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Overview

The purpose of this document is to provide a centralized resource for research related to Automotive Seat Design. Included content is primarily: recommended dimensions (widths, height, length) though other content such as: recommended cushion contours, ideal cushion properties and pressure distribution are also described. Feel free to add more content to this to expand it so the next Seats Form Factor DRI(s) will have more resources to use!

The recommendations here are to be used in conjunction with both ASC and WSC regulations. If for some reason there is a conflict between those regulations and these recommendations, the ASC and WSC regulations supersede the recommendations in this document

Most of the guidelines here are recommendations, not hard restrictions (with the exception of explicit safety related ones - which will be mentioned). Thus, if the physical space or geometry does not allow for them to be met, do not worry and aim to optimize the design so it can be as close as it can be to the guidelines

Note: Links to all the sources used in this document can be found at the bottom

Note: In text citation will be done in an IEEE style, with a citation number inserted in square brackets beside the text/table

Note on Sources

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 reviewed, such as papers, studies and published books. 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

 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.

  • 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

      • 1 & 2: Shoulder Belts

      • 3 & 4: Lab Belts

      • 5: Anti Sub Belt

  • 6 Point Harness

    • 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)

  • 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.

  • 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 pound-force

    • European measurements are in newtons

Occupant Geometry

 This section describes the desired angles between the legs, torso, head etc. of the occupant

[4]

Location of H Point

 Click here to expand

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

59

50th Percentile Female

122

81

99th Percentile Female

132

99




1st Percentile Male

104

66

50th Percentile Male

122

86

99th Percentile Male

135

97

[11]

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


Seatback (Structure)

 Click here to expand...

Widths

Height from H Point (mm)

Minimum Recommended Width (mm)

220

384

318

471

534

545 (see note below)

[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

[4]

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

Seatback (Cushioning)

 Click here to expand...

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

      • 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 

        • 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

    • Prominence for fixed lumbar support of this type: 15-20mm

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

    • Prominence for radius adjustable lumbar support of this type: 0-30mm


Headrest (guidelines in the headrest section are safety related and should be explicitly followed*)

 Click here to expand...

If for some reason this cannot be possible, discuss with relevant stakeholders how this can be accommodated

Width of Headrest: Minimum 127mm on either side of the centreline (measured at 65mm below the top of the headrest)  [10]

  • Important that the headrest is wide enough to cover the width of the occupant with a helmet on, otherwise it may be too easy for the occupants head to be off centre with respect to their body

Height of Headrest: At a minimum should be 60mm below the top of the helmet the occupant is wearing (helmets may add 2 inches - 2.5 inches in additional height to the occupant) [8]

  • Diagram below is for conventional passenger car where occupant is not wearing a helmet, but in our case the occupant must wear a helmet when the car is driving - thus imagine the guide on the right (in the image below) is shifted 2.5 inches up to account for the helmet

  • This is to help prevent and mitigate whiplash injuries from occurring in a rear impact collision

Seatpan

 Click here to expand...

Widths

Location along the Length

Minimum Recommended Width (mm)

Back (where seatpan and seatback connect)

460mm

Front

525mm

[6]

Length:

  • Length of seatpan: 440mm [4]

    • Measured along the thigh line from depressed seatback cushion contour to edge of seat

  • Distance between end of seatpan and back of occupant knee: 25.4mm - 101.6mm  [4]

    • After placing occupant model into the seat model, use this measurement to double check if length is appropriate

    • If for some reason the 440mm seatpan length comes into conflict with this measurement,  this measurement takes precedence over the 440mm seatpan length (i.e. change the seatpan length value so that this distance between end of seatpan and back of occupant knee is within 25.4mm - 101.6mm for all occupants who will sit in the seat)

Bolsters

 Click here to expand...

Seatback Bolsters Height: Maximum 288mm above H Point  [4]

NOTE: All dimensions (below the one above) in the bolsters section are NOT explicit recommendations, rather these are values taken from a 1990 Nissan Maxima Seat 

Please take these values with caution - the purpose of these measurements is to give a ballpark number of dimensions for bolsters.

While the below measurements are from a 1990 Nissan Maxima Seat, Appendix A within source 9 also has these measurements for seats from the following cars: 1990 Chevrolet Camaro, 1990 Nissan 240SX, 1990 Cadillac Seville. The dimensions for the Nissan Maxima were used as they seemed to be the most appropriate though looking at the dimensions for the seats from the other vehicles can give an intuition as to the range of dimensions for bolsters

  • Schematic Diagram of a typical production car seat  [9]

    • Section C represents H Point as viewed on the seatpan

    • Section D represents H Point as viewed on the seatback

Seatback Bolsters  [9]

  • NOTE: Main width is superseded by the other recommended seatback widths in this document, they are only used to calculate the angle of the side bolsters in this case


Depth

Inside Width

Outside Width

Main Width

Section D

41mm

432mm

514mm

292mm

Section E

64mm

457mm

521mm

292mm

Section F

74mm

457mm

521mm

292mm

  • Rough Angle of Side Bolsters (with respect to horizontal)


Angles

Section D

120.3581

Section E

127.8028

Section F

131.8911

Seatpan Bolsters  [9]

NOTE: Main Cushion width is superseded by the other recommended seatpan widths, they are only used to calculate the angle of the seatpan bolsters in this case


Cushion Depth

Inside Cushion Width

Outside Cushion Width

Main Cushion Width

Section A

56mm

432mm

508mm

279mm

Section B

53mm

419mm

483mm

279mm

Section C

43mm

381mm

470mm

279mm


  • Rough Angle of Seatpan Bolsters (with respect to horizontal)


Angles

Section A

126.2051

Section B

127.1309

Section C

130.1355


Foam Stiffness

 This section describes a way to approximate how much the foam will compress and what foam stiffness to use for the seat

To approximate the stiffness of the foam needed (if there is a desired compression), the formula below can be used  [4]  (Note: This will give the 50% ILD/IFD value in Newtons)

T = maximum thickness of the foam (mm or inches)

P = peak pressure

Type of Occupant

Peak Pressure (psi)

Small

1

Medium

1.25

Large

1.5

Source 4 did not specify what qualifies as a small, medium or large occupant. thus it was assumed

  • Small = 5th Percentile Male/Female

  • Medium = 50th Percentile Male/Female

  • Large = 95th Percentile Male/Female

C = the amount of compression (in same units as T )

0.0462 = conversion from psi to N

Below is a sample calculation:

  • We have a large sitter (95th Percentile Male/Female) - peak pressure is 1.5 psi

  • Max thickness is 58mm of cushioning

  • We want 32mm of compression

    To convert to pound-force (divide by 4.448)

    To determine the compression (with a known stiffness of foam), the above formula can be rearranged into:

    With ILD representing the 50% ILD value in Newtons

Pressure Distribution

 Click here to expand...

Being able to measure the pressure distribution when the occupant is in the seat requires specific equipment and/or specific software that can simulate this. Thus, the information in this section is mainly to give an intuition of what to aim for rather than something that can be actively measured against

  • Preferred pressure distribution across multiple areas of the occupant’s body  [5]

      • Below is more specifics on the distribution of pressure that largely corroborates the table from source 5

        • Pressure should not be directly on the spine, rather it should be on either side of the spine  [4]

        • Highest pressure (in the seatback area) should be at the apex of the lumbar support - or around 150mm above the H Point  [4]

        • Beyond the 325mm line above the H Point there should be minimal pressure  [4]

          • This is why the seatback and cushioning should largely be flat above the 325mm line

        • Highest pressure (in the seatpan area) should be at the area of the Ischial Tuberosities (these muscles are most resistant to pressure)  [4]

          • Ischial Tuberosities bones shown in red below

            • From 200mm in front of the H Point - to the front of the seatpan, pressure should be minimal  [6]

  • Pressure should be distributed as evenly as possible, as opposed to local concentrated areas [6]

    • Softer cushioning can achieve this  [6]

      • However too soft of cushioning used will prevent the driver from performing small changes in seat position, leading to pressure buildup and discomfort

Cover Material / Trim

 Click here to expand...

Temperature Regulation [6]

  • If bare skin will be touching the cover material, the material should not go above 33°C 1.4°C during operation

  • Minimum surface heat flux of cover material: 75W/m^2

    • Perforating the cover material in specific areas can greatly increase its surface heat flux value

Sources

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