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Information About Hub Bearings
The hub bearing is the component that connects the tire (rotating part)/brake disc (rotating part) to the steering knuckle (fixed part). Its main function is to reduce the friction caused by rotation and also to transmit force. Wheel bearings can withstand extremely high radial loads (vehicle weight) and axial loads (lateral tire forces or lateral impact forces during steering). Hub bearings are divided into ball bearings and tapered roller bearings. The main difference between the two is whether the rolling media (rollers) are balls or cones. Unless it is a vehicle with a particularly large load (engineering vehicles, heavy-duty SUVs, pickup trucks, etc.), ball bearings are usually used for wheel bearings in general passenger cars.
The first generation wheel hub bearing
The first generation of bearings has the simplest structure, mainly consisting of an inner ring, an outer ring and steel balls, and its cost is also the lowest. It has the advantages of simple structure and low cost, but it also has many disadvantages:
The first is the inconvenience of assembly. Since the bearing is independent of the steering knuckle and wheel hub, it is necessary to press the inner ring of the bearing into the hub and the outer ring of the bearing into the steering knuckle during assembly. Due to the complexity of the assembly process, the technical requirements for equipment and process control are high. The second is performance degradation. Since the installation process cannot be accurately controlled, the performance deviation of the press-fit rear hub bearing is large and the overall performance is lower. Due to the above-mentioned shortcomings of the first-generation bearings, their production has declined year by year, except for some car manufacturers who still use the first-generation bearings due to cost considerations. Finally, with the development of the automobile industry, it should gradually disappear.
Second generation wheel hub bearing
The structure of the second-generation bearing is slightly complicated, and the wheel hub is integrated on the basis of the first-generation bearing. Compared with the first generation wheel hub bearing, the press fit process of the wheel hub during assembly is omitted, but an interference fit with the steering knuckle is still required, so the assembly accuracy will be slightly higher than that of the first generation bearing. At the same time, it also has the disadvantage of reducing performance. Currently, some car manufacturers still insist on using second-generation bearings on rear wheel hubs, but they will eventually become less and less like the first-generation bearings and eventually no longer used.
Third generation wheel hub bearing
As the use of first- and second-generation wheel hub bearings decreases, the third-generation wheel hub bearing can be said to be the mainstream wheel hub bearing. The hub of the third-generation bearing is integrated with the inner ring, the flange connecting the steering knuckle is integrated with the outer ring, and the steering knuckle can be fixed with bolts. Assembly accuracy is greatly improved. Additionally, all dimensions are precisely controlled by the supplier, resulting in excellent performance. Although these two advantages increase costs, third-generation bearings are favored by almost all major automakers.
Fourth generation wheel bearings?
Many in the industry are currently working on integrated solutions. Someone proposed the concept of fourth-generation bearings. This is to integrate the third generation bearings with the constant velocity joints on the drive wheels. The concept of fifth-generation bearings is also proposed, which is the integration of bearings and brake discs. There should be no technical problems with these solutions, and whether they can be promoted depends on market acceptance.
Key points in wheel hub bearing design
•Interference and clearance design
•Bearing strength/stiffness
•Bearing drag torque
•Bearing life
•Tight sealing
Wheel hub bearing strength:
The strength of all bearings is very important because bearings are subject to large radial and axial loads. We usually perform stress and strain analysis through CAE, plus a certain safety margin.
Hub bearing stiffness:
If the rigidity of the bearing is poor, when a lateral force is applied to the bearing, the flange surface connecting the bearing and the brake disc will deform, causing problems such as uneven wear of the friction plate.
Wheel hub bearing drag moment:
Bearing drag torque refers to the resistance when the bearing rotates, and its size will affect the fuel consumption of the car and the cruising range of the new energy vehicle.
Hub bearing life:
Bearings are maintenance-free throughout the life of the vehicle, so their lifespan must be longer than the life of the entire vehicle. The formula for life calculation is very complex and is the proprietary technology of each parts supplier.
Hub sealing:
The sealing ring that prevents external water and dust from entering the bearing will affect the lubrication of the steel ball and ultimately affect the life of the steel ball. The design of the sealing ring is very important. Good sealing design and poor design will cause the bearing life to be extended several times and even lead to a lower failure rate.
How to determine if a wheel hub bearing is damaged
1. Place the vehicle on a lift, rotate the wheels vigorously, check whether the wheels are stuck, and evaluate whether the drag torque on the wheels is normal. If the ball is poorly lubricated or round, stagnation or drag torque will increase.
2. During normal vehicle driving, pay attention to whether there are any abnormal noises in the direction of the wheels. If the steel ball has poor lubricity, abnormal noise will first occur. If there are no unusual noises, there is usually no problem.
In addition, most wheel speed sensor signal sources (magnetic poles or rings) are now integrated into the bearings, so if there is a problem with the wheel speed signal, the instrument panel will report a fault code and the ABS fault light will illuminate, as shown below. If the ABS fault light is always on, the magnetic pole of the bearing may have been damaged.