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In a hybrid vehicle having an internal combustion engine that is assisted by an electric motor powered by a traction battery, the electric motor is operated in a generating mode to charge the vehicle battery during periods when neither acceleration assist nor regenerative braking are being performed

In a hybrid vehicle having an internal combustion engine that is assisted by an electric motor powered by a traction battery, the electric motor is operated in a generating mode to charge the vehicle battery during periods when neither acceleration assist nor regenerative braking are being performed. Torque of the electric motor is adjusted by a controller to generate a battery charge current which regulates the voltage of the battery to a selected setpoint. The setpoint is determined as a function of vehicle operating parameters, including but not limited to battery temperature.

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1. A method for regulating a charge state of a traction battery in a hybrid vehicle having an internal combustion engine that is assisted for acceleration by an electric traction motor energized by the traction battery, said method comprising:detecting operation of said traction motor in one of an a

1. A method for regulating a charge state of a traction battery in a hybrid vehicle having an internal combustion engine that is assisted for acceleration by an electric traction motor energized by the traction battery, said method comprising:detecting operation of said traction motor in one of an acceleration assist and regenerative braking modes;only when said electric motor is not operated in one of said acceleration assist and regenerative braking modes, applying torque from said engine to operate said traction motor in a generator mode to supply a charging current to said battery; andcontrolling operation of said traction motor in said generator mode such that said charging current charges the traction battery to a selected voltage regulation setpoint. 2. The method according to claim 1, wherein said controlling step comprises:detecting a voltage output from said traction battery;calculating an error signal by subtracting said voltage output from said voltage regulation setpoint;utilizing said error signal for generating a torque demand signal; andcontrolling operation of the traction motor according to the torque demand signal. 3. The method according to claim 2, wherein said step of controlling operation of said traction motor comprises controlling torque of said motor. 4. The method according to claim 3, wherein controlling torque of said traction motor is performed by adjusting motor phase current of said traction motor. 5. The method according to claim 1, wherein said voltage regulation setpoint is determined based on operating parameters of said vehicle. 6. The method according to claim 5, wherein said operating parameters include at least a temperature of said battery. 7. The method according to claim 1, wherein said step of controlling operation of said traction motor comprises:a control unit generating a torque command as a function of vehicle operating parameters, including traction battery voltage; andcontrolling said traction motor to generate a torque corresponding to the torque command. 8. The method according to claim 7, wherein controlling operation of said traction motor is performed by adjusting a motor phase current of said traction motor. 9. An apparatus for regulating a charge state of a traction battery in a hybrid vehicle having an internal combustion engine that is assisted for acceleration and deceleration by an electric traction motor that is energized by the traction battery, said apparatus comprising:detector means for detecting operation of said traction motor in one of an acceleration assist and regenerative braking modes;a computer receiving signals from said detector means, and having a memory encoded with a program foronly when said traction motor is not operated in one of said acceleration assist and regenerative braking modes, causing said traction motor to operate in a generator mode by absorbing torque from said engine, thereby generating a charging current to said battery; andcontrolling operation of said traction motor in said generator mode such that said charging current charges the traction battery to a selected voltage regulation setpoint. 10. The apparatus according to claim 9, wherein said controlling operation of the traction motor is performed via a closed loop controller, based on an error signal generated by subtracting a traction battery output voltage from said voltage regulation setpoint. 11. The apparatus according to claim 10, wherein the controller is one of a P, P.I. and a P.I.D. controller. 12. The apparatus according to claim 9, wherein said controlling operation of said traction motor is performed by controlling torque of said traction motor. 13. The apparatus according to claim 12, wherein torque of said traction motor is controlled by adjusting a phase current of said traction motor. 14. The apparatus according to claim 9, further comprising a lookup table for determining said voltage regulation setpoint as a function of vehicle operating parameters, wherein sa id computer determines said voltage regulation setpoint by accessing said lookup table. 15. The method according to claim 14, wherein said operating parameters include at least a battery temperature of said traction battery.