Rpm control device and rpm control method for a general-purpose engine

An rpm control device for a general-purpose engine, for controlling an intake-air amount to be supplied to an engine by using an electronic throttle to control an rpm of the engine, the rpm control device comprising:

• an rpm detecting section for detecting the rpm of the engine;
• an intake-air temperature detecting section for detecting a temperature of intake air of the engine;
• an intake-air detecting section for detecting one of an intake-air amount and an intake pressure of the intake air;
• an engine-load detecting section for detecting a load of the engine by using the temperature of the intake air of the engine, detected by the intake-air temperature detecting section, and one of the intake-air amount and the intake pressure, detected by the intake-air detecting section;
• a basic target-rpm calculating section for calculating a basic target rpm of the engine based on input of an accelerator operation;
• a target decrease-rate calculating section for calculating a rotation decrease rate based on the basic target rpm and the load of the engine;
• a target-rpm calculating section for calculating a target rpm based on the basic target rpm and the rotation decrease rate;
• a target throttle opening-degree calculating section for calculating a rotation deviation between the rpm of the engine and the target rpm so as to calculate a target throttle opening degree of the electronic throttle based on the rotation deviation;
• and
• an electronic-throttle control section for controlling an opening degree of the electronic throttle so that an actual opening degree of the electronic throttle becomes equal to the target throttle opening degree,
• wherein the target rpm is made smaller than the basic target rpm by reducing the rotation decrease rate in accordance with an increase in the load of the engine, and isochronous control is performed by using the electronic throttle so as to achieve the obtained target rpm to perform droop control in a pseudo-manner.