Apparatus for controlling the switch-over of hydraulic cylinders

An electro-hydrostatic drive for realizing a rapid movement during a rapid movement phase, a force-building movement during a force-building movement phase and a transition phase between the rapid movement phase and the force-building movement phase, comprising:

• a hydro-machine having a variable volume and/or a variable speed, wherein the hydro-machine is driven by an electric motor, and wherein the hydro-machine is arranged to provide a flow of a hydraulic fluid;
• a first cylinder having a piston chamber, a rod chamber, and a rod;
• a second cylinder having a piston chamber, a rod chamber, and a rod, wherein the rod chamber is arranged as a reservoir;
• a pressure source in selective fluid connection with the first cylinder and the second cylinder;
• a relief valve;
• a check valve;
• a fluid connection between the piston chamber of the first cylinder and a piston-chamber-side port of the hydro-machine;
• a fluid connection between the rod chamber of the first cylinder and a rod-chamber-side port of the hydro-machine;
• a fluid connection between the piston chamber of the first cylinder and the reservoir;
• a fluid connection between the rod-chamber-side port of the hydro-machine and the reservoir;
• a fluid connection, through the relief valve, between the reservoir and the pressure source;
• wherein the relief valve is operable to provide pressure safety to the reservoir, and the check valve has a fluid connection from the pressure source to the rod-chamber-side port of the hydro-machine;
• during the rapid movement phase, a first part of the hydraulic fluid is communicated via the fluid connection between the piston chamber of the first cylinder and the piston-chamber-side port of the hydro-machine and the fluid connection between the rod chamber of the first cylinder and the rod-chamber-side port of the hydro-machine, and a second part of the hydraulic fluid is communicated through the fluid connection between the piston chamber of the first cylinder and the reservoir;
• during the force-building movement phase, a first part of the hydraulic fluid is communicated via the fluid connection between the piston chamber of the first cylinder and the piston-chamber-side port of the hydro-machine and the fluid connection between the rod chamber of the first cylinder and the rod-chamber-side port of the hydro-machine, and a second part of the hydraulic fluid is communicated through the fluid connection between the rod-chamber-side port of the hydro-machine and the reservoir;
• and
• the rod of the first cylinder and the rod of the second cylinder are mechanically connected via a mass, and during the transition phase wherein the first and second cylinders are substantially stationary, the fluid connection between the piston chamber of the first cylinder and the reservoir is closed, and the fluid connection between the rod-chamber-side port of the hydro-machine and the reservoir is closed, wherein the hydraulic fluid does not flow between the reservoir and the rod-chamber-side port of the hydro-machine when the fluid connection therebetween is closed during the transition phase.