BRINGING THE ST1 rAGON INTO LINE.
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The Developments in Design and Meth Resulted in Types of Steam Vehicle NI struction of the Past Few Years Have anicany are on a Par with the Best ;.
T"rapid strides made in the design and manufacture of petrol lorries daring the last decade led many transport engineers to believe that this great and striking progress would ultimately lead to the extinction of the steam-driven goods vehicle, just as has happened in the case of the private car. This belief was very strongly supported when the petrol lorry invaded the heavy-load class which, up to a few years ago, had been considered the most favourable field for the steam wagon. It was often argued that it was not an economical proposition to use a trailer with a petrol lorry, owing to excessive wear and tear. That this is not strictly true is shown by the number of these lorries in use hauling trailers.
Very great efforts are also being made at the present time to popularize the use of the six-wheel vehicle, especially as this type can be legally driven at 12 miles per hour, and carry loads of 10 to 12 tons. If, however, the recommendations of the Departmental Committee on the Taxation and Regulation of Ttoad Vehicles are adopted, and a vehicle hauling a trailer be allowed to travel at higher speeds, the position of the six-wheel type will be open to challenge. In special cases this type is, without doubt, a very useful proposition, but the separate trailer has many points in its favour.
In view of all these developments in the heavyload class, the steam-wagon makers were put upon their mettle, and the number of new models recently placed upon the market, in addition to others which are shortly to be introduced, shows how very much alive the steam wagon is at the present time.
Without doubt, the price of petrol and the uncertainty as to the future trend of prices owing to the rapid production of pleasure cars, is a very strong factor which haulage contractors have to bear in mind. Another factor which may seriously influence the economic position of the transport vehicle is the fact that the steam wagon uses a fuel which is entirely home-produced.
It was generally considered that the steam wagon was a slow-speed vehicle, but, when one hears of some of these new models attaining speeds of over 20 miles per hour and covering 50 miles on one tank of water, one realizes that speed and ability to perform a large daily mileage are not the exclusive prerogatives of the petrol lorry.
In order to attain these high running speeds, the design and manufacture of the transmission gears have had to be very carefully considered. This problem was first tackled by Mr. Clarkson, and his interesting vehicle is well known to all transport engineers. This design was practically the application of a lightweight steam generator and power unit to a petrol type or chassis.
The next step was the introduction in 1922 of the 7-ton Yorkshire wagon with totally enclosed shaft-drive transmission. The well-known double-ended loco-type c32
fire-tube boiler was retained, but the compound engine and three-speed gearbox were made in a unit, with all parts enclosed and running in an oil-bath. The power is transmitted by a universally jointed cardan shaft to a double-reduction bevel-and-spur drive in a fullfloating live back axle. This was aptly described in The Commercial Motor as a milestone in steam-wagon design, and the performance of this machine induced many other steam-wagon makers to bring out models of a similar type.
The appearance of the new Yorkshire model was closely followed by the Super-Sentinel wagon, which was placed upon the market in 1923. In this model, however, chain transmission is adhered to, but the most important innovation was the embodiment of tilt differential gear in the crankshaft, with a doublechain drive direct from this shaft to the rear wheels, the latter being carried on a solid dead back axle.
Shortly after the introduction of the Yorkshire enclosed-drive wagon, the Mann Express wagon, with a similar type of transmission, was introduced. In this case a new feature in design was the placing of the engine across the chassis in a horizontal position, with an offset cardan-shaft drive to a double-reduction bevel-andspur full-floating live ,axle. The engine and gearbox are constructed in a unit, with a two-speed gear and double high-pressure cylinders. A vertical water-tube type of boiler is also used, in place
of the loco type previously used on all their previous models.
The Garrett undertype-wagon was also introduced at about the same time, but in this model the final drive is by a chain to each rear wheel on a solid dead back axle. The engine and gearbox are totally enclosed, with a two-speed gear and differential gear mounted on the countershaft, and is placed horizontally along the chassis. Here, also, there is used a vertical water-tube boiler of the Hopwood type, with one set of cross tubes, access to which is provided through two large manholes one on each side of the boiler. All the shafts in the power unit and both front and rear wheels are carried on taper roller bearings.
Another enclosed transmission type of wagon is the Fowler, which was introduced in 1924. In • this machine a Veo-twin compound engine is used, combined with a three-speed gearbox similar in style to the layout of the earlier Clarkson wagon. The final drive is by overhead worm, designed by Bostock and Bramley, and manufactured by Messrs. Buckton and Co., Leeds. An unusual type of boiler is used, having vertical curved fire tubes, an additional water compartment being formed round the top of the shell to ensure that the tubes shall not be uncovered, because of fluctuation of the water level. In this wagon the overall length is reduced by placing the engine under the driver's seat close up to the boiler. This object, however, seems to have been obtained at the expense of accessibility and also cab space for the driver. The latest wagon with enclosed drive is the leoden undertype, which is shortly to be placed on the market.
In general layout it somewhat resembles the Mann Express wagon, as it embodies a horizontal engine placed across the chassis, but the final drive is by overhead worm. The boiler is of the vertical watertube type. Particulars of this machine will, no doubt, be available shortly.
It will be seen that, in these new models, the most important diversity of design is in the final transmission and back-axle gear, for, where some makers pin their faith to the all-enclosed gear drive, others still favour the open chain drive. This naturally creates a very interesting position, and is bound to lead to lively discussions as to the respective and relative merits of chain drive and shaft gear drive transmission. A similar position occurs in petrol-vehicle design, where both types of transmission are employed.
As previously pointed out, the chief objects sought after in these new steam models are speed, coupled with quieter running, better control arrangements for the driver and cleanliness. It is, however, not yet proved that this new breed of steam wagon will entirely supersede the older types. The robust design of the latter, coupled with lower initial cost, is bound to appeal to many users, particularly where the machines are required to operate on rough ground and to negotiate such awkward places as stone quarries and building sites.
Another important point which must not be overlooked regarding vehicles for use in this country is the group of recommendations of the Departmental Committee afore
mentioned. According to the last report issued, it is proposed to increase the maximum axle weight from 8 to 10 tons, but the maximum speeds proposed are 12 miles per hour for vehicles up to 8 tons axle weight and 8 miles per hour for vehicles over 8 and up to 10 tons axle weight. It is useless manufacturing highspeed heavy-weight vehicles unless they will be allowed to exercise their better capabilities.
It is impossible, therefore, at the present time to say with any degree of certainty what the outcome will ultimately be. Refinement in design is very laudable, but the real problem is an economic one and depends upon what is considered to be the best commercial practice. The initial factor with the majority of users is first cost, and that is where the older types score very heavily. Very little consideration is needed to show that these refinements must increase the cost of production. For instance, the fitting of ball or roller bearings to the transmission gear and road wheels involves an expenditure of between 160 and £80 for bearings alone, apart from the extra cost of other fittings to accommodate this type of bearing.
It is -a very difficult problem to try and persuade a purchaser to pay for refinements in design, especially c33
in connection with stetun wagons, whose chief selling point, as compared with petrol lorries, has always been lower first cost.
Whether the newer types will justify their extra cost by greater economy in operation and upkeep still remains to be proved, and only experience in their use will tell.
The Trend Towards the Vertical Boller.
Dealing now with details in design, a noticeable feature is the tendency towards the vertical type of boiler. The loco-type boiler has given excellent service in the past, and in the early days, when boiler trouble was one of the most serious defects, it saved the day and laid the foundation of the present successful position of the steam wagon. No doubt this was due to the fact that Its construction had been well established on railway locomotives, traction engines and portable engines. It was well understood by drivers, and engineers were alive to its weak points and knew how to carry out repairs. Although not a very efficient boiler thermally, it can stand a great deal bf rough usage and forcing under the strenuous conditions often met with in the work of road haulage. Its greatest defect is the amount of space it occupies In, chassis length and the attendant disadvantage of a longwheelbase. It does not readily lend itself to a convenient cab accommodation for the driver and mate, and it weakens •the chassis frame, especially at the point between the boiler and the body.
The majority of vehicle boilers are of the watertube type, the exceptions being the Yorkshire doubleended horizontal fire-tube boiler and the Fowler boiler with vertical curved tubes. All the water-tube boilers have straight-through tubes, with the exception of the Clarkson thimble-tube boiler. It is interesting to note, however, that the Sentinel Waggon Co. have taken out a patent for the thimble-tube boiler of the type shown on the next page. Further news as to whether this type will supersede the vertical tube boiler first employed on the Super-Sentinel model will be awaited with interest, but probably it will not.
The Use of Superheaters.
All boilers, with the exception of the ordinary loco type, are now fitted with efficient superheaters. The only loco type fitted with a superheater is the Garrett overtype model. To obtain maximum economy the steam should be superheated to between 500 degrees and 600 degrees F. With steam at this temperature, the ordinary flat slide valve is unsuitable, and either piston valves or poppet valves have to be adopted.
Water-heaters are also used on many steam wagons, but, if these are heated by the exhaust steam from the engine, care must be taken to avoid emitting too much wet steam at the boiler chimney, especially in cold weather. All boilers are designed to operate with either coal or coke as fuel, and in a few instances oil-burning apparatus has been installed. The latter, however, has made practically no headway, and there is very little likelihood of it ever doing so in this country, on account of the high cost of fuel oil.
As previously pointed out, opinion is fairly evenly divided regarding the most suitable type of final transmission. The relative merits of chain drive and shaft drive have been very freely discussed-in The Commercial Motor recently, but it must be admitted that, at the present moment, the majority of steam wagons employ the chain drive. Makers who have introduced the shaft-drive models still manufacture their chaindrive models, the only exception being Messrs. Fowler, of Leeds, who are practically newcomers to the steamwagon market, their shaft drive being the first model they have produced. It will also be noticed that, even amongst the shaft-drive models, both spur drive and worm drive are employed. In the former case, doublereduction bevel-and-spur gear is used, with the differential gear mounted on the driving shafts.
In the issue of The Commercial Motor dated August 25th last attention was drawn to the marked variation e34 in back axle design and the need for standardization. It was also very truthfully pointed out that back-axle trouble is one of the most frequent causes of breakdown with commercial vehicles where the built-up gear-driven axle is employed. On the chain-driven models, whether of the single-chain type with rotating axle or doublechain type with fixed axle, the only cause of axle trouble is breakage, due to overloading.
The Merits of Chain Drive for Certain Work'
Chain drives are certainly more flexible than shaft drives, and are undoubtedly more suitable for rough work. If a machine be operating on bad roads or soft, uneven ground, the transmission gear is subjected to enormous shocks. With the chain drive these shocks are damped out by the flexibility of the driving chain, -and, consequently, no part of the transmission gear is loaded beyond its elastic limit. With the shaft drive, unless some kind of flexible coupling is employed, the transmission is " solid " metal to metal; there is not sufficient give in the gear teeth or the driving shafts to lessen the .blow of impact and so to reduce the stresses to a workable factor within the limit of the material employed. So soon as any wear occurs on the splines of the driving shafts or in the universal joint, this defect is aggravated, for the backlash which then occurs simply increases the intensity of the shocks. h'ven where flexible couplings are employed, the degree of torsional elasticity is very small compared with the flexibility of a driving chain.
Where a machine is only required to operate on good roads and where silence is greatly desired, then the shaft-drive type shows to best advantage. It must be borne in mind, however, that this type involves the use of high-class alloy steels, and great care has to be exercised in their manufacture, for unless these steels are given the proper treatment they are useless.
Bali Bearings Call for Expert Care in Many Ways.
This means that only highly skilled labour can be employed on their repair, Ball and roller bearings are also extensively used on this type of machine, and these also call for expert care in fitting, adjustment and repair. These bearings are not everlasting, and will not stand rough usage. The slightest amount of moisture or grit will ruin them completely. They certainly reduce the friction to some extent, but not so much as is generally thought. Recent tests at the National Physical Laboratory have shown that, although the momentary starting friction is much less with ball or roller bearings than with plain bearings, the running friction is nearly the same. In fact. a recent trial on the Midland Railway showed that a train fitted with white-metal bearings actually used less fuel on a test run between London and Leicester than did a similar train equipped with roller bearings.
On many of the new models the engines are fitted with two high-pressure cylinders of equal size. This is rather difficult to understand, because the compoundcylinder engine is undoubtedly more economical. With the high steam pressures now in use, a large ratio of expansion is required to obtain full use of the energy put into the steam. This cannot be obtained in one cylinder, for the cut-off would be too early, and the turning moment on the crankshaft too uneven. Another valuable feature of the compound engine is that, by fitting double high-pressure gear to the cylinders, the power develbped at slow speeds can be nearly doubled, a very valuable asset when maineuvring on soft ground.
The majority of steam wagons are fitted with two or three-speed gears, and this I. consider necessary where a wagon is to be used on contractors' work, or in hilly districts. The single-speed machine is very good on level roads, but, when steep gradients and difficult places such as stone quarries have to be negotiated, the multi-speed wagon may score very heavily.
The tendency is now for all engines to be of the
totally enclosed type running in an oil-bath. Apart from the advantage of less wear and tear, there is a decided gain in cleanliness. Although the working parts are not so accessible, they require less attention for adjustment and repair than the open type, whilst they are more economical in oil consumption and are quieter when running. The use of poppet valves in engines is increasing, but piston valves are also used on the majority of the new models.
The majority of steam wagons, whether of the undertype or overtype, now employ Ackerman steering for the front wheels. On the undertype wagons two side springs are used in all cases, but on the overtypes a single cross-spring is employed.
The Improvement in Steering Gear.
Some makers use the ordinary swing arm swivel bearings commonly used on all Petrol lorries, but the central pivot stub is gradually being adopted. The latter type is a better mechanical job, and, with the heavier loads usually carried on steam-wagon front axles, reduces the effort required to operate the steering gear. With -the ordinary swing-arm type, this difficulty can be partly overcome by inclining the front-wheel journal so that the tread of the wheel is brought nearer to the centre line of the pivot pin. If this angle be made too great, however, too much castoring effect will be produced, which increases the steering effort when the wheels are set in either lock for turning.
Practically all the steering gears on the new models have the screw and nut, or worm and wheel, whichever type be employed, it is totally enclosed and works in an oil-bath. This is a great improvement on the old open type where the backlash in the operating gear, due to wear, caused the steering to be too erratic and unsuitable for the high speeds now in vogue.
All road wheels are now made of cast-steel, with spokes of either cruciform section or hollow circular pattern. Steel-tyred wheels have entirely disappeared, except in a few special circumstances, such as, for instance, on tar-spraying machines.
Considerable improvement has been made in the cab accommodation both as regards the protection of the driver and the convenience of controls. Windscreens can now be fitted to many types of steam wagon thus giving the driver protection equal to that provided on any petrol machine.
All wagons are now arranged so that one man can drive and steer ; on short journeys he can also attend to the fuel and water supplies to the boiler. The capacity of the coal bunker has been considerably increased ; in some cases sufficient fuel for 150 to 200 miles can be carried. With the use of highly super-heated steam and more efficient engines, it is also possible to travel 40 to 50 miles on one tank of water. These conveniences all tend to increase the radius of action of the steam wagons, as is shown by their increasing use for long-distance work.
The brake gear has also been considerably improved, and the usual practice is to fit both hand and foot
brakes of the internal-expanding type, acting on largediameter drums bolted direct to the road wheels. The Westinghouse air brake has been used in many cases, particularly on six-wheel types, but the majority of users will not go to the extra expense of this type of brake gear. Most hand brakes are now of the pull-on lever type, in place of the old screw type previously employed, this latter having been found to be too slow in action when the speed of these heavy vehicles was increased to 12 miles per hour.
A further development of steam wagons is the manufacture of tractors fitted with solid rubber tyres, for employment where it is more economical to use separate trailers. In some classes of work, particularly where the ground is soft,' a tractor pulling its load c a n operate where a wagon, carrying the load on its own chassis, would become bogged owing to the excessive wheel pressure on the ground. Owing to the lesser axle loads, the tractor will negotiate rougher places and safely pass over bridges where a fully laden wagon would be unable to operate. It can also pass over very bad places alone and haul the trailers through afterwards. Where the distances are short and the loading facilities poor—a condition which is often found abroad—a tractor can be worked with two or more sets of trailers. The object is to keep the tractor, which is the most expensive part of the outfit, continually at work hauling one set of trailers while the other trailers are being loaded or unloaded.
For operating on exceptionally rough ground or soft places where the ordinary driving wheels would sink in, these tractors can be fitted with a caterpillar attachment to reduce the bearing load on the ground. We illustrate a Super-Sentinel tractor fitted with the attachment made by Roadless Traction, Ltd. This type of vehicle is particularly adapted for use abroad, where roads and railways are non-existent and it is necessary to haul loads over long distances from the interior to the railhead or seaport.
The enclosed steering gear fitted on the SuperSentinel steam wagon.
The Use of Up-to-date Methods of Production.
Apart from the development of improved designs, considerable progress has been made in methods of manufacture. Makers have found that the class of workmanship good enough in previous days for traction engines was not altogether satisfactory for steam wagons. Also, successfully to compete with other types of transport vehicles, the price must be reduced to the minimum. This result can only be obtained by using the most up-to-date methods of production, and by the standardization of the various units used in the construction of the many types of vehicle. It is rather significant that all the wagons employing shaft-drive transmission are using the Kirkstall rear axle. Some makers assemble their own units and others purchase the complete assembled unit from the Kirkstall Forge, Ltd.
In spite of these recent developments, it cannot be said that practical perfection in design has yet been reached. The greatest scope for improvement is, undoubtedly, a reduction in chassis weight. The first step in the attainment of this greatly desirable feature is the production of a lightweight boiler of practicable design. The water-tube boiler, no doubt, offers the greatest scope for development, and it will pay anyone interested in this subject to refer to the boilers constructed for steam carriages by Mr. Goldsworthy Gurney a hundred years ago. Several types were wade, and some of these worked at as high a pressure as 70 lb. per sq. in.—a remarkable figure when one considers the materials and methods of construction available at that period.
Several attempts have been made since that time to produce a purely water-tube type of boiler, the most notable being the Purrey boiler, made in France. Although many vertical boilers in use at the present time are called water-tube type, they are not so in reality. Strictly speaking, they are the ordinary type of vertical boiler, with water-tubes fitted in the firebox, and a large proportion of the heating surface is composed of the firebox itself. The weight of these boilers differs little from that of the loco type.
An interesting development which may affect steam wagon design is the Brunler internal-combustion boiler, which is being developed at the present time. Sufficient data is not yet available concerning this boiler, but as it will probably only be able to operate on oil fuel or gas, its suitability for steam wagons is rather doubtful, although, from the point of view of weight and efficiency, some remarkable claims are made.
With the introduction of a suitable lightweight boiler, it will be a simple matter to produce a high-speed engine of either reciprocating or turbine type of lighter weight even than present-day petrol engines. These, coupled with a suitable condenser, would effect a saving of probably between 11 to 2 tons in chassis weight. In present-day steam wagons the weight of the boiler, engine and water tank in full working order is in the neighbourhood of 3 tons. A saving in weight in these units would materially affect the rest of the chassis, and it is fairly obvious that there is considerable scope for improvement. The only practicable attempt to produce a lightweight vehicle within recent years was the Clarkson wagon. When this object is fully accomplished commercially, a great deal will be due to Mr. Clarkson, whose efforts seem to have been too much in advance of his time. HEpniEsTos.