Patent ID: 6176126
Filing Date: 2001-01-23
Classification: E02F

Abstract:
An engine speed control system for a construction machine, said system being for arrangement in association with a hydraulic circuit of said construction machine,said hydraulic circuit being provided with an engine, plural main hydraulic pumps driven by said engine, plural actuators driven by hydraulic fluid supplied from said main hydraulic pumps, and directional control valves for controlling flows of the hydraulic fluid to be supplied from said main hydraulic pumps to said actuators, respectively, in which:said plural actuators comprises a pair of travel motors and plural other actuators different from said travel motors, said directional control valves comprises a first directional control valve for controlling drive of one of said pair of travel motors, a second directional control valve for controlling drive of the other one of said pair of travel motors and plural third directional control valves for controlling drive of said plural other actuators, predetermined ones of said first directional control valve and plural third directional control valves are connected to a first one of said plural main hydraulic pumps, and other ones of said second directional control valve and plural third directional control valves are connected to a second one of said plural main hydraulic pumps,said system being provided with an engine controller capable of controlling a speed of said engine, a pilot pump capable of supplying a pilot pressure, a pilot line for guiding said pilot pressure supplied from said pilot pump, pilot valves arranged in said pilot line in association with said directional control valves, respectively, such that said pilot valves are operated association with their corresponding directional control valves, and a pressure detection device for detecting a pressure developed in said pilot line upon change-over of at least one of said pilot valves and then outputting a detection signal to said engine controller,whereby based on the detection signal outputted from said pressure detection device, said engine controller performs automatic idling control to maintain said speed of said engine at an idling speed of a predetermined low rpm or performs control to cancel said automatic idling control, wherein:said hydraulic circuit of said construction machine is provided further with a communication line, through which an input port of said first directional control valve and an input port of said second directional control valve are connected with each other, and also with a travel-controlling communication valve capable of maintaining said communication line in either a communicating state or a cutoff state,said pilot line comprises a first pilot line and a second pilot line,said first pilot line is provided with said pilot valve operable in association with said first directional control valve and also with said pilot valve operable in association with said second directional control valve,said second pilot line is provided with said pilot valves operable in association with their corresponding ones of said plural third directional control valves for controlling the drive of said plural other actuators, respectively,a signal line for guiding a pressure, which is developed in said second pilot line, as a change-over pressure for said travel-controlling communication valve, andsaid travel-controlling communication valve has a changed-over position where, when said change-over pressure is guided to said signal line, said communication line is maintained in said communicating state.