Note: Descriptions are shown in the official language in which they were submitted.
~ lC,57082
AIR PISTON DIFFERENTIAL LOCKOUT
Back~round of the Invention
Field of the Invention. This invention relates generally to an -~
axle assembly and, more particularly, an axle assembly having a differential
with a differential lockout mechanism.
Description of the Prior Art. Truck differential mechanisms and
the like are found in various types of axle assemblies and may come
equipped with or without means to bypass or lockout the differential ;~
action of the differential. Many trucks in use today are equipped with
automatic lockout mechanisms which allows for the transfer of power to
one of the wheels when the other is slipping as on an icy pavement. A -
typical example of a no-slip type of differential is found in United
States Patent 3,390,593 entitled "Traction Equalizer", patented on July
2, 1968. As before noted, this latter mentioned patented differential
contains an automatic differential lockout feature There are situations
when it is desirable to provide the operator of the vehicle with selectlve
lockout means which can be energized by suitable control means provided
in the cab.
The typ1cal prior art approach to providing a differential lockout
mechanism is to provide an air pneumatic cylinder external of the differential
housing to engage and disengage certain operational parts of the differential.
These prior art forms of lockout have been generally satisfactory, they
are, however, ln an exposed position with respect to the differential and
axle housing. In such a position, they are not only exposed to the elements ;
but also to flying projectiles that may be encountered on the road.
Summary of the Invention
It 1s, therefore, a primary object of the present invention to provide
an axle assembly comprising a differential having a housing, an input
drive pinion rotatably mounted in the housing and in driving meshing
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engagement with a drive gear rotatably mounted in the housing, the
drive gear carrying a differential spider having rotatably thereon
four differential pinions, a differential casing attached to said drive
gear enclosing the differential spider and the differential pinions,
a differential side gear also is enclosed within said differential
casing and is in meshing engagement with the differential pinions,
the internal bore of which is splined to accept an axle shaft through
an opening in the differential casing, the improvement comprising a
cylindr;cal piston surrounding the axle shaft and splined thereto, the
differential casing hav;ng a splined extension thereon to rece;ve a
comparably spl;ned port;on on the piston, biasing means b;as;ng
the piston along the longitudinal axis of the axle shaft to d;sengage
the p;ston from the d;fferential cas;ng at their mating splined areas, a
cylindrical cylinder surrounding the piston to provide an airtight
chamber for compressed air received from air compressing means, the
compressed air acts on the piston within the airtight chamber to drive
the piston in splined engagement with the splined portion of the differential
casing to bypass and lockout the d;fferent;al action of the differential
p;n;ons on the sp;der.
It ;s a further object of th;s ;nvent;sn to prov;de an axle assembly
where;n the p;ston rotates w;th the axle shaft and the cyl;nder rema;ns
stationary with respect to the housing and the spl;ned port;on prov;ded
on the outer surface of the differential casing mating with the spl;ned
portion provided on the inner surface of the piston.
It is a still further object of the present invention to prov;de
an axle assembly wherein at least one 0-ring is provided between the
surfaces of the piston and the cylinder and the cyl;nder provided with a
threaded opening to receive a threaded fitting connected to the compressed
a;r system of the vehicle w;th wh;ch ;t is associated.
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It is also an object of this invention to provide an axle
assembly wherein the biasing means is a spring surrounding the piston
and is retained thereon by holding means, the spring contacting at
one end the cylinder and at its other end the holding means.
~ t is another object of this invention to provide an axle asse~bly
where;n there are two 0-ring seals, one at each end of the cylinder and
the cylinder being concentric with the piston and the axle shaft.
It is another object of the present invention to provide an axle
assembly wherein the piston is normally biased out of contact with the
differential casing by the biasing means, the compressed air being introduced
into the chamber to overcome the biasing means to meshingly engage the
piston with the differential casing and the compressed air being remotely
controlled by valving means provided in the compressed air service
system.
It is a sti11 further object of the present invention to provide
an axle assembly wherein the piston moves longitudinally in and is
guided by the splines provided on the outer surface of the axle shaft.
It is also an object of the present invention to provide an axle
assembly wherein the piston and the cylinder are totally enclosed within
the housing assembly, an air fitting in communication with the air
chamber provided in the cylinder, and the air fitting protruding
through and outwardly of the housing.
It is still a further object of the present invention to provide
an axle assembly wherein the plston is an elongated sleeve whose
longltudinal axis is coincident with the longitudinal axis of the
axle shaft, the elongated sleeve having a shoulder thereon whose radially
extending surface provides the area against which the compressed air acts
to drive the piston in splined engagement with the differential casing.
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It is also an object of the present invention to provide an axle
assembly wherein the elongated sleeve is provided with two coaxial
splined surfaces, the inner of which is in engagement with the splined
surface provided on the outer surface of the axle shaft and the outer of
which is adapted to be in splined engagement with the splined portion
provided on the outer surface of the differential casing.
It is another object of this invention to provide a differential
lockout mechanism which is simplistic in design and inexpensive to
manufacture.
It is yet another object of this invention to provide a differential
lockout mechanism which is easy to maintain and reliable over a long
period of time.
It is a still further object of this invention to provide a differential
lockout mechanism which may be adapted to various types of differentials
as, for example, multiple reduction and single reduction drive units.
These and other advantages of the present invention will become
apparent as it is further described and explained in the following
disclosure and as shown in the accompanying drawing.
Description of the Drawing
Figure 1 is a partial sectional view of the present invention,
showing a portion of a differential including the differential lockout
mechanism contemplated by this invention.
Detailed Description of the Preferred Embodiment
Referring now to the drawing, there is shown a portion of a single
reduction drive unit. ~he drive unit 10 is particularly adapted to be
assembled with an axle assembly and operably connected to a drive shaft,
neither of which are shown.
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The differential drive unit 10 is of the type found in Rockwell
International "Field Maintenance Manual No. 5" dated March, 1975. -
Before proceeding further, however, it should be noted that the below-
described invention is applicable to other forms of reduction drive
units (differentials) and may be applied to multiple reduction drive
units as well as single reduction drive units.
The differential drive unit 10 includes a housing 12 which encloses
the various operational parts of the differential drive unit 10. The
housing 12 may include a number of parts (not shown) which may be suitably
fastened together to form the entire enclosure and, in general, to form
an axle assembly. The different1al drive unit 10 has a number of parts
including, generally, an input drive pinion (not shown) wh;ch ;s rotatably
mounted within the housing 12. The input drive pinion is connected
either directly or through some intermediate means to the drive shaft or
power train of the vehicle with which it is associated. The input drive
pinion is in driving, meshing engagement with a drive gear (also not
shown) which is also rotatably mounted in the housing 12. The drive
gear typically carr1es a differential spider for mounting thereon four
different;al p;n;ons. A d;fferent;al casing 14 is provided in the
differential drive unit 10 to enclose the differential pinions and
maintain the operational position of the differential spider. The
differential casing 14 is typically bolted to the above-mentioned drive
gear. The differential drive unit 10 also is provided wlth two differential
side gears 16, one of which is shown in Figure 1. The differential side
gear 16 is enclosed within the differential casing 14 and is provided
with teeth whieh are in meshing engagement with the differential pinions
and is driven thereby. The differential side gears 16 are provided with
a splined central bore 18 and are to be adapted to accept a splined end
of an axle shaft 22 through the opening 24 in the differential casing
14.
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It may be generally stated at this juncture of the description of t
the present invention that the above-noted structure is generally in
conformity with the prior art and the main thrust of the present invention
is to provide a new and novel means to bypass the differential action
of the differential drive unit 10 and that new and novel means is to be
described below.
One component of this new and novel mechanism is the cylindrical
piston 26 which, generally, surrounds the axle shaft 22. The
cylindrical piston 26 has a longitudinal axis coincident with that of the
10axle shaft and is coaxial with the axle shaft 22. The cylindrical piston
26 is provided with several series of splines at different locations
thereon. A first series of splines 28 are in engagement and interlock with
complementary splines 30 provided on outer surface o~ the axle shaft
intermediate its ends. The interlocked relationship of the splines 28
and 30 locks the piston 26 on a rotatable basis to the axle shaft 22,
i.e., as the axle shaft 22 turns the piston 26 will turn with it. A second
series of splines 32 is provided at one end of the piston 26 and are
adapted to mesh with a complementary series of splines 34 provided on the
outer surface of the differential casing 14. All of the series of splines
28, 32 and 34 are parallel with the longitudinal axis of the axle
shaft 22, thereby, allowing the piston 26 to move longitudinally with
respect to the axle shaft 22. The significance of this longitudinal motion
of the piston 26 will be further explained below.
A cylindrical cylinder 36 is provided within the housing 12 surrounding
the piston 26. The cylinder 36 ls in airtight relationship with the piston
26 to define an air chamber 38. The top 40 of the air chamber 38 is
defined by a radially extendlng portion of the cylinder 36, the portion
being formed integrally with the cylinder 36. A shoulder 42 on the piston
26 defines the other end of the air chamber 38. The cylinder 36 is held in
floating position by holding means (not shown) such that it may move slightly
in a radial or lateral direction to accommodate for misalignment or
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or eccentricity of the axle shaft 12. An air fitting 44 connects the
air chamber 38 with the service air of the vehicle with which the
differential drive unit 10 is associated. The service air is used to
provide the motive force for the brake system and other related accessory
systems on the vehicle.
The piston 26 as shown by the solid lines in Figure l is in
engagement with the differential casing 14 and the axle shaft 22. The
p;ston 26 is also shown in dotted form 26' and in that position is out
of engagement with the differential cas;ng 14; but still ;n engagement
with the axle shaft 22. These are the two basic operational positions
of the piston. The normal position being shown by piston 26'. The
piston 26' is moved to the extended or disengaged position by biasing
means thereon, particularly by helical spring 46 surrounding the piston 26
and held in place by holding means, such as ring 48 which abuts a snap ring
50. It can be seen, therefore, that the force of the spring is exerted on
the top of the cylinder 36 and against the ring 48 to drive the piston to
its disengaged position as denoted by 26'. The application of service
air to the air chamber 3B through the air fitting 44 will overcome the
blasing force of the spring 46 and drive the piston toward the differential
caslng 14 to engage the splined portions 32 and 34, respectively.
Obvious1y, whi1e the piston is in its disengaged position, i.e.,
disengaged from the differential casing 14, the differential drive unit
lO and its various operational parts are again in a normal position, i.e.,
permitting wheels to rotate at different speeds. If one of the two
wheels attached to the axle shafts operably connected to the differential
drive unit lO experiences a slipping condition and that wheel begins to
spin, the operator may lockout the differential action of the differential
drive unit lO which is causing the spinning by charging the air chamber
with service air. A suitable control valve or the like (not shown) may
be provided in the vehicle cab readily accessible to the operator for
this purpose. Once the chamber is charged with the service air the
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piston will be driven toward the differential casing 14 and the splined
portions 32 and 34 will mesh and interlock. At this point power will be
transmitted through the differential unit lO to the axle shaft directly
from the drive gear to the differential casing to axle shaft bypassing
the action of the differential pinions on the differential side gear.
This locking out of the differential pinions will result in power being
transmitted to the wheels thereby effecting traction to move an otherwise
immobilized vehicle, i.e. the locking out of the differential will result
in both the wheels operating at the same speed. If the operator
inadvertently leaves the locking out mechanism engaged, he will experience a
change in the steering characteristics of the vehicle during cornering or
other similar maneuvers because of the dragging of a wheel around such
corner. This change in steering characteristic will be quickly sensed
by the operator and he can appropriately deactivate the locking out
mechanism. It can be seen, therefore, that the vehicle operator can
selectively activate the piston to 10ckout the differential action of
the differential drive unit lO. This feature has provided the vehicle
operator with the above-described new and novel lockout mechanism, which
is simplistic in design yet reliable in service and relatively impervious
to the environment encountered externally of the housing 12.
The present invention is not to be limited to the specific details
as herebefore described but is capable of many other modifications and
changes without departing from the spirit and scope of the appended
claims.
