Patent ID: 7441613

Claim:
An electric drive system having an electric motor, comprising: a first output member; a second output member; a driving shaft drivable by the electric motor and having an axis of rotation; a differential steering system operably disposed between the driving shaft and the first and second output members such that the driving shaft conveys torque from the electric motor to the differential steering system, the differential steering system including a first planetary gear assembly operatively engaged between the driving shaft and the first output member and operatively engaged between the driving shaft and the second output member, the first planetary gear assembly having an axis of rotation that substantially aligns with the axis of rotation of the driving shaft; a steering motor operatively engaged with the differential steering system and operable to simultaneously adjust the rotational speed of both of the first and second output members to change the rotational speed of one of the first and second output members relative to the other of the first and second output members; a second planetary gear assembly operatively engaged between the first planetary gear assembly and the first output member, the second planetary gear assembly having a sun gear connected to a sun gear of the first planetary gear assembly and having an axis of rotation that substantially aligns with the axis of rotation of the driving shaft, wherein the steering motor is operatively engaged with the second planetary gear assembly and operable to modify the rotational speed of the second planetary gear assembly to thereby simultaneously adjust the rotational speed of both of the first and second output members to change the rotational speed of one of the first and second output members relative to the other of the first and second output members; a third planetary gear assembly operatively engaged between the first planetary gear assembly and the second output member and configured to have a rotational axis that substantially aligns with the rotational axis of the driving shaft; a reaction member connecting sun gears of the second and third planetary gear assemblies, wherein the driving shaft is hollow and the reaction member extends therethrough; and a fourth planetary gear assembly disposed between the electric motor and the differential steering system, the fourth planetary gear assembly being configured to reduce the rotational speed of the driving shaft.