Spark Plug Cap Apparatus

This invention relates to a spark plug cap apparatus which primarily is adapted for vehicle engines having vertical or near vertical openings of substantial depth in the top of the engine for the spark plugs, such as in overhead cam type engine.

One conventional apparatus of this kind is shown in U.S. Pat. No. 4,267,811 and consists of a spark plug cap including a plug pipe having a bush at the lower end and an expanding head cover of an elastic material, such as rubber, at the upper end. The plug cap is removably inserted into the spark plug bore which is formed in the engine head from the upper side such as to have a near vertical longitudinal shape and the opening at the upper end of the plug bore is closed by the head cover. It is preferable that the head cover of an apparatus of this type provide the opening at the upper end of the plug bore with a good seal for excluding moisture, water, oil and other foreign materials.

Accordingly it is an object of this invention to provide an improved apparatus of this type, which provides the spark plug bore opening at the upper end with a good seal.

A further and more detailed object of this invention is to provide an improved spark plug cap apparatus wherein the opening at the upper end of the spark plug bore is formed with an annular protrusion at its peripheral edge and the head cover is formed with a bent flange at the outer peripheral edge which engages with the annular protrusion, and further, an annular seal lip is provided on the head cover for inserting into the inner peripheral surface of the opening. A still further object is to provide such a spark plug cap apparatus with a ventilation opening that is effective without allowing foreign material into the bore.

Embodiments of the invention will be explained with reference to the accompanying drawings wherein:

FIG. 1 is an elevation view of the cylinder head of an overhead valve engine with portions shown in cross-section to illustrate the location of the spark plug and the apparatus of this invention.

FIG. 2 is an enlarged sectional elevation of the spark plug cap of this invention shown in FIG. 1.

FIG. 3 is an enlarged sectional elevation of the head cover portion of the spark plug cap shown in FIGS. 1 and 2.

FIG. 4 is a plan view of a modified form of the spark plug cap shown in FIGS. 1, 2 and 3.

FIG. 5 is an enlarged sectional elevation view taken substantially on the line V--V in FIG. 4.

Referring now to the drawings, the spark plug cap, generally designated 1, includes a plug cap pipe 2 with a bush 3 at the lower end and an expanding head cover 4 of an elastic material, such as rubber, at the upper end. A spark plug wire 5 extends outwardly through the cover. The cap 1 is removably inserted into an elongated spark plug bore 7 which is formed in the cylinder head 6 of an engine such that its length is disposed in the vertical direction, with the bush 3 being placed over the spark plug 8 removably mounted at the bottom of the bore 7 and with the cover 4 closing the opening 9 at the upper end. The head cover 4 is placed over the top portion of the pipe 2 and they are bonded together at a boss 10 on the center of the lower surface of the cover 4.

The spark plug cap structure as thus far described is not strikingly different from a conventional one, but according to the present invention the opening 9 at the upper end is formed with an annular protrusion 11 at its peripheral edge, and the head cover 4 is formed with a bent flange 12 at the outer peripheral edge which engages the annular protrusion 11. Further an annular seal lip 14 is provided for inserting into the inner peripheral surface of the opening 9 and protrudes from the lower surface of the head cover 4 with a slight annular clearance 13 between the lip 14 and the outer peripheral surface of the boss 10.

The outer diameter of the bush 13 is preferably made comparatively large such as to prevent the plug cap 1 from oscillating when it is inserted into the plug bore 7 and to thereby assure the proper insertion and removal of the cap 1.

FIG. 3 illustrates the relationship formed between the head cover 4 and the opening 9 at the upper end when the cap 1 is inserted into the plug bore 7. The bent flange 12 of the cover 4 engages the outer peripheral surface of the annular protrusion 11 and the seal lip 14 tightly engages the inner peripheral surface of the opening 9. Since the lip 14 has the small clearance 13 between its inner surface and the central boss 10, a good sealing and inserting effect is obtained by slight inward compression of the lip 14 while maintaining elasticity.

As has been described above, according to the present invention, the bent flange of the outer peripheral edge of the head cover engages the outer peripheral surface of an annular protrusion from the upper end of the plug bore and a seal lip on the inner periphery of the cover engages the inner peripheral surface of the plug bore, whereby the head cover is securely located in the plug bore and provides a good double seal.

A modification of this invention is shown in FIGS. 4 and 5 to provide ventilation of the sapce within the spark plug bore 7. A cylindrical protrusion 15 extends upwardly from the top surface of head cover 4 and a hole 16 extends through protrusion 15 and cover 4. Hole 16 is prefeably of about 1 mm. diameter and opens into the annular space 13 at its lower end. Since the hole 16 is located above seal lip 14, the inward compression of seal lip 14 to accomplish the seal with bore 7 does not tend to close hole 16. Thus, the cap 1 may be installed without the captured air resisting the insertion of seal lip 14 and removed with the vacuum resistance that might otherwise occur without vent hole 16. The location of the open end of hole 16 on top of protrusion 15 inhibits the entry of any foreign fluid or material.