Rather than develop a range of transmissions to meet the different requirements of its global markets, Mazda’s drive- train engineers took the bold decision to develop just two all-new six-speed Manual and Automatic transmissions to effectively deliver market demands.
Vehicle transmissions are not only extremely important for improving fuel economy, they also exert a major influence on driving performance. The performance demands on automatic transmissions vary greatly depending on the market, and since there is not a single transmission in existence that satisfies all these varied demands, automakers deploy a variety of systems, each matched to a particular market. Employing the world’s most commonly-used combination - a torque converter and stepped automatic transmission - as the basic structure, and by using technology that substantially reduces slip in starting devices, Mazda has brought together the benefits of each system and developed a highly efficient automatic transmission with a substantially direct drive feel that will be perfectly suited to conditions in numerous global markets.
- A next-generation highly efficient automatic transmission that achieves excellent torque transfer efficiency through a wider lock-up range and features the best attributes of all transmission types
- Combines all the advantages of conventional automatic transmissions, continuously variable transmissions, and dual clutch transmissions
- A dramatically widened lock-up range improves torque transfer efficiency and realizes a direct driving feel that is equivalent to a manual transmission
- A 4-to-7 percent improvement in fuel economy compared to the current transmission
All the Advantage of Conventional Step CVT, Dual Clutch, and Step AT
Automatic transmissions(AT) can be categorized into three types:
- CVT: generates various gear reduction ratios with a pair of pulleys
- Dual Clutch: 2 separate clutches for odd and even gear sets.
- Conventional AT: generates varios gear reduction ratios with planetary gear sets
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:
Improvement in Fuel Economy and Achievement of Direct Feel with Full Range Lock-Up
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.
- Is a light and compact new-generation manual transmission with crisp and light shift feel like that of a sports car, using a common second and third input gear and removing the reverse idle shaft has reduced the number of moving parts and trimmed its overall weight by 3kg.
- Short stroke and light shift feel
- Significantly reduced size and weight due to a revised structure
- More efficient vehicle packaging thanks to its compact size
- Improved fuel economy due to reduced internal friction
Technical Aims & Concept
Automatic transmissions dominate the North American and Japanese markets, but in Europe, MTs are widely used. To meet global demand, two types of MT (“Large” and “Mid” sizes) have been newly developed. The development concept was to create a “light and compact MT with improved shift feel and better fuel economy”. The goal was to achieve an MX-5-like sporty and brisk shift feel.
For a quick shift feel, both a short shift-lever stroke and light shift effort had to be achieved. By pursuing the ideal structure of manual transmissions, 16% at maximum of weight reduction was achieved. Furthermore, internal friction losses were significantly reduced to achieve a 1% improvement in fuel economy.
Quick and Crisp Shift Feel
To achieve lighter shift effort with a short shift lever stroke, the lever ratio must be increased. However, a larger lever ratio reduces the internal stroke. To achieve precise synchronizer and torque transmission even with a short internal stroke, a small module spline is used.
Also, the shift effort gradually reduces through the stroke, providing reassuring resistance as the lever is first pushed, then getting lighter so it feels as if the shift lever is automatically moving into gear. With the current shift lever, shift effort in the select direction (right-left direction) increases with the movement of the shift lever, but with the new shift lever, a stable shift effort is achieved. Binding is minimized when shifting diagonally.
Light and Compact MT
Since the structure of an MT is relatively simple, completely new ideas and logical thinking are required to achieve further weight reduction and higher efficiency.
The triple-shafted gear train with a common gear for 2nd and 3rd was selected from approximately 30 different configurations due to its potential to achieve lightness, light shift effort, high efficiency, and a wide gear ratio. Based on this selection, the lightest structural specifications were selected from over 10,000 alternatives. By reviewing the function of each component, commonization of the 1st and reverse gears was newly adopted.
This enabled the length of the secondary shaft to be reduced by 20%. A common 1st and reverse gear made possible the removal of the reverse idle shaft. As a result, by reexamining gear configurations, the number of components decreased and the gear train weight was reduced by roughly 3kg.