Lecture 9 - Train Resistances I

Question 1

Tractive Force

Answer 1

The tractive force Z of the traction unit must suffice to overcome the train resistance Rtrain
Z = Rtrain = ERi = Rtu + ERwg

Question 2

Traction or Drive Power

Answer 2

Product of the tractive force and the current velocity

Ptrain = Rtrain * V

Question 3

Wheel Resistance - RWh

Answer 3

According to Mitschake, the wheel resistance Rwh comprises:
Rolling resistance Rro
Sliding resistance Rsl
Bearing Resistance Rbe
Flexing Resistance Rfl
Dynamic Resistance Rdy
Acoustic Resistance Rac

Question 4

Dependency of the Rolling Resistance coefficient

Answer 4

On wheel load: increases (directly proportional)
On driving speed: increases
On wheel diameter: decreases (inversely proportional)

Question 5

Sliding Resistance

Answer 5

The causes of Sliding Resistance between wheel and rail are longitudinal sliding forces due to the different tread diameters of coupled wheels
Note: for a driving wheel the sliding resistance is not part of the vehicle resistance

Question 6

Bearing resistance related to wheel-rail contact

Answer 6

Assumptions:
• Outer bearing ring fixed to bearing housing
• Inner bearing ring fixed to wheel set stub axle
Note: Bearing resistance is often included in the rolling resistance

Question 7

Dynamic Resistance

Answer 7

Depends on the driving velocity due to the unroundness of the wheels and the track irregularities

Question 8

Acoustic Resistance

Answer 8

Acoustic resistance describes the acoustic losses radiated by the vehicle

Question 9

Flexing Resistance

Answer 9

Flexing resistance represents the energy loss due to the damping and warming of the wheel rubber

Question 10

Wheel or total wheel resistance

Answer 10

Is the sum of the single resistance components on the wheel

Question 11

Starting resistance

Answer 11

Resistance due to overcome the static friction in the axle bearings