Hybrid work machine

A hybrid work machine comprising:

• an engine;
• a hydraulic pump driven by the engine;
• a hydraulic actuator driven by hydraulic fluid delivered from the hydraulic pump;
• a generator motor coupled to the engine, the generator motor being able to act both as a generator and a motor;
• an electric storage device that transmits and receives electric power to and from the generator motor;
• an engine controller that controls the engine on a basis of a target engine revolution speed;
• a power controller that controls action of the generator motor by controlling charge and discharge of the electric storage device;
• a controller that controls the engine controller and the power controller;
• and
• a target engine revolution speed change instructing device that gives instructions on a change in the target engine revolution speed to be used in the engine controller on a basis of an operator's operation, wherein
• the engine controller controls a revolution speed and an output torque of the engine on a basis of a regulation characteristic set per target engine revolution speed if the target engine revolution speed has been changed by an instruction of the target engine revolution speed change instructing device to be lower than a target engine revolution speed set before change while the engine is in an unloaded state,
• the regulation characteristic has a characteristic that the output torque of the engine is increased at a predetermined rate in proportion to a reduction in the revolution speed of the engine, wherein
• the controller controls, if the target engine revolution speed has been changed by an instruction of the target engine revolution speed change instructing device to be lower than a target engine revolution speed set before change while the engine is in an unloaded state, the engine controller and the power controller to cause the generator motor to act as the generator on a basis of a same regulation characteristic as the regulation characteristic of the engine controller until an actual revolution speed of the engine is reduced to a revolution speed in response to a target engine revolution speed after the change.