Plug cap for internal combustion engines

Abstract: The invention relates to a plug cap freely mountable on or removable from an elongated bore 21 for the ignition plug in internal combustion engines or the like. The plug cap is provided with a rain cover portion 27, a sealing portion 12 and a pipe-holding portion 15. The latter is provided, on its internal circular face, with a circular groove 13 and a plurality of protrusions 14 projecting towards the central axis. These grooves and protrusions and subsequent deflection thereof, give an elasticity to the sealing portion 12 and to the pipe-holding portion 15. When the plug cap is pressed into the elongated bore 21 for the ignition plug, there is not curling up of the sealing portion 12 occurring as this was the case heretofore, thereby ensuring a reliable sealing. After insertion, the protrusions 14 of the pipe-holding portion 15, which are formed integrally with the sealing portion 12, are pressed onto the external circular face of the ignition pipe 19, so that the latter can be held more reliably.

Description: The present invention relates to the field of internal combustion engines for vehicles or the like, of the type having an elongated bore receiving an ignition plug. The invention more particularly relates to a plug cap that can be freely mounted onto and removed from such an elongated bore. Such a type of plug cap has been described in the past, for example in Japanese Utility Model Publication Showa 61-61778. Figure 3 shows such a known plug cap, in which an ignition pipe 19 (also called "plug cap pipe") is fitted at one end into an ignition plug and receives the plug cap on an external circular face at the other end. The above-mentioned plug cap also incorporates a rain cover 27. A pipe holder 15 is arranged to fit on the external circular face of the ignition pipe 19. A seal 12 is provided between the external circular wall of the pipe holder 15 and the internal circular wall at the opening of an elongated bore 21 adapted to receive the ignition plug. A narrow gap 26 is formed between the pipe holder 15 and the seal 12. The plug cap is provided with a circular peripheral cover portion 11 at its external circular face. This cover portion engages above and around the opening via a ring-shaped spigot 17 formed on a rim zone surrounding the opening. The ignition pipe 19 receives an ignition cable 18 which passes through the rain cover 27 and extends outwardly. The above plug cap thus fits over the elongated ignition plug bore 21 e.g. in a vehicle engine 20 such that it can be freely mounted or removed. In such prior art device, proper sealing is ensured by covering the ignition plug bore 21 with the circular peripheral cover 11. The gap 26 between the pipe holder 15 and the seal 12 gives the resiliency required for easy insertion of the plug cap into the ignition plug bore 21, and also prevents any compressive strain from forming in the plug cap during insertion. However, in such a prior art device, the pipe holder 15 and seal 12 are partially separated from each other by the above gap 26. This tends to make the seal 12 very thin. Consequently, when the plug cap is inserted into the ignition plug bore 21, it tends to curl up at the periphery or otherwise get deformed, resulting in the ignition plug bore no longer being sealed properly. Considering the document DE-A-3 302 878, there is provided a plug cap for an internal combustion engine of the type comprising an elongated bore for fitting an ignition plug and an ignition pipe, the plug cap comprising a rain cover portion, a pipe-holding portion, a bore sealing portion and a through-hole, the pipe-holding portion and the sealing portion being integrally formed and the pipe-holding portion comprising a first recessed circumferential portion at an inner surface thereof and an underlying base portion. However, in such prior art plug cap, the grip of the ignition pipe is not important enough to prevent movement between the ignition pipe and the plug cap. It is therefore an object of the present invention to provide a plug cap in which the seal is prevented from curling up when the plug cap is inserted into the elongated spark plug bore, while the elasticity needed to facilitate the insertion operation and to avoid compressive strain in the plug cap after insertion can still easily be obtained. It is therefore another object of the present invention to provide a plug cap with an easily obtainable elasticity needed to facilitate the insertion operation, to avoid compressive strain in the plug cap after insertion and to reinforce the grip of the ignition pipe. In order to solve the above mentioned problems, the plug cap according to the present invention is characterized by an underlying base portion having a plurality of protrusions, the protrusions being disposed at intervals along the circumference of the surface of the pipe-holding portion and projecting towards a central axis, thereby gripping the ignition pipe. Preferably, the sealing portion has a cross-section exceeding that of the opening of the elongated bore to a degree such that the plug cap snugly fits in the opening while being freely mountable on and removable from the opening. To this end, the plug cap may be made of an elastic material. The plug cap may optionally be provided with a circular peripheral cover depending from its side wall and covering a surface portion around the opening of the elongated bore. The circular peripheral cover may be adapted to cooperate with a circular spigot of the engine in a rim zone outside the aperture of the elongated bore, so that the circular peripheral cover is engageable with the spigot. The ignition pipe may comprise an outwardly splayed lip portion at an end proximal to the plug cap, the plug cap comprising a second recessed portion at its inner surface, at a position such that the second recessed portion engages with the lip when the plug cap is fitted into the elongated bore. The protrusions at the base part of the pipe-holding portion can be configured to grip on a shrunken portion of the outer wall of the ignition pipe. The plug cap may also further comprise a vent. The through-hole can be traversed by an ignition cable, the plug cap defining an internal passageway whereby the ignition cable can enter into the ignition pipe and thereby connect with said ignition plug. According to another aspect of the present invention, there is also provided a method of sealing an opening of an elongated bore receiving an ignition plug in a vehicle engine using the present plug cap. The above and other objects, features and advantages of the invention will be apparent from the following description of the preferred embodiment, given as a non-restrictive example, with reference to the accompanying drawings, in which : Figure 1(a) is a cross-sectional side view of the plug cap according to an embodiment of the present invention; Figure 1(b) shows a view from the underside of the plug cap shown in figure 1(a); Figure 2 shows plug cap of figure 1, when mounted on an engine; and Figure 3 shows a known type of the plug cap according to the prior art. In figure 2, there is shown an engine 20 in which an adapted elongated bore 21 is formed to accommodate an ignition plug 23 therein. The ignition plug 23 is installed at the base portion of the elongated bore 21. An ignition cable 18 which connects to the ignition plug 23 extends upwardly through the elongated bore 21 and towards the outside. An ignition pipe 19, also called "plug cap pipe", is provided with a first end fitted onto the ignition plug 23 and a second end vertically above the ignition plug 23 at the level of a plug cap 22. The plug cap 22, which is preferably made of an elastic material such as rubber, is fitted on the second end of the ignition pipe 19. A hollow circular part of the plug cap 22 is made to fit around the bore 21. An inner surface of that part fits over the ignition pipe 19, and thereby forms a pipe-holding portion 15. The outer surface of the hollow circular part fits inside the elongated bore 21, and thereby forms a seal portion 12. The pipe-holding portion 15 and the seal portion 12 thus constitute the two sides of a same integrated hollow part without any gap or slit present between them, in contrast with the prior plug cap. The pipe-holding portion 15 is also provided with a circumferential recessed portion or groove 13 on its inner circular face. A part of the pipe-holding portion underlying the circular recessed portion 13 is configured so as to form a plurality of protrusions 14 disposed at intervals along its surface, the protrusions projecting towards the central axis (figures 1a and 1b). The sealing portion 12 is adapted to close the elongated bore 21, having a diameter which is a little larger than the opening of the latter. The plug cap is provided with a circular flange portion extending from its side wall above the sealing portion 12 and forming peripheral cover 11. The peripheral cover fits around a circular spigot 17 formed on a rim zone outside the opening of the elongated bore 21 and thereby covers that rim zone. A rain cover portion 27 is formed at the top central portion of the plug cap, directly above the spark plug bore 19. An ignition cable 18 is received in the ignition pipe 19 and projects outwardly through a side hole 16 at the upper side of the plug cap, in the vicinity of the rain cover portion. Preferably, the rain cover portion 27 is provided with air evacuation vents 10 at appropriate locations. Thus, when the air inside the elongated ignition plug bore 21 is heated or otherwise tends to expand, it can be evacuated through the vents. The installation of the plug cap shall now be explained with reference to figures 1 and 2. The pipe-holding portion 15 of the plug cap 22 fits over the second end of the ignition pipe 19 before plug cap is fully received into the elongated bore 21. The second end of the ignition pipe 19 is formed into an outwardly splayed annular lip 24 which lodges in a receiving slot 25 in the form of an annular recess which is located just above the pipe-holding portion 15. The projecting parts of the protrusions 14 of the pipe-holding portion 15 come into contact with the outer circular wall of the ignition pipe 19, as shown in dotted lines in Figure 1(b), so that the pipe-holding portion 15 grips the ignition pipe 19 firmly by the outside. As shown in Figure 2, the first end of the ignition pipe 19 fits on the ignition plug 23 which is located at the base of the elongated bore 21. The sealing portion 12 is pressed into the opening of the elongated bore 21, and the circular peripheral cover 11 is engaged with the circular spigot 17 formed on the rim zone outside the opening. The plug cap is thereby firmly seated while remaining freely mountable or removable from the elongated bore 21. The annular recess or groove 13 of the pipe-holding portion 15 also surrounds the ignition pipe 19. Thus, when the plug cap is inserted into the bore 21, the sealing surface 12 is deflected inwardly to provide a snug fit with the inner wall of the bore 21, while the protrusions 14 just beneath this recess are pressed against the ignition pipe 19, thereby forcing the base of the cap into a compressed state. Because the sealing portion 12 is deflected inwardly, the protrusions 14 are pressed firmly onto the outer surface of the ignition pipe 19, whereby the latter is held very reliably. The circular groove 13 thus cooperates with the protrusions 14, thereby conferring the required elasticity for the plug cap, and in particular for the pipe-holding portion 15, while reducing the force necessary to insert the plug cap into the elongated bore 21. This elasticity also makes it possible to avoid the formation of a compressive strain in the plug cap after insertion. A remarkable feature of the invention is that there is no need to form a gap between the sealing portion 12 and the pipe-holding portion 15, which thus allows the sealing portion 12 to be thicker. Consequently, when the plug cap 22 is inserted into the ignition plug bore 21, there is no curling-up of the sealing portion 12, and a reliable seal of the elongated bore 21 is thereby obtained. As a result, there will be no need to increase the overall size of the plug cap, and optimum bore sealing conditions can thereby be maintained. Further, the diameter of the sealing portion 12 is a little larger than the opening of the elongated bore 21. Therefore, when the plug cap is pressed-fitted into the elongated bore 21, the outwardly bulging part of the sealing portion 12 is pushed inwardly towards the central axis of the plug cap. Because the pipe-holding portion 15 is formed integrally with the sealing portion 12, the pipe-holding portion 15 and the protrusions 14 formed thereon are pressed onto the external circular face of the ignition pipe. This integrated configuration, in combination with the groove-and-protrusion structure of the pipe-holding portion 15, further reinforces the grip of the ignition pipe 19. The circular peripheral cover 11 around ignition plug bore 21 is an optional part of the invention which can be implemented when a corresponding circular spigot 17 is formed on the rim zone outside bore opening. Such a configuration helps to maintain a reliable seal against the ingress of water, dust or the like.

Claims: A plug cap (22) for an internal combustion engine (20) of the type comprising an elongated bore (21) for receiving an ignition plug (23) and an ignition pipe (19), said plug cap comprising a rain cover portion (27), a pipe-holding portion (15), a bore sealing portion (12) and a through-hole (16), said pipe-holding portion (15) and said sealing portion (12) being integrally formed and said pipe-holding portion comprising a first recessed circumferential portion (13) at an inner surface thereof and an underlying base portion, characterized in that, said underlying base portion has a plurality of protrusions (14), said protrusions being disposed at intervals along the circumference of the surface of said pipe-holding portion and projecting towards a central axis thereby gripping said ignition pipe (19). The plug cap (22) according to claim 1, wherein the sealing portion (12) has a cross-section exceeding that of an opening of said elongated bore (21) to a degree such that the plug cap snugly fits in said opening while being freely mountable on and removable from said opening. The plug cap (22) according to claim 1 or 2, which is made of an elastic material. The plug cap (22) according to any one of claims 1 to 3, wherein said plug cap is further provided with a circular peripheral cover (11) depending from a side wall thereof and covering a surface portion around said opening of the elongated bore (21). The plug cap (22) according to claim 4, wherein said circular peripheral cover (11) is adapted to cooperate with a circular spigot (17) of the engine (20) in a rim zone outside said opening of the elongated bore (21), so that the circular peripheral cover (11) is engageable with said spigot. The plug cap (22) according to any one of claims 1 to 5, wherein said ignition pipe (19) comprises an outwardly splayed lip portion (24) at an end proximal to said plug cap and wherein said plug cap comprises a second recessed portion (25) at an inner surface thereof, at a position such that said second recessed portion engages with said lip when said plug cap is fitted into said elongated bore (21). The plug cap (22) according to any one of claims 1 to 6, wherein said protrusions (14) at said base part of said pipe-holding portion (15) are configured to grip on a shrunken portion of the outer wall of said ignition pipe (19). The plug cap (22) according to any one of claims 1 to 7, wherein the plug cap further comprises a vent (10). The plug cap (22) according to any one of claims 1 to 8, wherein said hole (16) is traversed by an ignition cable (18), said plug cap defining an internal passageway whereby said ignition cable can enter into said ignition pipe (19) and connect with said ignition plug (23). A method of sealing an opening of an elongated bore (21) receiving an ignition plug (23) in a vehicle engine (20) using a plug cap (22) as defined in any one of claims 1 to 9.

Inventors: MATSUO YOSHIYUKI, MATSUO, YOSHIYUKI, Matsuo, Yoshiyuki, c/o Sumitomo Wiring Systems Ltd
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1995
Main classification: H01T13
IPC codes: F02F11, H01T13