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
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