1. Technical Field
The present invention relates to a control apparatus that controls pump torque so as to raise engine speed from low engine speed to target engine speed quickly in a construction machine such as an excavator.
2. Description of the Related Art
A related art of the present invention is explained with reference to an excavator as an example.
The engine speed during no load of an engine mounted on the excavator is usually set according to an operation applied to an engine speed setting device called acceleration potentiometer, selection of a work mode, and the like. When there are a plurality of determination elements, a lower value is selected. By use of the set engine speed as a target engine speed, a fuel injection quantity in the engine is controlled.
On the other hand, in an excavator with an auto-deceleration function, there is performed an auto-deceleration control for reducing engine speed to set engine speed, i.e., deceleration engine speed, when a predetermined deceleration condition (e.g., a fixed time elapses after lever operation is stopped) is met. When the deceleration condition is not met, for example, when a lever operation is performed, performed is a return-from-deceleration control for raising the engine speed to target engine speed.
In this case, if an actuator is operated during a return from deceleration, the engine speed is not smoothly raised because of a pump load and the engine speed is delayed in reaching the target engine speed. As a solution to this problem, Japanese Patent Application Laid-open No. H5-312082 discloses a technique for reducing an engine load and quickening a rise of engine speed by minimizing pump torque, which is absorption torque of a hydraulic pump, during the start of an engine; however, minimizing the pump torque in this way makes it impossible to substantially perform an actuator operation, i.e., excavator work until the engine speed completely rises. This problem can occur not only during the return from deceleration but also during raising of the engine speed from low engine speed to target engine speed including engine start.