Using advanced digital measuring equipment, the former Forest Operations Institute, performed a series of measurements of tractive force and power requirement on mounted scarifier units. Previous measurements had only been done on trailed units.
In addition to conventional dynamometer equipment used for trailed units, two new methods were tested. The first involved measuring the braking pressure in the mattock-wheel drive motors on disc type scarifier wheels as used on the Bräcke B390 and the Donaren 870H. The second and better method was based on measuring the power, i.e. the pressure and flow in the hydrostatic transmission on the base machine. A whole series of calculations and corrections had to be made in order to obtain reliable data. Measuring the pressure in the hydrostatic transmission is the most widely applicable method, partly because the only requirement is that a machine is equipped with hydrostatic transmission and partly because it can be used for measuring other operations as well.
The tractive force required for scarification is surprisingly small and usually takes only a small proportion of the surplus drawbar pull available on the base machine. Most of the power is needed to move weight of the base machine through the terrain. The peak forces, which are evident from a jerky forward movement of the machine, could be dampened by using an alternative to the rigid mounting of the unit on the base machine. Not only would the surplus power available on medium duty forwarders then be more than ample for scarification but the overall efficiency of the system, in terms of energy used for scarification divided by fuel energy input, would also be enhanced. The current figure is below 10%.
Key words: scarification, tractive force.
Correspondence: Ulf Hallonborg, The Forestry Research Institute of Sweden, Glunten, S-751 83 Uppsala, Sweden
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