As environmental awareness continues to increase, the industry has also imposed restrictions on the size, quality and fuel consumption of auto parts. To meet these requirements, wheel bearing units are constantly evolving. The following focuses on what NTN has done in terms of mass reduction and fuel consumption (low torque) in the hub bearing unit. 1. Market demand for wheel hub bearing units According to the needs of automobile manufacturers (installation method, allowable space and bearing size, bearing capacity, low torque performance, mud resistance, stiffness and strength, etc.), there are many design specifications for wheel hub bearing units. kind. The requirements for bearings can be classified as follows: a) easy assembly; b) simplification or elimination of bearing clearance adjustment; c) compact structure, light weight, and high load carrying capacity; d) maintenance-free, especially for no longer lubricated operations and with Externally sealed sealed bearings; e) reduce the number of parts; f) reduce the overall cost, including the bearing unit, secondary parts and labor costs. To meet the above requirements, NTN has been developing, producing and selling 1st, 2nd and 3rd generation products for nearly 40 years. As many countries continue to enforce environmental regulations that require improved fuel efficiency to reduce CO2 emissions, in addition to the above requirements, light weight and low torque of wheel bearing units need to be considered. 2. Development history of wheel hub bearing units 2.1 History of bearing types Until the 1970s, two sets of single-row roller bearings were still the standard configuration, but single-row roller bearings had limitations in reducing mass and size. Therefore, the evolution of unitized products is to simplify assembly to suit quality and packaging requirements. The first designs of such products were sealed double row angular contact ball bearings and sealed double row tapered roller bearings, which were later named 1st generation wheel hub bearings and were widely used in specific environments in the late 1970s. In the 1980s, bearings and their secondary components such as hubs and bearing housings (knuckles) were assembled to reduce the number of components. This also helped reduce mass, resulting in the 2nd generation of hub bearings. In order to further reduce the number of separate parts, the third generation of wheel hub bearings was born. Since the 3rd generation bearing contains more components than the previous 2nd generation, the installation of the wheel hub bearing unit on the automobile assembly line is simplified. The evolution and characteristics of NTN hub bearing units are shown in Table 1, including the era of using 2 sets of single row bearings (before unitization started). Table 1. Evolution and characteristics of NTN wheel hub bearing units. Through multiple generations of bearing upgrades, more secondary components have been incorporated into a single product. This helps reduce the total number of individual components, resulting in a more compact design and a lighter overall axle weight. With the further evolution of hub bearing units, it is no longer necessary to press-fit the inner/outer rings onto the secondary components. On drive bearings, preload management is made easier by rolling the inner ring in place, resulting in significantly less variability. The optimized improvement of the preload results in a reduction in torque. 2.2 Development of the next-generation wheel hub universal joint After the third-generation wheel hub bearing was manufactured, NTN completed the development of the fourth-generation wheel hub bearing unit. The bearing combines a hub bearing unit with a constant velocity joint (CVJ). The technology has not yet been adopted due to major improvements to the automakers' assembly lines. To this end, NTN has developed a new method of assembling the CVJ and wheel bearing units, which can be carried out without changing the existing assembly line of the car manufacturer. The method of crimping the hub joint (PCS H/J) achieves a significant reduction in mass (Figure 1). Figure 1 Structure of PCS H/J Normally, the CVJ and the hub bearing unit are connected by splines and tightened with nuts. Spline teeth are generally designed to have an interference fit with the helix angle to eliminate backlash, which requires a longer spline fit length. The new press fit method completes the tightening of the splines by tightening the bolts, which results in a tighter interference fit than the CVJ stem splines to the hub bearing bore. This allows torque to be applied to the entire spline area, significantly reducing the spline fit length. Using the PCS H/J method can reduce the length of the CVJ stem by 65% ​​and the mass by up to 12%. This is because the inner diameter of the hub ring is a hollow structure, the nut is converted into a bolt, etc., and there is no spline fit clearance. 2.3 Development of Lightweight Bearings NTN reduces the size and mass of the entire axle structure through multiple generations of increasingly integrated wheel hub bearing units. After the third generation is adopted as the mainstream product, the bearing mass still needs to be further reduced, but the unitization becomes more difficult. As a reinforcement, the third-generation wheel hub bearing unit is different from the single-set bearing in terms of the strength of the hub ring, the strength of the outer ring, and the overall stiffness of the bearing. Strength must be maintained while reducing mass, especially the 3rd generation. The mass of the hub ring and outer ring accounts for more than half of the entire unit, so the optimized design of these parts is very important to reduce the mass. NTN employed finite element analysis to determine weight loss while maintaining strength and stiffness to meet the required performance requirements. The optimal shape is obtained by topology optimization