Abstract: A vehicle hydraulic system includes a lube circuit, a pump supplying hydraulic fluid from sump to first and a second hydraulic control circuits and a filter circuit. The filter circuit includes a first outlet connected to the lube circuit, a sump line, and a second outlet connected to the pump. A suction filter is connected between the sump line and second outlet. A return filter is connected to the first control circuit outlet. A return line having an orifice is connected between the return filter and the first outlet. A backpressure valve has a member, an outlet connected to the second outlet, and an inlet and pilot line connected to the return filter outlet. A pressure sense line has one end connected to the return line between the orifice and the first outlet, and a second end connected to the member in opposition to the pilot line.

Abstract: A vehicle includes steerable front wheels, an interaxle differential for transmitting torque from an engine to the front wheels and to rear wheels. The differential includes a controllable clutch operable to control a ratio of front wheel speed to rear wheel speed. A control unit controls the clutch as a function of sensed steering angles and stored information including steering angles and corresponding front to rear wheel speed ratio values. The control unit is automatically calibrated. The control unit periodically obtains steering angle values, periodically obtains front and rear wheel speed values, periodically generates new front to rear wheel speed ratio values, and replaces one of the stored front to rear wheel speed ratio values with one of the new ratio values if the steering angle values indicate that the vehicle has been in a straight ahead travel mode for at least a certain time period.

Abstract: A PTO transmission transmits power from an engine-driven shaft to a PTO shaft. The transmission includes a variable displacement hydraulic pump driven by the engine-driven shaft. A planetary transmission unit includes a ring gear driven by the engine-driven shaft, a planet carrier drivingly coupled to the PTO shaft, planet gears rotatably mounted on the planet carrier and in meshing engagement with the ring gear, and a sun gear in meshing engagement with the planet gears and drivingly connected to a fixed displacement variable speed hydraulic motor hydraulically driven by the pump. A one-way clutch is coupled to the sun gear. The one-way clutch allows the sun gear to rotate in only one direction so that at rated engine speed all power is transmitted mechanically.

Abstract: A PTO transmission includes a split power transmission unit having an output member connected to a PTO shaft, a first input connected to an engine output shaft and a second input connected the output of a variable speed drive unit. A control unit controls the speed of the variable speed drive unit as a function of sensed engine speed and maintains the PTO shaft at a constant speed. The split power transmission is preferably a planetary gear unit. The variable speed drive unit preferably includes a variable displacement hydrostatic pump driving a fixed displacement hydrostatic motor which drives a sun gear of the planetary gear unit. This system transmits power to the PTO shaft from both the engine and from the variable speed drive unit. The control unit may also control the variable speed drive unit so that the speed of the PTO shaft is maintained at a desired ratio with respect to the ground speed, or so that the speed of the PTO shaft is maintained at a speed set by an operator.

Abstract: A tractor has an interaxle differential which transmits torque from an engine driven transmission to a front axle and to a rear axle. A differential includes a planetary gear set coupled to a modulating clutch. The modulating clutch is coupled between a pair of the planetary gear elements, and is used to bring the front to rear speed differential within desired limits. A control system for controlling the clutch includes a steering angle sensor, a front wheel speed sensor and a rear wheel speed sensor. From these sensors the control system determines a desired maximum speed difference between the front and rear wheels, and controls the differential to keep the front to rear speed ratio within the desired limit.

Abstract: A PTO transmission includes a split power transmission unit having an output member connected to a PTO shaft, a first input connected to an engine output shaft and a second input connected the output of a variable speed drive unit. A control unit controls the speed of the variable speed drive unit as a function of sensed engine speed and maintains the PTO shaft at a constant speed. The split power transmission is preferably a planetary gear unit. The variable speed drive unit preferably includes a variable displacement hydrostatic pump driving a fixed displacement hydrostatic motor which drives a sun gear of the planetary gear unit. This system transmits power to the PTO shaft from both the engine and from the variable speed drive unit. The control unit may also control the variable speed drive unit so that the speed of the PTO shaft is maintained at a desired ratio with respect to the ground speed, or so that the speed of the PTO shaft is maintained at a speed set by an operator.

Abstract: A system and method are provided for monitoring a vehicle hydraulic system having a plurality of hydraulic function elements. The hydraulic system includes a hydraulic pump for supplying pressurized hydraulic fluid to the plurality of hydraulic function elements via a corresponding plurality of hydraulic element control valves, an electronic control unit for controlling the element control valves. The pump also supplies lube fluid to a lubrication circuit if requirements of the hydraulic function elements are met. The method includes sensing a hydraulic pressure (preferably the lube pressure of lube fluid in the lube circuit), and comparing the sensed pressure to a threshold pressure. If the sensed pressure is less than threshold pressure, then actively engaged hydraulic elements are tested by disengaging the elements in a predetermined manner, checking to see if the sensed low pressure condition is eliminated.

Abstract: A modulation control valve includes a modulating valve coupled by springs to an accumulator piston with both fluidly connected to a reservoir valve. The modulating valve is moved by pressurized fluid in an inlet port connected thereto when a predetermined fill pressure is reached. The fluid in the outlet port pressurizes the accumulator piston to move it to urge the modulating valve to pressure modulate fluid flow between the inlet and an outlet ports. Pressurized fluid in the outlet port acts on a return spring end of the reservoir valve to prevent the accumulator piston and on the other end of the reservoir valve from being relieved to a fluid reservoir. When the accumulator piston abuts the modulating valve, the inlet and outlet ports will be placed in full fluid communication to end modulation.