Boosted hydro-pneumatic drive

Boosted hydro-pneumatic drive having a rapid traverse and a power stroke for driving punching tools comprising

• a cylinder housing having a first section and a second section separated by a fixed partition;
• a working piston slidably mounted in an annular space in said first section, said working piston including a central bore and having an attached piston rod extending out of said housing;
• connections provided to said annular space in said first section to selectively apply compressed air pressure to opposite surfaces of said working piston;
• said second section having a disc piston and an annular piston slidably mounted therein, said disc piston having a plunger portion extending from one side thereof and adapted to slide into said central bore of said working piston upon application of pressure to the other side of said disc piston, and said annular piston being located at an intermediate position between said disc piston and said partition;
• an oil reservoir formed between said annular piston and said partition and having a fluid connection with said central bore;
• a compression spring mounted between said disc piston and said annular piston to assist in rapid traverse movement of said working piston and in the return stroke of said disc piston;
• said second section having an opening in said housing to the atmosphere and being located to provide atmospheric pressure in said second section throughout the drive cycle;
• said second section including a cover portion at the end remote from said partition, said cover and said disc piston having a working space formed therebetween;
• means providing a compressed air connection between said working space and that part of said annular space adjacent said partition;
• and
• said connecting means including a valve arrangement that is actuable during the power stroke to cause movement of said disc piston whereby said plunger portion slides into said central bore, and is further actuable to allow the return stroke of said disc piston.