Controlling steer-by-wire steering apparatus

1 . A microprocessor system for a steer-by-wire steering apparatus for a vehicle, the microprocessor system comprising:

a hand wheel actuator controller, comprising a first hand wheel microprocessor and a second hand wheel microprocessor, and arranged to provide control signals for a hand wheel actuator of the steering apparatus,

a front axle actuator controller, comprising a first front axle microprocessor and a second front axle microprocessor, and arranged to provide control signals for a front axle actuator of the steering apparatus;

a first private bus connecting the first hand wheel microprocessor to the first front axle microprocessor, the first private bus comprising a physical layer over which data can be transmitted using a first data link layer format and a second data link layer format different from the first data link layer format; and

a second private bus connecting the second hand wheel microprocessor to the second front axle microprocessor, the second private bus comprising a physical layer over which data can be transmitted using the the first data link layer format or the second data link layer format;

wherein the microprocessor system has:

a first state in which the first private bus uses the first data link layer format and the second private bus uses the second data link layer format; and

a second state wherein at least one of:

the first private bus switches to use the second data link layer format; or

the second private bus switches to use the first data link layer format;

wherein the microprocessor system is arranged to switch from the first state to the second state upon one of the first or second hand wheel microprocessors or the first or second front axle microprocessors determining that there is a fault on the first private bus or the second private bus.

2 . The microprocessor system of claim 1 , in which, when a fault is detected, only one of the private busses switches data link layer format.

3 . The microprocessor system of claim 2 , arranged so as to switch the other one of the first private bus or the second private bus to the data link layer format not currently used by that bus after a predetermined period of time has elapsed.

4 . The microprocessor system of claim 1 , in which the first and second data layer formats are unrelated.

5 . The microprocessor system of claim 1 , in which the first and second data layer formats do not comprise both CAN and FlexRay.

6 . The microprocessor system of claim 1 , in which the first data layer format is CAN and the second data layer format is UART.

7 . The microprocessor system of claim 1 , wherein the microprocessor system is arranged to operate in the second state only for a period of time.

8 . An actuator controller for a steer-by-wire steering apparatus for a vehicle, the actuator controller being arranged to provide control signals for an actuator of the steering apparatus and comprising:

a first microprocessor and a second microprocessor;

a first transceiver for a first private bus connecting the first microprocessor to another actuator controller, the first private bus comprising a physical layer over which data can be transmitted, the first transceiver being arranged to transmit data over the first private bus with a first data link layer format and a second data link layer format different from the first data link layer format; and

a second transceiver for a second private bus connecting the second microprocessor to another actuator controller, the second private bus comprising a physical layer over which data can be transmitted and the second transceiver being arranged to transmit data over the second private bus with the first data link layer format or the second data link layer format;

wherein the actuator controller has:

a first state in which the first transceiver uses the first data layer format and the second transceiver uses the second data layer format; and

a second state where:

the first transceiver switches to use the second data layer format;

the second transceiver switches to use the first data layer format; or

the first transceiver switches to use the second data layer format and the second transceiver switches to use the first data layer format;

in which the actuator controller is arranged to switch from the first state to the second state upon one of the first or second microprocessors determining that there is a fault on the first or second private bus.

9 . A method of operating a steer-by-wire steering apparatus for a vehicle comprising:

providing a hand wheel actuator controller, comprising a first microprocessor and a second microprocessor, and arranged to provide control signals for a hand wheel actuator of the steering apparatus;

providing a front axle actuator controller, comprising a first microprocessor and a second microprocessor, and arranged to provide control signals for a front axle actuator of the steering apparatus;

providing a first private bus connecting the first microprocessor of the hand wheel actuator controller to the first microprocessor of the front axle actuator controller, the first private bus comprising a physical layer over which data can be transmitted with a first data link format and a second data link format different to the first data link layer format; and

providing a second private bus connecting the second microprocessor of the hand wheel actuator controller to the second microprocessor of the front axle actuator controller, the second private bus comprising a physical layer over which data can be transmitted with the first data link format or the second data link format;

the method comprising:

in a first operating mode, transmitting data over the first private bus with the first data layer format and over the second private bus with the second data layer format; and

in a second operating mode:

switching to transmit data over the first private bus using the second data layer format;

switching to transmit data over the second private bus using the first data layer format; or

switching to transmit data over the first private bus using the second data layer format and over the second private bus using the first data layer format;

wherein switching from the first operating mode to the second operating mode occurs upon one of the first or second microprocessors of the hand wheel actuator controller or the front axle actuator controller determining that there is a fault on the first or second private bus.

10 . The method of claim 9 , in which, when a fault is detected, only one of the private busses switches data link layer format.

11 . The method of claim 10 , comprising switching the other one of the first private busses or the second private bus to the data link layer format not currently used by that bus after a predetermined period of time has elapsed.

12 . The method of claim 11 , comprising operating in the second state only for a period of time.

13 . The method of claim 9 , in which the first and second data layer formats do not comprise both CAN and FlexRay.

14 . The method of claim 13 , in which the first data layer format is CAN and the second data layer format is UART.

15 . The method of claim 14 , in which, when a fault is detected, only one of the private busses switches data link layer format.

16 . The method of claim 9 , in which the first and second data layer formats are unrelated.

17 . The method of claim 9 , in which the first data layer format is CAN and the second data layer format is UART.