What is HIL Testing?

What is HIL Testing?

Introduction

Hardware-In-the-Loop (HIL) refers to the process of testing a vehicle’s hardware by integrating it into a software environment and simulating real-world scenarios for the hardware to respond to. A vehicle’s components and subsystems interact with each other cooperatively, so the functionality of smaller components will affect how the entire vehicle operates.

Table of Contents

• How Does the HIL Testing Process Work?
• Who is involved in this process?
• Why is HIL Testing Important?
• Summary

By testing and validating vehicle components across different scenarios, organizations can continue producing vehicles that prioritize safety and reliability. This testing can be done on vehicles with traditional internal combustion engines (ICE), electric vehicles (EVs), and even motorcycles.

Since manufacturers are currently deep in the development of hybrids and EVs, HIL testing will remain essential for validating component behavior now and in the future.

The purpose of HIL testing tools

The overall purpose of HIL testing tools, whether a custom or ADAS HIL solution, is to verify and validate that automotive products operate as intended. From an organizational standpoint, this process helps accelerate product development and reduce any potential expenses from errors or hardware damage.

This testing benefits the overall product lifecycle development process by identifying issues with a component's operation and allowing engineers to address them. Whether pertinent to design or functionality, they can make changes early on to mitigate as many risks as possible. In turn, vehicles are developed with a minimized chance of failures and safety hazards.

HIL testing vs. SIL testing

Differentiating this process from Software-In-the-Loop (SIL) testing may provide additional insight into what HIL testing is and how it works. The main difference between the testing methods is that the vehicle’s hardware and software will be in separate loops.

In addition, one process often occurs before the other. In the product lifecycle development process, software is typically tested before hardware because the software's coding and calibration must function properly. At the same time, test benches will allow for both hardware and software devices to be integrated, which is necessary for integration.

For example, engineers may use an EV test bench to test the interaction between a Battery Management System (BMS) and a Vehicle Control Unit (VCU). There are different phases in which hardware and software can be tested together, but the most significant difference is that HIL testing simulates and tests the hardware itself.

How Does the HIL Testing Process Work?

When thinking about HIL testing and how the process works, an immediate question may arise: What does 'in-the-loop' mean? The in-the-loop aspect of this testing process reflects how the hardware is simulated. By using a test bench—a stationary gearbox or workstation full of equipment—hardware can be tested in a controlled environment.

There are various test benches available, depending on whether the goal is to test components, subsystems, or vehicles. HIL test benches often include relevant vehicle components that can be used in simulation.

Performing HIL testing in the context of the Functional Safety standard ISO 26262, from the International Organization for Standardization (ISO),  is a method many engineers and product developers are familiar with. This methodology incorporates HIL testing within the overall product lifecycle development process.

The first step is establishing the functional safety for how the hardware and software should perform. The next step is to design and develop each based on the previously established requirements. After that, engineers perform HIL testing by placing the hardware within the closed loop of the test bench.

HILs are automated to the point that they can run scenarios simultaneously, executing hundreds of tests in a short period. At the end of the tests, HILs provide a detailed testing report that engineers use to determine whether vehicle components are operating in compliance with their requirements.

The software, equipment, and tools used for HIL testing

Since many organizations perform HIL testing, along with several hardware and software suppliers, this process can be done with various tools and equipment. It depends on what the organizations are most familiar with or most comfortable using for their hardware.

For example, dSPACE—a company that designs HIL hardware—is a resource that engineering teams may use for an HIL test bench. In addition, there are several custom HIL testing tools and solutions, as well as different National Instruments (NI) software options that can be utilized, such as:

• LabVIEW
• VeriStand
• TestStand

Organizations should choose what is best for them based on what they are trying to test and what they are trying to achieve. There are several options to choose from, all of which play a role in HIL testing. The hardware must be connected to the chosen software program for the testing simulation to run. The decision about which software and tools to use may rest with the employees directly involved in this process.

Who is involved in this process?

Like many other automotive processes, HIL testing can involve different employees at different times.

The initial employees involved in HIL testing are software engineers, as they create the simulated testing environment. They dictate which scenarios hardware will test and how it will react. In addition, power electronic engineers may be involved with the construction of the HIL itself. There is a lot of wiring involved in HIL testing because the hardware must be integrated with sensors, actuators, or input/output (I/O) devices that emulate the scenarios previously established by software engineers.

Some engineers can be involved based on the level of hardware being tested. For example, a systems engineer will be directly involved with systems-level HIL testing to test how several systems function cooperatively. Other parties may include product developers who establish requirements and build test scripts. This is how engineers can determine whether components and systems are performing as intended within the testing environment. If not, they may have to go back and adjust the requirements or rewrite new ones entirely.

Different aspects of HIL testing require responsibility from different employees, and each is essential in guaranteeing a safe and efficient product development process.

Why is HIL Testing Important?

The evolution achieved within the automotive industry has continued to place safety at the forefront of product development. HIL testing is important because it is controlled in a simulated environment. The process can focus on vehicles’ hardware functionality at the component and system levels, verifying and validating that the overall vehicle hardware is operating as designed. As vehicle design, software, and technology grow in complexity, HIL testing can mitigate harm to these systems by testing them in a controlled environment.

There are immediate organizational benefits that highlight the importance of HIL testing. The process is meant to save organizations both time and money. The simulation runs many tests that would take longer in real road-testing environments. In addition, costs could increase if there is frequent or cascading damage to the hardware during actual road tests. Though some HILs may require more human intervention than others, the overall process is highly automated, allowing multiple tests to be run at once.

HIL testing also remains important for verifying the compliance of certain hardware with safety requirements. For example, part five of ISO 26262 addresses functional safety at the hardware level. HIL testing enables organizations to verify designs and requirements developed during the early stages of the product lifecycle to comply with the standard. Likewise, part six of ISO 26262 addresses safety at a software development level. This verification is one way to assess the safety and reliability of vehicles that manufacturers continue to develop.

If organizations performed manual testing instead of HIL testing, or its software-focused counterpart, the hardware and software integrated into vehicles could be more tedious to verify and validate against previously established testing requirements. Once these vehicles were in the market for consumers to buy, manufacturers could no longer ensure their reliability. That could lead to component and software failures, resulting in product recalls. Since manual testing would most likely require more time and money, HIL testing is the more efficient option.

Debugging

Another part of HIL testing focuses on identifying issues and uncovering unexpected errors. Debugging is the process of correcting these issues found in the testing results of this process. HIL testing won’t uncover every issue, but engineers can run hardware through simulations repeatedly to ensure it complies with the requirements. This is important because it uncovers hardware failures and provides the opportunity to implement safety in the design (e.g., adding redundant hardware, watchdogs, etc.).

Engineers can assess the overall robustness of hardware by testing and debugging. If a component is producing unexpected results or identifying multiple errors, engineers can run fault-mitigation tests to provide context for the issues. Identifying faults and testing how the component reacts determines which changes need to be made in the design, or even the requirements established beforehand, to safely mitigate those faults. This debugging process mitigates additional hardware faults by uncovering issues frequently and providing engineers with opportunities to consider safety and performance more closely. This is another example of the opportunities HIL testing can provide, but organizations may also face constraints within this process.

Constraints and considerations

There are some considerations to keep in mind when undergoing HIL testing. One initial constraint involves setting up the HIL itself. Engineers have to set up the HIL test bench with all the equipment needed for testing and simulation, which can be time-consuming. In addition, significant code must be written to automate the HIL system. The labor is tedious at the front end of this process, but it is necessary to start integrating the hardware and simulating it. The setup may take some time, but the HIL testing itself accelerates the product development process overall, so the payoff is worth the immediate constraints.

Another consideration for HIL testing is its role in the future of automotive development. The electrification of vehicles is well underway, and HIL testing will have a significant role in EV development as it continues to evolve. Some organizations have facilities dedicated to EV testing and development, meaning they most likely have, or plan to have, a HIL integrated into their facilities as well. EV components and subsystems can be tested to ensure they operate as intended and that their designs are robust. More specifically, HIL testing will be essential for verifying the safety and operability of electrified components such as batteries and BMSs.

Suppliers and manufacturers must ensure that the EV components they produce can operate without harming other systems or people. These considerations will remain relevant as the industry continues making significant investments in electrification in the years to come.

Summary

The advancement of modern transportation has established different milestones in software and technology. Vehicles are safety-critical systems that will become even more critical as their complexity evolves. By using processes such as HIL testing, engineers can test components’ functionality in simulated environments and address any issues identified. By addressing these issues, they can ensure that vehicles meet safety requirements and reduce the risk of safety-related failures on the roads humans use daily.