Proportional pressure reducing valves with intrinsic fail safe function

Transcription

1 Proportional pressure reducing valves with intrinsic fail safe function Dr. Jörg Schneider Dr. Jens Krallmann Daniel Ferres 1

2 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

3 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

4 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

5 Introduction and Motivation What to do for continuous improvements? 2) Integration of more functionality Standard PPCD04 Fail Safe version

6 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

7 PPRVs as pilot valves for sectional valves Functional principle of a PPCD06 P P P T P C F M 7

8 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

9 Functional principle of Fail Safe versions PPCD04 P P Tank armature bar P C < P SF 9

10 Functional principle of Fail Safe versions PPCD06 P P Tank P C < P SF pressure pin 10

11 Functional principle of Fail Safe versions 11

12 Functional principle of Fail Safe versions First Design Final Design Filter: mesh width of 125 µm Flow restricting bore 12

13 Limits and Restrictions PPCD04 13

14 Limits and Restrictions PPCD04 Vol. = 6 ml 14

15 Limits and Restrictions Vol. = 6 ml 15

16 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

17 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

18 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 not opening acc. Table C , S safe state 0 0, , ,76 450,00 ISO not closing acc. Table C , Y detection possible - transition to safe state to be done by higher ranking system SF(2), DF(10) 0, , change of pressure ctrl behavior fault exclosure due to use of proven 0,76 450,00 ISO acc. Table C , S spring acc Table C.6 0 0, , change of pressure ctrl behavior by unwanted change of set-value current and position ctrl /validation by 0,76 450,00 ISO acc. Table C.6acc. Table C , Y several SF/DF DF(10), DF(13) 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 parts acc. Table C , S 0 0, , ,76 450,00 ISO leakage acc. Table C , S fault exclosure acc Table C.6 0 0, , ,76 450,00 ISO change of the leakage flow during long operation time acc. Table 100 C , S no critical influence 0 0, , burst of valve housing or break of detection possible - transition to safe state to be done by higher ranking 0,76 450,00 ISO moving valve parts acc. Table C , N system 0 0, SF(2), DF(10) short & open --> safe state Pilot valve electrical part 0,76 450,00 ISO , S no critical influence 0 0, , (λs i) 0, Detectable and EHA can be brought into safe state (λ di) λ ddc = (λ ddi) MTTF dc = 1/ (λ di) in years 0, , , Possible failure modes due to table C.6 in ISO

19 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

20 Thank you for your attention! Contact: Dr. Jörg Schneider Thomas Magnete GmbH 20