Q&A: Craig Balis
Honeywell Turbo Technology's engineering chief explains how his team's next-generation turbochargers will boost gasoline engine downsizing
- Published in Features.
"We think this could spark a technology revolution in gasoline"
How did the programme begin?
We started from again scratch. We put in a special innovation team around gasoline. It's an advanced engineering group and has some of our current engineers but we've also put in some guys from aerospace – we tried to tap into certain areas of aerospace knowledge. It's sparked a lot of innovation.
What were your key development targets?
Two things we had to have were very high responsiveness, which we translate to lower inertia, and much more flow capacity because there are operating points where gasoline engines don't really need the turbocharger but you still need to be able to flow the air without choking the engine.
Why were these so important?
Under part-load cruising conditions for example, when you just need 10-15 horsepower, you don't need to boost the engine significantly. In a standard configuration you can open the wastegate but it's still not free flowing enough: the backpressure affects fuel consumption.
And you need low inertia because you're downsizing the engine and increasing gear ratios: to ensure good driveability the transient torque response of the engine has to be very fast.
What are the main differences between this technology and current gasoline turbochargers?
We realised that we could reconfigure the turbocharger's aerodynamics and the wheels to get the same horsepower ratings and much higher flow capacity in the design. We looked at concepts such as axial flow wheels and back-to-back wheels such as the ones in our DualBoost diesel turbos. We've been able to cut inertia by 70% compared to today's turbos for the same power rating.
You introduced ball bearings to Daimler's V6 diesel: could you apply this technology here too?
Not necessarily. I'd consider this an add-on technology for premium applications.
What about turbocharger control?
In addition to the DualBoost concept we've also looked at the wastegate. This is essentially an on/off valve but even when it's open at high engine rpm or at at part-load it's not necessarily flowing as much as you'd like.We came up with another concept which we call Rotopass, which is an entirely different design of a bypass function for the turbo that lets us increase the flow capacity by a factor of two while using less high temperature material than a standard wastegate.
It's simpler, and we've also lowered the actuation forces by about 90%, enabling system cost reduction. And there's more flexibility on how you package the actuator and the bypassing function.
