The PTU Fuse Drill
#1
09-01-2010, 08:06 AM
The PTU Fuse Drill
After much wrangling and other stuff...
Here's the best I can determine on this. The Power Transfer Unit is little more than a right angle gear drive. All elements in it turn if the front wheels are turning. So there is no issue of lubrication with it.
The propeller shaft thus is turning all of the time the wheels are turning. The Active Torque Coupling, located on the front of the rear differential, connects the rear axle into the drivetrain as signaled by the FEH traction control software.
The rear differential is a typical, open style differential. It does not add any feature of positraction, traclok, or other traction improving elements to the rear axle.
So, pulling the fuse for the PTU (which really powers the Active Torque Coupling) only deactivates this unit, putting it at 0% coupling. Since all other elements of the drive train remain turning, and thus adding friction and torque loading to the drive train, there is little reduction in total friction load on the engine.
The required torque and power loading on the engine remains the same at a given speed. Pulling the fuse does shift where in the drive train its appears but it does not change its total amount and effect on required engine power at the same speed.
The illustration in one post of a jack and the load change on it when jacking is just wrong.
As I see it pulling the fuse neither adds nor subtracts from those things that affect mpg. There may well be something else causing this.
Here's the best I can determine on this. The Power Transfer Unit is little more than a right angle gear drive. All elements in it turn if the front wheels are turning. So there is no issue of lubrication with it.
The propeller shaft thus is turning all of the time the wheels are turning. The Active Torque Coupling, located on the front of the rear differential, connects the rear axle into the drivetrain as signaled by the FEH traction control software.
The rear differential is a typical, open style differential. It does not add any feature of positraction, traclok, or other traction improving elements to the rear axle.
So, pulling the fuse for the PTU (which really powers the Active Torque Coupling) only deactivates this unit, putting it at 0% coupling. Since all other elements of the drive train remain turning, and thus adding friction and torque loading to the drive train, there is little reduction in total friction load on the engine.
The required torque and power loading on the engine remains the same at a given speed. Pulling the fuse does shift where in the drive train its appears but it does not change its total amount and effect on required engine power at the same speed.
The illustration in one post of a jack and the load change on it when jacking is just wrong.
As I see it pulling the fuse neither adds nor subtracts from those things that affect mpg. There may well be something else causing this.
#2
09-01-2010, 08:43 AM
Re: The PTU Fuse Drill
Well one 4WD FEH user here must be lying because they claim a 2MPG gain when the fuse was pulled which is a little less than the EPA difference between FWD and 4WD.
#3
09-01-2010, 12:41 PM
Hybrid and Ethanol Expert
Join Date: Mar 2005
Location: All over the Central U.S.
Posts: 3,616
Re: The PTU Fuse Drill
Placebo effect. You pull the fuse then drive ever so slightly more conservative, knowing in the back of your mind you have no traction on the rear. Would you drive more gently after pulling the air bag fuse?
#4
09-01-2010, 02:01 PM
Re: The PTU Fuse Drill
I suppose you think that FWD get the MPG as 4WD too???
#5
09-01-2010, 02:51 PM
Re: The PTU Fuse Drill
GPSMan1: Your response indicates that you don't understand that the FWD version doesn't have the additional "stuff" like the PTU, the propeller shaft (with two U Joints) & the rear differential. All of these components add friction and load to the drive line*reducing mpg somewhat.
So, in a word: No.
The FWD version should get somewhat better mpg.
Did you read the other series of posts on the PTU fuse pulling issue? I made this kind of apparent there.
So, in a word: No.
The FWD version should get somewhat better mpg.
Did you read the other series of posts on the PTU fuse pulling issue? I made this kind of apparent there.
Last edited by Bill Winney; 09-01-2010 at 02:59 PM.
#6
09-01-2010, 03:43 PM
Ridiculously Active Enthusiast
Join Date: Sep 2006
Location: Beautiful Pacific NW
Posts: 1,678
Re: The PTU Fuse Drill
After much wrangling and other stuff...
Here's the best I can determine on this. The Power Transfer Unit is little more than a right angle gear drive. All elements in it turn if the front wheels are turning. So there is no issue of lubrication with it.
The propeller shaft thus is turning all of the time the wheels are turning. The Active Torque Coupling, located on the front of the rear differential, connects the rear axle into the drivetrain as signaled by the FEH traction control software.
The rear differential is a typical, open style differential. It does not add any feature of positraction, traclok, or other traction improving elements to the rear axle.
So, pulling the fuse for the PTU (which really powers the Active Torque Coupling) only deactivates this unit, putting it at 0% coupling. Since all other elements of the drive train remain turning, and thus adding friction and torque loading to the drive train, there is little reduction in total friction load on the engine.
The required torque and power loading on the engine remains the same at a given speed. Pulling the fuse does shift where in the drive train its appears but it does not change its total amount and effect on required engine power at the same speed.
The illustration in one post of a jack and the load change on it when jacking is just wrong.
As I see it pulling the fuse neither adds nor subtracts from those things that affect mpg. There may well be something else causing this.
Here's the best I can determine on this. The Power Transfer Unit is little more than a right angle gear drive. All elements in it turn if the front wheels are turning. So there is no issue of lubrication with it.
The propeller shaft thus is turning all of the time the wheels are turning. The Active Torque Coupling, located on the front of the rear differential, connects the rear axle into the drivetrain as signaled by the FEH traction control software.
The rear differential is a typical, open style differential. It does not add any feature of positraction, traclok, or other traction improving elements to the rear axle.
So, pulling the fuse for the PTU (which really powers the Active Torque Coupling) only deactivates this unit, putting it at 0% coupling. Since all other elements of the drive train remain turning, and thus adding friction and torque loading to the drive train, there is little reduction in total friction load on the engine.
The required torque and power loading on the engine remains the same at a given speed. Pulling the fuse does shift where in the drive train its appears but it does not change its total amount and effect on required engine power at the same speed.
The illustration in one post of a jack and the load change on it when jacking is just wrong.
As I see it pulling the fuse neither adds nor subtracts from those things that affect mpg. There may well be something else causing this.
You seem to be coming along well, coming around. But you still do not seem to grasp that a driveline, drive "section" just freewheeling along, for a free ride as it were, is under less stress than if actively DRIVEN.
So let's talk about torque stear, okay...?
Torque stear results from having different length front drive halfshafts. Under the torque of acceleration the shorter halfshaft will have less windup/"twist" and therefore the drive wheel associated with the shorter halfshaft will "lead" the opposite wheel by a few degrees in roadbed drive traction.
That's why you must now only "stiffen" your grip on the stearing wheel in a tight accelerating turn moreso on a FWD vehicle, you must also "counter-stear" again this effect on order to hold the "line" you desire.
So, in this case which halfshaft, tire, & bearing set is going to get the most stress and therefore higher wear rate..?
#7
09-01-2010, 03:50 PM
Ridiculously Active Enthusiast
Join Date: Sep 2006
Location: Beautiful Pacific NW
Posts: 1,678
Re: The PTU Fuse Drill
Yet another point: The 2011 F/awd RX350 factory shop/repair manual states that should the F/awd control system determine that there is a difference of more than 3% between front tire circumference average and rear tire circumference average then it will disable the rear drive clutch and turn on a fault indication for the driver.
Why do "you" suppose that is...?
Why do "you" suppose that is...?
#8
09-01-2010, 05:42 PM
Re: The PTU Fuse Drill
Oh my, comic relief is so nice once in a while.
Free wheeling "stuff" still adds resistance to the driveline. Like my illustration of why 4WD vehicles have some kind of front axle unlocking hubs. Warn made their initial way as a company with such hubs after WWII...
Its measurable, in fact its the major contributor to the difference between 2WD & 4WD mileage.
Free wheeling "stuff" still adds resistance to the driveline. Like my illustration of why 4WD vehicles have some kind of front axle unlocking hubs. Warn made their initial way as a company with such hubs after WWII...
Its measurable, in fact its the major contributor to the difference between 2WD & 4WD mileage.
#9
09-01-2010, 10:55 PM
Re: The PTU Fuse Drill
But this did not make new york asian escort people forget their early customs.On the eve of All Hallows,Oct.31,people continued new york asian escorts to celebrate the festivals of Sam hain and Pomona Day.Over the years the customs new york escort from all these holidays mixed.October 31st became know as All new york escorts Hallow Even,later All Hallow's Eve.halloween .and then Halloween.
#10
09-02-2010, 07:02 AM
Re: The PTU Fuse Drill
Oh my, comic relief is so nice once in a while.
Free wheeling "stuff" still adds resistance to the driveline. Like my illustration of why 4WD vehicles have some kind of front axle unlocking hubs. Warn made their initial way as a company with such hubs after WWII...
Its measurable, in fact its the major contributor to the difference between 2WD & 4WD mileage.
Free wheeling "stuff" still adds resistance to the driveline. Like my illustration of why 4WD vehicles have some kind of front axle unlocking hubs. Warn made their initial way as a company with such hubs after WWII...
Its measurable, in fact its the major contributor to the difference between 2WD & 4WD mileage.
