When it comes to developing safe connected, autonomous vehicle technology, interfacing an autonomous driving system with any given vehicle has always been an industry challenge, especially when considering how to make the entire autonomous system as safe, scalable, and flexible as possible.
The system enabling this interface is known as the ‘drive-by-wire’ (DBW) system. DBW provides the means to control the throttle, steering, braking, gears and ancillary systems of a vehicle, and involves electronic replacement of traditional mechanical linkages connecting the vehicle to the driver.
In the autonomous vehicle (AV) world, control methodology is used to steer, brake, accelerate and change gear where necessary, whilst also passing back data on the current vehicle “state”. This is done via the autonomous software, or teleoperation software, enabled by the drive-by-wire system.
Whilst extensive resources have been dedicated into autonomous software development, it is the “automotive” technology stack present in the vehicle that enables the autonomous software to “drive” a vehicle. Therefore, the most critical hygiene factors for autonomous vehicles are the drive-by-wire system and the safety analysis of that system, with huge implications for safety, reliability, scalability and time-to-market.
The most important elements of a retrofit DBW system
Front and centre of the drive-by-wire challenge is safety. Building the DBW system in line with ISO 26262 standards, the existence of independent channels of sensors to detect faults, ensuring the system can be disabled when needed, having a functional safety analysis document that comes with the drive-by-wire system, are just some of the myriad of points that might arise when considering safety implications around DBW systems. What is sure, is that being able to rely on drive-by-wire is essential to build a wider safety case around autonomous vehicle deployments.
- Operating “Level”
Related to the safety pointers above, are considerations around the “level” of the drive-by-wire system. Those familiar with the SAE levels of autonomy will have some idea of the reference here which focuses on the level of maturity of autonomous technology and the presence of a “safety” driver. Most DBW systems in the market today are termed as “Level 2” and require an alert, trained safety driver to be ready to take over at all times. Some suppliers are developing Level 4 systems, where you can take the safety driver out of the loop, within certain scenarios also called Operational Design Domains.
An important consideration is the usage of the drive-by-wire system. Most systems are based on “CANBus”, the standard for on-vehicle communications, but some suppliers will provide other interfaces, such as ROS – see an example here, which act as a translator between CAN and the chosen programming language for the autonomous driving stack.
An important part of the drive-by-wire system, particularly when looking at R&D applications, is system usability, centred around the human-machine interface. How a safety driver can arm and initiate the system, and how that safety driver then disables the system in case of error is key to all occupants and engineers having confidence in the vehicle.
Disabling a DBW system is an important part of the wider safety considerations, with the best drive-by-wire systems offering intuitive takeover methods, such as grabbing the wheel, or pressing the brake as easy ways to disable the system if the autonomous driving software has not performed as expected.
- Reliability and Support
In order to deploy autonomous vehicles on the road, developers need to be able to access test vehicles as and when they need them. A big part of this is ensuring that the system is reliable, with maximum uptime to ensure that developers can maximise their road miles.
An important part of this is having detailed documentation, maintenance schedules and dedicated support to troubleshoot integration issues, and keep the vehicle available for testing as and when required.
- Legality and Regulations
Each and every country is different when it comes to the regulation of retro-fit drive-by-wire systems, destined for public-road trials. In the UK, such systems need to comply with UK Construction and Use laws. Different territories take different approaches to this, with organisations such as TÜV SÜD providing licenses in countries such as Germany.
However, there should be a solid safety analysis that can be applied to the relevant laws, regulations and approval processes for the designated country, behind each and every deployment of a drive-by-wire vehicle for research purposes.
A developer may aim to be using a drive-by-wire to develop a system relevant to many vehicle types, and suitable for wider deployment. As such the scalability of such systems to multiple different vehicle types, across use cases and manufacturers.
Even when starting with one test vehicle, it should be considered how the CAV technology will ultimately end up in the field.
The vehicle platform chosen for the drive-by-wire system is a vital component in the development and deployment of CAVs. Does the drive-by-wire solution allow work to commence on an “easy-to-use” test vehicle, before migrating to a use-case specific vehicle? Choosing a supplier that has the vehicles “off-the-shelf” or going for a bespoke vehicle can hugely impact on the time it takes to deploy the AV on the road.