Note: Descriptions are shown in the official language in which they were submitted.
CA 02656761 2008-12-02
flat sections which may allow it to be easily and conveniently manipulated
with a wrench or
other suitable tool.
Description:
FIELD OF INVENTION
1. The invention describes an eccentric bottom bracket for a bicycle. It is
desirable to adjust
chain tension in bicycles so that related drivetrain components may function
properly. This
invention allows one to install an eccentric bottom bracket into a frame with
a standard
bottom bracket shell, as understood within the industry. The present invention
has a more
limited range than traditional eccentric bottom brackets, but offers the
advantage of being
able to be installed into any bicycle frame with a standard sized threaded
bottom bracket
shell. It does not require a frame with an oversized bottom bracket shell, as
is usually needed
to install an eccentric bottom bracket on a bicycle. It is further
advantageous in that it does
not require a separate oversized eccentric bottom bracket to be installed
into.
BACKGROUND OF THE INVENTION
1. A bicycle drivetrain must maintain optimal chain tension in order for the
chain and related
components to function properly. Chain tension is achieved by a number of
methods. One of
these uses a device known within the industry as an eccentric bottom bracket.
In a traditional
eccentric bottom bracket, a standard bottom bracket is installed within a
secondary cylinder.
The housing for the standard bottom bracket is eccentrically offset from the
central axis of the
secondary cylinder. Rotating the secondary cylinder within its oversized frame
shell positions
the axle fore or aft of the shell center. The resulting orientation provides
greater or lesser
tensiori on the drive chrin of the bicycle. Once oriented, the main cylinder
is locked into
position by diverse means, allowing the chain to retain it's set tension.
The present invention addresses the need within the bicycle industry for an
eccentric bottom
bracket of that may be installed into a standard bottom bracket shell, and is
of a unitary
design. Current designs for eccentric bottom brackets require that a bottom
bracket of
standard size be installed into a secondary, oversized cylinder. This
secondary cylinder
features an offset chamber into which the standard bottom bracket is installed
(US PATENT
4,808,147, US PATENT 697,944). This prevailing method requires that the
bicycle frame be
fitted with an oversized bottom bracket shell to accommodate the secondary
cylinder. Said
arrangement contributes weight, complexity, and cost to the incorporation of
an eccentric
bottom bracket. There is one known eccentric bottom bracket with some similar
features as
the proposed invention, but no patent or patent application is known. This
product is known as
the Exzentriker, and is manufactured in Germany by a company called
Trickstuff. This present
invention contains features not found on the Trickstuff eccentric bottom
bracket, which make
the present invention advantageous and unique.
By combining the bearing assembly of a standard bottom bracket with a cylinder
incorporating
offset housing for said assembly, the present invention results in a unitary
design. Said unitary
eccentric bottom bracket eliminates the secondary cylinder typical of
traditional eccentric
bottom brackets. A further important benefit of the unitary eccentric bottom
bracket is that a
compact arrangement is achieved. This compact unitary eccentric bottom bracket
can easily
be installed into a bicycle frame bottom bracket shell of standard width and
diameter, as
understood within the bicycle industry.
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Further, the proposed positioning and retaining system for the present
invention allows simple
installation into a standard bottom bracket shell without modification of the
bottom bracket
shell. This system provides for an extremely compact and robust method of
maintaining
rotational position of the unitary eccentric bottom bracket discs, well
understand by those
skilled in the arts of bicycle component design.
SUMMARY OF THE INVENTION
1. An eccentric bottom bracket for a bicycle that may be installed into a
standard bottom
bracket shell, as understood within the bicycle industry. Said eccentric
bottom bracket utilizes
the threads contained within a standard bottom bracket shell for installation
into the frame of
a bicycle. The eccentric bottom bracket can be installed into a bicycle frame
bottom bracket
shell of standard width and diameter, as understood within the bicycle
industry. No specialized
frame details or modifications such as set screws or pinch bolts are required.
The frame
attachment elements of the eccentric bottom bracket are two similarly
configured tubular
threaded cups. The threaded cups are externally threaded so that they may be
installed into a
standard threaded bottom bracket shell of a bicycle, just as any standard
bottom bracket
would. The invention does not depend on an oversized bottom bracket shell in
which to be
installed. The eccentric bottom bracket is composed of two similar assemblies,
each of which
thread into one end of a threaded bottom bracket shell of a bicycle. Together
the assemblies
support the crank arm spindle of the bicycle, at both ends of the spindle.
2. An eccentric bottom bracket for a bicycle that is of a unitary design and
construction. The
bearing and spindles of the crank arms are fitted directly within said
eccentric bottom bracket,
eliminating the need for a second, oversized cylinder for a bottom bracket to
be installed
eccentrically into. The unitary eccentric bottom bracket may be installed
into, but is not
restricted to, a bottom bracket shell of standard size and width, as
understood within the
bicycle industry. The eccentric bottom bracket incorporates bearings within
it, and does not
require a separate bottom bracket to be installed within it in order to
support the crank arm
spindle. Each threaded cup of the invention contains a receptacle in which a
disc is installed,
at either end of the bottom bracket shell in order to support the crank arm
spindle. In each
disc is an offset bore. In each offset bore is installed a bearing. A spacer
ring separates each
bearing from the inner face of the crank arm attached. This spacer ring
rotates with the crank
arm during pedaling, and prevents the crank arm from contacting the non
rotating elements of
the eccentric bottom bracket. The spacer rings have a secondary purpose, and
that is to locate
the crank arm at the correct distance from the bottom bracket shell, in order
to assure that
correct chain line is achieved between the front and rear drive sprockets of
the bicycle. By
rotationally positioning the two bearing discs, the crank arm spindle may be
positioned
forward or aft of the bottom bracket shell center. By positioning these discs,
the installed
crank arm spindle is moved forward or back relative to the center of the
bottom bracket shell.
This position adjustment moves the front drive sprocket of the bicycle forward
or back relative
to the drive sprocket of the rear wheel. This position adjustment allows the
eccentric bottom
bracket to impart greater or lesser tension onto the attached drive chain of
the bicycle, which
is advantageous for maintaining optimal chain tension.
3. An eccentric bottom bracket for a standard bicycle frame with a unique and
advantageous
method for rotationally adjusting and positioning the crank spindle in order
to optimize chain
tension. This method utilizes a pair of similar attachments that do not
require tools in order to
be manipulated. Said attachments are affixed to the discs that contain the
bearings which
support the crank arm spindle. The attachments may contain features such as
notches along
their perimeter, or other features that provide for gripping by hand or with
tools, in order to
rotationally position the attached discs and bearings contained within them.
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4. An eccentric bottom bracket for a standard bicycle frame with a simple
method for fixing
the spindle into the desired orientation. Said eccentric bottom bracket may be
installed into a
bicycle bottom bracket shell of standard width and diameter, as understood
within the bicycle
industry. The method for fixing the discs into position utilizes a plurality
of fasteners such as
set screws. These fasteners are distributed around the perimeter of the
retaining cups. The
fasteners are of sufficient quantity, and of uniform distribution that they
may be tightened
against the bearing disc regardless of it's rotational orientation without
damaging the bearing
disc. The fact that there are a plurality of fasteners, and their distribution
is essentially
uniform, means that one or more may be left untightened, or only lightly
tightened, so that no
damage is done to the thin section of the bearing disc wall.
5. An eccentric bottom bracket with a nominal 1/4 inch total adjustment range.
That is,
nominally 1/8 inch forward of the center position, and nominally 1/8 inch
rearward of the
center position of the bottom bracket shell. The actual range may be
fractionally less or more,
varying with manufacturing and assembly tolerances.
6. An eccentric bottom bracket that incorporates spacer rings between the
bearings and the
crank arms. The rings assist in locating the crank arms at the correct
distance from the bicycle
bottom bracket shell. The rings also allows the crank arm to press against
them, imparting
thrust against the bearings so that there is no lateral play within the
assembly. The ring is of a
sufficient thickness that it prevents the rotating crank arms from contacting
the non rotating
elements of the eccentric bottom bracket.
7. A dedicated tool to facilitate the installation, adjustment, and removal of
the eccentric
bottom bracket invention with economy and simplicity. The tools is affixed to
the threaded
cups in the same manner as the bearing discs are, that is by means of
fasteners such as set
screws or other threaded fasteners. After installation or removal, the tool
may be removed
from the threaded cups. The installation and removal tool has features such as
raised parallel
flat sections which may allow it to be easily and conveniently manipulated
with a wrench or
other suitable tool.
BRIEF DESCRIPTION OF THE DRAWINGS
1. Figure 1 is a side view of the bottom bracket of a typical bicycle frame.
The circular feature
at the junction of the three tubes is known as the bottom bracket shell of the
frame. For
purposes of clarity, this threaded tube will be referred to in this patent as
the bottom bracket
shell. In the case of the present invention, the bottom bracket component
being claimed is
known as an eccentric bottom bracket. The present invention will be described
by it's full
description of eccentric bottom bracket in this patent for purposes of
clarity.
The frame shown is a typical "double diamond" frame design. The present
invention is not
limited to any type of frame configuration. It is suitable for installation in
any bottom bracket
of standard size, as understood within the bicycle industry.
2. Figure 2 is a side view of the present invention installed into a bottom
bracket. The bearing
discs are in their rearward most position relative to the bottom bracket
center.
3. Figure 3 is a side view of the present invention installed into a bottom
bracket. The bearing
discs are in their forward most position relative to the bottom bracket
center,
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4. Figure 4 is a section view of the eccentric bottom bracket installed in a
bottom bracket. The
attached crank arms and spindle are shown to illustrate the complete assembly.
The eccentric
bottom bracket is depicted in it's neutral position. The bearing discs are
capable of being
moved nominally 1/8 inch forward of this position, or nominally 1/8 inch
rearward of this
position.
5. Figure 5 is an exploded section drawing showing all the component elements
of the
eccentric bottom bracket, as well as the bottom bracket into which they are to
be installed.
The eccentric bottom bracket is depicted in it's neutral position. The bearing
discs are capable
of being moved nominally 1/8 inch forward of this position, or nominally 1/8
inch rearward of
this position.
6. Figure 6 is a section view of the bottom bracket with eccentric bottom
bracket installed. The
eccentric bottom bracket is depicted in it's neutral position. The bearing
discs are capable of
being moved nominally 1/8 inch forward of this position, or nominally 1/8 inch
rearward of this
position.
7. Figure 7 is a side view of the component elements of the eccentric bottom
bracket.
8. Figure 8 is a side view of the installation tool, with the flats for tool
attachment facing the
viewer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is composed of similar left side and right side
elements, with the
exception of the installation tool. In order to simplify the descriptions, the
preferred
embodiments described below refer singularly to the elements of one side only,
but apply
equally to both the left and right side elements of the eccentric bottom
bracket.
1. A threaded retainer which is tubular in nature. The inside diameter is
large enough to
accommodate a 24mm diameter spindle, with room to move the spindle radially in
relation to
the central axis of the bottom bracket shell. The range of motion of the
spindle is nominally
1/8 of an inch forward or nominally 1/8 of an inch rearward, or to any point
in between, in
order that an attached crank and chainring assembly may impart adequate
tension on the
drive chain of the bicycle.
2. A threaded cup which is tubular in nature. One end is narrower on the
outside, and
externally threaded to install into a bottom bracket shell.
3. A threaded cup which is tubular in nature. One end is wider. The wider end
of the threaded
cup has a plurality of threaded holes located radially around it such that set
screws or other
fasteners may be used to fix a disc into a desired position within.
4. A threaded cup which is tubular in nature. One end is wider. The wider end
of the threaded
cup has a plurality of threaded holes located radially around it such that set
screws or other
fasteners may be used to fix a disc into a desired position within. The
threaded holes are of a
sufficient number that the disc may be fixed into any position without any of
the fasteners
placing undue pressure against the thin wall region of the disc.
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5. A disc that fits into the large end of the threaded cup. The disc may be
fixed into place
within the threaded cup by means of set screws or other fasteners.
6. A disc that fits into the large end of the threaded cup. This disc has an
offset or eccentric
hole to accommodate a bearing. The hole is offset nominally 1/8 of an inch
from the center of
the disc so that the disc, when being rotated, may impart adequate tension on
the drive train
of the bicycle. The disc may then be fixed into place within the threaded cup
by means of set
screws or other fasteners, as described in embodiment 4.
7. A bearing that supports the spindle element of the crank arm assembly. The
bearing is
installed into the disc, as described in embodiment 6.
8. A ring which transfers thrust loads from the crank arm to the bearing. The
ring has an inner
diameter which is no smaller than the inner diameter of the spindle. The ring
has an outer
diameter that is small enough that it may not interfere with other elements of
the eccentric
bottom bracket assembly. The ring assists in locating the crank arm at the
correct distance
from the bicycle bottom bracket shell. The ring also allows the crank arm to
press against it,
imparting thrust against the inner race bearings so that there is no play
within the assembly.
The ring is of a sufficient thickness that it prevents the rotating crank arms
from contacting
the non rotating elements of the eccentric bottom bracket.
9. A manipulation disc which is attached to the bearing disc described in
embodiment 5.
10. A manipulation disc which is attached to the bearing disc described in
embodiment 5. This
attachment allows the bearing disc to be manipulated into the desired position
after the crank
arm and spindle assembly has been installed. The manipulation disc is attached
to the bearing
disc by fasteners or other means. The inside surface of the manipulation disc
attaches to the
outside surface of the bearing disc.
11. A manipulation disc which is attached to the bearing disc described in
embodiment 5. This
attachment allows the bearing disc to be manipulated into the desired position
after the crank
arm and spindle assembly has been installed. The manipulation disc has
features and or a
texture which allows it to be manipulated by hand or by tools such that it hay
be rotated in
order to rotate the attached bearing disc into the desired position.
12. An installation tool that consists of a disc with features for
manipulation by a tool such as
a wrench, spanner, pliers, or other device. The installation tool fits
temporarily into the
threaded cup, in the location where the bearing disc is normally placed. The
fixing screws of
the threaded cup hold the installation tool in place. Rotating the
installation tools allows the
threaded cup to be threaded into the bottom bracket shell with adequate
torque.
VARIANTS
1. The invention embodies principles that can be applied to various bottom
bracket shell and
thread standards. The bicycle industry defines a standard bottom bracket shell
as one being
68mm or 73mm or sometimes 100mm in width, with a so called English (also known
as British
and I.S.O.) thread of 1.37 inches diameter with a thread pitch of 24 threads
per inch. This
standard uses right hand threads on the left side of the bottom bracket shell,
and left hand
threads on the right side of the bottom bracket shell. The various other less
typical thread
standards, known commonly as Italian, French, Swiss, Raleigh, and others can
also be covered
under this patent, since all that is required to work with those standards is
a minor change in
thread diameter, thread pitch, and thread direction.
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2. A manipulation disc described in embodiment 9. may also be integrated as
part of one
single component with the bearing disc to which it is attached. This unitary
manipulation disc
and bearing disc would function exactly as described in the preferred
embodiments where they
are described as separate elements.
3. An installation or removal tool as described in claim 6 may be configured
to allow for
interface with tools other than a standard wrench, such as hex wrenches or
even custom
designed tools.
