The current is then said to be " ou the end "—that is, both the motor coils are in circuit.
The earlier form of Shortrail way motor is shown in Fig. 10. The arrangement of the field magnets is similar to that of the Brush arc dynamo. The arma ture is readily accessible for re pairs, but the form of the motor necessitates a different construc tion of truck, as shown in the cut.
In the summer of 1890 the electric railway art took an im mense stride forward, The Westinghouse Electric Co. brought out a motor pos sessing some unique mechanical features. The motor proper, Fig. 11, is within a square Iron frame that serves both to sup port it and to furnish bearings for the countershafts for gearing. The body or skeleton of the motor consists of only five parts : The cast-iron frame, the keeper, the two pole pieces, and the brass casting joining the upper and lower pole pieces, forming a mechanical framework of a very strong and simple character. The cast-iron frame carries the car axle.
the intermediate axle, and the armature in perfect alignment and parallelism. thus enabling the gears to mesh with great exactness. The pole pieces are hinged to the keeper, and both are firmly held in position by the retaining bolts through the brass casting that joins them at their extremities. The gears arc encased in cast-iron boxes, oil-tight, and partially filled withgrease. They are thus entirely free from the access of dust and grit, and can be con tinually and thoroughly lubricated. The armature is of the usual drum type; the core is built up of plates, each of which is cut with a key-way, so that the entire inner structure of tile armature can be locked firmly upon the shaft. The double wires of the arma ture are equivalent in conductivity to No. 7 wire, so that there is little danger of undue heating under the severest strain of service.
The Rae electric railway system presents some radical differences from any of the others heretofore mentioned. A single motor is used, r:gidly attached to the truck, and the armature spindle is parallel to the length of the car. The power is transmitted to both axles from the same motor through beveled gearing. Fig. 12 gives an idea of the princi pal characteristics of the system. The motor is placed cross-wise of the car, midway between
the wheels, and fastened rigidly to the framework of the truck. The armature pinion drives i an intermediate gear that, through the bevel-wheels, turns the axles. The motor is of 30 horse-power. with a Siemens armature ; it is thoroughly insulated at the sides by oak bars saturated with asphalt. and the employment of raw-bide or fiber armature pinions still further frees the machine from danger of a ground. The whole truck is put together as rigidly as possible, no attempt whatever being made to secure the usual The motor is series wound. The regulation of speed is effected through the interposition of a rheostat, consisting of four coils that are successively thrown in parallel arc with each other, and finally short-circuited. The rheostat, with its switch, is placed under the ear, as in the Thomson-Houston. Short. and Westinghouse systems, and is operated from the car platform by a simple handle, '• Single-reduction" Car Gear.—The standard Wenstrom street-ear motor, Fig. 13, is a O pole machine, the magnetic circuit being cast of initis metal in one piece. it is rated at 25 horse power, and weighs, complete, very nearly 1 ton. Owing to t he powerful magnetic field practicable with the Wenstrom construction, and to the fact of the motor• being a 4-pole machine, its speed is only 400 revolutions per minute. The armature is consequently geared directly to the car axle, without the intermediate countershaft. Another ingenious modi fication of street-car practice due to the WenstrOM CO, is to be found in the Atwood hydraulic gear which forms the connection between the split gear and the driven axle. Its purpose is to furnish a varia ble clutch between the driving and the driven axle, so that in starting the motor it may be allowed to run free and its power be applied gradually to start the car, and in addition, to provide a sort of mechanical safety valve, so that when there is a severe overload the hydraulic clutch will slip and allow the arnmtm•e to rotate fast enough to save it from the excess of current, instead of subjecting it to the dangerous overloading which would otherwise follow, Fig. 14 shows a section of this hydraulic gear.