French Retarder Demonstrated
Page 11
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rHE French Telma electric retarder was demonstrated in London on -uesday by the sole concessionnaire or this equipment for the United Cingdorn and Eire, Trico-Folberth Ltd., lrentford. Middx. The retarder was nstalled in a Bedford 41-scat diesel:ngined coach with an unladen weight if 5.tons 15 cwt., and 21 people were :board (including the driver) so the gross veight would have been in the region of 'tons. Tapley-meter readings of up to 6 per cent were obtained when the etarder was used to full effect, whilst ong gradients of at least 1-in-10 severity :ould be descended at low speeds withnit use of the wheelbrakes, thereby =ring out the claims made for this :quipment.
Telma brakes have been in use in -7rance for a considerable number of rears, but have been available in this :ountry only since the middle of last rear, when Trico became concessionnaire, in example being exhibited by Trico at he Earls Court Show last September. [he retarder assembly is basically fairly iimple, consisting of a stator which is nounted to the chassis frame and inside Nhich there is a rotor carrying two softteel discs. the rotor being bolted to the ?ropeller shaft. The retarder acts, in effect, as both a cross-member and a :entre bearing.
It is controlled by a four-position ;witch which can be mounted on the steering column, this acting through a contactor box which energizes the inductor coils, so producing a strong magnetic field which drags on the soft-steel discs and so produces a distinct retardation effect. Seven sizes of Telma brake arc available, these being suitable for vehicles with gross weights of 6, 11. 14, 19, 25, 40 and 55 tons, and weights range from 220 lb. to 810 lb., whilst prices range from £255 to £483, excluding fitting charges which would be in the region of £60 to £100.
Compared with an exhaust brake —the other form of retarding device in most common use in Europe—the Telma offers several advantages to help offset its disadvantages of bulk, weight and cost. For one thing, it is not necessary to use the gearbox to obtain the differing braking effects, in fact, being behind the gearbox, the retarder is fully effective even when the gearbox is in neutral. For another thing, the retarder is quite silent in operation, which is a big advantage for passenger-vehicle applications.
Because it has a four-stage control, the braking effect can be instantly selected to suit prevailing road conditions. the first stage giving a retardation of approximately 7.5 per cent, the second stage 11 per cent and the third stage 16 per cent. In theory the fourth stage should give about 20 per cent, but the retarder in the demonstration vehicle gave the same effect in fourth as in third. so presumably there was a fault. With the fourth stage in use the C.80 brake as demonstrated can absorb over 200 b.h.p., this brake weighing 320 lb., costing £255, and being suitable for 11-ton-gross vehicles. Current consumption is staled to be in the region of 60/70 amp, when using the retarder in the fourth setting.
J.F.M.