1.  Field of the Invention
This invention relates to a battery-operated vehicle, such as an industrial truck having an electronic control unit and with a built-in charging function. 
2.  Technical Considerations
Battery-operated electric vehicles, such as electric industrial trucks, must generally be brought to a charging station to recharge the battery.  That is not always easy or convenient to do, especially if the next charging station is a significant distance away.  Therefore, the designers of electric industrial trucks have attempted, since the very early days of such units, to include built-in charging units.  These units have the advantage that the battery can be recharged at any time, anywhere there is a suitable electrical outlet. 
The known art describes industrial trucks with built-in charging units.  The traction battery of the vehicle can then be recharged at the next electrical outlet when the truck is not in use.  It therefore becomes unnecessary to replace the battery or to provide a recharging station.  These on-board charging units are generally installed in the industrial trucks in the form of separate units.  The function of a charging unit is the isolated conversion of the line voltage into a direct-current voltage and of the controlled adjustment of the charging voltage or of the charge current so that it corresponds to the charge status and charging requirements of the battery.  Modem units generally contain a primary switched and higher-frequency transformer.  The process is controlled by a microprocessor. 
DE 199 22 137 A1 describes an industrial truck with a battery block that has a data storage unit.  A standard charging unit is necessary to recharge the battery. 
DE 196 52 950 A1 describes an industrial truck in which the recharging device is carried by the vehicle in the form of a component of the drive control system.  The traction motor has a very special winding that is also used for charging.  A specially equipped motor of this type with a special winding and taps is relatively expensive on account of the small size of the manufacturing runs. 
On the other hand, the known art also describes battery-operated industrial trucks that are equipped with one or more electronic control units.  The most important functions of the control units include: actuation of the drive motors; actuation of hydraulic elements such as proportional valves; interfaces for control and operator information; additional functions, e.g., actuation of relays or brakes; and monitoring and control of the vehicle. 
Current control systems are generally equipped with one or more microprocessors.  The scope of the functions and the size of the control units vary with the complexity of the vehicle.  Under increasing cost pressure, just as with the other components of an industrial truck, emphasis has been placed on minimizing the cost and complexity of the hardware used in the control units, especially for mass-produced vehicles in the lower power range. 
Because built-in recharging units represent a significant cost factor precisely in these small units, it is an object of the invention to provide a battery-operated industrial truck with a built-in recharging unit that can be manufactured more economically.