1999-2009 [Subscribe to Daily Digest] |
Torsen:
A far more efficient (and expensive) 4WD layout is the one involving a TorSen ( which stands for TORque SENsing) differential. This extraordinary device, invented by the American Gleasman (patent pending, 1958) and manufactured by the Gleason corporation, is based on the non-reversibility of worm gears and worm wheels (i.e. when you turn the worm wheel the worm gear turns but not vice versa). The TorSen is the only mechanism which acts like a differential and locking device at the same time. It has the advantage of being fully mechanical which guarantees its instantaneous response and progressiveness. Its main advantages therefore resume to:
Instantaneous response
The linear character of its locking to speed difference curve (smoothness)
No locking or speed difference inhibition under braking (it acts only when power is applied to it)
Integrates a "free" differential and a locking device in one part
Its compactness, the TorSen has only 8 moving parts
No wear as opposed to more traditional self-locking differentials based on friction plates
There are mainly two drawbacks in Torsen differentials:
They are expensive devices
They tend to generate more heat under heavy use than an open differential
Due to its inherent design if one wheel is completely off the ground or completely loses traction the TorSen will act as an open differential
Is extremely difficult to assemble. Although it only holds 8 moving parts there is only one way to fit them together
The TorSen splits torque in a 50:50 proportion in no-slip conditions and can manage slips up to 20:80 ratios between the wheels it drives.
Viscous coupling:
A viscous coupler can be seen as a tube containing a pressurized viscous fluid in which discs are rotating. Half of the discs are attached to the incoming axle while the other half to the outgoing one to the tube's walls. Each pair of discs faces each other i.e. a disc attached to the incoming axle faces its counterpart attached to the outgoing axle. The discs are pierced and the viscous fluid completely surrounds them. Minor speed differences are allowed between discs. Increased slip (i.e. rotational speed difference between discs) leads to a rapid increase in the viscosity of the fluid which, in turn, locks up the coupling.
Viscous couplers are convenient devices mainly because they are not very expensive and do not require extensive maintenance. Their major drawbacks are:
An exponential increase of their locking to speed difference curve (their are not very progressive)
A delay in their locking ability induced by the time the viscous fluid needs to increase its viscosity
Are difficult to handle under braking (they lock in braking situations)
The close relation of their locking abilities to that of the viscous fluid temperature (its viscosity decreases as temperature increases)
So:
The most important difference between TorSen differentials and viscous couplers is that the TorSen has a torque sensing characteristic while the VC has a rotation sensing characteristic. That's why TorSen differentials only lock when power is applied to them whereas viscous couplers lock both when power is applied and while braking.
I think that should cover the basics...
As you see... torsen as a center diff. is not a bright idea.
Regards,
Coolknight
posted by 212.77....
, Sat, 19 Jan 2002 19:20:26, Sun, 20 Jan 2002 18:24:19
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
