Patent GB-773401-A (GB)
Title: Improved power operating system for tractor hitch linkages
IPC: A01B63/112
Filed: 1952-11-03
Abstract: 773,401. Tractor power lift mechanisms. FERGUSON, Inc., H. Nov. 3, 1952 [Nov. 1, 1951], No. 27571/52. Class 79(1). [Also in Group XXIV] In a tractor power lift mechanism having a pressure fluid operated actuator 40 for the lift linkage under the control of a valve 59, the valve being actuated through a link 66 by a control member 32 under the influence of draft load on the linkage, the link 66 is adjustably guided in order to vary the range of movement of the valve for a given movement of the member 32. As shown the upper link of the power lift mechanism is connected to the draft control member 32, Fig. 3, acted on by a spring 31 and pivoted at 126 to an arm 127, Fig. 4, on a shaft 128 also carrying an arm 129 having a shoe 130 to which is secured at 130<SP>1</SP> one end of a flat metal strap 132. The strap passes round a sheave 133 and has its other end secured to a sheave 135 keyed to a hollow shaft 136 connected by a one-way locking means to a manually operable quadrant lever 65. The locking means comprises a pair of lugs 143, Fig. 11, on the shaft 136, a lug 144 on a shaft 146 carrying the lever 65, and a key 147 between the lugs urged into engagement with a casing 141 by a spring 148 guided by a pin 149, whereby torque applied to the shaft 136 by tension in the strap 132 acts through the lugs 143 to further wedge the key against the casing and torque applied to the shaft 146 by the lever 65 acts through the lug 144 to release the key from its wedging position and permit rotation of the shafts 136, 146. The sheave 133 is rotatably mounted on a pin 134 carried by an element 100 pivotally connected by a pin 101 carried between bars 97 of a link 95. The bars 97 also carry rollers 70, 98, the roller 70 normally engaging a cam surface 71 carried by a bracket 72 secured to an engine driven pump 52, and the roller 98 engaging a cam surface 99 formed on a plate 105 confined with a circular opening 107 in the bracket 72. The plate 105 is adjustable within the opening 107 by means of fingers 108 carrying a pin 111 arranged within a slot 112 in the bracket 72. The pin 111, Fig. 12, is carried by a crank arm 117 on a shaft 118 also carrying a hand lever 121. A pin 96 which carries the roller 70 carries pairs of strips 151, 152 constituting the link 66. Each strip is formed with an aperture 153 and a slot 154, and a spring 159 is arranged between lugs 157, 158 on each pair of strips and tends to shorten the combined length of the pair of strips. A pin 75 at the other end of the link 66 engages a crank arm 76 non-rotatably fixed to a shaft 77 journalled in the bracket 72. The shaft 77 also carries an arm 87 and rotatably mounts a sleeve 80 having arms 79 and a finger 89. A one-way operating connection is provided between the shaft 77 and sleeve 80 by means of the finger 89 and arm 87, the arm 87 adjustably carrying a bolt 90 engageable with a flange 88 on the finger 89. The arms 79 are connected to a valve plunger 60 co-operating with ports 61, 62 in the valve 59 whereby, when the ports 61 are open, fluid is taken by the pump 52 from a sump 63 and fed through a pipe 51 to the actuator 40 comprising a cylinder containing a piston 43 connected by a rod 44 to an arm 47 on a shaft 27 carrying further arms 28 connected by links (not shown) to the lower links of the power lift mechanism, and, when the ports 61 are open, fluid in the cylinder is discharged to the sump 63. With the plunger 60 in the position shown in Fig. 3 fluid is locked in the cylinder and the power lift links are retained in position. A spring 92 is provided urging the arms 79 into a position in which the ports 61 are open and the power links raised. The spring 92 also urges the link 66 upwardly and forwardly whereby a cross member 81 on the arms 79 engages the pump 52. Outward movement of the piston 43 relative to the cylinder (i.e. the uppermost raised position of the power lift links) is limited by the piston 43 engaging and moving the hooked end 163 of a bar 161 slidably guided by members 162 mounted on the actuator 40, such movement being transmitted by a shoulder 164 on the bar 161 to a lever 166 pivoted at 167 on the pump 52 whereby the rear edge of the lever engages bushings 168 carried by the pin 96 and the plunger 60 is moved to the position shown in Fig. 3 through the link 66 and arms 76, 79. In operation the depth of operation of an implement carried by the power lift links is determined by the lever 65 which rotates the sheave 135 and hence varies the length of the strap 132, thus determining the neutral position of the plunger 60 for any position of the draft control member 32. Movement of the member 32 under the effect of draft variation is transmitted through the strap 132 and sheave 133 to the link 66 and hence through the arms 76, 79 to the valve plunger 60. Movement of the lever 121 varying the position of the cam 99 between substantially horizontal and vertical positions alters the movements of the rollers 70, 98 along their respective cam surfaces on a movement of the draft control member 32, and hence varies the movement ratio between the member 32 and plunger 60 to take account of differing ground reactions of implements. In order that excessive tension in the upper link of the power lift mechanism does not cause excessive movement of the plunger 60 the strips 151, 152 lengthen against the action of the springs 159 and in the event of further movement the roller 70 leaves the surface 71 to engage a further cam section 71<SP>1</SP> having an arcuate contour centred on a bolt 73 securing the bracket 72 to a lug 74 on the pump 52, the contour permitting the roller 70 to be brought back to the section 71 by the springs 159 after the removal of the excessive tension. In order to unload the system when the draft load on the lift linkage becomes excessive (e.g. implement striking obstruction) the pressure fluid in the cylinder is released by automatically opening a valve 170. The valve is opened by an arm 176 on the shaft 128 pushing a rod 174 guided by a bracket 175, the rod 174 co-operating with a valve actuating lever 171.