•SANJAY KUMAR

LECTURER/STC/GKP

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.

• 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.

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.

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

• Unnecessary air consumption avoiding characteristics : Achieved by designing delayed reaction levelling valve

Vertical Spring Action

Lateral Spring Action

Self Damping Characteristics

• 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.

Modifications for Air Spring Fitment

Schematic diagram of Air Suspension Equipments

Actual diagram of Air Suspension Equipments

Air spring

Leveling valveBolster

Working Principle• Rubber bellows containing pressurized air and emergency rubber spring provide various suspension characteristics including damping.• Air springs are height –controlled load levelling 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.

Working principle of Pneumatic Suspension

No flow of air

Working principle of Pneumatic Suspension

flow of air

flow of air

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 bar.• 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 an air spring burst on one side, this valve will ensure

no severe tilt or twist occurs during movement of the coach.• 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.

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.

•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

Any Question