Electric Locomotives

The geared quill drive with single or twin motors secures com pletely spring-borne frame mounting of the motors, the elevation of the motors from the roadbed and their better placement as to overall weight distribution of the locomotive. The motors are less exposed and opportunity is afforded for twin motor mounting which secures certain advantages, notably those of simplified gearing, less space restrictions, reduction in voltage across corn mutators and better opportunity for motor groupings. With the use of twin motors the maximum possible output for an indi vidually driven axle may be realized.

With frame mounting and individual universal rod and pin con nection from gears to drivers the same advantages of placement obtain as with the geared quill drive with the substitution of mechanism for the springs.

The direct side rod drive was the result of the natural attempt to get away from the limitations of the street railway type motor and to follow the design of the steam locomotive in order to retain certain of its favourable characteristics such as high centre of gravity, favourable wheel spacing, etc. It has been used experi mentally on several locomotives usually with direct connected oblique main rods. Under certain dynamic conditions, excessive stresses in rods or pins are developed.

The direct side rod drive with scotch yoke has the advantage of permitting vertical movement between motors and drivers and also admits of motor mounting somewhat above the centre line of drivers. This drive is well adapted for the direct connection to large slow speed motors and is in extensive use on a large number of Italian locomotives. The same principle of sliding rod bushing has been used in various adaptations of side rod drive for single phase locomotives.

The jack shaft side rod drive was the logical development of the direct side rod drive. By its use certain stresses due to the static and dynamic characteristics of the general type of drive were better taken care of. It is limited to the higher speed locomotives on account of the low weight efficiency of the motors at the lower speeds. It has found a limited number of applications both with d.c. and a.c. motors.

The geared jack shaft drive is a modification of the direct jack shaft drive through the employment of gears which admits the use of higher speed and lighter motors and main rod with minimum angularity relative to the side rods. The use of flexible gears secures the advantageous cushioning of drive. It is now, with some variation in design, in successful operation in all classes of service.

The common disadvantage of all drive connections between the rotating masses of the motors and those of the wheels is due to changes in angular velocity between the two, each having its own inertia. Rod drives are in particular more susceptible to this, owing to the inclusion of more driven wheels, larger motors and more elements with clearance, together with transfer of load from one side to the other due to the use of crank motion. The difference in these respects from those obtaining with steam loco motives is that the electric drive is a mechanically closed system while the steam drive is an open system. This is a vital difference and one which must be provided for in order to take care of all conditions and speeds.

For the larger locomotives the running gear may comprise a single wheel base alone or several connected by hinges, or by coupling either with or without buffers. For the slower speed locomotives auxiliary trucks are often not needed but where operation is required over a considerable amount of critical curva ture, guiding is improved by the use of hinge connection. For the heavier and higher speed locomotives auxiliary trucks are employed ; these are of varied types, both two-wheel and four wheel. They serve various functions such as carrying weight,

easing track stresses, providing stability on tangents at high speeds and guiding on curves. The last two may be supplemented by hinge or special connections.

The general practice in America follows the steam practice of supplying restraint to trucks by the use of heart links or rockers.

without provision for special driver axle play. The usual conti nental practice, on the other hand, is to employ spring or inclined plane, or combined motion with adjacent driver. Long rigid wheel bases are commonly employed even with high curvature by the provision of ample lateral play of the driving axles involved and of their driving rods. The two-way operation of electric loco motives having restraint elements in auxiliary trucks imposes greater difficulties in securing favourable guiding on heavy curva ture than is the case with steam locomotives with one-way opera tion. This may be overcome or eliminated by adequate attention to design. Practice as to permissible axle loading differs widely and has not been definitely established. However, owing to the complete counterbalance for all speeds obtainable on electric locomotives (due to the absence of reciprocating parts), loading is considered to be less severe on structures and permanent way than a steam locomotive, even with its lesser static loading. For conditions of high speed or heavy axle loading, due provision can be and usually is made to minimize the non-spring-borne weight, and also to secure the most favourable wheel spacing for minimiz ing track stresses.

For the control of the motors and various other purposes, switches and other apparatus and equipment are required. There are two general types of mounting; one, with a self-contained cab, mounted on two or more trucks or running gears, and carry ing and housing the auxiliary apparatus ; the other, with the cab structure borne by and integral with each running gear. The first type having relative movement requires a much heavier cab structure with special supports, and also flexible connections for the electrical circuits, air, sand and oil lines and forced ventila tion system. In the case of the integral cab these flexible con nections are not required. Owing to the absence of relative move ment between motors and control apparatus it becomes possible to mount control and ventilating equipment directly upon the motors and all other equipment may be mounted directly upon the locomotive frame. The cab structure thus becomes merely a housing for the protection of the operators and apparatus. The electric locomotive, on the other hand, is dependent on and con trolled, both as to design and possible limits of operation, by the other necessary component elements of a railroad electrification. Conclusions on electric locomotives are consequently a com promise to realize the overall objective; therefore, discrimination is necessary when comparisons of electrifications are based solely on locomotive design, costs or performance. The general trend of locomotive design is influenced by the need for greater horse power per train especially in America. This is occasioned by the progressive trend for heavier trains and higher speeds in both freight and passenger services. The approximate number of loco motive units throughout the world in 1929, aggregated about 3,000, two-thirds of which are alternating current including some 500-3 phase units. D.c. units are divided approximately in the ratio of low voltage to high voltage. (F. H. SH.)