Portal axle

Portal axles (or portal gear) are an offroad technology where the axle tube is above the center of the wheel hub. [http://findarticles.com/p/articles/mi_m0FZX/is_7_65/ai_55438454 New Spicer portal axles for compact utility tractors - introduced by Off-Highway Systems Group of Dana Corp - Brief Article | Diesel Progress North American Edition | Find Articles at BNET.com ] ] Compared to normal layout, this enables the vehicle to gain a higher ground clearance, as both the axle tube and differential casing are tucked up higher under the vehicle. [ [http://www.portal-tek.com/index.php?go=faq Portal-Tek Custom Axle Assemblies, Domination Through Innovation ] ] [ [http://rockthis.org/tech/avportaxle.asp RockThis Off-Road! ] ]

Due to the gear reduction at the wheel which lessens the torque on all the other drivetrain components, the size of the differential casing can be reduced to gain even more ground clearance. Additionally, all drivetrain elements, in particular the transfer gearbox and driveshafts can be built lighter. This can be of use in reducing the centre of gravity for a given ground clearance.

As it requires a heavier and more complex hub assembly, however, these systems can result in an increased unsprung weight and require robust axle control elements to give predictable handling. In addition, at higher speeds the hub assembly can overheat. [ [http://www.exaxt.ca/faq.asp#5 Exaxt 4WD ] ]

Some examples of off-road vehicles fitted with portal axles are:

*Mercedes-Benz Unimog [ [http://unimogcentre.com/unimogprinc.html#portalaxle The Unimog Principle ] ]
*Steyr Puch Haflinger
*Steyr-Daimler-Puch Pinzgauer [ [http://www.a1.nl/phomepag/markerink/portal-compare.htm portal-compare.htm ] ]
*Volkswagen Kübelwagen
*Volvo C303
*AM General HMMWV [ [http://www.ebroadcast.com.au/ecars/FAQ.html 4WD Glossary & FAQ ] ]
*International FTTS [http://www.internationaldelivers.com/assets/PDFs/FTTS_Specs.pdf]

They are also used in railroads and low floor buses. [ [http://www.railway-technology.com/contractors/bogies/ghh/ghh3.html Railway Technology - Portal axle with SAB V60 rubber-sprung wheels and sound absorbers ] ] [ [http://english.chinabuses.com/news/0710/24004.htm ArvinMeritor Reveals New Second Generation Inverted Portal Axle ] ] . Although in the case of buses, the device is engineered in the opposite way to those fitted to off-road vehicles - the axle is below the center of the wheel. This, the "Inverted Portal Axle", allows the floor of the bus to be lowered, thus easing access to the bus and increasing the available cabin height.

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