THE NAPIER-CAMPBELL TRANSMISSION SYSTEM. CONSTRUCTION OF THE EPICYCLIC GEAR-BOX DESIGNED BY MR MAINA.
NOT long ago the world was thrilled with accounts of Captain Malcolm Campbell’s defence at Daytona, Florida, U.S.A., of Britain’s title to the holding of the world’s speed record for the flying mile, which was established by Major Segrave last.year at 203 miles per hour, and beaten by him at 205-05 miles per hour. Knowing that these trials would interest our readers, and that particulars of the gear-box and transmission would be appreciated, we endeavoured to obtain particulars of design, manufacture and assembly. With this object in view we visited the workshops of Messrs. Beard and Fitch, Ltd., 34, Aylesbury Street, Clerkenwell, amd were there favoured with, the opportunity of witnessing the various operations in progress, similar in all ways to those performed upon the” Bluebird” transmission gearing, though, of course,
not upon the actual parts, as these were installed in Captain Malcolm Campbell’s ” Bluebird” car now at Daytona.
We were greatly impressed with the extensive range of gear-cutting which was passing through their shops, and particularly by the fact that all types of gearing including worms and racks were actually generated. We were shown forms of fine toothed spur and helical gearing of 132 diametral pitch, such as is used in precision instruments ; then, again, heavier forms in alloy steels for use in automobiles ; and yet heavier forms of two diametral pitch for use in mill gearing. All sizes of teeth are actually generated with accurately-ground tools as distinct from the more usual method of cutting gears with formed-cutters. It was interesting to watch the gradual development of a worm as the blank was fed slowly past the ground cutter, and equally so to watch the generation of a rack upon another type of machine. We believe these to be quite new commercial
applications of the method of generation as applied to worms and racks.
Straight and spiralloid bevel-gearing is generated upon modern shaping machines, and here, again, gears were being produced for delicate distance-finding instruments, now in use by the Admiralty and War Office, in contrast to those for heavy commercial vehicles capable of hauling as much as 15 tons.
Helical or spur-gears are made in all kinds of material ; pinions are made in special compressed fabric, which is self-lubricating to ensure silence and long life. Beard and Fitch, obviously, have the equipment and ability to execute any type of scientific or commercial engineering proposition from telescope and model making to heavy lorry parts, and that no time, trouble, or expense in machinery is spared to produce the best
possible -results in gearing of all types.
Having inspected the methods of manufacture, we turned our attention to the epicyclic gearing of the Bluebird.” The whole of the transmission abaft the engine was manufactured in these shops and turned from special alloy-steel forgings provided by Messrs. Tickers to the instructions of Mr. Joseph Maim, of the F.B.M. Gear Syndicate of 15, Victoria Street, The plate clutch is of massive design and is coupled to the gear-box by means of a large bell-joint. From the gear-box to the back axle the power is transmitted through a shaft enclosed in a massive torque tube machined from a solid forging. The final drive, through spiralloid bevel gearing, is of interest because of the original design by which the actual housing serves only as a cover, the gearing it encloses being so arranged and mounted as to obtain maximum strength with a minimum of weight and to be practically self-supporting. The
static axles, live axles and brake drums are all :machined from solid alloy-steel forgings of very high. tensile strength, so that again maximum strengths are obtained with the least possible weight.
The gear-box itself, being described as epicyclic gearing, probably conveys the impression that it is of an extremely intricate nature, but there are many advantages attached to it, and it can be simplified and made less costly to produce, and cheaper for the user.
The accompanying illustration is of the gear-box in its most elaborate and expensive form, as fitted to the Napier-Campbell car, which is now in America.
The system upon which the box functions is really simple and an explanation of its operations will be given, commencing with the Reverse. Fig. r.—The driving shaft has on it a gear A and drum C, the driven shaft carries a drum B cut with internal teeth. The brake drum C carries a pinion D meshing with A and B. When C is held stationary, gear A turns in the one direction and the driven shaft B in the reverse direction, the motion being transmitted
through gears D and B. If C is free, it would revolve in the same direction as the driving shaft, and cause the driven shaft B to rotate at a less speed in the same direction, thereby obtaining the forward gears.
For the 1st speed forward, Fig. 2 shows gear E (on driving shaft) which engages into F and G carried by drum H. Drum H is held stationary so that E drives F and and so drives drum C by means of pinion j, and C, as explained above, turns the driven shaft through pinions D and H. Other similar gearing is introduced and brought into
action, increasing the speed of C, and thereby reducing the ratio between engine and rear axle speeds.
The controls are operated, as in the ” Bluebird,” by means of gears and clutches, or in commercial type by means of hydraulic controls.
The whole transmission system is an example of brilliant design, which, combined with the known efficiency of the Napier engine, proved so successf. .1 in the race for the world’s speed record.
In conclusion, we might say that, in our opinion, one would have to travel a long way to find a workshop so completely equipped with modern tools applicable to the gear-cutting industry, and the directors are technical and practical men, working in co-operation with a well-trained staff of mechanics.