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 pounds-force

  • European measurements are in newtons

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

[4]

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

[11]

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

Widths

[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

• Based on diagram below

[4]

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

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

  • 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

    
    

    

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 parallel to the top of the occupants head  [8]

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

Widths

[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)

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

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

  • 

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

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

  • 

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

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
  

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

Temperature Regulation [6]

• If bare skin will be touching the cover material, the material should not go above33°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

[1] https://ijret.org/volumes/2015v04/i06/IJRET20150406076.pdf 

[2] https://www.academia.edu/24947390/AUTOMOTIVE_SEAT_DESIGN_BASIC_ASPECTS

[3] Design specifications and ergonomic evaluation of car seat (A review) - A Jhinkwan, J Singh - 2014

[4] https://deepblue.lib.umich.edu/bitstream/handle/2027.42/1114/88879.0001.001.pdf?sequence=2 

[5] https://books.google.ca/books?hl=en&lr=&id=Kf0ubyntMZ0C&oi=fnd&pg=PA231&dq=automotive+seat+guidelines&ots=n2RFt6_Gx6&sig=iHhwXU79GqIhhaU35sJUAadgItI#v=onepage&q&f=false 

[6] https://www.researchgate.net/profile/Matthew_Reed/publication/30817199_Survey_of_auto_seat_design_recommendations_for_improved_comfort/links/00b4952b47b66354fb000000.pdf 

[7] https://www.ewiworks.com/wp-content/uploads/2017/12/ChairStandards_Report.pdf 

[8] https://trl.co.uk/sites/default/files/INS008_secure.pdf 

[9] https://deepblue.lib.umich.edu/bitstream/handle/2027.42/918/81163.0001.001.pdf?sequence=2 

[10] https://www2.tc.gc.ca/media/documents/roadsafety/202_tsd_rev_1r.pdf 

[11] The Measure of Man and Women - Alvin R. Tilley, Henry Dreyfuss Associates