Compound Wound Motor

Windshield wiper operation is controlled by a dash or steering column mounted switch. The wiper feed circuit is protected by a fuse which is located in the fuse block on most models, or in an Inline fuse holder on some models with pulse wipers. A circuit breaker, integral with the motor brush holder, protects the motor against overload. Pulse wipers, available on most models, use a variable resistor, a pulse control module, and/or a modified wiper motor to provide a delay wipe mode.

Fig. 1 Compound Wound Rectangular Windshield Wiper Motor. Shown W/washer Pump Installed:

Fig. 2 Windshield Wiper Motor Electrical Connections. Compound Wound Rectangular Motor:

RECTANGULAR MOTOR

The rectangular motor, Fig. 1, consists of an armature, brush plate assembly, field coils and a housing which is attached to a gear housing. The motor electrical connections, park switch, and on some models a washer pump are also mounted on the gearbox. A gear on the commutator end of the armature drives an intermediate gear and pinion assembly, which in turn drives the output shaft. A crank arm on the output shaft operates wipers through a pivot link (transmission) assembly.
When ignition is on, battery voltage is supplied to motor terminal 2, Fig. 2. Current flows through the series field to a splice where it is divided, and part passes through the armature and part through the shunt field. The armature and shunt field circuits are completed to ground through the wiper switch, with motor speeds determined by resistance in the shunt field ground path.

Standard (Non-Pulse) Wiper Operation

Placing wiper switch in low position grounds motor terminals 1 and 3, Fig. 2, at the wiper switch. Shunt field current flows directly to ground through terminal 3, armature current flows to ground through terminal 1 and the motor runs at low speed. Placing wiper switch in high position grounds terminal 1, but terminal 3 remains open. Armature current flows directly to ground through terminal 1, shunt field current flows to ground through a resistor connected between terminals 1 and 3, and the motor runs at high speed due to the weakened shunt field.
When wiper switch is turned off, and wipers are not in park position, terminal 1 is grounded through the closed motor park switch contacts. Terminals 1 and 3 are connected through the wiper switch, and the motor runs at low speed. When wipers reach their lowest point of travel, a cam on the motor output shaft opens the park switch, and the motor stops.

Pulse Wiper Operation

On models with pulse wipers, a pulse control module provides a delay wipe mode through the low speed circuit. When wiper control is in delay position, battery voltage is supplied to a capacitor in the module through a variable resistor. When the capacitor is fully charged, it activates a switching circuit which provides a ground to begin wiper operation. As the motor operates, park switch contacts close, the capacitor discharges, and the motor ground is maintained through the park switch. When wipers complete their cycle, the park switch opens and the capacitor begins to recharge. Delay between wipe cycles is determined by a variable resistor, which controls charging current to the capacitor. Higher resistance produces a longer delay.

Fig. 3 Compound Wound Round Windshield Wiper Motor:

Fig. 4 Compound Wound Round Windshield Wiper Motor W/modified Pulse System:

Fig. 5 Compound Wound Round Windshield Wiper Motor W/multiplex Pulse System:

ROUND MOTOR

The 4 or 4 1/2 inch long, round motor assembly consists of an armature, field coil and end cap assembly, and a brush plate which fits over the armature and is connected to the field coils. The motor assembly is attached to a gearbox housing which also provides a mount for the washer pump. A worm gear on the armature commutator end drives the output shaft at a 90° angle through a drive gear and pawl assembly.
The gearbox assembly contains a magnet switch, relay and terminal board assembly (gearbox relay) which provides electrical connections and controls current flow through the motor. On standard (non-pulse) motors, Fig. 3, the two motor leads to the gearbox relay are concealed and routed through a cavity in the gear housing. On pulse type motors, Figs. 4 and 5, the two motor leads to the gearbox relay, and the feed wire to the pulse relay are exposed. Both standard and pulse motors used on Corvette have an additional ground lead to ground the motor housing to the wiper switch.

Standard (Non-Pulse) Wiper Operation

When ignition is on, battery voltage is supplied to gearbox relay terminal 2, Fig. 3. When terminal 1 is grounded, relay contacts close and current is supplied to the motor. Current flows through the series field to a splice where it is divided, and part passes through the armature to the motor housing ground, and part through the shunt field. Motor speeds are determined by the amount of current flowing through the shunt field.
Placing wiper switch in low position grounds gearbox relay terminals 1 and 3. The relay contacts close, shunt field current flows directly to ground at the switch through terminal 3, and the motor runs at low speed. Placing wiper switch in high, or medium position on Cadillac, grounds relay terminal 1, but terminal 3 remains open. Shunt field current flows to ground through a 20 ohm resistor connected between terminals 1 and 3, and the motor runs at a higher speed due to the weakened shunt field. Medium speed on Cadillac models results from a 13 ohm resistor in the wiper switch, wired parallel with the gearbox relay resistor, which produces approximately 8 ohms resistance in the shunt field circuit.

Fig. 6 Gearbox Relay And Drive Gear Assembly, Shown Out Of Park Position. Compound Wound Round Windshield Wiper Motor:

Fig. 7 Gearbox Relay And Drive Gear Assembly, Shown In Park Position. Compound Wound Round Windshield Wiper Motor:

Placing wiper switch in off position opens the circuit to the gearbox relay magnet switch. This allows a spring loaded arm to move into the path of the output gear drive pawl, Fig. 6, while relay contacts remain closed. The shunt field is grounded through the wiper switch and the motor operates at low speed, allowing the gear mechanism to park the wipers and stop the motor.
As the output gear rotates, the drive pawl engages the latch arm on the gearbox relay, and the output gear is unlocked from the drive pawl, lock pawl and driveplate. Since the output shaft and gear shaft are off center, continuing rotation causes a cam action which moves the drive pawl into a slot in the gearbox relay and allows wipers to move below their lowest point of normal travel. The drive pawl pushes the latch arm against the gearbox relay contacts, opening the contacts and stopping the motor in park position, Fig. 7.

Multiplex Pulse Wiper Operation

Models with pulse wiper use a motor similar to the one used on standard systems, but with modifications to provide a delay wipe mode. The multiplex system, while similar to earlier pulse wipe systems, uses an integrated circuit timer and the voltage feed to the wiper switch has been eliminated. In addition to standard wiper system components, the multiplex system uses a variable resistor in the wiper switch, a pulse relay and holding switch mounted in the washer pump, and a timer circuit. The timer, consisting of a capacitor and integrated circuit, is mounted on a circuit board in the washer pump or contained in a separate module.
The gearbox relay functions in a similar manner on both standard and multiplex systems. However, on pulse systems the gearbox relay supplies voltage to the pulse relay, current to the motor windings is controlled by the pulse relay, and voltage is supplied to the timer circuit from motor terminal 2. In all switch positions except delay, the gearbox relay, pulse relay and timer capacitor circuits are completed directly to ground through the wiper switch. This deactivates the timer circuit and allows the motor to operate as outlined in Standard (Non-Pulse) Wiper Operation.
Placing wiper switch in delay position grounds gearbox relay terminals 1 (relay) and 3 (shunt field), and the timer capacitor is partially grounded through the variable resistor, allowing it to charge at a controlled rate. When the timer capacitor is fully charged it activates the integrated circuit. The integrated circuit completes the pulse relay ground circuit, and current flows through the motor windings.

Fig. 8 Pulse Wiper System Holding Switch. Compound Wound Round Windshield Wiper Motor:

As the motor begins to operate, holding switch contacts close, the capacitor discharges partially, and the pulse relay ground is maintained by the holding switch. As wipers complete their cycle, a fin on the washer pump drive cam opens the holding switch, Fig. 8, wipers stop and the timer capacitor begins to recharge. This cycle repeats as long as wiper switch is in delay position. Delay between wipes is determined by varying resistance between the timer capacitor and ground.