THAT automakers’ proving grounds are located in remote spots makes sense; this allows such places to sit on vast tracts of land, not to mention keeping them away from prying lenses. These are venues, after all, on which new models and technologies are tested before any of them get to showrooms.
One of Mazda Motor Corp.’s proving grounds (located in Mine, Yamaguchi, more than 900 kilometers southwest of Tokyo, Japan) is no exception. On May 27 it was where Mazda demonstrated the latest developments regarding its new generation of SkyActiv technologies. This involved technical presentations and test-drives of current Mazda 3 hatchbacks which have been fitted with the prototype versions of the upcoming SkyActiv power train. Key takeaways from the activity point to promising technologies.
SkyActiv is Mazda’s catchall term for its collection of systems which reduce fuel consumption and emission, as well as make its models safer — all while keeping to the brand’s preference for cars that are fun to drive. SkyActiv, to one degree or another, is presently fitted on virtually all Mazda vehicles meant for the global market.
Presented by the car maker in Mine was the latest version of the SkyActiv-G gasoline engine, branded as SkyActiv-X. Scheduled for release in 2019 under the hood of the new generation Mazda 3 (and eventually on other models), SkyActiv-X is touted by Mazda as retaining the clean emissions of the current SkyActiv-G engines while improving their response and power. Mazda also promised a “drastic improvement in fuel consumption rate.”
A key feature of the SkyActiv-X is its spark-controlled compression ignition system, or SPCCI. It basically takes the ignition method on which diesel engines rely — the high heat created by compressing air in the cylinder combusts the fuel mixed into it — and combines this with the use of a spark plug, by which component the air/fuel mixture in gasoline engines are ignited.
The way SPCCI fuses the two ignition methods is by compressing the air/fuel mixture in the cylinder to the point where it would nearly combust, then ignites this mixture with a spark plug. Because the timing and amount of compression vary endlessly according to driving conditions (or even how hard or light a driver presses the throttle pedal), something conventional compression engines cannot always manage well, the SPCCI keeps such factors in check by also constantly controlling when exactly the spark plug should fire (the engine can also operate in compression ignition mode under certain conditions). This way, the system never lets compression get so high as well. Plus, Mazda said using a spark ignition also means it could get away with not using complicated systems for its engine, like those which vary valve timing or compression ratio.
While more grunt is guaranteed by using SPCCI — torque output has not only significantly increased but also arrives sooner (at around 2,000rpm) and extends farther in the rev range (to 6,000 rpm) when compared to that outputted by the current SkyActiv-G — cutting fuel use and emission is also the goal of SkyActiv-X. And, according to Mazda, relying partly on the inherent characteristics of a compression ignition engine has allowed it to achieve this. Because through compression ignition, the SkyActiv-X mill can resort to using a lean air/fuel mixture, meaning the charge that is used for combustion is composed of vastly more air than fuel.
This, of course, presents its own challenges — like ensuring the ratio between the air and fuel that will be combusted is always kept ideally lean no matter how fast the engine spins. For this, the SkyActiv-X engine depends on a trick fueling system that boasts a “super-high-pressure” injector, which through multiple ports sprays a fine mist of fuel thoroughly and quickly throughout the cylinder, and a two-part injection process — one made during intake and the other during compression of the air/fuel mixture.
To stabilize the amount of air entering the engine, a hot rod-staple belt-driven supercharger is used, making sure there will always be sufficient air — enough to keep the air/fuel mixture very lean — regardless of how vigorously the engine is revving. Simply the faster the engine spins (requiring more air), the faster the supercharger pumps air into the engine. Meanwhile, helping keep the engine’s temperature in check — compression ignition relies on heat to ignite the air/fuel mixture in the cylinder — is an exhaust gas recirculation system.
As Mazda put it; the SkyActiv-X engine is a “crossover” engine that fuses the high-revving power and cleaner emission of a gasoline engine with the grunt and fuel-miser ways of a diesel-burner.
Taking further advantage of the added oomph produced by the SkyActiv-X engine is an automatic transmission that has lower gear ratios compared to that bolted on the current SkyActiv-G mills. This, Mazda said, would let a future SkyActiv-X-endowed car be zippier.
Meanwhile, the next evolution of SkyActiv components not directly related to the operation of the engine and gearbox will, Mazda promised, make its models even more pleasurable to drive as they intently consider kinetics and physiology. Speaking about a “vehicle architecture that optimizes [the] human ability to balance,” new developments are focusing on diverse areas like advanced seat design, and structural and suspension bits which return clearer feedback to the driver, absorb uneven surfaces better and behave on pavement more stably while filtering out noise, vibration and harshness.
BEHIND THE WHEEL
Mazda’s Mine proving grounds used to be one of Japan’s main race tracks, so it already has several facilities designed for different types of motor sports. On top of these, Mazda has either altered or built new sections which simulate public roads. In short, it’s an excellent venue in which to properly test cars.
Over most of these courses the Mazda 3 cars propelled by the 2.0-liter prototype SkyActiv-X engines (with automatic and manual transmissions) stacked up well against their counterpart current-production 3s that run on 2.0-liter SkyActiv-G engines.
All right, the SkyActiv-X engine still has rough edges — it was prone to “knocking,” or that noise usually caused by a lean mixture. This can even be induced by flooring the throttle pedal when the engine is spinning at low revs and the automatic transmission is caught in a high gear. The shift from one mode of combustion to another (Mazda thoughtfully installed a makeshift monitor on which the transition could be viewed graphically) also wasn’t as seamless yet.
Well, audibly, at least. Because there appeared to be no discernible loss of power, or a lag in its delivery, as the SPCCI went about its business of firing its spark plugs. Fact is, the SkyActiv-X engine created noticeably less vibration than the SkyActiv-G, and was also markedly peppier all throughout the rev range.
Aiding in the SkyActiv-X-propelled cars’ higher level of refinement were some of the structural and suspension components set to prop the 2019 production 3 (well, it didn’t hurt the cars were fitted with more insulation, too). Even in prototype form, it was easy to tell the changes did produce a more pliant, more absorbent ride quality while letting the car be agile and predictable in high-speed driving. Certainly, it can be expected that Mazda — as the car maker has committed — will have fixed the SkyActiv-X’s flaws by the time the upcoming 3 goes into production.
By which time then Mazda would have completed reinventing the wheel — or the internal combustion engine, to be precise. — Brian M. Afuang