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FOUR-WHEEL BRAKES ON LONDON BUSES.

9th November 1926, Page 117
9th November 1926
Page 117
Page 118
Page 117, 9th November 1926 — FOUR-WHEEL BRAKES ON LONDON BUSES.
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Details of the Servo Device and Other Features the New Dennis Admiral Bus. of

L.:kTTuesday saw an event which adds another 'Milestone to the progross of 'passenger travel in the London area. This was the placing into service o.g. the first London:kis equipped with front-wheel brakes. Only a few weeks before little hope had been entertained that the licensing authorities at Scotland Yard would permit the running of a bus equipped in this manner, but tests conducted in the presence of the officials concerned proved so satisfactory that a

muck decision was made, sanction being given on the Saturday before running commenced.

The vehicle is a handsome Dennis, forming a unit of the Admiral fleet of 34 buses owned by A. T. Bennett and Co., Ltd. Already sanction has been obtained for 10 of these four-wheelbraked buses to be employed; actually the company have bought seven, and six of these will be put into service before the end of the year. So far the brakes are permitted on single-deck buses only.

The front brakes are operated through a servo device, which is made by Dennis Bros., Ltd.; tinder licence from the patentees, Rolls-Royce, Ltd., and is the same as is used on Rolls-Royce cars.

The servo device consists of a rim formed in one with an inwardly' projecting ring and bolted to a driving plate rotated by skew-and-spur gearing from the .gearbox third shaft, which, being corriected direct to the propeller shaft, ensures movement until the vehicle iN actually arrested. outer disc and forms a bearing for a lever, which has on the inner side of its boss a double-faced cam similar to the dogs on a starting handle. A similar lever, bearing against a sleeve, is also carried on the centre spindle with its cam turned towards and meshing with that on the first lever. At the inner end of the sleeve are mounted two rockers, the upper ends of which are practically in contact with a projection on the outer disc, whilst the lower ends are linked to the horizontal arm of a bell-crank lever connected to the front and rear brakes, the arrangement being such that whichever way the disc endeavours to rotate it hears against one or other of the rockers and thus ensures operation of the brakes whether the bus fbe travelling forward or in reverse.

The outer lover is secured to the brake pedal, the inner one to the rear brake. It will be realized that the fact of pulling the outer lever and the resistance to movement of the inner lever will tend to separate the two through the action of the cams, and advantage is taken of . this movement to grip the revolving ring between the friction faces, which are stationary in the ordinary course. If no means was employed to govern this separating movement the plates of the servo would be clutched together immediately. To prevent this, a strong spring is utilized at the back of the inner lever and no separation of the levers occurs until the strength of this spring is overcome. Actually, if the spring were made strong enough, the braking would be all 011 the rear wheels and the servo would not be brought into operation at all so that by modifying the spring pressure any degree of braking, as between front and rear brakes, can be arranged.

In actual practice, on the bus in question, the braking power is 60 per cent, on the rear wheels and 40 per cent, on the front. On first applying the brake by foot, 20 per cent, is imposed on the rear wheels, and as the foot pressure is increased the servo comes into operation and an extra 40 per cent, is imposed on the rear wheels, whilst the remaining 40 per cent. acts on the front wheels.

It will be noted that whilst the bell crank of the servo device has entire control of the front brakes, it 'only shares in the operation of the rear brakes, and in these circumstances no front brake can be applied until after the rear brakes have been brought into operation.

We had a test on this hoe, and were agreeably surprised at its wonderful braking efficiency. Hard braking at 80 m.p.h. ensured a rapid but smooth stop, whilst at 12 m.p.h. stopping was so smooth that one could hardly realize that the brakes had been applied.

It is interesting to note that it was a Dennis bus which was first permitted to operate in London on pneumatic tyres, and the makers were the first, so long ago as 1904. to have a worm-driven bus in London service.

A few notes on the new Admiral bus will be of interest. It is a 30-seater with forward drive and a body built by Christopher Dodson, Ltd... The drop windows are handle-operated, but the handle can be retained in the conductor's possession. Side ventilators open outwards and the wide windows at the front have three cross-barS. The floor height is 31 ins. and there are two steps to the wide entrance at the near-side back, The turning circle is 55 ft.

The vehicle is British-built throughout and includes the C.A.V. 11-type dynamo with voltage regulator, a machine which has given wonderful service. The magneto is a Simms instrument and the tyres are run under contract with the Dunlop Co. They are straight-Sided, 36-in, by 6-in, pneumatics, which are inspected by the makers three times a week,, A small but important feature of the vehicle is that the silencer is encased with asbestos to keep the heat from the body: Those who would like to try this-bus will find it on the No. 529 service—Vietuna to Muswe11 Hill.

It will be of interest to users of Dennis vehicles to know that A. T. Bennett and Co., Ltd., keep a large stock of Dennis spare 'parts to the value of several thousand noun& at their works in Willow Walk, London, N.15.

Tags

Organisations: Scotland Yard
Locations: LONDON

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