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Portal axle
A portal axle (or portal gear lift) is an off-road vehicle suspension and drive technology in which the axle tube or the half-shaft is offset from – usually above – the center of the wheel hub and driving power is transferred to each wheel through a simple gearbox built onto each hub. It has two advantages over a non-offset axle: first, ground clearance is increased, particularly beneath the low-slung differential housing of the main axles; second, any hub reduction gearing allows the axle half shafts to deliver the same power but at reduced torque (by using higher shaft speed), which reduces load on the axle crown wheel and differential.
The portal gear configuration is also sometimes called a drop gear or drop gearset configuration (which, despite its similarity to the term dropped axle, produces the opposite effect).
Compared to a normal layout, portal axles enable the vehicle to gain higher ground clearance, as both the axle tube and differential casing are tucked up higher under the vehicle.
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 results in lowering the center of gravity for a given ground clearance. In a vehicle that also requires a reduced top speed in at least one gear, the gear ratio can also have this effect. The military Kübelwagen of WWII used a ratio of 1.4:1 to provide a 2.5 mph walking speed in first gear, as well as a useful lift of 50 mm.
As they require a heavier and more complex hub assembly, however, portal axle systems can result in increased unsprung weight and require robust axle-control elements to give predictable handling. In addition, at higher speeds the hub assembly can overheat.
They are also used in railways and low floor buses although, in the case of the latter, the device is engineered in the opposite way to those fitted to off-road vehicles - the axle is below the center of the wheel. Thus, the inverted portal axle allows the floor of the bus to be lowered, easing access to the bus and increasing the available cabin height.
Bolt-on portals (or drop boxes) are a housing with a set of gears which bolts onto the final flange of the axle tube. This approach allows existing vehicles to be converted to use portal gear lifts without modifying the axles (Volvo C303 or Unimog 404).
Vehicles fitted with portal axles include:
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Portal axle AI simulator
(@Portal axle_simulator)
Portal axle
A portal axle (or portal gear lift) is an off-road vehicle suspension and drive technology in which the axle tube or the half-shaft is offset from – usually above – the center of the wheel hub and driving power is transferred to each wheel through a simple gearbox built onto each hub. It has two advantages over a non-offset axle: first, ground clearance is increased, particularly beneath the low-slung differential housing of the main axles; second, any hub reduction gearing allows the axle half shafts to deliver the same power but at reduced torque (by using higher shaft speed), which reduces load on the axle crown wheel and differential.
The portal gear configuration is also sometimes called a drop gear or drop gearset configuration (which, despite its similarity to the term dropped axle, produces the opposite effect).
Compared to a normal layout, portal axles enable the vehicle to gain higher ground clearance, as both the axle tube and differential casing are tucked up higher under the vehicle.
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 results in lowering the center of gravity for a given ground clearance. In a vehicle that also requires a reduced top speed in at least one gear, the gear ratio can also have this effect. The military Kübelwagen of WWII used a ratio of 1.4:1 to provide a 2.5 mph walking speed in first gear, as well as a useful lift of 50 mm.
As they require a heavier and more complex hub assembly, however, portal axle systems can result in increased unsprung weight and require robust axle-control elements to give predictable handling. In addition, at higher speeds the hub assembly can overheat.
They are also used in railways and low floor buses although, in the case of the latter, the device is engineered in the opposite way to those fitted to off-road vehicles - the axle is below the center of the wheel. Thus, the inverted portal axle allows the floor of the bus to be lowered, easing access to the bus and increasing the available cabin height.
Bolt-on portals (or drop boxes) are a housing with a set of gears which bolts onto the final flange of the axle tube. This approach allows existing vehicles to be converted to use portal gear lifts without modifying the axles (Volvo C303 or Unimog 404).
Vehicles fitted with portal axles include: