RHD models have a different gear box!.

[oab_au]

RHD models that have the fuse, called DIFF LOCK. have a different AWD section to the US models, where the fuse is called FWD.

The system that the rest of the world have is a compound planetary gearset that provides a 36% front / 64% rear torque split. This is due to the number of teeth on the pinions and sun gears that provide that split.

The drive comes in to the front sun gear, the rear wheel drive is from the rear sun gear. The front drive is from the carrier, so the torque split is fixed by the gear ratio. A multi plate clutch is between the rear sun gear and the carrier to bring the torque back to 50/50.

The US system is different because, you can't turn one set of wheels off, in the RHD system, to run it on a two wheel dyno.
In the early 90s FWD dynos were not common in the US, so Subaru took the front wheel drive box, fitted the multi plate clutch to the back, to add torque to the rear wheels.

I would suspect that we will not get the 'binding' problems that the US have due to the different system and can't have the delay before the rear wheels engage, as they are all ways engaged.

So if you thought that yours behaved differently to the US one. Rest easy you were right.

Section drawing and write up, are in my locker.

Harvey.

[Trevor]

Please keep the info on this one coming Harvey. You have started a very interesting and important thread. Thanks, Trevor.

[svx_commuter]

Hi Harvey,

They will never find your post over here down under.

So.... Does your tranny have a front to rear differential or not? I can't tell from your discription. The USA cars use the transfer clutch for this function. So when we are in a corner the clutch plates have to slip.

I'll be waiting for the pictures.

John

[oab_au]

Originally posted by svx_commuter
Hi Harvey,

They will never find your post over here down under.

So.... Does your tranny have a front to rear differential or not? I can't tell from your discription. The USA cars use the transfer clutch for this function. So when we are in a corner the clutch plates have to slip.

I'll be waiting for the pictures.

John

I don't think they, would want to know, John it might worry them.
It's mainly for all the RHD, European and Japanese owners, that have wondered, why their gearbox seems to work differently, to what we read on the board, from US owners.
eg. the fuse doesn't disconnect the rear drive, it locks it in 4WD!. It handles differently, not like a front wheel drive with rear assist.

The center diff acts like a final drive diff, with the drive going to the front and rear wheels, the ratio of the number of teeth on the sun, pinions and ring gear being different, for front and rear output .This doesn't mean that the wheels turn at different speeds, because the carrier is not fixed and can rotate. It just alters the torque delivered to the front and rear wheels, to the ratio of 36% front to 64% rear, This is fixed by the planetary ratio.

The clutch is fitted between the 2nd sun gear, which drives the rear wheels, and the carrier,which drives the front wheels. The clutch doesn't carry the drive torque to the rear wheels, that is handle by the planetary set. The clutch is used to alter the torque split to the wheels by braking the 2nd sun gear and the carrier together to change the split to any ratio from 36/64 to 50/50.
If the clutch stopped working, the torque split would stay at 36/64.

I always wondered why members talked about the car under steering, as I could not find a trace of it. It is the most balanced road car I have ever driven.

Harvey.

[Trevor]

Originally posted by oab_au



I always wondered why members talked about the car under steering, as I could not find a trace of it. It is the most balanced road car I have ever driven.

Harvey.

I agree Ioo% Harvey.

This is the exact reason I purchased my car, certainly not for its looks.

[svx_commuter]

Originally posted by oab_au


The clutch is used to alter the torque split to the wheels by braking the 2nd sun gear and the carrier together to change the split to any ratio from 36/64 to 50/50.
If the clutch stopped working, the torque split would stay at 36/64.
Harvey.

Okay, so if you lock your car in 4WD and turn the steering wheel all the way left and drive in a circle, the drive train does not bind-up?

[oab_au]

Originally posted by svx_commuter


Okay, so if you lock your car in 4WD and turn the steering wheel all the way left and drive in a circle, the drive train does not bind-up?

Gid'ay John. If the fuse is fitted, the clutch is applied and the front and rear are locked together, in 4WD. Drive in a circle, the trans binds, digs the grass up and sighs in relief when I take the fuse out.

I guess the best way to describe the action is to compare it to a normal final drive differential. The drive comes in through the crown wheel (ring gear?) to the differential carrier, driving the pinions.The pinions are meshed with the sun gears, one each side, so the pinions don't rotate, they just turn as a unit, driving both wheels. If one wheel is held, the pinions are still rotated by the carrier to drive the other wheel. Plus the pinions have to walk around the stopped sun wheel, thus spinning the other wheel at twice the input speed.

In the planetary set, the drive comes in through the front sun wheel, to drive the pinions on the carrier. The front and rear pinions are one piece, so the rear pinion drives the rear sun wheel. The carrier is connected to the front wheels, the rear sun wheel is connected to the rear wheels and the wheels are connected together through the road. If there is no slip, the whole unit turns together, driving both wheels.

If you held the back wheels, the drive from the front sun gear, turns the pinions, but because the rear sun gear and wheels are held, the rear pinion has to walk around the rear sun gear, to rotate the carrier and drive the front wheels.

Just like a normal diff, you could spin the front or back wheels. So the multi plate clutch is used like a limited slip center in a normal diff. The clutch is connected between the carrier (front wheels) and the rear sun gear (rear wheels) to control wheel spin and torque split.

In a normal diff the sun gears have the same number of teeth, so do the pinions, to give equal torque to each wheel.
In this unit the front sun gear and its pinion have a different number of teeth than the rear sun gear and it's pinion. Thus giving different leverage to front and rear wheels.

This is how the torque is split in an uneven 36/64 ratio.

I have scaned other pages that shows the gear set up better, there in my locker.

Harvey.

[Trevor]

As I see it Harvey, incredible as it is, a wonderful system was stuffed up in respect of LH drive models on information from the sales dept. insisting that the car should and must be able to be run on a rear wheel dyno.
The mind boggles ! In point of fact US owners do not have a true SVX i.e. the car as it was described in most of the motoring press.

The idea of a clutch being used in this way makes me shudder and I wonder if the constant slippage and friction dissipates enough extra heat to cause the heat problems we hear so much about. I also wonder how many older cars are in fact putting the designed power to the back wheels hence the understeer reported. You have put the cat among the canaries!

[oab_au]

I wrote this in 2002, but it is still relative to how it does work. I thought I would up date it with some more info that explains how this VTD changes the tight corner handling of the SVX.

The default torque split of 36% front, 64% rear torque can be altered by applying pressure to the clutch which spans the front/rear drive shafts. As the pressure is increased the it adds rear torque to the front wheels. This is different to the US Transfer system as the VTD clutch does not carry the torque to the rear wheels, so it does not have to slip as the car is cornering.

The mechanical gearing of the epicyclic gear train will alter the torque split as the car turns tighter, without any input form the TCU or clutch. As the car is turned tighter the front wheels travel a larger circle than the rear. To do this the front wheels rotate faster that the rear, thus have a lower ratio that adds torque to the front.

It is most noticeable when driving around tight 'hairpin' corners. The torque shifts to the front to pull the front into the corner, and the drive from the rear powers the car around the bend. As we can swap the VTD on to the rear of the Transfer box, a 4.44 version with the VTD would make an Awesome Auto crosser, It would accelerate around the cones faster than the Transfer system, can.

This is a link to a conversion of a Transfer system to a VTD with a US TCU.
http://www.subaruforester.org/vbulle...version-37441/


Our box has a greater torque split than the later model.

[McTaff]

I have a sudden urge to pull an SVX drivetrain out in entirety, drop twin turbo's on it and squeeze it into a Caterham. It'd never fit, and you'd never get four wheel drive, but could you imagine a little light car like that with all that power, and distributing torque like that?

[TomsSVX]

sorry I look at this thread title and giggle a little

Tom

[1986nate]

Originally Posted by TomsSVX

sorry I look at this thread title and giggle a little

Tom

all the information we know now, yet in a few years we'll look back on the things we are discussing now and think the same thing

[BRADY]

Originally Posted by Trevor

As I see it Harvey, incredible as it is, a wonderful system was stuffed up in respect of LH drive models on information from the sales dept. insisting that the car should and must be able to be run on a rear wheel dyno.
The mind boggles ! In point of fact US owners do not have a true SVX i.e. the car as it was described in most of the motoring press.

The idea of a clutch being used in this way makes me shudder and I wonder if the constant slippage and friction dissipates enough extra heat to cause the heat problems we hear so much about. I also wonder how many older cars are in fact putting the designed power to the back wheels hence the understeer reported. You have put the cat among the canaries!

OK. This fills in a piece of the puzzle. When I took my SVX to have the transmission rebuilt, I supplied the repairer with a massive print out on the 4EAT and everything I could download from here.

Upon completion, the repairer informed me that the gearbox in my SVX was NOT the same one that I had provided the information on.

I am happy to hear that the RHD SVX have the superior drive-train!!

[subbieatnz]

Is this for all RHD SVXs?
Is it the same for Fulltime 4wd auto and AWD auto?

[NiftySVX]

Originally Posted by oab_au

I would suspect that we will not get the 'binding' problems that the US have due to the different system and can't have the delay before the rear wheels engage, as they are all ways engaged.

Harvey.

I don't mean to hijack, but I wanted to add something to what you said initially because it is important that all understand the difference between the very good system that is ACT4 dating back to model year 1987.5 which remains much more advanced than what is found on modern models from other manufacturers, though sadly, is horribly inferior to VTD.

While I agree that the binding phenomenon is far less likely in a VTD trans, it should be noted that the ACT4 system is a dynamic variable system, not a passive system like those found on many vehicles. The important distinction is that other vehicles are "passive", meaning they only activate one set of wheels after the others slip. Subaru takes it one step further by keeping the rear wheels are always engaged to some degree, varying on driving conditions (This can be observed by a test drive of one of these vehicles with a line pressure gauge connected to the transfer clutch test port.) Subaru has never had a passive system on a production vehicle that does not drive all 4 wheels at all times, excepting the old school driver switched 4WDs. They do have the passive system that incorporates the viscous clutch pack but it drives in a split of near 50/50.