Technology

Technology

Railway Technology Today 7 (Edited by Kanji Wako)

Braking Systems
Izumi Hasegawa and Seigo Uchida
Early Brakes

All rolling stock has some form of braking device, so that it can decelerate andstop when necessary. The first cars witha braking system were apparently small
trucks running on rails in mines. The
miners used a lever to push a wood blockagainst a wheel. However, such manual
devices became insufficient as the massand speed of rolling stock increased, so
braking systems using motive power wereintroduced.
By the 1860s, express trains were achieving speeds of about 80 km/h in England.
But at that time, brakes were not used on
all cars in a train. The engine driver anda brakeman in the last passenger car
would each apply a hand brake, with thedriver using the whistle to signal to thebrakeman when it was time to brake. Thisrudimentary system caused many accidents
that might have been avoided. Realizing
this, railway companies began installing

Figure 1 Early Braking System

braking equipment, generally using either
vacuum brakes or air brakes. Of these
two systems, only air brakes still remain
in use.
George Westinghouse, an American,
invented the air brake. In April 1869, heinvited the public to a trial run of a Pennsylvania Railroad train fitted with his air
brake system. The train had to make anemergency stop to avoid hitting a horsecarriage that had stopped on a levelcrossing. This famous incident ensured
that all major railways in the USA would
adopt Westinghouse’s new air brakesystem. In 1878, Westinghouse participated in a famous experiment conducted
by Galton in England. During this experiment, a train travelling at 96 km/h cameto a complete stop in the amazingly
short distance of just 183 m, a record thatstill stands today. The triple valve thatWestinghouse developed in 1879 for his
air brake system was of such a high design
standard that it remained in use with only
slight modifications until very recently.

In an air-brake system, compressed airforces a piston-driven brake shoe against
the wheel. The brake shoes can be madefrom a number of different substances,including cast iron and synthetic materials.
In some modern systems, the braking force
is not applied directly to the wheel. For
example, in a disc brake system, the force
is applied by clamping brake calipers toboth sides of axle-mounted or wheelmounted discs, thereby stopping thewheel.

Braking Systems of Japanese
Railways
A steam locomotive with a steam brakepulled the train on Japan’s first railway
from Shimbashi (Tokyo) to Yokohama
opened in 1872. Only the locomotive,
which generated the steam, had a steam
brake (Fig. 1), so the last car had a handbraking device. A vacuum brake poweredby a steam ejector was later developed,
making it possible to apply braking force

Figure 2 K Triple Valve Air Brake Device in Japan

Main piston

Steam pipe
(Brake cylinder)

SpringSlide valve

Emergency
pistonEmergency
valve

Lever

52

Brake shoe

Lever

Brake shoe

Japan Railway & Transport Review 20 • June 1999

Check
valve

Copyright © 1999 EJRCF. All rights reserved.

to each car using the difference between
atmospheric pressure and the vacuum.
Train travel became safer after this system
was introduced on passenger cars in about
1895.
When Japan’s railways were nationalized
in 1906, the total track length was 7153
km. In 1918, the Ministry of Railways
stipulated that air brakes were to beinstalled on all rolling stock, because they
were easier to maintain than vacuum
brakes. To meet this regulation, rollingstock braking systems were modified overa period of about 10 years, starting in
1920. By 1931, all Japanese trains had
air brakes based on the K triple valve(Fig. 2), which was itself based on
Westinghouse’s triple valve.
Today, most of Japan’s passenger trains areelectric; of the approximately 2000 carriages
manufactured each year in Japan, 97% arefor electric trains. Air brakes with solenoid
valves were introduced in every car ofelectric rolling stock in 1955, providing amore efficient braking system.
Dynamic brakes, which generate
electricity, were introduced at the sametime. When the Tokaido Shinkansen
opened in 1964, it had a combination of
two systems: an air brake system and a
dynamic brake system. The more efficientelectric command air brake system wasintroduced around 1970, and is used inrecent shinkansen and narrow-gauge
EMU trains.

Figure 3 Automatic Air Brake System
First car
Brake valve

PressureMainAir
regulator air reservoir compressor
ExhaustBrake pipe
Control valve

Auxiliary
air reservoir

Brake cylinder

Figure 4 Straight Air Brake System
First car
Brake valve

PressureMainAir
regulator air reservoir compressor
ExhaustMain air reservoir pipe
Straight air pipe
Brake cylinder

Basic Principles of Air Brake
Systems
Figure 3 shows the arrangement of an
automatic air brake system. Air compressors
mounted every two to four cars supply
compressed air to the air brakes. The air,which is compressed to 700 to 900 kPa,
is piped under the car floors to main air
reservoirs. The air pressure is lowered to
490 kPa by a pressure regulator and the
air is fed via the brake valve, brake pipes,
and control valves to the auxiliary air

Copyright © 1999 EJRCF. All rights reserved.

reservoirs. When the compressed air inthe brake pipes and auxiliary air reservoirsof each car is at 490 kPa, the brakes are
not activated. However, the activatedbrake valve cuts the flow of air from thepressure regulator, so the air pressure in
the brake pipes falls. The fall in airpressure is detected by the control valves
on each car. The control valves thenregulate the flow of compressed air fromthe auxiliary air reservoirs to the brakecylinders. The brake cylinders activate
the basic braking mechanisms (explainedlater) to slow down and stop the car. The
control valves regulate the flow of air fromthe auxiliary air reservoirs to the brakecylinders at a pressure that is proportional
to the pressure drop in the brake pipes.
Figure 4 shows a straight air brake system.
Unlike the automatic air brake system

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Technology

Figure 5 Braking Mechanisms

Adhesion brakes

Mechanical brakes(essential for safe andreliable rolling stock braking)Tread brakes
Axle-mounted disc brakes
Wheel-mounted disc brakes

Electric brakes
Non-adhesion brakes

Dynamic brakes
Regenerative brakes

Air resistance braking
Rail brakes

described above, the straight air brakesystem does not have a control valve or
auxiliary air reservoir in each car.
Activation of the brake valve forcescompressed air through the straight air
pipe to the brake cylinders, activating thebasic braking mechanism.
However, since the straight air pipes do
not contain compressed air during normal
running conditions, the brakes would failif cars became uncoupled. To avoid thisproblem, the straight air brake system canbe used in conjunction with the automatic
air brake system. It can also be avoided
by running another pipe, called a main
air reservoir pipe, from the first to the lastcar. The air pressure in this pipe acts likethe compressed air in the brake pipes of
the automatic air brake system. If thecompressed air in this main air reservoir
pipe falls, or if it leaks from air pipes orfrom air hoses between cars, etc., thepressure drop is detected and the brakes
are applied automatically. For example,
in shinkansen, the brakes are applied
automatically if the air pressure in thepiping falls to 600 kPa.

Braking Mechanisms
Government regulations specify braking
distance and deceleration rates to ensure

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Japan Railway & Transport Review 20 • June 1999

safe operation of rolling stock. Japanese
regulations require that narrow-gauge
trains travelling at maximum speed must
be able to stop within 600 m. To ensure
this short braking distance, narrow-gauge
trains presently have a maximum speedof 130 km/h, but research is now being
conducted into development of more
efficient braking technologies that willachieve shorter braking distance, meaning
faster speeds for the same braking
distance. Shinkansen regulations specify
deceleration rates for each speed slot, so
here too new braking technologies must
be developed to permit deceleration at
rates greater than those currently specified.
If trains were not equipped with fail-safe
mechanisms to ensure quick stops, they
could not run at high speeds, and transit
systems could not operate trains at shortheadway. The 300 km/h speeds ofshinkansen and the two-minute headwayof Tokyo commuter trains are only possible
due to the precision and superior responseof their braking systems. It is worth
remembering that earlier brake failures
and improper use of braking systems
resulted in many trains overrunning the
bumpers at the end of track sections,causing serious damage.
The amount of energy produced bybraking is tremendous. This can beillustrated by one example. A 16-car

Series 500 shinkansen with all seats
occupied weighs about 509 tonnes. The
amount of energy that must be absorbed
when this train is stopped from its
maximum speed of 300 km/h is 1.77 x
109 joules. This is enough to raise thetemperature of 4200 liters of water fromfreezing point to boiling point and isequivalent to 1,000 to 2,000 times theamount of energy used by an automobile.
When a braking force is applied to stop
the cars, the force must be transmitted tosomething other than the cars, forexample, to the rails. The braking force
can be transmitted either through adhesion,
which makes use of friction at the point
where the wheels touch the rails, or
through ways that do not involve adhesion(Fig. 5). Most rolling stock in Japan
currently uses adhesion braking methods.
Non-adhesion methods do not use friction
at the point where the wheels touch therails and include mounting panels on cars
to increase air resistance, or the direct
application of pressure from the car to therail, using shoes. This latter techniqueinvolves a device called a rail brake.
Most rolling stock braking systems use
either electrical brakes, or mechanicalbrakes.

Electric Brake Systems
Another braking system used by electrictrains is electrical dynamic braking thatconverts the motor into a braking generator dissipating the kinetic energy as heat.
Regenerative braking uses the generated
electricity instead of dissipating it as heat,and is becoming more common due toits ability to save energy.
Figure 6a shows the principles of theelectrical traction, dynamic braking andregenerative braking systems. Although
the traction motor drives and accelerates
the train, during braking, it acts as anelectric generator instead,forming part ofa circuit that consists of a main resistor

Copyright © 1999 EJRCF. All rights reserved.

(rheostat), armatures and a field system.
Electricity flows through the circuit and isconsumed by the main resistor, whichconverts the kinetic energy of the train into
heat and thereby acts as a brake.
Regenerative braking uses the same typeof circuit, but the electricity generated bybraking is not consumed by the main
resistor. Instead, it is transmitted to theoverhead wire. The flow of this electricity
is controlled by a controller under the

pantograph that opens and closes withsplit-second timing.
Electrical brake systems are economical
because they do not use friction elements,
unlike mechanical brake systems. The
regenerative braking system is even more
economical because the electricity
regenerated from the train’s kinetic energy
is transmitted to the overhead wire, andbecomes available to power other rollingstock (Fig. 6b). The problem withelectrical brake systems is that theyoccasionally malfunction because they
have complex circuits. For this reason
they cannot be used as emergency brakes.
In an electrical braking system, thebraking force of the traction motor(generator) is transmitted to the wheels via
gears (Fig. 7). The generated electricity is
adjusted to control braking force.

Figure 6a Principles of Electrical Braking
Electrical traction

Dynamic braking

PantographRegenerative braking

Pantograph

Main resistor(rheostat)

Traction motor
M1

M2

M3

M4

M1

Pantograph

Power generator(Traction motor)
M2

M3

Power generator(Traction motor)
M4

M1(Current direction)

M2

M3

M4

(Current direction)(Current direction)

Figure 6b Recycling Regenerated Electric Power
Decelerating by regenerative braking

Power running
Current

STATION

Overhead wire
PantographController
Power generator(Traction motor)
Wheelset

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Japan Railway & Transport Review 20 • June 1999

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Technology

Figure 7 Transmission of Braking
Force from Traction
Motor to Wheels
Bogies
Flexible Small
coupling gear
Traction
motor

Wheel

Large gear

Mechanical Braking Systems
The basic braking devices used bymechanical braking systems are: wheeltread brakes (Fig. 8), axle-mounted discbrakes (Fig. 9), and wheel-mounted discbrakes (Fig. 10). All these mechanisms
use an object (a brake shoe or lining) thatapplies friction to the disc. The appliedpressure is adjusted to control the braking force. In the wheel-tread brake, thebrake shoe applies friction to the wheel
tread, creating a sliding effect. High-speed
trains cannot use this type of brake, since

Figure 8 Wheel-Tread Brake Systemdoing so would damage the wheel tread.
Instead, they use axle- or wheel-mounted
disc brakes. Axle-mounted disc brakes
are used on trailer bogies, because they
have sufficient space to accommodate
such a system. Wheel-mounted discbrakes are used on motor bogies that must
accommodate the traction motor and haveinsufficient space for an axle-mounted
brake. In both systems, compressed air
or oil is applied to a brake cylinder thatforces the brake lining against the disc.
Brake discs are dead weight that are useful
only during braking, so operators are keen
to install lighter discs. Carbon/carbon-

Figure 9 Axle-Mounted Disc Brake System
Hydraulic or air pressure

Air pressure

Brake cylinder

Brake lining

Wheel

Brake disc

Brake shoe

Axle

Figure 10 Wheel-Mounted Disc Brake System

Figure 11 Carbon/Carbon-Composite Multi-Disc System

Hydraulic or air pressure

Brake cylinder

Brake lining
Wheel

Traction motor
Brake disc

Axle

Disc brake unit
(RTRI)

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Japan Railway & Transport Review 20 • June 1999

Copyright © 1999 EJRCF. All rights reserved.

Figure 12 Digital Electric Command System

Figure 13 Examples of Air Command lines

First carBrake
controller

Brake notches
SB1
SB2
SB3
EB

Command lines

1

2

3

4

5

6

7

EB

SB1
SB2

BCU
(Brake control unit)

BCU

BCU

SB3
EB

BC
(Brake cylinder)

BC

composite multi-discs and aluminium
composite discs offer lighter weights andare viewed with considerable interest.
The carbon/carbon-composite multi-dischas alternate sections of carbon-fiber
rotors and stators. During braking, they
rub against each other to create a frictional
force that slows down the wheel or axle.
The disc is lighter than conventional
materials and has excellent heat-resistantproperties. (Fig. 11)
Aluminium-composite brake discs can bemade much lighter than today’s forgedsteel and cast-iron brake discs. In
addition, their structure is the same forboth axle- or wheel-mounted discs,
achieving a much lighter disc without
design changes.

SB: Service brake
EB: Emergency brake

BC

Figure 14 Brake Control Unit (BCU) System
Service brakes
Emergency
brakesBrake control unit
Brake demand
operating device
Braking force
calculation

Copyright © 1999 EJRCF. All rights reserved.

Pressure
sensorVariableload valve

Electro-pneumatic processing
Emergency
solenoid valve

Braking Command

From airspring

Ex

Electro-pneumaticconverter valve
Regenerative brake

Brakes must function on every car at thesame moment and at the exact required
force. The timing and the braking force
are controlled by an electrical command
system or an air command system.
Figures 12, 13 and 14 show a digitalelectric command system, an air pressurecommand line, and the systems in a brake
control unit (BCU) system, respectively.
The digital electric command system
controls braking force by applying
digital voltage through wires running thefull length of the train. The air command

electric command system is used inshinkansen and other new trains, andoffers lighter weight and better response
times, even in long trains. The BCU
system keeps the braking force at the
optimum level by adjusting it in accordancewith braking commands, electricalsystem, otherwise known as an analog
dispatcher system, controls the air pressurein pipes that also run the full length of the
train. The air command system is used in
freight wagons and some passenger cars,and can transmit braking commands inrolling stock with no power supply. The

Relay valve
Ex
Ex

Main air reservoir

Electric air
compressor

Supply air reservoir

Brake cylinder

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Figure 16 Wheel Slide
Protection Device

Figure 15 Shinkansen Deceleration Rates

Wheel slide protection device

Deceleration rate (km/h)/s

Adhesion base values = 13.6/(V+85)
Adhesion base values
Series E1 and E4
Series 700
Series 500

3.0

Wheel rotation
speed

Rollingstockrunning
speed

Brake cylinderpressure

1.0

50

100

150
200
250
Train speed km/h

300

Figure 17 Ceramic Particle Jetting System
Direction of train
Emergency braking signal,
slide signal, slip signal

Ceramic particles

CompressedairNozzleReservoir

Figure 18 Rail Brake SystemAirpressure

S

N

S

N

S

Eddy current
Direction of eddy current braking force
Direction of electromagnetic rail braking force

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Japan Railway & Transport Review 20 • June 1999

During rain and snow, wet rails make it
impossible to apply a strong braking force
at the front of a train. If such a force wereapplied, the result would be similar to theskidding of an automobile when it brakes
suddenly on an icy road. To prevent thissliding, adhesion base values determinedusing data from rolling stock and benchtests, provide norms that must not be
exceeded (Fig. 15). Incidentally, braking
force is not applied uniformly to all cars,
but to a greater extent to rear cars.
If brakes are applied too strongly in wet
conditions, the wheels stop turning but thetrain continues to slide forward, wearing
down the wheel and creating small flat
sections that become the source of noiseand vibration. To prevent this wear, awheel slide protection device that detects
wheel sliding and automatically reduces
the braking force has been developed(Fig. 16). It has been installed on
shinkansen from the first models and is
now used on conventional and special
express trains, and even on new commuter
trains.

Ceramic particle jetting system

Electromagnetic rail
braking force
N

Improving Brake Performance
Compensating for adhesion loss
and sliding

2.00braking force (regenerative braking),
number of passengers, and speed, etc.

Direction of train

The wheel tread and top surface of therail have minute surface unevenness that
promotes adhesion and facilitates transmission of the driving power from thewheels to the rails. However, if there is awater film at the point of contact between
the wheel tread and rail, the adhesion islost. Higher train speeds and lower temperatures increase the water film; atspeeds of 300 km/h, the film thickness isestimated to be approximately 1 µm.
To improve wheel-rail adhesion undersuch conditions, a ceramic particle jetting

Copyright © 1999 EJRCF. All rights reserved.

system uses compressed air to spray fineceramic particles (about 10-µm diameter)
between the wheel tread and rail. The
ceramic particles act as tiny wedges,
increasing adhesion. This system is usedon the Series 500 Nozomi shinkansen andon conventional rolling stock operating
on steep gradients (Fig. 17.)

Rail brakes
Current train braking systems depend
heavily on adhesion between the wheel
tread and the rail. But in the case of
shinkansen and other high-speed rollingstock, adhesion decreases as speeds
increase, making it necessary for the train
to reduce braking force to avoid wheel
sliding. The end result is longer braking
distances. To solve this problem, a rail
brake system that does not depend onadhesion was developed.
The rail brakes developed for the firstshinkansen were never put into use. It
would have produced a braking force byusing magnetic repulsion obtained fromeddy currents generated on the top surfaceof the rails. It was not installed becauseof the fear that the eddy currents would
heat small sections of the rail to such a
degree that the rail would bend sideways.
The problem has been solved bydevelopment of a rail brake that uses eddy
currents and frictional force. Figure 18
shows the structure of this system. The
rail brake on the bogie is connected toRail brake system(RTRI)

batteries that create alternating north andsouth poles forming magnetic fields
between the poles. The magnetic fields
generate eddy currents in the top surfaceof the rails, creating a force acting in an
opposite direction to the movement of the
train, in other words, a braking force. This
type of rail brake system shows considerable
potential as a non-adhesion braking
mechanism able to complement adhesion
braking.
■Kanji Wako
Mr Kanji Wako is Director in Charge of Research and Development at Railway Technical Research Institute (RTRI). He joined JNR in 1961 after graduating in engineering from Tohoku University.
He is the supervising editor for this series on Railway Technology Today.

Izumi Hasegawa

Seigo Uchida

Mr Hasegawa is Chief Engineer in the Brake Control Group of the

Mr Uchida is Senior Engineer of the Vehicle Technology Division ofRailway Technical Research Institute (RTRI) where he has worked

RTRI, which he joined after graduating in mechanical engineering

since 1972. He joined JNR in 1968 after graduating in mechanicalfrom the Railway Technical College.

engineering from Hosei University.

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