From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Detailed explanation of the carburetion, oiling, and cooling systems of the Liberty Twelve engine, including ignition and oil pump diagrams.
| Identifier | ExFiles\Box 37\2\ scan 084 | |
| Date | 5th February 1919 | |
| FEBRUARY 5, 1919 Aeronautical Engineering (Supplement to THE AEROPLANE) 599 CARBURETION. Two Zenith duplex carburetters are used on the Liberty Twelve. This is equivalent to four single carburetters, each one supplying three cylinders of the engine. Each duplex carburetter consists of a single float chamber and a single air inlet joined to two separate and distinct spray nozzles, venturi and idling devices. As the V-type engine is, in a sense, two separate engines joined together for greater utility, so the Zenith is built in double form for the purpose of supplying each one of these two engines with its exact requirements. Each of the two barrels of each carburetter is fitted with a throttle valve of the butterfly type. The shafts of the throttles are parallel with the centre line of the engine, and are interconnected by means of gear sectors pinned to the throttle shafts and meshing together. The two pairs of throttles are operated simultaneously by a shaft, provided with an adjustment at each end by means of which the pairs may be synchronised. Each duplex carburetter is fitted with an “altitude adjustment” which affects both barrels equally. OILING SYSTEM. Oil supply is carried in a reservoir provided with a suitable means for cooling it. Oil is led from this reservoir to the connection on the right side of the oil pump body marked “Oil In.” It is filtered at this point through a large area fine mesh screen. A delivery pump of the geared type takes the oil up after it has passed through the screen and delivers it under considerable pressure to a distributor pipe running the entire length of the crankcase. Opening out of the passage between the pump and the distributor pipe is a pressure regulating valve designed to maintain a pressure not to exceed 50 pounds per square inch on the oiling system. Pipes are fitted in the case leading from the distributor pipe to the main crankshaft bushings. The crankshaft is hollow and in the centre of each main bearing a radial hole is drilled through the shaft into the hollow centre. This hole in the shaft registers with the corresponding hole in the bearing bushing once every revolution of the shaft, at which time a small quantity of oil is forced through into the hollow crankshaft. A passage leads from each hollow main bearing to the adjacent crank pin, which is also hollow. A radial hole is also drilled through each crank pin and carries the oil out on the surface of the pin. Oil grooves and passages in the connecting rod bushings ensure proper lubrication for both the forked and plain connecting rods. The excess oil thrown off the rapidly moving connecting rod ends forms a mist which lubricates the piston pins and the cylinder walls. Part of the oil conducted to the main crankshaft bearing at the propeller end of the engine goes through a passage around this bearing and up through the pipes to the propeller end of the camshaft housings. From the end of the camshaft housings it is led around the end camshaft bearing to a passage drilled diametrically through the bearing midway of its length. Once every revolution of the camshaft a hole drilled through the camshaft into its hollow centre registers with the oil passage through the bearing. Thus once every revolution a small quantity of oil is forced into the hollow camshaft. The oil is led through drilled in it to each camshaft bearing. The excess works out of the ends of these bearings and collects in small reservoirs to a depth of about ¼ in. The cams in revolving, dip into this oil and splash it over the cam roller and into pockets in the rocker lever shafts. From these pockets it is led through the hollow rocker shafts to the rocker shaft bearings. The excess oil eventually finds its way to the gear end of the camshaft housings, over the gears and down the drive shaft housing into a chamber just above the oil pump. The excess oil thrown off in the crankcase by the connecting rods collects in this same chamber when the engine is inclined so that the propeller end is high. If the propeller end of the engine is low, this oil collects in a small sump or chamber at the propeller end of the crankcase. Immediately above the oil delivery pump is located on oil return pump consisting of three gears, and driven by the same shaft as the delivery pump. The function of this oil return pump is to halves of the pump deliver oil to the connection on the left side from the sump at the distributor end of the crankcase. Both draw the excess oil out of the crankcase and return it to the oil reservoir. One-half of this pump draws oil from the sump at the propeller end of the crankcase and the other half draws oil of the oil pump body marked “Oil Out,” from which point it returns to the oil reservoir. COOLING SYSTEM. Cooling water is circulated through the Liberty engine by means of a centrifugal pump running at one and one-half times engine speed. The capacity of this pump is 100 gallons per minute at 1,700 r.p.m. The cooling system from the pump inlet to and including the water outlet header will hold 5½ gallons of water. The water pump is provided with a single inlet, the outside diameter of which is 2 ins., and two outlets, each one delivering water to a header supplying the right and left hand cylinders respectively. Water is forced into each cylinder jacket tangent to its outside surface. This construction gives the water a whirling motion inside the jacket and ensures uniform cooling. The water outlet pipe for each cylinder extends inside the jacket to a point very close to the exhaust valve chamber, which guarantees the proper cooling of the exhaust valve. The cooling water then goes through a passage cored in the intake headers. This serves to warm and further vaporise the incoming gas as well as assist in cooling the water. These passages in the intake headers are connected by two water outlet headers, the final outlet of which has an outside diameter of two inches. (To be continued.) [Diagram Labels - Ignition Connections of the Liberty Engine] Ignition Connections of the Liberty Engine. CYLINDERS-LEFT: 6L&1R-D, 5L&2R-D, 4L&3R-D, 3L&4R-D, 2L&5R-D, 1L&6R-D PROPELLER END, DISTRIBUTOR END, DIST. & BAT. DIST. CYLINDERS-RIGHT: 6R&1L-D, 5R&2L-D, 4R&3L-D, 3R&4L-D, 2R&5L-D, 1R&6L-D MAG. & BAT. DIST., BATTERY DISTRIBUTOR, MAGNETO DISTRIBUTOR TO SPARK PLUGS ON EXHAUST SIDE OF CYLINDERS, TO SPARK PLUGS ON INTAKE SIDE OF CYLINDERS IGNITION SWITCH BRIDGE-S, IGNITION SWITCH BRIDGE-M BATTERY, T, M, B IGNITION RELAY, VOLTAGE REGULATOR, AMMETER GENERATOR, GENERATOR FIELD, FIELD RESISTANCE DELCO IGNITION SYSTEM: CONTACT POINTS 'Y' MAKE & BREAK SIMULTANEOUSLY, CONTACT POINTS 'X' MAKE & BREAK SIMULTANEOUSLY, BREAKER CAMS, DELCO [Diagram Labels - Oil Pump Assembly] OIL PUMP ASSEMBLY SECTION A-A, SECTION B-B, SECTION C-C OIL IN, OIL OUT | ||