Power or economy? Disc or drum?
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Retarders or bigger brakes?
P.A.C. Brockington, MIMechE, surveys the trends indicated by contributors' comments and adds some of his own
HOW much power will operators want? How much power will they have to have by law? How much fuel consumption can be economically sacrificed to payload? How important is long engine life? How valid is the ''Gardner engine mentality"? Could a later generation of diesel engines challenge the gas turbine in terms of power /weight ratio and space requirements? To what extent will the export imperative dominate the UK market? Will the independent vehicle maker survive? Will the computer dominate the design .scene and could it frustrate design progress in some ways?
These are random questions inspired by a close look at the comments made by contributors to "The Next 10 Years" series published in CM over the past eight months. They indicate the complexity of the "thinking trendson the part of designers and development engineers. And in some cases known operator views and prejudices give point to the question. After all, it's the operator who pays and who sets the pace. The total number of vehicles in the 32 /40-ton-plus category in use in the world at the end of the next 10 years will be relatively small. But the engines developed for larger home-based vehicles and for heavier types designed for overseas markets might well set a design trend that could spread downwards if their economy, power /weight ratio and overall life were acceptable. Mr. Walter Manning of Fords forecast that the successful application of the gas turbine to long-distance vehicles requiring 250 /300 bhp (Commercial Motor, January 12) would later be followed by applications of turbines with outputs as low as 200bhp to non-trunking as well as trunking vehicles. Looking ahead over a period of possibly more than 10 years, Volvo technicians forecast (CM. March 22) that the next generation of power units would be lowcompression diesels that would have weight and space advantages over the gas turbine and a much better fuel economy. If this promise materializes, their application would undoubtedly spread downwards.
Or will the "Gardner approach" spread upwards?
In only one case was the Gardner engine mentioned by name in an article. The make was discussed in most of the interviews and a number of those discussions were important because they centred on the exploitable value or operational disadvantages of a high powerto-weight ratio. It is significant that Mr. E. Twemlow and Mr. J. B. Mills of Fodens observed that the typical vehicle user specified a Gardner 6LX 150bhp engine in place of a 6LXB 180bhp unit on the score of fuel economy (CM, February 9) and that the lower-powered engine could provide an "ample" cruising speed of 40150mph on the motorways.
The definition of an "ample" cruising speed by operators generally (and Governments) is crucial. Mr. G. K. Martlew of Dennis gave 60mph as the maximum cruising speed that will be required by the majority of operators for an indefinite period (CM, August 16) which appears to be the more realistic. And it is pertinent that Dr. A. Fogg of Leyland emphasized the need to provide power units with a longer life as a means of obtaining compatability with other major chassis components (CM, January 5).
On the same theme, Mr. P. M. Yates and Mr. J. E. Cooke of Atkinson noted the recently awakened interest in America in the "custom-torque" engine (CM, May 17) which is a high-powered unit de-rated some 15 per cent to give a long wearing life combined with a good torque back-up. And in common with the majority they claimed that a legallyrequired power-to-weight ratio of upwards of 6bhp /ton would stimulate design progress in this country. While Mr. Ty.remlovv and Mr, Mills anticipated a legal requirement of 8bhp /ton in due course, they warned that powers of this order would increase operating costs unless a suitable transmission were fitted and mph restricted by a road-speed governor. This is sensible thinking but, in general, comments in the series on power and life requirements were indicative of a rather woolly approach.
In only one or two cases was the role of the turbocharger considered to be of limited importance. Mr. A. Williamson of Vauxhall Motors (CM, January 26) emphasized that increasing the cubic capacity of an engine was the best means of providing a higher power. And in particular this contrasted with Mr. Martlew's comment that in the not-toodistant future operators would ask for a turbocharged engine in preference to a naturallyaspirated type because of its economy and low smoke and noise levels. In the opinion of the majority of contributors, operators will undoubtedly accept turbocharging without quibble, whether or not the constant-horsepower engine gains ground. In my opinion they'll have to.
Pending the development of low-compression diesels or if development is frustrated or delayed, the "in-line versus the V" conflict will probably be the main preoccupation of vehicle makers and users for some years. While the V8 is undoubtedly here to stay, its relatively short stroke and high speed are generally accepted as disadvantageous factors with re gard to the rated fuel economy that can be obtained compared with the economy of a highly-turbocharged in-line six. it is noteworthy, however, that Dr. A. E. W. Austen of CAV (CM, June 21) said that no one had so far demonstrated that the consumption of a direct-injection diesel having a short stroke was necessarily inferior to that of a longstroke engine and he pointed out that diesels had successfully been operated up to 4,00Orpm.
While a cross-section of the views quoted suggest that the useful peak bhp of an in-line six is around 250 /260 bhp, Volvo technicians were confident that the peak could go up to 400bhp, which would be sufficient for the heaviest vehicles apart from "specials". It is notable that Dr. Austen's comment on the future of the CH P engine—"why throw away horsepower"—accords with the Volvo view, In the case of the custom-torque engine mentioned by Mr. Yates and Mr. Cooke, however, horsepower is being thrown away to obtain a longer life as well as good low-speed torque. This would have a big appeal to the average operator—if he could afford to pay the extra for the big engine and was willing to sacrifice some payload.
The development of a low-compression diesel is, it would seem, an "if-only" project, the if-only being the availability of an efficient loVv-weight variable-compression-ratio piston or the equivalent. But if such a piston were produced it could benefit the petrol engine more than the diesel. The equivalent (for diesel engines) is the dual-compression-ratio engine, mentioned by Mr. C. H. Bradbury of Simms Group Research (CM, July 261. Mr. Manning stated that the future scope of the petrol engine in heavy trucks was the subject of intensive research, and Dr. Fogg said that the petrol engine could make a come-back for heavy vehicles. Will these projects depend on the long-sought-after development of a stratified-charge combustion system? This system has been "round-the-corner" for so long that I am inclined to Mr. Bradbury's view of its potential. He referred to it as the "bane of so many inventors for so many years."
I forecast that a power of at least 300 /340bhp will be required for trucks destined for the Continent (this is the figure given by Mr. F. Hedlund of Scania-Vabis in the March 8 issue of CM) and possibly higher powers for vehicles in some developing countries. Outputs up to 250 /260bhp will cover a large majority of heavy-truck requirements and here the turbocharged in-line six will be generally preferred to the V8 (partly on the score of a lower noise level) particularly if the solid-head engine mentioned by Mr. Bradbury proves a success. Although the low-compression diesel will eventually materialize it will not do so commercially within a period of 10 years. Despite Mr. Manning's claim that a commercially applicable gas turbine will be available with ratings down to 200bhp, a lower practical limit of, say, 300bhp is prob-, ably the more realistic.
The future of the power unit has so far been considered in isolation. Whether or not a particular type of engine gains operator favour could depend on the suitability of the engine/gearbox package. A good torque back-up and a limited speed range favours the use of a gearbox with a reduced number of ratios and if Mr. Martlew's view is accepted, turbocharging reduces cyclic torque variations and thus gives the gearbox an easier life. No contributor to the series mentioned higher engine rpm as a transmission advantage. In theory an increase in rpm should permit a lighter transmission to be used but the extended rpm range necessitates a larger number of ratios.
Future transmission trends may therefore depend on engine characteristics. But if sophisticated transmissions are successfully developed for commercial use, the trend may be "the other way round". Of special note, the availability of efficient hydrostatic transmissions would give engine designers a great deal more latitude because the transmission would accommodate any rpm range. And a hydrostatic transmission with separate wheel motors would enable the engine to be in any convenient position without complicating the drive line and would provide differential action. Any type of hydrostatic transmission could be employed to give full-torque braking of the driven wheels, More immediately, the advantages offered by the wheel-motor hydrostatic transmission for special multi-wheel-drive applications may well initiate developments that will later be applied to single-axle or tandem drives. Dr. Fogg observed that the only type of system that would be approved would be a wheelmotor transmission and forecast the possibility of its being used for vehicles employed mainly for site work. But after stating that there could be a future for a hydrostatic transmission, Waiter Manning said that it would be of the combined pump-and-motor type that could be fitted as an option to replace an existing clutch /gearbox assembly.
In my view, the productionof an efficient wheel-motor hydrostatic transmission at the right price would be -truly revolutionary" in that thorough exploitation of its merits would involve designing the vehicle round the transmission. While it is highly doubtful whether
this could happen in the next 10 years, applications to trailer axles of off-the-road vehicles and in some special cases to front axles should be fairly commonplace in a few years' time.
A revolutionary suspension development in the relatively near future is far more likely and this is indicated by a comment by Mr. Stanley Dews of BMC (CM, January 19). Mr. Dews stated that employing an interconnected sus pension system for heavy vehicles of the type that had been developed for cars could not be regarded as fantasy and he pointed out that such a system would provide optimum suspension characteristics together with automatic compensation according to static and dynamic load changes. I suspect that Mr. Dews' comment was based on a very much more realistic attitude of mind than that suggested by his words. He was obviously thinking of the BMC Hydrolastic suspension and was quite confident that it could be applied with considerable advantage to heavier vehicles. If his comment can be taken as a forecast, it could well be one of the most important forecasts made in the series.
Be that as it may, Waiter Manning's statement that the only problem in the application of the single-leaf spring arises from unfamiliarity among operators, and the tribute he and other contributors paid to recent improvements in leaf springs, augurs well for the continued acceptability of leaf springs in competition with air or any other established system for applications to rigids and tractive units.
Apart from Mr. E. Sherratt of ERF (CM, April 12) contributors were generally lukewarm or critical in their appraisal of air suspension, and its general application to prime-movers may well depend on whether the system can be used to control brakingforce distribution. Mr. Sherratt said that it could; and of major importance it could also be used to provide an accurate axle load sensing system with dials in the cab. Like turbocharging, the haphazard application of untried units in the early days created an unfavourable bias against the principle. There are roll problems to be overcome, in part associated with chassis flexing, and whether application to steered wheels can be completely successful has yet to be demonstrated. Will ERF lead the way?
The statement by Mr. D. W. Redmond of Seddon (CM, February 23) that limitation of the load on a single axle to 10 tons might necessitate the production of six-wheeled tractive units with tandem drive is symptomatic of vehicle makers "traction problems". And they are very pressing problems. Mr. A. J. Smith of Rootes ICM, February 2) had a stab at the subject without coming to grips with it, when he said that the load-transfer type of suspension used on 6x2s in Europe merited further appraisal. Many makers must be having similar thoughts and be wondering whether temporary overloading of an axle will be permitted by law.
With the prospect of saving a ton of pay load and of reducing tyre scrub, a load-transfer system is an extremely attractive alternative to tandem drive. Surely a legal formula could be found to sanction axle overloading temporarily in adverse weather conditions and on rough ground if its abuse could be prevented? I am doubtful whether leading UK vehicle makers are giving due thought to its development.
Of allied importance indirectly, the selfsteering axle and the linkage-controlled steered axle represent another type of development that probably warrants more intensive and practical thought than is being given to the systems. Mr. Redmond observed that if single-axle drive provided sufficient traction, a second rear axle of the self-steer type might well be suitable for tractive units. He also said that such an axle might well find a Place as the third axle of a three-axle semi-trailer but his first comment is the more significant because the axle would be a corporate part of a basic structure rather than an alternative appendage. Mr. Sherratt also stated that the axle could have a future (fitted with big-single tyres) for multi-wheeled rigids.
Mr. Cooke pointed out that jack-knifing of an articulated vehicle with a tandem-axle trailer could be eliminated and cut-in reduced if a linkage-controlled rear axle were employed and here again the system would be an integral part of the vehicle, in that the chassis would have to be designed to accommodate it. Applications of both types of system in this country have been rather haphazard.
To forecast that leading UK makers will take the potential of the self-steering and steered axle more seriously might not be realistic. It is to be hoped that they do.
Although service-brake requirements were reviewed in detail by most of the contributors there were few significant variations of viewpoint. The value of load-sensing valves (notably for artics) was acclaimed unequivocally by the majority with the provision that the anti-locking system could be regarded as the ultimate. How long to wait? That's the question! And will the system be of the electronic type?
Dr. Fogg observed that there was "no magic in discs" and this view is fairly typical of the comments made. Of more direct significance, Mr. Hedlund pointed out that a shield was required for a disc brake to prevent the ingress of mud and that this negatived its fade advantage. Because the availability of brakes having improved fade characteristics would be a boon to the vehicle industry, it is to be hoped that Mr. Martlew was nearer the truth when he said that disc brakes might well make a come-back and that they could prove suitable for rear wheels as well as front wheels. He noted that friction materials had been developed that would withstand the high temperatures created by a shielded brake.
When Mr. Smith said that he did not rule out -the possibility of a power-assisted hydraulic brake system being developed for heavy vehicles, he implied an opinion that did not accord with the general view. But in my view an hydraulic system will be fitted to most vehicles in 10 years' time. The announcement by Clayton Dewandre a few weeks ago (not mentioned in the series) that an accumulator-assisted hydraulic system would be a feature exhibit at Earls Court gives point to this contention.
What of the future of lock actuators, spring brakes and vehicle retarders? Many contributors stated that a low-weight, low-cost, efficient retarder was urgently required (Mr. Smith said it would be a Godsend) but no great enthusiasm was shown for lock actuators or spring brakes. Fairly typical of the comments made, Mr. Manning emphasized that the lock actuator had not been sufficiently developed to earn general acceptability and that the spring brake had a limited potential because of its weight and cost.
A challenge
That brake "auxiliaries" have a useful potential is surely a challenge to braking equipment makers to evolve a system (perhaps an hydraulically-operated disc brake type) that would make them unnecessary! This should be possible but the availability of efficient low-cost auxiliary units has an appeal to vehicle makers in that it facilitates catering for individual requirements by "hanging things on" to a low-cost basic chassis. So the spring brake in improved form will probably survive indefinitely and an acceptable retarder will be developed sooner rather than later. Mr. Redmond was right, however, when he referred to brake systems as a complex conglomeration of hits and pieces. Mr. Manning's forecast that new types of high-tensile steel would play an important part in the development of lightweight frames, springs and axles should be viewed in conjunction with Mr. Dews' forecasts on the use of new materials. Mr. Dews said that rationalization of model derivatives, such as tippers and tandem-axle vehicles, would be aided by the availability of high-tensile steels with a yield strength up to 80,000 p.si. He claimed that heavy-duty frames of high-tensile steel could be built having identical dimensions to the standard type and produced by the same tools.
Is the development of the techniques required for such projects essentially an exercise that only the big producers can exploit to the full? This is an important question. The independents are in a better pOSiti011 to cater for individual requirements and for changes in demand. But if the big producers can tackle the weight problem more realistically than the independents the latter will be at a distinct disadvantage in producing vehicles for a substantial proportion of their potential customers. Mr. Manning said that the computer revolution was the most important of all technical revolutions since the development of the steam engine. The computer can be expeditiously applied to matching exercises and good matching is the secret of weight saving.
It is likely therefore that within a few years the big producers' vehicles will be lighter and stronger than they are today and that derivatives will cater for non-standard requirements. But it is probable that the independents will have a rather larger share of the market in 10 years' time. Traffic is getting more specialized and matching the vehicle to the job is getting more important. If the flexibility provided by the computer in design exercises is conditioned by the inflexibility of flow-line production methods, changes that cannot be planned a long way ahead are extremely costly.
The extent to which the container revolution could effect vehicle design is problematical. Related contributors' comments mainly centred on the possible role of the drawbar trailer, given that one-man operation is legalized. Mr. Alan Dawson of Ford forecast that drawbar outfits would be employed to transport 20ft containers in multiples, but Mr. Redmond and his colleague Mr. W. Booth maintained that the future of drawbar outfits was a doubtful one. They pointed out that a prime-mover carrying one 20ft container coupled to a trailer with two 20ft containers would have an overall length of 70ft which would be excessive. I find difficulty in getting the implications of the container revolution into proper focus, and feel that I am one of many. And this is borne out by Mr. Redmond's observation that few operators had sufficient experience of container traffic to forecast future requirements accurately. Maybe a lot will depend on the development of airborne traffic which would favour the use of road transport between supplier and air terminal.
As a footnote. I could pose the question: -Are UK vehicle manufacturers sufficiently European-minded?" Little was said in the series about European practice: much more was said about American practice. The quiet confidence of Volvo and Scania-Vabis was obviously derived from a closer knowledge of European operators' requirements and a willingness to learn from anybody without prejudice but with a confidence in their own know-how. Volvo technicians stated that it would be increasingly necessary to design vehicles for a selected route or routes. Is this the pattern of the future and if so, have UK manufacturers a proper awareness of the trend? And the flexibility to cope with it?