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A NEW TRACTOR-LOR ETH NOVEL FEATURES.

9th October 1923, Page 14
9th October 1923
Page 14
Page 15
Page 16
Page 14, 9th October 1923 — A NEW TRACTOR-LOR ETH NOVEL FEATURES.
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The Latest Product of the A.E.C. Works Iias a New Turntable Arrangement, Westinghouse Air Brakes and a Large Reserve of Power.

WELL OVER,12 months have been devoted by the staff of the Associated Equipment Co. to the design and production of a tractor-lorry which, complying with all legal requirements, should have an ample reserve of power and strength, and which should be entirely free from.the defects which are liable to occur in the design of an articulated vehicle which, unless they are successfully eliminated, materially reduce its value, because the advantage of the tractor-lorry lies in the ability to move a full load at 12 m.p.h. with a minimum of driving staff, The designers of the A.E.C. tractor-lorry have aimed at the same standard of performance as that which is given by the A.E.C. four-tonner, with the carrying of heavier loads as the general a' dvantage. The successful mastering of a gradient of 1 in 5 is now laid down as a part of this standard performance, and tests that have been made with the A.E.C. production have shown that the vehicle can success-fully negotiate this gradient and maintain a high average speed ; thus the high tractive factors of the A.E.C. four-tonner have not been lost in the new production. With the legal axle weights', the tractorlorry will carry eight tons at 12 m.p.h. and from 10 to 12 tons at 8 m.p.h., but, as a matter of fact, its capacity is in excess of the figures mentioned.

Such a. high aim naturally calls for ample powef, and the engine with which the vehicle is equipped is four-eylindered (cast in pairs), the cylinder dimensions being 135 mil), bore and 170 mm. stroke, 65 b.E.p. being developed at 1,000 r.p.m.

The other most notable points about the vehicle are, first, its extreme simplicity of design, which makes for economy in production ; secondly, the Method of supporting the forward end of the trailer portion and connecting it to the tractor ; and, thirdly, the employment of Westinghouse air brakes.

To deal with the details of the power unit first, however. The engine is of simple, straightforward design, its valves and valve gear being situated an the left side, the governor being totally enclosed and sealed. In order to render starting easy, the Delco system has been adopted, and we have ourselves seen the engine start from cold at about the third revolution of the crankshaft. This ease of starting, considering the large dimensions of the engine, is quite remarkable. As an instance of the simplification of the design, scarcely any water piping is to be seen, because the centrifugal water-circulating pump is

mounted on the same shaft that drives the fan, being contained in the single housing which ats;.ommodates the timing wheels and the dynamo. Water passages are cast through this housing, a short pipe connects from the radiator to the intake, and, by means of rubber joints, the pump is connected to passages cast in the cylinder units just below the exhaust valve pockets. Thus, at first sight, the only water piping that can be seen is the outlet to the radiator.

The engine has a cast-iron crankcase, with a cast-aluminium base chamber.. The dynamo is raised high in the housing already referred to, is in a most accessiblys position and completely protected, and it provides for the lighting circuit as well as for ignition, the lighting consisting of five electric lamps.

Mounted on the same

sub-frame as the engine are the cone clutch and its gear and the gearbox, four forward speeds being provided, the top gear being direct, the third gear having a ratio of 1.685 to 1, the second gear 2.875 to 1, and the lower gear 5.12 to 1. There is no transmission brake, all brakes acting

direct on the wheel• drums, as will be seen. from our referenee to the braking system later on.

From the gearbox the power is transmitted by a propeller shaft, which is totally enclosed, to an overhead worm gear having a ratio of 9.33 to 1 and carried in a detachable worm casing. The forward end ef the tubular torque member surrounding the propeller shaft is carried in a spherical ball housing supported by a powerful cross-member of. the frame, the universal joint of the Spicer type being rendered easily accessible by the detachment Of a. ring and a divided.cover. These, when unbolted, can be.slid rearwards along the tubular torque member, rebushing of the jeint without dismantling being possible.

As we view the A.E.C, tractor-lorry, we end the tractor, portion at the cros-:emember carrying, the spherical ball joint, because the turntable carrying the trailer portion is mounted on the central. .springs, the pads Of which swivel on the central axle casing, the extension of the tractor frame behind the cross.member aforementioned virtually being allowed to float, as it is

merely hung on four double volute springs carried in brackets on the frame. Thus the rear wheels drive the tractor portion through the torque tube and draw the trailer through the king-pin and the front ends of the central pair of springs.

The advantages of this method of design are Many. In the first place, a very large turntable is possible, thus giving the utmost lateral stability to the forward end of the trailer portion and, consequently, the maximum width is given between the springs supporting the front end of the trailer. SeconoUy, the tractor frame can be light. In fact, we were rather surprised, to see how light the frame was, but immediately understood when we had examined the vehicle in detail. The frame is deep, and stiffened in the centre, where the maximum bending comes, by plates, one .of which serves the additional purpose of sup-porting the brake gear. Then, last, but not least, the riding comfort when the vehicle is carrying its i full load s beyond the normal. The double volute springs, however, have to be stiff enough to take the torque reaction, so that there is no increase in comfort when the vehicle is unloaded or only lightly , loaded, but there is an undoubted benefit with full load.

To revert to the turntable, this consists of two members connected by a king-pin which has a groove turned in it ; into the two sides of this groove there slides a substantial pin of hair-pig shape. This can be pulled out from the side of the vehicle, thus disconnecting the trailer portion from the tractor portion. The turntable is wide, and the lower member_ of it has its rear ends curved inwards, two strong arms, at the forward end of the trailer acting as guides, so that when the tractor is backed up to the trailer each member (that is to say, the Tractor and the trailer) gives a little, and they are guided into. their relative positions. A couple of jacks lowered on o " elephant's feet" serve to support the trailer portion when it is detached. from the tractor portion. With regard to the control of the vehicle, we remarked the very comfortable angle of the steering wheel caused by the sloping of the etterig column, due to the fact that the steering gear is mounted at the forward end of the frame just behind the radiator. This gives also a lot of room in the cab for pedals and controls. The gear lever and brake lever are centrally dispositioned, and mounted on the

• steering column are the connections to the Westinghouse air brake We will deal with the braking now as a whole. The brake pedal operates the brakes on large drums on the driving axle. The-Westinghouse air brakes act on the whole of the four load-carrying wheels. By means of the 'brake lever the brakes can be applied on the driving wheels, by means of a screwon gear the brakes on the rear wheel can be applied as a precautionary measure when the trailer portion is detached from the tractor portion. The brake normally used would be the Westinghouse brake, acting on all four load-carrying wheels, and this would be supplemented, if necessary, by the foot brake acting on the central or driving wheels.

In order to prevent the central wheels skidding through harsh application, the brake drums on the central wheels are made smaller than those on the rear wheels ; thus, a greater braking effect is obtained on the hind axle, and, should any skidding take place, the wheels on,the hind axiC would skid first. The hand. lever is interconnected with the arms of the brake gear operating the brakes on the central wheels, so that when the brakes have been applied by the Westinghouse air-brake system, all that the hand brake has to do is, first, to take up lost motion and then hold the brakes on by hand power or by ratchet and pawl. It has been found by experience, after 18 months' testing of the Westinghouse brake system, that absolute compensation is provided for and that there is a uniform pressure on the brakes and none of the tightening or slackening that must occur with any mechanical system of brake application. In the case of a breakaway the brakes on the trailer are automatically applied.

The unladen weight of the vehicle, complete with body, is.7 tons 19 cwt. With an 8-ton'useful load up, the axle weights are as follow :—Front axle, 2 tens 17 cwt. ; driving axle, 6 tons 10 cwt..; trailing axle, 6 tons 9 evrt. The tractor-lorry which we have examined and which we here describe has a body space of 21 ft. by

7 ff., and the vehicle was mounted on 920 mm. by 140 mm. solid tyres, singles on the front wheels only. Throughout, the design and workmanship are of the best, and we are quite 'sure that the A.E U. tractor-lorry will give excellent service.

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