(2)
When the transmission is in overdrive, the fixed hydraulic unit functions as a hydraulic motor. High pressure oil pumped from the variable unit forces the fixed unit pistons to slide down the inclined wobbler face causing the cylinder block to rotate. The rotation forces the input ring gear to turn in a direction opposite to the carrier shaft rotation and adds to the speed of the engine gearbox through the differential, maintaining constant output speed.
(3)
As the input speed increase and the need to add speed to the output decreases, the variable hydraulic unit pumps less oil to the fixed hydraulic unit until the cylinder block stops rotating. At this time the transmission is in straight through drive.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. CONSTANT SPEED DRIVES ú
24-11-00
ú CONFIG ú 01 Page 7 ú Nov 15/90
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
(4) When the transmission is in underdrive, the fixed hydraulic unit functions as a pump. The variable wobbler in the variable hydraulic unit is positioned so the variable unit can receive oil from the fixed hydraulic unit. The fixed hydraulic unit's pistons are forced into the cylinder block as they slide up the inclined wobbler face thus pumping high pressure oil to the variable hydraulic unit and allowing the cylinder block to rotate in the direction opposite to that of overdrive operation. The opposite rotation allows the input ring gear to turn in the same direction as the carrier shaft rotation and subtracts speed from the speed of the engine gearbox through the differential, maintaining constant output speed.
4. Governing System (Fig. 2)________________
A. The basic governor is a spring-biased, flyweight-operated hydraulic control valve. It controls porting of transmission charge oil to the control cylinder. The rotating sleeve in the governor is driven by the output gear and responds to transmission output speed. Flyweights pivoted on this sleeve move a valve stem within the sleeve against the bias of a spring. During steady state operation, supply pressure is reduced to the required control pressure by orificing action at the edges of the stem control groove. Depending on valve stem position, charge oil is ported to the control piston or control oil is drained to the transmission case.
B. The control cylinder is the actuator which responds to the porting functions of the governor. The affective area of the spring loaded side of the piston in the control cylinder is less than the opposite end. Therefore, the piston will compress the spring with equal pressure on both sides of the piston. When the governor allows the oil to drain from the control cylinder, the spring assisted by charge pressure on the small area of the piston allows the spring to relax. Small increments of such piston movement result in speed control within narrow limits.
5. Hydraulic System (Fig. 2)________________
A. The hydraulic system consists of the charge pump, the scavenge pump, and the charge relief valve.
B. The Charge Pump
(1)
The charge pump is in the hydraulic circuit between the all-attitude reservoir and the transmission. The charge pump supplies oil to the cylinder blocks, governor, control piston, and the lubricating system.
(2)
For the hydraulic unit to function properly and be properly lubricated, the charge pump must maintain above 200 psi at the stationary port plate. The pressure sensor downstream from the port plate signals the caution light on the overhead panel when oil pressure is below 100 to 150 psi. When the low pressure light comes on, the master caution light also comes on. Both lights should be off during normal operation.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. CONSTANT SPEED DRIVES ú
24-11-00
ú CONFIG ú 01 Page 8 ú Nov 15/90
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
C. The Scavenge Pump
(1)
The scavenge pump is in the hydraulic circuit between the transmission sump and the external oil cooler. The scavenge pump picks up lube oil and internal leakage and pumps it through the external oil cooler into the all-attitude reservoir.
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