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New in continuous variable transmissions

Punch Powertrain makes transmissions, but not the kind we all know. It develops and produces a new generation of Continuous Variable Transmissions (CVTs). These are different because instead of the usual 4–6 gears, they have a continuous number of gears and a system that automatically adjusts the ratio for the best performance.

Stefan Geusens, (age 44) has been working at Punch Powertrain for six months, and he has been at TMC for almost four years. He is contributing to the development of the control and software system for the newest generation of their CVT, called the VT5. “Engines are constantly getting stronger, so we needed to make our transmission stronger as well. Dimensioning everything in such a way that it can handle these increased forces. But unfortunately that’s not enough by itself to make the system work. Because when you make materials and components bigger and stronger they start to behave differently.”

Punch Powertrain has its heritage in DAF. As well as its trucks, DAF was also known for its small cars. These had a special continuous transmission that made them drive as fast backwards as forwards. “With those little DAFs you didn’t have gears. That system used a belt that pulled. We now use a belt that pushes, because when you pull at something, it can break. Pushing can withstand much bigger forces. When the engine pushes on this belt, little metal plates come together and form a metal rod. What you get is a very stiff connection, more so than you would have with a belt that pulls, and thus you get better performance.”

Stefan and his team are responsible for the development of the system controls: all the software and algorithms that make the transmission work smoothly and automatically. “The system is mainly aimed at comfort and decreasing fuel-consumption. To make the algorithms we get very accurate specifications. For example, at a temperature of -10 degrees Celsius and at an inclination of 20 degrees, the car needs to drive off without jolting and without riding backwards. We need to translate these specifications to numbers for the software. And then we need to develop the algorithms to implement this in the transmission and make it behave the way we want. Of course we were involved in the designing of the hardware, but now that we are at implementation stage, only minimal adjustments are possible on the hardware. It’s up to us now to get the control systems right to make it all work.”

Control is the new frontier in car technology according to Stefan. Every component of the hardware now has specific software that makes it work better.

“The CVT is a hydraulic system. Almost all of the actuation happens hydraulically. So temperature has a high impact on the system. Also the friction of the clutch behaves very differently at different temperatures. All those things and more are evened out with software that we develop. You see this more and more in modern design. Software and algorithms are used to increase comfort and to surpass the limitations of the hardware. So our job is to stretch the transmissions’ potential further when the hardware has reached its limits.”

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