Note: Descriptions are shown in the official language in which they were submitted.
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AUTOMATIC LOCKING CLUTCH
This invention relates generally to clutches. More
particularly, it relates to a clutch for use in effecting locking
engagement between a front drive axle and a front wheel of a four-
wheel drive vehicle in response to the application of power to thefront drive axle. The clutch automatically effects disengagement
upon cessation of the application of power to the front drive axle,
together with a direction reversal thereof.
Heretofore, various clutching mechanims have been used
for engaging a front drive axle with its associated wheels in a
four-wheel drive vehicle. One such mechanism normally is dis-
engaged to allow the wheels to rotate independently of the front
drive system. This requires that the operator lock each clutch
manually to engage the front drive axle and wheels, and to unlock
them manually to disengage.
Another such mechanism provides an overrunning clutch
which engages automatically when power is applied to the front
drive axle and when operation is in the drive mode. However, such
an overrunning clutch disengages automatically upon operation in
the coast mode. In other words, the overrunning clutch engages
when the rotational speed of the axle tends to exceed the rotational ;
speed of the wheel, but disengages when the rotational speed of the
wheel tends to exceed that of the axle. Such overrunning clutches
generally provide some means by which the operator may override
manually to insure locking engagement between the axle and wheels.
Yet another such mechanism provides a clutch which
operates in response to the application of torque to the front
drive axle to move pins into slots so as to engage the axle
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with its associated wheels. Although a mechanism of this
type will effect engagement in either the drive or coast
mode of operation, there is the possihility that the pins
will slip out of the slots during movement between drive and
coast, in which case the clutch would disengage and then
re-engage automatically. At normal operating speeds such
disengagement and re-engagement could cause severe shocks
to the clutch components and, indeed, to the entire
front driveline. This would result in a dangerous and possibly
destructive condition. Further, in a float condition wherein
the axle is rotating but no torque is transferred between the
axle and wheels, an inadvertent tendency for movement between
the drive and coast modes of operation could develop. This
could cause the clutch to disengage and then re-engage, and
establish the same dangerous condition.
Canadian Application 302,899 filed May 9, 1978
is directed to an automatic locking clutch which overcomes
the deficiencies of the prior devices. As disclosed therein,
the clutch will automatically engage a front drive axle
and an associated wheel in response to engagement of the
front-wheel drive system will maintain engagement positiveiy
in the drive and coast modes of operation as well as during
the transition hetween drive and coast, will maintain
engagement positively in forward and reverse operation as well~
as during the transition between forward and reverse, and
will disengage automatically when the front-wheel drive system
is disengaged.
The automatic locking clutch includes a ring for
developing frictional drag sufficiently high to cause clutch
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engagement. Thereafter, this high drag continues, although
it is not required to maintain engagement. Thus, in order
to conserve power, reduce heat, ease the problems of material
selection, etc., there remains a need for an automatic locking
clutch of this type which will develop relatively high
frictional drag initially to effect automatic clutch engagement,
and which will develop relatively low frictional drag thereafter.
A primary object of this invention is to provide
an improved automatic clutch which will meet the need noted
above. The invention is directed to an improved clutch for
automatically effecting engagement between driving and driven
members in response to rotation of the driving member. The
clutch maintains positive engagement between members so long
as the driving member rotates, and disengages automatically
~hen rotation of the driving member is discontinued. The
clutch of the present invention is adapted for use in four-
wheel drive vehicles where it is desirable to provide auto-
matic engagement of the front wheels when the operator engages
the front-wheel drive system. The clutch is operative when
the vehicle is engaged in forward or reverse, and maintains
engagement positively until the operator shifts out of four-
wheel drive and reverses direction~
The present invention resides in an automatic
clutch including first and second rotatable members forming
drive and driven members with first and second clutch elements
respectively rotatable with the first and second members, the
elements being engageable in drive and coast modes, the first
element being movable relative to the first member toward and away
from engagement with the second element. First means is
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provided for movinq the first element toward engagement with
the second element upon rotation of the first member in one
direction and for maintaining the first and second elements
engaged in the drive and coast modes when the first element
is subject to rotation. Second means is provided for moving
the first element away from engagement with the second
element when the first member is not subject to rotation.
The first means includes camming means having a rotatable
cam, a cam follower rotatable with the first element and
means for developing a force tending to retard rotation
of the cam. The camming means is effective sequentially for
moving the first element toward engagement with the second
element upon relative rotation between the cam and cam follower
and for rotating the cam with the cam follower in opposition
to the retarding force. The camming means reduces the magnitude
of the retarding force upon the rotation of the cam with the
cam follower.
In a specific embodiment of this invention, there
is included a movable clutching sleeve associated with the
driving member and a fixed clutchina sleeve associated with the
driven member. The movable clutching sleeve is positively
cammed into locking engagement with the fixed clutching sleeve
upon rotation of the driving member. A blocking device
prevents inadvertent disengagement of the clutching sleeves in
the event of a tendency for the driven member to overrun the
driving member. As a result, the positive locking relationship
is maintained in the drive and coast modes of operation as well
as during transition between drive and coast. Furthermore,
the arrangement is such that engagement is maintained when the
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driving member is rotated in forward or reverse as well
as during transition between forward and reverse drive.
The elutch of this invention also includes
an improved mechanism for developing a frictional drag force
to cause camming of the movable elutehing sleeve. The mechanism
incorporates a wrapped spring type of clutch characterized
as having relatively high re-
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sistance to slippage in the spring tightening or wrapp;ng direction,
and relatively low resistance to slippage in the spring loosening or
unwrapping direction. Upon initial rotation of the driving member,
the spring is caused to tighten, thereby causing camming of the
movable clutch sleeve. After camming is completed, the spring is
caused to loosen, thereby reducing frictional drag to a minimum.
One way of carrying out the invention is described in -;
detail below with reference to drawings which illustrate only
one specific embodiment, in which:- :
FIGURE 1 is a sectional view showing details of the
improved automatic locking clutch;
FIGURE 2 is a sectional view taken along the line 2-2
of FIGURE 1 showing additional details of the clutch,
FIGURE 3 is a developed view taken along the line 3-3
of FIGURE 1 showing the clutch in its disengaged position;
FIGURE 4 is a developed view similar to FIGURE 3 showing
the clutch at an initial stage of movement toward its forward
drive position,
FIGURE 5 is a developed view similar to FIGURE 3 showing
the clutch at a later stage of movement toward its forward drive
position;
FIGURE 6 is a developed view similar to FIGURE 3 showing
the clutch in its forward drive position,
FIGURE 7 is a developed view similar to FIGURE 3 showing
the clutch in its reverse drive position; and
FIGURE 8 is a schematic view showing an associated
transfer case for use in conjunction with the clutch.
While this invention is susceptible of embodiment in
many different forms, there is shown in the drawings and herein
will be described in detail a preferred embodiment. It should be
understood that the present disclosure is considered to be an
exemplification of the principles of the invention and is not
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intended to limit the invention to this embodiment.
Referring to the drawings now in greater detail, and
with particular reference to FIGURE l, 2, and 3, there is shown a
driving member or shaft lO, which in one preferred form of the
invention is the front axle of a four-wheel drive vehicle. Axle lO
is rotatably supported in a conventional manner within an axle
housing 12. Axle 10 extends outwardly beyond the spindle of
housing 12, and a spring retainer 14 is secured to the outer end
thereof by a bolt 16 or the like. A collar 18 is secured to axle
lO for rotation therewith, and is located between the spindle of
housing 12 and spring retainer 14.
A driven member 20, which in one preferred form of the
invention is the front wheel hub of a four-wheel drive
vehicle, is supported by a conventional bearing, not shown, for
rotation about housing 12. Lock nuts 22 secure this bearing in
the usual manner. An end nut 24 is fastened to the spindle of
housing 12 and defines a smooth cylindrical surface 26.
A hub extension sleeve 28 is secured to wheel hub 20
for rotation therewith. Hub extension 28 extends outwardly
beyond spring retainer 14 and bolt 16, and a suitable cap 30
closes its outer end. Hub extension 28 defines a plurality of
clutch teeth 32.
An axle clutch sleeve 34 is splined to collar 18 for
rotation therewith and sliding movement relative thereto. Sleeve
34 defines a plurality of clutch teeth 36 adapted for meshing
engagement with teeth 32 of hub extension 28. Sleeve 34 also
defines a plurality of cam followers in the form of outwardly
radially extending pins 38. A suitable spring 40 reacts against
spring retainer 14 and biases sleeve 34 inwardly such that teeth
36 normally are out of meshing engagement with teeth 32.
An annular cam 42 is spaced from the spindle of housing
12 and from sleeve 34 so as to be rotatable relative thereto. Cam
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42 defines a plurality of pairs of outwardly diyerging ramp
surface portions 44 and 46, each pair being connected by a flat
surface portion 48. A pin 38 is cooperable with each pair of ramp .
surface portions 44 and 46. Cam 42 also defines a pair of spaced
slots 49 and 50 in alignment with cylindrical surface 26 of nut
24. Slot 49 is partially defined by surfaces 52 and 54, and slot
50 by surfaces 56 and 58 of cam 42.
An annular stop member 60 is concentric with cam 42.
Member 60 defines a plurality of pairs of outwardly diverging
surfaces 62 and 64 parallel to but spaced farther apart than
surfaces 44 and 46 of cam 42. Surfaces 62 and 64 terminate in
outwardly extending projections 66 and 68. Projection 66 and 68
respectively extend outwardly beyond flat surface 48 of cam 42
adjacent the junction with ramp surfaces 44 and 46. Member 60 also
defines a notch 70 in alignment with slots 49-50 of cam 42, and
with surface 26 of nut 24. Notch 70 is partially defined by
surfaces 72 and 74 of member 60 such that notch 70 extends beyond
slots 49-50 with surfaces 72 and 74 spaced farther apart than
surfaces 52 and 58 of cam 42.
A friction drag mechanism of the wrapped spring clutch
type includes a multi-turn drag spring 76 wrapped around cylindrical
surface 26 of nut 24 with a slight interference fit so that some
residual frictional drag force is developed therebetween. Spring
76 has ends 78 and 80 respectively extending radially through
slots 49 and 50 of cam 42 and into notch 70 of member 60. In the
disengaged position shown in FIGURE 3, spring ends 78 and 80 are
spaced from surfaces 54 and 56, respectively. With pins 38 and
ramp surfaces 44-46 in the position shown in FIGURE 3, sleeve 34
is in the position shown in FIGURE 1. Teeth 32 and 36 are out of
mesh, and wheel hub 20 rotates freely about axle 10, which is
stationary when the associated vehicle is in two-wheel drive.
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When the operator desires to establish four-wheel
drive, he directs power to axle 10. Collar 18 and sleeve 34
rotate with axle 10. Assuming that forward rotation of axle
10 results in downward movement of sleeve 34, as shown in
FIGURE 3, pins 38 will abut ramp surfaces 46 and drive cam 42
downwardly, as shown in FIGURE 4. Surface 56 will abut spring end
80 and carry spring 76 around surface 26 of nut 24. As spring 76
tightens, or tends to wrap around surface 26, the frictional drag
force tending to retard downward movement of cam 42 is increased,
lC and a relatively high frictional drag results. Pins 38 move up
ramp surfaces 46 to the position shown in FIGURE 5, thereby
sliding sleeve 34 outwardly until teeth 36 are in alignment with
teeth 32. Pins 38 abut projections 68 and drive member 60 downwardly
as they move along flat surface 48 to the position shown in
FIGURE 6. Oam 42 no longer is driven by pins 38. However,
surface 72 of member 60 abuts spring end 78, moving it downwardly
into abutment with surface 54 of cam 42. Spring end 80 is moved
downwardly away from surface 56, and spring 76 loosens, or tends
to unwrap around surface 26. The frictional drag force tending to
retard downward movement of member 60 is decreased, and a relatively
low frictional drag results. Cam 42 also is carried downwardly
with very little energy loss, heat buildup, etc.
Sleeve 34 is moved outwardly against the biasing force
of spring 40 from the position shown in FIGURE 3 to the position
shown in FIGURE 6. Teeth 36 are moved outwardly into alignment
with teeth 32, and positive engagement is established between axle
10 and wheel hub 20 in the drive mode. Teeth 32 and 36 are
constructed such that the backlash therebetween is smaller than
the distance between pins 38 and the top of ramp surfaces 46 along
flat surface 48.
When the vehicle shifts from drive to coast, as for
example when the operator lifts his foot off of the accelerator,
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hub 20 tends to overrun axle 10. In this condition teeth 32 shift
from the full-line position shown in FIGURE 6 to the dotted-line
position of FIGURE 6. In effect, an engine braking condition is
established, and hub 20 drives axle 10. Pins 38 continue to abut
projections 68, and member 60 continues to carry cam 42 through
spring end 78. Spring 76 continues to loosen, and frictional drag
remains relatively low. The vehicle may shift back and forth
between drive and coast, but teeth 32 and 36 will remain in
meshing alignment, thus ensuring that four-wheel drive operation
lo is maintained.
When the operator desires to move in reverse, he stops
the vehicle, shifts the transmission into reverse, and then starts
the vehicle once again, all the while remaining in four-wheel
drive. Because the backlash between teeth 32 and 36 is smaller
than the distance between pins 38 and the top of ramp surfaces 46,
tooth contact is established before pins 38 start to ride down
ramps 46. Sufficient pressure is established between teeth 32 and
36 such that sleeve 34 is held against the biasing force of spring
40. Pins 38 move directly from the position shown in FIGURE 6 to
the position shown in FIGURE 7, in which they abut projections 66.
Pins 38 do not ride down ramps 46 and up rams 44, due to the
windup in teeth 32 and 36. Four-wheel drive operation is maintained.
When in reverse, the vehicle may shift between the drive and coast
modes while remaining positively engaged for four-wheel drive
operation.
An important advantage of the arrangement disclosed
herein is that a positive drive condition is maintained in both
the drive and the coast modes, either in forward or reverse. This
positive drive is established automatically, thereby eliminating
any need for manually locking the wheel hubs.
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When the operator desires to establish two-wheel drive,
he stops the vehicle, discontinues the transfer of power to axle
10, and moves the vehicle in the opposite direction slightly to
relieve the windup in teeth 32 and 36, and to bring pins 38 into
contact with either ramps 44 or 46. Spring 40 biases sleeve 34
inwardly to the position shown in FIGURES 1 and 3. The operator
may then proceed in either direction in two-wheel drive.
In one preferred form of the invention, direct drive may
be established from an engine to a rear drive axle, for example,
with offset drive being established to a front drive axle, for
example. As shown in FIGURE 8, such an arrangement includes a
transfer case having an input 82 adapted to receive power from the
transmission of a four-wheel drive vehicle. A rear output 84 is
connected directly to input 82, and is connected through a rear
propeller shaft to the rear axle. A sprocket 86 is journalled for
rotation relative to input 82, and a complimentary sprocket 88 is
secured to a front output 90 which is connected through a front
propeller shaft to front axle 10. A suitable chain 92 couples
sprokets 86 and 88 for power transfer therebetween. A clutch 94
is controllable by the vehicle operator through a suitable actuating
mechanism 96. In one position, clutch 94 disengages sprocket 86
from input 82 such that power is transferred from input 82 to
output 84, but not to output 90. Two-wheel drive is established.
In another position, clutch 94 engages sprocket 86 with input 82
such that power is transferred from input 82 to both outputs 84
and 90. With clutch 94 engaged and power transferred to output
90, front axle 10 rotates and four-wheel drive is established
automatically.
Thus it will be seen that positive drive is established
automatically in both the drive and coast modes of operation when
four-wheel drive is engaged. The automatic feature eliminates any
necessity for manual lock-up in order to insure positive drive.
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The automatic feature maintains four-wheel drive in either the
drive or coast modes, and during the transition between drive and
coast. Similarly, four-wheel drive is maintained in either
forward or reverse operation, and during the shift between forward
and reverse.
A friction clutch incorporating a drag spring is arranged
to develop a relatively high frictional drag force which is used
to cam the automatic locking clutch into engagement. The drag
spring is arranged to develop a relatively low frictional drag
force after automatic clutch engagement.
It should be apparent that although the invention
provides a novel arrangement for clutching the front drive axle
and its associated wheels in a four-wheel drive vehicle, it is
readily available for use in any environment where automatic
clutching between driving and driven members is desired.
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