Abstract:
The object of the present invention is to provide a mono-block cylinder head structure of a water cooled engine which can effectively prevent a reduction in strength of a joint portion due to a concentration of stress of a combustion load on the joint portion between a cylinder portion and a cylinder head ceiling portion without reducing the cooling efficiency by a water jacket, the structure being provided with a water jacket having a water jacket outer wall covering a cylinder upper end portion and a cylinder head ceiling portion in a water cooled engine wherein a reinforcing rib is provided in said Joint portion with said cylinder upper end portion and said cylinder ceiling portion to hold the load generated by combustion in a combustion chamber in said cylinder and release the beat generated by said combustion to a water jacket.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mono-block cylinder head structure of a water cooled engine, and more particularly, to a mono-block cylinder head structure of a water cooled engine wherein a mono-block cylinder head portion which constitutes a water cooled engine is provided with a reinforcing rib. 
     2. Description of the Related Art 
     In recent years, there have been adopted many mono-block cylinders for aircraft engines. 
     In producing the engine body, in general, as shown in FIG. 6, an engine body  43  is constituted by joining a cylinder block  40  and a cylinder head  41  with bolts through a cylinder head gasket  42 . In the figure, reference numeral  44  denotes a head cover, and reference numeral  45  denotes an oil pan. 
     The mono-block cylinder is made by integrally molding a cylinder portion and a cylinder head of a cylinder block, which obviates the need for a plurality of bolt boss portions, corresponding bolts and cylinder gaskets for joining the cylinder block and the cylinder head which are necessary when the cylinder block and the cylinder head are separated from each other. Thus, as it is possible to make the engine body lightweight, which is why such mono-block cylinders are much adopted, especially in aircraft engines. 
     In the mono-block cylinder head  46  of a water cooled engine, as shown in FIG. 7, a water jacket outer wall portion  50  is provided on a cylinder head portion  47  from an upper end of a cylinder wall portion  48  to a cylinder head ceiling portion  49  with a predetermined space between the cylinder wall portion  48  and the cylinder head ceiling portion  49 . A water jacket  51  is then formed with cooling liquid stored between the cylinder wall portion  48  and the cylinder head ceiling portion  49 . 
     In such a mono-block cylinder  46 , combustion load generated during combustion in a cylinder body  53  acts in concentration on a joint portion  52  between the cylinder head ceiling portion  49  and the cylinder wall portion  48 . 
     In order to avoid this situation there may be, for example, a method for enlarging a thickness of the above cylinder head ceiling portion  49  or the cylinder wall portion  48 , or for expanding a radius of curvature of the above joint portion  52 . 
     However, when the wall thickness is set large, the cylinder head portion  47  including the joint portion  52  shows a temperature increase during combustion because the cooling effect by the cooling liquid in the water jacket  51  is decreased. Consequently, such a temperature increase may bring about a loss in material strength of the joint portion  52  and induce non-uniformity of heat distribution in the cylinder head portion  47 , and reduce the strength of the cylinder head portion  47  itself. 
     Further, when the radius of curvature of the joint portion  52  is made larger, it is necessary to make an escape of the end portion of pistons larger to correspond to the inner shape of the joint portion  52 , thereby there was a possibility to lower a combustion efficiency and lower the engine performance such as fuel consumption, etc. 
     In particular, when the cylinder block is cast with aluminum alloy, the temperature of the combustion chamber side wall portion in the cylinder head portion  47  becomes 200° C. to 300° C. during combustion. However, since the strength of aluminum rapidly declines from about 150° C., the aforementioned condition becomes noticeable, such that some countermeasure has been desired. 
     SUMMARY OF THE INVENTION 
     In view of this, an object of the present invention is to provide a mono-block cylinder head structure of water cooled engine that makes it impossible to effectively prevent a reduction in strength of a joint portion due to a concentration of stress from a combustion load on the joint portion between a cylinder portion and a cylinder head ceiling portion without reducing the cooling efficiency by a water jacket. 
     Further, another object of the present invention is to provide a mono-block cylinder head structure of a water cooled engine which aims to alleviate uneven thermal stress by improving thermal uniformity in a cylinder body, while also enabling the cooling efficiency to be improved. 
     In order to solve the foregoing objects, in the invention, there is provided a mono-block cylinder head structure provided with a water jacket having a water jacket outer wall portion  14  covering a cylinder upper end portion  12  and a cylinder head ceiling portion  13  of a cooling-water type engine, comprising a reinforcing rib  19 , which can hold a load generated by combustion in a combustion chamber  18  formed in a cylinder  21  and which can release heat generated by combustion to the water jacket  11 , at a joint portion  16  between the cylinder upper end portion  12  and the cylinder head ceiling portion  13 . 
     Accordingly, in the invention, even when a combustion load is generated by combustion in the combustion chamber  18  formed in the engine cylinder  21  and acts upon the joint portion  16  between the cylinder upper end portion  12  and the cylinder head ceiling portion  13 , the reinforcing rib  19  which can hold the load generated by combustion enables the joint portion  16  to sufficiently withstand the generated stress, so that a loss in strength in the joint portion  16  can be prevented. Furthermore, as the heat generated in the combustion chamber  18  formed in the cylinder  21  can be radiated to the water jacket  11 , there is no loss in cooling effect by the water jacket  11 . 
     Consequently, in the invention, a loss in strength in the joint portion  16  between the cylinder upper end portion  12  and the cylinder head ceiling portion  13  can be effectively prevented without lowering the cooling efficiency by the water jacket  11 . 
     According to one form of the invention, there is provided a mono-block cylinder head structure of a water cooled engine provided with a water jacket  11  having a water jacket outer wall portion  14  covering the cylinder upper end portion  12  and the cylinder head ceiling portion  13 , comprising a reinforcing rib  19 , which is formed so as to be continuously rising from the cylinder upper end portion  12  at the joint portion  16  between the above cylinder upper end portion  12  and the cylinder head ceiling portion  13  in the water jacket  11 , for joining a space between the joint portion  16  and the water jacket outer side wall  14 . 
     Accordingly, in this form of the invention, when stress by combustion load generated in the combustion chamber  18  of the cylinder  21  has acted on the above joint portion  16 , the stress is retained by the joint portion  16  and the reinforcing rib  19 . Furthermore, the stress is input to the water jacket outer wall portion  14  through the reinforcing rib  19  and is hold also by the water jacket outer wall portion  14 . Accordingly, since it is possible to distribute and hold at the plural portions the stress generated by the combustion load, the stress caused by the combustion load does not concentrate on the joint portion  16 . 
     As a result, a loss of strength in the joint portion  16  can be effectively prevented. 
     Also, as the reinforcing rib  19  is joined to the water jacket outer wall portion  14 , it can effectively transfer the heat generated in the combustion chamber  18  to the water jacket  11  side without the heat remaining within the reinforcing rib  19 , and thus can prevent the cooling efficiency of the cylinder head  15  from being reduced. 
     In a yet another form of the invention, the reinforcing ribs  19  are disposed radially in a plane over the entire area in the peripheral direction of the combustion chamber  18  with predetermined intervals therebetween. 
     Accordingly, in this form of the invention, since the reinforcing ribs  19  are disposed radially in a plane over the entire area in the peripheral direction of the combustion chamber  18  with predetermined intervals therebetween, a plurality of radially disposed ribs  19  sustain the combustion load generated at the central portion in the combustion chamber  18 , and further, can transfer the stress radially to the water jacket outer wall portion  14 , such that it is possible to reliably distribute and hold the generated stress at the plural portions. 
     In still yet another form of the invention, the reinforcing ribs  19  are formed in a continuous planar annulus ring shape over the entire area in the peripheral direction of the cylinder head ceiling portion  13  on the outside of the cylinder head ceiling portion  13 , the water jacket  11  is formed in division into the inner water jacket portion  33  and the outer water jacket portion  34 , and the cooling liquid for the inner water jacket portion  33  is able to circulate in the outer water jacket portion  34 . 
     Accordingly, the inner water jacket portion  33  is positioned at a cylinder head ceiling wall central portion  35 , and the outer water jacket  34  is positioned at a cylinder upper end portion  37  whose temperature is lower than that of the central portion. 
     As a result, the cooling liquid inside the water jacket  11  circulates in the inner water jacket portion  33  disposed at the cylinder head ceiling wall portion  35  having a high temperature to cool a cylinder head ceiling wall portion  35 , and thereafter the cooling liquid which showed a temperature increase to a predetermined temperature by heat exchange circulates into the outer water jacket portion  34  and cools the cylinder upper end portion  37 . In this case, as the cylinder upper end portion  37  has a relatively lower combustion temperature than does the cylinder head ceiling wall central portion  35 , even when the cooling liquid temperature has risen to the predetermined temperature, the cooling action is not impaired. 
     As a result, it is possible to achieve sufficient cooling by supplying a cooling liquid of the lowest temperature to the cylinder upper end portion  37  which has the highest temperature and the greatest need for cooling, while supplying a cooling liquid of not so low a temperature to the cylinder upper end portion  37  which does not have as high a temperature as the cylinder head ceiling wall central portion  35 . As a result, cooling efficiency of the entire cylinder head  15  can be improved. 
     Furthermore, as it is possible to cool the cylinder head  15  by flowing the cooling liquid used for cooling the cylinder head ceiling wall central portion  36  at the cylinder head upper end portion  36  of the water jacket  11  directly into around the cylinder head upper end portion  37 , it is possible to cool the cylinder head  15  with high cooling efficiency by effectively utilizing the cooling liquid. 
     Moreover, as described above, it is possible to achieve sufficient cooling by supplying the cooling liquid of the lowest temperature to the cylinder head ceiling wall central portion  35  which has the highest temperature and the largest need for cooling, while supplying the cooling liquid of not so low a temperature to around the cylinder upper end portion  37  which does not have as high a temperature as the cylinder head ceiling wall central portion  35 . As a result, it becomes possible to make the thermal distribution of the cylinder head  15  uniform by cooling. Therefore it is possible to aim to alleviate the thermal stress generated by combustion and more effectively prevent a loss of strength of the cylinder head  15 . 
     In still another form of the invention, the joint portion  16  is formed with a predetermined curvature. The reinforcing rib  19  is disposed so as to extend across an extended surface  22  formed continuously on a cylinder inner wall surface  20 , and a space L between a reinforcing rib inner side surface  23  and the extended surface  22  is formed equal to or longer than the width of a radius of curvature R of the joint portion  16 . A space L 1  between a reinforcing rib outer side surface  24  and the extended surface  22  is formed equal to or greater than one-third of a thickness L 2  of the cylinder upper end portion  12 . 
     The purport of the thickness conditions of the reinforcing rib  19  in this form of the invention is as hereinafter described. 
     The range in which the stress of the load generated by combustion in the combustion chamber  18  formed in the cylinder  21  is concentrated on the joint portion  16  corresponds to the range over which the radius of curvature R of the joint portion  16  covers. Accordingly, the space L between the reinforcing rib inner side surface  23  and the above extended surface  22  must be formed equal to or greater than the radius of curvature R of the joint portion. 
     In addition, in order to sustain the stress acting on the joint portion  16  the instant of the combustion in the cylinder  12 , analysis results reveal that one-third of the wall thickness of the cylinder upper end portion  12  during non-combustion is necessary. Therefore, it is necessary for the space L 1  between the reinforcing rib outer side surface  24  and the above extended surface  22  to be formed equal to or greater than one-third the thickness of the cylinder upper end portion  12 . 
     As a result, according to this form of the invention, when the stress by the combustion load generated in the combustion chamber  18  of the cylinder  21  acts on the joint portion  16 , the stress is reliably retained by the joint portion  16  and the reinforcing rib  19 . Further, the stress is input to the water jacket outer wall portion  14  through the reinforcing rib  19 , and is hold also by the water jacket outer wall portion  14 . 
     Accordingly, because it is possible to distribute and hold stress generated by a combustion load, the stress by combustion load does not concentrate on the joint portion  16 . As a result, the joint portion  16  can sufficiently withstand the generated stress, such that a loss in strength in the joint portion  16  can be effectively prevented. 
     Moreover, since the above reinforcing rib  19  is joined to the water jacket outer wall portion  14 , it is possible to effectively transfer the heat generated in the combustion chamber  18  to the water jacket  11  side, thereby preventing the cooling efficiency of the cylinder head  15  from decreasing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view schematically showing an embodiment of a mono-block cylinder head structure of a water cooled engine according to the present invention. 
     FIG. 2 is a plan view showing an embodiment of the mono-block cylinder head structure of a water cooled engine according to the present invention. 
     FIG. 3 is a sectional view showing an embodiment of the mono-block cylinder head structure of a water cooled engine according to the present invention, taken along line III—III in FIG.  2 . 
     FIG. 4 is a plan view showing another embodiment of the mono-block cylinder head structure of a water cooled engine according to the present invention. 
     FIG. 5 is a sectional view showing an embodiment of the mono-block cylinder head structure of a water cooled engine according to the present invention, taken along line V—V in FIG.  2 . 
     FIG. 6 is an exploded perspective view showing in general the structure of an engine body in an exploded state. 
     FIG. 7 is a sectional view schematically showing a conventional mono-block cylinder head structure. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In this embodiment, there is shown as in FIG. 1 a mono-block cylinder structure of a water cooled engine. 
     In the mono-block cylinder structure according to this embodiment, a water jacket  11  is provided around the outer wall of the combustion chamber  18  of a mono-block cylinder  10 . This water jacket  11  has a water jacket outer wall portion  14  covering a cylinder upper end portion  12  and a cylinder head ceiling portion  13 , and a cooling liquid is stored in the inside, so as to enable cooling of the cylinder head  15 . 
     The cylinder upper end portion  12  and the cylinder head ceiling portion  13  are joined at approximately right angles, and the joint portion  16  with the cylinder upper end portion  12  and the cylinder head ceiling portion  13  is formed with a predetermined radius of curvature. 
     Also, in the present embodiment, a reinforcing rib  19  which can hold the load generated by combustion in the combustion chamber  18  formed in the cylinder  21 , as well as radiate the heat generated by the combustion to the water jacket  11  is formed at the joint portion  16  with the cylinder upper end portion  12  and the cylinder head ceiling portion  13 . 
     This reinforcing rib  19  is provided in the water jacket  11 , and is formed continuously rising from the cylinder upper end portion  12  at the joint portion  16  between the cylinder upper end portion  12  and the cylinder head ceiling portion  13 , so as to join the space between the joint portion  16  and the water jacket outer wall portion  14 . 
     The reinforcing rib  19  is disposed so as to extend across an extended surface  22  formed continuously in the axial direction of the cylinder  21  in a cylinder inner wall surface  20 . The space L between the inner side surface  23  of the reinforcing rib  19  and the extended surface  22  is formed equal to or greater than the width of radius of curvature R forming the joint portion  16 . The space L 1  between an outer side surface  24  of the reinforcing rib  19  and the extended surface  22  is formed equal to or greater than one-third the thickness L 2  of the cylinder upper end portion  12 . 
     That is, the thickness L 3  of the reinforcing rib becomes the sum of the thickness from the extended surface  22  of the cylinder inner wall surface  20  toward the inside of the cylinder from the extended surface  22  of the cylinder inner wall surface  20  and the thickness from the cylinder inner wall. surface toward the outside of the cylinder. The respective lengths are required to satisfy the following conditions: 
     (1) Thickness from the extended surface  22  of the cylinder inner wall surface  20  toward the inside of the cylinder. 
     To be equal to or greater than the width of radius curvature R from a terminal point  26  of the radius of curvature of the joint portion  16  between the cylinder upper end portion  12  and the cylinder head ceiling portion  13  to the joint portion inner peripheral surface  27 . 
     (2) Thickness from the extended surface  22  of the cylinder inner wall surface  20  toward the outside of the cylinder 
     To be of a length equal to or greater than one-third the thickness L 2  of the cylinder upper end portion  12  forming the water jacket inner wall. 
     In this case, the purport of condition (1) above is that, because the range in which the stress is concentrated on the joint portion  16  of the load generated by combustion in the combustion chamber  18  in the cylinder  21  corresponds to the range until the radius of curvature R of the joint portion  16 , at the very minimum this range must be ensured. 
     The purport of condition (2) above is that, in the same manner as in the cylinder  21  as the load generated by combustion, in order to reliably hold the load which acts on the joint portion  16  at the instance of combustion, analysis results reveal that it is necessary for the cylinder head ceiling portion  13  and the cylinder upper end portion  12  to be formed equal to or greater than one-third the thickness of the cylinder upper end portion  12  during non-combustion. 
     As a result, in the present embodiment, as shown in FIG. 1, the reinforcing rib outer side surface  24  is disposed in the approximately same position in the direction of cylinder diameter as the outer side surface  28  of the cylinder wall portion  17 , while the reinforcing rib inner side surface  23  is disposed in the position separated by the width of the radius of curvature R of the joint portion  16  from the extended surface  22  of the cylinder inner wall surface  22 . 
     Also, in the present embodiment, as shown in FIG.  2  and FIG. 3, the reinforcing ribs  19  are disposed radially over the entire range in the peripheral direction of the combustion chamber  18  with predetermined intervals therebetween on the upper side of the cylinder head ceiling portion  13 . 
     The functions of the mono-block cylinder head mechanism of water cooled engine according to this embodiment will hereinafter be described. 
     In the mono-block head structure of water cooled engine according to this embodiment, when a load generated by combustion acts as stress on the joint portion  16  when combustion takes place in the cylinder combustion chamber, that stress is hold by the joint portion  16  and the reinforcing rib  19 , and further input to the water jacket outer wall portion  14  through the reinforcing rib  19 . A lower end portion  29  of the water jacket outer wall portion  14  is, as shown in FIG.  1  and FIG. 3, at the upper end of the cylinder head  15 , joined to the cylinder wall portion  17  in a position lower than the cylinder head ceiling portion  13  to form a joint portion  30 , such that the stress transferred to the water jacket outer wall portion  14  is further transferred to the cylinder wall portion  17 . 
     The stress by the combustion load is primarily hold in the reinforcing rib  19 , and thereafter is further transferred to the water jacket outer wall portion  14 . It is further hold in the joint portion  30  of the water jacket outer wall portion  14  with the cylinder wall portion  17 . As a result, the combustion load becomes distributed to and hold in a plurality of locations on the cylinder head  15 . Therefore, the stress by combustion load acting on the joint portion  16  can be alleviated. 
     Consequently, in the present embodiment, the stress generated in combustion is distributed and absorbed without being concentrated on the joint portion  16 . 
     In addition, because the reinforcing rib  19  is joined to the water jacket outer wall portion  14 , it can effectively transfer heat generated in the combustion chamber  18 , so that the heat transferred to the reinforcing rib  19  is not confined in the reinforcing rib  19 , and the heat resistance strength of the reinforcing rib  19  and the joint portion  16  per se can be ensured. 
     Further, because the heat is transferred to the water jacket outer wall portion  14  by the reinforcing rib  19 , cooling can be conducted by dissipating the heat of the cylinder head  15 , such that the cooling efficiency of the entire cylinder head  15  can be improved. 
     Moreover, in the mono-block head structure of water cooled engine according to this embodiment, as shown in FIG. 2, on the cylinder head ceiling portion  13 , the reinforcing ribs  19  are provided radially over the entire area of the combustion chamber  18  with predetermined intervals therebetween in the water jacket  11 . Therefore, a plurality of reinforcing ribs  19  disposed radially hold the combustion load generated at the central portion in the combustion chamber  18 , and further, transfer that stress radially to the water jacket outer wall portion  14 . As a result, the stress by the generated combustion load can be reliably distributed and hold. 
     Furthermore, in the mono-block cylinder head structure of a water cooled engine according to the above embodiment, the die molding property during casting of the cylinder block can be improved. 
     That is, when casting a conventional mono-block cylinder head  46  by die molding, molten metal is poured into a mold from the direction of the lower part of the mono-block cylinder. In this case, as the cylinder head portion  47  is in a position separated by a distance from the pouring in point of the molten metal, the pressure of the poured molten metal gradually lowers. 
     In addition, because of the constitution is such that the water jacket  11  formed on the cylinder head  15  is to be molded into a thinner wall thickness than the cylinder head body portion  31 , there have been cases in which the molten metal channel formed in the die for forming the water jacket outer wall portion  50  is narrow and the molten metal does not spread sufficiently, making it difficult to make a complete die molding. 
     However, in the mono-block cylinder head structure of a water cooled engine according to this embodiment, as shown in FIG.  1  and FIG. 3, since the reinforcing ribs  19 ,  25  are formed between the water jacket outer wall portion  14  and the cylinder head ceiling portion  13 , a direct molten metal channel is formed from the cylinder upper end portion  12  to the upper surface  32  of the water jacket outer wall portion  14 , so that the molten metal easily spreads over the water jacket outer wall portion  14 , thus making it possible to reliably perform die molding of the water jacket outer wall portion  14 . 
     The foregoing embodiment was described using an example in which the reinforcing ribs  19  are provided radially over the entire area of the combustion chamber  18  with predetermined intervals therebetween. However, the invention is not limited to this embodiment but as shown in FIG. 4, the reinforcing ribs  25  may be formed in a planar annulus ring shape continued over the entire area in the peripheral direction of the cylinder head ceiling portion  13  on the outside of the cylinder head ceiling portion  13 . The water jacket  11  may be formed divided into the inner water jacket portion  33  and the outer water jacket portion  34 , such that the cooling liquid in the inner water jacket portion  33  can circulate in the outer water jacket portion  34 . 
     Accordingly, in the mono-block cylinder head structure of the water cooled engine according to the present embodiment, the cooling liquid in the water jacket  11  is first supplied to the inner water jacket portion  33  disposed on the cylinder head ceiling wall central portion  35  to cool the cylinder head ceiling wall central portion  35 . Thereafter, the cooling liquid, whose temperature has been elevated to a predetermined temperature by heat exchange, is circulated to the outer water jacket portion  34  disposed on the side portion of the cylinder head  15  to cool a cylinder upper end portion  37 . 
     In this case, the cylinder upper end portion  37  has a relatively low combustion temperature compared with the cylinder head ceiling wall central portion  35 . Accordingly, even when the cooling liquid temperature has risen to a predetermined temperature, the cooling action is not impaired. 
     As a result, it is possible to achieve sufficient cooling by supplying cooling liquid of the lowest temperature to the cylinder head ceiling wall central portion  35  which has the highest temperature and the greatest need for cooling, while supplying cooling liquid of a comparatively not so low temperature to the cylinder upper portion  37  wherein the temperature does not become as high as in the cylinder head ceiling wall central portion  35 , thereby making it possible to improve the cooling efficiency of the cylinder head  15 . 
     Furthermore, as the cooling liquid that cooled the cylinder head ceiling wall central portion  35  on the upper part of the cylinder head  15  of the water jacket  11  can be supplied directly to the cylinder upper end portion  37  to cool the cylinder head  15 , the cooling liquid can be effectively utilized to efficiently cool the cylinder head. 
     Also, as described above, it is possible to achieve sufficient cooling by supplying the cooling liquid of the lowest temperature to the cylinder head ceiling wall central portion  35  which has the highest temperature and the greatest need for cooling, while supplying the cooling liquid of not so low a temperature to the peripheral portion  38  of the cylinder head wherein the temperature does not become as high as in the cylinder head ceiling wall central portion  35 . As a result, it becomes possible to make the thermal distribution in the combustion chamber  18  uniform by cooling, such that it is possible to aim to alleviate uneven generation of thermal stress generated by combustion.