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03 - Coastdown test theory

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The test is performed in accordance with European Directive 70/220/EEC – Annex III and is based upon statistical evaluation of a minimum of 4 test runs.

The test results are considered to be valid when the statistical accuracy of the average test values is ≤ 2%.

The test can be performed at any speed according to the manufacturer’s requirements, but must follow the general procedure below:

 

CoastTheory.png

1 Accelerate the vehicle to a speed 10km/h greater than the test start speed (user definable – 125km/h in the diagram)
2 Place gearbox in neutral
3 Measure the time taken for the vehicle to decelerate from the start speed to the stop speed (user definable – 85km/h in the diagram). This is time t1.
4 Repeat steps 1-3, but in the opposite direction. This is time t2
5 Take the average time of these two test runs (t1 + t2)/2. This is the time T

Repeat steps 1 to 5 until such time that the statistical accuracy of the average is not more than 2%

 equ1.png

 

The statistical accuracy (p) is defined by:

 equ2.png

Where:

equ3.png= Coefficient given by the table below,

n = Number of tests

s = standard deviation 

 

n 4 5 6 7 8 9 10 11 12 13 14 15
t 3.2 2.8 2.6 2.5 2.4 2.3 2.2 2.2 2.2 2.2 2.2 2.2
equ4.png 1.6 1.25 1.06 0.94 0.85 0.77 0.73 0.66 0.64 0.61 0.59 0.57
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Last modified
17:08, 22 Oct 2014

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