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.
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.
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.