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).
Examination and modification report on a solenoid type starter main switch.
| Identifier | ExFiles\Box 168a\2\ img414 | |
| Date | 11th March 1939 | |
| To By/Rb.{R. Bowen} c. to By.{R.W. Bailey - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} 6139 Am/KC.o/Jn.11.3.39. re Solenoid type of Starter Main Switch to D.O.692. On a previous examination of a switch to this scheme the solenoid action was found to be inadequate, and for this reason a modification was issued for increasing the pull on the plunger, see Da.{Bernard Day - Chassis Design}O/G.16.11.38. and By/RL.1/B. 8.12.38. We received a switch in the modified condition 7.2.39. We have carried out bench tests on the switch and find it still unsatisfactory, in that at times the voltage necessary to operate the switch is excessive, i.e. 12.0 volts. Failure occurred after 2230 operations on an endurance test due to binding of the plunger at the top of the bore, the result of too much play between plunger and bore, allowing the plunger to move out of centre axially; the result of this is an uneven air gap between the 60° male and female cones, with a consequent side thrust on the plunger. The above failure also caused the carbon contact spring to collapse due to overheating of the carbon. At this stage the voltage required to operate the switch was found to vary between 6.2) - 12.0 volts. The switch was then dismantled and the diameter of the plunger increased .020" by nickel plating, also the brass rod replaced by one an 1/8" longer, to provide an improved guide for the plunger. This considerably reduced the amount of play. These modifications effected a reduction in operating voltage, the switch now pulling in at 3.15 volts. The endurance test was then recommended and has now completed nearly 10,000 operations. We shall stop the test at 10,000 operations for examination of the switch parts with a view to discussing further improvements with the D.O. We recommend that modifications be carried out by - (1) Using 30° cones instead of the existing 60°. (2) Trial with plain plunger and stop. | ||