H-drive

An H-drive drivetrain is a system used for heavy off-road vehicles with 6×6 or 8×8 drive to supply power to each wheel station.

H-drives do not use axles but rather individual wheel stations, usually carried on a punt chassis. A single differential splits the drive into separate left and right drive shafts, which each run fore and aft inside the bottom corners of the chassis. At each wheel station a bevel box drives the half shaft out to the wheel.

H-drive is not commonly used for 4 wheel vehicles, as it is relatively complicated for small vehicles. It has been used most widely for military 6×6 chassis in the West. Vehicles of the Warsaw Pact, such as the Tatra 813 and MAZ-535 series, were instead based on narrow backbone chassis with a central propeller shaft.

H-drive was first developed by Hub van Doorne of the Dutch truck maker DAF. It was a derivative of their Trado conversion to produce a 6×4 off-road truck from a commercial 4×2 chassis. The Trado used a bogie rear suspension for both sets of rear wheels. This suspension, best known through the Scammell Pioneer of 1927, uses a single central axle, or driveshaft, that in turn drives two walking beams (balanceur, in Dutch) one on each side. The wheels are supported by overhung stub axles. The conversion added the walking beams to the ends of the original truck beam axle. From that point, the drive between the axles of each side was separated side by side.

In 1938, a later version of the Trado 3 conversion added drive to the front wheels and so converted a 6×4 vehicle to 6×6 drive. Unlike most all-wheel-drive vehicles, the front axle was no longer a live beam axle with added articulation for steering, but used two separate drive shafts, one to each front hub.

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