Valve system for a multi-valve internal combustion engine

Abstract: A valve system for a multiple valve internal combustion engine that permits a low engine height even though two of the valves (101; 99,102) reciprocate along axes (A,B) that are not parallel to each other. However, the configuration is such that the loading on the valve actuating mechanism and specifically the followers 143 and tips of the valves is minimized and so that wear on the tips of the valves is equalized.

Description: The present invention relates to a valve system for a multi-valve internal combustion engine and more particularly to an improved valve operating system which enables to avoid an uneven wear within said system and moreover, enables to reduce the engine height by reducing the height of the valve operating arrangement. More specifically the present invention relates to a valve system for a multi-valve internal combustion engine, comprising first and second valves which reciprocate between closed and opened positions along their first and second reciprocal axes, said reciprocal axes extend inclined at different acute angles to a plane containing the axis of an associated cylinder of the engine, said first valve defining a first acute angle to said plane whereas said second valve defines a second acute angle to said plane, said first acute angle being less than said second acute angle, a rocker arm means for operating said valves, said rocker arm means being pivotable about a rocker arm axis, said rocker arm means having respective first and second follower portions engaging the tips of the valve stems of the first and second valves, said tips being disposed substantially in a common plane with said rocking arm axis when said first and second valves are in their closed positions. It has been recognised that the performance of an internal combustion engine can be improved by increasing the number of intake valves for the engine. The use of two intake valves for a high performance engine has been widely accepted. Although an even greater number of intake valves may improve the induction efficiency there are some difficulties in providing more than two intake valves for a given cylinder, said difficulties, however, can be overcome by selecting a different angle of inclination of reciprocal axes of a given pair of intake valves or even a group of three intake valves among two of them disposed in a common plane defining an acute angle with the axis of the cylinder bore whereas the third valve disposed as a center valve between the two other side intake valves is disposed more steeply such that the reciprocal axis of said center valve defines a smaller angle of inclination to the axis of the cylinder bore than the other intake valves. In such a valve operating arrangement, generally the side intake valves and the center intake valve are disposed perpendicularly to a camshaft and a rocker arm shaft which is disposed to pivotally support at least two rocker arms adapted to operate the valves in response to the rotational position of the associated cams of the camshaft. Conventionally, the afore-indicated valve operated arrangement is designed in such a manner that the more upright center intake valve has an upper end which is positioned at a level high than the upper ends of the both side intake valves. Moreover, it is common practise that the respective rocker am is rocked through the controlling camshaft both up and down through an equal angle i.e. at an equal amount upwards and downwards with respect to a reference rocking position which is determined to provide an angle of 90° in between the axis of the valve stem and a notional action line connecting the rocking axis of the rocking arm shaft to the point of contact in between the valve stem and the rocker am operating member engaging said tip end, respectively. Even though the afore-described system operates satisfactorily with the reference rocking position sub-dividing the valve operating stroke in equal upwards and downwards lift portions such a layout of the valve operating arrangement is relatively space consuming, specifically in view of the tip end of the center intake valve stem being positioned higher than the tip ends of the side intake valve stems, respectively. Accordingly, the increased height of the valve operating arrangement adds to the overall height of the engine which should be kept as low as possible. Moreover, in some cases, an uneven wear at the engaging surface of the tip end of the valve stem which is in abuttingly depressing contact with an adjusting screw disposed at the operating end of the rocker arm frequently occurs, said adjusting screw having usually a spherical contact surface to establish the point of contact with the tip end of the valve stem. Considering the travel of the point of contact between the adjusting screw and the valve stem along the engaging surface thereof to be substantially perpendicular to the rocking axis of the associated rocker arm, it has been usual so far to position the point of contact on the axis of the valve stem, i.e. on the reciprocal axis of the valve selecting the transitional reference rocking position as a reference position for said positioning. In EP-A1-0 237 295 a five-valve type internal combustion engine is shown, wherein the tip of the valve stem of a central intake valve, disposesd between two lateral intake valves extends beyond the tips of the stems of the lateral intake valves, increasing the height of the engine. If the height of the tip of the center intake valve above the cylinder head sealing surface is reduced, than the angular relationship of the intake valves can become disadvantageous and give rise to added stress on the valve actuating components. From US 4660 529 and also US 4624 222 intake valve rocker arm arrangements of the type described at the beginning are known wherein the angle between the valve stem axes and said notional action line connecting the rocking axis to said point of contact between the valve stem and the rocking arm starts from a right or even obtuse angle when the valve is in closed position and then progresses to an obtuse angle when the valve is opened, causing a comparatively high cylinder head construction and also substantially increasing the wear and stress on the components. From JP-A-6111407 it is known to design a rocker arm valve arrangement in such manner as to minimize the sliding distance of a point of contact between a rocker arm and the tip of a valve stem in order to decrease the lateral load of the valve. Accordingly, the offsets from the reciprocal axis of the valve stem in both the valve opening and valve closing position are equidistant and on the same side so that during a single rotation of the camshaft causing a single reciprocation of the valve the point of contact four times passes the same locations leading to wear of the contacting surfaces. A similar construction is disclosed by US 4 809 663 wherein the points of contact between the rocker arm and the tip of the valve stem in both opening and closing position of the valve lie on the same side with respect to the reciprocal axis of the valve. Accordingly, it is an objective of the present invention to provide an improved valve system for a multi-valve internal combustion engine, preferably for a five-valve engine, as indicated above enabling to reduce the height of the valve-operating arrangement and, accordingly, of the entire engine assuring a high durability and smooth operation of the valves as well. Moreover, the intended valve system should simultaneously provide the opportunity to influence the travelling of the point of contact in between the valve stem of each of the valves and the associated rocker arm means in such a manner that an uneven wear of the tip end of the respective valve stem can be prevented by appropriately locating the point of contact in response to the positional relationship in between each of the valves and the associated bearing structure of the rocker arms. In order to accomplish the afore-indicated objective, there is provided a valve system for a multi-valve internal combustion engine of the type as indicated above which is improved in that a transitional reference rocking position for each of the valves is determined by an angle of action of 90° connecting the rocking arm axis to the point of contact between follower portions and the tips of the valve stems, and a reciprocal axis of the first and second valves, and that the follower portions comprise spherical contact portions to establish said points of contact with the tip end of the associated valve, said points of contact are substantially equidistantly offset oppositely with respect to the reciprocal axis of said valve in both the valve closing and valve opening positions of the respective valve. Within the meaning of the present invention, the term "common plane" (or a corresponding term "generally on an identical plane") used to define the location of the contact points including the rocking axis of the rocking arm shaft also covers a layout which results in some gap occurring between the contact points of different valves caused in case where the inclination angles of the valves are different from one another considering the contact section of each of the contact portions of the rocker arms pushing the tip end of the valve stems, respectively, to be generally formed spherically. In such a case, even if the points of contact have been set on a strictly identical plane in the fully closed valve condition, such a slight gap is caused between said points of contact and such a notional common plane. Accordingly, such a case is considered to be covered by the teaching of the present invention as well and in any case the term "common plane" or "identical plane" whenever used in this application such small deviations from the precise state are considered to be included as well. Accordingly, the valve operating arrangement according to the present invention ensures those valves having a different inclination to an axis of a cylinder bore, to be simultaneously moved with the rocking motion of the rocker arms as the upper ends of all valves are located in such a manner that all points of contact to the rocker arms are positioned at least nearly on an identical plane including the rocking axis. Accordingly, those valves having different inclination are moved from their fully closed states through the transitional reference rocking position which is different for valves of different inclination and is characterized through an angle of 90° being defined between the respective reciprocal axis of each of the valves and a line connecting the tip end of the valve stems to the rocking axis, respectively, to their fully opened conditions. For each of the valves the points of contact of the spherical contact portions of the push members of the rocker arms with the tip ends of the valve stems are equidistantly offset oppositely with respect to the reciprocal axis of each of the valves in both the valve closing and valve opening positions. In this way, the point of contact of the push member of the respective rocker arm travels on the engaging surface (tip end of the valve stem) of the valve from the side closer to the rocking axis of the associated rocker arm to the side remoter from said rocking axis than the reciprocal axis of the valve and, accordingly, the push member will evenly engage the entire engaging surface of the tip end of the valve stem of each of the valves and an uneven wear of said engaging surface can be prevented, adding to an improvement of the durability of the valve operating arrangement. The latter aspect is specifically obtained by means of that the point of contact between the valve operating push member and the associated operating tip end of the valve stem of the relevant poppet valve established when the valve assumes the reference rocking position is selected such that the amount of offsetting the point of contact from the associated reciprocal axis of the valve to a side remoter from or closer to the associated rocker axis is selected in response to the different angle of inclination of said valve relative to the axis of the cylinder bore. In case the diameter of the valve stem of each of the valves is relatively small and, accordingly, the area of its engaging surface at the tip end of the valve stem is correspondingly small in particular with multi-cylinder engines or engines establishing small displacement, a design according to the present invention considerably improves the durability and accurate operation of the valve operating arrangement. Although the lift of the rocker arm or rocker angle in between a rocker reference position and the fully closed state of the valve or the fully open state of the valve clearly differs for valves of different inclination the invention enables to equally divide the total travel of the point of contact along the tip end surface of the valve stem between the fully closed valve state and the fully opened valve state to both sides relative to the reciprocal axis of the respective valve. According to a preferred embodiment of the present invention a ratio of the rocker angles which are the angles between a tangent to the path of motion of a rocker arm and the reciprocal axis of the respective valves, between the opening and closing valve positions with respect to the reference rocking position differs depending on the angle of inclination of the reciprocal axes of the valves to the axis of the cylinder bore, respectively. Moreover, as the rocker angle defined between the reference rocking position and the valve closing position of the valve that defines a smaller acute angle of inclination to the cylinder axis, than the other valves, i.e. which is disposed in a more upright position than the other valves, is smaller than the rocker angle between the reference rocking position and the valve opening position of said valve, an upward movement thereof beyond the reference rocking position into the fully closing condition of the valve is relatively small and, accordingly, the valve operating arrangement exhibits a lower height adding to restrain the increase of the interior height of the engine. In accordance with another feature of the invention, the angle between a line passing between the point of contact of the first follower with the tip of the first valve and the rocker arm axis and the first reciprocal axis passes from an acute angle when the first valve is in its closed position to a right angle before the first valve is one half open and to an obtuse angle when the first valve is in its fully opened position. In accordance with another feature of the invention, the point of contact of the first follower with the tip of the first valve lies on one side of the first reciprocal axis when the first valve is closed and at an equal distance on the other side of the first axis when the first valve in fully opened. Other preferred embodiments of the present invention are set out in the subclaims. Further objectives, features and advantages of the present invention will become apparent from the following description of a specific embodiment thereof in conjunction with the accompanied points: Figure 1 is a partial side elevational view of a motorcycle powered by an internal combustion engine constructed in accordance with the first embodiment of the invention, Figure 2 is a top plan view, with portions broken away, showing the cylinder head assembly of th engine with portions shown in section, and the cam cover removed, Figure 3 is a cross sectional view of the complete cylinder head assembly and a portion of the associated cylinder block taken along the line 3-3 of Figure 2. Figure 4 is a cross sectional view taken along the line 4-4 of Figure 2. Figure 5 is a cross sectional view of the cylinder head taken through the intake and exhaust ports to show the configuration of their passages. Figure 6 is a side elevational view, with portions broken away, on a further enlarged scale in part similar to Figures 3 and 4 and shows the relationship between the rocker arms followers and intake valves. Figure 7 is a still further enlarged view showing the relationship between the follower and tip of the center intake valve during its opening and closing operation. Figure 8 is a further enlarged view, in part similar to Figure 7, showing the relationship between the follower and the side intake valves. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Referring first to Figure 1, a motorcycle powered by an internal combusion engine constructed in accordance with an embodiment of the invention is identified generally by the reference numeral 21. The invention is described in conjunction with a motorcycle since it has particular utility in conjunction with such this type of vehicle. It is to be understood, however, that certain facets of the invention may be utilized in conjunction with internal combusion engines that power other types of vehicles or, for that matter, other applications for internal combustion engines. The motorcycle 21 includes a welded frame assembly 22 having a head pipe 23 that journals a front fork 24 for steering movement. A front wheel (not shown) is journaled by the front fork 24 in a known manner. The frame 22 further includes a main frame tube 25, a down tube 26, a seat rail 27 and a seat pillar 28. At the lower end of the frame, an underguard 29 spans the down tube 26 and the seat pillar 28. A fuel tank 31 is positioned behind the head pipe 23 and ahead of a seat 32 that is carried by the seat rail 27. A small body assembly comprised of a side cover for the tank 31 and air scoop 33, a side covering for the lower portion of the seat 34 and a roar cover 35 are suitably affixed to the frame 22. A trailing arm 36 suspends a rear wheel 37 from the frame assembly in a suitable manner, including a combined spring shock absorber 38 that lies generally on the longitudinal center plane of the motorcycle 21. The rear wheel 37 is powered by an engine unit 39 which is comprised of a water cooled, single cylinder, four cycle, five valve, single overhead cam engine. A crankcase assembly 41 of the engine unit 39 contains a change speed transmission which is driven by the engine crankshaft and which drives the rear wheel 37 through a chain 42. Although the details of the engine unit 39 and specifically the engine portion of it will be described by references to the remaining figures, the engine unit 39 includes a cylinder head 43, a cam cover 44 and a cylinder block 45 in addition to the crankcase 41. This engine unit is mounted in the frame 22 with the cylinder block 45 inclined slightly forward in a suitable manner by means including a support pipe 46 that is positioned beneath the main pipe 25 and which is joined to the main pipe 25 and the down tube 26. As will become apparent, the engine unit 39 has a pair of forwardly facing exhaust ports from which a pair of exhaust pipes 47 and 48 extend into an exhaust system, indicated generally by the reference numeral 49 and which includes a side mounted muffler 51. The engine unit 39 also includes an induction system including in air box which is not shown in Figure 1 that supplies air to a pair of carburetors which serve three rearwardly facing exhaust ports, as will be described by reference to the remaining figures. The induction system (Figure 5) includes a primary induction system 52 including a primary carburetor 53 and a secondary system 54 including a secondary carburetor 55. Both carburetors 53 and 55 draw air from the aforenoted air box. The configuration of the components is such that the exhaust pipes 47 and 48 extends on opposite sides of the down tube 26 while the air box encircles the spring shock absorber unit 38 so as to provide a very compact assembly and yet one which will not interfere with the basic construction of the motorcycle or adversely affect the design of the engine. Referring now to Figures 3 and 4, it will be noted that the cylinder block 45 is formed with a cylinder bore 59 which is formed by a pressed or cast in liner 61. A piston (not shown) reciprocates within the cylinder bore 59 and drives the crankshaft (not shown) contained within the crankcase 41 in a well known manner. Since the invention deals primarily with the cylinder head 43 and valve train associated with it, those components of the engine which are considered to be conventional have not been illustrated and further description of them is not believed to be necessary to enable those skilled in the art to practice the invention. The cylinder head 43 has a lower surface 62 that is sealingly engaged with a head gasket 63 so as to provide a seal with the cylinder block 45 around the cylinder bore 59. In addition, the cylinder head 43 is formed with a generally central recess 64 which recess is defined by a surface 65 surrounded by the lower cylinder head surface 62. This recess has a generally spherical configuration although it assumes a pent roof type of configuration as may be best seen in Figures 3 and 4. Referring now primarily to Figures 2 through 5, the cylinder head 43 is formed with a pair of forwardly facing exhaust passages 66 and 67 each of which extends from the combustion chamber 66 through a valve seat 68 formed by a pressed in insert 69. These exhaust passages 66 and 67 terminate in forwardly facing exhaust ports 71 to which the respective exhaust pipes 47 and 48 are affixed in a suitable manner. A pair of exhaust valves 72 each of which has a head portion 73 and a stem portion 74 are slideably supported for reciprocation within the cylinder head 43 by a respective pressed in valve guide 75. The exhaust valves 72 reciprocate within a common plane that is inclined at an acute angle to a plane containing the axis D (Figure 2) of the cylinder bore 59. The axes of reciprocation also lie in planes that are parallel to each other and to the cylinder bore axis D. This facilitates operation of the valve although they may be slightly inclined if desired. The exhaust valves 72 are urged to their closed positions by means of respective coil compression springs 76 that engage wear plates 77 bearing against the cylinder head 43 and keeper retainer assemblies 78 affixed in a known manner to the upper ends of the exhaust valve stems 74. The exhaust valves 72 are opened in a manner which will be described. It should be noted that the exhaust passages 66 and 67 are disposed at an angle to the plane containing the cylinder bore axis D and thus diverge from a plane perpendicular to this plane and also passing through the cylinder bore axis D. This permits the exhaust pipes 47 and 48 to clear the down tube 26 and also provides a better and less flow resistant path for the entire exhaust system. A spark plug well 81 is formed in the cylinder head 43 between the exhaust passages 66 and 67 and terminates at a threaded opening 82 in which a spark plug 83 is received. The spark plug 83 is disposed so that its gap lies substantially on the cylinder bore axis D. A corresponding well 64 is formed in the cam cover 44 so as to facilitate insertion and removal of the spark plug 83 without removing the cam cover 44. The spark plug 63 is fired by a suitable ignition system. A primary intake passage 85 extends through the opposite side of the cylinder head 43 from the exhaust side already described. The passage 85 extends from an intake port 86 formed in the side of the cylinder head 43 and terminates at a valve seat 87 formed by a pressed in insert. As may be best seen in Figure 5, the primary intake passage 85 has a central axis that is generally perpendicular to the aforenoted plane containing the cylinder bore axis D and hence as a relatively short length from its intake port 86 to its valve seat 87. As a result, good, low and mid range performance and good response may be achieved. This passage 85 and its central axis is disposed at a distance from a plane which plane contains the axis of the cylinder bore D and is perpendicular to the aforenoted plane. The significance of this will be as described. A siamese type secondary intake passage 88 extends from an intake port 89 formed in the intake side of the cylinder head 43 and branches into a pair of passages 91 and 92 each of which terminates at a respective valve seat comprised of a center valve seat 93 and a side valve seat 94. The center of the intake port 89 as extended by a spacer, to be described, is disposed at a distance from the place which distance is the same as the distance of the primary intake port 86. The carburetors 53 and 55 are affixed to these respective intake ports 86 and 89 through the intermediary of respective spacers 95 and 96 (Figure 5) which have respective passage ways 97 and 98 that form extensions of the cylinder head intake passages 85 and 88. By utilizing the spacers it is possible to have this equal distance between the centers of the ports even though the actual port 89 is closer to the perpendicular plane than is the inlet of the passage 98 and its spacer. This construction permits the induction system to clear the shock absorber and spring assembly 38 and avoids interference between the carburetors 53 and 55. A central effective line or bisector of the secondary intake passage 88 lies at an acute angle to the perpendicular plane while the portion 92 extends generally perpendicularly to the plane containing the axis of the cylinder bore D as aforenoted. As a result, the intake passages serving the side valve seats 87 and 94 are relatively short while the passage 91 is somewhat longer. This variation in length can be employed so as to achieve the desired flow pattern in the engine as will be described. The carburetor 53 is sized and jetted and has a throttle valve (not shown) that functions to control both the low speed and mid range performance of the engine as well as the high speed performance. The throttle valve (not shown) of the carburetor 55 is operated in a staged sequence with the carburetor of the throttle valve 53 and the carburetor 55 may only have high speed circuits since this carburetor supplies the fuel air charge only to the engine under high speed operation. Either a staged linkage system or some form of load or speed responsive control (such as a vacuum responsive servo motor) can be employed for operating the throttle valve of the carburetor 55 in this staged sequence. First, second and third poppet type intake valves 99, 101 and 102 have respective head portions 103, 104 and 105 which cooperate with the valve seats 87, 93 and 94 for controlling the flow through them. The intake valves 99 and 102 are side valves and have their respective stem portions 106 and 107 slidable supported in guides, to be described, for reciprocation about axes B which are in a common plane disposed at an acute angle ϑ s (Figure 6) to the plane containing the cylinder bore axis D which acute angle may be substantially the same as the acute angle of reciprocation of the exhaust valves 72. The center exhaust valve 101 has its stem portion 108 supported for reciprocation about an axis A which is disposed also at an acute angle ϑ c (Figure 6) to the aforenoted plane containing the cylinder bore axis D but which acute angle is lesser than the angle of reciprocation B of the valves 99 and 101. The angular disposition of the reciprocal axes A and B is such that these axes intersect a line C which is parallel to the plane containing the cylinder bore axis D but which is spaced from the tips of the individual intake valves 99, 101 and 102. As a result of this, the angular configuration of the side valves 99 and 102 relative to the center valve 101 is relatively small. This configuration permits the adjacent area between the intake valves to be relatively smooth and thus provide a smooth combustion chamber configuration that will avoid hot spots and still permit a generally spherical configuration. The axes A and B of reciprocation of the intake valves 101 and 99 and 102 all lie in parallel planes which planes are parallel to the axis of the cylinder bore D. This permits ease of operation. However, if desired, these axes may be slightly skewed from parallel planes as is also possible with the exhaust valve 72, as previously noted. The valve guides that slidable support the stems 106, 107 and 108 of the intake valves 99, 102 and 101 are each indicated by the reference numeral 109. Intake valve springs 111 engage bearing plates 112 that bear against the cylinder head 43 and keeper retainer assemblies 113 affixed to the upper ends of the respective valve stems for urging the intake valves 99, 101 and 102 to their closed positions. The intake valves 99, 101 and 102 are operated by means of rocker arm assemblies to be described. The exhaust valves 72 and intake valves 99, 101 and 102 are all operated by means of a single overhead camshaft 114. The camshaft 114 is journaled, in a manner to be described, for rotation about an axis E which is offset to the intake side of the cylinder head from the cylinder bore axis D by a distance O1 (Figure 2). The axis E is parallel to the plane aforementioned that contains the axis of the cylinder bore D. The camshaft 114 has end bearing surfaces that are journaled in bearing surfaces 115 and 116 formed by the cylinder head 43 and corresponding bearing surfaces formed by the cam cover 44. In addition, there is provided a central bearing surface on the camshaft 114 that is journaled by a bearing surface 117 formed in the cylinder head 43. A corresponding bearing surface is partially formed in the cam cover 44 and has its center offset a discance O2 from the cylinder bore axis D so as to provide clearance for other components of the cylinder head assembly to be described and specifically one of the rocker arms. The camshaft 114 is driven from the engine crankshaft by means of a drive chain (not shown) and sprocket 118 that is affixed to one end of the camshaft. A decompression device 119 is associated with the sprocket 118 and serves to reduce the starting torque on the engine by lifting slightly one of the exhaust valves 72 during starting operation. A pair of exhaust cam lobes 121 are formed at the outer ends of the camshaft 114 adjacent the bearings that engage the cylinder head bearing surfaces 115 and 116. These cam lobes 121 are engaged by follower surfaces 122 of exhaust rocker arms 123. These exhaust rocker arms 123 are journaled on stub rocker arm shafts 124 each of which is supported by a boss 125 formed on the inner surface of the cam cover 44. The outer ends of the rocker arms 123 are provided with taped portions 126 that receive adjusting screws 127 for providing lash adjustment between the exhaust rocker arms 123 and the tips of the stems 74 of the exhaust valves 72 for clearance adjustment. Access openings 128 are provided in the cam cover 44 for facilitating valve adjustment without removal of the cam cover 44. These access openings 128 are normally closed by closure plugs 129 which are affixed in place in a suitable manner. In addition to the exhaust cam lobes 121, the camshaft 114 is provided with a first intake cam lobe 131 and a second intake cam lobs 132 which lobes 131 and 132 are disposed on opposite sides of the central camshaft bearing surface which is journaled in the cylinder head bearing surface 117. The cam lobes 131 and 132 cooperate with respective rocker arms 133 and 134 for opening the intake valves 99, 101 and 102, respectively, in a manner to be described. The rocker arms 133 and 134 are both journaled on a single rocker arm shaft 135 that is journaled within the bearing surfaces formed by lugs 136 of the cam cover 44. These lugs 136 also form the bearing surfaces which cooperate with the cylinder head bearing surfaces 115, 116 and 117 for journaling the camshaft 114. It has already been noted that the intake valves 99 and 102 reciprocate about respective reciprocal axes B and the intake valve 101 reciprocates about the axis A. As has been noted that the axes A and B intersect at a line C which is parallel to the aforenoted plane containing the cylinder bore axis D which point C is spaced from the tips of all of the intake valves. The center intake valve 101 has its tip spaced outwardly in a horizontal direction a greater distance 12' than the tips of the side intake valves 99 and 102 which valves lie at the distance 11' from the plane and also from the pivotally axes of the respective rocker arms 133 and 134. Also, it should be noted that the center intake valve 101 and specifically its axis B is at a perpendicular distance 11 from the rocker arm shaft 113 whereas the axes of reciprocation A of the other intake valves is a perpendicular distance 12 from this axis. This distance 11 is less than the distance 12. These differences in distance permit the smooth combustion chamber configuration previously noted and also permit a variation in the amount of lift for the two valves operated from the same cam lobe and same rocker arm, this being the cam lobe 132 and rocker arm 134 in this embodiment. As a result of the greater distance to the center intake valve 101 than the side intake valves 99 and 102 a greater amount of lift may be achieved for this valve than the other two. As a result, there can be generated more air flow through the center intake passage than the side intake passages. However, since the center intake passage is longer than that of the side intake passages due to the fact that the side intakes passages extend perpendicularly whereas the center intake passages disposed at an angle, it is also possible to obtain equal flows. However, the geometric relationship described permits the designer to achieve desired flow patterns within the combustion chamber under varying running conditions. Although the tip of the center intake valves 101 is spaced different distances from the tips of the side intake valves 99 and 102 from the rocker arm axis E and also from the cylinder bore axis D, the tips of all of the stems of the intake valves 99, 101 and 102 lie at substantially the same vertical distance above the cylinder head sealing surface 62 and lie in a common plane with the pivot axis f of the rocker arms 133 and 134. This is done so as to reduce the overall height of the cylinder head assembly and of the engine, as will be described. Rocker arm 133 has an enlarged taped portion 137 that receives an adjusting screw 138 that cooperates with the tip of the stem 106 of the intake valve 99 that is associated with the primary intake passage 85. As has been previously noted, the intake passage 85 is designed primarily to accommodate low and mid range performance and hence the cam lobe 131 may be configured to provide a lift characteristic that is better tuned for low speed performance. The rocker arm 134 has a pair of bifurcated arms 139 and 141 with the arm 139 having a threaded end 142 that received an adjusting screw 143 that cooperates with the tip of the stem 108 of the center intake valve 101. The arm 141 has an enlarged taped portion 144 that receives an adjusting screw 145 that cooperates with the tip of the valve stem 107 of the intake valve 102 for clearance adjustment. The cam cover 44 is provided with elongated opening 146 for accessing each of the adjusting screws 138, 143 and 145 so that the valve adjustment may be made without removing the cam cover. A removal closure plug 147 normally closes the opening 146 and is removed for servicing. The cam lobe 132 associated with the rocker arm assembly 134 is configured so as to provide a greater degree of lift for both of the valves and also a longer event. This is because the rocker arm 134 is associated with the secondary or high speed intake passage 88 of the cylinder head 43. As has also be noted, due to the difference in length of the arms 139 and 141 the center intake valve 101 may have an even greater lift than the side intake valve 102. This configuration may be done so as to improve or generate swirl in the combustion chamber. Of course and as has been previously noted, those designers in the art may incorporate these features to provide different types of valve operation and different types of tuning. The cam cover 44 is affixed to the cylinder head 43 by a plurality of fasteners, most of which are accessible from externally of the cam cover 44. However, the cam cover 44 is provided with an inwardly extending bosses 148 (Figures 2 - 4) into which threaded fasteners 149 are received for affixing the cam cover 44 to the cylinder head 43. These fasteners 149 are readily accessible through the surface opening 146 when the cover 147 is removed. A corresponding lug 151 is formed on the exterior of the cam cover 44 between the two exhaust rocker arms and is secured to the cylinder head 43 by a threaded fastener 152. Further threaded fasteners, indicated by the reference numerals 153 not only serve to hold the cam cover 44 to the cylinder head 43 but also serve to prevent rotation of the rocker arm shaft 135. Other threaded fasteners 154 serve to hold the cam cover 44 to the cylinder head 43 and also serve to prevent rotation of the rocker arm shafts 124. Further threaded fasteners 155 are fastened into the cam cover and serve only the purpose of preventing rotation of the rocker arm shafts 124. It has been noted that the intake valves 99, 101 and 102 may have the same head diameter and the center intake valve 101 may have a greater lift than the others so as to compensate for the longer flow path to it and the greater flow resistance. The same effect can be provided by reducing the head diameters of center intake valve 101. This will permit the use of smaller diameter valve springs and so on for this valve and thus facilitate the freedom of design in the valve operating system. Because two valves are operated by the rocker arm 134 while only a single valve is operated by the rocker arm 133, the stress on the rocker arm 134 is larger. However, because the cam shaft 134 is shifted to the intake side of the engine this stress can be reduced by reducing the total length of the rocker arms. It has been noted that the tips of the stems of the intake valves 99, 101 and 102 all lie substantially on a common plane that contains the pivotal axis f of the rocker arms 133 and 134. However, this is done without substantially increasing the wear or loading on the valve actuating assembly and specifically the adjusting screws 143 and 145 and the tips of the stems of those valves. This relationship may be best understood by reference to Figures 6 through 8. Referring first to Figures 6 and 7, the relationship between the adjusting screw 143 and the center intake valve 101 may be best understood. It should be noted that the adjusting screw 143 has a spherical end portion 156 which when the intake valve 101 is in its fully closed position has its line of action G is disposed at an, acute angle to the tip of the intake valve 101. The point of contact is indicated as T c1 to one side of the reciprocal axis A and toward the rocker arm pivot axis f. A line "a" circumscribes the plane in which the rocker arm axis f and the tips of the stems of the valves 99, 101 and 102 lie when they are in their closed position. As the rocker arm 134 pivots to open the intake valve 101, there will be a rolling action between the spherical end 143 and the tip of the stem of the valve 101 through an angle ϑ as shown in Figure 7 which corresponds to the angular movement of the rocker arm 134 as the valve 101 is lifted. At an angle ϑ₃, indicated by the broken line "b" the line of action G of the adjusting screw 143 will be disposed parallel to or in line with the reciprocal axis A and perpendicular to the plane b containing the tip of the valve stem and the rocker arm axis f. Continued movement then causes the valve 101 to continue opening as the rotation of the rocker arm 134 moves through the angle ϑ₄. During this movement, the point of contact of the spherical end 143 with the stem 101 moves to the point T c3 on the left hand or outer side of the reciprocal axis A is seen in Figure 7. It should be noted that the points T c1 and T c3 are disposed at distances which are equal distance from the reciprocal axis A and this make more uniform the wear over the tip of the valve stem. When the angle is at a right angle, the point of contact is at the point T c2 which is at a distance D C from the plane A and still on the right hand side. That is, when the valve 101 is moved from its closed position to the point where the adjusting screw axis G is parallel to the axis A, the tip will move the distance D c1 which is still a distance D c displaced from the center axis A. Continued rotation causes the movement through the distance D c2 to affect full opening of the valve. As a result of this operation, it is possible to still minimize wear but keep the overall height of the engine low. A somewhat similar situation exists between the adjusting screw 138 and 145 and the tips of the valves 99 and 102 and shown in Figures 6 and 8. In this condition, the angular relationship between the line of action H of the adjusting screw 138 or 145 and the plane A is at an acute angle and the point of contact T s1 is to the right side of the line of action B of the valve 99 and 102. On this side, the adjusting screw 138 and 145 rotates through an angle ϑ until the point of contact is at the point T s3 at a distance D f to the left hand side of the line of action B wherein it is parallel to this axis. Continued opening movement causes the tip to move to the point T s3 which is equal distance from the line of action B as the point T s1 . As a result, even though the right angle line of action is offset from the center of the tip of the stems of the valves 99 and 101 there will be uniform wear across the face of the valve stems. In the illustrated embodiment, the valve 99 is operated by a single rocker arm 133 while the valves 101 and 102 are both operated by a single rocker arm 134. A reverse condition can be employed and also each valve can be operated by its own rocker arm. However, the described geometric relationship permits uniform wear and reduced loading on the valve actuating elements without increasing the height of the engine. The invention has been described in conjunction with a single cylinder but it should be readily apparent to those skilled in the art how the invention can be practiced in conjunction with multiple cylinder engines.

Claims: A valve system for a multi-valve internal combustion engine, comprising first and second intake valves (99,101,102) which reciprocate between closed and opened positions along their first and second reciprocal axes (A,B), said reciprocal axes (A,B) extend inclined at different acute angles to a plane containing the axis of an associated cylinder of the engine, said first valve (101) defining a first acute angle (ϑ c ) to said plane whereas said second valve (99,102) defines a second acute angle (ϑ s ) to said plane, said first acute angle (ϑ c ) being less than said second acute angle (ϑ s ), a rocker arm means (133,134) for operating said valves (99,101,102), said rocker arm means (133,134) being pivotable about a rocker arm axis (f), said rocker arm means (133,134) having respective first and second follower portions engaging the tips of the valve stems of the first and second valves (99,101,102), said tips being disposed substantially in a common plane with said rocking arm axis (f) when said first and second valves (99,101,102) are in their closed positions, characterized in that a transitional reference rocking position for each of the valves (99,101,102) is determined by an angle of action of 90° connecting the rocking arm axis (f) to the point of contact (T s1 ,T c1 ) between follower portions and the tips of the valve stems (106, 107, 108), and a reciprocal axis (A,B) of the first and second valves (99,101,102), and that the follower portions comprise spherical contact portions (156) to establish said points of contact (T s1 ,T s3 ; T c1 ,T c3 ) with the tip end of the associated valve (99, 101, 102), said points of contact (T s1 ,T s3 ; T c1 ,T c3 ) are substantially equidistantly offset oppositely with respect to the reciprocal axis (A,B) of said valve (99,101,102) in both the valve closing and valve opening positions (A,D) of the respective valve (99,101,102). A valve system for a multi-valve internal combustion engine as claimed in Claim 1, characterized in that a ratio of the rocker angles (ϑ₁,ϑ₂;ϑ₃,ϑ₄) between the valve closing and opening positions (a,d) with respect to the reference rocking position (b,c) differs depending on the angle of inclination (ϑ S ,ϑ C ) of the reciprocal axes (A,B) of the first and second valves (99,101,102) to the cylinder bore axis (D), respectively. A valve system for a multi-valve internal combustion engine as claimed in one of Claims 1 or 2, characterized in that the angle (ϑ) between a line (a) passing between the point of contact of said first follower with said tip of said first valve (101) intersecting said rocker arm axis (f) and said first reciprocal axis (A) passing from an acute angle (ϑ') when said first valve (101) is in its closed position to a right angle before said first valve (101) is one half opened and to an obtuse angle when said first valve (101) is fully opened. A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 3, characterized in that the rocker arms means (133, 134) comprises a single rocker arm (134) having a pair of arms (139,141) each carrying a respective one of the first and second followers. A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 4, characterized in that the rocker arm means (133, 134) comprises separate rocker arms. A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 5, characterized in that said engine is a five-valve engine, comprising three intake valves (99,101,102) and two exhaust valves (72) wherein said first valve (101) is a central intake valve disposed between said second valves (99, 102) forming lateral intake valves wherein the angle of inclination (ϑ S ) of the reciprocal axis (B) of the lateral second valves (99,102) is substantially equal whereas the central first valve (101) is disposed more steeply to form an angle of inclination (ϑ C ) between its reciprocal axis (A) and said cylinder bore axis (D) which is smaller than the acute angle of inclination (ϑ S ) formed by the second valves (99,102). A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 6, characterized in that the rocker angle (ϑ₁) defined between the reference rocking position (c) and the valve closing position (a) for the second valve (99,102) is larger than the rocker angle (ϑ₂) between the reference rocking position (c) and the valve opening position (d) of said second valve (99,102). A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 7, characterized in that the rocker angle (ϑ₃) defined between the reference rocking position (b) and the valve closing position (a) for the first valve (101) is smaller than the rocker angle (ϑ₄) between the reference rocking position (b) and the valve opening position of said first valve (101). A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 8, characterized in that the valve operating follower portions are adjusting screws (138,143,145) that cooperate with the tip of the valve stems (106,107,108) of the first and second valves (99,101,102), respectively, said adjusting screws (138,143,145) having a spherical contact portion (156) abuttingly contacting the tip end of the valve stem (106,107,108) of each of the first and second valves (99,101,102) A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 9, characterized in that a third valve (99,102) is provided to be supported for reciprocation relative to the cylinder head assembly (43) along an axis (B) that lies in a common plane with the reciprocal axis (B) of the second valve (102,99) of the first and second valves (99,101,102) operated by said rocker arm means (133,134). A valve system for a multi-valve internal combustion engine as claimed in Claim 10, characterized in that the rocker arm means (133,134) includes a third follower means for operating the third valve (99, 102). A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 11, characterized in that the rocker arm means comprises a first rocker arm (134) carrying the first and second follower means and a second rocker arm (133) carrying the third follower means. A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 12, characterized in that each of the follower means is carried by a separate rocker arm. A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 13, characterized in that the distance (ℓ₂) between the rocker arm axis (f) and the reciprocal axis (A) of the first valve (101) is greater than the distance (ℓ₁) between the rocker arm axis (f) and the reciprocal axis (B) of the second or third valve (99,102). A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 2 to 14, characterized in that in the reference rocking position (c) the point of contact (T S2 ) between the valve operating follower portion and the associated operating tip end of the valve stem (106, 108) of the second or third valve (99,102) is spaced from the rocker axis (f) of the associated rocker arm (138,143) at a distance larger than the distance between the reciprocal axis (B) of said valve (99,102) and the rocker axis (f). A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 2 to 15, characterized in that in the reference rocking position (c) the point of contact (T C2 ) between the valve operating follower portion and the associated operating tip end of the valve stem (108) of the first valve (101) is spaced from the rocker axis (f) of the associated rocker arm (133,134) at a distance smaller than the distance between the reciprocal axis (A) of said valve (101) from the rocker axis (f). A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 16, characterized in that the point on contact of the first follower with the tip of the first valve (101) lies on one side of the first reciprocal axis (A) when the first valve (101) is in its closed position and at an equal distance on the other side of the first reciprocal axis (A) when the first valve (101) is in a fully opened position. A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 17, characterized in that the point of contact of the second follower with the tip of the second valve (99,102) lies on one side of the second reciprocal axis (B) when the second valve (99,102) is in its closed position and at an equal distance on the other side of the second reciprocal axis (B) when the second valve (99,102) is in its fully opened position. A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 18, characterized in that the tips of the stems (106,107,108) of the first and second valves (99,101,102) are disposed at different distances (ℓ₁,ℓ₂) from the rocker axis (f) of the associated rocker arm shaft (135). A valve system for a multi-valve internal combustion engine as claimed in at least one of the preceding Claims 1 to 19, characterized in that the rocker arm means comprising a pair of rocker arms (133,134) for a set of three intake valves (99,101,102), two (99, 102) of them being inclined differently from the remaining one (101), and a pair of rocker arms (123) for a set of exhaust valves (72), said rocker arms (133,134; 123) being pivotally supported about axes extending parallel to the axis (E) of the camshaft (114) such that the reciprocal axes (A,B) of the intake valves (99,101,102) being spaced at different distances (ℓ₁,ℓ₂) from the associated rocker axis (f) of the rocker arms (133,134).

Inventors: NONOGAWA KENICHI, NONOGAWA, KENICHI
Applicants: YAMAHA MOTOR CO LTD, YAMAHA HATSUDOKI KABUSHIKI KAISHA
Application year: 1990
Main classification: F01L1
IPC codes: F01L1