Page 50 - Gear Technology Solutions

4 Conjugate Bevel and Hypoid Gears

4.1 Why are Today’s Hypoids Perfect Crossed-Axes Gear Pairs?

In 1924, Ernest Wildhaber, a well-known gear scientist, invented hypoid gear-
ing. Compared to spiral bevel gears, hypoid gears provide an offset that allows
lowering of the body of rear-wheel-drive vehicles by 50mm or more. This is
possible because the propeller shaft between engine/transmission and the
driving axle is not positioned at the center of the drive axle but is lowered by
the offset amount (Figure 1). This allows the vehicle designer to lower the floor
of the vehicle and subsequently the entire body by the same amount. Lowering
the center of gravity of a passenger car by 50mm reduces the inertia responsi-
ble for sideways rolling by more than 10% which provides better vehicle han-
dling and more active safety. The lower body also reduces the CV coefficient
for air resistance, providing higher gas mileage. Less than five years after the
invention of hypoid gearing, all large automotive manufacturers around the
world had converted their passenger cars and trucks to hypoid drive axles with
a lower vehicle body.

Figure 1: Features of pinion offset

Ernest Wildhaber emigrated from Switzerland to the USA in 1919 and was
hired by The Gleason Works as a gear theoretician. Wildhaber received 279
patents, many of which changed the world of gearing. The cylindrical gear tooth
profile that is today called Wildhaber-Novikov gearing was invented by Ernest
Wildhaber in 1926. Mikhail Novikov, a Russian scientist with no access to western

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