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).
The efficiency of a large diameter nut and worm for a steering system.
| Identifier | WestWitteringFiles\N\July1925-September1925\ Scan180 | |
| Date | 12th June 1925 | |
| R.R. 493A (50 H) (D.D. 31, 12-6-25) J.H.D. EXPERIMENTAL REPORT. Expl. No. REF: Ha/ACL1/LG31825 To R.{Sir Henry Royce} from Ha/ACL. c. to C.J. R.J. c. to Hu. E.{Mr Elliott - Chief Engineer} c. to N.A. BY.{R.W. Bailey - Chief Engineer} c. to Wor.{Arthur Wormald - General Works Manager} STEERING. X8430 EFFICIENCY OF LARGE DIA. NUT & WORM. We have tested the efficiency of a large diameter nut and worm (N.sch.2024) in a similar manner to the way in which we tested the standard i.e., by finding the torque necessary to be applied to the nut to raise a given load. The particulars of the nut are as follows :- Thread - outside dia. 1.941 Thread - bottom dia. 1.555 Linear pitch .240 Lead .720 Pitch dia. 1.800 Angle of thread with axis 82º 44' 37" on pitch line. 3 starts. White metal lined. Angle of thread in plane normal to threads 29º Oil lubricated. The efficiency was taken for various loads corresponding to axial thrusts of 200 to 1200 lbs. where 1200 lbs. is approx. the axial thrust required to steer a car round a corner at 20 m.p.h. The results obtained are as follows :- Mechanical effcy. of screw = 57% average. The corresponding average value of the actual coefficient of friction (μ) considering the double inclination of the thread is .091. The above values for the efficiency and μ are taken for the nut in motion, and higher values for the friction and lower values for the efficiency are obtained when starting from contd :- | ||