DIAPHRAGM TYPE FUEL PUMP FOR GENERAL PURPOSE ENGINE

Abstract

A diaphragm type fuel pump includes a rod, one end of which is coupled to a diaphragm, a plunger which is slidably fitted with respect to the other end of the rod, and a plunger biasing member which biases the plunger toward the other end of the rod. The other end of the rod has a first pin extending outward radially. A through hole extends through the plunger in a radial direction. The through hole has a size which allows the first pin to move in a longitudinal direction of the rod. The first pin is in contact with one edge of the through hole. A gap is formed between another edge of the through hole and another end surface of the rod. A second pin in parallel to the first pin can be fitted into the gap.

Claims

1. A diaphragm type fuel pump for a general purpose engine, the diaphragm type fuel pump comprising: a housing; a diaphragm configured to divide a space inside the housing into a pump chamber and an air chamber; a rod slidably supported by the housing, one end of the rod being coupled to the diaphragm, another end of the rod protruding from the air chamber to outside of the housing; a plunger positioned concentrically with the other end of the rod and configured to be slidably fitted with respect to the rod; and a plunger biasing member configured to bias the plunger toward the other end of the rod, wherein the other end of the rod includes a first pin extending radially outwardly of the other end; the plunger includes a bottomed tubular shape having a tubular portion, the other end of the rod being fitted into the tubular portion; a through hole extends through the tubular portion in a radial direction of the tubular portion; the through hole is configured to have a size which allows the first pin to be displaced in a longitudinal direction of the rod relative to the through hole; a part of an edge of the through hole closer to the diaphragm is referred to as one edge, and another part thereof closer to a bottom of the plunger is referred to as another edge; the first pin is in contact with the one edge; a gap is formed between the other edge of the through hole and another end surface of the rod for allowing a second pin in parallel to the first pin to be fitted into the gap; and the second pin is fitted into the gap to restrict movement of the other end of the rod in a longitudinal direction of the rod relative to the plunger by the first pin and the second pin.

2. The diaphragm type fuel pump for the general purpose engine according to claim 1, wherein a spacer is fitted between the second pin and an inner bottom of the plunger.

3. A diaphragm type fuel pump for a general purpose engine, the diaphragm type fuel pump comprising: a housing; a diaphragm configured to divide a space inside the housing into a pump chamber and an air chamber; a rod slidably supported by the housing, one end of the rod being coupled to the diaphragm, another end of the rod protruding from the air chamber to outside of the housing; a plunger positioned concentrically with the other end of the rod and configured to be slidably fitted with respect to the rod; and a plunger biasing member configured to bias the plunger toward the other end of the rod, wherein the other end of the rod includes a first pin extending radially outwardly of the other end; the plunger includes a bottomed tubular shape having a tubular portion, the other end of the rod being fitted into the tubular portion; a through hole extends through the tubular portion in a radial direction of the tubular portion; the through hole is configured to have a size which allows the first pin to be displaced in a longitudinal direction of the rod relative to the through hole; a part of an edge of the through hole closer to the diaphragm is in contact with the first pin; a gap is formed between another end surface of the rod and an inner bottom of the plunger, for allowing a spacer to be fitted into the gap; and the spacer is fitted into the gap to restrict movement of the other end of the rod in a longitudinal direction of the rod relative to the plunger by the first pin and the spacer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is a diagram schematically showing an air intake line, an air discharge line, and a fuel supply line of a general purpose engine having a diaphragm type fuel pump for the general purpose engine according to the present invention;

[0030] FIG. 2 is a cross sectional view showing the diaphragm type fuel pump for the general purpose engine used in a high pressure application shown in FIG. 1;

[0031] FIG. 3 is an enlarged view showing the other end of a rod and a plunger shown in FIG. 2, as viewed in a longitudinal direction of a first pin;

[0032] FIG. 4 is a cross sectional view showing the diaphragm type fuel pump for the general purpose engine used in a low pressure application shown in FIG. 1;

[0033] FIG. 5 is an enlarged view showing the other end of a rod and a plunger shown in FIG. 4, as viewed in a longitudinal direction of a first pin; and

[0034] FIG. 6 is a cross sectional view showing the diaphragm type fuel pump for the general purpose engine used in a high pressure application in shown in FIG. 2, according to a modification of the embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] A general purpose engine 10 is, e.g., mounted in a general purpose machine such as an outboard engine or a work machine. As shown in FIG. 1, the general purpose engine 10 includes a crankcase 11, a cylinder block 12, a head cover 13, a crankshaft 14, and a piston 15. The cylinder block 12 has a cylinder 16 where the piston 15 moves back and forth in a reciprocal manner. Further, the general purpose engine 10 includes a power generator 17 driven by the crankshaft 14. FIG. 1 schematically shows an air intake line 31, an air discharge line 32, and a fuel supply line 40 of the general purpose engine 10.

[0036] An ignition plug 18 is attached to the head cover 13. Further, the head cover 13 includes an air intake port 21 and an air discharge port 22. The air intake port 21 is opened/closed by an air intake valve 23, and the air discharge port 22 is opened/closed by an air discharge valve 24. The air intake valve 23 and the air discharge valve 24 are opened/closed by a rocker arm shaft 25 through a valve rocker arm 26. The rocker arm shaft 25 is a type of a camshaft, and driven by the crankshaft 14. Hereinafter, the rocker arm shaft 25 will be referred to as the “camshaft 25” as necessary.

[0037] The air intake line 31 is connected to the air intake port 21, and the air discharge line 32 is connected to the air discharge port 22. The air intake line 31 includes an air cleaner 33, a throttle body 34, and an intake manifold 35. A throttle valve 36 and an electronic control injection apparatus 37 are installed in the throttle body 34.

[0038] The fuel supply line 40 includes a fuel tank 41, a diaphragm type fuel pump 42 for the general purpose engine, a fuel filter 43, a fuel pressure regulator 44, and the electronic control injection apparatus 37. The diaphragm type fuel pump 42 for the general purpose engine (hereinafter simply referred to as the fuel pump 42) is a type of a mechanical fuel pump driven by a cam 25a (cam nose 25a) of the camshaft 25.

[0039] The fuel in the fuel tank 41 is supplied to an intake port 42a of the fuel pump 42 by a fuel intake pipe 45. The fuel discharged from a discharge port 42b of the fuel pump 42 flows through a fuel discharge pipe 46, and then, the fuel is supplied to the electronic control injection apparatus 37 through the fuel filter 43 and the fuel pressure regulator 44. The fuel atomized by the electronic control injection apparatus 37 is supplied into the throttle body 34, and supplied to a combustion chamber 19 of the general purpose engine 10 together with combustion air.

[0040] The fuel discharged from the fuel pump 42 pulsates. The fuel pressure regulator 44 levels (equalizes) the discharge pressure of the fuel. The redundant fuel is returned to the fuel tank 41 through a return pipe 47.

[0041] A control unit 48 receives electrical energy from the power generator 17, and at least controls the ignition plug 18 and the electronic control injection apparatus 37.

[0042] As shown in FIGS. 2 and 3, the diaphragm type fuel pump for the general purpose engine (fuel pump) 42 is used as a fuel pump in a “high pressure” application. The fuel pump 42 includes a housing 50, a diaphragm 60, a rod 70, a plunger 80, a plunger biasing member 91, and a first pin 92.

[0043] The housing 50 includes two separate bodies, i.e., a first housing half body 51 and a second housing half body 52, which are fixed together by bolts. The housing 50 includes a diaphragm chamber 53, an intake chamber 54, a discharge chamber 55, the intake port 42a, and the discharge port 42b. The diaphragm chamber 53 is formed between the first housing half body 51 and the second housing half body 52. All of the intake chamber 54, the discharge chamber 55, the intake port 42a, and the discharge port 42b are formed in the first housing half body 51.

[0044] The diaphragm 60 is provided between the first housing half body 51 and the second housing half body 52, i.e., in the diaphragm chamber 53. The diaphragm 60 divides the diaphragm chamber 53 (a space 53 inside the housing 50) into a pump chamber 56 and an air chamber 57.

[0045] The air chamber 57 communicates with external air. The pump chamber 56 communicates with the intake port 42a through the intake chamber 54 and an intake check valve 58, and communicates with the discharge port 42b through the discharge chamber 55 and a discharge check valve 59. The intake check valve 58 allows only the fuel to flow from the intake chamber 54 to the pump chamber 56. The discharge check valve 59 allows only the fuel to flow from the pump chamber 56 to the discharge chamber 55.

[0046] The rod 70 is slidably supported by the second housing half body 52 (housing 50). One end 71 of the rod 70 is coupled to the diaphragm 60, and the other end 72 of the rod 70 protrudes from the air chamber 57 to the outside of the second housing half body 52 (housing 50), i.e., toward the cam 25a.

[0047] The plunger 80 has a bottomed tubular shape including a tubular portion 81. The other end 72 of the rod 70 can be fitted into the tubular portion 81. A bottom 82 of the plunger 80 faces the cam 25a. The plunger 80 is positioned coaxially with the other end 72 of the rod 70, and fitted with respect to the rod 70 slidably relative to the rod 70.

[0048] The plunger biasing member 91 comprises a compression coil spring wound around the rod 70, and the plunger biasing member 91 biases the plunger 80 toward the other end 72 of the rod 70 (i.e., toward the cam 25a).

[0049] The first pin 92 is provided at the other end 72 of the rod 70, and extends radially outwardly of the other end 72. That is, a pin fitting hole 73 extends through the other end 72 of the rod 70 in the radial direction. The first pin 92 is fitted into the pin fitting hole 73, and extends both in opposite radial directions of the rod 70.

[0050] A through hole 83 extends through the tubular portion 81 of the plunger 80 in the radial direction. The through hole 83 is formed to have a size which allows the first pin 92 to be displaced relative to the through hole 83 in the longitudinal direction of the rod 70. The through hole 83 is a perfectly circular hole. It should be noted that the through hole 83 may be a long hole elongated in the longitudinal direction of the plunger 80.

[0051] A part 84a of an edge 84 of the through hole 83 closer to the diaphragm 60 will be referred to as the “one edge 84a”, and another part 84b thereof closer to the bottom 82 of the plunger 80 will be referred to as the “other edge 84b”. The first pin 92 is in contact with the one edge 84a.

[0052] A gap 75 is formed between the other edge 84b of the through hole 83 and an end surface 74 (the other end surface 74) of the other end 72 of the rod 70. A second pin 93 in parallel to the first pin 92 can be fitted into the gap 75. By adopting a structure where the second pin 93 is fitted into the gap 75, movement of the other end 72 of the rod 70 in the longitudinal direction of the rod 70 relative to the plunger 80 is restricted by the first pin 92 and the second pin 93. Preferably, the length of the first and second pins 92, 93 is equal to or less than the outer diameter of the tubular portion 81 of the plunger 80.

[0053] In operation of the fuel pump 42 used in the high pressure application, the plunger 80 moves back and forth in a reciprocal manner relative to the diaphragm 60 in accordance with rotational displacement of the cam 25a. Thus, the rod 70 locked to the plunger 80 moves back and forth in a reciprocal manner together with the plunger 80 to thereby displace the diaphragm 60 elastically. Consequently, the volume of the pump chamber 56 is changed, and the fuel suctioned from the intake port 42a is discharged to the discharge port 42b.

[0054] As described above, the diaphragm type fuel pump 42 for the general purpose engine used as the fuel pump in the “high pressure” application is the optimum for supplying the fuel to the “electronic fuel injection apparatus 37 for injecting the fuel at high pressure (see FIG. 1)”.

[0055] Next, in the case where the diaphragm type fuel pump 42 for the general purpose engine used as the fuel pump in the low pressure application, as shown in FIGS. 4 and 5, only the first pin 92 is provided, and the second pin 93 shown in FIGS. 1 and 2 are not provided. Further, in this case, a “diaphragm biasing member 100” for biasing the diaphragm 60 from the air chamber 57 to the pump chamber 56 is provided. The other structure is the same as that of the diaphragm type fuel pump 42 used in the high pressure application shown in FIGS. 2 and 3, and detailed description is omitted.

[0056] In operation of the fuel pump 42 for use in the low pressure application, the plunger 80 moves back and forth in a reciprocal manner relative to the diaphragm 60 by rotating displacement of the cam 25a. Therefore, when the plunger 80 is displaced toward the diaphragm 60, the rod 70 is movable freely in the axial direction relative to the plunger 80. The rod 70 and the diaphragm 60 are displaced elastically toward the pump chamber 56 by the biasing force of the diaphragm biasing member 100. Thereafter, in the case where the plunger 80 is displaced toward the cam 25a, the rod 70 and the diaphragm 60 are returned to the cam 25a side in opposition to the biasing force of the diaphragm biasing member 100. As a result, by the change of the volume of the pump chamber 56, the fuel suctioned from the intake port 42a is discharged to the discharge port 42b.

[0057] The diaphragm type fuel pump 42 for the general purpose engine used as the fuel pump in the “low pressure” application as described above is the optimum for supplying the fuel to the “carburetor (not shown) for atomizing the fuel utilizing the negative pressure”.

[0058] As described above, in the embodiment of the present invention, the diaphragm type fuel pump 42 for a general purpose engine can include, in addition to the first pin 92, the second pin 93 which is in parallel to the first pin 92. Regardless of whether the second pin 93 is present or not, the plunger 80 is biased by the plunger biasing member 91 toward the other end 72 of the rod 70. The first pin 92 is contact with the part 84a of the edge 84 (one edge 84a) of the through hole 83 closer to the diaphragm 60 at all times.

[0059] As shown in FIG. 4, in the case where only the first pin 92 is used, the other end 72 of the rod 70 can move in the longitudinal direction of the rod 70 relative to the plunger 80. In this case, the “diaphragm biasing member 100” for biasing the diaphragm 60 from the air chamber 57 toward the pump chamber 56 is provided. Therefore, when the plunger 80 is pushed up toward the diaphragm 60 by the cam 25a of the general purpose engine 10, the diaphragm 60 is biased by the diaphragm biasing member 100 toward the pump chamber 56. The resulting discharge pressure of the fuel pump 42 is a relatively low pressure which depends on the biasing force of the diaphragm biasing member 100.

[0060] As shown in FIG. 2, in the case where both of the first pin 92 and the second pin 93 are used, the second pin 93 is interposed between the other part 84b of the edge 84 (other edge 84b) of the through hole 83 closer to the bottom 82 of the plunger 80 and the other end surface 74 of the rod 70, and comes into contact with the other edge 84b and the other end surface 74. That is, the second pin 93 is in contact with the other part 84b of the edge 84 (other edge 84b) of the through hole 83. Movement of the other end 72 of the rod 70 in the longitudinal direction of the rod 70 relative to the plunger 80 is restricted (i.e., locked) by the first pin 92 and the second pin 93. As a result, the rod 70 is directly connected to the plunger 80, regardless of whether or not the diaphragm biasing member 100 (see FIG. 4) is present.

[0061] Therefore, when the plunger 80 is pushed up toward the diaphragm 60 by the cam 25a of the general purpose engine 10, the diaphragm 60 is forcibly displaced elastically toward the pump chamber 56 by the plunger 80. Therefore, the resulting discharge pressure of the fuel pump 42 is a relatively high pressure which does not depend on the biasing force of the diaphragm biasing member 100.

[0062] In this manner, the discharge pressure of the fuel pump 42 can be changed optionally depending on whether or not the second pin 93 (see FIG. 2) is present. Further, simply by selecting the presence or absence of the second pin 93, with the simple structure, the discharge pressure of the fuel pump 42 can be changed very easily. Additionally, even when the discharge pressure of the fuel pump 42 is changed, the shape and the dimensions of the fuel pump 42 remain exactly the same. That is, simply by switching between the fuel pump for use in the low pressure application and the fuel pump for use in the high pressure application, the pump can be used as is, without any modification. Therefore, in the fuel supply line 40 of the general purpose engine 10, it is possible to easily switch between the line having the specifications for the carburetor and the line having the specifications for the electronic control injection apparatus.

[0063] Further, by selecting the presence or the absence of the second pin 93, one type of diaphragm type fuel pump 42 can be switched between the low pressure application and the high pressure application. Therefore, improvement in the mass production efficiency is achieved. Consequently, it becomes possible to reduce the cost of the diaphragm type fuel pump 42 for the general purpose engine.

[0064] As shown in FIG. 2, preferably, a spacer 94 is fitted between the second pin 93 and an inner bottom 85 of the plunger 80. In this manner, the central portion of the second pin 93 in the longitudinal direction can be supported by the inner bottom 85 (inner bottom surface 85) of the plunger 80 through the spacer 94. Accordingly, it is possible to enhance the bending strength of the second pin 93.

[0065] Next, a modification of the diaphragm type fuel pump 42 will be described with reference to FIG. 6. A diaphragm type fuel pump 42A for a general purpose engine according to the modification is different from the fuel pump 42 shown in FIGS. 2 and 3 only in the following points, and has the same structure as the fuel pump 42 in the other points.

[0066] The first different point is that a gap 95 is present between the other end surface 74 of the rod 70 and the inner bottom 85 of the plunger 80. A spacer 94A can be fitted into the gap 95.

[0067] The second different point is that, by adopting the structure where the spacer 94A is fitted in the gap 95, movement of the other end 72 of the rod 70 in the longitudinal direction of the rod 70 relative to the plunger 80 is restricted by the first pin 92 and the spacer 94A.

[0068] In the diaphragm type fuel pump 42 for the general purpose engine according to the modification, it is possible to provide the spacer 94A in addition to the first pin 92. Regardless of whether or not the spacer 94A is present, the plunger 80 is biased toward the other end 72 of the rod 70 by the plunger biasing member 91. The first pin 92 is in contact with the part 84a of the edge 84 (one edge 84a) of the through hole 83 closer to the diaphragm at all times.

[0069] As shown in FIG. 4, in the case where only the first pin 92 is used, the other end 72 of the rod 70 can move in the longitudinal direction of the rod 70 relative to the plunger 80. In this case, the “diaphragm biasing member 100” for biasing the diaphragm 60 from the air chamber 57 to the pump chamber 56 is provided. In the structure, when the plunger 80 is pushed up toward the diaphragm 60 by the cam 25a of the general purpose engine 10, the diaphragm 60 is biased toward the pump chamber 56 by the diaphragm biasing member 100. The resulting discharge pressure of the fuel pump 42 is a relatively low pressure which depends on the biasing force of the diaphragm biasing member 100.

[0070] As shown in FIG. 6, in the case where both of the first pin 92 and the spacer 94A are used, the spacer 94A is interposed between the other end surface 74 of the rod 70 and the inner bottom 85 of the plunger 80, while in contact with the other end surface 74 and the inner bottom 85. Movement of the other end 72 of the rod 70 in the longitudinal direction of the rod 70 relative to the plunger 80 is restricted (i.e., locked) by the first pin 92 and the spacer 94A. As a result, the rod 70 is directly connected to the plunger 80, regardless of whether or not diaphragm biasing member 100 (see FIG. 4) is present.

[0071] Therefore, when the plunger 80 is pushed up toward the diaphragm 60 by the cam 25a of the general purpose engine 10, the diaphragm 60 is forcibly displaced elastically toward the pump chamber 56 by the plunger 80. Therefore, the resulting discharge pressure of the fuel pump 42 is a relatively high pressure which does not depend on the biasing force of the diaphragm biasing member 100.

[0072] In this manner, the discharge pressure of the fuel pump 42 can be changed optionally depending on whether or not the spacer 94A is present. Further, simply by selecting the presence or absence of the spacer 94A, with the simple structure, the discharge pressure of the fuel pump 42 can be changed very easily. Additionally, even in the case that the discharge pressure of the fuel pump 42 is changed, the shape and the dimensions of the fuel pump 42 remain exactly the same. That is, simply by switching between the fuel pump for use in the low pressure application and the fuel pump for use in the high pressure application, the pump can be used as is, without any modification. Therefore, in the fuel supply line 40 of the general purpose engine 10, it is possible to easily switch between the line having the specifications for the carburetor and the line having the specifications for the electronic control injection apparatus.

[0073] Further, by selecting the presence or the absence of the spacer 94A, the same diaphragm type fuel pump 42 can be switched between the low pressure application and the high pressure application. Therefore, improvement in the mass production efficiency is achieved. Consequently, it becomes possible to reduce the cost of the diaphragm type fuel pump 42 for the general purpose engine.

[0074] The diaphragm type fuel pumps 42, 42A for the general purpose engine can be adopted suitably for the general purpose engine of a general purpose machine such as an outboard engine or a work machine.

[0075] While the invention has been particularly shown and described with reference to the preferred embodiments, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the scope of the invention as defined by the appended claims.