flange 60 and below the flange 60 a pair of cam lobes 62 the cap 50 the flange 60 and the cam lobes 62 together form an oscillating member which rotates with the drive shaft 42 the upstanding barrel 34 the skirt 32 and the vanes 36 each of the cam lobes 62 is formed with a first driving surface 64 extending generally in a circumferential direction and a second capture surface 66 extending generally in a radial direction the driving surface 64 comprises a spiral which proceeds radially inwardly in the direction of the driving rotation shown by arrow 67 the capture surface 66 is tilted forwardly in the direction of the non driving rotation from a line radial to the axis of the assembly carried outwardly of the cam lobes 62 are a pair of clutch shoes or members 68 each clutch shoe 68 is retained axially about the cam lobe 62 between the flange 60 and an upper side of a support rim 70 of the driving barrel 56 the clutch shoes 68 are restrained from radially outward movement by surrounding cylindrical engagement surface 72 formed on an inner surface of the driving barrel 56 the engagement surface 72 of.