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Seven steps to the right drive-by-wire system

Dataspeed Vehicle Interior

Getting started in the autonomous vehicle (AV) industry can seem daunting to most, especially when trying to determine how to actuate an entire vehicles control system. To successfully perform important functions for autonomous driving there are many considerations for product development and engineering. First of all, what does by-wire control of vehicles for research and development (R&D) mean? It is the acceleration, braking, steering, and shifting control of the vehicle. Being able to control those electronically is essential for the development of autonomous vehicles. Secondly, why is this needed? Currently, most R&D for autonomous vehicles is done at a functional level – developing the software for autonomous driving, not the by-wire system. However, the by-wire system is needed to allow that development to take place.

One of the most significant decisions a developer must make is to either engineer their Drive-by-Wire (DBW) system or install a plug-and-play kit, such as the Dataspeed By-Wire Kit. Several factors must be considered before any development to assess against the capabilities, the budget, the resources, and the risk for the project. Project teams should consider actuation, communication architecture, electronic hardware, software, power, reliability, and safety.

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The ADAS (Advanced Driver Assistance Systems) Kit is a complete hardware and software system that allows seamless electronic control of a vehicle’s brake, throttle, steering, and shifting to enable testing for autonomous vehicle applications.

Actuation

For any by-wire system, the actuation that converts the driver’s commands from electronic signals to motion is the core. Actuators are integrated with automotive controls to help optimise the performance of the vehicle. Their presence is key to prevent human interaction to be necessary for driving. Dozens of sensors will be essential to obtain information from the surroundings, and it will be these sensors that will activate the various actuators, which in turn will generate the order to activate the final component. The same conversion from signals into motion needs to be done for the steering, acceleration, braking and the shifting for a by-wire system to work.

Passenger vehicle steering actuation can be done one of two ways: by adding an external motor to the steering and a controller to allow electrical signals to control the steering, or to utilise the electric power steering that is already built into the vehicle. If utilising the electric power steering difficulties may include communication with the motor as well as potential safety issues. The power steering on a vehicle can overpower human input, which needs to be taken into consideration to prevent a bad signal being sent, causing unexpected vehicle motion. Acceleration is straight-forward as many vehicles now having an acceleration sensor, or a pedal sensor, that sends a message to the engine controller which in turn controls the acceleration of the engine. Braking can also be done in a few different ways – you can place a motor and an outside device on the pedal or somewhere on the braking apply system, or for a safer option, you can utilise the motors and the electric braking that is already built into the vehicle.

Several vehicles have electronic stability control which can be utilized for applying brakes on request. However, the drawback is the stability control not being sized to rapidly stop the entire vehicle rather for stopping or controlling one or two wheels at a time. Therefore, the trade-off is you will receive a lower response time for applying the brakes and a bit of motor noise because it is not a continuous running system. The second and best option with the built-in braking is to start with a vehicle that has a brake-by-wire system built into it, as with hybrid and electric vehicles. These have full response time equal to the capabilities of a human emergency brake stop. Like steering, the shifting actuation can be done by adding an external component to allow electrical signals to control the shifting or you can use emerging electronic shifters, though there have been safety issues identified with production vehicles implementing the shift-by-wire systems. Major hazards associated with this type of system is the vehicle not achieving a park state and the vehicle moving in the wrong direction.

Therefore, the best course of action is for the actuation element to utilise what is already in the vehicle due to the convenience of taking advantage of any existing safety measures, and the reliability that has been designed and built into those devices.

Communication Architecture

If you are utilising these actuators that are built into the vehicle, how do you communicate with them? How do you send signals? How do you control them? How do you avoid disrupting other systems that are also communicating and causing faults?

To utilise these actuators, you have to get into the communications architecture which are the protocols of the vehicle. You need an understanding of the Computer Area Network (CAN). There are often multiple CANs communicating with different devices on the vehicles. 

It is important to be familiar with the embedded ADAS (Advanced Driver Assistance Systems) on the vehicle so that you are not deactivating any key safety features as you are changing command levels. Production command protocols and logic need to be understood and addressed to keep all operational systems functional as well as prevent any faults that may occur. Communication can be one of the biggest hurdles in developing a DBW system as it takes knowledge that is often available only through the original OEM or the Tier 1 supplier who created that particular subsystem. 

Knowledge of the vehicle communication systems is required to pass control signals successfully and safely for actuation.

Electronic Hardware

These are controllers that are needed for communication throughout the vehicle, used to process the low-level motion controls, the safety monitoring, and the over-ride that are built into the system. Whether the by-wire vehicle conversion is being done in-house or selecting an off-the-shelf DBW kit, ensuring the electronic hardware is functioning correctly is crucial.

If the vehicle will be used on public roads the safety concept will often drive the design of your processor – meaning the safety plan and safety measures that need to be put in place are often engrained at the controller level. Additionally, you must determine if those safety requirements are within the current electronics or if they need to be additional components.

Software

By-wire software considerations include communication interfaces, basic low-level motion controls, and the designed-in safety measure setting. Speed and steering control methods are required for basic low-level control, with speed control methods including maintaining a speed with minimal oscillation. Steering, or yaw control, methods involve how you are controlling the yaw, either through angle or for steering torque.

Safety measures also need to be developed within the software of the by-wire system – this is where most of the safety elements exist for this type of vehicle control. New safety measures such as driver over-ride settings, control signal limits, and vehicle speed dependencies need to reside in the by-wire system software.

Power

Power management and power distribution are often two of the most overlooked challenges when developing a by-wire equipped vehicle. AVs are typically developed on a retrofitted production vehicle designed with a traditional 12V system. An AV needs an array of specialised sensors to see the world, including cameras, radar and LiDAR. Additionally, the vehicle then needs to process the data by way of advanced computing systems.

Each of these AV components consumes electrical power. While individual sensors might not pose a significant load on the electrical system, the power consumed by an array of sensors and the by-wire system can be substantial. Without sufficient and reliable power, self-driving vehicles could experience hardware faults – potentially causing a substantial risk to both the vehicle and the surrounding environment. To ensure the AV remains functional and dependable it is imperative to verify there is ample power supply for the by-wire system components, as well as the sensors and other hardware.

Reliability

Reliability of a base system for an R&D project is critical to the success of any active safety or AV development. Will the development work every day once it is built? When / if it does not work, is it easy to diagnose and repair? Are there resources available to complete the repair?

The cost in downtime can add up rapidly for AV/ADAS development. Consequently, when the vehicle is the primary development platform and issues arise, all progress is halted until it is fixed.

Safety

What are the safety concerns when executing a by-wire conversion on a vehicle? Having engineered a new product, the by-wire equipped vehicle, generates several classes of hazards which need to be addressed. To address these hazards there are many processes and guidelines to follow, but it can be broken down into four basic steps, starting with conducting a hazard analysis. The team needs to assess what harmful events can happen or be caused by this new device. Next, perform a safety analysis of the system to see how those hazards could be caused by this design and how often they may occur. Subsequently, safety measures need to be added to mitigate these risks and to lower the chance of them happening. Finally, those safety measures need to be verified that they work as intended.

The primary safety measure for nearly all on-road AVs is the safety driver, in combination with the by-wire system. Safety for the end-user is equally important as for the engineers developing the AV. Custom in-house DBW systems generally have a focus and architecture intended for engineer-use only, but who all will be riding in the vehicle? Will the developing engineer always be behind the wheel as the primary safety driver? If there is any chance this answer could be “no” it is imperative that there are proper safety switches and stopping mechanisms available. Should a salesperson perform a demonstration, they should have the capability to stop the vehicle quickly and easily from the autonomous driving mode. Most turn-key DBW systems allow for intuitive emergency stopping through turning the steering wheel, pressing the brake, or triggering an e-stop button.

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A fleet of Autonomous Vehicles kitted out by Dataspeed

Engineering teams then should consider seven factors when deciding between engineering an in-house DBW system or implementing an already available DBW kit, such as the Dataspeed By-Wire Kit. These considerations include actuation, communication architecture, electronic hardware, software, power, reliability, and safety. 

Dataspeed’s By-Wire Kit provides a unique and compatible research and development platform for AV technologies. It allows for seamless control over a vehicles accelerator, brake, steering and shifting to enable testing for AV applications. It features full electronic control with little modification to the vehicle, and without adding any actuators, ensuring all production-level safety features remain intact and fully functioning. By deploying the Dataspeed By-Wire Kit, a development team can reallocate time to focus on sensor and algorithm development instead of the resources and risks as associated with engineering a custom system.