Hello,

I have an '08 fit sport. Every day, I drive on the highway, and come to a hill that gets gradually steeper. At 60 MPH with cruise control on, I'm at 2,200 RPM. The fit downshifts to 3,000 RPM, and finally downshifts to 3,500 RPM.

If I climb the hill by setting the cruise at 60MPH in "S" mode, and paddle to 5th gear, I'm at 2,200 RPM. As the hill get steeper, I downshift using the paddle. The RPM jumps to 3,500 RPM, and the indicator says I'm in 4th gear.

If 5th gear is 2,200 RPM, and 4th gear is 3,500 RPM, then what is the gear that runs at 3,000 RPM when I climb the hill in "D" mode without using the paddles?

Am I crazy?

Thanks,

-Ben

 

http://en.wikipedia.org/wiki/Overdrive_(mechanics)

"S Mode" likely locks out the overdrive gear to keep the revs up for spirited driving.

 

It's one of two things:

Remember your transmission has a torque converter. The RPM at any given speed can very slightly as the load changes due to the torque multiplying action. This reduces the number of actual gears you need. It's not quite a CVT but a difference of 500RPM as the load increases is not so surprising. Since it happens in the torque converter it doesn't matter whether you select the gear manually with the paddles or not.

If the Fit has a lock-up torque converter, what you may be seeing is the lockup disengaging and then the transmission shifting down.

Can anyone confirm or am I talking rubbish?

 

I noticed the same thing, and it actually occurs 3rd-5th gears for me. You can try it out. Drive around 2500 rpm in any of those gears in S mode and then gas it hard/floor it and the rpms will jump up just a tad and it feels like the car did a half shift.

There is no 6th gear though.

 

but it can SURE use one! especially on the highway with the manual transmission. I hate how i'm at such high revs when im just cruising along on the hwy keeping pace with traffic

 

high revs for manual models are typical...even with 6sp manuals.
My friends with manuals always drove 500-1000 rpm's higher than me at cruising gear/speed compared with my autos.

 

Honda automatic transmissions have an internal program called 'gradient control' that downshifts when the fuel delivery exceeds a certain amount for a given gear, indicating that the engine is 'loading up' and not being very economical. As soon as the grade levels out it returns to the gear you selected. Its like you shifted from sport to auto yourself.
Its normal.

 

Correct, lockup is controlled by the PCM. All new automatics are like that, though not all unlock the torque converter before downshifting (all Hondas do though).

 

You need to get a Fit shop manual and spend some time in the automatic transmission section. Start with the mechanical layout on page 14-36.
There are 5 hydraulic clutches to engage the 5 entry gears from the torque cionverter. Lockup ocurs to eliminate fluid losses in the torque converter when shifting is not needed and improve mechanical transfer. The difference between lockup and not locked is only a few rpm; perhaps 50 rpm. Probably yields 1 more mpg.
When you see the gradient program in action it is changing the input gears via the hydrulic clutches from 5th to 4th because the engine has trouble generating enough power (torque) to maintain speed.. Naturally, when the shifting is occurring the torque converter unlocks so the input can change easily but the change from 2200 to 2800/3000 rpm in 5th in due to the clutches changing 5th to 4th gear. Note the gear ratios of 4th to 5th will also show an rpm increase of 2200 to 3000. (0.756:1 and .550:1. That's ((.756/.550) x 2200 = 3024). The torque converter in simplistic terms is nothing but a liquid clutch that disconnects the engine driveshaft from the auto gearbox so the hydraulic clutches can shift the various gears. The hydraulic clutches are nothing more than hydraulic actuators controlled by the computer program reacting to its internal program or to your paddle switches sequentials aka like motorcycle shifters.

 

just so you all know there is a high and low side to the fits gears its not a 10 speed by any means its just how the Computer does it its no big deal "it just fits"

 

Lockup can yield a LOT more than 50 rpm at low engine speeds. Not so much at high speeds though. I'd bet it's better than a 1mpg gain too- I'd wager more like 3-4 on a little car like the Fit.

CR-V 4 spd auto, 2400 rpm at cruise, go up a hill when it releases the lock and it's at 2700. Turn overdrive off to put in 3rd gear when not under heavy load, 3200 rpm.

Biggest case I've seen was the E4OD Ford. When the speedo fuse blew on me it disabled the lockup since the PCM only allowed it over 35mph; at 55 mph instead of the low 1700 rpm it usually did it was churning at a pretty high 2200. I can count-- it was definitely in OD. Thank goodness for GPS otherwise I probably would have gotten a ticket.

Even at cruise, when there's a decent amount of power put to it (hill, wind resistance, whatever) the converter still excels at torque multiplication and that's what Honda is taking advantage of here.

Of course, that may be the cause of the 30k mile change interval too. Lots of heat.

 

Each of the 5 gears has a 'working range' 1500 to 6500 although in the automatic you'll never see much over 4000 rpm, if that. Not enough power to pull the car with such overgearing.

 

uhh what?

high side... low side... makes no sense. It's just planetary gearsets and clutches! If it's locked in gear, it's locked, if not, then not.

The type of gear is different from a manual's mainshaft/countershaft design, but when it's in gear, it may as well be the same! Ratio of rpm in to rpm out is always constant per gear. The only variable is the torque converter provided all clutches are in good working order.

 

...And that's what is causing the variation here. A torque converter does just that, it magnifies the torque of the engine up until the coupling point where the slip is minimum, at the expense of some loss of efficiency as heat.

The only transmissions in modern cars that I know of that have a simple fluid clutch are some Mercedes Benz (and even then maybe not anymore with their newer ones). Everyone else uses a three part torque converter with curved blades and a reactor.

Newer higher revving engines in small cars have relatively high stall speeds and therefore the coupling point is also higher.

Anyone know what the stall speed of this converter is? (hey, if you are going to actually test it rather than research, be safe!) My Jazz is a manual.

 

There's too much variation 1700 to 2200 unless the truck was heavy enough to have the fluid coupling so inefficient it was unable to transfer enough power until it reached 2200 rpm.
In the case of the Fit the rpm increase precisely matches the gear change from 5th to 4th at 60 mph (.756:.550). If the torque converter were so inefficient that merely unlocking would need an increase in rpm how does it know how many rpm would be needed? The power transfer of the converter would have enough variability that there would be no consistent rpm change. On my Fit whether its a moderate grade or a slight grade the rpm increase is always 2200 to 3000 and that alone says to me its downshifting, not unlocking the converter. Besides my old hydramatic design manuals pretty much say the same thing. Only the throttle plate position changes.

 

Yeah, I was wondering about this, because when on the interstate with cruise control on, it will downshift on pretty small hills (and twice on some larger ones), and even if I put it in S mode and manually select 5th gear, it will still downshift once going up hills, and it says it's still in 5th gear.

 

It was a 4wd 4400lb truck that got 8 mpg, so yeah it had a LOT of efficiency loss to drivetrain and wind. It wasn't constant at all when the converter was unlocked-- move my right foot, and that tach would go all over the place. It just didn't go over 2200 rpm at that road speed because that's when the converter finally had enough speed to be efficient at that load.

The Honda converter would do the same thing, but in the only condition it's in gear unlocked and stalled, any more throttle would result in a downshift, and letting off lets the tach gradually fall until the PCM decides to lock it again (which is the evidence pointing to the converter itself).

After looking at the previous posts and calculating where gear rpm should be like you did... I'm betting it downshifts to 4th and THEN unlocks the converter if more torque is required. You are right, 4th would put the tach at 3024, but 3rd would be 4268, from 2200 rpm 5th.

Got it backwards in my own head, drove too many miles in the CR-V. It definitely unlocks the converter in 4th... a LOT. There is no mistaking it.

Now that I think of it, my sis' civic does it just as often.

 

....

Definitely, the phenomenon experienced by the original poster is a 5-4 downshift, almost immediately followed by the unlocking of the torque converter. I once had a 2001 VW Passat V-6. Their Tiptronic had an extremely 'flexible' torque converter. On one occasion, I was definitely in 5th gear, and I accelerated from 35 mph to 55 mph, while the tachometer showed a virtually constant 2500 rpm. The converter was going from a fairly high amount of slippage (and torque multiplication) to a very modest amount as speed increased. MyBMW 335i shows virtually no torque converter slippage under any circumstances except immediate motion from a dead stop, i.e., the converter is almost always locked up or nearly so, and the transmission control is via proper selection of one of the six forward gears.

Our on-order Sport 5AT won't be delivered till late January. My impression during test drive is that the converter is fairly tight, like the BMW's, and not loose like the VW's. This translates into a small boost in fuel efficiency, all other factors being equal.

 

Mahout and I have had this conversation before, and I remain skeptical. In what is now my daughter's Cherokee, 3d locked actually produces fewer revs than 4th unlocked; something like 4-500 turns difference.
It puzzles me in Sport that the indicator would continue to say '5' if that isn't the gear you're in...
Mahout, I'm not meaning to argue...think I told you before, the A/T guy at a Dodge garage where I worked in my youth was viewed as the Witch Doctor...weird stuff in auto trannies, and weirder now that Hal has a word in it.
Moon

 

Maybe that's why the manual Fit doesn't have same ratio for 5th gear as the auto. People are just too lazy to down shift on moderate inclines once in cruise control mode. I never did when I had my manual Civic and the rpm at 60 mph was about 26000 rpm. There is just not that much power for climbing at low 2000 rpm for Fit auto's taller gear without down shifting.