Failsafe steering device for steer-by-wire system

A failsafe steering device for a steer-by-wire system includes a main Electronic Control Unit (ECU) that detects manipulating states of a main steering wheel and a rack mechanism via a plurality of sensors, actuates a reaction motor that provides the reaction force to the main steering wheel in relation to a driver's steering force, and controls a steering motor that executes the steering by actuating the rack mechanism. The failsafe steering device further includes a battery providing power to the steering motor, a relay restraining the power supply between the battery and the steering motor, a failsafe ECU that determines the malfunction state of the main ECU and controls the relay accordingly, and a steering shaft that transmits the rotational force of a supplement steering wheel to the rack mechanism.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on, and claims priority from, Korean Application Serial Number 10-2004-0046736, filed on Jun. 22, 2004, the disclosure of which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to a failsafe steering device for a steer-by-wire system. More particularly, the present invention relates to a device adapted to safely steer the vehicle in case the steer-by-wire system malfunctions.

BACKGROUND OF THE INVENTION

Generally, a steer-by-wire system actuates a rack mechanism to steer the vehicle in response to a driver's steering manipulation via electric signals without a steering column.

Test vehicles (used for developing vehicles) having the steer-by-wire system are typically equipped with a failsafe steering device to help ensure the safety of the steer-by-wire system.

If the steer-by-wire system fails to function properly, the steering can be performed safely in the test vehicles via the failsafe steering device.

A mechanical failsafe steering device is conventionally used to transmit the rotational force of a supplement steering wheel to the rack mechanism through a steering shaft.

SUMMARY OF THE INVENTION

Embodiments of the present invention are provided to easily steer a test vehicle even when a steer-by-wire system of the test vehicle malfunctions, thereby improving the safety of the test vehicle.

A failsafe steering device for a steer-by-wire system includes a main Electronic Control Unit (ECU) that detects manipulation states of a main steering wheel and rack mechanism via a plurality of sensors. The main ECU actuates a reaction motor that provides reaction force to the main steering wheel in relation to the driver's steering force and controls a steering motor that executes the steering by actuating the rack mechanism. A battery provides power to the steering motor. A relay restrains the power supply between the battery and steering motor. A failsafe ECU determines whether the main ECU malfunctions and controls the relay accordingly. A steering shaft transmits the rotational force of a supplement steering wheel to the rack mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first toFIGS. 1 and 2, a main steering wheel1is installed to be manipulated by a driver. A rack mechanism3, constituted by a rack and pinion, manipulates a steering knuckle. A steering motor5is installed on the rack mechanism3and activated according to the rotational state of the main steering wheel1for steering purposes. A reaction motor7provides the reaction force to the main steering wheel1.

A steering angle sensor9and torque sensor11detect the manipulated state of the main steering wheel1. A rack sensor13detects the operation state of the rack mechanism3. A main Electronic Control Unit (ECU)15receives signals from the steering angle sensor9, torque sensor11, and rack sensor13and controls the steering motor5and reaction motor7.

A supplement steering wheel17is located in front of a front passenger for assisting the main steering wheel1. The rotational force of the supplement steering wheel17is directly transmitted to the rack mechanism3through a steering shaft19in a mechanical manner.

The main steering wheel1and rack mechanism3are connected electronically while the supplement steering wheel17and rack mechanism3are mechanically connected to each other.

If the main ECU15operating the rack mechanism3in response to the steering state of the main steering wheel1malfunctions or improper steering is executed due to a failure or damage on other electric devices, then the steering of a test vehicle may manually be manipulated via the supplement steering wheel17.

A battery21provides power to the steering motor5and reaction motor7. A relay23restrains the power supply between the battery21and steering motor5. The relay23is controlled by a failsafe ECU25that determines whether the main ECU15is in a malfunction state.

Accordingly, even in case the main ECU15sends a signal to drive the steering motor5, if the failsafe ECU25manipulates the relay23to cut off power delivered from the battery21to the steering motor5, the steering motor5does not generate torque.

The main ECU15receives signals from the steering angle sensor9, torque sensor11and rack sensor13. The steering angle sensor9measures the steering angle of the main steering wheel1, the torque sensor11detects the steering torque of the main steering wheel1, and the rack sensor13detects the operational state of the rack mechanism3. By comparing the signals of the steering angle sensor9and rack sensor13, the main ECU15determines at all times whether the rack mechanism3operates according to the driver's manipulation of the main steering wheel1. The main ECU15also measures via the torque sensor11a torque generated by the reaction force (provided to the reaction motor7) and rotational force (provided by the driver's manipulation) to thereby feedback control the reaction motor7.

The failsafe ECU25, just like the main ECU15, receives signals from the steering angle sensor9and rack sensor13and compares the signals to monitor in real time whether the main ECU15properly performs the control operation.

Provided that the manipulation of the main steering wheel1is improperly applied to the rack mechanism3due to a malfunction of the main ECU15, then the failsafe ECU25detects the malfunction state and controls the relay23as shown inFIG. 3, thereby preventing power supply from the battery21to the steering motor5.

Therefore, the steering motor5prevents generation of an erroneous torque, and the front passenger manipulates the supplement steering wheel17in abnormal conditions of the main ECU15, thereby ensuring the safe steering of the test vehicle.

As the erroneous torque of the steering motor5is not applied to the rack mechanism3, the supplement steering wheel17can easily and appropriately be manipulated.

Another embodiment of the present invention shown inFIG. 4is identical in configuration to the above embodiment ofFIGS. 2 and 3. However, these embodiments are different since the failsafe ECU25may receive the malfunction signal that the main ECU15generates by itself.

The failsafe ECU25determines whether the main ECU15malfunctions by receiving the signals from the steering angle sensor9and rack sensor13or by receiving a malfunction signal that the main ECU15generates by itself in the second embodiment of the present invention. Once it is determined that the main ECU15is improperly operating, the failsafe ECU25controls power provided to the steering motor5by manipulating the relay23.

As apparent from the foregoing, there is an advantage in that test vehicles are easily and properly steered even when the steer-by-wire system malfunctions, resulting in an improvement of the safety of the test vehicles.