1. Field of the invention
The present invention relates to a deflector of an automobile sunroof which protrudes upward from front the edge portion of a sunroof opening provided in an automobile roof and changes the airflow direction.
2. Description of the Related Art
When an automobile is running at a high speed in a state where the opening of the roof is opened by removing a sunroof panel or a sunroof glass of the sunroof, unpleasant noise referred to as wind throb is generated by hitting of the airflow against the edge portion of the roof located at the back of the opening. The deflector is used to avoid such situation.
Referring to the sectional view in FIG. 21, a conventional deflector 20 is formed such that it protrudes upward from an opening 21 when a sunroof panel or a sunroof glass is removed from the opening 21. The deflector 20 has a guide face 22 which deflects the airflow 24 upward. The airflow 24 which has flown from the front along the roof 23 is prevented from hitting against the edge portion of the roof located at the back of the opening 21 by enlarging the angle of inclination a formed by the guide face 22 and a roof 23 or enlarging the protrusion amount h of the guide face 22 from the roof 23 (refer to Japanese Patent Application Laid-Open HEI 7-285343).
When the airflow is deflected upward by the deflector, the direction of flow is changed by the deflector. It is known that the speed of the slip stream separated by the deflector, or the vortex flow is increased as the curvature for changing the flow direction is made larger. On the other hand, the wind noise generated by the deflector becomes larger in proportion to the sextuplicate of flow velocity. Accordingly, referring to FIG. 22 showing the characteristics of sound pressure level against deflector protrusion amount, the wind throb A at vehicle speed of 55 km/h is decreased as the deflector protrusion amount increases, while the wind noise B at vehicle speed of 100 km/h is increased as the deflector protrusion amount increases. As apparent from FIG. 22, wind throb A and wind noise B are contradictory items.
Conventionally, the airflow from the front is changed upward by the deflector to prevent the airflow from hitting against the edge portion of the roof located at the back of the opening. However, after repeating the experiment while varying the position and shape of the deflector, an equivalent effect was proved to be achieved by restricting the airflow behind the deflector from going downward.