Camshaft arrangement for multiple valve engine

Abstract: A valve train arrangement for an internal combustion engine comprising a cylinder defining a bore (32) for receiving a piston, a cylinder head affixed relative to said cylinder and having a surface defining with said bore and the piston a combustion chamber, a pair of poppet valves (37,38) supported for reciprocation relative to said cylinder head about axes (A,B) that are disposed non parallel to each other, one of said axes being inclined at an acute angle only to a first plane containing the axis of said bore, the other of said axes being inclined at an acute angle to said first plane and also at an acute angle to a second plane perpendicular to said first plane and passing through said bore axis, and a camshaft (55) supported for rotation about an axis parallel to said first plane, a first cam lobe (57) on said camshaft for operating said first valve, and a second cam lobe (56) on said camshaft for operating said second valve, said second cam lobe (56) having its cam surface extending in a direction inclined to the axis of rotation of said camshaft (55).

Description: This invention relates to a cylinder head assembly for an internal combustion engine having at least two camshafts journaled for rotation about respective axes, each of said camshafts operating a plurality of valves reciprocably supported in said cylinder head assembly, first drive means for driving at least a first one of said camshafts from an engine output shaft, and a cylinder head casting for supporting an integral cam carrier which rotatably supports said at least two camshafts. It has been basically understood that the performance of an internal combustion engine can be improved by improving the breathing of the intake charge into the combustion chamber and the exhaust charge from the combustion chamber. It is also well known that the breathing and volumetric efficiency of an engine can be improved by increasing the number of valves rather than merely providing a single extremely large intake valve and a single extremely large exhaust valve. By using multiple smaller valves, the inertia can be reduced and higher engine speeds obtained. However, there still is a significant problem in placing all of the components within the combustion chamber and also insuring that the combustion chamber has a proper configuration. In high perfcrmance engines at the present time, four valves per cylinder are now becoming increasingly common. Such arrangements all employ two intake valves and two exhaust valves per chamber. It has been proposed also to employ arrangements with five valves (three intake and two exhaust) so as to permit even further increases in performance. Although it was thought that five valves per cylinder might be the optimum number, considering the problems in connection with valve placement and valve actuation, it is now believed that the provision of six valves (four intake and two exhaust) can offer still further performance increases. However, there are a wide variety of problems in connection with the provision of So many valves in a single combustion chamber. In connection with the utilization of multiple valves, it is, of course, desirable to minimize the number of camshafts employed for operating all of the valves. Generally, it has been the practice with four and five valve per cylinder engines to employ two camshafts, one for operating the intake valves and one for operating the exhaust valves. However, when one camshaft is called upon to operate more than three valves, then the placement of the valves can be compromised. Specifically, if there are four valves per cylinder operated by a single camshaft, it is normally the practice to align the valves so that they all reciprocate along axes that lie in a plane that will intersect or pass near the rotational center of the camshaft axis. This means that the actual length of the camshaft and specifically the lobes require the valves to be all positioned so that the combustion chamber configuration tends to be large and provide large surface areas. This obviously reduces the possible compression ratio of the engine and, accordingly, its performance. In conjunction with the use of a single camshaft for operating multiple valves, it is frequently the practice to employ separate cam lobes for operating each individual valve or groups of valves. However, where there are multiple valves and the use of multiple cam lobes, then the rotational support for the camshaft presents some problem. That is, the highest axial loading on the camshaft occurs in the area of the cam lobes where they engage the valve actuating elements. However, if the cam lobes are all placed close to each other, it is difficult if not impossible to provide a bearing surface adjacent the cam lobes in order to take these side loadings. Conventional camshaft arrangements simply do not afford the opportunity to provide adequate bearing surfaces for the camshafts under these circumstances. In some instances with multiple valve engines, it may be desirable to employ more than two camshafts for driving all of the valves of the engine. Where such an arrangement is employed, however, then it becomes important to insure that all of the camshafts are driven in the same timing relative to the engine output shaft. However, the timing drive should be relatively simple, uncomplicated and afford ready access to the components of the engine. EP-0 320 233 A1 for example shows a cylinder head for an internal combustion engine supporting three intake valves and two exhaust valves actuated by a pair of intake camshafts and a single exhaust camshaft. EP 0 063 385 A2 shows a cylinder head assembly for an internal combustion engine of the type indicated in the preamble of claim 1. The engine performance of the engine according to said document, particularly under high speed operating conditions, however still appears to be unsatisfactory because of the limited breathing and volumetric efficiency of the engine. Accordingly, it is an objective of the present invention to provide an improved cylinder head assembly for an internal combustion engine that permits an improved breathing and volumetric efficiency of the engine with a still compact valve arrangement. According to the present invention, this objective is performed in that the cam carrier rotatably supports a first and a second intake camshaft in a common plane for operating four intake valves per cylinder and at least one exhaust camshaft, in that a first pair of said four intake valves is smaller in diameter than a second pair of said four intake valves and in that a second drive means is provided for driving said second intake camshaft from said first intake camshaft. The provision of a pair of intake camshafts permits many possibilities of arranging and positioning the intake valves. According to a preferred embodiment of the present invention, the first drive means is disposed at one end of the first intake camshaft and the second drive means is spaced from said one end of said first intake camshaft, preferably it is disposed at the other end of said first intake camshaft. Further preferred embodiments of the present invention are laid down in further dependent claims. In the following the present invention is explained and illustrated in greater detail by means of preferred embodiments of the invention in conjunction with accompanying drawings, wherein: Fig. 1 is a cross-sectional view showing a cylinder head assembly for an internal combustion engine according to a preferred embodiment of the present invention, which view is taken along line XV-XV of fig. 3; Fig. 2 is a top plan view, with portions shown in section, of the valve and porting arrangement of the embodiment according to fig. 1; Fig. 3 is a top plan view, with portions, particularly a head cover removed and other portions shown in phantom, showing an embodiment of the invention; Fig. 4 is a partial top plan view, in part similar to fig. 3 of a cylinder head assembly constructed in accordance with another preferred embodiment of the invention, with portions broken away and with the cam cover removed; Fig. 5 is a partial cross-sectional view, in part similar to fig. 1, of the embodiment of fig. 4; and Fig. 6 is a top plan view of the embodiment according to fig. 5 showing the valve and spark plug placement in solid lines with the porting in phantom lines. Referring first to figs. 1 and 2, an internal combustion engine depicted in accordance with this embodiment is illustrated partially. Since the invention relates primarily to the construction of the cylinder head assembly, only this portion of the engine has been shown in detail. It is to be understood, however, that the cylinder head assembly, which in this embodiment is identified generally by the reference numeral 31, is associated with a cylinder block having a plurality of aligned cylinder bores, shown in phantom in Figures 1 and 5 and identified generally by the reference numeral 32. In the illustrated embodiment, the engine is of the in line type. It is to be understood, however, that the invention can be utilized in conjunction with engines having other cylinder configurations. Also, certain facets of the invention can be utilized in conjunction with engines having cylinders that are not cylindrical bores. For that reason, the term "bore" as used in the specification and claims is intended to encompass cylinders having openings in which pistons are supported for reciprocation regardless of the cross sectional configuration. In the illustrated embodiment, the cylinder head assembly 31 is made up of a plurality of light alloy castings including a main cylinder head casting 33 in which recesses 34 are formed so as to define combustion chambers with the cylinder bores 32 and the pistons reciprocating therein. The pistons are not illustrated in the drawings. In addition to the main cylinder head casting 33, the cylinder head assembly further includes a cam carrier 35 which, as will be noted, contains the valve actuators and camshafts and a pair of cam covers, each indicated generally by the reference numeral 36. The cam covers 36, the camshaft carrier 35 and cylinder head 33 may be affixed to the associated cylinder block in any known manner. The cylinder head assembly 31 is provided with a set of four intake valves 37, 38, 39 and 41, each of which has stem portions that are slidably supported for reciprocation within a respective guide pressed into the cylinder head portion 33. It will be noted that the items of the side intake valves 38 and 39 reciprocate about respective axes that extend parallel to each other and which define a common plane that is disposed at an acute angle to a plane passing through the center of the bore 32, extending perpendicularly to the plane of Figure 1. The outer or center intake valves 37 and 41 reciprocate about axes that are in a common plane in a direction parallel to the plane of reciprocation of the axes of reciprocation of the side intake valves 38 and 39 and which are disposed at an acute angle to the aforenoted plane of the cylinder bore. The acute angle of the side intake valves 38 and 39 relative to this plane is greater than the acute angle of the plane defined by the axes of reciprocation of the center intake valves 37 and 41. However, the axes of reciprocation of the center intake valves 37 and 41 also lie at an acute angle to a plane perpendicular to the aforenoted plane and passing through the cylinder axes. This perpendicular plane is parallel to the plane of Figure 1. As a result of this acute angle, it should be noted that the tips of the stems of the valves 37 and 41 are disposed outwardly of the periphery of the cylinder 32. The intake valves 37, 38, 39 and 41, and specifically the head portions thereof, open and close respective valve seats formed by pressed in inserts. These valve seats define intake ports which all are served by a common, siamese intake passage 43 that extends from an oval opening in a face 44 of the cylinder head to these valve ports. As may be best seen from Figure 2, the side intake valves 38 and 39 are much closer to the inlet opening of the intake passage 43 and the gales flowing to the intake valves 38 and 39 have a straighter path than the situation with respect to the center intake valves 37 and 41. If it is desired to provide substantially uniform flow into the cylinder 32 through all of the intake ports served by the valves 37, 38, 39 and 41, then the valves 37 and 41 should be made with their heads of a larger diameter than the heads of the valves 38 and 39. Generally, if the size of the side intake valves 38, 39 equals to the size of the center intake valves 37, 41 over 50% amount of all air-fuel mixture which flows into the combustion chamber flows into the chamber from the side intake valves 38, 39. On the other hand, the amount of the mixture from the respective intake valves is relatively averaged, when the size of the side intake valves 38, 39 is smaller, that is, the engine is tuned to middle speed. And in the case of Figure 2, the swirl effect is strengthened. The cylinder head assembly 31 also supports a second set of valves comprising exhaust valves 45 and 46 which lie generally on the opposite side of the first mentioned plane when these valves are in their closed position. The valves 45 and 46 have their stem portions supported for reciprocation within pressed in guides 47 and reciprocate along parallel axes that lie in a common plane that is disposed at an acute angle to the aforenoted plane. The exhaust valves 45 and 46 control the flow through one or more exhaust ports 48 formed in the side of the cylinder head portion 31 opposite to the intake port 43. With respect to the configuration of the intake port 43, it has been noted that it starts from a common opening but as it approaches the valves 37 and 38 and 39 and 41, it will branch into two portions. The intake valves 37, 38, 39 and 41 are all operated by respective thimble tappets 51, 52, 53 and 54 that are slidably supported in bores formed in the cam carrier 35. These bores are disposed so as to be parallel to the respective valve stems of the valves which they operate. As a result, the bores that support the tappets 52 and 53 have their central axes disposed in a common plane, that is at an acute angle to the first noted plane passing through the center of the cylinder bore, while the axes of reciprocation of the tappets 51 and 52 lie in a plane that is at an acute angle to this plane and also at an acute angle to the perpendicular plane aforenoted. As a result, the head portions of the tappets 51, 52, 53 and 54 will not all be in a common plane. Those of the tappets 52 and 53 are in a common plane, but those of the tappets 51 and 54 are skewed to this common plane. Coil compression springs and keepers act to urge the valves 37, 38, 39 and 41 toward their closed positions. The valves are opened by means of a camshaft assembly now to be described. A pair of intake camshafts, indicated generally by the reference nuneral 302, 306 is journaled for rotation, in a manner to be described, by the cylinder head assembly 31 and specifically between the cam carrier 35 and bearing caps which will be described. The camshafts rotate about an axis that is disposed parallel to the axis of rotation of the engine crankshaft (not shown). The exhaust valves 45 and 46 are actuated in a generally similar manner to the intake valves 37, 38, 39 and 41. However, due to their alignment, the exhaust valves 45 and 46 are operated by respective thimble tappets 62 that are slidably supported within bores formed in the cam carrier 35 and which bores have their center lines lying in a plane common to the plane of the axis of reciprocation of the valves 45 and 46. An exhaust camshaft 63 is journaled in an appropriate manner in the exhaust side of the cam cover 36 by means of bearings formed integrally in the cam carrier 35 and bearings formed by bearing caps 301 that are affixed in a suitable manner within the cam chamber. As can be seen from fig. 2, the embodiment according to figs. 1 through 3 is provided with a single spark plug 65 which is disposed substantially centrally with respect to the cylinder bore 32. Consistent with the desire to provide high performance, the combustion chamber 34 may be provided with a pair of spark plugs 65 that are disposed, in the embodiment of Figs. 4 through 6, with their gaps in side by side relationship aligned axially along the axis of rotation of the output shaft and lying substantially on the first mentioned plane containing the axis of the cylinder bore 32. The spark plugs 65 are accessible through spark plug wells 66 (Figure 4) formed centrally in the cylinder head assembly 31 and which may be opened through the area between the cam covers 36. The center intake valves 37 and 41 and specifically the tappets 51 and 54 associated therewith are operated by means of a first intake camshaft 302. The intake camshaft 302 has a drive sprocket 303 at its forward end and a similar drive sprocket 304 is connected to the exhaust camshaft 63. The exhaust camshaft 63 and intake camshaft 302 are driven by a chain or belt 305 from the engine output shaft in a known manner. Moreover, as shown in Figure 2 the size of the center intake valves 37, 41 is smaller than those of the side intake valves 38, 39, thus, an improved swirl effect can be obtained. As indicated in Figure 1 the spark plug 65 is positioned inclined with respect to a vertical center axis of the associated cylinder enabling the cylinger head to become more compact. A second intake camshaft indicated generally by the reference numeral 306 is supported for rotation, in a manner to be described, about an axis that is parallel to the axis of rotation of the exhaust camshaft 63 and the first intake camshaft 302. The intake camhafts 302 and 306 have affixed to the end opposite from the sprocket 303 timing gears 307 and 308 which drive the intake camshaft 306 from the intake camshaft 302. Obviously, the camshafts 302 and 306 will rotate in opposite directions and the cam lobes thereon can be formed accordingly. If desired, an intermediate gear (not shown) may be employed so that both camshafts will rotate in the same direction. Particularly, the first intake camshaft 302 is provided with a first cam lobe 51 for operating the valve 37 and a second cam lobe 54 for operating the valve 41. Said cam lobes 51 and 54 may have their cam surface extending in a direction inclined to the axis of rotation of said first intake camshaft 301, particularly when the center intake valves 37 and 41 are supported for reciprocation relative to the cylinder head assembly about axes that are disposed non-parallel to each other and inclined at an acute angle to a first plane containing the axis of the cylinder bore 32 and the axis of the engine output shaft and also at an acute angle to a second plane perpendicular to said first plane and also containing said cylinder bore axis. In a similar manner, the second intake camshaft 306 is provided with another pair of cam lobes 52 and 53 for operating the side intake valves 38 and 39, wherein the first and second cam lobes 51 and 54 on the first intake camshaft 302 are spaced apart from each other further than the cam lobes on the second intake camshaft 306. The camshafts 302 and 306 are supported for rotation relative to the cam carrier 35 by a plurality of bearing caps 309 and 311 which are affixed to the cam carrier 35 in a known manner and which cooperate with bearing surfaces on each of the camshafts 302 and 306. Alternatively, if desired, individual bearing caps may be provided. The bearing surfaces on the camshafts 302 and 306 are preferably provided between the respective pairs of cam lobes 51, 54 and 52, 53, as can be seen from figs. 3 and 4. Figures 4 through 6 show another embodiment of the invention which is generally the same as the embodiment of Figures 1 through 3. With this embodiment, however, the valve placement may be different from those previously described. In this embodiment, the intake valves 37 are 41 are disposed at a rather substantial acute angle to the vertical plane passing through the axis of the cylinder 32. On the other hand, the side intake valves 38 and 39 are disposed so that their reciprocal axes are nearly vertical. This configuration permits a more compact combustion chamber and can permit higher compression ratios. As result of this different valve placement, the camshaft 306 operates the center intake valves 37 and 41 while the first intake camshaft 302 operates the side intake valves 38 and 39. In all other regards, this embodiment is the same as that of Figures 1 through 3 and, for that reason, the same reference numerals have been utilized to designate the same components. The embodiments thus far described have employed thimble tappets for operating the intake and exhaust valves. Of course, the invention can also be utilised in conjunction with engines having rocker arm valve actuation, wherein a plurality of cam followers are provided for operating the plurality of valves, said cam followers being engaged with the surface of the cam lobes on the intake and exhaust camshafts. It should be noted that in that case the spark plug 65 is positioned inclined again, thus enabling an improved compact structure of the cylinder head.

Claims: A cylinder head assembly (31) for an internal combustion engine having at least two camshafts (63, 302, 306) journaled for rotation about respective axes, each of said camshafts (63, 302, 306) operating a plurality of valves (37, 38, 39, 41, 45, 46) reciprocably supported in said cylinder head assembly (31), first drive means (303, 305) for driving at least a first one of said camshafts (63, 302) from an engine output shaft, and a cylinder head casting (33) for supporting an integral cam carrier (35) which rotatably supports said at least two camshafts (63, 302, 306), characterised in that said cam carrier (35) rotatably supports a first and a second intake camshaft (302, 306) in a common plane for operating four intake valves (37, 38, 39, 41) per cylinder (32) and at least one exhaust camshaft (63), in that a first pair of said four intake valves (37, 41) is smaller in diameter than a second pair of said four intake valves (38, 39) and, in that a second drive means (307, 308) is provided for driving said second intake camshaft (306) from said first intake camshaft (302). A cylinder head assembly (31) as claimed in claim 1, characterised in that said first drive means (303, 305) drives said first intake camshaft (302) and said at least one exhaust camshaft (63). A cylinder head assembly (31) as claimed in claims 1 or 2, characterised in that the first drive means (303, 305) is disposed at one end of said first intake camshaft (302) and said second drive means (307, 308) is spaced from said one end of said first intake camshaft (302). A cylinder head assembly (31) as claimed in at least one of the preceding claims 1 to 3, characterised in that said second drive means (307, 308) is disposed at the other end of said first intake camshaft (302). A cylinder head assembly (31) as claimed in at least one of the preceding claims 1 to 4, characterised in that said second drive means comprises a gear drive (307, 308) for driving said second intake camshaft (306) from said first intake camshaft (302). A cylinder head assembly (31) as claimed in at least one of the preceding claims 1 to 5, characterised in that said first drive means comprises a flexible transmitter (305). A cylinder head assembly (31) as claimed in at least one of the preceding claims 1 to 6, characterised in that said first intake camshaft (302, 306) is provided with a first cam lobe (51) for operating a first valve (37), and a second cam lobe (54) for operating a second valve (41), said cam lobes (51, 54) having their cam surface extending in a direction inclined to the axis of rotation of said camshaft (302, 306), and said first and second valves (37, 41) are supported for reciprocation relative to said cylinder head assembly (31) about axes that are disposed non parallel to each other, said axes being inclined at an acute angle to a first plane containing the axis of a cylinder bore (32) and the axis of the engine output shaft, and also at an acute angle to a second plane perpendicular to said first plane and also containing said bore axis. A cylinder head assembly (31) as claimed in claim 7, characterised in that the cam lobes (51, 54) are formed with a bearing surface therebetween for rotatably journaling the camshaft (302, 306). A cylinder head assembly as claimed in claims 7 or 8, characterised in that a third valve (38) and a fourth valve (39) are supported for reciprocation about axes that are inclined at an acute angle to said first plane, a third cam lobe (52) for operating said third valve (38) and a fourth cam lobe (53) for operating said fourth valve (39) are provided on said second intake camshaft (302, 306). A cylinder head assembly (31) as claimed in at least one of the preceding claims 7 to 9, characterised in that the first and second cam lobes (51, 54) are spaced apart further than the second and third cam lobes (52, 53). A cylinder head assembly (31) as claimed in at least one of the preceding claims 7 to 10, characterised in that said third and fourth intake valves (38, 39) are inclined relative to said first plane by a smaller angle than said first and second intake valves (37, 41). A cylinder head assembly (31) as claimed in at least one of the preceding claims 7 to 11, characterised in that a spark plug (65) is disposed with its gap substantially on the axis of the cylinder bore. A cylinder head assembly (31) as claimed in at least one of the preceding claims 7 to 11, characterised in that a pair of spark plugs (65) have their gaps lying substantially along said first plane. A cylinder head assembly as claimed in at least one of the preceding claims 7 to 11, characterised in that a pair of spark plugs (65) are disposed with their gaps lying substantially along said second plane. A cylinder head assembly (31) as claimed in at least one of the preceding claims 1 to 14, characterised by a plurality of cam followers for operating the plurality of valves (37, 38, 39, 41, 45, 46), said cam followers being engaged with the surfaces of said cam lobes (51, 52, 53, 54). A cylinder head assembly as claimed in at least one of the preceding claims 1 to 15, characterised in that the first intake camshaft (302), centrally disposed between the second intake camshaft (306) and the exhaust camshaft (63), is adapted to operate two center intake valves (37, 41) of the four intake valves (37, 38, 39, 41). A cylinder head assembly as claimed in claim 16, characterised in that the second intake camshaft (306), disposed between the first intake camshaft (302) and a side wall of the cylinder head assembly (31) is adapted to operate two side intake valves (38, 39) of the four intake valves (37, 38, 39, 41).

Inventors: ONODERA HIROKI, ONODERA, HIROKI, ONODERA, HIROKI, C/O YAMAHA HATSUDOKI K.K.
Applicants: YAMAHA MOTOR CO LTD, YAMAHA HATSUDOKI KABUSHIKI KAISHA
Application year: 1990
Main classification: F01L1
IPC codes: F02B23, F01L1, F02F1, F02B1