Dynamic Force Measurement Vehicle

The DFMV is a vital element in NATC's arsenal for understanding vehicle and tire dynamics and quantifying terrain inputs to vehicles. The DFMV is equipped with longitudinal, lateral and vertical force transducers, a vertical accelerometer and a wheel speed sensor at each wheel end, allowing continuous measurement of all forces, accelerations and speed involved with the dynamic measurement activity. The force measurements are made at the tire/ground interface on tires ranging from small all-terrain-vehicle, high-flotation tires... to medium-duty truck tires... to agricultural tractor tires.... to military specification heavy equipment tires.

The first DFMV was built in 1973 based on a need to better understand tire/vehicle performance parameters. To insure methodology acceptance, guidance was obtained from the automotive and tire industries, tire companies, and government agencies. Since 1973, NATC has built 15 DFMVs, either for clients or for in-house use, and has conducted numerous studies. The DFMV is a proven tool that has been used by NATC for different tire and terrain measurements, including:

1. Profiling paved and off-road test courses for government and commercial sponsors
2. Accelerated tread wear measurements
3. Catastrophic tire failure force measurements
4. Dynamic tire response and mobility measurements
5. Separation of bound and unbound tire-slip energy
6. Quantification of drive train performance and integration of tire and suspension dynamics for optimum performance.

Because the load cells at each wheel end measure the wheel-vehicle interface impedance, the DFMV has been used for numerous vehicle and tire dynamics studies. For example, the frequency response functions between the wheel attachment and any location on the vehicle structure can be computed accurately using the wheel-axle interface force measurements as the input. This procedure is used to develop a transfer function between the ground and the wheel end to describe the tire, thus eliminating the need to have a tire in a wheeled vehicle simulation model. The advantage to this procedure is that the natural filtering characteristics of a tire are included in the transfer function, as well as tire deflection, tire temperature, etc. A complex model to describe a tire and all its variations is eliminated.