Truck engineering gets more
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sophisticated by Graham Montgomerie THE FACT that the Commercial Motor Show is taking place at all, in spite of all the complications imposed by the three-day working week earlier this year, is a compliment to the efforts of the British commercial vehicle and component manufacturers. The industry is putting on a good display at Earls Court, many firms exhibiting completely new vehicles.
The maximum interest is once again in the upper end of the weight scale, although the lower categories have not been overlooked.
The major launch of the Bedford TM range is a sign that the giant General Motors combine is now ready for a fullscale assault on the European market. At Earls Court in 1972 Bedford showed a 32-tonner, but it was more of a tentative sounding out of operator reaction to the Detroit Diesel two-stroke engine than a serious attempt to break into the market. The investigation has now been completed, and the resultant TM range is a display of major importance at Earls Court this year.
The 32.5-tonne (32-ton) 4x2 tractive unit weighs in at 5.35 tonnes (5.27 tons) kerb weight, which puts it in a very competitive position in terms of payload. The power unit has proved itself to be a reliable motor over the past two years, although many operators might still need convincing on the two-stroke principle. The 6V-71 unit produces 161kW (216 bhp) at 2,100 rpm from only 6.98 litres (426 cuin). At a price of £10,028 the TM3250 is certainly competitive and the new cab is at least as good as, if not better than its UK and Continental competitors.
Eight from GM Although the TM range will eventually cover trucks with gcw up to 42 tonnes, "only" eight models are released at present, all with the regular "D" cab. Due in 1975 will be the wider "F" cab with interior dimensions which take full advantage of the legally permitted limits at home and in most export markets. Also in 1975 the "H"-type sleeper cab will be released. Based on the full-width "F" cab, this will have an additional 508 mm (20 in) overall depth to provide sleeping accommodation.
The Detroit Diesel engine is installed in all the eight models of the first phase. This means that the 16-ton-gvw TM 1700 also has 161kW available, but it must be remembered that this particular vehicle is also suitable for drawbar operation at the full 32 tons gcw that the UK allows. The well-proven and familiar Fuller 9509 range-change gearbox is specified in conjunction with single-reduction axles for use in the 15 to 25 tonnes (14.8 to 24.6 tons) models which will make their appearance in 1975. A significant feature of the TM range is that Bedford has produced a UK 32tonner as well as a European model designed for the heavier gvw instead of using the maximum-weight model for both markets.
The independent Cheshire manufacturers of ERF and Foden both make it quite clear that they do not intend to be left behind by the opposition. The new "B" series from ERF is unique in using a glassfibre cab on a metal frame, but the company has avoided the obvious pitfalls of such a design. Previous glassfibre cabs have been hand laid up which is time consuming and expensive and produces variations in section thickness. The new ERF cab uses panels made from hot-pressmoulded glassfibre from the Duple company of Bifort, where the raw resinimpregnated material is put into a matched tool-press where it is heated and clamped. ERF claims that final sanding of the panels is unnecessary for painting and also that oJe panels and spare panels will be completely interchangeable as it is simple to maintain the required dimensions by this process.
The subframe of 14 swg steel answers all the questions on the subject of impact strength as the prototypes were tested to all the likely EEC regulations without failure. To ease production of chassis frames, fitted bolts are now replaced by clearance holes and anti-vibration nuts.
Departure from tradition
The "other" manufacturer from Sandbach shows a distinct departure this year from traditional Foden practice in the transmission field. The new four-model tractive unit range uses a Fuller gearbox, the nine-speed rangechange 9509, instead of the usual eightspeed with overdrive unit of Foden's own design. With an eye to improving the overal mechanical efficiency by reducing transmission losses, Foden has chosen a Rockwell hypoid-bevel singlereduction rear axle. This change in policy is said to be on the grounds of the wider servicing facilities available in Europe for the proprietary units. In the case of the gearbox, Foden says that fitting the Fuller box will ease production demands for its own unit in other models in its vehicle range; for example the eight-wheeler. But I wonder if this is the beginning of the end of Foden's staunch policy of using as many of its own components as possible and that in the future the proprietary units will be used in all the models.
An interim cab called the S83 is used which is an adaptation of the present S80 plastic cab with modified mountings to make it interchangeable with the new S90 pressed steel cab. It is interesting to compare the policies of ERF and Foden on cab design, especially on the use of steel and grp as constructional materials.
The distinction between 32-tonners and 38-tonners operating at the UK limit is well defined at Earls Court. Most of the Continental exhibits are to 38 tonnes (37.4 tons) gcw, which, in most cases, means they carry an extra burden in kerb weight. One exception is the DAF FT2000 which is a "lightweight" maximum-capacity truck. Fully equipped with derv, oil, water and fifthwheel, it turns the scales at 5.1 tons. If this were coupled to an all-aluminium trailer such as the Welford design, the allowable payload would be in the region of 23 tons. The "heavy" manufacturers argue that loads usually come in 20-ton lots anyway and that higher payload capacity is often unused. Also operating a 38-tonner at 32 tons gew is claimed to lead to a long breakdownfree life as the truck is operating on a lower stress level. This would indicate that all the Continental vehicles should have a higher level of reliability than the UK counterparts, but I am not sure that many operators would agree with this.
Volvo, one of the early leaders of the foreign assault on the British market, shows its uprated power units for the F86 and F88 vehicles, both familiar in this country. Two years ago most engine manufacturers with the most notable exceptions of Daimler-Benz and Fiat were hard at work on turbocharged engine designs. Now most of the initial design parameters have been established and manufacturers are concentrating on detail refinements to obtain the most efficient combustion from their blown engines. Volvo has developed an exhaust back-pressure regulator for better light-load running together with a number of detail improvements which have boosted the power output of the F85 from 172 to 217kW (230 to 291 bhp). A higher turbocharger boost is used but to restrict increases in peak cylinder pressures, the compression ratio is reduced from 15 to 12.5 to 1 which has necessitated an induction heater for starting.
The AT regulator, as the back-pressure control is known, provides an additional artificial engine load at light-load conditions. By eestricting the exhaustgas flow and hence increasing the back pressure, the combustion temperature is maintained at a high level comparable with the full-load condition.
The DAF refinement for turbocharged engines is the use of an air-toair charge cooler on the DKS 11.6-litre (708 cu in) engine. With power being proportional to the mass of inlet charge, any reduction in inlet air temperature is obviously beneficial and DAF claims a reduction in air temperature of some 50°C with its system. Although the installation is somewhat cumbersome compared with the integral radiator system employed by Garrett AiResearch on the American Mack engine, the DAF layout can be used without modification to the turbocharger itself.
As I mentioned earlier, Mercedes and Fiat stick resolutely to naturally aspirated designs, although the former continied overleaf probably has no immediate need for any extra power as its V10 engine develops 239kW (320 bhp).
Earlier in the year, Perkins released details of the "Squish lip" combustion chamber designed to reduce emissions and noise. Following on from this is a development in engine cladding to further cut down noise levels. The cladding material comprises a thin leadsheet-filled sandwich of asphalt-bonded asbestos sheet. Perkins suggests that typical cladding applications would be tappet, cover, sump and timing-case on a conventional diesel engine.
The entry to the UK market of two new eight-wheelers from MAN and DAF is a move which I personally find rather surprising. The production of four-axled machines last year amounted to less than 2,000 units, of which Foden alone accounted for over 40 per cent, with the British Leyland Group adding another 30 per cent. For such a relatively small market, remembering that the UK is really the sole area for eightwheelers, I am curious at the interest shown by the two companies. On the other hand, most of the components, mechanical and otherwise, are common to other vehicles in their respective ranges so the design work required would be relatively small.
That the British builders have fast caught up with the European competition is especially obvious in the area of cab design. Without going into too much detail on the subject (see page 30), compare the new Seddon-Atkinson MkIII cab, for example, with any of the Scandinavian trucks which have been long regarded as leaders in this particular field. I would now suggest that the boot is now on the other foot and new British cab designs, especially those of Seddon-Atkinson and Bedford, are setting the standards. Certainly, I feel that the time is right for a face-lift on the Volvo F88 cab.
An example of a more original approach to cab design is the result of a co-operation between Motor Panels (Coventry) Ltd and Ogle Design. The cab is certainly futuristic and, leaving out some of the more obvious showtime gimmicks, puts forward some useful ideas. The central driving position is suggested for on-site operation with right or left-hand drive for road use. Although the makers say that all their design innovations have been achieved in a cab only 11 inches longer than a standard unit, these 11 inches are important when it comes to squeezing into the 15 m overall limits for an artic unit.
The Leyland Marathon has a mechanical specification equal to anything in Europe, although its cab looks as if it was designed for another vehicle. But I wonder how seriously we are meant to take the Marathon Special with its super de luxe interior trim incorporating washing and cooking facilities?
Taper-leaf-spring suspension is gradually becoming more widespread on vehicles ranging from the new Leyland van to the TM Bedfords and, although air suspension is almost non existent on vetiicles, it is quite familiar on trailers. With its advantages of height adjustment, less variation between laden and unladen condition for ride height, and lower weight, I am surprised that air suspension does not find greater acceptance; presumably it is because of the cost penalty.
Bedford uses taper-leaf springs on the front suspension of the TM's which, it claims, saves around 40 per cent on weight compared with a conventional multi-leaf design. But Bedford hedges its bets by retaining multi-leaf assemblies with taper-leaf helpers at the rear. On the Leyland CV306 range, taper-leaf springs are similarly used in the front, although in this case a single-leaf design is featured.
This Leyland light van range is a really determined display at Earls Court even if only assessed on the sheer number of variants on show. The chassis-cab version of the Leyland makes an interesting comparison with the Toyota Hi-Ace and Mercedes-Benz L306D equivalents. The advantage of the front-wheel-drive layout of the German chassis in lowering the chassis height can be seen by comparing the three versions.
Increasing the load carrying space of a light van is treated by Simca and Volkswagen in different ways. VW has extended the interior floor length by some 3ft, while the French section of the Chrysler empire has increased the interior height of the new Simca "High Top" van to 1,270 mm compared with 914 mm of its standard van (50 in against 36 in). This is a sensible approach as vans in this category are usually limited by load volume rather than weight and are seldom operated up to their full weight limit.
Automatic transmissions are still few and far between, especially in the maximum and medium-capacity field. Allison transmissions are utilized in the Unipower fire-crash tender and the Motor Panels futuristic cab — although it is present in the latter in control layout form only. The transmission of the Unipower C44-20 is fully automatic with five forward speeds and one reverse, with an integral hydraulic retarder incorporated in the system.
Although multi-speed gearboxes are an accepted fact, there is no evident agreement on the suitability of rangechange or splitter units. Most manufacturers whether using their own designs or proprietary ones, tend to specify both systems somewhere in their ranges. Mercedes-Benz, for example, uses an eight-speed range-change gearbox on the new 1626 model while the 1932 model is fitted with a 12-speed splitter unit, both components being of ZF manufacture. It is not unknown for both systems to be used on the same