Electric machine having continuously-variable magnetic characteristics and method of controlling the same

A vehicle comprising:

• a load;
• a transmission connected to the load, and configured to provide an output torque to the load responsive to an input torque;
• an electric machine operable for producing the input torque to the transmission, the input torque being a total motor torque having continuously-variable magnetic and reluctance torque components, the electric machine including:
• a stator assembly having a stator core with an axial length;
• a return spring attached to the rotor hub;
• and
• a rotor assembly including a rotor shaft and a cylindrical rotor hub each having a respective axial length, the cylindrical rotor hub having a first end with a first magnetic field strength and a second end with a second magnetic field strength, wherein the second magnetic field strength is weaker than the first average magnetic field strength;
• wherein the rotor hub is splined to the rotor shaft, the axial length of the rotor hub exceeds the axial length of the stator core, and the rotor hub is configured to translate along the axial length of the rotor shaft, via an apply force from an actuator or via introduction of a flux-weakening stator current to the stator windings, at different speed and torque operating points of the electric machine, and to translate in a second direction via operation of the return spring;
• and
• a controller configured to receive a set of input signals, including a speed and a torque of the electric machine, and to command a translation of the rotor hub along the axial length of the rotor shaft responsive to the set of input signals to thereby continuously vary a relative contribution of the magnetic and reluctance torque component to the total motor torque.

A method for controlling an electric machine operable for producing a total motor torque that includes continuously-variable magnetic and reluctance torque components, the electric machine having a stator assembly and a rotor assembly, the method comprising:

• determining a speed and a torque of the electric machine via a controller and at least one sensor;
• determining a desired axial position of a cylindrical rotor hub of the rotor assembly via the controller using a lookup table, the desired axial position corresponding to the received speed and torque, wherein the cylindrical rotor hub has a first end with a first magnetic field strength and a second end with a second magnetic field strength, wherein the second magnetic field strength is weaker than the first magnetic field strength;
• and
• translating the rotor hub in a first direction along the axial length of a rotor shaft of the rotor assembly to the determined desired axial position such that a relative of the magnetic and reluctance torque components to the total motor torque is continuously varied in real time responsive to the determined speed and torque, including energizing an actuator connected to the rotor hub or introducing a flux-weakening stator current into stator windings of the stator assembly;
• and
• translating rotor hub in a second direction via operation of a return spring connected to the rotor hub.