The present subject matter relates to Yaw dampers and specifically to improved Yaw damper system to prevent lateral skidding of wheels of a railway vehicle on curved and irregular tracks.
BACKGROUND
Wheel shelling is well known worldwide problem in which Rail wheels get damaged and useless without serving its full life. In India the problem is specifically with LHB trains. The LHB trains were introduced in India in 2000. LHB design coaches are lighter in weight, have higher carrying capacity, speed potential, and better safety features as compared to ICF coaches. According to reports, India has only 6,000-7,000 LHB coaches. Gradually shall replace the entre stock of ICF coaches in the time to come. Indian Railways is increasingly replacing old ICF-design rakes with new LHB design coaches. The Indian Railways stopped inducting the relatively unsafe ICF-type coaches, which consisted of less than 10% of its 60,000-strong fleet in 2017, by the middle of 2018.
However, the wheels of LHB trains serve only 25% (maximum 4 years) of life as compared to ICF trains where the wheels last for at least 16 years. This results in huge losses to the Indian railways and the Government funds. The loss is estimated to be about 180 crores (75% loss of 8 wheels X 6000 X each wheel costing Rs 50000) at present and shall multiply as the ICF coaches are being replaced by LHB coaches.
Wheel shelling and spalling are metallurgical phenomena due to rail wheel interaction, which happens in all railways systems. The small pieces of metal continuously brake out of the tread surface at several places in the peripheral area. This requires frequent tyre turning at small intervals. The possible reasons were attributed to- Higher braking force Low Rail-wheel adhesion Ineffective wheel slide protection device Low hardness of wheel Low yield strength of steel Railways have

been reporting the problem of wheel shelling since the LHB coaches were introduced in service. Research Design and Standards Organization (RDSO) had already taken the following measures in 2001 to overcome the problem of wheel shelling: Specification R-19/93 Part II for Forged steel wheel has been revised. Brake cylinder pressure has been reduced to 3.0 kg/cm2 from 3.8 kg/cm2 on Shatabdi and Rajdhani coaches. The steps taken by RDSO are in line with international literature. After these measures, there has been little improvement in kilometer earning per tyre turning and corresponding increase in wheel life. Further, especially casted alloy wheels of robust were also tested but could not prevent wheel shelling. A Japanese company SUMOTOMO (Japan) provided 16 set of wheels free of cost with the assurance that wheel shelling and track damage will not happen. But wheel shelling still continues on LHB coaches and wheels serve only 25% of its life as compared to ICF coaches.
Further, it is very much obvious that the damage to the wheels which occurs due to wheel-rail interaction is bound to cause damage to the rail tracks as well. No study has been carried out till date for rail wear & tear by the wheels of LHB coaches and the volume of losses it is causing.
Besides shelling, breakage of wheel disk during run is very dangerous. More than 20 cases on 4000 coaches are recorded till now. Wheel disk of LHB coaches are being imported from foreign countries which is also another issue for the Indian Economy.
OBJECTIVES OF THE PRESENT INVENTION
To provide improvements in Yaw dampers to prevent lateral skidding of wheels of a railway vehicle on curved and irregular tracks.
To provide a system for balancing the pressure in the opposite Yaw dampers, of same trolley.

BRIEF DESCRIPTION OF THE FIGURES
The detailed description is described with reference to the accompanying figures. The same numbers are used throughout the drawings to reference like features and components:
Fig. 1 illustrates the hunting movement in rail vehicles.
Fig. 2 illustrates the inefficiency of the vehicles mounted with yaw dampers in curve negotiation.
Fig. 3 illustrates the plan of the Yaw damper system, in accordance with first embodiment of the present subject matter in sectional view.
Fig. 4 illustrates the plan of the Yaw damper system, in accordance with first embodiment of the present subject matter during expansion (Fig 4a) and contraction (Fig 4b) stages.
Fig. 5 illustrates the plan of the Yaw damper system, in accordance with first embodiment of the present subject matter.
Fig 6 illustrates the plan of the Yaw damper system, in accordance with second embodiment of the present subject matter.
Fig 7 illustrates the plan of the Yaw damper system, in accordance with second embodiment of the present subject matter.
DETAILED DESCRIPTION
The trolley design of LFffi coaches is rigid due to its design, which does not allow sinusoidal movement (hunting movement) of trolley. We can say relation between wheels and rail does not behave healthily as desired which leads to lateral skidding of wheel during movement on curved and irregular rail tracks.

Hunting Movement-The hunting movement (Fig 1) is a consequence of the reversed conic shape of the rolling surfaces. For instance, if the axle is transversally displaced, the wheel rolling on a larger diameter will advance quicker than the other one, which always stays behind because the wheels are fixed in a rigid manner to the axle's body (Fig.l). The axle spins compared to the vertical axis and, eventually, will approach the track's middle axis. In this moment, the axle spinning angle will be at its highest value and both wheels will roll on even diameters. Next, the axle will continue its movement, leaving the center position to the opposite side from the initial lateral displacement, forcing the wheel to roll on smaller and smaller diameters and the other one on increasingly larger diameters. Both wheels will reach the same level at the precise moment when the axle center is situated at the maximum distance from the rail longitudinal axis. From now on, the movement will repeat itself in reverse. The axle center's trajectory is a sinuous curve.
The hunting movement helps movement of the train on the irregular and curved tracks but also causes excessive swaying of the bogies. At higher speed the hunting movement may lead to accidents and therefore maximum allowable speed for such trains is 120 kms.
Four Yah Damper are provided two on each side of the trolley in new type vehicles such as LHB trains. These are disposed between Trolley and Coach body which almost make integral part in between and create hindrance to negotiate irregularities and curve of the track in the new LHB coaches (Fig 2). This leads to wheels being skid forcibly (lateral displacement) by the coach. The use of such Yaw dampers has resulted in rigidity in coach wheel interaction leading to skidding at curves and wheel shelling as well as damage to tracks. Thus it is important to balance the stiffness of these dampers to allow flexibility during movement on curved and irregular tracks while retaining effective longitudinal damping during braking and acceleration.
Novel damper has been designed which do not create hindrance of sinusoidal movement of wheels during movement on curved and irregular tracks. It is

5 understood that during movement on curved track the pressure in chamber (103) of
the damper of the outer damper becomes low and in the in chamber (103’) of inward damper it becomes high thus preventing the flexibility in movement of the wheels (the outer wheel should move to larger diameter). The invention provides a system to control the pressure difference between the pair of dampers of opposite side of the
10 trolley by coupling the two. This design will allow angular motion to the trolley or
sinusoidal movement for axle that’s why wheel will not skid laterally so that wheel life & rail life will increase tremendously.
In an embodiment of the invention connections are provided between the chambers of two (for each trolley) opposite yaw dampers (100 &100’) for allowing flow of fluid
15 from chamber of high pressure to Chamber of low pressure. The Chamber (103)
towards the distal end of the piston (102) of yaw damper of one side is connected with chamber (103’) on the opposite side with the help of regulator (105). Similarly, Chamber (101) at proximal end of yaw damper of one side is connected with corresponding chamber (101’) on the opposite side with the help of regulator (105’).
20 Regulator (105) works with difference of pressure and controls the flow of oil
between the chambers (103&103’) at distal end of the two opposite Yaw dampers to equalize the pressure between them.
In another embodiment of the invention the pressure difference between the two opposite dampers (100 &100’) is controlled through provision of valves (108 & 108’)
25 in the piston of the damper which can control the movement of fluid from Chamber
(109) at distal end to Chamber (106) at proximal end. The valves (108 & 108’) are operated and controlled by a microprocessor (111), based on analysis of pressure inputs from pressure transducers (110&110’) provided in the pairs of opposite Yaw dampers. In an example the pressure transducer (110) may be provided in either of
30 chamber A or chamber B of opposite pair of Yaw dampers. In an embodiment of the
invention the valves (108) are solenoid valves.
5

The novel damper system will dampen the longitudinal forces during acceleration of engine and during braking but will not create hindrance to lateral forces and prevent skidding of wheels. This will effectively reduce wheel shelling and ensure a longer wheel life.
In another embodiment of the invention a rail trolley system has been designed wherein the yaw dampers are connected between crosstube of the trolley and bogie bolster to take a central position for preventing lateral skidding.

claim:

A novel assembly for preventing shelling in wheels and rail track in rail vehicles, comprising of: i. a pair of Yaw dampers (100 &100') disposed laterally between the
between bogie frame and car body, corresponding to each wheel set of the
bogie;
a. wherein the chambers at the first end (101 &101') of each of the
pair of Yaw dampers are adapted by a means (104) to allow flow
of the fluid from high pressure to low pressure; and the chambers
at the second end (103&103') of each of the pair of Yaw dampers
are adapted by a means (104') to allow flow of the fluid from high
to low pressure; and a regulator(105) for controlling the flow of
fluid based on pressure difference from chamber (101) and (101'),
to allow the pressure to be equal in both chambers (101&101');
and chambers at the second end of the yaw dampers (103 & 103');
b. alternatively a valve (108) each is disposed in each Yaw damper
of the pair between chamber at first end of the yaw damper (106)
of the pair and chamber at second end of yaw damper (109) of the
pair of yaw dampers; wherein the valve (108) controls the flow of
the fluid between Chamber (106) at first end of the yaw damper
and chamber (109) at second end of the yaw damper; wherein the
valves (108&108') are operated by a microprocessor^ 11); and
wherein the microprocessor operates the two valves (111&1H')
based on inputs from a pressure transducers (110&110') disposed
in the chambers (109 & 109') at the second end of each Yaw

damper of the pair of yaw dampers to control the difference in pressure;
ii. alternatively a trolley system wherein the yaw dampers are connected between crosstube of the trolley and bogie bolster to take a central position for preventing lateral skidding.
An novel damper system as claimed in claim 1, wherein the valves (108&108') are preferably solenoid valves.
An novel damper system as claimed in claim 1, wherein the valve (108) is disposed within the piston (109).