| 摘要 |
A double arch center frame employs a depending center arch to mount by a ball and socket connection the leading end of a draw bar and yoke assembly. Bell cranks pivotably mounted to yoke plates borne by the arched center frame intermediate of the center arch and the rear arch have arms pivotably coupled to respective hydraulic lift cylinders disposed on opposite sides of the center frame and to a like member common to the bell cranks. A side shift hydraulic cylinder is pivotably connected at one end to one side of a subframe rotatably supporting a mold board assembly and at the other end to a link member intermediate of its pivot connections to a second arm of the bell crank members. The forward arched end of the center frame is articulated to a front single axle tractor for rotation about right angle, vertical and horizontal axes, and the rear arched end of the center frame is hinge connected to a rear single axle tractor for pivoting about a horizontal axis. Multiple hydraulic crab steering cylinders force angulation of the tandem wheel tractors relative to respective ends of the double arch center frame to move the unit selectively into laterally offset crab steering conditions for the dual tractors for soft ground grading. In a further embodiment, a cab is provided on the rear tractor. Also, the rear steering cylinder mounts are moved closer to the center of the cross bar and the king pin hinge joint brackets are advanced forward of the rear end of the center frame.
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