Audi 100/A6

1990-1997 of release

Repair and car operation

Sliding bearings almost only serve in modern automobile engines as support for cranked and camshafts. Kacheniye bearings (ball, roller, needle) apply to the similar purposes only in small motorcycle motors.

Necessary operability of bearings of sliding is reached by use of so-called effect of an oil wedge. At rotation of a smooth shaft in a gap between shaft and an opening oil moves. As the loading operating on a shaft, causes its excentric shift, oil is as though tightened in a being narrowed part of a gap and forms the oil wedge interfering contact of a shaft with walls of an opening. The more pressure and viscosity of oil in a gap, the big loading (before contact of surfaces) maintains the sliding bearing.

The actual pressure of oil in a zone of a wedge reaches 50–80 MPas (500–800 ^kg/cm2), and in some designs and it is more. It in hundreds times is higher, than in submitting system. However it is not necessary to think that pressure of giving influences operation of the bearing a little. The it is more, the there is an oil pumping via the bearing and the better it cooling more intensively.

Under certain conditions the operating mode with the minimum friction (it also call liquid) can be broken. It happens at ponizheniy to viscosity of oil (for example, because of its overheat owing to insufficient giving) and decrease in frequency of rotation at loading increase.

Quite often, especially after engine repair, not optimum geometry of knot affects also. At an insignificant deviation of a form of surfaces from cylindrical, at a distortion of axes and other defects of details probably local increase of specific loading (that is the loading carried to the area of a surface) above an admissible limit. Then the oil film in these parts becomes thin, and surfaces of a shaft and the bearing start to adjoin on microroughnesses. There is a mode of the semi-liquid greasing, being characterized increase of a friction and a gradual warming up of the bearing. Further it can lead to a so-called boundary friction with complete contact of the surfaces the overheat, skhvatyvany (teases), jamming, fusion and bearing destruction will be which consequence.

It is clear that in operation the mode of a boundary friction is unacceptable. Nevertheless it appears at violation of supply of oil, and it occurs because of its shortage in a case, that is or owing to oversight of the driver, or at damage of the pallet of a case as a result of arrival on an obstacle more often.

The mode of semi-liquid greasing is admissible only for short time when he does not manage to affect wear of the bearing. An example – start-up of the cold engine. However, there is other danger: at very low temperature oil можеты to be too viscous and its normal giving is restored long (20–30 seconds and more). Here already semi-liquid greasing is capable to affect wear of details considerably.

Improvement of automobile engines is connected with continuous growth of frequency of rotation and increase in capacity. Increase of compactness of designs, including reduction of width and diameter of bearings is at the same time observed. It means that specific tension grows in knot. And as load of the bearing at operation of the engine cyclically changes on size and the direction, there is real a so-called fatigue failure of details. To provide operability of bearings in such conditions, special designs, materials and technologies are required.