James Hayes outlines how vehicle development can be accelerated by using vehicle-in-the-loop testing
You may have come across the term ‘in-the-loop’ before, as it is commonly used in automotive development together with different subjects such as model-, software- and hardware- to create a brand-new sentence. But what does that phrase actually mean? An English dictionary will tell you that if someone is the ‘in-the-loop’, they are part of a group of people who make decisions about important things, or they know about these decisions. This also applies in automotive terms, where, by putting a model, software, hardware or even a vehicle in-the-loop together with other subsystems, we can understand how it behaves under various scenarios and conditions.
In a traditional V-cycle development process, the in-the-loop would follow a sequential path starting with models, progressing through various steps of software- and hardware-in-the-loops up to a vehicle that is then driven on the road. The V-cycle has proven itself over many decades but is now being challenged by alternative development processes, such as agile development, which, by nature, is more gradual and is usually visualised as circular. The in-the-loop exists in this type of process as well, but then also in parallel.
With record-high fuel prices and government incentives for low-emission vehicles, the consumer adoption of electric vehicles has accelerated, reaching an 8% share of new European vehicle registrations, according to a recent study by McKinsey. The pressure to develop new vehicle platforms, together with the increasing complexity of vehicle systems such as advanced driver assistance systems (ADAS), makes OEMs look at alternative methods to be able to increase their development pace and capacity, shortening the time to market. One way to achieve higher development efficiency is to use the concept of vehicle-in-the-loop (ViL) testing, a method that OEMs and Tier 1s are adopting to a greater extent.
The company Rototest has been supplying solutions for vehicle-in-the-loop for many years. In Rototest’s case, the object that is put in-the-loop can be anything, such as part of a powertrain, a prototype vehicle or a production vehicle. While the focus in the early days was on durability and track simulations, the main focus today tends to be more advanced configurations, including the full ADAS architecture of the vehicle.
This architecture can generally be described as being composed of three subsystems: the perception system, the decision system and the actuation system. The perception system is responsible for monitoring the surroundings of the vehicle and can include anything from a single camera to multiple cameras, short-range and long-range radars, ultrasonic sensors and LIDARs, etc. Depending on specific architecture, the perception system may also include the functionality of sensor fusion, meaning that the perception system takes information from multiple sensors and fuses it together to supply the next system in the chain – the decision system – with better information. An example could be a camera that detects an object in view. Together with a radar that determines the distance to the object, the information could be fused together and provided to the decision system.
The decision system does exactly what you’d expect – it makes decisions. Should we warn the driver of the object in front? Should we apply the brakes as we are approaching too quickly? Should we apply steering to keep the vehicle in the lane?
These are typical decisions for the system to make and then provide the actuation system with the appropriate task for action. The actuation system executes the decision that has been decided. A simplified comparison of the ADAS architecture with a human driver would be that the perception system would be the eyes, the decision system the brain, and the actuation system the muscles operating the accelerator, brake pedal and steering wheel.
A typical vehicle-in-the-loop configuration for ADAS applications built upon Rototest’s technology and an open platform would in general include Rototest’s high-dynamic powertrain dynamometer, a simulation environment of choice and a stimuli system such as over-the-air simulators or bus-injection, depending on access. The simulation environment is responsible for simulating the vehicle’s surroundings, i.e., what the vehicle would ‘see’ if it was driven on the road. This means that the simulation environment feeds the stimuli system with information of how the vehicle is travelling in the simulated environment and how it is interacting with other objects such as other vehicles or vulnerable road users. The dynamometer’s responsibility lies in providing the correct response and load back to the vehicle’s powertrain so that it represents actual road driving.
The main benefit of Rototest’s vehicle-in-the-loop platform is that the decision and actuation systems can be fully tested, optimised and, thanks to the truly road-like behaviour of Rototest’s dynamometer, calibrated before bringing the vehicle to a test track – thereby enabling a huge time-saving potential. This, as in the controlled environment of the lab, means that precise repetitions of complex manoeuvres can be made repeatedly without losing time repositioning the test vehicle and test objects on the track. And, naturally, weather is not a concern in a vehicle-in-the-loop scenario as any weather can be simulated, allowing you to decide if and when you want rain.