HR-8-12

Static Backset Measurement

Comparison of methods

2

Aims

• Comparison of static backset measurement of head restraints• Evaluate EuroNCAP protocol• Evaluate UTAC alternative• Recommendations for a method

3

Methods

Measure backset using five methods• Proposed EuroNCAP protocol using

• H-point SAE Manikin (OSCAR)• Head Restraint Measuring Device (HRMD)• No preload to head restraint

• Proposed EEVC WG20 procedure• Similar to EuroNCAP, but with 10 N preload to backset probe

• Alternative proposal from UTAC (not used in the end)• Explained in next pages

• 3D FARO measurement without HRMD• Like UTAC, but seat loaded with SAE manikin

• 3D FARO measurement without HRMD, without SAE manikin• Like UTAC without preload• Like UTAC with 10 N preload to backset probe

4

UTAC proposal: replace HRMD with 2 link bar

Car manufacturer

design torso angle

505.5

mm

205 m

m

292 mm

Line through H-point of the dummy and rotation point of the HRMD

rotation point of the HRMD to align it horizontally

Head to HR distance

73mm

-3°

5

UTAC proposal, simplified tool

Torso bar

Neck bar

Backset Probe

6

UTAC proposal made even more simple

• Use SAE manikin to determine H-point (or start from R-point in the car) and seat back angle

• Measure H-point on 2 sides of manikin with 3D FARO arm• Determine:

• Probe height which is needed for backset measurement• Virtual location of the back of the HRMD head• Using mathematical equations + manikin and HRMD dimensions

• Adjust the probe to calculated height

• Push probe against the head restraint (3 methods evaluated)• With SAE manikin in the seat, without probe preload• Without SAE manikin, without probe preload• Without SAE manikin, with 10 N probe preload

• Measure backset with 3D FARO arm

7

Comments to UTAC proposal

• Method should work fine, but the values found were different from those proposed by UTAC

• Average distance from H-point to HRMD rotation point was 505.9 mm (TNO) instead of 505.5 mm (UTAC)

• Average angle difference between seat back angle and line through H-point and HRMD rotation point was -1.9 deg (TNO) instead of -3 deg (UTAC)

• Ending up with backset differences of 13 -15 mm• Of course these values are related to combined SAE machine

and HRMD!• Standardising the analytical values solves these problems and

does not interfere with any combinations of these tools!

• For the static measurements presented here, the height of the probe as measured with HRMD was taken for valid comparison

8

Test rigs: HRMD and PortalMeasurements done with FARO

• Regular measurement• With SAE manikin and HRMD

• Without preload (EuroNCAP)• With preload of 10 N (EEVC)

• Portal measurement @ height of HRMD

• With SAE manikin loading seat• Without manikin

• Without preload (UTAC)• With preload 10 N for comparison

9

Comparison of methods

• Largest difference is between seats of one type, not method used

45.0

50.0

55.0

60.0

65.0

70.0

B1 B2 B4 C3 C4 C7 E10 E15 E1

Seat Type

Hea

d re

stra

int d

ista

nce

[mm

]

HRMD + Manikin + 0 N(EuroNCAP)

HRMD + Manikin + 10N (EEVC WG20)

No HRMD + Manikin +0 N

No Manikin + 0 N

No Manikin + 10 N

10

Comparison with EuroNCAP method (1)

Head restraint distance

50.0

55.0

60.0

65.0

70.0

50.0 55.0 60.0 65.0 70.0

HRMD + Manikin + 0 N preload [mm]

Alte

rnat

ive

[mm

]

HRMD + Manikin + 0N preloadHRMD + Manikin + 10N preloadNo HRMD + Manikin +0 N preloadNo manikin + 0 NpreloadNo manikin + 10 Npreload

11

Comparison with EuroNCAP method (2)

• Applying 10 N preload is used to prevent very soft head restraints. This always increases the head restraint distance measurement by average 3.5 mm.

• Not using the HRMD, but with the SAE manikin in the seat decreases the head restraint distance by average 0.1 mm (average absolute deviation is 0.6 mm). Not significant!

• Not loading the seat with a manikin decreases the head restraintdistance by average 3.6 mm

• Applying a 10N preload with an unloaded seat causes a decrease of 0.7 mm with respect to the EuroNCAP measurement

• The error within one seat type (3 seats) is 3.8 mm on average• This means that all deviations are within the range of

measurements of one seat type

12

Comparison with EuroNCAP method (3)

Deviation from EuroNCAP protocol

-6,0

-4,0

-2,0

0,0

2,0

4,0

6,0

8,0

10,0B1 B2 B4 C

3

C4

C7

E10

E15 E1

ABS

AVG

Seat type

Dev

iatio

n fro

m E

uroN

CA

P [m

m]

From averageEuroNCAPHRMD + Manikin +10 NNo HRMD + Manikin+ 0 NNo Manikin + 0 N

No Manikin + 10 N

13

Causes of head restraint distance variations:H-point x location

• Seat C and E: no influence of H-point x with HR distance

• Seat B: IncreasingH-point x ~ decreasing HR distance

Deviation from average

-8.0

-6.0

-4.0

-2.0

0.0

2.0

4.0

6.0

8.0

10.0

-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0

H-point x [mm]

HR

dis

tanc

e N

CA

P [m

m]

Seat type BSeat type CSeat type E

14

Causes of head restraint distance variations:H-point z location

• Seat B and C: no influence of H-point z with HR distance

• Seat E: IncreasingH-point z ~ decreasing HR distance

Deviation from average

-8.0

-6.0

-4.0

-2.0

0.0

2.0

4.0

6.0

8.0

10.0

-4.0 -2.0 0.0 2.0 4.0

H-point z [mm]

HR

dis

tanc

e N

CA

P [m

m]

Seat type BSeat type CSeat type E

15

Causes of head restraint distance variations:Torso angle

• Seat B, C and E:Increasingangle ~ increasing HR distance

Deviation from average

-8.0

-6.0

-4.0

-2.0

0.0

2.0

4.0

6.0

8.0

10.0

-1.0 -0.5 0.0 0.5 1.0 1.5

Torso angle [deg]

HR

dis

tanc

e N

CA

P [m

m]

Seat type BSeat type CSeat type E

16

Main results summary

• The deviation caused by the seat (of one type) and SAE positioning (reproducibility) is larger than the deviation caused by a change of measurement method.

• Head restraint distance varies with• Seat back angle• H-point location

• This relation is not similar for all seat types.• Small differences in H-point location (within specs) may result in

large changes of the head restraint distance• Example Seat B: H-point location ranges from -3 to +2 mm, but

HR distance -6 to +9 mm

17

Conclusions

• Measurement method is not mainly determining head restraint distance

• SAE manikin positioning has large influence on head restraint distance

• Need for more tight requirement on SAE manikin positioning or use more straightforward point in car, like R-point

• No preference for any method with regard to current results• UTAC method is more straightforward, not more accurate• UTAC method cannot be varied easily for different occupant

sizes

• Preference for simple (analytical) method