What is vehicle-in-the-loop testing?

Successful software development in the automotive industry — where the physical safety of drivers, passengers and pedestrians is paramount — is heavily dependent on code verification and validation. As advanced safety and autonomous driving programs become increasingly complex and interdependent, simulation testing can only go so far. And road testing is both expensive and time-consuming.

Vehicle-in-the-loop (VIL) testing is an approach that fills the gap between software or hardware simulations and full road testing. Common VIL testing applications include:

  • Verifying features such as parking assist, lane changing, emergency braking and evasive steering, along with autonomous driving functions.
  • Providing a safe environment to perform dangerous and risky maneuvers requiring target vehicles without the worry of collision.
  • Using repeatable scenarios for edge case tuning.
  • Reducing the cost of real target vehicle drivers by virtualizing them.
  • Using in-vehicle automated test case loading and real-time data post-processing to significantly reduce vehicle testing times by as much as 70 percent.

VIL is actually one of the last steps in the testing process. In the early phases of software development, testers will often first use software-in-the-loop (SIL), which simulates the vehicle and its entire environment. These software-based simulations can run faster than real-time tests and are effective in verifying multiple scenarios quickly. The next phase of testing is hardware-in-the-loop (HIL), a more complex process that uses physical test benches in a lab environment that send inputs from actual radars and cameras to an electronic control unit (ECU).

The next step is VIL testing, which typically occurs on a closed test track using a real vehicle. A human driver sits behind the wheel, but the inputs that the vehicle’s ECU responds to are simulated. In other words, the pedestrian carelessly stepping in front of the vehicle is not really there — but an ECU under test doesn’t know that. The ECU will still send a signal to apply the brakes, and testers can measure the effectiveness of the whole vehicle working as a system.

VIL has several benefits:

  • VIL enables the testing of complex software systems without the need to physically construct a test environment, which can be a significant cost saver. For example, without VIL, a test environment might require the use of a dummy to represent a pedestrian.
  • VIL enables repeatable testing of multiple scenarios in a vehicle environment.
  • VIL allows the testing of critical and dangerous driving situations for a vehicle.
  • The VIL environment reduces the amount of time needed for vehicle test integration and for the use of test tracks and special test environments to verify functionality changes and feature enhancements during software development iterations.
  • VIL supports the qualification of a system to be ready for time-consuming and extensive on-road vehicle tests.

How it works

VIL testing is extremely complex. It requires testers to create a simulation environment that can accurately represent real-world situations. A VIL environment will include traffic, road signs, road markings and so forth. The test equipment then presents that simulated environment to a real vehicle — that is, testers drive the vehicle on a test track, but the inputs for its sensors come from the simulation.

To make that work, VIL needs to be able to synchronize the simulation environment with the real environment. For instance, if the simulation scenario requires that a vehicle apply its brakes, the real-world vehicle should stop in time to avoid hitting the simulated object.

In an autonomous driving scenario, testers could measure how smooth the handoff is between the autonomous system and the human driver. VIL testing enables testers to analyze and factor in human behavior in real-world situations without putting anyone at risk.

Other benefits of VIL include risk-free testing of critical vehicle maneuvers, the ability to reproduce real-world conditions at will, and the ability to measure real vehicle dynamics. In addition, there are opportunities to leverage augmented and virtual reality technology, where the driver wears a headset rather than looking at a screen mounted on the dashboard.