US20080044302A1 - Electromagnetic fuel pump - Google Patents

Abstract

The invention can secure an improved pump operation while minimizing a loss of a magnetomotive force generated by an electromagnetic coil and making it possible to achieve a compact structure and a weight saving of an apparatus, in a plunger type electromagnetic fuel pump. In an electromagnetic fuel pump (1) which pressure-feeds a fuel by controlling a current application to an electromagnetic coil (5) and repeating generation and elimination of a magnetic force so as to slidably reciprocate a plunger (3) arranged in a cylinder (4) and having a proximal end side urged by a return spring (41), an insertion hole (35) for inserting the return spring (41) is provided from the proximal end surface of the plunger (3) at a predetermined depth along the center axis of the plunger (3), and the inner peripheral surface of the insertion hole (3) is formed as a spring guide retaining the outer peripheral leading end side of the return spring (41).

Description

BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates to an electromagnetic fuel pump used for delivering a liquid fuel reserved in a fuel tank to a combustion apparatus, more particularly to a plunger type electromagnetic fuel pump.
• 2. Description of Related Art
• Conventionally, a fuel pump has been employed as a fuel delivery means of a combustion apparatus such as an oil heater, an engine or the like, and as described in Japanese Unexamined Patent Publication No. 5-79452 and Japanese Unexamined Patent Publication No. 2002-39067, there has been generally widely spread a plunger type electromagnetic fuel pump which can achieve a stable fuel delivery and an accurate flow rate control by repeating generation and elimination of a magnetic force to slidably reciprocate a plunger urged by a return spring for pressurizing a fuel in a fuel passage.
• In the plunger type electromagnetic fuel pump, for example, as shown in a longitudinal cross sectional view, shown inFIG. 3, of an electromagnetic fuel pump used for supplying a liquid fuel such as a gasoline or the like to an engine, aplunger7 constituted by a magnetic material and arranged slidably in acylinder4 is moved backward on the basis of a magnetomotive force caused by a current application to anelectromagnetic coil5 against an urging force of areturn spring43, and acheck valve32 provided in a leading end side of theplunger7 is opened so as to introduce the fuel into a pressurizingchamber6 formed in a front side of theplunger7 from anintake port46 formed in a proximal end of thecylinder4.
• Further, the urging force of thereturn spring43 overcomes the magnetic force by reducing or stopping the current to theelectromagnetic coil5, and theplunger7 is moved forward, thereby pressurizing the fuel in the pressurizingchamber6 and acheck valve33 arranged on the downstream side of the pressurizingchamber6 is opened. The fuel is delivered toward the engine from adischarge port47 formed in the leading end of thecylinder4 by repeating the operation mentioned above.
• As mentioned above, the magnetomotive force by theelectromagnetic coil5 passes through theplunger7 while passing throughtubular bodies42 and42 constituting a part of the cylinder arranged around theelectromagnetic coil5 and the magnetic material constituting acoil cover8 as shown by the thick arrow, thereby theplunger7 is slidably attracted in a proximal end direction against an urging force of thereturn spring43 so as to drive the pump.
• In this case, as shown in an enlarged partial view of the proximal end side in theplunger7 shown inFIG. 4, the conventional plunger type electromagnetic fuel pump is structured such that areturn spring guide36 annularly protruding from a proximal end surface of theplunger7 for retaining a leading end side of thereturn spring43 is formed to guide thereturn spring43 in a state that thereturn spring guide36 closely contacts the inner peripheral side of thereturn spring43. Accordingly, an air gap Y formed between theplunger7 made of the magnetic material and thetubular body42 forming a magnetic part of thecylinder4 tends to become larger during a non-exciting time, and a loss of the magnetomotive force generated from theelectromagnetic coil5 becomes large. Therefore, it is not easy to achieve a compact structure and a weight saving of the electromagnetic fuel pump on the basis of necessity for securing a desired magnetic force.
• Further, thereturn spring43 arranged over a comparatively long distance along a center axis within thecylinder4 is flexed within the cylinder and an urging direction thereof is not stable during actuating the pump, because a guide portion formed by thereturn spring guide36 is short. Accordingly, there is a problem that a smooth sliding movement of theplunger7 is prevented and it is hard to secure an accurate pump operation.
SUMMARY OF THE INVENTION
• The prevent invention is made for solving the problem mentioned above, and an object of the present invention is to secure an accurate pump operation while minimizing a loss of a magnetomotive force generated by an electromagnetic coil and making it possible to achieve a compact structure and a weight saving of an apparatus, in a plunger type electromagnetic fuel pump.
• In accordance with the present invention made for solving the problem mentioned above, there is provided an electromagnetic fuel pump comprising: a cylinder having a discharge port provided with a check valve on a leading end side and an intake port on a proximal end side thereof; a plunger slidably fitted in the cylinder, the plunger having a fuel passage formed along an axis thereof and provided with a check valve therein; a return spring arranged on the proximal end side between the plunger and the cylinder for urging the plunder in a leading end side direction; and an electromagnetic coil arranged on the outside of the cylinder, a current application to the electromagnetic coil being controlled so as to repeat generation and elimination of a magnetic force to cause the plunger to slidably reciprocate for delivering a fuel under pressure; wherein an insertion hole for inserting the return spring is provided in a proximal end surface of the plunger at a predetermined depth along a center axis of the plunger, and an inner peripheral surface of the insertion hole is formed as a spring guide retaining an outer peripheral leading end side of the return spring.
• As mentioned above, the spring guide in the present invention is different from the conventional structure retaining the inner peripheral side of the return spring annularly protruding from the proximal end surface of the plunger, and is structured so as to retain the outer peripheral leading end side of the return spring by the inner peripheral surface of the insertion hole pierced from the proximal end surface of the plunger. Accordingly, an air gap formed between the plunger and the magnetic portion on the cylinder side for attracting the plunger becomes small, and it is easy to minimize the loss of the magnetomotive force. Further, it is possible to make the guide portion retaining the return spring longer than the conventional spring guide so as to make it easy to stably retain the return spring.
• Further, in the electromagnetic fuel pump, in the case that a second insertion hole for inserting the return spring is provided in an inner proximal end surface of the cylinder at a predetermined depth along the center axis of the cylinder, and an inner peripheral surface thereof is formed as a spring guide retaining an outer peripheral proximal end side of the return spring, both end sides of the return spring can be stably held.
• In accordance with the present invention structured such that the outer peripheral leading end side of the return spring urging the plunger is held by the inner peripheral surface of the insertion hole provided in the plunger, it is possible to reduce the air gap between the plunger proximal end side and the magnetic portion of the cylinder, and it is easy to achieve a compact structure and a weight saving of the apparatus while minimizing the loss of the magnetomotive force generated by the electromagnetic coil. Further, it is possible to make the guide portion of the return spring longer, and it is possible to secure an accurate pumping operation.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a longitudinal cross sectional view showing an embodiment in accordance with the present invention;
• FIG. 2 is an enlarged partial view of the proximal end side of the plunger inFIG. 1;
• FIG. 3 is a longitudinal cross sectional view showing a prior art; and
• FIG. 4 is an enlarged partial view of the proximal end side of the plunger inFIG. 3.
DESCRIPTION OF PREFERRED EMBODIMENTS
• The description will be given below of a best mode for carrying out the present invention with reference to the accompanying drawings.
• FIG. 1 shows a longitudinal cross sectional view of anelectromagnetic fuel pump1, for example, in the case that the present invention is used in a fuel supply system of a gasoline engine. Theelectromagnetic fuel pump1 introduces and pressure-feeds a fuel corresponding to a gasoline reserved in a fuel tank (not shown) so as to supply it to an engine via a fuel piping by an injector, and is called as a so-called plunger type electromagnetic fuel pump.
• Further, theelectromagnetic fuel pump1 is structured such that anelectromagnetic coil5 is provided around acylinder4, and acylindrical plunger3 is slidably provided in thecylinder4 so as to be slidable in a horizontal direction in the drawing. Areturn spring41 is arranged on a rear end side of theplunger3 in a compressed state, and urges theplunger3 toward the downward side, i.e., toward the left in the drawing.
• Afuel passage38 passes through theplunger3 along center axis thereof, acheck valve32 is arranged on a leading end side (left side in the drawing), acheck valve33 is also provided in the same manner in a fuel passage in thecylinder4 on the downward side of thecheck valve32, and a pressurizingchamber6 is formed between these twocheck valves32 and33. The above structure is similar to the conventional plunger type electromagnetic fuel pump and is well known.
• Further, in the present embodiment, aninsertion hole35 is provided along the center axis of theplunger3 at a predetermined depth from the proximal end surface of theplunger3, and the inner peripheral surface thereof is formed as a spring guide retaining the outer peripheral leading end side of thereturn spring41. This point is one of great features of the present invention.
• With reference to an enlarged partial view of the proximal end side of theplunger3 inFIG. 2, thefuel passage38 passes through theplunger3 in conformity with the center axis thereof, and theinsertion hole35 is provided by enlarging the proximal end side of thefuel passage38 so that its inner diameter is slightly larger than the outer diameter of thereturn spring41 and the latter can be inserted in theinsertion hole35.
• Further, the leading end side of thereturn spring41 is inserted in theinsertion hole35, the leading end of thereturn spring41 is brought into contact with the ring-shaped seat surface formed on a bottom surface of theinsertion hole35 on the basis of a difference between the original inner diameter of thefuel passage38 and the inner diameter of the enlarged portion, and theplunger3 is urged toward the leading end side of theelectromagnetic fuel pump1.
• FIG. 2 shows a state before theelectromagnetic coil5 is excited, in which an air gap X in term of a passage of a line of magnetic force is formed between the proximal end side of theplunger3 constituted by the magnetic material, and thetubular body42 constituted by the magnetic material, however, the width of the air gap X becomes significantly smaller than the air gap Y in the conventionalelectromagnetic fuel pump2 shown inFIG. 4.
• This is because in the prior art, since the inner peripheral side of thereturn spring43 is held and guided by the outer peripheral surface of thespring guide36 annularly protruding from the proximal end surface of theplunger7, the proximal end surface of theplunger7 is positioned close to the leading end within thecylinder4 and the air gap becomes large, but in the present invention, since the leading end side of thereturn spring41 is inserted in theinsertion hole35 provided from the proximal end surface of theplunger3, and the outer peripheral side of thereturn spring41 is held and guided by the inner peripheral surface of theinsertion hole35, the proximal end surface of theplunger3 is positioned closer to the proximal end within the cylinder than the prior art, and the air gap can be reduced.
• Accordingly, it is easy to restrict the loss of the electromotive force generated by theelectromagnetic coil5 to the minimum, and it is possible to achieve a pump performance equal to or more than the conventional one by the lighter and more compact apparatus.
• Further, as shown inFIG. 2, the guide portion formed by the inner peripheral surface of theinsertion hole35 becomes widely longer than the guide portion of the annularly protrudingspring guide36 in the prior art, it is possible to stably retain thereturn spring41 tending to deflect in a centrifugal direction in accordance with the pumping operation, it is easy to stably actuate theplunger3, and it is easy to secure an accurate pumping operation.
• Further, as shown inFIG. 1, aninsertion hole45 having a predetermined depth is provided from the inner proximal end surface of thecylinder4 with which the proximal end side of thereturn spring41 is brought into contact, in the similar manner to theinsertion hole35 of theplunger3, and the proximal end portion of thereturn spring41 is inserted in theinsertion hole45 so as to retain the outer peripheral proximal end side of thereturn spring41 by the inner peripheral surface of theinsertion hole45, so that both end sides of thereturn spring41 are guided at the predetermined depths, the motion of the plunger becomes further stable, and it is possible to secure a more accurate pump operation.
• As mentioned above, in the plunger type electromagnetic fuel pump, it is possible to minimize the loss of the magnetomotive force generated by the electromagnetic coil in accordance with the present invention, and it is possible to secure the accurate pump operation while making it possible to achieve the compact structure and the weight reduction of the apparatus.

Claims (2)

1. An electromagnetic fuel pump comprising:

a cylinder having a discharge port provided with a check valve on a leading end side and an intake port on a proximal end side thereof;

a plunger slidably fitted in the cylinder, the plunger having a fuel passage formed along an axis thereof and provided with a check valve therein;

a return spring arranged on the proximal end side between the plunger and the cylinder for urging the plunder in a leading end side direction; and

an electromagnetic coil arranged on the outside of the cylinder, a current application to the electromagnetic coil being controlled so as to repeat generation and elimination of a magnetic force to cause the plunger to slidably reciprocate for delivering a fuel under pressure;

wherein an insertion hole for inserting the return spring is provided in a proximal end surface of the plunger at a predetermined depth along a center axis of the plunger, and an inner peripheral surface of the insertion hole is formed as a spring guide retaining an outer peripheral leading end side of the return spring.

2. The electromagnetic fuel pump as claimed inclaim 1, wherein a second insertion hole for inserting the return spring is provided in a proximal end surface of the cylinder at a predetermined depth along the center axis of the cylinder, and an inner peripheral surface of the second insertion hole is formed as a spring guide retaining an outer peripheral proximal end side of the return spring.

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