Abstract:
A ceramic auxiliary combustion chamber for an internal combustion engine where a ceramic nozzle body with an integrally fitted gasket is mounted into an opening in the cylinder head.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an improved ceramic auxiliary combustion chamber. More particularly, the present invention relates to an auxiliary combustion chamber having a nozzle body mounted onto a cylinder head of an internal combustion engine such as a diesel engine or the like. 
     Engines which use an auxiliary combustion chamber to complete combustion in a relatively short time have been widely used in order to respond to the demand for miniaturization and high speed. In such engines, it is necessary to use a heat-resistant metal alloy as material for the body forming the nozzle of the chamber because it is subject to a high temperature in operation. Such heat-resistant metals are expensive and this results in increased cost thus causing a limited use. 
     In a auxiliary combustion chamber for a diesel engine or the like, in order to improve the combustion efficiency thereof by thermally insulating the same or to prevent parts thereof exposed to a high temperature from melting, ceramic auxiliary combustion chambers which are superior in adiabatic and heat-resistant properties have been studied and partly put to practical use. 
     Ceramics, however, have shortcomings in that they may be apt to be broken by thermal stress and they are brittle. To reduce thermal stress by reducing temperature gradients and to reduce assembling stress, a proposed device, as shown in FIG. 7, has been provided. In such a device, a ceramic nozzle body 3, having a nozzle 2 formed at its lower portion, is attached to a cylinder head 1 through a gasket 5 disposed on the upper portion of the nozzle body 3. A space 4 is maintained between the cylinder head 1 and the ceramic nozzle body 3 (Japanese Patent Unexamined Publication No. 59-200012). 
     In this proposed device, the nozzle body 3 is inserted after the gasket 5 has been mounted to the cylinder head 1, and therefore the side surface of the nozzle body 3 might come directly in contact with the cylinder head 1. When this occurs, thermal stress can arise by local heat removal from the nozzle body. Further, the gasket 5 and the ceramic nozzle body 3 are separately formed, and therefore the attaching of the gasket might be erroneously omitted. In the drawing, the reference numeral 6 designates a fuel injection nozzle, and the reference numeral 7 designates a glow plug. 
     SUMMARY OF THE INVENTION 
     The above mentioned problems in the prior art have been solved by integrally fitting an annular gasket onto the ceramic nozzle body at its shoulder portion. 
     Further, the possibility of contact between the cylinder head and the nozzle body is completely obviated by providing a axially extending portion on the gasket. 
     Since the annular gasket is integrally fitted onto the shoulder portion of the nozzle body, the assembling process is improved and a predetermined space can be maintained between the cylinder head and the nozzle body while the nozzle body is being mounted. 
     In the present invention, the auxiliary combustion chamber for internal combustion engine has a cylinder head with an opening therein. This opening has an internal surface. The auxiliary combustion chamber includes a ceramic nozzle body disposed in the opening, having an external surface dimensioned to fit in the opening while allowing a space to be maintained between the external surface of the nozzle body and the internal surface of the opening. An annular gasket is integrally fit on the external surface of the nozzle body to seal the space between the internal surface of the opening and the external surface of the nozzle body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIGS. 1 and 3 are longitudinal sectional views showing the mounting of the ceramic nozzle bodies mounted to the cylinder heads, according to the present invention. 
     FIGS. 2 and 4 are partial perspective views showing the structures of the gaskets used in FIGS. 1 and 3, respectively. 
     FIGS. 5 and 6A &amp; 6B are perspective views showing examples of other structures of annular gaskets to be used in the present invention. 
     FIG. 7 is a longitudinal view showing a conventional ceramic nozzle body mounted to a cylinder head. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, the reference numeral 1 designates a cylinder head. A fuel injection nozzle 6 and a glow plug 7 are inserted into the upper portion of the auxiliary combustion chamber in the cylinder head 1. In the lower portion of the cylinder head, there is mounted a ceramic nozzle body 3 having a nozzle 2 in the lower portion thereof. An annular gasket 5-R is integrally fitted onto the shoulder portion and inserted into an area between the portion of the cylinder head 1 and the nozzle body 3 defining the auxiliary chamber. A space 4 is maintained between the nozzle body 3 and the cylinder head 1. As shown in FIG. 2, the annular member 5-R used herein has a U-shaped cross section opened outward at its upper portion with an axially extending flange portion 5-L so that the necessary space 4 can unconditionally be maintained between the ceramic nozzle body 3 and the cylinder head 1. 
     A construction as described above was examined in real operation under a whole load condition for 100 hours and no abnormality could be seen in the metal surrounding the ceramic auxiliary combustion chamber or in the gasket. 
     The gasket material may be SUS 631 or any other heat-resistant metal alloy. 
     In FIG. 3, the ceramic nozzle body 3 is formed to have a larger diameter at its lower portion and a smaller diameter at its upper portion. The nozzle body 3 has two annular gaskets 5-R integrally mounted onto the upper and lower shoulder portions. In this embodiment, the gaskets work more effectively to prevent inclination of the nozzle body. In FIG. 3, the same items as those in FIG. 1 are correspondingly referenced and description about them will be omitted. 
     Each of the annular gaskets used herein has an inward bent P-shaped cross section including an axially extending flange portion 5-L so that the necessary space 4 can unconditionally be maintained between the ceramic nozzle body 3 and the cylinder head 1. 
     A construction as described above was examined in real operation under a whole load condition for 100 hours and no abnormality could be seen in the metal surrounding the ceramic auxiliary combustion chamber or in the gaskets. 
     FIG. 5 shows a gasket 5-R provided with notches C at the lower end of the axially extending fitting portion of the gasket so as to obtain the above mentioned effects with low cost, as well as to improve workability in fitting the nozzle body. 
     FIG. 6 shows a gasket 5-R made of a metal plate by cutting off along the outward and inward portions of a ring so the gasket can be more reduced in cost than that of FIG. 5 with the same effects as described above. 
     According to the present invention, as described above, the annular gasket (or gaskets) is (are) integrally fitted to the shoulder portion (or portions) of the ceramic nozzle body which is excellent in thermal resistance. Thus, it is possible to simplify the mounting of the nozzle body onto the cylinder head to perform mass production, to prevent the gasket from being erroneously omitted in assembly, and to easily and accurately maintain a necessary space between the nozzle body and the cylinder head.