DESIGN AND INNOVATION The diff debate
Cost, weight, functionality and longevity are all considered by the student engineers when choosing which limited slip differential to use
The Drexler limited slip differential is considered the state-of-the-art by current Formula Student / FSAE teams, primarily due to its weight advantage
utilised differentials from Drexler, Quaife or Torsen, but there is much debate over the best route to choose. Unusually (for Formula Student at least) the most expensive unit is currently the most popular, so we decided to ask the students the reasons behind their choices. The basic aim of a differential
M
The Drexler diff has been a favourite for a long time. This is the previous generation Drexler diff that is still in use with some teams today
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www.racecar-engineering.com • September 2011
is to provide a compromise between transmitting power from a single source to two driven axles and to allow independent rotation between the two driven axles (differentiation). In the majority of designs, this is done with an automatic torque biasing (ATB) characteristic, which instantly reacts to unequal traction conditions between the driven wheels by delivering an increased amount of torque to the wheel with higher traction, ideally before the other wheel
ore than two thirds of the cars entered into class 1 and 1A at Formula Student
BY GEMMA HATTON
exceeds its traction limit, thereby avoiding spinning. There are two main types
of differential design used by Formula Student teams – Torsen and Salisbury. The Torsen (torque sensitive) design originates from the centre differential of the 1986 Audi Quattro, of which a developed form is still currently used in Audi models. The Torsen company is a differential manufacturer that has developed this design into a ‘University Special’, intended specifically for Formula SAE teams. The Salisbury differential
is custom made by German motorsport manufacturer Drexler, which also supplies a differential specifically for Formula Student. A third popular differential supplier is UK-based Quaife Engineering, which offers its standard motorsport unit. All three types are limited slip differentials.
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