Note: Descriptions are shown in the official language in which they were submitted.
CA 02456633 2004-02-02
OVERLOAD C~UpLING
CROSS REFERENCE TO RELATED API?Z.,h::ATION
[0001]. This application relates to and claims priority to U.S. Provisional
Patent
Application No. 60/443,841, filed on January 31, 2003, which is incorporated
herein specifically
by reference.
BACKGROUND OF THE IN'VENTIO:(V
1. Field of the Invention
[0002] The present invention relates to a drive assembly for a vehicle having
an overload
coupling between a drive shaft and a driving pinion to limit the transmission
of excessive and
damaging torques through the drive assembly. The overload coupling includes an
overload
clutch.
2. Description of Related Art
[0003] Various manual transmissions for internal combustion engine driven
vehicles axe
known in the art. Zn a typical arrangement, an internal combustion engine
provides a driving
force to drive a drive shaft through suitable engine gearing (i.e., drive
assembly). This can be
accomplished by a belt-driven constant velocity transmission {"CVT") that
acts, preferably
through a manual transmission, on a driven shaft that is connected to at least
one driving wheel.
A forward gear, a reverse gear, or neutral positions can be selected as
desired by the manual
transmission.
[0004] In known drive assemblies, a centrifugal clutch and a. CVT provide
variable
transmission ratios. The clutch and CVT are incorporated between l:he internal
combustion
engine and the toothed gearing of the drive assembly. The CVT drives the
toothed gearing of
the drive assembly and thus moves the vehicle. It is preferred that the
driving assembly provide
a plurality of speeds, for example, a fast forward gear, a slow forward gear
and a reverse gear.
One particular problem with this drive concept has been that, in particular
when the transmission
is subjected to large impact loads in the drive train, such as those that
occur, for example, when
the vehicle jumps, the gearing will fail or be damaged and possibly destroyed
after a number of
such load reversals, These load peaks in the drive assembly are caused in
particular because the
high moment of inertia of the CVT and the gear ratio of the toothed ,gearing
of the drive
assembly make the drive assembly particularly stiff so that it cannot
attenuate the load peaks that
occur. This leads to load peaks, in particular at the output of the drive
assembly of the output
shaft. These impact loads. stem from the difference between the absolute speed
of the motor
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vehicle that is jumping and the circumferential velocity of the wheels of the
motor vehicle
which, when they land after the jump, dig into the ground with almost no slip.
[0005] Conventional drive assemblies such as the one disclosed in U.S. Patent
No.
3,997,043 include an overload clutch disposed between the transmission and the
wheel of the
vehicle. The overload clutch disengages when a torque transmitted.
therethraugh exceeds a
predetermined value so that the overload torque does not damage the
transmission. Such
overload clutches must be large to withstand the relatively large torques that
are generated in the
gear train between the transmission and the wheels.
SUZY OP THE INVENTION
[0006] It is therefore one aspect of one or more embodiments of this invention
to proviide
an overload clutch that is smaller, more durable, and/or less expensive than
conventional
overload clutches.
[0007] It, is another aspect of one or more embodiments of the present
invention to
provide an overload clutch that is positioned between the engine and the
transmission, instead of
between the transmission and the wheels.
[0008] It is another aspect of embodiments of the present invention to create
a drive
assembly of the type described heretofore for a motor vehicle wher<: excessive
load peaks in the
drive train can be avoided without having to abandon the proven drive concept.
It is also to be
possible to avoid peak loads of this kind by retrofitting existing drive
trains.
[0009] This obj ective is achieved by embodiments of the present invention
whereby an:
overload clutch is included as part of the drive assembly. This solves the
problem by
suppressing excessive torques and load peaks in the drive assembly in a
particularly simple and
elegant manner without any negative effects on the normal operation of the
drive assembly. The
design of the overload clutch 15 Such that it can transfer the maximal engine
torque and any
minor shock loads that may occur reliably. The arrangement only reduces
excessive shocks
whereby it releases the connection between the CVT and the drive shaft of the
wheels {i.e., the
output shaft)-which is rigid during normal operation-for brief periods so as
to reduce the
load peaks.
[0010] Depending on the amount of space that may be available, the overload
clutch is
installed in the drive assembly between the input shaft and the output shaft
of the drive
assembly. It is particularly advantageous if the overload clutch is arranged
on the input shaft
because the output torque that is to be limited to a maximum value o~z the
output shaft can be
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reduced by the transmission ratio of the drive assembly so that the torque
that is to be limited in
the drive train is also reduced by this transmission ratio, which means that
the overload clutch
can be made smaller. This in turn also reduces production costs.
[0011] In order to minimize the installed size, it is an advantage if a drive
pinion for the
drive assembly be mounted on the input shaft so as to be able to rotate
thereon, the drive pinion
is positively connected to the drive shaft by way of the overload clutch so as
to form a drive
connection. According to one advantageous configuration of the present
invention, on the drive
side the overload clutch is connected to the input shaft so as to rotate in
unison with it, and on
the output side it is connected to the driving pinion of the toothed gearing
so as to rotate in
unison with it. As an alternative to this, the overload clutch could be built
into a two-part drive
shaft, on both the output side and the input side.
[0012] In accordance with an aspect of embodiments of the present invention, a
drive
assembly for a vehicle having at .least one wheel and an engine is disclosed.
The drive assembly
transfers a driving force from the engine to the at least one wheel. 'lf'lhe
drive assembly includes
a rotatable input drive shaft. The input drive shaft is operatively coupled to
the engine. The
drive assembly further includes a rotatable output drive shaft. The output
drive shaft is
operatively coupled to the at least one wheel. The drive assembly also
includes a first
transmission operatively connecting the input shaft to the output shaft. The
first transmission
has a plurality of transmission ratios. An overload clutch is operatively
disposed between the .
input shaft and the first transmission to transfer a driving force from. the
input drive shaft to the
first transmission. The overload clutch has an engaged position such that the
overload clutch
transfers the driving force from the input drive shaft to the first
transmission during a first
operating condition. The overload clutch also has a disengaged position such
that the driving
force is not transferred from the input drive shaft to the first transmission
during a second
operating condition.
[0013] During the first operating condition, the torque transferred through
the input drive
shaft is below a predetermined threshold value. During the second operating
condition, the
torque transferred through the input drive shaft exceeds the predetermined
threshold value.
[0014] The drive assembly can also include an engine and a second transmission
operatively connecting the engine to the input shaft. The second transmission
is a continuous
variable transmission having a continuously variable transmission ratio. The
second
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transmission includes a drive pulley and a driven pulley coupled by a coupling
member. The
driven pulley of the second transmission may be positioned on the input shaft.
[0015] The first transmission may include one or more forward gears, a neutral
gear, and
a reverse gear. The first transmission may be a manual gear shifting device.
[0016) The overload clutch shifts to the first operating condition when a
torque
transferred theretlarough falls below a predetermined threshold value.
Conversely, the overload
clutch shifts to the second operating condition when the torque excE;eds the
predetermined
threshold value.
[001'1] The drive assembly can further include a driving pinion operatively
connected to
the input drive shaft. The overload clutch operatively connects the driving
pinion to the input
drive shaft, whereby the driving force is selectively transmitted from the
input drive shaft
through the overload clutch to the driving pinion. During the first operating
condition, the
torque transferred through the input drive shaft is below a predetermined
threshold value,
whereby the driving force is transferred from the input drive shaft to the
driving pinion. During
the second operating condition, the torque transferred through the input drive
shaft exceeds the
predetermined threshold value, whereby the driving force is not transferred
from the input drive
shaft to the driving pinion.
[0018] In accordance with the present invention, the overload clutch can
include at least
one friction plate operatively connected to the drive pinion and at least one
clutch plate
operatively connected to the input drive shaft. At least one spring is
provided for applying an
engaging force such that the at least one friction plate is.eoupled to the at
least one .clutch plate.,
whereby the driving force is transferred from the input drive shaft tc~ the
driving pinion. The
predetermined threshold valve is defined by the engaging force applied by the
at least one
spring.
[0019] The input drive shaft can include a flange formed thereon. The at least
one clutch
plate is operatively coupled to the flange by a connecting pin.
[0020] A reduction of construction casts can be achieved if the driving pinion
is
mounted on the drive shaft between tire overload clutch and a disk spring
pack, so as to be able
to rotate thereon, and optionally the disk spring pack causes a spring; force
to act on the driving
pinion in the direction of the drive shaft axis, against the overload clutch,
in the closing direction
of the overload clutch. The at least one friction plate, the at least one
clutch plate and the at least
one spring can be positioned between the flange azxd the drive pinion. The
spring can be
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positioned between the flange and either the at least one friction plate or
the at least one clutch
plate. The at least one spring can alternatively be positioned between the
drive pinion and either
the at least one friction plate or the at least one clutch plate. It is also
contemplated that the
drive pinion, the at least one friction plate, and the at least one clutch
plate can be positioned
between the flange and the at least one spring.
[0021] According to a further aspect of one or more embodiments of this
invention, the
drive assembly is incorporated into an all-terrain vehicle. The all-terrain
vehicle has a frame,
four wheels disposed on the frame, a straddle scat supported by the frame, and
an engine
supported by the frame. The drive assembly operatively connects the engine to
at least one of
the four wheels.
[0022] Such an overload clutch can also be retrofitted to existing drive
assemblies by
replacing'some minor components in existing drive assembly without having to
incur any great
costs. Using such measures, it is possible to significantly increase the
service life of a drive
assembly, since the loading on all shafts, wheels, and bearing can be limited
to an insignificant
maximal value.
BRIEF DESGR1PTION OF THE DRA.W1NGS
[0023] The invention will now be described in conjunction with the following
drawings
in which like reference numerals designate like elements and wherein:
[0024] Fig. 1 is a partial side cross-sectional view of an overload coupling
for a drive
assembly in accordance with an embodiment of the present invention;
[0025] Fig. 2 is a side schematic view of the input drive shaft for the
overload coupling
of Fig. l;
[0026] Fig. 3 is an end schematic view of the input drive shaft of Fig. 2;
[002'n Fig. 4 is side schematic view of an outer clutch plate for use in
embodiments of
the overload coupling;
[0028] Fig. 5 is side schematic view of an internal geared friction plate for
use in
embodiments of the overload coupling;
[0029] Fig. 6 is a side cross-sectional view of a drive pinion for use in the
overload
coupling of Fig. 1;
[0030] Fig. 7 is a partial side cross-sectional view of an overload coupling
for a drive
assembly in accordance with another embodiment of the present invention; and
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[0031] Fig. 8 is a partial side cross-sectional view of an overload coupling
for a drive
assembly in accordance with another embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0032] A drive assembly 10 for use in connection with an internal combustion
engine is
illustrated in Fig. 1. The drive assembly 10 can be used in connection with a
suitable vehicle
including but not limited to an all terrain vehicle, a go-kart, a three-
wheeled vehicle, a
snowmobile, a motorcycle or any other suitable vehicle. The drive assembly may
be
incorporated into an all-terrain vehicle such as the ones disclosed in. IJ.S.
Patent Nos. 6,296,073
and 4,699,234, the contents of which are incorporated herein by reference. The
drive assembly
is operatively connected to the wheels) of the vehicle to drive the same.
[0033] The drive assembly 10 includes an input drive shaft 11. The input drive
shaft 11
is operatively carmected to a driver pulley of a CVT 2, as disclosed, for
example, in TLS. Patent
Application No. 101395,844 entitled 'Braking Mechanism for a Gear," which is
assigned to the
Assignee of the present application and incorporated herein specifically by
reference. The CV'T
2 is operatively connected to the internal combustion engine 1. The engine 1
may be either a
two cycle or a four cycle engine. The present invention is not limitf:d to
internal combustion
engines; rather, other engines are considered to be within the scope of the
present invention.
[0034] The ingut drive. shaft 11 is rotatably mounted to a gearbox 3. The
gearbox 3 has
a gearbox cover 31. The input drive shaft 11 can be formed as a single
component or two or
more interconnected components. The input drive shaft 11 is operatively
connected to an
intermediate drive shaft 12, as described in greater detail below. Th.e
intermediate drive shaft 1.2
is rotatably nrxounted within the gearbox 3. The intermediate drive shaft 12
is operatively
connected to an output drive shaft 13. The output drive shaft 13 is rotatably
mounted to the
gearbox 3. The rotational drive force of the output drive shaft 13 is
transferred to the wheels)
through an appropriate sprocket or linkage 14 secured to the end of the shaft
13. The sprocket or
linkage 14 includes a toothed gear 141, which receives a chain 15 far driving
the wheel(s). The
present invention is not intended to be limited to the linkage 14; ratluer, it
is contemplated that
other suitable means for transferring the drive force to the wheeI(s),
including but not limited to
a direct connection to the wheel or a gear linkage without chains are
considered to be well
within the scope of the present invention.
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[0035] The intermediate drive shaft 12 is operatively coupled to the output
drive shaft 13
by a transmission that includes three transmission ratios, which include a
slow forward gear, a
fast forward gear, and a reverse gear. The intermediate drive shaft 12
includes a slow forward
gear 121, a first forward gear 122 and a reverse gear 123. The output drive
shaft 13 includes a
slow forward gear 131, a fast forward gear 132 and a reverse gear 133, which
are aligned with
the gears 121, 122, and 123, respectively, a shown in Fig. 1. The slli$ing
between gears can be
performed using a shifting mechanisrtn such as, for example, the mechanism
disclosed in U.S.
Patent Application No. 10/395,844, the disclosure of which is incorporated
specifically herein
by reference, or any conventional shifting mechanism including but not limited
to gear shift
forks. The shifting mechanism may alternatively comprise any other shifting
mechanism that is
known to those of ordinary skill in the art without deviating from the scope
of this invention.
[0036] The intermediate drive shaft 22 further includes an i~atermediate drive
pinion 124.
The intermediate drive pinion 124 is operatively coupled to a driving pinion I
11 mounted on
one end of the input drive shaft 11. '1"he rotational force of the input drive
shaft 11 is transferred
through the driving pinion 111 to the intermediate drive pinion 124 and the
intermediate drive
shaft 12.
10037] The interaction between the input drive shaft 11 and the driving pinion
111 will
now be described in greater detail. The driving pinion 111 is rotatanly
mounted to the input
drive shaft 11 via an appropriate bearing, such as a bushing or roller
bearing. The input drive
shaft includes a flange 112, as shown in Fig. 1. The flange 112 includes a
plurality of openings
113 formed therein, as shown in Figs. 2 and 3. A retaining ring 17 is provided
to limit the axial
movement of the driving pinion 111 on. the drive shaft 11. The drive shaft 11
is operatively
coupled to the da-iving pinion 1 I 1 through an overload clutch 16. The
overload clutch 16
includes a plurality of outer clutch plates 161, as shown in Fig. 1, .Each
outer plate 161 bras a
plurality of openings 162 formed therein, as shown in Fig. 4, which correspond
to the openings
113 in the flange 112. The overload clutch I6 limits the transmission of
excessive torque loads
between the input shaft 11 and the shafts 12, 13.
[0038] A pin 163 is received within each of the openings 11:3, I 62 to link
the clutch
plates 161 to the flange 112. Each pin 163 is attached to the flange 112 by
force fitting or other
suitable attachment mechanism. A plurality of internal geared friction plates
164 are positioned
between the clutch plates 161 such that each friction plate 164 is sandwiched
between the two
adjacent clutch plates 161. As shown in Fig. 5, each friction plate 164 has an
internal gear 165
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that engages a complementary gear 118 on the driving pinion 111. At least one
disc spring 166
or pack, which contains a plurality o:f springs is provided between the flange
112 and one of the
outer clutch plates 161 to provide the necessary axial force between the
friction plates 164 and
the clutch plates 161. The overload clutch 16 limits the excessive torque
that. can be transferred
from the input drive shaft 11 to the intermediate drive shaft 12. The;
overload clutch I6, the drive
pinion 11 I and the drive shaft 1 I together form an overload coupling.
[0039] During normal operation, the drive force from the engine 1 is
transferred to the
drive assembly 10 through the CVT 2 such that input drive shaft 11 rotates.
The rotational force
of the drive shaft 11 is transferred to the drive pinion 111 through tlhe
overload clutch 16. In
particular, the rotational force is transferred to the pins 163 that connect
the flange 112 to the
clutch plates 161. The axial force is supplied by the spring pack 166 causing
the plates 161 to
frictionally engage the friction plates 164 such that the rotational force is
effectively transferred
from the plates 161 to the plates 164, which in turn rotate the drive pinion
11 I . The shafts I 1
and drive pinion 111 therefore rotate in unison and the drive pinion drives
the intermediate shaft
I2.
[0040] When an excessive shock or torque occurs during, for example, vehicle
jump or
abrupt change of gears, the rotational force exceeds a threshold torque value
whereby the
friction plates 164 slip with respect to the clutch plates 161, which
c;ffectively prevents the
passage of excessive torques through the overload clutch 16. As such,
excessive loads may not
be transferred from the drive shaft 1 I to the intermediate drive shaft 12 or
vice versa. The shafts
11 and 12 momentarily do not opez-ate in unison. This avoids potential damage
to the pinions
1 I l and 124 and the gears in the event of an excessive load or shock.
[0041,] The transmission includes various transmission ratios that increase
the torque and
decrease the speed of the input shaft 11 relative to the output shaft 1. 3.
The overload clutch 16
experiences significantly lower torque than the output shaft 13. Consequently,
the overload
clutch 16 can be more compact and less expensive than conventional overload
clutches, which
are positioned on the higher torque output shaft 13 (or elsewhere between the
transmission and
the wheels of the vehicle} and must therefore be constructed to withstand
significantly higher '-
torque.
[0042] The drive assembly ICI may also include additional clutches. For
example, as
disclosed in U.S. Patent Application lVo. 10/395,844 entitled "Bra'king
Mechanism for a Gear,'A a
free wheel clutch and a centrifugal clutch may be disposed between the driven
pulley of the
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CVT 2 and the input drive shaft 11. however, unlike overload clutches, such
free wheel and
centrifugal clutches do not prevent torque shocks.
[0043] The input drive shaft 1 l, the, drive pinion 111 and the overload
clutch 16 can be
easily retrofitted into an existing drive assembly. The existing drive shaft
and drive gear can hre
replaced with the above-described drive shaft 1 l, drive pinion 111 and
overload clutch 16. As
such, an existing drive assembly can be retrofitted with an overload.
coupling.
[0044 An overload coupling according to another embodiment of the present
invention
will be described in connection with Fig. 7. in Fig. 7, the overload coupling
includes an input
drive shaft 21. Like the drive shaft 11, the drive shaft 21 is rotatably
mounted within the
gearbox 3. A driving pinion 211 is rotatably mounted on the drive shaft 21.
The driving pinion
21 I operatively engages the interFnediate drive pinion 124 to transfi~r the
rotational force from
the drive shaft 21 to the intermediate drive shaft 12.
[0045] A fixed bush 212 is connected to one end of the input drive shaft 21.
The fixed
bush 212 can be secured to the end of the shaft 21, molded onto shaft 21,
force f tted, integrally
formed with the shaft 21, or otherwise secured to the shaft 21. The driving
pinion 211 is
positioned between the fixed bush 212 and at least one spring pack .266. The
spring packs) 266
apply a force on the driving pinion 2 i 1 in direction F towards the fixed
bush 212.
[0046] An overload clutch 26 connects the driving pinion 211 to the input
drive shaft 21.
The overload clutch 26 includes at least one outer clutch plate 261. The outer
clutch plate 261
can have the same construction as the outer clutch plate 161. A pin 213 that
extends fronn the
fixed bush 212 is received within an opening in the clutch plate 261, as shown
in Fig. 7. The pin
213 can be integrally formed with the fixed bush 212 or formed as a separate
component. The
overload clutch 26 further includes at least one friction plate 264. T'he
friction plates 264 have a
similar.construction to the friction plate 164, shown in Fig. 5. The fxiction
plates 264 are
positioned between the fixed bush 2I2 and the outer clutch plate 261, and
between the outer
clutch plate 261 and the splines of the driving pinion 211, as shown in Fig.
7. 'The force exerted
by the spring packs 266 causes the friction plates 264 to engage the outer
clutch~plate 261 such
that the rotational forces transmitted from the bush 212 to the clutch, plate
261 through pin 213 is
transferred to the friction plates 264 which causes the driving pinion 211 to
rotate in unison with
the drive shaft 21.
[0047] Vhhen excessive shocks or loads occur, the rotational forces exceed a
threshold
torque value (i.e., the force exerted by the spring packs 266), whereby the
friction plates 264 slip
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CA 02456633 2004-02-02
with respect to the clutch plates 261, which effectively prevents the passage
of excessive torques
through the overload clutch 26. As such excessive loads may not be transferred
from the drive
shaft 21 to the intermediate shaft 12 or vice versa. The shafts 21 ar,~d 12
momentarily do not
operate in unison.
(0048] An overload coupling according to another embodiment of the present
invention
will be described in connection with Fig. 8. In Fig. 8, the overload coupling
includes an input
drive shaft 11 having a flange 112 formed thereon. A retaining ring 1? is
provided to limit the
axial displacement of the driving pinion 311 with respect to the drive shaft
11. As shown in
Figs. 2 and 3, the flange 112 includes a plurality of openings 113. 7Che
drive. shaft 11 is
operatively coupled to the driving pinion 311 through an overload clutch 36.
The overload
clutch 36 includes a plurality clutch plates 161 and friction plates ld4_in
the manner described
above in connection with the clutch 16. . The friction plates 164 engage the
gear 31$ on the
pinion 311. The location of the spring packs differ. In the overload clutch
36, the spring packs
366 are positioned between the splines of the driving pinion 311 an<i the
clutch plates 161 and
friction plates 164. With this arrangement, the clutch plates 161 and the
friction plates 164 are
compressed between the spring pads 366 and the flange 112. With such an
arrangement, the
maximal torque can be transmitted from drive shaft 11 to the driving pinion
311 through the
overload clutch 36 whereby the shaft 11 operates in unison with the pinion
211.
[Ofl49] When excessive shocks or Ioads occur, the rotational forces exceed a
threshold
value (i.e., the force exerted by the spring packs 366}, whereby the friction
plates 164 slip with
respect to the clutch plates 161, which effectively prevents the passage of
excessive torques.
[0050] While the invention has been described in connection with what is
presently
considered to be the most practical and preferred embodiments, it is to be
understood that the
invention is not to be limited to the disclosed embodiments and elements, but,
to the contrary, is
intended to cover various modifications, equivalent arrangements, and
equivalent elements
included within the spirit and scope of the appended claims. The input drive
shaft 11 and 21
could also be formed in two parts, the overload clutch 16, 26, 36 them being
arranged between
the two parts of the input drive shaft.
Spec.DOC
