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Mazda’s Sky technology secrets revealed

Blue is green: Mazda's forthcoming Sky petrol and diesel four-cylinder engines.

Inside Mazda’s groundbreaking Sky engine and transmission technologies

Mazda logo30 Aug 2010


A PAIR of cracking yet super-efficient new four-cylinder petrol and diesel engines are the headline acts of Mazda’s groundbreaking new Sky engine architecture, which will power a range of all-new models using a redesigned chassis that is stronger yet considerably lighter.

Revealed as part of an unprecedented insight into Mazda’s future vehicle plans during a ‘technology forum’ attended by GoAuto in Germany last week, the new engines will both run an outstanding compression ratio of 14:1.

First off the mark in production form will be a 2.0-litre Sky G four-cylinder petrol – installed in next year’s facelifted Mazda3 – as Mazda pursues a commitment to reduce the average fuel consumption of its new-vehicle fleet by 30 per cent between 2008 and 2015.

Smaller-displacement 1.3 and 1.5-litre versions of the Sky G petrol engine (for the next Mazda2) and a larger 2.5-litre petrol four for the next Mazda6 in 2013 will follow.

However, the revolutionary new Sky engine strategy will be spearheaded by Mazda’s first all-alloy diesel engine, a bristling new 2.2-litre Sky D four-cylinder twin-turbo oil-burner for the next Mazda6.

Benchmarked against the finest diesel engines from BMW and VW-Audi, Mazda’s next-generation common-rail direct-injection clean-diesel engine will feature piezo injectors, variable exhaust valve lift control and lower 14.0:1 compression (down from 16.3:1 in the current engine).

22 center imageLeft: Mazda's Sky line-up includes (from top) diesel engine, petrol engine and six-speed auto transmission.

It will still deliver 136kW of power, but torque will increase to 420Nm (up from 400Nm), while fuel consumption will be as low as 4.2L/100km and CO2 emissions just 105g/km.

Both the Sky G and Sky D engines benefit from reduced exhaust, cooling, pumping and mechanical losses thanks largely to a more efficient combustion process, but in the diesel’s case the lower compression ratio and shorter piston skirts – which in this case avoids traditional low-compression diesel problems like cold-start misfiring by recirculating hot exhaust gas – results in reduced mechanical friction and a higher 5200rpm redline.

As such, Mazda says the Sky D 2.2 powerplant, now 25kg lighter despite being fitted with twin sequential turbochargers, will return similar real-world fuel consumption to a B-segment vehicle and comply with Euro 6 emissions standards without expensive NOx after-treatment technologies.

But it will be cheaper to produce than comparable Euro 5-compliant engines or hybrid drive systems because it will be manufactured on the same production line as the Sky G engine.

The direct-injection Sky G petrol four comes with the same 14.0:1 compression ratio, but adds a new motorcycle-style four-into-two-into-one exhaust system and multi-hole fuel-injectors to improve combustion efficiency, reduce exhaust losses and, according to Mazda, return diesel-like fuel consumption and torque.

Its high-pressure die-cast alloy block features steel cylinder liners and more tightly spaced bore centres to reduce engine length by about 20mm, while the crankshaft is now forged rather than cast steel, all of which helps save more than 5kg.

Internal friction is claimed to be reduced by 50 per cent thanks in part to an electric oil pressure regulator and roller finger valvetrain followers.

Sky G engines destined for Australia and Japan, where standard unleaded petrol is 91 RON rather than 95, will be recalibrated to run 13:1 compression, which Mazda says will reduce performance outputs by up to three per cent.

Nevertheless, Mazda says the first Sky G engine will reduce fuel consumption by 15 per cent while improving torque output by the same amount, resulting in performance outputs of about 121kW and 210Nm while increasing fuel economy to less than 6.0L/100km with the new six-speed Sky Drive automatic transmission.

Mazda says that its next new C/D-segment vehicle equipped with a Sky G petrol engine will emit about 130g/km of CO2.

At the same time, it claims the slightly longer-stroke Sky G engine delivers at least 13Nm more torque across the entire engine speed range than before while offering more low-end and mid-range torque than any premium European 2.0-litre petrol engine.

Apart from producing smooth, linear response without the added expense of turbocharging, Mazda says its Sky G petrol engine line-up will also be less expensive to produce than equivalent downsized forced-induction petrol engines because a wide variety of displacement derivatives can come with similar calibration due to their common combustion, ignition and air-flow characteristics.

Mazda says the conventional torque converter-equipped Sky Drive automatic transmission, which was designed and developed in-house, was chosen because it combines the best attributes of traditional, dual-clutch and continuously-variable automatic transmissions.

Lighter and more compact than the five-speed auto it replaces, Mazda says the new six-speed auto contributes a fuel economy improvement of between four and seven per cent by incorporating a wider lock-up range in all gears (82-88 per cent – up from 49-54 per cent).

Sky Drive is claimed to deliver the direct feel of a manual gearbox with a smoother launch feel than a dual-clutch transmission.

New transmission technologies include direct linear solenoid-controlled oil pressure, larger damper springs, a twin-plate clutch with greater heat capacity and more compact torque converter to more precisely control low-speed lock-up, broaden the overall lock-up range, better absorb engine speed fluctuations and reduce noise, vibration and booming associated with lock-up.

Two versions of the Sky Drive auto will be produced, with the larger being 4.5kg lighter and offering increased torque capacity of 460Nm (up from 440Nm), while the smaller version increases from 220 to 270Nm.

Petrol auto vehicles will have a final drive ratio of 4.367:1, while the diesel auto will run a taller 3.841:1 differential ratio.

Mazda’s upgraded six-speed manual transmission, which will soon be available in Europe, has a final drive ratio of 4.388:1 and features 5mm-shorter (45mm) shift throws and more precise shift feel.

Manufactured on the same production line as the Sky Drive auto, Mazda’s next-generation manual features a small spline module, lock ball-type hub and a new shifting mechanism to reduce sleeve travel and syncroniser size respectively.

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