Hydraulic cylinder for a hydraulic drawing cushion

Hydraulic drawing cushion (20) of a drawing press (10), the drawing press (10) including an upper tool part (14) and a lower tool part (15), the hydraulic drawing cushion (20) for exerting a clamping force on a sheet metal part (B) for forming a formed metal part, comprising:

• a cylinder arrangement (22) including a hydraulic cylinder (23) including a cylinder housing (30) having an internal cylinder space (31) including a first hydraulic operating chamber (47), a second hydraulic operating chamber (48), and a third hydraulic operating chamber (53),
• a piston rod (33) slidably supported in a cylinder opening (32) of the internal cylinder space (31), the piston rod (33) for connection with a metal sheet support ring (25) of the drawing press (10),
• between the first hydraulic operating chamber (47) and the second hydraulic operating chamber (48), an annular piston (45) is arranged which extends annularly around and attached to the piston rod (33),
• the annular piston (45) having a first piston surface (49) adjacent first hydraulic operating chamber (47) and having a second piston surface (50) adjacent the second hydraulic operating chamber (48), the first piston surface (49) and the second piston surface (50) are of essentially a same surface area and movable simultaneously together with the piston (33),
• the piston rod (33) having a front face which is an integral part thereof and housed within the cylinder opening (32) delimiting a third piston surface (54) having a surface area larger than either the first and the second piston surface (49, 50) and which defines an upper border of the third hydraulic operating chamber (53),
• a first hydraulic circuit (55) in hydraulic circuit connection with the first hydraulic operating chamber (47) and the second hydraulic operating chamber (48),
• a second hydraulic circuit (56) in hydraulic circuit connection with the third hydraulic operating chamber (53),
• the first hydraulic circuit (55) controls a position and/or movement of the piston rod (33) before the upper tool part (14) abuts the sheet metal part (B),
• the second hydraulic circuit (56) controls a sheet metal part (B) clamping force upon the upper tool part (14) abutting the metal sheet part (B),
• the hydraulic drawing cushion (20) is operated by a position and/or movement control before the upper tool part (14) abuts the metal sheet part (B),
• the hydraulic drawing cushion (20) is operated by a sheet metal part (B) clamping force control as soon as the upper tool part (14) abuts the sheet metal part (B), and,
• an electrically controllable control valve (61) connected in hydraulic circuit arrangement with the first hydraulic circuit (55) and the second hydraulic circuit (56), the electrically controllable control valve (61) in a first position (I) enables the position and/or movement control of the hydraulic drawing cushion (20) and the electrically controllable control valve (61) switches over to a second position (II) to enable the sheet metal part (B) clamping force control of the hydraulic drawing cushion (20) upon the upper tool part (14) abutting the metal sheet part (B).