Bicycle crank and pedal structure

An extender arm for a bicycle crank arm consists of a generally cylindrical structure suitable for being slidably mounted on the crank arm of the bicycle. The distal end of the extender includes an opening for the mounting of a bicycle pedal. The extender arm contains at least one opening in its side for receipt of a bolt or fastener which will extend through the extender arm and into the opening at the end of the crank arm for receipt of a pedal. In one embodiment, the extender also includes a set screw at the proximal end opposite the distal end on which the pedal is mounted for stabilizing the extender arm on the crank arm.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a bicycle crank and pedal structure and in 
particular to a bicycle crank capable of being adjusted for use with legs 
of different lengths. 
2. Prior Art 
A number of different techniques exist for adjusting the crank of a 
bicycle. U.S. Pat. Nos. 4,648,287; 4,599,915; 4,446,753; 3,922,929 and 
3,888,136 all disclose structures for adjusting the length of a bicycle 
crank arm. However, each of the structures disclosed in these patents is 
relatively complicated and sophisticated and therefore expensive. A need 
exists for a simple, adjustable bicycle crank arm. 
SUMMARY OF THE INVENTION 
This invention overcomes certain of the disadvantages of the prior art by 
providing an extender for a bicycle crank arm which is simple and 
economical yet easy to use. Moreover, the adjustable bicycle crank arm of 
this invention is adjustable over a range of distances up to the length of 
the crank arm to which the bicycle pedal is attached. 
In accordance with this invention, an adjustable bicycle crank consists of 
a hollow tubular structure with an opening formed at one end through the 
tubular walls for receipt of a pedal. The inner surface of the hollow tube 
is adapted to slide longitudinally along the bicycle crank arm. Holes 
through the sides of the tubular structure are placed so as to allow the 
passage of a pin (typically a bolt) through the holes into the opening at 
the end of the bicycle crank arm in which the bicycle pedal is usually 
inserted. The tubular extension contains at its distal end an opening, the 
interior surface of which is, if desired, threaded to receive the mounting 
bolt of the bicycle pedal. Thus the bicycle pedal can be mounted on the 
distal end of the extension in the same manner as it is normally mounted 
on the end of the crank arm. 
This invention will be more fully understood in conjunction with the 
following detailed description taken together with the attached drawings.

DETAILED DESCRIPTION 
While two embodiments of this invention will be shown, other embodiments of 
this invention will be obvious in view of the following description. 
FIG. 1 illustrates the cylindrical bicycle crank arm extender 13 of this 
invention mounted on a bicycle crank arm 11a. By "tubular" is meant only 
that the extender 13 is hollow with an interior shape such that extender 
13 slides easily over crank arm 11a. The external surface of extender 13 
can be any desired shape in cross-section, such as round, square or 
rectangular. Crank arm 11a is mounted in a well-known manner in a housing 
12 containing bearings and lubricant and is symmetrically balanced with 
crank arm 11b extending from the opposite side of mounting structure 12. 
Extender 13 contains a plurality of holes 14-1, 14-2, 14-3, 14-4 and 14-5 
through which a mounting pin 16 (typically a bolt) can be inserted. Holes 
14-i are perpendicular to the plane of rotation of crank arm 11a. Bolt 16 
is shown in hole 14-1. Bolt 16 can be threaded on the shank 16b to allow 
it to be mounted in the threaded opening 11c (FIG. 3) formed in the bottom 
of crank arm 11a' to receive pedal 17. Should the opening in the bottom of 
crank arm 11a not be threaded, bolt 16 extends through the opening and is 
attached to crank arm 11a with nut 16a (FIG. 2b). As shown in FIG. 2b, 
bolt 16 has nut 16a mounted on its inner end to hold the extender 13 in 
place on crank arm 11a. By "inner end" is meant the end of bolt 16 facing 
inward away from the leg of the rider to prevent the pant leg of the rider 
from snaring on the threaded end of bolt 16. For the same reason, head 16c 
of bolt 16 is preferably smooth and rounded. 
To adjust the crank arm extender 13, bolt 16 is removed from the opening 
14-1, the crank arm extender 13 is slid up crank arm 11a until the desired 
one of openings 14-1, 14-2, 14-3, 14-4 or 14-5 align with the pedal 
opening (FIG. 3) in the bottom of crank arm 11a. Bolt 16 is then 
reinserted through the desired opening 14-i into the opening 11c in the 
bottom of crank arm 11a and the extender is thus mounted firmly on crank 
arm 11a. 
FIG. 2a shows a top view of the extender with pedal 17 mounted in opening 
13a (FIG. 2b) in the bottom of extender 13. Opening 13a is adapted to 
receive end 18a of the pedal mounting bolt 18 (FIG. 1). Nuts 18b and 18c 
(FIGS. 2a and 2b) are shown in FIG. 2b as holding pedal 17 on extender 13. 
Should the opening 13a (shown in dashed line in FIG. 2b) be threaded, then 
the extension 18a of pedal bolt 18 is also threaded so as to rotatably 
mount in the opening 13a. 
FIG. 3 shows an exploded view of the bicycle crank arm extender 13' of this 
invention in relation to regular bicycle crank arm 11a'. The cross-section 
of the interior opening of extender 13' is contoured to match the 
cross-section of bicycle crank arm 11a'. Openings 11c and 11d are shown at 
the ends of crank arms 11a' and 11b' for receipt of either the end 18a of 
pedal mounting bolt 18 or the bolt 16 used to mount the extender arm 13' 
on crank arm 11a' or 11b'. While not shown, in practice, two extenders 13' 
will be used at the same time, one on crank arm 11a' and one on crank arm 
11b'. Of interest, the two extenders can beadjusted differently to allow a 
person with two legs of different lengths to ride a bicycle more 
comfortably. 
As shown in FIG. 4, in an alternative embodiment, extender 13' has set 
screws 19a and 19b mounted in the proximal end (i.e., the end furthest 
from the pedal 17) to stabilize and center the extender 13' on crank arm 
11a'. The center line along the longitudinal axes of set screws 19a and 
19b is in, or parallel to, the plane of rotation of crank arms 11a' and 
11b'. 
The extender 13 of this invention will fit existing bicycle pedal crank 
arms such as arms 11a and 11b and is adjustable to fit the length of each 
leg of the person riding the bicycle. The extender arm 13 of this 
invention is particularly useful on a children's bicycle because it 
extends the useful life of the bicycle by a substantial period of time. 
Naturally the extender arm 13 can only be extended on the crank 11a to a 
distance which does not allow the pedal 17 to hit the pavement or road 
when the bicycle is being ridden either straight or around corners. 
However, the extender arm 13 of this invention does allow the bicycle 
crank to be adjusted for the particular leg length of the bicycle user. 
Thus as a child grows, the seat on a bicycle can be adjusted and now, with 
the extender arm 13 of this invention, the pedals can also be adjusted. As 
the extender 13 is extended the torque applied to pedal 17 about center 
line 12a (FIG. 3) through crank housing 12 increases, making the bicycle 
somewhat easier to ride but increasing the stress loads on crank arms 11a 
and 11b. 
In mounting the extender 13 on the crank arm 11a, the pedal 17 is removed 
from opening 11c in crank arm 11a, the pedal 17 is fastened to the bottom 
of extender arm 13 in the opening 13a (FIG. 2b) provided for end 18a of 
pedal bolt 18, the substantially cylindrical extender arm 13 is then slid 
over crank arm 11a until the desired opening 14-i lines up with opening 
11c. Extender 13 is then fastened to crank arm 11a by inserting bolt 16 
through opening 14-i into opening 11c of crank arm 11a. If set screws 19a 
and 19b are used, these screws are properly tightened down to center and 
firmly hold extender arm 13 on crank arm 11a. 
The above description is meant to be illustrative and not limiting.