Volume 1, numéro 1, july 1989

EN :

The effect of terrain factors on productivity in subgrade preparation by excavator was studied. The data, collected in a follow-up time study of 57 road sections, was analyzed using multiple linear regression. A prediction model that has soil moisture class and boulder frequency as independent variables was derived. The results also show that productivity varies considerably among operators. It is also apparent that the effect of the terrain is partly levelled out as the quality requirements for the performance of the subgrade are normally adjusted to the terrain conditions. It is suggested that, within a certain region, a fairly simple model can be sufficient for practical use in road network planning.

EN :

The required road width around curves on forest roads is largely determined by the difference in wheel paths between the inside front tractor wheel and the inside rear trailer wheel. This difference, known as offtracking, is a function of the vehicle and road geometry. This paper presents a method for determining the offtracking of fixed and variable length multiple unit vehicle combinations travelling over forest roads. The computational method numerically integrates the differential equations which compute the path (tractrix) that the rear of a vehicle follows from a given steering curve. A unique three-point solution method is used to determine the instantaneous center of rotation for trailers in the vehicle combination. The method is shown to have good agreement with experimental data. It is suitable for use on microcomputers for single and multiple curves. A microcomputer program, OFFTRACK, was developed using this methodology.

EN :

This paper explains why it has been difficult to get high mechanical availability with multi-function-machines. Simplified reliability theory is applied to demonstrate the relationship between Mean Time Between Failures of components and mechanical availability for machines of various complexities. The design engineer should reduce the number of components and find the right compromise between high reliability and low weight/low cost, thereby designing more reliable and cost-effective multifunction machines.