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Engine mountings

Engine mountings


Background

The balancer shafts are most effective within the most common working range of the engine, i.e. from 1800 rpm and above (the B206i engine has no balancer shafts). At slower engine speeds, in the range between idling speed and up to 1800 rpm, the balancer shafts are unable to counteract engine vibration.

To provide effective damping of engine vibration within this engine speed range, the rear and right-hand front engine mountings are of hydraulic type (except on the B206i engine, which has ordinary rubber mountings). They are designed to provide maximum damping effect within this range, i.e. between idling speed and about 1800 rpm.

Hydraulic mountings have the following advantages:


• improved damping of horizontal engine movements during acceleration

• improved damping of vertical engine movements on bumpy roads

• improved damping of engine movement when idling

• reduction of structure-borne sound between engine and body


Description

The hydraulic mounting has two chambers filled with a special hydraulic fluid. Interposed between the two chambers are a diaphragm and a passage, the length and diameter of which determine the damping characteristics of the mounting. The diaphragm absorbs the forces generated by small and normal movements of the engine.

If engine movement is more pronounced, the damping action of the diaphragm is insufficient and fluid is forced from the upper to the lower chamber, thus equalizing the pressure. This gives the hydraulic mountings a progressive damping action, the resistance of the mountings increasing as the load on them increases.