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SKYACTIV: Keeping the Zoom in Zoom-Zoom

Mazda takes a total approach to design.
Thursday, July 31, 2014 - 07:00
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This allowed them to not only do the pre-, main and post-injection most diesels do, but to modify the injection times per cycle for operating conditions and allow for precise high pressure injections for cold starts. The highly atomized fuel helps cold starts, but also Mazda adopted super-fast heating ceramic glow plugs to insure quick starts. To overcome cold run misfires, Mazda adopted Variable Valve Lift (VVL) on the exhaust. Knowing that only a single combustion cycle was needed to make exhaust temps rise, they open the exhaust valve on the intake cycle to pull exhaust back into the chamber for rapid cylinder heating. Most manufactures use the exhaust gas recirculation system for this, but that takes too much time for heating to occur. This technology is instant.

Most every diesel today has turbochargers, but Mazda went to new lengths again looking at performance engines that use a two-stage turbo charger design adapting these ideas to meet needed technology for clean/efficient operations under all conditions. Most diesels have some form of turbo lag, so the two-stage turbocharger enabled them to have smooth responsive torque output while decreasing emissions.

A two-stage turbo is one small and one large turbo mounted together sharing the same exhaust and intake pipes. This allows for switching between turbo profiles giving the best air charge for the operating conditions. A small turbo will spool up using less exhaust to give good boost at low rpms, and the large turbo produces boost at higher engine speed giving a great torque curve over the entire driving range. This turbo design also gave Mazda better boost control helping to lower both NOx and soot output. 

Without the need for the expensive and fuel robbing regeneration of after-treatment systems Mazda is way ahead of the game. All of the advances Mazda did to their diesel engine allowed them to change to an all aluminum block and a thinner cylinder head, cutting a whopping 62 pounds (28kg) of weight plus shaving the pistons’ weight by 25 percent.

SKYACTIV-Drive (automatic transmission)
Mazda took aim at combining all the best advantages of each transmission type to make each one better. They looked at the advantages of a conventional (step shifting) automatic transmission, continuously variable transmission (CVT) and a dual clutch transmission (DCT). It improved fuel economy 4 to 7 percent by reducing slip, cutting weight and reducing friction losses. It wanted a smoother shift, but also wanted to keep the fun in driving no matter which transmission choice the driver wants.

Everyone knows that a torque converter gives smooth starts and shifts but robs mpgs. Mazda wanted to get rid of slippage between shifts, so it improved the torque converter. To reduce the slippage, it locked the converter up just after takeoff. This required tighter electronic controls of both the engine and transmission plus better cooling of the multi-disc lock up clutch. The engineers controlled Noise, Vibration and Harshness (NVH) by providing a damper and compact torus (vane) in the torque converter, but also did a redesign of everything from the engine to the exhaust system.

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