1. Field of the Invention
The present invention relates to a hybrid working machine using an engine power and a battery power in combination.
2. Description of the Background Art
There is known a hybrid shovel as disclosed in e.g. Japanese Unexamined Patent Publication No. 2005-237178 as a hybrid working machine. The hybrid shovel includes an engine, a hydraulic pump and a generator motor connected to the engine, a hydraulic actuator driven by hydraulic fluid ejected from the hydraulic pump, and a battery for charging an electric power generated by the generator motor. The battery supplies the electric power to the generator motor as necessary to let the generator motor perform as a motor to thereby assist the engine.
The hybrid shovel is further provided with a means for detecting a battery SOC (State of Charge) indicating a charging state (charging amount) of the battery, and a means for controlling a charging power so that the charging power approaches a targeted value of SOC in accordance with the detected battery SOC. Here, since the charging performance of the battery also depends on a battery temperature, battery SOC/charging power characteristics also change depending on the battery temperature.
The hybrid working machine performing the above battery charging control, however, may involve an excessive load of the battery. Specifically, in the conventional hybrid working machine, in order to swiftly recover the battery SOC to a targeted value or stabilize the battery SOC in a condition that the battery SOC is sharply lowered by discharging during a working period, performed is a control for rapid charging by full use of the battery performance determined by the detected battery temperature and SOC, in other words, performed is setting the contents of battery control based on the control at the time of discharging; this may cause an increase in the load of the battery due to continuous rapid charging in a stand-by period with no discharging, thereby damage the battery and lower the battery life.