December 16, 200718 yr Pardon me if this post seems rambling. Topic pertains to 06-07 maybe earlier non vdc 4eat transmisions. I'm not sure how to calculate a friction coefficient. Isn't an effective end to end friction coefficient what the clutch pack is varying? What would the value be to achieve 60/40torque biasing? What would be the value for 100% lock up and what would be the value for 0% lock up? Subaru claimed a 60/40 torque bias on the recently made automatic 4eat transmissions. Did they lie? Why is it that there are so many people saying that it is really only 90/10? Do those people just really hate autos? Did subaru change this bias from 90/10 to 60/40 after a certain date ? What is the truth and who can prove it?
December 16, 200718 yr Your not reading correctly. 4eats are variable torque split at all times 10/90 11/89 12/88 (you get the idea) 15/85 20/80 25/75 30/70 35/65 40/60 45/55 50/50 The newer 4eats may be at 60/40 to bias the cars towards front wheel drive, with all the new widgest they have, 50/50 may not be necassary anymore (traction control etc etc etc). When there is no demand for the AWD as the TCU determins, its 10/90 split. This is the default, everything is right in the world, going straight at 40 mph setting. The TCU uses a very complicated algorytem to determine when more is needed. The TCU is over ridden if the car is in low, at full throttle, or in reverse, then its the maximum split. www.endwrench.com in the archives has some techy peices to explain in detail. http://www.cars101.com is also another source of information Be cautious about calling anyone or anything a liar untill you are fully informed, just some advice . There is more then enough information here and explinations ad nausim to explain how the 4eat works (so don't flame me please). nipper
December 17, 200718 yr Author Not calling any one a liar. The folks who espouse the 90/10 are calling Subaru a liar not me. Nipper in a sense I would agree with You. The front is normally pulling the car around at 1.5x the rear. This saves wear and tear on the clutch pack and imparts certain handling characteristics which are safe and predictable, if not boring. The 60/40 thing is as subaru has stated. The 90/10 thing is also true but only to enhance breaking and cornering performance. Mostly I would think to discourage rear wheel lock up. Under normal circumstances the computer allows a controlled amount of torque to be transmitted by varying the friction coefficient of the clutch pack to push up to two fifths of the vehicle from the rear. Other Subaru cars which do 45/55 have 7 clutch plates or something while the 60/40 ones have 5. I found the rest from Subaru. Active All-Wheel Drive is used on all Subaru models powered by the naturally-aspirated four-cylinder boxer engine and equipped with the four-speed automatic transmission, as well as on the turbocharged Forester 2.5L XT equipped with this transmission. An electronically managed continuously variable transfer clutch actively manages power distribution and ensures that the wheels with the best traction receive more power. Power transfer is governed by slippage in the clutch plates.The Transmission Control Module (TCM) controls the multi-plate transfer clutch. Active All-Wheel Drive can adjust the power split in an instant, depending on many input factors. If the front wheels begin to slip, the TCM increases hydraulic pressure on the transfer clutch, reducing slippage of the plates and transferring the power to the rear wheels. As the front wheels regain traction, the TCM reduces pressure on the clutch, increasing slippage of the plates and transferring power to the front. The TCM monitors input from speed sensors on the front and rear drive shafts and also takes input from the throttle position and the transmission. All of these factors cause the TCM to select a software strategy that determines how aggressively it adjusts the power distribution. Active All-Wheel Drive varies the power distribution according to driving conditions. When throttle input signals acceleration, the system responds by transferring more power to the rear wheels to account for rearward weight transfer. When releasing the throttle indicates deceleration, power transfers to the front wheels to enhance braking performance. The system enhances cornering performance as well. When the driver lifts off the throttle and applies the brake to enter a turn, power transfers to the front wheels for greater steering control. As the car exits the turn and accelerates, power transfers to the rear wheels for added traction.
December 17, 200718 yr darndarndarndarn, i had a really good link that explained it, BUT it was one of those links that when you clicked it it didnt go to the same place twice. I hate some subaru websites. lets try this again http://www.subaru.ca/WebPage.aspx?ArticleID=460&WebPageID=4998&WebSiteID=282 towards the bottom it explains the AWD. nipper
December 17, 200718 yr Author http://www.subaru.ca/WebPage.aspx?ArticleID=460&WebPageID=4998&WebSiteID=282 Subaru Active All-Wheel Drive varies the power split according to driving conditions. Under most conditions, 60 per cent of the engine torque is transferred to the front wheels and 40 per cent to the rear; this is to match the vehicle’s weight distribution.
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