21 Jul 2022
21 Jul 2022

How hybrid testing speeds up transmission development

Testing transmissions can be a complicated business. Transmissions need to align with every other component of a car, while some parts are still in development and not available for testing. Which is where hybrid test beds come in. Here Punch Powertrain tests its transmissions in a partly physical, partly virtual set-up, where software simulates certain components. A state-of-the-art technology that allows for quick turn-around and flexibility.

One area where this comes in handy is acoustic testing. Engineers here test the shifting noise a transmission makes. Which they can start doing even when they don't have key components, like the engine, yet. Virtually simulating the engine also offers the advantage that there's less noise from a combustion engine, allowing for better assessment of the transmission noise.

Punch Powertrain can simulate a range of conditions using its software. "We can for example give the car more slope or load, and we can play with the speed and forces", says Ilyas Barrou, test rig software developer. "It's like we have a real car on the test bed."

There's two big ways to do hybrid testing. One in which a real engine is present in the test bed, the other in which a virtual engine is simulated. But simulation is of course not just limited to the engine. "Before you can test a transmission, you also need to simulate components like the ABS", says Pepijn Peeters, test rig engineer. "We also simulate the load on the wheels, so the transmission experiences conditions similar to an actual vehicle. We even go so far that if you suddenly accelerate, the test bed will simulate the car pushing, which has a small effect on the transmission."

This testing capacity has made Punch Powertrain into a global technology leader. "It's pretty unique", says Peeters. "There are for example only 12 acoustic NDTS test beds like ours in the world, and most of them are in China."

Safety and speed

So why is this combination of virtual and physical testing so useful? It's, of course, faster, since engineers don't need to wait for components that are still under development. But there's more to hybrid testing than just speed. "You also don't have fuel lines lying around, which makes it 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 do 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 hybrids

One of Punch Powertrain's next 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 ICU and the transmission with a TCU, you also have the e-machine with an MCU and a battery, with an associated management system. On top of that there's a powertrain control unit, or PCU. So there's a much larger amount of components that need to be simulated."

Designing a hybrid test bed that can handle this was complicated, but Punch Powertrain's new technology should be ready for production in a 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 simpler. So if you know how to simulate a hybrid, you're ready for EV's."

The point of all of this testing is of course to serve Punch Powertrain's customers in a better way. "It gives a development project the maximum degree of flexibility", concludes Peeters. "We are ready for the future with our new testing rigs. If you compare our company to five years ago, we are taking huge steps. Customers are seeking us out for this t