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FURTHER DETAILS OF THE AUTOVAN.

10th November 1925
Page 10
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Page 10, 10th November 1925 — FURTHER DETAILS OF THE AUTOVAN.
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A Radial Engine with Vertical Crankshaft, Final Drive to the Front Wheels via Cardan Shafts from a Worm Gear and Four-wheel Braking, the Leading Features of an Unusual Vehicle.

.TN our issue dated October 20th we were able to publish the first particulars of a new 21-ton Scammell vehicle designed as a town runabout, and particularly intended for short-distance work, such as that to and from docks and in general delivery. In this chassis an engine of much smaller power, and affording greater economy, can be employed as compared with the more normal type of vehicle which may have to run to every part of the country. That there is a need for such a vehicle is shown by the great interest which was displayed by the many visitors to the 8cammell stand at the Exhibition which has just closed, and the orders which have already been placed for it.

The leading features of the machine are that front-wheel drive is employed, and that the whole of the driving mechanism, including the gearbox and the steering, is carried at the front of the chassis, so that the rear portion can be made of any desired length or height, and can be equipped with either small or large wheels.

So far as the rear portion is concerned, the design is very

simple, consisting of a tubular axle, above which are mounted laminated springs, and the drums on the rear wheels contain expanding shoes with mat-operating levers having three holes to afford a large scope for adjustment.

The power unit consists of a stationary radial engine having a vertical crankshaft of the built-up type. This crankshaft has only one crankpin, and what may be called the main connecting rod carries a bush which runs on this pin ; the other two connecting rods bear on subsidiary pins carried by the main big-end. This engine has aluminium pistons, each with four narrow rings, and aluminium cylinder heads, cast with each of which is a cowl forming a guide through which air from a six-bladed fan, with a diameter of 26 ins., secured to the top of the crankshaft, throws a blast of air, each cylinder thus being given an effective cooling area of approximately 2 sq. ft.

At the bottom of the crankshaft is a clutch consisting of a single disc, into which are pressed Ferodo plugs f in. thick. The gearbox is underneath the engine, and, being vertical,. special lubricating arrangements have had to be made. For this purpose a pump lifts oil through the layshaft to the constant-mesh gears, from which it is distributed over the rest of the box.

The worm is, of course, also mounted vertically, the .differential being inserted from the front end of the unit.

Reverting to the engine, much interest attaches to the valve gear, which is of the Bugatti type with a cam ring running at a quarter engine speed, and operating curved tappets running in grooves forming arcs' of a circle, six grooves being machined in a phosphor-bronze plate secured to the inner side of the crankcase.

The arrangement of the front drive and the mounting of the front wheels are unusual. Taking the place of the front axle are two wide, laminated springs, one Felted to the upper portion of the main casing forming the crankcase and gearbox, whilst the other is carried below it. Each stub axle has long arms in the vertical plane, which terminate in balls carried in spherical seatings at the ends of these springs, thus forming fulcrum points.

From the differential the drive is taken by short cardan shafts, having block-and-die universal joints at their inner ends and star-type joints at their outer ends. A brake drum is also carried at each side of, and externally to, the main housing, the cardan shafts protruding from the centres of these drums.

The steering column is mounted right forward, but it operates through a steering arm carried at the front of the main casing and comniunicating with the steering arms on the wheels through the medium of independent drag links.

An interesting point in the design is that the large lock of 40 degrees is obtained by slightly offsetting the drive by carrying the cardan shafts three or four degrees forward instead of setting them in line one with the other.

We have not yet menticTned the magneto and dynamo. These are mounted one at each end of a cross-shaft driven by -worm gearing from the crankshaft; they are thus carried high, and are in most accessible positions.

The starting handle is carried by a large aluminium cover above the cylinders and fan, and the crankshaft rotates in the anti-clockwise direction, starting being effected from the driver's seat, using the right hand.

The braking, of course, takes place through all four wheels, the brakes being applied by a pedal, and a slight lag being permitted to the front brakes to avoid risk of front-wheel skid. The rear brakes can also be applied by hand only.

The front driving unit is attached to the main frame through the medium of a very strong cast-steel cross-member, and the whole unit is practically balanced over the front springs constituting the axle.

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