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).
Analysis of crankshaft vibration and distortion, with a suggested new design for a 20 HP engine.
| Identifier | WestWitteringFiles\T\November1928\ Scan126 | |
| Date | 13th November 1928 guessed | |
| contd :- -11- the shaft, and thus affected by the presence or absence of the blocks. Owing to the nature of the vibration as observed we are inclined to put it down to distortion, as the sole remaining cause to our knowledge. We think that since the centre pair of weights are balanced by those at either end, they created a tendency towards 'hogging' and 'sagging', of the crankshaft in spite of the bearings, and that this was worst at [word struck through] one particular frequency. We think that although we observed little difference whether the blocks were fitted or not, perfect local balancing of each crank might have eliminated it, in the same way as a parallel shaft did. One thing very noticeable was that we only had to motor the engine over for 5 - 10 mins; (without pistons and rods) for the whole crankcase and cyl. block, together with a sumpful of oil, to become almost too hot to touch. SUGGESTED TYPE OF CRANKSHAFT FOR THE 20 HP. --------------------------------- We put forward a shaft shewn in fig.4. which we think should give very much smoother running up to nearly 4000 r.p.m. Particulars are :- (1) Balance of all rotating weight. i.e. big end, crank pin, and webs and hence : (2) Practically negligible main bearing loads at high r.p.m. giving prolonged life. (3) Torsional vibration period estimated at 4300 r.p.m. (Stiffness 62,100 lbs.ft/rad, inertia of shaft .0835 slugs.ft2. (4) 80% increased big end area. contd :- | ||