The tooth profiles of a high-power density differential gear set should be conjugate in the center and feature a pre-determined tip relief. A new function in Coniflex Pro allows creating a higher order tip relief which preserves a low transmission error and protects better against edge contact as the traditional circular profile crowning. A typical Coniflex Pro tooth contact analysis is shown in Figure 5. The Ease-Off has higher order relief areas along tip and root. The flank center around the Mean Point is nearly conjugate and the tooth contact is full and centered. The motion transmission graph in Figure 5 shows very small amplitudes of 25 μrad (compared to the traditional 300 to 2,000 μrad).

Until now, in bevel and hypoid gears, the same amount of positive profile shift used to reduce pinion undercut had to be applied to the gear, but with a negative sign. This was required to maintain the desired shaft angle. For differential gears, where the gear has also a low number of teeth, the profile shift had to be limited to small amounts to avoid undercutting the gear teeth. The newly developed independent profile shift allows positive profile shift for pinion and gear which results in stronger tooth profiles and increases the contact ratio by up to 50 percent. The principle is shown in Figure 6. Pinion and gear pitch cones are smaller by the equivalent amount of desired profile shift which reduces the shaft angle: Σ1 – Xγ1 – Xγ2 = Σ2 (Figure 6 left side). After the profile shift is applied, the reference pitch cones (working pitch cones) include the correct shaft angle Σ1 (Figure 5 right side) and the gear set has the advantages of a positive profile shift in both members. To demonstrate the dramatic improvement of this technology, the tooth contact of a differential gear set without profile shift is shown in Figure 7. The tooth contact of the same gear set with double positive profile shift X1 = X2 = +0.7 is shown to the right in Figure 7. The contact pattern increased in profile direction by about 30 percent. The result is an increased contact ratio, a reduced root bending stress and a reduced flank surface contact stress.