Mazda: motori SKY-G e SKY-D e la trasmissione automatica Sky-Drive

beckervdo · 29 Settembre 2009

Mazda presenterà in anteprima al prossimo salone di Tokyo importanti novità tecniche riunite sotto la denominazione SKY Concept : saranno infatti svelati i nuovi propulsori SKY-G e SKY-D e la trasmissione automatica Sky-Drive. Si tratta di una nuova generazione tecnologica votata al rispetto dell’ambiente: il motore SKY-G è un benzina ad iniezione diretta, lo SKY-D è un diesel ecologico mentre la nuova trasmissione automatica Sky-Drive, un 6 rapporti con convertitore di coppia, promette un ulteriore taglio del 5% nei consumi ed un feeling di guida sportivo e diretto.
Il propulsore a gasolio, in particolare, è stato studiato per ridurre gli attriti interni ai livelli di un propulsore a benzina ed è dotato di iniettori piezoelettrici, turbina a doppio stadio ed una curva di erogazione particolarmente favorevole. I consumi sono inferiori di circa il 20% rispetto all’attuale 2,2 litri ed i primi prototipi montati su Mazda 6 hanno ottenuti valori di consumo comparabili con quelli della piccola Mazda 2.
Secondo Mazda il progetto SKY Concept porterà ad una riduzione di consumi ed emissioni delle vetture di serie del 30% entro il 2015, senza dimenticare il piacere di guida e con ulteriori miglioramenti circa il peso complessivo delle vetture. Al salone di Tokyo sarà anche esposta nuovamente la concept Kyora, dotata del propulsore SKY-G 1,3 litri benzina e capace di un consumo medio di 3,1 l/100km ed emissioni inferiori a 90 g/km, senza ricorrere a sistemi di trazione ibrida.

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Via Autoblog.it

beckervdo · 31 Agosto 2010

Primo contatto per i propulsori Sky-G e Sky-D

In addition to those equipped with Sky-G gasoline engines, Mazda handed us keys to yet more Mazda 6 development mules, these ones sporting the Sky-D diesel engine. And believe us when we say that this 2.2-liter diesel is poised to make a splash when it shows up here in the US in the brandy-new 2013 CX-5 cute-ute (basically a tall Mazda 3 hatchback).Mazda benchmarked Europe's best diesels in the development of Sky-D and reckons they've got the establishment beat all around.

Torque is the calling card of a diesel, and the Sky-D delivers. In US-spec guise it will churn out 310 lb-ft of torque at approximately 1,800 rpm and generate a peak of 167 horsepower at 4,500 rpm. It'll rev all the way to 5,200 rpm, which is pretty darned high for a diesel, permitting gearing that doesn't necessarily have to be super tall.

Sky-D said to return 43 mpg on the US highway cycle in these cars. Mazda hasn't confirmed the existence of the CX-5, so take your best guess on its fuel economy.

On The Autobahn

Our driving route in Berlin included an unrestricted portion of the autobahn. Here, the Sky-D pulled with authority. Its powerband is broad and immediate and there was really no need to downshift to get back up to speed after a bit of light traffic materialized ahead. We could just leave it in 6th and give it wood. With little effort, we were cruising at just shy of 140 mph.

Around town the Sky-D similarly impressive. There's precious little waiting around for boost to arrive. Sure, you can force it below its boost threshold by laying into the throttle at 1,500 rpm in 4th, but even then the engine doesn't exactly go flat. In actual practice, a meaningful swell of thrust is always just a toe-dip away.

This engine doesn't feel like a boat anchor in the nose of the car since the block is aluminum. It's quite smooth, too, thanks to a counter-rotating balance shaft. You call, however, tell this is a diesel by the way it sounds. Not because it is clattery -- it isn't. Thrummy is a better description. In the diesel-averse United States, Mazda would do well to spend some more time on the Sky-D's aural signature. This diesel's got the kind of power delivery and response that will win over skeptics, so why not make it a trifecta of win?

A lot of clever thinking went into the Sky-D. Hit the jump to learn more.

How Mazda Beat The NOx Specter

Emissions-wise, the biggest hurdle for diesels nowadays is NOx. And when it comes to batting down NOx levels, automakers have generally settled on exhaust aftertreatment as the prescription.

Mazda approached the NOx issue in an unconventional manner. They set the the Sky-D's compression ratio to a relatively-low-for-a-diesel 14:1. If you're an engine geek, this approach might appear counterproductive to efficiency. However, it turns out that Mazda engineers are a shrewd bunch.

Consider the beneficial cascade effect of the reduced peak cylinder pressures (and temperatures) associated with low compression -- primarily, it allows for earlier injection timing without the usual penalty of elevated NOx formation.

Injecting the brunt of the fuel charge earlier in the cycle also frees up more time for the gases to expand, providing work. The lower peak cylinder pressures induce lower forces in the sliding and rotating interfaces of the crankshaft, pistons and connecting rods. Consequently Mazda was able to make these components significantly lighter than they would be in a high-compression ratio diesel, making for a freer-revving engine.

The end result of this craftiness is that the Sky D diesel meets U.S. emissions standards without the need for a de-NOx catalyst of any kind. This greatly simplifies the exhaust system, reducing cost and eliminating the need for a urea (aka diesel exhaust fluid or DEF) storage and injection system.

Other Techy Nuggets

Twelve-hole piezo injectors are supplied fuel at a maximum of 2900 psi. The block is a high-pressure die cast piece. The exhaust manifold is integrated into the head, to which two series-operation turbochargers are bolted.

Cold starts are improved with a clever two-step variable lift system applied to one of each cylinder's exhaust valves. This recycles hot exhaust gases into the combustion chambers during starts in order to shorten warm-up time.

In addition to a cooled high-pressure EGR system, US-bound Sky-D engines receive a low-pressure EGR loop in order to meet our stringent NOx emission standards. As a result, U.S models lose about five horsepower compared to Sky-D engines sold elsewhere in the world. Peak torque is unaffected.

Engines Like Legos

The Sky-D engine architecture shares bore spacing and key bearing dimensions with the gasoline-fed Sky-G engine, and accordingly Mazda can and will create offshoot powertrains. For example, a gas engine with a diesel block will form the basis of an upcoming HCCI configuration. And boosted Sky G variants will use the high-torque gearboxes initially slated for the Sky-D.

For now, well have to wait until mid-2012 before we can drive Sky-D in its debut guise. Things are looking promising so far.

--Jason Kavanagh, Engineering Editor
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Per quanto riguarda il benzina Sky-G

Here's some background. Sky-G (the G is for gasoline) and Sky-D (diesel) are a new series of all-aluminum direct-injected four-cylinder engines wholly conceived and developed by Mazda. These engines will, over time and in different guises, supplant the company's current entire powertrain lineup save for the rotary.

The first Sky-G we'll see in the US will be a 2.0-liter version, debuting in the facelifted 2012 Mazda 3. For the Mazda 6 and CX-7, Sky-G will be expanded to 2.5-liters. Another version of Sky-G with a lower deck height will displace 1.3- and later 1.5-liters for the Mazda 2. And in the coming years, a boosted Sky-G of some flavor will replace the V6 currently used in the CX-9. All of these engines will share a common bore to stroke ratio along with other key relationships in order to retain a fundamentally scalable combustion system. Only fine-tuning will be needed this way, shortening development cycles dramatically, say Mazda engineers.

In a novel twist of powertrain forethought, the Sky-D and Sky-G fundamentally share the same architecture and they are built on the same manufacturing line. This commonality will permit cross-pollination in upcoming variants. More on that later. Also, Sky-D will be covered in a follow-up post.

For now, hit the jump for a closer look at Sky-G including driving impressions.

Sky-G: 2.0-liters in 2012

In normally aspirated 2.0-liter form, Sky-G produces 158 horsepower at 6000 rpm and 151 lb-ft at 4000 rpm.

This is intended to a bread-and-butter engine, and although fuel economy is the engine's raison d'etre, the spread of torque available is said to be at the top of the 2.0-liter class. Its combination of efficiency and power is owed primarily to a stratospherically high 13:1 compression ratio.

Note that the figures above are for the US version, which will run without complaint on 87 octane -- other parts of the world get 14:1 compression which requires higher octane and produces 163 hp and 155 lb-ft while returning a tick better fuel economy.

Mazda is bullish on the high-compression normally aspirated approach in lieu of downsizing plus boosting as, the company says, it's equally fuel-efficient and more cost effective. Such a strategy means that knock abatement was a priority during development. As such, direct knock sensing has been integrated into the ignition coils, while a horny-looking tri-Y exhaust manifold -- together with VVT on both cams -- was said to be instrumental in preventing the crosstalk of hot exhaust gases between cylinders. A cooler cylinder is a more knock-resistant cylinder.

Friction reduction, too, was an area of intense focus. This resulted in roller finger followers in the valvetrain, a two-stage oil pump and myriad other details we weren't allowed to photograph. The high-pressure die-cast block is open-deck, and the rods and crankshaft are forged, saving some 13 pounds in the bottom end alone.

All-new transmissions include a 6-speed auto and a 6-speed manual, also lighter than the current gearboxes. Both transmissions will be produced in two flavors -- a 200 lb-ft (max) version and a high-torque variant that can handle up to 339 lb-ft. Key point: all gearboxes are interchangeable from Sky-D to Sky-G and vice versa. If you're thinking dirty thoughts, you're not alone.

Driving Sky-G

At a briefing in Berlin, Germany, we drove various development mules (TPVs or Technology Proveout Vehicles in Mazda-speak) of the next-generation Mazda 6 equipped with the 2.0-liter Sky-G coupled to the new gearboxes. These were the higher-compression ratio versions, not the US-spec ones.

Right away, the thing you notice is that this is not an engine that needs revs to deliver the goods. Torque is ample even at the low end of the tach, and it is delivered brightly all the way through the midrange and near the upper reaches.

In its current guise this is not intended to be a performance-car engine, but for everyday use it provides the right kind of motivation -- solid and linear thrust from low revs. The combination of direct injection and high compression provides sharp throttle response, too. It's the kind of engine that will serve Mazda's workaday applications quite well.

It could use a bit more personality like a more mellifluous intake note as today it sounds fairly prosaic. Final calibration and NVH work is still underway, though, so maybe there's a chance Mazda can fruitify the engine note. Yes, fruitify.

40 MPG On The Highway

Perhaps the best part about the engine is its frugality -- Mazda tells us that with the 14:1-compression 2.0 Sky-G, the next-gen Mazda 6 returns 40 mpg on the US highway cycle according to their simulations.

They also tell us that their simulations tend to err on the slightly conservative side.

--Jason Kavanagh, Engineering Editor
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beckervdo · 8 Settembre 2010

Al lavoro anche per un nuovo "Renesis" Rotativo.

Si chiamerà SKY- Rotary

The rotary engine is a love-it or hate-it piece of engineering. Marvelously simple and compact yet viciously inefficient, variants of the spinning triangle have seen use in Mazda's cars for over 40 years. But that robust classic tech won't do the job anymore. The next Mazda rotary will have to be a radical redesign to stay alive in the modern era of carbon footprints, ratings, and ever-escalating performance wars.

That's what Mazda's director of R&D, Seita Kanai, told press in Germany this week, according to GoAuto. Accordingly, the engine is under deep redesign, going down to the most fundamental elements of the rotary concept. The rotary is important to Mazda as a point of uniqueness amongst the increasingly homogenized car market, but if it can't meet emissions targets and fuel economy regulations, it'll go the way of the dinosaur.

We've heard news of Mazda's next-gen rotary before. Centered around a 1.6-liter displacement (up 0.3 liters from the current but soon-to-be-deceased RX-8's rotary) the engine is expected to turn up the wick on performance with output close to 300 horsepower. Some reports have hinted the boost in power and efficiency would come courtesy of forced induction, including possibly an electric supercharger, though Kanai refused to confirm that detail.

Getting more out of the rotary design while decreasing emissions and fuel use is certain to be a hefty challenge--especially while still meeting necessary cost and durability goals. It's not clear whether Mazda's success or failure in developing the new rotary for production applications will have an impact on its use in motorsports, though it's likely the production-based classes at least would eventually lose the use of the rotary without a production model to build from.

Mazda has had tremendous success with its rotary power from GT to formula cars in numerous series, including being the first non-U.S. or European engine and car to finish the 24 Hours of Le Mans with the 1974 rotary-powered Sigma MC74. The 2.6-liter four-rotor Mazda 787B remains the only non-piston-engined to win Le Mans overall.

We'd love to see Mazda's rotary live on as there are few sounds on earth like a race-prepped rotary popping and crackling at redline.
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[GoAuto]

matte · 7 Ottobre 2010

Letto con molto interesse l'approfondimento su 4R.

Dopo una prova su strada vedremo se le promesse....

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