Patent GB-833672-A (GB)
Title: Improvements relating to power lift systems for tractors
IPC: A01B63/14
Filed: 1956-07-03
Abstract: 833,672. Agricultural implements. ALLISCHALMERS MANUFACTURING CO. July 3, 1956 [July 11, 1955], No. 20550/58. Class 6(1). [Also in Groups XXIX and XXXI] In a power lift for an implement such as a harrow 41 towed by a tractor, and including two servomotors, one a pair of rams 21 mounted one on each side of the tractor and serving to lift the implement about its hitch point 33 on the tractor to transfer weight from the implement and front wheels 4 of the tractor to its rear wheels 3 for increasing tractive adhesion, the other a single ram 81, mounted on the implement and thrusting down a pair of ground wheels 49 to lift and support the implement, to reduce the depth of cut, and also for transport, the rams are controlled. as follows. Both rams are controlled by draught-responsive means which increases the lift with increase in draught, but the implement ram 81 is subject to a limit device so that it only comes into action after the tractor rams 21 exceed such a lift force as would result in undue transfer of weight from the front wheels. Except as regards the control of the implement ram 81 the entire arrangement is identical with that of Specification 833,670. Three alternative methods are used for the control of the implement ram 81. In the first of these the pressure line 141, 143 of the tractor rams 21 feeds the implement ram 81 through a limit valve 200, the piston 202 of which is pressed by a spring 231 into an upper position, shown, in which the implement ram 81 is connected to exhaust 241. When pressure in the tractor ram line 141, 143 reaches a value beyond which excessive transfer of weight from the front wheels would result, the pressure 143, acting in a hollow bore of the valve piston 202, thrusts the latter down, closing the exhaust line 241 and communicating the implement ram 81 with the pressure line 143, to extend the ram 81 and raise the harrow on its wheels 49. When, on reduction of pressure, the valve piston 202 returns to its upper position, collapse of the implement ram 81 is rendered gradual by saw-cut passages 238 on the exhaust land and by restrictors, one 239 in the exhaust outlet, the other in a passage 242, 244 leading from the chamber at the lower end of the valve piston. The upper position of the valve piston 202 is adjusted by a screw abutment 222, and operating pressure is adjusted by shims 243 at the upper end of the loading spring 231. In the second method, Fig. 10 (not shown), the implement ram 81 is fed directly in parallel with the tractor rams (as in Specification 833,670), but expansion of the implement ram is opposed by a strong tension spring, acting between the frame and a pivotal arm supporting the implement wheel 49 in such a way as to have a decreasing effective leverage as the wheel is lowered. In the third method, Fig. 11 (not shown), the pressure line 143 communicates with the implement ram 81 through a valve-block including an adjustably spring-pressed ball-valve for forward flow and a lightly spring-pressed ball-valve for return flow. Specifications 672,701 and 833,671 [Group XXIX] also are referred to.