| 摘要 |
A camshaft is provided having longitudinally spaced cams for operating the valve lifters of an engine. Each cam has juxtaposed first and second cam lobes for operating at low speed conditions (city driving) and high speed conditions (highway). The profile of each cam lobe has a base circle area and the base circle areas of the lobes on each cam are of the same radius and overlap to provide a cross-over zone. While the engine is running and the camshaft is rotating, the camshaft can be shifted longitudinally between a first position in which the valve lifters contact the profiles of the first cam lobes of the cams and a second position in which the valve lifters contact the profiles of the second cam lobes. The positions of the valve lifters longitudinally of the camshaft in relation to the angular positions of the cross-over zones of the cams is such that during the simultaneous rotation and longitudinal shifting of the camshaft the valve lifters will traverse the cams from the profile of one cam lobe to the other at the cross-over zone.
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