This paper reports the vertical dynamic response of two heavy vehicles to three different types of terrain under various load and speed conditions. The vehicles studied were (i) a heavy vehicle with conventional leaf springs at the front and rear (ii) the same heavy vehicle with the rear leaf springs replaced by hydropneumatic suspensions. The roads considered for the study were three 1km stretches of premixed bituminous carpet road, water-bound macadam gravel road and granite paved herringbone road which were characterized using a fifth wheel bump integrator. The speeds covered were 20, 30, 40 and 60 kilometres per hour (kmph). The tests were carried out for no load as well as for 1/3,2/3 and full loads, and also for extra load on one side of the vehicle. Vibration measurements were made at a few points on the chassis directly above the suspensions as well as on the axle and the driver's seat. Typical power spectral density (psd) plots of acceleration have been reported. Graphs of root mean square (rms) acceleration as a function of frequency for various roads, loads and speeds have been compared with ISO 2631. It is seen that for loads beyond 2/3 of full load, the hydropneumatic suspension gives better ride quality than the leaf spring, whereas the latter gives superior results at no load.
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