Lecture 14 - Train Protection and Brake Systems Flashcards
Definition of brakes
Generally, brakes are meant to reduce or limit the speed of moving machine parts or vehicles
How brakes work?
Most brakes work by transforming supplied kinetic energy in thermal energy through friction
Brakes types on rail vehicles
Electric motor braking, wheel tread brakes, disc brakes and magnetic or eddy-current brakes
Tasks of the brakes
Decelarating the vehicle
Keeping the vehicle stationary
Keeping constant velocity (downhill)
Braking distance in Regional Transport
Depends on the velocity Trammway at 70 km/h : ca 70 m Subway at 70 km/h: ca 120 m Regional train at 70km/h : ca 240 m This is because breaking capacity for a trammway is higher than for a subway or a regional train,
Braking distance in Long-distance transport
In the worst case
Freight train at 100 km/h: 1 km
Regular passenger train at 160 km/h: 1 km
High speed trains at 300 km/h: 3 km
Block signalling system
1) First we divide the track into blocks
2) A distant signal announces the next block start, normally at 1 km. So that a train can definitely stop in front of that signal
Signalling
Driving on site is not viable because of long braking distance and missing deviation possibilities. Max allowed speed withouth train protection is 50 km/h
v < 160 km/h intermittent automatic train control (in Germany PZB)
v > 160 km/h continuous automatic train control (in Germany LZB)
Continuous Automatic Train Control (LZB)
Control center knows at all times the exact positions of the trains it’s supervising
Advantages
• Paying attention to trackside signals is not necessary
• Knowing the status of various blocks ahead allows driving with efficient energy
• An inmediate reaction to danger situations is possible, instead of waiting until approaching a trackside signal
European Train Control (ETCS)
Is a Train control system and fundamental component of the future Standarized European Railway Traffic Management System ERTMS.
Exist currently in 3 downward compatible levels
ECTS Level 1
Level 1: Discontinuous communication similar to PZB, light signals are not necessary since are showed on driver’s console
Conventional clear track signalling with axle counters or direct current circuits
Necessary:
Track: Eurobalise or Euroloop for continuous signal transmision along the complete distant signal domain
Vehicle: Eurocab with receiver of balise signals, ETCS board computer and console display
ETCS Level 2
Level 2: Continuous communication with the signal box, similar to LBZ but via GSM-R.
Vehicle tracking with odometry and fixed balises (track).
Conventional clear track signalling with axle counters or direct current circuits
ETCS Level 3
Level 3: Continuous communication with the signal box, mostly without lineside equipment, fixed block segmentation unnecesary, driving beyond braking distance possible. Vehicle tracking like level 2 clear track signalling with train integrity monitoring system (TIMS)
Advantages and disadvantages of ETCS
+ With level 2 or 3 no wayside signals neccesary
+ Knowing the status of various blocks ahead allows driving with efficient energy use
+ An inmediate reaction to danger situations is possible
+ Block sections can be reduced, resulting in an increased capacity of the line
- Equiping a traction unit with the system is very expensive
- ETCS is not identical in all European countries
Braking force generation in train with pure Air brake
First occurs a brake force generation lag, the delay in braking force generation at the rear of the train leads to high compression forces along the train. Risk of derailment exists if threshold values are excedeed on curves
Brake Regime
A slow-acting brake is neccesary for long trains. Pressure impulse reach the last car of a 700m long train in about 3-4 seconds. This means that the front part of the train breaks considerably while the rear part has not yet started braking
Braking force generation in train with electro-pneumatic brake
The electric remote control line sends an air brake activation command to the control systems of the individual cars, this leads to a simultaneous brake force generation of all cars
What limits the braking force that can be transfered to a wheel?
The maximum adhesion between wheel and rail
Wheel-Rail Adhesion
Is a random magnitude, which is predetermined by nature
Rarely constant along the entire braking distance, fluctuates between right and left rail
Depend on temperature, humidity, rail contamination
Hard to determine
What is the Wheel Slide Protection for?
Helps to prevent the blocked wheel and the risk of flat spots
Classification of Rail Vehicle Brakes
Dependent on wheel-rail contact condition, wheel brakes: Wheel disk brakes, Axle disk brakes, Flange disk brakes, Separate shaft disk brakes, drive shaft disc brakes.
Independent on wheel-rail contact condition, track brakes: Electromagnetic track brake, Linear Eddy-curremt brake, Linear motor brake
Wheel Brakes
Braking force is limited by the wheel-rail adhesion Tread brake vs. Disc Brake: \+ Simple, economical contruction \+ Cleans wheel tread - Increases wheel wear - Strong heating of wheel
Dynamic break:
+ No additional components
- Cannot be used for holding braking
- Only available on powered wheelsets
Brake system at high-speed train and trammway
Electric vehicles brake with the electric motor in operation and use the mechanic wheel brakes and the track brakes as emergency and/or parking brakes
For v>160 km/h an electromagnetic track brake or an Eddy-current brake must be additionally installed
All trams are equipped with electromagnetic track brakes to achieve high brake requirements
Track brakes
Eddy-current
+ no friction, no wear, no abrup stop
- can interfere with track signalling equipment, strong heating of the rails
Electromagnetic track brake
+ Simple contruction
- Friction and wear, abrupt stop
