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Page 19
Lotus Service Notes
Section EH VALVEMATIC System The principle of the VALVEMATIC system is that a conventional inlet camshaft with a single (rotary) cam for each cylinder operates a roller arm on a pivot shaft. On each side of the roller arm is an oscillating cam, each of which opens, via a finger follower, one of two conventional inlet valves for that cylinder. The two valves are operated at all times as a pair. The connection between the roller arm and the two oscillating cams is made via a common pivot sleeve machined with three separate sections of helical splines, which correspond with splines in the bores of the roller arm and oscillating cams. By sliding the sleeve axially, within the roller arm and cams, the opposite helix angle used for the cams compared with that for the roller arm, results in a phase shift between arm and cams. A 'lost motion' damper ensures that the roller arm stays in contact with the rotary cam profile at all times. The position of the oscillating cams at the start of a valve opening event however, is dependent on their phasing with the roller arm. In the low lift mode, where the cams are phased counterclockwise in relation to the roller arm as viewed from the rear, the finger follower roller is in contact with the base circle of the oscillating cam, which must turn through a large part of its range before the cam starts to lift the valve, resulting in only the first portion of the cam profile being used. In high lift mode, the oscillating cams are phased clockwise in relation to the roller arms such that the cam profile immediately starts to lift the valve as soon as the roller arm is depressed by the rotary cam, continuing then to utilise the full profile of the oscillating cam for maximum lift. The concomitant variation in valve timing as the lift changes, is managed by the separate VVT-i system (see earlier). Valves shown at full lift (camshaft omitted for clarity) Pivot shaft Roller arm Camshaft Oscillating cam operates against this roller Finger follower Inlet valves Hydraulic pivot post |