DE69005276T2 - Method for producing a spark plug opening in a cylinder head of an internal combustion engine. - Google Patents

Description

The present invention relates to a method for producing spark plug wells in a cylinder head of an internal combustion engine obtained by molding, a spark plug well element intended for use in carrying out this method, and an assembly of elements intended for forming spark plug wells.

At present, the design of the valve control in certain internal combustion engines requires the creation of wells formed in the cylinder head to accommodate the spark plugs. One such design, which is shown in document FR-A-2.581.703, is shown, for example, in Figure 1, where the reference numeral 1 indicates a part of an internal combustion engine cylinder head made from a light alloy cast using the so-called "gravity mold" process, either under low pressure or by gravity, and comprising an oil chamber 2, a water chamber 3 located below the chamber 2 and an intake channel 4a. The cylinder head 1 also comprises spark plug wells 5, only one of which is shown and which are made during the molding of the cylinder head 1. However, this design has numerous disadvantages:

- The shaft 5 is hollowed out to point A by means of a mandrel 6 pressed in at the time of casting the metal of the cylinder head 1, but this mandrel has a relatively small cross-section so that it tends to deform under the effect of the heat developed by the molten metal, which has the consequence of preventing the dimensional tolerances from being met, resulting in a high percentage of rejects:

- The spindle mandrel 6 cannot be inserted deeper than point A and it is therefore necessary to carry out the reworking of the hole between point A and point B, which is located approximately at the bottom of the shaft 5; and

- when withdrawing the spindle mandrel 6 after casting, there is a risk of adhesion between the metal of the spindle mandrel and that of the cylinder head 1, which results in premature wear of this device type.

Figures 2 and 3 show another valve control design in which the cylinder head 1 is no longer completely penetrated by a hole P running perpendicular to the shafts 5, but these are penetrated at their lower ends in order to allow air circulation avoiding any condensation that could cause poor ignition. However, this known design, in addition to the disadvantages already mentioned above with regard to Figure 1, also has the disadvantage that the hole P communicating with the spark plug shafts 5 is expensive and is made in a mass of material of the cylinder head reserved for this purpose in the water chamber, which complicates molding and increases the risk of defects in the material, in particular the appearance of cracks.

GB-A-1.256.401 describes a cylinder head of an internal combustion engine obtained by molding, which comprises a spark plug well in the form of a tubular workpiece inserted after the molding of the cylinder head. Thus, this pre-published document does not pose the task of producing spark plug wells during the molding of the cylinder head.

GB-A-1.075.951 concerns the mounting of intake and exhaust ports in a cylinder head, but this document remains silent on the manner in which the tubular member 19 or 20 is positioned with respect to the sand mold core 22.

FR-A-2.431.335 mentions the difficulties of positioning metallic inserts in a mold, but proposes a process completely removed from the process forming the subject of the invention, which consists in hot-spraying a metallic layer onto a previously hardened mold core.

The present invention aims to eliminate the above-mentioned disadvantages by providing a method for producing at least one spark plug shaft in a cylinder head of an internal combustion engine obtained by moulding, of the type in which the cylinder head mould comprises a plurality of different cores corresponding to hollowed-out parts of the cylinder head to be cast, which cylinder head comprises in particular inlet and outlet channels and oil and water chambers, the cores being made of compressed sand and having been previously manufactured in core boxes, and which consists in introducing a tubular element forming the spark plug well into the appropriate one of the cores, firmly holding this tubular element in the core by means of a holding element firmly connected to the tubular element, this holding element being fixed in the core after compressing the sand forming the core, and then inserting and holding the core and tubular element assembly in the cylinder head mould during the operation of casting the latter.

According to a feature of the invention, the holding element is formed by a collar firmly connected to the body of the tubular element.

According to another feature of the invention, the tubular element is held in the core of the aforementioned oil chamber and is also inserted with its lower part into the core of the water chamber located below the core of the oil chamber.

The tubular element is advantageously positioned in the cylinder head mold by means of a positioning foot firmly connected to the lid of the mold, which foot is inserted into the upper part of the tubular element until it comes to rest with a shoulder on the edge of the upper opening of the tubular element.

According to a second embodiment of the invention, the aforementioned holding element is formed by a tubular support element which is firmly connected to the core of the aforementioned water chamber and is fastened approximately to the lower part of the tubular element.

The tubular spark plug housing element is held in a fixed position in the casting mold of the cylinder head during the casting process of the latter by the aforementioned tubular support element, which remains in the cylinder head in its final state and puts the spark plug housing element in contact with the outside air.

According to a feature of the invention, in order to produce a plurality of spark plug wells each associated with a plurality of cylinders of the engine, the spark plug well elements are supported by a plurality of successively aligned support elements which are connected to one another through the spark plug well elements, the two end support elements being firmly connected to the mold of the cylinder head during the casting of the latter.

According to another characteristic, the various tubular elements mentioned above are secured together before being inserted into a core box, the cores of which are intended to form the water chambers of the cylinder head during molding, the lower part of each tubular spark plug box element being captured in the corresponding core formed by compressed sand, the assembly of tubular elements and cores then being positioned in the cylinder head mold.

Advantageously, the tubular support elements have a rectangular or square cross-section and the various tubular elements are firmly connected to one another by welding.

Each tubular spark plug housing element is positioned in the cylinder head mold by a positioning foot that is firmly connected to the mold cover and inserted into the upper part of the tubular spark plug housing element.

After the cylinder head has been cast, the tubular element is drilled in its bottom to communicate with a threaded hole provided in the cylinder head for the passage of the threaded housing of a spark plug and its fastening in the cylinder head.

The invention also proposes a core and spark plug housing element assembly intended for use in carrying out the method of the first embodiment defined above, characterized in that it comprises a tubular body with a base, an upper opening opposite the base for the passage of a spark plug and a collar secured to the body of the tubular element, which ensures that the tubular element is held in position in the core of the oil chamber after compression of the material forming the said core.

Advantageously, the edge of the upper opening of the tubular element has a flange.

The side wall of the tubular element has a relatively small thickness, e.g. of approximately 1 to 1.5 mm.

The collar is either attached to the tubular element by welding or obtained by deformation of the latter and the tubular element is made of steel or aluminium.

According to a variant, the tubular element is made of ceramic and the collar is molded onto the tubular element.

The invention also proposes an assembly of elements intended to form at least one spark plug shaft according to the second embodiment, which is characterized in that it comprises at least one tubular spark plug shaft element and at least one tubular element supporting the spark plug shaft element, which support element preferably by welding, perpendicular to and attached to this spark plug shaft element and terminating in it.

In the case of several spark plug shafts to be formed, the whole comprises several tubular elements for supporting successively aligned tubular spark plug shaft elements, wherein two successive support elements open into the same spark plug shaft element.

Advantageously, each of the aforementioned tubular elements has a relatively small thickness of approximately 1 to 1.5 mm.

The invention will be better understood and further objects, features, details and advantages thereof will appear more clearly in the course of the explanatory description which follows and is made with reference to the accompanying schematic drawings given only as an example illustrating several embodiments of the invention and in which:

Figure 1 shows a cylinder head part in which the spark plug wells are manufactured during the molding of the same according to a previously known method;

Figure 2 is a longitudinal sectional view through a cylinder head part in which the spark plug wells are manufactured during the molding of the cylinder head according to a previously known method;

Figure 3 is a sectional view taken along the line III-III of Figure 2;

Figure 4 is a simplified view in cross section through a mold of a cylinder head according to a first embodiment of the invention;

Figure 5 shows a core box of an oil chamber of the cylinder head for carrying out the method according to the first embodiment of the invention in cross section;

Figure 6 shows a variant embodiment of a spark plug housing element according to the invention;

Figure 7 is a cross-sectional view similar to that of Figure 4 and showing the finished cylinder head;

Figure 8 is a cross-sectional view of a finished cylinder head according to a second embodiment of the invention;

Figure 9 is a longitudinal section through part of the cylinder head along the line IX-IX of Figure 8; and

Figure 10 is a cross-sectional view through a cylinder head mold according to the second embodiment of the invention.

Figure 7 represents a part of the cylinder head 1 of an internal combustion engine intended for installation in a motor vehicle. The cylinder head 1 is made, for example, of a light alloy cast using the so-called "gravity mold" method, either under low pressure or by gravity, and generally comprises, as is already known per se, an oil chamber 2, a water chamber 3 located below the oil chamber 2 and inlet and outlet channels 4a and 4b. The dot-dash lines symbolize the protective covers C of the engine valve control (not shown) which are attached to the cylinder head 1. The oblique axes X1-X2 and X3-X4 symbolize, respectively, the axes of the passage of the guides of the exhaust and inlet valves (not shown) which are actuated by the valve control through which the intake and exhaust of the engine gas takes place.

The oil and water chambers 2 and 3 surround approximately coaxially a spark plug shaft 5 intended to accommodate a spark plug 7, the upper part 7a and threaded housing 7b of which have been shown. The spark plug shaft 5 has a bore 8 on its bottom for the passage of the threaded housing 7b of the spark plug 7, which is screwed into a corresponding threaded hole 9 of the spark plug 1, so that the electrodes of the spark plug 7 are located in the combustion chamber 10 delimited by the cylinder head 1.

According to the invention, the spark plug well 5 comprises a tubular element 11 of rotational cylindrical shape which is inserted into the cylinder head 1 during the molding of the same. The element 11, which in the present case is arranged vertically in the cylinder head 1, has a relatively thin thickness, for example from 1 to 1.5 mm, in its side wall 11a forming a body and can be made of steel, aluminum or ceramic. The tubular element 11 has a collar 11b which in the present case is attached to the body 11a of the same by welding, but which can also be made by deforming the tubular element 11, as shown in Figure 6. The collar 11b can also be molded onto the tubular element 11 in the case where it is made of ceramic. The tubular element 11 also has a flange 11c formed by bending the edge of the upper opening of the element 11 opposite its base having the bore 8.

The method according to which the tubular element 11 is inserted into the cylinder head 1 will now be explained with reference to Figures 4 and 5.

Figure 4 represents the mold for casting the cylinder head 1, which is of the type comprising various cores corresponding to the hollowed-out parts of the cylinder head to be cast, formed in particular by the inlet and outlet channels 4a and 4b, the oil chamber 2 and the water chamber 3. Thus, the cores 12-15 correspond respectively to the oil and water chambers 2 and 3 and the inlet and outlet channels 4a and 4b and are preferably made of materials which allow the reservation of these hollowed-out parts during casting. compressed sand. These cores 12-15 are previously manufactured in core boxes, the most important of which for the invention is the core box 16 of the oil chamber 2 shown in Figure 5. The box 16, which thus allows the manufacture of the core 12 of the oil chamber 2, comprises three parts 16a, 16b and 16c defining an inner chamber in which the sand of the core 12 is formed and compressed when they are assembled. Once the core 12 has been manufactured, the parts 16a-16c of the core box 16 are extracted to recover the core 12, as shown by the arrows F1 to F3.

The tubular element 11 is inserted into the sand forming the core 12, in which it is firmly held by the collar 11b after the sand has been compressed in the box 16 so as not to slide after the box 16 has been withdrawn during the stripping of the core 12. The tubular element 11 is thus captured in the core 12 by its upper part comprising the flange 11c and its lower part lying outside the core 12. The collar 11b is located halfway up the tubular element 11, but it is obvious that its position is determined by its function, which is to ensure that the element 11 is held in the core 12.

The assembly of core 12 and tubular element 11 is then inserted into the cylinder head 1 mold, the tubular element also being introduced with its lower part into the core 13 of the water chamber 3, in which a corresponding through hole has been previously made to allow this introduction. The cylinder head 1 mold is conventionally composed of a base 17 comprising a metal part 18 ensuring the compression effect during the molding of the cylinder head 1, a mold side part 19 and a cover 20. The various cores, in particular the cores 12 and 13, are held in the cylinder head 1 mold by suitable means (not shown) which also allow the tubular element 11 to be held in position during the molding of the cylinder head 1. The cover 20 has a support 21 located approximately in its center and firmly connected thereto. connected foot 21 with shoulder 22 inserted in the upper part of the tubular element 11 to ensure its positioning or centering in the mold of the cylinder head 1 with the shoulder 22 supported on the flange 11c of the tubular element 11.

After the cylinder head 1 has been cast and cooled, the tubular element 1 is partially embedded in the cylinder head 1, as shown in Figure 7, and the bore 8 has been formed in the bottom 11d of the tubular element 11 in order to communicate with the threaded hole 9 into which the housing 7b of the spark plug 7 is screwed.

The relatively thin thickness of the tubular element 11 mentioned above gives this element good mechanical properties, while allowing a gain of approximately 3 mm in this thickness with respect to the well obtained by molding according to the process shown in Figure 1. This gain in thickness makes the presence of the areas corresponding to the water chamber 3 in which the cooling water circulates between each spark plug well and the valve guides less critical. In certain engine designs, in particular when it is necessary to incline the spark plug well 5 towards the exhaust or intake ducts of the cylinder head 1, there are in fact places where there is practically no room to create the water passage. The gain of 3 mm in thickness achieved thanks to the tubular element 11 of the invention allows the water film required for cooling to be created more easily.

Referring to the embodiment of Figures 8 to 10, where the same reference numerals as those used in the previous figures designate the same workpieces, each spark plug well 5 is also formed by a tubular element 11 of rotationally cylindrical shape inserted into the cylinder head 1 during the molding of the same. The element 11, which in the present case is arranged vertically in the cylinder head 1, has a relatively small thickness in its side wall, for example from 1 to 1.5 mm and can be made of steel, for example. The tubular elements 23, preferably made of a material similar to that of the elements 11 and with a rectangular or square cross-section, are also inserted into the cylinder head 1 during its molding and are aligned one after the other transversely to the longitudinal axis of the tubular spark plug housing elements 11. Two successive elements 23 open into a same spark plug housing element 11 at the lower part of the latter and the two tubular end elements 23 are in communication with the outside air to allow air to circulate in the cylinder head 1 through the tubular elements 11 and 23. The number of elements 23 obviously depends on the number of cylinders in the engine.

The method according to which the tubular elements 11 and 23 are inserted into the cylinder head 1 will now be explained with reference to Figure 10.

This figure represents the mold for casting the cylinder head 1, which is the different type comprising cores corresponding to the hollowed-out parts of the cylinder head to be cast, formed by the inlet and outlet channels 4a and 4b, the oil chamber 2 and the water chamber 3. Thus, the cores 12-15 correspond respectively to the oil and water chambers 2 and 3 and to the inlet and outlet channels 4a and 4b and are preferably formed from compressed sand allowing the reservation of these hollowed-out parts during casting. The cores 12-15 are previously manufactured in core boxes known per se, which cores, once formed, are held in the mold of the cylinder head 1 by suitable means known per se and not shown.

The various tubular elements 11 and 23 are inserted into the box to form the cores 13 corresponding to the water chambers 3 of the cylinder head 1. Before being inserted into this box, the tubular elements 23 are firmly connected to the tubular elements 11 by welding in order to form an inseparable unit with controllable known geometric and dimensional characteristics. Once the unitary assembly thus formed has been positioned in the core box, the sand is Formation of the core 13 around the lower part of the spark plug box elements 11. The assembly of elements 11, 23 and cores 13 is then removed from the core box and inserted into the mold 1 to be held there in a fixed position. Naturally, each tubular element 11 is introduced through a corresponding passage hole previously formed in the corresponding oil chamber core 12 and the two free ends of each of the two end support elements 11 are suitably secured to the mold. The latter is conventionally composed of a base 17 comprising a metallic part 18 ensuring the compression effect during the casting of the cylinder head 1, a side mold part 19 and a cover 20. The latter has feet 21 arranged approximately in its centre and firmly connected thereto, each inserted into the upper parts of the tubular element in order to ensure its positioning or centred in the casting mould of the cylinder head 1.

After casting the cylinder head 1 and cooling the latter, each tubular element 11 is embedded in the cylinder head as shown in Figure 8 and the bore 8 is formed in the bottom of the tubular element 11 to communicate with the threaded hole 9 into which the housing of the spark plug 7 is screwed.

The cylinder head 1 according to the invention is thus provided with elements 23 which form channels for ventilation by air circulation, which are molded into the spark plug chamber elements 11, and the water circulation in the chamber 3 will be optimal, since better cooling of the cylinder head during operation is achieved thanks to the relatively low thickness of the spark plug chamber elements 11.

Claims (21)

1. Method for producing at least one spark plug well in a cylinder head of an internal combustion engine obtained by molding, of the type in which the mold of the cylinder head (1) has several different cores (12-15) corresponding to hollowed-out parts (2, 3, 4a, 4b) of the cylinder head to be cast, which cylinder head has in particular inlet and outlet channels (4a) and (4b) and oil and water chambers (2) and (3), the cores (12-15) being made of compressed sand and having been previously produced in core boxes (16), and which consists in introducing a tubular element (11) forming the spark plug well into the appropriate one (12; 13) of the cores, pressing this tubular element (11) into the core (12 ; 13) by a holding element firmly connected to the tubular element (11). (11b, 23), which holding element is fixed in the core (12; 13) after compression of the sand forming the core (12; 13) and then to insert the assembly of core (12; 13) - tubular element (11) into the mold of the cylinder head (1) during the process of casting the latter and to hold it there. 2. Method according to claim 1, characterized in that the aforementioned holding element is formed by a collar (11b) firmly connected to the body (11a) of the tubular element (11). 3. Method according to claim 1 or 2, characterized in that the tubular element (11) is held in the core (12) of the aforementioned oil chamber (2) and is also inserted with its lower part into the The core (13) of the water chamber (3) is inserted below the core (12) of the oil chamber (2). 4. Method according to one of the preceding claims, characterized in that the tubular element (11) is positioned in the mold of the cylinder head (1) by a positioning foot (21) firmly connected to the cover (20) of the mold, which foot is inserted into the upper part of the tubular element (11) until it comes to a stop with a shoulder (22) of the same on the edge of the upper opening of the tubular element (11). 5. Method according to claim 1, characterized in that the aforementioned holding element is formed by a tubular support element (23) which is firmly connected to the core (13) of the aforementioned water chamber (3) and is fastened approximately to the lower part of the tubular element (11). 6. Method according to claim 5, characterized in that the tubular spark plug housing element (11) is held in a fixed position in the mold of the cylinder head (1) during the casting process of the latter by the tubular support element (23) which remains in the cylinder head (1) in its final state and puts the spark plug housing element (11) in contact with the outside air. 7. Method according to claim 6, characterized in that for the manufacture of a plurality of spark plug shafts (5) each associated with a plurality of cylinders of the engine, it consists in supporting the spark plug shaft elements (11) by a plurality of successively aligned support elements (23) which are connected to one another through the spark plug shaft elements (11), wherein the two end support elements (23) are firmly connected to the mold of the cylinder head (1) during the casting of the latter. 8. Method according to claim 6 or 7, characterized in that it consists in firmly connecting the various aforementioned tubular elements (11, 23) to one another before inserting them into a core box (13) whose cores are intended to form the water chambers (3) of the cylinder head during molding, enclosing the lower part of each tubular spark plug box element (11) in the corresponding core (13) formed by compressed sand and then positioning the assembly of tubular elements (11, 23) and cores (13) in the mold of the cylinder head (1). 9. Method according to one of claims 6 to 8, characterized in that the aforementioned tubular support elements (23) have a rectangular or square cross-section. 10. Method according to one of claims 5 to 9, characterized in that the various aforementioned round-shaped elements (11, 23) are firmly connected to one another by welding. 11. Method according to one of claims 5 to 10, characterized in that each tubular element (11) is positioned in the mold of the cylinder head (1) by a positioning foot (21) firmly connected to the cover (20) of the mold and inserted into the upper part of the tubular element (11). 12. Method according to one of the preceding claims, characterized in that, after the casting of the cylinder head (1), the tubular element (11) in its bottom (11d) is drilled through in order to communicate with a threaded hole (9) provided in the cylinder head (1) for the passage of the threaded housing (7b) of a spark plug (7) and its fastening in the cylinder head (1). 13. A core (12) and spark plug housing element assembly intended for use in carrying out the method as defined in at least claim 1, characterized in that it comprises a tubular body (11a) with a base (11d), an upper opening opposite the base (11d) for the passage of a spark plug (7) and a collar (11B) firmly connected to the body (11a) of the tubular element (11) which ensures that the tubular element (11) is held in position in the core (12) of the oil chamber (2) after the material forming the said core (12) has been compressed. 14. Core (12) and spark plug housing element assembly according to claim 12, characterized in that the edge of the upper opening of the tubular element (11) has a flange (11c). 15. Core (12) and spark plug housing element assembly according to claim 13 or 14, characterized in that the side wall of the tubular element (11) has a relatively small thickness, for example of approximately 1 to 1.5 mm. 16. Core (12) and spark plug housing element assembly according to claim 13, characterized in that the collar (11b) is attached to the body (11a) of the tubular element (11) by welding or obtained by deformation of this body. 17. The assembly of core (12) and spark plug housing element according to claim 16, characterized in that the tubular element (11) is made of steel or aluminum. 18. The assembly of core (12) and spark plug housing element according to one of claims 13 to 17, characterized in that the tubular element (11) is made of ceramic and the collar (11b) is molded onto the tubular element (11). 19. For forming at least one spark plug shaft according to the method as defined in at least claim 6, an assembly of elements, characterized in that it has at least one tubular spark plug shaft element (11) and at least one tubular element (23) for supporting the spark plug shaft element (11), which support element is preferably fixed by welding perpendicular to the spark plug shaft element and opens into it. 20. Assembly according to claim 19, characterized in that, in the case of several spark plug shafts 1 to be formed, it comprises several tubular elements (23) for supporting tubular spark plug shaft elements (11) aligned one after the other, two successive support elements (23) opening into the same spark plug shaft element (11). 21. Assembly according to claim 19 or 23, characterized in that each of the aforementioned tubular elements has a relatively small thickness of approximately up to 1.5 mm.