THE MOTOR WORLD.

Otago Daily Times, Issue 19947, 15 November 1926, Page 5

THE MOTOR WORLD.

By ACCELERATOR. {Continued from page 4.) TWO-STROKE REVIVAL. RACING AND AVIATION. WHAT EXPERTS ARE DOING. Considerable attention is being paid at tho present time, in technical circles, to the improvement of the two-stroko engine. The fact that Fiat has been working along these lines for the last two years has naturally existed much interest (says tho Autocar) although information regarding the engines which has been allowed to leak out is of the most meagre nature. In America Duesenberg is producing twostroko engines for racing purposes, and was sufficiently advanced to start a car fitted with one of the engines in the recent Indianapolis race, while in France, although few two-strokes have been produced, the experimental work is, nevertheless, interesting, whether it applies to car engines or to avaition power units.

There appears to he a feeling that a practical application of improved types of twostroko engines can be made with less difficulty to aviation than to road vehicles, although economy, in certain cases, indicates that experiments should be carried out on thg road before bigger units for the air are put in hand. Nearly a dozen welldeveloped types of aviation two-strokes have been presented to tho French military authorities during tho past year; all these plans are treated as State secrete, some of them have proved useless, but others oiler possibilities. Among the engines which have been actually built, either in their definite form, or as experimental models, are tho SimaViolcts, which are expected to make their first appearance in the European Grand I’rix at San Sebastian this' month, the Jiloriot, and the Causan. Quite recently tho engine designed by M. Causan appeared in England aboard a motor boat designated the Etchegoin-Causan, and although the craft did not make a brilliant display, the defects wore in the hull and not in the power-plant. The existing Etchegoin-Causan engine is a horizontal four-cylinder havin'- a piston displacement of 1500 ex. (bore nd stroke 60 by 66 mm), with two pistons, a cylinder, and two crankshafts. The explosions take place between two opposed pistons, which are of the normal type without a deflector, and the two crankshafts, which revolve in the same direction, are united by an intermediate pinion from winch the drive is taken.

The crankshafts, which are carried in three plain bearings, have their . throws at 90 degrees, considered spirally, and one of these is described as the intake crankshaft, for its pistons uncover the intake ports, while the other is the exhaust crankshaft, with pistons uncovering the exhaust ports. The cylinder block is a simple casting weighing 601 b, compared with 2001 b for the entire engine; there are intake and exhaust ports on both faces, and the plugs are mounted vertically in the centre of the combustion chamber.

With a symmetrical design the inlet and the exhaust ports would be uncovered simultaneously, but to avoid th : and to assure tho evacuation of tne exhaust gases before the fresh mixture is admitted, the exhaust crankshaft has n advance of 12 degrees on the opposite shaft. In this way the exhaust pons are uncovr before the fresh 1 carge is admitted. A Roots blower, turning at engine speed, is driven off the intermediate pinion and delivers the mixture through the ports to tho combustion chamber. The magneto is driven from one extremity of the intake crankshaft, and the oil pump from the end of the opposite shaft. There is a certain peculiarity about the lubrication owing to the fact that while the crank-case on the exhaust side is at atmospheric pressure, the same pressure is maintained ■ the opposite crank-case as in the intake manifold. The engine has developed 136.5 horse-power at 4400 revolutions, but can, it is maintained, be made to give off 150 horse-power. A direct development of the Causan horizontal four-cylinder engine is the aviation model box-typo, eight cylinder, 16piston engine, foiming two parallel squaies and having four crankshafts with two throws at ISO degres. The principle of this engine is the same as that of the smaller one already in existence. A Roots blower is used, and the pistons connected to tho upper and the lower crankshafts assure the opening of the exhaust ports, while those to left and right uncover the intake ports. The upper and the lower crank-cases are open to atir ospherio pressure, and the loft and right ones are under the sarr o pressure as tho intake manifolds.

The Sima-Violet engine may be described as a double flat-twin, its four cylinders having a bore and stroke of 75 by 84 mm. A central crank-case is used, the poston is of the deflector type, and there is crank-case compression with a rotary distributor. It, is intended, later, to make use of a Roots blower. While the crankshaft is of the normal four-cylindod type, with throws at 180 degrees, there >.ro simultaneous explosions in cylinders 1 and 2 and cylinders 3 and 4. When cylinders 1 and 2 are at upper dead centre, cylinders 3 and 4 are at lower dead centre, and when pistons 1 and 2 are moving outwards on the compression stroke, mixture is being draAvn into the crankcase common to these two. cylinders. The Blcriot two-stroke is similar to the Causan in having no deflector, but is distinctive by reason of the use of a reciprocating sleeve, which can be driven either by a train or gears or by an eccentric. IMPROVING THE CAR. Research into riding qualities of the car is a subject that is engaging the serious attention of automotive engineers. The term has a broad application that includes easy, smooth riding, quietness, and general comfort of body and mind. It embraces both physical and mental effects, which are exceedingly difficult to measure and correlate with mechanical causes. The preliminary work has been devoted largely to the development and study of instruments for measuring vibrations of the engine, transmission and driving gears, body panels and roof; of acceleration and deceleration when starting and stopping the vehicle, of vertical and gyratory motions of the body, and the measurement of sounds arising from the various vibrations set tip by the and driving mechanism. By the use of' these instruments the periodical vibrations of the engine crankshaft and the reciprocating parts a.e being studied with the object of securing better balance. Xoise produced by meshing gears is being analysed, and the tooth pitch and contour arc being improved. Attention is devoted to spring suspension, and the effect of balloon tyres to avoid synchronisation of vibrations and prevent shimmying and tramping. Longer and more flexible front springs, it has been found, will aid in correcting some of the unpleasant motions. Vibration damping devices, shock absorbers, and even the springs in the seat cushions are undergoing close scrutiny and experimentation with the object of reducing excessive car motion and even minor high frequency in the engine. Some engines are now mounted on cushions on the frame to prevent transmission of vibration to the frame. Squeaking, chattering, and grunting of brakes, which noises are a common source of much annoyance to car drivers and passengers, are undergoing investigation that no doubt will result in the use of a higher grade of tool in the drums, greater care in making the drums truly circular and the hand:; concentric with thorn, better protection from dirt, and means of damping the vibrations of the drums, which arc the cause of the noises. Much of the work of the engineers has a direct bearing on the safety of the occupants of the vehicles and of other users of the highways. This applies to specifications for materials, to many recommended practices, low centre of gravity, efficiency of brakes, and especially to hcadlighting, which is being investigated intensively now in co-operation with illuminating engineers and others. The increase in night driving, in speed, due to better highways and faster cars, and in congestion of traffic, the lowering of car bodies and other factors have brought the headlighting problem very definitely to the front. How to give adequate lighting for fast night driving without throwing a dangerous glare into the eyes of approaching drivers is the crux of the question. Dimming of the lights is recognised ns a dangerous expedient because the eyes of the "driver do not adjust themselves quickly enough to sudden changes in intensity of the road lighting.