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The Influence of Car Design on Commercial Motors
Page 77
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A Summary of the Improvements Noticed in the Cars Displayed at Olympia By the Technical Editor of "The Motor" T"private -cars staged at the annual Olympia Car Show (which closes to-morrow) are technically notable for the progress revealed in body construction, springing and frame design. There are many other features of wider popular appeal, but it is these three fundamentals which are of primary interest to engineers.
There is no doubt that, in some cases, car practice is reflected in commercialvehicle design. In others the maker of the heavier machine has worked on independent lines. I leave my readers to draw their own conclusions from this review of modern car practice as revealed at Olympia.
Steel Bodies Popular.
The coachwork of the car produced in quantities at a moderate price is now made almost entirely born steel pressings welded together. The influence of streamlining is seen in smooth external contours and in the desire to enclose luggage and the spare wheel. In several instances the body forms virtually a unit with the chassis, being either welded or riveted to the sidemembers of the frame. The most advanced design is that of the frontdrive Citroen, in which the body structure is itself so rigid as to make a separate frame unnecessary. The Americans have taken the all-steel fashion to a further stage by forming the roof from a steel oressing.
Independent front springing, which has become widely used on the Continent and in the U.S., has gained fresh adherents, amongst British manufacturers, in the Rolls-Royce, Humber and Hillman companies. It has, of course, been employed for some time by Alvis, B.S.A., Singer and Vauxhall. Half a dozen different types are in current use and leaf springs, coil springs and torsion bars are all represented.
The Germans have already applied independent springing to the rear end of many chassis, and in one well-known German car—the Wanderer, made by Auto-Union—it is used at the back but not at the front. So far, most of the big producers retain conventional axles. Chassis fames display many interesting features, notably the wide use of
welding in place of rivets. BoX sections, usually formed by the assembly of a channel and plate, are very-popular for side-members and provide a great increase in torsional rigidity.
Transmission systems show little change, the two popular mechanisms being the sY•hchromesh box and the epicyclic sell-changing Wilson system. A new epicyclic gearbox—the De Normanville—is an optional extra on Humber models; the brakes are, in this case, operated hydraulically. The Cotal epicyclic gearbox is also represented at Olympia; this is now fitted in a number of well-known French cars. It has electro-magnetic clutches.
The over-drive principle is now used for most of the Chrysler and Dodge chassis and comes into action automatically -to provide a super-top for cruising. It is obtained by planetary gearing controlled by centrifugal weights. Alternative plans are represented by the Mercedes-Benz (constantmesh helical gears with dog engagement) and Auburn (dual-ratio axle).
Free wheels are not so prominent as formerly, but find a new application in the Triumph under Warren patents. In this scheme the free wheel is normally locked by dogs but comes into action to facilitate gear-changing when the clutch pedal is depressed.
Engines have been improved mainly in detail, but there is a widespread tendency to use higher compressions and aluminium-alloy heads. In most
cases 14-mm sparking plugs have replaced the previous 18-mm. type. The number of V-type engines has been increased by the new 40-60 h.p. 12-cylindered Rolls-Royce and_ by an eight-cylindered 18 h.p. Riley. Superchargers are found on five makes. • A "Flat Four" Engine.
Amongst the novelties may be mentioned a four-cylindered 11) hp. jowett of the horizontally opposed type. There are also the two-cylindered twostroke D.K.W. (made by Auto-Union) and a rear-engined car, called the Mastra, built by Trojan. The latter has a six-cylindered engine, also of the two-stroke type, with the cylinders paired to employ three combustion chambers.
The use of liners is increasing for private-car engines; wet liners are employed in the new 12-cylindered Rolls-Royce and have been used for some time in the Siddeley Special, A.C. Ace and Citroen engines. A feature of the Rolls-Royce, incidentally, is the use of three relief valves in series, whereby lubricant-is supplied at 50 lb. per sq. in. to the main bearings and crank pins, at 10 lb. to the valve gear, and at 1! lb. to the timing gears.
Summed up, the Motor Show reveals much practical progress, albeit with fewer sensational exhibits than on certain previous occasions. In this respect it will bear a resemblance to the forthcoming Commercial Motor Show, and it is interesting to study those points in which the one industry leads the other, or vice versa, and the influences at work behind the designs.