Solenoid valve and fuel injection valve having the same

A solenoid valve includes a movable core, a magnetic opposed portion opposed to the movable core, a nonmagnetic cylindrical portion, a first magnetic cylindrical portion axially close to the movable core, and a second magnetic cylindrical portion located radially outside of the magnetic opposed portion. The nonmagnetic cylindrical portion surrounds radially outside of a gap between the magnetic opposed portion and the movable core. A coil is provided radially outside of the nonmagnetic cylindrical portion. A thickness t of the nonmagnetic cylindrical portion, a cross-sectional area S1 of the magnetic opposed portion, and a total cross-sectional area S2 of both the magnetic opposed portion and the second magnetic cylindrical portion having the thickness t satisfy the relationships of t≦0.6 mm and 0.55≦(S1/S2).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and incorporates herein by reference Japanese Patent Applications No. 2007-78478 filed on Mar. 26, 2007 and No. 2008-15037 filed on Jan. 25, 2008.

FIELD OF THE INVENTION

The present invention relates to a solenoid valve. The present invention further relates to a fuel injection valve having the solenoid valve.

BACKGROUND OF THE INVENTION

For example, U.S. Pat. No. 5,769,391 (JP-A-11-500509) discloses a fuel injection valve having a solenoid valve including a stationary core, a movable core, a valve element, and a coil. When the coil is energized, the stationary core and the movable core therebetween generate magnetic attractive force to manipulate the valve element together with the movable core so as to control communication in a fluid passage for intermitting fuel injection. In U.S. Pat. No. 5,769,391, a movable core side magnetic portion surrounds an outer circumferential periphery of the movable core. The movable core side magnetic portion and a stationary core side magnetic portion therebetween define a magnetism throttle. The movable core side magnetic portion, the stationary core side magnetic portion, and the magnetism throttle are integrated into one component. In U.S. Pat. No. 5,769,391, the magnetism throttle restricts the movable core side magnetic portion and the stationary core side magnetic portion from magnetically short-circuiting therebetween when a coil is energized. Thus, the movable core and the stationary core generate magnetic attractive force in a gap therebetween.

In U.S. Pat. No. 5,769,391, the magnetic throttle is formed from a magnetic material, whereby the movable core side magnetic portion and the stationary core side magnetic portion can be restricted from magnetically short-circuiting, nevertheless magnetic flux may leak through the magnetism throttle. As a result the magnetic attractive force between the movable core and the stationary core may decrease.

Alternatively, it is conceivable to provide a nonmagnetic portion, instead of the magnetic throttle, which is formed from the magnetic material. In this case, the nonmagnetic portion is provided between the movable core side magnetic portion and the stationary core side magnetic portion to surround radially outside a gap, which is defined between the movable core and the stationary core. In the present structure, the nonmagnetic portion is capable of restricting the movable core side magnetic portion and the stationary core side magnetic portion from magnetically short-circuiting therebetween.

However, in the present structure, an eddy current may arise in the nonmagnetic portion when the coil is de-energized and magnetic flux quickly reduces in the gap. When an eddy current arises in the non-magnetic portion, which is located radially outside the gap, magnetic flux may be induced in the magnetic portion in the vicinity of the gap. Consequently, magnetic attractive force between the stationary core and the movable core may be retained for a long period. Consequently, response of the valve element of the solenoid valve may be impaired when the coil is de-energized.

SUMMARY OF THE INVENTION

In view of the foregoing problems, it is an object of the present invention to produce a solenoid valve configured to quickly actuate a valve element when being de-energized. It is another object of the present invention to produce a fuel injection valve having the solenoid valve.

According to one aspect of the present invention, a solenoid valve comprises a movable core. The solenoid valve further comprises a valve element configured to move together with the movable core so as to control fluid communication. The solenoid valve further comprises a magnetic opposed portion located farther away from the valve element than the movable core and opposed to the movable core, the magnetic opposed portion and the movable core being configured to therebetween define a gap. The solenoid valve further comprises a nonmagnetic cylindrical portion surrounding radially outside of the gap. The solenoid valve further comprises a first magnetic cylindrical portion located axially closer to the movable core than the nonmagnetic cylindrical portion. The solenoid valve further comprises a second magnetic cylindrical portion located around an outer circumferential periphery of the magnetic opposed portion, the magnetic opposed portion being located axial farther away from the first magnetic cylindrical portion than the nonmagnetic cylindrical portion. The solenoid valve further comprises a coil located around an outer circumferential periphery of the nonmagnetic cylindrical portion, the coil being configured to generate magnetic attractive force between the magnetic opposed portion and the movable core when being energized. The nonmagnetic cylindrical portion has a thickness t. The magnetic opposed portion has a cross-sectional area S1. The magnetic opposed portion and a cylindrical member which retains the magnetic opposed portion and has the thickness t, have a total cross-sectional area S2. The thickness t, the cross-sectional area S1, and the total cross-sectional area S2satisfy t≦0.6 mm and 0.55≦(S1/S2).

According to another aspect of the present invention, a solenoid valve comprises a movable core. The solenoid valve further comprises a valve element configured to move together with the movable core so as to control fluid communication. The solenoid valve further comprises a magnetic opposed portion located farther away from the valve element than the movable core and opposed to the movable core, the magnetic opposed portion and the movable core being configured to therebetween define a gap. The solenoid valve further comprises a nonmagnetic cylindrical portion surrounding radially outside of the gap. The solenoid valve further comprises a first magnetic cylindrical portion located axially closer to the movable core than the nonmagnetic cylindrical portion. The solenoid valve further comprises a second magnetic cylindrical portion located around an outer circumferential periphery of the magnetic opposed portion, which is located axially farther away from the first magnetic cylindrical portion than the nonmagnetic cylindrical portion. The solenoid valve further comprises a coil located around an outer circumferential periphery of the nonmagnetic cylindrical portion, the coil being configured to generate magnetic attractive force between the magnetic opposed portion and the movable core when being energized. The nonmagnetic cylindrical portion has a thickness less than or equal to 0.6 mm. The nonmagnetic cylindrical portion has at least one recess.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First Embodiment

As shown inFIGS. 1,2, a fuel injection valve10is provided to, for example, a gasoline engine. A cylindrical member12is a substantially cylindrical member formed from a magnetic material or a nonmagnetic material. The cylindrical member12has a fuel passage100, which accommodates a valve body20, a valve element24, a movable core26, a spring28, a stationary core30, and the like.

Referring toFIG. 2, the cylindrical member12has a first magnetic cylindrical member14, a nonmagnetic cylindrical member16, and a second magnetic cylindrical member18, which are arranged in this order from the valve body20located on the lower side thereof. The first magnetic cylindrical member14, the nonmagnetic cylindrical member16, and the second magnetic cylindrical member18are integrally joined with each other by, for example, laser welding. The first magnetic cylindrical member14, the nonmagnetic cylindrical member16, and the second magnetic cylindrical member18respectively correspond to a first magnetic cylindrical portion, a nonmagnetic cylindrical portion, and a second magnetic cylindrical portion. The cylindrical member12is located radially inside of a coil44to surround the outer circumferential peripheries of both the movable core26and the stationary core30. The first magnetic cylindrical member14, the nonmagnetic cylindrical member16, the second magnetic cylindrical member18, the valve element24, the movable core26, the spring28, the stationary core30, and the coil44configure a solenoid valve in the fuel injection valve10.

The first magnetic cylindrical member14surrounds the outer circumferential periphery of the movable core26. The second magnetic cylindrical member18surrounds the outer circumferential periphery of the stationary core30. Together with the movable core26and the stationary core30, the first magnetic cylindrical member14and the second magnetic cylindrical member18form a magnetic circuit. The movable core26and the stationary core30therebetween define a gap200. The nonmagnetic cylindrical member16surrounds radially outside of the gap200to restrict magnetic flux tom being short-circuited between the first magnetic cylindrical member14and the second magnetic cylindrical member18. The first magnetic cylindrical member14and the second magnetic cylindrical member18are formed from a magnetic material such as electromagnetic stainless steel, SUS430, Fe—Co alloy, or the like. The nonmagnetic cylindrical member16is formed from a nonmagnetic material such as SUS304, SUS305, or the like. The first magnetic cylindrical member14, the second magnetic cylindrical member18, and the nonmagnetic cylindrical member16are preferably greater than or equal to 60 μΩ·m in specific resistance value. As shown inFIG. 3, the nonmagnetic cylindrical member16is formed from nonmagnetic metallic powder. Specifically, the nonmagnetic metallic powder is molded by metal injection molding (MIM) to be in a predetermined shape, and the molded form is thereafter sintered to be a product of the nonmagnetic cylindrical member16. The nonmagnetic cylindrical member16is formed with pores210therein by sintering the molded form, which is produced by the MIM process.

The valve body20is fixed to an inner circumferential periphery of a tip end of the first magnetic cylindrical member14on the side of nozzle holes by welding or the like. A nozzle plate22, which has the nozzle holes, is joined with an outer bottom surface of the valve body20by welding of the like. The valve body20has an inner circumferential periphery defining a valve seat21to which the valve element24is configured to be seated. The valve element24is a closed-end cylindrical hollow member, which is configured to be seated to the valve seat21of the valve body20. When the valve element24is seated to the valve seat21, the nozzle holes of the nozzle plate22are blockaded, whereby fuel injection is terminated. The valve element24has multiple fuel holes24aeach passing through a sidewall of the valve element24. Fuel flows into the valve element24, and the fuel flows out of the valve element24through the fuel holes24a. The fuel is lead to a valve portion, which is configured with the valve element24and the valve seat21.

The movable core26is fixed to the valve element24on the opposite side of the valve body20by welding or the like. The spring28as a biasing member applies load to the valve element24via the movable core26to bias the valve element24to be seated to the valve seat21. The stationary core30as a magnetic opposed portion is substantially in a cylindrical shape and accommodated in the cylindrical member12. The stationary core30is provided farther away from the valve body20than the movable core26. The stationary core30is opposed to the movable core26.

An adjusting pipe32is press-fitted to the stationary core30to retain one end of the spring28. Load applied from the spring28is regulated by adjusting press-insertion of the adjusting pipe32. Magnetic members40and42are located radially outside of the coil44and magnetically conducted with each other. The magnetic member40is magnetically conducted with the first magnetic cylindrical member14. The magnetic member42is magnetically conducted with the second magnetic cylindrical member18. The stationary core30, the movable core26, the first magnetic cylindrical member14, the magnetic members40,42, and the second magnetic cylindrical member18form a magnetic circuit.

The coil44is wound around an outer circumferential periphery of a spool46to surround outer circumferential peripheries of the nonmagnetic cylindrical member16and the second magnetic cylindrical member18. A resin housing50surrounds outer circumferential peripheries of the cylindrical member12and the coil44. A terminal52is electrically connected with the coil44to conduct a driving current to the coil44. A fuel filter60is accommodated in a fuel inlet of the cylindrical member12to remove a foreign matter from fuel, which flows into the fuel injection valve10. Fuel flows into the fuel passage100through an upper portion of the cylindrical member12inFIG. 2. The fuel further flows through fuel passages, which are defined in the stationary core30, the movable core26, and the valve element24. Thereafter, the fuel passes through the fuel holes24aand a clearance, which is formed between the valve seat21and the valve element24when the valve element24is lifted from the valve seat21, whereby the fuel is injected through a nozzle hole of the nozzle plate22.

In the fuel injection valve10, when the coil44is de-energized, the valve element24moves in a closing direction downward inFIG. 2by being exerted with the load of the spring28, whereby the valve element24is seated to the valve seat21. Thus, the nozzle hole of the nozzle plate22is blockaded, and fuel injection is terminated. When the coil44is energized, magnetic flux flows through the magnetic circuit, which is formed of the stationary core30, the movable core26, the first magnetic cylindrical member14, the magnetic members40,42, and the second magnetic cylindrical member18. Thus, the movable core26and the stationary core30therebetween generate magnetic attractive force. Thus, together with the movable core26, the valve element24moves against the load of the spring28toward the stationary core30, whereby the valve element24is lifted from the valve seat21. Thus, fuel is sprayed through the nozzle hole of the nozzle plate22. The movable core26makes contact with the stationary core30, thereby the lift of the valve element24is regulated.

FIG. 4is a graph showing relationships between the magnetic attractive force as magnetic force, which is exerted between the movable core26and the stationary core30, and elapsed time after de-energizing of the coil44. InFIG. 4, the relationships are indicated correspondingly to values of a thickness t of the nonmagnetic cylindrical member16determined at 0.1 mm, 0.2 mm, 0.4 mm, and 0.6 mm. According toFIG. 4, as the thickness t of the nonmagnetic cylindrical member16becomes small, the magnetic attractive force, which is exerted between the movable core26and the stationary core30, promptly decreases with respect to the elapsed time. Therefore, referring toFIG. 5, as the thickness t of the nonmagnetic cylindrical member16becomes small, a valve-closing time of the valve element24becomes short, since as the magnetic attractive force between the movable core26and the stationary core30decreases. The valve-closing time is defined between a time point, at which the coil44is de-energized, and a time point, at which the valve element24is seated to the valve seat21by being exerted with the load of the spring28whereby the fuel injection from the nozzle hole is terminated. According toFIG. 5, in a range, in which the thickness t is greater than 0.6 mm, the valve-closing time is not significantly reduced correspondingly to reduction in thickness t of the nonmagnetic cylindrical member16.

Here, the nonmagnetic cylindrical member16has the thickness t. The stationary core30has a surrounded portion, which is surrounded by the nonmagnetic cylindrical member16, and the surrounded portion of the stationary core30has a cross-sectional area S1. The second magnetic cylindrical member18has an overlap portion on the side of the nonmagnetic cylindrical member16with respect to an axial direction, and the overlap portion of the second magnetic cylindrical member18and the stationary core30have a total cross-sectional area S2. According to the present embodiment, the thickness t, the cross-sectional area S1, and the total cross-sectional area S2are preferably determined to satisfy the following equations (1), (2).
0.15 mm≦t≦0.6 mm  (1)
0.55≦(S1/S2)≦0.9  (2)

In the present structure, the thickness t of the nonmagnetic cylindrical member16, which is located on the radially outside of the gap200, can be effectively reduced by regulating the upper limit of t≦0.6 mm to the thickness t of the nonmagnetic cylindrical member16. Therefore, the volume of the nonmagnetic cylindrical member16is reduced, so that eddy current caused in the nonmagnetic cylindrical member16can be also reduced when the coil44is de-energized. In the present structure, the nonmagnetic cylindrical member16, which is located on the radially outside of the gap200, can be restricted from causing therein the eddy current. Therefore, magnetic components such as the movable core26and the stationary core30located in the vicinity of the gap200can be restricted from inducing magnetic flux, by reducing the eddy current. When the coil44is de-energized, magnetic flux passes between the movable core26and the stationary core30through the gap200. In the present structure, the magnetic flux can be promptly eliminated in response to de-energization of the coil44. Therefore, the magnetic attractive force exerted between the movable core26and the stationary core30can be promptly decreased in response to the de-energization. Consequently, response of the closing motion of the fuel injection valve10can be enhanced, whereby the valve-closing time can be reduced when the coil44is de-energized. Furthermore, mechanical strength of the nonmagnetic cylindrical member16can be secured by determining the lower limit of the thickness t of the nonmagnetic cylindrical member16to satisfy 0.15 mm≦t.

Here, as described above, the nonmagnetic cylindrical member16may be produced by metal injection molding (MIM) of nonmagnetic metallic powder and thereafter sintering the molded form. In the present manufacturing method, the pores210are formed inside the nonmagnetic cylindrical member16, whereby the substantial volume of the nonmagnetic cylindrical member16can be reduced. Consequently, the eddy current caused in the nonmagnetic cylindrical member16when the coil44is de-energized can be further reduced.

In addition, the total cross-sectional area of both the stationary core30and the second magnetic cylindrical member18is possibly reduced by determining the cross-sectional area S1and the total cross-sectional area S2to satisfy the relationship of 0.55≦(S1/S2). In the present structure, electromagnetic energy retained in both the stationary core30and the second magnetic cylindrical member18can be possibly reduced. Thus, the magnetic flux, which passes between the movable core26and the stationary core30, promptly disappears in response to the de-energization of the coil44, so that the magnetic attractive force exerted between the movable core26the stationary core30also promptly decreases. Consequently, response of the fuel injection valve10when the coil44is de-energized can be enhanced.

The outer diameter of the second magnetic cylindrical member18is secured by determining the cross-sectional area S1and the total cross-sectional area S2to satisfy the relationship of (S1/S2)≦0.90. Thus, the outer diameter of the second magnetic cylindrical member18is sufficiently greater than the outer diameter of the stationary core30. In a structure where the outer diameter of the second magnetic cylindrical member18is excessively reduced to be smaller than the outer diameter of the nonmagnetic cylindrical member16, the coil44and the second magnetic cylindrical member18therebetween have a gap to cause resistance in the magnetic circuit. As the second magnetic cylindrical member18is further reduced, the gap becomes larger, and consequently the resistance caused by the gap in the magnetic circuit becomes large. As a result, the magnetic attractive force between the movable core26and the stationary core30decreases.

Therefore, according to the present embodiment, the cross-sectional area S1and the total cross-sectional area S2are determined to satisfy the relationship of 0.55≦(S1/S2)≦0.90. That is, the lowest limit of the outer diameter of the overlap portion of the second magnetic cylindrical member18on the side of the nonmagnetic cylindrical member16is determined with respect to the outer diameter of the stationary core30. In the present structure, the magnetic flux between the movable core26and the stationary core30promptly disappears when being de-energized, while the magnetic attractive force between the movable core26and the stationary core30is maintained.

In general, a fuel injection valve has a coil applied with a driving signal such as a pulse signal. In such a fuel injection valve, fuel injection quantity is controlled by manipulating a pulse width of the driving signal in a range, in which an injection rate characteristic is in proportion to the pulse width. However, when the response in the closing motion of the fuel injection valve is lowered, a time period between terminating of the driving signal and closing of the fuel injection valve to terminate fuel injection becomes long. Consequently, fuel injection quantity is hard to be controlled. For example, when fuel consumption is small in an idling operation, the pulse width of the driving signal applied to the coil becomes short. However, in a conventional fuel injection valve, when the pulse width of the driving signal becomes short, the pulse width is increased to inject extra fuel so as to secure required fuel injection quantity. Consequently, the internal combustion engine consumes excessive fuel.

By contrast, according to the present embodiment, the response of the closing motion of the fuel injection valve10can be enhanced. Therefore, an injection quantity can be maintained in proportion to the pulse width of an operation signal of the coil44at small injection quantity compared with a conventional structure. Thus, in the present structure, the injection quantity in idling operation can be reduced, whereby fuel consumption can be reduced.

In the cylindrical member12of the present embodiment, the first magnetic cylindrical member14, the nonmagnetic cylindrical member16, and the second magnetic cylindrical member18are initially separate components from each other. The first magnetic cylindrical member14is joined to the nonmagnetic cylindrical member16by welding. The nonmagnetic cylindrical member16is further joined with the second magnetic cylindrical member18by welding. Each of the first magnetic cylindrical member14, the nonmagnetic cylindrical member16, and the second magnetic cylindrical member18, which is a component initially separate from another, can be formed by at least one of various processes such as sintering, cutting, and cold forging. Therefore, the cylindrical member12, which is constructed of the first magnetic cylindrical member14, the nonmagnetic cylindrical member16, and the second magnetic cylindrical member18, can be formed by combining the various processes such as sintering, cutting, and cold forging.

Second to Fourth Embodiments

As shown inFIG. 6, according to the second embodiment, the outer circumferential periphery of a nonmagnetic cylindrical member70has a recess72. The recess72is substantially in an annular shape and axially extends.

As shown inFIG. 7, according to the third embodiment, the outer circumferential periphery of a nonmagnetic cylindrical member80has multiple recesses82each being substantially in an annular shape. The outer circumferential periphery of the nonmagnetic cylindrical member80is in a wave shape in cross section. That is, the nonmagnetic cylindrical member80has a substantially corrugated outer periphery.

According to the second and third embodiments, the nonmagnetic cylindrical member70,80having the recess72,82are reduced in volume compared with the nonmagnetic cylindrical member16in the first embodiment. In the present structure, an eddy current caused in the nonmagnetic cylindrical member70,80in response to the de-energization of the coil44can be reduced. Therefore, the magnetic attractive force between the movable core26and the stationary core30can be promptly eliminated in response to the de-energization of the coil44. Thus, the response of the closing motion of the fuel injection valve10can be enhanced. According to the present second and third embodiments, the depth of the recess72,82of the nonmagnetic cylindrical member70,80is preferably less than or equal to 0.6 mm. The depth of the recess of the nonmagnetic cylindrical member70,80is preferably greater than or equal to 0.15 mm.

As shown inFIG. 8, according to the fourth embodiment, a magnetic opposed portion92and a second magnetic cylindrical portion94are integrally formed to be a single component as a stationary core90. The magnetic opposed portion92is opposed to the movable core26. The second magnetic cylindrical portion94is located farther away from the first magnetic cylindrical member14than the nonmagnetic cylindrical member16with respect to the axial direction. The second magnetic cylindrical portion94is located radially outside of the magnetic opposed portion92. In the present structure, the number of components of the stationary core90can be reduced, whereby a manufacturing process of the fuel injection valve can be reduced.

The nonmagnetic cylindrical member16has the thickness t. The surrounded portion of the stationary core30, which is surrounded by the nonmagnetic cylindrical member16, has the cross-sectional area S1. The overlap portion of the second magnetic cylindrical member18, which is located on the side of the nonmagnetic cylindrical member16, and the stationary core30have the total cross-sectional area S2. According to the present embodiment the thickness t, the cross-sectional area S1, and the total cross-sectional area S2are preferably determined to satisfy the relationships of 0.15 mm≦t≦0.6 mm and 0.55≦(S1/S2)≦0.9, similarly to the first to third embodiments.

Other Embodiment

In the above embodiments, the thickness t, the cross-sectional area S1, and the total cross-sectional area S2are preferably determined to satisfy the relationships of 0.15 mm≦t≦0.6 mm and 0.55≦(S1/S2)≦0.9. The relationships need not be fully satisfied. It suffices to determine at least the thickness t so as to satisfy the relationship of t≦0.6 mm. In a structure, in which the nonmagnetic cylindrical member is not provided with a recess, it suffices to determine the cross-sectional area S1and the total cross-sectional area S2so as to satisfy the relationship of 0.55≦(S1/S2), in addition to satisfying the relationship of t≦0.6 mm.

In the above embodiments, the solenoid valve having the above-described structure is applied to the fuel injection valve. The above-described structure is not limited to the above-described solenoid valve and may be applied to any other solenoid valve, which requires high response when the being de-energized.

According to the above embodiments, the outer diameter of the nonmagnetic cylindrical member, the outer diameter of the first magnetic cylindrical member, and the outer diameter of the second magnetic cylindrical member are substantially equal to each other. Alternatively, at least one of the nonmagnetic cylindrical member, the first magnetic cylindrical member and the second magnetic cylindrical member may be different in outer diameter from the other.

In the first embodiment, the first magnetic cylindrical member14, the nonmagnetic cylindrical member16, and the second magnetic cylindrical member18are initially separate components and are integrated to one components by welding or the like. Alternatively, the cylindrical member12may be initially provided as a single magnetic component, which is formed of a magnetic compound material to be substantially in a cylindrical shape. In this case, a portion of the magnetic cylindrical member12, which corresponds to the nonmagnetic cylindrical member, may be applied with, for example, quenching and demagnetized, whereby the de-magnetized portion of the magnetic cylindrical member12is configured to function as the nonmagnetic cylindrical member. In the present structure, the cylindrical member12is initially provided as the single component, consequently leakage of fuel through a seam between the cylindrical components can be further reduced. Furthermore, the number of components of the cylindrical member12can be reduced, whereby a manufacturing process of the fuel injection valve can be reduced.

In the second and third embodiments, the recess72,82is provided in the outer circumferential periphery of the nonmagnetic cylindrical member70,80, thereby reducing the volume of the nonmagnetic cylindrical member70,80. Alternatively, a recess may be provided in the inner circumferential periphery of the nonmagnetic cylindrical member to reduce the volume of the nonmagnetic cylindrical member.

In the first to third embodiments, the outer diameter of the first magnetic cylindrical member14at a side of the nonmagnetic cylindrical member16and the outer diameter of the second magnetic cylindrical member18at a side of the nonmagnetic cylindrical member16may be greater than the outer diameter of the nonmagnetic cylindrical portion16.

The above structures of the embodiments can be combined as appropriate. In particular, the second and third embodiments may be combined with the fourth embodiment. That is, the recess in the second and third embodiments may be provided to the nonmagnetic cylindrical member in the fourth embodiment.

Various modifications and alternations may be diversely made to the above embodiments without departing from the spirit of the present invention.