Hydraulic knockout device

A hydraulic knockout device comprising:

• an energy conversion section configured to convert a part of kinetic energy during lowering a slide of a press machine into hydraulic energy;
• an energy storage section configured to store the hydraulic energy converted by the energy conversion section;
• and
• a knockout section configured to take out a product worked by the press machine from the press machine, the knockout section configured to convert the hydraulic energy discharged from the energy storage section into kinetic energy to knock out the product,
• wherein the energy conversion section includes:
• a cushion pin pressed down with lowering operation of the slide;
• and
• a first hydraulic cylinder having a piston rod which comes into contact with the cushion pin,
• wherein the energy storage section is a first accumulator configured to store hydraulic fluid displaced from a rising side pressure generating chamber of the first hydraulic cylinder through the cushion pin when the slide is lowered,
• wherein the knockout section is a second hydraulic cylinder having a rising side pressure generating chamber to which the hydraulic fluid stored in the first accumulator in knockout operation is fed,
• wherein the hydraulic knockout device further comprises a second accumulator configured to store hydraulic fluid having second system pressure lower than hydraulic fluid having first system pressure stored in the first accumulator,
• wherein the second accumulator stores hydraulic fluid displaced from a lowering side pressure generating chamber of the second hydraulic cylinder in the knockout operation, and feeds the hydraulic fluid to the rising side pressure generating chamber of the first hydraulic cylinder with rising of the slide to raise the cushion pin,
• wherein a hydraulic closed circuit in which the hydraulic fluid is pressurized and filled is comprised of the first hydraulic cylinder, the second hydraulic cylinder, the first accumulator and the second accumulator, and
• wherein the hydraulic closed circuit does not include a hydraulic pump configured to pressurize and feed the hydraulic fluid.