Automobile door window lift motor control system - has obstruction detector circuit comparing motor load current with set proportion of most recent starting current

摘要

The system is for controlling an electric motor (1) whose load current produces a voltage (V) across a shunt. This is first amplified (12), then passed directly to a comparator (13,14). The amplifier output (S1) also reaches the comparator through an attenuator (15) with a reduction factor (K) of e.g. 0.75, and a memory unit (16), reset (21) at each motor start. The latter provides a constant output (S2) equal to K x the maximum amplified signal (S1), representing thus (18a) KIM, IM (19) being effectively the motor starting current. If during lifting (17a) the window jams or is obstructed, current rises sharply (17c). When it exceeds the stored value (KIM,20), the comparator output signal, time delayed, stops the motor (36). An end-of-travel switch and a detector on a slightly different principle are also provided. ADVANTAGE - Cyclically resetting comparison signal allows for variable mechanical load due to frost, etc.