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To say that the Ford Transcontinental uses a Berliet cab

29th July 1977, Page 24
29th July 1977
Page 24
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Page 24, 29th July 1977 — To say that the Ford Transcontinental uses a Berliet cab
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Which of the following most accurately describes the problem?

is basically true: but it is not quite that simple. The cab structure has had a number of modifications made for the Ford application — notably the provision of a four-point sprung cab mounting.

Ford went, straight away, for a full sleeper cab version — there is no short cab available in the Transcontinental range. Due to the extra height of the Cummins engine over the Berliet unit, the cab has had to be raised relative to the ground. Because of this, extra panels of glass fibre have been added below the waistline of the Berliet cab which is all-steel.

It is easy to tell which part is which when you see a Transcontinental on the road the glass fibre skirt panels are always painted white whatever the body colour.

Nothing lost

In 1974, Mercedes-Benz announced the New Generation range of vehicles with which they made a deliberate attempt to get away from a lorry which 'looked big'. I say 'looked big' .because a glance at the drawing of the interior dimensions of the New Generation and the cab it replaced will show that no space had been sacrificed at all.

The basically rounded shape of the cab was intended by the .Mercedes stylists to do away with 'optical aggressiveness' as they put it.

The New Generation cab was designed for the complete Mercedes-Benz range from about 14 to 44 tons gross. As with most manufacturers, Mercedes offer a sleeper cab version that adds an extra 600m (21 in) to the depth.

To eliminate holes in the cab floor which can act as noise sources, Mercedes-Benz designed the gear linkage on the New Generation machines extend telescopically as the cz is tilted.

Some manufacturers ha \ ;arranged it so the gear linkac automatically disconnects itse at a ball joint as the cab tilt Others accept the presence of hole in the cab floor and go 1 great lengths with insulatir materials to seal off any not: sources.

This is merely another exan ple of how cab engineers sho< off in different.directions to fin a solution to a common prot .lem

New groups

Another new truck range t a announced during 1974, the RE series, breaks new round in the cab construction 'ea by combining steel and lass fibre in the form of a 'elded steel frame and hot ressed glass fibre panels.

The frame is built up from aven main sub-assemblies sing both spot and gas Tiding. The SMC (sheet loulding compound) is formed to panels on large presses at a i-nperature of 140 t 1284 F)

nd a pressure of ,729kNisqm (1,120psi). ERF Iaims that the process prouces panels of a consistent arid pritrolled thickness and to 'exact size.

Glass fibre has, of course, been used before in commercial vehicle cab production, but in hand laid up form.

The advantages of this method were the relatively low tool costs and the ability to make rapid changes in the mould design as and when required. But there were disadvantages as well.

Control of the panel thickness was difficult and a high degree of trimming was necessary after the panels came out of the mould. Production time was longer and a large floor area was required. At the same time, though, the glass fibre concept was still considerably cheaper.

During the design stage of the 'B' series, ERF considered several possibilities for construCtion. These included a steel monocoque, steel panels on a steel frame, aluminium panels on a steel frame, aluminium panels on a composite aluminium / steel frame and plastic panels on a steel frame.

It was estimated that tooling up for an all-steel monocoque cab would have cost in the region of £1.5 million (1969 costing figures) so the final decision was made to go for a steel frame clad with plastic panels, hence the designation SP (steel / plastic) cab.

In more detail, it was decided to adapt hot press moulded glass fibre components on the steel frame for the reasons of panel thickness consistency already referred to. Total tooling cost for the frame and the S MC panels was £475,000.

ERF claim that the final cab is lighter than an all-steel design and only marginally heavier than an aluminium clad version. The production cab has been tested at MIRA and has withstood impact and static loadings greater than the existing and proposed EEC Safety Standards. The SP cab has actually been tested with a 17 tonne (16.7 ton) static roof load and a frontal impact using a pendulum of 1,500kg (3,3001b).

In contrast to ERF, Seddon Atkinson went for the all-steel construction. The cab, an SA design, is manufactured by Motor Panels Ltd, of Coventry.

One neat design feature concerns the windscreen pillars which are 140mm (51/2in) wide at their base but are angled to appear slim to the driver's eye.

An interesting aspect of the total design was that Seddon Atkinson called in an outside consultant — Ogle — to style the interior.

As with Mercedes-Benz, Seddon Atkinson uses the same cab for heavy and light machines. Unlike the German firm, however, the small cab is not absolutely identical although it shares the vast majority of common pressings with the 400 series

High praise

When. Bedford joined in the heavyweight market, in 1974, with the TM range, the cab rapidly received high praise. It won the 'Concours de la Cabine du Vehicule Utilitaire' at the 1 974 Paris Motor Show and followed this up the next year by collecting a Design Council award — the first such award for a cab.

The TM range is unique in that, as well as providing a choice of depth in the cab (for sleeper and standard), a choice of width is also available.

I had an excellent insight into how a commercial vehicle cab is designed from scratch when talked to Ron Cooper.

Bedford differed from Scania, Seddon Atkinson, ERF and Mercedes-Benz because TMs, besides being new vehicles, represented a totally new market. Previously, of course, Bedford had concentrated on machines in the lighter sectors.

So as well as designing a new cab for a new range, the Bedford engineers were entering an area where they had little experience.

It was fairly obvious when the heavy range was first mooted that the existing TK cab was inadequate both from the interior dimensions point of view and because it could not really cope with the bulk of the Detroit Diesel engine. Bedford were well aware of the standards set by the opposition in the area of cab design, so they spent a long time assessing market requirements at home and abroad.

Revealing

-It was important for the operator to tell us what he wanted,said Ron Cooper, describing this stage Of the exercise. The discussions were interesting and revealing with the operators very firm about what they did and did not want.

An example concerns window winders. Bedford were considering several alternatives including electric operation, the conventional winding handle and the 'quick release' tYpe favoured by Leyland with the Ergomatic cab some years ago. When asked what they wanted, truck operators all over the world were adamant that the traditional winding handle was best because of its lack of complication.

So, the TM range has standard window winders.

Because of the constraints in dimensions imposed on the cab designer by vehicle legislation — an overall limit of 15m (49ft. 2.6in) which has to include provision for a 12.2m (40ft) trailer doesn't leave a great deal of room for a cab — every manufacturer ends up with approximately the same shape and dimensions.

The manufacture • •.of any component in sheet metal is expensive especially ,when it is

something the size of a cab. The difference between producing a cab and a passenger car is a difference in volume. Cars are produced in relatively short model runs , but at a rate of 100,000 a year. Commercial vehicle vehicle production is obviously a lot slower so the return on capital expenditure is also slower.

Because of the massive initial outlay required for tooling up to produce an all-steel cab, Bedford looked at alternative solutions: buying a proprietary cab modified to suit their individual requirements or a glass fibre construction.

But after a long, hard look, it was decided to proceed with an all-steel design made by themselves. The major parameters were then identified: • All-steel structures for maximum strength and to utilize existing factory equipment; • 11/1inimal cab length to permit maximum cargo body 'length within the legal overall length consistent with adequate space for the driver; • To meet all current and future potential legislation; • Minimal weight consistent with high durability and occupant protection; • Commonisation between cab types of major components to keep tooling costs to a minimum; • Easy replacement of parts vulnerable to damage.

Other items on the 'things to do' list include providing a tilt cab, easy access for routine servicing and good driver access to the cab.

Where the crunch comes on this list is in trying "to meet all current and future potential legislation".

If designers knew what form future potential legislation was likely to take, they would have a much easier job. Present regulations are bad enough.

Take minimum seating space for the driver as a classic example. There are 40 different sets of national regulations alone formulated with no consultation between countries.

Having decided on the major chassis units to be used e.g. engine, gearbox etc, a vehicle gene—arrangement drawing was made to 1/4 scale, locating these units in relation to the axles within the limits imposed by legislation on weight distribution.'

Nowadays, cab heating and ventilating have become very complex so it's no good designing a cab, then trying to fit all the bits in afterwards. The position of the heater and ventilation ducts has to be decided before the engineers can finalise on the construction of the cab.

Because of the intrusion of the Detroit Diesel engine into the cab, a centrally-mounted heater unit was not possible, so two units (one above the driver and one above the passenger footwells) were decided on. The Bedford engineers were not prepared to accept raising the cab to allow a single central heater unit and, anyway, they found that the air distribution was better with the dual system.

Wood and clay

At this point, the basic cab outline — still essentially a square box — was handed over to the Bedford design department for styling where various full-size models were produced in wood and clay.

The next stage was to make a full-size wooden model of the cab with seats, controls, instrument panel and doors to confirm the acceptability of the overall design. Obviously, final acceptance could only be obtained 'under actual driving conditions on the open road, but a static model is still useful for fixing things like step location and cab entry.

To obtain the required running experience a pre-prototype chassis with a composite wood and metal cab was made. The vehicle was subjected to intensive motorway and local traffic conditions: consequently, modifications were made to the • siting of instruments and controls in response-to suggE tions made by the testi' personnel.

As far as production w concerned, it was decided concentrate on obtaining thr

• major sub-assemblies before t final assembly took plac Simplifying it slightly, th comes .down to A. tom* underbocly assembly; a fro end assembly; a rear assembl,

Bring these three maj sub-assemblies together, p the roof on and the cab complete . . more or less!

The Bedford designers ft light weight very much in mil when the TM cab was first p down on paper. Great care w taken in areas where joints con together to achieve a gra& strength transition at the points..

The finaldesign fell margi ally short of the Swedish impa requirements so, for this mark only, certain basic membe were increased in gauge ar some simple angle reinforc ments were added.

As far as the future concerned, Ron Cooper thin the major change in cab desic will centre around having a hic plastic content in the finish( product. And not just from ti cosmetic point of view — I thought that a structural foa sandwich Could be used whic would allow the use of simpl inexpensive tools at the produ tion stage.

Strict control

In effect, he suggested that would be b.etter to have minimum number of cab cor ponents which would ease th problems at the assembly stag With modern vacuum mouldir tethnology, it would be comp ratively easy to produce pane complete with brackets, bosse etc, all in one piece.

Whatever designers want • do, though, will still be ye, strictly controlled by what tF legislators allow them to do.

• Graham Mon tgomeri

Tags

Organisations: Design Council
People: Ron Cooper, Bedford
Locations: Coventry

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