Planetary gear transmission systems or components – Differential planetary gearing – Bevel gear differential
Reexamination Certificate
2000-01-11
2001-09-04
Wright, Dirk (Department: 3681)
Planetary gear transmission systems or components
Differential planetary gearing
Bevel gear differential
Reexamination Certificate
active
06283889
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a differential assembly, and more particularly to a pre-loaded clutch pack for a limited slip differential (LSD).
2. Description of the Prior Art
Limited slip differentials are well known in the prior art. Typically, clutch assemblies provide required slip limiting properties in the limited slip differentials. A conventional limited slip differential usually comprises a case rotatable about an axis, housing two bevel side gears coaxial with the case. Each of the side gears is intermeshing with bevel planet gears which are supported in the case on an axis perpendicular the axis of the side gears. Between the differential case and the side gears are interposed the respective clutch assemblies, usually in the form of clutch packs comprising alternately stacked clutch plates and discs, and Belleville springs, to provide the limited slip action. The two clutch packs pilot on side gear hub. The plates are keyed to the case, whereas the discs are splined to the side gear hub. Since these plates are alternately stacked, any rotation of the differential gears causes the frictional surfaces of the plates to turn against each other. The LSD clutch packs are provided with a certain initial pre-load. The pre-load is accomplished by using a biasing means (such as Belleville springs) and plates of various thickness, which cause the Belleville springs to compress when the differential is assemble. The pre-load increases the turning resistance between the clutch plates. The LSD clutch pre-load is currently measured in terms of a torque-to-rotation measurement for the differential case assembly. This is a combination of the Belleville spring force and the frictional characteristics of the plates and discs.
The existing designs of the limited slip differentials do not provide proper control of the clutch pack pre-load, because pre-load can not be controlled individually. Only the torque-to-rotation of the fully assembled differential assembly can be measured. This could allow the differential assembly to be built with differently pre-loaded clutch packs (one tighter than the other), and still have the total torqueto-rotate value within specifications. This results in a larger amount of torque available at one wheel than at the other.
Typically, current differential designs require the selecting from four selective thickness plates to obtain the necessary overall clutch pack thickness to compress the Belleville springs. Then the differential gear is assembled. If the desired torque-to-rotate is not achieved, the differential is disassembled and new plates selected. That makes correct pre-loading of the clutch pack of LSD a very laborious process.
Moreover, any wear which occurs in the differential components, such as spherical radii and side gear thrust faces, spherical washers, pinion mates, cross pin, side gears, discs or plates, etc., results in loss of pre-load.
The existing limited slip differential assemblies are usually provided with a spring means (such as Belleville springs) to urge the side gears away from one another to induce frictional engagement of the clutch assemblies. However, under high torque conditions, side gear separating forces overcome the spring force. This extra force can hamper differentiating, and is detrimental in a truck or light utility vehicle application where heavy loads or trailer tow is involved, even though it may be beneficial in a high performance application.
Therefore, the conventional design renders the existing limited slip differential assemblies quite complex in manufacturing, cumbersome and expensive.
SUMMARY OF THE INVENTION
The present invention alleviates the drawbacks of the prior art by providing a self contained clutch pack and side gear assembly for limited slip differential.
The limited slip differential in accordance with the present invention includes two clutch packs that pilot on hub portions of side gears. Each of the clutch packs includes a plurality of friction plates and discs pre-loaded with a Belleville spring. The present invention provides an accurate pre-load by compressing the clutch pack (the plates, the discs and the Belleville spring) on the side gear, then press-fitting a lock ring on the hub of the side gear.
Thus, the present invention allows accurate control of a clutch pack pre-load by controlling the compression of each clutch pack individually. Consequently, the need for selective thickness plates is eliminated, and the additional torque caused by gear separating force can be eliminated. Also, the present invention eliminates the pre-load drop-off due to wear of the differential case, pinion mates, side gear teeth, spherical washers, cross pin, etc. Moreover, because this clutch pack pre-load is set prior to its assembly into a differential case, the assembling process is simplified.
Thus, the present invention improves the performance of the limited slip differential assemblies and reduces production cost thereof.
REFERENCES:
patent: 3308685 (1967-03-01), Wojcikowski
patent: 3326064 (1967-06-01), Ordorica, Jr.
patent: 4040271 (1977-08-01), Rolt et al.
patent: 4245525 (1981-01-01), LeBegue
patent: 4876921 (1989-10-01), Yasui et al.
patent: 5045038 (1991-09-01), Sherlock
patent: 5741199 (1998-04-01), Tanser et al.
Dana Corporation
Liniak Berenato Longacre & White
Wright Dirk
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