Position control for parallel hydraulic systems on an agricultural implement

Claim 1

In an agricultural implement including a transversely extending frame adapted to be moved forwardly over the ground and rockably mounted on transversely aligned forward wheels, a toolbar mounted on a rear portion of frame and adapted to carry earthworking tools whereby rocking movement of the frame about the forward wheels will raise and lower any tools mounted on the toolbar between working and transport positions, a plurality of gauge wheel means mounted on a rear portion of the frame for generally vertical movement with respect to the rear portion of the frame, the gauge wheel means being interconnected with the frame by a plurality of double-acting extensible and retractable hydraulic motors each comprising a cylinder having rod and anchor ends and a rod reciprocally mounted within the cylinder and projecTing from the rod end thereof, whereby extension and retraction of the motors will raise and lower the rear portion of the frame by rocking the frame about the forward wheels, first fluid line means connecting the anchor ends of the cylinders in parallel, second fluid line means connecting the rod ends of the cylinders in parallel, third and fourth fluid line means connected respectively to the first and second fluid line means and being alternately connectible with a source of fluid pressure and a fluid reservoir whereby the toolbar can be raised and lowered by connecting the third and fourth fluid lines respectively to the source of fluid pressure, the improvement comprising: valve means movable between open and closed positions interposed in the third fluid line means, and means responsive to the retraction of the rod of one of the motors to a predetermined position to move the valve means to the closed position whereby after the toolbar has been lowered to a predetermined position additional lowering movement is prevented and the gauge wheel means will equally share the weight of the rear portion of the frame irrespective of the ground contour beneath the frame.