fit. 
     The pop pin  152  is operably connected with the front wall  158  of the head tube  30 . A boss  170  extends forwardly from the front wall  158  of the head tube  30  and defines a threaded aperture  172  for receiving a threaded sleeve  174 . The sleeve  174  is cylindrical with the outer surface being threaded and adapted to threadably engage the threaded aperture  172  defined by the boss  170 . The inner portion of the sleeve  174  is partially threaded, adjacent its front portion and is adapted to receive the pop pin  152 . The pop pin  152  is milled at one end, opposite a handle  176 , to define an engaging cylinder  178  and a collar  180 . The engaging cylinder  178  is adapted to insert into one of the apertures  150  along the front wall  158  of the handlebar stem  142 . The sleeve  174  is connected with the tightening bolt  152  by a spring  182  biased to insert the engaging cylinder  178  into one of the plurality of apertures  150  in the handlebar stem  142 . 
     Both the insert  154  and the head tube  30  define apertures large enough for the collar  180  to pass through. The apertures in the front of the handlebar stem  142 , however, are large enough to only receive the engaging cylinder  178  and not the collar  180 . Accordingly, when the engaging cylinder  178  is in one of the apertures  150  of the stem  142 , the collar  180  abuts the front wall  164  of the handlebar stem  142 . The spring  182  forces the pop pin  152  into this position when properly aligned with one of the apertures. When the engaging cylinder  178  is through one of the apertures  150 , an outer threaded portion  184  of the pop pin  152  abuts the threaded portion of the sleeve  174 . Using the handle  176 , the pop pin  152  may then be further tightened into the sleeve, which forces the collar  180  to press rearwardly on the stem  142  and thereby further secure the stem  142  in the head tube  30 . The head tube  30  and stem  142  may be rearranged so that, for example, the wide walls of the tube and stem are to the rear and the pop pin extends forwardly. 
     As best shown in  FIG. 8B , the distance between the front wall  164  and the rear wall  166  of the handlebar stem  142  is configured so that when it is inserted in the head tube  30  there is a front gap  184  between the front wall  158  of the head tube  30  and the front wall  164  of the handlebar stem  142  and a rear gap  186  between the rear wall  160  of the head tube  30  and the rear wall  166  of the handlebar stem  142 , in one example. The distance between the sidewalls of the of the head tube, i.e., the width, is configured so that when the tightening bolt  176  is not engaged, such as when the handlebar stem  142  is first inserted in the head tube  30  or when the handlebar is being vertically adjusted, the handlebar stem  142  rests forwardly in the head tube  30  to provide the gaps as described. 
     When the pop pin is tightened into the sleeve  174 , the handlebar stem  142  is wedged rearwardly in the head tube  30  widening the front gap  184  and closing (or nearly closing) the rear gap  186  as shown in  FIG. 8A . Due to the inter-engaging trapezoidal tubing, when being wedged rearwardly, the side walls of the handlebar stem engage the respective side walls of the head tube. In one example, the sidewalls and the front and rear walls of the handlebar stem  142  are configured so that each sidewall will positively engage a substantial portion of the length of the sidewalls of the head tube  30  thus providing at least two walls of positive engagement. The head tube  30  and handlebar stem  142  may be configured to provide positive engagement between the rear wall of the head tube  30  and the rear wall of the handlebar stem  142  in the most rearward position within the head tube  30 . In this manner, there is positive engagement between three walls of the head tube and the handlebar stem. 
     Other tube shapes, such as a triangle, a trapezoid with curved walls, a triangle with curved walls, and a star or other complex shape, may be used to provide the wedging effect achieved by the trapezoidal configuration described herein. Alternatively, the exercise bicycle of the present invention may also be fitted with a conventional cylindrical head tube and corresponding cylindrical handlebar post or a conventional square type head tube and corresponding square handlebar post. However, the trapezoidal tubing configured to provide a wedging effect provides a plurality of points of positive contact along entire longitudinal faces of the interengaging tubes, which reduces wobble, squeaking, and imparts overall improved stability to the structure as compared with cylindrical or square tubing. In the case of cyclindrical tubing there is typically only a limited area of positive engagement provided by a circumferential collar at the very top of the head tube (which is used to fix the cylindrical handlebar post at a particular height). Moreover, cylindrical tubing based head tube and handlebar post structures (and seat tube and seat post structures) can sometimes result in the handlebar being unintentionally rotated within the head tube during use, which is not possible with the trapezoidal tubing of embodiments of the invention. In the case of square tubing, there is typically only positive engagement along one wall of the square tube opposite the pop pin. As with the trapezoidal tubing, square tubing based head tubes and handlebar posts cannot result in unintentional rotation of the handlebars. 
     Referring to  FIGS. 1–3 , the seat assembly  36  includes a seat post  190  adapted to be adjustably mounted within the seat tube  34 . A seat tube pop pin  192  is operably connected with the front wall of the seat tube  34 . The seat tube pop pin  192  operates in the same manner as the pop pin  152  on the head tube  30 , including having trapezoidal interengaging tubes. The seat post defines a plurality of apertures  194  along a front wall adapted to receive the seat tube pop pin  192  when the engaging cylinder is and aligned with one of the apertures. The apertures  194  in the front wall of the seat post  190  are sized to receive the engaging pin, but not the collar so that the collar will abut the front wall of the seat post when the engaging pin is inserted in one of the apertures, the same as the pop-pin structure in the head tube  30 , as described above. 
     A rearwardly extending lateral adjustment tube  196  is connected with the top of the seat post  190 . The lateral adjustment tube  196  defines an aperture  198  adapted to receive a lateral adjustment post  200 . The seat  38  is connected to an S-shaped post  202  that extends rearwardly and upwardly from the front portion of the lateral adjustment post  200 . In one example, a bottom wall of the lateral post  200  defines a plurality of apertures adapted to receive a seat pop pin  204  mounted on a bottom wall of the lateral tube  196 . Accordingly, the seat  38  may be adjusted forwardly or rearwardly by disengaging the seat pop pin  204  and sliding the seat post  200  forwardly or rearwardly within the seat tube  196  and engaging one of the apertures in the seat post  200  corresponding with the desired lateral (forward or rearward) position of the seat  38 . 
     A seat post insert  206 , in one example, is fit between the seat tube  34  and the seat post  190 . The seat tube insert  206  defines a flange  208  along its upper rim configured to rest on the top rim of the seat tube  34 . A single large aperture  207  is defined along the front wall of the insert which aligns with the seat tube pop pin  192 . The aperture is sized to receive both the engagement pin and the collar of the pop pin. A lateral tube insert  212 , in one example, is also fit between the lateral tube  196  and the lateral post  200 . The lateral insert  212  defines a flange  213  along its rear rim configured to engage the rear rim of the lateral tube. A single large aperture is defined along the lower wall of the insert which aligns with the seat pop pin  204 . As with the other inserts, the aperture is sized to receive the engagement pin and the collar of the pop pin. 
     In one example, the seat tube  34  and the seat post  190 , and the lateral tube  196  and the lateral post  200  use interengaging trapezoidal tubing structure described above to facilitate wedge engagement like the head tube  30  and handlebar stem  142  described earlier. As shown in  FIG. 4 , a front wall  215  of the seat tube is wider than a rear wall  217  of the seat tube, forming a trapezoid. A left  219  and a right  221  sidewall of the seat tube  34  converge toward each other between the outer edges of the front wall and the outer edges of the rear wall to define a trapezoidal aperture. The seat post  190  includes trapezoidal tubing adapted to fit within the trapezoidal aperture defined by the seat tube  34 . In one example, the front wall of the seat post  190  is wider than the rear wall of the seat post, and the sidewalls taper inwardly between the outside edges of the front wall and the outside edges of the rear wall. 
     The seat post  190 , in one example, is configured to be wedged rearwardly in the seat tube  34 . The seat tube pop pin  192  is substantially similar to the pop pin  152  described as the head tube  30  and related structure and operation as shown in  FIGS. 7A ,  7 B,  8 A, and  8 B. The engaging pin is adapted to engage one of the apertures  194  on the front wall of the seat post  190  to vertically position the seat. The spring is biased to push the engaging pin into one of the apertures. Biased in such a manner, the pop pin snaps into whatever apertures it is aligned with when the user is not pulling outward on the handle. Again, the operation of the interengaging trapezoidal seat tube  34  and seat post  190  work with the pop pin structure  192  identically to that shown in  FIGS. 7A ,  7 B,  8 A, and  8 B. 
     Referring to  FIG. 3 , the lateral seat tube  196  extends rearwardly from the seat post  190  and is positioned generally horizontal when the seat post  190  is mounted within the seat tube  34 . In one example, the seat mounting tube  196  includes a lower wall  223  having a greater width than an upper wall  225 , and with a left side wall  227  and right sidewall  229  tapering upwardly from the outer edges of the lower wall to the outer edges of the upper wall to define a trapezoidal aperture  198  adapted to receive the lateral seat post  200 . 
     The lateral seat post  200  is generally trapezoidal with an upper wall  230 , a lower wall  232 , and sidewalls  234  adapted to cooperate with the trapezoidal aperture defined by the lateral seat tube. In one example, when the lateral seat post  200  is loosely positioned within the seat mounting tube  196 , there is an upper gap between the upper wall of the lateral seat mounting tube  196  and the upper wall of the lateral seat assembly post  200 , and the lower wall of the lateral seat post  200  rests on the lower wall of the seat mounting tube  196 . 
     The pop pin  204  extends downwardly from the rear portion of the lower wall of the lateral tube  196 , and is housed in a boss  236  with a sleeve substantially similar or described with reference to the head tube  30 . The lateral seat post  200  may be adjusted forwardly or rearwardly by moving it forwardly or rearwardly within the lateral seat tube  196  and fixing the seat assembly post in a desired position with the pop pin  204 . The pop pin  204  is biased to draw the engaging pin into one of the apertures in the bottom of the lateral seat post  200 . The pop pin  204  may then be tightened to force the collar upwardly against the bottom wall of the lateral seat post  200  and wedge the lateral seat post  200  upwardly between the sidewalls of the seat mounting tube  196 . As the lateral seat post  200  is wedged upwardly, the upper gap closes and a lower gap opens, until the left and right side walls  234  of the lateral seat post firmly engage the left  227  and right  229  sidewalls of the lateral seat tube  196 . In this manner, at least two sidewalls of the lateral seat post positively engage at least two sidewalls of the lateral seat tube. The tubes may also be configured so that the upper wall  230  of the seat assembly post  200  positively engages the upper wall  225  of the seat mounting tube  198  thereby providing three walls of positive engagement. 
     An alternative embodiment of the seat assembly  36 ′ is shown in  FIG. 9 . In this example, the lateral seat tube  196 ′ includes a lower wall  223 ′ having a lesser width than the upper wall  225 ′, and with a left side wall  227 ′ and a right sidewall  229 ′ tapering downwardly from the outer edges of the upper wall to the outer edges of the lower wall to define a elongate trapezoidal aperture adapted to receive the lateral seat post  200 ′. The lateral seat post  200 ′ is also rearranged so that the upper wall  230 ′ of the lateral seat post is wider than the lower wall  232 ′, and the sidewalls  234 ′ taper downwardly from the outside edges of the upper wall to the outside edges of the lower wall. The lateral seat post  200 ′ defines a plurality of apertures  239  along its upper wall  230 ′. 
     The pop pin boss  236 ′, in this embodiment, extends upwardly from the rear portion of the upper wall  225 ′ and defines a threaded aperture that extends through the upper wall and is adapted to receive the sleeve. In this embodiment, when the pop pin  204 ′ is tightened within the sleeve, it engages the upper wall  230 ′ of the lateral seat post  200 ′ and wedges the seat post downwardly within the lateral seat tube  196 ′. As the lateral seat post  200 ′ is wedged downwardly, the left and right sidewalls  234 ′ of the lateral seat post  200 ′ firmly engage the left and right sidewalls ( 227 ′,  229 ′) of the lateral seat tube  196 ′. As with the first embodiment, at least two sidewalls of the lateral seat post positively engage at least two sidewalls of the lateral seat tube. The tubes may also be configured so that the lower wall  232 ′ of the seat assembly post positively engages the lower wall  223 ′ of the seat mounting tube thereby providing three walls of positive engagement. Again, in this embodiment, the pop pin and trapezoidal structure and operation are identical to that shown in  FIGS. 7A ,  7 B,  8 A, and  8 B. 
     For either embodiment of the seat assembly or the handlebar assembly, additional pop pins may be provided, such as an additional pop pin near the forward portion of the lateral seat tube adjacent the downwardly extending seat post. In this manner, the lateral seat post may be wedged within the lateral seat tube in at least two locations. 
       FIG. 10  illustrates an additional alternative embodiment of the monocoque frame structure. In this embodiment, the bottom support and bottom tube structure is removed. The monocoque frame member  210  extends from the rear support  212  to the head tube  214  and forks  216 , with the top support  218  being connected with the head tube  214 . The seat support  220  extends upwardly between the rear support  212  and the top support  218 . In this embodiment, the top support  218  may have a greater vertical dimension than the top support shown in  FIGS. 1–5 , to properly support the frame. This type of frame has a linearly extending profile made of the monocoque construction, and only has a rear support  212 , a front support  218 , and a drive assembly extending between the main body  222  and the flywheel. The rest of the structure of the exercise bicycle frame has the same structure and operation as previously described. 
     Although the present invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made by way of example, and changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims.