The present invention relates to a multi-point spark plug capable of facilitating the attachment of a plug cap. The multi-point spark plug is made up of two center electrodes, an insulator for accommodating the center electrodes, a housing for holding the insulator and earth electrodes located at one end portion of the housing and each disposed in opposed relation each of the center electrodes in a state where a discharging gap is interposed therebetween. Moreover, first and second terminals to be electrically connected to the center electrodes are provided in a head portion of the insulator. In an outside configuration composed of the head portion and the first and second terminals, a contour between a location of the second terminal and a location of the first terminal is formed axis-symmetrically with respect to an axis of the head portion.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a spark plug for an internal combustion engine which ignites an air-fuel mixture in a combustion chamber, and more particularly to a multi-point spark plug including a plurality of center electrodes.

2) Description of the Related Art

For example, as disclosed in Japanese Patent Laid-Open No. SHO 57-208084, there has been known an ignition device for an internal combustion engine having a center electrode and a third electrode disposed in parallel with the center electrode.

In addition, as shown inFIG. 20, there has been designed a multi-point spark plug100having a pair of center electrodes. This multi-point spark plug is made up of an insulator104internally including two center electrodes102and103in a parallel configuration, a housing105for holding the insulator104and two earth electrodes106and107located at one end portion of the housing105and disposed in opposed relation to the tip surfaces of the center electrodes102and103in a state where a discharging gap is interposed therebetween. Moreover, two terminals121and122, respectively connected electrically to the two center electrodes102and103, are put in two axial holes111and112made in the insulator104, respectively.

There is a problem which arises with the above-mentioned multi-point spark plug100, however, in that, since the two terminals121and122are respectively placed in the two axial holes111and112made in the insulator104, difficulty is encountered in making a connection easily to a plug cap. This will be described hereinbelow with reference toFIG. 21.

FIG. 21is an illustration of a plug cap130to be connected to the multi-point spark plug100shown inFIG. 20. This plug cap130is composed of a blind-end cylindrical cap portion131to be set to cover up (cap) a head portion114of the multi-point spark plug100, and an ignition coil portion132for generating a voltage to be applied to the multi-point spark plug100.

A first contact terminal133and a second contact terminal134, each of which comprises a spring provided at a tip surface of a bar-like base, protrude from a bottom surface of the cap portion131, and the first and second contact terminals133and134are brought into contact with the first and second terminals121and122of the multi-point spark plug100, respectively, thereby supplying a voltage to the multi-point spark plug100.

The ignition coil portion132has a box-like casing for internally accommodating an ignition coil, and a fitting hole139is made in one side surface of the casing138so as to permit the insertion of a bolt thereinto.

Secondly, a description will be given hereinbelow of the attachment (connection) of the plug cap130to the multi-point spark plug100. The multi-point spark plug100is fixedly secured to an engine in a manner such that a male screw108formed in the housing105is put into a threaded engagement with a female screw formed in a cylinder head (not shown). The plug cap130is set to cover the head portion114of the multi-point spark plug100. At this time, the first contact terminal133and the second contact terminal134are inserted into the axial holes111and112, respectively. Following this, a bolt (not shown) is inserted into the fitting hole139attached to the casing138, and this bolt is placed into a threaded engagement with a female screw set on the cylinder head (not shown), thus fixedly securing the plug cap130thereto.

However, in the case of this multi-point spark plug100, for setting the plug cap130, there is a need to insert the first contact terminal133and the second contact terminal134into the axial holes111and112. Therefore, it needs that, after the plug cap130and the multi-point spark plug100are disposed so that their axes align with each other, the plug cap130is rotated around its axis to align the first contact terminal133with the axial hole111and further to align the second contact terminal134with the axial hole112and the plug cap13is pushed into the multi-point spark plug100to be fitted thereto. This makes it difficult to accomplish the attachment of the plug cap130easily.

In addition, since the attachment of the multi-point spark plug100is made in a manner such that the male screw108formed in the housing105and the female screw formed in the cylinder head are placed into engagement with each other, the positions of the axial holes111and112do not settle when the multi-point spark plug100is fixedly secured to the cylinder head. This is because, when two members are fixedly coupled to each other through screws, the relative positions of the male screw side member and the female screw side member in rotating directions vary according to the tightening torque and, even if the tightening torque is controlled to stand at a constant value, the precise screw processing is a necessity to making the rotating-direction relative positions constant. Thus, in a case in which the positions of the axial holes111and112do not settle, the position of the fitting hole139attached to the plug cap130engaging with the axial holes111and112does not settle. For this reason, the fitting hole139does not necessarily align with the position of the female screw formed in the cylinder head and, hence, difficulty is experienced in fixedly securing the plug cap130through the use of a bolt.

SUMMARY OF THE INVENTION

The present invention has been developed with a view to eliminating these problems, and it is therefore an object of the invention to provide a multi-point spark plug capable of facilitating the attachment of a plug cap.

For this purpose, in accordance with an aspect of the present invention, there is a provided a multi-point spark plug comprising a plurality of center electrodes, an insulator for internally accommodating the center electrodes, a housing for holding the insulator, and earth electrodes located at one end portion of the housing and each disposed in opposed relation each of the center electrodes in a state where a discharging gap is interposed therebetween, wherein the insulator includes a head portion protruding from an end surface of the housing opposite to the side in which the earth electrodes exist, a plurality of terminals each to be electrically connected to each of the plurality of center electrodes are provided in the head portion and, in an outside configuration (figuration) composed of the head portion and the terminals, a contour (outline) between a location (site) in which the terminal closest to the housing exists and an end portion remotest from the housing is formed axis-symmetrically with respect to an axis of the head portion.

Thus, since the plurality of terminals are provided on the head portion of the insulator and the contour of the outside configuration composed of the head portion and the terminals is formed axis-symmetrically with respect to the axis of the head portion, in installing the plug cap, there is no need to make the alignment by rotating the plug cap around its axis, which facilitates the connection between the multi-point spark plug and the plug cap. Moreover, even if a plug cap integrally having an ignition coil is installed thereto, it is possible that, after the plug cap is arbitrarily attached to the multi-point spark plug, the fixture can be made through a bolt by rotating the ignition coil portion so that a fitting hole made in the casing of the ignition coil portion aligns with the position of the female screw made in the cylinder head. This facilitates the fixing of the ignition coil portion.

In this case, the “in an outside configuration composed of the head portion and the terminals, a contour between a location at which the terminal closest to the housing exists and an end portion remotest from the housing is formed axis-symmetrically with respect to an axis of the head portion” signifies, for example, that only a contour of an outside configuration composed of the head portion and the terminals has an axial symmetry, and it does not require that the insulator itself and the terminal itself have an axis-symmetrical configuration. Moreover, it does not require that all the contour of the outside configuration composed of the insulator and the terminals are axis-symmetrically formed, but the axis-symmetry of only the contour from a location at which the terminal closest to the housing exists and an end portion remotest from the housing is acceptable. This construction can facilitate the attachment of the plug cap. Still moreover, in this specification, the “axis-symmetry” does not signify a strict geometrical axis-symmetry, but, even if irregularities slightly exist as compared with the ideal geometrical axis-symmetrical shape, the “axis-symmetry” includes it. Therefore, cases equivalent to the present invention in light of the facilitation of the attachment of a plug cap are to be included therein.

In addition, in accordance with another aspect of the present invention, there is provided a multi-point spark plug comprising a plurality of center electrodes, an insulator for internally accommodating the center electrodes, a housing for holding the insulator, and earth electrodes located at one end portion of the housing and each disposed in opposed relation each of the center electrodes in a state where a discharging gap is interposed therebetween, wherein the insulator includes a head portion protruding from an end surface of the housing opposite to the side in which the earth electrodes exist, and a plurality of terminals each to be electrically connected to each of the plurality of center electrodes are provided in an intermediary member attached to the head portion and, in an outside configuration (figuration) composed of the intermediary member and the terminals, a contour (outline) between a location at which the terminal closest to the housing exists and an end portion remotest from the housing is formed axis-symmetrically with respect to an axis of the head portion. This can provide the effects similar to those of the above-mentioned construction.

Still additionally, according to a further aspect of the present invention, the plurality of terminals have a disc-like configuration or a ring-like configuration. Therefore, the electrical connection with the plug cap is securable at any point on the circumference.

Yet additionally, according to a further aspect of the present invention, the plurality of terminals are disposed in a state separated from each other in an axial direction. Therefore, the insulation between the plurality of terminals is easily securable.

Moreover, according to a further aspect of the present invention, the plurality of terminals are made to have a smaller outer diameter as their positions are remoter from the housing. Therefore, the terminal separated from the housing does not hinder the coupling with the plug cap, which achieves the easy connection of the plug cap.

Still moreover, according to a further aspect of the present invention, at least one of the plurality of terminals is constructed with a ring member showing an elastic force to reduce its diameter. Therefore, when, in a state where a force is applied to the ring member to enlarge its diameter, the insulator or the intermediary member is inserted thereinto and the diameter-enlarging force is removed therefrom, the ring member can be fixed by the diameter-reducing elastic force, thus providing easy assembling of the terminals.

Yet moreover, according to a further aspect of the present invention, at least one of the plurality of terminals is placed in a cavity portion made in the insulator or the intermediary member. This prevents the terminal from displacing and dropping out.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a vertical cross-sectional view showing a multi-point spark plug according to a first embodiment of the present invention, andFIG. 2is a horizontal cross-sectional view showing the multi-point spark plug ofFIG. 1, and taken along a line A—A therein.

The multi-point spark plug, generally designated at reference numeral1, is made up of a pair of center electrodes2and3, an insulator4internally accommodating the center electrodes2and3, a housing5for holding the insulator4and earth electrodes6and7located at one end portion of the housing5and each disposed in confronting relation to each of the center electrodes2and3in a state where a discharging gap is interposed therebetween.

Each of the center electrodes2and3is made of a metallic material, such as an Ni-base alloy, having a high heat resistance and a high corrosion resistance, and has a cylindrical configuration. A tip surface thereof confronting the corresponding earth electrode6,7has a convergent (tapered) configuration, and a chip11,13, made of a noble metal or an alloy containing it is joined thereto through laser welding.

The insulator4is made of alumina ceramics, and it is composed of a fork-like leg portion23protruding from one side of the housing5, where the earth electrodes6and7exist, and a generally cylindrical head portion24protruding from an end surface of the other side thereof opposite to the side of the existence of the earth electrodes6and7.

In the interior of the insulator4, a pair of axial holes21and22are made and, in the order from the leg portion23toward the head portion24, there are disposed the pair of center electrodes2and3, a pair of resistors15an16, and stems17and18. On both end portions of the resistors15and16, there are placed a plurality of copper glass layers19.

The upper end surface of the stem18is positioned in the same plane as the upper end surface of the insulator4, and a disc-like first terminal31made from an SCM material is joined with the upper end surface of the stem18. The overall length of the stem17is approximately half the overall length of the stem18, and an insulating material20is interposed between the stem17and the first terminal31.

A circumferential groove26is formed in an outer circumferential surface of the head portion24, and a through hole27is made to extend from a bottom surface of the circumferential groove26to the axial hole21. In this circumferential groove26, there is fitted a ring-like second terminal32having a cross section shown inFIG. 2. The second terminal32is made by machining a plate material made of phosphor bronze or stainless steel, and it has a diameter smaller than the diameter of the circumferential groove26in a state where an external force is not applied thereto and, in a state placed in the circumferential groove26, it shows an elastic force so that its diameter reduces. A contact piece35bent into a U-like configuration is formed at an end portion of the second terminal32. This contact piece35is positioned in the interior of the through hole27to come into contact with the stem17.

The second terminal32is located at an approximately intermediate position between the first terminal31and the head portion24side end surface of the housing5, and the insulation of the second terminal32is secured with respect to the first terminal31and the housing5. Moreover, the first terminal31disposed more remotely than the second terminal32with respect to the housing5has an outer diameter smaller than that of the second terminal32so as not to hinder the engagement with the plug cap.

The housing5includes the pair of earth (ground) electrodes6and7each formed into an L-like configuration and fixed through welding to one end surface thereof. These earth electrodes6and7are made of an Ni-base alloy, and chips12and14made of a noble metal or an alloy containing it are joined through welding with the tip side surfaces thereof, respectively. The chips12and14welded to the earth electrodes6and7are placed in opposed relation to chips11and13welded to the center electrodes2and3, respectively, in a state where a discharging gap is interposed therebetween. a male screw8is formed in an outer circumferential surface of the housing5to engage with a female screw formed in a cylinder head (not shown).

Secondly, a description will be given hereinbelow of the effects of this embodiment.FIG. 3is an illustration of the connection between the multi-point spark plug1and a plug cap40.

In the interior of a cap portion41made of a silicone rubber, there are disposed a core material42made of a thermoplastic resin, a first contact terminal43including a bowl-like member made of an aluminum alloy and a spring placed on a bottom surface thereof, a ring-like second contact terminal41made of an aluminum alloy, and lead wires45and46electrically connected to the first and second contact terminals43and44, respectively. This plug cap40is formed by the insert molding.

In the multi-point spark plug1according to this embodiment, the first terminal31and the second terminal32are provided at the head portion24of the insulator4, and in an outside configuration (figuration) made by the head portion24, the first terminal31and the second terminal32, a contour (outline) between a location (site) at which the second terminal32closest to the housing5exists and the first terminal31forming an end portion remotest from the housing5is formed axis-symmetrically with respect to the axis of the head portion24. Therefore, in attaching the plug cap40thereto, there is no need to rotate the plug cap40around its axis for the alignment and, hence, the easy connection between the multi-point spark plug1and the plug cap40becomes feasible. Moreover, even in the case of the installation of a plug cap integrally having an ignition coil portion, after the plug cap is arbitrarily set to the multi-point spark plug1, the fixture can be made through the use of a bolt in a manner such that the ignition coil portion is rotated so that a fitting hole made in a casing of the ignition coil portion aligns with the position of a female screw formed in a cylinder head, thereby enabling the ignition coil portion to be fixedly secured to the cylinder head.

As described above, the first contact terminal43and the first terminal31are brought into contact with each other and the second contact terminal44and the second terminal32are brought into contact with each other and, hence, the multi-point spark plug1, to which the plug cap40is attached, can supply voltages to the center electrodes2and3. In response to the voltage application to the center electrodes2and3, the spark discharge takes place between the chips11and12and between the chips13and14to ignite the air-fuel mixture in the combustion chamber.

FIG. 4is a front view showing a multi-point spark plug50according to a second embodiment of the present invention,FIG. 5is a horizontal cross-sectional illustration of the multi-point spark plug50taken along a line B—B ofFIG. 4, andFIG. 6is a horizontal cross-sectional illustration of the multi-point spark plug50taken along a line C—C ofFIG. 4.

A difference from the first embodiment shown inFIGS. 1 and 2is only that the multi-point spark plug50is equipped with three center electrodes51,52and53, three earth electrodes56,57and58, and a first terminal61, a second terminal62and a third terminal63electrically connected to the center electrodes51,52and53, respectively. Detailed description of the other members will be omitted for brevity.

The first terminal61has a disc-like configuration and is joined with a stem66electrically connected to the center electrode51. The second terminal62has a ring-like configuration having a cross section shown inFIG. 5and has, at its end portion, a contact piece65bent into a U-like configuration. This contact piece65is brought into contact with a stem68electrically connected to the center electrode53, thereby securing the electrical connection between the second terminal62and the center electrode53. The third terminal63has a ring-like configuration shown inFIG. 6and has, at its end portion, a contact piece65bent into a U-like configuration. This contact piece65is brought into contact with a stem67electrically connected to the center electrode52, thereby securing the electrical connection between the third terminal63and the center electrode52.

The multi-point spark plug50according to this embodiment is a multi-point spark plug capable of three-point ignition and facilitates the attachment of a plug cap as well as the first embodiment.

FIG. 7is a front view showing a multi-point spark plug71according to a third embodiment of the present invention,FIG. 8is a horizontal cross-sectional illustration of the multi-point spark plug71taken along a line D—D, andFIG. 9is a partial cross-sectional view showing the joining of the multi-point spark plug71and a plug cap40.

A difference from the first embodiment shown inFIGS. 1 and 2is only a construction of a second terminal72and a construction of an insulator4in the vicinity of the second terminal72. A detailed description of the other components is omitted for simplicity.

The second terminal72is formed by means of the drawing and formed into a ring-like configuration having a cylindrical surface and an upper end surface as shown inFIGS. 7 and 8. In the inner circumference of the second terminal72, there are provided a conducting contact piece73formed by bending a claw portion made to protrude toward the inner-diameter side of the upper end surface and two holding pieces74. These two holding pieces74are provided at positions shifted by 90 degrees in opposite directions with respect to the position of the conducting contact piece73to be in opposed relation to each other.

A step portion is formed at a central portion of a head portion of an insulator4in its axial direction so that the second terminal72is put thereon. In the location of the disposition of the second terminal of the insulator4, a chamfer is formed at a position confronting each of the holding pieces74, and a through hole extending from an outer surface of the insulator4to an axial hole in which a stem17exists is made at a position confronting the conducting contact piece73.

The holding pieces74of the second terminal72are brought into elastic contact with the chamfered portions to prevent the displacement of the second terminal72by means of the elastic force thereof. Moreover, the conducting contact piece73is brought into elastic contact with the stem17through the through hole, thereby achieving the electrical connection (conduction).

In the multi-point spark plug71, since the second terminal72has the upper end surface, the electrical connection with a plug cap40is securable through this upper end surface. Therefore, when, as shown inFIG. 9, the plug cap40equipped with a second contact terminal44comprising a spring expanding and contracting in a cap portion41is attached to the multi-point spark plug71, a lower end surface of the second contact terminal44comes into elastic contact with the upper end surface of the second terminal72, thus effecting the electrical connection therebetween.

In the multi-point spark plug71according to this embodiment, in an outside configuration comprising the head portion24, the first terminal31and the second terminal72, the contour between the location of the second terminal72closest to the housing5and the first terminal31forming an end portion remotest from the housing5is formed axis-symmetrically with respect to the axis of the head portion24, thus providing easy attachment of the plug cap as in the case of the first embodiment.

FIG. 10is a front view showing a multi-point spark plug75according to a fourth embodiment of the present invention,FIG. 11is a horizontal cross-sectional illustration of the multi-point spark plug75taken along a line E—E ofFIG. 10, andFIG. 12is a partial cross-sectional view showing the attachment of the multi-point spark plug75and a plug cap40.

A different point from the first embodiment shown inFIGS. 1 and 2is only a construction of a second terminal76and a construction of an insulator4in the vicinity of the second terminal76. A detailed description of the other components is omitted for simplicity.

The second terminal76is formed by means of the drawing and has a semicircular (semi-cylindrical) configuration as shown inFIG. 11. A conducting contact piece73formed by bending a claw portion made to protrude toward the inner-diameter side is provided at a central portion of the second terminal76in its circumferential direction. Moreover, at both circumferential end portions of the second terminal76, there are provided holding pieces74formed by bending the end portions.

A cavity portion is made at a central portion of a head portion of an insulator4in its axial direction so that the second terminal76is put thereon. Engaging (fitting) holes are made at positions confronting the holding pieces74in the location of the disposition of the second terminal76of the insulator4, and a through hole extending from an outer surface of the insulator4to an axial hole in which a stem17exists is made at a position confronting the conducting contact piece73.

The second terminal76has an elastic force to reduce its diameter, and the holding pieces74engage with the engaging holes, thereby preventing the displacement of the second terminal76. Moreover, the conducting contact piece73comes into elastic contact with the stem17through the through hole, thereby securing the electrical connection therewith.

The second terminal76has the semicircular configuration and, hence, does not have an axis-symmetrical configuration. However, in the multi-point spark plug75according to this embodiment, since, in the outside configuration made by the head portion24, the first terminal31and the second terminal76, the contour between the location of the second terminal76closest to the housing5and the first terminal31forming an end portion remotest from the housing5is formed axis-symmetrically with respect to the axis of the head portion24, the easy attachment of the plug cap becomes easy as in the case of the first embodiment.

In addition, the second terminal76has the semicircular configuration and, hence, only an area corresponding to the half of the circumference contributes to the electrical connection with the plug cap40. However, as shown inFIG. 12, when the plug cap40having a ring-like second contact terminal44is attached thereto, the electrical connection between the multi-point spark plug75and the plug cap40is securable without rotating the plug cap40around its axis for the alignment.

FIG. 13is a side view showing a multi-point spark plug77according to a fifth embodiment of the present invention,FIG. 14is a horizontal cross-sectional illustration of the multi-point spark plug77taken along a line F—F ofFIG. 13, andFIG. 15is a partial cross-sectional view showing the attachment of the multi-point spark plug77and a plug cap40.

A different point from the first embodiment shown inFIGS. 1 and 2is only that a second terminal is formed integrally with an insulator4. A detailed description of the other components is omitted for simplicity.

At a central portion of a head portion of the insulator4, there is formed a through hole78which extends from an outer surface of an insulator4to an axial hole in which a stem17exists. Moreover, an electrically conductive metallized film is formed at a portion in the vicinity of a circumferential edge of the through hole78, an inner circumferential surface of the through hole78and a portion confronting the through hole78(sites indicated by a two-dot chain line inFIG. 14). This metallized film constitutes a second terminal79. This second terminal79can be made according to the well-known metallizing technique to be used for the joining of ceramics and metal.

The multi-point spark plug77according to this embodiment has the through hole78at axial central portion of the head portion24of the insulator4and, strictly speaking, a contour of an outside configuration made with the head portion and the terminals does not have a geometric axis-symmetrical configuration. However, even if the through hole78exists, it does not hinder the attachment of the plug cap40. Therefore, the multi-point spark plug77can provide the effects of the attachment of the plug cap40being made easy.

Accordingly, it is possible to interpret the multi-point spark plug77as the contour of the outside configuration made by the head portion24, the first terminal31and the second terminal79has an axis-symmetrical configuration.

FIG. 16is a front view showing a multi-point spark plug80according to a sixth embodiment of the present invention,FIG. 17is an enlarged cross-sectional view showing a portion, indicated by character G, in the multi-point spark plug80, andFIG. 18is an illustration of the connection between the multi-point spark plug80and a plug cap40.

A difference from the first embodiment shown inFIGS. 1 and 2is only a construction of a second terminal81and a construction of an insulator4in the vicinity of the second terminal81. A detailed description of the other components is omitted for simplicity.

At a central portion of a head portion of the insulator4, there is formed a through hole which extends from an outer surface of the insulator4to an axial hole in which a stem17exists. Moreover, the through hole accommodates a second terminal81including a semicircular conducting contact piece82positioned on an outer surface side of the insulator4and a seating83positioned on a back side of the insulator4. The second terminal81is welded so that the seating83is embedded in a fixing hole made in the stem17.

In the multi-point spark plug80according to this embodiment, the second terminal81protrudes from an outer surface of the insulator4and, hence, the contour of the outside configuration does not have a strictly geometric axis-symmetrical configuration. However, the conducting contact piece82of the second terminal81is supported to be elastically deformable so that, at the attachment of the plug cap40, the conducting contact piece82can be pushed in the back side of the insulator4. Therefore, it does not obstruct the attachment of the plug cap40and, hence, the multi-point spark plug80can provide the effects of the present invention which facilitate the attachment of the plug cap40.

For this reason, it is possible to interpret the multi-point spark plug80as the contour of the outside configuration made by the head portion24, the first terminal31and the second terminal81is formed into an axis-symmetrical configuration.

FIG. 19is a partial cross-sectional perspective view showing an intermediary member90constituting a multi-point spark plug according to a seventh embodiment of the present invention. The seventh embodiment relates to a multi-point spark plug comprising a combination of the intermediary member90and the multi-point spark plug100shown inFIG. 20.

The intermediary member90is made of a silicone rubber and is composed of a blind-end cylindrical cap portion91which is made to cover a head portion114of the multi-point spark plug100and a proximal (base) portion95made of a thermoplastic resin and having a generally column-like (cylindrical) configuration. A first contact terminal92and a second contact terminal93, each of which comprises a bar-like proximal portion and a spring provided on tip surface of the bar-like proximal portion, protrude from a bottom surface of the cap portion91. On an outer surface of the proximal portion95, a third terminal96and a fourth terminal97are provided which are electrically connected to the first contact terminal92and the second contact terminal93, respectively. The intermediary member90is attached to the multi-point spark plug100so that the first contact terminal92and the second contact terminal93are brought into contact with a first terminal121and a second terminal122in the multi-point spark plug100.

The combination of the intermediary member90and the multi-point spark plug100made in this way also can facilitate the attachment of the plug cap as in the case of the first embodiment.

It should be understood that the present invention is not limited to the above-described embodiments, and that it is intended to cover all changes and modifications of the embodiments of the invention herein which do not constitute departures from the spirit and scope of the invention.