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).
Modifications to a starter motor for EAC.7 to improve the vigour of its end motion.
| Identifier | WestWitteringFiles\Q\April1927-June1927\ 84 | |
| Date | 16th May 1927 | |
| TO EFC.) FROM R.{Sir Henry Royce} HS.{Lord Ernest Hives - Chair}) C to BJ. WOR{Arthur Wormald - General Works Manager} BY.{R.W. Bailey - Chief Engineer} E.{Mr Elliott - Chief Engineer} re. STARTER MOTOR FOR EAC.7. TO IMPROVE VIGOUR OF END MOTION. X7625 SPRING. To enable this to move better endwise I have suggested that we reduce the spring to 66% of its present force and make the rating as slow as possible. OUT OF CENTRE. It appears from the drawings that the armature is finally .125 out of centre. This should be increased to .25" by moving the pole pieces if the clearance in the winding would permit it - i.e. drill fresh holes in the carcase. TAPER BORE. The third and most important point is to machine the outside of the armature and the bore of the poles taper so that the armature has the present clearance when in a running position, but has .050" greater air space when out of gear. This will increase the end pull and decrease the torque until fully engaged. We believe these three modifications will make sufficient difference to enable full engagement to take place. PINION SPRING. The spring behind the pinion should also be reduced but this need not be done until after the other modifications, and then only if found an advantage. Regarding the relative end pull and torque in this starter motor we could easily keep the end pull to the maximum and reduce the torque to half the amount by winding two of the teazer coils for half the current, and join these in series with the armature, and the other half of the teazer coils similarly wound could be connected to frame. In this way the present teazer circuit would be divided into two, all giving end pull and half the current giving torque. Owing to the complication of this arrangement I should not use it unless it were found necessary, but it seems a simple idea to halve the torque. Regarding the arrangement of the field windings we consider that the four separate coils are slightly superior to the two only series coils and two only teazer coils on separate poles, as used in the Bosch machine. But we should certainly try if this simpler scheme of two coils only of each kind will give equally good results. In conclusion, you will realise that in this memo. the most hopeful suggestion is the taper bore which at once reduces the torque about half, and increases the end pull to about double - i.e. four times the difference. The taper bore may be a patentable feature of this scheme. R.{Sir Henry Royce} | ||