from the driving shaft to the driven shaft through
thrust collar; therefore, eight separate wedge-
the dental clutch. This engagement sequence is
shaped oil films are formed on each thrust face.
controlled by the control air system (COAS).
Since the bearing shoes are free to tilt slightly, the
Figure 8-6 shows the brake/clutch assembly.
oil automatically assumes the taper required by
shaft speed, loading, and oil viscosity. One thrust
Control Air System
shoe on each side is fitted with an RTE.
Thrust is transmitted from the rotating thrust
Each brake/clutch assembly has one COAS
collar to either (depending on ahead or astern
unit mounted on each side of the MRG on the
propeller pitch) of the two stationary eight-shoe
base flange below the lower second-reduction
thrust rings. The rotating thrust collar is an
pinion. Each COAS unit contains all of the
integral part of the second-reduction (bull) gear.
pneumatic and electronic components required for
Besides transmitting propeller thrust to the
automatic control and monitoring of the
ship's hull, the main thrust bearing also positions
brake/clutch assembly. Input requirements are
the other elements in the gear train. Since double
28-volt dc power from the propulsion local
helical gear teeth inherently trail together in mesh,
control console (PLCC) and 95 psig minimum
the limited axial clearance permits the main thrust
control air pressure from the ship's service air
bearing to locate all rotating elements in the
system (SSAS).
casing space. This arrangement allows elimination
The control components for each COAS unit
of thrust bearings on the HS rotors with attendant
have three solenoid air valve assemblies, two
reduction of maintenance and power loss. In
printed-circuit boards (PCBs) that control the
operation, the LS gear is positioned by the main
operation of the valves, and two air-pressure
thrust bearing directly. The LS gear positions the
regulators. The primary regulator is set at 100 psig
four LS pinions through the gear mesh. The gear-
to provide pressure for brake and clutch
type couplings on the lower intermediate
operation. The other regulator is set at 20 psig
assemblies are designed to position the lower HS
to provide a soft initial actuation of the brake.
gears through the quill shaft. The lower HS gears
The input parameters to the speed differential
position the HS pinions and upper HS gears
relay PCB are the input shaft and first-reduction
through the gear mesh.
pinion speed signals from magnetic speed pickups
on the clutch housing. The speed differential relay
BRAKE/CLUTCH ASSEMBLY
controls the clutch engagement sequence. It
(DD AND DDG-993 CLASS SHIPS)
inhibits friction clutch engagement if the clutch
input and output shaft speed differential is greater
Presently, two identical brake/clutch assem-
than 1,500 rpm and inhibits the dental clutch
blies are mounted on each MRG assembly, one
engagement if the speed differential is greater than
for each HS input shaft. These units will
11 rpm.
eventually be replaced by the SSS clutch used on
Both brake and clutch operation is inhibited
the FFG and CG, and DDG-51 class ships. The brake and clutch
(can be overridden by key switches in CCS) if the
in each assembly provide independent functions.
oil inlet temperature is greater than 130F and oil
The brake is a pneumatically operated,
inlet pressure is less than 14 psig. If control air
multiple-disc type of brake. When applied, it locks
pressure is less than 95 psig, brake and clutch
the input shaft to prevent rotation of the GTE's
operation is inhibited and cannot be overridden
power turbine rotor (turbine braking). The brakes
by the CCS. Brake and clutch status is indicated
may also be used to stop and prevent rotation of
at the PACC and PLCC. A clutch cycle counter
the propeller shaft. This can be accomplished only
is also mounted in the COAS enclosure.
when both brakes are applied and both clutches
are engaged. This process is called shaft braking
Clutch Sequencing
and is controlled by the ECSS.
Magnetic speed pickups are mounted in the
The clutch is a pneumatically operated, oil-
clutch housing and located directly over the teeth
cooled, forced-synchronization, combination
in the outside diameter of the sleeve gear and
friction and dental type of clutch. The multiple-
clutch cup. They produce electrical impulses
disc friction element is used to bring the input
proportional to the speed of the respective shafts.
shaft speed to within 11 rpm of the first-reduction
These signals are inputs to the electronics
pinion. The dental clutch then mechanically
enclosure in the COAS for automatic sequencing
couples the input shaft with the pinion. When the
of the clutch operation.
dental clutch is engaged, all torque is transmitted
8-8
