Audi 100/A6

1990-1997 of release

Repair and car operation

14.8.8.2. As the bearing is arranged

THE GENERAL DATA

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

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

Materials for loose leaves can be different. Their choice co-ordinates with a material of a cranked shaft and its heat treatment, degree форсировки 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 in the various ways put a layer (or layers) a special antifrictional material in the thickness of 0,3-0,5 mm. The basic requirements to an antifrictional material – a low friction on a shaft, high durability and heat conductivity (that is from a surface heat is good to spend to the bearing case ability). The first requirement is better provide soft metals, for example, alloys with the big maintenance of tin and lead (in particular, widely known баббиты).

In the past баббиты were widely applied on малофорсированных низкооборотных engines. With growth of loadings durability of such loose leaves with a thick layer баббита has appeared insufficient. The problem has been solved by replacement of all this layer by an original sandwich – свинцовооловянистую the bronze covered thin (0,03–0,05 mm) a layer of the same баббита. The loose leaf became multilayered. In modern engines "сталебронзобаббитовые" loose leaves usually carry out 4-layer (under баббитом very thin intermediate layer of nickel still lies) and even 5-layer when for improvement extra earnings from above the most thin layer of tin is put on a working surface. So bearings on many foreign engines look.

Along with it the wide circulation was received also by steel-aluminium loose leaves. As an antifrictional material alloys of aluminium with tin, lead, silicon, zinc or cadmium, both with coverings, and without them here serve. Most often in world practice the alloy of aluminium 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 simultaneously possesses satisfactory "softness". Nevertheless steel-aluminium loose leaves are more rigid, than баббитовые (or with баббитовым a 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 баббит or bronze without a covering. Frequently these bearings at all have no plugs or loose leaves and are formed directly растачиванием apertures in a head of the block of cylinders. In such designs the head is executed from an alloy of aluminium 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, conformity of a material and a design of loose leaves to a material and shaft working conditions (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 dare at such step, it is necessary to have the corresponding information.

Loose leaves are very exact (прецезионные) details. To guarantee small (but quite concrete – on the average 0,03–0,06 mm) working backlashes in bearings, at manufacturing a thickness of the loose leaf maintain with accuracy of an order 5–8 microns, and length – 10–20 microns. Infringement of these requirements can lead to change of a working backlash 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.