Hi All,

Was wondering if someone out there can tell me what a electronic locking rear differential is?

How does this compare to the standard Limited slip or Non Limited Slip?

From days past, I believe a limited slip allows the fixed wheel to take the power when the other is slipping, right?

 

"Electronic locking differential": As you will find in new vehicles, this is simply a traction control device that uses the brakes to limit wheelspin on an open differential. This is simply an electronic, computer-controlled update of the two brake pedal set up found on old farm tractors. One pedal for each side. Great for sharp turns, but also usefull if one wheel started to spin. The electronic system does not allow for the sharp turns.

"Standard Limited Slip": As found under the names "Positraction" or "Trac-loc" or "Equal loc" etc. These use spring-loaded clutches to "lock" the axles together. The spring tension and friction properties allow the clutches to slip during cornering, allowing differential action. Under power, they turn both wheels--when new. These are subject to wear and lose effectiveness with age. There are several designs.

"Non-limited slip": An open differential.

There are also truck "locking" axles that use air or electric controls to mechanically lock the axle temporarily under adverse conditions.

And mechanical lockers like the Detroit Locker that use more aggressive locking mechanisms than limited slips.

 

The standard clutch type limited slip differentials use the side forces generated by the spider gears against the side gears on each axle to activate the clutches. They need some resistance in the axles to activate. They use springs to preload the clutches so that if one tire is on a completely frictionless surface, a little torque is sent to the other tire, which hopefully will have more traction. In general, the greater the torque applied to the axles, the harder the clutches grab (until they wear out). So if you accelerate hard around a turn, you can spin both rear tires, instead of just the inside tire with an open differential.

The most common electronic locking rear differential would use some kind of electrically activated clutch, either with a magnet or air pressure.

The Detroit locker uses two gears that have teeth facing each other. Each gear is splined to an axle, and are pushed against each other by springs, so both axles are usually locked together. When the vehicle turns, and the inside and outside wheels move at different rates, the stress between the two sides will overcome the spring pressure on the gears, and cause them to pop apart, allowing differentiation, abruptly.

Another type uses either spiral or worm gears with the teeth pitch designed to allow one gear to easily turn the other, but more difficult the other way. One brand is Torsen, or torque-sensing. It's like an open differential that allows toque multiplication between the two axles, so again, if one tire is stuck on a completely tractionless surface, it will just spin. It also needs a spring loaded clutch to help in those situations. The Quaif brand uses this design.

There is also a type of differential that uses a viscous coupling that locks the two axles together when they try to turn at different speeds. Each axle is connected to a set of plates which are placed very close to each other in alternating order inside a closed container filled with a thick silicone oil that gets more viscous when subjected to the shear stress between the spinning plates.

Ford had an experimental differential using essentially an oil pump to apply the clutch. The pump activates when the two axles turn at different speeds.

 

The Quaife differentials I have seen are helical gear torque sensing and do not have any springs. They are comparable to the Torsen T2 and the Eaton Detroit TruTrac. The single wheel spin can be overcome with a light application of the brakes, true for both a torque sensing and a clutch-type limited slip.

Eaton makes an electronic locking rear that locks with the flip of a switch using an electromagnetic device in the differential itself. It functions similarly to an air-operated locker in that it is selectable with an on-off switch. Both the e-locker and air-locker usually function as an open differential when not engaged. Auburn makes something called ECTED that is both a clutch-type limited slip and a selectable electronic locker.

I would consider the automatic engagement of brakes to be part of traction control and not an electronic locking differential.

 

Sorry, I said "spiral", I meant "helical". I thought the Quaife had preloaded springs; guess I was wrong.

I've never been able to successfully get an open diff going when one wheel was stuck by the gentle brake application technique. In my case, the parking brake was non-functional due to a frozen cable, and I only had two feet to apply throttle, brake, and clutch at the same time. But I can imagine a Torsen or Quaife with 2X or 4X torque multiplication would be a lot more effective with this technique.

 

[quote=EPNCSU2006;12132007......................... .....

I would consider the automatic engagement of brakes to be part of traction control and not an electronic locking differential.[/quote]

I do not disagree with you, but some manufacturers label this set up as an "Automatic limited slip differential".