Note: Descriptions are shown in the official language in which they were submitted.
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1270.001 BACKGROUND OF INVENTlON
The most commonly used automo~ive vehicle differential is of the
bevel gear confirguration. This dif~erential is coupled to the vehicle engine drive
shaft and divides the engine's output and torque equally to both drive wheel
axles. This differential permits the speeds of the driven shafts to change
according to demand.
The conventional differential does not permit any larger amount
of torque to be transmitted to the~ ground than twice the amount that may be
- transmitted to the wheel with the Iesser traction. Consequently, when the
traction of either wheel is æro, such as~ when the wheel is spinning on ice, there
is no power or torque transmitted~ tcs the- ground by either of the wheels or driven
axles. As is well known, when one wheel spins, the opposite wheel does not
rotate at~ll with this-conventional differential.
Consequently, ~ various types of power-dividing or limited slip
differentials have~ been developed~ for the purpose of powering one wheel when
the opposite wheel spins, i.e., has lost traction. By way of example only, one
form of such a;- power-di-iding differential is disclosed in my prior~patent
No. 2,720,796 issued January 18, 1955.
However, avallable limited~ slip power-div~ding differentials are
relatively expensive and complex in construction and tend to wear out sooner
than the above conventional differential. Moreover, they typically do not
perform satisfactorily at low ground frictlon when the vehicie goes around a
curve where the outer wheel must rotate faster than the inner wheel, in which
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cases, there is a tendency to lose control due to lock up of wheels causing
scuffing of the~ tires. Further, problems tend to arise when a wheel momentarily
leaves the ground while the other remains in contact with the ~round. Further,
when one wheel looses traction, there Is still a tendency for it to spin to some
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_70.0Ql extent. Consequently, there has been a need for an improved di~ferential
capable of instantaneously transmitting torque to the wheel having traction while
the other wheel looses its traction and also to handle the problem of one wheel
rotating faster than the other, without further complica~ing or increasing the
cost of the differential and preferably reducing same.
SUMMARY OF INVENTION
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ll~e- invention herein relates to what may be called a positive
clutch differential. The differential housing is of the size and shape of a
conventional differential.. However, within the differential are two self-locking
and torque responsive friction clutches, each connected to one of the driven
shafts~ or axles~ When the vehicle is driven straight forward, both clutches are
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locked and torque is distributed substantially equally to both output shafts or
axles so that the driven wheels rotate equally. However, when the vehicle moves
along a curve or turns, the wheel on the outer side of the curve is disengaged,
that is, its clutch unlocks, so that such wheel is free~ wheeling. Consequently, all
power and torque flow to the inner wheel in the turn whlch inner wheel now
transmits all of the torque to the graund.. Likewise, should either wheel lose
traction, all driving torque will be di5tributed to the opposite wheel. The
performance of this differential is the same in either driving direction, that is,
whether the vehlcle travels forwardly or reversely.
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1270.001 The differential includes a center driving ring-shaped thrùst
coupling member that is secured within a conven~ional differential casing for
rotation therewith. Such casin~s are normally rotated by means of a beYel gear
secured to the casing which engages a pinion mounted upon the engine propeller
or output shaft. The center driving ring is located between a pair of pressure
rings, each of which is movable towards and away from ~he adjacent face of the
center ring.
Each of the opposite faces of the center dri~in~ rin~ is provided
with wedge-shaped cam-like teeth. Th'ese ~eeth couple with corresponding teeth
formed on the adjacent faces of the pressure rings.
Each of the pressure rings is connected to the inner end of one of
the axles or shafts which extends into the casing. This conr~ection is through a
friction clut~-h which locks or engages when the respective pressure ring moves;
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outwardly, i.e., away from the centèr driving ring, and disengage or unlock when
the pressure rings move- inwardly towards the driving ring.
When the vehicle' wheels are rotating at the same speed, as when
the~ vehicle is moving on a straight path, the center ring rotates with the
differential casing due to the power received from the engine. The center ring
teeth engage and'wedge outwardly the corresponding teeth of the two pressure
rings. Because of the axially outward wedging orce upon the pressure rings,
these in turn,~ press outwardly to positively engage their respective friction
clutches. ~These clutches are connected to the axles so that power is transmitted
to the axles.
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However, when one of the axles rotates faster than the other, as
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for example when the~vehicle is going around a curve wherein the wheel on the
outside of the curve must rotate faster, then the pressure ring of that wheel
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~70.001 over-runs or rotates more rapidly than the center ring. ConscquentJy, the
pressure ring wedge-like teeth, moving faster than the teeth of the center ring,disengage ~herefrom. That disengagement results in the pressure ring moving
axially inwardly, that is, towards th~ center driving ring, which results in thedisengagement of that pressure ring's clutch. When its clu~ch disengages, its axle
no longer receives power or torque and all of the torque is transmitted to the
opposite axle. Consequently, while one of the axles is "free wheeling" the othercarries all of the torque and transmits it through its wheel to the ground.
Because the pressure ring teeth over-run or speed-up relative to
the center ring teeth~ which they engage, there is a normal tendency for the teeth
to re-engage. That is, the teeth disengage on one surface and tend to re-engage
on the opposite surfaces. In order to prevent this from happening, that is to
maintain a gap between the teeth during the over-run or speed-up condition7 a
stop ringis provided; The stop rlng, which is~ als~called a 'ibalking" ring extends
through the middle of the center driving ring and connects the two pressure rings
together. Each connection`is provided by interengaging splines formed on the
surface of the stop ring and within openings in the pressure rings through whichthe stop ring is inserted. These splines, that is the teeth making up the splines,
'I are~ relatively Ioose to provide a predetermined amount of backlash. Such
backlash permits the pressure ring ~to move sufficiently so that its teeth
disengage from the corresponding teeth on the center driving ring, but then the
spline teeth engage to hold the specific pressure ring against further rotàtional
movement reiative to the center driving ring. This results in the gapping or
spacing apart of the opposite surfaces of the meshing wedge-like teeth of both
the pressùre ring and the~center rlng. That is, the backlash in the splines permit
limited movement and then hoid each pressure ring agains~ further movement
with respect to the center drivmg ring.
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~70.001 Restated in more detail, the differential of this invention
normaLly transmits torque substantially equally to both of the axles or drive
shafts through a thrust coupling, which is made up of the center driving ring and
the pair of pressure rings which are coupled together because of thcir meshed
wedge-like teeth. The pressure members each are ~rictionally clutched to their
respective axles or shafts. However, during over-runs or speed-ups of one axle,
such as when going around a curve or when a wheel spins due to lack of traction,i~s pressure ring rotates faster than the center ring so that the trailing faces of
the pressure ring teeth move ahead of the leading faces of the center drive ringteeth which they otherwise contact during normal operation. Momentarily, a gap
appears between the respective teeth which disengages the thrust mechanism.
Continued advancing movement of the pressure ring is stopped by
the spacer ring whose backlash permits a gap to appear between the tralling
faces of the pressure ring teeth and the leading faces of the center ring teeth but
then prevent the opposite teeth faces from engaging during the over-run. Now
that the wedge-shaped teeth are disengaged, that axle and its wheel are "free
wheelin~" and all torque is transmitted to the opposite axle or shaft and its
wheel. The disengagement occurs because the pressure ring, which is no longer
being wedged outwardly due to the released teeth contact, moves axially
inwardly to release its clutch.
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When the over-run axle slo~s down to the speed of the casing and
the center driving ring, its pressure ring teeth again re-engage the teeth of the
center driving ring and norrnal power transmission takes place again. This occurs
because the re-engaging teeth again wedge or move outwardly the pressure rin~
teeth so that the pressure ring clutch re-engages.
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The differential of this invention is formed of essentially five
elements which are of relatively simple and inexpensive construction. These
elements are: First, a conventional appearing, that is, conventional size and
shape, casing or housing which is rotated in the conventional m~nner throu~h the
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_70.001 usual gearing from the engine drive shaft or propeller shaft. Second, a flat disk-
like or ring-shaped center driving ring which rotat~s with and is fastened within
the interior of the casing. Third, a pair of pressure rings located on opposite
sides of the center ring. Fourth, a stop ring which extends through the axially
aligned pressure rings and center driving ring, interconnectin~ with the pressure
rings through the loosely meshed corresponding splines. Fifth, a coil spring is
arranged around the stop ring and between the pressure rings, extending through
a central opening in the center driving ring, to exert a slight amount oE axially~
outwardly directed pressure upon the pressure rings. The springs provide for
virtually instantanenous engagement of the clutches when drivin~ power is
applied.
These five elements, particularly the rings, are extremely simple
in construction and simple and inexpenslve to construct. For- example, their
wedge-like teeth may b~ made through the use of forging processes with minimal
machining required. Moreover, the clutch- engagement and disengagement
requires movemen~ of a small amountj such as within a few thousandths of an
inch and the movement is virtually instantanenous whereby there is practically
no wear upon the clutches during engagement or disengagement so that the
differential is expected to wear far better and longer than currently available
differentials.
Among the objec* of this invention is to provide an automotive
type differential with improved traction under slippin~ conditions, and
eliminatlng ~e spinning of either wheel when it looses traction and which
provides a higher efficiency and safer operation. This type of differential is
particularly useful in four-wheel drive vehicles and off the road vehicles.
Nevertheless, despite its subst~ntially improved operation, its construction is so
simplified as to be less costly to produce than other locking type differentials.
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1270.001 Another object of this invention is to provide a differential which
is quiet under all driving conditions or when the power is shifted from one to
another of the driYen axles due to slippery conditions or drivinO about curves or
turns. Further, this differential construction eliminates the ne~ative torques
which are induced in the unit and the so-cal~ed ~stick-slip" conditions which are
common in currently available limited slip type of differentials.
These and other objects and advantages will become apparent
upon reading the following description, of which the attached drawings form
part.
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_/0.001 DESCRIPTION OF I~RAWINGS
Fig. 1 is a cross-sectional view schematically illustrating the
differential herein. ,
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Fig. 2 is a diagramatic view of the differential center driving ring
and the ~wo pressure rings during normal power drive conditions, ~hat is, with
b~th axles driven at the same speed.
Fig. 3 is a diagramatic view of the stop ring and the two pressure
rings showing the relative positioning of their respective T~eshed teeth during
normal power drive conditions as illus~rated in Fig. 2.
Fig. 4 is a diagramatic view, sirnilar~ to Fig. 2, but illustraffng the
right side pressure ring disengaged~ from the center driving rin~ and with its
clutch disengaged for free-wheeling of the right-hand anxle.
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Fig. 5 Is a diagramatic view9 similar to Fig. 3, showing the
relative~positioning of the meshed teeth of the stop~ ringland the two pressure
rings during the condition shown in Fig. 4.
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Fig~ 6 is a~ partial cross-sectional, disassembled view of a nurnber
of the parts which make up the differential.
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Fig. 7 is a~ partial~ cross-sectional, schematic view of a modified
differential having~a dlsk type~dutch.
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Fig. g is a fragmentary cross-sectional view of certain of t~e
parts which make up the disk clutch type dlfferential of Fig. 7.
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?70.001 DETAILED DESCRIPTION
Fig~ I illustrates an embodiment of the differential of this
invention which utilizes a cone type clutch. This differential includes a rotatable
outer casing or housing 10. The casing is made of a flanged part 11 and an
opposite part 12, between which is positioned a flat ring-like member 13. The
two casing parts are fastened together by bolts 14 which pass through aligned
openings in each of the parts and also through openings 15 in the flat ring. The
openings in the opposite part 1Z are threaded so that the bolts may mechanically
secure the two parts together into the hollow casing shape.
Each of the casing parts is provided with a sleeve-like bearing
end 16 around which a bearing 17 is mounted. The bearings ~7, in turn, are
secured within the~ differential outer structure or outer housing which is
s~ationaryjso that the casing 10 may rotate within~it about the bearings 17. The
stationary housing is omitted from this~ d~sclosure since it is convent;onal. For
illustration purposes, the construction shown in my above-mentioned~ patent
No. 2,720,796 includes such a support.~
A conventional bevel gear 18 is fastened to the flange 19 which is
formed integral with the flanged part 11 of the caslng. Suitable bolts 20 are used
to fasten the bevel gear to the flange. The bevel gear meshes with a drive~pinion
21 secured on the end of the power drive shaft 22 which may be the propeller
shaft or engine drive shaftj as is conventional.
A pair of axles or shafts 25 extend into the casing through the
bearing ends 16. The inner ends of the axles are provided with splines 26. Axle
hubs or axle rings 27 having spline~ teeth 28 fit over and mesh with ~e splined
inner ends 26 of the axles so that the hubs may slide axially of the axles.
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`70.Q01 The center drive ring or chrust member 30 is integral with the flat
ring 13 that separates ~he two casin~ parts. Thus, the center drive ring rotateswith the casing as if it ~vere part of the casing. The opposite faces of the center
drive ring are provided with wed~e-shaped teeth 31, which are V-shaped in cross
section.
The center drive ring is located between a pair of pressure
rings 32, each of which has wedge-shaped teeth 33 for meshing with or coupling
with the ~ee~ 31 of the center drive ring.
Each of the pressure rings is also provided with an internal
spline 34.
The stop ring or so-called "balking" ring 35 is located within the
casingS co-axially with and extending ~hrough the centers of the pressure rings
and the center drivin~- rin~. Spline teeth 36 formed- upon the stop ring,
particularly at:its opposite edges, Ioosely mesh with the teeth of spline 34 of the
pressure rings 32. The spline teeth 36 of the stop ring may be formed as a pair of
spaced apart gear-like formations or alternatively as a unitary tooth formation
extending completely across the surface of the ring.
The rims 37 of the pressure rings 32 are widened considerably and
each is provided with an internal conical clutch face 39 which engages an
external conical clutch face 40 on its adjacent axle clutch hub 27. Each hub is
also formed with an outer conical portion 41 which fits within a conical seat 42formed within the casing parts 11 and 12 tsee Fig. 1).
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A coil spring 43 encircles the~ stop rin~ and its opposite ends abut
against the opposed pressure rings. The coil spring provides a small amount o~
axially outwardly directed pressure upon the pressure rings so that they normally
tend to virtually instantaneously move outwardly for clutch engagement.
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~270.001 The operation of the differential is diagramatically illustrated in
Figs. 2 through 5. Thus9 referring to Fig,. 2, the center driving ring 30 is
rotatably driven by the rotating casing, as illustrated by the large arrow. As the
center drive ring 30 rotates, its wedge-shaped teeth 31 engage and wedge againstthe adjacent wedge-like teeth 33 of each of the adjacent pressure rings 32. The
wedging force is illustrated by the small arrows drawn at the enga~ing teeth.
Thus, the ro~ational movement of the center drive gear results in ~e pressure
rings likewise rotating. The pressure conical clutch surfaces or clutch faces 38engage ~e corresponding conical clutch faces 40 on the double cone clutch
hubs 27. Therefore, the hubs rotate with the pressure rings and because they arespline connected with the axles, the axles rotate at the same speed, which wouldcorrespond to the vehicle moving along a straight path.
The arnount of movement axially outward by the pressure rings,
due to the wedging action of the engaging wedge-like teeth, may be on the order
of 20-30 mousandths of; an inch~ The lesser amount of movement, the shorter the
tirne of engagement. Ordinarily, the engagement time is Yery small so tha~ thereis virtually instantaneous engagement for all practical purposes which
substantially increases the time that both driven axles share the torque output to
the differential.
During the driving cgnditions shown in Fig. 2, the stop ring or
balking ring 35 has its spline teeth 36 centered relative to the teeth of the
spline 34 of the pressure rings. The meshed teeth of the spline 34 and the stop
ring spline are loosely interfitted so that there is sufficient backlash to permit
the teeth to be centered, as illustrated in diagramatically exaggerated form in
Fig. 3.
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Next, turning to Fig. 4, the right hand pressure ring 32 is shown as
disengaged from its clutch connèction with the axle hub. A condition like this
comes about when the vehicle makes a left turn or travels about a Jeft
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0.001 directional curve so that the right-hand wheel must rotate at a faster speed than
the left-hand wheel. During the time of that faster speed, the shaft of the right-
hand wheel rotates at a greater speed than the center driving rin~ 30 and the
differential casing 10.
When the shaft rotates faster than the driving ring, because of the
clutch connection between the axle hub 27 and the adjacent pressure ring, that
pressure ring tends to over-run or go faster than the center drive ring~ This
results in the meshing teeth separating (see Fig. 4) because the pressure ring
teeth advance more rapidly than the wedge-shaped teeth of the center driYing
ring. Thus, the trailing surface of the teeth o the pressure ring advance away
from the lead teeth surfaces of the center driving ring teeth. That advancement
could very well result in the teeth continuing until they again engage on their
opposite surfaces. That is, continued movement could result in ~e lead surfaces
of the pressure ring teeth engaging the~ trailing surfaces of the center ring teeth.
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However, to prevent the now momentarily separated wedge-
shaped teeth from re-engaging on thelr opposite faces, the stop ring 35 is now
located so that its teeth engage the surfaces of the teeth of the two pressure
rings. As can be seen in Fig. 5, the trailing surfaces of the teeth on the right-
hand pressure ring engage the leading surfaces of the spline teeth of the stop
ring. The converse occurs on the left-hand teeth. That i5, the backlash is over
come and the teeth engage so that they form a stop and thereby maintain the
wedge-shaped teeth in the condition shown in Fig. 4.
Because the wedge-shaped teeth shown in Fig. 4 are not engaging
on the right-hand side, the right-hand pressure rlng tends to move inwardly
axially, that is to the left, and center itself in an unloaded position.
Consequently, the interengaging clutch surfaces separate. Now, the axle hub is
disengaged from the pressure ring so that it is free to turn independently of the
center drive ring. As a result, the right hand axle is now free wheeling, i.e., not
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!270.001 powered. However, the left-hand axle remains powered, with the left-hand
pressure ring having its teeth still in contact with the wedge-shaped tee~h of the
- center drive ring and operating normally.
As can be seen, the interengaging, but loosely meshed teeth of the
stop ring and the pressure ring splines, work together to forrn a stop. In one
situation, that stop permits ~e wedge tee~ of the center ring to engage the
pressure ring teeth. In another situation, that is, when one axle over-runs the
speed of th~ casing, ~at stop allows the wedge-shaped teeth to disengage and
holds them disengaged.
During the. hme that the wedge-shaped teeth are engaged, the
wedging action forces the respective pressure rlngs outwardly. However, when
they are not interengaged, there is an~inherent tendency for the pressure rings ta
move inwardly.. In order to provide for.. instantaneous- response of the clutch.
engagement, the coi1 sping 43 IS relied upon to provlde a slight amount of spring
pressure which normally urges the two pressure rings apart and axially outwardly
into clutch engagement:positions.
The~relative proportions required of the differential's elements in
order to make the cone type~ differentials' clutches self-locking may be expressed
in the following mathematical relationship~
Tan B tan Ar
Where:
B = Thrust angle, cam angle
r = Mean radius, thrust coupling
R = Mean radius clutch facings
U = Friction coefficient
A = Cone angle
The thrust angle 6 refers to the angle of the surface of a wed~e-
.shaped tooth relative to the altitude or line which bisects the triangle formed by
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70.001 the opposed faces of adjacent teeth. That is, it is the angle between the
hypotenuse (tooth surface) and altitude of the equilateral triangle ~ormed by
adjacent wedge-shaped tooth surfaces.
Although the clutches are illustrated as being o~ the conical type,
disk type clutches rrlay also be used, depending upon the requirements of the
differential. Thus, Figs. 7 and 8 illustrate a modification which is similar in
operation an~ construction to that shown in Figs. 1 through 6, but utilize disk
type clutches instead of conical clutches. Fig. 7 illustrates the differential
which includes the~ casin~ 10 made of opposing parts 11 and 12 similar to the
casing shown in Fig. 1. Opposed axles or shafts 25 are inserted within the casing
in the same manner as described above, and each axle includes an axle hub 27
having internal splines which mesh with splines formed on the inner ends of the
shafts 25.
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-- The inner or facing ends of the axie hubs 45 are- reduced in
diameter and are surrounded by- the stop ring 46 which has an external spline
tooth arrangement 47. The coil spring 48 surrounds the~ splined stop ring and fits
within the open~ center of the center driving ring 30 which is slmilar to the center
driving- ring described in connection with Fig.- 1.
The pressure rings 32a have wedge-shaped teeth 33 which mesh
with the correspondingly shaped wedge-shaped teeth 31 on the center driving
ring 30 as above.
The pressure ring 32 includes an internal splined tooth
configuration 34 which meshes with the stop ring spline teeth 47 in the same
manner as that set forth above in connéction with Figs. 3 and 5 in the
embodiment of Fig. 1. However, a second spfine or tooth configuratlon 49 is
formed on the exterior of the pressure rings. These teeth 49 mesh with internal
splines 50 formed on clutch rings 51 which surround the pressure rings.
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70.001 A plurality of flat clutch plates 52 surround each hub 45 and are
engaged between the pressure rin~ outer plate engaging face 53 and an anvil or
rib annular formation 54 formed within the casing (see Fig. 7).
The clutch plates 52 alternate between plates that have outer
notches which receive the teeth of the spline 50 of the outer clutch ring S1 andreduced diameter plates which have inner notches that receive spline teeth 55 ofthe hub 45. Thus the clutch plates 52 alternate between larger diameter
plates 56 an~ smaller diameter plates 57 which are squeezed together by the
pressure of the face 53 of `the pressure ring directed towards the annual anYil 54.
This pressure occurs when the pressure ring tee~h 33 are engaged with and are
driven by the wedge-shaped teeth 31 o. the center driving ring as illustrated inFig. 2.
When an axle over-runs, its pressure plate moves into the gapped
apart position illustrated in Fig. 4, i.e., where the wedge-shaped teeth disengage
and the flat pressure or clutch surface 53 moves axially inwardly towards the
center drivin~ ring so as to release the pressure on the clutch plates and thereby
open the clutch.
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The inner spline 34a of the pressure ring 32a is engaged with and
ax~ally slides relative to the spline 47 of the stop ring 46 to provide for the
stopping and spacing action which is illustrated in Fig. 5.
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As in the cse of~ the cone type of clutch, a small amount of
movement in the axial direction of the pressure rin~, such as in the range of a
Iew thousandths of an inch is sufficient~ to engage or disengsge the clutch for
that particular axle. Thus,~ ~there is minimal wear on the clutch faces and
clutching and de-clutching is virtually instantanèous. In the disk type clutch, as
well as in the cone type clutch, the clutch faces enga8e when the parts are at the
same speed which substantially eliminates wear due to engagement or
disengagement.
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1270.001 The relative proportions required of the elements of the disk type
different;al of Fig. 7 and 5 to make the diferentials' clutches self-locking is
slightly different than the proportions expressed in the mathematical relatiohship
given above in connection with the cone type clutch. lllis relationship is as
f ollo~s:
Tan B = r
Where:-
B - Thrust angle~ cam angle
r = Means radius,. thrust coupling
R = Means radius clutch facings
N- = Number of friction surfaces
U - Friction coefficien~
l~ie~ construction of the differential described herein, whether of
the cone clutch type o~- the plate clutch type, is not complex and the parts are
produceable by relati.vely inexpensive manufæturing processes.- Consequently,
the construction is economical. to. produce and is more efficient, more wear
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resistant and substantially better in operation than prior cornparable
differentials. ~ ~
Having fully described. an operative embodiment of this inven~ion,
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