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A fuel pump includes a housing having therein a suction passage and a pressurization chamber into which fuel from the suction passage flows, a plunger held in the housing to be reciprocable so as to pressurize the fuel flowing into the pressurization chamber, and a diaphragm device located in a suct

A fuel pump includes a housing having therein a suction passage and a pressurization chamber into which fuel from the suction passage flows, a plunger held in the housing to be reciprocable so as to pressurize the fuel flowing into the pressurization chamber, and a diaphragm device located in a suction chamber that is provided in the suction passage. The diaphragm device includes a pair of first and second diaphragms that are arranged to define an inner space therebetween and air-tightly sealed at its entire peripheries. A mass addition member may be attached to an inside surface of at least one of the first and second diaphragms, so that the first and second diaphragms with the mass addition member have different characteristic frequencies. Accordingly, pressure pulsation of the fuel in the suction chamber can be effectively reduced by the pulsation damper.

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1. A fuel pump comprising: a housing having therein a suction passage through which fuel is drawn, and a pressurization chamber into which the fuel from the suction passage flows;a plunger held in the housing to be reciprocable, the plunger being configured to pressurize the fuel flowing into the pr

1. A fuel pump comprising: a housing having therein a suction passage through which fuel is drawn, and a pressurization chamber into which the fuel from the suction passage flows;a plunger held in the housing to be reciprocable, the plunger being configured to pressurize the fuel flowing into the pressurization chamber;a diaphragm device located in a suction chamber that is provided in the suction passage, wherein the diaphragm device includes a pair of first and second diaphragms that are arranged to define an inner space therebetween and air-tightly sealed at its entire peripheries,the first and second diaphragms are made of metal, and generally have the same shape and the same thickness, andthe first and second diaphragms each have an inside surface portion, the inside surface portions are disposed to oppose each other and spaced apart from each other by the inner space; anda mass addition member attached to the inside surface portion of one of the first and second diaphragms, wherein the mass addition member is a flat, planar member, and the mass addition member is spaced from the inside surface portion of the other of the first and second diaphragms. 2. The fuel pump according to claim 1, wherein the mass addition member is made of a material having flexibility, said material being one of a resin film and a thin metal plate. 3. The fuel pump according to claim 1, wherein the mass addition member is a metal film that is bonded to said inside surface portion via a flexible adhesive. 4. The fuel pump according to claim 1, wherein the mass addition member is attached to the inside surface of the second diaphragm to be integrated to each other such that a total characteristic frequency of the second diaphragm and the mass addition member is different from that of the first diaphragm. 5. The fuel pump according to claim 1, further comprising a plate located between the first and second diaphragms to partition the inner space into two space parts. 6. The fuel pump according to claim 1, wherein the mass addition member is attached to said inside surface portion of said one of the first and second diaphragms with an adhesive. 7. The fuel pump according to claim 1, wherein the mass addition member is attached to said inside surface portion so as to be spaced apart from said air-tightly sealed periphery. 8. The fuel pump according to claim 1, wherein the mass addition member is disposed substantially in parallel with the inside surface portion of the other of the first and second diaphragms. 9. The fuel pump according to claim 1, wherein the mass addition member is positioned without being exposed to the fuel. 10. A fuel pump comprising: a housing having therein a suction passage through which fuel is drawn, and a pressurization chamber into which the fuel from the suction passage flows;a plunger held in the housing to be reciprocable, the plunger being configured to pressurize the fuel flowing into the pressurization chamber;a diaphragm device located in a suction chamber that is provided in the suction passage, wherein the diaphragm device includes a pair of first and second diaphragms that are arranged to define an inner space therebetween and are air-tightly sealed at its entire peripheries,the first and second diaphragms are made of metal, and generally have the same thickness while having different shapes in cross section, andthe first and second diaphragms each have an inside surface portion, the inside surface portions are disposed to oppose each other and spaced apart from each other by the inner space; anda mass addition member attached to the inside surface portion of one of the first and second diaphragms, wherein the mass addition member is a flat, planar member, and the mass addition member is spaced from the inside surface portion of the other of the first and second diaphragms. 11. The fuel pump according to claim 10, wherein the first diaphragm has a circular deformable portion and a peripheral end portion at a radial outside of the circular deformable portion, andthe circular deformable portion of the first diaphragm has a plurality of concentric grooves that are recessed toward the inner space of the diaphragm device, so as to have a wave shape in cross section. 12. The fuel pump according to claim 11, wherein the second diaphragm has a circular deformable portion and a peripheral end portion at a radial outside of the circular deformable portion, andthe circular deformable portion of the second diaphragm has a flat shape in cross section. 13. The fuel pump according to claim 10, wherein the mass addition member is made of a material having flexibility, said material being one of a resin film and a thin metal plate. 14. The fuel pump according to claim 10, wherein the mass addition member is a metal film that is bonded to said inside surface portion via a flexible adhesive. 15. The fuel pump according to claim 10, wherein the first and second diaphragms are configured to have characteristic frequencies different from each other. 16. The fuel pump according to claim 10, wherein the mass addition member is attached to said inside surface portion so as to be spaced apart from said air-tightly sealed periphery. 17. The fuel pump according to claim 10, wherein the mass addition member is disposed substantially in parallel with the inside surface portion of the other of the first and second diaphragms. 18. The fuel pump according to claim 10, wherein the mass addition member is positioned without being exposed to the fuel. 19. A fuel pump comprising: a housing having therein a suction passage through which fuel is drawn, and a pressurization chamber into which the fuel from the suction passage flows;a plunger held in the housing to be reciprocable, the plunger being configured to pressurize the fuel flowing into the pressurization chamber;a diaphragm device located in a suction chamber that is provided in the suction passage, wherein the diaphragm device includes a pair of first and second diaphragms that are arranged to define an inner space therebetween and are air-tightly sealed at its entire peripheries,the first and second diaphragms generally have different thicknesses in cross section, while having the same outer shape, andthe first and second diaphragms each have an inside surface portion, the inside surface portions are disposed to oppose each other and spaced apart from each other by the inner space;a first mass addition member attached to the inside surface portion of one of the first and second diaphragms, anda second mass addition member attached to the inside surface portion of the other of the first and second diaphragms,wherein the first and second mass addition members are both flat, planar members that are different from one another in size, and the first and second mass addition members are spaced apart from one another. 20. The fuel pump according to claim 19, wherein each of the first and second diaphragms has a circular deformable portion and a peripheral end portion at a radial outside of the circular deformable portion, andthe circular deformable portion of each of the first and second diaphragms has a flat shape in cross section. 21. The fuel pump according to claim 19, wherein the first and second mass addition members are each made of a material having flexibility, said material being one of a resin film and a thin metal plate. 22. The fuel pump according to claim 19, wherein at least one of the mass addition members is a metal film that is bonded to said inside surface portion via a flexible adhesive. 23. The fuel pump according to claim 19, wherein the first and second diaphragms are configured to have characteristic frequencies different from each other. 24. The fuel pump according to claim 19, wherein at least one of the first and second mass addition members is attached to said inside surface portion so as to be spaced apart from said air-tightly sealed periphery. 25. The fuel pump according to claim 19, wherein the first and second mass addition members are each positioned without being exposed to the fuel.