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As Automotive Seat Design deals with accommodating a wide range of people in addition to seat ergonomics (which still relies on much subjective testing) it is best to use sources that are verified and/or peer reviewed, such as papers and studies. Typically the researchers behind these have the resources and equipment to survey a large number of people and measure metrics that the average person would be unable to. That being said, conducting in house research (if possible) is highly recommended. Finding information from a website is still perfectly acceptable if it comes from a reputable source, can be verified or you are using it to get more familiar with the topic before delving deeper into papers/studies. 


Terms

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This section provides description for some common terms that will be used throughout the document

  • H Point: The theoretical location of the occupant’s hip. This is the pivot point of both the torso and the upper leg. Many dimensions will be relative to this.

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  • 5 Point / 6 Point Harness: A seatbelt with 5 or 6 belts in total. It restrains the movement of the occupant more than a 3 Point Seatbelt and is safer

    • 5 Point Harness

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        • 1 & 2: Shoulder Belts

        • 3 & 4: Lab Belts

        • 5: Anti Sub Belt

  • 6 Point Harness

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      • Similar setup to 5 Point Harness however Antisub Belt is two separate belts

  • Passthroughs: Cutouts in the seat to allow the belts of a 5 or 6 Point Harness to pass through the seat uninterrupted (as shown by the red circles in the image below)

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  • Seatback: The portion of the seat which supports the back and shoulders of the occupant

  • Headrest: The portion of the seat which supports the head and/or neck of the occupant

    • In race/bucket seats this will be the area above the shoulder belt passthroughs

  • Seatpan: The portion of the seat which supports the buttock and upper leg of the occupant

  • Bolsters: Protrusions/barriers typically found on the seatback or seatpan of the seat (shown by the red circles in the image below) They keep the occupant centered in the seat during cornering.

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  • Undepressed Seat Contour: The shape of the seat cushioning (typically viewed from the side) when no occupant has sat in it

  • Depressed Seat Contour: The shape of the seat cushioning (typically viewed from the side) when an occupant is sitting in the seat - causing the cushioning to compress

  • ILD/IFD: Acronym for Indentation Load Deflection or Indentation Force Deflection. A test to determine the stiffness of a foam. Manufacturers will typically specify the stiffness of their foam in ILD/IFD

    • In this test a circular flat indenter is pressed against a foam sample of standardized width, length and height. 60 seconds after the indenter has achieved 25% or 50% compression, the force is measured 

    • Higher ILD/IFD values = stiffer foam

    • 25% ILD/IFD is for a 25% compression

    • 50% ILD/IFD is for a 50% compression

    • US measurements are in pounds-force

    • European measurements are in newtons

Occupant Geometry:

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Desired angles between the legs, torso, head etc. of the occupant

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[4]

Location of H Point

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Location of the H Point will depend on the type of occupant sitting in the seat at that time (e.g. 5th Percentile Female vs 75th Percentile Male) 

If you know generally which type of occupant will be sitting in the seat the most, you can use their location of the H Point (e.g. you know a 50th Percentile Male will sit in the seat the most - so use their location of H Point in design)

Note: The location of the H Point as per ASC/WSC is different from what is described in this document. For all ASC/WSC regulations use their location of the H Point. For all guidelines in this document use the H Point location described in this document

Type of Occupant

Distance from Depressed Seatback  Contour (mm)

Distance from Depressed Seatpan Contour (mm)

1st Percentile Female

102

58.5

50th Percentile Female

122

77.5

99th Percentile Female

132

97.79




1st Percentile Male

104

61.5

50th Percentile Male

122

80

99th Percentile Male

135

98.5

[11]

Unfortunately, the source for this data does not include the above measurements for 5th Percentile and 75th Percentile Male and Female


Seatback (Structure):

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Widths

Height from H Point (mm)

Minimum Recommended Width (mm)

220

384

318

471

534

545*

[6]

  • Not from source 6 - but from in house testing and CAD analysis

Shoulder Belt Passthroughs:

  • Shoulder Belt Passthroughs should be just above the occupants shoulders and must accommodate ASC and WSC regulations as well as anthropometric data below

  • Note: If you are designing for a different set of occupants (e.g. 5th Percentile Female to 75th Percentile Male) the upper and/or lower bounds for the shoulder belt passthrough will change

Height from H Point (mm)

Type of Occupant

Approx. 480mm

5th Percentile Female

Approx. 580mm

95th Percentile Male

  • Based on diagram below

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[4]

Height (not including headrest): 410mm - 515mm above H Point  [6]

Seatback (Cushioning):

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General Guidelines

  • Seatback should provide full contact from: Top of Pelvis to Shoulder  [4]

    • Headrest will provide contact for Head and/or Neck

  • Beyond the 325mm line that is above the H Point (will be shown in diagrams further below) the geometry should be fairly flat  [4]

    • Ergonomics of this will be described in Pressure Distribution Section

Lumbar Support

  • Preferred apex of lumbar support (i.e. where it protrudes out the most): 152mm above the H Point  [4]

    • Or 150mm above the H Point [6]   (only a 2mm difference, doesn’t really matter which one is used)

  • Preferred prominence of a fixed, non-movable lumbar support (i.e. how much it protrudes): 20mm  [6]

  • Preferred prominence of a movable lumbar support: 30mm  [6]

  • Range of motion for a movable lumbar support: 100mm - 200mm above the H Point  [6]

  • Lumbar Support Cushioning should not compress more than 80%  [6]

    • Greater than 80% compression leads to decrease in water vapor diffusion, leading to increase in local humidity

Depressed Seatback Cushion Contour  [4]

  • Assumed this was approximately 99th Percentile Male, thus H Point is 135mm away from Depressed Seatback Cushion Contour

  • Depressed Cushion Contour is the bolded black line that is pointed at by the red arrow in the image below

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      • Steps to recreate this Depressed Cushion Contour in CAD

        • Draw torso line (a line emanating from the H Point, at the angle that you have determined the occupant will be sitting at)

        • Draw three perpendicular lines to the torso line

          • At 115mm, 160mm and 325mm from the H Point

          • Each of these lines (in this case) are 135mm long though depending on the occupant it may be a different length for you

        • Draw a line connecting the endpoints of the 325mm and 115mm line

        • At the endpoint of the 115mm line, construct an arc with 100mm radius that will stop at the stiffer/base layer foam below it

Undepressed Seatback Cushion Contour [4] & [6]

  • Still under assumption we are using a 99th Percentile Male as the occupant - H Point is 135mm away from the depressed seatback cushion contour

    • Source 4 undepressed seatback cushion contour 

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        • NOTE: For MSXIV a fixed lumbar support was used, thus to have a 20mm prominence all Y-values above were multiplied by 0.4

  • Source 6 undepressed seatback cushion contour

    • Due to manufacturing concerns, source 4’s undepressed seatback cushion contour may be too complicated to make, source 6’s is merely an arc - which makes manufacturing much easier

    • Radius for fixed lumbar support: 300mm

    • Radius for lumbar support of this type that can adjust its radius (separate from adjusting the height of the apex): 240mm - 400mm

    • Note: Guidelines for the prominence of the lumbar support still apply with this type of undepressed seatback cushion contour


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