IMPROVED TORQUE CAPACITY
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates, generally, to locking differentials for automotive
cles, and more specifically to features of a locking differential that result in increased torque
lcity and density for a given size of the differential.
2. Description of the Related Art
[0002] Locking differentials of the type contemplated by the present invention are
loyed as a part of a drive train and generally include a pair of clutch members supported for
ion in a housing. A pair of side gears are splined for rotation to corresponding axle half
ts. A clutch mechanism is interposed between the clutch members and the side gears. A
s pin is operatively mounted for rotation with the housing and is received in a pair of opposed
ves formed on the inwardly facing surfaces of the clutch members. In the event of excess
:rential rotation between the axle half shafts, such as when one tire is supported on a slippery
tee, the cross pin acts on the associated clutch member to engage the clutch mechanism
eby coupling the pair of axle half shafts together.
[0003] While locking differentials of this type have generally worked for their intended
oses, certain disadvantages remain. More specifically, the size of the components of the
rential are often dictated by the amount of torque that can be transmitted thereby. Higher
re requirements typically require larger, more robust components such as the cross pin,
h members, etc. This design limitation ultimately increases the cost of a differential for the
amount of torque capacity and density required in any application.
[0004] Thus, there remains a need in the art for a locking differential that is designed so
as to increase its torque capacity and density without the need for increasing the size of the
related components, thereby reducing the cost of the differential.
SUMMARY OF THE INVENTION
[0005] The present invention overcomes the disadvantages in the related art in a locking
differential for an automotive vehicle that includes a housing and a differential mechanism
supported in the housing. The differential mechanism includes a pair of clutch members
disposed in spaced axial relationship with respect to one another and operatively supported for
rotation with the housing. A pair of side gears is operatively adapted for rotation with a
corresponding pair of axle half shafts. A pair of clutch mechanisms is operatively disposed
between the corresponding pair of clutch members and the side gears. The clutch members are
axially moveable within the housing to engage a respective clutch mechanism to couple the axle
half shafts together in the event of a predetermined amount of differential movement between the
axle half shafts. Each of the pair of clutch members presents an inwardly directed face. Each
face includes a groove disposed in facing relationship with respect to the other. A cross pin is
received in the grooves and operatively connected for rotation with the housing. Each of the
grooves includes a pair of working surfaces extending laterally relative to each other. In one
embodiment of the present invention, the working surfaces define a screw involute surface such
that the cross pin contacts the working surfaces along a line extending in the direction of the
cross pin in the event of differential rotation of an axle half shaft. In another embodiment of the
present invention, the working surfaces define a slightly convex surface in one plane such that the
cross pin contacts the working surface at a point defined thereon in the event of differential
rotation of one axle half shaft. In still another embodiment of the present invention, the working
surfaces define a slightly convex surface in two planes such that the cross pin contacts the
working surface at a point defined thereon in the event of differential rotation of one axle half
shaft.
[0006] In this way, the locking differential of the present invention employs clutch
members having working surfaces having screw involute working surfaces that allow for line
contact between the cross pin and the working surface; a working surface that may be slightly
convex in one plane; or a working surface that may be topologically modified to be slightly
convex in two planes that allows for point contact between the cross pin and the working surface.
This structure significantly reduces the edge stress generated by the interaction of the cross pin
and the working surface and thereby increases the torque density that may be generated through
the differential for a given size of the cross pin and clutch member. Accordingly, the present
invention reduces the necessity of increasing the size of the related component and by association
the cost of the differential for a given torque capacity of the differential.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Other objects, features and advantages of the present invention will be readily
appreciated, as the same becomes better understood after reading the subsequent description
taken in connection with the accompanying drawings wherein:
[0008] Figure 1 is a cross-sectional side view of a locking differential illustrating a
driveshaft, pinion gear and ring gear of the drive train in phantom;
[0009] Figure 2 is a cross-sectional side view of a locking differential illustrating the
disposition of the cross pin relative to the clutch members;
[0010] Figure 3 is an exploded view of the differential mechanism of the present
invention;
[0011] Figure 4 is a perspective elevational view of a clutch member of the present
invention;
[0012] Figure 5 is a perspective elevational view of a clutch member illustrating the areas
of contact between the cross pin and the working surfaces as well as areas of edge stress
generated in locking differentials known in the related art;
[0013] Figure 6A is a perspective elevational view of one embodiment of the clutch
member of the present invention illustrating a screw involute working surface;
[0014] Figure 6B illustrates the generation of a screw involute surface;
[0015] Figure 6C is a cross-sectional end view illustrating the line contact between a
cross pin and a screw involute working surface;
[0016] Figure 7 A is a perspective elevational view of a clutch member of the present
invention illustrating a working surface that is slightly convex in one plane;
[0017] Figure 7B is an enlarged representative cross-sectional view taken alpng lines 7B
- 7B of Figure 7A illustrating the slightly convex working surface in one plane;
[0018] Figure 8A is cross-sectional end view illustrating the contact between a cross pin
and a working surface that is slightly convex in two planes; and
[0019] Figure 8B is cross-sectional side view illustrating the contact between a cross pin
and a working surface that is slightly convex in two planes.
DETAILED DESCRIPTION
[0020] One embodiment of a locking differential of the type contemplated by the present
invention is generally indicated at 10 in Figures 1-2. The locking differential 10 is designed to
be employed as a part of a drive train for any number of vehicles having a power plant that is
used to provide motive force to the vehicle. Thus, the differential 10 includes a housing,
generally indicated at 12. The housing 12 may support a ring gear 14 that is designed to be
driven in meshing relationship with the pinion gear 16 fixed to a drive shaft 18. The ring gear 14,
pinion 16 and driveshaft 18 are shown in phantom in Figure 1. The housing 12 may be
composed of a main body 20 and a cap 22 that is fixedly mounted to the main body 20 at a pair of
mating annular flange portions 24A and 24B via bolts 26 or any other suitable fastening
mechanism. The ring gear 14 may also be mounted to the housing 12 at the mating flanges 24A,
24B via the fastener 26. Those having ordinary skill in the art will appreciate from the
description that follows that the housing may be defined by any conventional structure known in
the related art and that the present invention is not limited to a housing defined by a main body
and a cap portion. Similarly, the housing 12 may be driven by any conventional drive mechanism
known in the related art and that the invention is not limited to a housing that is driven via a ring
gear, pinion, and drive shaft.
[0021] The main body 20 defines a hub 28 that supports one 30 of the pair of axle half
shafts 30, 32. Similarly, the cap 22 defines an opposed hub 34 that supports the other one 32 of a
pair of axle half shafts. Together, the main body 20 and cap 22 of the housing 12 cooperate to
define a cavity 36. A differential mechanism, generally indicated at 38, is supported in the cavity
36 defined by the housing 12. The differential mechanism 38 is also illustrated in the exploded
view of Figure 3 and includes a pair of clutch members 40 disposed in spaced axial relationship
with respect to one another. The clutch members 40 are operatively supported for rotation with
the housing 12. A pair of side gears 42, 44 is operatively adapted for rotation with a
corresponding one of the pair of axle half shafts 30, 32. To this end, the side gears 42,44 define
splines 46 on the inner circumference thereof that are matingly received in corresponding splines
defined on the axle half shafts 30, 32. A pair of clutch mechanisms, generally indicated at 48 and
50, is operatively disposed between each corresponding pair of clutch members 40 and side gears
40, 42. To this end, the side gears 42, 44 include splines 52 on the outer circumference thereof.
The clutch mechanism 48, 50 includes a plurality of friction disks 54 that are cooperatively
splined to the outer circumference of the side gears 42,44 and are rotatable therewith. Similarly,
each of the pair of clutch members 40 includes a plurality of splines 56 formed on the inner
circumference thereof. A series of plates 58 are operatively supported on the splined inner
circumference 56 of the clutch members 40 and are interleaved between the plurality of friction
disks 54 supported on the side gears 42,44. The pair of clutch members 40 are axially moveable
within the housing 12 to engage a respective clutch mechanism 48, 50 to couple their associated
axle half shafts 30, 32 together in the event of a predetermined amount of differential movement
between the axle half shafts as will be described in greater detail below. One embodiment of the
locking differential of the type contemplated by the present invention may also employ a plurality
of biasing members 60 that are disposed between the clutch members 40 and receiving in cavities
61 to urge the clutch members 40 away from one another.
[0022] As best shown in Figures 3-5, each of the pair of clutch members 40 presents an
inwardly directed face 62 disposed in spaced axial relationship to one another. Each of the
inwardly directed faces 62 of the pair of clutch members 40 includes a groove, generally
indicated at 64, disposed in facing relationship with respect to the other. A cross pin 66 is
received in the grooves 64 and is operatively connected for rotation with the housing 12. To this
end, the differential 10 may also include a tubular mounting sleeve 68 (Figures 1 - 2) splined to
the inner circumference of the main body 20 of the housing 12. The cross pin 66 may be fixed to
the tubular sleeve at corresponding apertures 70 formed in the sleeve 68 for this purpose.
However, those having ordinary skill in the art will appreciate from the description set forth
herein that the cross pin 66 may be operatively mounted for rotation with the housing 12 in any
suitable manner.
[0023] Referring now specifically to Figures 4-5, each of the grooves 64 is defined by a
groove bottom 72 and a pair of working surfaces 74 extending laterally relative to one another.
The groove bottom 72 is disposed between and operatively interconnects the pair of working
surfaces 74. In addition, in one embodiment, the working surfaces extend at an obtuse angle
relative to each other. However, those having ordinary skill in the art will appreciate from the
lescription that follows that the grooves 64 do not necessarily need to define a groove bottom 72
in order to function in the way intended by the present invention. The working surfaces also
define inner and outer radial edges 75, 77, respectively. In its operative mode, the cross pin 66
engages the working surfaces 74 to drive the clutch members 40 axially outwardly to thereby
engage the clutch mechanisms 48, 50 and couple the axle half shafts 30, 32 together as will be
described in greater detail below.
[0024] More specifically, the locking differential 10 of the type described above allows
for a certain amount of limited slip between the axle half shafts 30, 32 to which it is mounted.
However, in an automotive context, for example, when one of the tires is solidly supported and
the other one is slipping (such as when one tire is on the pavement and the other is supported on a
slippery surface, such as ice) the differential acts to transfer torque from the slipping tire to the
solidly supported tire. This occurs when the cross pin 66 engages the working surfaces 74 of the
groove 64 disposed on opposite sides of the centerline Cl of the groove 64 to move the associated
clutch member 40 into engagement with an associated clutch mechanism 48,50 thereby coupling
the axle half shafts 30, 32 of the spinning tire to the other solidly supported shaft. In this way,
torque is transferred from the slipping tire to the solidly supported tire thereby allowing the
vehicle to be driven even though one of the tires is slipping. The opposed working surfaces 74
that are engaged by the cross pin 66 in this operational embodiment are shaded as designated at
76 in Figure 5 and are disposed on opposite sides of a centerline Cl bisecting the groove 64
(Figure 4).
[0025] When there is differential movement of the axle half shafts supported by the
locking differential of the type known in the prior art, the cross pin and the working surface of the
groove operate to create areas of increased stress at the radial edges of the working surface.
These areas of increased stress are illustrated in the arcuately stippled portions indicated at 78
illustrated in Figure 5. These areas of increased stress 78 limit the amount of torque that can be
generated for a given size of differential. Thus, where increased torque is required for any given
application, the clutch members and cross pins must be increased in size and thickness and may
also require additional heat treat and other processes in order to handle the increased torque
applied to the differential.
[0026] On the other hand, the locking differential 10 of the present invention employs a
groove 64 with specially designed working surfaces 74 that are calculated to eliminate or reduce
the edge stress at the radial edges of the working surfaces. Thus, a locking differential 10
employing the specially designed working surfaces of the present invention is capable of
transmitting more torque for a given size of differential, thereby reducing the cost of
manufacturing the differential.
[0027] More specifically, and referring now to Figures 6A - 6C, one embodiment of the
locking differential of the present invention employs working surfaces 74 that define a screw
involute surface representatively designated at 80 in Figure 6B. In this case, the cross pin 66 will
contact the screw involute working surface 80 along a line 82 extending in the direction of the
cross pin 66 in the event of differential rotation of an axle half shaft relative to the housing 12.
More specifically, and with continuing reference to Figure 6A - 6C, the screw involute surface
80 defines an imaginary point A located near the outer radial edge 77 of the clutch member 40
adjacent to the groove bottom 72 and an imaginary point B located near the inner radial edge 75
of the clutch member 40 remote from the groove bottom 72. The screw involute surface 80 is
slightly convex between the imaginary points A and B such that an imaginary plane P may be
defined orthogonal to the working surface 74 and intersects an imaginary point C at the outer
radial edge 77 of the working surface 74. The imaginary plane P defines a line 82 extending
radially across the working surface. In this operative mode, and as noted above with reference to
Figure 4, the cross pin 66 engages the working surfaces 74 disposed on opposite sides of the
center line illustrated in that figure. The use of screw involute working surfaces 80 produces line
contact between the cross pin 66 and the working surface 74 thereby substantially reducing the
problem of edge stress generated by the interaction of the cross pin 66 and the working surfaces
74. However, it is also true that, while ideal, screw involute working surfaces are difficult to
manufacture. Thus, those having ordinary skill in the art will appreciate that the use of
theoretically perfect screw involute working surfaces may not be completely practical in a
commercial embodiment of the present invention.
[0028] In recognition of this difficulty, Figures 7A - 7B disclose another embodiment of
the present invention where like numbers are used to designate like structure and same are
increased by 100. This embodiment also reduces the edge stress generated between the cross pin
66 and the working surfaces 174 but is more feasible to manufacture in a commercial
embodiment. More specifically, the working surfaces 174 defined in Figures 7A and 7B are
slightly convex in one plane, such that the cross pin 66 contacts the working surface at an
imaginary point F defined thereon in the event of differential rotation of an axle half shaft relative
to the housing. For example, and as illustrated in these figures, the working surface 174 defines
an imaginary point D located near the outer radial edge 77 of the clutch member 40 adjacent to
the groove bottom 72 and an imaginary point E located near the inner radial edge 75 of the clutch
member 40 remote from the groove 72. The working surface is slightly convex between the
imaginary points D and E such that an imaginary plane P defined orthogonal to the working
surface 174 intersects an imaginary point F on the working surface. The cross pin 66 establishes
point contact between the annular surface of the cross pin 66 and the working surface 174 of the
clutch member 40. In this context, and as best representatively illustrated in Figure 7B, the radius
of convexivity of the working surface 174 should be as large as possible. A large radius of
curvature of the convex working surface 174 substantially reduces the edge stress on these
surfaces.
[0029] Another embodiment of the working surface of the locking differential of the
present invention is also illustrated in Figures 8A and 8B where like numerals are used to
designate like structure and where same reference numbers have been increased by 200 relative to
the embodiment illustrated in Figures 6A - 6C. In this embodiment, the working surfaces 274
have been topologically modified so that they are slightly convex in two planes. In this
embodiment, the cross pin 66 will contact the working surface at an imaginary point F defined
thereon during differential rotation of the clutch member relative to the housing.
[0030] In this way, the locking differential of the present invention employs clutch
members having working surfaces having screw involute working surfaces that allow for line
contact between the cross pin and the working surface; a working surface that may be slightly
convex in one plane; or a working surface that may be topologically modified to be slightly
convex in two planes that allows for point contact between the cross pin and the working surface.
This structure significantly reduces the edge stress generated by the interaction of the cross pin
and the working surface and thereby increases the torque density that may be generated through
the differential for a given size of the cross pin and clutch member. Accordingly, the present
invention reduces the necessity of increasing the size of the related component and by association
the cost of the differential for a given torque capacity of the differential.
[0031] 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 having ordinary skill 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.
We Claim:
1. A locking differential (10) for automotive vehicle comprising:
a housing (12) and a differential mechanism (38) supported in said housing (12), said
differential mechanism (38) including a pair of clutch members (40) disposed in spaced axial
relationship with respect to one another and operatively supported for rotation with said housing
(12);
a pair of side gears (42, 44) operatively adapted for rotation with a corresponding pair of
axle half shafts (30, 32), and a pair of clutch mechanisms (48, 50) operatively disposed between
each corresponding pair of clutch members (40) and said side gears (42, 44);
said pair of clutch members (40) being axially moveable within said housing (12) to
engage a respective clutch mechanism (48, 50) to couple the axle half shafts (30, 32) together in
the event of a predetermined amount of differential movement between the axle half shafts;
each of said pair of clutch members (40) presenting an inwardly directed face (62), each
face including a groove (64) disposed in facing relationship with respect to the other, and a cross
pin (66) received in said grooves (64) and operatively connected for rotation with said housing
(12);
each of said grooves (64) including a pair of working surfaces (74) extending laterally
relative to the other, each of said working surfaces (74) defining a screw involute surface (80)
such that said cross pin (66) contacts said working surfaces (74) along a line (82) extending in the
direction of the cross pin (66) in the event of differential rotation of an axle half shaft (30, 32)
relative to said housing (12).
2. A locking differential (10) as set forth in claim 1 wherein said groove (64)
includes a groove bottom (72) disposed between and that interconnects said pair of working
surfaces (74).
3. A locking differential (10) as set forth in claim 2 wherein said screw involute
surface (80) defines an imaginary point A located near the outer radial edge (77) of said clutch
member (40) adjacent said groove bottom (72) and an imaginary point B located near the inner
radial edge (75) of said clutch member (40) remote from said groove (64), said screw involute
surface (80) being slightly convex between said imaginary points A and B such that an imaginary
plane C defined orthogonal to said working surface (74) defines a line (82) extending radially
across said working surface (74).
4. A locking differential (10) as set forth in claim 1 wherein said working surfaces
(74) extend at an obtuse angle relative to each other.
5. A locking differential (10) as set forth in claim 1 wherein said each pair of clutch
mechanisms (48, 50) include a friction clutch member having a plurality of friction disks (54)
supported for rotation with said side gear (42, 44) and a plurality of plates (58) supported for
rotation with a corresponding one of said clutch members (40) and interleaved between said
plurality of friction disks (54), said clutch mechanisms (48, 50) operable to be compressed to
engage said friction disks (54) with said adjacent plates (58) to couple said clutch member (48,
50) to an associated one of said side gears (42, 44).
6. A locking differential (10) as set forth in claim 1 wherein said groove (64) defines
a centerline (CL) and said cross pin (66) engages working surfaces (74) disposed on opposite
sides of said centerline.
7. A locking differential (10) for automotive vehicle comprising:
j a housing (12) and a differential mechanism (32) supported in said housing (12), said
differential mechanism (38) including a pair of clutch members (40) disposed in spaced axial
relationship with respect to one another and operatively supported for rotation with said housing
(12);
a pair of side gears (42, 44) operatively adapted for rotation with a corresponding pair of
axle half shafts (30, 32), and a pair of clutch mechanisms (48, 50) operatively disposed between
each corresponding pair of clutch members (40) and said side gears (30, 32);
said pair of clutch members (40) being axially moveable within said housing (12) to
engage a respective clutch mechanism (48, 50) to couple the axle half shaft (30, 32) together in
the event of a predetermined amount of differential movement between the axle half shafts (30,
32);
each of said pair of clutch members (40) presenting an inwardly directed face (62), each
face including a groove (64) disposed in facing relationship with respect to the other, and a cross
pin (66) received in said grooves (64) and operatively connected for rotation with said housing
(12);
each of said grooves (64) including a pair of working surfaces (74) extending laterally
relative to each other, each of said working surfaces (174) defining a slightly convex surface in
one plane such that said cross pin (66) contacts said working surface (174) at a point defined
thereon in the event of differential rotation of an axle half shaft (30, 32) relative to said housing.
8. A locking differential (10) as set forth in claim 7 wherein said groove (64)
includes a groove bottom (72) that interconnects said pair of working surfaces (174).
9. A locking differential (10) as set forth in claim 8 wherein each of said working
surfaces (174) defines an imaginary point D located near the outer radial edge (77) of said clutch
member (40) adjacent said groove bottom (72) and an imaginary point E located near the inner
radial edge (75) of said clutch member (40) remote from said groove (64), said working surfaces
(174) being slightly convex between said imaginary points D and E such that an imaginary plane
defined orthogonal to said working surface intersects an imaginary point F on said working
surface (174).
10. A locking differential (10) as set forth in claim 8 wherein said working surfaces
(174) extend at an obtuse angle relative to each other.
11. A locking differential (10) as set forth in claim 8 wherein each of said pair of
clutch mechanisms (48,50) includes a friction clutch member having a plurality of friction disks
(54) supported for rotation with said side gear (42,44) and a plurality of plates (58) supported for
rotation with a corresponding one of said clutch members (40) and interleaved between said
plurality of friction disks (54), said clutch mechanisms (48, 50) operable to be compressed to
engage said friction disks (54) with said adjacent plates (58) to couple said clutch member (40) to
an associated one of said side gears (42, 44).
12. A locking differential (10) as set forth in claim 8 wherein said groove (64) defines
a centerline (CL) and said cross pin (66) engages working surfaces (174) disposed on opposite
sides of said centerline.
13. A locking differential (10) for automotive vehicle comprising:
a housing (12) and a differential mechanism (38) supported in said housing (12), said
differential mechanism including a pair of clutch members (40) disposed in spaced axial
relationship with respect to one another and operatively supported for rotation with said housing
(12);
a pair of side gears (42, 44) operatively adapted for rotation with a corresponding pair of
axle half shafts (30, 32), and a pair of clutch mechanisms (48, 50) operatively disposed between
each corresponding pair of clutch members (40) and said side gears (42, 44);
said pair of clutch members (40) being axially moveable within said housing (12) to
engage a respective clutch mechanism (48, 50) to couple the axle half shaft (30, 32) together in
the event of a predetermined amount of differential movement between the axle half shafts (30,
32);
each of said pair of clutch members (40) presenting an inwardly directed face (62), each
face including a groove (64) disposed in facing relationship with respect to the other, and a cross
pin (66) received in said grooves (64) and operatively connected for rotation with said housing
(12);
each of said grooves (64) including a pair of working surfaces (274) extending laterally
relative to each other, each of said working surfaces (274) defining a slightly convex surface in
two planes such that said cross pin (66) contacts said working surface at a point defined thereon
in the event of differential rotation of an axle half shaft (30, 32) relative to said housing (12).
14. A locking differential (10) as set forth in claim 13 wherein said groove (64)
includes a groove bottom (72) that interconnects said pair of working surfaces (274).
15. A locking differential (10) as set forth in claim 14 wherein said working surfaces
(274) extend at an obtuse angle relative to each other.
16. A locking differential as set forth in claim 14 wherein each of said pair of clutch
mechanisms (48, 50) includes a friction clutch member having a plurality of friction disks (54)
supported for rotation with said side gear (42, 44) and a plurality of plates (58) supported for
rotation with a corresponding one of said clutch members (40) and interleaved between said
plurality of friction disks (54), said clutch mechanism (40) operable to be compressed to engage
said friction disks (54) with said adjacent plates (58) to couple said clutch member (40) to an
associated one of said side gears (42, 44).
17. A locking differential (10) as set forth in claim 14 wherein said groove (64)
defines a centerline (CL) and said cross pin (66) engages working surfaces (274) disposed on
opposite sides of said centerline.

ABSTRACT

A locking differential (10) for an automotive vehicle including a housing (12) and a
differential mechanism (38) supported in the housing (12). The differential mechanism (38)
includes a pair of clutch members (40) disposed in spaced axial relationship with respect to each
other wherein each clutch member includes a groove (64) disposed in an opposed inwardly
directing face (62) that is adapted to receive a cross pin (66). Each of the grooves (64) includes a
working surface (74, 174, 274) extending laterally relative to each other. Each of the working
surfaces defines a screw involute surface such that the cross pin (66) contacts the working surface
along a line extending in the direction of the cross pin in the event of differential rotation of an
axle half shaft relative to the housing.