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a British premium tractive unit
1y D. Lloyd, BSc
Part I: What are we looking for?
/HAT IS a "premium" tractive unit? It is ot an easy vehicle to define in precise ;rms, but any long-distance freight perator will have his own picture of what le term implies. And I think that all such perators would agree that one is talking bout a long-distance vehicle with ower-to-weight ratio and braking erformance well above the present UK gal minima; smoke emission well below le legal maximum; a cab giving a high egree of driver comfort, with certain !atures not found on domestic vehicles; obust construction and, above all, png-term reliability.
Reference to premium specification tends 3 make many operators immediately ssume that such a vehicle is solely for TIR iork but, especially with the growth of lritish motorways, this is too narrow a iew. It is, after all, farther from Aberdeen o Plymouth than from the Belgian coast to
■ witzerland. The fact that British operators ,re customers for considerable numbers of mported premium specification tractive inits should not be overlooked.
Certainly, the premium-spec unit is a ype made by all the leading Continental wavy commercial vehicle manufacturers, )ut this series of articles will set out my idea )f a specification for such a vehicle which :ould be British made. The component parts ire already in production in Britain. In ;ome cases I have considered American or 77erman parts because they are more fully ieveloped or because Continental service 'or them is better; but in fact it would be possible to assemble a premium specification tractive unit (in my terms) of which every major component was British.
Before setting out the engineering aspects 3f such a vehicle in detail, let us take a look at what it should be capable of achieving in service.
Stopping and going A braking efficiency of 70 per cent is possible for heavy lorries and nothing less will do, since this figure is still well below the performance of car brakes. An effective retarder and, for artics, an anti-jack-knife Jevice should be included in the braking system. The legal minimum power /weight ratio of 6 bhp /laden ton results in a hopelessly underpowered vehicle, as has been emphasized in CM on numerous occasions, and the proposed EEC standard of 7 bhp /tonne is still inadequate for present-day traffic conditions. The US Department of Transportation has issued several proposals on this subject and, although there is not sufficient data to justify a requirement in America at present, the figure of 11 bhp /ton — equivalent to 12.3 bhp /British long ton, is more like it. Unfortunately this would be unattainable at 32 tons gcw with engines currently made in Britain, so a compromise of 10 bhp/ton is suggested for our premium vehicle.
Drive-past noise level should ideally not exceed 80 dBA but since this figure is about half the current noise levels it will probably be too expensive to reach initially (though in view of UK Ministers' recent comments about lorry noise I'm surprised that no British manufacturer has come forward with a quiet lorry). Like bhp /ton, we shall have to accept a compromise figure on noise, aiming for the minimum practicable level. Smoke emission should not be a problem. as most new engines are well within the BS AU 141a: 1971 limit for exhaust gas opacity.
A premium specification vehicle should also have a cab with a high degree of driver comfort, several features which increase operational efficiency should be fitted as standard, for example, automatic chassis lubrication, and models intended for TIR operation should have equipment to deal with Continental driving conditions. However, by far the most important premium specification feature is, as I suggested earlier, long-term reliability. Mechanical reliability is achieved by every part of the vehicle being on top of its job, but electrical reliability is more of a problem. Possible solutions will be considered in the section of the specification covering electrical equipment.
New models Following the demise of the AEC Mandator V8 there was, in my opinion, no British vehicle remotely approaching "premium" specification in the terms that I have stated, but there are signs that this state of affairs will change. Most of the leading manufacturers are thought to be working on "Continental" model heavy tractive units which are rumoured to be nearer a premium specification than their predecessors, and ERF has shown the 64 CU 335 at the Brussels Show with a much improved cab. The new models are the NGC 360 and 420, but a comfortable cab does not, by itself, constitute a premium spec, and at 7.7 bhp/tonne the NGC 420 does not match the power of the German vee tens. Also, in a model intended for the French market among others, the lack of a Telma retarder as standard is surprising However, there is a choice of Continental tractive units which meet premium specification requirements as regards engine power, cab comfort and reliability. Best known in Britain are the Scania 140 and Volvo F89, but there is also the Berliet TR 320, DAF 2800 DKTS, Fiat 619 TI and Magirus Deutz and Mercedes-Benz tractive units with V 10 engines. The air-cooled Magirus Deutz is probably noisier than desirable, but the diesel-fuel-fired cab heater is an important advantage to a driver delayed somewhere in the depths of winter.
These models were designed to meet the German power weight ratio requirement of 8 bhp/tonne at 40 tonnes in anticipation of 40-tonne vehicles being allowed in EEC countries, but the increased productivity available from a higher power /weight ratio has made them economic at lower gross weights. For example, in Germany traffic congestion is so bad in summer that traffic jams on the autobahns are routine and the Frankfurt-Koln autobahn is often best avoided. Under these conditions an underpowered vehicle would not be able to average the 35 mph necessary to cover the EEC regulation 450km maximum in 8 hours' driving.
When Continental trucks were first imported into Britain five or six years ago they sold because they were available, this being the time when some British models were on 12 months or more delivery. However, British operators engaged on TIR work had seen how Continental trucks• left them behind on the hills so bought them because of their superior specification. Their lead was soon followed by UK trunk operators, because a vehicle suitable for TIR work is also suitable for long-distance UK work and this is the main application of a premium specification vehicle.
Virtually everything over 120 miles radius from base constitutes long distance, and reliability is the greatest advantage. The degree of mechanical reliability is more or less proportional to power/weight ratio, it being obvious that an underpowered vehicle working flat out all the time is going to start breaking down sooner than one which is usually only working at part load. Expressed another way, a 30-ton truck powered by a 180 bhp engine will be driven harder than a 16-ton truck with a similar 180 bhp engine, or than the 30-ton truck if it had a 320 bhp engine. At best, a breakdown a long way from base is expensive, there being not only the cost of the repair, but possible late deliveries affecting the reputation of the haulier or a lost load while the vehicle is off the road under repair. More serious is a breakdown such as a wheel falling off, a prop shaft breaking or simply brake failure which can result in an accident.
Thus the second major advantage of a premium specification is increased safety, not only from the reduced possibility of serious mechanical failure, but because the vehicle will usually be running with an ample reserve of performance so the driver will be more relaxed and able to pay better attention to road and traffic conditions.
Where power pays Low maintenance costs and long life are obvious major advantages of a premium specification vehicle and a high power engine in particular. In fact the higher the engine power, the lower the overall long-term costs of the vehicle.
Another advantage, that of reduced running time, is insignificant over the shorter distances such as Birmingham tc Southampton (130 miles), London tc Brussels (140 miles) or Cardiff tc Nottingham (150 miles) but on longer runs such as the 600-mile trip from Aberdeen tc Plymouth or the similar distance from the French or Belgian Channel ports to the Bodensee, half a day can easily be saved. On the really long-distance runs to Southern Italy, Eastern Europe or the Near East, not only are days saved but in the last case. only a premium specification will stand up to the road conditions. A DAF model 260C DKA has done the round trip to Pakistan and back in six weeks and regularly runs to Teheran.
Numerous specific examples of days saved by the use of premium specification tractors can be quoted. In one a Scania does Le Havre to Concorezzo in one and a half days with no night driving while a Ford D1000 pulling an identical load takes two and a half days. If the Scania can pick up his return load and get clear of Italy before Sunday, another day is saved. A more extreme case is the run from Zeebrugge to Voralberg, regularly done in one day by an operator using Scania 110 and 140 units; whereas another operator using Volvo F86 tractive units usually takes two days pulling similar trailers. Allowing one day for the Austrian turnround, the first operator can complete the round trip in three days and each unit can do two trips in a six-day week, whereas the second operator does one trip in a five-day week. Of course, in this case the first operator is breaking Common Market driving laws while the second is observing them, but the Belgian view is that the chances of getting caught are negligible.
Germany is the only country in which any real attempt at enforcement is made and the Germans are very unimaginative, always tending to use the same parkplatz or "LKW Kontrolle" checks. Also, the two rips in six days' schedule does not allow for my delays due to loading or unloading, :ustoms, traffic congestion or weather, but n the absence of these the premium ipecification tractors are earning money at .wice the rate of the small Volvos.
An old chestnut usually dragged out in iny discussion about premium specification -chides is that "power costs money" but his is a perfect example of the 1930s mage mentality resulting from pre)ccupation with miles per gallon figures which, on their own, mean nothing. The .echnical press helps to perpetuate the Thsession with mpg by emphasizing mpg igures in road tests of lorries instead )f the true fuel consumption. In this :ontext true fuel consumption is gallons )er mile per ton per mile per hour nultiplied by 100,000. To explain this, irst dispense with miles per gallon, which s an unsatisfactory term for fuel onsumption because the figure moves in he opposite sense to the parameter of which it is a measurement, and use gallons ser mile.
rrue consumption
The true fuel consumption is the fuel :onsumption relative to the gross weight if the vehicle, hence gallons per mile )er ton, and to the average speed for he run so the final term is gallons per nile divided by the weight and by the iverage running speed and multiplied by 100,000 to give convenient figures.
A term like "per mile per ton per tile per hour multiplied by 100,000" s too cumbersome for regular use, so it would be better to call it a "unit" and true fuel consumption is then measured in gallons per unit or GPU. In metric measurements this becomes litres per metric unit, the metric unit being per kilometre, per tonne, per kilometre per hour times 100,000. The figures are not much different, 1 GPU being 1.73 LPU.
Numerous road tests of lorries have shown that, for similar running times over the same route, total fuel consumption increases with gross weight, but true fuel consumption decreases with gross weight. This only proves that a heavy lorry is more economic than a light one, as is already generally accepted. At the same gross weight, total fuel consumption increases with average running speed, but true fuel consumption is not necessarily increased by higher engine power or power weight ratio. My table shows the results obtained in Commercial Motor road tests of 32-ton vehicles in 1971-72 (CM May 15) and comparison of the power weight ratio and true fuel consumption columns shows that, although one of the two vehicles with the lowest power weight ratio is the most economic, the other is less economic than two more powerful vehicles.
The Scania at 8.6 bhp /ton has the same true fuel consumption as the Scammell at 6.5 bhp /ton and less than the AEC at 6.4 bhp /ton, while the DAF with the second highest power weight ratio has the second lowest true fuel consumption. Thus there is no correlation between true fuel consumption and power /weight ratio, as expected, and the most significant difference in performance is from one make to another. This is thought to be due to variation in transmission efficiency.
In general terms the same power is needed to move a given load at a given speed irrespective of whether the maximum power of the engine in use is 220 or 340 bhp. This assumes other things being equal such as trailers with a 4 x 2.5 metres cross-section in each case and the vehicles having the correct gear ratios. Perusal of performance curves will show that overall fuel consumption will be the same in each case. In fact specific fuel consumption of the more powerful engine is sometimes lower, balancing out the higher power which the heavier-duty transmission absorbs.
In the case of the Rolls-Royce Eagle 220 and 340 engines when • both are producing 220 bhp, the specific fuel consumptions are 0.390 and 0.3581b /bhp / hour respectively giving fuel consumptions of 9.4gal/hour for the 340 bhp engine and 10.2gal/hour for the 220 bhp engine. These figures would be reflected on motorway running, provided the more powerful vehicle was not undergeared, and even at the same engine speed the turbocharged engine is more economical as the part load specific fuel consumption, when producing 220 horsepower at 2100 rpm is 0.375 lb /bhp /hour.
Time is money
Fact, of course, does not bear out theory, because the driver of the more powerful vehicle will use his extra power to reduce his running time, thus increasing his fuel consumption. But time is money and the time saved could be particularly valuable if it enabled a run to be completed in one day instead of running into a second day. There is more than one operator whose drivers regularly work a 14-hour day at present on day runs. This consists of up to 1+ hours refuelling and swopping trailers because no yard ' shunter is employed, trailer winding handles and number plates can never be found and usually both vehicles are boxed in, followed by a 12+-hour "spreadover" to complete the run in a day with underpowered tractive units. If there is any delay extending the run beyond 124 hours, a "breakdown" is booked on the log sheet which is quite plausible considering the state of the units used by most operators of this type. These people will have to use premium specification tractive units to stay in business when tachographs become mandatory unless they can think of ways to fiddle the tachograph records.
For the increased productivity obtainable from a higher power /weight ratio vehicle to result in more economical operation, it is necessary for vehicle utilization to be high and there must be incentive for drivers to do the extra work.
Apart from economy the environmental advantages of premium specification vehicles are important. A few years ago protesters against pollution of the environment were completely ignored, but a few recent examples have shown that if protest is properly organized and can get the support of public opinion, the developer can be checked.
The premium specification vehicle, with a power /weight ratio of 10 bhp /ton or more, a noise level of 80 dBA and considerably better brakes, could be road transport's answer to accusations of "juggernaut". The introduction • of a premium specification vehicle with maximum publicity is the way for road transport to improve its public image.
The component parts for such a tractive unit are already in production and a practicable model could be built at a realistic price, based on the frame of the current 32-ton, four-wheel, models produced by the quality makers. The
resulting specification could read as follows:—
Engine Cummins NTC 350 or NTA 400 or Rolls-Royce Eagle 340 double-capacity cooling system and thermostat-controlled fan or fans. High level air intake and exhaust with extra silencers. Cylinder head surrounded with acoustic cladding.
Transmission ZF or Brockhouse torque converter and five-speed gearbox or twin plate clutch and Eaton nine-speed range change gearbox. A Spicer SST splitter gearbox is an alternative to the range change gearbox.
Front axle One-piece I-section with ZF power steering. Rated 6.0 tonnes.
Rear axle Eaton 19120 rated 10 tons or 19128 or 19320 rated 11.5 tonnes.D.A.P. differential lock.
Suspension Semi-elliptic springs with shock absorbers.
Braking system Three line, full air, giving 70 per cent efficiency, Maxaret operating on both axles and Telma Retarder, Wheels and tyres 7.5 x 22.5in. with 22.5 x 11.00 tyres.
Frame Channel section with cross-members. Wheelbase 3.5 metres. Automatic lubrication. Double front bumpers. Twin fuel tanks. Catwalk, Susies and fifth-wheel fitted.
Cab Based on Motor Panels "Transcontinental" cab, non sleeper, right-hand drive, tilt, version. Flat floor to front of seats and three-man passenger seat. Luggage shelf behind the passenger seat with space underneath for stowing the service aids. The cab heater should be capable of sustaining a temperature of 30degC aboire ambient and operate independently of the engine. Aeroflow ventilation. Maximum interior noise level BO dBA at 60 mph.
Electrical Possibly a 12V system with 24V starter. Two heavy-duty 12V batteries.
Instruments Smiths ergonomic heavy commercial vehicle instrument layout.
Service aids Every tractive unit should carry a set of tools and spares of consumable items.
For units intended for TIR work to Central Europe, some extra equipment is necessary. This is:—
El Engine cold start for temperatures down to —30degC.
LI Better suspension, possibly rubber or air; built-in sanding boxes, El Cab heater capable of keeping the cab temperature 50degC above ambient, El Head and spotlights for driving on the right of the road, and a comprehensive set of spares, tools and cold weather equipment.
Scandinavian countries in winter and Mediterranean countries in summer, impose greater extremes of temperature, so the engine cold start and cab heater would need to cope with temperatures down to —40degC in the former case, also gearbox and differential heaters are necessary, while a Kysor air-conditioning unit would be available for the very hot weather application.
This specification will be discussed in detail in subsequent articles, beginning next week with the engine and transmission.