Estimate of Truck Drag
Forces from Roll-Down
Tests
Peter Hart
Hartwood Consulting
What Is Roll-Down Testing ?
•  The vehicle is rolled down (i.e. without engine power) from a high speed (100km/h) to a low speed (e.g. 20 km/h) on a flat road. Put your logo here
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What Is Roll-Down Testing ?
•  The vehicle is rolled down (i.e. without engine power) from a high speed (100km/h) to a low speed (e.g. 20 km/h) on a flat road. •  The speed v ?me trace is captured. Put your logo here
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What Is Roll-Down Testing ?
•  The vehicle is rolled down (i.e. without engine power) from a higher speed (100km/h) to a low speed (e.g. 20 km/h) on a flat road. •  The speed v ?me trace is captured. •  The drag force is es?mated from the computed dV/dt. Put your logo here
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So What?
•  Want to determine the nature of the drag force speed dependence. Put your logo here
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So What?
•  Want to determine the nature of the drag force speed dependence. •  Par?cular drag mechanisms are modeled by par?cular speed dependence. Put your logo here
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So What?
•  Want to determine the nature of the drag force speed dependence. •  Par?cular drag mechanisms are modeled by par?cular speed dependence. •  Therefore it might be possible to quan?fy the the various drag force levels using simple tests. Put your logo here
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Fundamental Assumptions
•  The speed dependence that exists for a transient test is the same as that for a con?nuous-­‐speed test. Put your logo here
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Fundamental Assumption
•  The speed dependence that exists for a transient test is the same as that for a con?nuous-­‐speed test. •  The speed dependence is assumed to be: Put your logo here
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Loss Power Relationship
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Testing
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Testing
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Testing
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Testing
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Some Maths
•  First order Ricca? non-­‐linear DE. Count Ricca?, Italian noble circa 1650. Put your logo here
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Riccati Solution
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Riccati
•  According to Wikipedia: Put your logo here
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US EPA
•  Requires car manufacturers to report the
A , B and C coefficients Put your logo here
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The Riccati Map
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Practical Measurements
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Practical Measurements
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Drag Force Mechanisms
•  Aerodynamic Drag Assumed to be with V2 A -­‐ parameter Put your logo here
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Drag Force Mechanisms
•  Aerodynamic Drag Assumed to be with V2 •  Braking Drag Assumed to be constant force C -­‐ parameter Put your logo here
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Drag Force Mechanisms
•  Aerodynamic Drag Assumed to be with V2 •  Braking Drag Assumed to be constant force •  Engine, Bearings, etc may vary with V ? B -­‐ parameter ? Put your logo here
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Drag Force Mechanisms
•  Tyres. Modeled as a constant drag force but this is an approxima?on. B , C -­‐ parameters Put your logo here
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Drag Force Mechanisms
•  Tyres. Modeled as a constant drag force but this is an approxima?on. B , C -­‐ parameters •  Suspension Unknown varia?on with speed Put your logo here
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Drag Force Mechanisms
•  Tyres. Modeled as a constant drag force but this is an approxima?on. B , C -­‐ parameters. •  Suspension Unknown varia?on with speed. •  Hill climbing / descending drag B and C -­‐ parameters Put your logo here
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Comparative Tests
•  Tests can be conducted with only one variable changed. E.g. Laden and Unladen with no change in aerodynamic profile. With and without an extra trailer. With tyres under-­‐inflated and normal. Put your logo here
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Program Implementation
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Program Implementation
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Program Implementation
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Semi-trailer
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Semi-trailer (unladen)
•
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•
•
V3 3.8% -­‐ V2 54.4% 61.6% V 17.4% 18.9% V1/2 4.8% -­‐ Constant 18.7% 19.5% Put your logo here
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Review
•  Roll-­‐down tes?ng needs perfect condi?ons Put your logo here
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Review
•  Roll-­‐down tes?ng needs perfect condi?ons •  Can separate the various drag force components if the experiments are well-­‐
planned. Put your logo here
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Review
•  Roll-­‐down tes?ng needs perfect condi?ons •  Can separate the various drag force components if the experiments are well-­‐
planned. •  Can be conduced with minimal test infra-­‐
structure. Put your logo here
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Review
•  I’m looking for a rich patron to fund a project to quan?fy the drag force components on a Australia B-­‐double trucks Put your logo here
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St Patrick’s Day
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Italian Contribution
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Finally
Thank you for listening! Put your logo here
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