Page 73 - ATZ11 November 2019 Professional
P. 73
0.52
0.515
0.51 Avarage torque
lifting
0.505
Torque [Nm] 0.495
0.5
0.49
0.485
Bearing friction
0.48 Avarage torque
lowering
0.475
0.47
0 10 20 30 40 50 60
Time [s]
FIGURE 4 Torque curve of a calibration measurement (© UAS South Westphalia)
5 EFFICIENCY MEASUREMENTS hand, the system must not become so stiff even at low tempera-
tures that the window moves only very slowly or not at all. This
In the following, efficiency measurements on a gearbox of a car demonstrates the importance of efficiency and its influences for
window regulator drive are presented as examples. FIGURE 5 shows window regulator drive units.
the main components. The worm is conected directly to the As FIGURE 6 illustrates, efficiency is influenced not only by tem-
motor shaft and in combination with the wheel a ratio of i = 73 perature and lubricant but also by speed and torque. With the
results. Together with the gear efficiency of approximately 45 %, same lubrication condition and the same surrounding temperature
a typical stall torque of approximately 13 Nm could be provided (24 °C), the efficiencies increase with increasing torque and in -
to window regulator system. The operating point of the drive creasing speed from 30 to 47 %. These differences show that the
unit to lift the glass is approximately 3 Nm with an output speed specification of a gear efficiency is only meaningful if the operat-
of approximately 60 rpm. ing conditions are defined.
Further, the window regulator drive unit has to provide a self- The transmitted power increases the internal temperature. This
locking function. This is necessary to avoid unintended lowering leads to significant changes of the lubricant properties. So espe-
of the glass. To guarantee this, the efficiency of the worm gear has cially at the gearing and bearing points, the temperature should
to be less than 50 % for all operating conditions [5]. On the other be controlled. Therefore, the test system described before should
FIGURE 5 Main components of
a window regulator drive unit
(© UAS South Westphalia)
ATZ worldwide 11|2019 67
