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Chains for Power Transmission.*

21st April 1910, Page 14
21st April 1910
Page 14
Page 15
Page 14, 21st April 1910 — Chains for Power Transmission.*
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Continued from Page 118.

Referring part:La:aid:: to chain drives ia cormectien with automobiles, they were generally acknowledged, by the original designers, as a ready and convenient means to provide for transmitting the power to the road wheels, and to the chain must be credited no small part in the Early development of the motor vehicle. All of us doubtless recollect and can picture some of the early types of chain-driven ears with driving chain wheels as small as 6 teeth, which quickly lost their original form and became under-cut or " hooked," causing constant chain troubles. As time went on matters somewhat improved, the makers of motor vehicles being so progressive as to put 9 teeth in the driving pinions with certainly better results, but yet far from satisfactory. It will be conceded that at this time chain manufacturers made marked advancement. towards perfection of manufacture, especially in the matter of luau* life, nntwithstanding which the chains were rapidly destroyed, the owners of automobiles buying new chains often without a thought of the wisdom of renewing chain wheels ; thus the new chains were compelled to get out of pitch even quicker than the old ones which they had replaced. Gradually the motorcar manufacturers learnt by experience that if the wear was distributed over a greater area, the teeth would retain their correct form for a longer period, until eventually gears were being used with pinions as large as 20 teeth made of steel castings, or front mild steel, case-hardened, instead of bronza or malleable iron. Noise of transmission was reduced as the important conditions here detailed received attention, and the next improvement was naturally to provide for all chains being properly encased and given a. fair chance to prove their efficiency. During all this time the fact must not. be lost sight of that the horse-power of the engines of automobiles had rapidly increased, as much as 40-50 h.p. being transmitted through a pair of 11 in. pitch chains of the single roller type. whereas previously the same size of chain was being used for 6-9 h.p., and yet on the more powerful machines, under the improved conditions, the chains lasted much longer than on the lower horse-powered vehicles. No doubt automobile designers have many awkward problems to solve, and unquestionably one is the designing of a proper chain ease permitting cleanliness and reasonable lubrication. At last, several automobile manufacturers decided so to design their vehicles as to admit of suitable chain cases being provided, and the author is of the opinion that chain gearing, under these conditions, compares with distinct advantage as regards efficiency, and most favourably as regards silence, with live-axle vehicles. It is not too much to claim for chains a higher efficiency for transmitting power than high-reduction bevels or worm gears. Positive in their

ithtnre. :hey have some degree of flexibility, and even when fitted in cases are fairly accessible. Chains and chain wheels can be quickly renewed without great expense. and an alteration of gear ratios, to suit the particular district the car is generally required to travel in,

ran be easily effected. The flexibility of the chain drive permits of freedom for axle, spring and frame movement, without setting up undesirable strains, and enables the road wheel, when required, to be conveniently splayed. With the live axle practically the whole weight of the bevel drive (considerable) rests directly on the tires, that is to say, the weight is not spring supported, and is subjected to the direct shocks from the road wheels, with the result that the tires on the rear wheels generally wear much more rapidly on a car with shaft gear drive than on a ear with double chain drive. One pound weight added to the axle is harder on both tires awl axle than many pounds added above the spring.

The application of chain drives to heavy motor lorries and tractors simplifies many of the problems connected with the design and running of these particular vehicles, and permits of a drive which meets the most exacting requirements. During the period when the chain troubles previously alluded to were sufficient to make an impression, there were very few commercial-motor vehicles in existence, and by the time commercial cars began to command general attention, the chain drive had been greatly improved, and designers generally realized the importance of good chain wheels with correctlyformed teeth. It will doubtless be now conceded by the majority of automobile engineers that the chain drive for commercial vehicles has demonstrated its superiority to the ' live axle, and there is little prospect, at present, of its being superseded. The torsional strain put on the frames of this class of vehicle is very considerable, and the chain lends itself, to a great extent, to the distortion without appreciable harm.

The fitting of chains as a means of transmitting power to the driving wheels of such vehicles at once dispenses with the large and heavy axle case with split axle, necessary when gear drives are employed, and permits of the use of the only satisfactory axle that can be used for carrying heavy loads, viz., a solid one. While thus reducing the total unsprung weight on the driving wheels to a minimum, a. relatively stronger axle can conveniently he fitted, and the removal of the differential gear to the driving end of the chains, where it is protected from road shocks and axle strains, allows of a lighter gear being fitted, by reason of the increased speed at, which it transmits the necessary power, and incidentally permits of more efficient lubrication there.

_Axle clearance with gear drives is very limited, but with chain driving of the road wheels it is may to obtain an axle clearance practically equal to half the diameter of the driving wheels. The size of the road wheel can, with chain transmissien. be made suitable to carry the required load, without being influenced by the ratio of reduction between the gear hox and axle, by reason of the wide limits of ratios possible with this type of drive. The ratio of reduction can at all times be conveniently altered to suit varying conditions of road service, by the changing of sprockets and detachment or addition of one or more chain links. With chain drives torque rods are not required, and the absence of universal joints provides a transmission with an efficiency higher and more, easily obtained and retained than is possible with other iorms of mechanical drives,

To the, automobile designers of the present day,to get best re suits from chain drives to the wheels, the author would submit the following points:—The pinion wheel should have from 17-20 teeth to snit chains of the " Inverted-tooth " type for preference, and of a pitch and width suitable for the weight of the vehicle and power to be transmitted; the ratio of wheels not snore than 2-1; pinion wheel of mild steel, casehardened; the larger chain wheel, or wheels, should be made of steel castings, or mild steel, case-hardened, and for preference should be in the nature of a simpleplain ring to bolt on to the brake drum or bracket.

The automobile designer should consnit with the chain manufacturer as to correct tooth forms and wheel diameters. The whole chum gear should be cased in with a strong case easily detachable, or easily accessible, i.nci provision should be made for it drip lubricator on the top of the case which should only drop oil on the chain when the car is in motion. Such a drive would compare favourably for silence, and would be less severe on the tires, than the live axle. It would be cheaper to instal, and would have longer life; it is also easier to alter ratios.

The chain-driven gearbox, as fitted to some London motor omnibuses, is somewhat of an innovation. Spur gears proving troublesome for noise, the chain manufacturer came to the rescue. and the scheme has proved a great success.

The magneto drives come under th: heading of the minor uses to which the chain is applied oil a otos vehicles.

In conclusion, the author desires to express Isis sincere and grateful thanks to Hans Renold, Ltd., end the Westinghouse Brake Co., Ltd., for their descriptive matter relative to their into patented speeia:ities. and Mt their unfailing courtesy so cheerfully extended, and also to :11r. Searle, of the London General Omnibus Co., for his aid and advice in the designing of the chain-driven gearbox.

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