Fig. 33.—70 h.p. Six-cylinder Dennis Fire-engine with Gwynne Centrifugal Pump.
Fig. 34.—60 h.p. Six-cylinder Halley Fire-engine with Centrifugal Pump.
Fig. 35.—One of Barford & Perkins’s Water-ballast Rollers.
It is still the hope of some manufacturers that a form of infinitely variable change-speed device will be produced, which will replace the step-by-step movement of toothed gearing; the two chief directions in which this has been attempted are electrical and hydraulic. Of these two, electrical devices are really step by step, and the hydraulic method is apparently the only one that permits of infinite variation. Enormous sums of money have been spent in the search for an effective hydraulic gear; the work of Hall, Pittler, Jannay, Hele-Shaw, Renault and others is, perhaps, the best known. It must be confessed, however, that in 1910 none of these gears could be said to be on the market for motor vehicles, although hydraulic gears were being successfully applied in connexion with other problems, such as the steering of ships, the movement of turrets, &c.
Fig. 36.—Marshall’s 30 h.p. Agricultural Tractor.
Electrical transmission systems, too, have been tried, and appear to have been attended with more success than those of the hydraulic type. Such systems include Vehicles which carry heavy batteries of accumulators, the current from which is utilized for the driving of the vehicle by means of electric motors. Other variations include the Hallford-Stevens system, shown in fig. 32, in which it may be seen the petrol engine drives a dynamo, and the current is then caused to drive an electric motor at each side of the chassis. Each motor drives one of the back road wheels, through a worm and worm wheel. The changes of vehicle speed are effected by altering the method of grouping the electrical windings of the dynamo and motor field-magnets and armatures. This system of control is known as the series-parallel, and is effected by a single lever, which actuates a mechanical switch, or “controller.”
In one of the most-recently-introduced petrol-electric systems—the “K.P.L.” system, as worked by the Daimler Co., of Coventry—each of the rear road wheels is provided with a separate power unit, consisting of a four-cylinder petrol engine, which is direct coupled to a dynamotor, the armature of the latter being coupled to a worm which meshes with a worm wheel attached to the road wheel. A small electrical storage battery forms part of the system, and this receives the excess of current from the dynamotors when the whole power of the engine is not required for the propulsion of the vehicle. When the machine is being driven up a steep incline, or when it is required to travel in a reverse direction, the battery may be called upon to supply current to the dynamotor, and, in this manner, the power of the engine is augmented by the dynamotors’ working as electric motors.
