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Refinement in Commercial Vehicles

16th February 1951
Page 53
Page 53, 16th February 1951 — Refinement in Commercial Vehicles
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Which of the following most accurately describes the problem?

Mr. P. M. A. Thomas Outlines to I.R.T.E. Members the Latest Developments in Chassis Design

7HE paper, "Trends of Vehicle Design," read at Glasgow on ebruary 5, before the Institute of Road ransport Engineers by Mr. P. M. A. homas, M.I.R.T.E., high-lighted cerin aspects of the 40 makes of chassis -presented at Earls Court.

It was, he considered, unreasonable compare a light van for retail :livery over good roads with an outze tractor and trailer specially built aservice over deserts. Likewise, it ould have been foolish to compare le modern bus chassis with that of le maximum-load eight-wheeler, or to Jnclude that because one embodied a :rtain feature of design, it necessarily idicated a general tendency applicable all transport vehicles.

He could eliminate certain types not tidally designed for commercial work, hich, with minor modifications, perirmed their work well, but embodied Natures introduced primarily to meet rivate requirements.

Tests with I.F.S.

Thus, independent front-wheel susension in them was not indicative of trend towards this in the commercial ,here. Experiments with this were, owever, in progress on passenger chicks and impressive tests had been lade.

At one time synchromesh gearboxes 'ere found exclusively on cars, to-day tey were employed increasingly in ommercial vehicles.

It was necessary to be careful as to ow much notice was taken of vehicles or specialized purposes, which included eatures dictated by the nature of their iork. Power-assisted steering was one sample, but it might have a wider pplication. In Britain designers of batterylectrics had given more attention to lelivery-van design than had those lesigners whose main concern was with oetrol models.

There was a marked absence of freak lesign, and one might reasonably ask vhether vehicles with engines below floor level indicated a move from the orthodox, but there was no sign that other makers contemplated following this lead for heavy vehicles. Flat engines produced by several British makers might, however, ultimately find a place in the future designs of goods vehicles.

Except where good ground clearance amidships was essential, for goods vehicles the flat engine had some advantages. It permitted a full forward cab, unobstructed by the engine, and itnproved comfort, whilst the amidships engine could be more accessible for routine adjustment and removal than • that within the cab. There were also possible advantages in weight distribution and shortening of the propeller shaft: The petrol engine was the accepted unit for smaller vehicles. Oil engines for light vehicles had not been generally available. There might be a danger of oil fuel being curtailed through the increased consumption of kindred fuels by gas turbines, whilst it was not so readily available in some foreign countries.

The oil engine would continue to be demanded by the home operator and elsewhere where suitable fuels were available. An influence against its wider adoption for cheaper vehicles was the comparatively high initial cost. Credit for pioneering smaller units should be given to the makers of the Gardner 4LK and the Perkins P6, followed by a number of others. There was much in favour of four-cylindered units in the 41-5flitre class, and the case for supercharging was an attractive one.

There were trends towards simplifying gear changing, and providing live forward ratios. Additional ratios were often achieved by an auxiliary gearbox or two-speed axle. Traditinnal spiralbevel and worm final drives were giving way to the hypiaid bevel. An interesting axle was the double-reduction Kirkstall with hypoid bevels and planetary gears in the hubs.

• Better Brakes

Much improvement had been effected in brakes, but no new principle applied. Consideration had been given to transmission brakes on heavier vehicles, and servo devices were used on many vehicles over-5 tons.

There was a breakaway from traditional design in passenger chassis, many single-deckers having engines under the floor. To use these also for doubledeckers would simplify manufacture and maintenance. Given a free hand to design a horizontal engine, some very different results might have been obtained. The appearance of the rearengined Foden had stimulated argument as to which was the best place for the power unit.

There was a trend to reduce the effort needed to change gear, but until a more efficient torque converter be developed there was little likelihood of that form of transmission being adopted to any great extent.

If considerable reductions in unladen weight could be achieved by chassisless construction, resistance to its progress would not be prolonged.

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Organisations: Earls Court
Locations: Glasgow

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