A method of operating a vehicle powertrain system comprising an electric
motor and transmission where the electric motor is operably and
selectively coupled to the transmission and adapted to provide an output
torque contribution thereto, and the electric motor has a predetermined
maximum motor output torque and a predetermined minimum motor output
torque which are used to determine a range of permissible control points
for at least one transmission control parameter. The method includes
establishing a motor torque reserve by performing at least one of
decreasing the predetermined maximum motor output torque to a maximum
reserved motor output torque and increasing the minimum motor output
torque to a minimum reserved motor output torque, wherein the maximum
reserved motor output torque and the minimum reserved motor output torque
are used in place of the predetermined maximum motor output torque and
the predetermined minimum motor output torque, respectively, to determine
the range of permissible control points for the at least one transmission
control parameter.