Lifting gear, and method for adjusting the boom of such a lifting gear

A lifting gear comprising:

• a boom;
• a boom adjustment unit comprising at least one hydraulic actuator for adjusting the boom;
• and
• a control device for controlling the movement of the hydraulic actuator, the control device being provided with a displacement controller having a first pump and a second pump for adjusting the hydraulic actuator;
• and
• wherein:
• the hydraulic actuator comprises a synchronous cylinder with equal pressure chamber cross-sectional areas or has a pair of differential cylinders arranged in opposition, the oscillating volumes of which at least approximately compensate each other;
• the first pump is connected to a pressure chamber of the hydraulic actuator acting in one direction and to a tank;
• the second pump is connected to another pressure chamber of the hydraulic actuator acting in the opposite direction and to the tank;
• and
• the first and second pumps have displacement volumes whose ratio corresponds at least approximately to the cross-sectional area ratio of the pressure chambers of the hydraulic actuator.

A lifting gear, comprising:

• a boom;
• a boom adjustment unit comprising at least one hydraulic actuator for adjusting the boom;
• and
• a control device for controlling the movement of the hydraulic actuator, the control device being provided with a displacement controller having a first pump and a second pump for adjusting the hydraulic actuator;
• wherein:
• the first pump connects two pressure chambers acting in opposite directions of the hydraulic actuator with each other and circulates pressure medium from one pressure chamber into the other pressure chamber;
• the second pump is connected on the one hand to one of the pressure chambers and on the other hand to a tank;
• the first and second pumps have displacement volumes whose ratio corresponds at least approximately to the cross-sectional area ratio of the pressure chambers of the hydraulic actuator;
• and
• a synchronization stage is provided for synchronizing the drive speed or synchronizing the displacement volume adjustment between the first and second pumps.

A lifting gear comprising:

• a boom;
• a boom adjustment unit comprising at least one hydraulic actuator for adjusting the boom;
• a control device for controlling the movement of the hydraulic actuator, the control device being provided with a displacement controller having a first pump for adjusting the hydraulic actuator;
• and
• a flushing arrangement and/or a feeding arrangement for compensating for excess quantities and/or sub-quantities occurring during circulation of pressure medium between pressure chambers acting in opposite directions of the hydraulic actuator;
• wherein:
• the flushing arrangement and/or the feeding arrangement comprises a feed pump for feeding sub-quantities of the pressure medium occurring during displacement control of the hydraulic actuator;
• and
• a hydraulic circuit portion into which the feed pump feeds the pressure medium is connected to a tank via a pressure limiting valve.

A lifting gear comprising:

• a boom;
• a boom adjustment unit comprising at least one hydraulic actuator for adjusting the boom;
• a control device for controlling the movement of the hydraulic actuator, the control device being provided with a displacement controller having a first pump for adjusting the hydraulic actuator;
• and
• a check valve arrangement between the first pump and the hydraulic actuator for shutting off inflows and/or outflows of the hydraulic actuator and thus locking the hydraulic actuator;
• wherein;
• the check valve arrangement comprises two check valves provided for shutting off the inflows and outflows of the hydraulic actuator;
• the check valves are hydraulically operated under pilot control;
• and
• a pilot pressure of the check valves is limited by a pressure limiting valve in such a way that when a predetermined pressure is reached in the hydraulic actuator, the pilot pressure is frozen and/or limited.