| Before discussing the vehicle performance curves, interpreting the engine performance curves will be explained. |
Torque is the twisting or rotating force that the engine exerts on the crankshaft; it is normally expressed in terms of kg.m and is measured at a radius of one meter from the crankshaft'fs center.
For instance, when a braking force of 44kg is required to stop an engine, equipped with a flywheel one meter in radius, its torque is 44kg.m.
The torque curve of the 6D14-3A engine, mounted on the FK615 truck is given in Graph 1. |
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| The engine speed (revolutions per minute), ranging from 1,200 to 3,100 rpm is charted on the horizontal axis. The numerical value of the torque, ranging from 36 to 44 kgÅEm, is charted on vertical axis. As engine speed increases from 1,200 rpm, the torque describes a convex curve; the curve is approximately flat between 1,600 and 2,000 rpm. The maximum torque 44 kg.m is obtained at 1,800 rpm. The flatter the curve, the less will torque be affected by fluctuations in engine speed- this translates into relative ease of operation of the truck. In the case of an engine where the curve, in the shape of a peak, drops precipitously from the point of maximum torque, the shift of engine rpm from the point of maximum torque will cause a loss of power. Even if the maximum torque of the engine is great, with such an engine, a constant shifting of gears would be required to negotiate hills making tiresome operation. |
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The rpm range over which maximum torque is supplied by the engine is an important consideration. If the maximum torque range is established in a very low rpm range, starting the truck from a stop may be easy. But, when the engine rpm is raised beyond this range, power will decrease; in order to maintain power, a rapid shift-up of gears will be necessary. However, if on the other hand,the maximum torque is established too high in the rpm range, a small drop in rpm would require a shift down of the gears to avoid knocking of the engine.
From the foregoing, it is evident that in addition to high torque, the shape of the torque curve, and the range of the engine rpm at which effective high torque is obtained are also very important. |
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