CARS AND Mozons. One or more electric mo tors geared to the ear-axles and a controlling switch on each platform constitute the principal parts of a motor-ear of haying the journal-boxes attached to the car frame, as in horse-ears, the motors and running gear are attached to a ear-trnek, on which the car-body rests. The remarkable improvement which has been made in the design of street-car motors within the last ten years is the principal cause of the success of electric railways. The first car motors were entirely too light mechan ically and of too small capacity. Front a single liftcen-horse-power inot.oy driving one car-axle, the capacity of the car equipments ha. been g•adually increased up to the present practice of using two twenty-horse-power motors. one geared to either axle. A marked improvement has also been made in the reduction of armature speeds, so that the use of a double reduction in speed by s of a countershaft and two pairs of gears the armature shaft and the car axle is almost obsolete. Gearless motors. in which the armature is built on the car-axlc. have been introduced, but simde reduction motors hav ing the armature shaft geared directly to the car axle are the most commonly used at present. Almost all modern car motor: are of the multi polar type instead of the bipolar, as formerly. and the reduction in armature speeds is due to this change of design. The severe service to kit street-car motors are subject has led to making them very substantial in design. in order to avoid uocchanXal injury, and so-called iron clad motors. in which the field-magnets form a closed iron box, are largely used to prevent short circuiting by water. or by nails or scrap: of iron picked up by the magnets. Most of the single reduction four-pole motors are supported on one side on the car-axles by set in projecting lugs at each end of the motor frame. the armature shafts being parallel to the ear-axles. The op posite sides of the motors are connected to the frame of the ear-truck by means of springs. and a pinion on each armature shaft meshes with a gearwheel on either axle. The function of the springs is to avoid a shock on starting the ear, by permitting the motors to turn through a small arc about the axles. In gearless motors the armature shaft is a hollow tube, through which the car-axle passes, and to which it is flexibly connected by means of springs. Another method in use with some geared motors is to place the motor on the truck with it. shaft at right angles to the car-axles. The shaft carries a bevel pinion at each end which meshes with bevel gears on both of the ear-axles. With this
system a single motor of large capacity is used. A number of attempts have been made from time to time to connect the armature shaft and the axle by belt:, sprocket chains, friction clutches, etc., none of which has been able to stand the service. See illustration of street-railway motor under DYNA.M 0-ELECTRIC Al The starting and regulation of speed of the car is effected by means of the controlling switches on the car platforms. The methods of regulation of the different electric railway sys tems are too numerous to be described in detail, but the same general plan is common to them all. Series machines are always used in railway work, and the field-windings are wound in a number of separate sections. the ends of which are carried to •ontaet pieces in the controlling switches. In addition to the resistance of the field-winding. a resistance box is also in-ed. The contact pieces in the controller press against corresponding rows of metal plates, each row having its plate connected ,r) as to vary the con nection: of the wires front the motor. In start big the car, the resistance box, sections of the field-coils and armature are all ill series to prevent a too large passage of current through the armature. The next turn of the switch cuts out more or less of the resistance-box circuit, allowing more current to pass. and by successive movements of the switch, the field zis pass through various combinations, from all in series to all in multiple. the latter corresponding to the highest car speed. To stop the car, the switch is reversed. making the sante combina tions in reverse order. To change the direction of the car. a separate switch is generally pro vided. which changes the direction of the current through the armature with reference to its direc tion through the fields. in ',Ienls where there is no commutation of the field-coils. the changes in speed depend entirely upon the variable amounts of extra resistance thrown into the circuit. The ears used on electric railways vary from 10 feet to 35 feet long, and weigh 6 to 11 tons. For illustration of controller, see DY NAMO-ELECTRIC .1.1CIIINERY.
Consult: Electric Railways and Tramways (London, 1597) ; Bell, Power Dis tribution for Electric Railroads (New York, 1900) : Ilanchett, Modern Electric Railway Mo tors (New York. 1900) ; Herrick, Practical Elec tric Railway Handbook (New York. 1901) ; Herring. Recent Progress in Electric Railways (New York. IS97). For descriptions of the generator: used in power-houses, see DYNAMO ELECTRIC SIACIIINERY.