Electromagnetic fuel pump

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 in FIG. 3, of an electromagnetic fuel pump used for supplying a liquid fuel such as a gasoline or the like to an engine, a plunger 7 constituted by a magnetic material and arranged slidably in a cylinder 4 is moved backward on the basis of a magnetomotive force caused by a current application to an electromagnetic coil 5 against an urging force of a return spring 43, and a check valve 32 provided in a leading end side of the plunger 7 is opened so as to introduce the fuel into a pressurizing chamber 6 formed in a front side of the plunger 7 from an intake port 46 formed in a proximal end of the cylinder 4.

Further, the urging force of the return spring 43 overcomes the magnetic force by reducing or stopping the current to the electromagnetic coil 5, and the plunger 7 is moved forward, thereby pressurizing the fuel in the pressurizing chamber 6 and a check valve 33 arranged on the downstream side of the pressurizing chamber 6 is opened. The fuel is delivered toward the engine from a discharge port 47 formed in the leading end of the cylinder 4 by repeating the operation mentioned above.

As mentioned above, the magnetomotive force by the electromagnetic coil 5 passes through the plunger 7 while passing through tubular bodies 42 and 42 constituting a part of the cylinder arranged around the electromagnetic coil 5 and the magnetic material constituting a coil cover 8 as shown by the thick arrow, thereby the plunger 7 is slidably attracted in a proximal end direction against an urging force of the return spring 43 so as to drive the pump.

In this case, as shown in an enlarged partial view of the proximal end side in the plunger 7 shown in FIG. 4, the conventional plunger type electromagnetic fuel pump is structured such that a return spring guide 36 annularly protruding from a proximal end surface of the plunger 7 for retaining a leading end side of the return spring 43 is formed to guide the return spring 43 in a state that the return spring guide 36 closely contacts the inner peripheral side of the return spring 43. Accordingly, an air gap Y formed between the plunger 7 made of the magnetic material and the tubular body 42 forming a magnetic part of the cylinder 4 tends to become larger during a non-exciting time, and a loss of the magnetomotive force generated from the electromagnetic coil 5 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, the return spring 43 arranged over a comparatively long distance along a center axis within the cylinder 4 is flexed within the cylinder and an urging direction thereof is not stable during actuating the pump, because a guide portion formed by the return spring guide 36 is short. Accordingly, there is a problem that a smooth sliding movement of the plunger 7 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 in FIG. 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 in FIG. 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 an electromagnetic fuel pump 1, for example, in the case that the present invention is used in a fuel supply system of a gasoline engine. The electromagnetic fuel pump 1 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, the electromagnetic fuel pump 1 is structured such that an electromagnetic coil 5 is provided around a cylinder 4, and a cylindrical plunger 3 is slidably provided in the cylinder 4 so as to be slidable in a horizontal direction in the drawing. A return spring 41 is arranged on a rear end side of the plunger 3 in a compressed state, and urges the plunger 3 toward the downward side, i.e., toward the left in the drawing.

A fuel passage 38 passes through the plunger 3 along center axis thereof, a check valve 32 is arranged on a leading end side (left side in the drawing), a check valve 33 is also provided in the same manner in a fuel passage in the cylinder 4 on the downward side of the check valve 32, and a pressurizing chamber 6 is formed between these two check valves 32 and 33. The above structure is similar to the conventional plunger type electromagnetic fuel pump and is well known.

Further, in the present embodiment, an insertion hole 35 is provided along the center axis of the plunger 3 at a predetermined depth from the proximal end surface of the plunger 3, and the inner peripheral surface thereof is formed as a spring guide retaining the outer peripheral leading end side of the return spring 41. This point is one of great features of the present invention.

With reference to an enlarged partial view of the proximal end side of the plunger 3 in FIG. 2, the fuel passage 38 passes through the plunger 3 in conformity with the center axis thereof, and the insertion hole 35 is provided by enlarging the proximal end side of the fuel passage 38 so that its inner diameter is slightly larger than the outer diameter of the return spring 41 and the latter can be inserted in the insertion hole 35.

Further, the leading end side of the return spring 41 is inserted in the insertion hole 35, the leading end of the return spring 41 is brought into contact with the ring-shaped seat surface formed on a bottom surface of the insertion hole 35 on the basis of a difference between the original inner diameter of the fuel passage 38 and the inner diameter of the enlarged portion, and the plunger 3 is urged toward the leading end side of the electromagnetic fuel pump 1.

FIG. 2 shows a state before the electromagnetic coil 5 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 the plunger 3 constituted by the magnetic material, and the tubular body 42 constituted by the magnetic material, however, the width of the air gap X becomes significantly smaller than the air gap Y in the conventional electromagnetic fuel pump 2 shown in FIG. 4.

This is because in the prior art, since the inner peripheral side of the return spring 43 is held and guided by the outer peripheral surface of the spring guide 36 annularly protruding from the proximal end surface of the plunger 7, the proximal end surface of the plunger 7 is positioned close to the leading end within the cylinder 4 and the air gap becomes large, but in the present invention, since the leading end side of the return spring 41 is inserted in the insertion hole 35 provided from the proximal end surface of the plunger 3, and the outer peripheral side of the return spring 41 is held and guided by the inner peripheral surface of the insertion hole 35, the proximal end surface of the plunger 3 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 the electromagnetic coil 5 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 in FIG. 2, the guide portion formed by the inner peripheral surface of the insertion hole 35 becomes widely longer than the guide portion of the annularly protruding spring guide 36 in the prior art, it is possible to stably retain the return spring 41 tending to deflect in a centrifugal direction in accordance with the pumping operation, it is easy to stably actuate the plunger 3, and it is easy to secure an accurate pumping operation.

Further, as shown in FIG. 1, an insertion hole 45 having a predetermined depth is provided from the inner proximal end surface of the cylinder 4 with which the proximal end side of the return spring 41 is brought into contact, in the similar manner to the insertion hole 35 of the plunger 3, and the proximal end portion of the return spring 41 is inserted in the insertion hole 45 so as to retain the outer peripheral proximal end side of the return spring 41 by the inner peripheral surface of the insertion hole 45, so that both end sides of the return spring 41 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.