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).
Investigation into the cause and potential fixes for a gear rattle on the 25 HP model.
| Identifier | ExFiles\Box 181\M13\M13.2\ img060 | |
| Date | 29th May 1931 | |
| ORIGINAL. To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Crys. c. to Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. to E.{Mr Elliott - Chief Engineer} Da.{Bernard Day - Chassis Design} c. to By.{R.W. Bailey - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Crys.1/MJ.29.5.31. x634 x5310 GEAR RATTLE. 25 HP. We have noticed, particularly with the low inertia flywheel (Lec.2830), a rattle in the transmission between 30 and 40 m.p.h. on the overrun, and have carried out some experiments to locate and eliminate this rattle. The rattle is worst when the engine and gearbox are really hot. On good cars it is only noticeable under this condition. We understand from the Test Dept., that the rattle exists on most 25 HP. cars after continuous running at high speeds. They have found the noise curable by fitting a new bronze servo worm wheel. On the car on which we have been working (12-G4 - with light flywheel), which posses this rattle to a marked degree, we first removed one of the continuous gear pinions. This had no effect. We next also removed the servo bronze wheel. The rattle was then less in magnitude but not absent. We therefore thought that the rattle was due to a bad fitting top gear sliding dog and hence had a new one fitted with the minimum of backlash. This again had no advantageous effect. We have reason, therefore, to believe that this rattle from 30 down to 40 m.p.h. will take place provided there is any backlash in the various parts of the transmission. Thinking that the rattle might be due to relative movement between the engine flywheel, which does not rotate at a constant angular speed but has superimposed oscillations due to gas and inertia torques, and the flywheel effect of the propeller shaft. We have tried altering the inertia of the propeller shaft. This has been effected by first fitting the 3" diameter shaft giving an increase in inertia of about 15 lb.in.2 which had the effect of considerably reducing the rattle. Secondly we fitted to the ordinary 2 1/4" shaft a flywheel of 103 lb.in.2 total moment of inertia (to Hs.{Lord Ernest Hives - Chair}352) and with this fitted no rattle was detectable. The rattle is therefore capable of elimination by attention to the transmission rear of the gearbox but we have done experiments that show its cause to be in the engine. The rattle is at the same engine speed on all gears. No rattle is observable when running up the engine in the neutral, on the overrun declutched, or on the overrun full throttle with the ignition switched off. We concluded therefore that the piston motion is the root of the trouble and shall be able to verify this if the rattle gets worse on fitting cast iron pistons. | ||