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).
Engine vibrations, body booms, frame stiffness, and engine mounting.
| Identifier | WestWitteringFiles\V\March1931-September1931\ Scan100 | |
| Date | 1st April 1931 | |
| HS.{Lord Ernest Hives - Chair} E.{Mr Elliott - Chief Engineer}) FROM R.{Sir Henry Royce} DA.{Bernard Day - Chassis Design} ) (At Le CanadelHenry Royce's French residence.) C. to SG.{Arthur F. Sidgreaves - MD} LHS.{Lord Herbert Scott} WOR.{Arthur Wormald - General Works Manager} C. to PN.{Mr Northey} C. CX.{Major Len W. Cox - Advertising Manager} EP.{G. Eric Platford - Chief Quality Engineer} ORIGINAL P. 2. BODY BOOMS. R1/M8. 4. 31. x634 x7830 xpos It is now agreed that as regards body booms there is nothing we can do to the power unit that will make any difference, and the improvement must be looked for in the engine mounting, the construction of the body, and its mounting on the frame. We do however get some distinct increase in smoothness of the engine at very high speeds by stiffening up and other modifications to the flywheel. Therefore the vibrations which are our real anxiety come from torque reactions and over-running vibrations. These can only be reduced very little indeed in the power unit and are natural to all engines of this type. As pointed out in a previous memo. we are still in difficulties because if we mount the engine so that these vibrations do not reach the frame so accutely we cannot take advantage of the engine to stiffen the frame against torsion. If the side members are stiff enough we can do something, such as the cross behind the gearbox, or we can trust to the body to help us. Now the steel body may do this (as is the practice in the latest railway carriages,) but I think it is asking too much from the ordinary coachbuilt body, as we found in the French 10,000 miles test (previous to the underframe construction) it completely destroyed a body in one trial at high speed on the rough roads of France. You will remember that we spent much thought on the cross in the frame which should have been good especially with strong side members, and perhaps some increase in stiffness forward, and I think this should be re-tested because except that we may run into some unfortunate period which we can never foretell it ought to be good, but there is one other reason why the body may be better than the cross - i.e. the former is damped in its stiffness and our cross is undamped. I do not however believe that anything can approach the efficiency of the engine for stiffening the frame and we ought to see that in future work we can arrange to use the engine with a similar mounting to the present P. 2. which although it is hardly sufficiently good for a big six or even the 25HP., might make an excellent combination with an engine of greater natural smoothness. Bentley is now, I firmly believe, trusting to the body to help the stiffness and using our old 3 point mounting (P. 1. scheme.) I have for some time thought that without the assistance of the engine we are somewhat at a disadvantage with P. 2. because we have a combined gearbox which prevents our fitting a substantial cross member between engine and gearbox - i.e. we have a larger bay for the engine. I have for a long time thought that the engine feet near the dash are very likely to transmit vibrations to the dashboard and decided that the torque arms forward would be better. This was at the time we schemed torque reaction dampers as a temporary improvement to P. 1. and 20HP. (11) | ||