Battery control device and hybrid forklift truck equipped with the device

1. A battery control device of a hybrid forklift truck having a traveling section for driving wheels by means of either or both of an engine and a battery-operated motor generator and a cargo handling section provided with actuators driven by means of either or both of the engine and the battery-operated motor generator to perform lifting up-and-down of cargos, comprising:

a controller that has,

a battery SOC estimating device, by which SOC (state of charge, indicative of remaining capacity) of the battery is determined from an established relationship between battery voltage and SOC of the battery when the battery does not discharge current for at least a predetermined time period and SOC of the battery is also determined when discharge current is constant for at least a predetermined time period from an established relationship between battery voltage, battery current and SOC of the battery, SOC of the battery is revised and reset every time the battery does not discharge current for at least a predetermined time period or discharge current is constant for at least a predetermined time period, and SOC of the battery at any point of time in operation of the forklift truck is estimated by integrating battery current from the time point of SOC revision and subtracting the integrated current from said revised SOC, thus revision of SOC is repeated during operation of the forklift truck and current value of SOC of the battery is estimated with high degree of accuracy; and

a drive power allocation control device by which discharge/charge current from/to the battery is controlled based on said estimated SOC of the battery so that excessive discharging and charging from and to the battery is prevented by appropriately controlling allocation of drive power to drive the actuators to the engine and/or motor generator,

wherein a lift lever sensor and a tilt lever sensor are provided, and said controller detects whether battery discharge current has been constant for at least a predetermined time period based on controlled variables inputted from said a lift lever sensor and/or a tilt lever sensor.

2. A battery control device of a hybrid forklift truck according to claim 1 , wherein determination of SOC of the battery by said battery SOC estimating device to reset an initial SOC when the battery does not discharge current for at least a predetermined time period is performed when an ignition signal of the engine is outputted or when an operator of the forklift truck gets out of driver's seat.

3. A battery control device of a hybrid forklift truck according to claim 1 , wherein a standard to limit discharge/charge current from/to the battery depending on SOC of battery is prepared, and said drive power allocation control device controls allocation of drive power to drive the actuators to the engine and/or motor generator so that discharge/charge current from/to the battery is in limited range depending on SOC of battery based on said estimated current SOC of the battery.

4. A battery control device of a hybrid forklift truck according to claim 3 , wherein said drive power allocation control device appropriates a part of output of the engine to charge the battery when estimated SOC of the battery is smaller than a predetermined value.

5. A hybrid forklift truck equipped with a battery control device according to claim 1 .

6. A hybrid forklift truck equipped with a battery control device according to claim 2 .

7. A hybrid forklift truck equipped with a battery control device according to claim 3 .

8. A hybrid forklift truck equipped with a battery control device according to claim 4 .