Abstract: An anti-plug control for a drive to prevent jamming of a driven working element in response to an overload wherein said drive includes a hydrostatic transmission having a variable displacement unit and a fixed displacement unit connected in closed circuit. A servo control cylinder is connected to a swash plate of the variable displacement unit for causing positioning thereof. A normally closed pressure-responsive valve monitors the pressure in the high pressure side of the closed circuit and is openable when the pressure reaches a predetermined value to deliver fluid from the closed circuit to the servo control cylinder and modify the displacement of the variable displacement unit to increase the speed of the working element to attempt clearing the overloaded condition of the working element.

Abstract: The invention is directed to a unitary cage assembly annularly positioning a plurality of rollers in a pair of roller bearings supporting a cradle swashplate. By utilizing the unitary cage assembly, a parallel relationship between the rollers is assured and, furthermore, only a single locating mechanism for the unitary cage assembly is required.

Abstract: The invention relates to a swashplate leveling and holddown mechanism wherein an axially sliding leveling mechanism is biased into engagement with a swashplate of an axial piston variable displacement hydraulic unit to position the swashplate in a zero displacement position when there is no control input to the hydraulic unit. The leveling mechanism has a pair of contact points, one positioned on each side of the swashplate tilt axis in a manner that both contact points positively engage the swashplate when it is centered to its zero displacement position. Such mechanism requires no spring adjustment and has no backlash. Furthermore, the axial bias on the leveling mechanism helps seat the swashplate in its support bearings. Utilized in conjunction with the leveling mechanism is an axially biased control input which operates on the opposite side of the swashplate to further hold the swashplate in its support bearings.

Abstract: A thin valve plate for use in an axial piston hydraulic unit wherein valve plate ports are provided with slot shaped extensions passing through the valve plate to provide limited initial fluid communication between cylinder block ports and valve plate ports and wherein the thickness of the valve plate is no greater than one half the width of the slots. Furthermore, such valve plate facilitates economical manufacture wherein the slots and valve plate ports can be stamped in a hardened steel disk.