Machine element or mechanism – Gearing – Nonplanetary gearing differential type
Reexamination Certificate
1999-08-31
2001-09-11
Bonck, Rodney H (Department: 3681)
Machine element or mechanism
Gearing
Nonplanetary gearing differential type
C475S164000
Reexamination Certificate
active
06286391
ABSTRACT:
BACKGROUND OF THE INVENTION
It is known for a locking differential to have a differential carrier contained within a drive housing and rotatable around an axis, with two spaced-apart side gears also contained within the drive housing and rotatable relative to one another, and having a differential component which co-operates with the side gears by means of alternately engaging toothings.
The most commonly used type of differential drive is the bevel gear differential. To the extent that such a differential is to have a self-limiting or self-locking effect (both terms herein used in the sense of slip-limiting), it is necessary to provide a locking device, preferably a multi-plate coupling between two of the three basic components, i.e., the differential carrier and the two spaced-apart side gears, the latter being rotatable relative to one another around a common axis.
A new type of differential is known from WO 96/41088 in which side gears are provided with one or two inclined disc faces which face one another, with disc elements resting against the disc faces in a wobbly manner. Two of the disc elements are non-rotatably connected to one another, with one disc rotating with the differential carrier. It will be readily appreciated that the construction of such an assembly is extremely complex.
In European Patent 0 619 863 B1, there is disclosed a differential drive wherein a plurality of sliding blocks is arranged between two side gears with opposed end toothings. The sliding blocks are axially-displaceable relative to one another, and have double wedge faces at their ends. Again, it will be readily appreciated that the construction of such an assembly is extremely complex.
It is the objective of the present invention to provide a new type of differential drive with a self-inhibiting or self-locking ti effect, with a simple design and relatively few parts.
SUMMARY OF THE INVENTION
A The present invention is essentially embodied in and carried out by a locking differential in which the two side gears comprise end toothings facing one another, and the differential component is a differential disc with end toothings on both faces, with the end toothings on each face co-operating with one of the side gears' end toothings. The number of teeth of each pair of inter-engaging end toothings differs by one, and the ratio of the number of teeth of both pairs of toothings is unequal. The differential disc is mounted to wobble between the side gears so that, by means of diametrically-opposed portions of its two sets of end toothings, it engages the associated sets of end toothings of the side gears. Variations on this design are set forth herein.
The first type of locking differential wherein the differential element is non-rotatably coupled to the differential carrier so as to rotate therewith is preferably designed symmetrically, since it is preferably used as an axle differential. The side gears are connectable to plugged-in side shafts. The second type of locking differential wherein the differential element is non-rotatably coupled to one end of a driveshaft introduced into the differential carrier is suitable as a central differential. One of the side gears has to be connected to a hollow shaft which extends co-axially relative to the driveshaft, with the axial carrier only serving to accommodate axially the side gears and the differential gear. However, it is also possible for one of the side gears to be non-rotatably connected to the differential carrier.
The term “side gears” will be used for convenience throughout this application, although the axes of the disclosed locking differentials can also be arranged in the longitudinal direction of a vehicle.
The non-rotatable connection of the differential disc which wobbles with reference to the axis can be effected by designs which correspond to those of constant-velocity universal joints and, in particular, comprise circumferentially disposed journals at the differential element, which engage a longitudinal guide in the differential carrier, or by a hub secured to the driveshaft, with torque transmitting balls being retained in ball grooves on the hub and in the differential disc. Rollers or sliding blocks may be mounted on the aforementioned journals and angularly moveable thereon. Said torque transmitting balls may be secured in a ball cage in a common plane. The ball joint design mentioned above can also be used between a driveshaft hub and the differential disc, just as the ball joint design mentioned secondly can also be used between the differential disc and the differential carrier.
According to the aforementioned first embodiment, the desired ratios of the numbers of teeth exist if the differential disc is provided with end toothings with identical numbers of teeth (z=n), and one side gear comprises a set of end toothings having one tooth fewer (z=n−1) and the other side gear having one tooth more (z=n+1). It is thus possible to achieve an unequal distribution of torque between the two side gears. According to the aforementioned second embodiment, the desired ratios of the numbers of teeth are achieved by having both side gears provided with end toothings with identical numbers of teeth (z=n), and the differential disc is provided with end toothings with one tooth fewer (z=n−1) on one side and one tooth more (z=n+1) on the other side. By using side gears provided with end toothings with identical numbers of teeth, the number of different parts required for the locking differential is reduced.
Because of the rotating and simultaneously wobbling movement of the differential disc and the above-described different numbers of teeth, the side gears rotate in different directions. Also, there is sliding friction at the tooth surfaces which are positioned at identical sliding angles with reference to the respective gear or disc elements, thereby generating the required torque-dependent locking effect. The side gears are axially supported on the differential carrier. By using axial bearings between the side gears and the differential carrier, it is possible to keep the locking effect relatively slight. If simple sliding discs are used in lieu of the axial bearings, the locking effect is increased. If friction discs are used instead of either axial bearings or sliding discs, the locking effect can be increased even further.
When the interior of the differential carrier is sealed and filled with a viscous fluid, making it a sealed hydraulic unit, the inter-engaging end toothings act similarly to two gear pumps, but there are no suction and pressure channels, causing substantial hydraulic friction losses and thereby producing a differential-speed-dependent locking effect which increases the torque-dependent locking effect of the toothings of the differential drive.
REFERENCES:
patent: 2555044 (1951-05-01), Lewis
patent: 3548683 (1970-12-01), Fisher
patent: 3895540 (1975-07-01), Davidson
patent: 5022802 (1991-06-01), Yokoi
patent: 5913949 (1999-06-01), Valasopoulos
patent: 5983754 (1999-11-01), Tyson et al.
patent: 8805139 (1988-07-01), None
Bonck Rodney H
GKN Viscodrvie Gmbh
Ho Ha
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