Air suspension technology• 1956: First German Rail Bus fitted with Air Springs.• Presently, most of the high speed trains including French TGV running with max. speed of 515 Kmph has air springs.• With varying vehicle loading, there is a need to maintain “Ride Height” to have parity with the way side “Platforms” and “Coupling Height” for train formation

Need for adoption of Air suspension• Abnormal increase in pay load condition in suburban Rlys e.g. Trailer coach of EMU 18 T to 34 T(SDCL)

• Super Dense Crush Load reduces the bogie clearances to Nil resulting in severe hitting.• Failure of components due to hitting.• Poor riding behavior of coach • Since 1997, Pneumatic suspension used in DC-EMU, AC-EMU, HP-DMU• All future EMUs & DMUs

Comparison with existing coil suspension:• Unlike steel springs, air springs retain their height under changing loads. The low natural frequency of air spring suspension remains virtually constant.• In case of coil spring, deflection is proportionate to the load, therefore, under high payload situation, space constraint becomes critical, leading to the use of stiffer springs resulting in unsatisfactory ride behavior and reduced speed potential.• Air springs through their control mechanism, offer a load proportionate stiffness, constant floor height and prospects of better ride behavior with higher speed potential.

Achieving of its characteristics:• Soft flexible characteristics under vertical direction : Achieved by compression of the air• Excellent lateral spring characteristics : Achieved by variation in effective area in lateral direction Good self damping : Achieved by placing an optimized orifice between air spring and additional reservoir• To avoid unnecessary air consumption due to all modes of vehicle oscillation or change in air pressure : Achieved by designing delayed reaction levelling valve

Vertical Spring ActionSelf Damping Characteristics

Modifications for Air Spring Fitment• Installed at Secondary Stage.• In place of standard bolster suspension arrangement, a FIXED lower spring beam is used to accommodate air spring on bolster• Primary springs are made stiffer.• Additional air reservoir (20 litres) provided on bogie bolster.• Leveling Valve, Installation lever etc fitted as per schematic diagram.

Working Principle

• Rubber bellows containing presurised air and emergency rubber spring provide various suspension characteristics including damping.• Air springs are height –controlled load leveling suspension devices.• With changing loads, air spring reacts initially by changing the distance between air-spring support & vehicle body.• The height monitoring valve (levelling valve) in turn actuates , either getting the compressed air pressure to the air spring or releasing air pressure to atmosphere.• The process continues until the original height is restored.

Delayed reaction of Control valve (To avoid excessive air consumption )

Duplex Check valves• Fitted between two air springs of the same bogie• Pressure differential on DC valve is set at 1.5• Basically comprises of two check valves side by side, arranged so that air can flow in either direction when the air pressure differential exceeds the pre-set value.• Whenever a burst air spring occurs on one side, this valve will ensure that no severe tilt or twist occurs during movement of the coach

Duplex Check valves• Air springs can have differential pressures upto the preset value ( both check valves remain closed)• When the differential air pressure exceeds the preset value, the air at higher pressure overcomes the spring pressure and flows to the lower pressure via the check valve. The flow continues till the differential reaches the preset value.• In case of burst, the air leaks to atmosphere. Due to high pressure differential, air starts leaking from the intact air spring to the burst air spring via DC valve. Thus complete coach end will gradually come and rest on the emergency rubber springs.

Air Springs for Mainline ICF stock• 8th CMG approved fitment of Air Springs on mainline AC coaches

Advantages of Air suspension:• Capable to sustain Super Dense Crush Load of suburban traffic.• Constant floor height of coach.• Excellent ride comfort.• Safe running.• Virtually Constant natural frequency from tare to full loads.• Low design height.• Integral input signal for load dependent braking and acceleration.• Isolation of structure borne noise.• Improved reliability, reduced maintenance.• Great durability.• Possibility of voluntarily choosing air spring characteristics.

General Technical Data• Supplied by “Contitech” and “Firestone”• Static Vertical Load on Air Spring: Tare: 51 KN, Full load: 142 KN• Vertical Stiffness: Tare: 550 N/mm, Full load: 975 N/mm• Horizontal stiffness: Tare: 325 N/mm, Full load: 430 N/mm• Emergency Spring vertical stiffness: Tare: 4000 N/mm, Full load: 6000 N/mm• Air spring volume: 26 litres• Design height of air spring: 255 mm

Projects to improve riding quality Development of Air springs for EMUs Development of new suspension of Coaching Container Flat. Development of better suspension of existing ICF coaches.

Development of Air springs for EMUs

AC-DC, AC and DC EMUs retrofitted with state-of-the-art Air springs.

Ride comfort has improved substantially. Problems of peak loads variations i.e. normal load to SDCL

have been solved without compromising on riding comfort.

Development of New suspension for Coaching Container Flat.

CCF design needed suspension that would have acceptable ride indices and simultaneously cater to wide variation in payload (39.75t) at high running speeds. Such a variation was impossible to handle using conventional springs. Use of Air springs has successfully solved the problem of achieving acceptable riding with high payload and at high speed.Coaching Container Flat designDevelopment of better suspension of existing upper class ICF coaches Various modifications have been done over past decades to achieve better riding and higher reliability of standard design of ICF coach. Further ride comfort increase cannot be achieved without making major changes in the bogie design. Retrofitment of Air springs can improve the ride behaviour of existing ICF coach with little investment and minimal design change.Air springs for FAC…• Air springs provide

Excellent bogie-body isolation. Excellent noise reduction. Superior ride index.

Air springs characteristics have to be customized to suit specific coach weight. Customization of air spring characteristics for existing FAC has been done – its manufacturing feasibility is under study with M/s ContiTech® GmbH Germany. Optimized Air spring for FAC show superior ride comfort vis-à-vis present suspension.

• Fitment of air springs for secondary suspension of mainline ICF coaches. Design of Air Spring has been finalized.

RDSO has recently advised ICF to manufacture one power car (WLRRM) and one Executive Chair Car (WCZ FAC) for

conducting oscillation trials.

• Provision of hydro springs in primary eliminating the dashpot arrangement.

Thank You

1. Development of Air Springs in DC EMUs.2. Development of Coaching Container Flat with Air springs.3. Development of AC & AC-DC EMU with Air Springs.4. High Capacity BG DMU with Air springs.5. Development of variants of LHB coaches with Air springs.6. Retro fitment of air springs on standard ICF coaches.