Butterfly valve device

A butterfly valve device comprising a butterfly valve made of a resin material, said butterfly valve being rotatably supported by a rotating shaft in a fluid path, wherein: when the butterfly valve is located at a full-closed position facing a peripheral lower surface of the semicircular portion with respect to a rotating shaft of the butterfly valve, a partial annular projection is adapted to radially inwardly extend towards an inner wall surface of a fluid path, the partial annular projection including a plane that contacts the peripheral lower surface of the valve to form a fluid seal; the partial annular projection is formed in a specific area ranging from a pair of bearings which support the rotating shaft of the valve to an area in a circumferential direction; and the projection, at least part of which is lacking, extends over a remaining range including a position whose distance from the pair of bearings becomes equivalent in the circumference direction, wherein within a range of the lacking part, an area between the periphery of the valve and the inner circumferential wall surface of the fluid path, which faces the periphery, is provided with a minute gap used to adjust the minimum airflow; and the leakage airflow from the minute gap between the valve peripheral surface included in the lacking part and the fluid path inner wall surface is kept substantially constant while the valve is pressed down to a seat surface, and after the valve gets away from the seat surface to open, until the specific opening is exceeded.
However, in the case of the butterfly valve formed by resin molding, the deformation of the valve exerts a large influence upon flow control characteristics. The deformation of the valve is caused by various kinds of external force including the heat distortion and the thermal stress, which occur due to temperature influence, or the fluid pressure that acts on the valve. As a result, the adjustment of the minimum flow of the valve becomes unstable, and the minimum flow is easily susceptible secular change. For example, in the case of a butterfly valve used for a throttle device for controlling the airflow of an internal combustion engine, an allowable range of the minimum leakage airflow is set over an operation range from −40 degrees to +130 degrees. However, if a throttle valve made of resin is used, there arises a problem that the temperature influence causes a minute gap, which is formed in a fluid sealing member between a throttle valve and an airflow path wall surface, to change so that an allowable value is exceeded. To be more specific, when the ambient air temperature is −40 degrees, the temperature of air passing through an airflow path becomes about −10 degrees. On the other hand, the ambient air temperature (the temperature inside an engine room) around a throttle device becomes 80 degrees. At this time, the throttle valve contracts. On the other hand, although a body is cooled from the inside, the body is warmed from the outside. Accordingly, the amount of contraction is small. As a result, there is a possibility that a gap between them will be widened. In addition, if both of a molded body and a throttle valve, which constitute an airflow path, are formed by resin molding, when the temperature decreases at the time of resin molding, if the amount of contraction of the molded body constituting part of the airflow path is large, the throttle valve is closely contacted with to the molded body, with the result that the throttle valve cannot rotate. If the gap is set at a large value beforehand to avoid the above situation, the leakage airflow becomes larger, which causes the minimum airflow to increase. In addition, the leakage airflow is easily susceptible to secular change depending on the use state. Moreover, a gap made between a peripheral wall inside a bearing hole and an outer circumferential surface of a rotating shaft is easily susceptible to secular change. This is a bottleneck in the adjustment of the minimum flow. Furthermore, when the throttle valve is kept in a full-closed state, the operation of an intake stroke of a piston of an engine causes the high negative pressure to occur in the downstream of the throttle valve. If this negative pressure acts on the throttle valve that is kept in the full-closed state, it is also thought that the throttle valve made of resin will be deformed.

                                                                                                      Shanghai Remy Valve Manufacturing Co., Ltd.

2011-12-23 02:56