Rolls-Royce Archives
         « Prev  Box Series  Next »        

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).
Oil feed issues, advantages of internal-gear construction, and production challenges.

Identifier  ExFiles\Box 19\3\  Scan132
Date  11th January 1930 guessed
  
- 2 -

Oil feed - One of the minor troubles has been rattle (with 6 cyls. - not with 8) and development of "sing" after 100 miles continuous hard running. This has been traced to lack of sufficient oil feed to the interior of the spool gears which have been found almost dry when rapidly dismantled after a continuous run.

By several details a positive feed of two quarts a minute of oil to the inside of the first spool-gear has been arranged and the boxes immensely improved thereby.

Advantages - Basic advantages claimed for internal-gear construction are -
1. Silence inherent in the design, due to much lower rubbing speed of teeth, distribution of load on teeth, and oil-retaining effect of annuli, not dependent on extremely accurate workmanship, and therefore inexpensive. The smaller box costs Chrysler only 45 dollars in labor material, O.H. and departmental profit.

2. Great strength for a given weight of material due to unexpected sharing of load through numbers of teeth.
There is only a difference of 4 teeth between the internal and external gears. The speed of approach and recession of the gear teeth is therefore so low that although only two pairs of teeth may be theoretically in contact, two more pairs probably share the load by reason of the oil film between them. In other words the gears are a "partial dog clutch".

3. Freedom from wear even with "second rate" materials. The spool gears are made of an oil hardened MÁLÉTÁLÁL steel single-quenched to give about 73 scleroscope hardness. Further particulars on materials will be given later.

4. Ease of quantity production.- No gear grinding, or lapping, no stoning, and only very "average" production-machining methods. What the possibilities may be with improved production methods is not known. Gear-grinding on the externals was tried without any improvement in tone. Gear lapping was not tried. It appears that teeth of average commercial accuracy with the normal distortion are "good enough". But it is known that noise in most cases can be traced to inaccuracy in centering. Although a nominal tolerance of ±.001 is held between internal and external gears there have occurred much greater variations due to -
Inaccurate boring.
Spool gears ground undersize allowing spools to shift sideways and tilt.
Gear-cutting inaccuracies.

- continued -
  
  


Copyright Sustain 2025, All Rights Reserved.    whatever is rightly done, however humble, is noble
An unhandled error has occurred. Reload 🗙