AN ENTIRELY NEW TRACTOR-TRAILER.
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A Description of the Watson Adapter, for Converting an Ordinary Vehicle into a Tractor-lorry.
CONTINTJOUS improvements are being made in the design of tractor-lorries or of attachments by which 'ordinary, vehicles can be converted into this type of machine. The latest device, Of which we Are able to publish the first description, is one invented by Mr. G. W. Watson; M.I.M.E., the wellknown conSulting engineer.
The arrangement embodies several particularly interesting features, which have been protected, and Mr. Watson is prepared to grant licences for its manufacture. Messrs. Jas. Bartle and Co., Ltd., Lancaster Road, London, W.10, have already made arrangements to manufacture types suitable for any vehicle, whilst makers of motor vehicles can obtain a licence to build the attachment for their particular productions.
The first tractor-lorry of the Watson type is now being built by Jas. Bartle and Co., Ltd. In this vehicle the tractor portion is a Burford 2i-ton chassis with a 10-ft. wheelbase, and the complete machine is designed to carry 4:1 tons. The power unit -develops 30 b.h.p. and the final drive is by internal gears, as employed on standard Burford productions. The price of the complete vehicle will be £850.
The trouble with the ordinary-type tractor-lorry is that if the trailer wheels are not on the same plane as those of the tractor, racking of the body occurs, and this is very apt to cause rapid deterioration. In the Watson attachment the trailer chassis is coupled to the tractor by means of universal and swivelling joints, the effect of which is to ensure that the wheels of the trailer always track with the rear wheels of the tractor, and special means are provided for relieving the body from all torsional stresses.
This is attained by the provision of two turntables. The lower ring of each is secured to a square-section cross-shaft, the ends of which are turned and mounted in trunnion brackets bolted to the side channels of the tractor main frame, and also, in the case of the trailer turntable, to the side channels of its chassis. By this means the body and turntables are free to tilt in the trunnions without bending or otherwise unduly stressing the king-pins. Each of the last-named is flanged and is riveted to the upper member of its turntable.
In the ease of the front end of the body, the disc carrying the king-pin is secured to suitable cross-members on the body frame, but the disc over the rear turntable is stiffened by two angle brackets and carries a couple of simple plurnmer blocks, whilst the rear end of the body is provided with three crossbearers, to which three further plummer blocks are secured.
Threaded through these three b/ocks and securely fastened therein is a length of steel shafting, which also passes through the two blocks mounted on the top turntable disc, as is shown in the drawing which we reproduce. It will be seen, therefore, that the rear of the body is not only free to rock on this shaft, but can slide endwise in order to compensate for the variation in distance between the front and rear turntables when the vehicle is steered to either side.
In certain respects this arrangemeat resembles one made by another manufacturer, but there is this important difference : in the other type the rear turntable is mounted on a slide, and thus the point of application of the load is not always immediately over the rear axle, whilst in the Watson type no such alteration of position occurs, and the point of application remains the same, whatever the position of the body. The centre of the universal joint in the connection between the two portions of the vehicle is situated exactly midway between the second and third axles, and the whole of the tractive load is transmitted through this coupling, the king-pins merely serving to locate the body, except that the front king-pin resists the inertia load of the body when starting or when the brakes are applied. As the body is supported at three points, it cannot be distorted owing to the vehicle travelling over uneven ground. The arrangement tends itself to a simple means for operating the brakes. on the wheels of the trailer. This can be done by cable, or rods, supported or articulated at a point coincident with the centre of the universal joint.
The wheels, brakes, springs and spring brackets used on the trailer are duplicates of those used for the rear axle of the tractor portion, and thus the number of spare parts required to be held is reduced. This duplication is not essential, however, particularly as regards the wheels and tyres, as the wheels carry the load and do not drive, and are, therefore, not so highly stressed as the wheels of the tractor.