1. Field of the Invention
The present invention relates to a fluid control device which performs fluid control.
2. Description of the Related Art
International Publication No. 2008/069264 discloses a conventional fluid pump (see FIGS. 1A to 1E). FIG. 1A to FIG. 1E show operations of the conventional fluid pump in a tertiary mode. The fluid pump, as shown in FIG. 1A, includes a pump body 10; a vibrating plate 20 in which the outer peripheral portion thereof is attached to the pump body 10; a piezoelectric element 23 attached to the central portion of the vibrating plate 20; a first opening 11 formed on a portion of the pump body 10 that faces the approximately central portion of the vibrating plate 20; and a second opening 12 formed on either one of a region intermediate between the central portion and the outer peripheral portion of the vibrating plate 20 or a portion of the pump body 10 that faces the intermediate region.
The vibrating plate 20 is made of metal. The piezoelectric element 23 has a size so as to cover the first opening 11 and a size so as not to reach the second opening 12.
In the above mentioned fluid pump, by applying voltage having a predetermined frequency to the piezoelectric element 23, a portion of the vibrating plate 20 that faces the first opening 11 and a portion of the vibrating plate 20 that faces the second opening 12 are bent and deformed in opposite directions, as shown in FIG. 1A to FIG. 1E. This causes the fluid pump to draw fluid from one of the first opening 11 and the second opening 12 and to discharge the fluid from the other opening.
The above mentioned fluid pump, as is shown in FIG. 1A with a conventional structure, has a simple structure, and thus the thickness of the fluid pump can be made thinner. Such a fluid pump is used, for example, as an air transport pump of a fuel cell system.
At the same time, electronic equipment and apparatuses into which the fluid pump is incorporated have tended to be miniaturized. Therefore, it is necessary to further miniaturize the fluid pump without reducing the pump performance (the discharge flow rate and the discharge pressure) of the fluid pump.
However, the performance of the fluid pump decreases as the fluid pump becomes smaller. Therefore, there are limitations to miniaturizing the fluid pump having the conventional structure while maintaining the pump performance.
Accordingly, the inventors of the present invention have devised a fluid pump having a structure shown in FIG. 2.
FIG. 2 is a sectional view showing a configuration of a main portion of the fluid pump 901. The fluid pump 901 is provided with a base plate 39, a flexible plate 35, a spacer 37, a vibrating plate 31, and a piezoelectric element 32. The fluid pump 901 is provided with a structure in which the above components are layered in that order. The flexible plate 35 corresponds to the “plate” of a preferred embodiment of the present invention.
In the fluid pump 901, the piezoelectric element 32 and the vibrating plate 31 bonded to the piezoelectric element 32 constitute an actuator 30. A ventilation hole 35A is formed in the center of the flexible plate 35. The end of the vibrating plate 31 is fixed to the end of the flexible plate 35 by means of an adhesive via the spacer 37. This means that the vibrating plate 31 is supported at a location spaced away from the flexible plate 35 by the thickness of the spacer 37.
The base plate 39 is bonded to the flexible plate 35. A cylindrical opening 40 is formed in the center of the base plate 39. A portion of the flexible plate 35 is exposed to the side of the base plate 39 through the opening 40 of the base plate 39. The circular exposed portion of the flexible plate 35 can vibrate at a frequency substantially the same as a frequency of the actuator 30 through the pressure fluctuation of fluid accompanied by the vibration of the actuator 30. In other words, through the configuration of the flexible plate 35 and the base plate 39, the portion of the flexible plate 35 that faces the opening 40 serves as a movable portion 41 that is capable of bending and vibrating. Furthermore, a portion on the outside of the movable portion 41 of the flexible plate 35 serves as a fixing portion 42 fixed to the base plate 39.
In the above structure, when driving voltage is applied to the piezoelectric element 32, the vibrating plate 31 bends and vibrates as a result of the expansion and contraction of the piezoelectric element 32. Furthermore, the movable portion 41 of the flexible plate 35 vibrates with vibration of the vibrating plate 31. This causes the fluid pump 901 to suction or discharge air through the ventilation hole 35A. Consequently, since the movable portion 41 vibrates with the vibration of the actuator 30, the amplitude of vibration of the fluid pump 901 is effectively increased. This allows the fluid pump 901 to produce a high discharge pressure and a large discharge flow rate despite the small size and low profile design thereof.
However, with the fluid pump 901, the movable portion 41 of the flexible plate 35 is not supported by the base plate 39. Therefore, the movable portion 41 of the flexible plate 35 bends in a direction away from the vibrating plate 31 through a force such as tension applied to the movable portion 41, thus the distance may increase from the movable portion 41 of the flexible plate 35 to the region of the vibrating plate 31 that faces the movable portion 41.
In this case, it becomes difficult for the vibration of the actuator 30 to be transmitted to the movable portion 41, and the vibration of the movable portion 41 becomes small. Thus, with the fluid pump 901, there is a problem in which the discharge pressure is lower compared to ideal pressure-flow rate characteristics.
Accordingly, by making the distance narrower between the actuator 30 and the flexible plate 35 in advance to allow vibrations by making the thickness of the spacer 37 thinner, it may be possible to increase discharge pressure. However, this method has a problem in which the discharge flow rate will decrease as the discharge pressure increases, and it has been difficult to generate high discharge pressure without decreasing the discharge flow rate.