Differential device

   The development and use of differential mechanisms starts form the ancient times and evolves in our days to the most complex driveline systems. Historical evidence for the existence of an early differential device is the Antikythera mechanism (Mihailidis, et al., 2013). The device is dated back to 80 BC and it derives from many analyses that it contained a differential gear, which is interpreted as a mechanism with two degrees of freedom. Since the first automobiles were built, the implementation of a differential device on the drive axle became an urgent necessity. Historically, the invention of the differential is attributed to Onésiphore Pecueur, who patented in 1828 a steam vehicle that included a differential gear on the driving axle (Mihailidis, et al., 2013).

According to their special design features, the automotive differentials can be categorized into six categories: Bevel gear differentials, Crossed helical spur gear differentials, Parallel axes spur gear differentials, Parallel axes internal spur gear differentials, Gearless differentials with CAM curved surfaces and Gearless differentials with friction clutches  (Mihailidis, et al., 2013). Torque is applied to the driving wheels through a differential gearbox that allows the driving wheels of a vehicle to rotate at unequal rates while cornering (Mihailidis, et al., 2013). The most common type is the open differential, which distributes the driving torque equally to both driving wheels (Mihailidis, et al., 2013). It operates satisfactory when the wheels operate below the traction limit (Mihailidis, et al., 2013). When the traction limit of one wheel is exceeded, it slips and the torque on both wheels is reduced (Mihailidis, et al., 2013). A solution to this problem is the use of a limited slip differential (LSD) that limits the torque difference by introducing friction between the halfshafts and the differential’s body in terms of mechanical or hydrodynamic clutches (Mihailidis, et al., 2013). This design solves the problem of acceleration on road surfaces with different friction coefficient on each side (split l), where the traction of one wheel is limited (Mihailidis, et al., 2013). However, these types of differentials affect cornering ability towards under-steering (Mihailidis, et al., 2013).

Bibliography

Mihailidis, Athanassios and Nerantzis, Ioannis. 2013. Recent Developments in Automotive Differential Design. Thessaloniki, Greece : Springer Science+Business Media, 2013. DOI: 10.1007/978-94-007-6558-0_8.