I was just thinking about transmissions

[mwmorph]

With the new wave towards smaller cars and less power I'm starting to wonder if we're getting towards the "hump" where we wont see any more gar ratios. Manuals are at 6 speed and will obviously stay there due to ergonomic issues to moving up to more gears, Automatics are at 8 gears and sequentials are at 7.

I'm just wondering how many more will be added before we see a break even? or one the fitting of smaller transmissions in smaller cars will obviously decrease space for more gearing, but on he other hand, the torque requirement is going to stabilize or even decrease so the gears won't have to be as robust.

What are your thoughts? Will we see 10 gear sequential? 12 gears? Maybe we'll all transition to CVT for hybrid or electric powertrain and fuel economy reasons? At what point will be hit the maximum?

 

[vi edit]

I'm scared to know what the long term reliability and repair costs are on thos 6, 7, 8 gear transmissions a few years down the road.

 

[Billb2]

There are a few cars with CVTs now.

 

[sdifox]

Do we have any sort of reliability numbers on the CVTs yet or is it still too early? I imagine if they are designed properly they should be relatively trouble free.

 

[exdeath]

CVTs would be ideal as they solve or mask the inherent problem of the piston ICE that requires a transmission in the first place (narrow operating range engine powering a wide operating range requirement).

Actually, electric motors would be ideal and the "final evolution" as they deliver a constant maximum torque over an infinite range of speed and do not require a transmission at all.

Note that the output shaft of a CVT (driven by an ICE) would somewhat attempt to mimic the behavior of an electric motor, in that the engine is maintained at its peak torque position while the output road speed increases steadily.

 

[Howard]

Electric motors are speed-limited as well.

 

[Zenmervolt]

In all honesty, there's not a huge difference in mileage between 5-speed manuals and 6-speed manuals. The real advance was when we went from three-speed and four-speed units to transmissions with a 5th, overdrive, ratio.

First gear, whether a true gear, or the initial ratio of a CVT can only be so low before it almost ceases to be useful outside of specific cases (e.g. the old Chevy "three and a half speed" pickup transmissions that had an extra low "creeper" gear for farm/jobsite use) and the top gear can only be so high before it becomes almost impossible to do anything other than maintain speed with it (e.g. the super-tall 6th gear in the Corvette, even with that magnificent engine, you still need to downshift to pass). So, at some point, the return from extra gears becomes so small that it's not worth it in terms of efficiency. I honestly don't see efficiency driving us past 5 or 6 ratios in manual transmissions. Now, for sporting purposes I can see wanting more ratios as it can increase the ability to keep the car in the fattest part of the powerband, but that's not an efficiency reason.

Trucks like Semis have 12-24 gears because their engines have only about 1,500-2,00 RPM between idle and redline and because they need many very low gears to get their weight moving. The next time you're sitting beside a semi at a light, pay attention to how often the driver shifts as he takes off. It's a lot. They are basically working through all of the "creeper" gears they have.

The ultimate problem with a CVT, just like with an automatic, is the torque converter coupling which reduces efficiency when it's unlocked. As torque converters have improved and the lockup clutches began to be used in lower gears efficiencies have climbed significantly, but there's still a gap when the converter is unlocked.

ZV

 

[exdeath]

Originally posted by: Howard
Electric motors are speed-limited as well.

Not with the same limitations and complexities as a reciprocating and valved combustion engine.

An electric motor only has a single rotational mass, it doesn't have to deal with things like valve float, piston velocity, tensile and compression forces in the rods, rapid acceleration and deceleration of reciprocating parts, friction, balancing, etc.

You can spin an electric motor shaft and windings at 20,000 RPM much more easily than a reciprocating combustion engine. The only thing you have to worry about is brush longevity and shaft bearings. The same applies to constant combustion gas turbine engines, except they don't output constant torque.

An electric motor putting out constant torque from 0 RPM to 20,000 RPM covers about 3-4 gears on an average vehicle.

 

[Howard]

I haven't checked any electric motor specs lately but I really don't think you can find a motor that will spin to 20k RPM with any decent torque at higher speeds... if at all.

EDIT: I could be wrong.

EDIT2: http://en.wikipedia.org/wiki/Venturi_Fetish

Assuming the car has driven tires of 22" diameter, the speed of the motor works out to be about 2650RPM at top speed.

EDIT3: The hypens in your sig are placed incorrectly.

 

[91TTZ]

Originally posted by: exdeath
CVTs would be ideal as they solve or mask the inherent problem of the piston ICE that requires a transmission in the first place (narrow operating range engine powering a wide operating range requirement).

Actually, electric motors would be ideal and the "final evolution" as they deliver a constant maximum torque over an infinite range of speed and do not require a transmission at all.

Note that the output shaft of a CVT (driven by an ICE) would somewhat attempt to mimic the behavior of an electric motor, in that the engine is maintained at its peak torque position while the output road speed increases steadily.

If you want the best fuel efficiency you'd want to stay around the peak torque rpm, but for best acceleration you'd want to stay at the rpm where you make peak HP.

 

[91TTZ]

Originally posted by: Zenmervolt
In all honesty, there's not a huge difference in mileage between 5-speed manuals and 6-speed manuals. The real advance was when we went from three-speed and four-speed units to transmissions with a 5th, overdrive, ratio.

I thought most auto transmissions went to OD when they switched from 3 to 4 speeds? Nearly all auto cars had 4 speeds, the 4th being overdrive.

 

[JulesMaximus]

Originally posted by: mwmorph
With the new wave towards smaller cars and less power I'm starting to wonder if we're getting towards the "hump" where we wont see any more gar ratios. Manuals are at 6 speed and will obviously stay there due to ergonomic issues to moving up to more gears, Automatics are at 8 gears and sequentials are at 7.

I'm just wondering how many more will be added before we see a break even? or one the fitting of smaller transmissions in smaller cars will obviously decrease space for more gearing, but on he other hand, the torque requirement is going to stabilize or even decrease so the gears won't have to be as robust.

What are your thoughts? Will we see 10 gear sequential? 12 gears? Maybe we'll all transition to CVT for hybrid or electric powertrain and fuel economy reasons? At what point will be hit the maximum?

I doubt we'll ever see 10 or 12 gears. You lose too much time between gear changes for it to be worthwhile. Formula One cars have 7 gears and they can attain speeds of over 200mph. We'll see more seemless or CVT transmissions before we see more gears IMO.

Nobody wants to be rowing through more than 6 gears in a manual gearbox. It just becomes tedious after a while.

 

[Zenmervolt]

Originally posted by: 91TTZ

Originally posted by: Zenmervolt
In all honesty, there's not a huge difference in mileage between 5-speed manuals and 6-speed manuals. The real advance was when we went from three-speed and four-speed units to transmissions with a 5th, overdrive, ratio.

I thought most auto transmissions went to OD when they switched from 3 to 4 speeds? Nearly all auto cars had 4 speeds, the 4th being overdrive.

They did, but I was thinking about manuals, which generally have an OD 5th rather than an OD 4th.

Automatics can tolerate fewer ratios because of the torque multiplication accomplished by the Torque Converter when it's unlocked. However, that is at the expense of fuel efficiency. The more a torque converter can slip, the more it can multiply torque, but the problem is that this reduces efficiency. (And yes, I'm being very general here.)

ZV