1. Virtual Seat Design at Vehicle Concept
Mac Reynolds, Ph.D.
Professor Emeritus, Michigan State University
CEO, ERL LLC
Thanks for the opportunity to speak about virtual seat design at vehicle concept. Please note that I am a Retired Professor from MSU, not UM.
We are gathered here to talk about seat comfort and seat design. Interestingly, everyone can design a seat, just like everyone can hit a golf ball. But how many who can hit a golf ball to win money on the Tour? Not many, just like seat design. Both are very simple yet present very difficult problems.
The seat has to meet the same function for all drivers but has to look different for all cars. Seems to be a little bit of a conflict which again reminds me of golf—to hit the ball you have to relax and concentrate at the same time. Oxymorons, so how do we design seats for the same global driver function yet make them unique for the car model.
Today, I’d like to offer a new path to a solution that has been a struggle to achieve.

2. Seats and Sitting Seat position accommodates body size
Sitting is a driver preferred posture
Design sitting seat at concept for comfort
First, the design of interiors uses a position model based primarily on body size. Unfortunately, drivers use seated posture of the back to position themselves for the driving task. Sitting posture, in fact, affects seat position.
Second, seat design should be based on a model that accommodates how drivers sit to perform the driving task—operate the car with good vision. With virtual drivers that represent this functional behavior, seat design can start at vehicle concept before ergonomics and safety have already defined the interior on the basis of position models.
Third, the car exterior and interior can be designed in parallel, as opposed, to the linear model used today. This parallel development is possible only through the use of virtual models in CAD that provide objective representation of driver behavior, rather than relying solely upon the subjective experience of engineers and consumers.
Currently, ergonomic models and safety define the interior on the basis of position models. For comfort, then we need to start at vehicle concept before ergonomics and safety have defined the interior on the basis of these position models.

3. Evolution of driver seat design
Ergonomics
1893
Comfort
We evolved from the horse and buggy to the car. Interestingly, the Duryea car, built in 1893, used a wagon for a car body and the driver sat on the right hand side steering the car with a handle. The focus of the first car was to replace the horse and only eventually did we reach a point that comfort for the driver and passengers was a consideration.
Comfort began initially as an enclosure for driver and passengers, particularly with the Model T when it became a car for the masses. The focus remained on a loose definition of comfort until 1967 when DOT first released FMVSS that defined safety relative to driver and passenger positions. Certainly uncontested, but here we are today still trying to find a way to develop and design a comfortable seats that meet the requirements of safety and ergonomics.
1967
Safety
2012

4. 19th Century Seats Passenger Comfort Driver Ergonomics
In the 19th century and before, passenger comfort was more important than driver comfort. At some point in the development of horse drawn vehicles, however, it was realized that the driver had an ergonomic workstation. So, the seat was developed as well as a floor board orientation to support the driver in position to control the horses from the right hand side. Very important to be able to rein in the horses. No brakes or accelerator pedal, just reins and body weight against the pull of the horse.

5. Today, car designed and built before any driver sits in driver’s seat.
Today, the car is designed and built before any driver sits in the driver’s position. This statement is true because the act of sitting requires a seat that supports body weight. And, the only way for a driver and passengers to sit in the car before it is built is through the use of digital human body models and virtual seats in virtual cars. There are no models but ERL that uses virtual drivers to design a virtual seat in a virtual car.
Then, you might ask, why design a virtual seat at vehicle concept. In my opinion, there are two answers—Cost efficiency and driver comfort space established for engineers to protect while developing the car.

6. Seats designed by iteration for position and comfort
Source most useful for seat design and development? (LinkedIn Survey)
Experience
15 (48%)
Consumer surveys
6 (19%)
Driver ride tests
2 ( 6%)
DHM software
5 (16%)
Other
3 (10%)
Seats designed by iteration for position and comfort
In the current process, seats are designed in a position model either by iterations which optimize a subjective evaluation of driver comfort or rules from the OEM. The seat is verified by position tests: H-point and 202a, for example. The success of the solution is based primarily on experience as shown in the table. This LinkedIn survey is not scientific nor representative but merely illustrative. I asked the question in the Automotive Seating Group and 31 of the 2014 members replied and half of them rely on experience. This, in my mind, is not significantly different from the process that developed the Bel Aire seats in the 1950s and is the basic process for the Lexus seats in We know that all drivers want a comfortable experience behind the wheel but why in 2012 do we still base approximately 75% of seat design for comfort on experience, consumer surveys and driver ride tests? In today’s world, this seems very much out of date.

7. Virtual Contentment?
We think we know seated contentment when we see it, but is this really how the dog wants to sit or is this the seat the dog sits in?

8. Drivers evaluate car seats!
Drivers evaluate the seat. They adapt and sit in the seat as it is. Certainly, drivers provide critically important evaluation, but how do drivers evaluate the seat? The drivers can only base their evaluation on subjective opinions and these are biased by halo effects and their personal interface with the vehicle which is dependent upon body size and functional anatomy for the driving task.

9. Who are the drivers? Experts in prototype seats
Experts in production vehicles
Owners in production vehicles
These subjective opinions come from drivers who are either experts or owners. In the prototype seats, drivers are experts who subjectively test the seat in a mule vehicle. Then, when the vehicles are in production, experts at Consumer Reports, Motor Wheel, Detroit Free Press, etc. evaluate the seats in their review of the cars. Lastly, owners, who have the ultimate halo effect of financial investment, evaluate the vehicles through surveys. This is the state of seat evaluation and development. Let me show you an example of an expert who could have participated in the prototype seat development.

10. Small Female Expert in Production Vehicle says,
“…cushion - a little long
…head rest - a little hard to move, orientation bad
…too close to steering wheel
…back rest lateral too low and are pushing my arms”
Comfort Score: 3.5/5.0

11. Digital Human Model (DHM) in Production Vehicle says,
Virtual output:
Cushion too long;
Head restraint too close;
SW too close;
Seatback wings wide;
Cushion wide;
Pedal too far
Comfort Score 3.65/5.0
This small female virtual driver in the production vehicle shows how the small expert was sitting. The software outputs almost the same comments and calculated a 3.65 seat comfort score on a 5.0 scale. Now, if the data from this validation study had been known during development or the seat had been developed at vehicle concept, would the small female driver still have these issues? I don’t know, but it is certainly an interesting question for the use of digital human models because it would have given the manufacturer a choice.
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

12. DHM Represents Driver
Thus, digital human body models can represent the driver at vehicle concept to design a virtual seat that
minimizes sources of discomfort,
grades the seating package with an objective comfort score and
evaluates changes proposed in development at the OEM and/or Supplier.
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

13. Seat at Vehicle Concept
A virtual surface that deflects under body weight distributed
in preferred driving postures.
Now, what is a virtual seat at vehicle concept? A virtual surface that deflects under body weight distributed in preferred driving postures of the driver population. Remember, sitting requires a surface that supports body weight. The digital human models that are used by the industry today are either missing the act of sitting or the act of driving. Seat design for the driver requires not only a digital representation of the driver, but also the components of the driving task as well as a seat that supports the driver in this task. So what exactly is a virtual seat design?

14. Virtual Seat Design
Size, Shape and Stiffness of sitting surface on seat frame for all occupants.
A virtual seat design has the size, shape and stiffness of a sitting surface on a frame that are defined by regions (or patches) that represent equivalent anatomical locations for all drivers, independent of body size, gender or posture. To be applicable for the automobile where all drivers sit in the same seat to operate the vehicle, the seat size, shape and stiffness requirements must meet the needs of all drivers. Ok, so how do you do this at vehicle concept when all drivers are different in body size and shape. Well, the answer lies in the use of math models.

15. Models at Vehicle Concept
Digital Human (DHM)
Seat for Position and Posture
Interior Space & Controls
Comfort Score
Optimization
To use a design tool at vehicle concept to design a seat for the population, a number of models are needed.
First, digital human body models that represent the population of drivers must be defined by anatomical landmarks and a deflected shape of the seated body.
Second, a seat sitting model must be developed that consists of a load deflection model of the sitting surface on a frame.
Third, the task of operating the vehicle that the seated driver performs must be defined by controls for reach and targets for up and downward vision for which the driver finds an optimal seat position.
Finally, to provide a measure of objectivity to the results, a comfort model based on the math in the solution must be developed and validated.
All of this is used in a non-linear optimization engine to develop a virtual seat and adjustments for the population.

16. DHM Body Size & Back Posture
In order to design a seat that fits the population, the digital human body models need to represent at least body sizes and seated postures in the adult drivers. Now, there may be much discussion regarding the use of boundary manikins, but at the initial stage of a seating surface in the vehicle concept, there is little need for greater definition of the population. The biggest need in this boundary approach is actually not in representing body size, but in representing back postures. Please note the differences in back shape from buttocks to head in the illustration.
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

17. Unique Attributes of DHMsL4
In order to use DHMs to design a seat, comparable points are needed in all models. These comparable landmarks are defined by skeletal landmarks. With the skeletal landmarks, a biomechanical model that defines load bearing points and contact points in the seat can be created that is equivalent for all drivers. Thus, L4, or L2 in Japan, is used to define the location of lumbar support needed by all drivers. In addition, to create a manikin that represents the solid body in a seat that deflects under load, a set of landmarks are needed to create a systematically comparable representation of the body in each of the small to large body manikins. For example, the surface under the pelvis is defined at the pelvis ischium where the greatest load of the body is applied in sitting. This comparability allows for the measurement and definition of a deflected tissue shape that varies by body size and gender, but is equivalent in location in the seat. Thus, the seat deflection, insert width, and wings are all represented by deflected tissue shapes of the small female, medium male and large male.
Hip
Thigh CG IT
Deflected Tissue Shape
Skeletal Landmarks
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

18. Seat Sitting Model Load-Bearing Patch in Seat (L)
Head
Shoulders (T4)
Chest (T8)
Lumbar (L4)
A seat sitting model represents the biomechanical and ergonomic interface of the driver to the vehicle. Although the seat cushion and back are composed of continuous surfaces, the functional interface to the body is not the same throughout these surfaces. Load-bearing regions support body weight. Contact regions at the front of the seat provide a feeling of seat length, but space at the buttocks, shoulder and head in the seat back accommodates different postures and activities of the driver. For example, the cushion supports a large proportion of torso weight under the ischial tuberosities (IT in the figure) and to give the driver a feeling of support, the seat must support the weight of the thigh and make contact as far down the thigh as possible without interfering with the calf which is extended to reach the pedal. The head restraint, shoulder and buttocks region in the seat back are not to make contact with the driver, but need to be within a limited distance from the driver’s body. To optimize a sitting surface that fits the population of drivers, the same set of anatomical landmarks in all digital human models must be used to define equivalent support and contact regions in the seat for all drivers. Thus, seat design is based upon the same set of support and contact criteria for all drivers. The size and shape of the seat is defined by this interaction between landmarks and the sitting surface.
These patches provide boundary conditions for stylists to use in creating a seat appearance for the car that is comfortable for all drivers.
Front of Thigh
Buttocks (Hip)
Thigh CG
Pelvis (IT)
Load-Bearing Patch in Seat (L)
Seat Contact Patch in Seat (C)
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

19. Body Size & Posture defines Seat Patch
Patch Position on STO Seat Surface
Ischial Cross Section
Wing
In the seat sitting model, a group of small surfaces are defined on the STO that represent where drivers sit. The key to this process is the use of comparable anatomical landmarks.
The illustration shows development of the ischial patch under the pelvis. A biomechanical model calculates the distribution of body weight and a load deflection model of the seat calculates the deflection at the ischial tuberosites under body weight. The math model finds a surface within +/- 2 mm for all occupants sitting in the seat that deflects under the same landmark at the ischial tuberosity. The initial coordinates of this surface are defined by the user, but the optimization algorithm defines the coordinates on the STO surface that meets the +/- 2mm boundary conditions. This surface is on the STO and we call it a patch.
Deflection
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

20. Virtual Seat Engineering
Body
Frame
Foam Manufacturability
Meat-to-Metal
Penetration
There are a few unique properties of the sitting surface relative to the frame and driver that are needed for seat engineering. For the virtual seating surface to represent realistic boundaries for styling and engineering to use in developing the interior, the surface must be developed for a frame as well as the driver sitting in it. Thus, measurements of wing penetration, meat-to-metal and foam manufacturability are needed to verify that the surface represents boundaries that can be built for comfort.
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

21. Interior Space & Controls
Line of Sight
Reach
The position of the driver is defined by three components of the vehicle interior: reach to controls, vision and seat. The driver only has joint angles in the limbs and back for use to fit into this space. Thus, the joint angles are important but also the needs of the driver’s unique size and personal posture preference are equally important to define an interior that will accommodate each driver well as possible. The ideal would be equal, but that will rarely happen.
Seat
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

22. Reach & FMVSS 202a
Since reach is more than to the steering wheel, a globographic description of reach is also needed. At this point in the vehicle concept, safety is mainly structural. By incorporating FMVSS regulations, such as 202a and others, the geometric information needed by Tier 1, 2 and 3 suppliers is available for their preparation to manufacture parts that will meet the comfort and safety needs of all drivers.
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

23. USA & Northern Europe Comfort Score
TOTAL Score: 7.70
Seat Cushion: 4.78
Cushion contact length is short. (Rating: 1.03)
Cushion provides not enough thigh support. (Rating: 1.34)
Cushion insert stiffness is just right. (Rating: 0.00)
Seat Back: 8.77
The upper seat back is just right. (Rating: 0.01)
Overall Wing shape provides good support. (Rating: 0.03)
Seat back Insert shape provides good support. (Rating: 0.28)
Seat back insert stiffness is just right. (Rating: 0.07)
Head Restraint patch contact is far. (Rating: 0.86)
Lumbar patch contact is just right. (Rating: 0.31)
Package: 9.82
Travel window requires no additional travel. (Rating: 0.00)
Package provides comfortable head room. (Rating: 0.01)
Seat can support driver vision requirements. (Rating: 0.00)
Steering Wheel to chest is just right. (Rating: 0.06)
Steering Wheel to thigh is just right. (Rating: 0.00)
Driver can comfortably reach pedal. (Rating: 0.20)
Penalty Seat: 0.8 % Package: 1.6 %
USA & Northern Europe Comfort Score
The comfort score is based upon measurements in the math data of each of the DHMs in the seating package for the dimensions listed. In this example, the score is calculated for a US & Northern Europe population distribution of small, medium and large drivers.
The seat cushion, back and package are individually scored and if the seat or package adversely affects joint angles, a penalty is calculated for the comfort score. The comfort score is derived from 15 measurements representing the interface between driver and seating package. In this particular example, the cushion is at a stop development while the back and package are reasonably well designed for the driver. The penalties correspond to the seat design primarily for the back (hip and neck angles) and the package focuses on the limb angles (elbow and knee).
USA
TOTAL
Cushion
Back
Package
TOTAL (1-10)
7.70
4.78
8.77
9.82
Small Female
6.65
5.50
8.37
8.27
Medium Male
7.91
4.89
8.83
10.00
Large Male
7.26
3.20
8.72
9.93
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

24. Global Drivers Body Size
These graphs represent the distribution of stature, or standing height, in populations representing Japan, Italy, USA and Germany. You can see that the USA and Germany (i.e. Northern Europe) are very similar. This graph is composed of both men and women. Please note that it is a theoretical distribution calculated from combining the data in People Size 2000 for each of the four countries represented in those data. In general, the only differences are at the large and small ends of the distribution. That is, there are smaller people in Italy and Japan than in the US as there are larger people in the US and Germany than in Japan and Italy. However, after watching the Olympics a few weeks ago, is that true or are we making a very big assumption that designs need to accommodate body sizes that are actually not present in some countries. I think the question is more directed at the range that we want to accommodate in the car interior rather than the particular national population.
Now, some may object to combining male and female data but cars are built for drivers independent of gender. I’ve never seen a car labeled for men only. I’ve driving some that only large people can drive, but there are large women as well as large Japanese. Body size in design for the automotive industry needs to be re-examined in the face of non-gender specific anthropometrics. 24

25. Validate Model & Comfort Score
Lux Sedan
Mid Sedan
Mid Xover
Mid SUV
FST
Sm Xover
Above all else, the model must be validated by testing against the subjective results of drivers. Regardless of the scientific depth or quality, until the model is shown to perform as humans, it is of little value. After this level of performance is demonstrated, then the model has to be used to demonstrate its value as a tool. At this point, I know of no other digital human body model that has been validated by comparing its comfort score to the subjective driver’s scores. Thus, this validation of the ERL design tool sets a standard against which other models will need to meet or improve.
Sm Sedan

26. Global Drivers have Universal Needs
Vision
Operate Controls
Sitting comfort
All global drivers have the same universal needs: vision, reach to safely operate the controls, and sitting comfort. Difference in how drivers sit in the seat are primarily based on body size, personal posture preference and driving conditions.

27. Driving Conditions affect Cultural Behaviors
As we go around the world, we find that there are environmental differences in roads and weather that have a great influence on how drivers want to sit in the car. When the conditions are difficult, most drivers will take a more alert posture. When the conditions are good, most drivers will take a more relaxed posture to operate the car. What does this mean?

28. Skeletal postures represent “cultural” behaviors
Alert
Neutral
Relaxed
44.4 mm
An alert posture is an erect posture. A relaxed posture is a slumped posture. The effect of these postures on eye height is rather dramatic. When applied to small and large bodies, these eye height effects are critical. The small driver wants to sit more upright all the time, primarily for vision. The large driver can sit more relaxed, even when driving in conditions that call for a more alert posture, because the headroom is not sufficient in some vehicles for either a neutral, much less an erect posture.
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

29. Posture affects Packaging
(+)
20 mm
Neutral Seat Position
(-)
You can see in this illustration, the effect that posture has on seat position. If the seat is designed to accommodate a more upright posture, there is a direct correlation with the shape of the seat and sitting posture that affects seat position by the driver.
These data come from measurements in drive studies conducted at MSU in The last drive was to measure the effect of seat modifications shown.
Slumped Seat Position
Seat position:
19 mm forward

30. Competitive Vehicles in USA (Medium 50th %tile Male)
Saab 9-5
VW Passat
Cushion thigh region provides
Cushion ischial insert width is
Cushion thigh insert width is
Seatback shoulder region is
Head restraint surface is
no support
too much pressure
too narrow
too wide
too narrow
too wide
Seat design and seating comfort are basically an A/B comparison. There is the design (A) and then the competition (B). To have these data in math at vehicle concept would be extremely valuable in making decisions regarding car features and cost.
In this comparison, the medium male is compared in the two vehicles. In general, the medium male has reasonable comfort in the seat, except for the seat back in the Saab 9-5 which is not good compared to the VW Passat.
Data for the small female and large male would also be available as well as a total score the population as weighted by proportional distribution of body sizes and postural preferences.
too narrow
too wide
too far
too close
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

31. Design for Comfort in Math STARTS at Vehicle Concept
The ability to design for the driver in parallel with the manufactured components of the vehicle can only come from the use of digital human models used at the beginning of the vehicle design at concept. This starting point is important because it gives the Tier 1, 2, and 3 suppliers time to ramp up to manufacture a part that may have slightly different geometry than previously used. This obviously affects safety, ergonomics and comfort, but given the start at vehicle concept, there is time and resources to test and evaluate the effects on the overall design while generating a vehicle that will satisfy a larger proportion of the market than the current process.
US Patents: #6,840,125, #7,047,831, #7,347,114, #7,797,138

32. Conclusion Objectivity Driver comfort at concept
I don’t know how any individual wants to sit. I only know the ranges of sitting behaviors that the seat needs to support. Thus, I believe that we must define boundary conditions that encompass these driver behaviors objectively.
The industry largely relies on position for seat design but often asks why seats are so variable. My answer—seat design misses the objectivity criteria in its design and development activities. Using a virtual tool at vehicle concept that designs seats and calculates a comfort based on the results for comparison with a math score of measured competition will be very valuable to in reducing this variability.
In addition, the car exterior and interior can be designed in parallel, as opposed, to the linear model used today. This parallel development is possible only through the use of virtual modeling efforts in CAD but the benefits to consumer and manufacturer are enormous. Primarily because they bring objective tools to represent the driver, rather than relying solely upon the subjective experience of engineers and consumers.
In the current process, I have been informed by one seating engineer at an OEM that seats are the 2nd most expensive and the last component developed in the car. They are largely ignored when compared to exterior appearance, power train and fuels. They are typically developed with prototype seats that are built and tested iteratively with real drivers. By this time, the effects of posture are too late to accommodate because ergonomics and safety have already defined the seating package for the driver.

33. Acknowledgements ERL LLC (Ray Brodeur, D.C., Ph.D., et al.)
Michigan State University (George Stockman, Ph.D., et al.)
General Motors Corporation (Don Maertens, et al.)
I would like to acknowledge the contributions of many people. However, the list is too long and I have simply pointed out contributors who played a significant role in this research, development and business. One of the most important people in this list is Don Maertens. He, unfortunately, has passed away, but his contributions cannot go without comment. I am incredibly indebted to his support and contributions to the research at MSU and the start-up of ERL LLC in 2000.
I want to acknowledge General Motors Corporation, the old one, for their support in getting this effort started at MSU, without their help I wouldn’t have all this information to share today. I also want to thank all the staff members that worked at ERL over the years in taking an idea and developing it into a new approach to meeting the needs of the automobile user. The tools, software and processers that move the operator from the role of a afterthought into the front seat at the conception of a new vehicle are the result of their efforts.  I thank them all and hope that this effort will move forward as computer aided design has done and become a standard part of automobile design.