Piston motor with starting charge device

A fluid pressure driven motor having a rotatable driven piston barrel member containing a plurality of pistons reciprocable within cylinder bores in the piston barrel member, an output shaft connected to and driven by said piston barrel member and a fixed porting plate member abutting the barrel containing inlet and outlet arcuate shaped slots in alignment with said pistons to supply fluid to and receive fluid from said pistons, respectively, said porting member having bearing surfaces radially inwardly and outwardly of said inlet and outlet ports which receive fluid for lubrication and provide a hydrodynamic bearing surface, said porting plate member further containing a force pad along a radius passing through said inlet port, said force pad having an opening abutting said piston barrel member, the improvement comprising:

• a supplementary charge device having a charge chamber containing a quantity of fluid, passage means connecting said charge chamber to said opening formed in said force pad, and differential area piston means actuated by high pressure motor driving fluid to expel said quantity of fluid into said opening during the motor starting phase to induce temporary separation between the barrel and said porting member.