Phase delayed active motor damping to mitigate electric vehicle driveline oscillations

#The present invention relates to a motor control system and method for mitigating unwanted electric vehicle driveline oscillations.

#The term “electric vehicle” used herein encompasses vehicles such as battery electric vehicles (BEV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV). A BEV includes an electric motor, wherein the energy source for the motor is a battery that is re-chargeable from an external electric grid. In a BEV, the battery is the source of energy for vehicle propulsion. A HEV includes an internal combustion engine and an electric motor, wherein the energy source for the engine is fuel and the energy source for the motor is a battery. In a HEV, the engine is the main source of energy for vehicle propulsion with the battery providing supplemental energy for vehicle propulsion (the battery buffers fuel energy and recovers kinematic energy in electric form). A PHEV is like a HEV, but the PHEV has a larger capacity battery that is rechargeable from the external electric grid. In a PHEV, the battery is the main source of energy for vehicle propulsion until the battery depletes to a low energy level at which time the PHEV operates like a HEV for vehicle propulsion.

#As such, an electric vehicle has an electric motor and a battery. The motor is interposed between the battery and a drive shaft of the vehicle, wherein the motor is mechanically coupled to the driveline of the vehicle. The motor may be controlled to contribute positive wheel torque to the wheels of the vehicle in order to drive the wheels for vehicle propulsion. Conversely, the motor may be controlled to contribute negative wheel torque to the wheels in order to brake the wheels for vehicle braking.

#FIG. 1 illustrates a block diagram of a hybrid electric vehicle (HEV) powertrain capable of embodying the present invention;

#FIG. 2A illustrates a plot of the commanded motor torque from a motor controller and the actual motor torque delivered by a motor during an active motor damping operation in which the oscillation frequency of driveline oscillations is within the response capability of the motor controller and the motor;

#FIG. 2B illustrates a plot of the driveline oscillations as effected by the actual motor torque shown in FIG. 2A during the active motor damping operation;

#As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

#As indicated above, an active motor damping system controls the motor of an electric vehicle to output a counter-torque to the wheels in order to damp out driveline oscillations, particularly during an ABS operation. During active motor damping, the active motor damping system looks for differences between the motor speed and the wheel speeds. Certain differences are an indication of driveline “windup” (i.e., driveline deflections). When a driveline windup is detected, a motor controller of the active motor damping system commands a counteracting motor torque to slow the motor in order to reduce the driveline windup. This works well if the wheel speeds are provided at a high enough rate and the motor controller and the motor can respond fast enough to prevent a phase lag between the commanded motor torque from the motor controller and the actual motor torque delivered by the motor.

#For many electric vehicles, the resonant frequency of the powertrain system, and thus the oscillation frequency of the driveline oscillations, is in the range such as, for example, 6-10 Hz or 6-12 Hz. In this case, the oscillation frequency is within the response capability of the motor controller and the motor such that there is no more than minimal non-problematic phase lag between the commanded motor torque from the motor controller and the actual motor torque delivered by the motor. As a result, the actual motor torque delivered by the motor counteracts the driveline oscillations such that the driveline oscillations are reduced.