How hardware-in-the-loop testing speeds up transmission development

Developing transmissions is a complicated business. Transmissions need to work in harmony  with every other component of a car, while some parts are still in development and not available for testing. This is where hardware-in-the-loop testing comes in. Here Punch Powertrain tests its transmissions in a partly physical, partly virtual set-up, where software simulates certain hardware components in the loop. A state-of-the-art technology that allows for quick turn-around and flexibility.

One area where this approach is used is in acoustic testing. For example, the shifting noise a transmission makes. “Using the hardware-in-the-loop methodology we don’t need to wait until the development of vital components, like the combustion engine, is finished”, says Pepijn Peeters, test bench engineer. “In fact for the specific case of acoustic testing, the combustion engine is unwanted as it makes a significant amount of noise, making the acoustic measurement more difficult. By simulating the combustion engine, the behavior is replicated without the noise associated with a combustion engine, making the acoustic measurements more accurate.”

Punch Powertrain has full in-house capabilities for developing various software required to  simulate a range of conditions during testing.  “We can for example increase the slope to the simulated road, add load to the car, change the applied forces or the desired speed. Furthermore, this setup enables to adjust the characteristic and the dynamic of the car, such as weight, wheel radius etc”, says Ilyas Barrou, test bench software developer. “We are able to fully simulate any ‘real’ car  in ‘real’ environment.”

"Before you can even start testing a transmission, you need to simulate components like the ABS-unit"

- Pepijn Peeters

There are two major ways to execute hardware-in-the-loop testing. One in which a real engine is present in the test bench, the other in which an engine is emulated with a very dynamic motor, that has the advantage to not consuming oil or fuel and being very flexible: easier to change the application parameters of the motor than changing a real engine. But simulation is of course not just limited to the engine. , test bench engineer. “We also simulate the load on the wheels, so the transmission experiences conditions similar to an actual vehicle. We can go far in this. For example, if you suddenly accelerate, the test bench will simulate the engine moving in the engine mounts. This will lead to slightly lower forces on the transmission.”

This testing capacity has made Punch Powertrain into a global technology leader. ” Our approach is exceptional”, says Peeters. “There are, for example, only 12 acoustic NDTS test benches like ours in the world, and most of them are in China. The acoustic properties in combination with the extremely low inertia to simulate a combustion engine with a virtually silent electric motor”

Safety and speed

So why is this combination of virtual and physical testing so useful? It is, of course, faster, since engineers don’t need to wait for components that are still under development. But there is more to hardware-in-the-loop testing than just speed, “As you don’t have fuel lines or exhaust systems installed, there is no need for CO, CO2 and fuel leak detection, making testing safer”, says Peeters. “Virtual testing is more accurate than using older, non-representative models of certain components. And we can switch easily, allowing us to for example test a transmission with different types of engines.”

“To validate a transmission we need to conduct many tests”, adds Barrou. “Now we can do that partly using software. We can see how the transmission performs on the highway or in the city. Anything you can do in a real car we can simulate on our test bench.”

Testing hybrid vehicles

One of Punch Powertrain’s current engineering challenges is simulating a hybrid car, which is more difficult compared to one with just an internal combustion engine. “A hybrid transmission adds another layer of complexity”, says Peeters. “It’s not just the engine with the ECU (Engine Control Unit) and the transmission with a TCU (Transmission Control Unit), you also have the electric motor with an MCU (Microcontroller Unit) and a battery, with an associated battery management system. On top of this, there is a Power Control Unit, or PCU. So there is a much larger amount of components that need to be simulated and need to work together.”

Designing a hybrid test bench that can handle this was complicated, but Punch Powertrain’s new technology is ready and production of hybrid test benches will begin in few months. Which is a step on the way to making the company ready for the future. “Testing hybrid transmissions is the most complicated testing you can do”, says Peeters. “An EV on the other hand is somewhat simpler as it requires less hardware and software components in the loop.”

The key goal is to serve Punch Powertrain’s customers in a more flexible way, faster. “Our approach and equipment give a development project the maximum degree of flexibility”, concludes Peeters. “We are ready for the future with our new test benches and corresponding software engineering. In the last 5 years, we have taken huge steps in this field and customers are seeking us out for this technology”.