Drive axle assembly

A drive axle assembly including a housing structure having a fixed spindle, a nonrotatable spacer ring disposed about the spindle and a drive hub rotatably mounted on the spindle by bearings, one of which abuts the spacer ring. The spacer ring has a brake apply fluid inlet to an interior passage which opens to a first sealed annular cavity between the spacer ring and the hub. The exterior of the spacer ring defines in conjunction with the drive hub a second low pressure cavity therebetween enclosed by a radial face seal having a rotating portion disposed in the hub and a nonrotating portion disposed in the spacer ring. Lubricating and cooling fluid is pumped through the second cavity to cool the face seal and continues through passages in the drive hub to provide a nearly continuous flow to the drive and brake components in the hub assembly. The specific location of the brake apply cavity interiorly adjacent the lower pressure lubricating cavity also minimizes the effect of small leakages past the seals of high pressure in the brake apply cavity.

CROSS REFERENCE TO RELATED APPLICATIONS 
This application is related to the following applications assigned to the 
assignee hereof: 
Ser. No. 335,948, filed Dec. 30, 1981 entitled AXLE DRIVE AND BRAKE 
ASSEMBLY by Kenneth E. Houtz, William J. Pratt, and Robert E. King. 
Ser. No. 336,003, filed Dec. 30, 1981 entitled DRIVE AXLE FLUID SYSTEM by 
Kenneth E. Houtz. 
Ser. No. 336,218, filed Dec. 31, 1981 entitled INTERNAL BRAKE by Karl 
Salna, Donald F. Rudny and Stanley Urman. 
BACKGROUND OF THE INVENTION AND THE PRIOR ART 
This invention is related to drive axles for heavy vehicles, such as wheel 
loaders, of the type having drive hub assemblies rotatably mounted to the 
respective ends of the axle housing and having planetary gear drives 
therein and, more particularly, to an apparatus for transferring fluids 
from the nonrotating axle housing to the rotating drive hub assembly. 
It is previously known to use a nonrotatable spacer ring to fix the axial 
position of the inner bearing mounting the planetary gear drive hub 
assembly on an axle housing. Such is shown, for example, in Chamberlain 
U.S. Pat. No. 4,140,198. However, the prior art drive axle assemblies, as 
also shown in Keese U.S. Pat. No. 4,037,694, and Sidles, Jr. et al. U.S. 
Pat. No. 4,142,615, utilized a pool of oil for cooling and lubricating and 
hydraulic passages in the fixed spindle for actuating the brake pack. In 
the referenced copending applications, a brake pack is provided in the 
drive hub assembly wherein all portions of the brake pack and the 
actuating means therefor rotate relative to the spindle. Consequently, it 
requires that for actuating the brake, the actuating fluid be transferred 
from the nonrotating spindle to the rotating hub assembly. 
Accordingly, a primary object of the invention described and claimed herein 
is to provide a drive axle assembly of the type described with a means 
associated with the axle spindle for establishing a fluid tight transfer 
of operating fluid to the drive hub assembly. 
A more specific object is to provide a drive axle assembly with a structure 
for communicating brake actuating fluid pressure from the stationary axle 
structure to the rotatable wheel hub assembly. 
A further object of the invention is to provide in a drive axle assembly a 
structure for communicating lubricating and cooling fluid under pressure 
from the stationary axle structure to the drive and brake components in 
the rotating wheel hub. 
Still a further object of the invention is to provide the drive axle 
assembly with a housing for stationary portion of the primary oil face 
seal located between the environment and the interior of the axle 
structure. 
Yet another object of the invention is to circulate the pressurized fluid 
for the drive and brake components past the aforesaid seal to also effect 
cooling thereof. 
A more specific object is to provide in a drive axle assembly a single 
structure meeting, in cooperation with the surrounding structure, all of 
the above objects while also functioning as the prior art bearing spacer 
ring which eliminates a stress concentrating sharp corner on the spindle. 
The above objects and others which will become apparent hereinafter are 
specifically met in a drive axle assembly including a housing structure 
having a fixed spindle, a nonrotatable spacer ring disposed about the 
spindle and a drive hub rotatably mounted on the spindle by bearings, one 
of which abuts the spacer ring. The spacer ring has a brake apply fluid 
inlet to an interior passage which opens to a first sealed annular cavity 
between the spacer ring and the hub. The exterior of the spacer ring 
defines in conjunction with the drive hub a second low pressure cavity 
therebetween enclosed by a radial face seal having a rotating portion 
disposed in the hub and a non-rotating portion disposed in the spacer 
ring. Lubricating and cooling fluid is pumped through the second cavity to 
cool the face seal and continues through passages in the drive hub to 
provide a nearly continuous flow to the drive and brake components in the 
hub assembly. The specific location of the brake apply cavity interiorly 
adjacent the lower pressure lubricating cavity also minimizes the effect 
of small leakages past the seals of high pressure in the brake apply 
cavity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, there is shown in FIG. 1, a wheel loader 10 
having an articulated frame 12, the rear portion 14 of which contains an 
engine 15 and is supported by rear wheels 18. The front portion 20 of the 
frame is pivoted at 22 to the rear frame portion 14 and is supported by 
front wheels 24. A loader bucket 26 is mounted to the end of lift arms 28 
supported by the front frame 20. 
The invention is directed to a drive axle assembly incorporating a 
planetary gear system that can be used in conjunction with any of the 
wheels illustrated in FIG. 1 and preferably on all four of the wheels. 
Referring to FIG. 2, a drive axle shaft 30 which is driven from the engine 
15 through a transmission and a differential (not illustrated), is 
supported to rotate within a non-rotating axle and differential housing, 
portions thereof being shown at 32, trunnion mounted on a longitudinal 
axis to the frame 12 of the vehicle. An elongated spindle 33 having an 
axial bore is welded or otherwise nonrotatably secured in outwardly 
exending relation from the axle housing. A wheel hub assembly 34 is 
rotatably mounted on the spindle 33 as by inner and outer bearings 35 and 
36, the inner bearing 35 abutting a spacer ring 37, fixed against rotation 
as by pin 38, circumferentially disposed about the spindle and abutting on 
exterior shoulder 39 thereon. Inner bearing 35 rotates within inner race 
35A. The spacer ring 37 thus locates the bearing 35 without adding a 
stress concentrating small radius shoulder to the spindle at the bearing 
mounting. As will be obvious from the drawing, the spacer ring 37 has many 
other functions which will be described subsequently. The outer diameter 
of spindle 33 is reduced axially outwardly to permit easy installation of 
the inner bearing 35 thereon and terminates in a splined end beyond the 
outer bearing 36. 
The tire 40 of the vehicle wheels 18 or 24 is secured in place on a 
peripheral rim assembly 41 secured to the wheel hub assembly 34 exteriorly 
of a planet carrier 42, as by a large number of circumferentially spaced 
bolts 43 extending through both the rim and carrier into taps in the hub 
assembly, so that both will rotate with the hub assembly relative to the 
spindle 33 and stationary axle housing 32. The planet carrier 42 is a one 
piece casting disposed about the drive shaft 30 and has an exterior radial 
wall 44 and an interior radial wall 45. A cover 46 having a flanged outer 
perimeter sealed by O-ring 50 is secured by a plurality of removable bolts 
48 to the exterior radial wall 44 of the planet carrier 42. Thus, the hub 
assembly 34 has an interior chamber 52 partially enclosed by the planet 
carrier 42 and the cover 46. 
A planetary gear drive assembly 56 is disposed in the hub chamber 52 
between the rotating drive shaft 30, the stationary spindle 33 and the 
planet gear carrier 42 which carries the wheel hub. The planetary gear 
system includes a sun gear 60 keyed to or formed integrally on the drive 
shaft 30 at its outboard end and a ring gear 61 keyed against rotation to 
splines 62 on the peripheral edges of ring gear carrier 64, and secured 
against axial movement by bolts 63. The inner portion of the carrier 64 is 
keyed by internal spines 65 to the splined end of the spindle 33. An 
annular retainer plate 66 attached to the end of the spindle 33 by bolts 
67 in axial taps therein retains the ring gear carrier 64 on the spindle 
33. The hub of the ring gear carrier 64 further functions as a spacer 
working against the inner race of the outer wheel hub bearing 36 so that 
the bearing 35, hub 34, bearing 36, and spacer ring 37 are in continuous 
abutment to the spindle shoulder 39, shims being disposed between the 
spindle 33 and the ring gear retainer plate 66 to provide the desired 
amount of preload on the bearings. 
The planetary gear drive assembly 56 further includes a plurality of 
circumferentially spaced planet gears 68 (only one being shown) engaged 
with the sun gear 60 and with the ring gear 61, each planet gear being 
supported rotatably by bearings 70 on a stub shaft 71 secured between the 
radial walls 44 and 45 of the planet gear carrier 42, being locked therein 
by a bolted plate 72 received in a corresponding groove in the stub shaft 
71. Thus, the rotation of the drive shaft 30 and sun gear 60 causes the 
planet gears 68 to rotate, and the planet gear carrier 42 to rotate in 
turn relative to the stationary ring gear 61. The speed reduction ratio 
can be quite high in such a planetary gear arrangement, on the order of 
about eight to one for the arrangement shown, so that the wheel hub 34 is 
rotated at a slower speed, but with higher torque, than the input speed of 
the drive shaft 30. 
The planet gear carrier 42 has an integrally cast annular wall 74 disposed 
axially and concentrically about the outboard end of the drive shaft 30 
and defining a cylindrical cavity 76 opening outboardly or endwardly of 
the drive shaft. A brake pack 78 is fitted within the cavity 76 and 
includes two sets of discs 80 and 82 interfitted with one another. Each 
disc 80, which is provided with friction material on its surfaces disposed 
to engage the discs 82, has an internal spline that cooperates with the 
axially extended teeth 81 of the sun gear 60 thereby keying all the discs 
80 to the drive shaft 30 while allowing axial movement thereon. The 
friction material on the disc 80 is grooved in a crosshatch pattern to 
assist in drawing oil between the discs 80, 82. Each disc 82, which has a 
metallic surface disposed to engage the discs 80, has an exterior spline 
that cooperates with a mating internal spine 83 on the annular wall 74 of 
the planet gear carrier 42 so that all of the discs 82 are keyed to the 
planet carrier while being movable axially thereon. Since both sets of 
discs rotate, the materials of the discs 80, 82 could be interchanged with 
little effect. 
A brake actuating means is disposed in the planetary gear cover 46 which 
has a pair of spaced annular walls 86 and 87 defining a groove opening 
toward the brake pack cavity 76 which is axially and concentrically 
disposed relative to the drive shaft 30. An annular piston 88 fits between 
the annular walls 86 and 87, seals 90 in the piston walls establishing 
rearwardly of the piston and remotely from the brake pack 78, an annular 
pressure chamber or cylinder 92 for fluid actuation of the brakes. An 
annular backing plate 94 is disposed in the brake pack cavity 76 on the 
inboard end of the brake pack 78 and a split ring 96 fitted within an 
annular groove in the annular wall 74 of the planet gear assembly 42 holds 
the backing plate 94 against inboard axial movement. Optionally, the ring 
96 and even plate 94 could be integral with the planet carrier 42. A 
plurality of coiled compression springs, one of which is shown at 98, are 
located between the outboardmost brake disc 82 and the backing plate 94 
for the purpose of providing a mechanical release of the brake pack 78 
when the brake cylinder 92 is depressurized. It will be seen that upon 
pressurizing the annular brake cylinder 92, the annular brake piston 88 is 
driven axially inboard along the drive shaft and against the brake pack 78 
causing the two sets of brakes discs 80 and 82 to frictionally engage each 
other. Therefore, in the brake-engaged position, the input drive shaft 30 
and the sun gear 60 integral therewith is held against rotation relative 
to the planet gear carrier 42. When any two components of a three 
component planetary gear system are stopped relative to one another, the 
entire planetary gear system is stopped and locks up. Accordingly, by 
braking the relatively rotating members, i.e., the planet carrier and the 
sun gear, the planet gear carrier becomes locked relative to the ring gear 
and, accordingly, the wheel hub assembly 34 becomes locked relative to the 
fixed spindle 33 or the frame 12 of the vehicle. 
Automatic adjusting means are also incorporated in the cover assembly to 
preclude the unlimited release of the brake pack 78 upon its 
disengagement. This is accommodated by means of a slack adjuster 178 which 
includes a dowel pin 180 secured to the annular piston 88 and slidingly 
supported within a plug 182 held by a bolt 183 to the radial wall of the 
cover 146 and defining a cavity therebetween around the dowel pin 180 
which receives a washer 185 positioned with clearance over the dowel pin. 
A compression spring 187 mounted in the plug 182 engages one edge of the 
washer 185 and forces it into a canted position so that the inner portion 
of the washer 185 engages the dowel pin while the outer surface of the 
washer opposite the compression spring engages a raised corner in the 
cover 46 as at 186. Upon pressurization of the brake cylinder 92 and the 
axial displacement of the piston 88, the dowel pin 180 is caused to slide 
within the washer 185 and possibly shift its position inboardly relative 
to the washer. Upon depressurization of the cylinder 92, the springs 98 
release the brake and cause the brake piston 88 to be moved axially away 
from the brake pack 78. The washer 187 strikes the cover corner 186 and 
cants causing the inner diameter of the washer to engage the dowel pin 180 
thus precluding the complete return of the brake piston 88 into the 
cylinder 92. This automatically compensates for wear of the brake pack 
discs 80 and 82. Three or more of the slack adjuster assemblies 178 can be 
equally spaced around the circumference of the cover. 
The operating fluid for actuating the brake piston 88 is supplied to the 
drive axle assembly from a single fluid system providing brake apply 
pressure, cooling and lubricating fluid, and differential gear 
lubrication, which will be described in detail hereinafter, to an input 
port 100 in the spacer ring 37 disposed about the spindle 33 inboard of 
the wheel hub assembly 34. The port 100 communicates via a radial passage 
101 with an axially extending passage 103 in the spacer ring. The outside 
diameter of the nonrotatable spacer ring 37 reduces in size outboardly to 
an outboard end telescoping within the wheel hub assembly 34 and thereat 
is provided with an annular groove 107 defining a cavity between the hub 
assembly and spacer ring opened to the axial passage 103 and to the 
annular inner wall 108 of the hub assembly. Square section metal filled 
ring seals 110 of the type conventionally used in transmissions are 
located on opposite sides of annular groove 107 to maintain a pressurized 
fluid seal of the groove 107 while allowing the wheel hub assembly 34 to 
rotate relative to the spacer ring 37 and spindle 33. On the external side 
of the wheel hub 34, another port 111 communicates via radial passage 112 
with the annular wall 108 of the hub and cavity. The wheel hub port 111 
communicates by a pressure tube 113 with a port 114 at the entrance of an 
axially extending passage 115 in the circumferential wall of the hub 
assembly 34 which extends into the planet gear carrier 42. The radial wall 
44 of the planet gear carrier 42 in turn is provided with a radial passage 
117 communicating with the passage 115 and which in turn communicates with 
an axially extending passage 118 extending therefrom into the cover 46 to 
a radial passage 120 in the outboard wall thereof. The radial passage 120 
opens into the annular brake cylinder 92 formed in the cover 46 and with 
the base of the brake piston 88. Thus, a passage means is disposed in the 
hub which establishes fluid communication between the input port 100 on 
the spacer ring 37 and an outlet into the brake cylinder 92 so that brake 
apply pressure at the input port 100 will activate the brake pack 78. As 
is illustrated, the hub assembly 34, planet gear carrier 42 and cover 46 
are separate components secured together and, accordingly, at the 
interfaces in the passages 115, 117, 118, small O-rings are disposed in 
grooves to preclude leakage pass the abutting components. Additionally, a 
bleed orifice 122 is disposed in the radial passage 120 of the cover 46 
near the center of the axle shaft 30 for the purpose of allowing the brake 
fluid to continually circulate through the passages and lines described 
above in order to prevent congealing of the brake fluid under cold 
operating conditions. The orifice 122 bleeds to a cavity 124 defined 
within the cover 46 surrounding the outboard end of the drive shaft 30. 
Operating fluid for cooling and lubricating the brake pack 78, as well as 
the various bearings 35, 36 and 70, is also supplied from the same fluid 
system to an input port 126 (FIG. 3) which is located on the top side of 
the spacer ring 37, that is, rotated 90.degree. from the brake fluid input 
port 100 shown in FIG. 2. The input port 126 communicates with a second 
cavity 128 defined by the outside wall of the spacer ring 37, the hub 34, 
and a pair of face seals 129, of the conventional type shown, for example, 
in the aforementioned Sidles patent, each comprising a metal seal ring 130 
disposed within a rubber compression ring 131, the radial faces of the 
rings 130 being disposed in mating relation within the annular outturned 
edges 132 respectively of the seal ring 37 and wheel hub assembly 34. 
Thus, a seal is maintained between the hub and spacer ring sealing the 
exterior of the axle assembly from the interior while permitting relative 
rotation therebetween. The second cavity 128 is also sealed from the first 
cavity 107 by the seals 110. The wheel hub 34 is provided with a port 134 
communicating via radial passage 135 with the second cavity 128. Thus, a 
second fluid tight passage is provided between the fixed spacer ring 37 
and the rotating hub assembly 34 for the passage of lubricant which also 
has the benefit of cooling the seals 129. Further, due to its axially 
adjacent location, leakage from the adjacent high pressure brake apply 
cavity 107 will leak into the low pressure second cavity rather than 
exteriorly of the axle. A tube 136 connects the port 134 with a second 
port 137 opening into an axially extending passage 138 in the 
circumferential wall of the wheel hub assembly and extending into the 
planet carrier assembly 42 whereat the passage 138 intersects a radial 
passage 139 in the wall 44 of the planet carrier 42. The planet carrier 
passage 139 communicates with an axially extending passage 140 
predominately in the cover 46 intersecting a radial passage 142 in the 
cover which in turn has an unrestricted outlet as at 143 into the cavity 
124 adjacent the end of the drive shaft 30. This provides for relatively 
continuous lubrication and cooling of the gears, bearings and the brake 
discs. 
In the latter regard, the inner portion of the brake discs 80 and 82 are 
each radially slotted in a conventional manner to allow lubricant flow 
adjacent the spline 60 on the drive shaft 30 to permit flow to each disc 
and radially among the discs and filling at least the lower half of the 
cavity 76. The lubricant flows past the backing plate 94 to an internal 
cavity 144 formed within the planet gear carrier and lubricates the 
bearings 70 located between the stub shaft 72 and the planet gear 68. The 
lubricant further fills the ring gear containing cavity 146 of the wheel 
hub assembly and lubricates the wheel hub bearings 35 and 36. With all the 
cavities 76, 144, 146 filled up to the level of the bore of the spindle 
33, the lubricant is sent back to the differential housing 32 along the 
clearance space 148 between the axle shaft 30 and the spindle 33. In this 
connection it is noted that even though the cavities fill up only half 
way, since all of the bearings 35, 36, and 70 and the sun and planet gears 
60, 68, as well as both sets of brake discs 80 and 82, rotate during 
operation of the vehicle (except the inner races of bearings 35, 36), more 
than adequate lubrication and cooling of all of these components is 
maintained. As previously indicated, the metallic face seals 129 between 
the hub and spacer ring are also cooled by the lubricant passing through 
the cavity 128 behind them. Due to its pressurization, the cavity 128 is 
substantially filled during operation. 
Referring now to FIG. 4, there is shown schematically the combined 
operating fluid system which actuates the brake pack 78, provides the 
lubrication and cooling for the entire axle drive and brake assembly, and 
also lubricates the differential gearing (not shown) within the 
differential housing 32. (The term "operating" is used to distinguish from 
the vehicle hydraulic control systems and their fluids). Of significant 
note, is that a single operating fluid, preferably an extreme pressure 
(EP) gear lubricant of high viscosity such as 85W-140, is used to provide 
all these functions. Viewed in detail, the operating fluid is supplied to 
a transmission driven gear pump 150 from the differential housing 32 of 
the axle assembly which functions as a reservoir. The operating fluid is 
pumped through a filter 152 and a pressure line 153 into the input port 
schematically illustrated at 154 of a brake apply valve 156. The brake 
apply valve 156 has left and right output ports 158L, 158R respectively, 
which are connected via tubes 160 to the brake apply input ports 100 at 
the left and right wheels of the axle respectively. Adjacent the brake 
output ports 158 are lubricant output ports 162L and 162R which are 
connected respectively by tubes 164 to the lubrication input port 126 on 
the spacer ring 37. Further spaced from the brake apply ports 158 is an 
input port 166 which is connected to a pilot pressure line 167 in turn 
connected to a pedal actuated brake pilot control valve 168 having a 
linearly increasing pressure output with pedal stroke located in the 
operator's compartment of the vehicle. In the brake release position of 
the pedal, the control valve maintains a small amount of continuous 
circulation in the pilot control line 168 which flows through an orifice 
169 on the right side of the valve 156 back to the transmission hydraulic 
fluid reservoir 170. It is noted in this regard that the brake pilot 
control system operates on hydraulic fluid from the transmission hydraulic 
system pump 171 rather than on the gear lubricant used on the operating 
fluid side of the brake apply valve 156. A sliding valve spool 172 is 
disposed in a relatively close fit in spool bore 173, the valve spool 172 
being shown at the extreme limits of its travel respectively on the left 
and right sides of the valve 156 illustrated in FIG. 4. Since the pilot 
control system operates on transmission hydraulic fluid, an annular groove 
174 is disposed in the spool bore 173 between the pilot control input port 
166 and the operating fluid lubricating output ports 162. The groove 174 
is connected to the operating fluid inlet 154 as by an internal passage in 
the valve body (not shown) which should be sufficient to provide adequate 
separation of the fluids since the pressure differential across the spool 
body is zero because the control pressure and inlet pressure are nearly 
always equal. 
The valve spool 172 comprises a cylindrical body portion 175 slidingly fit 
in the valve bore 173 between the lubricant output ports 162 and the 
control pressure port 166, a short control side axial stem of smaller 
diameter than the body 175 extending therefrom to the control side and an 
elongated operating side axial stem 177 extending from the body portion to 
the operating fluid side. The relative axial lengths of the body 175, 
control side stem 176, and operating side stem 177 are configured so that 
a part of the body portion is always between the ports 162 and 166 and 
covering the annular groove 174, that when the control side stem 176 
contacts the end of the valve 156 on the control pressure side, as shown 
on the left side of the valve in FIG. 4, both operating fluid output ports 
162, 158 are open, and that when the operating side stem 177 contacts the 
end of the valve 156 on the operating side, as shown on the right side of 
the valve in FIG. 4, the body portion 175 closes off the lubricant output 
ports 162 while leaving the brake apply output ports 158 open. 
In operation of the operating fluid system, the pump 150 removes gear 
lubricant operating fluid from the differential housing 32 and pumps it 
through the filter 152 and into the operating side of the brake apply 
valve 156 at input port 154. Since the pilot control circuit pressure in 
the line 168 is maintained at a relatively low level in the absence of a 
braking signal from the operator, the valve spool 172 moves toward the 
control side limit of travel, the control side stem 176 preventing the 
body 175 of the spool 172 from closing off the pilot control pressure 
input port 166 and the orifice 169 so that control pressure hydraulic 
fluid is circulated through the control pressure side of the brake apply 
valve 156 continually. The valve spool acts as a pressure regulator to 
maintain the operating side at the same pressure as the control side and 
since there is little restriction in the lubricating fluid passages, the 
gear lubricant operating fluid will be pumped past the operating side stem 
177 of the valve spool 172 through the lubricating output ports 162 and 
circulated through the line 164 into the lubricating input port 126 on the 
spacer ring 37 (FIG. 3) and thereafter through the cavity 128 and the 
above-described hub assembly passages into the cavity 124 adjacent the 
drive shaft 30 and brake pack 78 at the outboard end of the axle assembly. 
A small amount of lubricant also flows through the brake apply passages 
and out the orifice 123 to the cavity 124. When the operator depresses the 
brake pedal, the pilot control valve 168 increases the pressure in the 
pilot control line 168, generally proportional to the brake pedal travel. 
This pressure forces the valve spool 172 momentarily to the operating side 
limit of travel, as shown in the right side of FIG. 4, so that the spool 
body 175 closes off the lubricating ports 162 while leaving the brake 
ports 158 open. Since the brake circuit is restricted, opening only to the 
brake cylinder 92 and the orifice 123, the pressure on the operating side 
of the valve spool 172 will quickly build up until it equals the pilot 
pressure in the line 166, simultaneously pressurizing the brake line 160 
and ultimately the brake annular cylinder 92 forcing the brake piston 88 
against the brake pack 88. The pressure at the operating fluid inlet 154 
will continue to increase until it overcomes the pilot pressure on the 
pilot side of the valve spool 172 causing the spool to move downwardly and 
opening the lubricant ports 162 so that the flow from the operating fluid 
circuit again exits through the lubricating output ports 162, the valve 
spool 172 reaching an equilibrium position with the ports 162 partially 
open. Thus, during braking, the flow of lubricant is momentarily cut off 
but is immediately resumed after the pressure in the operating fluid 
circuit 153 rises to equalize the pilot pressure in line 168. Then, 
lubrication is resumed no matter how long braking lasts. 
Thus, it will be seen that there has been provided in accordance with the 
invention, a drive axle assembly which fully meets the objects, aims and 
advantages set forth above. Although the invention has been described in 
conjunction with a preferred embodiment, it should be understood that the 
invention should not be limited thereto. For example, although described 
in conjunction with a wheeled vehicle, it will be apparent that the hub 
assembly could be coupled by a sprocket to an endless track. It is further 
appreciated that those of ordinary skill in the art in view of the 
foregoing description will note many other alternatives and modifications 
which may be made without departing from the true invention. Accordingly, 
it is intended to embrace all such alternatives and modifications as fall 
within the scope of the appended claims.