The present invention relates to cylinder-head covers for use in a water-cooled internal combustion engine, and particularly to the cooling system incorporated in such covers.
A diagrammatic view of one type of cylinder cover of the prior art is illustrated in Figure 1, and a cross-section of a long cylindrical leg of the same cylindrical cover is shown in Figure 2. In Figure 1, the cylinder cover is shown supporting an exhaust valve 2 over a cylinder, said cover being bolted down onto a cylinder liner 3 located within a cylinder jacket 4. The cylinder liner 3 and cover 1 define a combustion chamber 5 above the associated piston 6. Referring also to Figure 2, a large number of cooling holes 9 are formed in the cylinder cover 1 at a constant spacing around its circumference. Thus, in this arrangement, cooling water which has cooled the cylinder liner 3 enters into an annular cooling chamber 8 defined in the periphery of a long leg 1a of said cover and a surrounding sleeve 7 through an inlet path 10 in said sleeve 7. After cooling said long leg 1a, which is formed in the lower part of said cover, the water flows through the cooling holes 9 to cool the upper part 1b of the combustion chamber wall defined by said cover, and then flows out externally.
However, the aforementioned cooling system in the prior art had the following shortcoming.
Though the long leg 1a is cooled only by the cooling water in the cooling chamber 8, since only the outer peripheral portion of said long leg is cooled, the inner peripheral portion, that is, the portion along the part defining the combustion chamber wall 1c cannot be cooled sufficiently.
It is therefore an object of the present invention to provide a cylinder cover in which the aforementioned short-coming in the prior art is eliminated and a cooling effect for a long cylindrical leg of the cylinder cover can be enhanced.
In French Patent Application FR-A-2,164,304 there is described a cooling arrangement for a cylinder cover in which a single cooling chamber is provided around a cylindrical leg portion of the cover. The cover has upwardly-directed bores formed therein communicating with the cooling chamber and intersecting with respective radial ducts leading to a further cooling chamber remote from the cylindrical leg. The intersection of bores and ducts in this manner could lead to localised stress and weakening of the cylinder cover and is not considered satisfactory.
In German Patent Specification DE-C-959,866, there is described a cooling arrangement for an internal combustion engine cylinder of a kind having a cylinder liner which is closed at its upper end by an integral wall to define the combustion chamber rather than having a separate cylinder cover. The upper part of the cylinder liner is surrounded by a sleeve which, together with the liner, define two spaced cooling chambers around the outside of the liner, the uppermost chamber being connected through radial bores in the upper wall of the liner with a further cooling chamber formed above the upper wall. The two cooling chambers are interconnected by slanting grooves formed in the outer surface of the liner. Even though the liner is comparatively thin, the grooves in its outer surface extend no closer to the inner surface of the liner than the two chambers they interconnect and could not effectively cool the inner portion thereof adjacent the combustion chamber without seriously weakening the liner by increasing the depth of the grooves.
According to the present invention, there is provided a cylinder cover incorporating a cooling arrangement comprising annular cooling means in the outer peripheral portion of a long cylindrical leg portion of the lower part of the cylindrical cover, and a plurality of circumferentially spaced cooling ducts communicating between said annular cooling means and a further cooling chamber for cooling for example an exhaust valve, characterised in that the annular cooling means comprises upper and lower annular chambers provided in the outer peripheral portion of said leg portion, in that said cooling ducts are connected only from the upper chamber to said further cooling chamber, and in that a plurality of cooling bores are formed within the cylindrical leg portion which extend through the inner portion thereof and which are inclined with their opposite ends opening into the upper and lower annular cooling chambers respectively, the plurality of cooling bores being each drilled in the form of a straight line, from one position on the outer peripheral surface of the long cylindrical leg portion through the leg portion to another position obliquely in the horizontal section and being arranged around the cylindrical leg portion such that they do not intersect.
The above-mentioned and other features and objects of the present invention will become more apparent by reference to the following description of a preferred embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Referring now to Figures 3 to 5 of the drawings, the cylinder cover 11 constructed in accordance with the invention has a lower portion in the form of a long cylindrical leg 11a, the inner surfaces of the upper portion of the cover 11 and said leg (11c c and 11 d respectively) defining the upper part of a combustion chamber 5. A metal sleeve 12 is fixedly secured to the outer periphery of the long cylindrical leg 11a. A lower and an upper annular cooling chamber 14 and 15 respectively, are defined between the outer periphery of the long cylindrical leg 11a, and the inner periphery of the metal sleeve 12, and circumferentially spaced cooling holes 9 are provided which communicate the upper cooling chamber 15 which an exhaust valve cooling chamber 16, these cooling holes 9 being drilled in the cylinder cover 11 close to and parallel with the upper wall surface 11c of the combustion chambers 5.
In this embodiment further cooling holes 13 are drilled in the long cylindrical leg 11a from the lower cooling chamber 14 towards the upper cooling chamber 15 in an obliquely upward direction (see Figure 5) at an angle 8 with respect to the vertical direction, these cooling holes 13 thus communicating the respective chambers 14 and 15 with each other. A plurality of such cooling holes 13 are provided so as to encircle the combustion chamber as a whole. As shown in Figures 4 and 5 the cooling holes 13 are formed in straight sections without intersecting each other, that is, without connecting to each other along their length (see numerals 13, 13a and 13b) and they are arrayed at a constant circumferential spacing. The aforementioned respective cooling holes 13 are provided as close (at a distance / - see Figure 4) to the inner peripheral surface 11 d of the long cylindrical leg 11a as is permissable to ensure adequate mechanical strength to withstand gas pressure at this point. "O"-rings 17 and 18 are provided between the periphery of the leg 11a and the sleeve 12 for sealing of the annular water chambers 14 and 15.
In operation of the preferred embodiment, upon operation of the engine, cooling water entering, via the inlet 10 through the sleeve 12, into the lower cooling chamber 14 flows into the respective cooling holes 13 as it flows around through the lower cooling chamber 14, and while it is cooling the long cylindrical leg 11a, it flows into the upper cooling chamber 15.
The cooling water in the upper cooling chamber 15 enters into the cooling holes 9, and after it has cooled the combustion chamber upper wall portion 11b of the cylinder cover 11, it is fed into the exhaust valve cooling chamber 16.
Due to the above-mentioned arrangement, the long cylindrical leg 11a as well as the combustion chamber upper wall portion 11b of the cylinder cover 11 can be sufficiently cooled. Accordingly, the complete cylinder can be cooled uniformly; hence, unevenness of temperature distribution can be corrected, and thereby thermal stresses in the cylinder cover can be reduced.
In summary, the present invention provides the following advantages:
Since many changes and modifications could be made to the above construction, and other different embodiments proposed, within the scope of the present invention, it is intended that all matter contained in the above description and/ or shown in the accompanying drawings shall be interpreted as illustrative, and not as limiting the scope of the invention.