The present invention relates to a wheel hub unit particularly for a drive/steering wheel of a motor vehicle.
The wheel hub units of vehicle drive wheels are usually formed by the connection, with various degrees of integration, of a constant-velocity universal joint with a rolling bearing with two rings of balls, in which one of the rings of the bearing is adapted to fulfil the functions of a wheel hub while the other is fixed to the suspension strut (or itself fulfils the functions of the strut). The known solutions provide a simple mechanical coupling for the transmission of torque between the joint and the bearing, these latter remaining as two separate components or there being an integration of mechanical parts between the two components, with the use both of constant-velocity universal joints provided with a shank on which there is integrally formed at least one half-element of one of the rings of the bearing, and of bearings of which the inner ring, of suitably large dimensions and suitable conformation also fulfils the function of the outer cap of the joint (fourth generation units).
The integrated solutions reduce the number of component elements but are disadvantageous in the case of breakdowns of only one of the components of the unit (the bearing or the joint) in that they require the replacement of the entire unit with consequent increased costs. Moreover, the dimensions of the joint are constrained by the bulk of the bearing whereby it is not possible to use the same unit for vehicles (for example belonging to the same range) of substantially the same weight but of different powers, at least not without using a larger and heavier solution for the joint. When the inner ring of the bearing and the cap of the joint are formed as a single component, moreover, manufacture of the parts, assembly and testing of the unit are particularly complicated and onerous.
Finally, the known solutions make it impossible, or at least extremely difficult, to fit the wheel hub unit automatically to the vehicle since either the two elements (bearing and joint) must first be pre-assembled and handled as an inseparable unit or they are connected at the moment of assembly on the vehicle with the need to force fit the splined part of the joint in the hub and effect the axial clamping with a controlled torque on the assembly line, which operations are wasteful in terms of time and equipment.