Fuzzy Logic Gearboxes

By Brian Alexander
If your transmission could sing you a tune – not just rattle and buzz away beneath you as some have been known to do – most modern cars would probably serenade you with peculiar yet catchy mechanical rendition of Rodgers and Hammerstein’s "Getting to Know You." As strange as it may sound, every time you drive computer systems in your car are actually looking at your driving style and converting those unique behind-the-wheel habits – both good and bad – into unintelligible strings of ones and zeros which it processes into a shift pattern that closely correlates to your driving style. After all, no one likes jerky, jarring upshifts.

While that may have sounded excruciatingly technical, the system is actually not that difficult to understand once broken down into its core components. The key to this shift pattern wizardry is the transmission control unit (TCU). Think of it as the mission control center of your car’s gearbox. Essentially, the system looks at your driving inputs, analyzes them to disturbingly minute levels and uses several algorithms to work out a shift pattern that fits with your driving style.

“All electronic control systems take in a wide variety of sensor inputs and typically begin with a predetermined shift pattern, which is then modified to driver input, environmental and vehicle conditions,” says Hamid Vahabzadeh, director of advanced power transfer at General Motors.

Basically, your gearbox comes preprogrammed to certain specifications that can be dynamically adjusted based on how you drive and the prevailing road conditions. If excessive acceleration is your thing the transmission will sense rapid pedal movements that result from your merciless throttle mashing and develop a propensity to hold gears longer before shifting. It can also throw a delay on downshifts for improved engine braking. In that same manner, excessive wheel slip caused by wet or icy pavement will cause the system to shift earlier, using the bottom end of the powerband to minimize wheelspin.

If all that’s left you feeling a bit excluded from the driving experience, fret not.  There’s plenty of evidence that it’s really all about you, as shift patterns are determined by the following factors, descending in order of importance: driver and passenger comfort, transmission feel and fuel economy.

The same technology can also be used to protect vital moving parts. If the transmission is not yet up to operating temperature, the software will short shift through the gears to avoid overstressing the gears. It might not sound like a big deal, but it could add thousands of miles to the life of your drivetrain.

Don’t think that your car will get stuck in its ways if you don’t change up your driving habits, however. Most manufacturers build in redundancies so the TCU won’t map itself to one particular person’s driving habits.

“When the ignition is switched off, the memory is cleared so that if another driver gets in the car, it isn’t driving under someone else’s behavior,” clarifies Vahabzadeh.

Because many vehicles are shared by multiple drivers, it is important that all modifications to the TCU’s software are done in a temporary fashion and that the system always defaults to its base calibration when the ignition is switched off. Can you imagine using a company vehicle after the transmission has adapted to a coworker’s throttle-thrashing?

As Vahabzadeh explains, in GM products “all six-speed transmissions come from the factory with the same settings, which are then calibrated further depending on the vehicle.” SUVs and trucks, which are typically driven less aggressively, are set up to shift at lower revs and use more engine braking on a downward slope. Sedans are set up for comfort, leaving them somewhere in the middle ground, while performance cars are have an inclination to hold gears longer from the get go.

Not everyone out there sees this technology as being advantageous, however. Ford Motor Company would be one such example. “We don't have any gearboxes that ‘learn’ based on driver style and inputs,” says Alan Hall, car and powertrain communications manager at Ford.

“We see that often with those systems, it ends up being a nuisance because what was ‘learned’ is not always the driving style that the customer wants to experience. So, it ends up actually being a dissatisfier versus an advantage.”

Instead, Ford takes a very different stance, calibrating their transmissions to deliver the best mix of fuel economy, throttle response and refinement for the customer without dynamic software modifications while driving.

Next time you start up your car, make note of how those first few shifts go through. Are they jerky? Slow? Abrupt? Ten minutes later, check again. Chances are you’ll notice your transmission behaving closer to your ideal setup. Turn on some Rodgers and Hammerstein and sing along with your car. It knows more about you than you think.


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