Proportional pressure reducing valves with intrinsic fail safe function Dr. Jörg Schneider Dr. Jens Krallmann Daniel Ferres 1
1 2 3 4 5 6 Introduction and Motivation PPRVs as pilot valves for sectional valves Functional principle of Fail Safe versions Limits and Restrictions Influence on functional safety ratings Summary 2
Introduction and Motivation THOMAS Mobilhydraulic history: First cartridge valve developement in 1996 PPRV: 3/2-way proportional pressure reducing valve PPCD04 Proportional Pressure Control Direct operatred 04 = flow capacity 3
Introduction and Motivation What to do for continuous improvements? 1) Higher performance and/or more compact and/or more cost efficient design Standard PPRV New Generation 2006 High Performance Valve 4
Introduction and Motivation What to do for continuous improvements? 2) Integration of more functionality Standard PPCD04 Fail Safe version 2017 5
PPRVs as pilot valves for sectional valves Functional principle of a PPCD04 P P P T P C F S F M P C I 6
PPRVs as pilot valves for sectional valves Functional principle of a PPCD06 P P P T P C F M 7
PPRVs as pilot valves for sectional valves Safe situation for implement functions with electrohydraulically driven sectional valve P C < P SF -> Safe Situation P SF P C 8
Functional principle of Fail Safe versions PPCD04 P P Tank armature bar P C < P SF 9
Functional principle of Fail Safe versions PPCD06 P P Tank P C < P SF pressure pin 10
Functional principle of Fail Safe versions 11
Functional principle of Fail Safe versions First Design Final Design Filter: mesh width of 125 µm Flow restricting bore 12
Limits and Restrictions PPCD04 13
Limits and Restrictions PPCD04 Vol. = 6 ml 14
Limits and Restrictions Vol. = 6 ml 15
Influence on functional safety ratings Electrohydraulic Actuator - CAN Signal as input command - Position feedback signal by hall sensor - Rated according to ISO13849 MTTFd = 150 year 16
Influence on functional safety ratings Reliability model for the main Safety Function: Both pilot valves are generating a pilot pressure below P SF if neutral position is commanded 17
Influence on functional safety ratings MTTF i Dangerous MTTF di λ di Number Realization of detection/explanation Diagnostic or Safety λ dd λ s [1/years] Part No. Part description λ [1x10-6 /h] [years] Database failures [%] [years] [1/years] of parts Detected for assessment Function [1/years] Total [1/years] Pilot valve mechanical part 0,76 450,00 ISO 13849 100 not opening acc. Table C.6 450 0,002222222 1 S safe state 0 0,002222222 0,002222222 0,76 450,00 ISO 13849 100 not closing acc. Table C.6 450 0,002222222 1 Y detection possible - transition to safe state to be done by higher ranking system SF(2), DF(10) 0,002222222 0,002222222 0 change of pressure ctrl behavior fault exclosure due to use of proven 0,76 450,00 ISO 13849 100 acc. Table C.6 450 0,002222222 1 S spring acc Table C.6 0 0,002222222 0,002222222 change of pressure ctrl behavior by unwanted change of set-value current and position ctrl /validation by 0,76 450,00 ISO 13849 100 acc. Table C.6acc. Table C.6 450 0,002222222 1 Y several SF/DF DF(10), DF(13) 0,002222222 0,002222222 0 SF(2), unwanted screw-out of the moving fault exclosure due to missing adjusting device in the valve acc Table C.6 0,76 450,00 ISO 13849 100 parts acc. Table C.6 450 0,002222222 1 S 0 0,002222222 0,002222222 0,76 450,00 ISO 13849 100 leakage acc. Table C.6 450 0,002222222 1 S fault exclosure acc Table C.6 0 0,002222222 0,002222222 0,76 450,00 ISO 13849 change of the leakage flow during long operation time acc. Table 100 C.6 450 0,002222222 1 S no critical influence 0 0,002222222 0,002222222 burst of valve housing or break of detection possible - transition to safe state to be done by higher ranking 0,76 450,00 ISO 13849 100 moving valve parts acc. Table C.6 450 0,002222222 1 N system 0 0,002222222 0 SF(2), DF(10) short & open --> safe state Pilot valve electrical part 0,76 450,00 ISO 13849 100 450 0,002222222 1 S no critical influence 0 0,002222222 0,002222222 (λs i) 0,011111111 Detectable and EHA can be brought into safe state (λ di) λ ddc = (λ ddi) MTTF dc = 1/ (λ di) in years 0,006666667 0,004444444 0,004444444 150 Possible failure modes due to table C.6 in ISO 13849 18
Summary Introduction of valves with fail safe function Discussion of limits and restrictions Positive effects on functional rating of systems with integrated fail safe valves 19
Thank you for your attention! Contact: Dr. Jörg Schneider Thomas Magnete GmbH Email: joerg.schneider@thomas-magnete.com 20