OPINIONS FROM OTHERS.
Page 34
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The Editor invites correspondence on all subjects connected with the use of commercial motors. Letters should be on one side of the paper only and typewritten by preference. The right of abbreviation is reserved, and no resfronsibility for views
expressed is accepted.
The Inventions Exhibition at the Commercial Motor Show.
The Editor, THE COMMERCIAL MOTOR.
[2424] Sir,—The exhibition of inventions, which was organized by the Institution of Automobile Engineers and hqld during the Commercial Motor Show at Olympia, undoubtedly attracted a good deal of attention; but as the public is not used to looking for such an exhibition, many visitors must have missed this particular section.
Should the Institution decideto hold future exhibitions of the kind—they will, in all probabilitY—we think that the interest of the visitor will gradually and even rapidly be gained and the inventions looked upon as constituting a feature of the Show that should on no account be missed.
Although the number of exhibits was not what might have been expeeted, one quite understands that it was the first show of its kind and that many inventors hardly realized the very easy terms on which they had the opportunity of showing their ideas to the public.'
I think that something like this requires to be said by a Show visitor unconnected with the motor industry in order to encourage all concerned to continue their efforts.--Yours faithfully, EVERLEIGH. London.
The Need for Better Change-speed Gears.
The Editor, THE COMMERCIAL MO-TOR.
[2425] Sir,—There is nothing in the nature of an infinitely variable gear in a marketable form yet, and, in the opinion of the writer, there never will be. This may sound like a somewhat sweetang statement, but a very close study of the subject of infinitely variable gears Of all kinds and for all sorts of drives, extending over a very long and varied engineering experience, seems to convince me that, with our present knowledge, we cannot construct a gear that will vary speeds and torque infinitely, and yet stand up to the very 'severe stress to which all gearing, is subjected in commercial motors. It is an easy matter to construct a gear for demonstration purposes in which the action of ratchets or (to use the modern and more polite term) " valves " is employed, but for anything further than a demonstration of a principle I have not yet been able to find an instance in which ratchets of any kind have been actually used for the transmission of the main drive of a commercial vehicle, and I do not suppose that I ever shall.
If we dismiss this form of infinitely variable gearing, we have very little choice excepting electric and B50 hydraulic transmission. With regard to the former, it is now so well known and its good points so well demonstrated that I do not propose to discuss its merits and demerits here. As regards hydraulic transmission, as used by Hall and those who came after him, for the main drive of a commercial motor, so far as I know Hall's was the only gear of the kind that ever stood the test of time; as several of the vehicles equipped with it ran for many years in constant work ; yet, although all the principles governing such an application of hydraulic transmission are now perfectly clear, we see no further advance in this direction. It would seem that the only reasonable hope we can entertain of relief from the imperfections of the present changespeed gear will be something in the nature of a stepped gear, but with certain improvements which will make it more foolproof and easier to change.
Ignoring those gears which have not got beyond the experimental stage, we may take the Commer semiautomatic gear as one of the earliest examples of a departure from the ordinary sliding gear. This gear was introduced in 1907, and several thousand examples are still running. If handled with a little care, changes from gearto gear could be made without declutching, without any shock, simply by throttling down, but, unfortunately, the human element came in and changes were made with full throttle and without declutching, which was not always good for the transmission.
The next outstanding departure from the sliding gear seems to be the system used in the S.D. Freighter, in which clutches are employed on each pair of gears. This method is very much appreciated by those who have to drive the vehicles. Much in the same class, but operated by means of hydraulic pressure, is the 'gear of the Swiss Locomotive Works Co., in which a separate clutch is provided for each pair of gears. It is curious that so much effort should have resulted in so few gears ever reaching the stage of being standardized on a vehicle. Owing to the little success that has been attained in this direction, it has become a fashion among engineers to adopt the attitude of the fox which stood below a grape vine and spoke disparagingly and with every semblance of doubt and disapproval of the fruit that was out of reach. Because they could not solve the problem, the engineers are pleased to contend that the present system is all that is needed and that a little trouble in changing now and then adds interest to driving. This may be true with regard to private cars, but it is certainly not the case with commercial vehicles wheregloads are heavy, stresses are great and a supply of skilful drivers cannot be relied upon.—Yours faithfully, PERTINAX. London.