Patent Publication Number: US-6990943-B2

Title: Cylinder block of an engine

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to the structure of a cylinder block constituting an engine. 
   2. Related Art 
   A cylinder block is one of media which transmit the explosive power to a crank system, and the most important structural member which must support the inertia load etc. of the crank system. Moreover, the structure of the cylinder block influences size, weight, whole durability, noise, etc. of the engine. 
   Conventionally, an art for increasing thickness of a cylinder portion is mainly applied as an art for improving the rigidity of the cylinder block which constructs an engine. 
   For example, in the Japanese Patent Laid Open Gazette 2001-221098, a large range portion such as a portion from the same side with a crankcase to the center in the cylinder block is constructed thickly so that the art for improving the rigidity of the cylinder block is disclosed. The art for improving the rigidity of the cylinder block is disclosed also in the Japanese Patent Laid Open Gazette Hei. 6-213064, where many portions of the cylinder block are constructed thickly. 
   However, when the cylinder block is formed thickly in a wide range thereof, the weight of the engine increases. Conversely, when the cylinder block is formed thinly for weight saving, the rigidity of the cylinder block is reduced, thereby increasing the noise of the engine. 
   Therefore, it is desired that the noise and weight of the engine are decreased while the rigidity of the cylinder block is enhanced. 
   A cooling-water gallery is constructed in the cylinder block so as to surround a cylinder, and cooling-water flows in the cooling-water gallery so that the cylinder is cooled. A drain hole of the cooling-water gallery is formed in the cylinder block and open on the side surface of the cylinder block. However, the drain hole is not disposed in the bottom of the cooling-water gallery. The cooling-water gallery of the cylinder block is disposed higher than a lubricating-oil gallery considering its arrangement relationship with the lubricating-oil gallery constructed within the cylinder block. 
   However, as disclosed, for example in the Japanese Patent Laid Open Gazette 2001-152851, only cooling of the cylinder like the temperature control of the cylinder wall is considered for the cooling-water gallery constructed in the conventional cylinder block. The cooling of lubricating-oil etc. circulating in the cylinder block is not considered especially. Moreover, since the drain hole of the cooling-water gallery is constructed higher than the bottom thereof, it is difficult to drain cooling-water completely. In case cooling-water remains within the cooling-water gallery for a long time, there is the possibility that degradation of the cylinder block might occur. 
   Furthermore, in the cylinder block formed by casting, the periphery of a hole formed by a member supporting a core is tapered, and a plug is installed in the hole. 
   In case the plug is installed in the hole after the hole is tapered by the member supporting the core, there is the possibility of change in the installing position of the plug according to the casting state of the cylinder block, so the labor and time are required in order to improve the precision of installing the plug. 
   SUMMARY OF THE INVENTION 
   A cylinder block of an engine according to the present invention comprises a cylinder portion housing a piston; and a skirt portion covering a crankshaft, wherein the skirt portion is curved and a rib is formed on the inside of the skirt portion. 
   Due to the shape of the skirt portion, noise emitted from the skirt portion is reduced without increasing the thickness of the cylinder block, thereby enabling an engine to be compact while ensuring silence of the engine. 
   In the cylinder block according to the present invention, a vertical rib formed in the skirt portion is provided from a lower end of a cylinder-liner of the cylinder block to a lower or bottom end of the skirt portion. 
   Therefore, rigidity of the cylinder block is enhanced at the cylinder-liner portion thereof and a bottom surface thereof fitted to a spacer. 
   The cylinder block of an engine according to the present invention further comprises a boss for attaching an engine base to the cylinder block, wherein a vertical rib is formed in the skirt portion continuously from the boss. 
   Therefore, rigidity of the boss in the cylinder block is enhanced, thereby restraining deformation of the cylinder block when the engine base is attached to the cylinder block, and improving precision of assembling the engine. 
   A cylinder block of an engine according to the present invention comprises a cylinder portion housing a piston; a skirt portion covering a crankshaft; a plugged hole formed in the cylinder portion; and a rib, wherein the skirt portion is curved and a rib is formed on the outside of the cylinder block so as to be connected with the plugged hole. 
   Therefore, rigidity of the cylinder block is enhanced at a portion thereof close to the plugged hole, thereby restricting deformation of the cylinder block and improving precision of assembling the engine. 
   A cylinder block according to the present invention comprises a cylinder portion housing a piston; a skirt portion covering a crankshaft; a surface facing a flywheel; a surface to be connected to a gear case; and journal housings for supporting the crankshaft, wherein the journal housings on respective sides of the cylinder block toward the surfaces are thickened at the upper portions thereof. 
   Therefore, rigidity of the cylinder block is enhanced so as to restrict deformation of the cylinder block when crank journals are attached into the journal housings and to improve the precision of assembling the engine. Moreover, the rotational stability of the crankshaft is secured and the silence of the engine is improved. 
   A cylinder block according to the present invention comprises a cylinder portion housing a piston; and a skirt portion covering a crankshaft, wherein a water jacket is disposed in the cylinder portion and extends into the skirt portion. 
   Therefore, the capacity of the water jacket is increased so as to enhance the cooling effect thereof. Moreover, the cooling effect to the crankcase portion is improved, and noise from the inside of the cylinder block is shut off, thereby attaining the noise reduction. 
   The cylinder block of an engine according to the present invention further comprises a lubricating-oil gallery, wherein the water jacket is extended to a point below the lubricating-oil gallery. 
   Therefore, an area of the lubricating-oil gallery contact with the water jacket is increased, thereby improving the cooling effect to the lubricating-oil gallery. 
   The cylinder block according to the present invention further comprises a drain hole of cooling water provided below the lubricating-oil gallery. Therefore, the cooling effect to the lubricating-oil gallery is improved over the upper and lower sides thereof. Cooling water is easily and perfectly drained from the cooling-water gallery, thereby improving maintainability. The cooling-water is prevented from remaining in the cooling-water gallery, thereby preventing degradation of the cylinder block. 
   A cylinder block according to the present invention comprises a cylinder portion housing a piston; a skirt portion covering a crankshaft; and a portion to be plugged, wherein a cast surface of the portion to be plugged is spot-faced. Therefore, installation of a plug into the hole is improved so as to facilitate processing of an engine. Moreover, precision of the installed plug is improved so as to improve the durability of the engine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       FIG. 1  is a cross sectional side view of an engine.  FIG. 2  is a cross sectional front view of the same. 
       FIG. 3  is an exploded view of a cylinder block, showing the assembling construction thereof. 
       FIG. 4  is a left side view of an engine.  FIG. 5  is a right side view of the same.  FIG. 6  is a cross sectional side view of a cylinder block.  FIG. 7  is a cross sectional front view of the same. 
       FIG. 8  is a front view of the same. 
       FIG. 9  is an arrow sectional view of the line D—D in  FIG. 4 . 
       FIG. 10  is a cross sectional view of a cylinder block, showing the shape of cylinder-head-bolt bosses. 
       FIG. 11  is an arrow sectional view of the line B—B in  FIG. 5 . 
       FIG. 12  is an arrow sectional view of the line A—A in  FIG. 4 . 
       FIG. 13  is an arrow sectional view of the line C—C in  FIG. 8 . 
       FIG. 14  is an arrow sectional view of the line L—L in  FIG. 13 . 
       FIG. 15  is a cross sectional view of a cylinder holder, showing another arrangement of grooves formed in a cylinder holder portion. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In order to expound the present invention more in detail, explanation will be given on it in accordance with drawings. 
   First, explanation will be given on the outline construction of an engine in accordance with  FIGS. 1 and 2 . A cylinder head  1  is attached to the upper end portion of a cylinder block  15 , and a rocker arm room  2  is constructed above the cylinder head  1 . 
   A flywheel housing  27  storing a flywheel  28  is connected with one surface of the front and rear (left and right in  FIG. 1 ) side surfaces of the cylinder block  15 . 
   A gear case  23  for housing gears and the like is connected with the other of the front and rear side surfaces of the cylinder block  15 , and the gears transmit the driving force from a crankshaft  25  to a cam shaft  14 , a fuel-injection-pump  12 , etc. 
   An oil pan  21  for storing lubricating-oil is provided below the cylinder block  15 , and connected with the cylinder block  15  through a spacer  18 . 
   The spacer  18  is extended from one of the front and rear end sides of the cylinder block  15  to the gear case  23  and a gear case cover  29 . The gear case  23  connected with the cylinder block  15  and the gear case cover  29  connected with the gear case  23  are connected with the spacer  18 . 
   A lubricating-oil intake gallery  181 , which is one of lubricating-oil galleries, is formed inside the spacer  18 , and open for free passage with a lubricating-oil suction pipe  19  projecting from the spacer  18  inside the oil pan  21 , whereby lubricating-oil is drawn into the lubricating-oil pump  22  through the lubricating-oil suction pipe  19  and the lubricating-oil intake gallery  181 . 
   The crankshaft  25  is supported in the lower portion of the cylinder block  15 . The crankshaft  25  is journalled by journal housings  38  of the cylinder block  15  and respective metal caps  39  fixed to the cylinder block  15 . Each metal cap  39  is fixed at the front and rear ends hereof to the lower portion of the cylinder block  15  between cylinders so as to upwardly support the crankshaft  25 . 
   Next, explanation will be given on the construction of the cylinder block  15  in accordance with  FIGS. 3–5  inclusive. 
   The cylinder block is constructed by a cylinder portion  31  and a skirt portion  32 . 
   The cylinder portion  31  has an inner cylinder portion and an outer cylinder portion, which are integrally casted, and the pistons  33  are provided inside the cylinder portion  31 . A cooling-water gallery is constructed between the inner cylinder portion and the outer cylinder portion in the cylinder portion  31 , and a cam shaft case  53  is formed on one of the left and right (in the perpendicular direction to the crankshaft  25 ) sides of the cylinder portion  31 . 
   Clean outs  34 ,  45  are formed on the left and right sides of the cylinder block  15 , respectively, so as to communicate with the cooling-water gallery. 
   The clean outs  45  provided on the same side with the cam shaft case  53  is positioned below the cam shaft case  53  so as to construct the bottom of the cooling-water gallery. 
   The clean outs  34  and  45  are formed by a support member for supporting a core when the cylinder block  15  is cast. That is, in a mold, the core for forming the cooling-water gallery  37  is supported by the support member constructing the clean outs  34  and  45 . 
   Some of the clean outs  34  and  45  are partly used as galleries for intake and drain of the cooling-water, and the others of the clean outs  34  and  45  are plugged. 
   The clean outs  34  and  45  serves as openings communicating with the cooling-water gallery  37  in the cylinder block  15 . Hence, there is the possibility of reducing the rigidity near the clean outs  34  and  45 . However, ribs are connected with the clean outs  34  and  45 , thereby preventing the rigidity from reducing. 
   The lower portion of each cylinder is curved in the skirt portion  32 . The left and right side surfaces of the skirt portion  32  are curved in a front view as shown in  FIG. 7 , and curved also in a plan view as shown in  FIG. 9 . That is, the skirt portion  32  is curved in both transverse section and vertical section. 
   In addition, ribs are formed on the inside and outside of the skirt portion  32  so as to enhance the rigidity of the skirt portion  32 . Due to this increased rigidity, the skirt portion  32  is restrained from deforming when something is attached onto a surface thereof. 
   The ribs  35  are formed on the cylinder portion  31  and the skirt portion  32  of the cylinder block  15  in the front and rear direction of the cylinder block  15 . The ribs  36  are formed on the cylinder portion  31  and the skirt portion  32  in the vertical direction of the cylinder block  15 . 
   Each of the ribs is formed near a point of the cylinder block  15  to which something is fastened, thereby restraining deformation of the cylinder block  15  caused by the fastening. 
   The rib  35  on the cylinder portion  31  is formed near the clean out  34 , where the rib  36  disposed in the vertical direction of the cylinder block  15  is also formed. 
   In this way, the ribs  35  and  36  are provided near the clean out  34  so as to enhance the rigidity of the cylinder block  15  near the clean out  34 . 
   At least one of ribs  61  and  62  is connected with the plugged hole. Moreover, the skirt portion  32  is curved in a transverse section, and the rib formed outside the cylinder block is connected with the plugged hole constructed in the cylinder portion, so that the rigidity of the cylinder block near the plugged hole is enhanced, thereby restraining deformation of the cylinder block and easily improving the precision of assembling the engine. 
   The ribs  61  and  62  are formed inside the cylinder block  15  as shown in  FIGS. 6–8  inclusive. 
   Inside the skirt portion  32  of the cylinder block  15 , the ribs  61  are formed in the vertical direction of the cylinder block  15 , and the ribs  62  in the front and rear direction thereof. 
   In this way, the ribs  61  and  62  are provided inside the cylinder block  15  so as to enhance the rigidity of the cylinder block  15 . Moreover, the ribs  61  and  62  are provided inside the skirt portion  32  so that the inner surface shape is so complicated as to cause interference of sound, thereby reducing the noise of the engine. Also, in the outer surface of the skirt portion  32 , flat portions are reduced, thereby further diffusing the noise. 
   The vertical ribs  61  are provided from lower end portions of the cylinder-liners to a lower end portion of the skirt portion  32  so as to enhance the rigidity of the cylinder block at the cylinder-liners and at the surface fitted to the spacer. 
   The ribs  61  and  62  are mainly formed below the cylinders so as to enhance the rigidity of the skirt portion  32 . 
   In this way, the rigidity of the cylinder block is enhanced at the skirt portion  32  by constructing the ribs  35 ,  36 ,  61 , and  62  while the cylinder block  15  is light-weighed by constructing the skirt portion  32  thinly. 
   Furthermore, some of the vertical ribs  61  are formed on the cylinder block  15  continuously from respective bosses  81  for attachment of an engine base. Due to the vertical ribs  61  integrally connected with the bosses  81 , the rigidity of the cylinder block  15  is enhanced at the bosses  81 . 
   Therefore, the cylinder block is restrained from deforming at the time of its attachment to the engine base so as to improve the precision of assembling the engine. 
   Moreover, the journal housings  38  for supporting the crankshaft are constructed in the skirt portion  32 . 
   Each journal housing  38  supports the crankshaft  25  together with the metal cap  39  fixed to the lower portion of the cylinder block  15 . 
   Each journal housing  38  is formed by the cylinder block  15  at the front and rear surfaces thereof and each cylinder thereof. The journal housings  38  on respective sides of the cylinder block  15  toward of the gear case  23  and the flywheel  28  are thickened at their upper portions. 
   Therefore, while casting process of the cylinder block  15  is simplified, the rigidity of the cylinder block  15  is enhanced and the noise of the engine is reduced. 
   In this way, while the cylinder block has the surface facing the flywheel and the surface to be connected to the gear case, the journal housings on the respective sides toward the surfaces are thickened at their upper portions. Therefore, the rigidity of the cylinder block is enhanced so that the deformation thereof when it is attached to the engine base is restrained and the precision of assembling the engine is improved, thereby ensuring the rotational stability of the crankshaft and improving the silence of the engine. 
   Locating bosses  82  are formed at the lower portion of the skirt portion  32 , and are made thicker than other portion of the skirt portion  32 . The locating bosses  82  are formed with the ribs inside the skirt portion  32 . By forming the locating bosses  82  inside the skirt portion  32 , a mounting seat of the engine E is not projected outward and the engine E is constructed compactly in width. Moreover, the skirt portion  32  curved to swell outward in a transverse section is enhanced in rigidity by such an easy manner as to form the ribs therein. 
   The journal housings  38  are formed below the cooling-water gallery  37  as shown in  FIG. 6 , and constructed so as not to project either toward the crankcase or the flywheel. Therefore, the conventional crankcase and flywheel can be installed onto the present cylinder block  15 . 
   Furthermore, a space of the cylinder block  15  is used effectively so as to enhance the rigidity thereof and reduce the noise of the engine, thereby improving the engine performance while maintaining the engine compact. 
   Therefore, the weight of the cylinder block  15  is reduced so as to facilitate for weight saving of the engine. 
   Next, explanation will be given on the construction of the skirt portion  32  in accordance with  FIG. 9  in more detail. 
   The skirt portion  32  is curved outward in a front view and a plan view. The ribs are provided on both inside and outside surfaces of the skirt portion  32 , so that the rigidity thereof is improved. The skirt portion  32  is comprised of curving structures as known from a plan view, which are as many as the cylinders, are connected in series, thereby being enhanced in rigidity. The above-mentioned ribs further enhance the rigidity thereof. 
   Each of the curving structures of the skirt portion  32  is comprised of end portions  72  and a middle portion  71  therebetween. The horizontal ribs  62  are connected with the middle portion  71  and the end portion  72 , and each of the vertical ribs  61  is constructed between the middle portion  71  and each of the end portion  72 . 
   The curvature of the middle portion  71  in plan view is set gentler than the end portion  72 . Therefore, a region  63  connecting the cylinders is so shaped as to be connected smoothly to the end portions  72 . Sand for molding is hard to remain between the region  63  and the end portion  72 , thereby making the production process of the cylinder block  15  easy. 
   The curve structure of the skirt portion  32  not only improves the rigidity thereof but also diffuses the noise emitted from the skirt portion  32 . The skirt portion  32  is constructed by the curve structure, so the noise emitted therefrom is diffused radially from the surface of the skirt portion  32 , and reduced with the increasing distance from the skirt portion  32 . 
   Therefore, noise emitted from the engine is not enlarged locally so that the silence of the engine is improved. 
   A main gallery of lubricating-oil is constructed inside a lubricating-oil case  91 , which is provided in a side portion of the cylinder block  15  (as shown in  FIG. 11 ). 
   The lubricating-oil case  91  is disposed in the middle of the side portion of the cylinder block  15  along the direction of arrangement of the cylinders, and integrally formed by the cylinder block  15 . 
   Next, explanation will be given on the construction of the clean outs  34  and  45  in accordance with  FIG. 7  in more detail. 
   The clean outs  34  and  45  are spot-faced so as to improve the precision of processing of the clean outs  34  and  45  in the cylinder block  15 . 
   When the cylinder block  15  is constructed by casting, there may arise such a case where the outer side portions of the clean outs  34  and  45  are recessed in a bowl-like shape. In this case, the outer sides thereof are spot-faced so as to keep the shapes of the clean outs  34  and  45  constant, thereby improving the precision thereof to be plugged, enhancing the rigidity of the cylinder block  15 , and improving the durability thereof by preventing leak of cooling-water. 
   Next, explanation will be given on the construction of the cooling-water gallery in accordance with  FIGS. 6 ,  7 , and  10  in detail. 
   The cooling-water gallery  37  constituting a water jacket is provided in the cylinder block  15 , and the water jacket is extended to the crankcase portion. Therefore, the capacity of the water jacket is increased so as to enhance the cooling effect of the crankcase portion. 
   The water jacket shuts off noise from the inside thereof so as to reduce noise emitted outward from the engine. 
   The cooling-water gallery  37  is constructed on the left and right sides of the cylinders  95 , and on the front and rear ends of the cylinders  95  so as to be connected in the front and rear direction. 
   The cooling-water gallery  37  is constructed along the outer side surfaces of the continued cylinders  95 , and an outer wall  96  constituting the outside of the cooling-water gallery  37  is constructed so as to cover the continued cylinders  95 . Each of cylinder-head-bolt bosses  94  is formed in the outer wall  96  positioned between the cylinders  95 . 
   The upper portion of the cylinder-head-bolt boss  94  touching the cooling-water gallery  37  is formed approximately symmetrically in the front and rear direction in order to support a bolt for fastening the cylinder head, while the lower portion thereof is formed non-symmetrically in the front and rear direction of the cylinder block  15 . 
   The lower portion of the cylinder-head-bolt boss  94  includes one of the front and rear sides thereof formed along the cylinder  95  to some degree, and the other thereof recessed inward (apart from the cylinder  95 ). That is, the shape of the cylinder-head-bolt boss  94  differs between the upstream and downstream sides of the cooling-water gallery  37 . 
   The cylinder-head-bolt bosses  94  are shaped to turn the flow direction of cooling-water to the portion between the cylinders  95 . 
   Therefore, the cooling-water flows into the cooling-water gallery  37  so as to be smoothly supplied into the portion between the cylinders, thereby enhancing its cooling effect. 
   Next, explanation will be given on the construction of the cooling-water jacket in accordance with  FIGS. 11 and 12  in detail. 
   As mentioned above, the lubricating-oil gallery  97  is constructed inside the lubricating-oil case  91 , which is provided on the side portion of the cylinder block  15 . The lubricating-oil gallery  97  is connected with the journal housings  38  by the oil passage  98 , and the interior of camshaft case  53  is also connected with the journal housings  38  by oil passages  99 . 
   Therefore, it is possible to maintain the lubrication between the crankshaft  25  and the cylinder block  15 . 
   The cooling-water gallery  37  is constructed above the lubricating-oil gallery  97  in the cylinder block  15 . 
   However, as shown in  FIG. 12 , a drain hole  100  of the cooling-water connected with the cooling-water gallery  37  is positioned below the lubricating-oil gallery  97 . 
   Therefore, the drain hole  100  is located at the lowest position in the cooling-water gallery  37  so that the cooling-water may be efficiently discharged from the cooling-water gallery  37  into the cylinder block  15  through the drain hole  100 . 
   The drain hole  100  is connected with the cooling-water gallery  37  through a cooling-water drain gallery  101 . The cooling-water drain gallery  101  connects the cooling-water gallery  37  and the drain hole  100  inside the lubricating-oil gallery  97 . 
   Therefore, efficient drain of cooling-water is ensured without changing the construction of the lubricating-oil gallery  97 . Moreover, the cooling-water does not remain inside the cooling-water gallery  37 , thereby preventing degradation of the cylinder block. 
   In addition, the water jacket constructed by the cooling-water gallery is extended to the below of the lubricating-oil gallery so as to increase an area of the lubricating-oil gallery close to the water jacket, thereby improving the cooling effect to the lubricating-oil gallery. 
   Next, explanation will be given on the construction of the camshaft case in accordance with  FIGS. 8 ,  13 , and  14  in detail. 
   Grooves  110  are constructed inside the camshaft case  53 . The camshaft  14  is provided in a columnar space, which is extended in the front and rear direction of the cylinder block  15  and constructed inside the camshaft case  53 . Spaces opening in the vertical direction are provided in the upper portion of the space where the camshaft  14  is disposed, and push rods are provided in the respective vertical spaces. 
   Holder portions  111  are constructed inside the camshaft case  53  so as to hold the camshaft  14 . 
   After the cylinder block  15  is cast integrally with the holder portions  111 , the holder portions  11  are processed so as to have smooth and constantly shaped surfaces, thereby supporting the camshaft  14  smoothly. 
   As the processing after casting, cutting is mainly carried out. In cutting, the inner side surfaces of the holder portions  111  are cut by the cutting tool. 
   In the cast cylinder block  15 , each of the holder portions  111  is formed on the inner periphery thereof with a plurality of grooves  110  at irregular intervals so as to prevent burrs etc. when the cutting is applied to the holder portions  111 . 
   Therefore, impact is transmitted to the cutting tool at irregular intervals so as to restrict judder and chatter of the cutting tool in cutting the holder portion  111 , thereby improving the precision of cutting the holder portions  111  so as to reduce friction loss in the cylinder block  15 . 
   Moreover, the burrs and abatements generated in the processing are separated from the holder portion  111  into the grooves  110  and do not remain on the surface of holder portion  111 , thereby simplifying the work for removing them. 
   Next, explanation will be given on other construction inside the holder portion  111  in accordance with  FIG. 15 . 
   Four grooves  110  are provided at respective positions in the holder portion  111  as shown in  FIG. 15 . Intervals t 1 , t 2 , t 3 , and t 4  between the grooves  110  differ from one another. 
   The upper groove  110  is constructed at the upper end of the holder portion  111 . The lower groove  110  is shifted leftward at a little from the lower end of the holder portion  111  making symmetry together with the upper groove  10  with respect to the axis of the holder portion  111 . The left groove  110  is shifted upwardly leftward from the lower groove  110  at about 90° around the axis of the holder portion  111 . The right groove  110  is opposed to the left groove  110  but higher than the left groove  110 . 
   Therefore, the intervals t 1 , t 2 , t 3 , and t 4  between the grooves  110  are different from one another so that the impact transmitted to the cutting tool becomes irregular so as to restrict judder and chatter of the cutting tool in cutting the holder portion  111 . The arrangement of the grooves  110  may be also adapted to other portions such as holes under the liners. For example, the above-mentioned plugged hole may be provided on the inner periphery thereof with axial grooves  110  at irregular intervals so as to improve precision of cutting the plugged hole. Alternatively, the grooves  10  may be constructed in another direction about a hole to which they are provided. For example, they may be aligned in parallel in the axial direction of the hole, or they may be disposed slantwise. Alternatively, they may be made into a shape of steps. Any shape of the grooves is appreciated if it is considered so as to reduce impact onto a cutting tool when the cutting work. The shape of the grooves is not limited to the above-mentioned constructions. 
   The irregular intervals among the grooves  110  makes intervals of impact to the cutting tool irregular so as to restrict judder and chatter caused by resonation of the cutting tool with the impact. 
   INDUSTRIAL APPLICABILITY OF THE INVENTION 
   As mentioned above, the cylinder block according to the present invention is adaptable for engines such as a diesel engine.