The Hallford-Stevens Petrol-electric System.
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In our issue of the 21st, January, 1908, we recorded the inaugural trip of the "Ilford " petrol-electric omnibus before its entry upon public service for Thomas Tilling, Ltd. It will be remembered that the distinctive features of this vehicle consisted of a simple electrical transmission which is patented and manufactured by W. A. Stevens, Ltd., of Maidstone. The inter-polar dynamo is coupled direct to the " Hallford " petrel engine, and electrical energy is supplied by way of the Stevens patent " sparkless " controller to the electric motors mounted on each aide of the main frame; these motors drive, by means of cardan shafts, the " S.B. and S " patent back axle, the joint invention of Mr. P. Frost-Smith (engineer and manager of the Tilling motor department), Mr. Frank Brown (chairman of David Brown and Sons, Ltd., of Huddersfield) and Mr. W. A. Stevens (managing director of W. A. Stevens, Ltd.). This vehicle has now run considerably more than 60,000 miles in London public service, and, as a result of experience gained in the earlier days, modifications have been made in some of the details, though the general principle and design has remained unaltered. On the electrical side, trouble was experienced from one of the motors' taking more current than the other, and, in extreme cases, one motor's acting as a generator. This difficulty has been entirely remedied by an improved method of connecting up the series field-windings of the motors, so that, now, each motor is compelled to take its share of the work, and perfect differentiation has been ensured. Trouble was experienced, too, because the carbon brushes were too good a fit in the holders. The particular type of brush used—and which is still in use, giving excellent results—expanded considerably with a small increase of temperature. After this characteristic was noted, the brush channel in the holders was slightly enlarged, and, as a result, no further trouble has been experienced in this connection.
Turning to the mechanical side, an important improvement has been made to the " S.B. and S." back axle. The worm box, instead of being rigidly attached, is loosely mounted on it, so that all torsional strains on the axle are now obviated. This improvement was made because the original type of axle broke after a few months of work, but, since the new form has been adopted, no trouble in this direction has been experienced. The rardan shafts, instead of their being exposed, arc now carried inside the hollow torque rods. Owing to the absence of gearbox, differential and clutch, and the fact that the drive between the engine and the road wheels is of so elastic a nature, the cost of upkeep is now very small.
As a result ot the success of the " Hallford " petrolelectric omnibus, a working arrangement has been entered into between J. and E. Hall, Ltd., of Dartford, the manufacturer of the chassis, and W. A. Stevens, Ltd., of Maidstone, the manufacturer of the electrical equipment, for the joint manufacture of the vehicle, which has the registered trade mark of " Hallford-Stevens." The latter company acts as sole selling agent for both petrol-electric and electric vehicles, and Mr. W. A. Stevens is giving his personal attention to this side of the business. He has, as a result of a demonstration tour of rather more than a thousand miles in the Midlands and North of England, which was undertaken in October last, had many inquiries from municipalities and provincial omnibus companies, in addition to several from abroad. Definite steps are being taken, at Loughborough, to begin a local service.
For military work, for which it is already employed, it is claimed that the vehicle offers many distinctadvantages. These are :—(1) Service as a three-ton lorry; (2) the generating plant on the vehicle is available for searchlight ‘%orkthe generator is able to develop 16 kilowatts continuously with petrol, and 14 kilowatts with paraffin, as the engine fuel, and will supply one 40 in., or two 24 in., or four 18 in., electric projectors, which may either be mounted on the vehicle or trailed on separate carriages ; (3) the vehicle can carry a complete wireless apparatus, with sectional aerial equipment ; (4) with the power developed with the generator, signalling over land can be effected to distances of 250 miles.
By an arrangement with the Marconi Wireless Telegraph Co., Ltd., quotations can be given for complete equipments fixed on the vehicle, or Mr. Stevens will be equally pleased if the inquiry is sent to the Marconi Co. It should also be noted that the electrical energy supplied by the generator would be most useful for supplying Röntgen and high-frequency apparatus, in addition to general lighting. The generator will supply thirty 1,000-candle-power 'arc lamps, or two hundred 16-candlepower carbon-filament lamps, continuously.