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On riveting technology of automobile hub bearing

The main function of the automobile hub bearing is to bear the weight of the car and provide accurate guidance for the transmission of the wheel hub. Hub bearing is a very important safety part because it bears both radial load and axial load. At present, most domestic cars still use the traditional two sets of single tapered roller bearings or angular contact ball bearings. This kind of structure has to go through many procedures such as adjusting clearance, preloading, fatliquoring and so on during automobile assembly, which involves many artificial control factors and is difficult to assemble. As a result, the automobile assembly line is lengthened, the cost is too high and the reliability is poor, so it is difficult to adapt to the fierce market competition.

In recent years, with the rapid development of front drive cars, great changes have taken place in wheel hub bearings. Especially, the joint research and development of foreign well-known automobile manufacturers and bearing manufacturers has led to the emergence of new wheel hub bearing units, which has been the fourth generation.

In the traditional design of the third generation hub bearing unit, the two inner rings are firmly connected with locking nuts. The new structure developed by NSK is that the inner ring with flange is plastic deformed by the axial force of shaft end riveting forming, which is pressed tightly with the small inner ring. Removing the nut helps to reduce the weight and size of the hub unit and improve reliability. Both driving and non driving wheels are applicable. The reliability will be improved by using riveting and pressing technology. Even if the connecting nut is loose, the bearing itself can provide preload guarantee.

The riveting process (as shown in the figure) is adopted in riveting forming. When the inclined riveting head (upper die) is riveted on the bearing assembly, the shaft end of the inner ring with flange is subjected to the pressure from the lower part to produce plastic deformation until the small inner ring is firmly connected. In the forming process, the deformation of the wheel hub is divided into three stages: in the first stage, the rivet head drops, contacts with the hub shaft, and the deformation begins. In the second stage, the deformation is further extended, and the hub shaft extends along the radial direction and contacts with the inner ring chamfer. Finally, the riveting process is completed in the third stage. In the first stage, almost all the riveting head pressure is used for the initial forming of the hub shaft, and the inner ring load is small and constant. In the second stage, the pressure of rivet head is transferred to the inner ring, and the inner ring load increases rapidly. In the third stage, due to the pressure of the rivet head, the inner ring load increases gradually until it is saturated. After the riveting pressure is finished, even if the rivet head has been lifted, the inner ring load has not been eliminated, and some loads are still retained. It can be considered that the residual load forms the clamping force.

The traditional die forging makes the whole workpiece compress and produce plastic deformation. Therefore, it needs a lot of pressure to process large-size workpieces, and when applied to bearings, the deformation often exceeds the central area. Under this kind of huge pressure, the ball and raceway are squeezed, and the bearing is likely to be damaged in the process of processing, while the riveting process only produces local deformation and only a small amount of pressure. By controlling the loading pressure, this machining is very suitable for bearing assembly. The fatigue strength and creep resistance of the inner ring of the riveted flange were tested by the running durability test under heavy load. The static strength test is carried out to investigate the static strength of the riveted forming edge and the torque load stiffness test of the bearing, because the rigidity of the bearing will affect the handling stability of the vehicle when turning.

According to the results of various tests, the third generation of self-locking inner ring bearing developed by NSK is equal to or even better than the traditional hub bearing with locking nut. On the premise of ensuring high reliability, the weight and size are reduced to meet the current market demand and reduce vehicle fuel consumption.

  • Release: Goode bearings
  • Time: April 2011
  • Views: 5402