The Radiator Cooling Fan is used in Diesel Electric Locomotives to bring down the temperature of the diesel engine cooling water to the desired level. Drive between the engine and radiator fan consists of an Eddy Current Clutch (ECC) type DBOCN – F which is capable of providing variable speed and a Bevel Gear Box which provides mechanical coupling between clutch and the fan.

The constant speed member of the Eddy Current Clutch is a ferromagnetic Drum and is rigidly coupled to the prime mover. Here the prime mover is the engine shaft.


Construction & System Description

A multi-pole inductor made from special alloy steel and mounted on the Gear Box input shaft rotates freely within the ferromagnetic Drum maintaining a small and constant air gap. This forms the variable speed member of the drive.

When the excitation coil is energized, a space varying flux pattern is created on the inside surface of the Drum. The relative motion between Pole and Drum causes the flux concentrations to sweep the surface of the Drum. This results in creation of eddy current in the Drum material depending on the rate of change of magnetic flux caused by the relative difference of speed between the input and output members and the total magnetic flux generated by the ampere turns of the excitation coil.

TThe two parameters controlling the magnitude of the torque are the excitation current and slip between the fixed speed member and the variable speed member. So for a given excitation current the slip will adjust in a manner to produce the required load torque demand on the output shaft which is connected to the Radiator Cooling Fan through the Bevel Gear Box.

Features of Eddy Current Clutch

  • No copper coating on the inside surface of the Drum. This eliminates problems with copper coating peeling off or suffering other mechanical damage while handling during periodic maintenance.
  • The stationary coil eliminates the use of carbon brushes. Slip rings are avoided and control is effected by relatively low power.
  • The Eddy Current Clutch functions without the need for mechanical contact. This eliminates the main cause of wear.
  • The Eddy Current Clutch isolates prime mover from abnormal torque demands.
  • The variable speed clutch allows to vary the Fan RPM depending on demand. Since Fan RPM is directly proportional to the output torque, this reduces the parasite power requirement and thus enabling more Motive Power.