An experimental study of low-frequency motion in cars

Low-frequency acceleration can cause discomfort, instability and motion sickness, but there is little published information on this type of motion in cars. Accelerations in the fore-and-aft, lateral and vertical directions were measured continuously while driving around a fixed suburban route for 30 min. In separate studies, the variations in accelerations with the same driver driving the same car, the same driver driving different cars, and different drivers driving the same car were determined. The spectra of fore-and-aft and lateral accelerations were similar over the frequency range 0.1-0.5 Hz and, in consequence, motion sickness dose values (MSDVs) were similar in these axes when calculated using the frequency weighting in current standards. At frequencies less than 0.1 Hz, fore-and-aft acceleration was greater than lateral acceleration. The MSDVs for vertical acceleration were appreciably less than those for fore-and-aft and lateral acceleration. Acceleration in the Vertical direction was predominantly influenced by vehicle suspension dynamics, with peaks between 1.0 and 2.0 Hz, and the differences between vehicles were greater than the differences between drivers. The fore-and-aft and lateral acceleration (as reflected in the MSDVs) showed differences between drivers that were greater than the differences between vehicles. Although such low-frequency fore-and-aft and lateral acceleration in cars is dependent on the behaviour of the drivers, some human responses to these motions may be modified by vehicle design.