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 cures for vehicle vibrations and body booms.
| Identifier | WestWitteringFiles\V\March1931-September1931\ Scan048 | |
| Date | 14th March 1931 | |
| ORIGINAL cc. FROM R.{Sir Henry Royce} (At Le CanadelHenry Royce's French residence.) C. to MOR. & FW. C. to EH. HS.{Lord Ernest Hives - Chair} DA.{Bernard Day - Chassis Design} re. P. 2. & BODY BOOMS. R1/M14.3.31. x634 x7830 (1) Mr. Hives memo. re. booms just to hand. He evidently had satisfied himself some time ago that the flywheel had nothing to do with the particular vibrations of which you and our customers complain. These refer to something at much slower speeds - i.e. near 2000 (50 MPH.) rather than near 3000 (70 MPH.) engine revs. (2) For this particular trouble (which is not noticeable on 18-EX) the power unit does not seem to be defective. (3) To have cleared away the flywheel whirl makes progress easier. (4) The diamond mounting being a cure suggests quite clearly that the vibrations are torsional and not lateral, as the flywheel would be. (5) It is reported to be a period over a fair range, but above that becomes quieter, (before one arrives at my 65/75 vibration which is probably the flywheel.) (6) If the period was the engine crankshaft it would have altered its speed with some of the things HS.{Lord Ernest Hives - Chair} has done (7) We know for certain that we have a source of vibrations at all high speeds due to the pistons weight. This source is unavoidable and must be almost exactly the same in our engine as in Bentley and Hispano. In itself it has no period but increases in vigour with speed, best known as over-run vibrations. This is the source. (8) If however as stated the fault is at one particular speed (periodic) then we have some hope that something in addition to softer mounting can be done. (9) My own impression is that the period is due to the unavoidable elasticity of the frame side members. There is very little doubt that the frame determines the speed of the impulse period (known as torque reaction). A frame with less vertical rigidity would lower this period and also the one complained of, and might be a partial cure, so I wired HS.{Lord Ernest Hives - Chair} to remove tie-bars and add weights firmly attached to side members just behind the dash. (10) Now if we can prevent these reacting on the frame they would do no harm as far as the trouble we have in mind is concerned. P. l.had rubber rear feet and my old torque dampers which were fairly effective, but were discarded for these sandwich feet because better for steering etc, but they evidently are not good enough insulators. Derby would never use thick and soft enough rubber or they might be much better. (11) Bentley certainly had a bad frame in the 6 litre. It was reported to be torsionally - and I thought vertically - weak, and we thought at the time if we were satisfied with such a frame and steering (1) | ||