Patent GB-923334-A (GB)
Title: Improvements in devices for exerting a follow-up action on hydraulically operated lift systems of agricultural tractors
IPC: A01B63/111
Filed: 1960-07-07
Abstract: 923,334. Fluid-pressure servomotor control systems. C.C.M. COMPAGNIE CONTINENTALE DE MOTOCULTURE. July 7, 1960 [July 9, 1959], No. 23836/60. Class 135. [Also in Group XXXI] In an hydraulic lift system for an agricultural tractor selector means are provided for rendering operative any one of three follow-up linkages responsive, respectively, to the position of a tractor-mounted tool, to the force exerted on the tool, or to the linear displacement of a member external to the tractor. The latter member may be a gauge wheel in contact with the ground for maintaining a constant height of an implement such as a tedder frame, or it may be a member that is displaced as a function of any physical variable such as speed, force or pressure. Alternatively, it may be a jack additional to the lifting jack and controlled by the control valve of the latter. An input lever (not shown) is connected to a rack 21c which meshes with a pinion 20 to rotate a cam-shaft 19 carrying three cams 21a for co-operation with follower rollers 23e, 231, 23p, each of which is mounted on a respective plunger 24e, 241, 24p. The plunger 24p is pivotally connected at 18p to a floating lever 16p of which the upper end is connected to a rod 40p and the lower end, through a roller 15p, abuts a lever 11 which operates the control valve (not shown) of the lifting jack 4. The other plungers 24e, 24l are connected to similar floating levers which have connections with rods 40e, 401. The cam-shaft 19 can be moved axially by a hand lever (not shown) to bring any of the cams 21a into operative relationship with its respective roller. In one of its axial positions the cam-shaft, when rotated, causes the floating lever 16p to be swung about its connection with the rod 40p and thereby to move the lever 11 to operate the control valve to cause movement of the jack 4. Movement of the latter is transmitted through a cam 44 and the rod 40p to the floating lever 16p to return the control valve to its neutral position so that positional correspondence between the rack 21c and the jack 4 is obtained. When the cam-shaft is moved axially to bring a cam 21a opposite the roller 23e the feedback to the corresponding floating lever and thence to the control valve is through a rod 50 and the rod 40e. Movement of the rod 50, which is connected to a part of the tool carried by the tractor, is resisted by a spring 52 so that the followup linkage acts to maintain a substantially constant force on the tool. An overload valve (not shown) is operated by excessive compression of the spring 52. Axial movement of the cam-shaft to bring a cam 21a opposite the roller 23l enables a feedback signal to be applied through a plunger 71 and the rod 401. The plunger 71 may be connected through a Bowden cable with a gauge wheel to maintain an implement at a constant height above the ground or it may be responsive to any physical variable such as speed, force, pressure. Alternatively, it may be movable by a further jack which is operated by the control valve after the jack 4 has been locked. Stops (not shown) which can be adjusted by a lever 38 limit the movement of the lever 11 and therefore the speed of operation of the jack 4.