Lifting mechanism for farm tractors

摘要

A lifting mechanism for farm tractors has two lower links (2, 2a), on each of which engages a double-acting lifting cylinder (1, 1a) articulated on the tractor. The lifting cylinders (1, 1a) can be loaded via two solenoid valves (3, 3a) controllable by means of a controller (6). The controller (6) is connected to actual-value transmitters (7, 7a) for the position of the lower links (2, 2a) and to a switching device (8) for the lifting and lowering movement. In order to allow a pulling-force and position control without an appreciable increase in the technical outlay, the switching device consists of an electronic control device (8, 9, 9a, 10) for the pulling-force and position control. The two solenoid valves (3, 3a) are each assigned to a lifting cylinder (1a) and are connected in parallel. Finally, the two solenoid valves (3, 3a) are preceded by a third solenoid valve (5) which is likewise controllable by the controller (6) and which either opens the inflow and flow-off of the pressure medium to and from the solenoid valves (3, 3a) or provides a short-circuit line between the pressure-medium source (4) and return. <IMAGE>