Abstract: A hydrostatic transmission control system is provided of the type utilizing a main control valve to vary the control pressure being ported to the strokers which control the swashplate position of a variable displacement pump. The control valve includes a control port connected to a source of control pressure fluid and a pair of stroker ports, each of which is connected to one of the strokers. The control valve includes a valve member having a valve land associated with each of the stroker ports, the lands preferably being either zero-lapped or under-lapped and disposed to provide a substantially zero neutral band to provide an improved control response when it is necessary for the valve member to cross the neutral band and port control pressure to the opposite stroker.

Abstract: A fluid controller is disclosed of the type including a primary valve member, and a follow-up valve member. The controller includes a load signal port and a load signal chamber. Fluid is communicated from the inlet port to the load signal chamber, and the valve members define a neutral orifice communicating between the load signal chamber and the return port when the valving is in neutral. The valving defines operating orifices communicating fluid from the load signal chamber to the main fluid path, downstream of the main flow control orifice, when the valving is shifted away from neutral. The operating orifices have a smaller orifice area when the valving approaches maximum deflection. The result is a substantially higher differential operating pressure, and a higher flow rate than would otherwise be possible at that particular valve deflection.

Abstract: An electro-hydraulic control for a hydrostatic transmission including a variable displacement hydraulic pump, a fixed displacement hydraulic motor, and fluid operable strokers to vary the displacement of the pump. The electro-hydraulic control is in series between the charge pump and the standard manual controller and determines the pressure of the charge fluid ported to the standard controller. The electro-hydraulic control includes a spool biased toward a first position to port fluid from the charge pump to the standard controller, and biased toward a second position to relieve to tank the pressure of fluid ported to the manual controller. The biasing toward the second direction is accomplished, in part, by pressure in a fluid chamber exerting a biasing force on the spool, the fluid chamber being in communication with drain through a variable orifice which is variable in response to a pressure command signal.

Abstract: A controller for fluid pressure operated devices such as power steering systems. The controller is of the type having a primary, rotatable valve member and a follow-up valve member and including a fluid meter having a metering member coupled to the follow-up valve member. The valving defines a central reference plane perpendicular to the axis of rotation of the valving, the primary valve member defining a pair of meter grooves oppositely and equally disposed about the plane. The follow-up valve defines pressure porting adjacent the plane and connected to the fluid inlet port.

Abstract: A rotary fluid pressure device such as a motor or pump of the type utilizing a Geroler.RTM. gear set. The internal teeth of the Geroler.RTM. are tubular members mounted on bearings to be slightly movable. Between each adjacent pair of tubular teeth is a check valve in the form of a roller which is mounted to be movable slightly more than are the tubular teeth. A resilient band surrounds the rollers, biasing each of them inwardly toward engagement with the adjacent teeth, but permitting each of the roller check valves to move out of sealing engagement with the adjacent teeth when the fluid pressure in the adjacent volume chamber exceeds the combined biasing force of the resilient band and the fluid in the outer fluid chamber. The invention provides a low cost Geroler.RTM. gear set permitting greater manufacturing tolerances, and having improved low speed characteristics and volumetric efficiency, resulting from minimized tooth-tip leakage.