ENGINE – TD 12-1-18 DESCRIPTION AND OPERATION Operation By applying a vacuum, the Engine Control Module (ECM) controls the engine damping mounting in two stages: “Hard” Engine Mount In the basic setting no vacuum is applied to the hydraulic mount. The spring (13) acts on the support cup (12) to close the U-bellows against the upper nozzle plate (8). Hydraulic fluid flows from the upper hydraulic chamber (6) via the nozzle (9), the annular channel (4) and via nozzle (3) into the lower hydraulic chamber (The annular channel extends over approximately 300 degrees. Due to the length of the annular channel and the small nozzle orifice hydraulic oil flows between the upper and lower hydraulic chamber only in the case of vibrations up to the natural frequency of the engine (approximately. 10 Hz, thus producing a vibration absorber effect. At higher frequencies, the equalisation between the hydraulic chambers is inhibited by the length of the annular channel and the small nozzle orifices. In practical terms, equalisation between the upper and lower hydraulic chamber does not take place. Diaphragms (5) are fitted in the holes (7) of the nozzle plates in order to achieve good acoustic characteristics at high frequencies with small amplitude.