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Electromagnetic fuel pumpElectromagnetic fuel pump description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080044302, Electromagnetic fuel pump. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001]1. Field of the Invention [0002]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. [0003]2. Description of Related Art [0004]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. [0005]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. [0006]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. [0007]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. [0008]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. [0009]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 [0010]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. [0011]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. [0012]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. [0013]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. [0014]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 [0015]FIG. 1 is a longitudinal cross sectional view showing an embodiment in accordance with the present invention; [0016]FIG. 2 is an enlarged partial view of the proximal end side of the plunger in FIG. 1; [0017]FIG. 3 is a longitudinal cross sectional view showing a prior art; and [0018]FIG. 4 is an enlarged partial view of the proximal end side of the plunger in FIG. 3. DESCRIPTION OF PREFERRED EMBODIMENTS [0019]The description will be given below of a best mode for carrying out the present invention with reference to the accompanying drawings. [0020]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. Continue reading about Electromagnetic fuel pump... Full patent description for Electromagnetic fuel pump Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electromagnetic fuel pump patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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