Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
2001-11-29
2003-09-23
Freay, Charles G. (Department: 3746)
Pumps
Motor driven
Electric or magnetic motor
C417S413100, C417S542000, C417S557000, C417S521000
Reexamination Certificate
active
06623256
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a pump that moves a fluid by changing the volume of the inside of a pump chamber using, for example, a piston or a diaphragm.
2. Description of Related Art
A conventional example of such a type of pump typically has a structure that is similar to the structure disclosed in Japanese Unexamined Patent Application Publication No. 10-220357 including a check valve that is mounted between an entrance passage and an exit passage, and a pump chamber defining a volume can be changed.
An example of a structure of a pump that produces a flow in one direction by making use of the viscosity resistance of a fluid is disclosed in Japanese Unexamined Patent Application Publication No. 8-312537. In this Publication, a valve is provided at an exit passage, and the fluid resistance at an entrance passage is greater than the fluid resistance at the exit passage when opening the valve.
An example of a structure of a pump that is made to be more reliable without using a movable part at a valve is disclosed in Published Japanese Translations of PCT International Publication for Patent Application No. 8-506874. This Publication discloses a compression structural member in which an entrance passage and an exit passage have shapes that are formed so that the pressure drops differ depending on the direction of flow.
However, in the structure disclosed in Japanese Unexamined Patent Application Publication No. 10-220357, both the entrance passage and the exit passage require a check valve, so that there is a problem in that pressure loss is high when a fluid passes through the two check valves. In addition, since fatigue damage may occur due to repeated opening and closing of the check valves, there is another problem in that the larger the number of check valves used, the lower the reliability of the pump.
In the structure disclosed in Japanese Unexamined Patent Application Publication No. 8-312537, in order to reduce back flow that is produced in the entrance passage during a pump discharge stroke, it is necessary to make the fluid resistance at the entrance passage to be large. When the fluid resistance is made to be large, fluid enters a pump chamber against the fluid resistance during a pump suction stroke, so that the suction stroke takes longer than the discharge stroke. Therefore, the frequency of the discharge-suction cycle of the pump becomes considerably low.
A small, light, high-output pump can be formed by an actuation operation at a high frequency using a piezoelectric element as an actuator for moving a piston or a diaphragm in up and down directions. The piezoelectric element is such that the displacement is small during one period but the response frequency is high, and has the characteristic of providing higher output energy the higher the frequency at which the actuation operation is performed up to the time of resonant frequency of the element. However, in the structure disclosed in Japanese Unexamined Patent Application Publication No. 8-312537, as mentioned above, an actuation operation can only be performed at a low frequency, so that there is a problem in that a pump that makes full use of the features of the piezoelectric element cannot be realized.
In the structure disclosed in Published Japanese Translations of PCT International Publication for Patent Application No. 8-506874, in accordance with an increase or a decrease in the volume of the pump chamber, the net quantity of flow is caused to be in one direction due to differences in pressure drops depending on the direction of flow of the fluid that passes through the compression structural member. Therefore, the back flow rate increases as external pressure (load pressure) at the exit side of the pump increases, resulting in the problem that the pump no longer operates at high load pressure. According to the treatise entitled “An Improved Valve-less Pump Fabricated Using Deep Reactive Ion Etching” presented in 1996 IEEE 9
th
International Workshop on Micro Electro Mechanical Systems, the maximum load pressure is of the order of 0.76 atmospheres.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a small, light and high-output pump which can operate under high load pressure, which makes it possible to reduce pressure loss and to increase its reliability by decreasing the number of mechanical on-off valves used, and which makes full use of the features of a piezoelectric element when the piezoelectric element is used as an actuator that actuates a piston or a diaphragm as a result of reducing the period of increasing and decreasing the volume of a pump chamber.
In order to overcome the above-described problems, according to a first aspect of the invention, a pump is provided that includes a pump chamber whose volume is changeable by a member including a piston and a diaphragm, an entrance passage used to make working fluid flow into the pump chamber, and an exit passage used to make the working fluid flow out from the pump chamber. A combined inertance value of the entrance passage is smaller than a combined inertance value of the exit passage. The entrance passage is provided with a fluid resistance member in which fluid resistance when the working fluid flows into the pump chamber is smaller than fluid resistance when the working fluid flows out of the pump chamber.
An inertance value L is determined by the expression L=&rgr;1/S, wherein the cross-sectional area of a flow path is S, the length of a flow path is 1, and the density of the working fluid is &rgr;. When a passage pressure difference is P, and the flow rate in a passage is Q, and when the inertance L is used to transform the formula of the movement of a fluid inside a passage, the relationship P=L×dQ/dt is derived. In other words, the inertance value indicates the degree of influence that unit pressure has on the change in the flow rate per second. The larger the inertance value, the smaller the change in the flow rate per second, whereas the smaller the inertance value, the larger the change in the flow rate per second.
The combined inertance value for parallel connection of a plurality of passages and for series connection of a plurality of passages having different shapes is calculated by combining the inertance values of the individual passages similarly to the way the inductance values for parallel connection and those for series connection in electrical circuits are combined.
Here, the entrance passage refers to a passage that extends from the inside of the pump chamber to a fluid flow-in-side end surface of an entrance connecting tube that connects the pump to the outside. However, when a pulsation absorbing device, such as that described below, is connected, the entrance passage refers to a passage that extends from the inside of the pump chamber to a connection portion with the pulsation absorbing device. Further, when the entrance passages of a plurality of pumps merge as described below, it refers to a passage from the inside of the pump chamber to the merging portion.
In accordance with the operation of the pump having the structure such as that described above with regard to the first aspect of the invention, when the piston or the diaphragm operates in the direction in which the volume of the pump chamber becomes small, this direction is, at the entrance passage, the direction in which the fluid flows out, so that the fluid resistance of the fluid resistance member is large, thereby making the fluid flowing out from the entrance passage very small or zero. On the other hand, at the exit passage, when the pressure inside the pump chamber increases in accordance with the shrinkage ratio of the fluid, the flow rate in the direction in which the fluid flows out from the pump chamber increases in accordance with the difference between the pressure inside the chamber and the load pressure and the inertance value.
When the piston or the diaphragm operates in the direction in which the volume of the pump chamber incre
Seto Takeshi
Takagi Kunihiko
Yoshida Kazuhiro
Freay Charles G.
Sayoc Emmanuel
Seiko Epson Corporation
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