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;pension in Bogie Conversion

13th June 1958, Page 51
13th June 1958
Page 51
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Page 52
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Page 51, 13th June 1958 — ;pension in Bogie Conversion
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Which of the following most accurately describes the problem?

By John F. Moon,

A.M.I.R.T.1E.

LL-RUBBER suspension, giving maintenance-free

A,

operation and a high degree of inter-axle articulation,

is one of the main features of the Hendrickson RS series of tandem-axle conversion units now, being made by Eaton Axles, Ltd., Warrington.

The first example, of this bogie to be produced in Britain was tested recently as applied to a Leyland Comet forwardcontrol vehicle and it 'was shown to provide marked advantages in payload ton-rn.p.g., braking safety and in riding .properties both on and off the road.

Fuel-consumption figures taken over a 10.2-mile undulating route produced 12.25 m.p.g., with the outfit running at just over 174 tons gross. This gave the high time-loadmileage -factor of 6,060, which IS a commendable figure in view of the road conditions and the newness of the vehicle.

The conversion had been made by J. H. Sparshatt and Sons (Southampton), Ltd., Southampton, at the request of

Eaton Axle& Ltd., and the chassis chosen was the Leyland Comet ECOS2.112. I3-ft. 7-in.-wheelbase model, equipped with an Eaton 18500 two-speed axle. For the conversion this axle was incorporated in the Eaton bogie, with the centre line of the bogie on the same plane as the original rear-axle centre line so that the wheelbase remains unaltered by the conversion.

It is more usual with a third-axle conversion to leave the driving axle in its original position and thus extend the wheelbase, but this entails frame modifications which are unnecessary with the Eaton conversion, although these can be carried out on medium-wheelbase chassis if a body length of more than 20 ft. is demanded.

The Hendrickson bogie is of the walking-beam type. The beams are carried below the axle centre lines and the Outer pivot points are rubber-bushed. Rubber bushes are used also at the centre pivots. The pivot brackets are T-shaped and each carries two rubber cushions, which form the suspension medium.

The pivot brackets are located relative to the chassis frame by vertical drive pins, which are integral with the frame hanger brackets and are free to move up and down inside the pivot brackets on rubber bushes. Thus the toad cushions are Unstressed apart from vertical loadings, and they deflect only in. between the unladen and fully laden conditions, thereby presenting an almost Constant frame height.

Axle driving and braking torque reaction is provided by horizontal rubber-bushed torque arms which are attached to the tops of the axles and to -a special double-channel frame cross-member. These, in conjunction with the walking beams, provide a parallelogram form of linkage

316 which, whilst allowing maximum articulation, reduces the tendency for the rear axle to lift when braking..

The two walking beams are connected by a cross-tube, which ensures constant alignment between the two axles.

The beams themselves keep the axles parallel to each other and the wheels parallel to the frame, although the rubber bushes allow a certain lateral movement—some 21 in. transverse sideplay when on full steering lock. This sideplay is automatically corrected when travelling in a straight line, because of the hush stressings.

In order not to introduce too many non-standard components, the trailing axle of the Eaton bogie is fitted with the same brake units as are used. on the driving axle. Moreover, in many cases identical hub assemblies can be used on both axles, particularly when the driving axle is an Eaton two-speed unit. A compensating linkage is employed for the hand brake.

Chassis-frame modifications are restricted to the addition of the central double-channel cross-member, channelsection flitch plates in the immediate vicinity of the bogie, and the re-positioning of the two cross-members, which in the standard chassis are adjacent to the spring-hanger brackets.

Because all the joints in the bogie assembly are rubber

bushed and because the suspension medium itself is of rubber, no maintenance is required and the only items likely to need replacement are the load cushions, the estimated life of which is about 200,000 miles.

Other than the minor frame modifications and the addition of the bogie, the chassis was as supplied by Leyland Motors, Ltd. Its standard specification :includes the 0.350 100 b.h.p. six-cylindered oil engine, Albion five-speed direct-top constant-mesh gearbox, Girling twoleading-hoe hydraulic brakes with Clayton Dewandre vacuum servo, and all-steel forward-control cab. The Eaton axle fitted to the test rvehicle had ratios of 5.57 and 76 to 1 and was equipped with vacuum-operated changespeed mechanism.:

The bogie adds about 14 cwt. to the unladen weight of the chassis, including the additional four wheels and tyres. A Sparshatt 18-ft. light-Alloy platform body, with cabheight headboard, weighed approximately 11 cwt., bringing the kerb weight of the complete vehicle to 5 tons 11 cwt. The maximum recommended rating for the Leyland 6x2 is_16 tons, with a front-axle limitation of 4 tons, and thi! would allow a payload of about 11 tons.

Bearing in mind the likelihood of such a vehicle being overloaded, however, Mr. G. W. Sparshatt agreed to the vehicle carrying a 121-ton payload, consisting of .approximately .4,200 bricks. These could not, however, be stacked evenly along the length of the body for fear of overloading the front axle, although had the correct payload of 11 tons been carried there would have been no danger of doing so.

Thus, operators who wish to carry payloads of 12 tons or more will be well advised to ensure that the bogie carries a high concentration of the payload, the bogie capacity limit being 151 tons.

For the braking and acceleration tests the six-wheeler was driven to a disused aerodrome where the main runway, although slightly pot-holed, provided good facilities.

Acceleration runs were made with the low axle ratio engaged the whole time and the average time taken to reach 30 m.p.h. from a standstill, although not outstanding, was good in %view of the gross weight. As might be expected, direct-drive acceleration was somewhat sluggish.

Good retardation figures were obtained from 20 m.p.h. and 30 m.p.h., and there was little evidence of delay in the braking system. Despite the parallelogram linkage, the rear axle lifted sufficiently to allow the trailing wheels to lock, but this lift was probably because of incorrect brake adjustment and was not sufficient to affect stability.

Although I had misgivings about conducting emergency stops with a load of bricks, my fears were unfounded. Very few bricks moved and only one was chipped. This fact alone is sufficient testimony to the smoothness of the braking system and stability provided by the suspension.

Hand-brake performance was somewhat disappointing, but I do not blame the bogie for this. Leyland hand brakes are rarely very effective for emergency application, partly because of the short lever. It would be preferable to fit a multi-pull lever if sufficient power cannot be provided by a direct-acting control.

Turning-circle measurements were made on the airfield and when on full lock the amount of inter-axle displacement was observed. The amount of sideplay permitted by the rubber bushes would suggest that tyre scrub under such conditions is not likely to be a major problem.

Rufus Stone Hill, which has a maximum gradient of 1 in 7, was used for brief hill-climbing tests. The gradient was ascended in an ambient temperature of 66° F. The climb lasted just under four minutes, and the temperature of the coolant in the radiator header tank rose from 159° F.

to 170° F., showing sufficient cooling latitude. Bottom gear, low axle ratio, was employed on the steepest part of the hill. .

The Leyland was then reversed to the 1-in-7 section, where it was stopped. The hand brake held the vehicle and a reasonably smooth restart was made, although a certain amount of clutch slipping was necessary. Slight exhaust smoking was observed.

Fuel consumption was measured over the Undulating road between the Sparshatt works at Redbridge, and Ower, a distance of 5.1 miles. On the outward journey the Leyland was climbing most of the time and there were few stretches where it was possible to use top gear, high axle ratio. Furthermore, heavy traffic was encountered in Totton.

Nevertheless, the distance was completed at an average speed of 26.7 m.p.h. and the calibrated fuel-test tank employed showed that 3i pints of fuel had been used, indicating a consumption rate of 10.6 m.p.g.

Better figures resulted from the return run as the gradients were favourable, and a consumption rate of 14.75 m.p.g. was achieved at an average speed of 29.1 m.p.h.

E18 The overall figures for the complete 10.2-mile journey are 12.25 m.p.g. and 27.8 m.p.h., showing that under normal conditions with a 12f-ton payload at least 12.5 m.p.g. can be expected when the vehicle is fully run-in.

Operators in hilly areas would be advised to specify lower rear-axle ratios for optimum performance and economy, in which case laden consumption rates no worse than 11 m.p.g. should be returned.

Between fuel-consumption tests the Leyland was taken off the road on to a tietch of rough ground so that bogie articulation could be Studied. " At one point there was a difference in pub height of 81 in at one side of the vehicle, the trailing. axle being at an "angle of 61° to the chassis frame, but the rubber cushions at each side were equally dellected.andthere was no chassis or body distortion.

Whatever the inter-axle articulation, no. out-of-balance frame stresses are set up in the ,Hendrickson suspension Layout. Another important factor is that the axle loadings remain equal under all conditions, which, was why it was possible to maintain traction over the damp, grassy surface despite the single driving axle.

During all this off-the-road work not one of the bricks was displaced and there was no sign of relative movement between the body and the cab.

The Leyland 6. X 2 is a pleasant vehicle to handle. Although the Power-to-weight ratio is low and a fair amount of gear changing is necessary on hilly roads, the gear change .is first-rate and does not tend to discourage frequent use of the indirect ratios. Properly used, the 10 available ratios permit a surprisingly high average speed to be maintained, whilst in the highest available overall ratio the maximum road speed is in excess of 45 m.p.h. An overdrive-top gearbox is available on this chassis.

Steering is commendably light, with just the right amount of castor action. The brakes are fully progressive and even emergency stops can be made without excessive pressure on the pedal. The vehicle rides well and is steady on corners.

This particular Eaton-Hendrickson bogie conversion adds £515 to the list price of the standard Leyland Comet with the Eaton 18500 axle. Other conversions may vary in price slightly according to the type of chassis.

As was explained in The Commercial Motor on May 2 in a costing article dealing with third-axle conversions, there is an appreciable saving to be gained in terms of cost per ton payload from such vehicles. Therefore, if the operator's traffic justifies the addition of some 4 tons of payload without fear of illegal overloading, the extra initial outlay is soon recovered in terms of reduced ton-mile running expenses. A further consideration in respect of the Eaton bogie is the elimination of maintenance.

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Locations: Ltd., Southampton

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