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).
Analysis of different clutch sizes, unit pressures, and spring loads, with comparisons to Borg & Beck specifications.

Identifier  ExFiles\Box 130\3\  scan0139
Date  2nd December 1940
  
Ru/GS.6/ST.2.12.40. - 3 -

If a smaller clutch than the 18" twin disc is used, it is on our responsibility, and they fear that a clutch failure would reflect on their name.

Borg & Beck would like to be kept informed of our intentions in regard to clutches.

Borg & Beck do not like the high unit pressures which would be necessary on the smaller clutches. In this connection they design on a μ of .2. The unit pressures necessary on the various clutches for a torque of 1200 lb.ft. and a μ of .2 are given below.

Clutch size : 14" : 16" : 18" : 18" : 15.75x6.3 : 30.G.7.
: twin : twin : twin : single : twin :
Pressure on : : : : : :
discs in lb/ : : : : : : 29.2 *
sq. inch : : : : : :
(μ = .2) : 32.5 : 22.6 : 16.5 : 33 : 21.9 :

* This value is based on a torque of 264 lb/ft. (115 m.c.t.)

P.M. Heldt in his book "Motor Vehicles & Tractors" gives clutch disc pressures as 25-35 lb/sq.in. for cars and 18 lb. for commercial vehicles.

We take μ as .28. Since our task is to have a performance equal to that of a private car and since even the highest pressures for tank clutches listed above are not much higher than on 30.G.7, it would seem that high unit pressure does not bar any of the above clutches.

Of the clutches other than the 18" Twin) which are already designed, the 18" S. torque comes nearest to what we require, and so we are to start off with this.

The next table gives the total spring load required on each clutch. It is assumed that the pressure plate passes all of the spring load to the disc.

Clutch size : 14" twin : 16" twin : 18" twin : 18" single
Total Spring load: 3200 : 2770 : 2390 : 4780
  
  


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