In early 1960s, class DF50 diesel locomotives were operated as the standard diesel locomotive for the main track, but it was serious problem that they had much trouble and were too heavy to use on the semi-trunk lines. So JNR was investigating new diesel locomotive for the trunk lines. As the result, class DD51 diesel hydraulic locomotive was developed. Newly developed 1,000 PS diesel engines; DML61S, and newly developed hydraulic transmission gear; DW2 for high power diesel locomotive gives the sufficient performance DD51 diesel locomotive which is used on semi-truck lines. Although other counties excepting Germany adopt diesel electric locomotives, JNR dared to standardize diesel hydraulic locomotive in order to make its body lightweight. DD51 of mass production type adopts 1,100 PS diesel engines, DML61Z with the intercooler and improved hydraulic transmission gear, DW2A. At first DD51 was equipped with the steam generator, but later various types of DD51 omitting SG or equipped with the multiple header control equipment appeared. And bolster spring of its intermediate bogie was changed to air spring in order to make axle load variable with changing air pressure of air spring.
Sub classes are shown as below;
0~ with SG
500~ with SG and multiple header control equipment
800~ with multiple header control equipment but omitting SG
1000~ with SG and multiple header control equipment
1800~ with multiple header control equipment but omitting SG
Class DD51 diesel locomotives were decommissioning by decreasing freight trains and spreading electrified lines. In additional DD51 becomes too old to use, so we have to take notice of future DD51.
|
