ELECTRONICALLY ACTUATED LOCKING DIFFERENTIAL HAVING
NON-ROTATING STATOR AND ARMATURE
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to United States Provisional
Application No. 61/650,620 filed on May 23, 2012 and United States Provisional
Application No. 61/813,231 filed on April 18 , 2013 the content of which are
incorporated herein by reference in their entirety.
FIELD
[0002] The present teachings relate, in general, to electronically actuated
locking differentials and, in particular to an electronically actuated locking differential
having a non-rotating stator and armature for operation of the differential.
BACKGROUND
[0003] In automotive applications, an electronically actuated locking
differential of the related art may be actuated electronically and is designed for
forward-wheel-drive (FWD), rear-wheel-drive (RWD), all-wheel-drive (AWD), and
four-wheel-drive (4WD) vehicles to allow the differential to be locked or unlocked
when it is so desired. The driver can lock the front and/or rear wheels by manually
activating a switch or button mounted to a dash or console of the vehicle. In this
type of torque-controlling device, the armature is allowed to spin or rotate with the
differential and the armature is not mechanically attached to a lock plate within the
differential.
[0004] While locking differentials of this type have generally worked for
their intended purposes, certain disadvantages remain. More specifically, these
arrangements limit the ability to electronically sense the locked state of the
differential. Further, adding a sensor to a rotating armature might be a cause for
increased costs because the sensor is non-contacting. Also, wear and durability
become a concern with any sensor being attached to a rotating armature.
[0005] Thus, there remains a need in the art for an electronically actuated
locking differential that is capable of locking the right-hand and left-hand axles
independent of the driveline rotation and allow them to remain locked independent of
vehicle direction. In particular, there is a need in the related art for an electronically
actuated locking differential that incorporates these features.
SUMMARY
[0006] The present teachings include an electronically actuated locking
differential for an automotive vehicle including a gear case, a pair of side gears
disposed within the gear case and operatively adapted for rotation with a
corresponding pair of axle half shafts, and a lock plate disposed within the gear case
and operably associated with one of the side gears and being movable axially
relative to the one of the side gears. The electronically actuated locking differential
also includes a return spring disposed within the gear case and cooperating with the
lock plate to bias the lock plate axially away from the one of the side gears and an
electronic actuator cooperating with the lock plate, the electronic actuator having a
non-rotating stator disposed about a portion of the gear case, an electromagnetic coil
associated with the stator, and a non-rotating armature coupled to the lock plate and
being axially movable relative to the stator. When direct current (DC) power is
supplied to the electromagnetic coil, magnetic energy is generated within the stator
creating an attractive force between the armature and the stator to generate a force
transferred to the lock plate causing it to compress the return spring and engage the
side gear locking it to the gear case and thus locking the pair of axle half shafts.
[0007] In one aspect of the present teachings, the new non-rotating
electronic actuator enables ease of lock detection by repositioning a slip ring away
from an electromagnetic coil, allowing both the stator and armature to remain
stationary relative to the differential's rotation. By not allowing the armature to rotate,
parasitic losses can be eliminated when the differential is locked because any
fictional drag between the armature and stator is eliminated. The electronic actuator
of the present teachings also creates less heat within the differential due to less
friction. Since the armature is mechanically coupled to the lock plate, the electronic
actuator of the present teachings can detect or sense when the differential is locked
or unlocked based on the axial position of the armature. Since the armature does
not rotate, the electronic actuator of the present teachings is not concerned with
runout or gap changes when rotating when using contact sensors and not concerned
with a mechanical or electronic slip ring arrangement when using contact sensors.
DRAWINGS
[0008] Other aspects of the present teachings will be readily appreciated
as the same becomes better understood after reading the subsequent description
taken in connection with the accompanying drawings wherein:
[0009] Figure 1 is a partial perspective fragmentary view of an
electronically actuated locking differential of the present teachings; and
[0010] Figure 2 is an exploded view of the electronically actuated locking
differential of the present teachings.
DETAILED DESCRI PTION
[001 1] One representative example of an electronically actuated locking
differential of the type contemplated by the present teachings is generally indicated
at 10 in Figures 1 and 2 . As shown in FIGS. 1 and 2 , the differential 10 includes a
gear case, generally indicated at 12 , and an end cap (not shown), which may be
fastened to the gear case 12 by any suitable fastener, such as by a plurality of bolts
(not shown). The gear case 12 and end cap cooperate with each other to define a
gear chamber, generally indicated at 14. Torque input to the differential 10 is
typically by an input ring gear (not shown), which may be attached to a flange 16. A
gear set is supported within the gear chamber 14 and has at least a pair of input
pinion gears 18 . The pinion gears 18 are mounted rotatably about a pinion shaft 20,
which is secured relative to the gear case 12 by any suitable mechanism. The pinion
gears 18 are input gears of the gear set and in meshing engagement with a
respective pair of left and right side gears, generally indicated at 22, 24. The side
gears 22, 24 define respective sets of internal, straight splines 26 (only one shown
for gear 22) that are adapted to be in splined engagement with mating external
splines on a respective pair of left and right axle shafts (not shown). The gear case
12 defines annular hub portions 28, 30 on which may be mounted a respective pair
of bearing sets (not shown) that are used to provide rotational support for the rotating
differential 10 relative to an outer housing or carrier (not shown).
[0012] A rotation-prevention mechanism, generally indicated at 32, has a
generally annular collar member or lock plate 34 and is disposed entirely within the
gear case 12 and operably associated with side gear 22 (the first output gear). The
lock plate 34 is spaced from the side gear 22 and is slideable along the outer surface
of the side gear 22. An electronic actuator, generally indicated at 36, is disposed
primarily external to the gear case 12. More specifically, the electronic actuator 36 is
disposed at the end of and about the gear case 12 adjacent side gear 22 (the first
output gear). The electronic actuator 36 has a stator 38 primarily external to the
gear case 12. More specifically, the stator 38 is disposed at the end of and about
the gear case 12 adjacent to the flange 16. The stator 38 is stationary and nonrotating
relative to the gear case 12. The electronic actuator 36 also has an
electromagnetic coil, generally indicated at 40, that is disposed in a cavity 42 of the
stator 38. The electromagnetic coil 40 is energized by a pair of electrical leads 44
and receives direct current (DC) from a source (not shown). The electronic actuator
36 also has an armature, generally indicated at 46, spaced from the electromagnetic
coil 40 to form a gap 48 therebetween. The armature 46 is a generally circular plate
and has an outer flange 50 extending axially and an inner flange 52 extending axially
and spaced radially from the outer flange 50. The armature 46 is mechanically
coupled to the lock plate 34 by an annular slip ring 54. The inner flange 52 has a
plurality of cutouts 56 spaced circumferentially thereabout. The cutouts 56 arranged
radially in the armature 46 focus the magnetic energy and maximize the force
potential in these areas. The armature 46 also has a radially extending target flange
58 extending outwardly from the outer flange 50. The armature 46 is non-rotating,
but movable axially relative to the stator 38. The actuator 36 includes a sensor 60
attached to the flange 16 of the gear case 12 and disposed opposite the target
flange 58 of the armature 46 to sense when the differential 10 is locked or unlocked
based on the axial position of the armature 46. The sensor 60 is a contact sensor.
The lock plate 34 is biased toward the non-actuated, "unlocked" mode by a return
spring 62 such as a wave spring. It should be appreciated that other types of
sensors may be used such as non-contact sensors, for example, Hall Effect or
proximity sensors.
[0013] The cutouts 56 arranged radially in the armature 46 focus the
magnetic energy and maximize the force potential in these areas of the actuator 36
whereas some of the magnetic energy is bled off in the areas where there is pilot,
which does not turn into usable force. These cutouts 56 are one to one to optimize
the force potential of the present teachingsFig. 2 is a posterior perspective view of
the knee prosthesis of Fig. 1;
[0014] During normal, straight-ahead operation of a vehicle within which
the differential 10 is employed, no differentiation occurs between the left and right
axle shafts or side gears 22, 24. Therefore, the pinion gears 18 do not rotate relative
to the pinion shaft 20. As a result, the gear case 12, pinion gears 18, and side gears
22, 24 all rotate about an axis of rotation as if the gear case 12, pinion gears 18, and
side gears 22, 24 are a solid unit.
[0015] When direct current (DC) power is supplied to the electromagnetic
coil 40, magnetic energy is generated within the stator 38 which creates an attractive
force between the armature 46 and stator 38 starting at around 40 Ibf and ending at
around 250 Ibf and causing the armature 46 to move toward the stator 38. This force
is transferred through the slip ring 54 and to the lock plate 34 compressing the return
spring 62 until the lock plate 34 exerts a required retarding torque on the side gear
22, locking it to the differential case 12 and thus locking the LH and RH axle shafts
independent of driveline rotation. It should be appreciated in light of the disclosure
that the differential 10 allows the LH and RH axle shafts to remain locked
independent of vehicle direction. It should also be appreciated in light of the
disclosure that the differential 10 is preferred for applications where frequent rock
cycles or direction reversals are common such as during snow plowing. It should
further be appreciated in light of the disclosure that the differential 10 also enables
ease of lock detection by repositioning the slip ring 54 away from the
electromagnetic coil 40, allowing both the stator 38 and the armature 46 to remain
stationary relative to the rotation of the differential 10.
[0016] The differential 10 may be controlled manually, wherein a driver of
the vehicle manually selects "locked" mode (rather than "unlocked" mode) to operate
the differential 10 . For example, when, say the vehicle is at rest, the driver simply
manually activates a switch or button (not shown), such as a simple momentary-type
"on/off" toggle or rocker switch or push button, mounted to a dash or console (not
shown) of the vehicle. In this way, an electric circuit (not shown) is closed, thereby
turning on current in the circuit and a lamp (not shown) located in or near the toggle
switch or push button to indicate to the driver that the differential is actuated.
Current flows in the circuit and ultimately to the electromagnetic coil 48 of the
differential 10. The differential 10 then operates in the "locked" mode (i.e., when the
vehicle is in first gear or reverse). In this way, the first output gear 22 is locked
relative to the gear case 12, preventing any further differentiation between the first
output gear 22 and gear case 12.
[0017] By not allowing the armature 46 to rotate, parasitic losses can be
eliminated when the differential 10 is locked because any frictional drag between the
armature 46 and the stator 38 is eliminated. The electronic actuator 36 of the
present teachings creates less heat within the differential 10 due to less friction.
Since the armature 46 is mechanically coupled to the lock plate 34, locking and
unlocking of the differential 10 can be detected or sensed based on the axial position
of the armature 46.
[0018] The teachings have been described in great detail in the foregoing
specification, and it is believed that various alterations and modifications of the many
aspects of the present teachings 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 teachings, insofar as they
come within the scope of the appended claims.
[0019] The following is a list of reference numerals used in the disclosure:
10 differential;
12 gear case;
14 gear chamber;
16 flange;
18 pinion gears;
20 pinion shaft;
22, 24 side gears;
26 splines;
28, 30 hub portions;
32 rotation-prevention mechanism;
34 lock plate;
36 electronic actuator;
38 stator;
40 electromagnetic coil;
42 cavity;
44 electrical leads;
46 armature;
48 gap;
50 outer flange;
52 inner flange;
54 slip ring;
56 cutouts;
58 target flange;
60 sensor; and
5 62 return spring.

CLAIMS
What is claimed is:
1. An electronically actuated locking differential comprising:
a gear case;
a pair of side gears disposed within said gear case and operatively
adapted for rotation with a corresponding pair of axle half shafts;
a lock plate disposed within said gear case and operably associated
with one of said side gears and being movable axially relative to the one of said side
gears;
a return spring disposed within said gear case and cooperating with said
lock plate to bias said lock plate axially away from the one of said side gears; and
an electronic actuator cooperating with said lock plate, said electronic
actuator comprising a non-rotating stator disposed about a portion of said gear case,
an electromagnetic coil associated with said stator, and a non-rotating armature
coupled to said lock plate and being axially movable relative to said stator;
wherein direct current (DC) power is supplied to said electromagnetic
coil and magnetic energy is generated within said stator creating an attractive force
between said armature and said stator to generate a force transferred to said lock
plate causing it to compress said return spring and engage said side gear locking it
to said gear case and thus locking the pair of axle half shafts.
2 . An electronically actuated locking differential as set forth in claim 1
wherein said actuator has a target flange extending radially.
3 . An electronically actuated locking differential as set forth in claim 1
including a sensor attached to said stator opposite said target flange for sensing
whether a locked or unlocked condition exists based on the axial position of said
target flange relative to said sensor.
4 . An electronically actuated locking differential as set forth in claim 3
wherein said sensor is a contact sensor.
5 . An electronically actuated locking differential as set forth in claim 3
wherein said sensor is a non-contact sensor.
6 . An electronically actuated locking differential as set forth in claim 1
wherein said armature is a generally circular plate and has an outer flange extending
axially and an inner flange extending axially.
7 . An electronically actuated locking differential as set forth in claim 6
wherein said inner flange has a plurality of cutouts spaced circumferentially
thereabout to focus the magnetic energy and maximize the force potential in these
areas.
8 . An electronically actuated locking differential as set forth in claim 1
including a slip ring mechanically coupled to said armature and said lock plate.
9 . An electronically actuated locking differential as set forth in claim 1
wherein said stator has a cavity and said electromagnetic coil is received in said
cavity of said stator.
10. An electronically actuated locking differential comprising:
a gear case;
a pair of side gears disposed within said gear case and operatively
adapted for rotation with a corresponding pair of axle half shafts;
a lock plate disposed within said gear case an operably associated with
one of said side gears and being moveable axially relative to the one of said side
gears;
a return spring disposed within said gear case and cooperating with
said lock plate to bias said lock plate axially away from the one of said side gears;
an electronic actuator cooperating with said lock plate, said electronic
actuator comprising a non-rotating stator disposed about a portion of said gear case,
an electromagnetic coil associated with said stator, and a non-rotating armature
coupled to said lock plate and being axially moveable relative to said stator;
wherein direct current (DC) power is supplied to said electromagnetic
coil and magnetic energy is generated within said stator creating an attractive force
between said armature and said stator to generate a force transferred to said lock
plate causing it to compress said return spring and engage said side gear locking it
to said gear case and thus locking the pair of axle half shafts; and
a target flange extending radially from said armature and a sensor
attached to said stator opposite said target flange for sensing whether a locked or
unlocked condition exists based on the axial position of said target flange relative to
said sensor.
11. An electronically actuated locking differential as set forth in claim 10
wherein said sensor is a contact sensor.
12. An electronically actuated locking differential as set forth in claim 10
wherein said sensor is a non-contact sensor.
13. An electronically actuated locking differential as set forth in claim 10
wherein said armature is a generally circular plate and has an outer flange extending
axially and an inner flange extending axially, said target flange extending from said
outer flange.
14. An electronically actuated locking differential as set forth in claim 13
wherein said inner flange has a plurality of cutouts spaced circumferentially
thereabout to focus the magnetic energy and maximize the force potential in these
areas.
15. An electronically actuated locking differential as set forth in claim 10
including a slip ring mechanically coupled to said armature and said lock plate.
16. An electronically actuated locking differential as set forth in claim 10
wherein said stator has a cavity and said electromagnetic coil is received in said
cavity of said stator.