Method for controlling RPM of engine in hydraulic construction machine

In a hydraulic construction machine comprising an engine, means for setting an output characteristic of said engine, a motor for driving a throttle lever for said engine, an engine throttle control mechanism for transferring a drive force from said motor to said engine throttle lever, means for detecting RPM of said engine and control means for controlling the RPM of said engine, a method for controlling the RPM of said engine, comprising the steps of:

• (a) setting a reference engine RPM value in response to an output signal from said engine output characteristic set means to allow said engine to have a target output characteristic;
• (b) performing a control arithmetic operation in response to a present engine RPM value from said engine RPM detection means and the set reference engine RPM value to allow the present engine RPM value to be approximated to the set reference engine RPM value under the condition that a difference therebetween is within the range of a mechanical error of said engine throttle control mechanism;
• and
• (c) generating a control signal as a result of the control arithmetic operation and outputting the generated control signal to said motor to control the RPM of said engine.

In a hydraulic construction machine comprising an engine, means for setting an output characteristic of said engine, a motor for driving a throttle lever for said engine, an engine throttle control mechanism for transferring a drive force from said motor to said engine throttle lever, means for detecting a position of said engine throttle lever, means for detecting RPM of said engine and control means for controlling the RPM of said engine, a method for controlling the RPM of said engine, comprising the steps of:

• (a) setting a reference throttle lever position value in response to an output signal from said engine output characteristic set means to allow said engine to have a target output characteristic;
• (b) performing a first control arithmetic operation in response to a present throttle lever position value from said engine throttle lever position detection means and the set reference throttle lever position value to allow a difference between the present throttle lever position value and the set reference throttle lever position value to be within the range of a mechanical error of said engine throttle control mechanism;
• (c) generating a first control signal as a result of the first control arithmetic operation and outputting the generated first control signal to said motor to control the RPM of said engine;
• (d) setting a reference engine RPM value in response to the output signal from said engine output characteristic set means when the difference between the present throttle lever position value and the set reference throttle lever position value is within the range of the mechanical error of said engine throttle control mechanism;
• (e) performing a second control arithmetic operation in response to a present engine RPM value from said engine RPM detection means and the set reference engine RPM value to allow the present engine RPM value to be approximated to the set reference engine RPM value under the condition that a difference therebetween is within the range of the mechanical error of said engine throttle control mechanism;
• and
• (f) generating a second control signal as a result of the second control arithmetic operation and outputting the generated second control signal to said motor to control the RPM of said engine.