Getting started in the autonomous vehicle (AV) industry can seem daunting to most, especially when trying to determine how to actuate an entire vehicle’s control system. In order to successfully perform important functions for autonomous driving, there are many considerations for a product development and engineering team to consider. First of all, what does by-wire control of vehicles for research and development (R&D) really mean? It is the acceleration, braking, steering, and shifting control of the vehicle. Being able to control those electronically is necessary to do development on autonomous vehicles. Second, why is this needed and why is this being discussed? Currently, most R&D for autonomous vehicles is done at the functional level. What is being developed is the software for the autonomous driving, not the by-wire system. However, the by-wire system is needed to allow that development to take place.
That being said, one of the most significant decisions a developer must make is to either engineer their own Drive-by-Wire (DBW) system or install a plug-and-play kit, such as the Dataspeed By-Wire Kit. Several factors must be considered prior to any development to assess against the capabilities, the budget, the resources, and the risk for the project. Project teams should consider the actuation, communication architecture, electronic hardware, software, power, reliability, and safety.
The core of any by-wire system is the actuation that converts the driver’s commands from electronic signals to motion. Actuators are integrated with automotive controls to help optimize the vehicles’ performance. 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. It will be sensors that will activate the various actuators, which in turn, will generate the order to activate the final component. Essentially, the same conversion from signals into motion need 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 utilize the electric power steering that is already built into the vehicle. If utilizing the electric power steering, which many vehicles are now equipped with, difficulties may include communication with the motor as well as potential safety issues. The power steering on a vehicle has the capability to overpower human input, which needs to be taken into consideration in order to prevent a bad signal being sent, causing unexpected vehicle motion. Acceleration is fairly straight-forward since almost all 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, like steering, 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 utilize the motors and the electric braking that is already built into the vehicle.
Typically, all U.S. 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. Conversely, it is sized 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 option with the built-in braking, which is certainly the best option, is to start with a vehicle that has a brake-by-wire system built into it. The brake-by-wire production system is typically found on hybrid vehicles 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 utilize emerging electronic shifters. However, there have been safety issues identified with production vehicles implementing the shift by-wire systems, which have led to recalls. The major hazards associated with this type of system is the vehicle not achieving a park state and the vehicle moving in the wrong direction.
In summary, it is desirable for the actuation element to utilize what is already in the vehicle. This is due to the convenience of being able to take advantage of any existing safety measures, as well as the reliability that has been designed and built into those devices.
The second consideration is the communication architecture of the vehicle. If you are utilizing 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 utilize these actuators, you really 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 in order 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. In brief, knowledge of the vehicle communication systems is required to pass control signals successfully and safely for actuation.
The electronic hardware are the controllers that are needed for communication throughout the vehicle. Essentially, the electronics are 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 utilized 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 added components.
By-wire software considerations include communication interfaces, the basic low-level motion controls, and the designed-in safety measure setting. Speed and steering control methods are required for the basic low-level control. Speed control methods include maintaining a speed without too much 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. In fact, this is where most of the safety elements exist for this type of a 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 management and power distribution are often two of the most overlooked challenges when developing a by-wire equipped vehicle. Today, AVs are typically developed on a retrofitted production vehicle, which are designed with a traditional 12V system. An AV needs an array of specialized sensors to see the world, including cameras, radars, and lidars. Additionally, the vehicle then needs to process the data by way of advanced computing systems.
Each of these AV components consume 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 substantial risk to both the vehicle and the world in which it is driving. 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.
Often overlooked, the reliability of a base system for an R&D project is critical to the success of any active safety or AV development. There are a handful of important questions that should raise concerns: Will the development work every day once it is built? When/if it does not work, which is hopefully a rare occurrence, 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.
Last, but certainly not least, is safety. What are the safety concerns when executing a by-wire conversion on a vehicle? It should be noted that having engineered a new product, the by-wire equipped vehicle, generates several classes of hazards which need to be addressed. In order to address these hazards, there are many different 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. Lastly, those safety measures need to be verified that they work as intended.
The reality is that 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 by means of turning the steering wheel, pressing the brake, or triggering an e-stop button.
All in all, plug-and-play by-wire systems must include functional safety features out-of-the-box. With any DBW platform, it is important to refer to regional laws and regulations that may specify required safety measures and procedures for autonomous vehicles.
To conclude, engineering teams 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 the actuation, communication architecture, electronic hardware, software, power, reliability, and safety. Moreover, the capabilities, the budget, the resources, and the risks associated with engineering a custom drive-by-wire system is something that should deliberated from the very start.
Dataspeed’s By-Wire Kit provides a unique and compatible research and development platform for AV technologies. It allows for seamless control over a vehicle’s throttle, 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 utilizing 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.