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).
Discussion of engine lubrication and cooling system designs and their associated challenges.
| Identifier | ExFiles\Box 141\2\ scan0150 | |
| Date | 31th May 1936 guessed | |
| 6. Figure 19 illustrates an application of the angular bleed hole in the connecting rod designed to supply an additional quantity of oil to the cylinder walls, in addition to the leakage from the rod bearings, and particularly, when the engine first starts up with cold oil. Figure 20 illustrates a small reservoir groove employed in a radial aircraft engine master rod bearing designed to supplement the discharge from the crankpin during the interval between registration of the crankpin discharge with the highly loaded surface of the master rod bearing. It is expected that the transition from full fluid film to border line lubrication is delayed or prevented by the supply from the reservoir groove under critical load or supply conditions. Figure 21 illustrates a device used in the same engine, designed to remove foreign matter and sludge from the oil entering the master rod bearing. It is a tube extending from the center of the crankpin to the pin surface where the oil is discharged and at the moderate rotational speeds of regular operation with such engines is a very effective centrifuge. The generous reservoir in the crankpin hollow collects the material too heavy to discharge through the tube whence it can be removed at overhaul. Obviously, this device is not suited to the automobile engine with its normally infrequent overhaul. No matter how generous the reservoir for alien material, it might fill up before it would for other reasons be necessary to remove the crankshaft. Figure 22 shows an effective automobile engine oil cooling scheme which is reported to reduce the oil temperature 45°F.{Mr Friese} in its passage over the side walls and floor of the oil pan. Figure 23 illustrates a conventional type of aircraft engine oil cooler which is of the tube and header type, air occupying the tubes. Oil pressure through such coolers with cold oil is generally controlled by a by-pass line in or around the cooler. Methods of introducing oil to the journal represent a study in refinement of design which would fill a volume alone. The classic principle of introducing oil at the unloaded side of the bearing is generally employed. The degree of crank angle selected for the discharge, the angle of incidence at the surface of the oil film, flats or grooves in the crankpin, grooves in the bearings and number of discharge holes in the crankpin all tend to complicate the problem of the hydrodynamics of lubrication which cannot be attacked in this paper. Despite the effort, amounting almost to genius, lavished on lubrication system design to maintain full fluid film between friction surfaces, it is obvious that much boundary layer lubrication exists. Practically always for the upper piston rings, more of the time than is generally realized, for the crank assembly bearings, the lubricating film is thin enough to demand a better lubricant and the oil refiner must face his part of the problem squarely and supply oil adequate to separate friction surfaces with a partial film. | ||