FR2750736A1 - HEAD GASKET FOR AUXILIARY COMBUSTION CHAMBERS - Google Patents

Abstract

The invention relates to a cylinder head gasket (G) for an internal combustion engine comprising main combustion chambers and auxiliary combustion chambers. The gasket is formed from at least one metal plate (10) comprising a plurality of bores (Hc) and a plurality of beads (11, 12), each bead surrounding a bore and an area (X) located at it. below an auxiliary combustion chamber. Each bead comprises a first part (11b, 12b) located in an area between two adjacent bores (Hc1, Hc2), and a second part (11a, 12a) surrounding the area (X) and at a distance from the bore. The first part (11b, 12b) has a higher elasticity constant than that of the second part (11a, 12a).

Description

HEAD GASKET FOR AUXILIARY ROOMS OF

COMBUSTION.

  The present invention relates to a cylinder head gasket for an engine comprising auxiliary combustion chambers in addition to the main combustion chambers. In a diesel engine, it is known that auxiliary combustion chambers can be formed in a cylinder head to improve the combustion or ignition characteristics of the fuel in the main combustion chambers. A cylinder head gasket used in such an engine comprises a main bead formed to surround a main combustion chamber or bore of the cylinder and a portion below the auxiliary combustion chamber to provide a seal around an opening of the auxiliary combustion chamber and the main combustion chamber. Japanese Utility Model Publication (KOKAI) No. 3-77053 describes this structure. To obtain a powerful and lightweight engine, a cylinder head made of an aluminum alloy was manufactured. When using an aluminum alloy cylinder head with an iron cylinder block, the cylinder head may be deformed so that its middle part protrudes upwards when the engine is running, due to a difference in expansion. between the aluminum alloy and the iron. As a result, a strong bias is exerted on both longitudinal ends of the cylinder head. The beads formed at the longitudinal ends of the seal may therefore be damaged or broken, and no longer be able to ensure adequate sealing around the bores. Usually, to avoid this inconvenience, spacers are installed on the seal which have the effect of compensating for the deformation of the cylinder head. The main engine bead can also be modified so that the width and radius of curvature of the main bead, located at the longitudinal ends of the engine, are larger than those of the other bead, thereby improving the service life of the bead. beads, as described in the model publication

  of Japanese utility (KOKOKU) n 5-1728.

  But, the yoke being tightened by bolts around the bores and spaced apart from each other, it is understood that each of the beads around the bores is not uniformly compressed by the bolts. To be able to improve the engine, it is necessary that the

  bead is fixed as evenly as possible.

  More particularly, in the engine comprising the auxiliary combustion chambers, described and shown in Japanese Utility Model Publication (KOKAI) No. 3-77053, the bead surrounding the auxiliary combustion chamber may have a portion remote from the the bore and located outside an imaginary line connecting the

  centers of two bolts adjacent to the bore.

  The remote part can not be compressed and fixed satisfactorily by the bolts. As a result, the conventional seal includes factors that provide uneven pressures on the surface of the bead portions. It is therefore necessary to improve the

seal.

  The present invention aims to remedy these drawbacks and therefore relates to a metal sealing gasket for an engine comprising main and auxiliary combustion chambers, whereby the sealed fastening around the bores of the cylinders can be

  made as regular as possible.

  The invention also relates to a metal seal, as mentioned above, which continues to adhere perfectly around the main and auxiliary combustion chambers, even if the cylinder head deforms under the effect of

the heat.

  The invention also relates to a metal seal, as mentioned above, which is suitable for a cylinder head of

relatively low rigidity.

  Other objects and advantages of the invention will emerge

  best of the description of the invention which follows.

  A cylinder head gasket according to the present invention is used for an internal combustion engine having main combustion chambers and auxiliary combustion chambers. The seal is formed from at least one metal plate, and includes a plurality of side-by-side bores, and a plurality of beads formed on the metal plate. Each bead surrounds a bore and an area underneath

  an auxiliary combustion chamber.

  According to the invention, each bead comprises a first part situated in an area where two adjacent bores are close to one another, that is to say an intermediate zone between the two adjacent bores, and a second part, surrounding the area below the auxiliary combustion chamber and remote from the bore. The first part has a constant of elasticity

  higher than that of the second part.

  Each of the beads, located in the areas of the longitudinal ends of the seal, has a third portion, facing a longitudinal edge of the seal. This third part has a lower elasticity constant than that of the first part. The second and third parts may have the same elasticity constant. In the first part of the yoke, the beads are heated and subject to creep and, in addition, the cylinder head can not provide sufficient surface pressure due to the upward deformation. This is why the elasticity constant of the bead at the first part must be greater than for the other parts. In addition, in the second part, the bolts do not exert on the bead a sufficient clamping pressure and, in the third parts, a strong stress is exerted on the beads. It is for these reasons that the elasticity constant of the second and third parts is chosen relatively low. Thus, as a whole, the bead ensures a balanced surface pressure over its entire length. Preferably, in order to ensure a high surface pressure at the first part, the height of the bead is greater than in the other part. As a result, even if the breech is deformed, we obtain a

high surface pressure.

  Each of the beads located on the side opposite the second portion, relative to the bore, may have a fourth portion having an intermediate value elasticity constant with respect to the elasticity constants of the

first and second parts.

  The second portion is located on a side opposite the bore, with respect to an imaginary line connecting the centers of two adjacent bolt holes, formed around the bores, and extending in the opposite direction.

  longitudinal seal.

  The seal may comprise at least one additional plate placed on said at least one metal plate, thereby forming a laminated metal seal. The bead may have any shape of the cross-section, for example an upwardly arched protuberance, corrugations, trapezoidal shape, or the like, in a manner well known in the art. The elasticity constant of the bead can be adjusted as in the conventional method, for example by changing the width, height or curvature. When the width becomes narrower or the height is greater, the constant

  elasticity of the bead can be increased.

  Other features and advantages of the invention

  will emerge more clearly from reading the description

  hereinafter, with reference to the only appended FIG. 1 which is a plan view of a metal seal for a four-cylinder and four-chamber engine

  auxiliary combustion apparatus according to the present invention.

  The seal G shown in Figure 1 is formed from a metal plate 10. However, this plate can be combined with one or more other plates

  metal to form a laminated metal seal.

  The metal plate 10 has outer bores Hc1 and inner bores Hc2, as well as through holes Hb for bolts arranged around the bores. The seal G also comprises, in a manner known per se, holes for water, for oil, for pushers, etc., these holes not being shown in FIG. 1. The auxiliary combustion chambers are located above the zones X. The metal plate 10 includes outer beads 11 around the outer bores Hcl and

  inner beads 12 around the inner bores Hc2.

  These beads 11, 12 surround the bores and the zones X

  below the auxiliary combustion chambers.

  Each outer bead 11 comprises a portion 11a located outside an imaginary line L connecting the centers of the holes Hb for bolts and which extends along the lateral edge 10a of the seal. The outer bead 11 also comprises a portion 11b, located in an intermediate zone situated between two adjacent bores, zone in which two beads are close to one another, a portion 11c located at the transverse edge 10b of the seal, and a part lld located on the opposite side to the part lla. The elastic constants of parts 11a and 11c are identical and they are less than the elasticity constant of part 11b. The elasticity constant of the lld part has an intermediate value between those of the

parts 11a and 11b.

  Each inner bead 12 includes a portion 12a located outside the imaginary line L, portions 12b each located between the two adjacent bores and a portion 12d located on the side opposite to the portion 12a. The constants of elasticity of parts 12a, 12b and 12d are, respectively, the same as those of parts 11a, 11b and 11d. In the gasket G, the portions 11c located at the transverse edges 10b are strongly subjected to the influence of the thermal deformation of the cylinder head. On the other hand, since the parts 11a and 12a are located outside the imaginary line L, relative to the bores, they do not undergo high clamping pressures from the cylinder head. Therefore, according to the present invention, the parts 11a, 11c and 12a are made with a relatively low elasticity or mechanical strength, so that when the yoke is tightly clamped, the parts 11a, 11c and 12a

  can be compressed relatively easily.

  On the other hand, in the parts 11b and 12b situated in the intermediate zones between two adjacent bores, where the rigidity of the cylinder head is likely to decrease, it is difficult to obtain a surface pressure. According to the invention, the parts 11b and 12b are formed to have a relatively high elasticity constant or to have a high height to ensure the

  required surface pressure between bores.

  Thus, when the seal is installed in the engine and the engine is running, the beads can provide a relatively even surface pressure around all the beads. The seal can therefore seal and adhere, reliably, around the combustion chambers, main and auxiliary. According to the invention, each bead surrounds a bore and the area below the auxiliary combustion chamber. Since the different parts of a bead receive different clamping pressures from the yoke, when the bolts are tightened to a block, the elastic constants or the height of the bead portions are modified to correspond to the different tightening pressures. . The beads can therefore be compressed easily without risk of damage and they are able to seal reliably around the bores and the auxiliary combustion chambers. Although the invention has been described with respect to a preferred embodiment, it is evident that changes in form and detail can be made.

  without departing from the spirit or scope of the invention.

Claims (5)

  1. Head gasket (G) for an internal combustion engine having main combustion chambers and auxiliary combustion chambers, said gasket comprising at least one metal plate (10), a plurality of bores (Hc) formed in the metal plate and arranged side by side, and a plurality of beads (11, 12) formed on the metal plate, each bead surrounding a bore and a zone (X) below an auxiliary combustion chamber, said seal (G) being characterized in that each bead (11, 12) comprises a first portion (11b, 12b) located in an area in which two bores (Hcl, Hc2) are adjacent, and a second portion (11a, 12a) ) surrounding the zone (X) below the auxiliary combustion chamber and away from the bore, said first portion (11b, 12b) having a higher spring constant   higher than that of the second part (11a, 12a).   2. A cylinder head gasket according to claim 1, wherein each of the beads (11) at the longitudinal ends of the seal (G) has a third portion (11c) facing a transverse edge (10b) of the seal, said third portion having a constant of elasticity   weaker than that of the first part (11b).   3. Head gasket according to one of claims 1 and   2, wherein each of the beads (11, 12) located on the side opposite the second portion (11a, 12a), relative to the bore, comprises a fourth portion (11d, 12d) whose elastic constant is intermediate between the constants of elasticity of the first (11b, 12b) and second (11a, 12a) parts.   4. Head gasket according to one of claims 1, 2   and 3, wherein said second portion (11a, 12a) is located on a side opposite the bore with respect to an imaginary line (L) connecting the centers of two adjacent holes (Hb) for bolts, formed on the outside bores, said line extending along the longitudinal side (10a) seal (G).   A cylinder head gasket according to claim 1, 2, 3 or 4, further comprising at least one additional plate placed above said at least one metal plate (10) to form a laminated metal gasket.