ELECTRIC SPARK PLUG The present invention relates to an electric spark plug comprising a tubular ceramic body within which an electrode is fastenable such that the electrode projects from a head end of the ceramic body by a free end generating electric arcs.

The tubular ceramic body is used as an insulator for the electrode.

The electrode is currently fastened inside a ceramic insulator in several ways .

Generally the most used system is the fastening by means of high temperature resistant cement.

Cements can be of different type depending on the application.

A first type provides cements that lead to dimensional shrinkages upon drying.

These cements have the characteristic of being compact but the shrinkage can result in clearances in the fastening, in such case the electrode can move within such clearance or even in some cases it can allow the electrode to be removed from the ceramic body.

A second type provides cements that have the characteristic of drying which results in volume increases .

Such volume increases can cause the cement to unaesthetically leak out from the electrode-ceramic body assembly.

The removal of such unaesthetic defects involves additional operations, with an increase in the costs.

The application of the cement generally requires a particular experience as regards the application modes and as regards the keeping of the proper density allowing the space inside the ceramic body to be properly filled.

Therefore the process has a drawback resulting from the turnover of the workers inside the factory and it requires a constant training. Despite this however it can happen to have waste lots due to insufficiently skilled workers.

Cements further require a drying process that involves an increase in the time for passing throughout the factory in addition to energy costs due to the fact that such drying process occurs by applying heat.

The market is increasingly asking for waste rates of component supplies equal to zero PPM.

A manual process based on the human factor will never guarantee such quality levels.

Therefore there is the unsatisfied need for the currently known spark plugs to guarantee the fastening of the electrode in a simple and effective manner and in a manner that allows cements not to be used.

The present invention relates to the replacement of the system for fastening the electrode to the ceramic body, when possible, with a mechanical fastening system that can be performed by mechanical equipment handled manually or even semi-automatic ones, where the result from the qualitative perspective is no more based on the human factor.

The present invention aims at the above objects in order to overcome the drawbacks of the prior art described above, by providing a spark plug as described hereinbefore, wherein there are further provided snap- on means for locking the electrode inside the ceramic body.

The fact of providing a mechanical fastening of the electrode inside the ceramic body allows the use of fastening cements to be avoided.

The snap-on locking on one side allows the stable fastening of the electrode into the ceramic body to be guaranteed, and on the other side it allows the user to easily recognize when the electrode is placed in a stable fastening condition.

According to one embodiment there are provided pressing means for clamping the electrode in the ceramic body.

Thus in addition to a snap-on locking, the fastening of the electrode is guaranteed by a clamping due to the insertion by pressing of the electrode inside the cavity of the ceramic body.

According to a further embodiment the free end of the electrode is enlarged with respect to the body of the electrode and it has radial dimensions greater than the opening port of the head end of the ceramic body.

This allows the electrode to abut by the enlarged head on the edges of the opening port of the ceramic body and not to be inserted too much deeply in the cavity of the ceramic body.

This arrangement guarantees the electrode to always project by the predetermined extent from the head end of the ceramic body.

In a particularly advantageous embodiment there is provided an element for locking the electrode to the ceramic body, which locking element is insertable into the tubular ceramic body and it has a head end intended to be oriented in the direction of the head end of the ceramic body and a tail end intended to be oriented in a direction opposite to the head end of the ceramic body .

This locking element acts as a terminal to be crimped to an electric supply wire of the spark plug, and it has snap-on locking means for the electrode, keeping it tightened against the ceramic body.

As it will be clearly described below, by showing some embodiments, the locking element therefore is as a separated element intended to be inserted in the ceramic body before the electrode.

Particularly the ceramic body has a head end with an opening port for the insertion of the electrode and moreover it has a tail end, opposite to said head end, through such tail end the locking element is insertable.

In a further embodiment the electrode has abutment elements intended to cooperate by a form- fit with the locking element with the electrode and the locking element in the condition inserted in the ceramic body.

Such abutment elements are part of the locking means and of the pressing clamping means, cooperating with the locking element in the condition inserted into the ceramic body, when the electrode is inserted into the ceramic body.

According to a further embodiment the snap-on locking means comprise opposite locking tabs provided on the locking element, each locking tab having the free end faced in the direction of the tail end and inclined in the direction of the opposite locking tab, the snap-on locking means further comprising an end enlargement of the electrode, opposite to the free end, such that the insertion of the electrode in the locking element causes the locking tabs to spread apart and it causes subsequently the locking tabs to move near each other in proximity of the head side of the end enlargement .

The end enlargement of the electrode therefore acts as an abutment element in the coupling between the electrode and the locking element.

According to an improvement, the end enlargement is composed of a knurling on the shell surface of the electrode.

The knurling identifies a shell surface of the enlargement having a higher pliability and therefore it can be subjected to small deformations that can promote the passage of the tabs on the end enlargement and their positioning on the head side of the end enlargement .

According to a further embodiment the pressing clamping means comprise opposite clamping tabs provided on the locking element, each clamping tab having the free end faced in the direction of the head end of the locking element and inclined in the direction of the opposite clamping tab, the pressing clamping means further comprising a radial narrowing of the inner cavity of the ceramic body and a corresponding intermediate radial enlargement of the electrode, such that the insertion of the electrode in the locking element causes the clamping tabs to spread apart, which clamping tabs are pressed between the radial narrowing of the inner cavity of the ceramic body and the intermediate radial enlargement of the electrode leading to the pressing clamping.

Thus, when inserting the electrode in the ceramic body and therefore in the locking element for operating the locking tabs, the clamping tabs are also spread apart which perform a pressing clamping by being inserted between the radial narrowing of the inner cavity of the ceramic body and the intermediate radial enlargement of the electrode.

According to an embodiment the intermediate radial enlargement is composed of a knurling of the shell surface of the electrode.

Also in this case, such as described for the end enlargement of the electrode, the knurling is very advantageous due to its pliability against the clamping tabs during the insertion of the electrode, allowing a better pressing clamping.

In a further embodiment the clamping tabs before being spread apart are moved near each other at such an extent to allow the locking element to be inserted in the radial narrowing of the inner cavity of the ceramic body.

Such insertion occurs at the end of the ceramic body opposite to the head end.

In a further embodiment the end of each clamping tab is bent and inclined in a direction diverging with respect to the opposite clamping tab, such that the ends of the clamping tabs form a leading entrance of the locking element for the insertion of the electrode.

This allows the electrode to be easily inserted in the locking element when the clamping tabs are still one near the other, subsequently spreading them apart.

Therefore the ceramic body has an inner cavity shaped in such a manner that it provides opposing abutment surfaces and points for the locking element and for the electrode when it is inserted.

In one embodiment the radial narrowing of the inner cavity of the ceramic body is shaped in such a manner to have on the side faced towards the head end of the ceramic body abutment surfaces for the bent ends of the clamping tabs, when the latter are in the spread apart condition.

This characteristic has the great advantage of preventing the locking element, and consequently the electrode, from slipping into the inner cavity of the ceramic body during the insertion of the electrode.

The bent ends of the clamping tabs therefore act as a leading entrance when the clamping tabs are near one another before inserting the electrode, and act as an abutment element of the locking element on the abutment surfaces of the ceramic body when the clamping tabs are spread apart when inserting the electrode.

According to a further embodiment the radial narrowing of the inner cavity of the ceramic body is shaped in such a manner to have on the side opposite to the head end of the ceramic body abutment surfaces for corresponding abutment shoulders provided on the locking element .

This allows a stop for the insertion of the locking element in the inner cavity of the ceramic body to be created, such that the locking element is in the proper position for receiving the insertion of the electrode .

According to an improvement the distance between the shoulders and the bent ends of the clamping tabs is greater than the distance between the opposite sides of the radial narrowing of the inner cavity of the ceramic body, such that the locking element is movable from a first extreme position in the direction of the head end of the ceramic body to a second extreme position in the direction opposite to the head end of the ceramic body.

This allows a stop for the insertion of the locking element to be created such that the locking element and particularly the clamping tabs project by a predetermined limited extent past the position in which they are in the clamping condition, such to promote the insertion of the electrode.

The insertion of the electrode therefore causes the clamping tabs to spread apart and contemporaneously causes all the locking element to go back into the ceramic body up to the final position, wherein the bent ends of the clamping tabs abut against the abutment walls of the radial narrowing of the inner cavity of the ceramic body.

In one variant embodiment the distance between the shoulders and the bent ends of the clamping tabs is substantially equal to the distance between the opposite sides of the radial narrowing of the inner cavity of the ceramic body, such that at the beginning the locking element is already in the final position, and it is not subjected to any movements back into the ceramic body during the insertion of the electrode.

According to one embodiment the tail end of the locking element is provided with an electric connector for the electric coupling with a corresponding electric connector provided on a power cable.

In one variant embodiment the tail end of the locking element is electrically and mechanically coupled with a metal rod.

According to a preferred embodiment the locking element is made of metal .

This results in a fastening that guarantees mechanical resistances against the removal of the electrode from the ceramic body suitable for the aim.

These and other characteristics and advantages of the present invention will be more clear from the following description of some embodiments shown in the annexed drawings wherein:

Fig.l is a sectional view of the assembled spark plug;

Fig.2 is a detail of a first embodiment of the electrode;

Fig.3 is a detail of a second embodiment of the electrode;

Fig.4 is a detail of the locking element;

Fig.5 is a sectional detail of the ceramic body; Fig.6 is a sectional view of the spark plug before inserting the electrode;

Fig.7 is an external view of the assembled spark plug.

The electric spark plug of the present invention is shown in a sectional view in the assembled condition in figure 1, wherein a tubular ceramic body 2 is visible which acts as an insulator inside which an electrode 1 is fastenable.

The electrode 1 projects from a head end of the ceramic body 20 by a free end 10 generating electric arcs .

There is provided an element 3 for locking the electrode 1 to the ceramic body 2, insertable into the ceramic body 2.

The locking element 3, in combination with abutment elements provided on the electrode 1 and with a shape of the inner cavity of the cylindrical body 2, forms snap-on means for locking and means for clamping by pressing the electrode 1 in the cylindrical body 2, which therefore are of the mechanical type.

Figure 2 shows the electrode 1 or plug, composed of a cylindrical body with a diameter smaller than the diameter of the inner cavity of the ceramic body 2, such to be inserted therein.

The free end 10 of the electrode is enlarged with respect to the body of the electrode and it has radial dimensions greater than the opening port 21 of the head end of the ceramic body 20.

The abutment elements provided on the electrode 2 are intended to cooperate by a form- fit with the locking element 3 with the electrode 2 and the locking element 3 in the condition inserted into the ceramic body 2.

Such abutment elements comprise an end enlargement, opposite to the free end 10, composed of an end knurling 11 on the shell surface of the electrode 1, which is a part of the snap-on locking means .

Such abutment means further comprise an intermediate enlargement composed of an intermediate knurling 12 on the shell surface of the electrode 1, which is a part of the pressing clamping means.

Figure 3 shows an alternative embodiment of the electrode 1, which has the same enlarged head 10 as the electrode 1 of figure 2 but it has slightly different abutment elements.

Such abutment elements comprise an end enlargement, opposite to the free end 10, with a conical or truncated cone shape, which is a part of the snap-on locking means.

Thus the electrode has one end for the insertion into the locking element 3 that is sharpened, in order to facilitate the penetration, while the base edge of the cone or frustum of cone abuts with the locking tabs 32, for the snap-on locking.

The abutment elements further comprise an intermediate enlargement 12 on the shell surface of the electrode 1, which is a part of the pressing clamping means .

Figure 4 shows the locking element 3, which has a head end 30 intended to be oriented in the direction of the head end of the ceramic body 20 and a tail end 31 intended to be oriented in the direction opposite to the head end of the ceramic body 20.

The locking element 3 is provided with locking tabs 32, which are a part of the snap-on locking means.

Each locking tab 32 has the free end faced in the direction of the tail end 31 and is inclined in the direction of the opposite locking tab 32.

The insertion of the electrode 1 in the locking element 3 causes the locking tabs 32 to spread apart and it causes subsequently the locking tabs 32 to move near each other in the proximity of the head face of the end knurling 11.

The locking tabs 32 are made of any material elastically pliable if subjected to a force and which tends to return in the original position once the force is removed.

Preferably the locking tabs 32 are made of metal. The locking tabs preferably are two, opposite to each other and inclined one in the direction of the other one, but they can be provided in any number. The locking element 3 is further provided with opposite clamping tabs 33, that are part of the pressing clamping means.

Each clamping tab 33 has the free end faced in the direction of the head end 30 of the locking element 3 and inclined in the direction of the opposite clamping tab 33.

The end of each clamping tab 33 is bent and inclined in a direction diverging with respect to the opposite clamping tab 33, such that the ends of the clamping tabs 33 form a leading entrance of the locking element 3 for the insertion of the electrode 1.

The clamping tabs 33 are made of any pliable material that allows them to spread apart during the insertion of the electrode 1, preferably they are made of metal.

Figure 5 shows a sectional view of the tubular ceramic body 2 acting as an insulator for the spark plug .

The ceramic body 2 has a head end 20 with an opening port 21 for the insertion of the electrode, which electrode in the operating position projects from the ceramic body by its enlarged head 10.

The ceramic body 2 further has an opposite tail end 22 where the locking element 3 is insertable into the inner cavity.

The inner cavity of the ceramic body 2 is further provided with a radial narrowing 23.

The radial narrowing is provided at the intermediate knurling 12 of the electrode 1 in the complete insertion condition and at the clamping tabs 33 of the locking element 3.

Figure 6 shows a sectional view of the spark plug, with the locking element 3 inserted in the cylindrical body 2 and with the electrode 1 in the non- inserted condition.

Before inserting the electrode 1 and before the subsequent spreading apart of the clamping tabs 3, the latter are near each other at such an extent to allow the locking element 3 to be inserted in the radial narrowing of the inner cavity of the ceramic body, starting from the tail end 22 of the ceramic body 2.

The insertion of the electrode 1 into the locking element causes the clamping tabs 33 to spread apart, which pass from the condition one near the other one of figure 6 to the spread apart condition of figure 1.

The clamping tabs 33 are pressed between the radial narrowing 23 of the inner cavity of the ceramic body 2 and the intermediate knurling 12 of the electrode 1, resulting in the pressing clamping.

During the insertion of the electrode 1 in the ceramic body 2 and therefore in the locking element 3 for operating the locking tabs 32, also the clamping tabs 33 are spread apart which perform a pressing clamping by being interposed between the radial narrowing 23 of the inner cavity of the ceramic body 2 and the intermediate knurling 12 of the electrode 1.

The radial narrowing 23 of the inner cavity of the ceramic body 2 is shaped such to have on the side faced towards the head end 20 of the ceramic body 2 abutment surfaces for the bent ends of the clamping tabs 33, when the latter are in the spread apart condition.

This prevents the locking element 3, and consequently the electrode 2, from slipping towards the inside of the inner cavity of the ceramic body 2 during the insertion of the electrode 1.

Such as shown in the figures, the side of the radial narrowing 23 faced towards the head end 20 of the ceramic body 2 is inclined such to form a truncated cone step.

On the side opposite to the head end 20 of the ceramic body 2 the radial narrowing 23 of the inner cavity of the ceramic body 2 is shaped such to have abutment surfaces for corresponding abutment shoulders 34 provided on the locking element 3, clearly visible in figure 4.

Thus a stop is created for the insertion of the locking element 3 in the inner cavity of the ceramic body 2, such that the locking element 3 is in the proper position for receiving the insertion of the electrode 1, shown in figure 6.

In the example shown in the figures, the distance between the abutment shoulders 34 and the bent ends of the clamping tabs 33 is substantially equal to the distance between the opposite sides of the radial narrowing 23 of the inner cavity of the ceramic body 2.

Therefore the locking element 3 at the beginning is already in the final position for the insertion of the electrode 1.

The tail end of the locking element 31 can be provided with an electric connector for the electric coupling with a corresponding electric connector provided on a power cable.

The connector can be of any type, preferably the connector is of the faston type.

In the variant embodiment shown in the figures the tail end 31 of the locking element 3 is electrically and mechanically coupled with a metal rod 4.

The metal rod can be replaced by a rod composed of one or more materials, of which at least one having a high electric conductivity.

The locking element 3 is advantageously composed of a single body of metal, such not to require electrically conductive elements for connecting the electrode 1 with the power cable or with the rod 4.

Figure 7 shows an external view of the assembled spark plug, wherein the electrode 1 is housed in the ceramic body 2 and it projects only by the enlarged head 10.

The locking element 3 is hidden inside the ceramic body 2 and it guarantees a mechanical resistance against the removal of the electrode 1 from the ceramic body 2 suitable for the aim.

The ceramic body is externally shaped such to have ridges and depressions for fastening the spark plug to a bracket or an external structure.

The rod 4 for the electric connection of the spark plug to a power cable or circuit projects from the tail end 22 of the ceramic body.