Last year, Lexus became the first automaker to introduce a production eight-speed automatic transmission in the latest LS460. Recently, German transmission manufacturer ZF announced a new eight-speed of its own which is claimed to provide a 14-percent boost in fuel efficiency compared to a five-speed. It looks like Audi and BMW will likely be the first to directly challenge Lexus when they start using the ZF. Audi may be first out of the gate in 2009, with eight-speed installations in the A8, Q7 and the expected A7 coupe. BMW will probably follow a year later with the X6 and the next-generation 7 series getting the extra gears. Mercedes-Benz already has a seven-speed that it builds on its own. Mercedes' powertrain chief admits that an extra gear could be added to the unit but that the incremental improvement would be limited. As more gears are added, the weight and complexity of the system increases and the improvements become smaller and smaller. Seven and eight-speed transmissions will likely remain the maximum for the foreseeable future and six-speeds will probably take the bulk of volume in mainstream segments.

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German transmission supplier ZF has just started building production samples of a new electric motor that will be part of Mercedes-Benz new mild hybrid system. Mercedes co-developed the system with BMW and displayed it in several different vehicles shown at last fall's Frankfurt Motor Show. The first production application is expected to be the S400 hybrid which will pair a 3.5L gasoline V-6 with the 15kW electric motor/generator and a lithium ion battery to recapture energy from regenerative braking.

The motors are being manufactured by ZF's Sachs division at a plant in Schweinfurt Germany. ZF claims to be the first company to manufacture hybrid modules in Europe. Full production starts this fall at the rate of 35,000 annually and will eventually be ramped up to 200,000 a year. The Mercedes-BMW mild hybrid sandwiches the motor/generator between the engine and transmission to provide some low speed electric drive, electric power boost at higher speeds, auto start-stop and regenerative energy recapture. ZF currently has eight hybrid development projects with four manufacturers including Mercedes with production launches scheduled over the next four years.

[Source: ZF Friedrichshafen AG]

In the name of increased efficiency, and quite possibly playing the game of automotive one-upmanship, luxury automakers such as Mercedes Benz, BMW and Lexus have been adding more and more gear ratios to their automatic transmissions. By allowing a computer to choose the most appropriate ratio for any given scenario, the vehicle's engine is required to only make as much power as absolutely necessary, potentially saving fuel in the process. ZF, one of the largest transmission makers in the world, claims that their new 8-speed unit boasts an efficiency increase of eleven percent over its older 6-speed unit. The transmission giant has just developed a new modification, though, which could increase the overall vehicle efficiency even further. By adding a hydraulic impulse storage unit, the new ZF unit can support stop/start functionality, which they claim can result in an additional five percent reduction in fuel consumption.

[Source: Just-Auto - sub. req'd.]

Is it solely a case of one-upmanship that is driving the number of forward gear ratios forward in today's passenger cars? Or, are consumers choosing vehicles based on the number of gears in the transmission? I am not entirely sure, but I do know that I would consider passing on a vehicle just because it only has a four-speed transmission. As rare as they are today, some vehicles, like the GM full-size pickups, are still using four-speed automatic transmissions. Before you comment, I know that they are being phased out in favor of the new six-speeders. But, a little research shows that Mercedes and BMW offer seven speed automatics, and Lexus has an eight speed for their top-of-the-line model. Why so many gears? Efficiency is one reason, and performance is the other. We'll start with the latter.

Do you remember the old Power-Glide trannys that GM used when muscle cars were just hitting the scene? I'm not old enough to remember, but I have experienced them after-the-fact. They worked fine, but if you were cruising in second gear and hit the gas causing a downshift, it might be rather abrupt, because there was only one choice for the transmission to make. In the newer trannys with more gears, there are many choices. For instance, imagine cruising in gear eight, you hit the gas ... depending on how hard and at what speed you are traveling, you could drop to seventh for a gradual acceleration, or to fourth for fast pick-up. Conversely, only having two forward gears in the Power-Glide allows for excellent reliability and it also makes them predictable, which is why they are still popular transmissions for drag racing.

Now, as far as efficiency is concerned, if you are driving slowly, the transmission can up-shift to a lower numeric gear ratio, saving gas in the process. I have never driven a car with more than six forward gears ... so I can't say what the driving experience is like, but it is certainly a market trend to increase the number of forward gears. For maximum efficiency, a manufacturer may choose a CVT with an infinite number of ratios, but some consumers don't like the driving experience with them. So I would expect to see more and more new transmissions like this ZF with eight forward gears. The more the merrier?

[Source: Gizmag]