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, studies and studiespublished 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

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title	Click here to expand	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 Lap 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 poundspound-force
- European measurements are in newtons

Occupant Geometry

Desired

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

Image Modified

[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	58.559
50th Percentile Female	122	77.581
99th Percentile Female	132	97.7999

1st Percentile Male	104	61.566
50th Percentile Male	122	8086
99th Percentile Male	135	98.597

[11]

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

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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
- - 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 Prominence for fixed lumbar support of this typethat can adjust its : 15-20mm
- Radius for lumbar support of this type that can adjust its radius (separate from adjusting the height of the apex): 240mm 250mm - 400mm
- Note: Guidelines for the prominence of the lumbar support still apply with this type of undepressed seatback cushion contourProminence for radius adjustable lumbar support of this type: 0-30mm

Headrest (guidelines in the headrest section are

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safety related and should be

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**explicitly followed*)**

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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]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

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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

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title	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

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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