ABSTRACT: This paper discusses the problem with which automotive bearing are located and fixed in the housings of automotive engines. The solution is to make an eccentric groove on outer ring of bearing and place snap ring into the groove. By elastic force of snap ring, the bearings and housings are tensioned, and by using the stroke principle of cam, the clearance produced due to altering of tem-perature factor etc. can continuously be compensated by itself. This paper also analyzes in detail the operating conditions and arresting principle.
B series automobile bearings are installed on automobile generators. In addition to the accuracy and low noise requirements of general bearings in use, the outer ring of the bearing must also have a narrowing snap function to ensure the reliable installation and positioning of the bearing in the bearing housing. After the structure bearing is used by the user, the performance of the bearing and the installation and fixation of the bearing meet the technical requirements of the warping bearing of the automobile generator.
1. Installation and use requirements of automobile bearing outer ring
B series automobile bearings are installed on the bearing pedestal of an automobile motor with an aluminum alloy shell. The shell is a casting and will not be machined after molding directly submit the assembled bearing for use. Due to the limitation of casting accuracy, it is no longer possible for the bearing to be correctly positioned in the bearing housing, but more importantly The linear expansion coefficient of steel is only half of that of aluminum Obviously, at work, as the temperature rises There will be a gap between the original well matched bearing and the bearing housing, the bearing will crawl in the bearing housing, the relative movement between the outer ring and the aluminum shell bearing housing, the friction between aluminum steel and the wear of aluminum shell will affect the performance and service life of bearing and automobile motor.
2. Design and analysis of snap function of B2 series auto bearing outer ring
There is a certain clearance when the aluminum bearing housing is matched with the bearing outer ring. The bearing cannot be correctly positioned in the bearing housing, and the bearing outer ring rotates in the housing shell. In order to prevent this phenomenon, structural technical treatment must be carried out on the outer ring of the bearing, that is, a snap groove is opened on the outer ring of the bearing, and the snap ring is placed in the groove. The friction of elastic deformation is generated by the snap ring to position and fix the bearing in the shell. This technical structural treatment not only solves the problem that the original bearing cannot be positioned and fixed due to the clearance fit between the bearing and the bearing housing, but also brings convenience and quickness to the installation of the bearing into the shaft shell.
The snap ring plays an important role in the positioning and fixing of the bearing. In operation, the structure of the snap ring can make part of the ring belt of the snap ring higher than the outer ring of the bearing. Therefore, when the bearing is rotating, the shoe friction force generated by the pressing shape of the snap ring makes the outer ring of the bearing rotate relative to the bearing housing to zero, so that the bearing is fixed in the bearing housing. The working state of the snap ring is shown in Fig. 1.
However, the self-locking ability of this structure is limited, and there is no compensation function for the change of the gap between the bearing outer ring and the housing shell. The clearance will change with the increase of temperature, the generation of wear and the inclination of the main shaft installation. In particular, the clearance generated by different linear expansion coefficients of steel and aluminum is always changing.
In order to solve this key technical problem, certain technical measures are taken on the structure of the outer ring groove, that is, the center of the outer ring groove is deviated from the center of the outer ring of the bearing by a certain distance, resulting in a certain eccentricity e (Fig. 2). In this way, the outer ring groove becomes a cam with only the highest point and the lowest point. Using the principle of cam motion, the technical problems of bearing installation and clearance self-compensation can be well solved.
When the bearing needs to be installed, the snap ring is at the lowest point of the cam. As long as the snap ring is gently pressed to the center, the outer edge of the snap ring is lower than the outer ring, and the bearing can be installed into the shaft housing more conveniently and quickly. After entering the shaft housing, the snap ring is reset by elastic force, the shaft housing and bearing are tensioned, and the bearing is correctly positioned in the bearing housing.
When the bearing enters the working state, due to the high temperature rise, there is a gap between the bearing outer ring and the shaft housing. When the gap increases to, the bearing outer ring will slip in the bearing housing, and the bearing outer ring will rotate at an angle. At this time, under the action of the eccentric principle of the outer ring snap groove, the dynamic range variation of the cam is generated, and its principle analysis is shown in Fig. 3.
The mathematical expression of cam motion is
h - Cam dynamic range value, mm
R- Radius of outer ring groove, mm
E - Eccentricity, mm
0 - rotation angle of cam, (°)
At that time, that is, when the change of the cam travel is greater than the increment of the gap between the bearing and the bearing housing (the elastic force of the stop ring remains unchanged), the sliding phenomenon of the bearing outer ring in the bearing housing disappears. Under the elastic force of the stop ring, the bearing is positioned reliably in the housing shell.
The calculation formula of the variation of cam motion is
It can be seen that when the bearing is in the bearing housing, the cam motion principle formed by the eccentricity of the outer ring groove is used to continuously self- compensate the gap increment caused by temperature rise, friction and wear, so that the bearing can always be positioned correctly and reliably under the action of elasticity.
The snap ring is the key part for fixing the bearing outer ring. In order to make the stop ring meet the process requirements of deformation and tension, the structural dimension of the stop ring must be designed. The snap ring shall have both a friction working section in contact with the outer ring groove and a working section in contact with the housing shell. The working section of the former should be an arc related to the outer ring groove, and the working section of the latter is an arc related to eccentricity Therefore, the snap ring is designed as an annular belt with two different curvatures, and its structure is shown in Fig. 4.
R2is the arc radius of the contact between the snap ring and the outer ring groove, and its size directly affects the working performance of the stop ring. In order to ensure the reliable and stable installation of the snap ring in the outer ring groove, there must be a certain preload when the snap ring is installed in the groove. In this way, not only the snap ring is close to the outer ring groove to produce uniform and reliable friction to prevent the outer ring from rotating, but also when the snap ring is subjected to external force, the force can be transmitted downward along the outer ring groove. It is designed according to the radial elastic deformation generated by the preload, which can be calculated according to the following formula:
R2 - Arc semicircle contact between the stop ring and the outer ring groove, mm
T - Material shear stress, N / mm
A - Ratio coefficient between the length and width of stop ring
h - Cross section roughness of stop ring, mm
b- Cross section length of stop ring, mm
Pm - pre tightening force, N
After calculation, the value is less than the arc radius of the outer ring groove. This is conducive to the uniform and reliable transmission of friction.
3. Conclusion
(1) Setting an eccentric snap groove on the outer ring of the bearing and placing the snap ring can effectively solve the installation and positioning problem of the bearing in the extraction shell of different materials
(2) The clearance between the bearing and the bearing housing caused by temperature and other factors is continuously compensated by using the cam motion principle,
(3) The arc radius of the contact between the snap ring and the outer ring groove shall be less than that of the outer ring groove which can prevent the deflection of the snap ring in the groove and make the friction transmission uniform and reliable.
More about UNIM Auto Bearing:
Automobile bearing is a large part of its bearing industry, including hub bearing, air conditioning fan bearing, pulley bearing and so on. Automobile bearings have two main functions: one is to keep the shock absorber rotating with the wheel when the vehicle turns, so as to maintain the flexibility of steering; Second, the outer ring of the pressure bearing is made of rubber, which can maintain the soft connection between the vehicle body and the shock absorber and prevent the vibration from being transmitted to the vehicle body through the shock absorber due to the uneven road surface.
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2022-04-21
