Portal beam axles

[Swordman]

Can someone with a bit of engineering knowledge enlighten me about these? From what I can see, they allow solid axles to pack larger wheels, however, the struts look like they could be a weak point, so maybe they're only as strong as independent suspension set-ups. Which begs the question; do they have any advantage over independent suspension?

[mikeh501]

i think primarily their purpose is to raise the diff on the axle to gain more ground clearance which is usually the lowest point. The portal boxes would usually be bolted into stronger axle cases in the first place which helps make the unit stronger. The portal boxes themselves also allow changes of gearing. Dont believe they are for fitting larger wheels, although this is a side effect as the wheel needs to be larger enough to enclose the portal box.

[Swordman]

I see...

[C Lee Farquar]

They tend to be off Unimogs and similar sized kit so plenty strong enough for a 4x4.

If anything they are too strong and therefore too heavy, depending on your priorities.

[bigblock]

Portal axles allow the axle tube to attach above the centre of the wheel hub, this means that ground clearance is increased, particularly beneath the differential housing.

Secondly the reduction gearing in the hub allows the axle halfshafts to deliver the same power to the wheel (by using higher shaft speed) but also reduces the torque loading on the axle, crownwheel and differential.

Here is a photo of a basic portal hub so you get the idea...






Then depending on the application it can get a bit more complicated...




It is possible to have independent suspension with portals if you go for bolt on hubs instead of a full solid axle unit.

Edited by bigblock on Sunday 8th March 19:39

[Watchman]

bigblock said:

It is possible to have independent suspension with portals if you go for bolt on hubs instead of a full solid axle unit.

I'm intrigued by this. The Tibus website suggests they could make drop boxes to fit independent suspension too. Have you any examples of any that have been implemented? I am wondering how my ML would look/handle with a set. Just idle speculation - I've only clouted the bottom of it once and that was through stupidity getting the better of me.

[skyrover]

Watchman said:

bigblock said:

It is possible to have independent suspension with portals if you go for bolt on hubs instead of a full solid axle unit.

I'm intrigued by this. The Tibus website suggests they could make drop boxes to fit independent suspension too. Have you any examples of any that have been implemented? I am wondering how my ML would look/handle with a set. Just idle speculation - I've only clouted the bottom of it once and that was through stupidity getting the better of me.

You have to remember portal hub's place a huge amount of leverage on the drivetrain, so any independent suspension system would need to be very beefy to cope with the strain.

But why would you fit portal axles to an independent setup where you have no axle diff to worry about?

And more importantly, why would you go with independent suspension on an offroader?

[Watchman]

skyrover said:

You have to remember portal hub's place a huge amount of leverage on the drivetrain, so any independent suspension system would need to be very beefy to cope with the strain.

It's all speculative but compared with the leverage of "braking" I wonder how much more leverage portals exert. The ML is a surprisingly beefy piece of kit if you look underneath.

skyrover said:

But why would you fit portal axles to an independent setup where you have no axle diff to worry about?

Simply the fact that they advertise the availability of portals for independent suspension piqued my interest.

skyrover said:

And more importantly, why would you go with independent suspension on an offroader?

I absolutely don't need a full-on offroader. In fact, I inherited the ML which replaced my Legacy which is more suited to 95% of my use. The ML is a good road car, and is great for towing (powerful) where it beats the Legacy hands down. And although I wouldn't describe it as an offroader, it has a capable-enough 4WD system on the sort of non-paved areas I have used it.

Given that the portals described are £6K+, I wouldn't/couldn't afford/justify it anyway. I was just curious. It sort of appeals to my "upgrade for fun" mentality too.

It'll never happen.

[grizzly7]

Oldish topic but this I think has portals on an independent set up, at a cost http://www.seikel.de/en/products/seikel-vw-t5-extr...

Also, the fact that max torque is generated at the hub on a mog, allowing the rest of the drive train to be relatively small is I believe why you can have factory fit 395 85 R20 tyres for instance on such a "light" truck. 365s are more normal on equivalent sized MANs etc, 395s would need an 18ton range 4x4 truck chassis from MAN rather than more like 10-12 ton on a Mog. What gets done by individuals afterwards is another thing of course

[TooMany2cvs]

Watchman said:

but compared with the leverage of "braking" I wonder how much more leverage portals exert.

Both acceleration torque and braking torque would pass the same forces onto the end of the portal as goes onto the axle currently - but the leverage of the portal will multiply that when it reaches the actual axle.

And think about what forces'll be passed to the axle when/if that wheel hits something solid.

[PhillipM]

TooMany2cvs said:

And think about what forces'll be passed to the axle when/if that wheel hits something solid.

Less than before, since it's being geared down through the portal. VW Buses used to run similar years ago.

[battered]

skyrover said:

But why would you fit portal axles to an independent setup where you have no axle diff to worry about?

And more importantly, why would you go with independent suspension on an offroader?

Ask Steyr-Puch, they fitted IRS with portals to the Haflinger, AFAIK. A mate had one in the 80s, when they were still dirt cheap. I never went underneath but I think it had swing axles because when he jacked it up the wheels tucked under. I don't think it ever went fast enough to suffer tuckunder on the road, which was why his Dad had bought it for him. Genius choice, it was too slow to get into trouble, it was as cool as a penguin in shades (the lucky sod) and his Dad could use it to move junk around without giving a toss. Jealous, me? Jealous as hell. I borrowed my Dad's Mini van, which might be cool now but aged 18 in the 80s it was anything but.

[Cfnteabag]

Current in service Pinzguaer uses portal axles with independant suspension, Chassis is a tube with propshafts running inside with a diff at either end.

Works well off road but gives a strange "stance" with what appears to be excess camber and sometimes strange tyre wear and shaking when steering.

Can put a picture up on this computer but a quick google should find one!

[skyrover]

I suppose a relatively famous example of portal axles on independent suspension would be this...





Quite a beefy setup although maintenance can be a bit of a bugger apparently.

The US armedforces went this route to get as much ground clearence as possible.

It also explains why the H1 is so wide,as the gearbox, transfer case, driveshafts and exhaust all sit high up in between the driver and passenger

Edited by skyrover on Monday 27th July 10:26

[bigblock]

Cfnteabag said:

Current in service Pinzguaer uses portal axles with independant suspension, Chassis is a tube with propshafts running inside with a diff at either end.

Works well off road but gives a strange "stance" with what appears to be excess camber and sometimes strange tyre wear and shaking when steering.

Can put a picture up on this computer but a quick google should find one!

Here is a photo of mine to help you out

[GC8]

skyrover said:

I suppose a relatively famous example of portal axles on independent suspension would be this...





Quite a beefy setup although maintenance can be a bit of a bugger apparently.

The US armedforces went this route to get as much ground clearence as possible.

It also explains why the H1 is so wide,as the gearbox, transfer case, driveshafts and exhaust all sit high up in between the driver and passenger

Edited by skyrover on Monday 27th July 10:26

Probably even more famouser...