Automobile beltline portion sound insulating structure and automobile door glass

1. An automobile beltline portion sound insulating structure formed along a beltline of an automobile, comprising:

a door panel having an inner panel and an outer panel as two panel boards facing each other,

a door glass main body freely openable and closable between the two panel boards in a liftable manner, and

a first viscoelastic member mounted on a lower portion of at least one main surface of the door glass main body and constrained between a mounting region of the first viscoelastic member in the door glass main body and a part of a surface of the inner panel facing to the at least one main surface, at a door glass closed time, to insulate sound,

wherein

the first viscoelastic member comprises a foamed viscoelastic material,

the first viscoelastic member is elastically transformable and a thickness of the first viscoelastic member is decreased at the door glass closed time compared with a door glass opened time, and

the first viscoelastic member has a Young's modulus E in N/m 2 at 20° C. and a loss coefficient tan δ at 20° C. and 4000 Hz satisfying formula (2):

E

≧

1.65

×

10

5

⁢

1

+

tan

2

⁢

δ

tan

⁢

⁢

δ

.

(

2

)

2. The automobile beltline portion sound insulating structure according to claim 1 , wherein the first viscoelastic member has a laminated structure comprising a soft layer whose Young's modulus at 20° C. is lower than that of another layer.

3. The automobile beltline portion sound insulating structure according to claim 1 , wherein a cross-sectional shape in a vertical cross section in a direction from a door glass side to an automobile interior side of the first viscoelastic member is a tapered shape that tapers toward its upper end.

4. The automobile beltline portion sound insulating structure according to claim 1 , wherein

the at least one main surface of the door glass main body is a main surface on the automobile interior side; and

the first viscoelastic member is constrained between the mounting region of the first viscoelastic member in the door glass main body and the part of the surface of the inner panel facing to the door glass main body, at the door glass closed time.

5. The automobile beltline portion sound insulating structure according to claim 1 , further comprising

a second viscoelastic member mounted on a lower portion of the other main surface of the door glass main body,

wherein the second viscoelastic member is constrained between a mounting region of the second viscoelastic member in the door glass main body and a part of a surface on a door glass side of the outer panel facing the other main surface, at the door glass closed time.

6. The automobile beltline portion sound insulating structure according to claim 5 , wherein the second viscoelastic member is elastically transformable and a thickness of the second viscoelastic member is decreased at the door glass closed time compared with a door glass opened time.

7. The automobile beltline portion sound insulating structure according to claim 1 , wherein the mounting region of the first viscoelastic member extends in an entire horizontal direction of the door glass main body.

8. The automobile beltline portion sound insulating structure according to claim 1 , wherein the first viscoelastic member has a layer which contacts the inner panel and has adhesiveness to the inner panel.

9. An automobile door glass for a sound insulation structure formed along an automobile beltline and comprising a door panel having an inner panel and an outer panel as two panel boards facing each other, the automobile door glass comprising:

a door glass main body freely openable and closable between the two panel boards in a liftable manner, and

a first viscoelastic member mounted on a lower portion of at least one main surface of the door glass main body and constrained between a mounting region of the first viscoelastic member in the door glass main body and a part of a surface of the inner panel facing to the at least one main surface, at a door glass closed time, to insulate sound,

wherein

the first viscoelastic member comprises a foamed viscoelastic material,

the first viscoelastic member is elastically transformable and a thickness of the first viscoelastic member is decreased at the door glass closed time compared with a door glass opened time, and

the first viscoelastic member has a Young's modulus E in N/m 2 at 20° C. and a loss coefficient tan δ at 20° C. and 4000 Hz satisfying formula (2):

E

≧

1.65

×

10

5

⁢

1

+

tan

2

⁢

δ

tan

⁢

⁢

δ

.

(

2

)

10. The automobile door glass according to claim 9 , wherein the first viscoelastic member has a laminated structure comprising a soft layer whose Young's modulus at 20° C. is lower than that of another layer.

11. The automobile door glass according to claim 9 , wherein a cross-sectional shape in a vertical cross section in a direction from a door glass side to an automobile interior side of the first viscoelastic member is a tapered shape that tapers toward its upper end.

12. The automobile door glass according to claim 9 , further comprising

a second viscoelastic member mounted on a lower portion of the other main surface of the door glass main body,

wherein the second viscoelastic member is constrained between a mounting region of the second viscoelastic member in the door glass main body and a part of a surface on a door glass side of the outer panel facing the other main surface, at the door glass closed time.

13. The automobile door glass according to claim 9 , wherein the mounting region of the first viscoelastic member extends in an entire horizontal direction of the door glass main body.

14. The automobile door glass according to claim 9 , wherein the first viscoelastic member has a layer which contacts the inner panel and has adhesiveness to the inner panel.