GB829347A - Improvements in or relating to hydraulic power lift control means for tractors - Google Patents

Abstract

829,347. Tractor power-lift mechanisms.' INTERNATIONAL HARVESTER CO. OF GREAT BRITAIN Ltd. Jan. 22, 1958 [March 18, 1957], No. 8799/57. Class 79(1) A selector valve 6, Fig. 1, in a tractor power-lift system provides for the connection of a draft-responsive relief valve 16 providing draft-responsive load transfer. The valve 6 is slidable in a bore 3 and in the position for lowering (shown) hydraulic fluid supplied from a pump to a passage 2 is connected to pass freely to return passages 4, 5 communciating with a reservoir. For lifting, the valve is moved so that the passage 2 communicates with passages 7, 10 leading to the lifting ram cylinder 9. When the linkage is fully raised to transport position the pressure fluid passes to the return passages 4, 5 through a relief valve 33. For draft-responsive control the valve 6 is moved so that pressure fluid passes to the ram 9 and also to a passage 8 connected to the draft-responsive relief valve 16 which reduces the supply pressure in accordance with loads on a member 22 connected to the upper link of the three-point linkage. For depth limiting, the valve 6 is moved against a spring 34 to open a passage 26 leading to a follow-up valve 31 actuated according to the position of the lift arms 15 from an arm 27 on the cross-shaft 14. Variable settings are made for both draftresponsive and depth setting control by hand levers 18, Fig. 2, connected to points 24, 30 on the linkages 20, 28 operating the valves 16, 31.