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Automatics Closing Fuel Economy Gap On Manuals; Engines, Electronics Lending A Hand

Illustration for article titled Automatics Closing Fuel Economy Gap On Manuals; Engines, Electronics Lending A Hand

In a stringer piece for the Detroit News, Rex Roy makes the observation that automatic transmissions are finally beginning to catch up to stick shifts in fuel economy. While we say "it's about damn time," considering automatics make up more than 90% of the US new vehicle market, we simultaneously lament that same fact. Also, we think photog-cum-journo Roy misses out on an important component of the improvement: The interface between engine and transmission and the technologies that make the entire powertrain system more efficient. Join us after the jump for a look at why it's not just the two extra gears in your slushbox doing all the work. The first thing that had to happen for automatics to get closer to manuals in fuel economy was an improvement in automatic transmission design. Advances like variable line pressure and the addition of more than four forward gears were far too long in coming to mass-market vehicles in this country. But, five- and six-speed autoboxes are finally becoming the norm. Even the retro four-speed automatics many domestics saddle their low-end models with now have variable line pressure, which reduces the amount of power needed to drive the transmission. All these improvements lead to better efficiency and reduced fuel consumption. But the key, as with so many modern advances, has been in the software controlling the engine/transmission relationship. Old transmissions used a vacuum modulator and a mechanical governor to adjust shift points. New electronically controlled automatics take advantage of vast improvements in processor power to tailor shifts, internal pressures, and torque converter lockup to extract the maximum amount of efficiency possible. The engine helps, though: Cylinder deactivation, like Chrysler's MDS and GM's Active Fuel Management, only works effectively through constant communication with the transmission's requirements. You don't feel any of it happening: You just notice that your new automatic car gets close to the same mileage as your old 5-speed manual beater. So, Rex Roy, we agree that automatics have made exponential improvements in recent years. But let's not give short shrift to the software wizardry and all the black boxes that allow an engine and a transmission to function as an integrated modern powertrain. [Detroit News; Photo Credit: ZF]


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@timtoolman: It depends on the driving situation. Would I spend a minute or two at 3000 RPM before shifting to the next gear? No, I would not. Would I shift early at low RPM going up hills? No, I would not. Neither do most automatics I have driven. Shift points are a function of how hard you're mashing down on the gas. I don't mind having the machinery making this decision for me as long as it is doing so with maximum efficiency/performance in mind.

Otherwise, my decision whether to get an automatic or a standard is simple economics - how much extra is the automatic going to cost me when I take delivery of the vehicle. I'll gladly drive a stick to save $30/month in payments, even if I'm not really saving any gas, but it's not a deal killer either way. I would simply hope that computers were used to design the tranny just like every other part of the drivetrain. If properly designed, a transmission should last the life of the vehicle no matter who is shifting the gears.