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Aviation History
1944
1944 - 0609.PDF
MARCH 23RD, 1944 FLIGHT NAPIER SABRE I is sealed by a single taper-type pressure ring in the cylinder head. The drive for the 12 sleeve valves of each cylinder block is by a divided hollow shaft driven at crankshaft speed through an idler gear from the rear pinion of the upper airscrew reduction gears. Each half-shaft runs in bear ings bolted to the face of the cylinder block and has three integral worm gears for driving the sleeve cranks. A splined coupling joins the half-shafts at the centre. Sleeve cranks, arranged at 18c deg. and fitted with a bronze worm wheel to mesh with a drive-shaft worm, are mounted in roller bearings in pedestals which also form the caps for the drive-shaft bearings. The worm wheel has 22 teeth and is bolted to a vernier flange on the crank, which, in combination, furnish an adjustment of 1.48 deg. from the assembly datum for the timing of the sleeves. Each of these cranks actuates the sleeves of a vertical pair of cylinders. As will be seen from one of the illustra tions, the sleeve-drive gear remains intact when a cylinder block is removed from the crankcase. Actually, sleeve ^phasing and timing can be made on the bench and final adjustment for the twelve cylinders effected in the mesh ing of the drive shaft pinion with the idler wheel trans mitting the drive from the main reduction gears. Sleeve travel is somewhat longer than in common practice and, in fact, is almost equal to the piston stroke. Torsion Shaft Blower Drive Arranged within the hollow sleeve-drive shafts are the torsion shafts for the two-speed supercharger drive. At its forward end each torsion shaft is splined to the drive shaft; to the rear end is splined and bolted the first pinion for the supercharger drive. The shaft is freely sup ported in a bearing at the rear end and also by a steady- bearing in the splined coupling muff joining the sleeve drive half shafts. From the two torsion-shaft pinions the drive is trans mitted to co-axial medium- and high-speed gear shafts of the double-entry centrifugal blower. Each shaft ter minates in a cone, the two being spaced to accommodate centrally a floating double-conical member, slidably splined at its periphery to engage the driving drum of the blower impeller. Selective engagement of the two cones is effected hydraulically as shown in the sectional diagrams. micr 3*3 CLUTCH In the supercharger, medium- and high-gear ;shafts are both^^Sd^™ by the two torsion rods. Selective engagement is effected by a fluid-actuated conical clutch, as indicated. This view shows the lour compound reduction gears driven from the two crankshafts, the central rear bearing of the airscrew shaft, and the two pinions of the sleeve 4 drive shafts. Mixture is supplied by a special four-choke S.U. car burettor. Two chokes feed the block of 12 cylinders on each side of the engine. The instrument follows usual S.U. practice, embodying oil-warmed throttle valves and automatic altitude and mixture enrichment controls. An automatic boost control unit is a separate component mounted on the supercharger casing. From the volute collecting chamber of the supercharger the mixture passes through four tangential outlets to cast light-alloy manifolds, each serving a bank of six cylinders. Exhaust ports are arranged between the upper and lower banks of cylinders and each ver tical pair is fitted with an individual ejector-type nozzle. These damp the exhaust flames and the efflux has a propulsive effect which improves the performance of the aircraft in which the engine is installed. Considerable interest attaches to the airscrew-shaft reduction gear at the forward end of the unit. The rear bearing of the airscrew shaft, an un divided steel shell lined with lead bronze, is housed in the crankcase wall. This bearing receives two feeds from the general lubricating system and two separate feeds to the centre and the annulus of the shaft for the supply of pressure fluid for the pitch control of the Hydromatic airscrew. The four compound reduction gears arc- mounted in roller bearings in steel housings in the front wall of the crank case and a steel carrier plate. The upper and lower crankriiafts
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