Center Buffer Coupler for Coaching StockCenter Buffer Coupler for Coaching Stock

FUNCTIONS REQUIRED TO BE PERFORMED

Capable of gathering, engaging/coupling on horizontal curve as small as 175m and vertical curve of 1500m

Vertical Interlock to prevent vertical override of cars in case of derailment aligning wings prevent vertical

movement of mated couplers relative to each other

Coupling with adverse mismatch in car heightswheel wear, passenger loading, spring failure,service tolerances etc.

FUNCTIONS REQUIRED TO BE PERFORMED Damp unduly large dynamic deflections and associated forces

under normal and emergency train operation conditions.– Suitable energy absorption even at low normal condition

draw/buff forces - High energy absorption not required in draft mode even at very

high acceleration of 1.3 m/s2 Energy absorption capacity while shunting

– effort should be to absorb maximum energy possible on bumping of cars without compromising cushioning on lower impact loads

Draft/buff should absorb and dissipate impact energy keeping recoiling forces to minimum without exceeding the squeeze load strength of car body

In the event of excessive tensile forces, failure should be at coupler head junction

Uncoupling from track level by means of properly secured handle without need for staff to enter between cars.

FUNCTIONS REQUIRED TO BE PERFORMED

In some cases, pneumatic and electrical connections are automatically required through couplers.

FUNCTIONS REQUIRED TO BE PERFORMED

CRASHWORTHINESS

Coupler plays very very important role in crashworthiness of the coach at initial stages of impact

Coupler can provide vertical interlocking to avoid overriding

Energy absorption capability of the coupler gear to avoid damage of the coupler or car body up to a specified collision speed of loaded/empty trains

– effort should be to absorb maximum energy possible on bumping of cars without compromising cushioning on lower impact loads

– if need of high energy absorption becomes essential, then switch over to hydraulic gear so that lower impact loads are taken care of

FUNCTIONS REQUIRED TO BE PERFORMED

CRASHWORTHINESS Energy absorption by couplers at colliding speed through

the complete complete train is important than individual cars

– Provision of hydraulic coupler on the locomotives and on extreme ends of a train-set of of great advantage

Coupler is desirable to be associated with shear protection device behind the coupler bearing bracket

– impact energy is absorbed by deformation of the sleeves – In case of shear off, coupler is guided through guide rails

into the under frame structure– engage the anti-climber

FUNCTIONS REQUIRED TO BE PERFORMED

CRASHWORTHINESS

After collapse of the coupler device, balance energy, if any, should be absorbed at car body end

– A suitable car body end structure and collision post for suitable distribution of load to car body can be designed by very careful Finite Element Analysis of the shell

( IDEAS best suited)

– LS-DYNA or PAM-CRASH is to know the deformation details at various collision speeds so as to validate the above design

Coupler Issues

Centering spring keeps pin pressed against shank and absorbs negligible energy on impact

10mm gap between shank and buffing bracket would hit each other on mal-compression of centering spring

Stiffer centering spring is suggested-Travel.

SAB-WABCO

Centering spring

Coupler Issues

Higher pre-compression in draw gear - no cushion of impact load upto 8t Draft gear is designed to leave the back support on compression and hit

back on to it with pre-compressed load as soon as draft force is removed–causing reversal of load with metallic hitting

Intensity of hitting is low with lower pre-compress load but frequency would increase

Soft cushioning of draft impacts is desired during normal and emergency train operation without aiming to reach high energy absorption capability of the order of 40 KJ which is not required even with acceleration of 1.2m/sec2 with CBC

Jerks appear to be more frequent after continuous operation for longer period

ASF Coupler • Separate springs for

cushioning buff and draft impacts

• Close tolerances between bearing surface has to be

maintained

Uncoupling Handle - ASF

Chances of getting unscrewed and dropping out ASF - Handle not secured in grooveScrew on top instead of horizontal is suggested

along with its positioning in groove

Locking Screw

Uncoupling Handle - SAB-WABCO

Locking screw found to be loose - can drop out as it is in bottom quadrant

Suggested to be kept vertically upward

A Typical Draft/Buff gear patented by Scharfenberg

Cushions the draft and compression loads produced under train operation by shear stress of the rubber.

Absorbs energy generated during coupling/shunting process. Sudden travel stop only at high abnormal impact speeds -

not under train operation conditions