GB813204A - Improved hydraulic system for tractors - Google Patents

Abstract

813,204. Tractor power-lift mechanisms. FORD MOTOR CO. Ltd. June 21, 1957 [Oct. 29, 1956], No. 32873/56. Class 79(1) In an automatic depth control arrangement for ground working implement attached to a tractor the force in the upper link 3 is balanced by hydraulic pressure upon either end of a double acting piston 13, the pressure being derived from two streams of fluid passing over the opposite ends of the piston 13 and influenced by endwise movement of the piston 13, the derived pressures actuating a valve for controlling the depth of working through the lifting ram 10. The upper link 3 is attached to the tractor through a link 4 connected at its upper end to the piston 13 through an extension 13a. Two independent streams of fluid are fed to the cylinder 12 of the piston 13 from a pump 21 through a flow divider 21a and pipes 19, 20. The streams leave the cylinder through valve ports 15 partially covered by the piston 13 and leading to a common return 16. The lifting arm 6 for raising or lowering the links 1 is actuated by the ram 10 to which pressure fluid is supplied from a pump 44 through pipes 45, 47 and a servo control-valve assembly 24 actuated for raising and lowering the lift linkage by a lever 78. The valve assembly 24 comprises a coaxially slidable spool valve 41 and sleeve valve 26, spool valve 41 being operable through a floating lever 79 which is moved by the control lever 78 through a crank 77 engaging in a slot 79a. Followup is provided by a cam 74 on the crossshaft 7 of the lift linkage which moves the end 80 of the lever 79 through a pivoted finger 73 and spring loaded push rod 75. The lever 79 is loaded by a spring 81, the slot .79a permitting free movement when the lever 78 is set at the fully lowered position. Movement of the spool valve 41 by the lever 78 for raising the linkage results in passage of pressure fluid through a cross-port 37 of the sleeve valve 26 from. cross-ports 38, the fluid passing to the ram 10 over a non-return valve 48. For lowering the linkage, opposite movement of the valve 41 results in escape of ram fluid through a passage 46 and cross-ports 39 in the sleeve valve 26 leading to a common return bore 41a, b in the spool 41. During normal raising or lowering, or for positive depth control the sleeve valve 26 is locked axially by fluid trapped in end chambers 27, 28 which are connected by passages 29, 30 to a spool valve 51 under the manual control of a lever 69. For automatic depth control the lever 69 is actuated to move the spool valve 51 to a position located by a spring-loaded ball 54 at which, the end chambers 27, 28 of the sleeve valve 26 are connected through passages 17a, 18a to opposite ends of the piston 13 so that the sleeve valve 26 is moved under the influence of the draft load. Movement of the ram 10 therefor takes place to raise or lower the implement according to the draft load determined by the setting of the lever 78 until the spool valve 41 is again brought to the neutral position relative to the sleeve valve 26 through the follow-up system 74, 79. A bias spring 32 restores the sleeve valve to its normal central position when the draft load is released. Overload relief is provided by a blowoff valve 95 connected to the cylinder 12 of the piston 13 and may be set to different pressures by varying the loading on a spring 97 by cam 93 which is rotatable to different positions by a lever 92. Auxiliary hydraulic systems may be connected to the valve assembly 24 through a bobbin valve 57 the supply and return pipes 62, 63 being interconnected when the systems are not in use.