The world of automobiles today is radically different than it was a twenty years ago, based on several metrics. In the area of fuel efficiency, it was once an automotive maxim that if you wanted good fuel efficiency, manual transmission was clearly the best way to go. Automatic transmission was more convenient but far more wasteful of energy. Today a radically different result has been achieved, and curious observers can wonder what happened to suddenly make automatic transmissions more efficient. The answer, in a simplistic sense, boils down to the combined effect of multiple “incremental” innovations in automatic transmission design that together have propelled automobiles radically forward. In “Why do automatic transmissions now get better fuel efficiency than manuals?,” Green AutoBlog explores the changes that have turned things around so dramatically, but gradually.
In the last 25 years, there have been three major advances to automatic transmissions that have made the biggest difference in fuel economy gains: more gear ratios, lock-up torque converters and electronic controls. Lock-up converters incorporate a mechanical clutch that can hard-couple the pump and turbine when the vehicle is cruising with no transmission shifting. The clutch allows the torque converter to achieve near-100 percent efficiency. In recent years, engineers have also been able to utilize electronic controls to increase the proportion of time that the torque converter is locked, further increasing efficiency.
Those electronics have played a much bigger role than just controlling the torque converter clutch. Since the mid-1990s, engineers have integrated the management of the engine and transmission making the entire system work together. In combination with electronic throttle, spark and fuel control, engineers have been able to optimize how the engine behaves during shifts as well as during acceleration.
Since fuel efficiency is measured on standard driving cycles on a dynamometer, the engineers are able to calibrate how the throttle responds regardless of what the driver actually requests with the accelerator pedal. This way, actual vehicle response can be closer to the demands of the cycle so the transmission typically shifts at lower engine speeds. The increasing number of ratios â€“ automatics have gone from three speeds in the early-1980s to six, seven and eight speeds today â€“ has also allowed engineers to calibrate shift patterns that keep the engine closer to its most efficient speed regardless of vehicle speed.
Despite the mechanical efficiency advantages of manual transmissions, the transmission is controlled by the vagaries of the driver trying to follow the test protocol. The result is that in most cases, the automatic transmission can now match or beat the manual. Going forward, automatics are likely to improve even more as torque converter automatics are gradually supplanted by dual-clutch transmissions (DCT).
Sometimes innovators strike out for radical change all at once. One can imagine brainstorming teams in the 80s talking about doing away with transmissions altogether, or making them purely electronics, or coming up with entirely different systems that could improve performance. The wild ideas may elevate hopes before they are incinerated on the pyres of reality, while realistic engineers stayed focused on improving each element of the automatic transmission. The latter gave us important but arguably incremental gains, but cumulatively, they have delivered radical innovation that turns popular wisdom upside down, giving us automatic transmissions that are not only more convenient but now also more fuel efficient than manual transmissions.
There are lessons in their story for many other fields.