NON-SYNCHRONOUS GEAR MESHING EVENTS FOR LIMITED-SLIP
DIFFERENTIALS
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Patent Application No. 61/955,295
filed on March 19, 2013. The disclosure of the above application is incorporated herein
by reference.
FIELD
[0002] The present disclosure relates generally to differential gear assemblies and
more particularly to a differential gear arrangement having side gears that have staggered
meshing events.
BACKGROUND
[0003] A differential gear mechanism can be provided in an axle assembly and used
to transfer torque from a driveshaft to a pair of output shafts. The driveshaft can drive the
differential through the use of a bevel gear that meshes with a ring gear mounted to a
housing of the differential. In automotive applications, a differential allows the tires
mounted at either end of the axle assembly to rotate at different speeds. This is important
when the vehicle is turning because the outer tire travels over an arc of greater distance
than the inner tire. Thus, the outer tire must rotate at a faster speed than the inner tire to
compensate for the greater distance of travel. The differential includes a differential case
and a gear arrangement that allows torque to be transferred from the driveshaft to the
output shafts while concurrently allowing the output shafts to rotate at different speeds as
needed. The gear arrangement can generally include a pair of side gears that are
mounted for rotation with the respective output shafts. A series of cross pins or pinion
gear shafts are fixedly mounted to the differential case for rotation therewith. A
corresponding plurality of pinion gears are mounted for rotation with the pinion gear shafts
and are in meshing relationship with both of the side gears.
[0004] Some differential gear mechanisms include traction modifying differentials.
Typically, a clutch pack can be disposed between one of the side gears and an adjacent
surface of the differential case. The clutch pack or locking mechanism is operable to limit
relative rotation between the gear case and the one side gear. In such differentials,
engaging the clutch pack or locking mechanism (retarding differentiation) is achieved by
one of several different approaches. Some configurations include a piston that actuates
to cause the clutch pack to move between open, locked and partially locked conditions.
In some arrangements, hydraulic fluid is delivered to actuate the piston.
[0005] The background description provided herein is for the purpose of generally
presenting the context of the disclosure. Work of the presently named inventors, to the
extent it is described in this background section, as well as aspects of the description that
may not otherwise qualify as prior art at the time of filing, are neither expressly nor
impliedly admitted as prior art against the present disclosure.
SUMMARY
[0006] A differential gear mechanism constructed in accordance to one example of the
present disclosure can include a differential case, a first side gear, a second side gear a
first pinion and a second pinion. The differential case can define first and second output
shaft openings that are coaxially aligned along an axis of rotation of the differential case.
The first side gear can be rotatably mounted within the differential case and have a first
outer diameter. The second side gear can be rotatably mounted within the differential
case and have a second diameter. The first pinion gear can be meshed for rotation with
the first side gear during a first meshing event. The second pinion gear can be meshed
for rotation with the second side gear during a second meshing event. The first and
second pinion gears form a torque transfer arrangement configured for transferring torque
between the first and second pinion gears and the first and second side gears to rotate
the first and second side gears about the axis of rotation. The first and second outer
diameters are distinct such that the first and second meshing events are offset in time.
[0007] According to additional features, the first and second meshing events can occur
at distinct angular positions. The first and second meshing events can be out of phase.
The first side gear and the first pinion can collectively provide a first contact ratio. The
second side gear and the second pinion can collectively provide a second contact ratio.
The first and second contact ratios can be distinct. The first side gear and the first pinion
can collectively provide a first length of contact. The second side gear and the second
pinion can collectively provide a second length of contact. The first and second lengths
of contact can be distinct.
[0008] According to other features, the first pinion gear can include a first series of
pinion gear teeth each having a first pinion gear tip. A series of first contacts between the
respective first pinion gear tips and corresponding teeth of the first side gear occurs at a
first sequence of contacting times. The second pinion gear can include a second series
of pinion gear teeth each having a second pinion gear tip. A series of second contacts
between the respective second pinion gear tips and corresponding teeth of the second
gear can occur at a second sequence of contacting times. Each time of the first sequence
of contacting times is offset from each time of the second sequence of contacting times.
The first side gear and the first pinion can collectively provide a first line of action. The
second side gear and the second pinion collectively provide a second line of action. The
first and second lines of actions can be distinct.
[0009] A differential gear mechanism constructed in accordance to another example
of the present disclosure can include a differential case, a first side gear, a second side
gear a first pinion and a second pinion. The differential case can define first and second
output shaft openings that are coaxially aligned along an axis of rotation of the differential
case. The first side gear can be rotatably mounted within the differential case and have
a first outer diameter. The second side gear can be rotatably mounted within the
differential case and have a second diameter. The first pinion gear can be meshed for
rotation with the first side gear during a first meshing event. The second pinion gear can
be meshed for rotation with the second side gear during a second meshing event. The
first and second pinion gears form a torque transfer arrangement configured for
transferring torque between the first and second pinion gears and the first and second
side gears to rotate the first and second side gears about the axis of rotation. The first
side gear and the first pinion can collectively provide a first contact ratio. The second
side gear and the second pinion can collectively provide a second contact ratio. The first
and second contact ratios can be distinct.
[0010] According to other features, the first and second meshing events can be out of
phase. The first side gear and the first pinion can collectively provide a first length of
contact. The second side gear and the second pinion can collectively provide a second
length of contact. The first and second lengths of contact can be distinct. The first and
second outer diameters are distinct such that the first and second meshing events are
offset in time. The first side gear and the first pinion can collectively provide a first line of
action. The second side gear and the second pinion can collectively provide a second
line of action. The first and second lines of action can be distinct.
[001 1] A differential gear mechanism constructed in accordance to other examples of
the present disclosure can include a differential case, a first side gear, a second side gear
a first pinion and a second pinion. The differential case can define first and second output
shaft openings that are coaxially aligned along an axis of rotation of the differential case.
The first side gear can be rotatably mounted within the differential case and have a first
outer diameter. The second side gear can be rotatably mounted within the differential
case and have a second diameter. The first pinion gear can be meshed for rotation with
the first side gear during a first meshing event. The second pinion gear can be meshed
for rotation with the second side gear during a second meshing event. The first and
second pinion gears form a torque transfer arrangement configured for transferring torque
between the first and second pinion gears and the first and second side gears to rotate
the first and second side gears about the axis of rotation. The first pinion gear includes
a first series of pinion gear teeth each having a first pinion gear tip. A series of first
contacts between the respective first pinion gear tips and corresponding teeth of the first
side gear occurs at a first sequence of contacting times. The second pinion gear includes
a second series of pinion gear teeth each having a second pinion gear tip. A series of
second contacts between the respective second pinion gear tips and corresponding teeth
of the second side gear occurs at a second sequence of contacting times. Each time of
the first sequence of contacting times can be offset from each time of the second
sequence of contacting times.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present disclosure will become more fully understood from the detailed
description and the accompanying drawings, wherein:
[0013] FIG. 1 is a schematic view of an exemplary vehicle driveline incorporating a
differential gear assembly constructed in accordance to one example of the present
disclosure;
[0014] FIG. 2 is a sectional view taken through first and second side gears and first
and second pinion gears of the differential assembly of FIG. 1;
[0015] FIG. 3 is an exemplary gear meshing event between the first side gear and the
first pinion gear of FIG. 2; and
[0016] FIG. 4 is an exemplary gear meshing event between the second side gear and
the second pinion gear of FIG. 2.
DETAILED DESCRIPTION
[0017] With initial reference to FIG. 1, an exemplary vehicle driveline is shown and
generally identified with reference numeral 10. The exemplary vehicle driveline 10
described herein is for a rear wheel drive vehicle having a limited slip differential, however,
it will be appreciated that the teachings of the present disclosure may be used in other
differential gear mechanisms or gear mechanisms in general.
[0018] The driveline 10 can generally include a limited slip differential assembly 20
having a clutch assembly 22 and a differential gear assembly or mechanism 24. The
limited slip differential assembly 20 operates to drive a pair of axle shafts 30 and 32 that
are connected to drive wheels 40 and 42, respectively. In general, the limited slip
differential assembly 20 functions as a traditional open differential during normal
operating conditions until an event occurs where a bias torque is required. When a loss
in traction is detected or anticipated, the clutch assembly 22 can be selectively actuated
in order to generate the optimum bias ratio for the situation.
[0019] A ring gear 48 can be fixed to a differential case 50 of the differential gear
assembly 20. The ring gear 48 can be meshed for rotation with a drive pinion 52 of an
input pinion shaft 54. In general, the input pinion shaft 54 can be driven by an engine
(not shown) through a transmission (not shown). The input pinion shaft 54 can transmit
rotatable motion from the drive pinion 52 through the ring gear 48 to drive the differential
case 50.
[0020] The ring gear 48 is non-rotatably fixed to the differential case 50. The
differential gear assembly 24 includes a first and second side gear 60 and 62 that are
mounted for rotation with the axle shafts 30 and 32 (and first and second drive wheels 40
and 42), respectively. A first and second pinion gear shaft 64 and 66 are fixedly mounted
to the differential case 50 for rotation therewith. A corresponding first and second pinion
gear 68 and 70 are mounted for rotation with the pinion gear shafts 64, 66 and are in
meshing relationship with both of the side gears 60 and 62. While two pinion gears are
shown in the drawings, it will be appreciated that more than two pinion gears may be
included in the differential gear assembly 24. In an open configuration, described more
fully below, the differential gear assembly 24 acts to allow the axle shafts 30 and 32 to
rotate at different speeds.
[0021] The clutch assembly 22 can generally include a clutch pack 72 and a clutch
actuator (not shown). The clutch pack 72 includes a plurality of annular plates 74
interleaved between a plurality of annular friction disks 78. The plurality of annular plates
74 can be coupled for rotation with one of the differential case 50 and the differential gear
assembly 24. The plurality of annular friction disks 78 can be coupled for rotation with
the other one of the differential case 50 and the differential gear assembly 24.
[0022] The plurality of annular plates 74 and annular friction disks 78 are interleaved
between one another and act to rotate past one another in substantially non-contacting
relationship when the clutch assembly 32 is in its open position. However, it will be
appreciated by those skilled in the art that the term "non-contacting" as used herein is
relative and is not meant to necessarily indicate that the annular plates 74 and annular
friction disks 78 have absolutely no contact when the clutch assembly 22 is in the open
condition. The annular plates 74 and annular friction disks 78 are axially movable into
frictional engagement relative to one another, thereby reducing relative rotation between
the annular plates 74 and annular friction disks 78 when the clutch assembly 22 is in the
closed or partially closed configurations. In this manner, when the clutch assembly 22 is
in its closed position, the side gears 60 and 62, as well as the axle shafts 30 and 32 and
the drive wheels 40 and 42 rotate together.
[0023] The clutch assembly 22 can operate in an open configuration to allow the side
gears 60 and 62 to rotate independently from each other, e.g., at different speeds. The
clutch assembly 22 can also operate in a closed or partially closed configuration where
the side gears 60 and 62 rotate together or partially together (that is, not independently),
e.g., at substantially the same speed. The clutch assembly 22 can, for example, be a
hydraulic clutch assembly that utilizes pressurized hydraulic fluid that can act on a piston
(not shown) of the clutch actuator to selectively actuate the clutch pack 72 between the
open, closed and partially closed configurations. Other configurations are contemplated.
[0024] With additional reference now to FIGS. 2-4, additional features of the
differential gear assembly 24 will be described. The first side gear 60 is rotatably mounted
within the differential case 50 and has a first outer diameter 100. The second side gear
62 is rotatably mounted within the differential case 50 and has a second outer diameter
102. The first outer diameter 100 is distinct from the second outer diameter 102. In the
example shown, the second outer diameter 102 is less than the first outer diameter 100.
[0025] The first pinion gear 68 is meshed for rotation with the first side gear 60 at a
first gear mesh 110 (FIGS. 2 and 3) during a first meshing event. The second pinion gear
70 is meshed for rotation with the second side gear 62 at a second gear mesh 112 (FIGS.
2 and 4) during a second meshing event. The first and second pinion gears 68, 70 form
a torque transfer arrangement configured for transferring torque between the first and
second pinion gears 68, 70 and the first and second side gears 60, 62 to rotate the first
and second side gears 60, 62 about an axis of rotation 120. Because the first and second
outer diameters 100 and 102 are distinct, the first and second gear mesh 110 and 112
are distinct. In this regard, the meshing events are offset in time.
[0026] Turning now to FIG. 3, the first side gear 60 and the first pinion 68 are shown
at the first gear mesh 110 during a first meshing event. The first side gear 60 includes
first side gear teeth 130 each having a teeth tip 132. Corresponding roots 134 are
provided between adjacent first side gear teeth 130. The first side gear 60 defines a roll
angle 138. The first pinion 68 includes first pinion gear teeth 150 each having a teeth tip
152. Corresponding roots 154 are provided between adjacent first pinion gear teeth 150.
A line of action 158 is defined between the first side gear 60 and the first pinion gear 68.
[0027] Turning now to FIG. 4 , the second side gear 62 and the second pinion 70 are
shown at the second gear mesh 112 during a second meshing event. The second side
gear 62 includes second side gear teeth 170 each having a tooth tip 172. Corresponding
roots 174 are provided between adjacent second side gear teeth 170. The second side
gear 62 defines a roll angle 178. The second pinion 70 includes second pinion gear teeth
190 each having a tooth tip 192. Corresponding roots 194 are provided between adjacent
first pinion gear teeth 190. A line of action 198 is defined between the second side gear
62 and the second pinion gear 70.
[0028] When differential assemblies incorporate side gears having the same gear
geometry, meshing events with corresponding pinion gears are concurrent. That is, the
tip of one gear contacts with the root of its mate at a given position. All pinion gears will
share this rotational contact point. The position is specified in degrees of roll, which is an
angular rotation of the gear. The differential assembly 24 of the present disclosure
provides many advantages over differential assemblies having side gears with the same
gear geometries. Because the side gears 60 and 62 have different diameters, the
meshing events of the side gears 60 and 62 with the pinion gears 68 and 70 are
staggered. Again, it will appreciated that while the drawings identify two pinion gears,
more than two may be incorporated into the differential assembly 24. The timing of the
gear meshing events is therefore offset. The contact ratio, the length of contact and the
tip-to-root contact event will be different for both side gears 60 and 62. By providing side
gears 60 and 62 that have different diameters, the meshing events will occur at different
angular positions creating slight out-of-phase meshing event frequency for each side gear
60 and 62. In this regard, the first and second meshing events are not in phase. In one
example the first and second meshing events are offset between 2-4 degrees. The
differential assembly 24 can operate at reduced noise levels and encounter reduced
stress amplitudes during operation.
[0029] Returning now to FIG. 3, the first pinion gear 68 includes the first series of
pinion gear teeth 150 each having the first pinion gear tip 152. A first series of contacts
between the respective first pinion gear tips 152 and corresponding teeth 130 of the first
side gear 60 occurs at a first sequence of times. Similarly, referring to FIG. 4 , the second
pinion gear 70 includes the second series of pinion gear teeth 190 each having the second
pinion gear tip 192. A second series of contacts between the respective second pinion
gear tips 192 and corresponding teeth 190 of the second side gear 62 occurs at a second
sequence of times. Each time of the first sequence of contacting times is offset from each
time of the second sequence of contacting times. The line of action 158 is distinct from
the line of action 198. The roll angle 138 is distinct from the roll angle 178.
[0030] The foregoing description of the embodiments has been provided for purposes
of illustration and description. It is not intended to be exhaustive or to limit the disclosure.
Individual elements or features of a particular embodiment are generally not limited to
that particular embodiment, but, where applicable, are interchangeable and can be used
in a selected embodiment, even if not specifically shown or described. The same may
also be varied in many ways. Such variations are not to be regarded as a departure from
the disclosure, and all such modifications are intended to be included within the scope of
the disclosure.

CLAIMS
What is claimed is:
1. A differential assembly comprising:
a differential case defining first and second output shaft openings that are
coaxially aligned along an axis of rotation of the differential case;
a first side gear rotatably mounted within the differential case and having a
first outer diameter;
a second side gear rotatably mounted within the differential case and having
a second outer diameter;
a first pinion gear meshed for rotation with the first side gear during a first
meshing event; and
a second pinion gear meshed for rotation with the second side gear during
a second meshing event, wherein the first and second pinion gears form a torque transfer
arrangement configured for transferring torque between the first and second pinion gears
and the first and second side gears to rotate the first and second side gears about the
axis of rotation;
wherein the first and second outer diameters are distinct such that the first
and second meshing events are offset in time.
2 . The differential assembly of claim 1 wherein the first and second meshing
events occur at distinct angular positions.
3. The differential assembly of claim 1 wherein the first and second meshing
events are not in phase.
4 . The differential assembly of claim 3 wherein the first meshing event and the
second meshing event are offset between 2-4 degrees.
5. The differential assembly of claim 1 wherein the first side gear and the first
pinion collectively provide a first contact ratio and wherein the second side gear and the
second pinion collectively provide a second contact ratio, wherein the first and second
contact ratios are distinct.
6 . The differential assembly of claim 1 wherein the first side gear and the first
pinion collectively provide a first length of contact and wherein the second side gear and
the second pinion collectively provide a second length of contact, wherein the first and
second lengths of contact are distinct.
7. The differential assembly of claim 1 wherein the first pinion gear includes a
first series of pinion gear teeth each having a first pinion gear tip wherein a series of first
contacts between the respective first pinion gear tips and corresponding teeth of the first
side gear occurs at a first sequence of contacting times.
8. The differential assembly of claim 7 wherein the second pinion gear
includes a second series of pinion gear teeth each having a second pinion gear tip
wherein a series of second contacts between the respective second pinion gear tips and
corresponding teeth of the second side gear occurs at a second sequence of contacting
times, wherein each time of the first sequence of contacting times is offset from each time
of the second sequence of contacting times.
9. The differential assembly of claim 1 wherein the first side gear and the first
pinion collectively provide a first line of action and wherein the second side gear and the
second pinion collectively provide a second line of action, wherein the first and second
lines of action are distinct.
10. A differential assembly comprising:
a differential case defining first and second output shaft openings that are
coaxially aligned along an axis of rotation of the differential case;
a first side gear rotatably mounted within the differential case and having a
first outer diameter;
a second side gear rotatably mounted within the differential case and having
a second outer diameter;
a first pinion gear meshed for rotation with the first side gear during a first
meshing event; and
a second pinion gear meshed for rotation with the second side gear during
a second meshing event, wherein the first and second pinion gears form a torque transfer
arrangement configured for transferring torque between the first and second pinion gears
and the first and second side gears to rotate the first and second side gears about the
axis of rotation;
wherein the first side gear and the first pinion collectively provide a first
contact ratio and wherein the second side gear and the second pinion collectively provide
a second contact ratio, wherein the first and second contact ratios are distinct.
11. The differential assembly of claim 10 wherein the first and second meshing
events are not in phase.
12. The differential assembly of claim 11 wherein the first meshing event and
the second meshing event are offset between 2-4 degrees.
13. The differential assembly of claim 10 wherein the first side gear and the first
pinion collectively provide a first length of contact and wherein the second side gear and
the second pinion collectively provide a second length of contact, wherein the first and
second lengths of contact are distinct.
14. The differential assembly of claim 10 wherein the first and second outer
diameters are distinct such that the first and second meshing events are offset in time.
15. The differential assembly of claim 10 wherein the first side gear and the first
pinion collectively provide a first line of action and wherein the second side gear and the
second pinion collectively provide a second line of action, wherein the first and second
lines of action are distinct.
16. A differential assembly comprising:
a differential case defining first and second output shaft openings that are
coaxially aligned along an axis of rotation of the differential case;
a first side gear rotatably mounted within the differential case and having a
first outer diameter;
a second side gear rotatably mounted within the differential case and having
a second outer diameter;
a first pinion gear meshed for rotation with the first side gear during a first
meshing event; and
a second pinion gear meshed for rotation with the second side gear during
a second meshing event, wherein the first and second pinion gears form a torque transfer
arrangement configured for transferring torque between the first and second pinion gears
and the first and second side gears to rotate the first and second side gears about the
axis of rotation; wherein (i) the first pinion gear includes a first series of pinion gear teeth
each having a first pinion gear tip wherein a series of first contacts between the respective
first pinion gear tips and corresponding teeth of the first side gear occurs at a first
sequence of contacting times, and (ii) the second pinion gear includes a second series of
pinion gear teeth each having a second pinion gear tip wherein a series of second
contacts between the respective second pinion gear tips and corresponding teeth of the
second side gear occurs at a second sequence of contacting times, wherein each time of
the first sequence of contacting times is offset from each time of the second sequence of
contacting times.
17. The differential assembly of claim 16 wherein the first and second meshing
events occur at distinct angular positions.
18. The differential assembly of claim 16 wherein the first side gear and the first
pinion collectively provide a first contact ratio and wherein the second side gear and the
second pinion collectively provide a second contact ratio, wherein the first and second
contact ratios are distinct.
19. The differential assembly of claim 16 wherein the first and second meshing
events are out of phase.
20. The differential assembly of claim 16 wherein the first side gear and the first
pinion collectively provide a first length of action and wherein the second side gear and
the second pinion collectively provide a second length of action, wherein the first and
second lengths of action are distinct.