POINTERS ON CHASSIS DESIGN.
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A Continuation of Our Observations on Features Noted at the Commercial Motor Show.
rp HOSE interested in the de1 velopment of engines must have found much to intrigue them in the latest models. Perhaps one of the most startling points is the return in certain engines to a practice which was at one time condemned. We refer to the built-up crankshaft which, in a curious cycle of evolution, has again come to the fore in connection with two remarkable chassis, the Saurer and the Karrier. In the former, the crankshaft is actually in some seven sections, each joining flange forming a part of one of the ball bearings in which the shaft is carried; whilst in the Karrier—a single-sleeve-valve unit—the crankshaft is divided at Its centre, where the flywheel is carried. It is difficult to criticise the Saurer design, whilst the other
engine was designed by. Ricardo, who is, of course, an authority on the subject. The return is a venturesome one and only time will . prove its wisdom and whether our old prejudices will have to go by the board.
We rather regret that the new Leyland " Tiger" was not shown in chassis form, as its engine would then have attracted more attention. It vies successfully with many foreign-built vehicles in respect of cleanliness of design.
-Useful Ideas In Engines.
An interesting engine feature is to • be found in the Cottin Desgouttes, which, although not actually staged at Olympia, was examined by many visitors at premises just outside. One of the engine bearer arms of this unit is formed as a capacious reservoir for oil. A hand-operated cock enables this oil to enter the sump, and the indicator is mounted close by so that when shortage of oil Is noticed it is only necessary for . the driver to allow a portion of the reserve supply to run into the crankcase.
On the Garner engine both cylinders and head are detachable, as it
is considered that decarbonizing should not be confined to the piston heads and combustion chambers only, and in this we fully agree. The removal of the head only does not permit the scraping of the ring grooves, which often become choked with carbon. Another point in this connection is that there is often more carbon deposit within the piston than without, as the oil, being thrown up against the underside of the crown, is burnt into a thick cake which, if left, often flakes off and seriously contaminates the engine lubricant.
Although the Autovac instrument is still used on the majority of vehicles, we noted at least one, an Associated Daimler, in which use was made of the interesting AutoPulse electric device, which consumes approximately one-eighth of an amp., and if anything happened to the electrical system could be worked quite well off a flash-lamp battery. The instrument consists briefly of small bellows worked by a trembler.
Radiator design and construction showed certain interesting developments. For instance, in the AutoTraction radiator the separate block units are supported by coned rubber rings, there being no metallic contact with the main shell. This assists greatly in the prevention of leakage caused by vibration and distortion.
The Maudslay radiator block is mounted on two cantilever arms bolted to the underside of the crankcase of the engine, one of the arms forming a water lead. Thus the weight of the filled radiator must help to damp out engine vibration.
The polished shell of the radiator, however, is separate from the block and is secured to the chassis frame, the block being able to float in respect to the shell—a very good feature as the shell forms one support to the bonnet.
Unit Construction.
The method of Combining the engine and gearbox as a unit was to be seen on many of the new models —more than, in fact, we expected— as, although this arrangement has many advocates who claim for it that it ensures perfect alignment, a reduction of parts and a saving in weight, there is still a strong feeling against it amongst some of those who have to keep fleets of moderate size on the road, as, no matter how much its design may be simplified, any trouble with a clutch will always he a more serious matter than when a separate gearbox is employed, unless an open dutch pit
be provided, as in this case the accessibility could hardly be bettered.
There did not appear to be very striking modifications in springing except in the case of six-wheelers, with which we may deal later in another article.
There were more springs placed underneath the axles than we have seen in previous shows ; probably this is due to their being necessary in the low frames now made use of for special purposes, and having used them on one model it is convenient to adopt them on others, although a low load-line is not then essential.
There appears to be a tendency towards more camber in springs, and the extremely flat spring which had so many advocates a short time
hack is not so much in evidence; the more scientifically correct cambered spring seems to be increasingly popular.
More attention appears to have been given to what may seem a very unimportant point, but in reality one that affects the maintenance man— namely, the arrangement of the bolts that hold the springs to their beds. In the past these bolts were often made so that they pass through long holes to the end where the nuts are situated. The result of this was that in many cases a bolt would become rusted in its hole, and no effort with a spanner would have the effect of tightening the leaves of the spring down on their bed ; consequently, the spring often moved and sheared its centre-pin. All this is altered on most models, and the nut is on the end of the bolt near the plate which holds the spring.
Discussions of a more or less academical kind have from time to time taken place as to which end of 1140
the front spring should carry the shackle. Although there appear to be certain reasons why the shackle should be at the front end, we can only recall seeing one model where this was done, and we imagine that it is of as much real importance as the end at which an egg should be opened.
Splaying of the rear springs—a feature popular on the Continent— is to he found on the Citroen. This is claimed to give a. wider spring base and to assist in the prevention of roiling.
A modification has been made to the familiar cross-springing of the Renault. This used to be effected by two quarter-elliptic springs clamped within a channel-section cross-member. Now, each of the single springs has been replaced by two springs arranged side by side. The main object appears to be to provide greater safety, as the breakage of a single leaf would be of practically negligible importance.
Change-speed Gears and Free Wheels. There was very little that can bP called new in the way of changespeed gears excepting that the boxes seem to be better designed, several having a centre hearing and many using ground gears to ensure silence. We did not hear anything of the American method of burnishing the teeth.
very ingenious automatic gear was shown by a Swedish engineer, Mr. Ljungstriim, but being hardly out of the experimental stage can not yet be looked upon as a proved success. It is, however, an extremely clever invention, and I hope to hear more of it in the future, but as it depends upon impulses transmitted to the shaft from a reciprocating
member by unidirectional clutches, I, personally, am sceptical as to its future application ,to commercial vehicles.
The free wheel as applied to the Vulcan commercial vehicle is perhaps the only practical step shown towards making the change of gear easier. This device has also the advantage that it effects an appreciable saving in petrol. These two advantages will, I am prepared to prophesy, eventually overcome all foolish prejudices and wrongly conceived ideas and eventually make the free wheel in some form, perhaps not as it is at present, as general on the motor as it is on the bicycle.
Coloured Electric Wires.
Coloured electric wires are alinost universally adopted now. Considering the advantage this plan offers to the man who has to deal with the wiring, it is not easy to see why the adoption of the plan shOuld have been so long becoming general, especially as we can remember seeing it standardized on at least one make 20 years ago.
Air Cleaners.
• 'Air cleaners were shown on many makes, and I understand that they are usually fitted to any vehicle that Is likely to work under conditions which are calculated to render such a device necessary, a popular form being that in which a mass of thin strips of tangled metal is soaked in paraffin or thin oil and the dust is caught as a fly is on a flypaper. In annther pattern the air has to pass through and between hundreds of small copper cylinders. "Washing in petrol is the method adopted for cleaning the filter,