A glow plug having a capsule and a fastening bush, in particular for diesel engines with deep wells

Abstract: A glow plug for diesel engines, comprising a fixing bush (62) and a capsule (20) provided with a tubular housing (22) from which projects a sheath element (24) containing a heating resistor (26). The fixing bush (62) and the capsule (20) are two separate components, in order to improve concentricity and coaxiality tolerances for plugs with long bodies intended to be fitted into deep wells.

Description: The present invention relates to a glow plug for diesel engines, of the type comprising: a metallic body having a treaded portion for its engagement in a treaded portion of an engine head, a metallic sheath element projecting from one end of the body, and a heating resistor extending in said sheath element and having a first end connected to a power supply member extending through the body and a second end electrically connected to said sheath element. The new direct injection diesel engines require glow plugs with longer and longer bodies. This is due to the fact that the axis of the glow plug in these engines is parallel to the injector and the glow plug must cross substantially the whole thickness of the engine head. In the glow plugs of the most advanced type for pre-chamber engines, the cost of the body represents about 20% of the total cost of the glow plug. The increase of the cost of the body of the glow plug is proportional to its length and in the last type of plugs for direct injection diesel engines with deep wells the cost of the body represents about 50% of the total cost of the glow plug. In addition, with the increase of the length of the body there are always increasing difficulties for maintaining concentricity and coaxiality tolerances within the limits required by the automotive manufactures. DE-A-19630208 discloses a sheathed element glow plug having the features of the preamble of claim 1, including a plug shell, a connection element for the glow current and a tube fastened to said plug shell and closed at the its end facing away from the plug shell. The plug shell comprises two sections and, depending on the desired overall length of the sheathed element glow plug, an intermediate member of selectable length which connects with each other a first part and a second part of the plug shell. The object of the present invention is to provide a glow plug intended to be used in diesel engines with deep wells, which is more economical of a traditional glow plug and which maintains the manufacturing tolerances within much more restricted limits than the glow plugs of conventional design. According to the present invention, this object is achieved by a glow plug having the features forming the subject of the main claim. The present invention proposes to divide the body of the plug in two parts. A first part or lower part (papsule) has the function of supporting the sheath element and to avoid gas leaks from the combustion chamber. The second part or upper part (fastening bush) carries the treaded section necessary for engaging the treaded portion of the well and has only the function to push the lower section against the conical sealing end of the well and of holding the member for the power supply of the resistor which is housed in the lower portion. The solution according to the invention permits to obtain a reduction of the cost of very long bodies for glow plugs for applications in which the plug must be mounted in a very deep well. Furthermore, the invention permits to standardize the lower portion which together with the metallic sheath element forms a capsule which can be joined with upper portions of different dimensions. By providing only five or six different types of capsules it is possible to satisfy the functional and geometric requirements of the great majority of engines. The glow plug can be adapted to the particular type of engine by simply changing the upper portion. Another advantage of the present invention is the reduction of the cost of the resistor power supply member, which can be advantageously formed by a simple wire extending through the upper portion of the body. Further characteristics and advantages of the present invention will become clear in the course of the detailed description which follows, given purely by way of an example, with reference to the annexed drawings, in which: figure 1 is a partially sectioned lateral elevation view of a first embodiment of a glow plug according to the invention mounted in a well of an engine, figures 2 and 3 are partially sectioned lateral elevation view of the two parts which form the glow plug of figure 1, figure 4 is a partially sectioned lateral elevation view of a second embodiment of a plug according to the invention, and figures 5 and 6 are partially sectioned lateral elevation view of the two parts which form the plug of figure 4. With reference to figures 1 to 3, a glow plug for diesel engines is indicated at 10. The plug 10 is intended to be mounted in a well 12 formed in a head 14 of a diesel engine. The well 12 has two coaxial cylindrical portions 12a, 12b with a different diameter and connected to each other by a frusto-conical sealing surface 16. The cylindrical portion 12a with greater diameter has a treaded section 18, for example in correspondence with the upper end of the well 12. The glow plug 10 is formed by two distinct and separate parts. The lower part 20 is a capsule including a tubular housing 22 and a sheath element 24. Within the sheath element 24 is a spiral electric resistor 26 whose lower end is welded to the closed end 28 of the sheath element 24. The resistor 26 may be formed for example by two spirals of different materials connected in series to each other, as is well known in the field. The upper section of the resistor 26 is connected to a terminal 30 formed by a small metallic pin which projects from the upper end of the sheath element 24 through a seal 32 of elastomeric material. The sheath element 24, in a way per se known, is filed with an insulating powder for example of magnesium oxide. In the example shown in the figures, the sheath element 24 and the tubular housing 22 are two separate parts of different materials, fixed to each other by driving with interference the sheath element 24 in the through cavity 34 of the tubular housing 22. The sheath element 24 is formed by a metallic alloy resistant to the temperature and to corrosive gas, for example INCONEL, while the tubular housing 22 is for example made of steel. In a variant of the present invention, the capsule 20 can be produced in a monolithic form, as disclosed in European Patent Application No. 97830307.1 of the same Applicant. In this case, the tubular housing 22 and the sheath element 24 are made of the same material and are formed starting from a monolithic piece by shaping operations, for example by swaging. The tubular housing 22 has an outer cylindrical surface 36 with a diameter which is slightly less than the diameter of the portion 12a of the well 12. The cylindrical surface 36 finishes at its lower end with a frusto-conical surface 38 which is intended to be pushed against the corresponding frusto-conical surface 16 of the well 12. The terminal 30 is electrically connected to a power supply member 40 formed for example by a wire, solid or plaited, which projects from the upper end of the capsule 20. The power supply member 40 is connected to the terminal 30 by means of a metallic adapter 42 fixed to the member 40 and to the terminal 30 in any known manner, for example by welding or rolling. The power supply member 40 is insulated for example by a sheath of plastic or textile material. The power supply member 40 extends through a connection element 44 fixed for example by means of a tread 46 to the upper end of the tubular housing 22. The connection element 44 pushes downwardly an insulating bush 48 for example made of ceramic material or of bakelized fabric which in its turn pushes an o-ring 50 against the outer surface of the adapter 42. The o-ring 50 has the object to prevent that liquid or dirt enter into contact with the heating element 24. The connection element 44 has a hole 52 through which extends the power supply member 40. The connection element 44 has a pin 54 provided with one or more longitudinal slots 56 adapted to permit a radial deformation of the pin 54. The pin 54 has a head with a frusto-conical surface 58 and a shank with an undercut portion 60. The glow plug 10 according to the present invention further comprises an upper portion formed by a fixing bush 62 having a treaded portion 64 intended to engage the treaded portion 18 of the well 12. The fixing bush 62 has an hexagonal head 66 which can be engaged by a wrench for tightening or removing the plug from the engine head. The fixing bush 62 has a hole 67 through which extends the power supply member 40. On the upper end of the fixing bush 62 is preferably inserted a sealing element 68 which acts on the outer surface of the power supply member 40. The end of the power supply member 40 which comes out from the fixing bush 62 is connected to an electrical connector (not shown) which serves for the connection of the glow plug 10 to a power supply cable. The lower end of the fixing bush 62 has an engagement seat 70 with an undercut shape having an entry aperture 72 smaller than the head of the pin 54 and slightly greater than the diameter of the shank of the pin. The head of the pin 74 is intended to snap-engage the seat 70, in order to connect to each other in an axial direction the two parts of the plug 10. The fixing bush 62 and the tubular housing 22 together form the body of the plug 10 which in the traditional solution is formed by a single component. The glow plug according to the present invention can be supplied to the final user in an assembled configuration or with the two parts 20, 62 separated. When the plug is assembled, it has the configuration shown in figure 1, with the pin 54 engaged into the seat 70. If the plug is supplied already assembled, fitting or removal thereof are carried out in the same manner as any other known plug. If the two parts 20, 62 are supplied separately, the user must insert the power supply member 40 through the hole 67 of the fixing bush 62. The two parts are then inserted in the well 12 and the element 62 is screwed by means of a normal wrench. The downward thrust of the fixing bush 62 provokes the snap engagement of the pin 54 in the seat 70 as well as an axial thrust which bring the capsule 20 in abutment against the sealing conical surface 16 formed in the well 12. When the plug must be removed by the well, by unscrewing the fixing bush 62 the capsule 20 is extracted from the well 12, by virtue of the engagement of the pin 54 in the seat 70. In figures 4 to 6 is shown a variant of the glow plug according to the present invention. The elements identical to the ones disclosed above are indicated with the same numeral references. The main difference with respect to the previously disclosed embodiments consists in that the pin 54 is carried by the fixing bush 62, while the engagement seat 70 is formed in the tubular housing 22 of the capsule 20. The pin 54 can be obtained in integral form with the fixing bush 62, as shown in figures 4 and 6. The tubular housing 22 of the capsule 20 has a treaded section 74 in which is engaged a bush 76 which has the object to press the o-ring 50 against the connector 42. In the embodiment shown in figures 4 to 6, the wire forming the power supply member 40 is welded to the connector 42. In a further variant (not shown) could be used different systems for fixing the power supply wire to the terminal 30. For example, this connection could be carried out by means of a connector welded to the electrode 30 and an electrical plug connected to the wire 40 and a plug electrically connected to the wire 40 and carried by the fixing bush 62.

Claims: A glow plug for diesel engines, comprising: a metallic body (22, 62) having a treaded portion (64) for its engagement within a treaded portion (18) of an engine head (14), a metallic sheath element (24) projecting from an end of the body (22, 62), and a heating resistor (26) extending within said sheath element (24) and having a first end electrically connected to a power supply member (40) which extends through the body (62, 22) and a second end electrically connected to said sheath element (24), characterized in that said body is divided in two separated detachable parts a first of which (22) is fixed to the sheath element (24) and a second of which (62) has said treaded portion (64). A glow plug according to claim 1, characterized in that the first part (22) of the body has a cylindrical outer surface (36) terminating with a frusto-conical sealing zone (38) from which projects said sheath element (24). A glow plug according to claim 1, characterized in that the first and the second part of the body (22, 62) are provided with engagement means axially cooperating with each other for permitting the removal from a deep well of the first part of the body (22) by acting on the second part (62). A glow plug according to claim 3, characterized in that said engagement means comprise a coupling member (54) carried by one of the two parts of'the body (22, 62) and adapted to engage a seat (70) provided on the other part (62, 22). A glow plug according to claim 4, characterized in that said coupling member comprises a radially deformable pin (54) having an undercut portion (60) which snap engages in a seat (70) with an undercut profile. A glow plug according to claim 1, characterized in that it comprises an electric terminal (30) projecting outside the sheath element 24 and connected to an insulated wire (40) which extends through a hole (67) of said second part (62) of the body. A glow plug according to claim 6, characterized in that said wire (40) is connected to the terminal (30) by means of an adapter (42) and in that it comprises a sealing element (50) arranged between the outer surface of said adapter (42) and the inner wall of the tubular housing (22). A glow plug according to claim 7, characterized in that it comprises a treaded element (44, 74) which exerts an axial thrust on said sealing element (50).

Inventors: BALDELLI MARIO, TONELLI CLAUDIO, BALDELLI, MARIO, TONELLI, CLAUDIO
Applicants: FEDERAL MOGUL IGNITION SPA, FEDERAL-MOGUL IGNITION S.P.A.
Application year: 1998
Main classification: F23Q7
IPC codes: F23Q7