Patent ID: 7052427

Claim:
Electric screw actuator system usable in at least an electrically driven and controlled steering device, the system comprising: a screw actuator containing at least a nut and a screw; an electric motor engaging the screw actuator through a reduction gear mechanism; an electronic operating device for operating the screw actuator electrically; and a mechanical back-up system for operating the screw actuator in the absence of electric power due to at least one of an electric power failure and the electric power being intentionally switched off, the mechanical back-up system further comprises a manually controllable rotation member and an electromagnetic coupling, the coupling disengaging the rotation member from the screw actuator in the case of normal operation and availability of electric power, and engaging the rotation member with the screw actuator in the case of absence of electric power, wherein the coupling is connected to an auxiliary gear mechanism which engages the screw actuator in case of absence of electric power, the coupling is connected to an auxiliary drive gear wheel which engages the screw actuator, and the reduction gear mechanism and the auxiliary gear mechanism are integrated, and the reduction gear mechanism comprises a sun gear wheel which is driveable by the electric motor, a fixed ring gear wheel connected to one of the nut and the screw, satellite gear wheels which engage the sun gear wheel and the ring gear wheel and a carrier onto which the satellite gear wheels are rotatably mounted, the carrier engaging the other of the nut and the screw, and the auxiliary drive gear wheel engages an auxiliary carrier onto which auxiliary satellite gear wheels are rotatably mounted, said auxiliary satellite gear wheels engaging an auxiliary ring gear wheel which is fixed with respect to the fixed ring gear wheel, and an auxiliary sun gear wheel connected to the carrier.