Honda/Acura Automatic Transmission Design - Unique?
As I've come to grips with the idea that, to please my wife, our next car will have an auto' transmission, I've looked closer at a technology in which I've previously had no interest. I've learned that Honda's automatic design departs from most everything else on the planet (but then, they've never been shy about different technology). My info on Honda transmissions comes primarily from old, Accord and Acura Legend shop manuals but I've found nothing to suggest a radical departure later. Please correct me if you know differently. Are there any other manufacturers that employ a similar automatic design?
The following comparison ignores the torque converter since it is common to all automatics. While most (all?) other automatic (not CVT) transmissions use planetary gear-sets, Honda has used a mainshaft/countershaft arrangement of spur gears, not unlike a manual transmission. Advantages of planetary gear designs for automatics include constant-mesh gears and that multiple ratios, including reverse, can be derived from a single planetary gear-set. They have the disadvantage of being larger and more complex than paired spur gears and not as flexible in configuration, typically resulting in designs with a single shaft-axis that is not ideal for front wheel drive packaging. Consequently, automatic transmissions are usually large and heavy in comparison to manuals even without considering the torque converter and in spite of the fact that they usually have fewer ratios.
Honda design differs from a manual transmission in that the mainshaft gears do not form a single "cluster" gear but instead rotate independently on the mainshaft and are linked to it (or to other gears) as needed by individual clutches. In this arrangement the gears remain constant mesh (reverse is a special case) and unlike typical automatic transmissions, there may be only one pair of gears per transmission ratio (planetary gear-sets may be used in series in typical designs, reducing efficiency). Unlike a typical automatic where reverse is accomplished by stopping rotation of the planet carrier in one planetary gear-set, Honda uses a manual-like shift fork and collar to engage a separate reverse gear (does this relate to the metallic sound when engaging/disengaging reverse that some people comment (complain?) about?). Brake bands as used in planetary gear designs are not needed, but the number of clutches may be greater. This arrangement results in a more compact (and presumably lighter) automatic transmission, although it is still larger than a manual to accommodate the clutches (one per forward gear ratio) and control hydraulics.
An apparent challenge posed by the Honda design regards the clutches. Since the clutches cannot be larger in radius than the distance between shafts, they are necessarily smaller than in typical planetary designs where the clutches may be nearly the full diameter of the transmission (although perhaps with a narrower annulus). This means that a given torque must be handled by a smaller diameter clutch, which suggests higher operating pressure, greater component (and lubricant) stress and interesting control challenges. I'm not surprised that Honda ATF is "special".
I don't know whether Honda's design is inherently better or worse, but cars with this design have been in service for decades and Honda's reputation for quality has remained among the top in the industry. OTOH, in perusing the Internet, I have encountered references to Honda/Acura V6 transmission failures. Has engine power increased to the point that it exceeds some inherent design limitation? Are the transmission failures related to Honda's design or are they a QA issue? Was there a design change that caused a problem? OR, is the "problem" merely an artifact of an Internet that gives voice to a few who have experienced anomalous failures? How does one know?
I am a long-term Honda/Acura fan and owner (at least one has been in my "fleet" since '84), and I am now in the market for a new car, unfortunately with the dreaded "slush box" (although Honda's seem tighter than many). The Internet is a great place for information but it can be difficult to determine the acuracy and significance of what you find and those with complaints may be the most vocal so I hesitate to draw conclusions from forum discussions. Who has THE answer??
The following comparison ignores the torque converter since it is common to all automatics. While most (all?) other automatic (not CVT) transmissions use planetary gear-sets, Honda has used a mainshaft/countershaft arrangement of spur gears, not unlike a manual transmission. Advantages of planetary gear designs for automatics include constant-mesh gears and that multiple ratios, including reverse, can be derived from a single planetary gear-set. They have the disadvantage of being larger and more complex than paired spur gears and not as flexible in configuration, typically resulting in designs with a single shaft-axis that is not ideal for front wheel drive packaging. Consequently, automatic transmissions are usually large and heavy in comparison to manuals even without considering the torque converter and in spite of the fact that they usually have fewer ratios.
Honda design differs from a manual transmission in that the mainshaft gears do not form a single "cluster" gear but instead rotate independently on the mainshaft and are linked to it (or to other gears) as needed by individual clutches. In this arrangement the gears remain constant mesh (reverse is a special case) and unlike typical automatic transmissions, there may be only one pair of gears per transmission ratio (planetary gear-sets may be used in series in typical designs, reducing efficiency). Unlike a typical automatic where reverse is accomplished by stopping rotation of the planet carrier in one planetary gear-set, Honda uses a manual-like shift fork and collar to engage a separate reverse gear (does this relate to the metallic sound when engaging/disengaging reverse that some people comment (complain?) about?). Brake bands as used in planetary gear designs are not needed, but the number of clutches may be greater. This arrangement results in a more compact (and presumably lighter) automatic transmission, although it is still larger than a manual to accommodate the clutches (one per forward gear ratio) and control hydraulics.
An apparent challenge posed by the Honda design regards the clutches. Since the clutches cannot be larger in radius than the distance between shafts, they are necessarily smaller than in typical planetary designs where the clutches may be nearly the full diameter of the transmission (although perhaps with a narrower annulus). This means that a given torque must be handled by a smaller diameter clutch, which suggests higher operating pressure, greater component (and lubricant) stress and interesting control challenges. I'm not surprised that Honda ATF is "special".
I don't know whether Honda's design is inherently better or worse, but cars with this design have been in service for decades and Honda's reputation for quality has remained among the top in the industry. OTOH, in perusing the Internet, I have encountered references to Honda/Acura V6 transmission failures. Has engine power increased to the point that it exceeds some inherent design limitation? Are the transmission failures related to Honda's design or are they a QA issue? Was there a design change that caused a problem? OR, is the "problem" merely an artifact of an Internet that gives voice to a few who have experienced anomalous failures? How does one know?
I am a long-term Honda/Acura fan and owner (at least one has been in my "fleet" since '84), and I am now in the market for a new car, unfortunately with the dreaded "slush box" (although Honda's seem tighter than many). The Internet is a great place for information but it can be difficult to determine the acuracy and significance of what you find and those with complaints may be the most vocal so I hesitate to draw conclusions from forum discussions. Who has THE answer??
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Comments
is it advisable to put the gear in Neutral while
in idle, then in Drive when light is green?
i'm just concerned about wear and tear on the
auto tranny.
i know that for manual trannys, your pressure
plate would have a reduced life if you were a
clutch driver.
kinda stupid question but i have been driving
manuals for over 10 years and it's my 1st time
to own an automatic tranny vehicle. i'm also
used to the fact that when a manual stalls, you
can use the "push n throttle" method to start
the car (n/a on autos)
Only time I've ever shifted into neutral is when I'm slowing down and the car feels like it's about to stall out. I'll shift into neutral and rev the engine a bit to keep it from stalling.
The best way to make an automatic transmission last, though, is to make sure it's maintained properly, and when it's serviced that they put the correct fluid in. Even on cars where they have 50K, 100K, or even "tranny fluid for life", the stuff still has to be checked. And if it ever looks sooty, discolored, or smells burnt, it needs to be changed.
Just do what andre1969 says and your transmission will last.
read your post so i can learn from it
Barnone: wear occurs in auto trans clutches and bands as they're applying. Shifting to neutral then drive at every traffic light will reduce their service life.
My opinion on my Honda AT: I love the grade-logic. I can't recall it ever hunting back and forth for the right gear; it always seems to be in the correct gear given the speed, incline and throttle position. I also like the fact that you get some engine braking when you take your foot off of the throttle, just like in a manual transmission car. I never knew that it was due to the somewhat unique design until I read the first post in this thread - thanks daysailer!
After driving my Honda, I particularly notice in other cars that they remain at the same speed after I take my foot off the go pedal, and I have to use the brakes a lot more.
I also like the "abrupt" shifts in my Honda, although I realize a lot of people don't, particularly those used to GM and Toyota automatic cars. The shifting seems hard to some people.
I would have loved to get a stick shift with Honda's great V6 engine, but they don't offer that. I certainly hope they do with the next generation Accord. Otherwise, I will probably look at the competition that does.
have you used additives of some sort?
what say?
Chickoo: the type of transmission you describe is showing up on some high-dollar sports cars like Ferrari, Porsche (and BMW?). These are take-offs on the transmissions used on Formula 1 race cars. The driver uses little paddles to upshift and downshift, or you can have the car's computer do it for you automatically. But they differ from an automatic transmission because there is a clutch and manual gearbox. The paddle (or computer) actuates the clutch and gear changer to upshift or downshift, only much much faster than you or I can do with a clutch pedal and stick shift.
I don't know how quick (or if) this type of shifting system will work its way down to cheaper cars. It's expensive as heck now.
I would love to have that tranny come down to affordable cars.....will bring back th thrill of driving a car w/o getting laborious.....and maintenance would also be darned easy.