Audi 100/A6

1990-1997 of release

Repair and car operation

Usually bearings of cranked shaft in modern engines carry out in the form of thin-walled loose leaves or plugs in thickness of 1,0-2,5 mm (it is rare more). Loose leaves of radical bearings of a cranked shaft do to thickness because of need to place a circular flute for supply of oil to shatunny bearings. The general tendency – reduction of thickness of loose leaves which now averages 1,8–2,0 mm at radical and 1,4–1,5 mm at shatunny bearings. The loose leaves are thinner, the better they adjoin to a surface of the case (bed), that the heat-conducting path from the bearing is better, the geometry, less admissible gap and noise at work is more exact, it is more knot resource.

That at installation in a bed the loose leaf precisely accepted its form, in a free condition it should have a tightness on diameter of a bed (so-called straightening) and not cylindrical form of variable radius. Besides, the tightness is necessary for a good prileganiye to a surface and deduction from a provorachivaniye and on length of the loose leaf – it call a vystupaniye. All these parameters depend on thickness, width and diameter of loose leaves, thus straightening averages 0,5–1,0 mm, and a vystupaniye – 0,04–0,08 mm. However for reliable operation of the bearing and it still it is not enough. About the socket thickness of loose leaves reduce by 0,010–0,015 mm to avoid задиров in these parts. They can appear because of opening deformation in the case under the influence of working loading when the working gap in the bearing is small.

Materials for loose leaves can be different. Their choice coordinates with a material of a cranked shaft and its heat treatment, degree of a forsirovka of the engine and the set resource. To a certain extent affect here and traditions of automobile firm.

Loose leaves always do multilayered. A loose leaf basis – a steel tape which provides durability and reliability of landing in the case. On a basis with various ways put a layer (or layers) a special antifrictional material in thickness of 0,3-0,5 mm. The main requirements to an antifrictional material – a low friction on a shaft, high durability and heat conductivity (that is heat from a surface is good to carry out to the bearing case ability). The first requirement soft metals, for example, best of all provide alloys with the big content of tin and lead (in particular, widely known babbits).

In the past babbits were widely applied on the low-forced low-turnaround engines. With growth of loadings durability of such loose leaves with a thick layer of babbit appeared insufficient. The problem was solved by replacement of all this layer by a peculiar sandwich – the svintsovoolovyanisty bronze covered thin (0,03–0,05 mm) a layer of the same babbit. The loose leaf became multilayered. In modern engines "stalebronzobabbitovy" loose leaves usually carry out 4-layer (under babbit very thin intermediate layer of nickel still lies) and even 5-layer when for improvement extra earnings from above the thinnest layer of tin is put on a working surface. Exactly bearings on many foreign engines so look.

Along with it the wide circulation was received also by steel-aluminum loose leaves. As an antifrictional material aluminum alloys with tin, lead, silicon, zinc or cadmium, both with coverings, and without them here serve. Most often in world practice the aluminum alloy from 20 % of tin without a covering is used. It well resists to high loadings and speeds of rotation of modern engines, including diesel engines, and at the same time possesses satisfactory "softness". Nevertheless steel-aluminum loose leaves are more rigid, than babbitovy (or with a babbitovy covering) therefore are more inclined to teases in the conditions of insufficient greasing.

Auxiliary and camshafts of engines rotate, as a rule, with smaller frequency, than cranked and test much smaller loadings therefore it is easier than a condition of their work. Loose leaves and plugs of these shaft usually do of the materials, similar by the aforesaid. Besides, here sometimes apply babbit or bronze without a covering. Often these bearings at all have no plugs or loose leaves and are formed directly rastachivaniy openings in a head of the block of cylinders. In such designs the head is executed from an aluminum alloy with silicon which possesses quite good antifrictional properties.

The general for bearings of modern engines, especially if it is a question of support of cranked shaft, compliance of a material and a design of loose leaves to a material and operating conditions of a shaft (frequency of rotation, loading, a greasing condition etc.) is. Therefore any replacement of details when, for example, at repair put loose leaves from other engine, cannot be recommended. Otherwise the durability of the repaired unit can appear very small. To decide on such step, it is necessary to have the relevant information.

Loose leaves are very exact (precision) details. To guarantee small (but quite concrete – on the average 0,03–0,06 mm) working gaps in bearings, when manufacturing maintain thickness of the loose leaf with accuracy about 5-8 microns, and length – 10–20 microns. Violation of these requirements can lead to change of a working gap in the bearing or density of landing of the loose leaf in the case that is inadmissible because of decrease in reliability and a resource of all engine as a whole.