A 21-TON TOWN RUNABOUT.
Page 15
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Produced at the Scammell Works, the Autovan is a New Type of Chassis with Radial Engine, Vertical Worm and Cardan Shaft Drive to the Front Wheels, and Four-wheel Brakes.
A N INCREASING demand is show.tVing itself for chassis designed to carry fairly heavy loads, and yet particularly intended for short-distance work in towns, to and from docks, etc. Such a vehicle can be built with an engine of comparatively small power and, if well designed, can provide a loading space equivalent to that of a lorry with a bigger engine and of much more expensive construction.
It has already been proved that a chassis of this type meets a large variety of purposes, including the carrying, at moderate speeds, of passengers, as on coast town esplanade routes. Therefore, considerable interest attaches to the new-type four-wheeled vehicle built for loads of 2-4. tons and upwards by Seammell Lorries, Ltd., and which will be known as the Scammell Autovan.
This' machine presents the features of compactness, ease of handling, and a very low-loading line if desired. The layout is highly original, one of the leading points being that front-wheel drive is employed, and that the engine, gearbox and transmission mechanism form a compact unit from which each front wheel is driven direct through universally jointed shafts. The driver sits alongside the engine, which is of the three-cylinder radial type with a vertical crankshaft driving through a vertically arranged three-speed gearbox to a worm in a similar position.
In some respects the basic idea of the Scammell tractor-trailer is followed, In that whilst the rear portion of the vehicle is secured rigidly to the front portion; yet no machinery at all is attached to it, so that it can be made to any desired length and height.
High or Low Platform.
The standard low-load-line machine has very small back wheels and a low frame, the platform height being roughly 2 ft, but for general use large back wheels and a high frame can be employed, without altering in any manner the front portion, including the driving mechanism, which is standard for all types and has front wheels of normal size; this is a decided advantage, because where pneumatic tyres are required it has been found difficult to obtain such tyres of small diameter.
The rear suspension is of the normal type, and at the front the suspension is by two semi-elliptic springs which take the place of the front-axle. One is bolted to the upper portion of the casing forming the crankcase and gearbox, whilst the other is carried below this casing. Each stub axle is provided with arms in the vertical plane which terminate in balls carried in spherical seatings at the enels of the front springs, so that the whole stub axle can fulcrum on these, the`eontrol being through 10-in, steering arms and push rode of exceptional strength with large ball joints, there being no track rod in the ordinary sense of the term. The starting handle is at the top of the engine casing, at the left of the driver, and the crankshaft rotates in the anti-clockwise direction. Starting can easily be effected from the driver's seat, using the right hand.
The bore is 4 ins, and the stroke approximately 4 5-16 ins., but owing to the design of the engine and the fact that there is only one crankpin on the crankshaft, the stroke varies slightly in the different cylinders. The R.A.C. rating is, however, 19.2 h.p. The cylinders are of cast iron with cast aluminium heads, and each of these heads is extended and webbed to form a cowl open at the top and end. Above this cowl is a fan having six blades and a diameter of 26 ins. It is secured to the top of the crankshaft and, there-. fore, rotates at engine speed. The blast of air from this fan passes. along between the cowls and the cylinders proper, and each cylinder is thus given an effective cooling area of approximately
2 sq. ft. The crankshaft is of the built-up type and the crankpin is 11 ins. diameter.
Tested for 30,000 Miles.
An experimental vehicle built on similar lines has run for over 80,000 miles and, upon examination, the wear between the big-end bush and the crankpin was found to be only .0015 in. In the new engine the bearing areas have been greatly increased ; improvements have also been made tti the system of lubrication, and there seems no reason why the big-end bearings should not last as long as the vehicle. Incidentally, the connecting rods are of stamped duralumin.
The clutch is of somewhat unusual construction so far as commercial vehicles are concerned. It consists of a single disc into which are pressed Ferodo plugs I in. thick.
The lubricating oil is forced to the top main bearing and to the big-end, whilst a separate pipe conveys oil tinder pressure to the bottom main bearing. Incidentally, the main bearings are of the radial ball type and of unusually large size.
Ample strength is provided in the gearbox, the shafts of which are 4 ins, between centres, whilst the gears are of generous width. The gearbox being vertical, special provision has to be made for its lubrication, as it will not do merely to have a sump. It has, therefore, a double screw pump resembling the Archimedean type. This lifts oil through the layshaft to the teeth of the constant mesh gears, and from these it drops over the rest of the box.
The worm gear has 7-in, centres, and the differential is inserted from tlee front end of the unit to avoid large ...holes at the side.
Bolted to the front of the' main casting is the steering box, and the addition of lubricant to this box also oils the differential and worm gear. Above the steering box is the sump for the en gine oil. '
A cross-shaft, driven by worm gearing from the crankshaft, serves to drive the magneto and dynamo, the lastnamed giving an output of 6 volts.
It is not intended that the vehicle shall be run at high speeds, 20 m.p.h. being about the maximum. For this reason the final-drive gear ratios ',of 9-1 and 10-1 are being tried. In the same way, whilst the engine is of a fair size it is intended that it should be run fairly fast with a small throttle opening, thus reducing the loads on it and assisting the coding. It may be pointed out that an engine of this type has almost perfect balance, and can be run at high speeds without vibratide.
Four-wheel braking is provided, the brake shoes at the rear being enclosed in such a manner that although the entry of water and mud is prevented, any oil which may reach the drums can escape. Whilst at the rear the drums are secured to the hubs, at the front they are at the inner ends of the differential shafts, and are thus protected from dirt,,etc., and are not affected by the steering. All the shoes are of the internal-expanding type, operatine' in drums 13 ins. in diameter Trifriction material is die-pressed Ferodo, having a width of 2i ins. All four brakes are applied by a pedal, a slight lag being permitted to the front brakes to avoid any risk of front-wheel skidding. The rear brakes can also be applied by hand.
Large Timken bearings are utilized In the wheels, and it will be realized that whilst the vehicle is nominally constructed for 2i-tan loads its capacity can easily be increased by the provision of stronger wheels and the fitting of suitable tyres. Naturally, the wheelbase can be increased, within reason, to almost any extent desired, arrangements having already been made to modify the steering accordingly.
A Practicable Machine.
Because the design of this machine is so unusual it should not be looked upon in any way as a freak, for the system has been exhaustively tested and the construction is straightforward.
The front unit is attached to the frame proper through the medium of an enormously strong cast-steel crossmember, and the unit is practically balanced over the front springs which constitute the axle. Both front and rear brakes are compensated, and the method of compensation is such that if one brake-rod fails, sufficient pressure can he put on the other brake to stop the vehicle.
We have no doubt that this new product will find a ready market. As a matter of fact, the chassis has really been built to meet the expressed requirements of potential users, and quite a respectable number is already on order. It is certain to' create great interest at the commercial vehicle exhibition.