The Electric Drive as a Motorcoach Transmission 270040
THE engineering factors involved in the adaptation of the electric drive as applied to the motorcoach are presented by the author, who also enumerates the limitations of design. To raise the power curve at the higher engine-speeds and within the most efficient speed-range of the engine, which corresponds generally with a piston speed of from 1200 to 1600 ft. per min., without unduly sacrificing engine torque at the lower speed, the valve-timing must be changed. The author illustrates what effect this has by presenting data obtained with a four-cylinder engine of 4¼-in. bore and 5-in. stroke, together with other tabulated data and charts.
With regard to the advantages and disadvantages of the electric drive, it has been fairly well established that the greatest asset, as applied to the motorcoach, is the permissible increase in scheduled speed where traffic is congested. Other advantages are its quietness of operation due to the elimination of the selective-gearshift transmission and also to the ease of operation, because the driver has but two operations to perform in addition to steering. The last advantage has a tendenscy to increase safety, renders fare collecting easy, saves time, and lessens the physical fatigue and the mental strain on the driver of the motorcoach.
Some of the disadvantages of the electric drive are its high initial cost and its greater weight, the latter being from 1250 to 1650 lb. more than that for a vehicle equipped with the conventional clutch and gearbox. The greater weight requires that more pounds must be carried as dead-weight. It is stated that the electric drive is comparatively inefficient for vehicles having low power-weight ratio. There is a slight time-lag at the start of acceleration which is caused by the necessity of building up the necessary magnetism and potential in the generator, but it does not become serious until traffic conditions call for 15 or more stops per mile. It is stated also that the fuel consumption is greater with the electric drive and that, in the future, this drive must stand or fall on its economic merit.