Patent GB-743118-A (GB)
Title: Power operating system for tractor hitch linkage
Inventor: BUNTING ERNEST VIRDEN
IPC: A01B63/111
Filed: 1951-02-26
Abstract: 743,118. Fluid-pressure servomotor control systems. FERGUSON Inc., H. Feb. 26, 1951, No. 4577/51. Class 135. [Also in Group XXXI] Relates to a tractor hydraulic-lift system including a ram 36 for raising the lift arms 43, a plunger 101 connected to the upper hitchlink and movable, against the action of a spring 102, proportionally to the draught-load on the links, a valve 50 for controlling the flow of fluid to and from the ram and motiontransmitting linkage between the plunger 101 and the valve 50 so that valve is movable in response to draught-load changes. According to the invention the motion-transmitting linkage is relieved of the force applied by the spring 102 and is adjustable, without altering the position of the valve, so as to vary the sensitivity of the system to draught variations. The lift arms 43 are integral with a shaft 42 and an arm 41 pivoted to the piston-rod 40 of the ram. The valve-actuating linkage comprises a bar 100 pivoted at its lower end to a toggle-link system 140, 141 operating a lever 142 connected to the valve-stem 153. The toggle-links consist of the link 140 pivoted at its top end to a normally-fixed stirrup 143 and at its lower end to the bar 100 and the link 141. The link 141 is composite and includes a portion 184 pivoted at 18 to the main link and at 154 to the valve-actuating lever 142, the two parts abutting at a stop 188 and being held in contact by a spring 117. In the event of over-travel of the bar 100, during operation, the two parts of the link 141 act as an elbow-joint and separate pivotally until the ram-cylinder responds, to close the two parts of the link 141 together again. The bar 100 is moved longitudinally by two alternative mechanisms in one of which the arms 43 are raised and lowered in response to draught-changes (i.e. draught-control) and in the other of which the arms have a follow-up action on a lever 60 controllable by the tractor driver (i.e. position-control). The alternative mechanisms include coaxial pulleys 72, 73 carried on sleeves which can be selectively keyed to the shaft 70 in turn keyed' to the lever 60. Draught-control.-For draught-control, the pulley 72 is keyed to the shaft 70. A steel band 115 is secured to the pulley at both ends, the doubled loop being then passed over a pulley 114 and around a pulley 116. The pulley 116 is mounted between parallel arms forming the beam 100, and the pulley 114 is pivoted on an arm 112 freely pivoted on the shaft 70 and connected to the plunger 101 by a link 109. The rod 100 can therefore be moved to alter the valve-position by rotation of the shaft 70, through the hand-lever 60 or movement of the arm 112 under the action of the plunger 101, both movements having a tightening or slackening action on the band 115. When the hand-lever is set in any given position the lift-links will be raised or lowered until the draught-force on the implement compresses the spring 102 sufficiently for the linkage to return the valve 50 to its neutral position. Position-control.-With the pulley 73 keyed to the shaft 70 and the pulley 72 unkeyed, the band 115 becomes slack and control of the bar 100 is effected by a band 120 fixed at its ends to the pulley 73 and to a sleeve 121 integral with the rock-shaft 42. The band passes around a pulley 122 carried by one arm 124 of a bell-crank the other arm 127 of which is pivoted to the bar 100 at 128. Movement of the hand-lever 60 in either direction causes a tightening or slackening of the band 120 until the rock-shaft has followed up sufficiently to nullify the effect and return the valve 50 to neutral. Raising for transport.-In order to raise the lift-arms 43 to an upper limit for transport irrespectively of the type of control in use, the pulley 73 is associated with a pair of segmental plates 130 with which it has a pin and slot connection 131, 132, the plates being otherwise free on the shaft 70. Movement of the hand-lever 60 to its upper limit rotates the segments until an abutment 133 carried thereby contacts an adjustable screw stop 134 on the tractor casing. Subsequent rotation of the rock-shaft 42 winds up the band 120 to shut off the valvo as the lift-arms reach their uppermost position. The pin and slot connection 131, 132, renders this control inoperative during normal working. Sensitivity control.-The sensitivity of the system will depend upon the extent of the valve-movement for a given movement of the bar 100. This is adjustable by varying the angle between the links 140, 141. The stirrup 143 is pivoted at 162 coaxially with the pivot between the levers 140, 141, its upper end being connected to a hand-lever 165 accessible to the tractor driver. The maximum and minimum sensitivity-settings are shown in Figs. 6 and 7 respectively. Overload-release valve.-The hydraulic system includes an overload-release valve similar to that described in Specification 743,117, this valve being so positioned to spray the bands, pulleys and levers with oil in the event of overload. Specifications 470,068, [Group I], 470,069, 510,352, (both in Group XXXI], and 738,561 are referred to.