Tech Briefs

This transducer could ensure better testing of off-road vehicles.

Aconcept wheel force transducer has been developed that can measure the forces and moments between a tire and a road on a High Mobility Multi-purpose Wheeled Vehicle (HMMWV or Humvee) driven under off-road conditions. The proposed wheel force transducer is an important step in correcting the gap in current tire testing and modeling knowledge to ensure that future off-road vehicle models and simulation efforts are conducted with confidence. In order to obtain tire characteristics over off-road terrain, cost-effective field test equipment was required.

This model shows the Force Transducer mounted to the modified rim. The load cell inner ring is mounted to the modified rim using 12 bolts.
There are many derivatives of the HMMWV, with large differences in mass. The gross weight of the vehicle used in this work is 12,100 pounds. The first important step in the concept design was to determine the space envelope, and therefore basic dimensions available to fit the transducer. Due to the suspension components on the inside of the wheel, the transducer had to be mounted to the outside of the standard rim.

The wheel force transducer had to replace part of the rim so that the rim was connected to the hub via the force transducer. To achieve this, the standard rim had to be modified. Modification involved cutting out the center portion of the outer part of the original rim to the same diameter as the unmodified inner rim. The load cell inner ring was mounted to the modified rim using 12 bolts. On the unmodified rim, these 12 bolts were responsible for holding together the two parts of the split rim. These bolts were part of the inner rim. In this application, the bolts were replaced and screwed in from the inside of the rim into the load cell inner ring. The nuts on the outside were not used, as the load cell inner ring served this purpose.

The load cell outer ring was mounted to the hub using the hub mounting adapter, which connected the load cell outer ring to the vehicle’s hub with the existing eight hub bolts and nuts. The hub mounting adapter was also bolted to the load cell outer ring. The load cell inner ring and outer ring were connected to each other via six individual tension-compression load cells. The load cells were mounted such that the three tire forces and three tire moments could be calculated from the six tension-compression forces measured with the individual load cells and the geometry.

The possibility exists to mount the wheel force transducer to other rim sizes and designs. The exact possibilities depend on the geometry of the different rims, but basically entail designing and manufacturing adapters to connect the load cell inner ring to the rim, and the load cell outer ring to the hub. This can also be turned around so that the load cell inner ring is mounted to the hub, and the load cell outer ring is mounted to the rim.

This work was done by P.S. Els of the University of Pretoria, South Africa, for the US Army International Technology Center-Atlantic. ARL-0124

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Wheel Force Transducer Research and Development (reference ARL-0124) is currently available for download from the TSP library.

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