Concentric camshaft for variable valve timing and method of manufacturing by metal additive process and disintegrable barrier to preserve interstitial void spaces and method of removal

Abstract

This invention relates generally to a camshaft having dual independent banks of cam lobes which are azimuthally adjustable one with respect to the other over a small angle so as to allow separate control of intake and exhaust valve opening and closing events. Such a coaxial camshaft allows relative changes in the lobe centerline angle, or LCA, to vary the amount of valve overlap during operation. An outer shaft member containing one bank of cam lobes houses an inner shaft containing another bank of cam lobes which protrude and extend radially outward through windows of omitted material in the outer shaft. The concentric shafts containing banks of cam lobes are each a single piece being produced in their final shapes, simultaneously, by metal additive manufacturing, or MAM. The shafts being initially produced concentrically require no individual assembly operation, and are constrained by one another, inextricably bound in the assembled configuration upon their being formed. Furthermore, as exemplified in the invention, the requisite spacing between the inner and outer shafts of the coaxial camshaft may be preserved free of metal by the pre-placement of barrier material, or by placement of a non-metal interlayer during manufacture, as exemplified herein which may subsequently be disintegrated by industrial ultrasonic process to facilitate its removal. In either case, the small annular space having been formed maintains the radial alignment between the inner and outer shafts to within acceptable tolerance, and allows the flow of lubricating oil within the space during operation. Such a camshaft with the addition of a separate cam phasing mechanism may beneficially be fitted to engine blocks with a single traditional camshaft, which would otherwise be made from a single piece of material, with fixed LCA, thereby allowing older designs to be upgraded with fully universal Variable Valve Timing, or VVT.

Dependencies are inferred from the claim text.