Automatic transmissions (AT) can be categorized into three types:
The key requirements for ATs are “good fuel economy”, “quick start-up” (including hill climbing), “direct feel” and “smooth shifting”.The table below shows the drawbacks and advantages of each transmission.
SKYACTIV-DRIVE is the ideal AT with all the advantages of the various types of transmissions:
The torque converter transfers engine power to the transmission through fluid, making a smooth start-up and gearshifts possible. The drawback is that fuel economy worsens due to the loss of power transfer through the fluid, and slippage during rapid acceleration, which causes vehicle speed to lag behind engine speed. Therefore, a torque converter with a lock-up clutch was developed, which locks the torque converter’s turbine to the impeller to improve fuel economy and direct drive feel. To improve fuel economy and direct drive feel pointed as challenges of Step AT shown in Fig.1, the lock-up range has to be maximized. However, in order to do so, we had to ensure NVH performance and clutch reliability.
With extensive analysis, Mazda overcame NVH by improving the engine, mounts, exhaust, body, and system control as well as the AT itself. Furthermore, improvement in clutch response and precise lock-up control ensures reliability by preventing heat buildup due to slippage.