Proportional speed control of fluid power devices

Abstract

A hydraulic circuit for controlling the speed of multiple hydraulic fluid power devices when the flow demand of the devices exceeds the flow capacity of a pressure source supplying hydraulic fluid under pressure to the devices has multiple pressure controlled proportional flow supply valves for controlling the supply of hydraulic fluid to the power devices. Load sense pressures which indicate the pressure delivered by the valves to the corresponding devices are compared to determine the highest load sense pressure, which is compared to the supply pressure by a proportional speed sensing valve to regulate the pilot pressure. In the preferred embodiment, the pilot pressure is regulated by the proportional speed sensing valve to be equal to the differential between the supply pressure and the highest load sense pressure, and a limit control is provided in one form of the proportional speed sensing valve. Thus, when the differential between supply pressure and the highest load sense pressure starts falling, as occurs when the flow demand exceeds the flow capacity of the pump, the pilot pressure is reduced, which reduces flow to the power devices proportionally to reduce the speeds of the devices while maintaining substantially constant the proportions of the speeds to one another.