Abstract: Hydraulically actuated grapple tongs mounted to a log skidder are useful, for example, in gripping a bunch of logs that are being dragged from one site to another. Maintaining a grip on the logs during the dragging operation with known hydraulic systems generates heat within the hydraulic systems. The subject hydraulic system includes first and second variable displacement load sensing pumps commonly connected to a control valve which controls fluid flow to an actuator. A load pressure signal is directed through a first signal line to a displacement controller of the first pump and to a pressure responsive valve normally resiliently biased to a position at which the first signal line is communicated to a displacement controller of the second pump. When the load pressure signal in the first signal line exceeds a predetermined value, the valve is moved to a position blocking communication of the load signal to the displacement controller of the second pump.

Abstract: A flexible retention mechanism for maintaining a positional relationship between a bearing cage of an arcuate roller bearing assembly and a swashplate supported by the bearing assembly includes a flexible retainer connected to the bearing cage and having a pair of end portions resiliently engaging a pair of anchor pins extending outwardly from the swashplate.

Abstract: An electrohydraulic steering system has a three position pilot operated directional valve disposed between a variable displacement pump and a pair of steer cylinders. The directional valve controls the direction of fluid flow from the pump to the steer cylinders while the displacement of the variable displacement pump is controlled to vary the rate of fluid flow to the steer cylinders. The directional valve is moved to an on position in response to a pilot signal delivered thereto from a pilot valve device while the displacement setting of the variable displacement pump is varied by an electrical signal delivered to a displacement controller from a position sensor mechanism.

Abstract: An axial piston hydraulic device includes a holddown device for maintaining the slippers swivably connected to pistons in sliding contacting with a cam surface of a swashplate. The holddown device also includes a nested wave spring disposed to resiliently urge a holddown sleeve away from a cylinder barrel for biasing a holddown plate engaging the slippers toward the cam surface.

Abstract: An accumulator charging valve has a first valve spool determining a cut-in pressure level at which fluid from a pump is directed to an accumulator and a second valve spool determining the cut-out pressure level at which fluid is no longer directed to the accumulator. When the pressure at the accumulator reaches a predetermined high level, the second valve spool moves to a position communicating an inlet port with an intermediate passage. The first spool is normally at a position blocking the intermediate passage from an outlet port so that a flow path is established through a pair of orifices reducing the pressure in the intermediate passage and the inlet port. The reduced pressure is transmitted to an actuating chamber to hold the second valve spool in the above noted position and to a pump displacement controller to destroke the pump to a low standby pressure displacement.

Abstract: A steering control system for an autonomous machine has a manual steering control valve for directing fluid from a pump to either a head end chamber or a rod end chamber of a hydraulic steering actuator. In one embodiment, an electrically actuated steering valve device is disposed in series flow relationship between the pump and the manual steering control valve and is operative to direct fluid from the pump to the head end and rod end chambers. In another embodiment, a electrically actuated device mechanically actuates the manual steering control valve for steering the machine.

Abstract: An end-of-stroke bidirectional snubber for a suspension cylinder includes an elongate snubber element having a first flow regulating end portion co-acting with an annular edge for gradually restricting fluid flow from a head end chamber as the piston approaches an end wall of a casing to snub end-of-stroke retraction motion of a piston rod. The snubber element also has a second flow regulating end portion which coacts with a radial passage for gradually restricting fluid flow from a rod end chamber as the piston approaches an end of cap to snub end-of-stroke extension motion of the piston rod.

Abstract: An electrohydraulic steering system has a pair of proportional valves for controlling displacement of a steering valve for normal steering functions. The proportional valves are selectively energized by a position sensor in response to rotation of a steering wheel. However, should an electrical malfunction occur, rotation of the steering wheel beyond the normal operating range causes a steering control member to mechanically move an armature of the proportional valves through a spring to provide mechanical/hydraulic steering. Making the armatures of the proportional valves responsive to a mechanical input through the springs provides a simple, cost effective mechanical/hydraulic backup for the primary electrohydraulic steering control.

Abstract: A method of flushing a closed loop hydraulic system utilizes a pair of adapters temporarily disposed between a drive motor and a pair of hoses during the flushing procedure. The adapters block communication between the hoses and the motor and cover the inlet/outlet ports of the motor. By connecting a case drain line to one of the adapters and running the engine to drive a charge pump, oil is circulated through the hose connected to that adapter, the case drain line, a case drain line filter and is returned to a tank. The case drain line is then switched to the other adapter so that oil from the charge pump is circulated through the other hose.

Abstract: A hydraulic control system is designed to permit the use of a plurality of small substantially identical existing valve assemblies in place of a lesser number of larger valve assemblies. In one embodiment, a first pair of variable displacement load sensing hydraulic pumps communicate with a manifold connected to a first valve assembly and another pair of variable displacement load sensing hydraulic pump communicate with a second manifold connected to second and third valve assemblies. A crossover conduit interconnects the manifolds so that fluid from all four pumps can be used by any one of the valve assemblies or shared by two or all three of the valve assemblies. In another embodiment, a third pair of variable displacement load sensing hydraulic pumps communicate with the first manifold 12 which also has another valve assembly connected thereto.

Abstract: A force feedback popper valve has a valve element for controlling fluid flow from an inlet port to an outlet port. A meter-in orifice communicates pressurized fluid from the inlet port to a control chamber above the valve element. A pilot valve provides a meter-out orifice between the control chamber and the outlet port to selectively reduce the pressure level in the control chamber in response to a control force applied to the pilot valve. A feedback spring is disposed in the control chamber between the valve element and the pilot valve so that displacement of the valve element is proportional to the control force exerted against the pilot valve.

Abstract: Fluid regeneration circuits are useful for filling expanding sides of a hydraulic cylinder with fluid being exhausted from the other side. The currently available circuits pass the excess fluid not needed for filling the expanded side of the cylinder through the directional control valve to the tank such that the directional control valve must be actuated for the regeneration valve assembly to function. A combined meter-out and regeneration valve assembly of the present invention is used in a hydraulic system having a directional control valve for metering in pump to cylinder fluid flow and includes a meter-out valve to meter-out cylinder to tank fluid flow from a head end actuating chamber. The fluid passing through the meter-out valve passes through an exhaust conduit to a tank bypassing the directional control valve. This permits the meter-out valve to be used independently of the directional control valve to retract a hydraulic cylinder.

Abstract: Snubbers are useful in dampening inertia loads at the end of stroke movement of a hydraulic motor. The known snubbers usually restrict fluid flow therethrough in the non-snubbing mode thereby slowing the response of the motor in the opposite direction. The subject self-energizing snubber includes a snubber piston which is moved from a first operative position to an intermediate operative position by contact with an end surface and then hydraulically moved to a second position by differential pressure established between an actuating chamber and a fluid passage. The snubber piston defines a variable rate flow path continuously communicating the actuating chamber with the passage. A maximum flow rate is established through the flow path at the first operative position while a minimum flow rate is established through the flow path at the second operative position.

Abstract: Transmitting actuating forces from an actuator to a swashplate of an axial piston unit through a pin extending from a lever of the swashplate induces torsional stresses in the lever. The present invention overcomes this problem by securing a lever to a swashplate so that a distal end portion thereof extends into a slot of an actuator. The distal end portion has a cylindrical shaped surface pivotally seated in a mating socket formed in a slide block positioned within the actuator slot. The actuating forces transmitted from the actuator to the lever are thus transmitted in a straight line motion with minimal torsional stresses introduced into the lever.

Abstract: Filter devices are useful in hydraulic systems for removing contaminants or foreign particles from the oil in the hydraulic system. One of the problems encountered with such filters is that they are subjected to high pressure drops thereacross when the oil is cold. The subject filter device of one embodiment includes a pump driven by a two-speed electric motor. When the oil temperature is below a predetermined temperature, the pump is driven at a normal speed for increased efficiency and the pressure drop across the filter is within an optimal range. When the temperature of the oil is below a predetermined temperature, the pump is driven at a low speed so that the pressure drop across the filter remains within the optimal range. In another embodiment, an electric motor driving the pump is stopped when the oil temperature is below the predetermined temperature.

Abstract: A follow up mechanism for maintaining a timed positional relationship between a bearing cage of an arcuate roller bearing assembly and a swashplate supported by the bearing assembly includes a flexural elastic link pivotally connected to the bearing cage and having first and second ends slidably disposed within a first bore in a pump housing and a second bore in the swashplate, respectively. The bores are in axial alignment with each other when the swashplate is in the equivalent of its centered position thereby allowing blind assembly of the follow up mechanism thereby eliminating the need for an access opening in the side of the pump housing and the associated cover, gasket and bolts.

Abstract: Arcuate bearings are useful, for example, in pivotally supporting a cradle swashplate of axial piston variable displacement hydraulic devices. The bearings of known hydraulic devices have either been a pair of laterally spaced roller bearings assembly or a pair of laterally spaced sleeve bearings. The subject hydraulic device includes a roller bearing assembly positioned between the swashplate and the housing at the side of the swashplate subjected to high loads and a less expensive sleeve bearing positioned between the swashplate and the housing at the other side of the swashplate subjected to low loads. By using this combination of bearings, the overall cost of the hydraulic device is reduced without impairing the operation of the hydraulic device.

Abstract: Regeneration valves are useful in directing fluid expelled from a contracting chamber of a hydraulic actuator to its expanding chamber to increase the actuation speed of the actuator. The present remotely controlled regeneration circuit improves the controllability of the regeneration valve by positioning the regeneration valve between the pump and the control valve so that the fluid expelled from the contracting chamber and combined with the pump flow to the expanding chamber passes through and is controlled by the control valve. The regeneration valve is moved to its regeneration position by pressurized fluid from a solenoid valve which can be selectively energized by the operator manually closing a switch mounted to a control lever.

Abstract: A displacement controlled hydraulic proportional valve is provided with a dashpot disposed between a main valve spool and a pilot valve spool to stabilize the proportional valve. The dashpot includes a bore in a spring retainer engaging the main valve spool and a plunger axially extending from a spring retainer engaging the pilot valve spool with the plunger extending into the bore to define a dashpot chamber. The plunger is sized to permit restricted fluid flow thereby when the spools move relative to each other thereby dampening relative movement between the valve spools. Dampening the relative movement between the valve spools drastically reduces the amount of overshoot by the main valve spool.

Abstract: A displacement controlled hydraulic proportional valve has a spring retainer and a force feedback spring serially disposed between a pilot valve spool and a main valve spool in a control chamber. An arcuate convex end portion on the pilot valve spool extends into a cylindrical pocket in the spring retainer essentially defining a contact point through which force is transferred between the pilot valve spool and the retainer. The point contact minimizes side loading on the pilot valve spool due to buckling of the feedback spring to minimize tendency of the pilot valve spool to stick during operation.