Page 131 - Gear Technology Solutions

In Figure 18 the stress results of such a high abuse torque are presented. The
graphics for the bending stress results reflect still a 10% advantage in bending
stress of the cut side gear versus the forged version. Although the forged gear has
about the same surface stress values in the heel section, the high stress area is
smaller in profile direction and increased in the web area.

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Figure 18: Stress comparison, Coniflex Pro cut versus forged
(input torque = 5000Nm), [7]

Also interesting is the difference in surface stress. In the heel top area, the forged
version has about 22% higher stress values. This trend increases in the toe
direction, and at the toe the surface stress is even 87% higher compared to the cut
side gear. These results reinforce the statements made earlier regarding the
disadvantage of the webs when high torques are applied and the highest possible
power density is required. The linear elastic deflection of the forged teeth is
compromised by the webs. One result is the high surface and bending stress
concentration in the web area which can result in case crushing and cracks.

The second result is the lower load sharing with neighboring teeth which reduces
the effective contact ratio. In Figure 19 a comparison of the load sharing for a
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Coniflex Pro cut differential gearset and its forged predecessor is presented. The
green graph in Figure 19 is the maximum at the center of three consecutive tooth
pairs. The periodic shape of the graph represents in ordinate the amount of load
which this particular pair of teeth transmits in the current roll position (pitch
position). The blue and the red graphs represent the two tooth pairs neighboring
the tooth pair represented by the green graph. A vertical line in the upper diagram
(at the center of the graphic) intersects the green graph at 80% and the red and
blue graphs at 10%. This means that 80% of the input torque is transmitted by one
pair of teeth.

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