Assessing the compliance of Steer-by-Wire systems for Individual Vehicle Approval
Approval of vehicles through Individual Vehicle Approval (IVA) is regulated by the Road Vehicles (Approval) Regulations 2020 (SI 2020 No. 818). As detailed in this legislation, steering systems are required to provide evidence of compliance to Directive 70/311/EEC (as last amended by Directive 1999/7/EC).
The scope of Directive 70/311/EEC specifically excludes steering equipment with purely electric transmission, and so it is not possible to demonstrate compliance to this legislation for Steer-by-Wire systems. Safety of these systems therefore needs to be demonstrated through equivalent legislation, in this case UNECE Regulation No. 79 (R79). R79 was updated in 2003 to permit the approval of Steer-by-Wire systems (defined in R79 as ‘Full Power Steering’ systems), with supplement 3 to the 01 series of amendments (hereafter referred to as ‘R79.01.S3’). R79 has been regularly updated since and is now at the 04 series of amendments.
Steer-by-Wire systems are in scope of R79 Annex 6 – ‘special requirements to be applied to the safety aspects of electronic control systems’. Demonstrating compliance to Annex 6 requires an audit of “documentation, fault strategy and verification with respect to safety aspects of Electronic Systems and Complex Electronic Vehicle Control Systems”.
Compliance to R79 for Steer-by-Wire Systems needs to be in the form of evidence provided from the vehicle manufacturer or system developer. This will be either:
- An approval to R79.01.S3 or later, with sufficient attached documentation to confirm it covers the Steer-by-Wire system and applies to the vehicle presented.
Or,
- A test report to R79.01.S3 or later from a recognised Technical Service, with sufficient attached documentation to confirm it covers the Steer by Wire, applies to the vehicle presented, confirms compliance of the Steer-by-Wire system and includes the required documentation relating to Annex 6.
In lieu of not having either of the above the VCA can work with vehicle manufacturers or system developers to demonstrate compliance to R79.01.S3 or later, through the following:
- Review of Manufacturer Documentation
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- System explanation in the form of a formal document package as required by Annex 6
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- System architecture / wiring diagram
- Performance Evidence
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- Assessment of general and failure provisions for Full Power System Systems, including system tell-tales.
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- Testing of system in both intact and failed conditions.
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- If applicable, testing of braking performance for common energy sources.
- Auditing Evidence
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- Audit of the safety concept, development process and associated functional failure tests as required by Annex 6.
Involvement of the vehicle manufacturer or system developer is necessary due to the nature of Annex 6 auditing requiring provision of information on the system and on the development process. To help understand the need for this, here are two extracts from the legislation:
- R79.01.S3, Annex 6, 3.1.:
The manufacturer shall provide a documentation package which gives access to the basic design of “The System” and the means by which it is linked to other vehicle systems or by which it directly controls output variables. The function(s) of “The System” and the safety concept, as laid down by the manufacturer, shall be explained. Documentation shall be brief, yet provide evidence that the design and development has had the benefit of expertise from all the system fields which are involved. For periodic technical inspections, the documentation shall describe how the current operational status of “The System” can be checked.
- R79.01.S3, Annex 6, 3.4.4:
The documentation shall be supported, by an analysis which shows, in overall terms, how the system will behave on the occurrence of any one of those specified faults which will have a bearing on vehicle control performance or safety.
This may be based on a Failure Mode and Effect Analysis (FMEA), a Fault Tree Analysis (FTA) or any similar process appropriate to system safety considerations.
The chosen analytical approach(es) shall be established and maintained by the Manufacturer and shall be made open for inspection by the technical service at the time of the type approval.
To conclude, approving vehicles through IVA when fitted with Steer-by-Wire is possible so long as there is direct involvement of the vehicle manufacturer or system developer in providing evidence of compliance to R79.01.S3.
Regulatory and technology group
Vehicle Certificaiton Agency
E-Mail: RTG@vca.gov.uk