Gear ratio and its effect on traction motors

John C. Aydelott (General Electric Company, Erie, Pa.): At a particular state of the art, and with a given arrangement of gearing, gear reduction can be increased only to a point which in railway service we know as “maximum reduction,” at which the pinion is the smallest considered to be reliable. Most railway designs are worked out on the basis of maximum reduction. By changing from single reduction to double reduction or from double reduction to triple reduction, the designer has a whole new range of possibilities involving, of course, increased complication and more expensive gearing. In some cases the best solution is to use single-reduction gearing and to put enough material in the motor to do the job. In other cases the best solution is to use double-reduction gearing and much less motor material. There is a range in which these two solutions tend to overlap to some extent. As a rule of thumb, it may be stated that double reduction is particularly useful at speeds below 35 miles per hour, and that above 35 miles per hour single reduction generally will be found preferable. As indicated by Mr. Woods, however, the trend in railway motor design is still toward higher and higher speeds.