Chairs and seats – Bottom or back – Cushioned
Reexamination Certificate
2000-08-30
2002-10-01
Nelson, Jr., Milton (Department: 3636)
Chairs and seats
Bottom or back
Cushioned
C297SDIG001
Reexamination Certificate
active
06457777
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a seat cushion pad composed of polyurethane foam, especially a seat cushion pad for use of a vehicle, especially a car, where a vibration is accompanied with the use of the seat.
2. Description of the Related Art
With respect to the comfortability of a car seat cushion, JASO B-407 regulates a standard on the vibration transmissibility characteristics. For attainment of comfortable feeling, it is effective, in general, to remarkably damp the vibration in a frequency region that makes persons feel uncomfortable. The frequency of vibration that makes persons feel uncomfortable is in the region of 4-10 Hz, and the vibration transmissibility at 6 Hz is conventionally employed for estimating the degree of the uncomfortable feeling described the regulation in the JASO. It is said that the vibration at the frequency about 6 Hz tends to cause carsickness, especially. Therefore, also in the development of the car seat cushion pad composed of polyurethane, much effort are devoted to suppress the vibration transmissibility in such frequency region.
Japanese patent publication H03-140319(A1) discloses a polyurethane foam which have a lower resonance frequency than usual, so as to remove the uncomfortable feeling of seat cushion.
The seat cushion pad according to the above prior art, which has suppressed vibration transmissibility characteristics at 6 Hz, shows large resonance amplitude (resonance peak) at the frequency region of 2 to 4 Hz. Therefore, when person sitting on a seat cushion using such polyurethane foam disclosed in the prior arts, often feels an instability of the body according to the vibration while travelling. Namely, such polyurethane foam can not protect sufficiently the disagreeable feeling that person's body bounds up and down at a low frequency (feeling by shaking).
SUMMARY OF THE INVENTION
Accordingly, for the seat cushion pad for vehicle, a car for example, such characteristics listed below are required to prevent carsickness and fatigue of drivers and passengers.
i) suppressed vibration transmissibility characteristics at a frequency region about 6 Hz
ii) stability of the body of the person, who is sitting on the seat cushion and is driving the car
iii) a lower vibration transmissibility characteristics at a wider frequency region
However, according to a theory of a vibration engineering, in general, when the resonance amplitude in a vibration transmissibility characteristics at a frequency region of 2 to 4 Hz is lowered, the vibration transmissibility at a higher frequency (for example, 6 Hz), which is related to the agreeability of the seat cushion, increases. And the vibration transmissibility characteristics (vertical axis: vibration transmissibility; horizontal axis: frequency) shows broad curve as a whole. Namely, the lowering of the vibration transmissibility and the lowering of the resonance amplitude in a vibration transmissibility characteristics curve are contradictory requirements to each other.
Thus, the object of the present invention is to provide a seat cushion pad which shows lower resonance amplitude at 2-4 Hz and simultaneously shows the same or lower vibration transmissibility at a frequency region of about 6 Hz, compared to a conventional seat cushion pad. Thus, a seat cushion pad of the present invention shows a high damping characteristics.
The inventors of the present invention have studied eagerly the vibration transmissibility characteristics of a seat cushion pad made from urethane foam, and found that the aforementioned object can be achieved, when the hysteresis loss of a core layer of a urethane foam is less than 17% and the air permeability of the urethane foam including the skin portion falls in a special region. And the invention is accomplished.
A seat cushion pad according to the present invention is composed of polyurethane foam having a skin layer and a core layer, which is molded by supplying polyurethane foam raw material composition into a mould, characterized in that the seat surface has a single-layer structure, that the air permeability is between 0.05 and 1.5 cfm (cubic feet/min, i.e., ft3/min), and that the hysteresis loss of the core portion is 17% or below.
It is preferable that the air permeability of the seat cushion pad according to the present invention is between 0.1 and 1.5 cfm (2.81 to 42.2 L/min) and that the hysteresis loss is 15% or below. The air permeability shall be measured according to the regulation of ASTM D-1564 (DOW method).
The hysteresis loss of the core portion shall be measured using the sample which belongs evidently to the core layer, though the skin layer and the core layer is continuously formed and there is not any sharp boundary between them.
The seat cushion pad according to the present invention has a less resonance amplitude in the vibration transmissibility characteristics curve than that of a conventional seat cushion pad, and its vibration transmissibility at about 6 Hz is equal or less than a conventional seat cushion pad, as will be shown by evaluation results of the examples described later. Namely, according to the present invention, irrespective of the shape, it is possible to manufacturing a seat cushion pad, having a lower resonance amplitude and a lower vibration transmissibility at frequency of 6 Hz than conventional seat cushion pad.
The inventors of the present invention obtained new knowledge that the resonance amplitude in the vibration transmissibility characteristics is influenced by the air permeability: the lower the air permeability is, the lower the resonance amplitude is. And it is deduced that it is effective to lower the air permeability range, in such a manner as defined in the present invention, for lowering the resonance amplitude. Thus the range of the air permeability of the seat cushion pad according to the present invention is between 0.05 and 1.5 cfm (1.41 to 42.2 L/min). The lower limit of the air permeability range is defined with respect to the stability in the seat cushion pad forming. Namely, from a viewpoint of the stability of foaming, it is preferable that the air permeability is over 0.1 cfm, and particulary it is preferable that it is over 0.3 cfm (8.43 L/min). For lowering the resonance amplitude at 2 to 4 Hz, it is preferable that the air permeability is less than 1.5 cfm (42.2 L/min).
The measured value of the air permeability of polyurethane foam does not include the effect of the covering material of the seat cushion such as cloth, which will be applied to the seat cushion pad for producing the seat, the final product. However, the measured value of the air permeability includes the effect of the skin layer.
On the other hand, the hysteresis loss of the core layer, one of the physical properties defining the present invention, has almost no relation with the air permeability, and depends on the kind of the polymer which constitute the polyurethane foam. Further, the inventors obtained a new knowledge that the resonance frequency of a seat cushion pad composed of polyurethane foam depends on the hysteresis loss of the core layer, more precisely, the former is proportional to the later, and that the resonance frequency is inversely proportional to the resonance amplitude. Thus, it is deduced that an utilization of material having small hysteresis loss of core layer is effective in lowering the resonance frequency, in order to realize a seat cushion pad having a lower resonance amplitude and a lower vibration transmissibility at 6 Hz. It is preferable that the hysteresis loss of the core layer is 17% or below. And it is more preferable that the loss is 15% or below. The less the hysteresis loss of core layer is, the more preferable it is.
As explained above, for the first time, the object of the present invention is attained, by a seat cushion pad composed of polyurethane foam defined by the present invention, in which, on one hand, the air permeability as a whole of the foam including the skin layer, which is a physical properties to lower the resonan
Banno Masanobu
Kazuno Atsushi
Sato Katsuya
Sekita Kikuo
Sugie Takanori
Jr. Milton Nelson
Toyo Tire & Rubber Co., Ltd.
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