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30th September 1924
Page 24
Page 25
Page 24, 30th September 1924 — A SIX-WHEEL-DRIVE VEHICLE FOR ARMY USES.
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Details of an Interesting Model Conceived by the American Military Authorities Who Have Also Designed a Four-wheel-drive Vehicle Embodying Similar Features, Many of Which are Unusual.

DTIRING the past few months we have made many reference to.the several different makes of British 30-cwt. motor vehicle which have been designed to meet the exacting specification of the War Department, entitling their owners to a eubsicly grant. In recent issues we have been able to deal at some length with the performances of some of these vehicles in army exereises under mimic conditions of warfare, and in another part of this issue we make further reference to the use of these vehicles in connection with certain administrative branches of the Army.

Without searching for other reasons the time would, therefore, appear to be particularly opportune for a brief illustrated description of two new types of vehicle which have been designed by the Engineering Section, Motor Trans' port Division of the Quartermaster Corps of the United States Army.

There are several interesting and somewhat unusual features in the design of these vehicles, one of which is intended for 2-ton loads, and the other for 3-ton loads, and although they have been more particularly designed to meet army requirements, they are equally fitted for ordinary spheres of service, It is of more than passing interest, however, to note that one of the new vehicles is a six-wheeler of the rigid type, and, in so far as machines of this description may prove invaluable for specific military activities, we feel

that its design and construction will be closely studied.

As is more or less consistent with the general procedure in America, these vehicles have been built up so far as is practicable, of standard units, although certain components have been embodied in their layout to meet special needs. In the design of these new models the main aims of the army authorities have been concerned with securing maximum accessibility, and a reduction of the problems associated With maintenance work.

One of the new vehicles is driven on all four wheels, and the other, which possesses features closely resembling the lighter model, is very similar in design, the chief difference being resultant upon the employment " of six driving wheels, although with its wheelbase of 13 ft. 4 ins., the latter is 10 ins, longer than the four-wheeler. In the main, therefore, one description will suffice for the two machines.

The engine which is used in thest.4 vehicles is a four-cylindered Hinkley, which has a bore of 41 ins, and a stroke of 51 ins. The power is conveyed through a Covert clutch and thence through a four-speed gearbox and two Peters universal joints, and a shaft to a special auxiliary gearbox. • From the rear end of the latter, a shaft with two universal joints connects to the rear axle, and a second shaft is arranged for driving the winch.

The drive to the front axle is also through a shaft provided with twd Peters universal joints, one of which is carried at the front end of the auxiliary gearbox. In order to clear the bottom of the crankcase of the engine and to give ample space for the winch and its drive at the rear, the main driving shafts are offset from the centre line of the chassis.

An unusual feature is the use of a universal joint in the steering gear column. This form of construction is favoured in order to obtain easy steering and to facilitate assembly and disassembly of the steering gear and its column.

In the design of these new vehicles, special attention has been given to the question of braking. The foot brakes operate on two drums of large diameter which are disposed at the ends of the propeller shafts on each side of the secondary gearbox. The bands are contracted by toggle mechanism, and are extremely accessible. Brakes of the band type are also used on the rear wheels, and it is important to note that they are fully enclosed and arranged to run in oil. This procedure is the opposite ef that usually employed on vehicles which depend upon internal gearing for their final drive, and measures are usually taken to prevent the oil from reaching the brake bands. It is pointed out, however, that although the oil undoubtedly materially

reduces the co-efficient of friction against the lining and results, therefore, in the braking effort being lessened, it enables continuous application of the brakes to be made on long, steep gradients without the usual possibilities of overheating and resultant rapid wear which occur with the conventional form of braking mechanism.

Another feature in the braking arrangement is the mounting of the fabric on the heavy hralae drum to which the internal gearing is attached, instead of riveting it to the brake band, as is the more usual method. This construction has been, followed so that a band more nearly approaching a true circle can be obtained, and also to avoid the possibility of the band becoming distorted -when the friction material is being renewed. By completely enclosing the braking mechanism, dirt and water are excluded, and this is a factor of considerable importance in the case of a vehicle which is likely to be employed over all conditions of road surfaces; moreover, in a country where severe winters are experienced, it also avoids the possibility of mud-covered brakes freezing up. it is, perhaps, unnecessary to describe the general construction of the front

and rear axles, as their lay-out can be readily understood by referring to the illustrations which accompany this article. It should be mentioned, however, that certain front axle parts are interchangeable with those on the rear axle, and that a self-locking type differential is employed on the rear axles, although the conventional bevel-pinion type is -used in the central unit for front axles in order to avoid interference with the steering gear. In the six-wheeled vehicle the two axles comprising the rear unit are substantially the same in construction. They are connected by a shaft with two universal joints, and by a pair of semielliptic springs and a telescoping type of torque member of the pattern already used on certain American Army vehicles. This torque member, the disposition of which can be clearly seen in one of our illustrations, is pivoted about vertical axes at each end, and it permits the axles to move relative to one another as the springs-are flexed, The springs of this unt'e have no shackles, but are pivoted to the axles and attached to the chassis frame about

their centres by 'trunnions. Provision is made so that the two pairs of rear wheel brakes on the same side of the chassis, are applied simultaneously. The secondary gearbox of each vehicle has five shafts, all of which are mounted in ball hearings, and the centre of the five is driven from the main gearbox either by way of reduction gears in the larter, or by a double universally jointed shaft. On the primary shaft are two sliding gears, one keyed to the * shaft and the other free to turn upon it. In the centre is a pinion with a clutch at each side. When either sliding gear is engaged by the use of its respective clutch, the drive is transmitted through a gear of an idler shaft and thence to the shaft which is connected at the front to the propeller shaft driving the front axle, and at the rear to the propeller shaft driving the rear axle.

One of the two gears gives a much • greater reduction than the other, so that, in combination with the four speeds of the maid gearbox, a total of eight forward and two reverse speeds is available.

Any of the four speeds of the main gearbox can be employed to operate the winch, for details of which we -would refer our readers to the separate drawing included with the plan and side elevations of the six-wheeled chassis.

The writer of the article in " Automotive Industries" (to which we are indebted for the details and illustrations of the new American Army vehicles) who deals very thoroughly with these vehicles sees in the construction of the front axle a similarity to certain French and German designs, in which some of the bevel driving gears are concentric with the knuckle pivot. The American design differs from these Continental productions in so far as the gears in the knuckle axis are above the axle centre.

The live axle shafts of the front axle are similar to those used at the rear_ They are splined into the bevel differential carrier at their inner ends, and are flanged at their outer ends for bolting to the bevel driving pinions which mesh with ...bevel ring gears at the top of, and concentric with, the knuckle pivot. Attached to these gears are flanged sleeves with integral bevel pinions at their base. The pinions, in turn, mesh with bevel ring gears which are attached to the front wheel hubs, the mounting of which is identical with that of the rear wheels.

On the four-wheel-drive model the front and rear springs are interchangeable. The radiator and its guard form a separate assembly on both models, and the component rests on pads et rubber and fabric composite which act as cushion devices.

Bath of these new chassis have been designed to run on pneumatic tyres of 38 ins. by 7 ins, dimensions.

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