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).
Crankshaft balancing, crankchamber stiffness, and engine vibration for 25HP and 45HP engines.
| Identifier | ExFiles\Box 103\2\ scan0225 | |
| Date | 20th December 1930 | |
| E.{Mr Elliott - Chief Engineer} BY.{R.W. Bailey - Chief Engineer}) FROM R.{Sir Henry Royce} HS.{Lord Ernest Hives - Chair} } (At Le CanadelHenry Royce's French residence.) X('000 R2/1120.20.12.30. X.7000 X.634 X.5000 X.7010 X.5010 C. to SG.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} C. to RG.{Mr Rowledge} DA.{Bernard Day - Chassis Design} 25HP. AND 45HP. ENGINES. We have now settled that we must not use cast iron crank- chambers unless we do not care about weight and are going in for the cheapest job possible regardless of impressions. Our improved practice is to use the 4 weight balancing system which requires less than .7 of the total balancing weight and should not bring down the master period quite so much, though this may not be in proportion. If the torsional period is too low we must go on increasing the stiffness until it is higher than our useful speed range. It would seem that perhaps we need not go much above the speed of maximum HP. with open cutout because we ought soon to have the double top which permits of a higher top gear. The balanced crankshaft will save the main bearing and hence probably the life of the engine between repairs. Although the crankchamber is less stressed with the balanced crank we have decided to stiffen it by the system of box flange along the bottom as well as the increased depth, the reason being that we cannot completely balance the crank and big end, and it has lately been demonstrated that some of the vibrations causing booming come from the crankchamber deflection, which must be reduced. It will be realised that we have been increasing the diameter of the crankshaft, and especially the pins and big ends, to get greater stiffness, especially torsional, but we have increased the force of the couples and the load on the main bearing, and hence the deflection of the crankchamber, but we hope that it has just made possible the balancing of the crankshaft when stripped of con. rods and pistons. We do not expect to go further than this. It is probable that we shall have to fit 8 balance weights, but we should like to do the work with 4 - i.e. 2 in centre and 1 at each end. Prepare the shaft for 8., provide 8 for complete balance of shaft and big ends, 8 for shaft only, and we should expect the engine would prove to be best with 8 smaller ones or 4 of the larger ones. This seems to be the way of getting less high speed booms. Naturally it will not be expected to affect slow speed torque reactions or over-run vibrations; we shall reduce the former by the diamond suspension, and the latter by the increased proportions of the con. rod. (1) | ||