How Mazda Sky works

That's the compression ratio for their frugal petrol and diesel engines.  For a petrol engine, that's high compression - in fact the highest in the world for a mass-produced engine - but for a diesel, it's very low.  Mazda executive officer Kyoshi Fuziwara says the new Skyactiv engines will be produced in different capacities and configurations over the next decade, replacing the MZR engine introduced in 2002.

He says the new internal combustion engines and other "Sky" manufacturing technologies will help improve fuel economy of the Mazda fleet by 30 per cent and decrease emissions by 23 per cent by 2015.  The new engines will be introduced alongside developments in electric and hybrid powertrains.

Fuziwara says about 70 per cent of the potential energy in an internal combustion engine is lost due to unburnt fuel, cooling losses, exhaust gas, pumping losses and friction.  "The internal combustion engine still has great potential for improvement," he says.

Powertrain manager Susumu Niinai program says high compression means more air mixed with the fuel for a faster burn and reduced load.
Mazda brought out four technical officers from Japan headquarters to a technical briefing in Melbourne this week.

Niinai says the key point of the Skyactiv-G petrol engine is high compression without knocking or pinging by reducing residual gas in the cylinder and therefore reducing temperature.  To achieve this it uses a longer 4-2-1 exhaust manifold, direct injection and a specially designed piston head.

In the Skyactiv-D diesel engine, lower compression allows more time for the air and fuel to mix for a cleaner and more efficient burn that reduces soot and greenhouse gases.

These engines will be mated to new Skyactiv automatic and manual transmissions that technical officer Toshiyuki Kikuchi says will further improve economy by up to 7 per cent.

Mazda has chosen to reject continuously variable and double-clutch transmissions and stay with a torque converter automatic highly modified with less clutch slip and an expanded lock-up range.  Kikuchi says this gives it a manual transmission feel, smooth and powerful start-up performance, smooth shifting and a reduction of drive loss.

He claims it shifts gears faster than DCT.  The Skyactiv-MT manual is lightweight and compact with a "light and crisp feel like MX-5".

It has a common second and third input gear and first and reverse idling gear, plus a reduced shift stroke (from 9mm to 7.65mm), increased lever ratio, reduced inertia during synchronization, reduced load and modified gear geometry.

"It's has a quicker and more positive shift," he says.  The other major ingredient in improving economy and greenhouse gas emissions is reduced weight in the chassis and body as most other manufacturers are pursuing.

Vehicle development officer Norihiro Tomita says the Skyactiv chassis and body will by 30 per cent more rigid while weight is down 8 per cent.  The suspension and steering will include increased rear toe-in, higher steering gear ratio, and increased front caster angle and caster trail for better high-speed stability and low-speed agility.

The front cross bar member of the suspension will be 6.4 per cent lighter and 40 per cent more rigid while the rear is 4.5kg lighter but retains rigidity.