Patent Publication Number: US-6340294-B1

Title: Diaphragm type fuel pump

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a diaphragm type fuel pump which feeds fuel in response to reciprocations of a diaphragm. 
     2. Description of the Related Art 
     A diaphragm type fuel pump has been utilized as a fuel supply for feeding fuel to a fuel injector from a fuel tank. An example of such a fuel pump is shown in FIG. 8 of the accompanying drawings. 
     A diaphragm type fuel pump  10  comprises: a first body  16  including a fuel introducing path  12  and a fuel discharging path  14 ; a second body  18  arranged on one side of the first body  16 ; a cover  20  arranged on the other side of the first body  16 ; a diaphragm  22  sandwiched between the first and second bodies  16  and  18 ; and a membrane  24  sandwiched between the first body  16  and the cover  20 . 
     A pump chamber  28  is formed between the diaphragm  22  and the first body  16 , while a pulse chamber  30  is formed between the diaphragm  22  and the second body  18 . The pump chamber  28  communicates with both the fuel introducing path  12  and fuel discharging path  14  of the first body  16 . The second body  18  is provided with a pulse introducing path  32  in order to introduce pulse pressure to the pulse chamber  30 . The pulse pressure is generated by an engine and is supplied to the pulse chamber  32  via the pulse introducing path  32 . 
     A fuel sucking chamber  34  communicating with a fuel tank (not shown) and a fuel discharging chamber  35  communicating with a fuel injector (not shown) are formed between the membrane  24  and the first body  16 . Between the membrane  24  and the cover  20 , a damping chamber  36  faces the fuel sucking chamber  34  via the membrane  24 , and a damping chamber  37  faces the fuel discharging chamber  35  via the membrane  24 . 
     The fuel sucking chamber  34  communicates with the pump chamber  28  via the fuel introducing path  12  of the first body  16 , while the fuel discharging chamber  35  communicates with the pump chamber  28  via the fuel discharging path  14  of the first body  16 . A check valve  38  is provided in the fuel introducing path  12  in order to feed fuel only to the pump chamber  28  from the fuel sucking chamber  38 . Further, a check valve  40  is provided in the fuel discharging path  14  in order to feed fuel only to the fuel discharging chamber  35 . 
     In this diaphragm type fuel pump  10 , pulse pressure generated in a crank chamber (not shown) of the engine is introduced into the pulse chamber  30 , thereby reciprocating the diaphragm  22  between the pump chamber  28  and the pulse chamber  30 . As a result, fuel introduced into the fuel sucking chamber  34  from the fuel tank is supplied to the fuel injector via the pump chamber  28  and the fuel discharging chamber  35 . 
     The diaphragm  22  is generally made of a rubber or synthetic resin material. The rubber material becomes hard at a low temperature, and tends not to reciprocate smoothly, thereby reducing the flow rate of the fuel pump. On the contrary, a synthetic resin material that remains flexible regardless of temperature variations has been utilized for snow mobiles or the like which are structured so as to be usable in very cold areas. 
     FIG. 9 shows the diaphragm  22  made of only synthetic resin in the related art. The diaphragm  22  is flat, and has openings  42  at four corners in which screws (not shown) are received in order to fixedly hold the first body  16  and two lids  18  and  20 . 
     At normal temperatures, the synthetic resin is hard compared with the rubber material, so that the synthetic resin diaphragm  22  is less flexible than the rubber diaphragm, and takes time to reciprocate. The fuel pump including a synthetic resin diaphragm  22  therefore suffers from a reduced flow rate compared with a fuel pump including a rubber diaphragm  22 . 
     It is well-known that the flow rate of the diaphragm type fuel pump depends upon a size of an effective diameter X (shown in FIG. 8) of the diaphragm  22 . The term “effective diameter” means a diameter of the diaphragm in which the pumping operation is performed. Referring to FIG. 8, the effective diameter X of the diaphragm  22  is equal to a diameter of an inner wall of the second body  18  constituting the cylindrical pulse chamber  30 . 
     FIG. 10 is a graph showing the relationship (N-Q characteristics) between the number N of pulses and flow rate Q of pumps  10  having the synthetic resin diaphragm  22  and two different effective diameters X. In FIG. 10, black squares ▪ denote the N-Q characteristics of a fuel pump having a relatively small effective diameter diaphragm (for a maximum flow rate of 42 L/H), and black circles  denote the N-Q characteristics of a fuel pump having a relatively large effective diameter diaphragm (for a maximum flow rate of 72 L/H). Referring to the N-Q characteristics, it is understood that the effective diameter extensively affects the flow rate of the fuel pump. 
     In the related diaphragm type fuel pump  10 , a variety of second bodies  18  have been prepared in accordance with required flow rates of the fuel pump. Since the different flow rates mean the necessity of different effective diameters X, the second bodies  18  have been selected in accordance with the required flow rates. As a result, a plurality of dies have been required, which has caused an increase in manufacturing costs of fuel pumps. 
     The invention is intended to overcome the foregoing problems of the related art, and to provide a diaphragm type fuel pump that includes a single kind of body, meets requirements for a plurality of flow rates and can be manufactured at a reduced cost. 
     According to the present invention, at very low temperatures, the diaphragm of the fuel pump can assure strokes identical to those of the synthetic resin diaphragm of the related art and having an effective diameter X that is the same as that of the present invention. At normal temperatures, the diaphragm of the invention can assure large strokes compared with those of the synthetic resin diaphragm, and increases necessary flow rates. Therefore, the flow rates can be varied as desired only by exchanging the diaphragm but without replacing the second body. As a result, it is not necessary to prepare a plurality of dies, which is effective in promoting the use of just one type of second body and reducing manufacturing costs. 
     SUMMARY OF THE INVENTION 
     In order to accomplish the foregoing object of the invention, there is provided a diaphragm type fuel pump comprising: a fuel sucking chamber and a fuel discharging chamber; a first body having a fuel introducing path communicating with the fuel sucking chamber and a fuel discharging path communicating with the fuel discharging chamber; a diaphragm fixed to the first body using a second body; and a pump chamber constituted by the diaphragm and the first body and communicating with the fuel introducing path and the fuel discharging path. The diaphragm includes an outer diaphragm made of resin and having an opening formed within an effective diameter of the diaphragm, and an inner diaphragm arranged in the opening of the outer diaphragm. Further, the outer and inner diaphragms are mutually fixed using an elastic coupling member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of the diaphragm type fuel pump according to one embodiment of the invention. 
     FIG. 2 is a perspective view of the diaphragm used in the invention. 
     FIG. 3 is a sectional view of the diaphragm, taken along line  3 — 3  in FIG.  2 . 
     FIG. 4 is a schematic view showing strokes of the diaphragm of the invention. 
     FIG. 5 is a sectional view of another example of the diaphragm of the invention. 
     FIG. 6 is a sectional view of a further example of the diaphragm of the invention. 
     FIG. 7 is a schematic view showing strokes of the diaphragm in FIG.  6 . 
     FIG. 8 is a sectional view of the diaphragm type fuel pump of the related art. 
     FIG. 9 is a perspective view of the diaphragm of FIG.  8 . 
     FIG. 10 is a graph showing the N-Q characteristics of the diaphragm type fuel pumps of the related art and the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention will be described with reference to the drawings. FIG. 1 is a sectional view of a diaphragm type fuel pump according to one embodiment of the invention. FIG. 2 is a perspective of a diaphragm used in the invention. FIG. 3 is a sectional view of the diaphragm taken along line  3 — 3  in FIG.  2 . In FIGS. 1 and 8, like or corresponding parts are denoted by like or corresponding reference numerals. 
     The diaphragm type fuel pump  44  of the invention is composed of components which are similar to those of the related diaphragm type fuel pump  10 , with the exception of the diaphragm  46 . Components other than the diaphragm  46  will therefore not be described here. 
     The diaphragm  46  is composed of: an outer diaphragm  50  having a center opening  48  (see FIG.  3 ); an inner diaphragm  52  fitted into the center opening  48 ; and an annular coupling member  54  for fixedly coupling the outer and inner diaphragms  50  and  52 . Referring to FIG. 3, the inner diaphragm  52  and the outer diaphragm  50  are flush with each other as shown in FIG. 3, and are made of synthetic resin materials. The annular coupling member  54  is made of an elastic material such as rubber. 
     With the diaphragm  46 , the outer diaphragm  50  is sandwiched between a first body  16  and a second body  18 . A diameter of the opening  48  and an outer diameter of the coupling member  54  are designed such that an effective diameter X of the diaphragm  46  is equal to an outer diameter of the outer diaphragm  50 . In other words, the diameter of the opening  48  and the outer diameter of the coupling member  54  are small compared with the effective diameter X of the diaphragm  46 . 
     The inner and outer diaphragms  50  and  52  are hermetically coupled to the coupling member  54  using adhesives. Alternatively, these components may be hermetically molded or fused. The coupling member  54  should be as strong as the outer and inner diaphragms  50  and  52 . 
     The effective diameter X of the diaphragm  46  coincides with the outer diameter of the synthetic resin outer diaphragm  50  that is not hardened even at an extremely low temperature. Therefore, the diaphragm  46  can assure large reciprocation compared with the related diaphragm  22  made only of synthetic resin. 
     At normal temperatures, the inner diaphragm  52  reciprocates in an orbit which differs from an orbit of the related diaphragm  22 , i.e. the center (inside the effective diameter X) of the diaphragm  22 . This is because the inner diaphragm  52  is separated from the outer diaphragm  50  via the coupling member  54 . In other words, the coupling member  54  made of rubber is softer than the synthetic resin at normal temperatures, so that the inner diaphragm  52  easily performs vertical strokes in response to pulses. As a result, the diaphragm  46  of the present invention reciprocates extensively compared with the related diaphragm  22  made of only synthetic resin. Further, even when the diaphragms  46  and  22  have the same effective diameters X, the fuel pump  44  of the invention can have a much larger flow rate than that of the diaphragm  22  made of only synthetic resin. 
     FIG. 4 schematically shows how the diaphragm  46  reciprocates at normal temperatures. In FIG. 4, solid lines denote strokes of the diaphragm  46 , and dashed lines denote strokes of the related synthetic resin diaphragm  22 . Referring to FIG. 4, it is understood that the strokes of the diaphragm  46  are larger than those of the diaphragm  22 , which means that the fuel pump of the present invention can assure a large flow rate. 
     The N-Q characteristics of the diaphragm type fuel pump  44  including the diaphragm  46  are shown by black triangles ▴ in FIG.  10 . In FIG. 5, the fuel pump  44  is provided with the second body  20  having a relatively small effective diameter (i.e. the maximum flow rate of the pump is 42 L/H) which is equal to the flow rate shown by the black squares ▪. 
     As can be seen from the N-Q characteristics, the flow rate of the fuel pump  44  is substantially equal to the flow rate of the fuel pump including the second body  20  with the relatively large effective diameter (i.e. the maximum flow rate is 72 L/H). In short, the fuel pump  44  having the second body  20  with the relatively small effective diameter (i.e. the maximum flow rate of 42 L/H) can assure the flow rate that is equal to the flow rate of the related pump having the relatively large effective diameter (i.e. the maximum flow rate of 72 L/H). Therefore, according to the present invention, even when the same second body  20  is used, desired flow rates can be obtained by replacing the diaphragm  46 . In other words, one kind of the second body  20  is usable regardless of the required flow rates. 
     A further example of the diaphragm  46  will be described hereinafter. 
     In this example, the coupling member  54  is curved so that the synthetic resin inner and outer diaphragms  52  and  50  are not flush with each other at normal temperatures. If the coupling member  54  is made of synthetic resin, it cannot be curved but remains flat. On the contrary, if it is made of a rubber material, the coupling member  54  can be shaped as desired, which is effective in enlarging strokes of the diaphragm  46 . When the inner and outer diaphragms  54  and  52  are not flush with each other due to curving the coupling member  54  as shown in FIG. 5, the diaphragm stroke can be increased compared with the diaphragm in FIG. 3, so that the flow rate of the fuel pump can be increased. 
     The outer and inner diaphragms  50  and  52  are not always made of the same material, and may be made of different materials. For instance, the outer diaphragm  50  may be of a synthetic resin material while the inner diaphragm  52  may be made of an elastic material such as rubber. In the latter case, the inner diaphragm  52  (shown in FIG. 3) and the coupling member  54  may be integrally formed as an inner diaphragm  56  as shown in FIG.  6 . 
     Strokes of the inner diaphragm  56  at normal temperatures are schematically shown in FIG.  7 . In FIG. 7, solid lines denote strokes of the diaphragm  56  of the present invention, while dashed lines denote strokes of the related diaphragm  22  made of synthetic resin. Referring to FIG. 7, the rubber material is more elastic than the synthetic resin at normal temperatures, so that the rubber diaphragm  56  of the present invention can assure large strokes compared with those of the synthetic resin diaphragm  22  of the related art. 
     Further, it is not always necessary that the outer and inner diaphragms  50  and  52  have the same thickness. Still further, the inner diaphragm  52  may be in the shape of a plate instead of in the shape of a membrane (as long as the diaphragm  52  does not curl during the stroke operation).