estimate of truck drag forces from roll-down...

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.

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•  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.


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•  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.


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So What?

•  Want to determine the nature of the drag force speed dependence.


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So What?


•  Par?cular drag mechanisms are modeled by par?cular speed dependence.


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So What?


•  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.


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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.


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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:


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Loss Power Relationship


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Testing


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Some Maths

•  First order Ricca? non-‐linear DE. Count Ricca?, Italian noble circa 1650.


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Riccati Solution


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Riccati •  According to Wikipedia:


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US EPA

•  Requires car manufacturers to report the A , B and C coefficients


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The Riccati Map


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Practical Measurements


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Drag Force Mechanisms

•  Aerodynamic Drag Assumed to be with V2

A -‐ parameter


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•  Braking Drag Assumed to be constant force

C -‐ parameter


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•  Braking Drag Assumed to be constant force

•  Engine, Bearings, etc may vary with V ?

B -‐ parameter ?


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•  Tyres. Modeled as a constant drag force but this is an approxima?on. B , C -‐ parameters

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•  Tyres. Modeled as a constant drag force but this is an approxima?on. B , C -‐ parameters

•  Suspension Unknown varia?on with speed


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•  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


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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 n mastr template

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Program Implementation


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Semi-trailer


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Semi-trailer (unladen)

•  V3 3.8% -‐ •  V2 54.4% 61.6%

•  V 17.4% 18.9% •  V1/2 4.8% -‐

•  Constant 18.7% 19.5%


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Review

•  Roll-‐down tes?ng needs perfect condi?ons


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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.


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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.


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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


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St Patrick’s Day


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Italian Contribution


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Finally

Thank you for listening!


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estimate of truck drag forces from roll-down...

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