Differential and method for variable traction control

Details Differential and method for variable traction control Differential and method for variable traction control

1999-10-26

2002-03-12

Wright, Dirk (Department: 3681)

Planetary gear transmission systems or components

Differential planetary gearing

Bevel gear differential

C475S237000

Reexamination Certificate

active

06354978

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to differentials and more particularly, to differentials capable of controlled power transmission to multiple output shafts.
BACKGROUND OF THE INVENTION
The control of power output from a power source such as a drive shaft to more than one output (i.e., two wheels driven by respective output shafts) is a function accomplished in numerous ways in the prior art. A differential is typically used to transmit power to output shafts on opposing sides of the differential. For purposes of illustration only, the following discussion is with reference to a conventional differential having one input and two outputs in the form of co-axial output shafts driving respective wheels. However, it will be appreciated by one having ordinary skill in the art that the following discussion applies equally to other differential types having more outputs and having outputs which are different from shafts turning wheels.
In a conventional differential having two output shafts, rotational power is transmitted from a differential housing or ring gear to orbit one or more planet gears about a differential axis. The planet gears are engaged with side gears, each of which is connected to and turns an output shaft. When the planet gears orbit, they rotate the side gears to turn their respective output shafts. The planet gears normally do not rotate when the output shafts are equally loaded, and therefore the side gears rotate at the same speed. However, when the output shafts are loaded differently (e.g., when one wheel begins to spin faster than the other, when the traction of one wheel is significantly greater than the traction of the other, etc.), the planet gears rotate as they orbit, thereby turning the side gears at different speeds with respect to one another and driving the output shafts at different speeds. This speed differential can present problems in system performance, particularly when one output shaft spins with little or no load, thereby drawing power through the path of least resistance to that shaft.
Conventional differentials often employ limited slip devices to provide a minimum threshold torque resistance to each output shaft. When one wheel begins to slip and drain power supplied to the differential, a limited slip device on that shaft provides a minimum resistance. Power therefore continues to be transmitted to the opposite shaft rather than being drained to the shaft corresponding to the slipping wheel.
Most early differentials employ one or more elements which apply a constant force against the planet gears and/or the side gears to establish the above-mentioned minimum threshold torque resistance. These elements include pins which are threaded through the differential housing and which ride upon the rear surfaces of the gears, spring-loaded wedge blocks fitted between the planet gears and pressing with frictional engagement against the sides of the gears, and braking disks, disk packs, and/or Belleville springs pressed under spring force against one or more faces of the gears, etc. Although each of these elements function adequately to exert frictional force against the planet gears or side gears to inhibit spinning, they are either incapable of adjustment or must be adjusted manually after the equipment has been stopped. For example, the Belleville springs commonly used are often inaccessible without disassembling at least part of the differential, and have a spring force which is generally not adjustable. Also, the braking disks and disk packs are usually pressed by a conventional element (such as an adjustable threaded fastener or by an internal spring) which must be hand turned or adjusted as the disks or packs wear upon the gear surfaces. Such a differential design increases maintenance and operational costs of the differential, requires interruption of vehicle operation for adjustment, and results in a differential having braking effectiveness which varies as elements wear.
To address some of the drawbacks of older differentials, newer differential designs employ assemblies and devices for braking planet or side gears without manual adjustment and without the need to stop differential operation for adjustment. For example, U.S. Pat. No. 4,776,234 issued to Dennis W. Shea employs an energizing coil and magnet capable of adjusting pressure of a clutch pack against a side gear when the coil is energized. The electromagnetic control of this device enables a user to adjust the braking force of a desired gear through a range of frictional braking forces. As another example, U.S. Pat. No. 4,934,213 issued to Yoshikazu Niizawa uses oil pressure cylinders supplied by a controllable pressurized oil source to control pressure upon a frictional clutch having a number of frictional clutch plates between a differential housing and a side gear of the differential. By changing the oil pressure to the oil pressure cylinders, pressure upon the clutch plates can be changed to thereby change the frictional braking upon the side gear. Both the Shea and Niizawa devices represent improvements over the prior art in their ability to be adjusted without manually adjusting braking elements and without stopping the differential. But like other prior art devices capable of “on-the-fly” gear braking adjustment, these devices are relatively complex, particularly in comparison to their earlier counterparts. Such devices are expensive to manufacture, assemble, service, and repair. These problems are due at least in part to the design necessary for the anticipated applications of the differentials. The differentials must be able to operate on equipment such as cars, trucks, and off-road vehicles, and must therefore operate under demanding conditions of stress, power, and speed. However, these differentials are not well suited to less demanding applications in which the vehicles are not fast moving and are not exposed to heavy load conditions.
In light of the problems and limitations of the prior art described above, a need exists for a differential which is simple, easy and inexpensive to manufacture, assemble, service, and repair, well-adapted to low speed and normal loading conditions, capable of traction control adjustment (i.e., braking of planetary and/or side gears) without stopping the differential, and which is preferably infinitely adjustable over a differential braking range. Each preferred embodiment of the present invention achieves one or more of these results.
SUMMARY OF THE INVENTION
In each of the preferred embodiments of the present invention, an actuation element is movable during differential operation either directly or indirectly by a user to exert a braking force upon a side gear or a planet gear of the differential. The actuation element is most often a element accessible by a user, but in some embodiments is the side or planet gear itself. The braking force upon the side gear or the planet gear can be exerted directly upon a gear surface by a braking element or surface or upon an element (such as a pivot or an axle) to which the side gear or the planet gear is mounted. In either case, the amount of braking force applied is preferably controllable by controlled actuation of the actuation element through a range of positions. Therefore, a user can control the amount of braking force applied as desired or in response to different vehicle operating conditions (e.g. running upon and along a slope, operating in slippery or muddy conditions, and the like).
In a number of preferred embodiments, the actuation element is a lever, thrust rod, magnetic coil, or similar element which is movable or energized either to drive a brake element in harder or lighter frictional engagement with a planet or side gear or to drive a planet or side gear in harder or lighter frictional engagement with a brake element. In the first case, the actuation element can be a lever of a band brake which is tightenable around plant gear pivots, brake blocks in wedging relationship between planet gears, cone clutch elements fitted to planet or side gears in a cone cl

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