Now that manual transmission is quickly becoming a thing of the past, queries about the differing automatic transmission types have greater relevance.
First up, the fully automatic transmission is what most of us are familiar with. For years, the only two choices on the dealership floor were a manual or an automatic transmission. Unlike a manual transmission, an automatic transmission employs a torque converter – a coupler that transfers rotating power from the engine to the transmission using fluid instead of a mechanical connection like a clutch.
Bicycles are a great way to explain why gears are used in this style of transmissions. Your legs can only put out so much energy. Therefore, being able to select a low gear to get yourself moving from a dead stop is very different than the higher gear required once you are moving and maintaining steady cruising speed.
The key takeaway for this style of transmission is that all the gear ratios are fixed, and the only way to introduce a wider gear-ratio range is to physically add additional gear sets. Bicycles have evolved from the single fixed-gear units of my childhood to modern bikes with 18 speeds. Accordingly, automatic transmissions started out with two or three speeds and now regularly have 10.
The downside is that as your automatic transmission shifts gears, a noticeable drop in engine speed occurs. It is this drop in engine rpm that creates a moment where fuel economy suffers as the engine is temporarily moved out of its most fuel-efficient range.
Enter the continuously variable transmission (CVT), an idea that has been around for a while but was forced into the mainstream by manufacturers looking for a way to recover the lost fuel efficiency that occurs every time the typical automatic transmission shifts gears. The CVT employs a sophisticated, continuously variable metal belt system that varies the gear ratios without actually changing gears. Therefore, without the shifting of gears, there is no rpm drop, and the engine can be programmed to remain in its most fuel-efficient power range all the time.
The dual-clutch transmission (DCT) takes old-school manual transmission technology to the next level. Prior to the rise in popularity of DCT transmissions, manufacturers experimented with automated manual transmissions (AMT). Essentially, they were manual transmissions with automation that did the shifting for you and replaced the manual foot-operated clutch with a hydraulic unit. The AMT has essentially evolved into the DCT.
Internally, the DCT resembles its predecessor but adds a second gear shaft and a second, hydraulically operated, clutch. Hence, it’s labelling as a dual-clutch or two-clutch system.
The odd-numbered gears are located on one shaft and the even-numbered gears on the other. Both shafts work independently of each other. Instead of engaging a gear whenever necessary like we did when operating a manual transmission, the DCT‘s control module predicts shift points and pre-engages the next gear ahead of time. When the vehicle is travelling in first gear, shaft one is engaged while second gear waits patiently on the other. The on-board computer simply switches back and forth between shafts with each predicted gear, ready to go. Anyone who remembers driving a manual transmission will clearly recall the drop in rpm as one depressed the clutch pedal in preparation to shift to the next gear. Again, that drop hurts fuel economy.
So, which one is right for you? The CVT always wins the fuel-efficiency game, and most auto manufacturers already have multiple models featuring this style of transmission. Love them or hate them, they are not going away.
The automatic transmission still has use in pick-up trucks and heavier vehicles, as the amount of torque required to move these vehicles exceeds what current CVTs can handle. Manufacturers keep adding gears to smooth out the torque curve and keep the rpms from dropping significantly. For example, most full-size pickups now have 10-speed automatic transmissions.
Expect this to change in the next few years as progress is made with CVTs. Expect them to make an appearance in the truck market in the next few years.
The DCT is marketed towards driving enthusiasts and higher-horsepower vehicles, which are typically seen in the European car market.
You still have choices for now, but expect the CVT to become the most common transmission. That is, of course, until all-electric, gearless vehicles take over the world.
Your automotive questions, answered
Hey Lou,
With many cars today having paddle shifters, I am wondering your thoughts on shift points. From a maximum gas-mileage standpoint, the auto transmissions today shift to higher gears very quickly at what I see as relatively low rpm. Should these shift points be higher? Are the low shift points healthy for engine longevity?
Thanks for your thoughts.
Gord
I don’t know a single person who actually admits to regularly using paddle shifters. They exist for that small population of auto enthusiasts who still think they have some sort of control. What I find ironic is that many vehicles’ transmission control modules override the driver’s manual choices whenever the driver goes outside of allowed parameters. It will shift the transmission regardless of what the driver wants, which signifies to me that you are not truly in control after all. The shift points may seem too low, Gord, but your manufacturer has put a lot of effort into calculating what’s best for fuel economy and engine longevity.
Even the majority of my fellow autocross participants who compete in automatic vehicles don’t use the vehicle’s paddle shifters when competing. They just put their vehicle into its sport mode and let the computer do the work, as the computer’s reaction time is far faster than any human could ever be. I honestly don’t see a need for paddle shifters any longer.
Hi, I am happy with my 2013 Corolla with 197,000 km as it runs well. Now that it’s eight years old, it has two recalls. They are telling me this now! The first recall was about the air bag and was fixed in June, 2019. Now there’s another recall about the air-bag mechanism located between the front seats.
Is it a risk that I drove it for years with no issues?
What do you think?
Albert M
Recalls are now common for all vehicles, given their ever-increasing complexity. The latest recall I believe you are referring to has to do with the Supplemental Restraint System (SRS) control unit, which is located in the center console. The unit may fail to recognize certain types of crashes and fail to deploy air bags and pre-tensioners. From my research, the impact type that the SRS module has problems detecting is limited to a collision where the front of your vehicle is wedged underneath the rear of another vehicle. The SRS unit is manufactured by TRW and used by many auto manufacturers. Accordingly, all of them have been forced to recall this unit.
It is, however, a different SRS recall than the first one you had completed in June, 2019, which I believe was for premature airbag deployment. As far as specific risk goes, unfortunately, yes, you were at greater risk, regardless of how minute the chances were of actually being involved in that specific kind of accident. But we can’t leave the confines of our house without being exposed to some sort of risk, and both of the recalls you mentioned had incident odds similar to winning the lottery.
Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing “Lou’s Garage” in the subject line.
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