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The function of the car wheel bearing is mainly to bear the weight of the car and provide an accurate guide for the transmission of the wheel hub. The hub bearing bears both radial and axial loads, and is a very important safety component. At present, most domestic cars still use the traditional two sets of separate tapered roller bearings or angular contact ball bearings. This structure needs to go through many processes such as adjustment of clearance, preload, and grease during the assembly of the car, and there are many artificial controls. Due to factors, the assembly is difficult, resulting in the lengthening of the automobile assembly line, the high cost and poor reliability, and it is difficult to adapt to the fierce market competition.
In recent years, with the rapid development of front-drive cars, wheel hub bearings have undergone great changes, especially in the joint research and development of well-known foreign automobile manufacturers and bearing manufacturers, and new wheel hub bearing units are constantly emerging. , has now entered the fourth generation.
NSK riveting-formed third-generation hub uranium bearing In the design of the traditional third-generation wheel hub bearing unit, the two inner rings are firmly connected with a lock nut, while NSK developed In the new structure, the flanged inner ring is plastically deformed by riveting and forming axial force at the shaft end, and is pressed tightly with the small inner ring. Removing the nut helps reduce the weight and size of the hub unit and improves reliability. Both drive and non-drive wheels apply. With riveting forming technology, reliability will be improved, even if the coupling nut is loose, the bearing itself can provide a preload guarantee.
The riveting process adopts the riveting process (as shown in the figure). When the inclined riveting head (upper die) is riveted on the bearing assembly, the shaft end with the flanged inner ring is subjected to the pressure from the lower part. Plastic deformation until the small inner rings are firmly attached together. During the forming process, the deformation of the hub is divided into three stages: in the first stage, the rivet head descends and comes into contact with the hub axle, and the deformation begins. In the second stage, the deformation further expands, and the hub shaft expands radially, making contact with the inner ring chamfer. Finally, in the third stage, the riveting process is completed. In the first stage, almost all the rivet head pressure is used for the initial forming of the hub axle, and the inner ring load is small and constant. In the second stage, the pressure of the rivet head is transmitted to the inner ring, and the load of the inner ring increases rapidly. In the third stage, due to the pressure of the riveting head, the inner ring load gradually increases until it is saturated. After the riveting pressure is over, even if the riveting head has been lifted, the inner ring load has not been eliminated, and some load is still retained. It can be considered that the residual load forms the clamping force.
Traditional die forging compresses the entire workpiece, producing plastic deformation. Therefore, when machining large-sized workpieces, a lot of pressure is required, and when applied to bearings, the deformation often extends beyond the central area. Under the action of this huge pressure, the ball and the raceway are squeezed, and the bearing is likely to be damaged during processing, while the riveting process only produces local deformation and uses only a small amount of pressure. By controlling the loading pressure, this process is very suitable for bearing assembly. The fatigue strength of the riveted formed edge and the creep resistance of the inner ring were tested by the running durability test under heavy load. The static strength test was carried out to investigate the static strength of the riveted forming edge and the moment load rigidity test of the bearing, because the rigidity of the bearing will affect the steering stability of the vehicle when turning.
According to the results of various tests, NSK's newly developed riveted and formed inner ring self-locking third-generation hub bearing is equal to or even better than the traditional hub bearing with lock nut. On the premise of ensuring high reliability, the weight and size are reduced, which meets the current market demand and reduces vehicle fuel consumption.