1998-02-23

VAST: A New Variable Valve Timing System for Vehicle Engines 980769

VAST is a variable timing system developed for spark-ignition and compression-ignition engines.
It makes variable control of the intake and exhaust valves possible for SC and OHC engines.
The system is based on the principle of the purely mechanical effect of the cam's irregular angular speed. It makes it possible to vary the valve opening angle (up to approx. 50° crankshaft angle) and the spread (up to approx. 30° crankshaft angle) continuously for each valve lift movement.
When the valve opening period is prescribed, longer time profiles can be realized with this system than with any mechanical VVT system known to the authors.
The valve lift is influenced directly at the cam, which means this system can be used with all types of known valve gear- both for engines/cylinder heads with just one camshaft and for multi-valve cylinder heads with two camshafts.
The system is being tested on functioning spark-ignition and compression-ignition engines. The results show that the components of the VVT system meet the high requirements for series-production engines. The measured friction is on the same level as with conventional valve gear.
An adaptation of VAST to an American passenger car engine is planned.

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