Abstract: An axial piston hydraulic unit has a valve plate assembly positioned between a head and a rotatable cylinder barrel. The assembly includes a pair of valve plates stacked together to function as a single valve plate. The valve plate assembly defines a restricted flow path for providing initial communication between an approaching piston bore of the rotatable barrel and an intake port and a discharge port extending through the pair of plates. A first portion of the flow path is defined in the valve plate adjoining the head and a second portion of the flow path is defined in the valve plate adjacent the barrel. The stacked valve plates are hydraulically held together by a pair of pressure balancing devices.

Abstract: A variable displacement axial piston hydraulic unit includes first and second control pockets individually disposed between first and second arcuate shaped fluid passages, a first electrohydraulic valve for controlling fluid flow between the first control pocket and the first fluid passage and a second electrohydraulic valve for controlling fluid flow between the second passage and the second control pocket. A controller outputs first and second control signals to the first and second electrohydraulic valves in response to receiving a command signal so that the tilt angle of a swashplate is controlled to obtain a desired operating parameter. An angle detector, a pressure detector, and a speed detector provide feedback signals to the controller for determining when the desired operating parameter has been obtained.

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: 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: A pilot-operated pressure relief valve is provided for a hydrostatic transmission. The override valve is in the closed circuit loop, which includes a pair of multi-function valves and a displacement control valve. The pressure override valve includes a spool slideably mounted within a body so as to be responsive to a pressure differential created by pilot flow through the override valve. The spool is biased to a normal position which provides fluid communication between a pressure charge source and the displacement control valve. As the pressure differential in the override valve increases, the spool shifts so as to close such communication from the charge source to the control valve, thereby defeating the pressure signal from the control valve to the servos of the hydrostatic transmission pump.

Abstract: A spool valve has a valve body with an elongated cylindrical bore therein. Fluid passageways extend in a radial direction through the valve body and communicate with the interior bore. A peripheral port edge is defined by the intersection of the bore and the passages. A cylindrical valve spool is slidably mounted in the bore to close and open the passageways with respect to the bore. The valve spool has a cylindrical outer surface and at least one planar circular surface with a peripheral metering edge therebetween. The peripheral metering edge has a plurality of tapered notches therein which are adapted at times to overlap the peripheral port edge to permit fluid flow between the bore and the passages.

Abstract: A removable fluid seal has a first deforming pin seated on a dead end of a fluid passage and a second deforming pin positioned in the opposite end of the fluid passage, with a spherical elastomeric member positioned between the first and the second deforiming pins. A threaded plug is axially advanced through the fluid passage to force the deforming pins towards each other and resiliently distort the elastomeric member into a deformed state in which an outer surface of the sphere is forced into sealing engagement with the sidewall of the fluid chamber.

Abstract: A hydraulic displacement unit of the axial piston fixed displacement type having a rotatable cylinder block with axially reciprocal pistons, each of which has a slipper associated with a swash surface, as defined by a thrust plate, and structure for obtaining fixed maximum clearance between the slippers and the thrust plate. This fixed maximum clearance is achieved by the use of the controlled positioning of a slipper retainer bearing relative to the surface of the thrust plate by use of a tubular member positioned within the cavity of the unit housing which is securely located and positioned by assembly of an end cap to the housing to be located between the thrust plate and the end cap.