PHASE 6

VARIOUS CLAIMS OF THE CONCEPT:

2.3.2 IN-VEX GEARING:

Index gearing in a this differential includes a gear train arrangement comprised of two or more pairs of satellite gears (called element gears') in mesh with central helical gears (called 'side gears'). The pairs of element gears are interconnected with each other by means of spur tooth engagement. This particular arrangement consists of six element gears and two side gears. The number of element gear pairs used in a specific design is a function of overall torque capacity and space requirements.

The modified crossed axis helical gear mesh, element gear to side gear, is designed and processed to provide instantaneous elliptical contact for reduced tooth stress and increased tooth overlap engagement. In addition, gear tooth helix angle, pressure angle and tooth depth proportions are selected to further minimise stress and wear without sacrifice to function.

2.3.2 TORQUE BIAS RATIO

The maximum torque ratio which is supported by a particular differential design       is termed 'bias ratio'. This term is expressed as the quotient of the torque in the higher torque axle divided by the torque in the lower torque axle in proportion to unity.

The provision of bias ratio significantly affects the operative connection between drive axles and represents a careful choice for controlling torque transfers between drive axles to achieve optimum traction. A '4:1' bias ratio design means that the differential is capable of delivering, to the drive wheel having better traction, four times the amount of torque which can be supported by the lower traction drive wheel. In comparison with an open differential, this means that, under the same conditions, a '4:1' bias ratio differential is capable of delivering approximately two and one-half times more torque to the drive axles collectively than an open differential.

Other means are also known for modifying the operative connection between drive axles to provide for the transfer of additional torque to the drive axles collectively. For example, many limited-slip differentials provide for preloading friction clutches to oppose the transfer of torque between drive axles.

This frictional pre-load represents a particular minimum magnitude of resistance which must be overcome to permit any relative rotation between drive axles which may interfere with the operation of anti-lock braking systems. Also, since frictional forces are continually active to resist differentiation, the friction clutches tend to wear, resulting in a deterioration of intended differential performance.

In contrast to the limited-slip's continuous magnitude of frictional resistance to differentiation, the torque biasing characteristic of the differential provides for a maximum ratio of torque distributions between drive axles. For instance, as the amount of torque being conveyed by the differential decreases, the amount of resistance to differentiation also decreases. That is, even though the bias ratio remains relatively constant, a proportional division of a lower magnitude of torque being conveyed by the differential results in a smaller torque difference between drive axles.

In braking situations where little or no torque is being conveyed by the differential, a four to one apportionment of torque between drive axles amounts to little or no torque difference between drive axles. Thus, the differential will not support any appreciable torque 'wind-up' between drive axles during braking and so does not interfere with the operation of anti-lock braking systems. Another known approach to modifying the operative connection between drive axles is to provide for resisting differentiation as a function of the speed difference between drive axles.

It has long been appreciated that undesirable wheel slip is associated with very high rates of differentiation. Differentials have been designed using fluid shear friction, which respond to increased rates of differentiation by increasing fluid shear frictional resistance to differentiation. The obvious problem with such 'speed sensitive' differentials is that undesirable wheel slip has already occurred well in advance of its detection. Also, the fluid shear friction designs generally rely on the changes in fluid temperature associated with high differential shear rates to increase resistance to differentiation. However, similar temperature changes may be associated with extended periods of desirable differentiation, or may be influenced by changes in ambient temperature, so that resistance to differentiation may vary throughout ordinary conditions of vehicle use.

The bias ratio characteristic of the differential instantly reacts to unequal traction conditions by delivering an increased amount of torque to the drive wheel having better traction before the other drive wheel exceeds the limit of traction available to that wheel. The bias ratio characteristic also remains substantially constant over a wide range of torque conveyed by the differential, and is not sensitive to changes in ambient temperature or conditions of vehicle use.