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Simplicity and EXciency as

5th May 1933, Page 130
5th May 1933
Page 130
Page 131
Page 130, 5th May 1933 — Simplicity and EXciency as
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THE AIM OF

CHASSIS DESIGNERS

Complexity Can be Abolished in Modern Goods Vehicles without Interfering with Their Usefulness. A Review of What Has Been Done in This Direction, with a Few Pointers to Likely Developments in the Future SIMPLIFICATION is .undoubtedly the predominating aim of the commercial-vehicle designer of today. It reduces production cost, often increases efficiend and certainly facilitates maintenance operations. Simple and straightforward lines tend themselves to promote efficiency; a saving in weight naturally accrues from the simplification of any design, and if care be expended upon the layout of each component accessibility also is enhanced.

There arp two methods which can be employed to obtain clean lines. The first, and obviously the more desirable, method is to simplify the design of every separate unit. The other method, of merely enclosing a complex arrangement, is of little or no utility, because the fault of excessive elaboration is actually exaggerated and the problem of making each component as accessible as possible is aggravated.

An Illuminating Instance.

An instance comes to mind. On a beautifully laid-out private-car chassis it was desired to fit a new clutch spring. To do this the car had to be jacked up (under the frame), the rear-spring shackles disconnected, the axle moved rearwards and the clutch-gearbox assembly dismantled, in order to allow access to the offending component. Such a design, of course, although superficially appearing attractive, is anything but a blessing, yet one cannot help remarking that even the bad case quoted could have been improved enc.-7mously by the addition of one splined shaft in place of a fixture.

We will, however, turn -to a consideration of more constructive ideas. Commercial-vehicle designers have been helped greatly during the past few years by rapid strides in metallurgy. It is now possible to obtain awkwardly shaped castings and pressings in light

alloys which years ago would have been considered impossible to make. This means, of course, that castings can be used in place of built-up structures, a multiplicity of bolts, rivets and flanges being avoided.

Even so, the fullest possible use does not seem to have been made of the facilities offered in this direction, for one often notices a group of components which might easily have been built as a. unit without affecting the accessibility of essential parts or the cost of production.

One simple item seems to escape the notice of many designers—irregular shapes caused by " bossing " a casting to receive bolts can be formed on the inner surface, leaving the exterior quite plain. The result is increased strength, and a smooth outline gives an immediate impression of simplicity, whilst innumerable webs, recesses and bosses create exactly the opposite effect. On the Continent there seems to have been a fuller realisation of the possibilities in this direction, for in both car and commercial-vehicle design most of the prominent manufacturers have developed power units of exceedingly clean lines.

There is no sense whatever in attempting to enclose in a cover accessories such as the magneto, carburetter, dynamo, starter, etc., or, on an oiler, the fuel pump, but the manner in which they are grouped has a great bearing upon both the appearance and the usefulness of any particular power unit. There are, of course, many examples of cleanly designed engine, but, on the score of appearance alone, an orderly arrangement immediately attracts the eye of any discriminating. operator.

Whether to fit a unit-mounted or a separately constructed gearbox is a

problem which even now has not been universally determined, this being a matter for individual judgment in relation to each particular design. There is no doubt that a plain casting enclosing the clutch, and at the same time forming the gearbox is attractively simple, yet in a separately mounted gearbox arrangement the transmission layout often works out quite nicely, especially in long chassis.

Probably the greatest scope for simplification lies in the design of the chassis frame itself and the brake system. In this latter connection hydraulic or compressed air application has a distinct advantage, for on a pipe line it is unnecessary to provide numerous cross-shafts, rod steadies and adjusting links.' On the other hand, the quantity of mechanism is increased in other directions. Thus, the designer is left to display ingenuity in producing a tidy arrangement for the controls.

Simplified Servo Systems.

On the largest types of vehicle the principle of using a single servo for applying front and rear brakes seems to be dying out, it being the practice nowadays to provide a separate servo for each front wheel. This naturally tends to complicate matters, but one manufacturer has got over the difficulty in a satisfactory manner by mounting each servo cylinder on top of the kingpin.

Whilst dealing with the subject of brake controls, it might be mentioned that in a purely mechanical layout simplicity can be improved by keeping the various pull rods in a fair line with the chassis instead of carrying them up and down.. Another point is that thumb-screw adjusters at the forward ends of the rear rods are just as effective as other types of adjuster placed at the rear end of the rods, hut they have an advantage in that they can be made really accessible, and the screwed portion -of the rod is, moreover, protected from road dirt.

One of the most .important developments in brake layout has arisen out of the Construction and Use Regulations, as now worded. As two independent means for operating the same set of brakes now constitute acceptable equip

ment, a single pair of shoes can be utilized in the rear brake drums. The resultant simplification not merely cheapens production but also allows the designer an opportunity to produce a stouter set of brakes.

The requirement that the failure of any part of the system shall leave the driver with adequate braking powers over at least half the number of wheels (counting, for this purpose, only one front wheel) does not involve undue complication for, in most cases, it is possible to comply with this demand by instituting a really strong supporting bracket in between the end bearings of the main brake-application cross-shaft.

Nothing could be simpler to produce or to maintain—and nothing more likely to retain efficiency in long and hard usage. Clearly, the authorities now begin to appreciate the value of this simplicity —it eases the work of their examiners I Modern Chassis Frames. Chassis frames are really a study in themselves, but here one is confronted by a multiplicity of types with practically no uniformity of design. This seems to kndicate that finality is still a long way off, as, indeed, it must be, yet one can discern a definite tendency to brace the side-members rigidly' amidships, which helps to produce a stout structure, capable of dealing with all sorts of stressing, including lozenging and weaving.

Chassis frames with cruciform central cross-members are inherently of simple layout, yet the form of construction employed is not costly in production, nor does it involve an increased amount of labour, in manufacture of the components or during assembly.

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