Belts, chains, and gears: They’ve been the stuff of transmissions for 125 years. But today’s gearboxes have as much in common with the transmission on Henry Ford’s 1896 Quadracycle as your kid’s balsawood glider has with the gone-missing hypersonic Falcon HTV-2.
Today, traditional manuals and torque-converter-equipped automatics share the road with continuously variable transmissions (CVTs), dual-clutch automated manuals, electrified automatics, and power-split electric motor transmissions. And though two- and three-speed automatics and four- to five-speed manuals ruled for decades, new transmissions offer seven, eight and even nine forward gears. As the gear count in new cars approaches double digits, we have to wonder: What’s with the rush for more speeds, and how many is too many?
The Latest Gear Counts
The latest craze amongst manufacturers is the eight-speed automatic transmission. BMW, Audi, Lexus, and Porsche currently offer octo-geared automatic transmissions with traditional torque converters and planetary gearsets. Ford has committed to manufacturing its own eight-speed automatic in-house. Chrysler recently announced it would license ZF-built eight-speeds to pair with the Pentastar V6 as a $1000 option.
But you can always go higher. Fiat/Chrysler CEO Sergio Marchionne says ZF’s new nine-speed automatic could go into new front-wheel-drive offerings beginning in 2013. Mercedes-Benz is known to be developing a nine-speed version of its G-Tronic gearbox to back its AMG performance models.
It’s not just automatics that are seeing the gear count creep ever upward. Manual transmissions have been relegated to either performance or low-price fuel-miser cars in recent years, but even they are seeing the trend. Porsche unveiled its all-new 911 at the Frankfurt auto show, showing off a new seven-speed manual option.
Why More Gears?
According to Ford Motor Company’s chief engineer of transmissions, Craig Renneker, more gears give powertrain engineers more gear spread to work with. This means first gear can be shorter for better off-the-line acceleration while the top gears can be taller for better fuel economy. Having more gears allows smaller, more economical engines to power larger vehicles or improves the efficiency of existing engines.
“If you had asked me five years ago whether an eight-speed would give better efficiency, I would have said no,” Renneker says, “because the additional sixth clutch required for an eight-speed would have created more internal drag [parasitic energy loss] than the added gear span could offer. We’ve recently discovered how to reduce the clutch drag losses so that eight gears are beneficial. Now it makes sense to jump from the five clutches required for a six-speed, and the overall package saves 2 to 6 percent in fuel economy.”
Porsche spokesman Dave Engelman says his company’s bold step to a seven-speed manual—a highly modified version of the current Porsche PDK automated manual—was also motivated by fuel economy. “Traditionally, Porsche models with manual transmissions hit their top speed in top gear (sixth). The new seventh gear is taller, lowering engine rpm at any given speed, thereby decreasing fuel consumption and CO2 output without compromising acceleration or top speed.”
How Many Is Too Many?
Each manufacturer answers this question differently. Beyond offering smoother shifts, better fuel efficiency, and improved acceleration, a higher gear count also helps marketing simply by giving customers the impression that the car is packed with sophisticated technology (wow, seven speeds!) But some automakers eschew new and higher ratios in the name of product reliability.
Ford’s Renneker says, “Even though one of our competitors is coming out with a nine-speed, we felt the added complexity wasn’t beneficial. We can’t really find the value in using nine gears right now. We can do everything we want, and what we think the customer needs, with eight.”
As for more than nine gears, Renneker says, “In the future, we may come to find a good arrangement, say, for example, for an 11-speed transmission. This could make sense if we can get the losses low enough, but first we’d need to find a good use for 11 speeds. Perhaps some specialized operation like an ultralow first creeper gear? We’ll have to see.”
Shifting Into the Future
More speeds is only part of the picture. The new kinds of transmissions available are also changing how drivers think about changing gears. The continuously variable transmission can pick from a nearly limitless choice of ratios, theoretically making fixed-gear transmissions obsolete. Practically, however, scaling up CVTs to handle the power of bigger engines tends to eliminate their efficiency advantage compared to modern conventional automatics and dual-clutch automated manuals. CVTs also tend to leave customers feeling odd about the driving experience, as the engine and transmission don’t behave the way most drivers are used to.
So predictions of the ultimate extinction of the manual gearbox may be premature. Manual transmissions continue to be the most energy-efficient gearbox available, regardless of what fuel-economy labels say. The number of vehicles with manuals will continue to drop, but there will be a segment of the driving public that wants to shift for itself.
Electrified transmissions will certainly become more prevalent, as evidenced by BMW’s ActiveHybrid models, the Mercedes-Benz S400 Hybrid, and the Honda CRZ. When asked whether Ford’s new eight-speed would include a hybrid variant, Renneker said, “Any new transmission we do is developed with this in mind. It’s definitely on our radar that we would look at what it would take to electrify this transmission.”
All these transmissions will have their place, Renneker tells PM: “What’s interesting in the (transmission) industry today is while dual-clutch transmissions were under development, the planetary units were not standing still. They were getting better and better. As a result, there’s no one clear transmission type emerging as ‘The Future.’ DCTs, planetary, and CVTs are all alive and being developed, and all have a niche. As fuel-economy regulations become tougher and tougher, there’s going to be more customization that defines the optimum transmission for each application.