92908 Portal Axle - how does it work?

[Richard Dower]

I actually genuinely dont get what these do?.....it seems you can add gears to this, what is the point of that?

I am not a steering and geometry expert or a car person, are these designed to add some interesting new techniques and building options?

 

 

http://www.bricklink.com/catalogItemIn.asp?P=92908&in=S

 

 

Edited January 7, 2017 by Richard Dower

[syclone]

I'm not an expert in definitions, but basically you can lift up your model, increasing the clearance under the chassis by placing them vertically. 

Edited January 7, 2017 by LXF

[suffocation]

They also make it easier to gear down and gain torque where you need it the most; the trade-off is that it's very hard to get a decent pivot point.

[DrJB]

These were first introduced with the Unimog, for the so-called 'portal' axles. The goal there was precisely to increase the ground clearance (distance between ground and truck's underside).

They seem like they do not do much, but you can install a gear reduction AND a spindle (below) for a wheel (wheel hub connects to spindle).

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Edited January 7, 2017 by DrJB
added pics

[Dazenie]

It allows the axle to handle more torque

[suffocation]

Addendum: check out @nicjasno's brilliant rebuild of the Unimog's front axle for an example of how to achieve proper steering geometry with portal axles. 

[Blakbird]

Portal axles have two benefits in real vehicles.

1. By placing the gear reduction as close to the wheel as possible, you reduce the amount of torque required in the rest of the drivetrain making it more robust.
2. It allows the axles and differentials to be placed higher in the vehicle increasing ground clearance.  Usually the drive axle must enter at the center of the wheel, but with a portal axle it can enter significantly higher.

Only really heavy duty vehicles use this.  For example, the full size Humvee has portal axles.  If you look at one from straight on, the ground clearance is incredible.  No diff housing hanging down.

[Imanol BB]

Here is a very simple example of what the portal axles do: https://upload.wikimedia.org/wikipedia/commons/f/f1/NormalVsPortalAxle.svg

Another thing to consider about the portal axle (in addition to the great explanation made by Blackbird), is that the portal axles allow to increase the ground clearance without necessarily using bigger tires, which is good for medium and large vehicles where tire size can be a problem, that is why vehicles like unimogs or pinzgauers, despite having not too big tires (at least the standard versions) have a huge ground clearance similar to other large sized trucks.