Mark Hughes

Straight talk
The design details that separate Merc’s V6 turbo from the rest

Do you want to know why the Mercedes W05 had one second per lap on the opposition in the season’s opening race? It’s been conceived around a single, brilliant idea.

Brilliant ideas often seem so obvious once someone has come up with them. Usually they are simple, yet startlingly original. Mercedes came up with one about two years ago.

But sometimes just seeing the invention in isolation doesn’t explain its effectiveness. It’s only when you dig deeper into its implications that its full significance becomes apparent. Which is why the works team – in on the innovation since the start – has evidently been able to make more spectacular use of it than the three customers, McLaren, Williams and Force India.

The innovation is having the turbo’s compressor at one end of the engine and the turbine at the other, linked by a long shaft through the engine’s vee. Normally the two components are housed directly together, plumbed into the exhaust primary pipes somewhere near the back of the car. But in the Mercedes V6 only the turbine sits with the hot exhausts that drive it. That turbine drives a compressor up front, where the surrounding air is about 600-deg C cooler.

That temperature difference suggests one of the advantages of the system: the compressed air has to be cooled before being fed to the engine. Having it surrounded by cooler air in the first place helps this process, albeit only slightly. The less the air needs to be cooled, the smaller the bulky intercoolers (mounted in the sidepods) can be. But that’s only the beginning of the cascading series of benefits this innovation offers.

Consider: this new hybrid formula is all about filling up your battery’s capacity quickly and thereby having the engine require as little fuel as possible. The more electrical energy you have available to use, the less you dip into the fuel reserves to get your power. The harder you can brake without locking the wheels, the faster you can harvest energy for the battery.

So you need a car that has great braking stability and heats up its tyres quickly, particularly the fronts. That way you can harvest the energy more aggressively. The better your tyres work, the less fuel the engine needs – and the spare fuel can be used to employ more boost. So you get more power for a given fuel consumption. Feeding into this formula is aero efficiency – the less drag you create for a given amount of downforce, the less fuel you use… and the more boost you can deploy etc.

So returning to Merc’s trick turbo layout, the inlet air for the compressor is taken from a scoop above the cockpit. It now has a nice short distance to travel, improving the turbo’s response. But these new cars have an ersH electrical turbine on the same shaft as the turbo: this can be used either to feed excess turbo energy to the battery or in the other direction to spool up the turbo to eliminate lag. So if this already eliminates lag, what’s the benefit of the short inlet tract to the compressor? It means you will be asking less of the electrical power of the ersH because the turbo won’t need as much spooling. Which means you retain more stored electrical energy – which in turn makes more electrical power available, reducing fuel consumption and allowing greater boost.

With the compressor up front, it’s virtually alongside the intercooler. Again this improves turbo response – and also cuts down the plumbing necessary, creating more space, allowing everything to be shrink-wrapped for greater aero efficiency.

As a tangential feature, the W05 features air-water intercoolers. These are more compact but do not cool the air as much as the more traditional air intercoolers used by the other Mercedes teams.

Typically they will deliver charge air to the combustion chamber at about 20-deg C above ambient. The air intercoolers can get it down close to ambient. The cooler the better as far as power is concerned. But, with a regulation fuel flow limit, the cooling requirement is not as great as it would otherwise be. So the trade-off between power and the aero efficiency engendered by the smaller sidepod changes – in the direction of water-cooling.

So we now have a car with super-small sidepods and radiator inlets. It has more efficient energy use because of a) the superior turbo response and b) greater aero efficiency. But the cascading hasn’t finished. The compressor – which gets very hot – is no longer at the back, so the gearbox cluster can be brought forward. This centralises the car’s masses and makes more compact packaging feasible. The W05 is so tightly packaged it is the only car with bodywork blisters around the rear to comply with regulation dimensions.

The layout will also allow the weight distribution to be brought forward to the limit of the tolerance allowed by the regulations, helping heat the front tyres. Which, as explained, will help maximise energy harvesting under braking and – ultimately – deliver more power...