Wheel bearing uses novel spur gear tooth connection

Paul Boughton
The Schaeffler Group's new range of FAG wheel bearings is not only 10 per cent lighter than previous versions, but is also more compact, more precise and provides simplified mounting.
The FAG wheel bearings, which were first developed as a concept in 2004, have now moved into series production, with BMW already utilising the bearings on its new X1 model. A reduction in weight of 10 per cent typically amounts to an overall weight reduction of around 1kg for a four-wheel vehicle.
Schaeffler says the new bearing has a unique spur gear tooth design in which the wheel bearing and axle journal are connected axially rather than radially. This has resulted in a bearing module that is lighter and can be mounted clearance-free. Driving characteristics are therefore improved and automotive manufacturers benefit from a simple mounting process and associated cost reductions.
Previously the gear teeth of the axle journal of the input shaft were pushed axially into the wheel bearing. Here the drive torque was transferred via longitudinal gear teeth. This mounting method has proven itself over many years; however, it has a number of disadvantages. The relatively solid, heavy component requires a certain amount of clearance to enable easy mounting. Also, loads that occur during vehicle operation can result in the assembly becoming loose, resulting in loss of comfort and higher noise levels, as well as possible failure of the bearing.
Up to now, the solution to this problem has been to reduce the radial clearance to zero in the design phase. However, this requires the use of complex, costly mounting technology.
The new FAG wheel bearing with spur gear teeth is said to be better equipped to deal with the loads that occur during vehicle operation. The spur gear teeth ensure positive connection between the wheel bearing carrier and the input shaft, which simplifies mounting considerably. The self-centring axial gear teeth are simply placed on the axle journal and fixed in place by using a central screw. Unlike radial gear teeth, this mounting procedure does not require significant force. The bearing remains clearance-free, but securely held in place during vehicle operation.
Having four lighter wheel bearings on the vehicle reduces the unsprung mass, which improves the driving characteristics and contributes to a reduction in CO2 emissions.
Although the idea of using spur gear teeth in wheel bearings is not totally new, manufacturing these in an economical way is. The economical production of the FAG wheel bearing was made possible by the use of an orbitally-formed shoulder as the carrier of the gear teeth. The spur gear teeth are applied onto the orbitally-formed shoulder by high-precision cold forming. Schaeffler has developed a sophisticated method for the manufacture of this complex component that enables volume production to high quality standards.
Schaeffler expects the new innovation to replace conventional radial gear teeth. As Dr Manfred Krauss, chief engineer for chassis applications at Schaeffler Group Automotive, comments: "We are convinced that this groundbreaking invention will sooner or later become established with all the automotive manufacturers."
For more information, visit www.schaeffler.co.uk

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