GB2269633A - Exhaust passage for an internal combustion engine - Google Patents

Abstract

A ceramic liner for an engine part comprises an elliptical hollow tubular portion (10) and a bifurcated portion (111, 112). The ratio I/L of the length (l) of the tubular portion (10) to the length (L) of the liner is given by 0. 8>/= I/L >/= 0.25. <IMAGE>

Description

EXHAUST PASSAGE FOR AN INTERNAL COMBUSTION ENGINE The present invention relates to an exhaust passage for an internal combustion engine. More particularly the invention relates to an engine part comprising a cast main body and a ceramic liner provided within the main body to define an exhaust passage, the ceramic liner including a hollow tubular liner body and a plurality of tubular members branching from the liner body.

An engine part of this type is disclosed in Japanese Patent Application No 111985/1984, for example.

An engine part having a ceramic liner of the mentioned type used therein tends to be heated excessively during engine operation, due to exhaust gas at high temperature passing through the tubular members, at an area of the ceramic liner where adjacent tubular members branch apart from the liner body. It is preferable to reduce the radius of the inside surface of this branched area as much as possible so that the high temperature exhaust gas within the tubular members will be guided smoothly toward the liner body. This is difficult as regards molding and therefore there remains a disadvantage that exhaust gas at high temperature is liable to stay on the inner surface side of the branched area.

As a result, thermal stress is concentrated on the branched area and this leads to a problem that cracks tend to occur at the branched area since conventional engine parts have not been equipped with specific means for moderating or reducing concentration of such thermal stress. There is also a problem that the flowability of molten metal at the time of casting the main body is not good at the branched area since the molten metal is cooled by the ceramic liner and a core member.

From a first aspect the present invention provides an engine part provided with an exhaust passage, comprising a cast metal main body and a ceramic liner on or around which is cast the main body and which defines an exhaust passage, the ceramic liner including a hollow tubular liner body and a plurality of tubular members branching from said liner body, wherein a through portion is provided at an area of said ceramic liner at which adjacent tubular members branch apart, for providing communication between inside and outside of the ceramic liner, said through portion being filled with metal of said main body.

With the above arrangement, a metal portion which is formed continuous with the main body and fills the through portion serves as a heat transfer passage during engine operation and permits heat in the region of the branched area to be dissipated through the passage to the main body. Thereby, excessive heating of the branched area is prevented and concentration of thermal stress is moderated. In consequence, generation of cracks at the branched area can be avoided.

Additionally, at the time of casting the main body, molten metal which has flowed into the through portion exhibits a heat insulating action to improve the flowability of molten metal around the branched area of the ceramic liner. Adherence between the main body and the ceramic liner is enhanced thereby.

Further, according to a preferred feature of the invention, a guide portion is formed integrally with the main body and projects inside the ceramic liner through the through portion so as in use to guide exhaust gas, which has passed along the adjacent tubular members, toward the liner body.

In this arrangement, the guide portion formed on the main body serves also as a heat transfer passage during engine operation like the foregoing arrangement.

Heat generated at the branched area is dissipated to the main body through the passage and moreover exhaust gas at high temperature which has passed along the tubular members is guided smoothly by the guide portion toward the liner body. Accordingly, excessive heating of the branched area is prevented and thermal stress concentration is moderated. Simultaneously the discharge resistance of the exhaust gas is reduced.

In addition, at the time of casting the main body, the molten metal which fills the through portion can also exhibit a heat insulating action.

From a second aspect the invention provides an engine part provided with an exhaust passage, comprising a cast main body and a bifurcated ceramic liner on or around which is cast the main body and which defines an exhaust passage, the ceramic liner including a hollow tubular liner body and a pair of tubular members branching from the liner body, wherein said hollow liner body includes a tubular part of an elliptical cross section having an outlet for the exhaust passage, the ratio l/L between a length (L) of the liner body measured on a dividing plane which includes a long diameter of the elliptical cylindrical part and divides the ceramic liner substantially into two equal parts along the exahust passage and a length (1) of the tubular part being:: 0.8 2 l/L 2 0.25 The above arrangement provides advantages in that solidification and shrinkage forces generated at the time of casting the main body are carried on the cylindrical part of an elliptical cross section to prevent the occurrence of cracks at the branched area and that exhaust gas which has passed along the tubular members can flow into the liner body smoothly.

In contrast, if the ratio of the two lengths l/L > 0.8, the radius of the branched area as measured on the dividing plane becomes sufficiently large to hinder a smooth flow of the exhaust gas toward the liner body.

If the ratio 1/L < 0.25, the length 1 of the cylindrical part-is so short that the cylindrical part cannot support the solidification and shrinkage forces generated at the time of casting the main body, thus permitting cracks to be generated easily at the branched wall.

Thus at least in preferred embodiments the flow of exhaust gas is smooth and an engine part obtained has a ceramic liner which is free of defects and does not suffer from cracks at the branched wall thereof.

Preferably, the ceramic liner is formed of alumina titanate.

From a third aspect, the invention provides an engine part provided with an exhaust passage, comprising a cast metal body and a bifurcated ceramic liner on or around which said metal body is cast, and which defines said passage, said liner having a first tubular portion of substantially constant elliptical cross-section, and a second bifurcated portion leading therefrom wherein the ratio l/L of the length of the first tubular portion (1) to the length of the liner (L) is given by 0.8 2 l/L > 0.25 said lengths being measured along the longitudinal axis of the liner.

From a fourth aspect, the invention provides a ceramic liner for casting into an engine part, comprising a hollow tubular liner body and a plurality of tubular members branching from said liner body, wherein a through portion is provided at an area of said ceramic liner at which adjacent tubular members branch apart, for providing communication between inside and outside of the ceramic liner.

From a fifth aspect, the invention provides a ceramic liner for casting into an engine part, comprising a first tubular portion of substantially constant elliptical cross-section, and a second bifurcated portion leading therefrom wherein the ratio l/L of the length of the first tubular portion (1) to the length of the liner (L) is given by: 0.8 > l/L 2 0.25 said lengths being measured along the longitudinal axis of the liner.

It will be seen therefore, that the present invention at least in its preferred embodiments provides an engine part in which the concentration of thermal stress on the branched area of the ceramic liner is moderated and generation of cracks at the branched area is avoided. Furthermore the engine part advantageously permits the flowability of molten metal around the branched area when casting the main body to be improved and therefore serves to enhance the adherence between the cast main body and the ceramic liner.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

In the accompanying drawings, Figst 1 - 9 show a first group of embodiments wherein Fig. 1 is a longitudinally sectioned, front view of a cylinder head according to an embodiment, corresponding to a sectiona-l view taken along a line I - I of Fig. 2, Fig. 2 is a view taken along a line II - II of Fig. 1, Fig. 3 is a perspective view of a ceramic liner, Fig. 4 is a plan view of the ceramic liner, Fig. 5 is a sectional view taken along a liners --V of Pig. 4, Fig, 5A is an end view seen in a direction of arrow Va of Fig. 5, Fig. 5B is an end view sectioned along a line Vb - Vb of Fig. 5, Fig. 6 is an enlarged view:. of that portion of Fig.S as indicated byan arrow.VIafter casting, Fig. 7 is an enlarged view of that protion of Sig. 6 as indicated by an arrow VII, and Figs. 8 and 9 are perspective views of other two examples of ceramic liner.

Figs. 10 - 19 show a second group of embodiments wherein Fig. 10 is a longitudinally sectioned view of a cylinder head according to an embodiment, which.:cor'responds to a sectional view.taken along a line X - X of Fig,- 11, Fig. 12 is a sectional view taken along a line XII - XII of Fig. 10, Fly. 13 is an enlarged view of that portion, of Fig. 12 as indicated by an arrow XIII, Fig. 14 is a perspective view of the ceramic liner, Fig. 15 is a, plan view-of the ceramic liner, Fig. 16 is a sectional view taken along a line XVI - XVI of Fig. 15, Fig. 17 is a sectional view taken along a line XVII - XVII of Fig. 16, Fig 18 is an enlarged view of that portion of Fig. 17 as indicated by an arrow XVIII, and Fig. 19 is a plan view of another example of ceramic liner.

Figs. 20 - 23 show a modified formofoeramic liner wherein Fig. 20 is a plan view, Fig. 21.is a sectional view taken along a line XxI - XXI of Fig 20, Fig..-22 is an end view seen in a direction of arrow XXII.of Fig. 21, and Fig. 23 is an end view sectioned along -a line XXIII - XXIII of Fig. 21.

Figs. 24 and 25 show a modified fo.rm of, ceramic liner wherein Fig. 24 is a perspective view.and Fig,'25 is a plan view.

Fig. 26 is a graph showing a relationship between the surface roughness of ceramic liner and;that of cylinder head body.

Figs. 27 and 27A show a further modified form of ceramic liner wherein Fig. 27 is a sectional view and Fig. 27A is an enlarged view of that portion of Fig. 27 as shown by an arrow XXVI Ia.

Fiy. 28 is a sectional view of. a still further modified form of ceramic liner, corresponding to Fig..21.

In Figs 1 and 2, a cylinder head 1 for an engine is shown as an engine part according to one embodiment of the invention and it is provided with a manifold type intake passage which is in the illustration a bifurcated intake passage 4 having one inlet 2 and two outlets 3r and a manifold type exhaust passage which is in the jllustrat'ion a bifurcated exhaust passage 7 having two inlets 5 dnd one outlet 6. The cylinder head 1 comprises a cylinder head body 8 made of aluminum alloy as a cast main body ana a manifold type (bifurcated in the illustration) ceramic liner, 9 which is cast within the main body 8 and defines" the exhaust passage 7 therein.

In Figs. 2 to 5, the ceramic liner 9- is. formed by using alumina-titanate (AQ203-TiO3) as a ceramic material.

Alumina-titanate has a relatively small rupture stress 6B based on three-point bending test and a relatively low Young's modulus. It further has a small coefficient of thermal expansion and a small thermal' conductiv2ty and is superior in thermal shock resistance. Alumina-titanate is a material most suitable for forming this kind of ceramic liner 9.

Thc ceramic''liner 9 includes a hollow - tubular liner body 10 and a plurality of tubular. members branch in from the liner body 10, in the illustration a pair of first and second tubular members 111 and 112 As is clearly shown in Figs. 5, 5A and. 5B, the liner body 10 comprises a first tubular part 101 having the outlet 6 for the exhaust passage 7 and a second tubular part 102 located between the first tubular part 10 and the pair of tubular ' members lilt 1,12 As shown in Fig. 5A, the first tubular part 10i has a substantially track-shaped cross section formed by.a pair of parallel, mutually opposed straight portions and a pair of mutually opposed curved portions.As shown in 'Fig' SB, the second tubular part 102 has a pair of recess portions 12 which extend from the central portions of parallel, opposed walls of the first tubular part 10,1 toward a branched wall a disposed between both the tubular members Ili and 112 while increasing their depth gradually: .

A slit 13 is formed so as to extend continuously over a branched area R on the ceramic liner- 9 -at which area the adjacent first and second tubular members 111 and 112 are branched apart, and more specifically in- the illustrated embodiment over the branched wall a of the liner body 10 and opposed portions b of the peripheral wails of both the tubular members 111 and 112. This slit 13 penetrates through the branched wall a and the opposed portions b of the peripheral walls to provide communicatio.n between inside and outside of the liner 9. Reference numeral 14 denotes a through hole for receiving therethrough a valve guide 15.

As is apparent from Figt 6, the slit 13 is designed such that its opening on the inner side of the ceramic liner 9 has a width which is larger than a width c2 of its opening on the outer side of the ceramic liner 9, whereby the slit 13 has a cross section of dovetail groove shape.

As is clearly shown in Fig 7r glass is filled into spaces e such as holes and cracks present in the inner wall d of the slit 13. In this Figure, reference character g denotes particles of alumina-titanate.

As the glass f, at least one selected from silicate glass, borate glass and phosphate glass-is used When filling the spaces e with the glass f, a fluid of dispersion of glass particles is .coated. to. a ceramic molded article made of alumina-titanate-and is, then permitted to be impregnated into the spaces e by capillary action. Thereafter, the glass f is meited down in the process of sintering the ceramic molded article.It is useful to add alumina-titanate to the- fluid of dispersion as a formulation ingredient for the reinforcUment purpose and when added with alumina-titanat'e,'the-fluid of dispersion may be in a state of scurry, One example of the conditions for ma-nufacturing the ceramic liner 9 will be described as follows*- the diameter of alumina-titanate particles 0.1 - 10 pom; the method of molding ... slip casting; glass particles uSed in the fluid of dispersion ... silicate glass particles of a diameter not more than 1 pm, at a load of 20 weight % and in water as dispersion medium; sintering is conducted for five hours at a temperature of 1500 C after coating of the fluid of dispersion.

It is also possible, in filling the spaces with the glass f, to carry out coating and impregnation treatments after sintering and then a heating treatment, or to conduct first and second sintering -treatments' wherein a provisionally sintered ceramic article which corresponds to the ceramic liner 9 and which has been subjected to the first sintering treatment at a temperature out 300 to 14000C for 0.5 hours is coated and impregnated with the fluid of dispersion and thereafter is subj'ecte'd'to,the second sintering treatment.

In this case, when the coating treatment is conducted after sintering, the heating treatment is carried out at a temperature of 1100 - 14000C for 1.-' 5 hours in the atmosphere and the conditions of the second. sintering treatment are the same as of the afore-mentioned sintering treatment of alumina-titanate (1500 - 1600 C, 3 - 10 hours).

One example of the casting conditions for the cylinder head body 8 in which the ceramic liner 9 is 'used will be as follows the ceramic liner 9 is preheated at a temperature of 1S00C; molten aluminum alloy (-JIS AC2B) is at a temperature of 750 C and is poured under pressure of 0.25 kg/cm2; and the low pressure casting method is applied Thrh the afore-mentioned casting operation, the ceramic liner 9 is cast in the cylinder head body 8 and the molten metal is charged into the slit l3 as clearly shown in Fig. 6.Since the molten metal charged in the slit 13 can provide a heat insulating action, the flowing property of the molten metal around the branched area R of the ceramic liner 9 is good and the- a dberance between the cylinder head body 8 and the ceramic liner 9 is improved Moreover, since the opening edge portion h of the slit 13 on the inner side of-the ceramic liner 9 forms an obtuse angle, any compression stress acting on the ceramic liner 9 during solidifica'tkon of the molten metal cannot produce cracks at the opening -edge portion h.

With the arrangement described above a ridge 16 which is formed as a projecting portion continuous with the cylinder head body 8 and fills the slut 13 serves as a heat transfer passage during engine operation to permit heat at the branched area R to be released to the cylinder head body 8 through the heat transfer passage whereby the branched area R is prevented from bein'g heated excessively and concentration of the thermal stress thereon is moderated.

Owing to this, occurrence of cracks at the branched area R is prevented.

The ridge 16 is molded to have a dovetail crosssection and hence provides an anchoring effect which enables the cylinder head body 8 and the ceramic liner 9 to be adhered to each other in a preferable manner.

In addition, relative movement may be caused between the slit 13 and the ridge 16 during engine operation due to differences in coefficients of thermal expansion and thermal shrinkage between the aluminum alloy and the ceramic material. According to this embodiment, however, the glass f has been filled in the spaces e present in the inner wall d of the slit 13 as has been mentioned above for reinforcement of the wall d and this reinforcing action works to prevent the inner wall d from being damaged due to such movement.

When a ceramic liner is not formed with. the aforementioned slit 13, cracks resulting from tompression stress caused by solidification and shrinkage of the:.-molten metal may be generated on that inside sutface portion of the branched wall a which corresponds to the slit 13 due to a small radius of the arcuate wall a Provision of the slit 13, however, serves advantageously to eliminate occurrence of such cracks.

Fig. 8 shows an embodiment wherein an elongated through hole 17 is provided as a through portion at the branched area R of the ceramic liner 9 and Fig. 9 shows an embodiment wherein a circular through hole 18 is provided as a through portion at the branched area R of the ceramic liner and in this illustrated embodiment at the branched wall a. These through holes 17 and la may be provided on at least one of the opposed peripheral wall portions..b.of the tubular members 11 112.

Incidentally, engine parts to which the afore-mentioned embodiments are applied may include', exhaust manifolds. In this case, an exhaust manifold may comprise a manifold body made by casting and a manifold-shaped ceramic liner which is cast within the body.

Figs 10 - 19 show a second group of embodiments In these embodiments, a cylinder head 1-for an engine as an engine part has the same const-ruction as of the first group of embodiments and hence identicaL parts are indicated by identical reference numerals -and characters and their detailed description will be omitted here.

In Figs. 11 - 17, the ceramic liner 9 is formed of alumina-titanate (Al2-O3#TiO2) just like, the first group of embodiments and includes the hollow tubular liner body 10 and the pair of first and second tubular, members 11 and 112 which - branch -'---'- the liner body 10.

An elongated hole 19-is formed as a through portion continuously over the branched area R of the ceramic liner 9 at which mutually adjacent first. and second tubular members ill and 112 are branched, and more specifically in the illustration over an area from base ends i of the tubular members 111, 112 to both of opposed portions i of the peripheral walls of the recess portions 12 in the second tubular part 102, for providing communication between inside and outside of the ceramic liner 9.

As is clearly shown in Fig. 17, -the- elongated hole 19 is designed so as to have a width-kl of an opening on the inner side of the ceramic liner 9 (for.example, 9 - 11 mm) which is larger than a width ,k2 of, an opening located on the outer side of the ceramic liner 9 (for example, 3 - 5 mm), whereby the elongated hole 19 has a dovetail groove-shaped cross section Also gas rs apparent from Figs,14 andl5, each of longitudinal opposite ends of the elongated hole 19 is formed to have an inside surface m of arcuate shape.

Purthermore, Fig. 18 clearly shows bbat glass f of the same material as that of the first,group of embodiments has been filled in the same manner into the minute spaces e such as holes and cracks present in an inner wall d defining the elongated hole 19.

Like the first group of embodiments, at the time of casting the cylinder head body 8,. the ceramic liner 9 is cast into the body 8. In the process of such casting, the molten metal is poured into the elongated slit 19 as well as into a guide portion shaping cavity which is defined in a core member, not shown, located within the ceramic liner 9, as clearly shown in Figs. 12 and 13 so that a guide portion 20 integral with the cylinder head body 8 is formed so as to project inside of the ceramic liner 9 through the elongated hole 19. The guide portion 20 has a V-shaped inclined surface n which forms an extension of the inner side surface of each of the tubular members 111, 112.Heat insulating action obtained by the molten metal charged into the elongated hole. 19 works to improve the flow ability - of the melt around the, branched area R of the ceramic liner 9 thereby enhancing the adherence between the cylinder head body 8.and-the ceramic liner 9.

Owing to the above-described arrängement, the guide portion 20 formed on the cylinder head body 8 serves as a heat transfer passage during engine operation and permits heat around the branched area R to be dissipated to the cylinder hcad body 8 through the passage and. moreo,ve,r the exhaust gas of a high temperature which has passed both the cylinder members 111 and 112 is guided smoothly :toward the liner body 10 as shown by arrows in Fig 13. -Acco.rdingly, the branched area R is prevented from excessively heating and concentration of thermal stress on that area is moderated.

Thereby, cracks are prevented from occurring at the branched area R.

Furthermore, since the guide portion 20 is formed to have a dovetail groove cross section at a portion P thereof opposed to the elongated hole 19, the guide portion 20 exhibits an anctloring effect to keep the adhesive properties between the cylinder head body 8 and the ceramic liner 9 at a good level.

In addition, relative movement may occur during engine operation between the elongated hole 19 and the guide portion 20 due to differences in coeff-icjents;of thermal expansion and thermal shrinkage between aluminum alloy and ceramic material. However, since the inner wall d of the elongated hole 19 has been reinforced-by glass f filled into the spaces e present in the wall d, such movement cannot cause any damages to the inner wall d -as reinforced Moreover, due to formation of the insi.de surfaces m at the opposite ends of the elongated.hOle 19 as arcuate surfaces, it becomes possible to moderateconcentration of thermal stress on the opposite ends of the. hole.

Fig. 19 shows an embodiment wherein the inside surface m at each of longitudinal opposite ends of the elongated hole 19 is formed into an arcuate surface-of a notched circle so as to moderate concentration of, thermal stress Engine parts according to these embodiments may include e: < haust manifolds as in the first group of embodiments.

Figs. 20 - 23 show a further modifiedf,orm of the ceramic liner 9 though the ceramic liner -9 is made of aluminatitanate like the foregoing embodiments The ceramic liner 9 has substantially the same construction as those of the first group of embodiments, however, differs therefrom in the configuration of the hollow cylindrical liner body 10.

That is, the hollow tubular . liner body 10 according to this modified form comprises a first tubular part 10 having an outlet 6 for the exhaust passage ,7 defined therein and a second tubular . part 102 located between the first tubular . part 101 and first and second tubular members 111, 112.The first tubular - - portion 101 has an elliptical-shaped cross section The second tubular portion 102 has a pair of recess portions 12 which extend from the central portions of those. walls 'of -the first tubular part 101 which are opposed to each other with the long diameter of the elliptical section being; interposed therebetween and which increase their.depth gradually toward the branched wall a between the tubular. members 111, 112.

Assuming that L denote the length of the liner body 10 at its portion including the long diameter of the first cylindrical part 101 and lying on-a dividing plane Q which divides the ceramic liner 9- substantiell-y into two equal parts along the exhaust passage 7 and 2 denote the length of the first tubular part 101, the ratio between both the lengths Q/L are set as follows.

0.8 > /L # 0.25 Ceramic liners 9 of the type according to the example of Figs. 20 - 23 have been formed of alumina-titanate of respective different solid state properties and they have been cast in cylinder head bodies 8 two produce cylinder heads 1, respectively.

- The following table show comparison between the solid state properties of respective alumina-titanates A to F and the results of casting Here, the length L of the liner body 10 has been set to 55 mm, the length l of the fir-st-tubular part 101 has been set to 38 mm, and hence the ratio l/L of both the lengths has been set to 0.69.

Also in the table, the term "good" means that the ceramic liner 9 had no cracks generated therein and the term "bad" means that cracks have been found in the branched wall a.

Alumina-titanate A B C D E F Young's modulus E 3.000 2.500 1,800 300 300 100 (kg / mm) Strength against 4.0 3.5 2.5 0.9 0.6 0.5 ge # @ / E 1.3 1.4 1.4 3.0 2.0 5.0 ( X 10-3 ) Results of mparison I 1 The following may be commented from this table Namely, in case of alumina-titanate A having a high Young's modulus E of 3,000 kg/mm2 or so, the strength against breakage of 6B t. 3.7 kg/mm2 can be used as the standard for selecting the material whereas in case of 'alumina-titanates D to F having a low Young's modulus E now more than 300 kg/mm2, the standard for material selection can-be- set to the strength against breakage/Young's modulus > 1.-8 It is considered that a ceramic liner fo,rmed of alumina- titanate A is of a relatively high strength and therefore is free of generation of cracks which may otherwise be generated by the solidification shrinkage-force at the time of casting the cylinder head body 8 and .that in case of ceramic liners made of alumina-titanates D to F, their strengths are relatively low and they. can absorb the solidification shrinakge force duping casting of the cylinder head body 8 and therefore they can be free of cracks.

Incidentally, the configuration of the liner bodies 10 of the ceramic liners 9 in the first and second groups of embodiments may be identical to tha.t of the example of Figs. 20 - 23.

Figs. 24 and 25 show a further modified form of the ceramic liner 9. This ceramic liner.9 is substantially of the same configuration as 6f Figs. 20 - 23.

When it is required to avoid a stress concentration on the branched area R of the ceramic liner 9 at the time of casting the cylinder head body 8, the outside surface of the area R should preferably be as smooth has possible whereas the outside surface of a remaining, area R1 other than the branched area R should be rough to an appropriate extent in order to achieve a good adherence between the area R1 and the cylinder head body 8.

From these points of view, the surface roughness Rmax of the outside surface r at the branched area R of the ceramic liner 9 and in the illustration åt the area including the branched wall a of the liner body 10 "and its adjacent portion (inclusive of a part of the, reccss.po'rtions 12) and further including the opposed portions b of the peripheral walls of the tubular - members 111 and 112 is set at less than 30 Sm while the surface roughness Rmax -of the outside surface s at the remaining area R1 -other, than the branched area R is set at not less than 30 pm but below 100 ,um.

Fig. 26 shows a relationship between the'surface rough nests of the outside surface s at the remaining area R1 of the ceramic liner 9 and the surface roughness of thc cylinder head body 8 which is established under application of the low pressure casting method.

In this figure, if the surface roughness Rmax of the remaining area R1 is set at not less than 30-,um, the depth of penetration of the molten metal into minute recess portions on the outside surface s of the remaining area R1 increases even under application of the low pressure casting method to make the surface-roughness- Rmax of the cylinder head body 8 not less than about 20 m, thereby strengthening the adhesion of the cylinder head body 8 with respect to the ceramic liner 9.On the-.other hand, if the surface roughness Rmax of the outside surface s of the remaining area R1 exceeds 100 m, gas generated at the time of casting operation stays 'w'ithin" the minute recess portions on the outside surface s of,the the area R thereby to lower the surface roughness of the cylinder head body 8 to a level below 20 m and as a result the adhesion of the cylinder head body -8 to the ceramic liner 9 is reduced.

This relationship in surface roughness will be the same under application of a gravity die casting method.

However, when a high pressure casting method is-applied, a high pressure acting on a molten metal enables the molten metal to be filled into the minute 'recess. portions on the outside surface of the ceramic liner 9 sufficiently so that the surface roughness of the ceramic liner 9 can be disregarded.

Figs. 27 and 27A show a further modified form of the ceramic liner 9. This ceramic liner ,i-s substantially identical to that of Figs. 20 - 23 in configuration.

When the ceramic liner 9 is cast. within the cylinder head body 8, a compression stress t1 acts on an outer wall side ul of each of the rccess portions 12 by the molten metal pressure and the solidification and shrinkage of the cylinder head body B as shown Ln Fig. 27A and this in turn causes a tensile stress t2-, to be .exerted on an inner wall side u2 of each recess portion 12.

The tensile stress t2 thus produced may become a cause for generating cracks at the-inner .wall side u2 of each recess portion 12 and hence it is required to construct the inner wall side u2 to have a high strength.

To meet this requirement, glass f of-the.same kind as of the afore-mentioned ones is filled into minute spaces such as holes and cracks present in the inner wall side u2 of each recess portion 12 in the same manner Owing to this arrangement, the inner wall sides u2 of both recess portions 12 which require a high, strength are formed to have a high density during the production process of the ceramic liner 9 and are reliably reinforced.

It will of course be apparent that glass may also be filled into other portions requiring a strength such as the outer wall sides u1 of the recess portions 12, the branched wall and the like or into the whole of the,ceramic liner 9.

As other reinforcing means for portions which require a strength (or the whole ceramic liner 9), there may be listed up such measures to form those portions to have a fine structure and/or to have metallic oxides dispersed at grain boundaries.

When obtaining a ceramic liner 9 of, such a structure as mentioned above, particles of alu'mina-titanate are used to shape a ceramic molded article as a Cetamic blank material corresponding to the ceramic liner 9,. then a solution including at least one kind of-.metallxc oxide to be dispersed in alumina-titanate which ; selected from the group consisting of SiO2, ZrO2, Mg' 0, Fe2O3 and SnO2 is coated and impregnated into spaces..pre-ent in predetermined portion(s) of the ceramic molded article and thereafter the article is subjected to a sintering treatment which serves also as a diffusion treatment.

The content of each metallic oxide such as SiO2 in the ceramic liner 9 is appropriately in a range.of 0.05 to 5 weight %. It is effective in-respect Of reinforcement to mix the metallic oxides with alumina-titanate and a small amount of CdO in the form of elements included in the aforementioned solution, When alumina-titanate is added to the solution, the solution may become slurry.

The measure proposed above causes SiO2 and the like to be diffused in alumina-titanate and-prede,tetmined portions of the liner 9 to have a fine structure and thereby metallic oxides are dispersed at the grain boundaries As other reinforcement means there may be listed up a measure to provide a fine structure at the predetermined portions and/or to diffuse metallic.oxides at grain boundaries and to provide a composite-of whisker w (diffusion at the grain boundaries) :: When a ceramic liner 9 of the-just-mentioned structure is to be achieved, particles of alumina-titanate and silicon carbide whisker as said whisker' are' employed for shaping a ceramic molded article which corresponds to the ceramic liner 9 and then a solution including said metallic oxides diffused in alumina-titanate is applied to and impregnated in the spaces present in the predetermined portions of the ceramic molded ar'Eicle-.-', Thereafter, the ceramic molded article is subjecte.d to .a diffusion treatment which serves also as a sintering treatment.

The content of silicon carbide whisker in the ceramic liner 9 is appropriately in a range of O-05-'to 5 weight %.

The content of each metallic oxide likewise stays appropriately in a range of 0.05 to 5 weight t. Moreover, similarly to the afore-mentioned case, alumina-titanate and a small amount of CaO may be added to the metallic oxides as elements to be included in the solution when desired.

This proposed measure causes SiO2 and the.like to be diffused in alumina-titanate, said predetermined portions to have a fine structure, the metallic oxides to be dispersed at the grain boundaries, and silicon - carbide whisker to become composite.

Fig. 28 shows a further modified form of the ceramic liner 9. This ceramic liner 9 is substantia-l-ly identical to that of Figs. 20 - 23 in its configuration and therefore the ratio of two lengths l/L is set to 0.8 # l/L > o,zs.

However, it has no slit 13. It is formed of alumina-titanate.

Claims (12)

CLAIMS:

1. An engine part provided with an exhaust passage, comprising a cast main body and a bifurcated ceramic liner on or around which is cast the main body and which defines an exhaust passage, the ceramic liner including a hollow tubular liner body and a pair of tubular members branching from the liner body, wherein said hollow liner body includes a tubular part of an elliptical cross section having an outlet for the exhaust passage, the ratio 1/L between a length (L) of the liner body measured on a dividing plane which includes a long diameter of the elliptical cylindrical part and divides the ceramic liner substantially into two equal parts along the exhaust passage and a length (1) of the tubular part being: 0.8

2 1/L 2 0.25 2.An engine part provided with an exhaust passage, comprising a cast main body and a bifurcated ceramic liner on or around which said metal body is cast, and which defines said passage, said liner having a first tubular portion of substantially constant elliptical cross section, and a second bifurcated portion leading therefrom, wherein the ratio 1/L of the length of the first tubular portion (1) to the length of the liner (L) is given by: 0.8 2 1/L 2 0.25 said lengths being measured along the longitudinal axis of the liner.

3. A ceramic liner for casting into an engine part, comprising a first tubular portion of elliptical cross section, and a second bifurcated portion leading therefrom wherein the ratio 1/L of the length of the first tubular portion (1) to the length of the liner (L) is given by: 0.8 2 1/L > 0.25 said lengths being measured along the longitudinal axis of the liner.

4. An engine part or ceramic liner as claimed in claims 1, 2 or 3, wherein a through portion is provided at an area of said ceramic liner at which said bifurcated portion branches apart, for providing communication between inside and outside of the ceramic liner.

5. An engine part or ceramic liner as claimed in claim 4, wherein the size of the through portion on an inner surface side of the ceramic liner is larger than on an outer surface side thereof.

6. An engine part or ceramic liner as claimed in claim 4 or 5, wherein glass is filled in spaces which are present in an inner wall of the through portion.

7. An engine part or ceramic liner as claimed in any of claims 4 to 6, wherein the through portion is a slit which extends continuously over a branched wall of the liner body and opposed portions of peripheral walls of the adjacent tubular members.

8. An engine part or ceramic liner as claimed in any of claims 4 to 6, wherein the through portion is a through hole.

9. An engine part as in any claims 1, 2, 4, 5, 6 or 7, wherein the cast main body is integrally formed with a guide portion which projects inside the ceramic liner through the through portion and serves in use to guide exhaust gas which has passed along the adjacent tubular members toward the liner body.

10. An engine part or ceramic liner as claimed in any preceding claim wherein the ceramic liner is formed of alumina-titanate.

11. An engine part, substantially as hereinbefore described with reference to Figures 1 to 7, or Figure 8, or Figure 9, or Figures 10 to 18, or Figure 19, or Figures 20 to 23, or Figures 24 and 25, or Figures 27 and 27a or Figure 28 of the accompanying drawings.

12. A ceramic liner substantially as hereinbefore described with reference to Figures 1 to 7, or Figure 8, or Figure 9, or Figures 10 to 18, or Figure 19, or Figures 20 to 23, or Figures 24 and 25, or Figures 27 and 27a or Figure 28 of the accompanying drawings.