PHASE 7

2.3.3 STRUCTURE FOR ACHIEVING TORQUE BIAS

As previously stated, the torque biasing characteristic of this differential is achieved by interconnecting the drive axles with an Index gearing configuration which selectively controls the generation of frictional torques within the differential.

It is important to note that there are no intrinsic forces or pre-loads within the differentials which affect transfers of torque between drive axles. All of the forces which are controlled to produce frictional resistance between drive axles are derived from transfers of torque between a single drive source and the drive axles.

The characteristic of torque bias is achieved in a very simple way. It is well known that frictional forces are determined by the product of the coefficient of friction of a given surface and the normal force applied to that surface. Frictional torque, of course, is merely the application of that normal force at an effective frictional radius. All of the forces which are active within the differential are derivable from the torque which is being conveyed by the differential and the friction coefficients of surfaces within the differential.

Therefore, all of the frictional forces which are generated within the differential, and all of the resulting resistant torques which oppose the transfer of torque between drive axles, are proportional to the torque being conveyed by the differential. Since the maximum difference in torque between drive axles which can be supported by friction is proportional to the combined torque of the drive axles, the maximum bias ratio remains constant with respect to changes in the combined drive axle torques.

In addition to providing a geared interconnection between drive axles which permits the usual opposite relative rotation between the drive axles, the gearing also distributes forces which may be generated to resist differentiation over a large number of different surfaces within the differential. The surfaces over which the Invex gearing distributes forces are designed with different coefficients of friction and the Invex gearing is designed to distribute different loads between the surfaces. Collectively, the surfaces and the gearing are designed to distribute wear evenly over the surfaces and to control the overall amount of friction within the differential needed to achieve a desired bias ratio.

The twenty-one components which make up the differential are shown in Figure 4. All components of the Index gear system are contained within the housing. Input power usually is transmitted to the housing by way of a ring gear (crown wheel) bolted to the housing itself. Trunnion are adapted to receive bearings by which the housing is rotatively supported and retained within the axle carrier assembly. These Trunnion also receive the respective axle ends which are spline to the side gears within the housing.

Each side gear meshes with element gears arranged at intervals about the periphery of the associated side gears; tangent to, and in engagement with, the pitch surfaces of the side gears. Each of these element gears is formed with a helical middle portion and spur gear end portion. Each side gear meshes with the middle portion of these associated element gears. At the same time, the integral spur gear portion of each element gear meshes with the spur portion of its adjacent element gear. Element gears are shaft-mounted by means of their associated journal pins. The number of element gears and associated hardware may vary.

However, the usual arrangement has three sets of element gear pairs arranged at 120 degree intervals as illustrated. It is this arrangement of In-vex gearing that provides for (a) connecting the drive axles for opposite directions of relative rotation with respect to the differential housing and, (b) controlling the transfer of torque between drive axles.

Completing the hardware complement are thrust washers used between each end of each side gear, between side gears and the housing. Selection of thrust washers is important in determining the operating characteristics for each application. Proprietary Gleason models permit pre selection of components with a high degree of accuracy with respect to actual vehicle characteristics.