LEC Drivetrain & Transmission 3

Question 1

In a diesel-hydraulic locomotive drivetrain, what component replaces the traction motors used in diesel-electric designs?

Accepted Answer

A hydraulic torque converter and mechanical gearbox

Answer

Diesel-hydraulic locomotives use a hydraulic torque converter (and sometimes a fluid coupling) combined with a mechanical gearbox to transmit power to the axles.

Question 2

What is 'dynamic augment' in the context of locomotive drivetrain forces?

Accepted Answer

The cyclic vertical force variation caused by rotating and reciprocating drivetrain components

Answer

Dynamic augment is the periodic variation in vertical wheel force caused by rotating wheel/axle imbalance and reciprocating parts, affecting track loading.

Question 3

What does the term 'gear ratio' refer to in the context of a locomotive axle drive?

Accepted Answer

The ratio of traction motor pinion teeth to bull gear teeth on the axle

Answer

The axle gear ratio is the number of teeth on the axle-mounted bull gear divided by the number on the motor pinion, determining the speed/torque trade-off.

Question 4

A locomotive with a higher axle gear ratio compared to a standard unit will MOST likely have:

Accepted Answer

Lower top speed but greater starting tractive effort

Answer

A higher gear ratio multiplies torque more at the wheels but limits rotational speed, resulting in more pulling power at the cost of maximum speed.

Question 5

What is the function of the traction motor suspension system (nose suspension) in a locomotive?

Accepted Answer

It permits the traction motor to move with the axle over track irregularities while transmitting torque

Answer

Nose-suspended traction motors are rigidly attached to the axle bearing housing on one end and pivot from the truck frame on the other, allowing axle movement while maintaining gear mesh.

(LEC) Locomotive Engineer Certification Practice Test

(LEC) Locomotive Engineer Certification Practice Test

LEC Drivetrain & Transmission 3