DIFFERENTIAL HAVING IMPROVED
TORQUE CAPACITY AND TORQUE DENSITY
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates, generally, to locking differentials for automotive
vehicles, and more specifically to features of a locking differential that result in increased torque
capacity 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
employed as a part of a drive train and generally include a pair of clutch members supported for
rotation in a housing. A pair of side gears are splined for rotation to corresponding axle half
shafts. A clutch mechanism is interposed between the clutch members and the side gears. A
cross pin is operatively mounted for rotation with the housing and is received in a pair of opposed
grooves formed on the inwardly facing surfaces of the clutch members. In the event of excess
differential rotation between the axle half shafts, such as when one tire is supported on a slippery
surface, the cross pin acts on the associated clutch member to engage the clutch mechanism
thereby coupling the pair of axle half shafts together.
[0003] While locking differentials of this type have generally worked for their intended
purposes, certain disadvantages remain. More specifically, the size of the components of the
differential are often dictated by the amount of torque that can be transmitted thereby. Higher
torque requirements typically require larger, more robust components such as the cross pin,
clutch members, etc. This design limitation ultimately increases the cost of a differential for the
given 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 including 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 members is operatively disposed between each 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 defines a first
predetermined radius of curvature. The cross pin defines a second radius of curvature wherein
the first predetermined radius curvature of the groove is greater than the second predetermined
radius of curvature of the cross pin. This interrelationship between the cross pin and the groove
dictates that contact between the cross pin and the groove defines a line extending along the axis
of the cross pin.
[0006] During normal, non-differentiated movement between the axle half shafts, such as
when a vehicle is driving in a straight path down a road, the line contact is more than sufficient to
transfer torque between the cross pin and the clutch members because all the components rotate
together. However, in the event of differential movement between one or the other of the axle
half shaft and its associated side gear, the cross pin moves relative to the groove and engages an
opposed pair of working surfaces. Making the radius of curvature of the groove larger than that
of the cross pin creates less resistance in the movement of the cross pin to the working surfaces of
the clutch members at the beginning of this differential movement. Accordingly, the specific
interrelationship between the cross pin and the groove reduces the shock that is generated at this
moment of differentiation. This results in smoother operation of the differential and reduced
wear between the cross pin and the groove of the clutch members.
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 cross-sectional end view illustrating the interrelationship between the
cross pin and a groove in the clutch members known in the related art; and
[0013] Figure 6 is a cross-sectional end view illustrating clutch members having a groove
with a radius of curvature larger than the radius of curvature of the associated cross pin of the
present invention.
DETAILED DESCRIPTION
[0014] 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.
[0015] 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 48, 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 received in pockets 61 formed in the
opposed clutch members 40 to urge the clutch members 40 away from one another.
[0016] Each of the pair of clutch members. 40 presents an inwardly directed face 62
disposed in spaced axial relationship to one another. As best shown in Figures 3,4 and 6, 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 splined to the inner
circumference of the main body 20 of the housing 12 (Figure 2). 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.
[0017] As best shown in Figure 6, each of the grooves 64 defines an arc having a first
radius of curvature Rg and a pair of working surfaces 74 extending from either side of the
grooves 64 laterally relative to one another. The groove 64 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 8 relative to each other. On the other hand, the cross pin 66
defines a second radius of curvature Rp. 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, thereby coupling the axle half shafts 30, 32 together as will be
described in greater detail below.
[0018] 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 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 disposed on opposite sides of a
centerline Cl bisecting the groove 64 (Figure 4).
[0019] Where there is no differential movement between the axle half shafts 30,32, the
cross pin 66 is positioned within the groove 64 of the clutch members 40 as illustrated in Figure
6. This is compared to differential mechanisms typically employed in the related art as illustrated
in Figure 5. There, the bottom of the groove G has substantially the same radius of curvature as
the cross pin P. In this disposition, the cross pin and the groove of the clutch member C establish
surface contact between each other. However, when all of the components of the differential are
rotating together, the significance of any surface contact between the groove G and the clutch
member C is irrelevant because there is no differentiation among the components. But surface
contact of the type illustrated in Figure 6 and typically employed in the related art resists
movement of the cross pin P relative to the clutch members C when differential movement is
required. This resistance to movement creates a shock force and increases wear between the
components.
[0020] On the other hand and as noted above, the present invention includes a pair of
clutch members 40 having a groove 64 that defines a first predetermined radius of curvature Rg
and a cross pin 66 that defines a second radius of curvature Rp. The first predetermined radius of
curvature Rg of the groove 64 is greater than the second predetermined radius of curvature RP of
the cross pin 66. Thus, the contact between the cross pin 66 and the groove 64 defines a line
extending along the axis of the cross pin 66.
[0021] During normal, non-differentiated movement between the axle half shafts 30,32,
such as when a vehicle is driving in a straight path down a road, the line contact is more than
sufficient to transfer torque between the cross pin 66 and the clutch members 40 because all the
components rotate together. However, in the event of differential movement between one or the
other of the axle half shafts 30, 32 and its associated side gear 42, 44, the cross pin 66 moves
relative to the groove 64 and engages an opposed pair of working surfaces 74. The groove 64
having a larger radius of curvature Rg than the cross pin 66 provides less resistance to the
movement of the cross pin 66 to the working surfaces 74 of the clutch members 40 at the
beginning of this differential movement. Accordingly, the specific interrelationship between the
cross pin 66 and the groove 64 reduces the shock that is generated at this moment of
differentiation. This results in smoother operation of the differential and reduced wear between
the cross pin and the groove of the clutch members.
[0022] 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 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) defining a first predetermined radius of curvature (RG), said
cross pin (66) defining a second radius of curvature (Rp) wherein said first predetermined radius
of curvature (RG) of said groove (64) is greater than the second predetermined radius of curvature
(Rp) of said cross pin (66) such that contact between said cross pin (66) and said groove (64)
defines a line extending along the axis of said cross pin (66).
2. A locking differential (10) as set forth in claim 1 wherein each of said grooves
(64) include a pair of working surfaces (74) extending laterally relative to each other and wherein
said first predetermined radius of curvature (Rg) of said groove (66) merges into said working
surfaces (74).
3. A locking differential (10) as set forth in claim 1 wherein said working surfaces
(74) extend at an obtuse angle relative to each other.
4. A locking differential (10) as set forth in claim 1 wherein each of said 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 (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).
5. 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 cross pin (66).

ABSTRACT

A locking differential (10) including a housing (12) and a differential mechanism (38)
including a pair of clutch members (40) that present an inwardly directed face (62). Each face
includes a groove (64) disposed in spacing 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).
The clutch members (40) are axially moveable within the housing (12) so that they may engage
respective clutch members coupled to a pair of axle half shafts (30,32). Each of the grooves (64)
in the clutch members defines a first predetermined radius of curvature (RG). The cross pin (66)
defines a second radius of curvature (RP) wherein the first radius of curvature of the groove (64)
is greater than the second radius of curvature of the cross pin (66) such that contact between the
cross pin (66) and the groove (64) defines a line extending along the axis of the cross pin (66).