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27th July 1920, Page 28
27th July 1920
Page 28
Page 28, 27th July 1920 — AN INGENIOUS VARIABLE GEAR.
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Which of the following most accurately describes the problem?

A Résumé of Recently Published Patents.

The epicyclic gear has, since the earliest days of the motorcar, -possessed ant irresistible fascination for the inventor who would solve that eternal riddle of how to construct a satisfactory and practicable infinitely variable gear. The gear in' its simplest form consists of a central wheel, called, for reasons which are fairly obvious, the sun wheel. A set of pinions, • termed for similes reasons, planetary pinions, are in mesh with the sun wheel, neing, as a rule, spaced equally around it., ard each is mounted on a spindle, the soave/ el spindles all being attached to a common spider, which -may -revolve con. centrically with the sun wheel. Yet another gearwheel is required for the set, and it is one having internal cogs. It meshes with the planetary pmions. Various combinations of these gears are possible ; we will consider one. Assume the sun wheel to be keyed to a driven shaft, and the planetary pinion spider to be similarly secured to the driving shalt, the outer gear, with the internal cogs, being subject to some form of control. Now if the outer gear be allowed to run free, it is dear that the planetary pinions will revolve idly between it and the sun wheel, when the driving shaft, with_the spider &Trying those pinions, is

revoked. There will consequently be no transmission of power. If, however, the outer wheel were to be held stationary., then the sun wheel, and with it the driven shaft, would be revolved at a speed duly proportionate to that of the spider, the ratio of the speeds of the driv. ing and dricen shafte being preciaely determined by the proportions of the various gearwheels. Clearly, too, any desired speed of the driven shaft, up to that defined by that ratio, would he attainable by varying the control of the outer wheel.

The arbitrary limit to this ratio may be removed, however, and an entirely variable gear attained, if the outer wheel, besides-being controlled between the limitsof running free and being held stationary, is caused to revolve in a negative direction, that is to say, in the reverse direction to that in which it runs when freed.. Specification . No. 144,349 (Maodoviald) describes a means of controlling the outer gear -sathat an infinitely variable gear ratio between the driving and driven shafts is attainable.. In the principal view of the drawing which is reproduced herewith, the righthand upper shaft is the driving shalt. The driven, shaft in line with it (being actually journalled on to its end), and carries the Sun wheel of the epicyclic gear. The driving shaft is connected, indirectly, by means of the gearing-shown, to the spider of the planetary pinions, and-the velocity ratio of those two shafts is varied by controlling the speed of revolution of the outer gear, On the hub of the latter is keyed a worm wheel, which is in engagement with another which is journalled on the layshaft shown, but is not keyed to it. Instead, it is secured to a peculiarly-shaved friction disc, one of a pair of which the other is keyed to the layshaft. Between the two friction discs are mounted.a pair of idler wheels, which may be. manipulated so as to vary the velocitY ratio be. -i,ween the two main discs. The layshaft, therefore, drives, indirectly and ata speed which may be gradually varied, the worm which is journalled on it. The pitch of the twe worms is such that, although neither will actually drive the other, nor can either revolve unless the other is turning. The outer wheel of the epicyclic gear, therefore, is controlled, through the worms, infinitely variable friction gear, and layshaft, of which the last-named is driven from the

main driving shaft. The construction thus affords, an infinitely variable gear between wide limits, and includes a reversing gear.

Detail Improvements.

The epicyclic gear is also the foundation of the starter gear the subject of specification No. 144,509' (deal). This is a unit dynamo and starter. The drive to the dynamo, which is also the motor, is direct, so that it revolves at engine speed when generating, When operating as a starter motor, however, it drivesthe engine' through an epicyclic train so arranged that the engine revolves more slowly than. the motor, which may thus develop the required torque without having to be cumbersome.

Electric starter gear is also the subject of 144,353 (Questa). The driving pinion of the gear is mounted on the customary screeced spindle, -and is retarded, when the motor commences to revolve, by a magnetic brake acting through a flexible medium, --Which takes the form of a coil spring. 144,436 (Bettinger) is a piston valve and gear, and is apparently a modification of a previous patent (131,847). The valve is very narrow, thus needing-hut a slight movement, and it is driven by a peculiar form of worm gear. The teeth of the driving warm are regular for portion of the circumference, but for the remainder resolve themselves into One teeth of no pitch. The consequence is that while the driving gear turns through that proportion of a revolution, no motion is transmitted, and the valve is stationary. An, ingenious carburetter is the subject of 144,363 (Grace). The butterfly valve contains the jets, of which. there are many in one half of the valve, for normal working, and few—pilot jets—in the other. The tubular spindle of the valve conveys the petrol to the jets, and can be revolved imithin the valve so as to vary the supply of fuel. The gear for this differentialmovement of valve and spindle is rather ingenious. It consists of a set of links and lovers, and is con-' trolledindependently by Bowden wire.

The clutch And accelerator pedals are combined in the arrangement desoribed kin 144,567 (Forneea). The pedal is .coupled to the throttle valve, and controls the clutch through the mediuha of cam.

144,444 (Sangster) is an arrangement of engine and transmission, the principal object of which appears to be that of attaining simplicity in the machining of tho various components


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