1. A Study of Parking Brake Cable Efficiency as Affected by Construction Type
Paul Stoloff
Brake Technical Lead
Chrysler Group, LLC
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2. Agenda Park Brake System Efficiency Cable Efficiency Cable Testing
Force Efficiency
Travel Efficiency
Cable Testing
Test Results
Force Efficiency, Travel Efficiency and Work Efficiency
Other Considerations
Summary
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3. Park Brake System Efficiency
The mechanical efficiency of a parking brake system is determined by the sum of the losses of all components in the system
Cables represent the greatest contribution to efficiency loss in a typical parking brake system.
Since a parking brake lever delivers force and travel, work efficiency should be understood in order to optimize a system.
Work is not simply the product of force and travel, but rather…
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4. Cable Efficiency
Input Force is limited by regulation and customer satisfaction
Input travel is limited by packaging constraints and customer satisfaction
Hence net work is limited.
Since cables consume both force and travel efficiency, small improvements in cable performance can have significant affect on system performance
Where to from here?
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5. Cable Testing
“Without data, you are just another person with an opinion”, Anonymous
“With data, you are just another person with an analysis”, Anonymous
Independent data from different (biased) sources is insufficient to perform an analysis or draw any conclusions.
Uniform testing is the proper method for gathering data.
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6. Cable Testing
A simple cable test stand was developed and validated to measure input/output force and input/output travel under a fixed set of conditions.
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7. Cable Testing
Cable samples from four leading cable suppliers were solicited.
The following constructions were tested:
Flat Wire Conduit
Twin Wire Conduit
1x19 Strand
3 Samples
7x7 Strand
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8. Test Validation – Travel and Force Efficiency
The test stand was validated using one sample each of three different constructions that were expected to have measurable differences in performance.
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9. Test Validation - Results
Travel efficiency differences were clear and statistically valid.
Force efficiency fell within a very narrow range and was repeatable.
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10. Test Results – Travel Efficiency
The testing was expanded to include all construction combinations from all suppliers; 48 pieces total.
ANOVA analysis of the results showed a strong correlation for strand type.
1x19 Strand – 68.1% Mean
7x7 Strand – 61.1% Mean
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11. Test Results – Force Efficiency
ANOVA analysis of Force Efficiency revealed a moderate effect from Supplier, driven primarily by the poor performance of Supplier D and the good performance of Supplier A.
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12. Test Results – Work Efficiency
Work efficiency was calculated using numerical integration.
Of the sixteen combinations, the top eight were all 1x19 strand.
Three of the top four were flat wire conduit.
The worst performer had both the worst travel and worst force efficiency, compounding to create the worst overall performer.
19%
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13. Cable efficiency is not the only consideration in cable design.
Other Considerations
Cable efficiency is not the only consideration in cable design.
Others include
Flexibility/Stiffness
Cost
Corrosion Resistance
Supplier Strategy
Application specific issues
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14. Summary
A method was demonstrated for quantifying parking brake cable performance.
The method is simple, quick, repeatable, and reliable.
Other variations of parts can be quickly evaluated and compared to previous results.
This procedure provides the engineer the tools to remove the guesswork from cable selection.
Proper selection of cable construction can result in significant improvements in parking brake system performance.
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