Abstract:
A prechamber cup for an internal combustion engine which is made of ceramic material and designed to have a sintered and surface finished exterior wall which is to be fit in a cylinder head, a sintered and surface finished passage portion through which a gas is passed and a sintered interior wall forming cup-shaped portion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a prechamber cup for an internal combustion engine. 
     2. Description of the Prior Art 
     A prechamber cup formed by ceramics is shown at pages 889-891 of &#34;CERAMICS FOR HIGH PERFORMANCE APPLICATION-II&#34; published in 1978 by Brook Hill Publishing Company. The above-mentioned prechamber cup is formed of reaction bonded silicon nitride. The main object of making a ceramic prechamber cup is to replace expensive nickel alloys by cheaper, non-strategic materials and to be able to operate the internal combustion engine at high temperatures. 
     However, it has been found to be necessary to improve the design in making the prechamber cup of ceramics. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of this invention to provide a prechamber cup formed of ceramic material having a desirable surface condition on the exterior wall. 
     A further object of this invention is to provide a prechamber cup formed of ceramic material having a gas passage portion with a desirable surface condition. 
     Another object of this invention is to provide a prechamber cup formed of ceramic material having a desirable surface condition along the interior wall of a cup-shaped portion. 
     These and other objects of the present invention have been attained by providing a prechamber cup made of ceramic material which is designed to have a surface finished exterior wall so as to be fit within a cylinder head, a surface finished gas passage portion and a sintered interior wall forming a cup-shaped portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various objects, features and attendant advantages of the present invention will become clear when considered in connection with the accompanying drawing wherein: 
     The sole FIGURE is a partial cross sectional view of an internal combustion engine utilizing the prechamber cup of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As seen from the sole FIGURE a prechamber cup 10 includes an exterior wall 11 which is to be fit within a cylinder head 12 wherein the interior wall 13 forms a cup-shaped portion and includes a gas passage 15. The prechamber cup 10 according to this invention envisions various surfaces for improving the surface condition thereof. The surface of the exterior wall 11 and the surface 16 of the gas passage 15 are surface finished in accordance with the present invention. 
     Where the surface of the exterior wall is surface finished, it is easy to fit the prechamber cup within the cylinder head 12. The preferable surface roughness of the exterior wall is below 2S (The dimension &#34;S&#34; is used to indicate the surface roughness of the members according to the Japanese Industrial Standard B 0601 in which S(m)=RMS(m)×4/1.1). More preferably, the surface roughness of the exterior wall is 0.8S to 2S, because where the surface roughness falls below 0.8S, the cost and time necessary for such surface finishing will become high and long. 
     Where the surface of the gas passage 15 is surface finished, the pressure loss of gas passing therethrough decreases. The preferable surface roughness of the surface of the passage is below 2S. More preferably, the surface roughness is 0.8S to 2S. 
     Where the surface of the cup-shaped portion is sintered, the surface roughness will be more than 2S. As the surface of the cup-shaped portion is increasingly roughened, the efficiency of the combustion and stirring of fuel will be increased. The more desirable surface roughness of the cup-shaped portion is between 2S and 10S. 
     The prechamber cup according to this invention is used in such applications as require great resistance to heat stress. Therefore, preferably, the ceramic body is formed of such nitride materials as silicon nitride, aluminum nitride, titanum nitride and zirconium nitride, oxynitride materials such as silicon oxynitride (Si 2  ON 2 ) and silicon aluminum oxynitride (SiAlON), carbide materials such as silicon carbide, boron carbide, titanium carbide and zirconium carbide, carbonitride materials such as silicon nitride--silicon carbide (Si 3  N 4  --SiC), and glass ceramics such as MAS (Mg--Al--Si oxide) and LAS (Li--Al--Si oxide). 
     Any sintering method can be applied to obtain the prechamber cup of this invention. For instance, hot pressing, reaction sintering and furnace sintering are well known as ceramic sintering methods. Preferable sintering methods for obtaining the prechamber cup of this invention are hot pressing or furnace sintering. Where the prechamber cup is formed by hot pressing or furnace sintering, it is easy to obtain the prechamber cup with a ceramic body having a density higher than 90% of the theoretical value. This value of density is the desirable value for the prechamber cup. Still more, where the ceramic material is silicon nitride, silicon carbide, aluminum nitride, silicon oxynitride, silicon aluminum oxynitride or silicon nitride--silicon carbide, it is relatively easy to obtain a ceramic body having a flexural strength greater than 50 kg/cm 2  at 800° C. This strength value is the desirable value for the prechamber cup. 
     EXAMPLE 
     A powder mixture consisting of 90% by weight of silicon nitride, 5% by weight of yttrium oxide and 5% by weight of aluminum oxide, the mean particle size thereof being 1.1, 1.2 and 0.5 microns, respectively, was prepared and 5% by weight of paraffin was used as a binder. The mixture was molded and sintered and sintering was performed by furnace sintering. The sintering condition was at a temperature 1800° C. for 1 hour in an atmosphere of nitrogen gas. The size of the sintered body having a prechamber cup shape as shown in the sole FIGURE was 40 mm for the outer diameter of base 17, 35 mm for the outer diameter of the outer or exterior wall 11, 28 mm for the inner diameter of the cup-shaped interior wall portion 13, 10 mm for the inner diameter of the gas passage 15 and 28 mm in height. The density was 97% of theoretical value and the flexural strength at 800° C. was 73 kg/mm 2 . 
     The outer or exterior wall surface 11 and the inner surface 16 of the gas passage 15 of the prechamber cup 10 formed by above-mentioned process, were ground. The surface roughnesses were 1.0S for the outer wall, 1.0S for the inner surface 16 of the gas passage 15 and 9S for the inner or interior wall surface 13 of the cup shaped portion, respectively. 
     The prechamber cup 10 was then set in the internal combustion engine and subsequently tested. As a result, highly desirable combustion efficiency was certified. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.