LIST OF ABBREVIATIONS
4. MEASUREMENT OF VEHICLE PERFORMANCE
4.2 Haulage Vehicle Performance Measurements
As outlined in the objectives of this project, in order to validate the SimTrans model, one would need to compare a measured dataset, captured from a haulage vehicle operating under normal conditions, to simulated data from SimTrans for the same vehicle. The haulage vehicle used for the performance tests was a Mercedes Benz 2637 V Series (shown in Figure 4.3) from the Unitrans Freight Sugar and Agriculture Company. The Mercedes Benz 2637 was fitted with an ADE 443N engine, which is a VI0 naturally aspirated 260kW diesel engine. The vehicle was coupled to a conventional set of interlink trailers used to haul timber.
The vehicle specifications are tabulated in Table H.l, page 124 in Appendix H. The graphs of torque versus engine speed and power versus engine speed for the ADE engine fitted to the truck are shown in Figure H.l and Figure H.2 respectively, on page 125 in Appendix H. The vehicle driver was experienced and operated the engine revolutions strictly within the greenband range.
Figure 4.3 The Mercedes Benz 2637 haulage vehicle used in the vehicle performance tests
The VPMS once designed and tested, was installed on this vehicle and used to gather performance data. The haulage tests were performed on the 15th and 16th of January 2004.
The vehicle was driven on two alternative routes between the Eston Sugar Mill and a timber compartment near Mid-Illovo, designated as Zone Three. The first route, referred to as Route One was via the Umbumbulu (R78) road and was tarred and in good condition throughout the distance. The second route, referred to as Route Two, was partly tarred with a worn tar surface in some sections, while the rest of the road surface was gravel. Route Two is shorter than Route One by 4.8 km. The vehicle was driven in both directions, on both routes unloaded. The vehicle was then driven to another timber compartment called Zone Four, where a load of 31 450 kg of wattle timber was loaded onto the vehicle. The vehicle was then driven on both routes in both directions loaded. Consult Table 4.1 for a listing of the routes travelled in the tests. The VPMS was active during the testing and recorded vehicle performance data for all trips.
Table 4.1 Observed vehicle trip details Trip#
1 2 3 4 M-Z4
Detail Mill to Zone 3 Zone 3 to Mill Mill to Zone 3 Zone 3 to Mill Mill to Zone 4
Route Short Long Long Short Short
Load Empty Empty Empty Empty Empty
Start time 08:27 08:52 09:23 09:47 10:45
Trip distance
(km) 11.8 16.6 16.6 11.8 20.0
Average speed (km/h)
36.5 42.4 46.0 36.1 37.3
Max speed (km/h)
66.6 72.4 76.6 73.3 76.4
End time 08:46 09:15 09:45 10:07 11:17
Trip time (min)
19.6 23.5 21.7 19.9 31.4 Timber Loaded at Zone 4
Z4-Z3 5 6 7 8 9
Zone 4 to Zone 3 Zone 3 to Mill Mill to Zone 3 Zone 3 to Mill Mill to Zone 3 Zone 3 to Mill
Short Short Long Long Short
Full Full Full Full Full Full
13:19 13:43 14:27 15:00 15:42 16:22
8.3 11.8 11.8 16.6 16.6 11.8
23.4 19.8 25.1 26.8 30.1 21.2
77.8 75.2 59.1 71.2 79.4 74.0
13:40 14:19 14:56 15:37 16:15 16:59
21.6 36.2 28.6 37.1 33.0 33.8 4.3 SimTrans Simulation
The SimTrans model requires the user to input three data files to describe the route and speed changes along the route and the vehicle details. The accuracy of the simulation results from SimTrans depends on the accuracy of the input data and thus careful consideration was given to the preparation of accurate data files (Clark, 1996).
The first input file required for SimTrans is the vehicle file, which is used to describe the engine, gear box, axles, the tyres and loading of the vehicle and the trailer, and other associated components of the vehicle. The vehicle specifications used for the simulation may be seen in Table H.l, page 124 in Appendix H.
The road profile was digitised by Green Belt Mapping using a Trimble Pro XRS mapping grade GPS with a sub-meter accuracy. Post processing was performed on the GPS data to enable the files to be compatible with SimTrans. The vertical route profiles are plotted in Figure 4.4 and Figure 4.5. The equivalent grade rolling resistance values, required for the road profile input file were estimated using Table 3.1, page 35.
800
750
700
650
600
550
Distance (km)
Figure 4.4 Vertical profile of Route One from the Eston Mill to Zone Three
850
600 H 1 1 1 1 1 1 0 2 4 6 8 10 12
Distance (km)
Figure 4.5 Vertical profile of Route Two from the Eston Mill to Zone Three
The speed limit file for the simulation was constructed by setting the observed vehicle's maximum speed over road sections varying from 10 m to 50 m, as the speed limit for the simulated vehicle in these road sections. The road segments were determined using the GPS position data from the observed vehicle dataset and since the GPS position data was collected on a timed interval, the distance between samples varied. The road was split into these sections to limit the number of speed variations on the route and make data processing manageable.
Through studying the observed performance data, it was decided that the most realistic method of simulating the driver's choice of gear changes was to run the SimTrans model in the "greenband" gear changing mode. The entire dataset of observed engine speed versus data point number of the observed engine speed values, as they appear in the observed dataset, was plotted in Figure H.3 on page 126 in Appendix H. From this plot it was determined the engine speed at which the gear up shifts occurred was approximately 1900 r/min, while down shifts occurred at approximately 1000 r/min. Thus these engine speeds were taken as the greenband upper and lower limit respectively for the SimTrans simulation.
A stationary start was applied in all simulations.