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B y THE mid-1970s the gas turbine will be in a

12th January 1968
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Page 50, 12th January 1968 — B y THE mid-1970s the gas turbine will be in a
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favourable competitive position, compared with the diesel, for application to long-distance heavy vehicles requiring a pdwer unit of 250/300 bhp. Later, units with outputs as low as 200 bhp will be acceptable on economic grounds for trunking and some nontrunking vehicles.

The gas turbine affords a payload advantage of approximately 20001b; it can be combined with a simple form of transmission to provide a clutchless drive offering sustained-torque acceleration; it will be reliable and will operate without undue smoke emission at a low noise level. It will also have a long life and a regenerative system giving a fuel consumption nearly comparable to that of a conventional diesel engine.

Oil consumption moreover, will be negligible, and the unit will be easy to start in cold weather, with full power instantly available. Drive-line shock will be reduced and it will have installation advantages.

Relating these claims for the gas turbine to the wider concept that "it is always possible to improve economy by reducing weight", and that vehicle weight reduction represents a dominant problem in designing for the future, Mr. Manning points out that saving weight in the case of the diesel (and of the associated drive line) is in part dependent on increasing the rpm. The implementation of the noise regulations, he says, will frustrate the development of high-speed high-output units, an increase in mechanically radiated noise with speed being inevitable.

Partly because of the speed limitation imposed by noise restriction, turbocharging will be increasingly applied to diesels and advances in turbocharging techniques will be exploited to the full, including, if appropriate,.the use of the exhaust-gate type and of turbocharging in series. The turbocharged constant-torque engine is not ruled out as a possibility.

The makers of turbochargers have overcome their teething troubles. Current units are very reliable and side benefits include a" somewhat reduced fuel consumption, a less noisy exhaust and a reduction in smoke at the upper end of the load /speed range.

Eventually the diesel will provide an output comparable to the power produced by a naturally aspirated petrol engine on a capacity basis, although it will always be a little heavier than its petrol equivalent. A variable-compression-ratio piston offers considerable benefits in terms of peak diesel-engine output and reduced mechanical stresses, while application to a petrol engine could improve part-load economy.

Existing designs are, however, far too complicated and heavy for practical use and there is little promise that an acceptable unit will be developed in the near future. The future scope of the petrol engine in heavy trucks is the subject of intensive research, notably by Ford Dearborn.

In a general forecast of piston-engine trends, Mr. Manning says the V diesel engine will take over from the larger in-line six and that production of the in-line four will be restricted to units of up to 250 cu.in. capacity. Because of its lower piston mass and good balance, the in-line six is preferred for medium-sized engines.

The four-stroke diesel will not be superseded by the two-stroke, despite a number of advantages offered by the latter which include a good torque back-up and high power at peak rpm. Progress in four-stroke combustion will enable torque back-up to be substantially improved and a seven-speed synchromesh gearbox will be more than adequate for the majority of applications.

Automatic transmission is a "very attractive" proposition for heavier vehicles in Mr. Manning's view and there is an urgent need for a lightweight automatic gearbox for non-motorway vehicles, weight rather than cost being the main disadvantage of established types. There may be a future for hydrostatic transmission as an option, which would take the form of a pump and motor, built as a unit, and which could replace an existing clutch /gearbox assembly.

While automatic control of the clutch would have obvious benefits, it could involve gadgetry of doubtful reliability and durability. Mr. Manning has reservations about gadgetry, particularly if it is electrical. He points out that occasional failure of a sensing unit, used as a guide to the driver, can cause more trouble than infrequent failure of the component because a doubtful warning is already suspect and may be disregarded by the driver. Therefore, he stresses that it is especially important for such instrumentation and components to be of high quality and reliability coupled to simplicity of design.

In an assessment of present and future operator requirements Mr. Manning states that, as an engineer, he favours the vehicle that is geared to provide optimum performance in top gear on the score that it will operate more economically and with less wear and tear than an undergeared vehicle.

In the development of lightweight vehicles, new types of high-tensile steel for frames, springs and axles will play a prominent part. They will be combined with matching advances in design and the use of cast aluminium wheels, light-alloy crossmembers and brackets, tubeless tyres and so on, aluminium for radiators being regarded as a "hopeful possibility". Lighter frame-members will have a greater deflection than existing types of frame, but this will not impair their life or create vehicle-handling or body-mounting problems that cannot be overcome by sophisticated system engineering.

Mr. Manning emphasizes that light equipment can only be developed by sophisticated engineering development—merely calculating requirements on a theoretical basis and hoping it will work when assembled is a hopeless approach.

In the case of lighter axles, the deflection characteristics of the steels will have to be countered by appropriate changes in design to stiffen the structure; a high deflection of a rear axle would be unacceptable because it would result in severe mechanical misalignments, and a rigid front axle is necessary to eliminate changes in steering geometry.

Of closely related interest, Ford of Dearborn has developed a new spring steel process for leaf springs that offers a weight saving of 24 per cent and enables the number of leaves to be reduced by 40 per cent, while in some instances fatigue life has been increased by 60 per cent. Although steels with a yield point of 110,000 p.s.i. have been successfully employed in America for frame-members, production in this country will be concentrated on frames of 65170,000 p.s.i. yield point that can be pressed cold, which obviates the costly heat treatment that has to be applied to the higher-yield-point steels.

Advances in leaf-spring design over the past seven to eight years are described by Mr. Manning as phenomenal. He believes that for heavy vehicles the leaf spring will retain its usefulness for considerably more than 10 years. The development of taper-leaf springs has contributed valuably to the progress made; the production of improved constant-periodicity multi-leaf springs can be expected, while the only problem in the application of singleleaf springs arises from unfamiliarity amongst operators. For vehicles of 30cwt to 3 tons capacity, coil springs may later be applied to the front-axle beams.

The durability and reliability of non-rolling lobe air suspensions are good, but the system will remain too costly for acceptance for other than single-deck public service vehicles (for which constant height is a big advantage), trailers and special vehicles. The need to provide power to operate the air bellows is regarded as a decided disadvantage when compared with steel springs or rubber suspension.

Elaborating on detailed aspects of frame design, Mr. Manning deplores the use and approval of flitch plates which are "only as good as the bolts or rivets that hold them in place" and add unnecessarily to the weight of the vehicle. Unfortunately, to the typical operator of a heavy vehicle at home, on the Continent and in most export areas, flitch plating is a sign of strength and he judges a chassis accordingly. Operators will have to be weaned from this concept; unflitched frames, designed for the job they have to do, are stronger, lighter and less prone to fracture than reinforced frames.

There is also operator resistance to tubeless tyres for reasons such as kerbing and parts stocking. For heavier vehicles in particular they offer significant weight savings and are completely satisfactory. Mr. Manning says they should cost less because of the reduced amount of rubber they contain and he contrasts the cost /weight factor in the production of tyres unfavourably with the balance between cost and weight in the case of steel parts. Although a more costly steel is employed for lightweight frames and so on, the saving in the amount of material used enables the part to be produced at a comparable or reduced cost.

There is room for revolutionary thinking with regard to light-delivery vehicles, according to Mr. Dawson, who points out that vehicles of this type are ancillary to a business in contrast to hauliers' lorries which may be regarded as a craftsman's tool.

The Ford Comuta experimental prototype car heralds a new 10-year era, in Mr. Dawson's view, in which the use of electric delivery vehicles could expand to an extent that they will cater for a substantial proportion of the lighter end of the commercial vehicle market. In the Ford longer-view concept, therefore, the piston engine will lose some ground to the gas turbine in heavy vehicle applications and to the electric in the case of lighter vehicles.

Mr. Manning elaborated on the advantages of a non-locking braking system applied to all axles (which are regarded as the ultimate). He points out that it gives automatic distribution of braking effort according to the load on each wheel. Its application to both tractive units and semi-trailers would solve the tractive unit /trailer matching problem, which currently creates difficulties with regard to the use of the most suitable tractive units. Load-apportioning valves enhance stability but are not "the complete answer". It is unlikely that disc brakes will be developed in the foreseeable future that are suitable for heavy vehicles.

Weight transfer on to the front axle is cited by Mr. Manning as a particularly serious problem in the case of heavier artics, a problem exacerbated in practice by limitation of front-axle loading. He emphasizes, however, that British manufacturers have produced articulated outfits that are second-to-none in world markets.

Mr. Manning states that although lock actuators have a favourable potential they have not been sufficiently developed to earn general acceptability. The spring brake "does the job" but has a limited potential because of its weight and cost. Braking problems have in the main been resolved in the past few years.

Mr. Dawson points to the very real problem under the new plating regulation of loading vehicles within their legal axle limits. Operators and drivers will have to pay most careful attention to methods of loading that give balanced weight distribution. Manufacturers will help by designing load latitude into axles and by the development of load cells.

In a comment on the effect of the "container revolution" on vehicle developments, Mr. Dawson foresees a greater swing towards draw-bar outfits as used in Europe, provided the law is changed to permit these outfits to be operated without a mate. Drawbar outfits would then be used for the transport of 20ft containers in multiples. The trailers would be coupled to highperformance motive units which could conveniently carry demountable bodies.

Dealing with trends in the application of plastics materials, Mr. Manning envisages the increased use of plastics for cab structures and panelling, for the noise-insulating panels of engine enclosures, for fuel tanks as well as fuel lines, fans and fan shrouds, as a means of reducing weight and cost. In some cases a single plastics panel could suitably replace double-sheet steel panelling.

The computer revolution is the most important of all technical revolutions since the development of the steam engine, in the opinion of both Mr. Manning and Mr. Dawson. It's the finest tool any engineer could have, according to Mr. Manning. He foresees that, in the not-too-distant future, it will "enable Sales to tell Engineering exactly what is required to be done by Engineering". Work that previously occupied two years can now be completed in less than 12 months and, in due course, the time factor for the same work may well be reduced to three months. "We have only lifted the curtain on the potential of the computer", is Mr. Dawson's view.

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