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Measuring Seating Comfort

A central question in the development of new seats is the seat comfort. Developers are very concerned about ways to measure the comfort objectively. Therefore, the focus of developers are models that establish a relationship between objective measures and subjective sensation which allows a virtual prediction of seat comfort. Mergl considers the measurement variables posture, microclimate, vibration and pressure distribution for detecting the seating comfort. He comes to the conclusion that the pressure distribution is the best parameter for determining the seat (dis)comfort in seat development.

Different aspects of seating comfort

Figure 1: Seating comfort (Click to enlarge)

Possible ways of measuring seating discomfort (see de Looze et al., 2003)

• Posture
• Microclimate
• Vibrations
• Pressure distribution

Comfort – Discomfort

Figure 2: Where does it start the discomfort? Source: Zhang and Helander (1996) (Click to enlarge)

Posture

Figure 3: Parameters of posture in a car (Click to enlarge)

Posture - basics

• There‘s an optimum range for each joint
• Determined by concept development of OEM by positions of
  • Steering column
  • Pedals
  • Seating Reference Point

Posture - Summary

• Posture is essential for seating comfort
• Small influence for seat developers
• Prediction of discomfort is possible (e.g. with digital human models). It‘s possible to optimize posture in virtual reality

Figure 4: Posture - Summary (Click to enlarge)

Microclimate

Figure 5: Microclimate – Overview
Source: BG Verkehr, BGI 7005 (Click to enlarge)

Aspects of microclimate

• Global thermal comfort
• Local thermal comfort
  • Draft
  • Asymmetric heat radiation
  • Vertical temperature gradient
  • Microclimate on seat
• Order of importance
  • Air condition in car has to ensure good global and local thermal comfort
  • Seat ventilation has to ensure good microclimate on seat. Temperature and humidity below limits, without draft.

Microclimate - Summary

• Trim has a big influence – if possible take textile fabric
• Measurement on seat prototypes possible – car environment is important
• Simulation is very complex
• Finding of useable correlations between objective measure and comfort in progress (vgl. FAT 257, 2013)
• Comparison with reference seat is possible

Figure 6: Thermal Dummy STAN (Click to enlarge)

Vibrations

Figure 7: Parameters of vibrations (Click to enlarge)

Figure 8: Measure Vibrations (Click to enlarge)

Vibrations - Summary

• Relationship to discomfort is known
• Measurement and simulation is possible (e.g. Pankoke 2013)
• Modifications of seat is hard to implement
  • Platform strategy for metal structures
  • Few available space in high end seats
  • Foam and trim can be optimized only in a small range

Pressure distribution

Figure 9:Pressure Distribution (Hartung 2006): (Click to enlarge)

• Basic research to objectify seating discomfort
• Questionnaire
• Evaluations with „0“ Discomfort. No correlation between pressure distribution and discomfort with seats of serial production.

Figure 10: Results (Mergl 2006) (Click to enlarge)

3 parameters are important:

• % of load
• Pmax
• Gradient

These results have been validated for short term and long term exposition.

Further validation of pressure distribution

Figure 11: Ideal pressure (Zenk 2009) (Click to enlarge)

Figure 12: Measuring with Pressure sensors Pressure sensors were implanted in a test subject. (Click to enlarge)

Summary pressure distribution

• Pressure distribution has direct influence on the pressure inside spinal discs; good pressure distribution leads to low pressure inside spinal discs.
• Developer can draw direct conclusion for the reason of discomfort
  • e.g. high pressure peak beneath buttocks can change foam parameters
  • no support of frontal thigh shows that seat pan is too short or too less tilt.
• These parameters can be directly influenced by seat developer.
• Seats can be optimized virtual with digital human models (e.g. Verver 2004)
• Measurement of pressure distribution can help to check quality in production (e.g. Pankoke 2013)

Figure 13: Further application of pressure distribution: Automatic seat adjustment (Zenk 2006) (Click to enlarge)

• Automatic seat adjustment by pressure distribution could be realized
• Validation of the adjustment was successfull (Pankoke 2013)

Design

Figure 14: Influence Design (Knoll 2006) (Click to enlarge)

What else can be done to get a comfortable seat?

• „Das Auge sitzt mit “ – liking has an influence on seating comfort
• Good ergonomics can be improved with good design

Summary

Seat developer has several measures for prediction of seating comfort

• Good posture should be ensured by concept development
• Pressure distribution is an important parameter for seat comfort and can be influenced by seat developer:
  • Travel ways of structure
  • Contour of foam
  • And can be used for quality management in production
• Design helps to build more comfortable seats