can you tell me what is vcu in differential?

pls discribe what does vcu do ?
is it useful transmission?

wich one is better transmission?

I am pretty sure that all it mean (as referring to ur pic) is it has a Viscous limited slip diff Aka "VLSD". it smiler to a clutch type LSD in its function but does it in a almost completely diffrent manner. A clutch type tries to keep the wheels locked (turning at the same RPM) by used clutch packs, were half the discs are connected to one wheel the over half is connected to the opposite wheel. now when the wheels try spin at diffrent speeds the discs try to spin against each other but friction tries to keep them locked. A VLSD tries to keep the wheels locked by using a viscous fluid, now in the clutch type u had all the disc touching but in a viscous there is a small gap in between the disc and there, so now when the wheels try to spin at diffrent speed the fluid tries to keep the disc spinning at the same RPM. So u see how they both try to keep the wheels locked but they do feel diffrent to drive a clutch style will all ways be trying to keep the wheels locked but the viscous will only generate friction when the wheels are already spinning at diffrent speeds so it almost a open diff until theres e-nuff slip to generate the friction.

hope that makes sence to u. but in short clutch style diffs almost allways a better diff but a viscous one is cheaper to make and to run, but is still a lot better then a open diff.....I am going to look for some pics to help u see what i am talking about..

In the case of the pictures you have included the VCU is a viscous coupling between the front and rear wheels. It is used in many AWD systems in place of a center differential. Just as a 2WD car needs a dif between the left and right wheels, an AWD car needs a "dif" between the front and rear axles. Older full time 4WD/AWD vehicles (Jeep, Audi, Subaru and others) used a center gear dif that split power between the front and rear axles. In a system like this there is a gear connection between all 4 wheels.
In recent times many AWD systems have moved to viscous or other slip type connections between the front and rear axles. These systems have a geared connection to one set of wheels (the front wheels in the pictures you provided). A viscous coupling connects the other set of wheels to the drive. The viscous coupling then transmits some torque to the other set of wheels (the back in this case) while also acting as a differential.
There are lots of technical differences and implications between using a gear dif vs a viscous coupling. One difference is that a viscous coupling can not send all the power to the rear wheels (again based on your pictures). With a center dif the center dif could send all the power to the rear axle while the front didn’t move. Think of having the rear wheels on ice. It’s kind of like having one wheel on ice in a 2WD car but this time it’s one axle on ice. In a car with a viscous AWD system one axle is gear driven by the transmission. It MUST spin when the gearbox tells it to spin. The other set of wheels may not spin. So if you have your AWD car stuck in mud the front wheels will/must spin when you give it gas. The rear wheels may not.

Disclaimer: I made sure to mention “as illustrated” because this system can work with non-front engined cars. Most of these systems are used on FWD based cars (Mazdaspeed6, Volvo, Some VW-Audis, most “soft-road” SUVs). These vehicles typically operate/feel like FWD cars with better than normal traction. But if the engine is in back, the system can act like a RWD car that sends just a bit of it’s power to the front. Porsche uses a viscous coupling on the 911. It transfers between 0 and I think 30% of the power to the front wheels. That means the Porsche can’t ever act like a FWD car. You get a RWD feel but some extra grip that helps the car produce great standing start acceleration numbers.

Thank you for your useful information :)
I find your mean about vcu in front differential :rolleyes: but if u can give me more information about this awd transmission. If u find any useful pics pls send it :confused: .
Thanks a lot

[QUOTE=gimydvd]Thank you for your useful information :)
I find your mean about vcu in front differential :rolleyes: but if u can give me more information about this awd transmission. If u find any useful pics pls send it :confused: .
Thanks a lot[/QUOTE]
No the pictures you posted show a VCU in the center differential. It just happens the "center" differential is right next to the front differential.

These might help:
[url]http://auto.howstuffworks.com/differential2.htm[/url]
[url]http://auto.howstuffworks.com/four-wheel-drive.htm[/url]
[url]http://www.autozine.org/technical_school/traction/tech_traction_4wd_2.htm[/url]

Take all of them with a grain of salt. They are not written by experts and their are always exceptions to what they say.

hello
we can use 2 differential in 4wd
why used 3 differential in this vehicle?
what do central differential?

For on road use you need a center differential because the front and rear axles don't always spin at the same speed. For off road use this isn't as important because you are going slow and you just let the tires slip on the ground. That's why many 4WD trucks are part time (can drive in 2WD mode)

Hello
I need a schematic of relative of components of this vcu/cd
You can see more information in this site
[url]http://www.stealth316.com/2-awd3.htm#cdvcu[/url]
I read all of them but I don’t know its completly
is this picture is right releative between componets? i think it is true