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).
Design dissatisfaction and proposed modifications for the speedometer drive and its reduction gear.
| Identifier | WestWitteringFiles\D\November1919\ Scan16 | |
| Date | 19th November 1919 | |
| To D.A. from E.{Mr Elliott - Chief Engineer} Copy to C.C. " " EFC. ORIGINAL. X.3685 RE SPEEDOMETER DRIVE - 3/19 GEAR BOX. E3/G19/11/19. Referring to drawing No. LeC.1158 sent to you on the 18th instant, shewing the above, would you kindly note that Mr. Royce is not entirely satisfied with it in respect to the casing which contains the reduction gear. Since it may be required to fit various pairs of gears at this point to suit different makes of speedometer, and that the centres will possibly vary a little, a scheme of rectangular aluminium box with a bronze cover containing the driven wheel spindle is considered by Mr. Royce to be more suitable. When we have the blue print back from you we will tackle this point. We further propose to cut out the small sliding sleeve between the spring and the hub of the large gear driven by the gear shaft. This will effect an economy by removing one piece and shortening the drilling operations on the shaft. The spring will then bear direct on the end of the large sliding gear. Referring again to the reduction gear, the wheels actually shewn have 18 and 50 teeth of No. 36 diametral pitch. This is suitable for the Elliott speedometer, assuming that the speedometer does 720 revs. per minute against 2,000 on the engine exactly. By altering the number of teeth in the big wheel by one, we have an adjustment in steps of 2%, which would give us a maximum error of 1% in adjusting the drive of the speedometer. Since 1% is only half a mile in fifty, it is considered near enough when the fact is taken into account that slip of the rear road wheels, and wear of tyres may have to be allowed for.(Cont.d) | ||