FACE GEAR DIFFERENTIALS INCORPORATING A TORQUE RING
TECHNICAL FIELD
[0001] The present invention relates to a gear set, including a first gear comprising a
helical face gear and a second gear comprising a helical pinion in meshing engagement with the
helical face gear. The gear set may be configured for use in a differential.
BACKGROUND
[0002] Helical face gears for use in differentials are known in the art, as set forth for
example, in U.S. Pat. No. 3,253,483 and U.S. Pat. No. 4,791,832. However, incorporation of
helical face gears into differentials has not been commercially utilized because of, for example,
limitations with respect to determination of gear tooth architecture and to the strength of the
gears, both of which may adversely affect performance of the gear set.
[0003] It may be desirable to utilize face gear technology that may overcome these
limitations. Face gear technology may allow for the option of more and/or larger diameter
pinions and more robust primary helical face gears that may be better supported. With respect to
the use of face gear technology in connection with a differential, the compact size of side gears
utilizing face gear technology in connection with a torque ring may allow for greater flexibility
in packaging and design. In this way, the overall strength of the differential for a given package
size can be increased. Furthermore, the compact nature of the gear set and a torque ring, in some
embodiments, may direct the dynamic forces in a more beneficial way and may allow the same
gear set and internal components to be used in connection with various packaging designs of
various rnodels of motor vehicles, thereby increasing the transportability of the differential.
SUMMARY
[0004] A gear set is provided including a side gear comprising a helical face gear with at
least one helical tooth and a helical pinion. The helical pinion may have at least one helical tooth
and may have an apex angle that is less than about 20°. The helical pinion may be configured for

meshing engagement with the side gear. A differential may also be provided. The differential
may comprise a differential case and a gear set. The gear set may include a side gear comprising
a helical face gear with at least one helical tooth and a helical pinion. The helical pinion may
have at least one helical tooth and may have an apex angle that is less than about 20°. The
differential may further include a torque ring configured to support the helical pinion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Embodiments of the invention will now be described, by way of example, with
reference to the accompanying drawings, wherein:
[0006] FIG. 1 is a perspective view of a first gear in accordance with an embodiment of
the invention.
[0007] FIG. 2A is front view of a second gear in accordance with an embodiment of the
invention.
[0008] FIG. 2B is a side view of the second gear of FIG. 2A.
[0009] FIG. 3A is a perspective view of a torque ring for use with the first gear of FIG. 1
in accordance with an embodiment of the invention.
[00010] FIG. 3B is a side view of the torque ring of FIG. 3 A.
[00011] FIG. 4 is a schematic illustrating the apex angle of a first gear in accordance with
an embodiment of the invention.
[00012] FIG. 5 is a schematic illustrating the tooth flank geometry of a first gear in
accordance with an embodiment of the invention.
[00013] FIG. 6A is a cross-sectional view of a gear set in accordance with an embodiment
of the invention incorporated into a differential.

[00014] FIG. 6B is a front view of a portion of the gear set of FIG. 6A.
[00015] FIG. 7 is a cross-sectional view of a gear set in accordance with an embodiment of
the invention incorporated into a differential.
[00016] FIG. 8 is an exploded view of an electrically selectable locking differential
including a gear set in accordance with an embodiment of the invention.
[00017] FIG. 9 is a cross-sectional view of a differential including a torque limiting fuse
and a gear set in accordance with an embodiment of the present invention.
[00018] FIG. 10 is a cross-section view of a differential including torque limiting clutch
plates and a gear set in accordance with an embodiment of the present invention.
[00019] FIG. 11 is a partial cross-sectional view of a differential including an air/hydraulic
actuator and a gear set in accordance with an embodiment of the invention.
[00020] FIG. 12 is a cross-sectional view of a differential including a gear set in accordance
with an embodiment of the invention.
DETAILED DESCRIPTION
[00021] 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.
[00022] A gear set 10 in accordance with the present invention may include a first gear 12
and a second gear 14. Referring now to FIGS. 1-2, the first gear 12 may comprise a helical
pinion, and the second gear 14 may comprise a side gear. In an embodiment, the first gear 12
may comprise a helical pinion for use in a differential. In this embodiment for a differential, the

first gear 12 may be provided to transmit torque from a torque ring 18 to second gear 14 (e.g., a
side gear 14). The torque ring 18 may be as shown in FIGS. 3A-B and may be configured as
described in further detail herein. Alternatively, the first gear 12 may be provided to transmit
torque from one side gear 14 to another side gear 14. Further, in this embodiment, there may be
a plurality of pinions 12. The number of the pinions 12 in gear set 10 may vary. However, there
may be at least two pinions 12 in gear set 10 when the pinions 12 are used in a differential. The
number of pinions 12 may be about six in an embodiment, although greater or fewer pinions 12
may be used in other embodiments. In contrast, the number of bevel pinions that may be utilized
in a conventional gear set for a differential may only be about four. The maximum number of
pinions 12 used in a differential may be determined using the following formula, where the outer
diameter of the pinion 12 is denoted as do.p' and the inner diameter of the corresponding side gear
14 is denoted as din.sg.

[00024]" The size of pinions 12 may also vary. However, in an embodiment, the pinions 12
may be about one half the size of a conventional bevel pinion gear used in a differential. In
addition, the pinions 12 may be configured to have a low apex angle θP as compared to
conventional gear designs. Referring now to FIG. 4, a schematic illustrating the apex angle of a
pinion 12 is shown. In an embodiment, the apex angle θP may be less than about 20°. The apex
angle θP may be subject to the following equation, in which do.p is the outer diameter of the
pinion 12, dl.p is the limit diameter of the pinion 12, d0.sg is the outer diameter of the side gear 14,
and din,sg is the inner diameter of the side gear 14.

[00026] The number of helical teeth 20 on pinion 12 and the geometry of the tooth flank of
the helical teeth 20 on pinion 12 may be flexible in accordance with an embodiment of the
invention. The helical teeth 20 may be formed by forging technology. The use of forging

technology instead of machine-cutting technology may significantly improve the strength of the
pinions 12. The use of helical teeth 20 also allows less emphasis to be placed on where the
pinions 12 are in their rotation as compared to conventional bevel pinions, which may eliminate
the requirement of indexing. The number of helical teeth 20 on pinion 12 may be considered a
low tooth count relative to the size of the pinions 12. For example, the tooth count (i.e., the
number of helical teeth 20) of pinion 12 may between about 4 to 10. Although a tooth count of
about 4 to 10 is mentioned in detail, the tooth count of the pinions 12 may be lower or higher in
other embodiments of the invention.
[00027] Referring now to FIG. 5, the geometry G of the tooth flank for the helical teeth 20
on pinion 12 may be determined in accordance with the following equation, in which rp = the
position vector of a point of the tooth flank of the pinion 12; Up, Vp = curvilinear (Guassian)
coordinates of a point of the tooth flank of the pinion 12; :rb.p = the radius of the base cylinder of
the pinion 12; and τb.p = the base helix angle of the pinion 12.

[00029] When the pinion 12 is stationary, then the tooth flank of the pinion 12 may be
analytically described by Equation 3. When the pinion 12 is rotated about its axis 22 through a
certain angle φp, and when it is moving around the axis 24 of the side gear 14, the position vector
of a point r*p of the tooth flank of the pinion 12 in a current position of the pinion 12 may be
expressed in the following form:

[00031] The pinions 12 may also be configured to provide flexibility with respect to
structural features to accommodate various embodiments. For example, the pinions 12 may be
modified to provide access for C-clips 26 as illustrated in FIGS. 6A-6B. C-clips 26 may be
provided for axially positioning side gears 14 on the axle shafts and retaining the axle shafts. In
another example, the pinions 12 may be modified to include a boss 28 at the first end 30 and a

counter diameter 32 at the second end 34, as illustrated in FIG. 7. The boss 28 and counter
diameter 32 may be configured to better support pinion 12 and may be provided to alter the bias
ratio. The boss 28 and counter diameter 32 may be configured to either increase and/or decrease
the bias ratio depending upon the desired end result. The pinions 12 may also be modified to
include an axially extending bore 36. The bore 36 may extend through the center of the pinion
12 along axis 22. The bore 36 may be configured to receive an axle for rotating the pinion 12.
Although a bore 36 is mentioned in detail and is illustrated, the pinion 12 may not have a bore 36
in other embodiments of the invention.
[00032] In an embodiment of the invention, the first end 30 of the pinions 12 may be flat,
and the second end 34 of the pinions 12 (i.e., opposing the first end 30) may be hemispherical in
shape. The second end 34 may be configured to have a hemispherical shape such that the second
end 34 has the same radius of curvature as the outer surface 56 of the torque ring 18 shown in
FIG. 3. In addition, the second end 34 of the pinion 12 may be configured so that it matches the
inner surface of a housing for the gear set 10 (e.g., a differential case). The shape of the pinion
12 may thus help control friction of the gear set 10, since no other device is necessary to
maintain the outer shape of the torque ring 18. Although the first end 30 of the pinion 12 is
described as flat, and the second end 34 of the pinion 12 is described as hemispherical in shape,
the pinion 12 may have other shapes in other embodiments of the invention.
[00033] The second gear 14 may comprise a helical face gear. The second gear 14 may be
configured to be in meshing engagement with the first gear 12. In an embodiment, the second
gear 14 may comprise a side gear for use in a differential. In this embodiment for a differential,
the second gear 14 may be configured to transmit torque from the first gear 12 to an output (e.g.,
axle shafts of a motor vehicle). Further, in this embodiment for a differential, there may be a
plurality (e.g., a pair) of side gears 14. Each side gear 14 may have a first annular hub portion
37. Each annular hub portion 37 may be configured to receive an axle shaft (not shown) of a
motor vehicle, for example. The annular hub portion 37 may define an inner axially aligned
opening 38. The inner radial surface of annular hub portion 37 of the side gear 14 that defines
the opening 38 may include a plurality of splines 40 (i.e., may be splined). The axle shafts (not
shown) may connect to side gears 14 through a splined interconnection with the splines 40 on the

inner surface defining the inner axially aligned opening 38. Accordingly, the side gears 14 may
be configured to be in splined engagement with a pair of axle shafts.
[00034] The plurality of side gears 14 (e.g., in an embodiment for use in a differential) may
be located on opposing sides of first gear 12. In particular, in an embodiment, the pair of side
gears 14 may be located on opposing sides of a torque ring 18 configured to retain the helical
pinions 12. Each side gear 14 may have a main portion 42 with an outer surface 43. The outer
surface 43 may extend circumferentially around the axis 24 of the side gear 14. The outer
surface 43 may have at least one projection 44 extending radially outwardly from the outer
surface 43. The projections 44 may be configured for supporting the side gear 14. In particular,
the projection 44 may be configured for supporting the side gear 14 in connection with a
corresponding element on the torque ring 18. The projection 44 may be configured to be
received by a corresponding recess in the torque ring 18. The side gear 14 may include about six
projections 44 as illustrated. Although six projections 44 are mentioned in detail, the side gear
14 may include fewer or more projections 44 in other embodiments. The projections 44 may be
configured to increase the robustness of the side gear 14.
[00035] The main portion 42 of the side gear 14 may further include a helical face 46.
Helical face 46 of each side gear 14 may face torque ring 18. The helical face 46 of each side
gear 14 may be in meshing engagement with the pinions 12. The pinions 12 and side gear 14
may thus share torque via gear meshing. In an embodiment, each side gear 14 may further have
a substantially flat surface 48 opposing the helical face 46. Although the surface 48 opposing the
helical face 46 is described as flat, the opposing surface may not necessarily be flat in
embodiments of the invention.
[00036] The helical face 46 may comprise a plurality of teeth 50. The helical teeth 50 of
side gear 14 may be forged. The use of forging technology in place of machine-cutting
technology may significantly improve the strength of the side gears 14. In addition, the use of
forging technology in connection with the side gear 14 allows the side gear 14 to have a hub 52.
Hub 52 may be integral with side gear 14 and may extend circumferentially around the inner
diameter din.sg of the side gear 14. The hub 52 may have a radially extending thickness T. The
radially extending thickness T may vary in accordance with different embodiments of the

invention. The hub 52 may be configured to improve the strength of the side gear 14 at its
otherwise weakest point. Each of the helical teeth 50 of side gear 14 may extend radially
inwardly toward the hub 52. The hub 52 may be integral with each of the helical teeth 50 of side
gear 14. In an embodiment, the top surface of each helical tooth 50 may be substantially flush
with the top surface of the hub 52. Although the top surface of the hub 52 may be substantially
flush with the top surface of each helical tooth 50 in an embodiment, the top surface of the hub
52 may be higher or lower than the top surface of each helical tooth 50 in other embodiments of
the invention.
[00037] The number of helical teeth 50 on side gear 14 and the geometry of the tooth flank
of the helical teeth 50 on side gear 14 may be flexible in accordance with an embodiment of the
invention. The tooth count (i.e., the number of helical teeth 50) of side gear 14 may be
considered a low tooth count. For example, the tooth count may be as low as 12. Although a
tooth count as low as 12 is mentioned in detail, the tooth count may be lower or higher in other
embodiments of the invention. The tooth flank for the helical teeth 50 on the side gear 14 may
be determined as an enveloping surface to successive positions of the pinion tooth flank when
the pinion 12 is rotating about its axis 22 and moving around the axis 24 of the side gear 14. An
expression for the position vector of a point rsg of the tooth flank of the teeth 50 on side gear 14
may be derived from an equation for pinion tooth flank (Equation 5) set forth below:

[00039] Substitution of φp may be required to determine rsg. This may be accomplished
through use of the equation of contact (Equation 6) set forth below:

[00041] In connection with Equation 6, np denotes the unit normal vector to the pinion tooth
flank, and VΣ denotes the vector of the resultant motion of the pinion 12 relative to the side
gear 14. Both np and VΣ are functions of φp as set forth in the equations below (Equations 7
and 8).


[00044] By solving for φp in Equations 7 and 8, the derived expression for φp may be
substituted into Equation 5, which then returns an expression for the tooth flank of the teeth 50 of
side gear 14.
[00045] The side gear 14 may further include a supporting diameter 53. In particular, the
supporting diameter 53 may comprise a second annular hub portion 53 (e.g., similar to first
annular hub portion 37). However, the supporting diameter 53 may have an outer diameter that
is larger than an outer diameter of the first annular hub portion 37. In addition, the supporting
diameter 53 may have an outer diameter that is smaller than an outer diameter of the main
portion 42 of side gear 14 that includes helical face 46. The supporting diameter 53 may be
configured to further reinforce side gear 14. Referring now to FIG. 8, an exploded view of an
electrically selectable locking differential incorporating a gear set 10 in accordance with an
embodiment of the invention is illustrated. The differential may further include a thrust washer
and/or shim 62. Shim 62 is configured to adjust proper side gear 14 orientation/placement
during assembly. Shim 62 may be disposed adjacent the supporting diameter 53 and around the
first annular hub 37. In conventional gear sets, the shim 62 may be located at the end of the hub
37. The location of the shim 62 in a differential that incorporates a gear set 10 including side
gear 14 in accordance with an embodiment of the invention may affect axial take-up.
[00046] As set forth above, in an embodiment, the first gear 12 may comprise a helical
pinion for use in a differential, and the first gear 12 may be provided to transmit torque from a
torque ring 18 to a second gear (e.g., side gear 14). Although the gear set 10 is described in
connection with the use of the torque ring 18 in an embodiment, the torque ring 18 may be
omitted in other embodiments of the invention and the first gear 12 may be supported on axles
extending through bores 36. In the embodiment utilizing torque ring 18, torque ring 18 may be
generally ring-shaped. Torque ring 18 may be made from one piece of material (i.e., comprise a
unitary, integral, and/or monolithic structure) in an embodiment of the invention. Torque ring 18
may be configured for locating one or more pinions 12 in a radial pattern between side gears 14.

The torque ring 18 may have a plurality of radially inwardly extending holes 54 extending into
the torque ring 18 from an outer radial surface 56 of the torque ring 18. The outer radial surface
56 of torque ring 18 may be cylindrical in shape, as may be best illustrated in FIG. 3B.
Accordingly, the outer radial surface 56 of torque ring 18 may not be spherical. While a
spherical outer radial surface 56 may make the assembly of the gear set 10 with torque ring 18
more difficult, the cylindrical shape of the outer radial surface 56 in accordance with an
embodiment eases assembly.
[00047] The holes 54 of torque ring 18 may each have an axis. The axis of holes 54 may
extend substantially radially outwardly. For example only, and without limitation, there may be
approximately six holes 54 extending through the torque ring 18. Although six holes are
mentioned in detail, there may be fewer or more holes 54 in other embodiments of the invention.
The holes 54 may be equi-angularly spaced around the circumference of the torque ring 18.
Although the holes 54 are described as being equi-angularly spaced around the circumference of
the torque ring 18, the holes 54 may be spaced in any alternate arrangements and/or
configurations in other embodiments of the invention. The pinions 12 may be disposed within
the holes 54 in the torque ring 18. In this way, the pinions 12 may be circumferentially spaced
around the torque ring 18. The number of pinions 12 may generally correspond to the number of
holes 54 in the torque ring 18, although fewer pinions 12 in relation to the number of holes 54
may be used in embodiments of the invention. In these embodiments of the invention, at least
one or more of the holes 54 may remain open. In the embodiments where at least one or more of
the holes 54 remain open, the open holes 54 do not necessarily have to be regularly (e.g., equi-
angularlyj spaced around the torque ring. Instead, the open holes 54 may be adjacent to each
other, spaced from each other, and/or arranged in any arrangement and/or combination.
[00048] The pinions 12 may be free to rotate within holes 54. The pinions 12 may be
axially trapped between an inner surface of a housing for the torque ring 18 (e.g., a differential
case) and a radially inward portion 58 of the torque ring 18. The housing for the torque ring 18
and the radially inward portion 58 of the torque ring thus restrain the pinions 12 from axial
movement. Radially inward portion 58 extends circumferentially around the torque ring 18,
thereby causing each of holes 54 to comprise a blind hole. A first end of hole 54 at the outer
radial surface be open, while a second end of hole 54 at the radially inward portion 58 may be

closed. The second end of the hole 54 may oppose the first end of the hole 54. Because holes 54
comprise blind holes, the amount of friction in connection with the gear set 10 may be reduced
since there is no additional friction from other moving parts (e.g., other moving parts of a
differential) acting on the pinions 12. In addition, the radially inward portion 58 allows the size
of the center axle shaft (not shown) to be modified without requiring modification to the torque
ring 18. In some embodiments of the invention, the torque ring 18 may include an opening
extending through the radially inward portion 58 to the center axle shaft. The opening may be
configured to allow tools and/or other instruments to access the center axle shaft without having
to require partial and/or complete disassembly of the gear set 10.
[00049] The torque ring 18 may further include channels 60 in the side surfaces of the
torque ring 18. The torque ring 18 may be configured to support the pinions 12 on their outside
surfaces and to confine the pinions 12 in meshing engagement with the side gears 14. The torque
ring 18 may exert pressure on the pinions 12 (e.g., the outside diameter d0.p of the pinions 12) to
move them radially about the axis 24 (e.g., an axial centerline) of the side gears 14. Due to the
meshing engagement between the pinions 12 and the side gears 14, the side gears 14 are forced
to turn about their axis 24. Because the output (e.g., axle shafts) are grounded and coupled to the
side gears 14, the motor vehicle incorporating gear set 10 may move. When the side gears 14 are
forced to rotate at different speeds by grounding through the output (e.g., axle shafts), the pinions
12 may rotate within the torque ring 18 and in mesh with the side gears 14 to compensate.
Helical teeth 20 of pinions 12 may extend into the channels 60 (e.g., the opposed channels 60) in
the side surfaces of the torque ring 18. Helical teeth 50 on helical face 46 of side gear 14 may
also extend into the channels 60 in the side surfaces of the torque ring 18. In this way, the helical
teeth 20 of pinions 12 may be meshed engagement with the helical teeth 50 of side gear 14.
[00050] The torque ring 18 may be configured to provide flexibility with respect to
structural features to accommodate various embodiments. For example, the torque ring 18 may
be modified to comprise features to access and retain axle shaft C-clips 26 as illustrated, for
example, in FIGS. 6A-B in an embodiment. For another example, the torque ring 18 may be
modified to include a mechanical fuse link 68 that is designed to fail at a predetermined shear
value which governs the amount of allowable differential torque that the torque ring 18 may
experience. For example, the mechanical fuse link 68 may comprise a shear pin which shears at

a predetermined torque. The mechanical fuse link 68 may be for torque fusing and/or limiting.
The mechanical fuse link 68 may retain the torque ring 18 to the differential case 64, for
example, until a predetermined torque is reached.
[00051] As set forth herein, the gear set 10 may be used in a differential. Although the gear
set 10 is described for use in connection with a differential, the gear set 10 may be used in other
applications in other embodiments of the invention. When gear set 10 is used in a differential,
the differential may be provided to allow a motor vehicle to negotiate turns while maintaining
power to both the left and right wheels of a drive axle. A differential incorporating gear set 10 in
accordance with the present invention may provide increased strength and robustness, and may
be especially robust relative to its compact differential size. The gear set envelope for a
differential incorporating gear set 10 may be relatively compact and may provide for great
flexibility in packaging. Furthermore, a differential incorporating a gear set 10 in accordance
with an embodiment of the invention may allow for greater commonality of parts (i.e., the
components may be common to various types of differentials) and transportability (i.e., the
ability to use the same gear set and internal components for various models of motor vehicles),
thereby improving ease of manufacture. Finally, a differential incorporating a gear set 10 in
accordance with an embodiment of the invention may reduce the need for higher cost materials
and may also reduce noise, vibration, and harshness ("NVH") that may be associated with other
conventional designs.
[00052] When the gear set 10 is incorporated into a differential, the differential may further
include a differential case 64. Differential case 64 may be provided to house the gear set 10
and/or any number of other components of the differential. In an embodiment, differential case
64 may not require pinion cross shaft bores which may increase ease of manufacturing.
Accordingly, the differential case 64 may be configured to have an opening only at each axial
end of the differential case in those embodiments that do not require pinion cross shaft bores.
The differential case 64 may be made from low cost materials. The differential case 64 may be
subjected to minimal loading. The differential may further include a ring gear (not shown). The
ring gear may be connected to an input source and/or drive source (not shown) in a conventional
manner for rotating the differential case 64. In an embodiment where the gear set 10 utilizes a
torque ring 18, the torque ring 18 may be mounted within the differential case 64 in any manner

conventional in the art so as to be configured for common rotation with the differential case. For
example, the torque ring 18 may include a plurality of axially extending apertures through which
a plurality of fasteners 66 may extend through the torque ring 18 and the differential case 64. In
this way torque from the ring gear may be applied to the torque ring 18 by means of a
mechanical connection and/or attachment to the ring gear (e.g., directly attached to the ring
gear).
[00053] The gear set 10 may be used in an open differential, a limited slip differential,
and/or a locking differential in various embodiments. An open differential may allow two axle
wheels to rotate at different speeds. However, an open differential may generally be configured
for torque to take the path of least resistance, which may provide the greatest risk of a motor
vehicle being stuck because of the inability to have torque transfer to the wheel that has the most
traction.
[00054] A limited slip differential may be substantially similar to an open differential, but
may further include a clutch pack 65 that is configured to limit the slippage associated with an
open differential by transferring a portion of the power from one wheel to another wheel (e.g., if
the side gears 14 are forced to different speeds by an imbalance of traction). The clutch pack 65
may best be illustrated in FIG. 10. The clutch pack 65 may be mechanically coupled to the side
gear 14, torque ring 18, and/or a differential case in order to limit slippage and restore tractive
effort. In a limited slip differential, as the pinions 12 rotate within the torque ring 18 in mesh
with the side gears 14, the separating forces may exert pressure forcing the side gears 14
outward. The force of the side gears 14 may be used to compress the clutch plates of the clutch
pack 65. In accordance with the present invention, the torque ring 18 and side gears 14 may be
configured to direct a greater proportion of the gear separating forces to thrusting the side gears
14 outward, thereby increasing the pressure available to compress the clutch plates of the clutch
pack 65. Alternatively, a limited slip differential incorporating a gear set 10 in accordance with
the present invention may be configured to induce drag on the pinions 12 as they rotate within
the torque ring 18.
[00055] A locking differential may be substantially similar to an open differential, but may
be configured to maintain free differential action during normal driving of a motor vehicle to

allow two wheels to operate at different speeds (i.e., like an open differential), but to fully lock
when excessive wheel slippage occurs. That is, if a wheel starts to slip, the drive axle may be
fully locked side to side, providing full power to both wheels. The locking differential may
comprise a selectable locking differential in accordance with an embodiment. However, the
locking function may also be automatic in other embodiments.
[00056] Referring back to FIG. 8, an exploded view of a locking differential is illustrated.
In an embodiment of the invention, the differential case 64 in which at least a portion of gear set
10 is housed may comprise a flanged body (e.g., as illustrated). In particular, the differential
case 12 may be configured to have an axial length L for housing components of the differential
that is relatively short compared to conventional designs. Accordingly, the locking differential
may be of a compact size, but may still be configured to house differential components. Without
the compact nature of the gear set 10 and torque ring 18, in certain embodiments, it could
otherwise be difficult to find sufficient space for the differential, as well as locking, components.
Still referring to FIG. 8, the locking differential may further include a cover 70. Cover 70 may
be configured for connection to the differential case 64. Cover 70 may comprise a hub 72 and a
flanged portion 74. The flanged portion 74 of cover 70 may be configured to correspond to the
flanged portion of differential case 64 in an embodiment of the differential.
[00057] Still referring to FIG. 8, a locking differential may further include a locking ring
76. Locking ring 76 may also be referred to as a lock collar. The locking ring 76 may be
configured to make the axles lock side-to-side when the locking ring 76 is engaged. The torque
ring 18 may be configured to provide the torque path to the pinions 12 or the locking ring 76,
depending upon the mode of operation or design. The locking ring 76 may be generally ring-
shaped and may include a plurality of axially extending protrusions 78. The protrusions 78 may
be circumferentially spaced around the circumference of the locking ring 76. In an embodiment,
the protrusions 78 may be equi-angularly spaced around the circumference of the locking ring
76. Although the protrusions 78 have been described as being equi-angularly spaced in an
embodiment of the invention, the protrusions 78 may be spaced in any alternate arrangements
and/or configurations in other embodiments of the invention. The locking ring 76 may be placed
at a substantially increased diameter and may be coupled directly to the torque ring 18.

[00058] Still referring to FIG. 8, a locking differential may further include an actuator 80.
The actuator 80 may be provided to engage the locking ring 76 and force the locking ring 76 into
engagement with the side gear 14 in order to make the axles lock side-to-side. The actuator 80
may be powered and/or signaled by one or more of the following methods: electricity, vacuum,
pneumatic, hydraulic, or mechanical means. Referring now to FIG. 11, an air or hydraulic
mechanical means for actuator 80 is illustrated. Referring back to FIG. 8, an electric means may
also be used for actuator 80 in an embodiment. The actuator 80 may include a stator housing 82
and an armature plate 84. The stator housing 82 may house a stator that is configured to activate
armature plate 84. Armature plate 84 may then, in turn, be configured to activate locking ring
76. In this way, actuator 80 is configured to relay its movement, when energized, to the locking
ring 76 that may be splined to a side gear 14 and may further be connected (e.g., coupled) with
the torque ring 18 through complementary face tooth profiles. The face tooth profiles may be
arranged with angled contact surfaces so as to exploit the torque applied and pull the locking ring
76 into full engagement.
[00059] A locking differential, for example, as illustrated in FIG. 8, may function as an
open differential until the actuator 80 is energized. When torque from the ring gear (not shown)
is applied to the torque ring 18, the locking ring 76 (e.g., connected to the torque ring 18) may
transfer torque to the side gear 14, and no relative motion can take place between the side gear
14 and the torque ring 18. With one of the side gears 14 coupled directly to the to torque ring 18,
the other side gear 14 cannot move relative to the torque ring 18 via the gear mesh with the
pinions 12. The locked condition will continue during the driving, coasting, forward movement,
reverse movement, stopping, and starting, so long as the power of the actuator 80 is maintained.
When actuator power and torque pressure are removed, a return spring (not shown) acting
between the side gear 14 and the locking component 76 may return the locking component 76 to
the default unlocked position. When the actuator 80 comprises an electric actuator, upon
deactivation of the stator in the stator housing 82, the armature plate 84 may retract and the
selectable locking differential may then return to an open differential state.
[00060] A locking differential, for example, as illustrated in FIG. 8, may require no external
equipment for actuation, other than a 12 V DC power supply (i.e., be self-containing). A locking
differential may have an improved actuation method with low backlash and may have a positive

lock indication using a common wiring harness, in some embodiments. A locking differential
may also be configured for installation in different and/or various differential cases with the only
necessary modification to the system being the actuator pins and/or length of the axle shaft
splined hub of the side gears 14 in order to achieve such transportability.
[00061] 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 gear set [10], comprising:
a side gear [14] comprising a helical face gear with at least one helical tooth [50]; and
a helical pinion [12] configured for meshing engagement with the side gear [14], wherein
the helical pinion [12] has at least one helical tooth [20] and an apex angle that is less than about
20°.
2. The gear set [10] of claim 1, wherein the helical tooth [50] of the side gear [14] and the
helical tooth [20] of the helical pinion [12] are forged.
3. The gear set [10] of claim 1, further comprising a plurality of helical pinions [12]
configured for meshing engagement with the side gear [14].
4. The gear set [10] of claim 1, wherein the apex angle is governed by the following
equation: θp < sin where do.P is the outer diameter of the helical pinion [12],
dlp is the limit diameter of the helical pinion [12], do.sg is the outer diameter of the side gear [14],
and din.sg is the inner diameter of the side gear [14].
5. The gear set [10] of claim 1, wherein the helical pinion [12] has a tooth count between
about 4 and 10.
6. The gear set [10] of claim 1, wherein the helical pinion [12] comprises a boss [28] at a
first end [30] of the helical pinion [12].
7. The gear set [10] of claim 1, wherein the helical pinion [12] is substantially flat at a first
end [30] of the helical pinion [12] and is substantially hemispherical at a second end [34] of the
helical pinion [12].
8. The gear set [10] of claim 1, wherein the side gear [14] comprises a first annular hub
portion [37] configured to receive an axle shaft.

9. The gear set [10] of claim 8, wherein the side gear [14] comprises a main portion [42]
with a circumferentially extending outer surface [43] with at least one projection [44] extending
radially outwardly from the outer surface [43].
10. The gear set [10] of claim 1, wherein the side gear [14] further comprises a hub [52] on
the helical face [46], the hub [52] extending circumferentially around an inner diameter of the
side gear [14] with the helical tooth [50] of the side gear [14] extending radially inwardly toward
the hub [52].
11. The gear set [10] of claim 10, wherein the hub [52] is integral with the helical tooth [50]
on the side gear [14].
12. The gear set [10] of claim 11, wherein a top surface of the helical tooth [50] on the side
gear [14] is substantially flush with a top surface of the hub [52].
13. The gear set [10] of claim 1, wherein the side gear [14] has a tooth count as low as about
12.
14. The gear set [10] of claim 9, wherein the side gear [14] comprises a second annular hub
portion [53], wherein an outer diameter of the second annular hub [53] portion is greater than an
outer diameter of the first annular hub portion [37] and an outer diameter of the second annular
hub portion [53] is less than an outer diameter of the main portion [42].
15. A differential, comprising:
a differential case [64];
a side gear [14] comprising a helical face gear; and
a helical pinion [12] configured for meshing engagement with the side gear [14], wherein
the helical pinion [12] has an apex angle that is less than about 20°.
16. The differential of claim 15, further comprising a torque ring [18] configured to support
the helical pinion [12].
17. The differential of claim 15, wherein the helical pinion [12] comprises a substantially
hemispherical end, and wherein the radius of curvature of the substantially hemispherical end of

the helical pinion [12] is substantially equal to the radius of curvature of an outer surface [56] of
the torque ring [18].
18. The differential of claim 16, wherein the torque ring [18] comprises at least one hole [54]
extending radially inwardly from an outer radial surface [56] of the torque ring [18], and wherein
the helical pinion [12] is disposed in the hole [54].
19. The differential of claim 18, wherein the at least one hole [54] comprises a blind hole,
such that hole [54] is open at a first end at the outer radial surface [56] of the torque ring [18] and
the hole [54] is closed at a second end opposing the first end.
20. The differential of claim 16, wherein the torque ring [18] includes at least one channel
[60] in the side surfaces of the torque ring [18] for allowing the helical pinion [12] to be in
meshing engagement with the side gear [14].

ABSTRACT

A gear set [10] is provided including a side gear [14] comprising a helical face gear with
at least one helical tooth [50] and a helical pinion [12]. The helical pinion [12] may have at least
one helical tooth [20] and may have an apex angle that is less than about 20°. The helical pinion
[12] may be configured for meshing engagement with the side gear [14]. A differential may also
be provided. The differential comprises a differential case [64] and a gear set [10]. The
differential may further include a torque ring [18] configured to support the helical pinion [12].