Title
TOOTHED SPROCKET HUB WITH ELASTIC CENTERING ELEMENT
Field of the Invention
The invention relates to a toothed sprocket, and
more particularly to a toothed sprocket with elastic
centering element having a first surface disposed on a
bending beam and radially moveable, a second surface
radially moveable to a lesser extent that the first
surface, and a third surface in cooperative relation to a
second surface, the third surface bearing upon the outer
surface of the input shaft, the third surface having a
clearance fit with the outer surface.
Background of the Invention
Chain drives are the predominant means of power
transmission on two-wheelers such as bicycles. Chains are
also used for power transmission on numerous machines.
Very often, the chain sprockets are connected to a shaft
via a form-fitting shaft/hub connection. In general,
these and other connections work with local elevations
and depressions with respect to a cylinder-shaped
connection surface. Some free play fit between the shaft
and hub is important for the proper function of these
connections. However, under load and if tolerances
between the shaft and hub are too large, it can lead to
wobbling between the two components. This is considered
negative. On the other hand high-quality fits are
relatively expensive to manufacture using machining
processes. This is a disadvantage when one has to
manufacture low-cost mass products.
The chain sprocket is usually thin on affordable
bikes with hub gears. This component is typically two to
three millimeters wide and is usually a stamped part made
of steel and has three or more drive cams with teeth
which engage grooves which are located on the input shaft
of the hub gear. The fit between these two components is
usually a clearance fit. This is necessary in order to
employ low-cost manufacturing methods such as sintering,
casting or stamping. To prevent the sprocket from moving
axially on the input shaft, it is typically held in
position by a lock washer or snap ring.
In recent years, many chain drives in automotive
technology and general drive technology were replaced by
toothed belt drives. Advantages include lower weight,
longer service life, less noise and operation without
lubricant. Especially in the field of bicycles with hub
gears, toothed belt drives according to EP000002289792A1,
CA000002749293A1 and US000007854441B2 are becoming more
prevalent .
Because a functioning toothed belt drive requires a
defined preload on the belt, a wobbling toothed belt disk
on the rear hub would not be able to maintain a constant
tension. If the toothed belt disk is not centered and
tightly fixed on the rear hub, there can be operating
noises as the toothed sprocket moves on the input shaft.
The consequence can be squeaking and creaking noises.
Rear hubs with hub gears from all major
manufacturers have a centering diameter, which, due to
low-cost manufacturing methods, have typical tolerances
of plus/minus 0.15 millimeters in the area of the input
shaft. If one intends to manufacture inexpensive toothed
sprockets without machining by sintering or investment
casting, then the manufacturing process requires also
bore tolerances in the area of plus/minus 0.15
millimeters. Considering the boundary conditions of the
assembly both components can thus be combined only with a
certain play. This is the problem of deficient centering
when using a toothed sprocket with a spline shaft profile
in combination with inexpensively available hub gears.
Means are available to absorb excess tolerance in
the component fit between a toothed sprocket and a hub
gear. The sprocket relies on a bending beam which
absorbs the fit tolerance. The art comprises a sprocket
having a first radially movable surface which has a
diameter slightly smaller than the hub to which it is
mounted. A second surface prevents relative rotation of
the parts. Representative of the art is US application
serial number US20150016880A1 which discloses a shaft/hub
connection for vehicles or for use in drive systems with
a cylinder-shaped shaft component, containing elevations
or depressions on the lateral surface and a hub component
having a bore, including inside the bore also elevations
or depressions, whereby the shaft component can be
mounted inside the bore of the hub component. It is
further distinguished in that inside the bore of the hub
component at least 2 surfaces are arranged such that an
elastic deformation of these surfaces in the radial
direction is possible and inside the bore of the hub
component at least 2 surfaces are arranged such that an
elastic deformation of these surfaces in the radial
direction is less possible. In addition, the shaft/hub
connection is characterized in that the elastically
deformable surfaces are connected in a materially bonding
manner with the elastically less deformable surfaces.
What is needed is a toothed sprocket having a first
surface disposed on a bending beam and radially moveable,
a second surface radially moveable to a lesser extent
that the first surface, and a third surface in
cooperative relation to a second surface, the third
surface bearing upon the outer surface of the input
shaft, the third surface having a diameter greater than
the diameter of the outer surface. The present invention
meets this need.
Summary of the Invention
The primary aspect of the invention is a toothed
sprocket having a first surface disposed on a bending
beam and radially moveable, a second surface radially
moveable to a lesser extent that the first surface, and a
third surface in cooperative relation to a second
surface, the third surface bearing upon the outer surface
of the input shaft, the third surface having a diameter
greater than the diameter of the outer surface.
Other aspects of the invention will be pointed out
or made obvious by the following description of the
invention and the accompanying drawings.
The invention comprises a toothed sprocket hub with
elastic centering element comprising an input shaft
having a receiving portion and a cylindrical outer
surface, a sprocket engagable with the input shaft, the
sprocket comprising at least two first surfaces each
disposed on a bending beam such that each first surface
is elastically moveable in a radial direction, the two
first surfaces bearing upon the outer surface, the two
first surfaces each having a radius d that is less than a
radius D of the outer surface, at least one second
surface that is radially moveable to a lesser extent than
a first surface, the second surface engaging the
receiving portion to prevent a relative rotation of the
sprocket with the input shaft, and a third surface in
cooperative relation to the second surface, the third
surface bearing upon the outer surface of the input
shaft, the third surface having a clearance fit with the
outer surface.
Brief Description of the Drawings
The accompanying drawings, which are incorporated in
and form a part of the specification, illustrate
preferred embodiments of the present invention, and
together with a description, serve to explain the
principles of the invention.
Fig. 1 shows a rear hub of a bicycle without spokes
or rim.
Fig. 2 is an exploded view of Fig. 1 .
Fig. 3 is an isometric presentation of the
embodiment of a toothed sprocket.
Fig. 4 shows a side view of a toothed sprocket.
Fig. 5 is a side view of the sprocket on an input
shaft.
Detailed Description of the Preferred Embodiment
FIG. 1 shows a rear hub 1 of a bicycle without
spokes or rim. Torque is transmitted to a toothed belt
drive via a foot pedal or crank (not shown) . The toothed
belt transfers torques to the toothed sprocket 7 , which
in turn drives the input shaft 2 .
This arrangement transmits torque via a shaft/hub
connection 4 into the hub input shaft. A bicycle rim
with tire (not shown) is driven by the rear hub 1 via
spokes that are mounted inside the spoke holes 3 . This
is a known structure on a bicycle wheel. Toothed sprocket
7 is held axially on the input shaft 2 via a snap ring 6 .
Sprocket 7 transmits torque via three receiving
portions or grooves 5 which are engaged by projections
10. Cylinder-shaped outer surface 16 provides for
correct centering of the toothed sprocket 7 on the input
shaft 2 . However, correct centering is only possible if
the bore 9 of toothed sprocket 7 is seated without play
in relation to the cylinder-shaped lateral surface 16.
This is achieved in the radial direction by elastically
movable bending beams 14 and thereby through each surface
12. Each beam surface 12 exerts pressure against surface
16 and in this manner absorb manufacturing tolerances.
Each bending beam 14 extends approximately tangentially
to the outer surface 16.
FIG. 2 is an exploded view of Fig. 1 . Input shaft 2
has at a shaft component 11 a shaft/hub connection 4 ,
which transmits torque from the toothed sprocket 7 into
the hub input shaft 2 . Lock washer 6 is shown in a
disassembled state. Grooves 5 on the input shaft 2 are
shaped such that projections 10 inside the bore 9 of the
toothed sprocket 7 accurately engage therein.
Within bore 9 are disposed three surfaces 12, which
are arranged such that an elastic movement of these
surfaces in the radial direction is possible. Elastic
movement of these three surfaces 12 is achieved through
three bending beams 14, which are shaped such that they
form the bore 9 with a radius "d" . In this embodiment
radius "d" of the toothed sprocket 7 disconnected from
the input shaft 2 is always less than the shaft radius
"D" of surface 16. Each of the three surfaces 12 of the
toothed sprocket 7 deform elastically radially outward
during assembly and thereby create precise centering of
sprocket 7 on input shaft 2 . Each bending beam 14
comprises surface 12, which can deform elastically
radially, and surface 13. Surface 13 is responsible for
the form-fitting torque transmission and cannot deform
elastically radially. Bending beams 14 with the elastic
movable surfaces 12 form the elastic centering elements
of the inventive sprocket.
FIG. 3 is an isometric presentation of the
embodiment of a toothed sprocket 7 . Bore surface 9
contacts surface 16 and grooves 5 from FIG. 1 with
surface 12, surface 13 and surface 17. Only radial
projections 10 with surface 13 are made with a clearance
fit with respect to the input shaft 2 of FIG. 2 .
Surfaces 12 can be considered moveable in terms of radial
deformability, because they are connected to the rigid
remaining body of the toothed sprocket 7 via bending beam
14. Elastically deformable surfaces 12 of bore 9 are
joined with elastically non-def ormable surfaces 13.
Elastically deformable surfaces 12 are joined with rigid
surface 13. Elastically deformable surfaces 12 and the
elastically rigid surfaces 13, which contact the input
shaft 2 on surface 16, are always smaller in diameter
than surface 16.
Each surface 17 bears upon surface 16. Each surface
17 is adjacent to each surface 13. Each surface 13 is
disposed between a surface 17 and a surface 12. Each
surface 17 adds support for loads caused by torque input
while maintaining a normal fit and manufacturing
tolerance range. By doing so surface 17 reduces stress
on each bending beam 14, thereby enhancing durability of
each bending beam 14 and the toothed sprocket 7 . Surface
17 does not engage groove 5 but instead engages outer
surface 16 directly.
FIG. 4 shows a side view of a toothed sprocket 7 .
Surfaces 13 of bore 9 are designed as a radial projection
10 and are manufactured with a clearance fit relative to
the grooves 5 of the input shaft 2 . Spline shaft profile
15 is represented here by a dashed line. The entire
surface of bore 9 does not contact the cylinder-shaped
lateral surface 16 from FIG. 2 . The profile
circumference of the bore is approximately 25% larger
than the surface of the shaft. In terms of radial
deformability, surfaces 13 can be considered rigid and
relatively inelastic. Here, the radial direction of
movement of surfaces 13 is shown with an arrow "B" .
Surfaces 12 can be considered elastic in terms of radial
deformability, because they are connected to the toothed
sprocket 7 via bending beam 14. The radial direction of
movement of the elastic surfaces 12 is shown with an
arrow "C" .
A toothed sprocket hub with elastic centering
element comprising an input shaft having a receiving
portion and a cylindrical outer surface, a sprocket
engagable with the input shaft, the sprocket comprising
at least two first surfaces each disposed on a bending
beam such that each first surface is elastically moveable
in a radial direction, the two first surfaces bearing
upon the outer surface, the two first surfaces having a
diameter that is less than a diameter of the outer
surface, at least one second surface that is radially
moveable to a lesser extent than a first surface, the
second surface engaging the receiving portion to prevent
a relative rotation of the sprocket upon the input shaft,
and a third surface in cooperative relation to the second
surface, the third surface bearing upon the outer surface
of the input shaft, the third surface having a diameter
greater than the diameter of the outer surface.
Fig. 5 is a side view of the sprocket on an input
shaft. In this view snap ring 6 is removed for clarity.
Each projection 10 engages a receiving portion 5 . Each
projection 10 prevents sprocket 7 from rotating relative
to the input shaft 2 . Surface 12 and surface 17 each
engage outer surface 16 of input shaft 2 . Surface 12 and
surface 17 properly locate sprocket 7 on input shaft 2 .
Each surface 12 is moveable radially inward and outward
due to the flexibility of each bending beam 14. This
embodiment illustrates three bending beams 14 by way of
example and not of limitation. This embodiment
illustrates three surfaces 17 by way of example and not
of limitation. This embodiment illustrates three
receiving portions 5 and three projections 10 by way of
example and not of limitation.
The inventive system is advantageous over splines
because it relies on fewer receiving portions 5 , which in
turn reduces the expense and need for controlling close
tolerances during manufacturing. Surfaces 12 and 17 are
used for centering alignment with input shaft 2 . This in
turn relies upon the accuracy of outer surface 16 which
is easily achieved in the art. The flexibility of each
bending beam 14 allows absorption of greater and
therefore less expensive manufacturing tolerances.
Although a form of the invention has been described
herein, it will be obvious to those skilled in the art
that variations may be made in the construction and
relation of parts without departing from the spirit and
scope of the invention described herein.

Claims
I claim:
1. A toothed sprocket hub with elastic centering element
comprising :
an input shaft having a receiving portion and a
cylindrical outer surface;
a sprocket engagable with the input shaft;
the sprocket comprising at least two first surfaces
each disposed on a bending beam such that each first
surface is elastically moveable in a radial direction,
the two first surfaces bearing upon the outer surface,
the two first surfaces each having a radius d that is
less than a radius D of the outer surface;
at least one second surface that is radially
moveable to a lesser extent than a first surface, the
second surface engaging the receiving portion to prevent
a relative rotation of the sprocket with the input shaft;
and
a third surface in cooperative relation to the
second surface, the third surface bearing upon the outer
surface of the input shaft, the third surface having a
clearance fit with the outer surface.
2 . The toothed sprocket as in claim 1 , wherein each
bending beam is oriented tangentially to the input shaft.
3 . The toothed sprocket as in claim 1 , wherein the
receiving portion comprises a groove in the outer
surface .
4 . The toothed sprocket as in claim 1 further comprising
at least three first surfaces, at least three second
surfaces and at least three third surfaces.
5 . The toothed sprocket as in claim 1 , wherein the
second surface is disposed between the first surface and
the third surface.
6 . The toothed sprocket as in claim 1 further comprising
a retaining member for axially retaining the sprocket on
the input shaft.
7 . The toothed sprocket as in claim 1 , wherein the
second surface comprises a projection for engaging the
receiving portion.