I feel incomplete if I haven't posted anything......

I've been scouring the forum to see if anyone has explained the Gearing in the X-Type, but I haven't found anything that really goes into detail. I understand, sort of, the viscous coupling for the AWD in models '01-'04, then it changed from '05 and on. But is the gearing in the tranny the same (not the same as viscous coupling, I just mean same as in goes from gear to gear without anything else like shifts in power at play)? I know on some cars the gear accepts the torque up to a desired rpm then shifts to the next gear, so on and so forth, but it seems/feels like the Jag handles power through each gear differently.

Maybe a silly question but how is the gearing set up? The X doesn't seem to be much of a city driver, more for cruising so far from my experience. The tranny shifts smoothly and it likes to get into 5th - I imagine for emissions and mpg, but I'm specifically curious what goes on in 4th. It always seems to adjust in a high/low torque kind of way and I'm not really sure if this is by design or if there is something going on with a shift in power from the transfer case since it's AWD. I've never owned an AWD before the Jag, always FWD, but I've been a passenger in a few AWD's and been in Trucks that have 4x4. So the shift in power, like it's going from a 4 low to a 4 high gear is intriguing to me. I'm not sure if it's the same concept as a truck, just in a car. Can anyone give a detailed - or somewhat detailed - explanation to how the Jag shifts and utilizes the power through the gears? This may be useful for any Jag novices that are feeling how the car drives and wondering what all is at play.

 

ugotmale, from my understanding of how modern day transmissions work, you have 2 worlds that are working against each other here. You still have the old day full hydraulic shifting that occurs (ie, no computers required, just once the fluid pressure reaches a certain point, the tranny will shift), but this is meant more for a backup than anything should the computer fail. You then have the shift tables (one for up shifts, one for down shifts). The tables are based on looking at engine loading and engine RPM and finding a gear that will work based on these parameters. Obviously, as you apply more gas (ie, increase the engine load), the computer is going to look at the downshift table and see if it crosses some "line" that would require the tranny to downshift to put the tranny into a more appropriate gear or if it is going to leave the gears where they are. Then, as the RPMs come up, the computer starts looking at the up shift table and seeing if it crosses some line there that would then tell the computer to shift the tranny into the next higher gear. It is all a balancing act of bouncing between these 2 tables.

Now, just to add more complexity into this, you have the torque converter (and this is where I think you are seeing your high/low power issue). In lower gears, the torque converter is left uncoupled. This allows the torque converter to convert engine RPM into torque. So, what you see is a higher RPM for a given speed. The more engine load that is applied, the more RPM that is converted into torque. The computer has a table for this that it looks at the gear, the engine RPM, and engine load to determine if it needs to have the torque converter coupled or uncoupled. As you are driving, you will notice that in first gear, the torque converter will almost never couple up (only when you are off the gas and coasting). Yet, in 5th gear, about the only time the torque converter will be uncoupled is under a hard acceleration at high speeds (even then not always).

Just to add more confusion into this whole thing, you have the "sport" mode button. But, this is rather easy to comprehend once you understand the shift tables. In short, in "SPORT" mode, the computer subtracts out a portion of the engine RPM (the amount of which is based on engine loading). So, the more you are on the gas (ie, engine loading, the more RPMs it will subtract). What this effectively does is cause the tranny to hold a given gear longer to get the engine RPMs up more and to generate more power.

Keep in mind that you also have some general fail safes built in too. If the engine RPM reaches a pre-determined RPM (normally redline or there abouts), there is a command that forces the tranny to shift to the next higher gear. Kinda like if the RPMs drop below a pre-determined point (about idle), that the tranny is forced to downshift to the next gear. You also have a low temperature override of the torque converter (you can see this when the motor is cold, get up to speed and watch the engine RPMs as you accelerate even at high way speeds, the engine RPMs will rise about 200-300 RPM without the car changing speed, but once warm, the RPMs will remain constant for the same acceleration).

As you can see, there is a lot of information that the tranny is trying to process to know what gear to be in and where it should be to maximize the desired effect (mileage, power, etc).

The below picture is to show you what a shift table may look like. In our case, you would have 5 gears (vice the 4 shown here).


Something else that you may find an interesting read is this: http://www.thejagwrangler.com/upload...on_control.pdf. While it is for the XK, the same principles apply to the X-Type. Granted, this goes into the clutch pressures and why they are controlled like they are to make the shifts smoother and the like.

 

Thanks for the info Thermo! Brings things into perspective quite a bit. Is there anything you don't know?!

 

ugotmale, I take each day and try to learn something new. After many years, you get quite a bit of info stored up here and there. There is tons of stuff I don't know. As an old saying goes, A smart man knows what he doesn't know, a dumb one thinks he knows everything.

I got to get into the tranny a bit when I was working on making my truck. I didn't need a truck that had 5,000 RPM power. That isn't very good for when you are out 4x4ing. So, I researched how the tranny worked and I was trying to figure out ways to take the tranny and maximize the 4x4 ability. Now I just apply that knowledge to the Jag as the concept is the same, just with different shift points.