5-speed automatic question

EMB1230 · #1 01-03-2011, 08:41 PM

Now call me crazy, but I thought the point of extra gears in a transmission was to lower RPM's and in turn raising fuel economy. That's what the case in the 1980's & 90's was when automakers transitioned from 3-speed to 4-speed units. What baffles me about the 5-speed auto Ford first installed in 1997 Explorers is that it gets the same, if not a little WORSE fuel economy than the 4-speed unit it replaced. They say the purpose of the then new 5-speed was to improve acceleration from a standstill. Is that in fact true?

01_ranger_4x4 · #2 01-03-2011, 08:46 PM

the additional gear was added somewhere between either 1st and 2nd or 2nd and 3rd, cant remember for sure. theres no reason the 5 speed would get worse mileage, the 4 speed and 5 speed are essentially the same transmission with just the addition of the extra gear. the 5 speed does provide for better acceleration, i will agree with that. BTW, lowering the RPM doesnt always make for better MPG's, it all depends on where the motor makes its power most efficiently.

rwenzing · #3 01-04-2011, 05:40 AM

In the case of the 5RxxE, the "extra" gear is the combination of 1st + overdrive and it is used between what used to be 1st and 2nd in the 4 speed version. It is only for enhanced performance at or near wide open throttle.

This new "2nd gear" in the 5-speed is skipped during part throttle driving, so the transmission behaves essentially as it did when it was a 4-speed.

The earlier change from 3-speed to 4-speed automatics usually involved the addition of an overdrive gear for higher speeds which did improve fuel economy significantly. Another improvement came from the use of a lockup arrangement to bypass the torque converter in one or more gears.

Quote:

Originally Posted by rwenzing

The 5RxxE can be thought of as 2 "mini" transmissions in series. It has a Simpson gearset providing 3 speeds, and an overdrive gearset providing 2 speeds, so there are actually six (2 x 3 = 6) possible gear combinations within the 5R55E, but one of the ratios is so close to the others that it is unusable. In a typical 4 speed auto, the Simpson gearset provides the 1st, 2nd, and 3rd gear ratios while the overdrive gearset is at a 1:1 ratio. Then for 4th gear, the Simpson set remains in 3rd while the overdrive set upshifts to its overdrive ratio (0.75 in the 5RxxE).

In the 5RxxE, the control system also upshifts the overdrive set to 0.75 while the Simpson set is in low gear, creating a "new" second gear (0.75 x 1st).

1st = Simpson 1st
2nd = Simpson 1st w/OD
3rd = Simpson 2nd
4th = Simpson 3rd
5th = Simpson 3rd w/OD

Comparison of 4R44E/4R55E 4-speed and 5R44E/5R55E 5-speed (current Ranger):

4R44E, 4R55E
1st 2.47
2nd 1.47
3rd 1.00
4th 0.75 (1.00 x 0.75)
5th ---

5R44E, 5R55E
1st 2.47
2nd 1.85 (2.47 x 0.75) <----(added gear in the 5-speed)
3rd 1.47
4th 1.00
5th 0.75 (1.00 x 0.75)