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).
Causes and potential solutions for engine vibrations and 'booming' in 25HP and 45HP car bodies.
| Identifier | ExFiles\Box 5\2\ 02-page357 | |
| Date | 26th December 1930 | |
| HS.{Lord Ernest Hives - Chair} E.{Mr Elliott - Chief Engineer} } FROM R.{Sir Henry Royce} BY.{R.W. Bailey - Chief Engineer} } (At Le CanadelHenry Royce's French residence.) X5830 RL/M26.12.30. C. to SG.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} CAR WORK - BOOMS IN BODIES. X.7830. C. to PN.{Mr Northey} DA{Bernard Day - Chassis Design}/EV.{Ivan Evernden - coachwork} 25HP. & 45HP. X.5830. X.634. We now better understand and agree that most of the above come from engine vibrations, some of which can be reduced: (1) By the engine mounting known as the 'diamond', at once available on the 25HP., and we must press forward a design for the 45HP. P. 2. (2) I believe that most of the flywheel vibration comes from crankchamber deflections, and we ought at once to fit such balance weights as the master period permits, even if they only half balance the bare crankshaft couples; these would be only one each at on the two middle, and one each on the end crank webs. (Although I agree we gain with smaller radius, and suggested it originally to E.{Mr Elliott - Chief Engineer}, I am afraid we cannot get much from it because of the disadvantage of the extra weight.) (3) We can at once slightly lighten the flywheel by reducing the most overhanging weight, because the inertia of the balance weights will enable us to run equally well with less inertia in the flywheel. This has been done on the 25HP. (4) We can at a very early date strengthen the existing crank-chambers which will reduce the deflection by something though I fear it will not show up very definitely, but I should press this forward. (5) The crankpins of the 45HP. are now smaller than we think best proportion to the journals. I should like to see the journals 2.750 and the pins 2.50 as soon as ever possible, with (2). It will be realised that contrary to expectations based on torsional rigidity that the lighter crankshafts seem better unless balance weights are fitted, but with these heavier cranks and big ends are possible without throwing too much load on main bearings, and stresses and deflection in the crankchamber. (Bentley's seem to get away with a light shaft, probably luckily, and may be now running into greater trouble by stiffening up both engine and chassis parts.) Still, we can never hope to avoid a really booming body, booming from some cause or another, and DA{Bernard Day - Chassis Design}/EV.{Ivan Evernden - coachwork} must strive to learn the law which makes bad ones. I am certainly of the opinion that parts with low periods will be found best - i.e. everything possible - roof, floor, etc. - should have low periodicity, and be well damped. It is wrong to attempt stiffening. R.{Sir Henry Royce} | ||