Windshield Wiper Circuit

DESCRIPTION OF CIRCUIT

Windshield Wipers (Front Wiper) And Washer:

The circuit is designed so that when the wiper switch is turned OFF the wiper blades automatically return to their specified level rest positions. In figure, when the wiper switch is turned ON with the ignition switch ON, current is supplied continuously from the battery (via lead Y/BI - switch - lead BI or BI/R) to the motor, running the motor to move the blades.

The gear-and-linkage mechanism, which converts the rotary movement of the motor to the wiping movement of the blades, has a contact plate on the shaft of its output gear.

The plate serves to connect the contact P(0) to the contact P(1) Although the plate thus serves to make and break the circuits containing the contacts P(0), P(1) and P(2), the wiper motor makes its rotation completely independent of this plate rotation. When the wiper switch is turned OFF (the switch is set to the OFF position) with the blades positioned at the rest positions, current supply is cut, causing the motor to stop with the blades staying at the same positions.

Even when the wiper switch is turned OFF (the switch is set to the OFF position) with the blades positioned other than at the rest positions, current is still supplied, though intermittently, through a different path from the battery (via lead Y/BI - contact P(2) - contact P(0) - lead BI/W - switch (OFF position) - lead BI) to the motor.

Therefore, the motor can still rotate supplied with this intermittent current, causing the blades to return to the rest positions.
As soon as the blades have returned to their rest positions, the plate connects contact P(0) to contact P(1), causing current to be shunted around the motor.

When current is no longer supplied to the motor, a counter electromotive force is generated in the motor armature, causing a current to flow through the motor-and-shunt circuit so that the motor is stopped with the blades staying at the specified level rest positions.