Overview

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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!

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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

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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, 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

Occupant Geometry

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Desired

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title Click here to expand	This section describes the desired angles between the legs, torso, head etc. of the occupant
Image Modified [4]

Location of H Point

Seatback (Structure)

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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)

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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 Image RemovedImage Added 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  Image RemovedImage RemovedImage AddedImage Added 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 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 60mm below the top of the occupants head  the helmet the occupant is wearing (helmets may add 2 inches - 2.5 inches in additional height to the occupant) [8] Image Removed This is to help prevent and mitigate whiplash injuries from occurring in a 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 Image Added This is to help prevent and mitigate whiplash injuries from occurring in a rear impact collision

Seatpan

Bolsters

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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 Image RemovedImage Added 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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To approximate the

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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

Pressure Distribution

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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 Image RemovedImage Added 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

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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

Sources