The invention relates to pantograph assemblies for supplying power from an overhead conductor to electrically-powered trains and other vehicles, and more particularly to methods of and apparatus for controlling the contact pressure of the contact brushes of the pantograph on the lower surface of the overhead conductor.
In pantograph assemblies of this general type, the brush is supported for vertical movement in a brush holder, which in turn is carried on the top of an upper link or rod of a scissors-type pivot structure associated with the top of the vehicle. Typically, the brush holder is hydraulically or pneumatically driveable, via a piston-cylinder set in a vertical direction with respect to a fixed-height scissors structure supporting it.
The hydraulic or pneumatic pressure is varied in correspondence to the deviation of an instantaneous contact pressure of the brush, which is sensed by a transducer carried on the brush holder, from a desired value of contact pressure represented by a reference signal.
Regulators of this type have been found to be insufficiently responsive to maintain the contact pressure within a desired range where, as in the usual case, the height of the overhead conductor above the top of the vehicle varies significantly in a random fashion as a function of distance along the path of movement of the vehicle.