Automobile hub outer frame oil seal, commonly known as iron shell oil seal. Because of its precise coaxiality and good sealing performance, it has been widely used in the automobile industry as a tight-fitting sealing system that requires high speed, precise fit, high coaxiality, harsh working conditions and long-term high temperature, and is gradually replacing the original lip sealing structure with built-in skeleton in China.

1, skeleton oil seal structure: skeleton oil seal-generally composed of oil seal body, reinforced skeleton and locking spiral spring. According to different parts, the sealing body is divided into bottom, waist, cutting edge, inner and outer sealing lips, etc. In the free state, the inner diameter of the skeleton oil seal is smaller than the shaft diameter, that is, there is a certain "interference" (see GB 9877.2-88). The function of the locking spiral spring is that after the hub skeleton oil seal is installed on the outer shaft diameter of the hub oil seal seat and the inner ring of the oil seal, the pressure of the oil seal cutting edge and the contraction force of the locking spiral spring generate a certain radial tightening force on the outer shaft of the inner ring, and after running for a period of time, the pressure will rapidly decrease or even disappear, so the self-tightening force of the oil seal can be compensated at any time after adding the locking spring.

2. Sealing principle of skeleton oil seal: There is an oil film controlled by the cutting edge of the oil seal between the hub skeleton oil seal and the outer shaft of the inner ring of the oil seal, and this oil film has fluid lubrication characteristics. Under the action of liquid surface tension, the stiffness of the oil film just makes the contact end of the oil film and air form a crescent surface, which prevents the leakage of the working medium, thus realizing the sealing of the rotating shaft. The sealing ability of the hub frame oil seal depends on the thickness of the oil film on the sealing surface of the hub frame. Excessive thickness, oil leakage of hub frame oil seal; If the thickness is too small, dry friction may occur, resulting in the wear of the hub frame oil seal and the outer shaft of the oil seal inner ring; There is no oil film between the sealing lip of the hub frame and the outer shaft of the inner seat ring of the oil seal, which is easy to cause heating and wear.

3. Installation of automobile axle hub skeleton oil seal: When installing the hub skeleton oil seal, it is necessary to coat some oil on the skeleton oil seal ring and ensure that the skeleton oil seal is perpendicular to the outer axis of the oil seal inner ring. If it is not vertical, the sealing lip of the hub frame oil seal will discharge the lubricating oil from the outer shaft of the inner ring of the oil seal, which will also lead to excessive wear of the sealing lip. During operation, a small amount of lubricating oil in the hub frame shell will leak out, thus achieving an ideal state of forming an oil film on the sealing surface of the hub frame. Scientific, professional and effective installation methods can improve the wear resistance and temperature resistance of the skeleton oil seal, and ensure that the automobile axle does not leak grease at 180℃ for a long time.

Hub skeleton seal is a very important link in automobile sealing system, but it is easily overlooked, and it is also a grease leakage problem that has long plagued our company. The leakage of lubrication system has caused huge economic losses, caused customer dissatisfaction, and caused a series of problems such as deterioration of braking environment. The correct installation and use of the hub frame oil seal is a very important work for reducing the cost and protecting the environment of the automobile sealing system.

Some time ago, the market reflected that the oil seal of the front axle hub of our company had hidden quality problems such as oil leakage, edge sticking and fracture, which affected the normal operation of the axle and also had a certain impact on the reputation of our products among customers. In view of this situation, we have conducted a comprehensive and in-depth investigation, on-site anatomical analysis, microscope observation and other scientific means to study the oil leakage of oil seals. Finally, we found that in the process of oil seal assembly, the main problem is that there is a big deviation between the axis of oil seal and the axis of hub due to unscientific assembly method and unreasonable assembly process design, and this eccentricity is difficult to check and find after oil seal assembly.

In this regard, we have improved the assembly process of the existing front axle hub oil seal, improved the assembly process and operation method, and designed a new assembly fixture to improve the assembly quality of the front axle hub oil seal. After more than half a year's investigation, the oil leakage caused by the installation process basically did not happen again, and the assembly quality of the front axle hub oil seal was greatly improved.

In the process of modifying the assembly process of the hub oil seal, we calculated the press-in force of the hub oil seal theoretically by using the found relevant information, formulated a new assembly scheme of the hub oil seal, improved the press-in design and structure, and ensured the assembly quality of the hub oil seal.

Second, the automobile axle front hub frame oil seal assembly process requirements and assembly process diagram.

1. Technical requirements for oil seal of automobile hub frame

Requirements for oil seal installation of automobile hub frame: the surface hardness of oil seal inner race shaft should be HRC ≥ 35 ~ 55, and the hardness depth should not be less than 0.33mm；; Machining of inner oil seal seat ring shaft and frame oil seal ring seat hole/assembly chamfering of kloc-0/5 ~ 30; The surface of the lip contact part of the skeleton oil seal should not be organically processed with thread marks; In order to prevent the oil seal from damaging the sealing lip during installation, special tools should be used for installation.

2. Installation process of hub skeleton oil seal

According to the requirements of EQl53 automobile hub frame oil seal assembly station of our company, as shown in the following figure:

Press the front hub oil seal into the hole φ 150mm on the left side of the front hub oil seal position (Figure 1).

The technical requirements of the hub skeleton oil seal are: after the front hub is pressed into the oil seal, the inclination angle between the oil seal and the hub axis is within 50' tolerance, and the oil seal shall not have assembly defects such as deformation, distortion and tearing.

Among them, the material of the hub oil seal skeleton is: 08 steel; The oil seal rubber is nitrile rubber; The front axle hub is made of QT500.

3. Installation process of hub skeleton oil seal

The positioning of the front hub on the fixture is based on φ 170mm outer cylindrical surface and rim stop, and the horizontal center line of the front hub is determined by placing it on two narrow V-shaped blocks. The left and right positioning is realized by the sides of two narrow V-shaped blocks.

Analysis and improvement of oil seal assembly process for front hub frame of automobile axle

1, structural analysis of the original press-fitting process of the hub frame oil seal

The design of power mechanism and pressure head structure of hub frame oil seal press-fitting is the key link of hub frame oil seal assembly, and whether its structure is reasonable or not determines the assembly accuracy of oil seal.

Firstly, according to the design theory, the pressure head of the press-fit oil seal moves linearly in the horizontal direction. In order to keep the hub frame oil seal vertically pressed into the hub oil seal hole (φ 150mm), its horizontal movement center and the hub oil seal hole center should coincide on the same half line, and the coaxiality requirement is ≤0.20mm, which is difficult to guarantee in actual assembly.

The horizontal movement of the piston rod of the second hub frame oil seal press-fitted power cylinder will not be absolutely horizontal. After working for a period of time, the deviation caused by piston wear will become larger and larger, which will gradually increase the inclination of the oil seal in the hole towel.

The piston movement of the third cylinder is instantaneous, and the dynamic stability is poor, which also brings difficulties to the accurate positioning of the vertical pressure of the hub frame oil seal into the hub oil seal hole.

When the fourth press-fitted hub frame oil seal enters the hub oil seal hole, there is some "interference" because the outer diameter of the hub frame oil seal is larger than the outer diameter of the shaft oil seal hole in the free state.

The oil seal of the fifth hub frame is fixed on the pressure head with the inner diameter of the oil seal rubber lip. Because the lip is a rubber seal with strong plasticity and large enough elastic deformation, the accurate positioning of the oil seal rigidly clamped on the pressure head cannot be guaranteed by elastic deformation positioning. When the oil seal of the hub frame is pressed into the hub oil seal hole, due to the interference fit between the outer diameter of the oil seal and the position of the hub oil seal hole, the oil seal will tilt under the action of friction, thus forming an assembly error, which makes the oil seal axis deviate greatly from the hub axis; Thus affecting the normal performance of the oil seal.

Based on the analysis of the above reasons, we put forward several measures for improvement and transformation.

2. The structure of the oil seal pressure head of the hub skeleton after the process improvement.

In order to solve the above problems, according to the structural principle of the hub skeleton oil seal, the particularity of the skeleton oil seal pressing operation and the actual working conditions, we have improved the installation mechanism of the hub skeleton oil seal, and the improvement scheme is shown in Figure 3.

1) Based on the reasons mentioned in the first, second and third items above, starting from the structural design of the power source, we adopted the hydraulic transmission power with stable movement, and replaced the original oil cylinder as the power actuator with the oil cylinder as the actuator; At the same time, the original horizontal pressing is replaced by vertical pressing, and the improved process is as follows:

① Improvement of special fixture and positioning mode

As shown in the above figure, the front wheel hub is placed on a special fixture. Fixture positioning is based on φ 1.20 mm bearing inner diameter hole and rim stop end face. By using the machining accuracy of the special positioning block and mechanism, the vertical movement center and the center of the hub oil seal hole should be on the same vertical line, that is, the movement center of the mechanism coincides with the positioning center of the fixture, so as to meet the requirement that the coaxiality of the hub oil seal is less than or equal to 0.20 mm, which simplifies the original positioning method.

② Calculation of axial compression force of oil seal and selection of oil cylinder.

Press-fitting quality, when the press-fitting force is too large, the pressure head and oil seal will be damaged; If the pressing force is too small, the oil seal tends to tilt, and people cannot be pressed to the required position. According to the empirical formula for calculating the oil seal indentation force, the surface friction coefficient (f), the elastic modulus of the front hub (E 1), the Poisson coefficient of the front hub (μ), the elastic modulus of the oil seal (E2) and the Poisson coefficient of the oil seal (μ) are reasonably selected according to the mechanical design manual, and the improved oil seal cylinder is calculated in combination with the drawings and technical requirements of the installed oil seal.

The calculation formula of axial indentation force is as follows:

Where the maximum axial pressure when P is pressed in (kg)

—— coefficient of surface friction during pressing.

—— Nominal diameter of mating surface (mm)

—— Length of mating surface (mm)

P—— compressive stress of contact surface during interference fit (kg/m)

but

Among them, the calculated interference of the mating surface (m)

-The actual interference of mating surfaces is determined by the selected mating ()

Average height of oil seal surface roughness ()

—— Average roughness height of hub oil seal hole surface ()

D—— Diameter of excircle at oil seal hole (mm)

—— Diameter of inner hole of oil seal (mm)

—— Elastic modulus of front wheel hub

—— Elastic modulus of oil seal

—— Poisson coefficient of front wheel hub

—— Poisson coefficient of oil seal

According to the specific parameter values of press-fitted parts, the corresponding calculation coefficient is selected, and the required axial compression force is about P= 1800Kg, multiplied by a correction coefficient. Finally, the oil cylinder with a diameter of 50 is selected as the driving power source, and the press-fit guide ram is used as the actuator.

2) In view of the fourth and fifth reasons mentioned above, starting with the design of clamping and positioning structure, the original clamping mode is improved by adopting positioning guidance, flexible floating joints, buffer springs and other measures. The improvement process is as follows:

① Selection and improvement of weir loading head position

A stroke positioning block is added to the outer ring of the press-fitting head, which plays the role of clamping and positioning the skeleton oil seal and controlling the press-fitting stroke of the press-fitting head.

(2) The flexible floating mechanism is adopted as the actuating mechanism.

In this process, the press-fitting pressure head is connected with the piston rod of the oil cylinder through the flexible floating joint, so that the press-fitting pressure head is flexible relative to the piston rod. When the press head blocks the excircle of the skeleton oil seal, the skeleton oil seal will not be stuck or twisted when it enters the inner cavity of the hub, thus eliminating the rigid stamping defect of the original process. At the same time, after adopting this technology level, even if there is a certain deviation between the center of the pressure head and the center of the oil seal, the pressure head can be automatically aligned, which greatly reduces the requirements for positioning during the installation process when the skeleton oil seal enters the inner cavity of the hub.

(3) Factory earth loading head and automatic alignment and positioning mode with buffer spring.

The cylindrical surface of the large bearing position (170mm) of the front hub is used for positioning and guiding when the press-fitting pressure head is pressed in, and the outer circle of the oil seal is used for positioning when the pressure head is installed (as shown in Figure 3). The movement of the press-fitting pressure head and the travel positioning block is completed by the spring between them. When the travel positioning block is located at the outer cylindrical end face of the large bearing position of the front hub, the pressure head overcomes the pressure of the spring to press the oil seal into the hub.

Oil seal is a very important link in automobile sealing system, and it is also a link that is easily overlooked, and it is also a problem that has long plagued China's automobile industry. This paper attempts to introduce the structural principle and improved assembly technology of the new-type hub skeleton oil seal (EQl53) imported from China, and explains that when importing, digesting and absorbing foreign advanced products, the oil seal manufacturing industry and other brother axle industries should fully consider the requirements of oil seal design, press-fitting head design and process flow between press-in parts, so as to find the best design scheme and avoid huge economic losses caused by leakage.