Control system for a hydraulic circuit

Abstract

A control system is provided for use in a hydraulic system to provide a simple arrangement with a limited number of elements that bypasses the system flow in the event of an electrical malfunction in the system and further allows other hydraulic circuits to operate even if one or more of the hydraulic circuits have experienced an electrical malfunction. The subject arrangement uses an electro-hydraulic fluid flow control valve mechanism in conjunction with directional valve mechanisms that have at least three functional positions and are controlled by associated electrically controlled displacement control mechanisms in response to receipt of electrical signals from an electrical controller. In the event of an electrical malfunction, each of the directional valve mechanisms are spring biased to one of its extreme positions in the absence of an electrical signal to the associated electrically controlled displacement control mechanisms and the electro-hydraulic fluid flow control valve mechanism bypasses all of the fluid from a source of pressurized fluid to a reservoir. With the directional valve mechanisms of one hydraulic circuit in their spring biased extreme positions, the electrical signal to the electro-hydraulic fluid flow control valve mechanism can be re-instated and the other hydraulics can be operated.