Dr Yan Sun - CQUniversity - Module 3: Suspension designs to optimize curving and hunting

Suspension designs to optimise

curving and hunting

Dr. Yan Quan Sun, Centre for Railway Engineering, CQUniversity

Tuesday 20 May 2014

Brisbane

CENTRE FOR RAILWAY ENGINEERING

Module 3 - Information about rail vehicle suspension design issues

Outline

Rail Vehicles – Passenger Cars & Wagons

Bogies & Suspensions

Principles for Selecting Suspension Parameters

Approaches for Preliminary Selection of Suspension

Parameters

Simulation Modelling for Optimum Selection of Suspension

Parameters

Closing Remarks


Rail Vehicles – Passenger Cars & Wagons Rail vehicles are used to transport human beings and various

types of cargo;

Rail vehicles referring to a vehicle car body with a pair of bogies

are presented and discussed;

Rail vehicle consists of a number of components which, depending

on the design and use, can include:• Car body;

• Vehicle frame (underframe);


• Couplings & draft gear;

• Bogies – unpowered bogies and

powered bogies: Bolster or bolsterless;

Suspension components;

Sideframes or bogie frame;

Wheelsets;

Brakes.



• Two types of wagons - heavy haul & freight wagons.

Heavy haul wagon [1] Freight container wagon [1]



• Two kinds of passenger trains - older style long distance

trains hauled by locomotives at the front & metropolitan or

inter-city trains with powered bogies at the front and rear of

the trains.

Long haul passenger train [1] High sped passenger train [1]



• Bogies for wagons and passenger cars are typically as

shown below:

Three-piece bogie for freight wagons [1] Bogie for passenger cars [2]



The main functions are:

• Transmission and equalisation of the vertical load from the wheels

of the vehicle to the rails;

• Guidance of vehicle along the track;

• Control of the dynamic forces due to motion over track

irregularities, in curves, switches and after impacts between the

cars;

• Efficient damping of excited oscillations;

• Application of traction and braking forces.

Bogies & SuspensionsCENTRE FOR RAILWAY ENGINEERING

For passenger bogies:

• Wheelsets are generally mounted in a rigid H-

shaped frame;

• Primary suspensions (PS) – elastic elements

connect axlebox to bogie frame (coil springs &

dampers), transmit forces from wheelsets to bogie

frame;

• Secondary suspensions (SS) – elastic elements between bogie frame and vehicle body

(air springs), transmit forces from bogie frame to car body;

• The principal functions of PS are guidance of wheelsets on straight track and in

curves, and isolation of the bogie frame from dynamic loads produced by track

irregularities;

• The SS provides the reduction of dynamic accelerations acting on the car body which

determines passenger comfort.



Modern passenger bogie designs:

• A smaller number of parts in the secondary suspension and thus reduced

maintenance costs – flexi coil springs, air springs;

• Bolsterless – car body directly mounts on secondary suspensions;

• Equipped with separate secondary dampers to damp oscillations in

vertical and lateral directions;

• Yaw dampers are often fitted longitudinally between the body and bogie to

damp hunting motion on straight track.



For wagon bogies:

• The frame of a three-piece bogie consists of bolster

and two sideframes, elastically connected by a coil

spring and friction wedge-type secondary

suspension (SS), which can resist asymmetrical

loads and holds the bogie frame square in-plane;

• Such SS allows independent pitch of sideframes

when negotiating a large vertical irregularity on one

rail, allowing bogie to safely negotiate relatively

poor track;

• SS consists of a set of nested coil springs and the

wedge arrangement, providing friction damping in

the vertical and lateral directions.

Secondary suspension [1]



• There are two types of friction dampers - constant friction

and variable friction dampers:

Three-piece bogie friction wedge type dampers [1]



• Clearances between adapter (or the axlebox) and

sideframe in longitudinal and lateral directions, allow

the wheelsets to move in curves and pass large

horizontal irregularities;

• Due to the absence of PS, such bogies have a large

unsprung mass which causes increased track forces;

• In curves, three-piece bogies demonstrate the

“lozenging” or “warping” effect, when the two

sideframes adopt a parallelogram position (in plan

view);

• In this instance, the wheelsets cannot adopt a radial

position in the curve, and generate large angles of

attack, leading to constant flange contact and causing

high levels of wear.

Clearances [2]



Understanding of Suspension Parameter Effect on Hunting &

Curving• Massive investigations on this area began in the 1950s;

• Early study showed that both lateral and yaw PS stiffnesses are increased, there being an optimum at which

stability is a maximum;

• With a careful choice of lateral suspension damping and lateral & longitudinal stiffnesses, it was possible to

eliminate the low-speed body instability (a strongly contributory factor in wagon derailments) so that the

vehicle operating speed was only limited by the wheelset instability;

• The use of yaw relaxation dampers could provide sufficient flexibility at low frequencies in curves and

sufficient elastic restraint at high frequencies to prevent wheelset instability;

• The design of a two-axle vehicle with a purely elastic suspension requires a compromise between stability

and curving;

• When linear theories of the curving of railway vehicles became available it became possible for the first time

to consider the best compromise between the requirements of stability and curving on a numerate basis;

• Generally, to achieve high speeds the longitudinal stiffness of PS should be high, whereas the lateral

stiffness may be lower to reduce dynamic force when negotiating lateral track irregularities.



Principles for Selection

• The parameters of a rail vehicle may be considered optimal if its

dynamic characteristics meet three groups of requirements:

There is sufficient reserve of critical speed with respect to design speed;

Ride quality, track forces, and safety factors satisfy the standards on straight

track and in curves for the full range of operational speeds;

Wear rate of friction elements and wheel profiles is within acceptable limits.(the requirements are specified in many standards. (e.g., RISSB, Australia))

• How to achieve the optimal design of suspensions:

At the preliminary stage the suspension parameters can be estimated using

simple engineering approaches;

To make sure that the parameters are optimised, further refinement is usually

done using computer simulations.

Approaches for Preliminary Selection of

Suspension Parameters





Selecting Lateral and Longitudinal Primary Suspension

Stiffness• Theoretical investigations and experiments show that wheelset stability increases with increasing stiffness of

the connection to the bogie frame;

• However, the character of this dependence is highly nonlinear and the relationship between suspension

stiffness and the mass and conicity of the wheels influences the critical speed;

• Increasing the longitudinal stiffness of the primary suspension impairs the guidance properties of the

wheelset in curves, whilst increasing the lateral stiffness reduces the ability of the wheelset to safely

negotiate large lateral irregularities.




Selecting Shear & Bending Stiffness• A fundamental conflict therefore exists between the requirements for

high speed stability on straight track and good curving with safe

negotiation of track irregularities;

• For a preliminary choice of bogie lateral and longitudinal stiffness, a

simplified approach providing the relationship between stiffness and

ride quality in analytical or graphical form would be useful;

• Two generalised parameters can be introduced to represent the

primary suspension:

1. A stiffness corresponding to relative lateral displacement

between the centres of wheelsets referred to as the shear

stiffness (Ks);

2. A stiffness corresponding to the relative yaw angle between the

wheelsets referred to as the bending stiffness (Kb).Shear & bending stiffness [2]

where 2a = wheelset centres, and

2b = wheelset journal centres.




Selecting Shear &

Bending Stiffness• Shear stiffness Ks has a greater influence

on critical speed of vehicle, whilst

bending stiffness Kb mainly determines

wheelsets’ angles of attack in curves;

• Solution of the stability problem shows

that the critical speed of a conventional

railway vehicle is a function of its shear

and bending stiffness;

• The quality of curving can be estimated

using relationship of wear number (the

sum of creep force power for all wheels of

vehicle) to shear and bending stiffness.

Ref. [2]




Selecting Suspension Damping• Damping is typically provided within the suspension by either friction or hydraulic devices;

• The selection of the optimum damping levels is more complicated than the choice of suspension stiffness;

• High levels of damping decrease the amplitudes of vibrations in resonances but significantly increase the

accelerations acting on vehicle body for higher frequency inputs such as short wavelength track irregularities;

• Considering the simplified case of linear dependence between the damper force and the velocity, the damping

coefficient is defined as the ratio of the real part of the eigenvalue to the corresponding natural frequency:

where [B], [M] are the damping and inertia matrices of the vehicle multi-body model, respectively,{vi} is the column-vector of ith

eigenmode and ωi is the natural frequency of ith eigenmode;

• Effective damping of vibrations of railway vehicles is typically obtained with damping coefficients which lie in

the following ranges: 0.2 – 0.3 for vertical oscillations; 0.3 – 0.4 for horizontal oscillations, and 0.1 – 0.2 for

vehicle body roll.




Selecting Suspension Damping

• In freight bogies, friction dampers are commonly used. When making the

preliminary choice of parameters, the friction force in the damper is estimated on

the basis that the amplitude should not increase in the resonance case;

• A relative friction coefficient is defined to be equal to the ratio of friction force to the

static vertical load. For freight cars the recommended value of relative friction

coefficient is typically in the range 0.05 – 0.15.

Simulation Modelling for Optimum Selection of



VAMPIRE

• A VAMPIRE wagon modelling contains 11 masses (one wagon car body, two

bolsters, four sideframes, and four wheelsets). The connections among these 11

masses have been modelled using 17 stiffness elements, 74 bumpstop elements, 13

viscous damper elements, 116 friction elements, and four shear spring elements,

which fully consider the nonlinear characteristics of the connections.

• There are some commercial software packages available for

comprehensive rail vehicle modelling to conduct suspension designs for

optimum curving and hunting, such as VAMPIRE, Gensys, NUCARS,

Simpack, Adams/Rail, etc.

• VAMPIRE and Gensys are available at CRE, CQU.




VAMPIRE• The natural frequencies of the wagon with loaded and empty condition are determined using VAMPIRE model.

Loaded Car Body Bounce Mode (1.998 Hz) Loaded Car Body Pitch Mode (3.04 Hz)

Empty Car Body Bounce Mode (5.373 Hz) Empty Car Body Pitch Mode (8.161 Hz)

Vampire wagon model [3]




Gensys

Whole Wagon Bogie

Bogie (Side View) Bogie (Front View)

Gensys wagon model [4]




Gensys• The wagon model includes 11 masses – one wagon car body, 2 bolsters, 4

sideframes and 4 wheelsets, which are modelled as rigid bodies;

• The connections include centre bowl and side bearers between wagon car body and

bolster, secondary suspensions between bolster and sideframes and primary

suspensions between sideframe and wheelsets;

• Each friction wedge is modelled as a massless block and the exact triangular shape

is considered;

• In the wheel-rail modelling, the Hertzian contact stiffness normal to the wheel-rail

contact surface is defined. Three different contact surfaces can be in contact

simultaneously. The calculations of creep forces are made in a lookup table

calculated by Fastsim.




Gensys• Hunting speed & curving analysis;

• The determination of critical hunting speed is through simulation using a

decreasing vehicle speed (e.g. from 200 or 300 km/h to 50 km/h) with an initial

lateral disturbance;

• The wheel-rail normal force and the L/V ratios during curving (radius = 300m with

lateral geometry irregularities).




Gensys

Determination of hunting speed [4]Simulation results during curving


Closing Remarks

• Only rail vehicles with a pair of bogies are covered, and the types and

use of passenger vehicle and freight wagon are discussed;

• The functions of their bogies & suspensions are described;

• The design of suspension significantly affects rail vehicle stability and

curving, requiring a compromise between them;

• In order to achieve the optimal design of suspensions, the initial

suspension parameters can be estimated using simple engineering

approaches, and then the optimum selection is usually done by

sensitivity analysis using computer simulation;

• Finally, rail vehicle modelling using VAMPIRE and Gensys simulation

programs are introduced and some simulation results are shown.


References

1. M. Spiryagin, C. Cole, Y.Q. Sun, M. McClanachan, V. Spiryagin and T.

McSweeney, Design and Simulation of Rail Vehicles, Ground Vehicle

Engineering Series, CRC Press, 2014. ISBN 978-146-657-566-0.

2. Simon Iwnicki, Handbook of Railway Vehicle Dynamics, CRC Press, Taylor &

Francis Group, 2006, ISBN 978-0-8493-3321-7 (Hardcover)

3. Y.Q. Sun, C. Cole and M. McClanachan, The calculation of wheel impact force

due to the interaction between vehicle and a turnout, Proc. IMechE, Part F,

Journal of Rail and Rapid Transit, Vol. 224, 2010, pp391-403.

4. Y.Q. Sun, M. Spiryagin, C. Cole and S. Simson, EFFECT OF WHEEL-RAIL

CONTACTS AND TRACK GAUGE VARIATION ON HUNTING BEHAVIOURS OF

AUSTRALIAN THREE-PIECE BOGIE WAGON. Proceedings of 23rd

International Symposium on Dynamics of Vehicle on Roads and Tracks, Aug.

19th ~ 23rd, 2013, Qingdao, China.


Thanks for Your Attention


Discussion Questions

• What are the main functions of bogie and suspension? What type of

bogie & suspension is used in your company?

• What are the principles for selection for the suspension parameters? Do

you know the requirements in RISSB standard?

• If you know the required natural bounce frequency is 2.5 Hz for loaded

vehicle and 4 Hz for the empty, how to determine the static deflections of

a suspension with linear characteristics?

• If the shear & bending stiffnesses are selected, how to deduce the lateral

and longitudinal stiffnesses of a primary suspension?

Dr Yan Sun - CQUniversity - Module 3: Suspension designs to optimize curving and hunting

Business

Transcript of Dr Yan Sun - CQUniversity - Module 3: Suspension designs to optimize curving and hunting