Abstract:
A crank assembly for fitness equipment includes a ductile spacer engaged between a crankshaft mounting surface and a crank arm mounting surface at the interface thereof and conforming respectively to each to maximize surface contact area to distribute loads across a larger area.

Description:
BACKGROUND AND SUMMARY 
     The invention relates to exercise fitness equipment, and more particularly to a crank assembly therefor. 
     The joint between a crank arm and a crankshaft is one of the most important joints on a piece of fitness equipment. On an upright stationary bike, for example, this joint supports the loads generated by the exercise and the user&#39;s body weight. The crank arm may be mounted to the crankshaft along a tapered square. The crank arm is typically steel or aluminum, and the crankshaft is typically steel. Assembly and disassembly of the parts reveal markings, which indicate less than optimal surface contact. 
     The present invention arose during continuing development efforts in the above technology and provides a simple, economical system for maximizing surface contact between the crank arm and the crankshaft, distributing the loads across a large area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view, partially exploded, of a portion of a piece of fitness equipment such as a stationary bike. 
         FIG. 2  is an exploded perspective view of a portion of the apparatus of  FIG. 1 . 
         FIG. 3  is an assembly view of the components of  FIG. 2 , partially in section. 
         FIG. 4  is a side sectional view of a portion of the structure of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a crank assembly  10  for fitness equipment  12 , such as a stationary bike or other exercise equipment. The crank assembly includes a crankshaft  14 ,  FIGS. 2-4 , extending along an axis  16  and rotational about the axis. The crank assembly includes a crank arm  18  mounted to crankshaft  14  at a keyed interface  20  and extending radially therefrom relative to axis  16 . The crank arm is mounted to the crankshaft by a threaded bolt  15 , which may be covered at its head by a protective and/or decorative cap  17 . In one embodiment, such as a stationary bike, a pedal  22  is mounted at the end of crank arm  18  in journaled rotational relation for engagement by the foot of the user. The crankshaft has an opposite end with a keyed interface  24  for engaging an opposite crank arm and pedal, not shown. 
     Crankshaft  14  and crank arm  18  each have a mounting surface  26  and  28 , respectively,  FIG. 2 , facing each other at interface  20 . A ductile spacer  30  is engaged between crankshaft mounting surface  26  and crank arm mounting surface  28  at interface  20 . Ductile spacer  30  has distally opposite facing surfaces, namely a first facing surface  32  facing and engaging crankshaft mounting surface  26 , and a second facing surface  34  facing and engaging crank arm mounting surface  28 . Ductile spacer  30  is of a constituent material softer than at least one of mounting surfaces  26  and  28 . In the preferred embodiment, the constituent material of ductile spacer  30  is softer and more malleable than both of the mounting surfaces  26  and  28 , such that first facing surface  32  conforms to crankshaft mounting surface  26  and maximizes surface contact area therewith, and such that second facing surface  34  conforms to crank arm mounting surface  28  and maximizes surface contact area therewith. In one embodiment, and as is typical, crankshaft  14  is steel, and crank arm  18  is steel or aluminum. In one preferred embodiment, ductile spacer  30  is copper. 
     Ductile spacer  30  has a keyed cross-sectional shape along a cross-sectional plane taken transversely to axis  16 . In  FIG. 4 , the noted cross-sectional plane extends into and out of the page. The noted keyed cross-sectional shape of ductile spacer  30  preferably has at least one straight side. Further in the preferred embodiment, ductile spacer  30  extends axially along axis  16  and is frustoconically tapered relative to axis  16 . Crankshaft  14  extends axially away from keyed interface  20  along a first axial direction, e.g. leftwardly in  FIGS. 2-4 . Frustoconically tapered ductile spacer  30  has first and second perimeters  36  and  38 . First perimeter  36  is larger than second perimeter  38 . First perimeter  36  is axially spaced from second perimeter  38  along the noted first axial direction, i.e. larger perimeter  36  is spaced axially leftwardly of smaller perimeter  38  in  FIGS. 2-4 . 
     In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different configurations, systems, and method steps described herein may be used alone or in combination with other configurations, systems and method steps. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims.