A variable displacement vane-type fluid pump is provided which permits improved
regulation of the pump discharge such that the pump can meet the various requirements
of lubrication for internal combustion engines at all speeds with minimized use
of power. Of course, the vane pump may also be utilized in a wide range of power
transmission and other fluid distribution applications. The variable displacement
vane pump of the invention may utilize both hydrostatic and mechanical assistance
in radially positioning its vanes to ensure efficient and quiet operation of the
pump and to facilitate priming of the pump. The vane pump of the invention may
also use both hydrostatic and mechanical actuators to control the position of its
containment ring or eccentric ring and hence, regulate the output of the pump.
According to yet another aspect of the present invention, to prevent inlet flow
restriction or cavitation, a valve may be provided to permit some of the pump outlet
or discharge flow to bleed into the pump inlet to provide needed velocity and energy
to the fluid flow into the pump inlet.
