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COMMERCIAL MOTOR DESIGN.

25th October 1921
Page 9
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Page 9, 25th October 1921 — COMMERCIAL MOTOR DESIGN.
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Some Notes by a Well-known Designer, who Desires to Preserve His Anonymity, Concerning the Tendencies Observable to Him at the Show.

THE Commercial Motor Vehicle Exhibition showed that designers are fast coming into line on mast points. Tho most suitable devices are being adopted, even, by firms who, some time back, pinned their faith to contrivances directly opposite to the practice of to-day. The adoption of a device introduced originally by anothertirm, or the abandonment of one even after many years successful use, need not be looked upon as a climb-down on the part of a manufacturer. Circumstances alter cases, and circumstances are continually altering in a comparatively new industry such as that of the commercial motor.

Where conditions alter, construction should alter. Many things are possible to-day in commercial motor construction which would have been but of the question some years back. The sip read of mechanical knowledge, improvements in steel, etc., have enabled the designers to make many alterations. The tendency of most of such alterations is towards simplicity. Many " fool-proof ' gadgets, which wercthought absolutely necessary some time back, have gone.

With the exception of matters which may be considered details, there is one outstanding point where designers do not seem able tie fall in, line, and that is the back axle and its surroundings. Here we see a greater difference of opinion than. in any other

part. • •

Chain Drives.—These were few in number, but when it is considered that the examplesshown were on the stands of some of the most experienced and practical firms, including Albion, Commerears„ HaIlford, etc., it it a question whether the tendency towards other methods of driving is altogether justified. In judging the trend towards an important point, like the final drive, it is not wise to take the numbers shown entirely as a criterion. The experience and character of the firms showing must be taken into consideration.

Worm Drives.—These were shown by almost every firm on some of their models exhibited. The construction and mounting of the worm drive seem to be thoroughly well understood now. The design in which bearings carrying worm and worm wheel are in one integral part, removable from the top of the box, is undoubtedly the correct, and almost universal form. Only in one case was an e±aanple of another design noticed. In this instance, the worm bearings were formed in the top cover, while the crown wheel bearings were in the box, the two parts being held together only by bolts. It is hard to account for this departure as it seems to offer no advantage. Double-reduction Gears.—In spite of the proved silence, durability and other advantages of the worm drive, one cannot help noticing a tendency towards the double-reduction type for heavier models. Here, again, the experience and character of the firms ex

hibitingmust be taken into consideration against mere numbers. The Leyland Motor Co. hare recognized the merits of this gear for many years for heavy vehicles. The illaudslay Co. showed a fine example.

Torque Rods, Torque Tubes and Radius Rods.—In earlier days of the industry, doubts were expressed as to the ability of the springs to stand the strain of the torque arising from the action of the brakes; still further doubts existed of their ability satisfactorily to withstand the severe strains of torque arising from the drive of a live axle, also the propelling of the car. Torque rodsand radius rods were looked upon as essential. When, however, We see such makes as De Dion, Daimler, Albion, Thornycroft, Berliet, Straker-Squire, and Dennis on the lighter model entirely doing away with these devices, it cannot be argued. that they play any useful part. Their absence tends to simplicity and silence, and reduces the parts to be lubrieated.

Gearboxes.—Here, once more, the tendency is towards simplicity. Engagement by means of dog clutches and similar devices seems to be on the decline, and the simplest forms of change-speed gearboxes with sliding gears were shown by most of the . firms, whose large output and experience entitle them to be considered the best judges. The improvements in the steels used for gear wheels is largely the cause of this change.

Engine Construction.—In this part of the exhibits there was little that was not 'shown last year. Opinions seem to vary considerably still on many points of engine construction. The very old question as to whether an engine should have one camshaft or two is not settled. Overhead valves and detachable cylinder heads have added to the unsettled points. As these points do not seem materially to affect the efficiency or durability of the engines, their unsettled state does not matter much to the purchaser.

Clutches.—The single plate clutch is growing in popularity, and seems destined to become even more popular on account of it requiring practically no attention. Most of the examples consist of a steel plate grippeirbetween rings of Ferodo, which works without lubrication. On the examples of cone clutches shown, Ferodo or similar fibrous material has almost entirely replaced leather. There still seems to be some difference of opinion as to whether

there should be one or two universal joints between the engine and gearbox, the exhibits showing about an even number of both.

Position of .Driver.—There is every sign that the placing of the driver, either by the side of the engine or partly over it, with the intention of lengthening the available space for load, is being very satisfactorily carried out. From the user's point of view, where light and bulky loads have to be carried, this is an important point. The A.E.C., Straker-Squire, and Maud.slay were good examples. Cooling.—The general trend seems to be in favour of large water pipes in which thermossyphonie action is assisted by a hustler or impeller. Springing.—There is a tendency to make springs wider, although the Continental practice of making extremely wide and flat springs does not seem to find favour. Each country finds by experience the/ spring% most suitable for its own roads. A slight camber has been found to give the best all-round results. A number of thin plates have been found bet, ter than a few very wide ones. As to the mounting of the springs, there seems to be a tendency to return. to slides or slippers instead of shackles. Whether this will be found to he a move in the right direction is doubtful., as it is practically impossible to keep grit out of slippers. With regard to shackle joints, there is a taqve in the direction of introducing oil instead of grease. Oil will run in all directions, while grease, once pressed away, will not return. Some good examples are to be seen on Straker-Squire and Halley models. Road Wheel Rearings.—Plain roller and ball bearings are all shown on models of repute. Good results have been, got from all three types. Each has its merits and demerits, no one system having proved its superiority sufficiently to become universally adopted.. General Rernarks.—Simplicity, accessibility, and low coat of renewable parts are studied, even if efficiency has to be sacrificed to a, small degree. The absence of fads and unnecessary fitments was most noticeable. This is a healthy sign and shows that designers are keeping more in touch with actual road conditions, and are being influenced less by mere ideals. All devices which, although they might tend to efficiency, increase complication and the number of working parts, or render vital parts inaccessible, are being done away with, so far as possible. A clean, simple, serviceable machine is the result.

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