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).
From 'The Motor' magazine detailing the mechanism and operation of a new magneto impulse starter.
| Identifier | ExFiles\Box 48\3\ Scan067 | |
| Date | 22th September 1920 | |
| X 4210 September 22, 1920. 339 The Motor A NEW MAGNETO IMPULSE STARTER. A Simple Mechanism, Combining the Action of a Flat Coil Spring and Two Steel Balls, for Giving Rapid Initial Movement to the Armature. THE new C.M.I. magneto impulse starter, just introduced by the Conner Magneto and Ignition Co., Ltd., Binley Road, Coventry, will doubtless create a great deal of interest by reason of the simple and effective means employed to give the armature a sharp initial movement in the magnetic field; and thus ensure a powerful spark at normal starting speeds. The additional mechanism is contained in a small casing at the driving end, the machine as a whole being practically of standard design. The principle involved is that of temporarily holding the armature against the tension of a clock spring and suddenly releasing it, the armature then receiving a very rapid impulse through 120 degrees, and thus producing a spark equivalent to that obtained in normal running at 500 revs. per minute. The device "cuts-out" at about 110 revs. per minute, that is practically at the instant the engine starts; the armature then being directly driven in the normal manner. The added weight of the starter is only 1 1/4 lbs., and it occupies but a small space (as shown on the illustration) between the coupling and end plate. The part played by the steel balls is important, and they come into action by centrifugal force in such a manner as to lock the armature drive solid after it has been "flicked" through 120 degrees by means of the energy stored in the spring. The illustrations depict the three main components of the starter (1) a trip plate screwed to the magneto end plate, (2) central part carrying the balls, (3) outer element keyed to the flexible coupling. The armature shaft is keyed to a central boss having grooves in which the balls normally rest. For starting up, the balls temporarily hold up the armature by engaging in semi-circular recesses formed in the fixed element. The spring is then wound up by the motion of the casing connected to the flexible coupling till the two cams shown on the central boss come in contact with the balls and force them out of engagement with the aforesaid recesses, thus suddenly releasing the armature and contact breaker, which receive a sharp impulse from the automatically wound-up spring. The balls are then thrown outward by centrifugal force, and couple the outer and free central elements together so that the armature is then driven practically direct, the spring being only partly wound up. In the unlikely event of the spring breaking, the machine can still be used by removing the spring and putting both balls into one groove, thus locking the two driving elements. For starting up with the device, it does not matter where the spark lever is placed, as there is no possibility of a back-fire occurring. In the course of its 120 degrees movement, the armature travels from the point of maximum magnetic flux through a complete range of advance and retard, the spark occurring when the piston is just past the upper dead centre. It is impossible to over oil the device, and we have seen one starter giving 90 impulses per minute when flooded with oil. Provision is made by means of wicks to oil the balls and cams, but as both these are made of hardened steel, this is only adopted as a precaution. Image Captions: Top Left Illustration: part section & interior view of Impulse-Starter. The interior mechanism of the device can be seen in this sketch. Middle Right Illustration: impulse starter, flexible coupling Showing the neat appearance of the magneto with starter, and flexible coupling. Bottom Illustration: spiral spring connecting 2 & 3, outer-casing attached to flexible-coupling, central section & balls., trip plate with recesses for balls., armature shaft. A dissected view, showing the simple mechanism. B31 | ||