ERTMS / ETCS Braking Curves - UIC
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ERTMS / ETCS Braking Curves - UIC

ERTMS/ETCSbraking curvesRobert DijkmanEEIG ERTMS Users Group15 - 17 December 2004 UIC ERTMS Conference Rome 1

Why are braking curves an issue?SRS 222:1. No feasible input defined to enable the driver toenter brake characteristics in trains with changingcomposition.2. Brake model (SRS chapter 3.13) defined only in aglobal way. Implementation is supplier dependent.3. Harmonised safety margin for the braking curves isnot defined.15 - 17 December 2004 UIC ERTMS Conference Rome 2

Who are the players?1. ERRI/UIC B126.15: brake experts.2. EEIG: ERTMS experts.3. Interested railways (SBB, OEBB, BV): specificoperational problems.4. UNISIG: ERTMS specifications.15 - 17 December 2004 UIC ERTMS Conference Rome 3

Finding the right balanceperformancesafetydriverergonomics15 - 17 December 2004 UIC ERTMS Conference Rome 4

Braking curve overviewVariable compositionETCS curves2Fixed composition- brake percentage- brake type: P/GDriver Data Entry- guaranteed deceleration- service deceleration- guaranteed brake delay timemeasured:- max deceleration- service deceleration- brake delay timeOnboard ETCSconversion model:-deceleration- brake delay time1Safety margin3Pre-programmedin onboard ETCS15 - 17 December 2004 UIC ERTMS Conference Rome 5

Conversion modelERRI model versus reality – example 1: passenger train2,5Deutsche Bahn AG - Passenger train with disc brakes (pneumatic brake accelerators off) in R2,0deceleration [m/s²]1,51,0Nominal speeds200 km/h180 km/h160 km/h140 km/h120 km/h100 km/h0,5Models for 135 %ERRI modelcalibrated model0,00 50 100 150 200 250velocity [km/h]15 - 17 December 2004 UIC ERTMS Conference Rome 6

Conversion model (2)ERRI model versus reality – example 2: freight train2,5Deutsche Bahn AG - Goods train with cast iron brake blocks (Minden 2004) in P2,0deceleration [m/s²]1,51,0Nominal speeds120 km/h0,5100 km/hModels for 101 %ERRI modelpossible model0,00 20 40 60 80 100 120 140velocity [km/h]15 - 17 December 2004 UIC ERTMS Conference Rome 7

Conversion model (3)Options for improvement:1. Delete the hidden safety margin. The output deceleration will beput at the average measured value instead of a conservativevalue. All neccessary safety margin will be concentrated in onepart of the whole braking curve model structure. The conversionmodel remains a “one size fits all” solution. The outputdeceleration is a single value independent from the train speed,because it is based on a single input: the brake percentage.2. Make the model brake type dependent. The output can be a moreaccurate representation of the deceleration of the specific braketype. This however requires the brake type to be an input to themodel. Is it realistic to expect the driver to input more detailedcharacteristics of the actual brake system of the whole train?15 - 17 December 2004 UIC ERTMS Conference Rome 8

ETCS brake modeldecelerationinterventionaudible warningpermitted speedindicationpre-indicationEOA15 - 17 December 2004 UIC ERTMS Conference Rome 9

Impact on approach of the EOAA flat braking curve will force the train toapproach the EOA with low speed,resulting in a long time to stop.steep curveshort stopping timegood performanceflat curvelong stopping timebad performanceEOAPlatform15 - 17 December 2004 UIC ERTMS Conference Rome 10

Impact on level 1 linesmodel notfully definedpermittedcurvedecelerationcurveWhere to putthe balise?DistantsignalEOAMainsignal15 - 17 December 2004 UIC ERTMS Conference Rome 11

ETCS brake modelActions:1. Decrease the time between the different curves to theabsolute minimum that is acceptable from ergonomic pointof view. This is done by the railways in the context of EEIGand B126.15 with the help of an SNCF simulator in Lille anda DB simulator in Munich. Tests with these simulators areongoing.2. Define the ETCS braking curve model in sufficient detail toguarantee a predictable braking distance of a given train,independent from the supplier of the onboard ETCSequipment. This is done in close co-operation betweenrailways (co-ordinated by EEIG) and UNISIG.15 - 17 December 2004 UIC ERTMS Conference Rome 12

Safety marginsOutput conversion modelorMeasured decelerationA guaranteed = K v * K r * A basicT guaranteed = K t * T basicA guaranteedA basicEOAK vK r(=1) - speed dependent factor for reduction of basic deceleration(=1) - train length dependent factor for reduction of basic decelerationK t(=1) - factor for prolongation of brake development timeA max- maximum deceleration when reduced adhesion is active15 - 17 December 2004 UIC ERTMS Conference Rome 13

Safety margins (2)The facts:Harmonised safety margin work ongoing in B126.15. Based on actualsafety margins used in existing systems. Results not available in timefor SRS300.Relation between performance requirements and safety requirementscan vary between the different railways, specifically in the case of anexisting line with level 1 overlay.The short term solution for SRS300:Implement the safety margins as a national value which can be sentto the train from trackside. This is a temporary solution, to besuperseded by the harmonised safety margin as soon as it becomesavailable.15 - 17 December 2004 UIC ERTMS Conference Rome 14

ConclusionsThe current pragmaticapproach gives the best possible mix of:¦ safety¦ performance¦ driver ergonomics¦ flexibility for the railways toimplement ERTMS in the waythat best suits their needs15 - 17 December 2004 UIC ERTMS Conference Rome 15

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