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INCREASING specialization on the part of operators of heavier vehicles

17th May 1968, Page 74
17th May 1968
Page 74
Page 75
Page 76
Page 74, 17th May 1968 — INCREASING specialization on the part of operators of heavier vehicles
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will favour "independent" manufacturers because they are in a position to match the best available major chassis components to the needs of specialized users--this is the view of Mr. Yates and Mr. Cooke. Higher powers and weights would benefit all UK manufacturers because they would foster a higher degree of compatibility between home and export models.

Mr. Yates and Mr. Cooke recently returned from a tour of America, Australia and South Africa (CM, May 3) and feel that a number of current developments in America will be a major influence on traffic and vehicle design trends throughout the world. They qualify this observation, however, with the comment that America has a lot talearn from this country and that these trends will not gain ground in the UK unless legislation is introduced stipulating a minimum bhp/ton rating and allowing the use of vehicles of higher gross weights on selected routes.

They say that contrary to the generally accepted concept of American awareness.

American transport men believe that thehigh. speed short-stroke engine, mated to a multi ratio box, has had its day. Makers are con centrating on the "custom-torque" engine in compliance with the needs of operators and to cater for individual needs.

The custom-torque engine takes the form of a slow-speed long-stroke turbocharged unit, the nominal bhp output of which is well in excess (say 15 per cent) of the power required. An improved torque back-up is provided that enables the number of transmission ratios to be reduced and a lighter, less costly gearbox to be employed. The bhp output of the engine is derated in accordance with the excess power available, and in addition to offering a good low speed torque the unit has a long wearing life.

Reliability and a long life are priority considerations in America—the reducing of down-time is regarded as far more important than reducing fuel consumption or saving on first cost. However, fuel consumption will continue to be a major selling factor in this country and in the majority of world markets; it is notable that the custom-torque engine promises to provide better economy than the higher speed units in current use.

While in-line six-cylinder engines predominate in custom-torque developments, long-stroke V engines have been developed in America that could readily be adapted to provide custom-torque ratings. Although they have created certain installation difficul ties in the case of Atkinson vehicles (CiMC two-stroke V engines are fitted in a number of Atkinsons operating in Australia). Mr. Yates and Mr. Cooke consider that the long stroke V may well have aft important role in future developments.

They point out Vehicle development has been stultified over the past few years in this country by vague indecision on the part of the Ministry of Transport regarding powerto-weight ratios. Consequently many operators have been specifying relatively low-powered engines for heavy vehicles to gain an immediate advantage in the form of reduced fuel consumption. A ratio of 6 or more bhp/ton (in America the average is about 7 bhp/ton) would stimulate design progress in this country and promote longterm economy in addition to facilitating compatibility with the type of vehicle required overseas.

In due course custom-torque engines of around 400 bhp derated to say 350 bhp and producing a torque of 900lb/ft, will probably be required on a worldwide scale. The legal yardstick of performance should not, however, be based on power-to-weight ratio (which would discourage the use of customtorque engines) but on a performance factor or gradabilii y rating. This could well be based on the American minimum rating of 20 mph on a 3 per cent gradient operating at maximum gross weight.

The gas turbine is unlikely to find general favour in any part of the world except possibly for operations on the turnpikes of America or equivalent roadways developed in other countries. Speeds of up to 70 mph are permitted on the turnpikes and the characteristics of a gas turbine could be exploited to the full, the efficiency of a turbine depending on sustained high-load ru mire .

Inevitably in this country the legislators will in due course sanction the use of vehicles

with overall lengths up to 100ft on selecte routes, and doubleor triple-bottom vehicles will be used on these routes for a shuttle service between depots at the ends of the route. The Transport Bill will have very little effect on the growth of heavy vehicle traffic; Licensing Authorities will use their power intelligently in the interests of national economy and will not favour the railways unfairly.

Double bottom vehicles carrying two 40ft containers (grossing at about 75 tons) and triple-bottomed combinations carrying three 27ft containers (grossing at about 70 tons) are being increasingly used on the American turnpikes. And this represents a trend that will find favour in many markets. It is assumed that in the 1..TK one-man operation of draw bar trailer outfits will eventually be allowed.

In America a guaranteed engine life of 300 poo miles is the target of the makers of higher powered units to meet the current demand for long life. The custom-torque engine should give a life of this order under arduous operating conditions.

In a trans continental run in Australia of 3,000 miles, only about 400 miles is on metalled roads and in the event of a breakdown it is often necessary to charter a plane to take parts and a mechanic to the stricken vehicle. Here again, therefore, durability and a long life take precedence over low weight or first cost

In the past Atkinson has been concerned in noise reduction for the benefit of drivers and it is noted that the level may be 12 to 16 dBA higher in the cab than on the outside. Apart from reductions of exhaust and intake noise, improvements are in the hands of engine makers and in some cases encapsulation wholly or in part may be required.

Employing a thermostatically-controlled type of fan drive would be favoured if the equipment were simple and reliable, the advantage envisaged being a reduction of a power loss. It is noted that a flexible blade type of fan is in common use in America. This has glass-fibre blades that automatically feather at higher speeds, which reduces the capacity of the fan and the power absorbed.

Atkinson does not favour tilt cabs but Mr. Yates and Mr. Cooke consider that improved accessibility should be given priority. They contend that this could best be provided by an installation system which enabled the engine and gearbox to be withdrawn from the front of the vehicle with the minimum of uncoupling.

In line with the uprating of gross loads, two distinct types of vehicle will be developed —a city vehicle of up to 26 tons g.v .w. and a train vehicle with a gross rating up to the maximum allowable.

Conventional types of automatic gearbox with torque convertor and planetary gears will increasingly be used for vehicles used in -congested areas. Conventional gearboxes will continue to be used for train vehicles as relatively little gearchanging will be required.

Infinitely-variable transmission will be developed for earth-moving machines powered by engines developing upwards of 500 bhp and may take the form of electric wheel motors supplied from engine-driven generators. If gas turbines are used for turnpike operations electric traction would be the ideal and might possibly be applied to dieselenginect vehicles in due course.

The general use in America of chassis dynamometers by garages and distributors has brought to the notice of operators that a lot of power is lost between the engine and road wheel (which often amounts to 25 per cent) and this has directed the attention of manufacturers to the need to improve the efficiency of transmission systems. Undoubtedly attention to detail could improve transmission efficiency by say 5/10 per cent.

There is an urgent need for a light and efficient brake retarder, low weight being more important than low cost. While disc brakes have higher fade resistance than the conventional drum-type, the problem of heat dissipation if a protective shield is fitted to eliminate the ingress of dust and grit particles is one which will probably limit the use of disc brakes to special applications. Shielding a disc brake inhibits heat dissipation and increases fade tendencies.

A lot of work has yet to be done on suspensions and the first necessity is to reduce the total unsprung weight which in the case of a heavy tractive unit may be as much as 21 tons. Reducing unsprung weight would have the double advantage of facilitating the development of improved suspensions and of augmenting payload.

Driver comfort

The increasing attention being given to driver comfort will necessitate the use of softer springs. Eventually more sophisticated types of suspension will be developed but in the meantime existing types can be greatly improved. Enforcement of the weight regulations will be of great benefit to vehicle manufacturers as it will eliminate the need to design for overloading.

Suspension problems are aggravated by the torsional flexibility of the current type of chassis based on conventional longitudinal members. While it would not be possible to build a non-flexing long-wheelbase chassis it would be feasible to design a tracuve unit with a rigid chassis based on all-welded pressed-steel components. This could be equipped with independent suspension at the front, of a type similar to the suspension of a typical private car, and with air suspension at the rear.

Air suspension is not suitable for applica ton to a flexing chassis or to a steering axle. in the latter case because it would impair stability. The use of i.f.s. would enable the height of the engine to be reduced and although it would necessitate a particularly stiff structure at the front to cater for high local stressing the pressed-steel frame would afford a weight saving.

Implementation of the proposed legislation regarding the centre of gravity of vehicle loads would be approved. This v. ould require that the maximum c of g height of the load be given by the vehicle maker. Loading that gave a higher c of g would constitute a breach of the regulations, and such regulation would undoubtedly be a aluable safety measure. The flexing characteristics of rigid-vehicle frames should be matched to the type of body carried and its torsional rigidity. For example a torsionally rigid tank can appropriately be mounted on a light chassis frame, while a light tank should be mounted on a heavy frame.

While low profile types are offered by Atkinson as an option and there is no objection to their use, they are not being eon• siderecl as original standard equipment, despite the weight saving they provide.

Although the load-transfer system would be favoured for vehicles up to say 30 tons g.v.w., combinations of 38/42 tons gross will need a double-drive bogie. The legality of a load-transfer system is in question and clarification by the MoT of the legal aspects of its application would be welcomed.

Lock actuators are preferred to spring brakes because the latter require continual adjustment. and residual drag can result from slow release of the braking force which could increase lining wear. Moreover, the driver cannot prevent automatic operation of a spring brake in the event of air failure and this loss of control is undesirable. It is pointed out that hill holding by spring brakes or lock actuators on the front axle is negligible on a steep gradient, such as a slope of 1 in 5, when the vehicle is facing up the slope.

The self-steering axle is not favoured but a linkage/turntable system of the Halo-type could be used with advantage on semitrailers, this could eliminate jack-knifing in addition to reducing cut-in. Tyre scrub with a three-axle rigid or tractive unit chassis is not serious and employing a self-steering axle (at the rear) is regarded as an unnecessary complication.

An axle load-sensing device would be a boon to operators, Mr. Yates and Mr. Cooke agree, but a device of reasonable accuracy is unlikely to be developed. In America and New Zealand load sensors of the hydraulic pad type are commonly employed on logging vehicles, and could easily be adapted to measure axle loads. It is doubtful, however, if the overall weight of the load would be gauged more accurately than + + ton.

In conclusion, Mr. Yates and Mr. Cooke predict that the American operator's order of priorities will increasingly apply to the rest of the world in areas where operating conditions of the American pattern apply, with the

probable exception of fuel consumption. In particular, -putting price last" will gain in acceptability as an exercise in true economy --so long as there is value for money.

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Organisations: Ministry of Transport
People: Cooke

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