All-round Improvements in the Lodekka
Page 49
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THE 1951 version of the Lodekka bus made by the Bristol Tramways and Carriage Co., Ltd., Bristol, has many improvements which provide for greater passenger comfort and an increase in transmission efficiency. The prototype. introduced in 1949, was the first lowheight double-decker with central gangways to both decks. This model was described in "The Commercial Motor" on October 7, 1949.
Provision is made in the latest version for overall body dimensions of 27 ft. length and 8 ft. width, and the wheelbase has been increased from 15 ft. 10 ins. to 16 ft. 5 ins. This new overall length has afforded a further II ins. of \pace between the seats on the lower deck' and ; in. in the upper saloon, whilst the platform length has been increased by 2 ins. to 4 ft. 2 ins.
New Transmission Line There has been a major alteration in the transmission, beginning at the gearbox, which now incorporates the differential unit and split drive to the wheels. This new gearbox, which is provisionally protected, has a light-alloy ease and forms a unit with the engine. It provides four forward speeds and a reverse ratio, the top gear giving a stepdown ratio of 1.2 to 1. It is designed for a torque of 350 lb. ft. A further reduction in ratio is obtained through the gears driving the propeller shafts. the overall ratio being 1.8 to 1.
The internal arrangement of the gearbox .consists of a clutch housing and two output shafts, which, in a normal case, would be the main and layshafis, the lower shaft acting as a layshaft for the first and second gears. At the rear of this shaft, and on the same axis, ar2 mounted the differential bevel gears.
The driving carrier of the planet ),‘ heels may be driven either by an outer gear ring giving top gear, or direct through the centre shaft of the carrier from the constant-mesh and output shaft, the ratio of constant mesh pro
viding third speed. This dispenses with the normal third-gear drive. First and second gears are obtained through the constant mesh in the conventional manner and the drive goes to the outer ring of the differential planet wheels.
Each of the sun wheels of the differential is directly attached to a gear which is in mesh with a larger wheel on each of the propeller driving shafts. These shafts are situated on each side of the gearbox output shaft and spaced to give the necessary clearance for the centre gangway in the lower saloon, the lower position in relation to the clutch housing permitting the propeller shafts to pass under the floor.
On the earlier prototype vehicle, there were two separate worm drives to the rear wheels. These have been replaced by spiral-bevel units to provide a wider gangway at the entrance to the lower saloon.
In conjunction with the increase of frame width from 3 ft. 8 ins. to 3 ft. 11 ins., and the new transmission arrangement, the sunken gangway is now parallel from front to rear and lit. 9 ins. wide.
Although similar in shape to the original, the frame has been modified, the cross-members and outriggers being steel channel pressings, bolted and strap-welded on assembly with the side members. The former light-alloy rearaxle beam is replaced by a tubular steel member, and the castings carrying the springs, back plates and drive assembly are spigotted and secured by clamp bolts at its extremities.
Vertical heights of the saloons and body have remained practically unchanged, there being 5 ft. 10 ins. headroom between the bottom of the gangway well and ceiling of the lower deck.
The special body for the Lodekka is made by Eastern Coach Works, Ltd., Lowestoft.