6% is not a whole lot. I imagine that is city driving. So if a car gets 20 mpg city with a conventional automatic (4 speed?) we're only talikg a potential of 1.2 mpg. Even if you are talking 25 mpg with a conventional 5 or 6 speed auto, CVTs and more speeds is probably only delivering around 1-1.5 mpg or less tops, and with some drawbacks.
GM, Ford teaming up for new transmissions
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6% less fuel used over a million units of a particular model is a lot of fuel! Engineers scrape for a few tenths of a MPG. A 1 mpg increase on a 20 mpg vehicle is huge!
In certain situations like going uphill there comes a point where a 4 or 5 speed automatic is holding the engine at too high RPM, throwing away fuel. Programmed well, a 9 or 10 speed transmission could get the engine into a more efficient speed faster without compromising hillclimbing power. It won't be "hunting" for gears nearly as much, which is something that annoys the daylights out of me.
In certain situations like going uphill there comes a point where a 4 or 5 speed automatic is holding the engine at too high RPM, throwing away fuel. Programmed well, a 9 or 10 speed transmission could get the engine into a more efficient speed faster without compromising hillclimbing power. It won't be "hunting" for gears nearly as much, which is something that annoys the daylights out of me.
Originally Posted By: sciphi
6% less fuel used over a million units of a particular model is a lot of fuel! Engineers scrape for a few tenths of a MPG. A 1 mpg increase on a 20 mpg vehicle is huge!
In certain situations like going uphill there comes a point where a 4 or 5 speed automatic is holding the engine at too high RPM, throwing away fuel. Programmed well, a 9 or 10 speed transmission could get the engine into a more efficient speed faster without compromising hillclimbing power. It won't be "hunting" for gears nearly as much, which is something that annoys the daylights out of me.
Agreed. Many new vehicles can't find the right gear under those conditions. However, that IS by design. AND, we don't spend a lot of fuel or a lot of time "climbing".
What many fail to see in that case, is that you NEED power to climb. An undersized engine will be operating in a mode pushes fuel/air ratio's even farther into the "power" mode. And, whether forced induction or not, the production of 50% or more torque is an inefficient place to operate for gasoline engines. With many operating F/A of 12 to 1.
The 17 speed transmission won't significantly help the engine operate more efficiently.
I'd like to direct y'all to a list of BSFC curves. Notice that many engines can operate efficiently over a somewhat wider range than you've been led to believe???
http://ecomodder.com/wiki/index.php/Brake_Specific_Fuel_Consumption_(BSFC)_Maps
6% less fuel used over a million units of a particular model is a lot of fuel! Engineers scrape for a few tenths of a MPG. A 1 mpg increase on a 20 mpg vehicle is huge!
In certain situations like going uphill there comes a point where a 4 or 5 speed automatic is holding the engine at too high RPM, throwing away fuel. Programmed well, a 9 or 10 speed transmission could get the engine into a more efficient speed faster without compromising hillclimbing power. It won't be "hunting" for gears nearly as much, which is something that annoys the daylights out of me.
Agreed. Many new vehicles can't find the right gear under those conditions. However, that IS by design. AND, we don't spend a lot of fuel or a lot of time "climbing".
What many fail to see in that case, is that you NEED power to climb. An undersized engine will be operating in a mode pushes fuel/air ratio's even farther into the "power" mode. And, whether forced induction or not, the production of 50% or more torque is an inefficient place to operate for gasoline engines. With many operating F/A of 12 to 1.
The 17 speed transmission won't significantly help the engine operate more efficiently.
I'd like to direct y'all to a list of BSFC curves. Notice that many engines can operate efficiently over a somewhat wider range than you've been led to believe???
http://ecomodder.com/wiki/index.php/Brake_Specific_Fuel_Consumption_(BSFC)_Maps
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That'll be the rub: "programmed well". Until they put in tilt mechanisms, so as to know the grade being tackled, and put in some way to sense how loaded the vehicle is, they won't be "programmed well". My six speed truck likes to double downshift, and IMO it's because it has no way of knowing it's being driven unloaded: it was cruising in top gear, just barely turning at 60mph, and then, because it just might be loaded up, aggressively downshifts on a hill when there was a spike in power required to maintain speed.
I suppose I could be proactive, and use sport mode, and downshift ahead of time. Kinda defeats the purpose...
But I think these 8+ speed transmission are going to be similar: they will drop two, perhaps even three gears, when encountering a grade. Simply because, let's say it downshifts one cog, and "tries" that cog for a few seconds before downshifting again. Who would put up with that? It'd be considered a slow-responding transmission. Again, w/o the ability to know what is ahead of the vehicle, it is always reacting to the road, it has no ability to plan ahead. And since it's reacting, it'll always be behind the curve.
Pure SWAG, but I have to wonder if in the end it'll downshift with jumps more akin to the older 4 speed autos--those gear ratios weren't stabs in the dark, after all. The big gain will be the ability to push the tallest gear possible when grades and speeds are "steady" and not changing rapidly.
I suppose I could be proactive, and use sport mode, and downshift ahead of time. Kinda defeats the purpose...
But I think these 8+ speed transmission are going to be similar: they will drop two, perhaps even three gears, when encountering a grade. Simply because, let's say it downshifts one cog, and "tries" that cog for a few seconds before downshifting again. Who would put up with that? It'd be considered a slow-responding transmission. Again, w/o the ability to know what is ahead of the vehicle, it is always reacting to the road, it has no ability to plan ahead. And since it's reacting, it'll always be behind the curve.
Pure SWAG, but I have to wonder if in the end it'll downshift with jumps more akin to the older 4 speed autos--those gear ratios weren't stabs in the dark, after all. The big gain will be the ability to push the tallest gear possible when grades and speeds are "steady" and not changing rapidly.
5 speed is enough for me. My 8 speed rental sucked! I'd rather pay a little extra for the gas I might be wasting with the 5 speed.
Originally Posted By: sciphi
[If] Programmed well...
This is truly the key. And others have mentioned it as well.
With the advent of these 8, 9, 10 speed transmissions (and even 6 speeds in my experience), manufacturers seem to have discovered that they can leverage the number of speeds now available to them and really "lock the engine down" in terms of fuel economy. There's only so much you can do with 4 or 5 forward gears and keep the car manageable. But with 8 or 9 or 10 speeds, you can now keep the engine to about 1,500 or 1,800 rpm all day long, and the car will drive just fine.
This is great for fuel economy. You're right: a 6% gain is absolutely HUGE, especially when multiplied across hundreds of thousands of cars. Follow the money: those CAFE credits are extremely valuable to each and every manufacturer.
On the downside, an 8 speed transmission keeping an engine at 1,500 rpm all day long makes for a very BORING drive. I know; I rented a car like that for a month. Super nice car, very quiet inside, very refined, very classy. The engine itself was very nice. The transmission itself was very nice. You couldn't feel most shifts; it did its business in a very smooth way. But the driving experience was a real snoozer. There was no emotion from the car, no playfulness, no excitement. The engine just lugged along at 1,500 rpm all day long. It returned good fuel economy, but it was a real snoozer.
I fear these transmissions not because of the transmissions themselves, but because of what they allow the computer programmers to do with the software.
[If] Programmed well...
This is truly the key. And others have mentioned it as well.
With the advent of these 8, 9, 10 speed transmissions (and even 6 speeds in my experience), manufacturers seem to have discovered that they can leverage the number of speeds now available to them and really "lock the engine down" in terms of fuel economy. There's only so much you can do with 4 or 5 forward gears and keep the car manageable. But with 8 or 9 or 10 speeds, you can now keep the engine to about 1,500 or 1,800 rpm all day long, and the car will drive just fine.
This is great for fuel economy. You're right: a 6% gain is absolutely HUGE, especially when multiplied across hundreds of thousands of cars. Follow the money: those CAFE credits are extremely valuable to each and every manufacturer.
On the downside, an 8 speed transmission keeping an engine at 1,500 rpm all day long makes for a very BORING drive. I know; I rented a car like that for a month. Super nice car, very quiet inside, very refined, very classy. The engine itself was very nice. The transmission itself was very nice. You couldn't feel most shifts; it did its business in a very smooth way. But the driving experience was a real snoozer. There was no emotion from the car, no playfulness, no excitement. The engine just lugged along at 1,500 rpm all day long. It returned good fuel economy, but it was a real snoozer.
I fear these transmissions not because of the transmissions themselves, but because of what they allow the computer programmers to do with the software.
Good point Cujet, although I thought 12:1 was around the optimal A/F for power? probably not for economy, but most hp per cubic inch.
I thought I had read of the Northstar(?) engines running upwards of 10:1 to prevent pistons from melting. With the trend towards higher compression ratios I wonder if some of the engines out there do just that: run really rich under peak conditions (and thus still rather rich under more moderate loads), since those are regions that are not heavily used for most drivers; but do allow the advertising of high peak power, while keeping engine weight low (because presumably something has to give in order to have a leaner running engine that is more efficent). Isn't that what goes on with some of the tuners, they pull out fuel at WOT, at least on some?
Maybe they run rich under those conditions for emissions, not to protect the engine.
I thought I had read of the Northstar(?) engines running upwards of 10:1 to prevent pistons from melting. With the trend towards higher compression ratios I wonder if some of the engines out there do just that: run really rich under peak conditions (and thus still rather rich under more moderate loads), since those are regions that are not heavily used for most drivers; but do allow the advertising of high peak power, while keeping engine weight low (because presumably something has to give in order to have a leaner running engine that is more efficent). Isn't that what goes on with some of the tuners, they pull out fuel at WOT, at least on some?
Maybe they run rich under those conditions for emissions, not to protect the engine.
Of course even a few tenths increase in mpg is attractive to automakers but is the rather small increase worth it to the vehicle owner/driver?
Anyway you slices, in order for 6+ speed automatic to get better milage it has to be continually upshifing into a higher gear and locking the converter. The car is going to be sluggish any time any grade is encounter or more acceleration is needed. This means unlocking the converter and downshifting OR sluggish performance and lugging.
You cannot get both more performance and more fuel economy at the same time. More speeds might get you slightly more performance potential and slightly more fuel economy potential, both not both at the same time. When it's giving you more economy (higher gear locked up converter), you're giving up performance and drivability, and when it's giving more performance you are giving up some economy. It's a trade off, and in everyday driving the trade off is performance and drivability for a small increase in economy.
Anyway you slices, in order for 6+ speed automatic to get better milage it has to be continually upshifing into a higher gear and locking the converter. The car is going to be sluggish any time any grade is encounter or more acceleration is needed. This means unlocking the converter and downshifting OR sluggish performance and lugging.
You cannot get both more performance and more fuel economy at the same time. More speeds might get you slightly more performance potential and slightly more fuel economy potential, both not both at the same time. When it's giving you more economy (higher gear locked up converter), you're giving up performance and drivability, and when it's giving more performance you are giving up some economy. It's a trade off, and in everyday driving the trade off is performance and drivability for a small increase in economy.
Originally Posted By: mechanicx
Of course even a few tenths increase in mpg is attractive to automakers but is the rather small increase worth it to the vehicle owner/driver?
In my opinion, no. That's why I won't buy one. At least not one without some user intervention, like a +/- shifter or paddles behind the steering wheel. Even then, you don't get much change in ratio when you have 10 speeds. I prefer wider spacing on the ratios. They let me "feel" the engine more.
I grew up on 2- and 3-speed transmissions. I never felt that those were enough. I yearned for more gears. 4- and 5-speeds fit the bill for me quite nice. I can live with a 6-speed, but the ratios have to be spread wide enough. More than 6 speeds, and all it's doing is shifting.
Of course even a few tenths increase in mpg is attractive to automakers but is the rather small increase worth it to the vehicle owner/driver?
In my opinion, no. That's why I won't buy one. At least not one without some user intervention, like a +/- shifter or paddles behind the steering wheel. Even then, you don't get much change in ratio when you have 10 speeds. I prefer wider spacing on the ratios. They let me "feel" the engine more.
I grew up on 2- and 3-speed transmissions. I never felt that those were enough. I yearned for more gears. 4- and 5-speeds fit the bill for me quite nice. I can live with a 6-speed, but the ratios have to be spread wide enough. More than 6 speeds, and all it's doing is shifting.
Originally Posted By: Hokiefyd
I grew up on 2- and 3-speed transmissions. I never felt that those were enough. I yearned for more gears. 4- and 5-speeds fit the bill for me quite nice. I can live with a 6-speed, but the ratios have to be spread wide enough. More than 6 speeds, and all it's doing is shifting.
Same here, I agree completely. 3-speed automatics with a decently low axle gear were fast to way over legal speeds (heck in a light enough car a 2-speed can be faster). But the 3-speed lacked reasonable highway engine speeds and didn't deliver maximum fuel economy. Enter the 4-speed with lower 1st, 2nd and overdrive with lock up you got 90-95%+ of the performance and economy you are going to get out of the engine, and drivability overall increased once the lock up converter scheme became smoother.
An increase to 5-speed seemed to not affect drivability and may even helped. But once you start goiing over 5-6 speeds it seems drivability increasingly suffers for a diminishing increase in economy. Can more sophisticated programming improve drivability? I'd say there's improvements to be made, but you're not going to increased fuel economy without trading off some performance and drivability.
I grew up on 2- and 3-speed transmissions. I never felt that those were enough. I yearned for more gears. 4- and 5-speeds fit the bill for me quite nice. I can live with a 6-speed, but the ratios have to be spread wide enough. More than 6 speeds, and all it's doing is shifting.
Same here, I agree completely. 3-speed automatics with a decently low axle gear were fast to way over legal speeds (heck in a light enough car a 2-speed can be faster). But the 3-speed lacked reasonable highway engine speeds and didn't deliver maximum fuel economy. Enter the 4-speed with lower 1st, 2nd and overdrive with lock up you got 90-95%+ of the performance and economy you are going to get out of the engine, and drivability overall increased once the lock up converter scheme became smoother.
An increase to 5-speed seemed to not affect drivability and may even helped. But once you start goiing over 5-6 speeds it seems drivability increasingly suffers for a diminishing increase in economy. Can more sophisticated programming improve drivability? I'd say there's improvements to be made, but you're not going to increased fuel economy without trading off some performance and drivability.
My '84 Cutlass had a 3-speed and a 2.14:1 axle ratio. Engine speed at highway speed was in the 2,500 range, which was reasonable. But 1st gear was good until about 45-50 mph, and it was quite doggish off the line.
I love the 5-speeds in our current cars. They have a short enough 1st gear to be usable off the line. They have tall enough 5th gears to maintain low engine speeds at quite fast road speeds (our MDX can reach about 75 mph at 2,000 rpm), and the ratio spread seems just perfect. It's close enough that there's not much shock during a shift, but it's wide enough that the engine feels free to rev as it works through the gears. That's good for a car guy, who likes to hear and feel the engine operate. That's not as good for fuel economy. But I'm okay with that. In fact, I prefer it.
I love the 5-speeds in our current cars. They have a short enough 1st gear to be usable off the line. They have tall enough 5th gears to maintain low engine speeds at quite fast road speeds (our MDX can reach about 75 mph at 2,000 rpm), and the ratio spread seems just perfect. It's close enough that there's not much shock during a shift, but it's wide enough that the engine feels free to rev as it works through the gears. That's good for a car guy, who likes to hear and feel the engine operate. That's not as good for fuel economy. But I'm okay with that. In fact, I prefer it.
I'd need some sort of manual intervention that worked. Flappy paddles are fine by me, since they are right there. I was tooling around in our Fit today, and needed more power. Mashing the gas got 4000 rpm, and it still needed more. Hitting the flappy paddle got a downshift to 5500 rpm, and the faster acceleration needed. The car redlines at 7200 rpm, with power up until 6700 rpm or so.
Program it well, give a working manual shift mode that will override the computer's gear choice as long as over-revving is not possible, and 9 speeds is fine with me.
Program it well, give a working manual shift mode that will override the computer's gear choice as long as over-revving is not possible, and 9 speeds is fine with me.
Many missed points here. First is A/F ratios. Note that many many vehicles run pig rich at any significant load. 10:1 is not unheard of, and the higher the specific output the more fuel is used for cooling.
Second is grade recognition. My new van has this, able to both provide grade braking downhill as well as recognize the tilt of the road in either direction, up or down. This is not an uncommon feature in GM products and has been around for years.
Programming is the key. With proper programming the 45 speed autobox will shuffle the gears seamlessly and you won't have much to complain about! The smaller displacement engines will benefit the most.
Note that my 2013 Chevy Express 3500 averaged 15.9 mpg across 1400 miles at an average speed of 69.7 mph. That is at least 4 mpg better than a comparable 4 speed drivetrain in a similar truck. Some of that is VVT but not much.
Second is grade recognition. My new van has this, able to both provide grade braking downhill as well as recognize the tilt of the road in either direction, up or down. This is not an uncommon feature in GM products and has been around for years.
Programming is the key. With proper programming the 45 speed autobox will shuffle the gears seamlessly and you won't have much to complain about! The smaller displacement engines will benefit the most.
Note that my 2013 Chevy Express 3500 averaged 15.9 mpg across 1400 miles at an average speed of 69.7 mph. That is at least 4 mpg better than a comparable 4 speed drivetrain in a similar truck. Some of that is VVT but not much.
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