Differential cross pin retention

Details Differential cross pin retention Differential cross pin retention

1999-11-23

2001-07-03

Marmor, Charles A (Department: 3681)

Planetary gear transmission systems or components

Differential planetary gearing

Bevel gear differential

C475S150000, C475S231000, C475S234000

Reexamination Certificate

active

06254505

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to differentials, and more particularly, to the retention of the cross pin, on which pinion gears are rotatably disposed, therein.
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. Typically, each of the axles is rotatably fixed to one of a pair of side gears, which are both intermeshed with a pair of first pinion gears. These pinion gears are rotatably disposed about opposite ends of a cylindrical cross pin which extends through diametrically opposite, holes in the circumferential wall of the rotating differential casing. The cross pin is fixed to the casing such that the first pinion gears revolve about the axis of rotation of the axles and side gears with the casing. As will be discussed further hereinbelow, typically, one end of the cross pin is provided with a cross bore which is aligned with holes in the casing; a bolt extends through the casing holes and the cross bore to retain the cross pin to the casing.
The casing is typically provided with a ring gear attached about its outer periphery, and which is intermeshed with a second pinion gear which is drivingly rotated by an engine. The cross pin, which is caused to rotate with the casing, imparts a driving force on the first pinion gears, the teeth of which impart a driving force on the teeth of the side gears intermeshed therewith. Hence, rotation of the axles, which are coupled to each other through the side gears and first pinion gears, is achieved. During differentiation, there is relative movement between the first pinion gears and the side gears, and the axles rotate at different speeds. Thus, a differential distributes the torque provided by the input shaft between the two axles and their respective driven wheels.
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 5,989,147 (Forrest et al.), issued Nov. 23, 1999, all 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.
A transfer block element disposed about the cross pin, between the pinion gears disposed thereon, is provided to transfer axial movement from the first side gear to the second side gear, which is disposed on the opposite side of the cross pin. The transfer block element is allowed to move laterally relative to the cross pin, along the axis of the axles. The transfer block element is abutted by the axially moving first side gear and is forced into abutment with the second side gear, to which is rotatably fixed a second clutch element which also operatively engages the rotating casing, thereby providing additional clutched engagement between the clutch elements and the casing. The following example, which describes a previous limited slip differential having first and second cone clutches and an electromagnetic initiating force, is illustrative:
FIG. 1
depicts differential
10
which comprises rotatable casing
12
constructed of joined first and second casing parts
12
a
and
12
b
, respectively, and providing inner cavity
14
, which is defined by the interior surface of the circumferential wall portion of first casing part
12
a
and end wall portions
16
,
18
of first and second casing parts
12
a
,
12
b
, respectively. Disposed within cavity
14
are side gears
20
,
22
and pinion gears
24
,
26
. The teeth of the side gears and pinion gears are intermeshed, as shown. Pinion gears
24
,
26
are rotatably disposed upon cylindrical cross pin
28
, which extends along axis
30
. Cross pin
28
is made of a suitable material such as, for example, heat treated 8620 steel. The ends of cross pin
28
are received in holes
32
,
34
diametrically located in the circumferential wall of casing part
12
a
. One end of cross pin
28
is provided with cross bore
36
, which is aligned with holes
38
,
40
in casing part
12
a
, as shown. Bolt
42
extends through hole
38
, cross bore
36
and hole
40
to retain the cross pin in its proper position relative to casing
12
. Portion
44
of bolt
42
is provided with threads which are engaged with hole
38
.
Axles
46
,
48
are received through hubs
50
,
52
, respectively formed in casing end wall portions
16
,
18
, along common axis of rotation
54
, which intersects and is perpendicular to axis
30
. Axles
46
,
48
are respectively provided with splined portions
56
,
58
, which are received in splines
60
,
62
of side gears
20
,
22
, thereby rotatably fixing the side gears to the axles. The axles are provided with circumferential grooves
64
,
66
in which are disposed C-rings
68
,
70
, which prevent the axles fr

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