portions 222 pass over the peaks 324 the spring 40 decompresses and drives the cam 30 back toward the cylindrical portion 221 with the finger portions 222 riding along the steep inclined planes 328 from the peaks 324 to the valleys 322 the cover 204 is thus rotated automatically to the fully open position or fully closed position under decompression force of the spring 40 accordingly the cover 204 is moved 180 degrees relative to the main body 202 with the finger portions 222 once again mating in the valleys 322 in this way the cover 204 is opened or closed preferably the structures of the cover 204 and the main body 202 are adapted to control the degree of rotation of the hinge assembly 10 such that the finger portions 222 can be held in one or more particular locations between the valleys 322 and the peaks 324 during the above described processes if the cam 30 is rotated relative to the spring 40 some oil flows from the oil storing receptacles 33 and lubricates the cam 30 and the spring 40 this reduces the friction between the cam 30 and the spring 40 referring to fig6 in an alternative embodiment a plurality of oil storing receptacles 82 can be provided on a washer 80 that is a first surface portion of the washer 80 defines the oil storing receptacles 82 and resists a cam 60 and an opposite second surface of the washer 80 resists the spring 40 each oil storing receptacle 82 is substantially a groove or has another suitable shape the cam 60 is similar to the cam 30 of the first preferred embodiment and includes a cam surface 62 and a protrusion 64 the cam surface 62 includes.