Hydraulic drive for multi-color sheet-fed rotary printing machines

In a multi-color, sheet-fed rotary printing machine including a plurality of consecutively arranged press units each having a plurality of sheet-processing cylinders, and gear trains for interconnecting said cylinders, a hydraulic driving device comprising a plurality of constant-flow radial piston type hydraulic motors each having an intake port and a discharge port for admitting and discharging pressure fluid and means for distributing the pressure fluid to respective radial pistons, a power output member directly connected to one of said cylinders in the assigned press unit for driving the same;

• an adjustable pump for supplying pressure fluid into said hydraulic motors;
• an electric motor for driving said pump;
• a first hydraulic control means including a main control valve and a switching control valve connected between said pump and said hydraulic motors;
• and second hydraulic control means provided in each of said hydraulic motors, said second hydraulic control means including a cylindrical bore, said ports communicating with said bore and forming with its inner wall control edges spaced apart in axial direction, a conduit opening into said bore between said control edges and leading to said distributing means, a reciprocating piston movable in said bore past said ports, said piston being formed on its jacket with an annular control groove which during the movement of said piston alternately connects one of said ports with said conduit, the axial clearance of said groove being shorter than axial spacing between said control edges so that during the reversal of working phase into discharging phase of respective radial pistons, said reciprocating piston positively overlaps for a short period of time the control edges of both ports.