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A

737-300/400/500
MAINTENANCE MANUAL

LOAD SENSING SOLENOID
SPRING
CABLE
TERMINAL

RETURN
SPRING

YOKE MOTORENERGIZING PIN
RETURN SPRING
BELLCRANK
RING GEAR LOAD SENSING SPRING
INPUT PLANETARY GEAR ASSEMBLY
OUTPUT SHAFT
CABLE ASSEMBLY
RING GEAR OUTPUT PLANETARY GEAR ASSEMBLY
Alternate Flap Electric Drive Unit Figure 11
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A 737-300/400/500MAINTENANCE MANUAL
S1 ALT FLAP MASTER ARM
FLAP

SWITCH

SWITCH S816 WFA FLAP(REF 27-58-01)
CONTROL CABLE TENSION SWITCH
Trailing Edge Flap Electric Asymmetry System Circuit
Figure 12

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T81266
A 737-300/400/500MAINTENANCE MANUAL

Flap Load Limiter System Circuit
Figure 13

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A 737-300/400/500MAINTENANCE MANUAL
SUPPORT

A
737-300/400/500MAINTENANCE MANUAL
 B.  The reduction gear train consists of a double planetary (epicyclic) gear (Fig. 11). The ring gear of the first planet system is fixed to the motor housing. The input planet system carrier gears rotate around an input sun gear cut on the motor drive shaft. The output sun gear is attached to the input planet system carrier gears. Rotation of the output sun gear drives the second planet system carrier gears attached to the output shaft. The output ring gear is a floating gear held fixed by a cable assembly during motor operation. The two terminals on the cable assembly are held by spring mechanisms consisting of a sensing spring, return spring, and a spring collar. A threaded collar is provided to adjust spring tension. Since the normal spring load on the cable is not sufficient to prevent rotation of the output ring gear, a mechanism is provided to accomplish this function. The mechanism consists of a yoke, energizing pin, bellcrank, and a solenoid. One arm of the bellcrank is attached to the solenoid and the energizing pin is inserted into a hole in the other arm of the bellcrank. The opposite end of the energizing pin is attached to the yoke. The ends of the yoke are attached to the cable terminals. The electric motor and solenoid are energized simultaneously from 115-volt rectified ac power. Energizing the solenoid places the cable under tension by mechanically increasing the distance between the yoke and the output ring gear. The increased cable tension locks the output ring gear, allowing the motor to drive the output shaft. If binding occurs in the gear train, an overload clutch prevents damage to the unit. The output ring gear will slip when the load exceeds 1200 pound-inches. This is accomplished through the load sensing spring which compresses to relieve tension in the cable. When the flap system is being driven hydraulically, a reduction gear in the power unit drives the output shaft. In this mode, neither the electric motor nor the solenoid is energized. With the solenoid de-energized, the cables are not under tension and the output ring gear is allowed to rotate with the carrier gears. This action prevents transmission of motion to the electric motor shaft.
 14. Limit Switches______________
 A.  Limit switches are used to open the circuit to the flap alternate drive unit at either extreme of flap travel. The limit switches are located on the forward side of the flap control unit (Fig. 1). The switches are actuated by cams mounted on the control valve follow-up mechanism drum shaft.
　
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