We want great performance
and great fuel economy. In
short, we pretty much would
like to have both! Are the two
mutually exclusive? Well, both
goals can be achieved if the
lower gears of a transmission
are short enabling good ac-
celeration and the upper gears
are tall to provide low rpm
cruising and thus fuel economy.
If enough gears are available
in a transmission, the engine
will better remain in the ‘sweet spot’ providing a very smooth coordinated driving
experience. Even today’s smaller engines are powerful and perform well with
What if today’s six-speed transmissions turned into eight speeds? Well, it is
coming to a vehicle near you! The eight-speed transmission is not new in the
automotive world. Toyota has offered eight speeds on its LS and IS F automobiles
for the last few years. BMW also offers an eight-speed transmission.
A challenge for the eight-speed transmission has been ‘packaging’ all the gears
in a reasonably sized transmission case, keeping the unit’s weight in check, but
also making certain the components are durable enough for long term service
(after all, thinner and lighter transmission parts for efficient packaging and weight
reduction would impact the transmission’s durability). However, the transmission
giant ZF located in Friedrichshafen, Germany will be bringing the eight-speed
transmission to the mass vehicle market.
The transmission is known as the ‘8HP kit’ and it will offer automakers a number
of options. This transmission is already in upper level offerings such as the BMW
760Li, and 5-Series GT. It will be in the soon to be released Rolls Royce Ghost,
Bentley Mulsanne, and Audi A8.
The transmission consists of four planetary gearsets that provide eight
speeds in all. These gearsets are engaged and disengaged with five shifting
elements. The Toyota eight-speed gearbox also has four planetary gearsets,
but it uses seven shifting elements (see what I mean by fewer parts, packaging,
weight reduction, etc?). The ZF unit has a simpler design than the current
offerings. It will be able to be configured as an automaker specifies
for optimum use in a specific vehicle. The transmission is designed
for longitudinal or north south vehicle installations and for rear-wheel
or all-wheel drive applications. Additionally, it will be equipped in
some applications with an electric ‘helper’ motor for hybrid vehicles.
To save weight, the electric drive motor will double as the starter for
gasoline or diesel engines.
ZF states that the 8-HP transmission will be six percent more efficient
that the six-speed and almost as efficient as the dual-clutch automated
manual which the company also manufactures. The 8-HP will cost about
20 percent less than the dual-clutch unit. Additionally, it will retain the
smooth operating torque converter (it will lock up however, to avoid
inefficient slippage) that American drivers favor.
In addition to manual gear boxes that contain more gears, and the dual-clutch
units, continuously variable transmissions (CVT) are starting to offer a wide
rage of ratios, a reduced number of parts and relatively low weight. However,
making the transmission units smaller is the CVT’s major challenge. The CVT
transmission also will be a major player in the mass automotive market.
Expect to see the 8-HP in hybrid cars by 2011 and plan on the 6-HP (six-speed)
transmission to disappear by 2014.
I can see it now. Honey, can you give me eighth gear overdrive fast? Wow,
what performance! Now, can you downshift three gears we are coming up
to a curve? Wow, we are always driving in the powerband!
Kyle Busch is the author of “Drive the Best for the Price…” He
welcomes your comments or car questions at his auto web site: