Abstract: In a preferred embodiment of the invention an extension section of a frame is held down in its locked position by the same mechanism that folds and unfolds the frame extension. When the frame extension is in its locked down position, it bears against a limit stop that precludes further movement in an unfolding direction. An operating link that is pushed and pulled by a hydraulic cylinder to manipulate the frame extension is controlled in such a way by a guide member that the line of action of the link is directed transversely toward a guide surface of the guide when the frame extension is in its unfolded position. Thus, only a small amount of force is required from the hydraulic cylinder at that time to maintain the link in its locked position, since most of the load from the link is born by the guide surface at this time. In a preferred embodiment, the line of action of the link is approximately perpendicular to the guide surface.

Abstract: In a preferred embodiment of the invention an extension section of a frame is held down in its locked position by the same mechanism that folds and unfolds the frame extension. When the frame extension is in its locked down position, it bears against a limit stop that precludes further movement in an unfolding direction. An operating link that is pushed and pulled by a hydraulic cylinder to manipulate the frame extension is controlled in such a way by a guide member that the line of action of the link is directed transversely toward a guide surface of the guide when the frame extension is in its unfolded position. Thus, only a small amount of force is required from the hydraulic cylinder at that time to maintain the link in its locked position, since most of the load from the link is born by the guide surface at this time. In a preferred embodiment, the line of action of the link is approximately perpendicular to the guide surface.

Abstract: The spring trip assembly has lever mechanism between the shank and the compression spring which causes the trip-out force of the shank to drop sharply once the relatively high, initial trip-out force level has been reached, thus permitting the shank to slide up and over obstructions without breakage. The compression spring is actuated from both ends simultaneously as the shank rises so that although the trip force drops off quickly, energy also builds up quickly in the spring. Thus, the trip force does not drop as low as it otherwise would, assuring that ample return force is available to reset the shank down into the soil in its working position. Various components of the assembly can be removed and replaced easily without disassembling the entire unit from the tool bar.