Coastdown measurement with 60-tonne truck and trailer: estimation of transmission, rolling and air resistance

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Ulf Hammarström
Mohammad Reza Yahya

By use of coastdown measurements, driving resistance parameters have been estimated for a truck with trailer (60t) and a box vehicle body. At a vehicle speed of 20 m/s, average meteorological wind conditions and a load factor of 50% the following distribution of the driving resistance components has been obtained:

  • transmission resistance (churning losses), 5%
  • rolling resistance (test route surface conditions), 41%
  • air resistance, 54%.

There are also measurements for the truck without a trailer. Rolling resistance is dependent on road surface conditions, in particular roughness (iri) and macro texture (mpd). The total rolling resistance consists of three parts: a basic, an iri and a mpd part. The road surface effect amounts to approximately 40% of the total rolling resistance. The iri effect seems to be the dominating part of the surface effects on the contrary to light vehicles.

Driving resistance parameters have been estimated by means of regression analysis. A major problem is how to avoid high correlations between explanatory variables. One objective of the experiment design has been to minimize such dependencies. This study might also be of interest for methodological reasons and in particular for including:

  • the introduction of high accuracy road gradients as well as other road surface properties
  • the estimation of vehicle mass from coastdown to coastdown
  • the equipment (based on Doppler technique) used in order to measure the coastdown driving pattern
  • the method used in order to separate parts of the driving resistance

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