Abstract: The disclosure relates to a pump having (a) a wobble plate, (b) a barrel, (c) a pair of piston assemblies reciprocated in the barrel by the wobble plate, and (c) a mechanism retaining the piston assemblies in contact with the wobble plate. In the improvement, the mechanism comprises a yoke member contacting the piston assemblies and a support member mounted to the barrel. The support member has a concave surface and the yoke member has a convex surface contacting the concave surface for bearing support. The support member coacts with the yoke member and permits oscillation of such yoke member in a plane substantially coincident with the barrel central axis. The new hold-down mechanism may be "cascaded" in that the pump may also include another pair of piston assemblies and a second yoke member contacting the second pair of piston assemblies. A bearing component, e.g., a spherical ball, is interposed between the yoke members.

Abstract: The disclosure relates to a pump having a wobble plate, at least one piston assembly reciprocated by the wobble plate, and a mechanism retaining the piston assembly in contact with the wobble plate. In the improvement, the mechanism includes a hold-down plate having a number of radially-extending retention fingers. Each finger extends into a fill opening of a separate piston assembly and retains such assembly in contact with the pump wobble plate. The piston shoe is maintained in sliding contact with the wobble plate; that is, separation of the piston assembly from the wobble plate is thereby substantially prevented.

Abstract: An electrohydraulic proportional valve wherein an electromagnetic force motor sends a mechanical signal to a pilot actuator which moves a main spool. The pilot actuator includes a pilot spool slidably received in a pilot sleeve. A feedback spool which is movable with the main spool has a camming surface against which the pilot sleeve rides. A load check valve is provided that isolates the load pressure from system pressure when desired.

Abstract: A servo valve having a pilot control balance network in which a variable orifice is established between the main control spool and the actuator member of a force motor wherein movement of said member causes the main spool to assume a new corresponding position that re-establishes the balance in said network.

Abstract: Disclosed is an electrohydraulic proportional valve comprising an electromagnetic force motor, a pilot actuator assembly, and a main spool and body assembly. The pilot actuator assembly comprises a pilot spool slidably received in a pilot sleeve and a feedback spool which has a camming surface against which the pilot sleeve rides. The camming surface comprises a first portion in which the position of the pilot sleeve is a function of the axial position of the camming surface and a second portion immediately adjacent the first portion in which the position of the pilot sleeve is constant regardless of the axial position of the camming surface.

Abstract: A method and apparatus for hydraulically driving and controlling a cooling fan.The apparatus includes a variable displacement hydraulic pump driven by a prime mover and a hydraulic motor connected to the pump and being driven thereby. The motor in turn is connected to a fan which serves to cool fluid passing through an associated heat exchanger. A temperature/force transducer monitors the temperature of fluid flowing from the exchanger and serves to control a pilot relief valve associated therewith. A pressure regulator is connected to the pump and acts in cooperation with the relief valve to control fluid pressure from the pump and thus torque of the motor and speed of the cooling fan.The method includes the steps of pumping hydraulic working fluid to a motor and driving the motor with the full hydraulic output of the pump to power a fan associated with a cooling system heat exchanger.

Abstract: Disclosed is an improved hydraulic control comprising a fail-to-neutral module. As is conventional, the hydraulic control comprises a main spool and a fluid flow path comprising a bridge circuit including a driver stage. The fail-to-neutral module comprises means defining a fail-to-neutral orifice which (a) is located in the fluid flow path upstream of the bridge circuit and (b) has a relatively large flow area but a maximum dimension smaller than the smallest orifice in the pilot stage. Preferably the means comprise a pin positioned through a hole, the pin and the hole both being circular in cross-section and coaxial, and the fail-to-neutral orifice is the clearance between the pin and the boundary of the hole.

Abstract: Disclosed is a method of preventing thermal shock to a hydraulic motor in an open-loop hydraulic system. The method comprises the step of circulating warm oil through the motor when it is not in use. Preferably the method includes the further step of returning the warm oil to the tank after it has passed through the motor, and where appropriate it may also include the preliminary step of lowering the pressure of the warm oil before it is passed through the motor.The method is disclosed as applied to a vane motor, and means for carrying it out in that context are also disclosed.

Abstract: An electromechanical force motor including an elongate magnetic casing which coaxially enhouses a magnetic armature. An annular electromagnetic coil surrounds the armature and is axially positioned between a pair of permanent magnets having axially directed poles. A magnetic pole is positioned at each end of the armature in a posture juxtaposed to but spaced from the ends of the armature to provide a magnetic flux gap between the armature and poles. A pushrod is connected to one end of the armature and projects outwardly from the casing to produce work upon excitation of the electromagnetic coil.