Transmission of vertical vibration through a seat: Effect of thickness of foam cushions at the seat pan and the backrest

Abstract The perception of vehicle ride comfort is influenced by the dynamic performance of full-depth foam used in many vehicle seats. The effects of the thickness of foam on the dynamic stiffness (i.e., stiffness and damping as a function of frequency) of foam cushions with three thicknesses (60, 80, and 100 mm), and the vibration transmitted through these cushions at the seat pan and the backrest were measured with 12 subjects (6 males and 6 females). With increasing thickness, the stiffness and the damping of the foam decreased. With increasing thickness of foam at the seat pan, the resonance frequencies around 4 Hz in the vertical in-line and fore-and-aft cross-axis transmissibilities of the seat pan cushion and the backrest cushion decreased. For the conditions investigated, it is concluded that the thickness of foam at a vertical backrest has little effect on the vertical in-line or fore-and-aft cross-axis transmissibilities of the foam at either the seat pan or the backrest. The frequencies of the primary resonances around 4 Hz in the vertical in-line transmissibility and the fore-and-aft cross-axis transmissibility of foam at the seat pan were highly correlated. Compared to sitting on a rigid seat pan with a foam backrest, sitting with foam at both the seat pan and the backrest reduced the resonance frequency in the vertical in-line transmissibility of the backrest foam and increased the associated transmissibility at resonance, while the fore-and-aft cross-axis transmissibility of the backrest was little affected. Compared to sitting without a backrest, sitting with a rigid vertical backrest increased the resonance frequency of the fore-and-aft cross-axis transmissibility of the seat pan cushion and increased the transmissibility at resonance. Relevance to industry The transmissibility of a seat is determined by the dynamic properties of the occupant of the seat and the dynamic properties of the seat. This study shows how the thicknesses of foam at a seat pan and foam at a backrest affect the in-line and cross-axis transmissibilities of the foams at the seat pan and the backrest. The findings have application to the design of vehicle seats to minimise the transmission of vibration to the body.

[1]  Brian R. Mace.  Statistical energy analysis, energy distribution models and system modes , 2003 .

[2]  Michael J. Griffin,et al.  Seat Dynamics and Passenger Comfort , 1989 .

[3]  Michael J. Griffin,et al.  The transmission of vertical vibration through seats: Influence of the characteristics of the human body , 2011 .

[4]  Michael J. Griffin,et al.  Nonlinearity in the vertical transmissibility of seating: the role of the human body apparent mass and seat dynamic stiffness , 2013 .

[5]  Michael J. Griffin,et al.  Vertical and dual-axis vibration of the seated human body: Nonlinearity, cross-axis coupling, and associations between resonances in transmissibility and apparent mass , 2012 .

[6]  M. Ashby,et al.  Cellular solids: Structure & properties , 1988 .

[7]  M J Griffin,et al.  The apparent mass of the seated human body: vertical vibration. , 1989, Journal of biomechanics.

[8]  Lanzhu Zhang,et al.  Measurement and identification of dynamic properties of flexible polyurethane foam , 2011 .

[9]  L. Wei,et al.  THE PREDICITON OF SEAT TRANSMISSIBILITY FROM MEASURES OF SEAT IMPEDANCE , 1998 .

[10]  M J Griffin,et al.  Qualitative models of seat discomfort including static and dynamic factors , 2000, Ergonomics.

[11]  Michael J. Griffin,et al.  Non-linear dual-axis biodynamic response to vertical whole-body vibration , 2003 .

[12]  M J Griffin,et al.  Factors affecting static seat cushion comfort , 2001, Ergonomics.

[13]  Michael J Griffin,et al.  Biodynamic responses of the seated human body to single-axis and dual-axis vibration. , 2010, Industrial health.

[14]  Michael J. Griffin,et al.  Handbook of Human Vibration , 1990 .

[15]  M. Griffin,et al.  Quantitative prediction of overall seat discomfort , 2000, Ergonomics.

[16]  Changki Mo,et al.  A VIBRATIONAL MODEL OF OPEN CELLED POLYURETHANE FOAM AUTOMOTIVE SEAT CUSHIONS , 1998 .

[17]  Ion Stiharu,et al.  Seated occupant interactions with seat backrest and pan, and biodynamic responses under vertical vibration , 2006 .

[18]  Rong Deng,et al.  Flexible polyurethane foam modelling and identification of viscoelastic parameters for automotive seating applications , 2003 .

[19]  Michael J. Griffin,et al.  Apparent mass of the human body in the vertical direction: Effect of seat backrest , 2009 .

[20]  M. Griffin,et al.  Resonance behaviour of the seated human body and effects of posture. , 1997, Journal of biomechanics.

[21]  Horst Peter Wölfel,et al.  Apparent mass of seated men : determination with single- and multi-axis excitations at different magnitudes , 2006 .

[22]  N. C. Hilyard,et al.  Mechanics of cellular plastics , 1982 .

[23]  E. Huygens,et al.  MDI comfort cushioning for automotive applications , 1994 .

[24]  Michael J. Griffin,et al.  Measuring Vibration on Soft Seats , 1977 .

[25]  M. Griffin,et al.  MOVEMENT OF THE UPPER-BODY OF SEATED SUBJECTS EXPOSED TO VERTICAL WHOLE-BODY VIBRATION AT THE PRINCIPAL RESONANCE FREQUENCY , 1998 .

[26]  Anil K. Bajaj,et al.  Nonlinear multi-body dynamic modeling of seat-occupant system with polyurethane seat and H-point prediction , 2008 .

[27]  M. Griffin,et al.  A MODAL ANALYSIS OF WHOLE-BODY VERTICAL VIBRATION, USING A FINITE ELEMENT MODEL OF THE HUMAN BODY , 1997 .

[28]  Mike Kolich,et al.  Automotive seating: the effect of foam physical properties on occupied vertical vibration transmissibility , 2005 .

[29]  Michael J. Griffin,et al.  Tri-axial forces at the seat and backrest during whole-body vertical vibration , 2004 .