Page 36 - Automotive Engineering Powertrain Chassis System and Vehicle Body

CH AP TER 2 .1 Measurement of torque, power, speed and fuel consumption

100% 100%
b c
b
c
Torque a d Power a d

e e

0 Speed 100% 0 Speed 100%

Fig. 2.1-13 Engine torque curves plotted on hydraulic dynamometer torque curves.
Minimum torque corresponding to minimum Fig. 2.1-15 shows the performance curves for an eddy-
permitted water flow. current machine, which lie between those of the previous
Fig. 2.1-14 shows the considerably different perfor- two machines:
mance envelope of an electrical machine, made up of the Low speed torque corresponding to maximum
following elements: permitted excitation.
Constant torque corresponding to maximum current Performance limited by maximum permitted shaft
and excitation. torque.
Performance limited by maximum permitted power Performance limited by maximum permitted power,
output of machine. which is a function of cooling water throughput and
Maximum permitted speed. its maximum permitted temperature rise.
Since these are ‘four-quadrant’ machines, power Maximum permitted speed.
absorbed can be reduced to zero and there is no mini- Minimum torque corresponding to residual magneti-
mum torque curve. zation, windage and friction.

100% a 100% b

b
a
Torque Power c

c

0 Speed 100% 0 Speed 100%

Fig. 2.1-14 Performance curve shapes of electrical motor-based dynamometers.

100% b 100% c

c
b d
Torque a Power

d

e a e

0 Speed 100% 0 Speed 100%
Fig. 2.1-15 Performance curve shapes of an eddy-current dynamometer.

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