Integrated control for electric lift trucks

摘要

A controller system for an electric lift truck that controls a traction motor (86) and a hydraulic pump motor (12) is disclosed. The speed of rotation of both motors (86, 12) is controlled by a pulse width modulated current supplied from a battery source (84) by the controller (80) in direct response to a demand communicated to the controller (80) through an interface (50) manipulated by an operator. A pump (13) driven by the pump motor (12) supplies pressurised hydraulic fluid to a lift mechanism (90) and a power assisted steering unit (17). A priority valve (14) ensures that the pressurized hydraulic fluid first satisfies the power assisted steering unit (17) before being used for other hydraulic functions. A joystick (52) with function switches (56, 58, 60 and 62) is provided so that the operator steers with one hand while controlling truck propulsion and all functions of the lift mechanism (90) with the other hand. The combination of direct control of the pump motor (12) speed and on-demand pressure switch (16) enables a fully proportional control of the hydraulic system. The system provides a compact structure with minimal cabling and ensures that the hydraulic system operates with energy efficiency and minimal wear.