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).
Article discussing the design and performance of a magneto for deluxe cars, including a comparison graph.
| Identifier | ExFiles\Box 48\3\ Scan066 | |
| Date | 22th September 1920 guessed | |
| A MAGNETO FOR THE CAR DE LUXE.—Contd. into action. The copper strip placed in the magnetic field constitutes an electrical circuit and exhibits the property of opposing the distortion of the field which the rotation of the armature tends to produce. It acts, as it were, as a barrier to the “bunching up” of the magnetic flux towards the extremities of the pole piece extensions. It keeps the lines of force where they are wanted, and governs their distribution. In this way a sufficient number of lines of force are present at that position of the armature rotation where the circuit is broken when the ignition control lever is at the position of maximum advance, to produce a spark of maximum intensity. Thus, throughout the range of control from full advance to full retard a maximum of ignition efficiency is obtained. Graph: Y-Axis: REVS PER MINUTE (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 140+) X-Axis: FULL ADVANCE to FULL RETARD (0, 10, 20, 30, 35, 40, 50) Curve A shows the approximate engine speeds at which an efficient spark is generated on an average magneto at various degrees of advance and retard. Curve B shows how the new type C.M.I. machine maintains a constant spark at about 80 r.p.m. through 50° of advance and retard. The machine in question will be known as the 620, and it is intended for use on six-cylinder engines, and by reason of its special characteristics will undoubtedly become popular on high-class cars. Conner Magneto and Ignition, Ltd., also make a very useful range of machines of the orthodox type. They consist of the C.M.I. 417 model, which is intended for use on heavy car and lorry engines of the four-cylinder type, and the C.M.I. 617, a similar machine, but of the six-cylinder type. Then there are two particularly neatly-designed machines known as the C.M.I. 418 and 618, these being respectively the four-cylinder and six-cylinder types and intended for use on light cars. On these machines the laminated pole pieces are cast in an aluminium casting together with the gunmetal inserts for the base plate holes. The casting also forms the end bracket for carrying the distributor gear. This form of construction, while being particularly neat in appearance, makes the machine very strong and rigid and at the same time comparatively light. Ball bearings are used throughout, and are carefully enclosed to exclude damp and dust. The machine has a one-piece sheet aluminium cover lined with impregnated felt, giving it a very neat and smooth exterior. No oil holes are provided, as the makers claim that the bearings retain sufficient of the high-grade grease with which they are filled to last for some years, and the lubrication of the cams and contact breaker is provided for by a patent felt lubricator. It is not necessary in this article to enlarge upon the great care and attention to detail which is exercised in the manufacture of these machines, as a brief description of the C.M.I. works and of the methods employed therein was given in our last week’s issue. The conditions under which the machines are made should be particularly conducive to the production of first-class work. An unusual amount of attention seems to be devoted to careful testing both of materials and of the finished article, in order to ensure absolute reliability under all conditions. Much thought has also been devoted towards obtaining easy starting characteristics in all the C.M.I. machines by efficient electrical design, and they are capable of producing a very hot spark at low speeds of rotation. | ||