Wheel hub bearing - one of the key parts of the car
The wheel hub bearing is one of the key parts of the automobile, its main function is to carry the weight and provide precise guidance for the rotation of the wheel hub, which requires it to bear not only the axial load but also the radial load.
1. Relevant background
The traditional automobile wheel bearing is composed of two sets of tapered roller bearings or ball bearings. The installation, oiling, sealing and clearance adjustment of the bearings are all carried out on the automobile production line. This structure makes it difficult to assemble in an automobile production plant, with high cost and poor reliability, and the bearings need to be cleaned, oiled and adjusted when the automobile is maintained at the maintenance point.
The wheel hub bearing unit is developed on the basis of standard angular contact ball bearing and tapered roller bearing. It integrates two sets of bearings, which has good assembly performance, can omit clearance adjustment, light weight, compact structure and load capacity. The advantages of large, sealed bearings can be pre-loaded with grease, omission of external hub seals and maintenance-free.
2. Development history
In the past, most of the wheel hub bearings of cars used single row tapered roller or ball bearings in pairs. With the development of technology, car wheel hub units have been widely used in cars. The range and usage of wheel hub bearing units are increasing day by day, and it has now developed to the third generation.
The first generation consisted of double row angular contact bearings.
The second generation has a flange on the outer raceway for fixing the bearing, and the bearing can be simply sleeved on the axle and fixed with a nut. Makes car maintenance easier.
The third-generation wheel hub bearing unit is a combination of the bearing unit and the anti-lock brake system ABS. The hub unit is designed with an inner flange and an outer flange, the inner flange is bolted to the drive shaft, and the outer flange mounts the entire bearing together.
3. Technology and development trends
High performance seal
Because the hub bearing is very close to the ground and high temperature brake discs and other parts, it needs to adapt to various complex road conditions and harsh driving environments. Therefore, the bearing sealing ring must have good anti-leakage performance, and must also have good heat resistance, anti-mud and sewage performance.
Rolling technology
The third-generation wheel hub bearings generally use the rolling technology to self-lock the half inner ring. When the rolling technology is used, the axial load causes the plastic deformation of the main shaft end of the hub, so that the main shaft of the hub and the half inner ring are connected as a whole. Compared with the traditional nut tightening, the third-generation wheel hub bearing using the rolling technology helps to reduce the volume and weight, while reducing the cost and improving the reliability of the wheel hub bearing. At the same time, it eliminates the step of adjusting the position of internal components when assembling into the car.
Lightweight and miniaturized
Finite element analysis should be carried out in the structural design of the second and third generation wheel hub bearings. While ensuring sufficient rigidity of the flange, its volume and weight should be reduced as much as possible. The rigidity of the third generation wheel hub bearing is the hub method. The inclination angle of the flange relative to the flange of the outer ring. Through the integration and miniaturization design to reduce the weight of the axle, the second-generation wheel hub bearing is 180g lighter than the first-generation, and the third-generation wheel hub bearing further reduces the weight of 120g.
Low friction torque
An important measure to reduce automobile fuel consumption is to design wheel hub bearings with low friction torque. The main factors affecting the bearing friction torque are the type of bearing and the preload load, and the bearing seal causes a large proportion of the friction torque. Therefore, improving the seal design and reducing the friction torque can significantly improve the performance of the hub bearing. The wheel hub bearing has developed from the first generation to the latest fourth generation, and the friction torque is obviously gradually reduced.
ABS technology
ABS is a kind of automobile safety control device with the advantages of anti-skid and anti-lock. It can automatically adjust the braking force to prevent the wheels from locking and shorten the braking distance by detecting the speed of the wheels during emergency braking. The detection of the rotational speed is carried out by means of magnetic sensors mounted on the parts that rotate with the wheels and fixed on the vehicle body nearby. The hub unit with ABS sensor is divided into two cases: one is placed inside the hub, and the sensor is installed on other parts; the other is placed inside the hub together with the sensor (called the hub unit with sensor).
4. Precautions
Worn or damaged hub bearings or hub units can cause unsuitable and costly failure of your vehicle on the road, or even harm your safety. Please pay attention to the following matters in the use and installation of wheel hub bearings:
1. In order to ensure maximum safety and reliability, it is recommended that you always check the wheel hub bearings regardless of the age of the car - pay attention to the early warning signs of bearing wear: including any friction noise when turning or the suspension combination wheel is turning Unusual deceleration.For rear-wheel drive vehicles, it is recommended that the front wheel hub bearings should be lubricated when the vehicle travels to 38,000 kilometers. When replacing the brake system, check the bearings and replace the oil seal.
2. If you hear the noise from the hub bearing, first of all, it is important to find the place where the noise occurs. There are many moving parts that may produce noise, and it may also be that some rotating parts are in contact with non-rotating parts. If it is confirmed that it is the noise in the bearing, the bearing may be damaged and needs to be replaced.
3. Because the working conditions of the front hub causing the failure of the bearings on both sides are similar, even if only one bearing is broken, it is recommended to replace it in pairs.
4. The hub bearing is more sensitive, and in any case, the correct method and suitable tools need to be used. In the process of storage, transportation and installation, the parts of the bearing cannot be damaged. Some bearings require greater pressure to be pressed in, so special tools are required. Be sure to refer to the car manufacturer's manual.
5. When installing the bearing, it should be in a clean and tidy environment. The entry of fine particles into the bearing will also shorten the service life of the bearing. It is very important to maintain a clean environment when replacing bearings. It is not allowed to hit the bearing with a hammer, and be careful not to drop the bearing on the ground (or similar mishandling). The condition of the shaft and bearing housing should also be checked before installation, as even a small amount of wear can lead to poor fit, which can lead to early failure of the bearing.
6. For the hub bearing unit, do not attempt to disassemble the hub bearing or adjust the sealing ring of the hub unit, otherwise the sealing ring will be damaged and water or dust will enter. Even the raceways of the sealing ring and inner ring are damaged, resulting in permanent failure of the bearing.
7. There is a magnetic thrust ring in the sealing ring equipped with the ABS device bearing, which cannot be collided with, impacted or collided with other magnetic fields. Take them out of the box before installation and keep them away from magnetic fields, such as motors or power tools in use. When installing these bearings, change the operation of the bearings by observing the ABS alarm needle on the instrument panel through a road test.
8. For the hub bearing equipped with ABS magnetic thrust ring, in order to determine which side the thrust ring is installed on, a light and small object can be used to approach the edge of the bearing, and the magnetic force generated by the bearing will attract it. When installing, point the side with the magnetic thrust ring inward, facing the sensitive element of the ABS. NOTE: Improper installation may result in the malfunction of the brake system.
9. Many bearings are sealed, and these bearings do not need to be greased throughout their life. Other unsealed bearings such as double row tapered roller bearings must be lubricated with grease during installation. Due to the different sizes of the inner cavity of the bearing, it is difficult to determine how much grease to add. The most important thing is to ensure that there is grease in the bearing. If there is too much grease, when the bearing rotates, the excess grease will seep out. General experience: During installation, the total amount of grease should account for 50% of the bearing clearance.
10. When installing the lock nut, the torque varies greatly due to the different bearing types and bearing seats. Pay attention to the relevant instructions.
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