A seal for sealing and automatically cleaning a sheathed element of a heater plug for Diesel engines

Abstract: The element comprises a hollow metal sheath (1) which is open at one end (6) and has an arched opposite end (2). A heating element (3) in the form of a metal coil is disposed inside the sheath (1). The cavity of the sheath (1) is filled with an insulating powder (4) and the open end (6) of the sheath (1) is closed by a seal (7) of elastomeric material having at least one annular projection (10) which exerts a vigorous cleaning effect on the seat of the seal (7) during the fitting of the seal (7).

Description: The present invention relates to a sheathed element for a heater plug for Diesel engines, of the type comprising a hollow metal sheath which is open at one end and has a closed, arched opposite end, and inside which a heating element in the form of a metal coil is disposed, the cavity of the sheath being filled with an insulating powder and the open end of the sheath being closed by a seal of elastomeric material, as for example EP-A- 0 365 258. The current technique for manufacturing sheathed elements for glow plugs for Diesel engines provides for the mouth of the sheath to be sealed by a rubber seal which, as well as being a suitable electrical insulator, has to ensure a perfect seal against infiltration of air into the sheathed element even at temperatures of 90-120°C which occur in this region when the plug is in operation. The absence of infiltrations of air into the sheathed element is very important since it constitutes one of the main factors for increasing the reliability of the element. The seal is achieved mainly as a result of three effects: suitable pressure exerted by the seal against the internal wall of the sheath, absence, in the seal seats, of scoring and roughness of dimensions comparable to those of the seal, and absence of impurities and dust particles. Whilst the first two requirements can be achieved by appropriate design solutions, by the adoption of suitable working techniques, and by effective control operations, the third is a typical process problem. In fact, the elimination of dust from the seal seat is a very significant problem since the interposition of dust particles between the wall and the seal creates paths through which air passes. The interior of the sheath is filled with insulating powder (typically magnesium or aluminium oxide) which has the function of electrically insulating the heating element and easily conducting the heat produced by the element to the exterior. The filling with magnesium or aluminium oxide powder is carried out through the seal seat, causing numerous oxide particles to be deposited on the walls of the seat. The cleaning of the seal seat is a very difficult operation since the insertion of a small spatula or brush alone is problematical, by virtue of the restriction of the spaces and the delicacy of the surrounding parts, even a small alteration of which involves large changes in the functional characteristics of the element. In order to overcome the aforementioned problems, the subject of the present invention is a sheathed element of the type defined above, characterized in that the seal has at least one annular projection which projects from a surface of the seal and establishes a sealing contact with the respective seat of the sheath so that, when the seal is fitted in the seat, the projection removes dust particles present on the internal wall of the seat. Further characteristics and advantages of the present invention will become clear in the course of the following detailed description given purely by way of non-limiting example, with reference to the appended drawings, in which: Figure 1 is a schematic, axial section of a sheathed element according to the present invention, Figure 2 is a plan view of the seal indicated by the arrow II in Figure 1, and Figure 3 is a section taken on the line III-III of Figure 2. Figure 1 shows a sheathed element for glow plugs for Diesel engines, comprising a sheath 1 formed by a hollow metal tube having a closed, arched end 2. Inside the sheath 1 there is a heating element 3 constituted by a metal coil connected electrically to the end 2 of the sheath 1. The interior of the sheath 1 is filled with an insulating powder 4 (typically magnesium or aluminium oxide) which has the function of electrically insulating the coil 3 from the sheath 1 and easily conducting the heat produced by the glowing coil to the exterior. The coil 3 is supplied electrically by a cylindrical rod 5 which extends through an open end 6 of the sheath 1. The open end 6 of the sheath 1 has a seat 6a for a sealing ring 7 made of elastomeric material, for example, hard rubber. As can be seen in greater detail in Figures 2 and 3, the seal 7 has an internal surface 8 which establishes a sealing contact with the rod 5 and an external surface 9 with a diameter such that it can be fitted with radial interference in the seat 6a. Two annular projections 10 with substantially triangular profiles project from the external surface 9 and exert a vigorous cleaning effect on the seat 6a for the seal 7 during the fitting of the latter. Similar projections may be provided on the internal surface 8 of the seal so as also to achieve a cleaning effect on the external surface of the rod 5. This solution avoids a specific cleaning operation and prevents the risk of breakage of adjacent parts.

Claims: A sheathed element for a heater plug for Diesel engines, comprising a hollow metal sheath (1) which is open at one end (6) and has a closed, arched opposite end (2), and inside which a heating element (3) in the form of a metal coil is disposed, the cavity of the sheath (1) being filled with an insulating powder and the open end (6) of the sheath (1) being closed by a seal (7) of elastomeric material, characterized in that the seal (7) has at least one annular projection (10) which projects from a surface (9) of the seal (7) and establishes a sealing contact with the respective seat (6a) of the sheath (1) so that, when the seal (7) is fitted in the seat (6a), the projection (10) removes dust particles present on the internal wall of the seat (6a). A sheathed element according to Claim 1, in which the seal (7) is annular and has an internal surface (8) which establishes a sealing contact with the outer surface of a rod (5) which supplies the heating element electrically, characterized in that the seal (7) has at least one projection projecting from the internal surface (8).

Inventors: RITI GIANFRANCO, TONELLI CLAUDIO, RITI, GIANFRANCO, TONELLI, CLAUDIO
Applicants: COOPER IND ITALIA, COOPER INDUSTRIES ITALIA S.P.A.
Application year: 1996
Main classification: F23Q7
IPC codes: F23Q7