Transmission

Abstract

A transmission having hydraulic components including a hydrostatic unit with a variable displacement component having a hydraulic displacement control with a lubrication circuit for the components and a charge circuit for supplying fluid under pressure. First and second pumps are connected in series, with the first pump having a larger volume than the second pump to provide fluid to the second pump and to a lubricating circuit. A fluid line connects between the charge circuit and the lubrication circuit and has a lubrication priority valve therein which operates to provide fluid flow from the charge circuit to the lubrication circuit when required to maintain pressure in the lubrication circuit. Additionally, the charge circuit has a pair of branch lines, with one branch line having a charge priority valve therein which functions to control the flow through the one branch line leading to the hydraulic displacement control for the hydrostatic unit and to thus provide pressure control in the other branch line. The charge priority valve additionally controls the pressure in said one branch line by modulating flow thereof relative to a drain port and also has provision for increasing pressure in the other branch line when the speed of the hydrostatic unit exceeds the overspeed rating thereof.