Andy Cowell's mid 2016 view on range extenders. It's from an ESPN interview, but I've heard him talk about vee twin mgu-h range extenders in several publications now.
https://www.espn.com.au/f1/story/_/id/1 ... -road-cars
How two-cylinder engines and F1 technology could redefine road cars
Formula One technology combined with small capacity engines could form the basis of future road car powertrains, according to Mercedes' F1 engine boss Andy Cowell.
The current F1 engine regulations were designed to promote hybrid technologies, and since their introduction in 2014 manufacturers have improved thermal efficiency from 29 percent to more than 45 percent, meaning more than 45 percent of the potential energy in the fuel is delivered to the crankshaft. Cowell believes those efficiency gains will start to filter down to road cars in the near future, allowing family-sized cars to be powered by small capacity, two-cylinder engines.
Asked what drivetrain he would use if he was designing the next generation of Mercedes C-Class, Cowell came up with a proposal quite different to the brand's current offering of straight fours, V6s and V8s.
"If I get the job of the next C-Class and we can get parts for free -- so somebody doesn't pull the cost out of it without destroying the efficiency -- you would definitely go for a very small capacity engine, tiny, maybe half a litre," he said. "It would be less than three cylinders, down at 400cc -- let's start talking about cc and not litres. So a 400cc, 90-degree, v-twin with 200bhp!"
Cowell's two-cylinder engine concept would be turbocharged much like the current F1 engines, with an F1-style MGU-H used to control turbine speeds and combat turbo-lag. Independent MGU-Ks would be fitted on the front wheels to harvest energy under braking and provide all wheel drive when necessary under acceleration.
"I hate brake discs getting warm on any vehicle, so it's probably going to have an electric machine at the front two corners -- if we are staying rear-wheel drive for a nice driving experience. So one electric machine on the powertrain, two electric machines on the front that have got enough power to absorb over half a G braking.
"You would have a miniaturised version of the F1 assembly to recover energy from the turbine and you would use that when you really want to get away from the traffic lights. So you'd have the front drive motors providing four-wheel drive, you'd have the engine pulling you away and then when you want to do your zero emissions around town, you would have used the engine in the suburbs to make sure the battery is full [for full electric use].
"You need a decent battery, efficient power electronics and then it's a question of how much would the engine actually be doing? At that point is it not just a range extender? Is it not that the C-Class has a 400cc, v-twin range extender that sits there and operates at full throttle with around 54% thermal efficiency?"
The MGU-H on an F1 car controls the turbine speed for optimum boost pressure, with excess energy either harvested and stored in the battery or delivered straight to the crank shaft via the MGU-K. One of the biggest differences between the demands on an F1 power unit and that of a road car is that a driver on the road is unlikely to employ full throttle or maximum braking on a regular basis. Cowell said that would have to be considered on the road car engine design.
"It's the drive cycle aspect of whether the electric machine recovering from the turbine is of merit, because how many of us drive our road cars at full throttle? Not many. And even if we do, it's only for a few seconds. The electric turbo recovering from the turbine needs full throttle, which is then where you are getting into the electric machine doing even more."
Despite the growing popularity of electric cars in recent years, Cowell sees hybrid gasoline engines as the future for journeys outside cities.
"I think there is a beautiful partnership between high-voltage hybrid systems and internal combustion engines where they can help each other," he explained. "There is a huge problem with the mass of batteries in pure electric vehicles. Cars need to have low aerodynamic losses and be lightweight [to be efficient], but as soon as you say 'lightweight' and 'electric vehicle' there is a huge conflict. So what you want is a system that recovers all that kinetic energy and a system that uses gasoline because gasoline has great energy density. But you want an engine that converts that at greater than 50% efficiency to useful work.
"If in the future we are all going to be living in cities and close together, then electric cars are fine. But we need to make sure that the electricity comes from an honourable source -- it's very important that we keep an eye on that. What comes out of our three-pin [wall] socket hasn't necessarily come from a great source.
"If it's coming from solar panels on all the buildings then fine, but if it's coming from coal-fired power stations or gas turbines, I don't think it's that honourable. In cities an EV [electric vehicle] with zero emissions is perfect, but as soon as we start doing say 100km or maybe even 80km -- not a big number -- then a hybrid makes more sense."