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In a hybrid electric vehicle (HEV), the available energy from a battery may be inadequate to drive a motor to generate additional torque sufficient for driveability upon a request for an increase in wheel torque. The motor may then be operated in a lossy, inefficient mode. When the motor operates in

In a hybrid electric vehicle (HEV), the available energy from a battery may be inadequate to drive a motor to generate additional torque sufficient for driveability upon a request for an increase in wheel torque. The motor may then be operated in a lossy, inefficient mode. When the motor operates in the lossy mode, engine power can be increased such that the sum of the engine power and the maximum available battery power may exceed requested wheel power. The increased engine power may be dissipated as heat in the motor until an increase in wheel torque is requested, whereby the motor may switch from the lossy mode back to a normal, efficient mode. By switching back to the normal mode, the excessive engine power that was being dissipated as heat in the motor may contribute to the output torque of the motor.

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1. A method comprising: receiving input indicating that an electric machine cannot generate additional machine torque sufficient to meet a request for an increase in wheel torque at one or more drive wheels;increasing an amount of power generated by an engine and decreasing an efficiency of the elec

1. A method comprising: receiving input indicating that an electric machine cannot generate additional machine torque sufficient to meet a request for an increase in wheel torque at one or more drive wheels;increasing an amount of power generated by an engine and decreasing an efficiency of the electric machine in response to the input;dissipating at least a portion of the engine power as heat in the electric machine;receiving a request for an increase in wheel torque; andincreasing the efficiency of the electric machine and transferring the engine power to be dissipated as heat in the electric machine to the drive wheels in response to the request. 2. The method of claim 1, wherein receiving input indicating that the electric machine cannot generate additional machine torque includes receiving input indicating that an energy storage device cannot supply additional energy necessary to drive the electric machine to generate the additional machine torque. 3. The method of claim 2, wherein the energy storage device is a battery and receiving input indicating that the energy storage device cannot supply additional energy includes receiving input indicating a state of charge of the battery. 4. The method of claim 1, wherein increasing the amount of power generated by the engine includes transmitting an engine control signal corresponding to an increase in engine torque. 5. The method of claim 1, wherein the efficiency of the electric machine is decreased without changing the current amount of machine torque generated by the electric machine. 6. The method of claim 1, wherein the step of decreasing the efficiency of the electric machine includes: receiving a first direct-axis current value and a first quadrature-axis current value associated with the electric machine that reduces the efficiency of the electric machine while maintaining the current machine torque; andtransmitting a first machine control signal corresponding to the first direct-axis current value and the first quadrature-axis current value. 7. The method of claim 6, wherein the step of increasing the efficiency of the electric machine includes: receiving a second direct-axis current value and a second quadrature-axis current value associated with the electric machine that increases the efficiency of the electric machine; andtransmitting a second machine control signal corresponding to the second direct-axis current value and the second quadrature-axis current value. 8. The method of claim 1, wherein the step of receiving a request for an increase in wheel torque includes receiving input from an accelerator pedal corresponding to a request for an increase in vehicle acceleration. 9. The method of claim 1, wherein the step of receiving a request for an increase in wheel torque includes receiving input from a gear shifter corresponding to a shift in gears. 10. The method of claim 1, further comprising: prior to increasing engine power and decreasing electric machine efficiency, receiving input indicating that the electric machine can dissipate additional engine power as heat in the electric machine. 11. The method of claim 10, wherein receiving input indicating that the electric machine can dissipate additional engine power as heat in the electric machine includes receiving input indicating that a temperature of the electric machine does not exceed a temperature threshold. 12. A vehicle comprising: an engine;a motor mechanically coupled to the engine; anda control system configured to: increase engine power generated by the engine;decrease motor efficiency and dissipate the increased engine power as heat in the motor;receive a request for an increase in wheel torque; andincrease the motor efficiency upon receipt of the request. 13. The vehicle of claim 12, wherein the increased engine power to be dissipated as heat in the motor is transferred to one or more drive wheels as torque from the motor when the motor efficiency is increased. 14. The vehicle of claim 12, wherein increasing the engine power generated by the engine includes transmitting an engine control signal corresponding to an increase in engine torque. 15. The vehicle of claim 12, wherein the motor efficiency is decreased without changing motor torque. 16. The vehicle of claim 12, wherein receiving a request for an increase in wheel torque includes receiving input from an accelerator pedal corresponding to a request for an increase in vehicle acceleration. 17. A method comprising: increasing engine power such that the sum of the engine power and battery power available to drive a motor exceeds requested wheel power;decreasing efficiency of the motor and dissipating at least a portion of the increased engine power as heat in the motor; andincreasing the efficiency of the motor upon receipt of a request for additional wheel power. 18. The method of claim 17, further comprising: upon increasing the efficiency of the motor, transferring the engine power to be dissipated as heat in the motor to one or more drive wheels in response to the request. 19. The method of claim 17, wherein the efficiency of the motor is decreased without changing an amount of torque generated by the motor. 20. The method of claim 17, wherein decreasing the efficiency of the motor includes switching operation of the motor from an efficient mode to a lossy mode and increasing the efficiency of the motor includes switching operation of the motor from the lossy mode back to the efficient mode.