Mazda’s SKY System: Reducing fuel consumption by 23%?

The reputation of Mazda’s engineers is solid. Over the last few years, they’ve impressed us with original vehicles that offer superior driving pleasure. Plus, they’re the only ones to have mastered the Wankel rotary engine, which you can still find in the RX8, an interesting four-seater sports car. And since the first Mazda6 was launched in 2002, they’ve adopted the Vroom Vroom philosophy that emphasizes driving pleasure, safety, environment and fuel consumption. In 2007, this philosophy translated into the development of a second generation of the Mazda6, which was released a year later.

Despite all this, Mazda recognized that its fuel consumption rates were not as good as they should be. This prompted the manufacturer to come up with the SKY project toward the end of 2006. SKY would allow Mazda to offer a 23% reduction in fuel consumption by 2015, compared to rates posted in 2008. We recently had the chance to learn more about this new technology and even to drive some prototype vehicles that will be sold with SKY system in 2011 (gas engine) and 2012 (diesel engine).

Simplicity first

Some manufacturers have made big efforts to quickly develop hybrid vehicles as a means of reducing fuel consumption and thereby reaching their targets with relative ease. However, according to Kiyoshi Fujiwara, Mazda’s Transmission Director, this would have meant developing onerous vehicles that would really only resolve a part of a bigger problem. By redefining the engines that will be used on most Mazda models, the majority of Mazda’s clients can benefit, as opposed to a select few.

Mazda engineers therefore concentrated their efforts on two engines, a 2.0-litre naturally-aspirated engine and a 2.2-litre diesel. In addition, they also proceeded to develop two transmissions, a six-speed manual and a six-speed automatic. None of these mechanical components feature exotic or onerous materials and the mechanical design is free of complex technology. The engineers from Hiroshima and those from the Mazda Research Centre in Frankfurt did everything possible to reduce the weight of the mechanical components and the internal friction, while optimizing engine performance. And as we’ll see a little later, the solutions they came up with for the gas and diesel engines are similar, yet different at the same time.

So that’s how Mazda came about improving their gas engine to the point that its fuel consumption is equal to their current diesel engine’s rate. The new SKY diesel, however, will consume 20% less than the current diesel motor. What’s more, the new SKY diesel won’t need any post-combustion accessories like a second catalytic converter or urea injection to meet European and American exhaust regulations.

Efficiency

To meet these lofty goals, Mazda engineers opted to revise the engine and how it works. In the case of the gas engine, they increased the compression rate (now 14:1 in Europe and 12:1 in North America, since we don’t have RON 95 fuel over here). This increased engine torque. Also, the engineers made the cylinder bore smaller and the course longer for faster exhaust evacuation and reduced heat load in the combustion chamber. Direct fuel injection also helps bring down the temperature in the combustion chamber. And the engineers developed a 4-2-1 exhaust system for the same reason.

For their diesel engine, Mazda adopted technology that was different from traditional diesel engines by reducing the compression rate to just 14:1, the same as the gasoline engine. Injection via pieza injectors, more efficient piston heads and better fuel distribution also help reduce consumption and prevent detonation. The lower compression rate means that lighter components can be used, and many of these are interchangeable with the gasoline engine components. Incidentally, the two engines are so similar that they are produced on the same assembly line. Both use lighter crankshafts, pistons and connecting rods, while the aluminum engine block also contributes to the weight reduction.
The SKY system’s pièce de résistance is its automatic transmission. The manual gearbox is lighter, more refined and simpler in terms of mechanics, but it doesn’t feature any innovative technical solutions. The engineers did, however, improve the gear shifting and made the synchronization smoother. In fact, they based themselves on the MX-5 transmission.

As for the automatic transmission, the goal was to combine CVT gentleness and dual-clutch speed. The engineers focussed on the torque converter, which now has four pressure plates instead of one, and a fully revamped hydraulic system. They also placed the electronic control module right inside the carter. This translates into very fast transmission reactions. The torque converter has an internal damper that absorbs the energy that results from locking.

In addition, the SKY system includes an all-new platform that’s been made lighter with simpler, yet stronger parts. Trident reinforcements under the body also make it stronger and lighter.

Proven efficiency

When new technologies are presented to us, we’re rarely given the opportunity to test them out on the road – and if we are, it’s not usually more than a spin around the block. But since Mazda likes to be different, they let us try each mechanical combination possible over 30 km each time.

Four development Mazda6s were made available to us. These included gasoline engine versions with either a manual or automatic transmission, or the same gearboxes with a diesel engine. These vehicles were equipped with the current Mazda6 body with the next-generation platform, which is why some body parts were held together with rivets on the front fenders and extensions between the hood and windshield. Inside the vehicle, there was a button on the dash instead of a horn, the windshield wipers had no intermittent setting and the turn signal had be deactivated manually. Everything else was just like a regular Mazda6, except that the driver’s side was over to the right...

Our four test drives are pretty easy to summarize. First, gear shifts on the automatic were not just smooth, but fast too. Even though we didn’t take it for an exhaustive trial, this transmission delivers on its promises. And that’s even more the case with the diesel engine. With this engine’s high level of torque, you might expect some jerking when changing gears with a traditional gearbox. The SKY transmission, however, is very discreet. The same can be said for the manual gearbox, which offers gentle synchro and a short and precise shifting distance.

The 2.0-litre gas engine delivers very linear accelerations. You’d think there was a compressor bolted on, but that’s not the case. Mazda has not released the power or torque levels of these engines, but both the accelerations and pick-up would make you think that this engine had nearly twice the number of cylinders. Even at speeds of almost 200 km/hr (the tests were done in the suburbs around Berlin), the engine purred gently, and there was still more energy awaiting under the accelerator, even in sixth.

The diesel engine was a little rougher than a Volkswagen TDI with the same number of cylinders, but the difference is really not that much. And once the revs pick up, it’s quieter. Since its compression rate is lower than the average diesel engine, max revs are higher (5,200 RPM), though the average is generally about half of that.
During our test runs, Mazda engineers recorded our fuel consumption rate at 4.8 L/100 km for the diesel and 5.4 L/100 km for the gasoline engine. That’s even more impressive when you consider that we reached speeds of nearly 200 km/hr on the autobahn. As for the new platform, we found it to be more rigid than the current Mazda6, the brakes were more powerful and progressive, while the electronic assist steering became firm at high speeds.

The first models featuring SKY technology will be sold in 2011. As years go by, it will be offered on all Mazda vehicles. Plus, i-Stop technology that cuts the engines when you stop and regenerative brakes will be included too. By 2020, Mazda will offer hybrids, plug-in cars and electric vehicles. But the majority of their vehicles will be powered by SKY technology engines, which will be the base for the entire system.