FREE FLOATING HYDRAULIC BULKHEAD WITH IMPROVED
SEALING AND ANTI-ROTATION
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional Application No. 61/251,949,
filed Oct. 15, 2009, which is hereby incorporated by reference as though fully set forth herein.
TECHNICAL FIELD
[0002] The present invention relates to a hydraulic bulkhead for an external hydraulic
limited slip differential that may be configured both as a hydraulic passageway to route hydraulic
fluid from the external pump to the differential and as a means to prevent rotation of the
hydraulic bulkhead and its components.
BACKGROUND
[0003] Limited slip differentials generally include a hydraulically actuated friction clutch
pack that may be actuated to retard relative rotation of at least one of the side gears relative to the
differential case. Limited slip differentials may include a non-rotating differential housing and a
differential case rotatably supported within the differential housing. The differential case may be
driven by an input shaft through a ring gear attached to a flange extending outwardly from the
differential case. The differential case may house a pair of side gears, a pair of pinion gears, and
a pinion shaft to allow speed differential between a pair of opposite output shafts. A friction
clutch pack may be disposed between the side gear and the differential case. The friction clutch
pack may comprise a plurality of friction discs that are alternately splined onto the side gear and
the differential case.
[0004] A hydraulically actuated piston may be disposed within a piston chamber and may
be configured to actuate (e.g., compress) the clutch pack and retard any speed differential
between the side gear and the differential case. This may result in a retardation of any speed
differential between the output shafts. A pump may be employed to provide pressurized
hydraulic fluid to actuate the piston and engage the clutch pack. For example and without
limitation, a gerotor pump may be provided with an inner gear attached to one of the side gears
and an outer gear rotating with the differential case. Whenever the side gear is rotating, the
pump may generate a pressurized flow of hydraulic fluid to the piston chamber. When the
hydraulic pressure reaches a predetermined value, a portion of the fluid being pumped into the
piston chamber is released and collected in a non-rotating plenum for recirculation through the
piston chamber.
[0005] When the pump is positioned outside of the differential housing or the axle housing
(i.e., an external hydraulic limited slip differential), some form of hydraulic bulkhead is
generally required to provide a passageway for the hydraulic fluid to be supplied to the
differential. The need for a hydraulic bulkhead may require that the axle housing have a
particular configuration and/or certain features to enable this hydraulic fluid passageway. The
axle housing may also generally be required to have a particular configuration and/or certain
features to prevent rotation of the hydraulic bulkhead and/or its components.
[0006] If the axle housing needs to meet these multiple requirements, it may make the
manufacturing of the axle housing more complex, complicated, and costly. For example, tight
tolerances and/or various additional seals may be necessary in order to ensure that seals (e.g., o-
rings) on the high pressure side of the hydraulic bulkhead are able to withstand the load from the
plenum resisting rotation and prevent leakage. It may be desirable to reduce and/or minimize the
manufacturing requirements for the axle housing that may still allow for the same level of
functionality as existing axle housings utilized in hydraulic limited slip differentials.
SUMMARY
[0007] A hydraulic bulkhead configured for use with a limited slip differential may
include a plenum comprising a passageway for hydraulic fluid and a boss. A first seal may be
located on an outer surface of the boss. The outer surface of the boss may be a low pressure area
relative to the inner surface of the boss. The plenum may be stationary relative to the limited slip
differential.
[0008] A differential assembly may comprise a differential case; a differential gear
assembly disposed within the differential case, the differential gear assembly may be driven by
an input shaft and may be configured to allow differential rotational speed between a pair of
opposing output shafts; a clutch pack disposed within the differential case, the clutch pack may
be configured to retard the differential rotational speed between the output shafts; and a
hydraulic bulkhead. The hydraulic bulkhead may comprise a plenum including a passageway for
hydraulic fluid for delivery to the clutch pack and a boss, wherein the plenum may be stationary
relative to the differential case; and a first seal may be located on an outer surface of the boss.
[0009] By providing a hydraulic bulkhead that combines the requirements for the
hydraulic passageway with anti-rotation features, it may simplify and/or reduce the cost
associated with the manufacturing of the axle housing. For example, a conventional axle
housing (e.g., transaxle housing) may only require relatively minor modifications for hydraulic
connections through the use of the inventive hydraulic bulkhead
BRIEF DESCRIPTION OF THE DRAWINGS
[00010] Embodiments of the invention will now be described, by way of example, with
reference to the accompanying drawings, wherein:
[00011] FIG. 1 is a partial cross-sectional view of a hydraulic bulkhead in accordance with
an embodiment of the invention.
DETAILED DESCRIPTION
[00012] Reference will now be made in detail to embodiments of the present invention,
examples of which are described herein and illustrated in the accompanying drawings. While the
invention will be described in conjunction with embodiments, it will be understood that they are
not intended to limit the invention to these embodiments. On the contrary, the invention is
intended to cover alternatives, modifications and equivalents, which may be included within the
spirit and scope of the invention as embodied by the appended claims.
[00013] Referring now to FIG. 1, a hydraulic bulkhead 10 for an external hydraulic limited
slip differential is generally illustrated. Hydraulic bulkhead 10 may be configured both as a
hydraulic passageway to route hydraulic fluid from an external pump (not shown) to the plenum
and to the limited slip differential and as a means of preventing rotation of the hydraulic
bulkhead components. While the hydraulic bulkhead 10 is described in connection with a
limited slip differential, the invention may also be suitable for use in connection with other
torque coupling mechanisms, other hydraulic couplings, axle and transaxle housings, and the
like.
[00014] The hydraulic bulkhead 10 may be configured for insertion in the axle housing 12.
Axle housing 12 may be configured to house the axles extending from the output shafts of the
limited slip differential, as well as the hydraulic bulkhead 10. The axle housing 12 may also be
configured to house a hose fitting 14 and a hydraulic fitting 16. Both the hose fitting 14 and the
hydraulic fitting 16 are generally not configured for rotation. The hose fitting 14 and hydraulic
fitting 16 may be conventional and known to those of ordinary skill in the art. The axle housing
12 may further include a hydraulic supply port and hydraulic bleed access port in connection
with embodiments of the invention.
[00015] The hydraulic bulkhead may comprise the plenum 18. The plenum 18 may be
configured to route hydraulic fluid to the piston chamber 20 and piston 22 for actuation of the
hydraulically actuated friction clutch pack 24 of the limited slip differential. The plenum 18 may
be configured to be sealed in fluid communication with the hydraulically actuated friction clutch
pack 24. The plenum 18 may be held stationary with respect to the differential. For example
and without limitation, the plenum 18 may be attached and fixed against rotation in relation to
the axle housing 12. The plenum 18 may comprise a cylindrical boss 26.
[00016] The cylindrical boss 26 may be configured for plugging into a through-hole in the
axle housing 12. The axle housing 12 may thus be configured with a single machined through-
hole for receiving the cylindrical boss 26 of the hydraulic bulkhead 10. The cylindrical boss 26
may comprise at least one seal 28 (e.g., o-ring) on the outer diameter of the cylindrical boss 26.
Seal 28 may be configured to seal the interface between the axle housing 12 and the plenum 18.
In an embodiment of the invention, the cylindrical boss 26 may comprise first and second seals
28, 30 on the outer diameter of the cylindrical boss 26. Second seal 30 (e.g., o-ring) may be
configured to add additional protection to the first seal 28 from outside contaminants, such as
dirt. The first seal 28 may be an inner seal disposed proximate the differential. The second seal
30 may be an outer deal disposed proximate the axle housing 12. Although two seals 28, 30 are
shown and generally illustrated, the hydraulic bulkhead 10 may include fewer or more seals in
accordance with various embodiments of the invention. Moreover, while the aforementioned
seals are generally illustrated as being round or oval, it is noted that the invention is not so
limited and one or more such seals (e.g., 28, 30) may be provided in various other shapes (e.g.,
square or cupped), which may be configured to provide an increased sealing surface.
[00017] The first and second seals 28, 30 disposed on the outer diameter of the cylindrical
boss 26 of the plenum 18 may be located in the low pressure area of the interface between the
plenum 18 and the axle housing 12. The first and second seals 28, 30 may be configured to seal
oil up to about only 15 psi in accordance with an embodiment of the invention. Sealing at such a
low pressure with seals 28, 30 allows for a relatively large e-gap 32 between the axle housing 12
and the plenum 18. For example and without limitation, the e-gap (e.g., the gap between the axle
housing 12 and the plenum 18) may be greater than 0.5 mm or greater than 0.02 inches in
accordance with an embodiment of the invention. Since a relatively large e-gap 32 is allowed in
connection with an embodiment of the invention, increased positional tolerance for the through-
hole of the axle housing 12 and/or the cylindrical boss 26 of the plenum 18 may also be allowed.
[00018] The through-hole of the axle housing 12 may serve as an anti-rotation means for
the plenum 18. The plenum 18 may thus be kept stationary relative to the differential and/or to
the axle housing 12. The anti-rotation requirement for the interface between the axle housing 12
and the plenum 18 may create a dynamic axial and/or side load on the seals 28, 30. The first and
second seals 28, 30 may not be dynamic seals in a traditional and/or conventional sense because
they are not disposed between two components characterized by relative rotation therebetween.
However, the first and second seals 28, 30 may be configured to withstand an axial load from the
plenum 18 resisting rotation and may be considered dynamic seals. Dynamic seals generally
have a greater leak potential than static seals.
[00019] This dynamic axial and/or side load on the seals 28, 30 may tend to make the e-gap
32 approach zero on a first side of the cylindrical boss 26 of the plenum 18 and generally double
on a second opposing side of the cylindrical boss 26 of the plenum 18. The durometer and/or
hardness of the seals 28, 30 may be optimized to limit the amount of squeeze and/or deformation
under the condition of dynamic axial and/or side load of the seals 28, 30. The first and second
seals 28, 30 may be configured to absorb the shock load when the plenum 18 exhibits a load to
cause rotation. By placing the first and second seals 28, 30 on the low pressure side of the
interface between the plenum 18 and the axle housing 12, the risk of leak may be reduced. In
addition, the placement of the first and second seals 28, 30 on the low pressure side of the
interface between the plenum 18 and the axle housing 12 may significantly simplify the interface
requirements for the purposes of manufacturing the axle housing.
[00020] The high pressure area and/or side of the plenum 18 may be the area where
pressurized fluid is channeled to the differential. The high pressure side of the plenum 18 may
be sealed with a high pressure seal 34 (e.g., o-ring). For example and without limitation, the
high pressure seal 34 may comprise a standard Eaton™ Aeroquip™ hydraulic fitting. The high
pressure seal 34 may be used at a static sealing surface. Since static seals have less leak potential
than dynamic seals, the static seal 34 may be located on the high pressure side of the plenum 18.
Seal 34 may remain static so long as there is sufficient friction applied to the seal 34 to overcome
the torque or side load from the plenum 18.
[00021] The foregoing descriptions of specific embodiments of the present invention have
been presented for purposes of illustration and description. They are not intended to be
exhaustive or to limit the invention to the precise forms disclosed, and various modifications and
variations are possible in light of the above teaching. The embodiments were chosen and
described in order to explain the principles of the invention and its practical application, to
thereby enable others skilled in the art to utilize the invention and various embodiments with
various modifications as are suited to the particular use contemplated. The invention has been
described in great detail in the foregoing specification, and it is believed that various alterations
and modifications of the invention will become apparent to those skilled in the art from a reading
and understanding of the specification. It is intended that all such alterations and modifications
are included in the invention, insofar as they come within the scope of the appended claims. It is
intended that the scope of the invention be defined by the claims appended hereto and their
equivalents.
We Claim:
1. A hydraulic bulkhead (10) configured for use with a limited slip differential, the bulkhead
(10) comprising:
a plenum (18) that is stationary relative to the limited slip differential, the plenum (18)
including:
a passageway for hydraulic fluid; and
a boss (26); and
a first seal (28) located on an outer surface of the boss (26).
2. The hydraulic bulkhead (10) of claim 1. wherein the boss (26) is substantially cylindrical.
3. The hydraulic bulkhead (10) of claim 1, wherein the boss (26) is configured for insertion
in an axle housing (12).
4. The hydraulic bulkhead (10) of claim 1, further comprising a second seal (30) located on
the outer surface of the boss (26).
5. The hydraulic bulkhead (10) of claim 1, further comprising a third seal (34) located on an
inner surface of the boss (26).
6. The hydraulic bulkhead (10) of claim 1, wherein an outer surface of the boss (26) is at a
lower pressure than an inner surface of the boss (26).
7. The hydraulic bulkhead (10) of claim 1, wherein the first seal (28) is configured for
operation up to about 15 psi.
8. The hydraulic bulkhead (10) of claim 3, wherein a gap (32) between the boss (26) and the
axle housing (12) is greater than about 0.5 mm.
9. The hydraulic bulkhead (10) of claim 5, wherein the third seal (34) comprises a static
seal.
10. The hydraulic bulkhead (10) of claim 1, further comprising a hydraulic fitting (16) in
fluid communication with the plenum (18).
11. The hydraulic bulkhead (10) of claim 10, further comprising a hose fitting (14) in fluid
communication with the hydraulic fitting (16).
12. The hydraulic bulkhead (10) of claim 11, further comprising a pump in fluid
communication with the hose fitting (14).
13. The hydraulic bulkhead (10) of claim 1, wherein the first seal (28) comprises an o-ring.
14. The hydraulic bulkhead (10) of claim 1, wherein the limited slip differential comprises:
a piston chamber (20);
a piston (22) located in the piston chamber (20); and
a clutch pack (24) configured for actuation by movement of the piston (22),
wherein the plenum (18) is in fluid communication with the clutch pack (24).
15. A differential assembly comprising:
a differential case;
a differential gear assembly disposed within the differential case, the differential gear
assembly driven by an input shaft and configured to allow differential rotational speed between a
pair of opposing output shafts;
a clutch pack (24) disposed within the differential case, the clutch pack (24) configured to
retard the differential rotational speed between the output shafts;
a hydraulic bulkhead (10) comprising:
a plenum (18) that is stationary relative to the differential case, the plenum (18)
including:
a passageway for hydraulic fluid for delivery to the clutch pack (24); and
a boss (26); and
a first seal (28) located on an outer surface of the boss (26).
16. The differential assembly of claim 15, wherein the hydraulic bulkhead (10) further
comprises a second seal (30) located on an outer surface of the boss (26).
17. The differential assembly of claim 16, wherein the hydraulic bulkhead (10) further
comprises a third seal (34) located on an inner surface of the boss (26).

ABSTRACT

A hydraulic bulkhead (10) configured for use with a limited slip differential includes a
plenum (18) comprising a passageway for hydraulic fluid and a boss (26). A first seal (28) is
located on an outer surface of the boss (26). The outer surface of the boss (26) is a low pressure
area relative to the inner surface of the boss (26). The plenum (18) is stationary relative to the
limited slip differential. A differential assembly including the inventive hydraulic bulkhead (10)
is also disclosed.