Electromagnetic fuel injection valve

Abstract
An electromagnetic fuel injection valve comprises a movable unit having a valve element, an electromagnetic coil, and a magnetic circuit for magnetically attracting the movable unit toward a valve opening side through energization of the electromagnetic coil. The magnetic circuit is composed of a hollow, cylindrical stationary core, which defines a fuel passage extending axially through an injection valve body, a hollow seal ring made of a nonmagnetic or a feeble magnetic material, a hollow nozzle housing, and a movable core constituting a part of the movable unit. The stationary core and the nozzle housing are joined together through the seal ring. This electromagnetic fuel injection valve has improved responsibility.
Description




BACKGROUND OF THE INVENTION




The present invention relates to an electromagnetic fuel injection valve for internal combustion engines.




Hitherto, electromagnetic fuel injection valves driven by electric signals from an engine control unit have widely been used in internal combustion engines for motor vehicles. The conventional fuel injection valves have a construction in which an electromagnetic coil and a yoke accommodating the coil are arranged around a stationary core of a hollow cylindrical shape (center core) and a nozzle body is mounted to the lower portion of the yoke. The nozzle body has fitted therein a movable unit having a valve element. The movable unit is urged toward a valve seat by force of a return spring.




A conventional electromagnetic fuel injection valves, as described in, for instance, JP-A-10-339240 is known to have a construction in which a magnetic fuel connector section, a nonmagnetic intermediate pipe section and a nonmagnetic valve body section are formed in one united body by magnetizing a single pipe made from a composite magnetic material and demagnetizing only an intermediate portion of the pipe through induction heating or the like in order to reduce the number of parts and improve the assemblability. In this electromagnetic fuel injection valve, a cylindrical stationary iron core is press-fitted into the fuel connector section, and a movable core with a valve element is installed in the valve body section. Further, an electromagnetic coil is arranged around an intermediate outer circumferential portion of the pipe, with the yoke mounted on the outer side of the electromagnetic coil. When the electromagnetic coil is energized, a magnetic circuit is established through the yoke, fuel connector section, stationary core, movable core, valve body section and yoke to magnetically attract the movable core toward the stationary core. The nonmagnetic section is employed to prevent a possible short-circuit of magnetic flux between the fuel connector section and the valve body section.




In the construction as described in JP-A-10-339240 that has the nonmagnetic intermediate pipe portion at an intermediate part of the pipe, however, magnetic flux leakage cannot be prevented sufficiently, resulting in a reduced magnetic force for attracting the movable core and therefore deteriorated the responsiveness.




In recent years, also in gasoline engines, fuel injection valves that directly inject fuel into cylinders have been put into practical use. As the direct injection type fuel injection valve, a so-called long nozzle type injector has been proposed in which a nozzle body provided on a lower portion of a yoke is made slender and long. When the long nozzle injector is to be mounted on a cylinder head in which an intake valve, an intake manifold and other components are closely arranged near the injector, only the slender nozzle body that does not occupy a large space can be installed in the cylinder head, so that large-diameter body portions such as the yoke and a connector mold are disposed apart from other components and cylinder head to have no interference therewith. This injector thus has an advantage of high degree of freedom for installation. However, a nozzle driven by the movable core inherently becomes long due to the long length of the nozzle body, and the nozzle weight also increases, thereby posing a serious problem of a response delay due to a reduced magnetic force.




BRIEF SUMMARY OF THE INVENTION




An object of the present invention is to provide an electromagnetic fuel injection valve with improved responsiveness.




(1) To achieve the above objective, the invention provides an electromagnetic fuel injection valve which comprises a movable unit having a valve element, an electromagnetic coil, and a magnetic circuit for magnetically attracting the movable unit toward a valve opening side by energizing the electromagnetic coil. The magnetic circuit is composed of a hollow, cylindrical stationary core which defines a fuel passage extending axially through an injection valve body, a hollow seal ring made of a nonmagnetic or a feeble magnetic material, a hollow nozzle housing, and a movable core constituting a part of the movable unit, wherein the stationary core and the nozzle housing are coupled through the seal ring.




With this construction, it is possible to reduce flux leakage and improve a magnetic force and the responsiveness.




(2) In the above (1), preferably the seal ring has a flange at a lower portion thereof, a lower portion of the stationary core is press-fitted into an upper portion of the seal ring and welded thereto for sealing fuel, and the flange of the seal ring is press-fitted into a socket portion formed at an upper end of the nozzle housing and is welded thereto for sealing fuel.




(3) In the above (2), preferably, an outer circumference of a lower end of the stationary core is formed with a rounded or a tapered portion serving as a curved guide surface for press-fitting into the seal ring, and has a hard coating formed from a lower end face of the stationary core to the rounded portion or tapered portion.




(4) In the above (2), preferably, a contact surface between the movable unit and the stationary core is provided near an upper end of the flange of the seal ring.




(5) In the above (1), preferably the seal ring has a lower end portion formed to gently increase in inner diameter toward a lower end thereof, and an inner diameter of the lower end portion of the seal ring is larger than an inner diameter of the nozzle housing.




(6) In the above (1), the movable core preferably has a thin-walled portion at a lower portion thereof.




(7) In the above (1), the movable unit preferably comprises the movable core, the valve element and a joint for connecting the movable core and the valve element, and the joint comprises an upper cylinder portion, a lower cylinder portion smaller in diameter than the upper cylinder portion, and a tapered or spherical junction portion with a small fluid resistance for connecting the upper cylinder portion and the lower cylinder portion.




(8) In the above (7), the junction portion of the joint preferably has resiliency.




(9) In the above (8), a leaf spring is preferably provided between the movable core and the joint.




(10) In the above (7), preferably the junction portion of the joint has a hole for passage of fuel, and a total cross-sectional area of this hole is larger than a cross-sectional area of an axial fuel passage hole formed in the movable unit.




Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.











BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING





FIG. 1

is a longitudinal section view showing the overall construction of an electromagnetic fuel injection valve according to an embodiment of the present invention.





FIG. 2A

is a section view showing a part of the fuel injection valve of FIG.


1


.





FIG. 2B

is a section view showing a modification of the part shown in FIG.


1


.





FIG. 3

is an exploded perspective view showing the overall construction of the fuel injection valve of FIG.


1


.





FIG. 4

is an enlarged view of a yoke assembly


52


for use in the fuel injection valve of FIG.


1


.





FIG. 5

is a section view of an internal combustion engine in which used is the electromagnetic fuel injection valve according to the embodiment of this invention.





FIG. 6

is an enlarged view showing a construction of an orifice plate


16


and a front end portion of a movable unit


12


for use in the fuel injection valve of FIG.


1


.





FIGS. 7A

to


7


C are top, section and bottom views showing in an enlarged scale a swirler


15


for use in the fuel injection valve of FIG.


1


.





FIG. 8

is a side view of the movable unit


12


for use in the fuel injection valve of FIG.


1


.





FIGS. 9A and 9B

are top and section views showing in an enlarged scale a joint


11


for use in the fuel injection valve of FIG.


1


.





FIGS. 10A and 10B

are top and section views showing in an enlarged scale a leaf spring


9


for use in the fuel injection valve of FIG.


1


.





FIG. 11

is an enlarged view of an essential part of a stationary core


1


and a movable core


10


for use in the fuel injection valve of FIG.


1


.





FIG. 12

is a response characteristic diagram of the electromagnetic fuel injection valve according to the embodiment of the invention.





FIG. 13

is a longitudinal section view of a movable unit of an electromagnetic fuel injection valve according to another embodiment of the invention.





FIG. 14

is a longitudinal section view of a movable unit used of an electromagnetic fuel injection valve according to still another embodiment of the invention.











DETAILED DESCRIPTION OF THE INVENTION




Referring to FIG.


1


through

FIG. 12

, an electromagnetic fuel injection valve according to an embodiment of the present invention will be now described.




At the outset, the electromagnetic fuel injection valve according to the first embodiment will be explained with reference to FIG.


1


.

FIG. 1

is a longitudinal section view showing an overall construction of the electromagnetic fuel injection valve of this embodiment.




As shown in

FIG. 1

, a fuel injection valve


100


is of a so-called top-feed type which, when it is open, allows a fuel to flow in from a top of an injection valve body and flow down the valve in its axial direction and ejects the fuel out of an orifice provided at a lower end of the injection valve.




An axially extending fuel path in the fuel injection valve


100


is mainly composed of a hollow cylindrical stationary core


1


for introducing fuel, a hollow seal ring


19


having a flange at a lower portion thereof, a hollow nozzle housing


13


with its outer circumference tapered, a nozzle holder


14


, and an orifice plate


16


with a valve seat.




Now, referring to

FIG. 2A

, a construction of an essential part of the electromagnetic fuel injection valve of the embodiment will be described.

FIG. 2A

is a section view of the essential part.

FIG. 2B

is a section view of a modification of the essential part of FIG.


2


A.




As seen in

FIG. 2A

, the seal ring


19


is press-fitted at its upper end portion over the stationary core


1


and welded thereto at a position indicated by reference sign W


1


. The seal ring


19


is formed with a flange


19




a


at its lower end, which is press-fitted into the nozzle housing


13


and welded thereto at a position indicated by reference sign W


2


. This welding is done in the circumferential direction before assembling of the injection valve. The press-fitting thus realizes secure fixing between the seal ring


19


and the stationary core


1


and between the flange


19




a


of the seal ring


19


and the nozzle housing


13


. The reason for welding them together in the circumferential direction is to form a fuel path by the stationary core


1


, the seal ring


19


and the nozzle housing


13


and to prevent the leakage of fuel from the fuel path formed. Compared with a case where the seal ring is fixed to the stationary core and the nozzle housing with the welding alone, welding them together after the press-fitting can reduce adverse effects of thermal distortion due to welding. Further, in this embodiment, an inner radius r2 of the seal ring


19


is set larger than an inner radius r1 of the nozzle housing


13


(r2>r1).




Next, as shown in

FIG. 1

, the nozzle holder


14


is received in a lower portion of the nozzle housing


13


through a stroke adjustment ring


17


. A lower end of the nozzle housing


13


is secured to the nozzle holder


14


by a metal flow due to plastic flow joining. A plunger rod guide


18


is fixed in the nozzle holder


14


by press-fitting.




As described above, the stationary core


1


, seal ring


19


, nozzle housing


13


, stroke adjustment ring


17


and nozzle holder


14


are securely coupled together to form a fuel passage assembly.




In the fuel passage assembly are incorporated a cylindrical movable core


10


, a slender valve element


5


, a joint pipe


11


, a mass body


8


, a return spring


7


, a C-ring pipe


6


and others. The valve element


5


includes a valve rod. The movable core


10


, the valve rod


5


and the joint pipe


11


are joined together to form the movable unit


12


. The return spring


7


urges the movable unit


12


toward a valve seat


16




a


. The C-ring pipe


6


has a cross section in a letter C shape and serves as an element for adjusting a spring force of the return spring


7


.




An electromagnetic coil


2


is arranged around an outer periphery of the stationary core


1


in an area where the seal ring


19


is press-fitted over the stationary core


1


. A yoke


4


is arranged on the outside of the electromagnetic coil


2


. A plate housing


24


is press-fitted over the stationary core


1


and welded to an upper end of the yoke


4


to form an assembly for accommodating the electromagnetic coil


2


.




The fuel injection valve


100


, when the electromagnetic coil


2


is energized, forms a magnetic circuit through the yoke


4


, the stationary core


1


, the movable core


10


, the nozzle housing


13


and the plate housing


24


. As a result, the movable unit


12


is attracted against the force of the return spring


7


to make a valve opening movement. When the electromagnetic coil


2


is deenergized, the force of the return spring


7


make the movable unit


12


engage the valve seat


16




a


, as shown in

FIG. 1

, closing the valve. In this example, a lower end face of the stationary core


1


serves as a stopper that receives the movable unit


12


when a valve opening movement.




Next, features of respective parts for use in the fuel injection valve


100


of this embodiment will be described.




The stationary core


1


is made from a stainless steel and formed into an elongate, hollow cylinder by press working and cutting. A hollow portion in the stationary core


1


provides a fuel passage, into an inner circumferential surface of which the C-ring pin


6


shaped like a letter C in cross section is press-fitted. Changing a depth by which the C-ring pin


6


is press-fitted may adjust a load of the return spring


7


. A fuel filter


32


is installed above the C-ring pin


6


.




The seal ring


19


is made of a nonmagnetic metal. Alternatively, a feeble magnetic metal may be used. The seal ring


19


, as shown in

FIG. 2A

, has the flange


19




a


at its lower end and is thus shaped like a letter L in cross section on each side. The stationary core


1


and the nozzle housing


13


are joined through the seal ring


19


. The lower end face of the stationary core


1


is roughly aligned in vertical position with the upper end face of the nozzle housing


13


.




The flange


19




a


of the seal ring


19


is received in a counterbore


13




b


formed in the upper end of the nozzle housing


13


. The height of the flange


19




a


and the depth of the counterbore


13




b


of the nozzle housing


13


are appropriately set at about 1-2 mm. The flange


19




a


of the seal ring


19


is so constructed as to shield a magnetic flux generated by the electromagnetic coil


2


and efficiently introduce it to the nozzle housing


13


, the movable core


10


and the stationary core


1


.




Conventionally employed is a construction in which the nozzle housing


13


and the seal ring


19


are formed in one united boy and a portion corresponding to the seal ring


19


is demagnetized. Hence, the shielding of magnetic flux is not sufficient, and resultant flux leakage reduces the magnetic force. The construction of the invention described above on the other hand can concentrate the magnetic flux in the nozzle housing


13


, the movable core


10


and the stationary core


1


which together form the magnetic circuit, thus producing an enough magnetic force to attract the movable unit


12


. This arrangement can improve the responsiveness when opening the valve.




It is also possible, as shown in

FIG. 2B

, to form a seal ring


19




c


into a hollow cylinder of a nonmagnetic or a feeble magnetic metal and to secure it to the nozzle housing


13


and the stationary core


1


. Also in this case, the magnetic circuit for attracting the movable unit


12


can be prevented from developing magnetic flux leakage.




As shown in

FIG. 2A

, the nozzle housing


13


is made of a magnetic material and has a tapered portion on its outer circumference. Further, the nozzle housing


13


has counterbores


13




b


,


13




c


. The counterbore


13




b


is for receiving the seal ring


19


press-fitted therein. With the seal ring


19


press-fitted in the counterbored recess


13




b


, the upper end face of the flange


19




a


of the seal ring


19


slightly protrudes above the upper end face of the nozzle housing


13


. This protrusion is for minimizing errors during welding.




After the seal ring


19


and the nozzle housing


13


are joined together, an inner circumference


19




b


of the seal ring is cut and ground for press-fitting over the stationary core


1


. This machining sets the radius (r2) of the seal ring inner circumference


19




b


larger than the radius (r1) of a nozzle housing inner circumference


13




a


. This setting enables a high level of coaxialness between the seal ring inner circumference


19




b


and the nozzle housing


13


. The assembly errors of the stationary core


1


can be reduced as less as possible, thereby making it possible to stabilize the operation of the fuel injection valve


100


and keep an O-ring


21


and a backup ring


22


, both serving as fuel seals, in an appropriate range of condition during use.




The seal ring


19


is welded to the stationary core


1


and the nozzle housing


13


at locations indicated by the reference signs W


1


and W


2


to seal their inner circumferences and thereby prevent possible leakage of fuel flowing through the fuel injection valve


100






Since the welding location W


1


is set at a thin-walled portion of the seal ring


19


, the thermal energy required for the welding can be reduced, thereby preventing thermal deformations from occurring in parts of the fuel injection valve due to the welding heat.




The nozzle housing


13


has the counterbore


13




c


to receive the stroke adjustment ring


17


and a part of the nozzle holder


14


. The housing also has an annular groove


13




d


necessary for joining with the nozzle holder


14


.




The joining of the nozzle housing


13


and the nozzle holder


14


shown in

FIG. 1

is done by pushing the end face of the nozzle housing


13


to cause plastic deformation thereof and its metal to flow into two grooves


14




a


formed in a maximum diameter portion of the nozzle holder


14


. Thus, the nozzle holder


14


is securely fixed, and their inner circumferences are sealed to prevent leakage of fuel passing through the fuel injection valve


100


.




As shown in

FIG. 2A

, the nozzle housing


13


has a stepped portion


13




e


on an outer circumference of an upper end thereof, which is adapted to receive the hollow, cylindrical yoke


4


of FIG.


1


. With this fitting portion provided, it is possible to prevent positional deviations between the yoke


4


and the nozzle housing


13


when they are to be welded together after the electromagnetic coil


2


is accommodated.




Then, the plate housing


24


is axially pushed under pressure over the stationary core


1


until it contacts the upper end of the yoke


4


. The contact surface between the upper end of the yoke


4


and the plate housing


24


is welded along the entire circumference.




Further, pin terminals


20


of the electromagnetic coil are bent and a resin molding


23


is formed to complete a yoke semi-assembly.




Now, referring to

FIGS. 3 and 4

, a process of assembling the yoke semi-assembly


52


will be explained.

FIG. 3

is an exploded perspective view showing the overall construction of the electromagnetic fuel injection valve of the embodiment.

FIG. 4

is an enlarged view of the yoke semi-assembly


52


which constitutes a part of the electromagnetic fuel injection valve of the embodiment.




The process of manufacturing the yoke semi-assembly


52


of this embodiment has a feature that respective parts are stacked sequentially in one direction. More specifically, when manufacturing the yoke semi-assembly


52


shown in

FIG. 4

, first, the seal ring


19


is press-fitted into the nozzle housing


13


from above and welded thereto. Next, the stationary core


1


is press-fitted into the seal ring


19


from above and welded thereto. Then, the yoke


4


is fitted from above over the nozzle housing


13


and joined thereto by welding. Then, the electromagnetic coil


2


is installed from above on the inner circumferential side of the yoke


4


. Further, the plate housing


24


is pushed under pressure axially from above of the yoke


4


over the stationary core


1


and joined by welding along its entire circumference. After that, the pin terminals


20


of the electromagnetic coil are bent and the resin molding


23


is formed. Thus, the yoke semi-assembly


52


as shown in

FIG. 4

is formed.




Since the yoke semi-assembly


52


of the embodiment is manufactured by sequentially stacking the respective parts from one direction, as described above, the manufacturing of the yoke semi-assembly


52


can be easily automated.




Next, as shown in

FIG. 1

, a lower portion


14




b


of the nozzle holder is formed with a seal member mounting groove


14




c


in an outer circumference thereof, in which a seal member


26


such as a chip seal is installed. The nozzle holder lower portion


14




b


is longer than a conventional one and forms a so-called long nozzle portion.




Now, referring to

FIG. 5

, a configuration of an internal combustion engine using the fuel injection valve


100


will be described.

FIG. 5

is a section view of the internal combustion engine in which the electromagnetic fuel injection valve of the embodiment is used.




In a fuel injection system in which a fuel injection valve is directly installed in a cylinder head


106


of an engine


105


, when an intake valve


101


, a drive mechanism


102


for the intake and exhaust valves, an intake manifold


103


and other parts are arranged close together, there are cases where a large-diameter injection valve body portion will interfere with these parts and the cylinder head


106


. In that case, the long nozzle portion


14




b


of the fuel injection valve


100


shown in

FIG. 1

allows the large-diameter injection valve body portion to be located remote from the engine parts and cylinder head


106


(i.e., at a position not interfered with), advantageously increasing the degree of freedom of installing the fuel injection valve.




When the fuel injection valve is mounted in the cylinder head, a conventional practice involves providing a gasket between the yoke bottom of a large-diameter and the cylinder head to prevent leakage of combustion gas from the engine. In the fuel injection valve


100


of the embodiment, the seal ring


26


installed on the outer circumference of the slender long nozzle portion


14




b


seals between the outer circumference of the long nozzle portion


14




b


and an inner circumference of an insertion hole for this nozzle portion (in the cylinder head


106


) to prevent a combustion gas leakage from the engine. Thus, a combustion pressure receiving area at the sealing position can be reduced, which in turn contributes to a size reduction, a simplified structure and a reduced cost of the seal member.




As shown in

FIG. 1

, at the lower end (front tip) of the nozzle holder


14


are provided an orifice plate


16


and a fuel swirler (hereinafter referred to as a swirler)


15


. These parts


14


,


15


and


16


are formed as separate members.




Now, referring to

FIG. 6

, description will be made on the orifice plate


16


.

FIG. 6

is an enlarged view showing the orifice plate


16


and the front end portion of the movable unit


12


, both for use in the electromagnetic fuel injection valve of the embodiment.




As shown in

FIG. 6

, the orifice plate


16


is formed of a disc-shaped chip of, for example, stainless steel with an injection hole or orifice


27


formed at the center thereof. The orifice


27


is connected with a valve seat


16




a


formed upstream thereof in the orifice plate


16


.




As shown in

FIG. 1

, the orifice plate


16


is installed by press-fitting into a recess


14




d


of a lower end of the nozzle holder


14


. The swirler


15


is formed from a sintered alloy and press-fitted in the recess of the lower end of the nozzle holder


14


.




Here, referring to

FIGS. 7A-7C

, the swirler


15


will be explained.

FIGS. 7A-7C

are enlarged views showing the construction of the swirler


15


for use in the electromagnetic fuel injection valve of the embodiment.

FIG. 7A

is a top view,

FIG. 7B

a section view taken along the line B—B of

FIG. 7A

, and

FIG. 7C

a bottom view.




As shown in

FIG. 7A

, the swirler


15


is of a chip which is in the shape close to a regular triangle with its vertices rounded. At the center the swirler


15


has a center hole (guide)


25


for slidably guiding the front end (valve element) of the movable unit


12


. On the upper surface of the swirler


15


is formed an annular groove


28




a


around the center hole


25


. Guide grooves


28


are formed to radially extend outwardly from the annular groove


28




a


to introduce fuel to chamfers


15




a


at outer three sides of the swirler.




As shown in

FIG. 7C

, on the bottom surface of the swirler


15


is formed an annular step (flow path)


29


along its outer periphery. A plurality of passage grooves


30


(six in this embodiment) for swirling fuel are formed between the annular flow path


29


and the center hole


25


. These passage grooves


30


extend from the outer circumference of the swirler


15


toward the inner circumference almost tangentially thereto so that the fuel injected from the passage grooves


30


to the lower end of the center hole


25


has a swirling force. The annular step


29


is provided to serve as a fuel reservoir.




Further, as shown in

FIG. 7A

, there are three chamfers


15




a


formed on the outer periphery of the swirler


15


. The chamfers


15




a


provide fuel passages between them and the inner circumference of the nozzle holder


14


when the swirler


15


is fitted in the front end of the nozzle holder


14


, and also serve as a reference when machining the grooves


28


,


30


. The rounded surfaces provided at the outer periphery of the swirler


15


engage the inner circumference of the front end of the nozzle holder


14


. When the swirler


15


is shaped like an almost regular triangle with its vertices rounded as described above, it has an advantage of being able to secure a greater fuel flow than that provided by a polygon chip with four or more angles.




As shown in

FIG. 1

, the front end of the nozzle holder


14


(the end on the fuel injection side) is formed with the recess having a receiving surface


14




e


(stepped recess),


14




d


, for mounting of the swirler


15


and the orifice plate


16


. The swirler


15


is fitted into the recess of the nozzle holder so as to rest on the receiving surface


14




e


of the nozzle holder


14


. Further, the orifice plate


16


is press-fitted into the recess


14




d


and welded thereto, so that it bears on the swirler


15


. Reference sign W


3


indicates a location where the orifice plate


16


is welded along its entire circumference.




With the swirler


15


and the orifice plate


16


mounted as described above, the swirler


15


is held between the receiving surface


14




e


and the orifice plate


16


. Although the upper surface of the swirler


15


is in press-contact with the receiving surface


14




e


of the nozzle holder


14


, the provision of the fuel guide grooves


28


, as shown in

FIG. 7A

, allows the fuel upstream of the swirler to flow through these grooves


28


to fuel flow paths


31


on the outer circumference of the swirler


15


.




Now, referring to

FIG. 8

, the movable unit


12


will be explained.

FIG. 8

shows a side view of the movable unit


12


used in the electromagnetic fuel injection valve of the embodiment.




In the movable unit


12


, as shown in

FIG. 8

, the movable core


10


and the valve element


5


are connected together through the joint


11


having a spring function. Further, a leaf spring (damper plate)


9


is interposed between the movable core


10


and the joint


11


.




Further, as shown in

FIG. 1

, a mass body


8


(also referred to as a weight or movable mass) is arranged to extend from an axial hole f constituting a fuel passage in the stationary core


1


to an axial hole in the movable core


10


. This mass body


8


is axially movable independent of the movable unit


12


. The mass body


8


is situated between the return spring


7


and the leaf spring


9


. Thus, a spring load of the return spring


7


is applied to the movable unit


12


through the mass body


8


and the leaf spring


9


.




As shown in

FIG. 8

, the movable core


10


has an upper axial hole


10




a


for accepting a part of the mass body


8


, and a lower axial hole


10




b


of a larger diameter than that of the upper axial hole


10




a.






Here, referring to

FIGS. 9A and 9B

, the joint


11


will be explained.

FIGS. 9A and 9B

are enlarged views showing a construction of the joint


11


used in the electromagnetic fuel injection valve of the embodiment.

FIG. 9A

is a plan view and

FIG. 9B

a longitudinal section view.




As shown in

FIGS. 9A and 9B

, the joint


11


is of a cup-shaped pipe which has an upper cylinder portion


11




a


, a lower cylinder portion


11




c


with a smaller diameter than that of the upper cylinder portion


11




a


, and a tapered portion


11




b


between the upper cylinder portion


11




a


and the lower cylinder portion


11




c


, all these portions formed in one united body. The tapered portion


11




b


has a function of a leaf spring.




Further, as shown in

FIG. 8

, the upper cylinder portion


11




a


is fitted into a lower axial hole


10




b


of the movable core


10


and welded thereto at a position W


5


along its entire circumference, thus securing the joint


11


to the movable core


10


.




There is an inner stepped surface


10




c


between the upper axial hole


10




a


and the lower axial hole


10




b


of the movable core


10


. The leaf spring


9


is interposed between the inner stepped surface


10




c


and the upper end face of the upper cylinder portion


11




a


of the joint


11


. An upper part of the valve element (valve rod)


5


of the movable unit


12


is welded to the lower cylinder portion


11




c


of the joint


11


at a position W


6


along its entire circumference.




Now, referring to

FIGS. 10A and 10B

, the leaf spring


9


will be explained.

FIGS. 10A and 10B

are enlarged views showing a construction of the leaf spring


9


used in the electromagnetic fuel injection valve of the embodiment.

FIG. 10A

is a plan view, and

FIG. 10

a longitudinal section view.




As seen in

FIG. 10A

, the leaf spring


9


is in a ring shape with its inner portions punched out as indicated by


51


. The punching forms a plurality of elastic pieces


9




a


protruding inwardly that are arranged at equal distances along the circumference. The lower end of the cylindrical, movable mass body


8


is received and supported by these elastic pieces


9




a


of the leaf spring


9


.




Further, as shown in

FIG. 8

, a thin-walled portion


10




d


is formed at the lower end portion of the movable core


10


along its entire outer circumference. The seal ring


19


shown in

FIG. 1

is formed of nonmagnetic material and thus does not constitute the magnetic circuit. But those parts of the nozzle housing


13


and the movable core


10


that are situated immediately below the seal ring


19


form the magnetic circuit. However, the lower end portion of the movable core


10


has a reduced flux density and thus does not function as a magnetic circuit. At this lower end portion of the movable core


10


that does not function as the magnetic circuit the thin-walled portion


10




d


is provided. Since the lower end portion does not function as the magnetic circuit, forming it into the small-thickness portion does not adversely affect the characteristic of the magnetic circuit. On the other hand, the reduction of the thickness can reduce the weight of the movable core


10


, which in turn leads to a reduction in the weight of the movable unit


12


and an improvement of responsiveness in opening the valve.




As described above, since in this embodiment the leaf spring


9


supports the mass body (first mass body)


8


and the leaf spring portion (tapered portion)


11




b


of the joint


11


supports the movable core (second mass body)


10


, the mass body and the leaf spring function for supporting it (damper function) are duplicated.




When during a closing operation of the fuel injection valve the movable unit


12


strikes against the valve seat


16




a


due to the spring force of the return spring


7


, the impact is absorbed by the tapered portion


11




b


of the joint


11


. Further, a kinetic energy of rebounding of the movable unit


12


is absorbed by an inertia of the movable mass body


8


and an elastic deformation of the leaf spring


9


to prevent a rebound. With this provision of the double damper structure as described above, even in the fuel injection valve of an in-cylinder injection type with a large spring load of the return spring


7


, the impact energy of the valve element during the valve closing operation can be sufficiently attenuated to effectively prevent a secondary injection due to the rebound of the valve element.




As shown in

FIG. 1

, the interior of the joint


11


as well as that of the mass body


8


constitutes a fuel passage f. The tapered portion


11




b


of the joint


11


has a plurality of holes lid formed for passage of fuel to the nozzle holder


14


, as shown in FIG.


9


B.




In this embodiment, a total sectional area of the fuel passage holes


11




d


is set larger than a sectional area of the fuel passage f defined inside the stationary core


1


and the mass body


8


. When the inner diameter of the fuel passage f is taken to be 2φ, setting the inner diameter of the fuel passage holes


11




d


to 1.5φ results in the total sectional area of the four fuel passage holes


11




d


being 7.1 mm


2


while the fuel passage f has a sectional area of 3.1 mm


2


. It is therefore possible to reduce a pressure loss at the joint in the fuel passage and to avoid excessive throttling of fuel flow. As a result, the movable unit


12


can be operated in a stable manner, and further the fuel pressure at which to operate the fuel injection valve can be increased.




Since the joint


11


is formed as a cup-shaped pipe having the upper cylinder portion


11




a


, the lower cylinder portion


11




c


and the tapered portion


11




b


between them formed integral as one piece, it has the shape which is small in stream friction. Hence, a fluid resistance of the movable unit


12


including the joint


11


caused as it is moved can be reduced, thereby improving the responsiveness of the valve during its closing operation. The shape of the tapered portion


11




b


is not limited to a taper and it may be semispherical.




As shown in

FIG. 1

, a part of the valve element


5


serves as a guide surface on the movable unit side. An inner circumference


18




a


of the plunger rod guide


18


and an inner circumference of the center hole


25


of the swirler


15


form a guide surface, which constitutes a so-called 2-point support guide system, for slide-guiding the valve rod


5


.




The yoke


4


shown in

FIG. 1

is made of a magnetic stainless steel by press working or cutting and in a cylindrical shape for accommodating the electromagnetic coil


2


. The electromagnetic coil


2


is installed through the upper end of the yoke


4


. A yoke lower portion


4




c


is fitted over a part of the outer circumference of the nozzle housing


13


, and the position of the electromagnetic coil


2


is determined by an upper end face or flange


19




a


of the seal ring.




In this embodiment, a stroke of the movable unit


12


is defined by the valve seat


16




a


and the lower end of the stationary core


1


. Since the lower end face of the stationary core


1


therefore abuts against the upper surface of the movable core


10


when the valve is closed, the lower end face of the stationary core


1


and the upper surface of the movable core


10


are subject to a hard coating treatment, such as chrome plated films


60


,


61


.

FIG. 11

is an enlarged view showing essential parts of the stationary core


1


and the movable core


10


used in the electromagnetic fuel injection valve of the embodiment.




As shown in

FIG. 11

, a lower end


1




b


of the stationary core


1


is formed with a rounded portion


1




c


that serves as a curved guide surface for press-fitting into the seal ring


19


. The rounded portion


1




c


extends in a range indicated by L


1


in

FIG. 11 and

, in this example, has a curvature of about R=2.5 mm. With the lower end


1




b


of the stationary core


1


thus narrowed by the rounded portion


1




c


, a smoother press-fitting can be assured than when the lower end of the stationary core


1


is tapered. That is, in the case of the tapered lower end, an intersecting point between a taper line and a straight line has a wide angle edge, so that there is a fear that a galling will occur in the press-fitted portion of the seal ring at the wide angle edge position during the press fitting. This example does not cause such a problem.




The hard coating treatment such as chrome plated film


60


made on the lower end face of the stationary core


1


extends to a lower end side surface of the stationary core


1


. More specifically, the hard coating is formed from the lower end face of the stationary core


1


to the rounded portion (curved guide surface)


1




c


(not exceeding the range indicated by reference sign L


1


) in such a manner that no difficulty is in the press-fitting, that is, an outer diameter of the lower end portion of the core plus a thickness of the hard coating is smaller than an outer diameter of the straight portion of the stationary core


1


. This provides wear resistance and impact resistance.




As shown in

FIG. 6

, the valve element


5


of the movable unit


12


has its front end in the configuration of combining a spherical surface


12




a


and a conical projection


12




b


. The spherical surface


12




a


and the conical projection


12




b


have a discontinuous portion at a position indicated by reference numeral


12




c


. The spherical surface


12




a


rests on the valve seat


16




a


when the valve is closed. Forming the surface that contacts the valve seat


16




a


into the spherical surface


12




a


prevents a gap from being formed between the valve seat and the valve element even when the valve element tilts. The conical projection


12




b


has a function of minimizing a dead volume of the orifice


27


and regulating the fuel flow. The provision of the discontinuous portion


12




c


has an advantage of facilitating, and increasing the precision of, a polishing finish when compared with a case where the conical portion and the spherical surface portion are formed continuous.




Next, referring to

FIG. 3

, a process of assembling the nozzle will be explained. First, the swirler


15


is placed in the front end of the nozzle holder


14


, and the orifice plate


16


is press-fitted into the front end and welded thereto. The movable unit


12


, which is already assembled as shown in

FIG. 8

, is inserted into the nozzle holder. The movable unit


12


, after being assembled, is formed with the chrome plated film


61


, as shown in FIG.


11


. When assembling the nozzle holder


14


into the yoke semi-assembly


52


which is already assembled as shown in

FIG. 4

, the stroke adjustment ring


17


is set to a desired dimension to easily determine the stroke of the movable unit


12


. Then, the nozzle housing


13


and the nozzle holder


14


are joined together by metal flow. In the last step, the mass body


8


, return spring


7


, spring adjustment member


6


, fuel filter


32


, O-ring


21


and backup ring


22


are assembled.




Then, referring to

FIG. 12

, a response characteristic of the fuel injection valve according to the embodiment will be described.

FIG. 12

is a response characteristic diagram of the fuel injection valve of this embodiment. An abscissa in the diagram represents time (ms) and an ordinate represents a displacement (μm) of the movable unit.





FIG. 12

shows a displacement of the movable unit when a close signal is given to the fuel injection valve


100


at time 0 ms. In the diagram, reference sign X represents a response characteristic of a conventional fuel injection valve when closing the valve, which took about 0.42 ms until it closes. This conventional fuel injection valve is of the type having a part of the nozzle holder demagnetized. Reference signs Y and Z represent response characteristics of the fuel injection valves according to the embodiment during the valve closing. The fuel injection valve indicated by reference sign Y is of the example having the thin-walled portion


10




d


formed at the lower end of the movable core


10


, as shown in

FIG. 3

, to reduce the weight of the movable unit. The response time of this valve is 0.405 ms, which is shorter than that of the conventional valve indicated by reference sign X. The fuel injection valve indicated by reference sign Z is of the example realizing a weight reduction of the movable unit by the thin-walled portion


10




d


shown in FIG.


3


and also a reduction in magnetic flux leakage by using the independent, nonmagnetic seal ring


19


shown in FIG.


1


. The response time of this valve is 0.37 ms, which is shorter than that of the conventional valve indicated by the reference sign X.




As described above, in this embodiment the fuel passage assembly is formed by welding the nozzle housing


13


and the seal ring


19


together as shown in FIG.


4


. Further, this assembly and the stationary core


1


are joined by welding. This arrangement enables the manufacture of the fuel injection valve without deteriorating the accuracy of assembling the nozzle housing


13


and the stationary core


1


. In addition, although the seal ring


19


has the flange


19




a


and is thus shaped like a letter L in cross section on each side, magnetic flux leakage from the magnetic circuit is minimized by adopting a nonmagnetic or a feeble magnetic material. The magnetic flux flows concentratedly between the lower end of the stationary core


1


and the movable core


10


, thus improving a magnetic attraction characteristic of the solenoid valve. This in turn improves the responsiveness during the valve closing operation.




Further, when a part of the nozzle holder


14


is received in and joined to the nozzle housing


13


, the stroke adjustment ring


17


is interposed between them. This arrangement can set the stroke of the movable unit


12


to a specified value, thus enabling the delivery of a volume of fuel required of the fuel injection valve.




Moreover, since the impact and rebound of the valve element at time of closing the fuel injection valve are effectively prevented by the double damper structure, the secondary injection can be prevented more effectively than ever. The yoke semi-assembly is of the construction in which its components are successively stacked in one and the same direction, the assembling procedure is simple and can be automated easily.




While the above description has been made on the fuel injection valve of in-cylinder injection type, the present invention can also be applied to a fuel injection valve arranged in an intake manifold.




Next, referring to

FIGS. 13 and 14

, the configuration of fuel injection valves according to further embodiments of the invention will be described.

FIGS. 13 and 14

are longitudinal section views showing the constructions of the movable units in the fuel injection valves of these embodiments. In the drawings, the same reference numerals as those of

FIG. 3

denote the same parts.




A movable unit


12


A shown in

FIG. 13

comprises a movable core


10


, a damper plate


9


, a joint


11


and a valve element


5


A. While the valve element


5


shown in

FIG. 3

is made by machining a round rod, the valve element


5


A is made from a pipe. This construction can reduce the weight of the movable unit


12


A and further improve the responsiveness. Since fuel flows also into the pipe valve element


5


A, fuel discharge holes are formed through a lower part of the valve element


5


A.




A movable unit


12


B shown in

FIG. 14

comprises a movable core


10


, a damper plate


9


, a joint


11


and a valve element


5


B. The valve element


5


B is shaped like a cotter pin with a slit formed in its side. This construction can reduce the weight of the movable unit


12


B and further improve the responsiveness. The valve element


5


B can easily be fabricated by curling a plate material while forming a slit in its side.




As described above, the present invention can improve the responsibility of the electromagnetic fuel injection valve.




It will be understood by those skilled in the art that the foregoing description has been made on the embodiments of the invention and that various changes and modifications may be made in the invention without departing from the spirit of the invention and the scope of the appended claims.



Claims
  • 1. An electromagnetic fuel injection valve comprising:a movable unit having a valve element; an electromagnetic coil; a magnetic circuit for magnetically attracting the movable unit toward a valve opening side by energizing the electromagnetic coil, said magnetic circuit including a hollow, cylindrical stationary core defining a fuel passage extending axially through an injection valve body, a hollow seal ring made from one of a nonmagnetic material and a feeble magnetic material, a hollow nozzle housing, and a movable core constituting a part of the movable unit; and said stationary core and said nozzle housing being joined together through the seal ring.
  • 2. An electromagnetic fuel injection valve according to claim 1, wherein said seal ring has a flange at a lower portion thereof, a lower portion of said stationary core is press-fitted into an upper part of the seal ring and welded thereto for sealing fuel, and said flange of the seal ring is press-fitted into a receiving recess formed at an upper end of the nozzle housing and is welded thereto for sealing fuel.
  • 3. An electromagnetic fuel injection valve according to claim 2, wherein one of a rounded portion and a tapered portion serving as a curved guide surface for press-fitting into the seal ring is provided on an outer circumference of a lower end of said stationary core, and a hard coating is formed from a lower end face of the stationary core to the rounded or tapered portion.
  • 4. An electromagnetic fuel injection valve according to claim 2, wherein a contact surface between said movable unit and said stationary core is provided near an upper end of the flange of the seal ring.
  • 5. An electromagnetic fuel injection valve according to claim 1, wherein said seal ring has a lower end portion thereof formed to gently increase in inner diameter toward a lower end thereof, and an inner diameter of the lower end portion of the seal ring is larger than an inner diameter of the nozzle housing.
  • 6. An electromagnetic fuel injection valve according to claim 1, wherein said movable core has a thin-walled portion formed at a lower portion thereof.
  • 7. An electromagnetic fuel injection valve according to claim 1, wherein said movable unit comprises the movable core, the valve element, and a joint connecting the movable core and the valve element, and said joint comprises an upper cylinder portion, a lower cylinder portion smaller in diameter than the upper cylinder portion, and a tapered or spherical joint portion with a small fluid resistance, which connects the upper cylinder portion and the lower cylinder portion.
  • 8. An electromagnetic fuel injection valve according to claim 7, wherein said joint portion of the joint has resiliency.
  • 9. An electromagnetic fuel injection valve according to claim 8, wherein a leaf spring is interposed between said movable core and said joint.
  • 10. An electromagnetic fuel injection valve according to claim 7, wherein said joint portion of the joint has at least one hole for passing fuel, and a total cross-sectional area of this hole is larger than a cross-sectional area of an axial fuel passage hole formed in the movable unit.
Priority Claims (1)
Number Date Country Kind
2002-031717 Feb 2002 JP
US Referenced Citations (5)
Number Name Date Kind
4403741 Moriya et al. Sep 1983 A
4409580 Ishigaki Oct 1983 A
5791630 Nakao et al. Aug 1998 A
6343751 Ito et al. Feb 2002 B1
6695233 Sekine et al. Feb 2004 B2
Foreign Referenced Citations (1)
Number Date Country
10-339240 Dec 1998 JP