Abstract: A hydraulic controller for a hydrostatic transmission to control a number of functions of a variable displacement pump or motor of the transmission. A valve includes a spool biased in one direction by a spring and in the opposite direction by fluid pressure in a chamber communicating with the charge pump. A variable orifice communicates the chamber with a drain. The size of the orifice is controlled electrically by a signal representative of swashplate position. Depending upon the pressure of the fluid in the chamber, the valve will directly vary the pressure ported from the charge pump to the standard controller. A needle roller has one end in contact with the end of the spool communicating with the chamber. A high pressure signal is provided via a shuttle valve across the high and low pressure conduits of the transmission to the other end of the needle roller.

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 control including a control valve and an override valve for use with a variable displacement pump or motor unit having a pair of strokers into and out of which fluid must be directed to vary the displacement of the unit. The control valve ports fluid from a high pressure source to a first control passage and from a second control passage to a low pressure source, reverses said flow, and terminates said flow. The override valve is interposed between the control passages and the strokes and defines a pair of override passages therein used to direct fluid from one control passage to one stroker and from the other stroker to the other control passage. The override valve is selectively movable between a first position directing such flow therethrough and a second position in which such flow is terminated between the control passages and the strokers.

Abstract: A valve having a body with two ports and a bore, a sleeve selectively movable within said bore and having two radially extending passages adapted for sequential communication with one of said ports upon movement of said sleeve, and a spool selectively movable within said sleeve and including a land to restrict fluid flow in said passages. The valve is used as a variable pressure control valve in a closed loop hydrostatic circuit to control the displacement of a variable displacement pump. The spool is actuated in response to a pressure difference between the high pressure and the low pressure lines of the circuit. The sleeve is manually movable. A charge pump is provided to provide control fluid to one of the ports of the valve whereby movement of the sleeve and spool within the body will result in the flow of fluid from the charge pump to one servo of the variable displacement pump and from the other servo to drain.

Abstract: A hydrostatic transmission is disclosed which includes a pump assembly in which a main pump, a charge pump, and an auxiliary pump are commonly housed and are drivingly connected to a single shaft assembly. An external fluid connection is provided through which fluid is directed from the auxiliary pump to a power take off, and valving is provided to short circuit the auxiliary pump when power is not demanded. Means of controlling the rate of operation of the valve are also provided to prevent excessive pressure rise rates at the outlet of the auxiliary pump upon actuation of the valving.

Abstract: A hydrostatic transmission system is provided which is particularly well adapted for use in driving vehicles employing skid-steer drives. In the system disclosed two independent hydrostatic transmissions, each employing a variable displacement motor are utilized; and a pressure responsive valve is employed to sense the magnitude of the load on each of the motors and to permit shifting the motors from minimum displacement toward maximum upon the sensing of a load in excess of a predetermined valve. The variable displacement motors of the system are configured to create forces during operation tending to urge the motors to maximum displacement, and the pressure responsive valve operates to bias the motors to minimum displacement when they are loaded at a magnitude less than the predetermined valve.

Abstract: A control valve for a variable displacement pump or motor. The valve includes a pair of solenoids which are independently actuatable to port relatively high pressure fluid to their respective servo motor. A shuttle valve actuated by the high pressure fluid is used to simultaneously port the fluid from the other servo motor to a low pressure fluid source. A manual valving system is also provided having a pair of balls each biased into engagement with a seat to seal a passage to one of the servo motors. Movement of either ball off of its seat allows high pressure to flow to the respective servo motor. The high pressure fluid actuates the shuttle valve to port fluid from the other servo motor to the low pressure fluid source.