ENGINE COMPRISING A CYLINDER HEAD GASKET

Abstract: A cylinder head gasket (1) includes two pieces of gasket base plates (3) providing a combustion chamber hole (3A), and a spacer (4) arranged surrounding a cylinder bore (2) in an endless manner and is held between the gasket base plates. Each gasket base plate has a full-bead portion (3a) and a half-bead portion (3b) within a range thereof that superposes on the spacer (4). The spacer, the full-bead portion and the half-bead portion are held continuously along the circumferential direction of the cylinder bore between the cylinder head (5) and the cylinder block (6). Due to the spacer, the full-bead portion and the half-bead portion are press-contacted to the opposing member with a high surface pressure and over a relatively wide contact area. Therefore, a favorable sealing performance is obtained despite the presence of a cavity or a scar in the junction surface of the opposing side.

Description: TECHNICAL FIELD The invention relates to an engine having a cylinder head, a cylinder block and a cylinder head gasket. BACKGROUND OF THE INVENTION A cylinder head gasket is known in the art comprising a pair of gasket baseplates held sandwiched between a cylinder head and a cylinder block and having a combustion opening formed therein in alignment with a cylinder bore, a spacer disposed around the cylinder bore to surround it in an endless manner and held sandwiched between the pair of gasket baseplates and a full bead and / or half bead formed at a suitable location or locations on the gasket baseplates (Japanese Laid-Open Utility Model Application No. 71,865 / 1992 and Japanese Laid- Open Patent Application No. 165, 167 / 1992). In the prior art, when only gasket baseplates are provided which are formed with a full bead and a half bead, they are readily susceptible to the influence of any blowhole in the casting or flaw on mating adjoined surface, causing likelihood that the sealing performance becomes degraded. An engine according to the preamble of claim 1 is known from JP-A-07-253 162. DISCLOSURE OF THE INVENTION In view of the foregoing, the invention provides an engine with a cylinder head gasket which assures and maintains a good sealing performance in the presence of any blowhole in the casting or flaw on the mating adjoined surface. According to the present invention there is provided an engine having a cylinder head, a cylinder block in which is formed a plurality of cylinder bores, and a cylinder head gasket sandwiched between the cylinder head and the cylinder block, the cylinder head gasket including a pair of gasket baseplates having combustion openings formed therein in alignment with the cylinder bores, a spacer disposed around each combustion opening to surround it in an endless manner and sandwiched between the pair of gasket baseplates, and, for each combustion opening, a full bead and a half bead formed on each of the gasket baseplates in the regions thereof overlapping the spacer, characterised in that, for each combustion opening, the spacer, the full bead and the half bead on each gasket baseplate are continuously held sandwiched between the cylinder head and the cylinder block around the cylinder bore with both the full bead and the half bead on each gasket abutting against the spacer, and the half bead being disposed radially outwardly of the full bead away from the cylinder bore. With the described arrangement, the full bead and the half bead on each of the gasket baseplates disposed around the combustion chamber opening are held sandwiched between the cylinder head and the cylinder block, and the spacer is interposed therebetween in such region. This allows the full bead and the half bead to abut against the mating member under a high surface pressure and over an increased area of contact, with consequence that they are less susceptible to the influence of any gross porosity in the casting or flaw on the mating adjoined surface, thus enabling a good sealing performance to be secured. The engine may include, for each combustion opening, a reinforcing plate of a thickness less than that of the spacer and disposed radially outwardly of the spacer away from the bore, the reinforcing plate being held sandwiched between the pair of gasket baseplates. At least one of the cylinder head and the cylinder block may be formed as an open deck with cooling water passages which, for each combustion opening, surround the spacer and the full bead and the half bead on each gasket baseplate. Each full bead may include a centre portion extending away from the spacer in the direction of the thickness of the spacer. The spacers around each opening may be integrally connected together to be continuous with one another. For each combustion opening the spacer may terminate radially outwardly of the opening in the region of the half bead. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal section of a first embodiment of the invention; Fig. 2 is a plan view of cylinder head gasket 1 shown in Fig. 1; Fig. 3 is a cross section, to an enlarged scale, of a pertinent portion shown in Fig. 1; and Fig. 4 is a longitudinal section of a second embodiment of the invention. BEST MODES FOR CARRYING OUT THE INVETION The invention will now be described below with reference to an embodiment applied to a linear four cylinder engine. Referring to Figs. 1 and 2, a cylinder head gasket 1 comprises a pair of gasket baseplates 3 having four combustion chamber openings 3A formed therein in alignment with respective cylinder bores 2 (see Fig. 1) and a spacer 4 disposed between the pair of gasket baseplates 3 to be held sandwiched therebetween. The spacer 4 is disposed around each cylinder bore 2 to surround it in an endless manner. However, in the embodiment shown, because a spacing between the cylinder bores 2, and hence, between the combustion openings 3A is reduced, four spacers 4 are integrally connected together between adjacent combustion openings 3A so as to be continuous to each other. Where there is an increased spacing between the combustion openings 3A, it will be obviously seen that the four spacers may be separate from each other. In a region overlapped by the spacer 4, each gasket baseplate is formed with a full bead 3a and a half bead 3b, each of which surrounds the respective combustion opening 3A and is formed as a projection from the spacer 4. The full bead 3a and the half bead 3b are formed in the sequence named as viewed in a direction from the combustion openings to the outside thereof. SUS 301-H having a thickness of 0.20 mm, for example, may be used for each of the gasket baseplates 3. Preferably, its opposite surfaces are coated with NBR layers 3c, as shown in Fig. 3. For the spacer 4, SUS 304 having a thickness of 0.08 mm may be used. However, it should be understood that the thickness and the material of the gasket baseplate 3 may be suitably selected depending on the variety of an engine to which it is applied. As shown in Fig. 1, the cylinder head gasket 1 is interposed between a cylinder head 5 and a cylinder block 6 of the engine and is held sandwiched therebetween to provide a sealing between the both by integrally connecting the cylinder head 5 and the cylinder block 6 by a clamping bolt 7. In this example, the spacer 4 as well as the full bead 3a and the half bead 3b on the respective gasket baseplates 3 are continuously held sandwiched between the cylinder head 5 and the cylinder block 6 along the circumference of the cylinder bore 2, thus providing a safeguard preventing a circum-ferential continuity from being interrupted or preventing part of the half bead 3b which is located on the outer side from being trapped into cooling water passages 5a, 6a formed in the adjoining surfaces of the cylinder head 5 and / or the cylinder block 6 to prevent such part from being held sandwiched. In the embodiment shown, the cylinder head 5 and the cylinder block 6 are formed as aluminum die-cast open decked blocks, and the cooling water passages 5a, 6a are formed in the adjoining surfaces of the cylinder head 5 and the cylinder block 6, respectively, so as to surround the four combustion openings 3A in an integral manner at a location on the outside of the outermost half bead 3b. With the described construction, each of the combustion chamber openings 3A can be surrounded by the full bead 3a and the half bead 3b in an endless manner. In addition, since the spacer 4 is disposed in the region where the full bead 3a and the half bead 3b are provided, the full bead 3a and the half bead 3b can be brought into abutment against the cylinder head 5 and the cylinder block 6 under a high surface pressure and over a relatively extensive area of contact. As a consequence, it is less susceptible to the influence of any gross porosity in the casting or flaw on the adjoining surfaces of the cylinder head 5 and the cylinder block 6, allowing a good sealing performance to be secured and maintained. Fig. 4 shows another embodiment of the invention in which a reinforcing plate 11 of a reduced thickness than the spacer 4 is disposed on the outside of the spacer 4 of the first embodiment. The reinforcing plate 11 is held sandwiched between the pair of gasket baseplates 3, and a difference in the thickness between the reinforcing plate 11 and the spacer 4 in this embodiment is chosen to be equal to the thickness of the spacer 4 in the first embodiment. Again, a similar function and effect is achieved as in the first embodiment, while allowing the rigidity of the entire cylinder head gasket 1 to be enhanced. INDUSTRIAL APPLICABILITY As described, according to the invention, the gasket is less susceptible to the influence of any gross porosity in the casting or flaw on the mating adjoined surfaces, permitting a good sealing performance to be secured.

Claims: An engine having a cylinder head (5), a cylinder block (6) in which is formed a plurality of cylinder bores (2), and a cylinder head gasket (1) sandwiched between the cylinder head (5) and the cylinder block (6), the cylinder head gasket (1) including a pair of gasket baseplates (3) having combustion openings (3A) formed therein in alignment with the cylinder bores (2), a spacer (4) disposed around each combustion opening (3A) to surround it in an endless manner and sandwiched between the pair of gasket baseplates (3), and, for each combustion opening (3A), a full bead (3a) and a half bead (3b) formed on each of the gasket baseplates (3) in the regions thereof overlapping the spacer (4), characterised in that , for each combustion opening (3A), the spacer (4), the full bead (3a) and the half bead (3b) on each gasket baseplate (3) are continuously held sandwiched between the cylinder head (5) and the cylinder block (6) around the cylinder bore (2) with both the full bead (3a) and the half bead (3b) on each gasket baseplate (3) abutting against the spacer (4), and the half bead (3b) being disposed radially outwardly of the full bead (3a) away from the cylinder bore (2). An engine as claimed in claim 1 and further including, for each combustion opening (3A), a reinforcing plate (11) of a thickness less than that of the spacer (4) and disposed radially outwardly of the spacer (4) away from the bore (2), the reinforcing plate (11) being held sandwiched between the pair of gasket baseplates (3). An engine as claimed in claim 1 or claim 2 in which at least one of the cylinder head (5) and the cylinder block (6) is formed as an open deck with cooling water passages (5a,6a) which, for each combustion opening (3A), surround the spacer (4) and the full (3a) bead and the half bead (3b) on each gasket baseplate (3). An engine as claimed in any one of claims 1 to 3 in which each full bead (3a) includes a centre portion extending away from the spacer (4) in the direction of the thickness of the spacer (4). An engine as claimed in claim 1 in which the spacers (4) around each combustion opening (3A) are integrally connected together to be continuous with each other. An engine as claimed in any one of claims 1 to 5 in which, for each combustion opening (3A), the spacer (4) terminates radially outwardly of the opening (3A) in the region of the half bead (3b).

Inventors: FUJIKI RYOSUKE, GOTO EISABURO, NAKATA KAZUYA, SINPO YOSHIKAZU, YAMAGUCHI KEN ICHI, FUJIKI, RYOSUKE, GOTO, EISABURO, NAKATA, KAZUYA, SINPO, YOSHIKAZU, YAMAGUCHI, KEN'ICHI
Applicants: TAIHO KOGYO CO LTD, TAIHO KOGYO CO., LTD.
Application year: 1997
Main classification: F16J15
IPC codes: F02F11, F16J15