Note: Descriptions are shown in the official language in which they were submitted.
1329497
TITLE
H~DRAULIC V~ BLE LOC~ DIFFERENTIAL
BAC~OUND OF T~IE INVENTION
The present ln~ention rel~tes in gelleral to n li~lted
slip differential for n vehicle ~nd, in pnrticular, to ~n
hydraulically actu~ted vnriable lock dlf~erential.
Early differential mechanisms consisted of a set of
planetary gears coupled between two half-shafts of a drive
axle. Such a drive axle has the advantages over a solid axle
that the wheels of the vehicle can travel at different speeds
and equal driving force can be applied to the driving wheels.
However, under certain conditions, this conventional
differential has a serious deficiency. For example, if one
drive wheel is on a sllppery surfAce, such as ice or ~ud,
that wheel will sllp and spin becnuse lts tlre can not grip
the road. Consequently, the sllpping wheel cnn 8pply very
llttle drlving torque to move the car. The opposite drive
wheel, which well may be on a surface that gives good
adhesion, can apply no more driving torque than the spinning
wheel because the differential delivers only an equal amount
of torque to both wheels. Thus, the total driving force can
never be more than twlce the amount applled by the wheel with
the poorest road adhesion.
Traction is ~lso adversely effected, especially during
hard driving, by other conditions that unbalance the weight
on the driving wheels. When driving at high speed around a
curve, the weight is transferred from the inside wheel to the
outside wheel. Hard acceleration coming out of a turn can
then cause the inside wheel to spin because it has less
weight on it and therefore less road adhesion. Similarly,
during any hard acceleration there is propeller shaft
reaction torque on the rear axle assembly. When one wheel is
partially unloaded and looses part of its traction
capability, the loss is not offset by gain on the opposite
side because the total can only be twice that of the wheel
with the lesser capabLlity.
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The limit~d slip liffer~ntial was lesigned to improve
the traction of a vehicle nde1 ad~erse trnction condltions
by nllowing the ~ifferential to cratlsmit torqle to the ~le
shnfts in ulleqlnl nmoullts wltholt ~nter~erill6 wlth th~
differentinl action on turlls. The most common limited slip
differential is the friction type which has clutch nssemblies
mounted between the two side gears and the differential case.
In a conventional differential, the side gears and the axle
shafts to which they are spllned always turn freely in the
case. The added clutches provide a means of transferring
torque from the faster spinning (usually slipping) wheel to
the slower spinning (usually better adhesion) wheel.
Typically, there nre two clutch pn.ks, each of which is
comprised o~ dlsks thnt are splinel to the side genr, and
plates that sre tanged to fit into the differential case.
Thus, the disks rotate with the side gear and the plates
rotate with the case. The clutches are applied or actuated
by two forces. One force is applied by springs compressed
between the two side gears which push the slde gears apart,
towards the case, and thus keep the plates and dlsks in
contact with each other. This force is relatively constant
and preloads the clutches. The other force results from the
tendency of the pinons and side gears to push themselves :
apart as they turn. This force is applied through the side ~^
25 gears and lncreases the pressure on the plates and disks. -
This force becomes greater as the drlving torque transmitted
from the pinons to the side gears increases and is therefore
a variable force.
The typical limited slip differentlal has a design limit
on the amount of torque transfer from the faster to the
slower wheel, so th~t the torque on the wheel with good
traction is about two and one half times that of the wheel
with poor traction. From the above description, several
shortcomings of the common limited slip differential are
apparent:
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1) During turning maneuvers, torque is trnnsferred to
the inside wheel at a rate generally proportional
to the driving torque. This results in a tendency
to understeer.
2) Under conditions where one driving wheel is on a
very sl~ppery surface while the other has good
traction, the amount of torque that can be
transferred is very limited, essentially determined
by the preload spring force on the clutch packs.
It is the Lntent of this invention to overcome these
shortcomings by providing an externally controllable limited
slip differential whose clutch actuating force is not
dependent on preload springs or side gear separatlng forces
caused by drive llne torque, but rnther is provided by
hydrnul~c pressure. This pressure may be regulated as
necessary to adJust the different1al from zero to full
locking as driving needs dictate.
.
SUMMARY OF THE INVENTION
The present invention concerns an hydraulically actuated
variable lock differential which utilizes a piston to actuate
a multidisk wet clutch to selectively lock the differential.
The clutch pack is mounted within a right side differential
case half and the clutch disks are alternately splined to a
sun gear and the case half. At the left side of the clutch
pack, a pressure plate is fitted and held in position by a
snap ring. The right side case half also contains an annular
cavity which retains a piston. When hydraulic fluid is
injected into the cavity, the piston moves axially to the
left and squeezes the clutch disks against the pressure plate
thereby providing resistance to relative rotation of the left
a~nd right output shafts of the differential.
The hydraulic fluid is provided to the pi~ton cavity by
means oi` passages formed in the right case half and leading
to an opening on the outer surface of the case half hub. A
ring-shaped manifold ls fitted external to the case half and ~ -
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suitably mounted so th~t it does not rot~t~. Tllis mnnifold
receives hydraulic fluîd under pr~ssure from ~n e~ternnl
supply. Tlle mnl~ifold is se~l~d to ~h~ rotntlng ll~b by
primary ~nd secon~lnry senls so thnt tlle fluid will enter
opening ln the case h~lf hub. A set of passnges in the
manlfold rlng allows any hydraulic fluld that leaks past a
prlmary seal to be captured by a secondary seal and returned
to the external fluld supply.
BRIEF DESCRIPTION OF THE DRAWINGS
The above, as well as other advantages of the present
invention, will become readily apparent to those skllled in
the art from the followlng detailed description of a
preferred embodiment when considered ln the light of the
accompanying dr~wings in wllich:
FIG. 1 is a sectional top plan view of a differential
assemb1y incorporating the present invsntion;
FIG. 2 is a right side elevational view of the planetary
gear wheel assembly shown in FIG. l; -
FIG. 3 is a schematic block diagram of the pressured
hydraulic fluid supply system for the present invention;
FIG. 4 is a right side elevational view of the hydraulic
fluid ~anifold shown in FIG. l;
FIG. 5 is an enlarged cross-sectional view as if taken
along the line 5-5 in FIG. 4; and
FIG. 6 is an enlarged cross-sectional view as if taken
along the line 6-6 of FIG. 4.
. DESCRIPTION OF THE PREFERRED EMBODIMENT
There is shown in FIG. 1 a vehicle differential gear
apparatus 11 incorporating an hydraulically actuated variable :
lock differential mechanism in accordance with the present
invention. The apparatus 11 includes an outer housing 12
enclosing a rotatable differential gear case 13. The case 13
is formed from a left half case 14 and a right half case 15
which abut at radially outwardly extending flanges 16 and 17
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respectively. The left half case 14 has an axially outwardly
extending hub 18 formed thereon which is rotatably reeained
by a tapered roller besring l9 mounted on the interior of the
outer houslng 12. Sl~ rly, the right hal~ cnse 15 hns nn
outwardly a~iAlly e~tending llub 20 whicll is rotntnbly
retained by a tapered roller bearing 21 ~ounted on the
interior of the housing 12. The bearings l9 and 21 are
mounted on opposite sides of the housing 12 concentrically
with a palr of openings through which the lnner ends of a
left half axle 22 and right half axle 23 respectively extend.
The half axles 22 and 23 are rotatably supported by a pair of
tapered roller bearings 24 and 25 respectively which are
mounted in the openlngs formed in the outer houslng 12.
An end of a drlve sh~ft 26 extel~ds through a front w811
of the outer housing 12 nnd terminntes in n drive pinion gear
27. A ring gear 28 is mounted on the outer surface of the
rlght half case 15 and abuts the flange 17. The case halves
14 and 15 are attached together and to the rlng gear 28 by a
plurality of threaded fasteners 29 which pass through
apertures formed ln the flanges 16 and 17 and threadably
engage threaded aper~ures in the rlng gear 28.
An annular gear 30 is formed at the base of the flange
16 on the left half case 14 and extends lnslde the right half
case 15. The annular gear 30 has a plurality of inwardly
facing teeth. The annular gear 30 cooperates with a
planetary gear assembly 31 mounted lnside the annular gear 30
and coaxlal with the left half axle 22. Referrlng to FIG. 1
and FIG.2, the planetary gear assembly 31 includes a pair of
spaced apart generally circular plates 32 and 33. The left
side plate 32 includes a generally tubular hub portion 34
which is coupled to the inner end of the left half axle 22 by
cooperating sets of splines. The right plate 33 is formed
with an enlarged central opening through which the hub
portion 34 extends.
Mounted between the facing inner surfaces of the plates
32 and 33 are a plurality of meshed pairs of planet gears 35
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and 36. The pl~llet ge~rs 35 n--d 36 ~re ench rotatnbly
mounted on An nssocinted one of a plurnlity of plns 3;' whlch
extend through apertures for?ned in the plntes 32 and 33 and
are retained by nny s~lltnble menns, perm~nent or relensable.
A plurality of web member~ 38 e~tend radially from the axis
of rotation of the plates 32 and 33 and are Attsched to the
inner surfaces of those plates to form a unit. The gear 35
of each psir of gears is positioned closer to the periphery : :~
of the gear assembly 31 than the gear 36. The outer gears 35
all mesh with the inwardly extending teeth of the annular
gear 30. The inner gears 36 all mesh with radially outwardly
extending teeth formed on an exterior of a sun gear 39 as
shown in FIG. 1. The gears 35 nnd 36 shown in FIC. 1 are
shown in cross-section as if taken along the line 1-1 in FIG.
2.
The sun gear 39 is generally tubular in shape and has a
center portion 40. An axially extending left end portion 41
extends over and is rotatably mounted on the hub portion 34 :
of the left plate 32. The left end portion 41 is externally
toothed to engage the planet gears 36. The teeth extend from
an outsr end of the left end portion 41 whlch abuts the inner
face of the leit plate 3Z to the right hand edge of the
center portion 40. An axially extendlng right end portion 42
is lnternally splined to the inner end of the right half axle
.25 23. The outer surface of the right end portlon 42 engages an
lnwardly faclng concentric bearlng surface formed in the end
of the right half case 15. A radially disposed annular
shoulder 43 is formed at the junction of the center portion
40 and the right end portion 42. The shoulder 43 bears ~: :
against a radially extending annular surface 44 formed inside
the rlght half case 15. -
An hydraulically operated multldls?k wet clutch assembly :
45 is positioned inside the right half case 15 concentric
with and mounted on the center portion 40 of the sun gear 39.
The clutch assembly 45 provides a variably controllable
reslstance to the relative rotation between the left half
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axle 22 And the ri~ht ~nlf a~le 23. The clutcll nssembly 45
includes A wet clutch p~c~ comprlsed of ~ plurAllty of
l~terally movable annular cl~ltch dis~s concentrlcally stacked
together side by slde. Alternnte disks 46 are slidably keyed
to the right half case 15 and are linked to the left hslf
axle 22 through th~ right half case 15, the left half case
14, the annular gear 30 and the planetary gear assembly 31.
The alternate disks 46 alternate with a plurality of
intermediate disks 47 which are slidably keyed by means of
radially inwardly pro~ecting teeth which engage the teeth
formed on the center portion 40 of the sun gear 39.
The left end of the clutch pack of the clutch assembly
45 abuts an annular pressure plate 48. The pressure plate 48
is prevented from Axial movement to the left by A snap right
49 which engA~es an inw~rdly fncing nntlulAr groove formed in
the interior surface of the right half case 15 ad~acent the
pl~netary gear assembly 31. The right end of the wet clutch
pack abuts an annular piston 50 retained in an annular piston
chamber 51 formed in an interior surface of a wall of the
right half case 15 and sealed with O-rings on its outer and
inner diameters. The piston 50 is free to move axially ln
the pi~ton chamber 51 to apply pressure to the wet clutch
pack tending to force it against the pressure plate 48.
The right end of the piston chamber 51 has an orifice
formed therein which is in fluid communication with an
hydraulic fluid passageway 52 formed in the wall of the right
half case 15. The opposite end of the fluid passageway 52 is
ln fluid communication with an orifice which opens to an :~
external surface of the right half case 15 at an inwardly
facing surface of a manifold 53.
The manifold 53 is shown in greater detail in FIG. 4
through FIG. 6. The manifold 53 has a radially extending
threaded inlet 54 formed in an outer surface thereof for
connection to an hydraulic fluid supply line and fitting ~not
shown). The threaded inlet S4 is in fluid communication w~th
an inwardly facing annular channel 55. The channel 55 faces
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the e~terior stlrfnce of tl~ rl~l~t l-nlf Cl-S~ 15 nnd ls sonl~d
along opposite sides by a pnir of n~n~llnr llp seals 56. The
lip seals 56 form a primary seal for the hydraulic fluid ~-
path. If any of the hydraulic fluid should leak past the lip
seals 56, it can be returned to the hydraulic fluid supply
through a threaded outlet 57 formed in the exterior surface
of the manifold 53. The threaded outlet 57 is adapted to be
connected to a threaded fitting and hydraulic line (not
shown) to return hydraulic fluid to a reservoir as will be
discussed below.
The threaded outlet 57 is connected to a pair of
radially extending passages 58 spaced between the threaded
outlet 57 and the opposite side surfaces of the manlfold 53.
The passages 58 e~tend from the outer peripheral surface to
the lnner peripheral surface of the mnnifold 53 and are
closed at thelr outer ends by threaded plugs 59. A pair of
0-ring (or other suitable) seals 60 are positioned in annular `
grooves formed in the inner peripheral surface of the
manifold 53 and are positioned between the lip seals 56 and
20 the side surfaces of the manifold 53. The lip seals 56 and ~`
the 0-ring seals 60 are exposed to opposite sldes of the
inner end of the radial passages 58. Thus, any hydraulic `
fluid which leaks from the annular channel 55 past the lip
seals 56 will enter the passages 58 and will be prevented by
the 0-rin~ seal 60 from leaking outside the manifold 53. The
threaded outlet 57 is in fluid communication with the radial
passages 58 through an axially extending passage 61 extending -~
from one side surface of the manifold 53 to the passage 58
ad~acent the opposite side surface. The outer end of the
passage 61 is sealed with a threaded plug 62. The manifold
53 can be mounted to the outer housing 12 by any suitable -
means to prevent rotation. Thus, the right half case 15
rotates within the central opening of the manifold 53 against
the lip seals 56 and the 0-rings 60. The 0-ring seals 60 ~;
function as a secondary seal which enables any hydraulic
fluid which leaks past the primary seal to be returned to the
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e~ternal hydraulic fluid S~lr~ly~
There is shown in FIG, 3 n schemntic block diagsam of ~n
hydraulic fluid supply and control system for use with the
present lnvent~on. An hydraulic fluid reservoir 63 ls
connected to a fluid supply line 64 below the fluid level in
the reservolr 63. The fluid supply line 64 is connected to
an inlet of an hydraulic pump 65 of the unidirectional, fixed
displacement type. An outlet of the hydraullc pump 65 is
connected to a system supply line 66. The outlet of the pump
65 is also connected through an ad~ustable pressure relief
valve 67 to a return line 68 which terminates in the
reservolr 63.
An accumulator 69 ls connected to the system supply line
66. This accumulator serves as a reservoir of hydraulic
flu~d under pressure to prevent frequent on/off cycllng of
the pump 65. A pressure-sensitive switch 70 controls the
operatlon of the pump 65. The limits of switch 70 are set to
obtain the desired hydraulic fluid pressure in supply line 66 ~,
and accumulator 69.
The supply line 66 is connected to one inlet of a three-
way normally closed solenoid actuated valve 71. An outlet of
the valve 71 is connected by a return line 72 to the
reservoir 63. An inlet/outlet of the valve 71 is connected
by a line 73 to the threaded inlet 54 on the manifold 53.
The hydraullc fluid exits from the manifold 53 into the
passageway 52 and from there into the piston chamber 51 to
act~ate the piston 50 which in turn actuates the clutch
assembly 45. Any fluid which passes the lip seals 56 of the
primary seal is trapped by the secondary O-ring seals 60 and ~-
exits the manifold 53 through the threaded outl'et 57. A
return line 74 is co,nnected to the threaded outlet 57 and
terminates at the reservoir 63.
When the valve 71 is actuated, pressured fluid in the
line 66 passes through the valve to the line 73 and flows to
the piston chamber through the path described above. The
clutch actuating fluid pressure is released when the
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energizing power is removed from the solenoid associated with
the valve 71.
Hydraulic fluid in the piston chamber 51 can now Elow
backward through the fluid passageway 52, through the
manifold 53, line 73, ~alve 71, and return line 72 to the
reservoir 63. The release of pressure in piston chamber 51
reduces the force on piston 50 to essentially z.ero, allowlng
the plates in clutch pack 45 to rotate freely against each
other. Thus, when the solenoid valve 71 i9 not energized,
the differential behaves essentially as an open or free
differential.
As the piston 50 is actuated by the application of
pressured hydraulic fluid, the clutch disks 46 and 47 are ~ ;
squeezed together against the pressure plate thereby ~ -
providing resistance to relative rotation between the left
half axle 22 and the right half axle 23. Thus, the
dLfferential will be locked for a range of torque wh~ch is
the difference in the torques applied to tha half axles. The
torque range will be from zero to an upper limit determined
by the torque at which the clutch slips. This upper limit i8
related to the hydraulic fluid pressure.
In this embodiment of the hydraulic supply, the degree
oi locking is set by the limits set on pressure switch 70.
The solenoid valve 71 could be controlled by an electronic
circuit, not shown, that activates valve 71 when wheel spin
occurs. It should be realized that other embodiments of the
hydraulic supply are possible within the scope of this
invention. For e~ample, if the solenoid valve 71 were
replaced by an electro-hydraulic proportional or servo valve,
it would be possible to electronically vary the pressure in
llne 73 from zero to the value of pressure in line 66, as set
by switch 70. This would permit the locking torque of the
differential to be varied as necessary to meet driving
requirements.
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In accordancs with the provisions of the patent
statutes, the present invention has been described in what is
considered to represent its preferred embodiment. However,
it should be noted that the invention can be practiced
S otherwise than as specifically illustrated and described
without d~parting from its spirlt or scope. ~:
