Patent Publication Number: US-6988480-B2

Title: Cylinder block for an internal combustion engine having a locally thickened end wall

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of commonly-owned provisional application No. 60/411,510 filed on Sep. 16, 2002. 

   TECHNICAL FIELD 
   The present invention is directed to a cylinder block for an internal combustion engine of the type having a water jacket surrounding one or more cylinder bores. 
   BACKGROUND 
   In conventional engine manufacture, the size of the cylinder block is normally dictated by the capacity of the cylinder bores. In particular, the surface area of the top deck of the block is affected by the diameter of each of the cylinder bores. As a result, increasing the capacity of a cylinder block by increasing the diameter of the cylinder bores requires a larger and heavier cylinder block to accommodate the larger bores. This increase in the size and weight of the block will negate to a certain extent the improvement in performance provided by the increased engine capacity created by the larger diameter bores. 
   As a result of this disadvantage, engine manufacturers have attempted to obtain greater cylinder bore dimensions, and hence engine cubic capacity, within an engine block without substantially adding to the size and weight of the block itself. The disadvantage of such arrangements is that increasing the bore diameters without lengthening the block means that the space between the end walls of the block and the walls of the outermost cylinder bores becomes limited. As a water jacket must be located between the cylinder bores and the end walls, the transverse portions of the water jacket between the end walls and outermost bores must be thinner than usual because of the reduction in space. 
   As will be understood by those skilled in the art, the conventional way in which to define a water jacket during cylinder block casting is to use moulded sand cores in the block mould. However, if the transverse portions of the water jacket between the end walls and outermost bores are too thin, the thinner sand cores needed to define the thinner transverse portions of the water jacket may not be strong enough during casting. If the cores are too thin they may tend to crack or deform. Thus, efficient block casting of compact but increased capacity blocks remains difficult. 
   A cast cylinder block is provided with a variety of internal volumes, apertures and recesses that define various elements within the block itself. In conventional engine block casting, the shape or profile of such internal features is dictated by the shape of sand cores which are pre-moulded and placed within a cylinder block mould prior to the metal being cast into the mould. These cores themselves are shaped in core boxes, which are conventionally split into two parts, with the split between the two parts at either the top or bottom of the box in order that the formed cores may be removed. However, the shape that the cores can be formed in—and hence the shape of the internal features in the cylinder block—is limited, as the cores must be easily removed from the core box prior to insertion into the cylinder block mould. With the split in the core box at either the top or bottom of the box, the cores must only taper longitudinally in one direction if they are still to be easily removed from the core box. 
   This problem of core shape is especially significant when considering the profile of a water jacket for a cylinder block, where the water jacket is positioned between the side wall of the block and the cylinder bores. As the cores can only taper in one direction, the water jacket created by the core also only tapers in one direction, narrowing when viewed in transverse section from the top deck of the block downwards. This presents problems in that the water jacket cannot be particularly deep given the single taper, and the cylinder bores must also be relatively far apart so that there is room on the deck of the block for machining additional features. Furthermore, with a water jacket which is wider at the top of the block the wall thickness between the bore and jacket will be relatively thin, which is not desired when the combustion—and hence greatest heat transfer—occurs at the top of the cylinder bore. 
   Conventional cylinder blocks are also cast such that the water jackets are closed at the top thereof. This is disadvantageous in the manufacturing process as it prevents easy cleaning and inspection of the block after both casting and machining. 
   It is an aim of the present invention to obviate or mitigate one or more of the aforementioned problems. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention there is provided a cylinder block for an internal combustion engine comprising at least one cylinder bore, a coolant jacket surrounding the at least one cylinder bore, a top deck, and first and second longitudinally opposed end walls, each of the first and second end walls having a substantially planar end wall surface arranged on respective first and second planes. The coolant jacket includes a first portion located between the first end wall and the at least one cylinder bore, and a second portion located between the second end wall and the at least one cylinder bore. At least one of the first and second end walls includes a projecting portion adjacent the top deck that projects longitudinally beyond the first or second plane. 
   According to a second aspect of the present invention there is provided an internal combustion engine including the cylinder block according to the first aspect of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a perspective view of a cylinder block; 
       FIG. 2  is a plan view of the cylinder block of  FIG. 1 ; 
       FIG. 3  is a transverse cross sectional view of the cylinder block of  FIG. 2  through line III—III; 
       FIG. 4  is a longitudinal cross sectional view of the cylinder block of  FIG. 2  through line IV—IV; 
       FIG. 5  is a vertical cross-section along the transverse axis of a sand core box used in the manufacture of the cylinder block of  FIG. 1 ; and 
       FIG. 6  is a cross-sectional view of the sand core box of  FIG. 5  through line VI—VI. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a cylinder block in accordance with the present invention. The block  30  is a one piece casting which includes an upper part  31  and a lower part  33 . The upper part  31  houses a number of cylinder bores  32  and a coolant jacket  34  surrounding the bores  32 . The coolant jacket  34  is referred to in the specification as a water jacket, but it is to be understood that any suitable coolant may be used, and that the jacket  34  may include any suitable chamber at least partially surrounding the cylinder bores  32 . In this embodiment, the bores  32  are linerless and have conjoined walls  39 , such that the water jacket  34  does not extend between the bores  32 . The block  30  is of open deck construction, whereby the water jacket  34  is open on the top deck  36 . During engine assembly a gasket (not shown) is placed directly on the water jacket  34  before a cylinder head (not shown) is attached to the block  30 . The block  30  is also provided with conventional features such as threaded apertures  40  for receiving cylinder head attachment bolts (not shown) and also ventilation passages  38  which allow for removal of casting material from the block following casting. The lower part  33  of the block  30  is of a conventional form which will be appreciated by the skilled person, and as such will not be further described herein. 
   The aforementioned features of the upper part  31  of the block  30  can be seen clearly in  FIG. 2 . The upper part  31  has a first end wall surface  42  and a second end wall surface  44  which have first  42 A and second  44 A planes, respectively. The first and second end wall surfaces  42 , 44  are generally co-planar with respective first and second end wall surfaces  46 , 48  of the lower part  33 . In other words, the first end wall surface  42  and second end wall surface  44  of the upper part  31  generally do not extend longitudinally beyond the first and second end wall surfaces  46 , 48  of the lower part  33 . However, each of the first and second end wall surfaces  42 , 44  of the upper part  31  are provided with first and second projecting portions  50 , 52  which curve outwardly from the respective planes of the first and second end wall surfaces  42 , 44 , generally following the curvature of the first and second outermost cylinder bores  32 A, 32 B. 
     FIG. 3  shows a cross section through the block  30  along line III—III of  FIG. 2 . From this figure the tapering of the water jacket  34  in the transverse direction can be seen. The water jacket  34  widens as viewed in this transverse section from a first upper width W 1  at upper portion  34 A, 34 B adjacent the top deck  36  downwards until it reaches a third intermediate width W 3  at intermediate portion  41 . The split or casting line  37  of the block, where the two parts of the block mould meet, is generally co-planar with the intermediate portion  41  of the water jacket  34 . 
   Continuing downwards, the water jacket  34  then narrows as viewed in this transverse section from the intermediate portion  41  to a second lower width W 2  at lower portion  34 C, 34 D adjacent its base, or floor  54 . The amount of narrowing or widening will depend on the degree of taper A,C of the water jacket  34  between the top deck  36  and intermediate portion  41 , which will correspond to that given to the sand cores in the core box  10 , as will the amount of taper B,D between the intermediate depth  41  and the water jacket floor  54 . The amount of taper A,B,C,D of the different portions of the water jacket  34  is preferably in the range of 1–10°. In the preferred embodiment the taper of each portion is 4°, but where appropriate the taper may be less than 1° or more than 10°. Although  FIG. 3  only shows a selected transverse cross section of the block  30 , the water jacket  34  is tapered in this manner along both longitudinal sides and both ends of the block  30 . The taper may vary according to the position on the block  30 . 
   The water jacket  34  has two substantially transverse portions  34 E, 34 F which lie between the first end wall surface  42  and first outermost cylinder bore  32 A and the second end wall surface  44  and second outermost cylinder bore  32 B, respectively, seen in section in  FIG. 4 . 
     FIG. 4  shows the block  30  in longitudinal section along line IV—IV of  FIG. 2 .  FIG. 4  illustrates the extent to which the projecting portions  50 , 52  project from the first and second end wall surfaces  42 , 44  of the upper part  31 . The purpose of the projecting portions  50 , 52  is to allow the first and second transverse portions  34 E, 34 F of the water jacket  34  to be wider—at least in part—without substantially adding to the overall size or weight of the cylinder block  30 . 
   The normal extent of the first end wall surface  42  is shown as a broken line  43  in  FIG. 4 . It can be seen that to accommodate larger cylinder bores in the existing compact block, the space for the water jacket would have been very narrow, given that the outer wall must be of sufficient width so as to provide strength to the block  30 . Thus, at the first end wall surface  42  of the upper part  31  of the block  30 , the first projecting portion  50  has been added to extend the length of the block  30  beyond the normal extent line  43 . The projecting portion  50  extends outwardly from the top deck  36  and down the first end wall surface  42 , but it should be noted that the vertical depth of the projecting portion  50  does not substantially exceed the depth of the water jacket  34 . The remainder of the first end wall surface  42  is still substantially co-planar with the first end wall surface  46  of the lower part  33 , but the transverse portion  34 E of the water jacket  34  is wider than would be possible without the projecting portion  50 . 
   At the second end wall surface  44  of the upper part  31  of the block  30 , the normal extent of the second end wall surface  44  is shown as a broken line  45 . The second projecting portion  52  projects beyond the normal extent line  45  and allows the transverse portion  34 F of the water jacket  34  to be widened in the same manner as at the first end wall surface  42 . However, although it too extends downwards from the top deck  36 , the second projecting portion  52  does not extend as deep as the depth of the water jacket  34 . This is so as not to interfere with a flywheel housing (not shown) which is located adjacent the second end wall surface  44  after the engine is assembled. As a result only an intermediate section  35  of the transverse portion  34 F of the water jacket  34  is widened, such that the width of the intermediate section  35  is greater than the widths of the upper and lower sections. 
   As can be seen in  FIG. 4 , the substantially transverse end portions of the water jacket  34 E,  34 F adjacent the two outermost cylinder bores are tapered in the same manner as the substantially longitudinal portions of the water jacket  34  illustrated in  FIG. 3 , although the magnitude of the taper may vary.  FIG. 4  illustrates the depth of the water jacket  34 , which terminates at the water jacket floor  54 . The depth of the water jacket  34  ensures that the combustion portion of each bore  32 —the portion which will experience the most extreme pressure and temperature—will be sufficiently cooled as the depth of the jacket extends at least as deep as the combustion portions of the bores  32 . 
   The core box  10  shown in  FIGS. 5 and 6  is comprised of an upper part  12  and a lower part  14  which are detachable from one another. The box  10  is provided with a split line  16  between the upper and lower parts  12 , 14  which, unlike conventional cylinder block core boxes, is at an intermediate height on the box  10 . In this particular embodiment, the split line  16  is located midway up the box  10 . With conventional cylinder block boxes, the split line is normally adjacent either the top or bottom of the box. 
   Each of the upper and lower parts  12 , 14  are provided with first and second shaped recesses  18 A, 18 B, 20 A, 20 B where the recesses  18 A, 20 A in the upper part  12  co-operate with the recesses  18 B, 20 B in the lower part  14  to form volumes  18 , 20  into which sand or other suitable material can be poured to create cores for use in casting. 
   Each of the recesses  18 A, 18 B, 20 A, 20 B has an inward taper such that the width of the recesses  18 A, 18 B, 20 A, 20 B reduces when viewed in transverse section in either the upward or downward direction away from the split line  16 . Each of the recesses  18 A, 18 B, 20 A, 20 B has a respective amount of taper A,B,C,D in the range of 1–10°, but in the preferred embodiment the taper is 4°. Where appropriate tapers outside the range of 1–10° may be used. Each recess can have an individual amount of taper depending on desired specifications for the engine block for which the cores are being formed. The tapers of the upper recesses  18 A,  20 A may differ from the tapers of the lower recesses  18 B,  20 B. As a result of the tapers A,B,C,D, the portions of the recesses  18 A, 18 B, 20 A, 20 B furthest from the split line  16  are narrower when viewed in transverse section than the portions at the split line  16 . Providing the split line in the middle of the box  10  allows this double taper of each volume  18 , 20  which is not possible with conventional core boxes. 
   In use, the sand cores are moulded in the conventional manner, and this process will not be further described here. However, as the volumes  18 , 20  narrow when viewed in transverse section in both the upward and downward directions, once the cores have been moulded the upper part  12  of the core box  10  can be lifted off leaving the cores in the lower part  14  of the box. The cores can then simply be lifted out of the lower part  14  when needed. 
   The block  30  of  FIG. 1  may be cast using the sand cores produced using the core box  10  of  FIGS. 5 and 6 . The intermediate portion  41  of the block  30  corresponds to the intermediate depth of the core box volumes  18 , 20  where the core box split line  16  is located, as the water jacket profile is defined by the sand cores created in the core box  10 . In addition, the parting line or casting line  37  of the block  30 —where the two parts of the block mould meet—is also co-planar with the intermediate portion  41  of the water jacket  34 . The taper the water jacket  34  corresponds to the taper of the sand cores in the core box  10 . It is to be understood that a cylinder block having a closed top deck (not shown) could also be cast in this way. 
   INDUSTRIAL APPLICABILITY 
   The provision of the projecting portions  50 , 52  on each end wall surface  42 , 44  of the upper part  31  of the block  30  means that the transverse portions  34 A, 34 B of the water jacket may be wider than if the diameter of the cylinder bores was increased without increasing the overall size of the block itself. From  FIG. 3 , it can be seen that at least part of each of the transverse portions  34 A, 34 B of the water jacket  34  lies in the plane of the first or second end wall surface  42 , 44 , respectively. This would clearly not be possible without the provision of the projecting portions  50 , 52 . 
   As previously discussed, it is desirable to increase the diameter—and hence the cubic capacity—of the cylinder bores without increasing the length of the block. However, if the external shape of the block is unchanged, the transverse portions of the water jacket are too thin over the whole depth of the water jacket for them to be successfully cast in the block. With the present invention, accommodation of wider transverse portions of the water jacket is possible but, as the dimensions of the block other than the projecting portions remain the same, the overall dimensions of the block are still compact. Thus, bores of greater diameter can be cast in a compact block without encountering casting problems due to the transverse portions of the water jacket being excessively thin. 
   The present invention provides a cylinder block with a water jacket which has a double taper when viewed in transverse section. This double taper permits the water jacket to be narrower at both top and bottom. Being narrow at the top allows more room for the addition of machined features post-casting, and also permits thicker bore walls in the combustion portion of the bore. Being narrow at the bottom allows for the jacket to have a greater depth than possible with the water jackets of conventional open deck cylinder blocks, which are usually moulded as part of the head core. 
   Having an open deck construction means that the engine will produce less noise during operation, as the combustion portion of the bores is isolated from the outer walls of the block by the water jacket. An open deck arrangement also allows easier visual inspection and cleaning of the block post-casting or machining. The combination of an open top deck and double tapered water jacket promotes better cooling around the cylinder bores, as the jacket extends to the top of the deck of the block. 
   Modifications and improvements may be incorporated without departing from the scope of the present invention. For example, although the water jacket on either longitudinal side of the block is shown to have the same degree of taper for both the upper and lower portions, the water jacket on one side of the block may have a different degree of taper within the 1–10° range for either one or both of its upper and lower portions than that of the other side, if desired. It will also be appreciated that although a four cylinder, in-line engine is described in the above embodiment, variations in terms of number of cylinders and layout thereof may also be employed with the present invention. Although the above embodiment describes projecting portions on both end walls of the block, the present invention could equally only have a projecting portion on one end wall of the block if desired. Furthermore, although only one of the transverse portions of the water jacket is shown to have an intermediate width greater than its upper and lower widths, both transverse portions of the jacket could be in this form. The transverse portions of the water jacket may also be widened further such that they are located at least partially within the projecting portions if necessary. It will also be clear that the present invention may also be applied to closed deck blocks if desired.