Steering system

1. A steering system, comprising:

a steering mechanism configured to turn a steered wheel in response to a steering operation;

a motor configured to apply a motor torque to the steering mechanism;

a prioritized torque sensor and a redundant torque sensor each configured to detect a steering torque based on a twist of a torsion bar provided on a steering shaft of the steering mechanism, the prioritized torque sensor including a first prioritized detector and a second prioritized detector each configured to output a prioritized detection value depending on the twist of the torsion bar, the redundant torque sensor including a first redundant detector and a second redundant detector each configured to output a redundant detection value depending on the twist of the torsion bar;

a controller configured to control actuation of the motor based on the steering torque;

a first signal line and a second signal line each connecting the prioritized torque sensor and the controller; and

a common signal line connecting the redundant torque sensor and the controller, wherein:

the prioritized torque sensor is configured to transmit, via the first signal line, a first prioritized detection signal containing the prioritized detection value output from the first prioritized detector;

the prioritized torque sensor is configured to transmit, via the second signal line, a second prioritized detection signal containing the prioritized detection value output from the second prioritized detector;

the redundant torque sensor is configured to transmit, via the common signal line, a first redundant detection signal and a second redundant detection signal containing the redundant detection values output from the first redundant detector and the second redundant detector, respectively; and

an information amount of each of the prioritized detection values contained in the first prioritized detection signal and the second prioritized detection signal is larger than an information amount of each of the redundant detection values contained in the first redundant detection signal and the second redundant detection signal.

2. The steering system according to claim 1 , wherein:

each of the first prioritized detector, the second prioritized detector, the first redundant detector, and the second redundant detector includes:

a detection element configured to output an analog value depending on the twist of the torsion bar; and

an A/D converter configured to output a digital value obtained through A/D conversion of the analog value; and

a number of bits for quantizing the analog value by the A/D converter of each of the first prioritized detector and the second prioritized detector is larger than a number of bits for quantizing the analog value by the A/D converter of each of the first redundant detector and the second redundant detector.

3. The steering system according to claim 1 , wherein:

the controller is configured to calculate a prioritized torque command value that is a target value of the motor torque based on the steering torque detected by the prioritized torque sensor;

the controller is configured to calculate a redundant torque command value that is a target value of the motor torque based on the steering torque detected by the redundant torque sensor;

the controller is configured to control the actuation of the motor so that the motor torque is a torque indicated by the prioritized torque command value or the redundant torque command value; and

a number of arithmetic processing operations for calculating the redundant torque command value by the controller is smaller than a number of arithmetic processing operations for calculating the prioritized torque command value by the controller.

4. The steering system according to claim 3 , wherein:

the controller is configured to calculate a target steering torque that is a target value of the steering torque detected by the prioritized torque sensor;

the controller is configured to calculate a torque feedback component by executing torque feedback control for causing the steering torque detected by the prioritized torque sensor to follow the target steering torque; and

the controller is configured to calculate the prioritized torque command value based on the torque feedback component.

5. A steering system, comprising:

a steering mechanism configured to turn a steered wheel in response to a steering operation;

a motor configured to apply a motor torque to the steering mechanism;

a prioritized torque sensor and a redundant torque sensor each configured to detect a steering torque based on a twist of a torsion bar provided on a steering shaft of the steering mechanism, the prioritized torque sensor including a first prioritized detector and a second prioritized detector each configured to output a prioritized detection value depending on the twist of the torsion bar, the redundant torque sensor including a first redundant detector and a second redundant detector each configured to output a redundant detection value depending on the twist of the torsion bar;

a controller configured to control actuation of the motor based on the steering torque;

a first signal line and a second signal line each connecting the prioritized torque sensor and the controller; and

a common signal line connecting the redundant torque sensor and the controller, wherein:

the prioritized torque sensor is configured to transmit, via the first signal line, a first prioritized detection signal containing the prioritized detection value output from the first prioritized detector;

the prioritized torque sensor is configured to transmit, via the second signal line, a second prioritized detection signal containing the prioritized detection value output from the second prioritized detector;

the redundant torque sensor is configured to transmit, via the common signal line, a first redundant detection signal and a second redundant detection signal containing the redundant detection values output from the first redundant detector and the second redundant detector, respectively;

the controller is configured to calculate a prioritized torque command value that is a target value of the motor torque based on the steering torque detected by the prioritized torque sensor;

the controller is configured to calculate a redundant torque command value that is a target value of the motor torque based on the steering torque detected by the redundant torque sensor;

the controller is configured to control the actuation of the motor so that the motor torque is a torque indicated by the prioritized torque command value or the redundant torque command value; and

a number of arithmetic processing operations for calculating the redundant torque command value by the controller is smaller than a number of arithmetic processing operations for calculating the prioritized torque command value by the controller.

6. The steering system according to claim 5 , wherein:

the controller is configured to calculate a target steering torque that is a target value of the steering torque detected by the prioritized torque sensor;

the controller is configured to calculate a torque feedback component by executing torque feedback control for causing the steering torque detected by the prioritized torque sensor to follow the target steering torque; and

the controller is configured to calculate the prioritized torque command value based on the torque feedback component.