Engine | R-2800 Overhaul Manual
Auxiliary Supercharger Section
Auxiliary Supercharger Case: The auxiliary supercharger case attaches by studs, washers, and nuts to the rear of the supercharger inlet case (Fig 2-18). A mounting pad for the water regulator of the combat power system is provided on the left side of the case. The breather outlet is located at the top of the rear face of the case, and a scavenge oil line strainer is provided in the
right bottom side of the case. The bowl shaped center wall forms an annulus which collects the supercharged air from the auxiliary impeller and directs it to an outlet port on each side of the case. The auxiliary impeller diffuser is attached to studs on the front of the center wall of the case. Bosses in the rear face of the wall support the front ends of the pressure oil transfer shaft and bearings for the hydraulic coupling shafts. A web in the lower rear of the case supports the front bearings for the vacuum pump, high speed generator drive, and accessory intermediate drive gears as well as the shafts for the three high speed generator
drive pinions. A steel liner in the center of the main wall accommodates the four auxiliary impeller shaft rear oil seal rings.
Auxiliary Impeller Assembly: The auxiliary impeller assembly is housed between the supercharger inlet and auxiliary supercharger cases. The auxiliary impeller shaft is of hollow steel with a bronze bearing pinned in the I.D. at each end. These bearings support the assembly on the accessory drive shaft. Splines for the auxiliary impeller, the auxiliary impeller drive gear, and lands for the four rear oil seal rings are
,machined on the O.D. of the shat. The auxiliary impeller drive gear is locked on the rear of the shaft, and the auxiliary impeller and locknut are installed on the front of the shaft. The auxiliary impeller locknut carries the five front oil seal rings of the auxiliary impeller.
Hydraulic Couplings: High and low ratio hydraulic couplings are mounted on each of two shafts which are supported on either side of the impeller shaft in the rear case and auxiliary supercharger cases (Fig 2-20). The two coupling shafts are driven by the accessory drive gear through a pinion which is splined on the rear of each shaft. The impellers of each coupling are splined to the shaft and the runners are splined to the respective coupling gears. Each coupling gear is free running on the coupling shaft and meshes with the auxiliary impeller shaft gear. When oil is directed into the high or low ratio couplings by the selector valve, power is transmitted through the oil from the impeller to the runner. The gear of the selected coupling accelerates as the coupling fills with oil, until it travels at the same rpm as the coupling shaft and drives the auxiliary impeller at the selected ratio. In shifting from the high ratio to the low ratio coupling, a circular sleeve valve located on the hydraulic coupling shaft between the low ratio runner and impeller, prevents the low ratio coupling from filling with oil until the auxiliary impeller has slowed to a point where the low ratio runner is traveling at a slightly lower rpm than the low ratio impeller. The low ratio coupling valve will rotate on the coupling shaft when the rpm of the low ratio impeller equals or exceeds the rpm of the low ratio runner.. The distance that the valve can rotate is controlled by a stop, and when the valve rotates on the shaft, the oil holes in the vale will line up with the oil holes in the shaft, allowing pressure oil from the shaft to enter the low ratio coupling. When the shift is made from low to high, the rpm of the low ratio runner will exceed that of the impeller which will cause the valve to rotate to the stop in the opposite direction. With the valve in this position, oil from the shaft will be blocked off and prevented from entering the low ratio coupling (Fig 2-20) (Fig 2-21 1of3) (Fig 2-21 2of3) (Fig 2-21 3of3).