RELIABILITY IN THE MECHANICAL DESIGN PROCESS
8.6 Clutch System Failure Rate Estimation Model
The clutch system failure rate is expressed by the following equation44:
𝜆c=𝜆cf+𝜆sp+𝜆bf+𝜆ss+𝜆ac (64) where 𝜆c=clutch system failure rate, expressed in failures/106h
𝜆cf=clutch friction material failure rate 𝜆sp=failure rate of springs
𝜆bf=failure rate of bearings 𝜆ss=failure rate of seals 𝜆ac=failure rate of actuators
The clutch friction material failure rate is given by
𝜆cf=𝜆bcfF1F2 (65)
where F1=factor that considers the effects on the base failure rate of ambient temperature
F2=factor that considers the effects on the base failure rate of multiple plates 𝜆bcf=clutch friction material base failure rate
The clutch friction material base failure rate is expressed by44, 48 𝜆bcf= nAE
2MawAcfmLth (66)
where AE=average energy dissipated per engagement, expressed in ft-lbf
Afm=total area of the clutch friction material on each disk, expressed in inches2 n=number of applications per hour
Maw=average wear of the material Lth=lining thickness, expressed in inches
9 FAILURE DATA AND FAILURE DATA COLLECTION SOURCES
Failure data provide invaluable information to reliability engineers, design engineers, manage- ment, and so on concerning the product performance. These data are the final proof of the success or failure of the effort expended during the design and manufacture of a product used under designed conditions. During the design phase of a product, past information concern- ing its failures plays a critical role in reliability analysis of that product. Some of the uses of the failure data are estimating item failure rate, performing effective design reviews, pre- dicting reliability and maintainability of redundant systems, conducting tradeoff and life-cycle cost studies, and performing preventive maintenance and replacement studies. Table2presents failure rates for selected mechanical items.13,49,50
There are many different ways and means for collecting failure data. For example, during the equipment life cycle, there are eight identifiable data sources: repair facility reports, devel- opment testing of the item, previous experience with similar or identical items, customer’s failure-reporting systems, inspection records generated by quality control and manufacturing
Table 2 Failure Rates for Some Mechanical Itemsa Item Description Failure Rate 10−6h
Roller bearing 8.323
Bellows (general) 13.317
Filter (liquid) 6.00
Compressor (general) 33.624
Pipe 0.2
Hair spring 1.0
Pump (vacuum) 10.610
Gear (spur) 3.152
Seal (o-ring) 0.2
Nut or bolt 0.02
Brake (electromechanical) 16.00
Knob (general) 2.081
Washer (lock) 0.586
Washer (flat) 0.614
Duct (general) 2.902
Guide pin 13
Hose, pneumatic 29.3
Heavy-duty ball bearing 14.4
Pressure regulator 2.4
aUse environment: ground fixed or general.
Table 3 Selected Failure Data Sources for Mechanical Items
Author(s)
Source title/ Document
Ref. No./Year Developed by
M. J. Rossi Non-electronic Parts Reliability Data, (Rept. No. NPRD-3, 1985)
Reliability Analysis Center, Rome Air Development Center, Griffis Air Force Base, Rome, New York.
— Component Reliability Data for
Use in Probabilistic Safety Assessment (1998)
International Atomic Energy Agency, Vienna, Austria.
R. G. Arno Non-electronic Parts Reliability Data (Rept. No. NPRD-2, 1981)
Reliability Analysis Center, Rome Air Development Center, Griffis Air Force Base, Rome, New York.
— Government Industry Data
Exchange Program (GIDEP)
GIDEP Operations Center, U.S.
Dept. of Navy, Seal Beach, Corona, California.
R. E. Schafer, J. E. Angus, J.M. Finkelstein, M. Yerasi, and D. W. Fulton
RADC Non-electronic Reliability Notebook (Rept. No.
RADC-TR-85-194, 1985)
Reliability Analysis Center, Rome Air Development Center, Griffis Air Force Base, Rome, New York.
groups, tests conducted during field demonstration, environmental qualification approval, and field installation, acceptance testing, and warranty claims51. Table3presents some sources for collecting mechanical items’ failure data for use during the design phase.13
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CHAPTER 7