An Air-sprung Lodekka
Page 43
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AtPROTOTYPE Bristol E.C.W. Lodekka incorporating severalnew features is shortly to be used in experimental service with Crosville Motor Services, Ltd. The sunken lower-saloon gangway of the earlier design has now been dispensed with, air suspension is used for the rear axle, and Cave-BrownCave fresh-air heating equipment has been incorporated.
The new vehicle is a 27,ft. 60-seater, but the flat gangway has also been incorporated in a 30-ft. bus. The principal drawback to the original design, in which the gangway was some 4-5 in, below the level of the seat floors, was that the collection of fares was difficult when standing passengers were being carried, passengers being reluctant to step up between the seats to give passage to the conductor.
Unobstructed Flooring
A flat floor has been achieved basically by reducing the depth of the main chassis side members, which now finish ahead of the rear axle. Body loadings after this point are carried by deep wheel-arch members which form part of the body framing (a similar layout has been applied by Willowbrook's in the Dennis Loline described on the previous page and above).
This flat floor will henceforth be a standard production feature and the rearend framing has been laid out so that air suspension can be offered as an alternative to leaf springs with little modification. The air-sprung Lodekka (type LDS) has a constant platform height of not more than 17-iin., whilst the constant overall height is 13 ft. 31 in, whether laden or unladen..
With air suspension, the conventional drop-centre rear axle is retained and is rigidly attached to two trailing arms pivoted at their front ends and attached to a transverse cross-beam at the rear. The arms arc slightly flexible, each consisting of three thick leaves. About I in. of movement is allowed within the length of each arm, permitting slight relative movement between the body and the axle without locally overstressing any of the members.
Firestone rolling-lobe diaphragm-type air springs are employed and Andre will be used in the second prototype. The springs are located at the outer ends of the cross beam and react against the wheel box structures. Thus a wide spring-base is achieved which helps to give good .anti-roll characteristics.
Th es e characteristics are further enhanced by setting the Westinghouse levelling valves without a delay period. so that any roll tendency is immediately corrected by the admission of more air into the bellows on the lower side of the vehicle. During tests the body tilted to only 32° when the axles were at 28°, which is 3° less than is achieved with a conventionally sprung Lodekka.
. Large Girling telescopic dampers are used with the air springs and a rubberbushed Panhard rod provides lateral axle location, The other bearings in the prototype have plain bushes but it is expected that rubber bushes will be incorporated later to eliminate the need for lubrication.
High-pressure Bellows
Each air bellows works at a maximum pressure of 110 p.s.i and is fed through a separate air reservoir, has an integral surge tank and gives a constant periodicity of approximately 90 c.p.m.
Unlike the normal 27-ft. Lodekkas, which have triple-vacuum-servo braking, the prototype bus has dual-circuit airpressure braking, as fitted to the 30-ft. buses. Thus, the incorporation of air suspension has not resulted in any undue complication.
The 7-cu.-ft. compressor fitted to the Gardner engine is stated not to be overworked, although the slightest relative movement between chassis frame and axle causes air to be exhausted from or emitted to either or both of the bellows. By piping the exhaust outlets away from the immediate vicinity of the bellows a commendable degree of silence has been obtained.
Lightweight Components
Other design improvements include a large reduction in the amount of timber in the body, the use of a one-piece plywood floor for the upper saloon in place of tongued-and-grooved boarding; aluminium sheeting for the rear platform floor instead of boards; an aluminium staircase; extensive use of plastics mouldings for body fittings; an increase in the number of interior lights and the employment of aluminium conduit tubing; E.C.W. hopper-type side ventilators in place of sliding lights; a new type of rear entrance door which eliminates piano hinges and dispenses with the bottom track; and a revised emergency exit, so that passengers leaving the vehicle are directed naturally towards the nearside pavement.