THE ELMA ELECTRICALLY-OPERATED GEARBOX.
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A Four-speed and Reverse Gearbox of the Double Differential Type Controlled by Magnetic Clutches and Brakes.
FEW PARTS of the chassis have received so much attention from designers as the gearbox, but, in spite of this, few radical changes have been incorporated since the time when the sliding spurgear type was brought out by Levassor.
In the earliest days changes of gear were obtained by the use of belts and stepped pulleys, but after a short time the sliding pinion type in conjunction with the leather-faced cone clutch practically swept the board. There are still in existence a, few successful gearboxes using epicyclic gear. These, though, are exceptions which prove the rule.
In spite of all the attention which has been paid to the subject, we have never got away from the unmechanical idea of meshing toothed gears running at different pitch line velocities to each other. Possibly this is due to most of the attention being paid to this standard type, of gear, which, both by improvements in design and in material, has 'been made extremely reliable. It would appear, however, that there is a large field open. to inventors who can produce a system of gearing other than the ordinary selective sliding and epicyclic types, and in which the gears are constantly in mesh.
Much attention is being paid of late to a type of gearing known as the Elma. This the invention of Mons. Perret, and consists of what is practically a combination of epicyclio and double differential gearing, in which the four sun wheels may be locked to either the flywheel of the engine or to the gearbox casing, by means of magnetic clutches and magnetic brakes respectively.
Electrioally-operated gearboxes have been produced in the past, but in these the electricity was used inerely to slide the gears into contact, in lieu of this being done by hand power. With this type the sliding gear forks were usually operated by solenoids. In the case of the Elma gear the electrical portion of the apparatus actually determines the gear. In order to assist the reader to obtain a clear understanding of how the various gear changes are effected, we reproduce a series of drawings in which everything but tlle actual gears in operation, and the means of controlling them, has been eliminated. We also reproduce a drawing of a specimen gearbox. In this case also all details which do not apply to the actual operation of the gears have been eliminated.
In all of the small illustrations we have followed the practice of blacking in those parts, excepting the shafts, which are in 'motion, and of stippling those parts which are purposely prevented from rotating. Certain of the gears which may revolve idly, but which do not affect the action of any one speed, are not included in individual diagrams.
In the Elma gear the flywheel is contained in the gearbox and attached to it are two electro-magnets.
What might be called the primary shaft, that is the shaft which conveys power from the engine to the propeller shaft, has its forward end running in a bearing situated within the flywheel, At the centre of this shaft is a cross shaft, upon which run two sets of double planetary pinions. This cross shaft passes vertically through, and forms one with, the primary shaft.
At each side of the planetary pinions are situated two sun wheels, which run independently of each ether. The two sun wheelsesituated next to the flywheel each carry a large diameter clutch ring, so that either wheel may be locked to the flywheel through the medium of the electro-magnets. The clutch ring en the larger wheel is double-faced and one face can be braked by an electro-magnet attached to the crankcase.
The two Sun wheels at the other side of the planetary pinions also carry rings, but in this case they are solely brake rings, 'because they can be locked to the crankcase independently, when required, through the medium of a pair of electro-magnets, thus preventing one or other of the sun wheels from rotating.
The first diagram shows how the first speed is obtained. Au electric current ls passed through the electro-magnet D, thus locking Dl firmly to the flywheel. A current is also passed through the electromagnet H, which locks the sun wheel 111 to the crankcase. The sun wheel Dl in revolving causes to revolve the planetary pinions K, and these being in one or interlocked with the planetary pinions J, cause the latter to react on or climb round the stationary sun wheel Hi, thus rotating the cross shaft B in the same sense as Dl, but at a lower speed, owing to the double reduction thus obtained between Dl and K, J and Hl. The cross shaft B, being in one with the primary shaft, the drive is thus taken through to the propeller shaft.
Fig. 2 shows how the second speed is obtained. In this case the action is very similar to that of the first speed, excepting that the large sun wheel El is clutched to the flywheel in lieu of the smaller wheel Di, and, of course, the reduction is less bcanse in this case the planetary pinions -3are driven by El.
The third arrangement is shown in Fig. 3. In this case the pinion El is again clutched to the flywheel, but the small sun wheel Il is locked to the crankcase by means of the electro-magnet I, and naturally a higher speed is obtained, because of the large planetary pinion K reacting on the small sun wheel Ii.
The fourth speed is the direct or straight-through drive, and is obtained by passing a current through both the electromagnets D and E. These clutch the two sun wheels Di and El, causing them to rotate with the flywheel ;' owing to the planetary pinions J and K having teeth the ratio of the numbers of which are different, the equal rotation of the sun wheels causes these to jam, with the result that the shaft B is driven at the same speed as the flywheel.
The arrangement of the gearing for the reverse is shown on Fig. 5. In this case a current is passed through the electro-magnets D and G, so that Di is compelled to revolve with the flywheel, while Et is locked to.the crankcase, DI rotating the sun pinions K, and consequently the sun pinions j causes the la,tter to react on the sun wheel El, rotating the cross shaft B in a direction opposite to thA of the flywheel.
The great advantages of the Elma gear lie in the fact that the gear wheels are few in number and are always in mesh, that no secondary shaft has to be employed, and that the action of changing speed can be graduated by electrical means, so that no shocks are sustained by the mechanism. In addition, it is possible to utilize the gearing as a brake, for which purpose a current is passed through the electromagnets H and I, which lock the planetary pinions J and K on the cross shaft B, and consequently prevent the primary shaft from rotating. The action of this brake ean also be graduated by means of the current applied to the electro-magnets.
The necessary. current can be obtained from a dynamo of the lighting type, which can conveniently be the one, if any, already-installed on the vehicle, but, if necessary, the ordinary flywheel can be replaced by means of a dynamo acting as a. flywheel. This gear dispenses with the need of any clutch other than the electrical ones, and the whole control being by electrical means, all levers, supports, tubes, forks, etc., required with the ordinary change-speed-gear are rendered unnegessary.
The question orbalance, which is of such vital importance when dealing with comparatively heavy masses of metal rotating at high speeds, is adequately dealt with in the E1n3a gear, and the gearing has the advantage of acting as a flywheel, so that the engine flywheel may be lightened to an appreciable extent, particularly as no clutch has to be incorporated beyond the light electrical ones.