Controlling device for controlling rotational speed of engine of hydraulic working machine

A controlling device for controlling the rotational speed of an engine of a hydraulic working machine provided with:

• a hydraulic pump driven by an engine;
• a plurality of actuators operated by oil supplied under pressure from the hydraulic pump;
• a plurality of actuator operating members for operating the plurality of actuators respectively;
• and rotational speed designating means for designating a rotational speed of the engine,
• the controlling device comprising:
• delay time setting means for setting a delay time in accordance with a shifting speed of at least one of the plurality of actuator operating members to a neutral position thereof when all the actuator operating members are shifted to their respective neutral positions when the engine is at a rotational speed designated by the rotational speed designating means;
• and
• rotational speed controlling means for measuring an elapsed time while controlling the engine to run at the designated rotational speed when all the actuator operating members are shifted to their respective neutral positions, and controlling the engine to run at a predetermined low rotational speed to save fuel in a case that the elapsed time reaches the set delay time and all the actuator operating members are maintained in the neutral positions whereas resetting the measurement of elapsed time and controlling the engine to run at the designated rotational speed in a case that at least one of the actuator operating members is shifted from the neutral position to a working position before the elapsed time reaches the delay time,
• wherein the delay time setting means sets a longer time in a case of low shifting speed when the shifting speed is lower than a predetermined value than in a case of high shifting speed when the shifting speed is higher than the predetermined value.