Draw hook performance
The Zughakenleistung is a characteristic that often for tensile and towing vehicles of rail and road traffic as well as for agricultural machinery , construction vehicles and tractors is specified.
The towing hook power refers to the maximum power available after deducting all losses and ancillary operations of the vehicle machinery on the towing device (towing hook, coupling, etc.). The size specification is given as a power specification in PS or kilowatts and should not be confused with the pulling force , which is specified in Newtons or N, kN etc. In catalogs of relevant machines and vehicles, under the title "Towing hook performance", however, a tensile force dimension is often and formally incorrectly stated. In this context, it would be more correct to use the term “hook pulling force”, which is used occasionally, especially for tugs.
Rail vehicles
On steam locomotives, the towing hook power was referred to as the mechanical power available on the towing hook and was specified in metric or imperial power units ( PS or hp ). The special designation indicates that different performance levels can be defined for a steam locomotive, depending on the starting point of the measurement. In addition to the boiler evaporation capacity , the indicated capacity is calculated based on the determined maximum steam or gas pressure and the piston pressure area. However, part of this output power is lost again in the downstream engine machinery in the form of frictional heat from the piston and drive rod bearings . The draw hook power thus allows, in particular, a determination of the efficiency of different parts of the drive, which in the case of steam locomotives is overall in the range of 10 to 15%, depending on the design and operating condition.
For other types of traction, draw hook performance data can basically also be given, but this is less common there, since other drives have a higher degree of efficiency and therefore the aggregate output is more likely to be stated (corresponding to the boiler output of the steam locomotive), for example, diesel locomotives usually use the installed power specified. Electric locomotives represent a special case, the max. Aggregate performance depends on the period over which this performance is called up; in addition to the continuous output, the higher value for hourly and short-term output is also given.
detection
If you multiply the indicated power P Zi by the mechanical efficiency of the piston machine , you get the effective draw hook power. Since the determination of the efficiency alone is rather complex, and the aerodynamic individual driving resistance must also be taken into account, the draw hook performance was mainly determined on test drives. For this purpose, a measuring car was coupled behind the locomotive and behind it a sufficiently heavy freight train or a brake locomotive with a correspondingly strong inertia brake (for example a counter-pressure brake ). The tensile force of the locomotive is determined by measuring the voltage on the coupling of the measuring car and the speed reached (distance per time span) is recorded. From this, the performance achieved in each case can be calculated as the product of force and speed (“performance = force times distance per period”).
The towing hook power, which is usually determined as a maximum value, is not a fixed value, but only applies to the respective operating state, with the speed and climatic conditions (e.g. altitude with thinner air) being the changing parameters. The information must always be accompanied by the values for these variables in order to allow a meaningful comparison.
literature
- Steam locomotive science , Volume 134 of the railway teaching library of the Deutsche Bundesbahn, 2nd edition, p. 197 f. (Reprint from 1983 ISBN 3-9800684-2-0 ).