Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
VARIABLE RATIO DRIVE SYSTEM
FIELD OF THE INVENTION
The present invention relates to drive systems. More
particularly, the present invention relates to a drive system including a
variable diameter sprocket.
BACKGROUND OF THE INVENTION
Variable diameter sprockets are well known in the art.
For example, Unites States patents numbers 4,030,373; 4,832,660;
5,041,061; 5,013,284; 5,094,653; and 5,104,357 all naming Hamlin
Leonard as an inventor, each describes variable speed drive systems for
bicycles provided with variable diameter pulleys. By modifying the
diameter of the variable diameter pulley, the ratio of the front to rear
pulleys is modified.
The systems described by Leonard do not use a
conventional bicycle chain but instead use a flexible driving means under
the form of a V-belt. The different mechanisms described by Leonard
have the same common drawback that the diameter changing
mechanisms provided to modify the diameter of the pulley are generally
complex. The use of a V-belt is also a drawback since it must be
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tensioned to prevent it from slipping. It is also to be noted that adverse
temperature conditions, such as rain, may nevertheless cause the V-belt
to slip in the pulleys.
OBJECTS OF THE INVENTION
An object of the present invention is therefore to provide
an improved variable ratio drive system.
It is a further object of the present invention to provide
a variable ratio drive system using a conventional chain.
It is also an object of the present invention to provide a
variable ratio drive system provided with an improved sprocket diameter
changing mechanism.
Other objects, advantages and features of the present
invention will become more apparent upon reading of the following non
restrictive description of preferred embodiments thereof, given by way of
example only with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the appended drawings:
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Figure 1 is a front elevational view of a variable ratio
drive system according to an embodiment of the present invention;
Figure 2 is a rear elevational view of the variable
diameter sprocket of the variable ratio drive system of Figure 1;
Figure 3 is a sectional view taken along line 3-3 of
Figure 1; and
Figure 4 is a schematic view illustrating the operation of
the sprocket diameter changing mechanism.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning now to Figures 1-3 of the appended drawings
a variable ration drive system 10 according to an embodiment of the
present invention will be described.
It is to be noted that while the variable ratio drive system
10 is illustrated and described herein as replacing the front sprocket of a
bicycle drive system, the general principles of the present invention could
as well be designed as a rear sprocket cluster replacement or as a
replacement of virtually any sprocket clusters for other applications.
The system 10 generally includes a variable diameter
sprocket 12 and a sprocket diameter changing mechanism 14.
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The variable diameter sprocket 12, better seen from
Figure 2, is configured and sized to be mounted to a conventional shaft
15 of a bicycle (shown in dashed lines in the figures) via a mounting
sleeve 17. The variable diameter sprocket 12 is provided with a support
16 including a central portion 18, a peripheral portion 20 and six (6) radial
branches 22a-22f extending from the central portion to the peripheral
portion in a symmetrical fashion. The branches 22a-22f are defined by
identical cutouts 24a-24f. The variable drive sprocket 12 also includes six
sprocket portions 26a-26f mounted to a respective branch 22a-22f of the
support 16.
For concision purposes and since the variable diameter
sprocket 12 is symmetrical, only branch 22a and its respective sprocket
portion 26a will be described in greater details hereinbelow.
Branch 22a includes a radial channel 28a and five (5)
radially aligned circular apertures 30, 32, 34) 36 and 38 provided in the
radial channel 28a.
The sprocket portion 26a includes a dented portion 40,
a channel engaging portion 42, better seen in Figure 3, integrally formed
with the dented portion 40 and provided with an internally threaded
aperture 44, a threaded pin 46 engaged to the aperture 44, including a
pan head 47, and configured and sized to enter any of the apertures 30-
38 and a spring 48 fixedly mounted to the shaft 15 and slidably mounted
to an aperture 50 of the pin 46.
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The width of the channel engaging portion 42 is slightly
smaller than the width of the channel 28a allowing the sprocket portion
26a to be radially and laterally moved therein. When a sufficient lateral
movement of the sprocket portion 26a is obtained, the pin 46 will egress
5 the aperture in which it is inserted (aperture 32 in Figures 1-3) and radial
movement of the sprocket portion 26a will be possible.
The direction of the force applied by the spring 48 (see
arrow 52 in Figure 3) maintain the pin 46 in one of the apertures 30-38
unless an external force is applied as will be described hereinafter.
Turning now more specifically to Figure 3 of the
appended drawings, the sprocket diameter changing mechanism 14
includes a fixed assembly 54 fixedly mounted to the bicycle and a
movable assembly 56 so mounted to the fixed assembly 54 as to be
longitudinally movable (see double-arrow 58).
The fixed assembly 54 includes a bracket 60 mounted
to the bicycle via a plate 62 and a fastener 64. The bracket 60 includes
a longitudinal slot 66 to which the movable assembly 56 may be mounted.
The movable assembly 56 includes a support 68 slidably
mounted to said slot 66 via a fastener 70, a first angled abutting element
72 and a second angled abutting element 74. As will be described
hereinafter in greater details, the first angled abutting element 72 has the
function to selectively reduce the diameter of the variable diameter
sprocket 12 while the second angled abutting element 74 has the function
to selectively increase the diameter of the variable diameter sprocket 12.
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The first and second angled abutting elements 72 and
74 respectively include bevels 76, 78 having angles similar to the angle
of the pan head 47 of the pin 46. The distance between the first and
second angled abutting elements 72 and 74 is slightly larger than the
width of the pin 46, therefore allowing the pin to thread between the first
and second angled abutting elements 72 and 74 when the pin 46 is
correctly positioned for the desired diameter of the variable diameter
sprocket 12.
Of course, as will be easily understood by one skilled in
the art upon reading the following description of the operation of the
sprocket diameter changing mechanism 14, the sprocket diameter
changing mechanism 14 also includes means (not shown), fixedly
mounted to the fixed assembly 54 to move the movable assembly 56 (see
double arrow 58) upon user's control, as will be described hereinbelow.
It is also to be noted that if variable diameter sprockets
according to the present invention are used to replace the front and rear
sprocket clusters of a bicycle, the movable assembly moving means (not
shown) could be linked to provide a single user's operable lever to
actuate both sprocket diameter changing mechanisms.
Turning now to Figure 4 of the appended drawings, the
operation of the variable diameter sprocket 12 will now be described.
It is to be noted that, in Figure 4, branch 22a is
illustrated twice in different positions as the sprocket 16 is rotated (see
arrow 80). More specifically, Figure 4 illustrates the sprocket portion 26a
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as it is moved from the second aperture 32 of the channel 28a to the third
aperture 34 of the same channel.
To cause the movement of the sprocket portion 26a, the
movable assembly 56 of the sprocket diameter changing mechanism 14
is moved outwardly (see arrow 82). This movement will place the second
angled abutting element 74 in the path of the rotating pin 46 of the
sprocket portion 26a. The head 47 will therefore contact the bevel 78 of
the second angled abutting element 74. Because of the physical
relationship between the sprocket diameter changing mechanism 14 and
the variable diameter sprocket 12 this contact will laterally move the
sprocket portion 26a so that the pin 46 egress the aperture 32. The angle
of the abutting element 74 will then radially move the sprocket portion 26a
inside its channel 28a. When the position of the variable diameter
sprocket 12 is such that the head 47 no longer contacts the abutting
element 74, the sprocket portion 26a is then moved back laterally causing
the pin 46 to enter the aperture 34, completing the displacement of the
sprocket portion 26a.
Of course, as will be easily understood by one skilled in
the art, upon a full rotation of the variable diameter sprocket 12, the six
sprocket portions 26a-26f will be moved from the aperture 32 to the
aperture 34 of their respective channels 28a-28f.
It is also to be noted that if the sprocket portions 26a-26f
were to be moved from the aperture 34 to the aperture 32, for example,
the first angled abutting element 72 would be the element contacting the
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head 47 of the sprocket portions in a similar fashion to lift, move and
finally release the sprocket portions.
It is also believed within the skills of one skilled in the art
to design a similar variable diameter sprocket where the sprocket portions
would be only movable radially in their respective channel and where the
pin 46 would not be fixedly mounted to the sprocket portions but would be
slidably inserted therein to provide the lateral movement.
Although the present invention has been described
hereinabove by way of preferred embodiments thereof, it can be modified,
without departing from the spirit and nature of the subject invention as
defined in the appended claims.
