Note: Descriptions are shown in the official language in which they were submitted.
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CHAIN TENSIONER FOR CH~IN DRIVES
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to chain tensioners, and partic-
ularly a chain tensioning device for chain drives, such as used
on motorcycles.
2. Description of the Prior Art
There has been a continuing problem created by the slack
required to be provided in the chain drive of motorcycles. The
slack is required because the distance between the motor drive
sprocket and the wheel sprocket varies depending upon the displace-
ment of the shock absorbers which extend between the rear wheel
mounting or swing frame and the base frame on which the motor
housing is secured. The existence of such slack in the chain drive
results in frequent derailment of the chain from the wheel or motor
sprocket which, if it occurs at high speed, can cause considerable
damage to the motor, the sprocket, the frame and the rider. Attempts
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to control the chain under high speed operating conditions have
been largely unsuccessful. For instance, United States Patent
1,962,223 teaches the use of a tensioning mechanism in conjunction
with a chain, however it is applicable to only one reach of the
chain, whereas slack appears in both reaches of the chain under
certain circumstances.
United States Patent 3,448,628 relates to a device for
tensioning the driving chain in a bicycle equipped with a coaster
break. The necessity for a tensioning device results from the fact
~0 that as the chain shifts from one larger gear to a smaller gear the
excess length of chain appearing in the lower reach of the chain
must be taken up in some way. This patent teaches independent
mechanisms for taking up the slack in the upper and lower reaches
of a bicycle chain.
!5 Krause U.S. Patent 3,575,058 teaches the use of independent
devices for tensioning the upper and lower reaches of a chain drive,
the devices including a bracket adapted to be mounted on a fixed
object such as a wall and projecting over the upper and lower reaches
of the chain in such a way that rollers mounted on the bracket come
~0 in contact with the upper and lower reaches of the chain. This
construction is primarily useful for the drive mechanisms for
equipment that is fixed in place and does not appear to be applicable
for mobile or motorcycle drive chains.
U.S. Patent 3,677,103 also relates to a tensioning device for
?5 bicycle chains but does not teach the concept of a device operating
in conjunction with both upper and lower reaches of such chains.
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U.S. Patent 3,785,219 relates to a device for tensioning the
upper reach of a bicycle chain when the main drive sprocket is
rotated in reverse to operate a coaster break. This patent does
not teach the concept of a single device engaging both upper and
lower reaches of the chain to accommodate slack in the chain.
United States Patent 3,913,410 relates to a tensioning
mechanism for a variable speed sprocket and chain drive assembly
in which two parallel chains are driven by (or drive) a variable
diameter sprocket. Spring pressed idler rollers are provided
independently associated with each reach of the chain to accommodate
slack in the chain when the effective diameter of the sprocket is
reduced.
United States Patent 3,463,022 also relates to a chain
tensioning device, however, it utilizes hydraulics to control the
slack in only one reach of the chain.
From the foregoing it will be apparent that the problems
created by slack in a chain drive have been in existence for a
long time. It is also apparent and surprising that no one has
considered the possibility of combining in one single mechanism
means for controlling the slack in both reaches of a motorcycle
chain under all operating conditions. Accordingly, it is one of
the principal objects of this invention to satisfy that need.
So far as is known, the relationship between the rotational
axis of the rear wheel sprocket assembly of a motorcycle and the
rotational axis of the motor drive sprocket is a variable one for
the reason that the swing frame member on which the rear wheel is
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mounted is pivoted about an axis spaced from the axis of rotation
of the motor drive sprocket so that the distance between the - -
rotational axis of the wheel sprocket and the rotational axis of
the motor drive sprocket varies in relation to the displacement of
5 the rear wheel or swing frame assembly in relation to the main
t frame as permitted by shock absorbers. Such variation in the
distance between the rotational axis of the sprockets causes
variation in the amount of slack in both the upper and lower reaches
of the chain, again depending upon the degree and direction of dis-
10 placement of the rear wheel in relation to the main frame as permitted
by the shock absorbers. Accordingly, it is one of the principal
objects of the present invention to provide a chain tensioning
device that may be easily mounted on the swing frame member and
which will control the slack in both reaches of the chain through
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15 all of its variations.
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;I During the operation of a motorcycle, different slack
conditions in the chain are created by different modes of operating
the motorcycle. For instance, when the motorcycle is under power
and is being driven by the motor, the top reach of the chain is
20 generally taut between the upper peripheries of the motor drive
and wheel sprockets, while the lower reach of the chain contains
all of the slack. Accordingly, it is another object of this invention
to provide a single chain tensioning device applicable to both
upper and lower reaches of the chain,which will accommodate all
25 of the slack that is transferred to the lower reach of the chain
when the motorcycle is being driven by the motor.
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Under a different circumstance, e.g., when the motorcycle
is driving the motor, the lower reach of the chain will be taut
between the lower peripheries of the motor drive and wheel sprockets
while the upper reach of the chain will contain all of the slack.
With the motorcycle traveling at high speed, and the chain rotating
rapidl~ under these conditions, there is a tendency for the chain
to be derailed from the motor drive sprocket because of the large
amount of slack. Accordingly, still another object of the invention
is to provide a single chain tensioning device that will accommodate
the transfer of slack from the lower reach of the chain to the
upper reach of the chain under these conditions and which will keep
sufficient tension on the upper reach of the chain to prevent its
being inadvertently disengaged.
When a motorcycle is being operated in rough terrain,
such as on dirt trails, it is normal operating procedure to accelerate
and decelerate suddenly so that the transfer of slack between the
upper and lower reaches of the chain will occur frequently and with
suddenness on a single ride. Additionally, because of rough terrain
and the necessity to lean the motorcycle precariously going around
sharp curves or bends in trails, because of the large amount of
slack in the chain, there is a tendency for the chain reaches to
shift laterally, thus causing derailment from the sprockets on
which it is mounted. In other words, there is a tendency for the
chain to be displaced laterally out of the plane of the sprockets.
Accordingly, still another object of the present invention is to
provide a single device capable of being attached to a frame member
of the motorcycle in association with the chain drive and which
will engage both reaches of the chain and prevent such lateral
displacement of the chain out of the plane of the sprockets while
simultaniously controlling the tension on the chain.
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Because of the necessity of having a great deal of slack
in the chain, there is a tendency for the motorcycle to respond
sluggishly to the throttle. Accordingly, it is another object of
the present invention to provide a dev~ce that controls the tension
S in both reaches of the chain so as to improve throttle response.
It has been found that when acceleration and deceleration
occur rapidly, such as in a race or on a trail, excessive slack
in the chain creates a considerable amount of drive line shock.
Accordingly, another object of the invention is to provide a device
easily attachable to a frame member of the motorcycle and which
is operative to control tension in both reaches of the chain as
to eliminate or materially diminish drive line shock.
The invention possesses other objects and features of
i advantage, some of which, with the foregoing, will be apparent
from the following description and the drawings. It is to be
understood however that the invention is not limited to the embodi-
ment illustrated and described since it may be embodied in various
forms within the scope of the appended claims.
SUM~qARY OF THE INVENTION
Broadly, the invention thus contemplates a chain tensioner
for chain drives which has upper and lower reaches revolving on
drive and driven sprockets. The tensioner comprises means forming
a support for the drive and driven sprockets, means on the support
comprising a pair of arms pivoted at corresponding ends about a
common pivot and divergent therefrom with the ends of the arms remote
from the common pivot adapted to engage the upper and lower reaches
of a chain adjacent the driven sprocket, and means resiliently inter- .
posed directly between the divergent arms and biasing the divergent
arms and the ends thereof remote from the pivot to engage the upper
and lower reaches of the chain whereby displacement in the plane of
the chain of either reach of the chain between the drive and driven
- ` sprockets effects automatic resilient displacement of the other
reach of the chain to eliminate slack from the upper and lower
reaches of the chain in correlation to one another.
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In a further em~odiment, the invention contemplates a
combination of a motorcycle drive train which includes a motor
drive sprocket and a rear wheel sProcket connected by a
drive chain with the rear wheel sProcket being mounted on a
swing frame member pivotally mounted about an axis spaced from
and disposed between the axes of rotation of the motor drive
and wheel sprockets, and a chain tensioner adapted to control
the slack in both upper and lower reaches of the chain. The
tensioner comprises means pivoted on the swing frame member
and engaging the upper reach of the chain, means pivoted on
the swing frame member and engaging the lower reach of the
chain, and means resiliently biasing the means engaging
the upper and lower reaches of the chain in directions to
eliminate slack from the upper and lower reaches of the chain.
In terms of broad inclusion, the chain tensioner of the
invention comprises a bracket for attachment to the rear wheel
swing arm member of a motorcycle frame in association with the
chain drive thereof, the bracket having pivotally mounted thereon
a cooperating pair of chain engaging arms, one for each reach of
the chain, the two arms being independently pivoted on the bracket
and being interconnected by a coil spring that controls the tension
imposed on both reaches of the chain simultaneously. Roller means
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are provided on the ends of the arms engaging the chain so as to
guide the chain and prevent lateral displacement of the chain out
of the plane of the sprockets on which it is mounted.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a side elevational view of a motorcycle drive
train, including the motor drive sprocket, the wheel sprocket and
the swing arm on which the rear wheel is rotatably mounted, showing
the chain tensioning device of this invention applying tension to
both reaches of the chain when the chain is at rest.
Fig. 2 is a view similar to Fig. 1, but showing the
relationship of the chain tensioning device to the upper and lower
reaches of the chain when the upper reach of the chain is tensioned
such as when the motor is driving the motorcycle.
Fig. 3 is a side elevational view similar to Figs. 1
and 2, and illustrating the relationship of the chain tensioning
device with the upper and lower reaches of the chain when the lower
reach of the chain is tensioned, such as when the motorcycle is
driving the motor.
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Fig. 4 is an enlarged fragmentary side elevational view
of the chain tensioner device shown in the at-rest position of
Fig. 1 as it is applied to the upper and lower reaches of a motor-
cycle drive chain.
Fig. 5 is a vertical cross sectional view taken in the
plane indicated by the line 5-5 in Fig. 4.
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Fig. 6 is a horizontal cross-sectional view taken in the
plane indicated by the line 6-6~in Fig. 4.
Fig. 7 is a vertical cross-sectional view taken in the
plane indicated by the line 7-7 in Fig. 6 and shown enlarged to
better illustrate the construction of the chain tensioning device.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
In terms of greater detail, the chain tensioning device
of the invention in one of its aspects is adapted to be mounted
on the swing arm 2 of the motorcycle on the free (rearj end 3
constituting the mounting bracket on which the rear wheel (not shown)
is mounted in coaxial relationship with the wheel sprocket 4. The
swing arm 2 is mounted about a pivot pin 5, on the main or base
frame 6, the pivot pin 5 being spaced from the rotational axis 7
of motor drive sprocket 8. The axis of rotation 7 Oc the motor
drive sprocket 8, the pivotal axis 5 of the swing arm 2, and the
pivotal axis 9 of the wheel sprocket 4 are illustrated in Figs. l
through 3 in alignment and lying in a common plane designated in
Figs. 1 through 3 by the broken line 12.
It should be noted that the pivot 5 on which the swing
arm 2 of the motorcycle frame is journaled is mounted on motorcycle
main frame member 6, while the pivot pin 7 for the motor drive
sprocket 8 is mounted on a drive shaft that projects from the
motor housing of the motorcycle, the motor housing also being
supported on the motorcycle main frame member 6. Thus, the relation-
ship of the pivot pin 5 and the pivot shaft 7 is constant. This
is not true however of the relationship between the rotational
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axis 9 of the rear wheel and wheel drive sprocket 4, and the
rotational axis 5 of the swing arm 2. Thus, the height between
the rotational axis 9 of the rear wheel sprocket 4 and the surface
of thé ground on which the wheel is supported generally is not
changed to any great extent.
Conversally, the relationship of the pivot pins S and 7
with the ground is not constant and does change, sometimes to the
extent of being displaced downwardly, six or seven inches below
the plane 12 indicated in the drawings. When this occurs, it will
be clear that the swing frame member 2 pivots counterclockwise
about the pivot pin 5. Since there is a space between the pivot
pin 5 and the pivot axis 7 of the motor drive sprocket, it will be
obvious that the distance between the rotational axis 9 of the rear
wheel sprocket 4 and the rotational axis of the motor drive sprocket
lS 8 will be somewhat less than when these parts are arranged in the
relationship illustrated in the drawings, in which they lie in a
common plane. It will therefore be understood that such displacement
of the rotational axis 7 of motor drive sprocket 8 and pivot pin 5
of the swing frame member 2 increases the amount of slack in the
chain, thus enhancing the problem of accommodating such slack
without derailment of the chain from the sprocket.
; To accommodate the variations in slack of the chain 13
that thus occur, there is provided a chain tensioning device
designated generally by the numeral 14 and including an upper arm
16 and a pair of lower arms 17, the upper arm having a lower mounting
or journal portion 16' and an upper chain-bearing portion 18
interconnected by a strap or body portion 19. The strap or body
portion 19 has struck therefrom a section 21 to provide an anchor
under which one leg 22 of a coil spring 23 may be caught.
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The spring possesses multiple coils as illustrated in Figs. 5,
6 and 7, and the other leg 24 o~ the spring is caught under a
section 26 struck from one of the pair of arms 17 to provide an
anchor for the spring leg 24.
As illustrated in Fig. 5, 6 and 7, the arms 16 and 17
are pivotally journaled on pivot pin 31 which extends through
sleeve 32 rotatably journaled in a bearing block 33 appropriately
welded to the underside of the swing frame member 2 as shown. Also `
mounted on the pivot pin 31 is a rubber bushing 34 that lies
concentrically within the coils of the spring as illustrated and
which keeps the coils concentrically centered with respect to the
pivotal axis of the arms 16 and 17, and which also accommodates
the increase and decrease of inside diameter of the spring coils as
they flex druing operation. The assembly is retained on the bearing
block 33 by a washer 36 and nut 37 as illustrated.
It should be noted that the length of the sleeve 32
rotatably journaled within the bearing block 33 is such that the
pair of arms 17 cannot be clamped down tightly upon the lateral
ends of the bearing block 33 to thus prevent their free pivotal
movement on the pin 31.
~ eferring to Figs. 1 through 4, it will be seen that with
respect to the upper arm 16, there is mounted on the free end of
the chain-bearing portion 18 a rotatable guide wheel 41 the outer
periphery of which is formed to provide a central flange 42 having
shoulders 43 on opposite sides thereof. As illustrated in Fig. 5,
the guide wheel is rotated about rotational axis formed by the
pin 44 and is positioned so that the flange 42 extends between the
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side flanges 46 of chain 13, the outer periphery of the flange 42
being in physical contact with the rollers 48 forming a part of
the chain construction. The height of the flange 42 above the
shoulders 43 is proportioned so that the shoulders 43 contact the
associated upper edges 49 of the side flanges 46 of the chain links,
to thus effectively guide the chain and confine it in the proper
plane, thus precluding its displacement laterally in a manner which
would result in its being derailed from the sprockets. To place the
guide wheel 41 in the proper plane, i.e., the plane in which the
chain lies, it should be noted that the central connecting section
1~ of the upper arm 16 is offset from the plane of the mounting
section 17' and the section 18 on which the guide wheel 41 is
journaled. The offset of the central connecting portion 19 of the
arm provides for clearance around the associated swing frame member
2 while insuring that the guide wheel 41 will be retained in a
position to properly control tracking of the chain in its proper
plane of operation.
Referring to Figs. 4, 5 and 6, it should be noted that
the lower pair of arms 17 are spaced apart to receive therebetween
a chain guide wheel 51 having a central flange 52 and shoulders 53
on opposite sides thereof for the same purpose as described above
with respect to the guide wheel 41. It should also be noted that
with respect to the pair of arms 17, the lower reach 54 of the chain
passes between the arms 17 and is guided therebetween by the wheel
51. Thus, even if the chain managéd somehow to disengage itself
from the wheel 51 it could not escape traveling in a proper track
because it is confined in such track by the pair of links 17 on
opposite sides thereof. Accordingly, in addition to forming a
pivotal support for the guide wheel 51, the arms 17 pexform an
additional function in that they insure retention of the lower reach
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of the chain in a proper track, cooperating with the guide wheel 51,
which is journaled on pin 54 as shown, that extends between the
arms 17 adjacent their free end. It should also be noted that the
guide wheel 41 engages the upper side of the upper reach of the
chain while the guide wheel 51 engages the bottom side of the
lo~er reach of the chain.
In operation, it will be seen from Fig. 1 that when the
motorcycle chain is quiescent or not operating, the tension in the
spring 23 biases the arms 16 and 17 toward each other so that the
wheels 41 and 51 in engagement, respectively, with the upper side
of the upper reach of the chain, and the lower side of the lower
reach of the chain, cause the chain to be confined between the two
wheels and wrapped to a greater extent about the outer periphery of
the wheel sprocket 4, thus imposing tension on both reaches of the
chain simultaneously and eliminating uncontrolled slack in the
chain. As soon as the motor is activated and the motor starts
driving the motorcycle, counterclockwise rotation of the motor
sprocket 8 imposes tension on the upper reach of the chain so that
the upper reach of the chain assumes a position substantially
tangential to the outer peripheries of the wheel drive sprocket and
the motor drive sprocket as shown. When this occurs, it will be
apparent that displacement of the upper reach of the chain causes
the upper arm 16 to pivot counterclockwise, elevating the wheel
41 so that it now tracks at a higher elevation above the swing
frame member 2.
At the same time, because of the resilient interconnection
of the upper and lower arms through the spring 23, the pair of
lower arms 17 will be elevated toward the underside of the swing
frame member 2. It should be understood however that the lower
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arms 17 are independently pivotal with respect to the upper arm 16
so that th lower arms are permitted to find their appropriate
position in view of the independent forces acting upon the lower
arms, such as the weight of the lower reach of the chain and the
centrifugal force exerted by the chain because of its high speed
movement. From this it should be clear that the spacing between
the wheels 41 and 51 that engage the upper and lower reaches of
the chain, respectively, is not constant but varies continuously
depending upon the conditions imposed by operation of the motorcycle.
Assuming that Fig. 2 illustrates the relationship of the
parts when the motorcycle is cruising under power, it may be
imagined what occurs if a sharp bump is encountered by the motorcycle.
The rear wheel and wheel sprocket bounce upward, pivoting the swing
frame member 2 upward or counterclockwise. The frame on which the
motor drive sprocket is journaled remains at the same elevation
because of inertia, and as a consequence, the distance between the
centers of rotation of the wheel sprocket and drive sprocket is
reduced. Such reduction causes the upper reach of the chain to
slacken somewhat, and the slack is taken up automatically by down-
ward movement of the upper arm 16 and wheel 41. But increased
slack in the upper reach of the chain results in increased tension
or a reduction of slack in the lower reach, and such variation is
automatically compensated by the lower arm 17 since it is resiliently
interconnected with the upper arm 16. Thus, an increase of tension
in the lower reach causes independent displacement of the lower arm
as modified by the resilient interconnection o~ the two arms.
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