Concentric camshaft arrangement

Abstract

A concentric camshaft arrangement comprises an inner shaft, an outer tube concentrically arranged around the inner shaft and rotatably supported in a cylinder head. A first set of lobes is fixed for rotation with the outer tube and a second set of lobes is rotatably supported by bearing journals on the outer tube and connected for rotation with the inner shaft. The outer tube is supported in the cylinder head by means of a roller bearing and an oil feed is provided for supplying oil for lubricating the bearing journals of the second set of cam lobes. At least part of the oil feed is defined by a radial clearance between the outer surface and an inner surface of the cylinder head that is sealed at its axial ends, the radial clearance being larger than any radial clearance at the roller bearing so that loads on the camshaft are supported at least predominantly by the roller bearing.

1 . A concentric camshaft arrangement comprising:
 an inner shaft,   an outer tube concentrically arranged around the inner shaft and rotatably supported in a cylinder head,   a first set of lobes fixed for rotation with the outer tube,   a second set of lobes rotatably supported by bearing journals on the outer tube and connected for rotation with the inner shaft,   a roller bearing mounted between the outer tube and the cylinder head, and   a camshaft oil feed for supplying oil for lubricating the bearing journals of the second set of cam lobes,   wherein at least part of the camshaft oil feed is defined by a radial clearance between the outer surface of the outer tube and an inner surface of the cylinder head that is sealed at its axial ends, the radial clearance being larger than any radial clearance at the roller bearing so that loads on the camshaft are supported at least predominantly by the roller bearing.   
     
     
         2 . The concentric camshaft arrangement as claimed in  claim 1 , wherein the radial clearance between the outer tube and the cylinder head is sealed by first and second sealing rings. 
     
     
         3 . The concentric camshaft arrangement as claimed in  claim 1 , wherein the outer tube includes a separately formed oil feed ring fixed securely to the outer surface of the outer tube for rotation therewith, the outer surface of the oil feed ring being the surface that is spaced from the inner surface of the cylinder head by the radial clearance forming the camshaft oil feed. 
     
     
         4 . The concentric camshaft arrangement as claimed in  claim 3 , wherein the diameter of the outer surface of the oil feed ring is substantially equal to the outer diameter of the roller bearing. 
     
     
         5 . The concentric camshaft arrangement as claimed in  claim 3 , wherein the oil feed ring serves to limit axial displacement of the roller bearing. 
     
     
         6 . The concentric camshaft arrangement as claimed in  claim 3 , wherein the oil feed ring serves additionally to limit axial displacement of the outer tube of the camshaft relative to the cylinder head. 
     
     
         7 . The concentric camshaft arrangement as claimed in  claim 1  wherein the camshaft oil feed comprises a plurality of discrete oil feeds defined by clearances between the outer tube of the camshaft and cylinder head, which plurality of discrete oil feeds are separated from one another by seals. 
     
     
         8 . The concentric camshaft arrangement as claimed in  claim 1 , further comprising a camshaft phaser and a phaser oil feed operable to supply oil to the camshaft phaser. 
     
     
         9 . The concentric camshaft arrangement as claimed in  claim 8 , wherein at least part of the phaser oil feed is formed by the camshaft oil feed. 
     
     
         10 . The concentric camshaft arrangement as claimed in  claim 8 , further comprising a phaser flow restrictor operable to control at least one of the oil flow rate and direction in the phaser oil feed. 
     
     
         11 . The concentric camshaft arrangement as claimed in  claim 1 , further comprising a camshaft flow restrictor operable to control the oil flow rate in the camshaft oil feed.