Planetary gear transmission systems or components – Electric or magnetic drive or control – Differential drive or control
Reexamination Certificate
2000-01-18
2001-10-30
Wright, Dirk (Department: 3681)
Planetary gear transmission systems or components
Electric or magnetic drive or control
Differential drive or control
Reexamination Certificate
active
06309320
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to limited slip differentials, and more particularly, to the retention of the electromagnet in a limited slip differential having a electromagnetically actuated clutch.
2. Description of the Related Art
Differentials are well known in the prior art and allow each of a pair of output shafts or axles operatively coupled to a rotating input shaft to rotate at different speeds, thereby allowing the wheel associated with each output shaft to maintain traction with the road while the vehicle is turning. Such a device essentially distributes the torque provided by the input shaft between the output shafts.
The completely open differential, i.e., a differential without clutches or springs which restrict relative rotation between the axles and the rotating differential casing, is not well suited to slippery conditions in which one driven wheel experiences a much lower coefficient of friction than the other driven wheel: for instance, when one wheel of a vehicle is located on a patch of ice and the other wheel is on dry pavement. Under such conditions, the wheel experiencing the lower coefficient of friction loses traction and a small amount of torque to that wheel will cause a “spin out” of that wheel. Since the maximum amount of torque which can be developed on the wheel with traction is equal to torque on the wheel without traction, i.e. the slipping wheel, the engine is unable to develop any torque and the wheel with traction is unable to rotate. A number of methods have been developed to limit wheel slippage under such conditions.
Prior means for limiting slippage between the axles and the differential casing use a frictional clutch mechanism, either clutch plates or a frustoconical engagement structure, operatively located between the rotating case and the axles. Certain embodiments of such prior means provide a clutch element attached to each of the side gears, and which frictionally engages a mating clutch element attached to the rotating casing or, if the clutch is of the conical variety, a complementary interior surface of the casing itself. Such embodiments may also include a bias mechanism, usually a spring, to apply an initial preload between the clutch and the differential casing. By using a frictional clutch with an initial preload, a minimum amount of torque can always be applied to a wheel having traction, e.g., a wheel located on dry pavement. The initial torque generates gear separating forces between the first pinion gears and the side gears intermeshed therewith. The gear separating forces urge the two side gears outward, away from each other, causing the clutch to lightly engage and develop additional torque at the driven wheels. Examples of such limited slip differentials which comprise cone clutches are disclosed in U.S. Pat Nos. 4,612,825 (Engle), 5,226,861 (Engle), 5,556,344 (Fox), and U.S. patent application Ser. No. 09/030,602, filed Feb. 25, 1998, each of which are assigned to the assignee of the present invention and expressly incorporated herein by reference.
Certain prior art limited slip differentials provide, between the first of the two side gears and its associated clutch element, interacting camming portions having ramp surfaces. In response to an initiating force, this clutch element is moved towards and into contact with the surface against which it frictionally engages, which may be a mating clutch element attached to the casing, or an interior surface of the casing itself, as the case may be, thereby axially separating the clutch element and its adjacent first side gear, the ramp surfaces of their interacting camming portions slidably engaging, the rotational speed of the clutch element beginning to match that of the differential casing due to the frictional engagement. Relative rotational movement between the ramp surfaces induces further axial separation of the clutch element and the first side gear. Because the clutch element is already in abutting contact with the surface against which it frictionally engages, the first side gear is forced axially away from the clutch element by the camming portions.
Certain embodiments of limited slip differentials utilize an electromagnet to actuate the clutch. The differential casing, in which the clutch is disposed, rotates within the housing and is rotatably supported by a pair of bearings. The electromagnet, which actuates the clutch, is mounted in fixed relationship to the axle housing and is rotatably supported on the differential casing by a separate bearing. An example of a prior electrically actuated limited slip differential is disclosed in allowed U.S. patent application Ser. No. 09/030,602.
FIG. 1
depicts an embodiment of prior axle assembly
10
having electrically actuated limited slip differential assembly
12
. Axle assembly
10
may be a conventional axle assembly or comprise part of a transaxle assembly. Therefore, it is to be understood that the term “axle assembly” encompasses both conventional (rear wheel drive) axle assemblies as well as transaxle assemblies. Differential assembly
12
comprises electromagnet
14
, rotatable casing
16
constructed of joined first and second casing parts
16
a
and
16
b
, respectively, and providing inner cavity
18
, which is defined by the interior surface of the circumferential wall portion of first casing part
16
a
and end wall portions
20
,
22
of first and second casing parts
16
a
,
16
b
, respectively. Disposed within cavity
18
are side gears
24
,
26
and pinion gears
28
,
30
. The teeth of the side gears and pinion gears are intermeshed, as shown. Pinion gears
28
,
30
are rotatably disposed upon cylindrical steel cross pin
32
, which extends along axis
34
. The ends of cross pin
32
are received in holes
36
,
38
diametrically located in the circumferential wall of casing part
16
a.
Axles
40
,
42
are received through hubs
44
,
46
, respectively formed in casing end wall portions
20
,
22
, along common axis of rotation
48
, which intersects and is perpendicular to axis
34
. Axles
40
,
42
are respectively provided with splined portions
50
,
52
, which are received in splines
54
,
56
of side gears
24
,
26
, thereby rotatably fixing the side gears to the axles. The axles are provided with circumferential grooves
58
,
60
in which are disposed C-rings
62
,
64
, which prevent the axles from being removed axially from their associated side gears. The terminal ends of the axles may abut against the cylindrical surface of cross pin
32
, thereby restricting the axles' movement toward each other along axis
48
.
Clutch element
66
is attached to side gear
24
and rotates therewith. Clutch element
66
is of the cone clutch variety and has frustoconical surface
68
which is adjacent to, and clutchedly interfaces with, complementary surface
70
provided on the interior of casing part
16
a
. Clutch element
72
is also of the cone clutch variety and has frustoconical surface
74
which is adjacent to, and clutchedly interfaces with, complementary surface
76
also provided on the interior of casing part
16
a.
Disposed between cone clutch element
72
and side gear
26
is annular cam plate
78
, which abuts thrust washer
82
adjacent end wall portion
22
. First ball and ramp arrangement
84
,
86
,
92
is comprised of a first plurality of paired spiral slots
84
,
86
located in cam plate
78
and primary cone clutch element
72
, respectively. Slots
84
,
86
define a helically ramping path followed by ball
92
, which may be steel, disposed in each slot pair and a first ramp angle. With electromagnet
14
de-energized, balls
92
are seated in the deepest portion of slots
84
,
86
by Belleville spring
94
. The actuation sequence is created by the momentary difference in rotational speed between cone clutch element
72
and cam plate
78
as frustoconical surfaces
74
and
76
seat against each other.
Second ball and ramp arrangement
104
,
106
,
108
is comprised of a second plurality of paired spiral s
Forrest James L.
Leeper Robert
Auburn Gear, Inc.
Baker & Daniels
Wright Dirk
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