Internal combustion engine

Abstract: A cylinder head (14) arrangement for an internal combustion engine wherein the cylinder head (14) has a generally I-shape and cross section so as to permit attachment of the cylinder head (14) to the cylinder block (12) without necessitating removal of any of the components of the cylinder head assembly or opening or accessing of the valve train (25, 34).

Description: This invention relates to an internal combustion engine comprising a cylinder block having at least one cylinder and a cylinder head assembly which comprises, a lower portion fixed to the cylinder block and an upper portion connected to the lower portion and supporting a camshaft arrangement, as well as a camshaft drive means for operating a plurality of poppet valves for each cylinder of the cylinder block , said camshaft arrangement comprising, two parallel camshafts for operating the intake and exhaust valves of the engine, said lower portion of the cylinder head assembly having a flat lower surface adapted to form a seal with an upper surface of the cylinder block , and a cylinder head fastening means , comprising a plurality of fasteners adapted to affix the cylinder head to the cylinder block. As is well known, the performance of an internal combustion engine can be improved by using overhead valves and direct valve actuation by overhead mounted camshafts. In many high performance engines, multiple intake and exhaust valves and multiple camshafts are also employed. Although such construction increase the performance of the engine, they also complicate significantly the construction of the cylinder head and particularly the manner by which it may be attached to the cylinder block. It is, of course, extremely important to insure that the clamping of the cylinder head to the cylinder block is uniformed around the cylinder bore so as to insure against gasket failures and leakage. However, this problem becomes particularly acute when overhead camshafts are employed. That is, the placement of the hold down fasteners for the cylinder head can be comprised due to the use of the overhead camshafts. In addition to the aforenoted problems, when overhead camshafts are employed it is frequently the practice to place the fasteners for the cylinder head to the cylinder block within the cam cover of the engine. This means that the cam cover must be removed to access the fasteners. In addition, frequently it becomes necessary to remove some of the valve train in order to access the fastener. In addition to the increased labor caused by such assembly methods, there is also the danger that when servicing the cylinder head fasteners that foreign material may enter into the valve train and cause eventual damage or wear. Since frequently it is the practice to require retorquing of the cylinder heads after a certain amount of running following rebuilds, the problems are not insignificant. From FR-A-2 527 270 it is known to affix the cylinder head to the cylinder block by stud bolts which penetrate sidewardly projecting flange portions of the cylinder head. Said stud bolts extend closely adjacent to a cylindrical liner of the cylinder block. Generally, the fixation struture need to combine a plurality of further requirements such as the cooling capacities of the cylinder head/cylinder block arrangement as well as the serviceability and assembly of the engine, simultaneously assuring sufficient stiffness and rigidity of the cylinder head in order to award appropriate bearing capacities for a camshaft bearing structure selected. An internal combustion engine as indicated in the preamble of claim 1 is known from EP-A-0 098 180, leading to an increased width of the cylinder head of said DOHC engine. Moreover, the fastening bolts are not easily accessable and, therefore, further improvement of such engines is required. Accordingly, it is an objective of the present invention to provide an improved internal combustion engine as indicated above, having a cylinder head construction that permits the cylinder head to be attached to the block without necessitating removal of any components of the valve train or with necessitating accessing the fasteners through the valve cover. According to the present invention, said objective is performed through an internal combustion engine of the type as is indicated in the preamble portion of claim 1 which is characterised in that the upper camshaft bearing portions and the lower cylinder head fixing portions of the cylinder head being integrally connected via a narrowed intermediate rib portion which has a smaller width in cross-section than the upper and lower portions , respectively, providing sidewardly accessible open recesses above the cylinder head fastening means , said recesses are positioned substantially beneath the camshaft supporting areas of the upper portion , enabling to operate the cylinder head fastening means between the upper and lower portions of the cylinder head , whereas the fasteners are disposed laterally offset outwardly with respect to the camshafts. In the following the present invention is explained in greater detail by an embodiment thereof in conjunction with the accompanying drawings, wherein: Figure 1 is a partial cross sectional view taken through an internal combustion engine constructed in accordance with an embodiment of this invention and generally along the line 1-1 of Figure 2. Figure 2 is a top plan view of the cylinder head assembly with the cam cover removed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION In the drawings the reference numeral 11 indicates generally an internal combustion engine constructed in accordance with an embodiment of the invention. Since the invention relates primarily to the cylinder head assembly in the manner in which it is affixed to the block, only this portion of the engine has been illustrated. In all other regards, it may be assumed that the engine 11 is of a conventional type. Also, the invention is depicted in conjunction with a portion of one cylinder of an in-line type of engine. It is to be understood, however, that the invention has utility with cylinder heads for engines other than in-line type engines and for engines having any number of cylinders. The cylinder block is identified generally by the reference numeral 12 and is formed with a plurality of longitudinally spaced cylinder bores (not shown) which open through an upper face 13 of the cylinder block 12. A cylinder head assembly, indicated generally by the reference numeral 14 is affixed, in a manner to be described, with a lower face 15 of a lower portion thereof 16 in sealing engagement with a gasket 17 that is interposed between the cylinder block 12 in the cylinder head 14 for sealing purposes. The lower face 15 of the cylinder head portion 16 may also be formed with recesses which cooperate with the cylinder bores and pistons that reciprocated therein to form the combustion chambers of the engine. Poppet type intake and exhaust valves (not shown) control the flow of gases to and from these combustion chambers through suitable intake and exhaust ports which have repective openings 17 in opposite sides of the cylnider head 14. There may be either one intake valve and one exhaust valve for each cylinder bore or multiple valves as desired. These valves are operated by lobes 18 and 19 formed on camshafts 20 and 21, respectively. These camshafts 20 and 21 are journalled in an upper portion 22 of the cylinder head assembly 14 in a manner to be described. It should be noted that the upper portion 22 is integrally connected to the lower portion 16 by an intermediate portion 23 which has a smaller width in the cross section shown in Figure 1 than the upper and lower portions 22 and 16 respectively. This gives rise to a generally I-shaped configuration for the cylinder head assembly and provides recesses 24 that are positioned beneath the camshafts 20 and 21 for a purpose to be described. The cylinder head upper portion 22 is formed with a generally concave recess 25 in which the valve actuating mechanism comprised of the camshafts 20 and 21 is contained. Respective bearing portions 26 and 27 formed in this recess 25 journal the camshafts 19 and 21, respectively. Each bearing portion 26 and 27 is comprised of a respective lower bearing surface 28 and 29 which is formed directly in the cylinder head material and thus forms half of the bearings for the camshafts 20 and 21. A plurality of space bearing caps 31 and 32, respectively, are affixed over the cylinder head bearing portions 28 and 29 by threaded fasteners such a bolts 33 or stud and nut assemblies. The chamber 25 in which the valve actuating mechanism described is contained is covered by means of a cover plate 34 that is affixed to the cylinder head 14 in a suitable manner. At the forward end of the cylinder head 14 there is provided a recess 35 that is defined by an upstanding front wall 36. This recess is defined on its rear side by an upstanding wall 37 and contains the mechanism for driving the camshafts 20 and 21 in a timed relationship. This mechanism includes a pair of timing gears 38 and 39 which are affixed to the camshafts 20 and 21 in a known manner. These timing gears 38 and 39 are immeshed with a further gear 41 which is journalled on a shaft 42 that extends through the front wall 36 of the cylinder head 14. It should be noted that the ratio between the gear 41 and the gears 38 and 39 may be either one to one or a ratio other than one to one so as to achieve the desired timing relationship between the crankshaft and the camshaft 20 and 21 so that the camshafts 20 and 21 rotate at one half of crankshaft speed, as is well known. A timing pulley or sprocket 43 is affixed to the front end of the shaft 42 and is driven from the crankshaft either by a belt or chain as desired. The ratio between the crankshaft and the pulley or sprocket 43 coupled with the ratio between the gear 41 and the gears 38 and 39 will obtain the aforenoted drive ratio between the crankshaft and the camshafts 20 and 21. The cylinder head 14 is affixed to the cylinder block 12 by means of a plurality of fastener assemblies 44 which, as have been aforenoted, are positioned so to be accessible through the recesses 24 and thus permit removal or insertion of the head 14 fron or on the cylinder block 12 without necessitating removal of any of the components of the head assembly or even removal of the cam cover 34. The fastener assembly depicted is of the stud type and includes studs 45 that are affixed to the cylinder block 12 in a known manner and have threaded upper portions 46 on which nuts 47 are received. The nuts 47 may be easily tightened and removed from the recessed areas 24 and thus the cylinder head assembly 14 can be removed as a unit as aforenoted. It should be understood that bolts rather than studs and nuts may be utilized for the fasteners 44, but the use of studs and nuts permits easier assembly and disassembly, as should be readily apparent. In defining the cylinder head upper and lower portions in both the Specification and Claims hereof the term "upper" is used to refer to the portion of the cylinder head more remote from the cylinder block while the term "lower" is intended to refer to the portion adjacent the cylinder block. Thus, the terms "upper" and "lower" are used only by reference to the associated cylinder block and not to the actual orientation of the cylinder head in space. Obviously if the cylinder block is inverted, then the upper portion of the cylinder head would actually be the lower portion and vice versa. However, the terms "upper" and "lower" are used by the reference as aforenoted to the relationship to the cylinder block rather than to the actual spatial relationship which is dependent upon how the engine is installed. As will become obvious to those skilled in the art, the aforedescribed construction provides a very compact cylinder head assembly and nevertheless one that can be easily serviced by installation and removal without requiring the removal of any components of the head assembly or accessing the valve actuating mechanism.

Claims: Internal combustion engine comprising a cylinder block (12) having at least one cylinder and a cylinder head assembly (14) which comprises, a lower portion (16) fixed to the cylinder block (12) and an upper portion (22) connected to the lower portion (16) and supporting a camshaft arrangement, as well as a camshaft drive means for operating a plurality of poppet valves for each cylinder of the cylinder block (12), said camshaft arrangement comprising, two parallel camshafts (20, 21) for operating the intake and exhaust valves of the engine, said lower portion (16) of the cylinder head assembly (14) having a flat lower surface (15) adapted to form a seal with an upper surface of the cylinder block (12), and a cylinder head fastening means (44), comprising a plurality of fasteners (45, 47) adapted to affix the cylinder head (14) to the cylinder block (12), characterized in that the upper camshaft bearing portion (22) and the lower cylinder head fixing portion (16) of the cylinder head (14) being integrally connected via a narrowed intermediate rib portion (23) which has a smaller width in cross-section than the upper and lower portions (22, 16), respectively, providing sidewardly accessible open recesses (24) above the cylinder head fastening means (44), said recesses (24) are positioned substantially beneath the camshaft supporting areas of the upper portion (22), enabling to operate the cylinder head fastening means (44) between the upper and lower portions (22, 16) of the cylinder head (14), whereas the fasteners (45,47) are disposed laterally offset outwardly with respect to the camshafts (20,27). Internal combustion engine as claimed in claim 1, characterised by a cam cover (34) for enclosing the area of the cylinder head (14) where the camshafts (20,21) are journaled. Internal combustion engine as claimed in claims 1 or 2, characterised in that, the threaded fastening means (44) comprises studs (45,47) affixed to the cylinder block (12) and nuts (47) bearing against the cylinder head lower portion (16). Internal combustion engine as claimed in at least one of the preceding claims 1 to 3, characterised by a timing gear means (38,39) affixed to the camshafts (20,21) and meshingly engaged with a timing gear (49) journaled in the cylinder head (14) and driven from the crankshaft of the engine for driving the camshafts (20,21).

Inventors: SUGIURA YOSHIAKI, SUGIURA, YOSHIAKI
Applicants: YAMAHA MOTOR CO LTD, YAMAHA MOTOR CO., LTD.
Application year: 1989
Main classification: F01L1
IPC codes: F01L1, F02F1