T HE GREAT development of the tractor-tPailer type of vehicle which
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has occurred during recent years in this country is merely one effort to solve the problem which is exercising the minds of road and transport engineers throughout the world. That problem is to decrease the cost of transport as represented by ton-mileage figures, and, at the same time, to reduce the wear on roads, which is proving such a great burden, not only to municipalities but to countries as a whole. In Britain our efforts regarding the development of the tractor-trailer type of vehicle are at present somewhat limited. The vehicle must not exceed an overall length of 33 ft., and although "a, passenger vehicle of this type was recently exhibited it cannOt yet be legally employed on the road for passenger work.
Many of our readers will be surprised to learn that a tremendous amount of work in connection with the tractor-trailer type of vehicle, and this type combined with Ackerman-steered trailers to form road trains, has been carried out by a well-known Dutch engineer, Mr. H. W. Jonkhoff, who resides at Semarang, Java.
This gentleman has travelled extensively and has obtained a very comprehensive view of the difficulties pertaining to those countries where mechanical transport can be employed. For years he has been convinced that the problem of road transport could not be solved by the ordinary type of vehicle, so he commenced to build vehicles with more than four wheels, on the principle that a number of cyclists weighing, with their machines, the same as a heavy lorry would not damage the road surface to anything like the same extent as the lorry, because of their weight being divided over so many wheels.
As a basis upon which to work, he took the tractortrailer, and the first thing he changed, in order to render this type of vehicle suitable to the serpentine roads of Java, was the steering. Many of the products of Java; such as kapok and quinine, occupy a large loading space, but are of light weight, and the ordinary type of transport vehicic,is expensive to run because of its initial weight, which renders the ratio of pay load to gross load most uneconomical.
The first vehicle built was an eight-wheeler, 'which might be termed a tractor-truck. This introduced a new element in shock absorption between the truck chassis and the loading platform, for the fourwheeled truck or trailer was provided with a central turntable with provision for rock. This central pivoting reduces the shocks on the platform by something like 50 per cent. The front end of the loading platform rested on the tractor portion, in the usual manner, through the medium of a turntable. So soon as the great advantage of this balanced
truck system:became clear to the inventor he manufactured a second vehicle, in which the loading platform was carried on two rocking turntables, each one mounted on a four-wheeled trailer chassis or bogie. By combining the first vehicle with the second he then formed a tractor-train capable of carrying 150 passengers, and a year or two ago, at an exhibition at Bandoeng (Java), this vehicle carried 30,000 passengers over a distance of five miles between the
city and the site of the exhibition.
After this demonstration the new road train was bought by the Dutch East Indian Government for military purposes: and for more than a year has given complete satisfaction ; in fact; the Government is considering the placing of orders for these trains for use in islands where railways have not yet been constructed.
It is stated that the passengers on the tractortrain were agreeably surprised at the smooth riding given by the eight, comparatively light, springs upon which each body is carried, and the way in which the bogies are balanced.
Turning his attention to freight trairks he took as a basis the fact that, as used for plantations, in order to carry a load of, say, 24 tons, from one place to another, a three-ton lorry would have to run eight times in one direction loaded and eight times hack unloaded, making a gross. weight of something like 80 tons to be transported, whereas by carrying the whole quantity of 24 tons in one trip by a tractortrain, with an unladen weight of 15 tons only, the gross weight to be carried would be 54 tons.
The inventor was also convinced that the average driving wheels of a motor vehicle are greatly overloaded, and lift endeavoured to reduce the weight on them so that it would give just over the necessary adhesion uncan the most severe conditions. Returning to the actual design of Mr. Jonkhoff's trailer-trucks, the inventor saw that every axle with non-steering wheels cut in at the corners to the extent of something like 20 ins., and with long trains having eight to ten axles this trouble was greatly accentuated-, However, he overcame it by adopting a simple and original method by which all the wheels could be steered automatically and made to track with those of the tractor. He did this by utilizing the loading platform in the manner, which we illustrate.
The tractor drawbaris fulcrumed at the same centre as the turntable and its position controlled by means of two cable connections _passing from the point (e) over pulleys at the end of the tractor frame, the ends being conducted to a point (h) on a bracket attached to the loading platform at a certain position below its longitudinal centre line. So soon as the tractor-truck turns from a straight course there is difference of direction between the longitudinal axis of the trailer chassis and that of the loading platform, and the point h moves away in a, lateral direction from the pulley at 'g and towards that at f, thus moving the drawbar in the opposite direction and to the same extent.
Automatic Steering Control.
The whole action is controlled by the distance between the fulcrum point of the turntable and the point h. The same system, carried out in a slightly different manner, can also be used as 'a stabilizer between the double-acting steering device of the two bogies of an eight-wheeled wagon, making it possible to use such a wagon at much higher speeds than can safely be attained by the ordinary trailer. Reference to the drawing which we reproduce will show how the wheels on the outer axles of each llogie are controlled by extensions from the drawbars of the inner and outer axles.
In The Commercial Motor for December 19th, 1922, we gave a brief description of the -accepted patent covering this portion of the invention • and we explained that in making curves an alteration is possible in the centre distance of, for example, two coupled four-wheel trailer chassis carrying a loading platform common to both chassis upon one fixed and one sliding turntable. Until then the sliding movement necessary to take up the difference in the curves had all been taken up by the sliding device on the turntable of the • second trailer chassis or bogie, the first turntable being fixed. • This, however, gives uneven distribution of weight and, apart from this, the loading platform may project too far beyond the rear bogie. This trouble being accentuated in a train consisting of a number of trailers and forming a positive danger.
The invention described made possible sliding movement in both turntables with spring connections balancing the horizontal stresses due to hauling and braking between the bogies and the loading platfcirm. The' springs utilized are of the 'laminated semielliptic type and cennected to the middle coupling rods, In starting one of these trailers, the front truck or bogie moves first, and after the drawbar springs are sufficiently compressed the second bogie starts ; finally, the movement of the coupling rods is transmitted to the cross-spring at the rear, thus putting pressure at the point (m) where the spring is connected to the loading platform, which is, consequently, caused to move. In stopping the trailer, the opposite action occurs, and the spring at the front end is in this case compressed. .
Saving the Road and Power Unit.
The principal matter of importance in this design is that the work done by the driving wheels of the tractor in starting the trailer from rest .is spread over a greater:road distance,thus preventing wheelspin and permitting the use of -a comparatively small
motor, owing to the small starting resistance or inertia.
One of the roost interesting features of the Jonkhoff train is the automatic brake system. In its simplest form this consists of utilizing the spring drawbar to pull on the brakes when it is compressed, so that if one truck tends to overtake another, as when descending a steep hill or when the tractor brakes are employed, it is -automatically retarded. This, of course, gives greater braking power towards the front of the train, as, at this point, the push exerted is from all the trailers behind.
It has been demonstrated that long trains with brakes designed on this principle can descend very steephills without folding double, and without giving the driver any , more trouble than is required for a single vehicle ; in fact, fully loaded trains with a total weight of 25 tons can be stopped almost immediately while going down hills of 15 per cent. The whole principle•is one of decentralization—the more wheels employed, the more,brakes are available.
Preventing Backward Running.
Another, of Mr. Jonkhoff's patents is for a quickworking brake which prevents his tractor-trains from 'running down hills backwards. The interesting point about this patent is that the regular brakes am employed, but the automatic regulation brings the brakes into action very rapidly, without depending upon the volition of the driver, and the inventor claims that no trick or train built to this design can reverse more than 10 ins in any circumstances and whatever the total weight may be, unless the backward running is intentional. At present the applications for the patent have not been completed, so that it is impossible to give full details.
So far, we have explained the balancing truck system in connection with the eight-wheeled wagon or trailer and pointed out that in the tractor-trailer combinations the bogie system is only employed at the rear end of the loading platform, but, later, further modification was made by carrying the front turntable of the loading platform in the centre of a two-wheeled chassis the front end of which is carried on the turntable of the tractor, thus making a 10-wheeled tractor-trailer combination, giving the same loading space as that on the eight-wheeled tractor-trailer and consisting of what might be called a four-wheeled tractor and a six wheeled trailer.
.Owing to the reduction of the weight on the driving wheels of the tractor it was considered that wheel slip might occur with only two driving wheels, unless these were ballasted. Therefore, in order to avoid this,' the 10-wheeled machine was constructed with four-wheel drive, the arrangement of which is clearly shown in one of the illustrations. It will be noted that this tractor-trailer to carry 12 tons on 10 wheels has eight steering wheels, six brake drums and automatic steering and braking-. The six trailer wheels on the axles (c, d and e) are all Ackermansteered and controlled, in the manner previously explained.
One of the most interesting features of the steering is its safety, for the reason that, in taking curves, the track of the vehicle is automatically widened to the extent of just over one yard, which makes it 'possible to take .the curves at high speed without danger of turning over.
Owing to the short space in which a vehicle of this description can be turned, it is seldom necessary to • Ba0 run in reverse, but, if this b-a required, the fastening of the steering cables can easily be disconnected at the poi-ht j, after which, the drawbar at the end can be. manipulated by hand. presume some means are provided for putting the automatic braking gear out of action when it is necessary to reverse, but in sending us the particulars Mr. Jonkleaff has not Mentioned this matter.
In the 10-wheeled .vehicle the intermediate sliding action between the turntable and loading platform is -found at the front end only, and in this case the drawbar springs are utilized forthe purpose of shock absorption between the tractor and the loading platform, instead of the ,laminated cross-springs previously described.
It was not easy to arrange; a four-wheel drive on two axles which are not always parallel to each other. This is done in the Goodyear construction, but in that vehicle the wheels are kept very close together. However, in the 10-wheeled vehicle the difference in direction betwuen the second axle and the third axle is always restricted, so that transmission in the regular way can be effected by extending the worm of the first axle and connecting it by a" second propeller shaft to a worm in the third axle.
By the use of eight-wheeled trailers, each with two bogies and with automatic steering, 'almost any size of train an be made up, providing that the tractor is sufficiently powerful for the work, and that its four driving wheels can obtain the necessary adhesion.
Road Trains versus Buses.
It is pointed out by the inventor that a vehicle to carry 240 passengers and comprising three Wagons would not have a length of more than 39 metres, (just under 100 ft.). Ordinary single-deck buses to. carry the same number of people would occupy about three times as much road space, whilst the saving in deadWeight is between 40 and 50 per cent.
On the average, each wheel of one of these multiwheel trailers carries only half the weight of that imposed on the ordinary lorry wheel, so that vehicles of this type could be used on roads built with. much lighter foundations. Another consideration is the great saving of man power. One man can actually drive a train carrying goods which would, if conveyed in ordinary vehicles, require the services of from four to eight drivers. • The inventor has other patents dealing with the use of his tractor-trains on the railway by the substitution of flanged wheels for the ptesent solidtyred type.
He is desirous of leaving Java and of making arrangements with manufacturers for the Construction of his vehicles under licence. At the moment
he is•wotking-on the perfection of rall-lessArolley
. . buses and trolley-trains.