Hydraulic control apparatus for injection molding fluent plastic material

Hydraulic control apparatus for controlling the injection speed and pressure of an injection molding machine having a hydraulic cylinder with a piston therein coupled to an injection molding nozzle, said apparatus comprising:

• a source of hydraulic fluid;
• a hydraulic fluid pump;
• a main hydraulic circuit comprising:
• a main line connected to said hydraulic cylinder, said pump being arranged to provide hydraulic fluid under pressure from said fluid source to said main line;
• and
• valve means in said main line between said pump and said hydraulic cylinder for controlling the application of hydraulic fluid to said cylinder for selective actuation of said piston in either direction;
• a pilot hydraulic circuit for controlling the pressure in said main line, said pilot circuit comprising:
• a plurality of pilot pressure control valves each having a pressure set point;
• a like plurality of pilot pressure control lines respectively connecting said pilot pressure control valves in parallel;
• a main pressure control valve, said parallel pilot pressure control lines being connected to said main line between said pump and said valve means through said main pressure control valve, said main pressure control valve being arranged to selectively provide hydraulic fluid under pressure to said pilot pressure control lines;
• and
• means in each pilot pressure control line for selectively and individually isolating and connecting the respective one of said pilot pressure control valves to said main pressure control valve;
• and
• means for sequentially and individually actuating said selective isolating and connecting means in said pilot pressure control lines for respective predetermined periods of time to sequentially adjust the main line pressure to the respective pressure set points by coupling said main line individually to said pilot pressure control valves through said main pressure control valve and through a respective isolating and connecting means, only one of each of said pilot pressure control valves and its respective pilot pressure control line and isolating and connecting means being coupled through said main pressure control valve to said main line at any one time, whereby the pressure within said hydraulic cylinder and the speed of movement of said piston therein is controlled.