Better Fuel Economy Through Better Transmissions

Arguably, the most complicated piece of machinery in the automotive world is a transmission. Transmissions transmit the power from the motor to the wheels in a way that prevents the engine from damaging itself while maximizing the power of the engine. Some battery electric vehicles may be able to skip the transmission all together using just two or three simplified set of gears. However, in internal combustion engines (ICE), the transmissions provide the gears to best capitalize on the power curve of the engine (as well as provide the reverse function).

In the quest to snatch every last joule of energy from each drop of fuel, ICE vehicles have been undergoing a lot of interesting developments recently, including turbo charging, lighter weight materials, and revising pistons and fuel injectors. All of these contribute to better fuel Economics do not have the same impact as an improved transmission.

Transmissions have evolved over the years. When I first started to drive, manual transmissions were considered much more fuel efficient than automatic transmissions. That difference has diminished significantly and now we are seeing automatics that beat or match manual transmissions for fuel economy. In the mid 2000's, the continuously variable transmission (CVT) emerged as the leader for fuel economy. These transmissions do not have the mechanical gears of a traditional transmission, instead using a chain on two v-shaped pulleys that move in and out making the chain rotate on a larger or smaller "gear." This allows the transmission to operate at an infinite number of gear ratios, which keeps the engine running at its optimum speed.

Meanwhile, transmission manufacturers like ZF Friedrichshafen have been adding additional gears to their transmissions while reducing the lag between shifting. This summer, ZF launched the first nine-speed automatic transmission for passenger cars with transverse mounted engines (typically used in front and all wheel drive cars). ZF's nine-speed transmissions have very fast shifts with only two open clutch events, all but eliminating the fuel wasting time between shifts. The new transmission is expected to improve fuel economy 15% or more compared to a six-speed transmission and do so with fewer parts.

Dual clutch transmissions (popular in Europe) typically improve fuel economy 4% to 12% over comparable traditional automatics with torque converters according to transmission-builder, Getrag Corporate Group. Getrag explains dual clutch transmissions on their website as "one gear is engaged, the system has already preselected the next. Once the relevant rpm has been reached, one clutch is opened while the second is closed simultaneously, precluding any interruption in tractive force." In addition, new torque converters and transmissions are being optimized to provide start/stop capabilities to automatic transmissions, all in the name of increased fuel economy.

  Source:reuter