Abstract: A tractor hydraulic power lift mechanism has a known manually adjustable flow control valve for regulating the rate of lowering an implement. However, when the valve is so adjusted that a heavy ground-working implement is lowered to ground level at a rate slow enough not to cause damage, the implement is then very slow to penetrate the ground to the desired working depth. A manually operable overriding mechanism preferably actuated by the main hand lever of the power lift mechanism is therefore provided to enable the valve to be moved temporarily into its fully open position and allowed to return to its adjusted position. The overriding mechanism is operated as the implement reaches ground level and released when it reaches its working depth.

Abstract: Tractor hydraulic power lift mechanisms may have automatic draft control signals fed back to them from lower link draft force sensing systems. One such system has two bowed rearwardly-extending leaf springs anchored to the tractor frame at their front ends, two laterally-spaced arms pivoted at their upper ends to the tractor frame and at their lower ends to the rear ends of the respective springs, a cross-bar universally supported by the lower ends of the respective arms and having two attachment points laterally offset from said arms to which the front ends of respective lower hitch links are universally connectible, and linkage for deriving a control signal from the fore and aft displacement of the mid-point of the cross-bar. However, the cross-bar is stressed in bending to the detriment of the control signal accuracy. To avoid this, a summating bar is universally connected between said arms and the control signal derived from a point on the unstressed summating bar.

Abstract: A power steering system for a wheeled agricultural tractor includes a pump circulating oil through a known steering-wheel-operated hydrostatic steering unit. A double-acting hydraulic cylinder communicates via conduits with the steering unit and is connectible to the tractor frame. A piston having a rod which projects from one end only of the cylinder is connectible to steer the tractor. A valve block interposed in the conduits causes oil displaced from the piston-rod end of the cylinder to flow to its other end when oil under pressure is supplied to said other end, and causes oil displaced from said other end to return directly to the steering unit when oil under pressure is supplied to the piston-rod end of the cylinder.

Abstract: Adjustable mixed automatic height and draft control apparatus for a tractor power lift mechanism includes a height control rocker actuated by the tractor's rockshaft, a draft control rocker actuated by the tractor's hitch linkage, and a first balance lever moveable relative to either one of the rockers by movement of the other. A control linkage has its point of connection to the first balance lever variable by a first hand lever to adjust the mixture of height and draft control, a second hand lever gives over-riding manual control of the power lift mechanism, and a second balance lever is moveable relative to either one of the control linkage and the other hand lever by movement of the second. The second balance lever actuates the control valve of the power lift mechanism.

Abstract: A tractor has a power lift mechanism controllable automatically in known manner by implement draft load sensing apparatus. This apparatus comprises two leaf springs which are spaced apart in a lateral direction relative to the tractor, the springs being connected at their front ends to the tractor and being adapted to flex in the lateral direction but being stiff longitudinally of the tractor and vertically; two hitch links each connected to the rear end of one of the springs; and equipment for transmitting to the power lift mechanism a control signal derived from any variation in the distance between the flexible portions of the springs.

Abstract: A compression spring capable of having a very high rate comprises co-axial annular plates alternating in an axial direction with diametrical strips adjacent ones of which are perpendicular to one another. The spring may comprise a stack of washers with diametrically opposed pads or radial ribs on their faces, said washers having non-circular bores enabling them to be located non-rotatably on a correspondingly non-circular central support. Alternatively, the spring may comprise a single tubular element with pairs of diametrically opposed tangential slots perpendicular to its axis which extend from its periphery into its bore.