T Technology echnolo Railway Technology Today 7 (Edited by Kanji Wako) Braking Systems Izumi Hasegawa and Seigo Uchida braking equipment, generally using either In an air-brake system, compressed air Early Brakes vacuum brakes or air brakes. Of these forces a piston-driven brake shoe against two systems, only air brakes still remain the wheel. The brake shoes can be made All rolling stock has some form of brak- in use. from a number of different substances, ing device, so that it can decelerate and George Westinghouse, an American, including cast iron and synthetic materials. stop when necessary. The first cars with invented the air brake. In April 1869, he In some modern systems, the braking force a braking system were apparently small invited the public to a trial run of a Penn- is not applied directly to the wheel. For trucks running on rails in mines. The sylvania Railroad train fitted with his air example, in a disc brake system, the force miners used a lever to push a wood block brake system. The train had to make an is applied by clamping brake calipers to against a wheel. However, such manual emergency stop to avoid hitting a horse both sides of axle-mounted or wheel- devices became insufficient as the mass carriage that had stopped on a level mounted discs, thereby stopping the and speed of rolling stock increased, so crossing. This famous incident ensured wheel. braking systems using motive power were that all major railways in the USA would introduced. adopt Westinghouse’s new air brake Braking Systems of Japanese By the 1860s, express trains were achiev- system. In 1878, Westinghouse partici- Railways ing speeds of about 80 km/h in England. pated in a famous experiment conducted But at that time, brakes were not used on by Galton in England. During this experi- A steam locomotive with a steam brake all cars in a train. The engine driver and ment, a train travelling at 96 km/h came pulled the train on Japan’s first railway a brakeman in the last passenger car to a complete stop in the amazingly from Shimbashi (Tokyo) to Yokohama gy would each apply a hand brake, with the short distance of just 183 m, a record that opened in 1872. Only the locomotive, driver using the whistle to signal to the still stands today. The triple valve that which generated the steam, had a steam brakeman when it was time to brake. This Westinghouse developed in 1879 for his brake (Fig. 1), so the last car had a hand- rudimentary system caused many accidents air brake system was of such a high design braking device. A vacuum brake powered that might have been avoided. Realizing standard that it remained in use with only by a steam ejector was later developed, this, railway companies began installing slight modifications until very recently. making it possible to apply braking force Figure 1 Early Braking System Figure 2 K Triple Valve Air Brake Device in Japan Main piston Spring Steam pipe (Brake cylinder) Slide valve Emergency piston Emergency valve Lever Brake shoe Lever Brake shoe Check valve 52 Japan Railway & Transport Review 20 • June 1999 Copyright © 1999 EJRCF. All rights reserved. to each car using the difference between atmospheric pressure and the vacuum. Figure 3 Automatic Air Brake System Train travel became safer after this system was introduced on passenger cars in about First car 1895. When Japan’s railways were nationalized Brake valve in 1906, the total track length was 7153 km. In 1918, the Ministry of Railways stipulated that air brakes were to be Pressure Main Air regulator air reservoir compressor installed on all rolling stock, because they were easier to maintain than vacuum Exhaust brakes. To meet this regulation, rolling Brake pipe stock braking systems were modified over Control valve a period of about 10 years, starting in 1920. By 1931, all Japanese trains had Auxiliary Brake cylinder air brakes based on the K triple valve air reservoir (Fig. 2), which was itself based on Westinghouse’s triple valve. Today, most of Japan’s passenger trains are electric; of the approximately 2000 carriages manufactured each year in Japan, 97% are Figure 4 Straight Air Brake System for electric trains. Air brakes with solenoid valves were introduced in every car of electric rolling stock in 1955, providing a First car more efficient braking system. Brake valve Dynamic brakes, which generate electricity, were introduced at the same time. When the Tokaido Shinkansen Pressure Main Air opened in 1964, it had a combination of regulator air reservoir compressor two systems: an air brake system and a Exhaust dynamic brake system. The more efficient electric command air brake system was Main air reservoir pipe introduced around 1970, and is used in recent shinkansen and narrow-gauge Straight air pipe EMU trains. Brake cylinder Basic Principles of Air Brake Systems Figure 3 shows the arrangement of an reservoirs. When the compressed air in the auxiliary air reservoirs to the brake automatic air brake system. Air compressors the brake pipes and auxiliary air reservoirs cylinders. The brake cylinders activate mounted every two to four cars supply of each car is at 490 kPa, the brakes are the basic braking mechanisms (explained compressed air to the air brakes. The air, not activated. However, the activated later) to slow down and stop the car. The which is compressed to 700 to 900 kPa, brake valve cuts the flow of air from the control valves regulate the flow of air from is piped under the car floors to main air pressure regulator, so the air pressure in the auxiliary air reservoirs to the brake reservoirs. The air pressure is lowered to the brake pipes falls. The fall in air cylinders at a pressure that is proportional 490 kPa by a pressure regulator and the pressure is detected by the control valves to the pressure drop in the brake pipes. air is fed via the brake valve, brake pipes, on each car. The control valves then Figure 4 shows a straight air brake system. and control valves to the auxiliary air regulate the flow of compressed air from Unlike the automatic air brake system Copyright © 1999 EJRCF. All rights reserved. Japan Railway & Transport Review 20 • June 1999 53 Technology Series 500 shinkansen with all seats Figure 5 Braking Mechanisms occupied weighs about 509 tonnes. The amount of energy that must be absorbed when this train is stopped from its Adhesion brakes Mechanical brakes Tread brakes maximum speed of 300 km/h is 1.77 x (essential for safe and reliable rolling stock braking) Axle-mounted disc brakes 109 joules. This is enough to raise the temperature of 4200 liters of water from Wheel-mounted disc brakes freezing point to boiling point and is Electric brakes Dynamic brakes equivalent to 1,000 to 2,000 times the Regenerative brakes amount of energy used by an automobile. Non-adhesion brakes Air resistance braking When a braking force is applied to stop Rail brakes the cars, the force must be transmitted to something other than the cars, for example, to the rails. The braking force can be transmitted either through adhesion, which makes use of friction at the point described above, the straight air brake safe operation of rolling stock. Japanese where the wheels touch the rails, or system does not have a control valve or regulations require that narrow-gauge through ways that do not involve adhesion auxiliary air reservoir in each car. trains travelling at maximum speed must (Fig. 5). Most rolling stock in Japan Activation of the brake valve forces be able to stop within 600 m. To ensure currently uses adhesion braking methods. compressed air through the straight air this short braking distance, narrow-gauge Non-adhesion methods do not use friction pipe to the brake cylinders, activating the trains presently have a maximum speed at the point where the wheels touch the basic braking mechanism. of 130 km/h, but research is now being rails and include mounting panels on cars However, since the straight air pipes do conducted into development of more to increase air resistance, or the direct not contain compressed air during normal efficient braking technologies that will application of pressure from the car to the running conditions, the brakes would fail achieve shorter braking distance, meaning rail, using shoes. This latter technique if cars became uncoupled. To avoid this faster speeds for the same braking involves a device called a rail brake. problem, the straight air brake system can distance. Shinkansen regulations specify Most rolling stock braking systems use be used in conjunction with the automatic deceleration rates for each speed slot, so either electrical brakes, or mechanical air brake system. It can also be avoided here too new braking technologies must brakes. by running another pipe, called a main be developed to permit deceleration at air reservoir pipe, from the first to the last rates greater than those currently specified. car. The air pressure in this pipe acts like If trains were not equipped with fail-safe Electric Brake Systems the compressed air in the brake pipes of mechanisms to ensure quick stops, they the automatic air brake system. If the could not run at high speeds, and transit Another braking system used by electric compressed air in this main air reservoir systems could not operate trains at short trains is electrical dynamic braking that pipe falls, or if it leaks from air pipes or headway. The 300 km/h speeds of converts the motor into a braking genera- from air hoses between cars, etc., the shinkansen and the two-minute headway tor dissipating the kinetic energy as heat.