Automatic vs. Manual

[Coolin]

From the FAQ:

The automatic transmission used in these vehicles increases fuel consumption by about 20% compared to the manual transmission.

Can anyone give me a good explanation as to why this is...with Highway and City examples...

 

[Geordi]

Here are the numbers for 2002 U.S. Jetta Wagon TDI

Manual: 1st 3.78:1, 2nd 2.12:1, 3rd 1.36:1, 4th 0.97:1, 5th 0.76:1 final 3.39:1

Auto: 1st 2.71:1, 2nd 1.44:1, 3rd 1.00:1, 4th 0.74:1, final 3.62:1

In order from "shortest" to "tallest" once final drive is factored in, they are:

M1 (12.81:1)
A1 (9.81:1)
M2 (7.19:1)
A2 (5.21:1)
M3 (4.61:1)
A3 (3.62:1)
M4 (3.29:1)
A4 (2.68:1)
M5 (2.58:1)

Note that the manual covers a wider range. On the highway, the auto will be revving higher (I recall on another thread seeing that the TDI goes open loop around 2600, at which point the fuel economy takes a sharp drop). On the other hand, starting from a dead stop it's got a taller ratio, so it needs a lot of slippage in the converter for a smooth start.

The difference is the lack of a 5th gear that could be taller than .74, say .70 perhaps taller than even that. The taller the final OD, the slower the engine spins. Final differential also makes a BIG difference. If you KNOW you will never tow anything other than passengers with these cars (not like you could anyway) then looking into the upcoming Tiptronic 6-speed Auto is worth it.

I know I am eagerly awaiting the new TipTronic, I WILL have 60+mpg at 80mph someday!

--Jim

 

[KdF Man]

Originally posted by Geordi 01JetTDI:
[QB]Here are the numbers for 2002 U.S. Jetta Wagon TDI

Manual: 1st 3.78:1, 2nd 2.12:1, 3rd 1.36:1, 4th 0.97:1, 5th 0.76:1 final 3.39:1

Auto: 1st 2.71:1, 2nd 1.44:1, 3rd 1.00:1, 4th 0.74:1, final 3.62:1

In order from "shortest" to "tallest" once final drive is factored in, they are:

M1 (12.81:1)
A1 (9.81:1)
M2 (7.19:1)
A2 (5.21:1)
M3 (4.61:1)
A3 (3.62:1)
M4 (3.29:1)
A4 (2.68:1)
M5 (2.58:1)

/QUOTE]

In addition to the gear ratios, they also get less MPG because of inherent inefiscienceies (sp?) of torque converters. You always loose some between the motor to transmission in an auto - excep for maybe truck types with locking convertors maybe? not sure.

Brian

 

[NB TDI]

ya what every they said

 

[VeeDubTDI]

The TDI automatics have locking torque converters.

 

[C Brown]

An itersting point I saw at the auto show in Detroit a few years back.. You may notice that the auto first gear isn't nearly as low as the manual. This is because the torque converter *slippige* as it is often called. But in reality it has a fluid path, which does it's best to convert speed loss into torque, using a longer path for the fluid.IIRC If only they could make the rest of the planatary transmission as efficent as a manual must be, considering a well designed torque converter should be as efficent as a clutch, when locked up on the freeway.

http://www.howstuffworks.com/torque-converter.htm
Look under (Benefits and Weak Points) on the fourt or so page, for the torque multiplication...

I had to look it up...
Check it out.
Regards
CB&Stoker

 

[C Brown]

see also
http://www.howstuffworks.com/automatic-transmission1.htm

and the cool shift lever and the color changes to show power flow.

Good presentation.

CB

 

[oilhammer]

German automatics have historically not been as efficient as others. GM had lock up convertors in the late '70s, and I am sure Ford and Chrysler were around that time as well. Some Japanese cars were using them by early '80s (and usually perfected auto trans durability, too).

Volkswagen, on the other hand, did not even have an automatic until 1968. And that was in the Type3. This was the "003" unit, and was used in conjunction with different differentials in Type3s, Type4s, '73 through '79 Busses, and early Dashers. Then the "010" came out, which was used with different differentials and final drive housings in everything from a Rabbit to a Vanagon to a Porsche 944 to an Audi 5000! This unit was still in use in the 1993 Cabriolet! But even then, it still did not have a lock-up convertor!!! And it was still only a 3 speed. I had an '88 1.8L gas Golf with that unit, and although it was reliable, it got lousy mileage...like only 23 around town and maybe 25 on the highway! But the same car with a 5 speed would have yielded 25 to 27 around town and over 30 easily on the highway.

The newer 01M automatics and its predecessor the 096 are better, with 4 speeds and lockup, but still not near as efficient as the good ol' stick shift!

 

[wkendrvr]

Talk to Jet Jock, he is getting 49mpg with Auto... Wife is getting 43 with 7500 miles... I am getting 39mpg with 3500 miles (that is chipped, and a lead foot

) I think a lot of it has to do with what you put in the tank... On Texaco we NEVER got decent MPG... On Ammoco Power Blend it runs quieter and economy is obviously not bad

 

[Derrel H Green]

Originally posted by Geordi 01JetTDI:
On the highway, the auto will be revving higher (I recall on another thread seeing that the TDI goes open loop around 2600, at which point the fuel economy takes a sharp drop). --Jim

<font size="2" face="Verdana, Helvetica, sans-serif">

Could you please explain what is meant by "the TDI goes open loop around 2600, at which point the fuel economy takes a sharp drop."

Interesting sidenote,

The gear ratios for the TDI automatics are the same as the ratios supplied in the VR6 2.8 liter 6 cylinder automatics that come with 195 ft/lb of torque. Wonder if the TDI automatic internals are the same as those in the VR6 with the exception of the ring and pinion ratio and the T/Cs?

Maybe that is why this box will stand up to being UPsoluted and larger injectors.

[ October 15, 2002, 18:13: Message edited by: WVWSP61 ]

 

[GoFaster]

Originally posted by Coolin:
From the FAQ:

The automatic transmission used in these vehicles increases fuel consumption by about 20% compared to the manual transmission.

Can anyone give me a good explanation as to why this is...with Highway and City examples...

<font size="2" face="Verdana, Helvetica, sans-serif">Transport Canada figures for city driving are 6.9 L/100 km automatic, 5.6 L/100 km manual (automatic 23% more consumption).

Transport Canada figures for highway driving are 4.8 automatic, 4.4 manual. (automatic 9% more consumption).

Every transmission needs a method of "slipping" to move the vehicle away from a standstill. The engine must continue rotating but the car is stopped and needs to get moving. Slippage means that power which the engine consumes fuel to produce is getting thrown away as heat. Slippage is NO GOOD for efficiency but you need at least a little bit to get away from a standstill.

With a manual this slippage is done by a mechanical clutch and the slippage is over with by 10 km/h and the engine speed going barely above idle during this process if the driver is any good. At anything above that speed it is pure mechanical gear reduction, which is very efficient. Also the manual transmission doesn't require any power to hold itself in gear. Once you put the tranny in gear it's there. No effort is expended by the engine to keep the transmission engaged.

With an automatic the slippage is done by a torque converter. It is basically a centrifugal pump driving a turbine. The faster you spin the pump the more force is developed at the turbine. To move away from a standstill this whole setup sloshes fluid around (the "slushbox" nickname for an auto tranny is well deserved) and it keeps sloshing this fluid around (slipping, and throwing away power in the process) until you are well into third gear and moving probably 50 to 70 km/h. In other words, if you are driving around town this tranny is throwing away a big percentage of the power produced by the engine.

At higher speeds, the converter has a lockup clutch that eliminates the slippage losses. But look at how an auto tranny engages this lockup clutch and the clutches that operate the gears: HYDRAULICS. Even on the highway, there is a little hydraulic pump running all the time, eating up a little bit of power, just to keep the transmission engaged via the hydraulic system.

Thus ... an auto tranny can't touch a manual for efficiency unless the manual tranny driver has no clue what to do.

And it also seems to be that this auto tranny is worse off for efficiency than others.

Why not lock the converter clutch as soon as the car moves away from a standstill, just like a manual? Because then you'll feel every gearshift with a slam. The converter acts like a big cushion. Most drivers of auto trannies don't want to know what the tranny is doing, and if the converter is locked, you'll feel every shift ...

Want optimum efficiency? buy a manual tranny.

 

[Derrel H Green]

Originally posted by GoFaster:

From the FAQ:

Why not lock the converter clutch as soon as the car moves away from a standstill, just like a manual? Because then you'll feel every gearshift with a slam. The converter acts like a big cushion. Most drivers of auto trannies don't want to know what the tranny is doing, and if the converter is locked, you'll feel every shift

<font size="2" face="Verdana, Helvetica, sans-serif">

The statement about feeling every upshift with a slam is NOT true.

The part about the T/C acting like a big cushion is correct, but our automatic transmissions do in fact lock up the torque convertor BEFORE upshifting from third gear (direct drive) to overdrive (fourth gear). The 01M trans will not upshift to fourth speed until the T/C is locked up in third speed. Do any of you that have this transmission feel it "slam" as it upshifts to fourth speed? I sure don't feel any harshness with mine. In fact, it upshifts very smoothly, and if I were not listening for it to change gears or lockup, and wasn't watching the tachometer, I would not be able to tell that it was shifting at all!

Even though the VW TDI automatic does not lockup the T/C prior to reaching approximately 28 mph under minimum throttle in third gear, other automatics do and have been doing so for years. As an example, many may recall the 3.8 liter turbocharged Buicks, and with the same powertrain in 1989, the 20th anniversary Poncho Trans-Ams with the TH tranny. These automatics locked up in every gear except first speed, and talk about power transmission, those last vehicles with this setup would run 102 mph in the quarter mile with an ET of 13.2 seconds right off the showroom floor, box stock! And they did not slam any shifts. The hotrodders would modified the ECU to get those trannies to lockup the torque convertors right off the line while still in first gear, but they then had to go to a beefed up T/C because the stock T/C could not stand that much torque/horsepower for long. Many run those motors with up to 30 pounds of boost. A good modified street machine that runs just like any stocker can easily turn 125 mph in the quarter mile, and their trannies are very smooth shifting indeed.

No one in the world can get the fuel economy like GM. Maybe that is one of the ways that GM gets such high city mileage estimates. For instance, the Buick Park Avenues are EPA rated at 20 city, and 29 Highway. This is a 3800 pound car with a 3.8 motor and a very efficient automatic transmission.

So it can be done if the engineers want to put their heads into it. But I guess that there isn't that much demand for slushboxes over yonder like there is here? If there were, I'll bet that we would see a much more fuel efficient set-up.

[ October 15, 2002, 22:58: Message edited by: WVWSP61 ]