Cylinder head and valve arrangement of a multi-valve internal combustion engine

Abstract: The present invention relates to an internal combustion engine and more particularly to an improved high efficiency induction system for a multi-valve engine (11) which preferably is a five valve engine. According to the present invention at least one of the intake valves seats (16,17,18) is of a different diameter than the other two intake valve seats and that said intake valve seats (16,17,18) in conjunction with the intake port means (41,42,43) and the intake valves (19,21,22) are tuned such that each of the valve seats (16,17,18) provides an intake flow that has optimum powering efficiency at different engine speeds.

Description: This invention relates to an internal combustion engine comprising a cylinder head and induction system having a cylinder head assembly defining three intake valve seats all adapted to communicate with same combustion chamber of the engine, three intake valves supported for reciprocation in said cylinder head and each controlling the flow through an associated one of said intake valve seats, and intake port means formed in said cylinder head and terminating at each of said valve seats for delivering a charge to the associated combustion chamber, at least one of said intake valve seats being of a different diameter than the other ones of the intake valve seats and fuel injecting means for injecting fuel. It is well known that it is possible to improve the breathing efficiency of an internal combustion engine by utilizing multiple intake valves. By using a greater number of valves per cylinder, it is possible to increase the flow area in a given space of the engine. For this reason, four valve per cylinder engines are very popular and five valve per cylinder engines, having three intake valves per cylinder, are also becoming very popular. When the number of intake valves is increased beyond two, several problems arise. One of these problems is insuring that the valve placement is such that the valves can open to a maximum height so as to permit good flow into the cylinder and, at the same time, to maintian a small combustion chamber volume so that the compression ratio for the engine can be kept high and so that undue quenching can be reduced. United States Letters Patent 4,660,529, now reissued as RE 33,787 is an example of how five valves per cylinder may be placed to provide optimum induction efficiency and high compression ratios. Although the use of multiple intake valves provides good high speed performance, such large valve areas and low flow resistance passges normally employed therewith tend to provide high power and high speed, but may have a torque curve that has too much emphasis on high end performance. One problem that is particularly prevalent with three intake valve engines is that the center intake valve (the one furthest from a plane passing through the center of the cylinder bore axis), tends to be masked by the other intake valves and this can reduce the induction efficiency. In conjunction with improving engine performance, particularly at the lower speed ranges, there is a desirabilitiy to promote turbulence in the combustion chamber. One type of turbulence is an action called "tumble". Tumble is a type of swirl which occurs around a horizontal plane that intersects the cylinder bore axis rather than around the cylinder bore axis. That is, the charge that flows into the chamber is directed toward the side of the charter opposite from the intake valve where it will be deflected downwardly by the cylinder bore and then back across the head of the piston and upwardly on the side where the charge is introduced. With conventional, three intake valve per cylinder engines, the center intake valve is disposed too far from the center of the cylinder bore axis to generate any tumble action. When multiple valve cylinder heads are employed the valve area requires such a large recess in the cylinder head, particularly with five cr more valves per cylinder, that squish action is not possible. Squish action is the action that occurs as the piston approaches the top dead center position. This is an area where there is minimum clearance volume and the gas that is trapped in this area is forced into the larger recessed area that forms the major portion of the volume of the combustion chamber at top dead center. This effect is called "squish action". It is normally difficult to obtain any significant squish action with conventional five valve per cylinder, cylinder heads. From document EP 0 340 834 A3 a conventional intake valve arrangement is already known. An internal combustion engine comprising a cylinder head induction system having a cylinder head assembly as mentioned above is already known from document DE 36 00 408 Al. Said cylinder head comprises three intake valve seats, which have different diameters and are tuned to different engine operating ranges. A fuel injecting means having three injecting nozzles associated with each of the intake ports and the intake valve seats respectively, so as to inject fuel into each of the intake ports when the throttle valve associated with the respective intake port is opened. It is a main objective of this invention to provide an internal combustion engine having a cylinder head and induction arrangement as indicated above that will further improve the efficiency of such engines, specifically by using the five valve technology, providing a good overall torque curve throughout the entire speed and load ranges of the engine and assuring optimum induction efficiency. Moreover, the engine should allow to be preferrably developed such that sufficient tumble action and significant squish action can be obtained. In order to perform said main objective the present invention provides an internal combustion engine as indicated above wherein said intake port means comprises a first siamesed intake port having an inlet opening at one side of the cylinder head and terminating at a pair of the intake valve seats and a second intake port having an inlet opening formed at one side of the cylinder head and terminating at the remaining valve seat and, wherein said fuel injecting means comprises a single injector for injecting fuel into said siamesed intake port towards said pair of intake valve seats while said remaining intake valve seat is served by intake air only. In accordance with a preferred embodiment the intake valve seats are disposed so that at least two of the intake valve seats are considered as side intake valve seats and lie closer to a plane passing through the center of the combustion chamber than the other of the valve seats, which other valve seat comprises a center intake valve seat. A center intake port is formed in the cylinder head and terminates at the center intake valve seat. This center intake port is inclined at an acute angle to a lower sealing surface of the cylinder head and extends generally straight up to the center intake valve seat for directing a charge into the combustion chamber toward the plane. In accordance with another preferred embodiment, two of the intake valve seats are considered as side intake valve seats and these lie closer to a plane passing through the center of the combustion chamber than the other of the valve seats which comprises a center intake valve seat. In accordance with this feature of the invention, a plane passing through the center of the side intake valve seats will pass through the center intake seat. Other preferred embodiments of the present invention are laid down in the further subclaims. In the following the present invention is explained in greater detail by means of several embodiments thereof in conjunction with the accompanying drawings, wherein: Figure 1 is a cross sectional view taken through a cylinder head assembly constructed in accordance with a first embodiment of the invention and is taken generally along the line I - I of Figure 2, Figure 2 is a partial bottom plane view of the clyinder head assembly, Figure 3 is a top plane view of the clyinder head assembly with the cam cover removed and the tappet diameters shown in phantom along with the clyinder bore in this same fashion, Figure 4 is a bottom plane view of another embodiment of cylinder head assembly which does not form part of the present invention and is, in part, generally similar to the embodiment of Figure 2. Figure 1 represents a cross sectional view taken along the line 1 - 1 of this Figure also, Figure 5 is a bottom plane view of a cylinder head constructed in accordance with another embodiment and is in part similar to Figures 2 and 4, but only shows the portion of the cylinder head falling within the clyinder bore axis, Figure 6 is a bottom plane view, in part similar to Figures 2, 4, and 5, and shows another embodiment Figure 7 is a bottom plane view, in part similar to Figures 2, 4, 5 and 6, and shows still further embodiment , and Figure 8 is a bottom plane view, in part similar to Figures 2 and 4 through 7, and shows a still further embodiment. Referring now in detail to the drawings and initially to the embodiment of Figure 1 through 3, an internal combustion engine constructed in accordance with this embodiment is shown partially and is identified generally by the reference numeral 11. The engine 11 is depicted only in conjunction with a single cylinder of the engine and since the invention relates to the cylinder head assembly, indicated generally by the reference numeral 12, only the portion of the cylinder head assembly associated with a single cylinder bore is shown in the drawings. For any details of the engine 11 which are not depicted, they may be of any conventional type. The cylinder head assembly 12 is affixed to a cylinder block in any known manner and has a combustion chamber recess 14 that is associated with a cylinder bore 15 of the cylinder block 13. Basically the left hand side of the cylinder head assembly 12 is the intake side and the recess 14 is formed with three intake valve seats comprised of a center intake valve seat 16 and side intake valve seats 17 and 18. The side intake valve seats 17 and 18 lie closer to a parallel plane containing the clyinder bore axis A and extending parallel to the axis of rotation of the associated crankshaft (which plane appears also coincident with the cylinder bore axis A in Figure 1) than the center intake valve seat 16. In fact, in all illustrated embodiments the side intake valve seats 17 and 18 may extend over this center plane onto the exhaust side of the recess 14. Poppet type intake valves 19, 21 and 22 are all mounted for reciprocation in the cylinder head assembly 12 along axes defined by valve guides, one of which appears in the Figures that is associated with the center intake valve 19 and which is identified by the reference numeral 23. These intake valves 19, 21 and 22 are all urged toward their closed positions by coil compression springs 24 held in place by keeper retainer assemblies 25. These intake valves 19, 21, 22 are opened by the respective lobes 26 of an intake camshaft, indicated generally by the reference numeral 27 and which is rotatably journalled in the cylinder head assembly 12 by one or more bearing caps 28 (Figure 3). The reciprocal axes of the intake valves 19, 21 and 22 may be disposed as noted in the aforenoted United States Letters Patent RE 33,787. Briefly summarized, the axis of reciprocation of the side intake valves 21 and 22 are parallel to each other and at a greater acute angle to a plane containing the cylinder bore axis A than the axis of reciprocation of the center intake valve 19. The axes of reciprocation of the intake valves 19, 21 and 22 each lie in planes that are parallel to each other and perpendicular to the aforenoted plane containing the cylinder bore axis A. As is clearly derivable from Figure 1, the intake valves 19, 21, 22 are disposed steeper than the exhaust valves 49 and a distance of a longitudinal axis L1 of the intake camshaft 27 from the above mentioned parallel plane containing the cylinder bore axis A is remarkably shorter than the distance of the longitudinal (rotational) axis L2 of the exhaust camshaft 56 from said plane. Moreover, as is clearly shown in Figures 1 and 3, the positions of the intake and exhaust camshafts 27, 56 with respect to the cylinder bore (and combustion chamber) - or vice versa - are such that the axis L1 of the intake camshaft 26 intersects a notional plan view projection of the cylinder bore while the axis L2 of the exhaust camshaft 56 does not. Similarily, the distance of the inside bolts 28a of the bearing caps 28 of the intake camshaft 27 from said afore-indicated reference plane is considerably smaller than that of the inside bolt 57a of the bearing cap 57 of the exhaust camshaft 56. In this way, shallower inclinations of the upper walls of the combustion chamber 14 can be obtained reducing the height of the combustion chamber 14 and leading to superior burning conditions of the charge supplied to said combustion chamber 14 while similiarly rendering the engine more compact. For compacting the cylinder head and valve operating arrangement as shown in Figure 3, the two inside bolts 28a of the two spaced bearing caps portions 28 of the intake camshaft 27 have generally the same minimal distance a from a center of a spark plug bore 62 as the inside bolt 57a of the bearing cap 57 of the exhaust camshaft 56. In this way highly compacted five valve engine arrangement is obtained having minimal dimensions in transverse direction which facilitates obtaining superior sealing conditions between the cylinder block and the cylinder head. Preferably, there is a single inside bolt 57a provided between two exhaust valve actuating cam lobes 55 of the exhaust camshaft 56 and there are two inside bolts 28a alternately disposed between three intake valve actuating cam lobes 26 of the intake camshaft 27 so that said three inside bolts 57a, 28a related to one cylinder are disposed on the corners of an isosceles triangle. In accordance with another important feature of this particular embodiment, each of the intake valve seats 16, 17 and 18 and their respective heads of their associated intake valves 19, 21 and 22 are of a different size. In this embodiment, the center intake valve 19 and its associated valve seat 16 is larger than the side intake valve 22 and its intake valve seat 18 and smaller than the side intake valve 21 and its intake valve seat 17. This difference in sizing coupled with the valve actuation and porting arrangement which permits each intake valve seats 16, 17 and 18 to be tuned so as to provide optimum charging performance for a different running speed of the engine 11. This coupled with the large effective intake valve area permits not only good torque and performance at the various speeds for which the individual intake valves 19, 21 and 22 and the porting are tuned, but also permits the attainment of good torque and power at wide open throttle due to the large total effective valve area. The intake valves 19, 21 and 22 are each operated from the cam lobes 26 through respective thimble tappets 29, 31 and 32 which have diameters that are different in the same proportion as the difference in the diameters of the heads of the valves 19, 21 and 22 and their respective valve seats 16, 17 and 18. The diameter of the valve springs 24 are also so interrelated. Generally, the diameters of the respective thimble tappets 29, 31, 32 are in the order of the diameters of the valve heads of the associated intake valves 19,21, 22. It should be noted that the center of the center intake valve seat 16 and the head of the intake valve 19 are offset by a distance C to a plane which is perpendicular to the aforenoted parallel plane at one side of the cylinder bore axis A, said perpendicular plane being identified by the broken line B in Figure 2. This offsetting permits the use of the larger center intake valve 16 than the smaller side intake valve 22 to which side the center intake valve 19 is offset. This also permits the center intake valve 19 to be positioned somewhat closer to the cylinder bore axis A than if its center were directly on the line B and also permits a somewhat larger diameter for its valve head. This offsetting also permits a squish area 33 to be formed between the intake valves 19, 21 and 22 on this side of the aforenoted plane containing the axis of the cylinder bore A so as to obtain some squish action. The larger side intake valve 21 and its corresponding valve seat 17 is provided with a single intake passage 34 which extends through the side of the cylinder head to a single inlet opening 35 that is served by an intake manifold 36 in a manner which will be described. The intake passage 34 is generally straight and on a line which is substantially parallel to a corresponding axis of theintake passage associated with the other side intake valve seat 18 and which will be described later. The intake manifold 36 is provided with an intake passage 37 in which a flow controlling throttle valve 38 is positioned so as to normally preclude flow to the combustion chamber through the intake valve seat 17 except under high speed, high load performance. Hence, the intake passage 34, intake valve seat 17 and intake valve 21 are configured and tuned to provide maximum charging efficiency at a relatively high speed. The center intake valve seat 16 and side intake valve seat 18 are served by a common intake passage siamesed configuration, having an inlet portion 39 which is served by an intake passage 41 of the manifold 36. The manifold intake passages 37 and 41 may be served by a common plenum chamber to which air is admitted through an atmospheric air inlet in which a throttle valve (not shown) is provided, which throttle valve will control the speed of the engine. The throttle valve 38 may be opened either through an interconnected linkage with lost motion or by means of a vacuum servo motor or in an other well known manner as are employed in staged throttle valve mechanisms. The intake passage 39 diverges into a pair of portions 42 and 43, respectively, which terminate at the valve seats 16 and 18. The passage portion 42 has a central axis G which is disposed at an acute angle to the lower seating face of the cylinder head 12, which seating face is indicated by the reference numberal 44, which is sealed to the cylinder block 13 in a well known manner with an interposed head gasket. Because of this inclination of the intake port 42 and the fact that it extends in a straight line from the inlet opening 39 to an area immediately adjacent the valve seat 16 with only a small curve portion at this valve seat, the charge flowing into the combustion chamber will be directed toward the center plane comprising the cylinder bore axis A and the opposite side of the cylinder bore 15. Thus, even though the center intake valve 19 and its valve seat 16 are disposed at the extreme opposite side of the cylinder bore, there will still be a substantial tumble action generated because of this configuration. By the way, the parallel plane serving as a reference plane to explain the different positions of the centre and side intake valve seats 16, 17, 18 and the different positioning of the intake and exhaust side valve operating machanisms needs not necessarily to be a symmetry plane of the cylinder bore containing the cylinder bore axis but may also be a plane in parallel to the crankshaft or the intake and exhaust camshafts 22, 56 which additionally or alternatively contains the center of the combustion chamber 14. The passageway 43 has its central axis H inclined at an acute angle to the lower sealing surface 44 and since the side intake valve 22 and its valve seat 18 are disposed closer to the cylinder bore center axis A, there will also be generated a substantial tumble action from this port as well as from the intake port 33 when it is flowing into the cylinder. The intake manifold 36 and cylinder head 12 are formed with a bore 45 that receives a fuel injector (not shown). This bore 45 terminates in a recess 46 that bridges the manifold portion 39 and extends toward the sections 42 and 43. It should be noted that these sections 42 and 43 are separated by a very small wall 47 so that they communicate with each other through substantially all of their length. It should also be noted that the sides of the passages 42 and 43 are disposed at angles  1 and  2 to the common inlet opening portion 39 with the angle  1 being greater than the angle  2 . The fuel injector has a spray axis F that encompasses an arc shown between the lines D and E in Figure 2, which arc intersects the center of the valve seats 16 and 18 and the center of the heads of the intake valves 19 and 22 so as to provide substantially equal fuel distribution between both intake passages. Although the intake passage 33 associated with the valve seat 17 has no fuel sprayed into it, the amount of fuel sprayed by the injector will be increased at the time when the throttle valve 38 is opened so that there will be adequate flow of fuel for the increased air flow to the combustion chamber. Also, because of the turbulence which is generated, the fuel/air mixture will be substantially homogeneous in the cylinder bore at the time of ignition. Turning now to the exhaust side of the cylinder head 12, there are provided a pair of exhaust valve seats 48 which have the same diameter and which diameter may be the same as the diameter of the side intake valve seat 17. Poppet type exhaust valves 49 are mounted in the cylinder head assembly 12 by means of valve guides 51. The exhaust valves 49 are urged to their closed positions by coil compression springs 52 that cooperate with keeper retainer assemblies 53 affixed to the stems of the exhaust valves 51. The exhaust valves are provided with bucket type tappets 54 that are mounted in suitable bore formed in the cylinder head and which are operated by cam lobes 55 of an exhaust camshaft 56. The exhaust camshaft 56 is rotatably journalled in the cylinder head assembly 12 by means of bearing caps 57 that are suitably affixed to the cylinder head assembly 12. Hence, the valve train is contained within a cam cavity 58 which is closed by a cam cover 59 that is fixed to the cylinder head in a suitable manner. A pair of exhaust ports formed in the outer side of the cylinder head assembly 12 cooperate with a suitable exhaust manifold (not shown). It should be noted that the positioning of the exhaust valves 49 and the exhaust valve seats 48 permits the formation of a squish area 61 on the exhaust side of the cylinder head around the recess 14 so as to further promote turbulence and improve combustion efficiency particularly at low speeds. A spark plug well 62 is formed in the cylinder head assembly 12 and terminates in the recess 14 at a point so that the gap of the spark plug will lie directly on the cylinder bore axis A. This spark plug is fired in any well known manner. Figure 4 shows another embodiment which does not form part of the present invention and differs from the embodiment of Figures 1 through 3 only in the positioning of the flow controlling throttle valve 38 and the fuel injector which goes into the recess 45 as aforenoted. Because these are the only differences between this embodiment and that of Figure 1 through 3, all components of this embodiment which are substantially the same are identified by the same reference numerals and will be described again only insofar as is necessary to understand the construction and operation of this embodiment. In this embodiment, the throttle valve 38 is positioned in the intake manifold passage 41 and thus the intake manifold passage 37 and cylinder head intake passage 34 forms the primary intake passage for the engine 11 as opposed to the previously described embodiment. For this same reason, the fuel injector is mounted in the recess 45 of the manifold 36 and cylinder head 12 which intersects the primary intake passage 34 serving the valve seat 17. Aside from this difference, this embodiment is the same as that previously described and has the same advantages. Again, each of the intake valve seats 16, 17 and 18 and their associated passages are tuned to suit a different range of engine running conditions. However, since the passage 34 and valve seat 17 is for the primary passage, this is tuned primarily to serve a low engine speed requirement while the remaining passages are designed so as to provide better induction efficiency at higher engine speeds. In the embodiments as thus far described, each of the intake valves has a different diameter with the center intake valve 19 having a diameter between those of the side intake valves 21 and 22. Figure 5 is a view in part similar to Figures 2 and 4 of another embodiment and in this embodiment the center intake valve 19 and its valve seat 16 are designed so as to have the largest diameter. The side intake valve 21 and valve seat 17 in this embodiment have the next largest diameter while the side intake valve 22 and its valve seat 18 have the smallest diameter. This arrangement may be employed with either the porting and valve arrangement as shown in Figures 1 through 3 or that shown in Figure 4. Again in this embodiment, the center intake valve 19 and its associated valve seat 16 are offset by dimension C from the center plane B although this offsetting is somewhat less than that of the previously described embodiment, there are provided two smaller squish areas 101 each between the center intake valve 19 and one of the side intake valves 21 and 22. In the embodiments as thus far described, each of the intake valves 19, 21 and 22 and their associated valve seats 16, 17 and 18 have a different diameter. Now will be described some embodiments wherein at least two of the intake valves have the same diameter. Since this is the only difference and since in each of these embodiments the porting, valving and fuel injection arrangements of either the embodiment of Figures 1 through 3 or the embodiment of Figure 4 may be employed, only bottom plan views of the combustion chamber recess and valves are believed to be necessary to understand the construction and operation of these embodiments and the valves and valve seats and other components have been identified by the same reference numerals as already employed. In the embodiment of Figure 6, the side intake valves 21 and 22 and their respective valve seats 17 and 18 are the same size and are larger than the center intake valve 19 and its valve seat 16. This permits the center intake valve 19 to be moved closer to the cylinder bore axis A and also permits the center of this port to be positioned directly on the plane B. This also permits the squish area 33 to be larger than with the previously described embodiments. The embodiment of Figure 7 employs an arrangement wherein the side intake valve 21 and its valve seat 17 are the same diameter as the center intake valve 19 and its valve seat 16. Hence, the remaining side intake valve 22 and its valve seat 18 are of a larger diameter. Because of this relationship, the center of center intake valve 19 and its valve seat 16 are offset by the distance I from the center plane B towards to the side intake valve 21. Also, this permits the positioning of the center intake valve 19 and its intake port 16 closer to the cylinder bore axis A in fact, the center intake valve 19 may be positioned so that its head overlies a plane J passing through the center of the side intake valves 21 and 22 as seen in Figure 7. Again, this construction also permits the squish area 33 to be enlarged. In this case, the angle between the axis of the centre intake valve 19 and the axis of the side intake valves 21, 22 is very small which adds to amplify the tumble action of the charge supplied into the combustion chamber recess 14. Moreover, by means of such an arrangement the masking effect is decreased as the center intake valve 19 is so far no longer somewhat shielded though the two more offset side intake valves 21, 22 and the smaller diameter of the center intake valve 19 against at least one side intake valve is compensated through the increase of the amount of flow into the combustion chamber 14 increasing the turbulence within the combustion chamber as well due to the enlarged squish area obtained by this arrangement. Figure 8 shows another embodiment which permits the center intake valve 19 and its valve seat 16 to be moved closer to the clyinder bore axis A and permits a larger squish area 33. This is done by making the side intake valves 21 and 22 and their respective valve seats 17 and 18 of the same diameter and smaller than the diameter of the center intake valve 19 and its valve seat 16. In the embodiments of Figures 6, 7 and 8 wherein at least two of the valves and valve seats have the same diameter, it is still possible to tune the intake passages with those valve seats and the operation of the valves in such a way that each valve seat and its associated intake passage and valve is tuned to obtain maximum charging efficiency at a certain engine speed with all of these being tuned to accommodate different engine speeds. Alternatively, those valves which are paired in their induction systems, may be tuned together to suit the same speed. Also, although arrangements have been disclosed with paired or siamesed intake passages for two of the valves, each valve may operate with its own intake passage or all of the passages may be siamesed. It should be readily apparent from the foregoing description that the described embodiments permit the use of a large intake valve area and, at the same time, permit tuning of the induction system for the engine so as to achieve good performance and good torque throughout the entire engine speed and load ranges. In addition, the construction permits the increase of turbulence in the combustion chamber at low speeds and low leads so as to improve the performance of the engine even under this condition, which is extremely difficult to obtain with high performance engines having large valve areas.

Claims: Internal combustion engine comprising a cylinder head and induction system having a cylinder head assembly (12) defining three intake valve seats (16,17,18) all adapted to communicate with same combustion chamber (14) of the engine (11), three intake valves (19,21,22) supported for reciprocation in said cylinder head (12) and each controlling the flow through an associated one of said intake valve seats (16,17,18), and intake port means formed in said cylinder head (12) and terminating at each of said valve seats (16,17,18) for delivering a charge to the associated combustion chamber (14), at least one of said intake valve seats being of a different diameter than the other ones of the intake valve seats and fuel injecting means for injecting fuel characterised in that said intake port means comprises a first siamesed intake port having an inlet opening (39) at one side of the cylinder head (12) and terminating at a pair of the intake valve seats (16,18) and a second intake port having an inlet opening (35) formed at one side of the cylinder head (12) and terminating at the remaining valve seat (17) and, in that said fuel injecting means comprises a single injector for injecting fuel into said siamesed intake port towards said pair of intake valve seats (16,18), while said remaining intake valve seat (17) is served by intake air only. Internal combustion engine as claimed in claim 1, wherein all of the valve seats (16,17,18) have different diameters. Internal combustion engine as claimed in claim 1, wherein two of the valve seats have the same diameter. Internal combustion engine as claimed in claim 3, wherein the centre intake valve seat (16) and one of the side intake valve seat (18) have the same diameter. Internal combustion engine as claimed in at least one of the preceding claims 1 to 4, wherein both of the side intake valve seats (17,18) have the same diameter. Internal combustion engine as claimed in claims 1 to 5, wherein the centre intake valve seat (16) has a smaller diameter than each of the side intake valve seats (17,18). Internal combustion engine as claimed in at least one of the preceding claims 1 to 6, characterised in that , the two side intake valve seats (17,18) are disposed closer to a parallel plane than the remaining centre intake valve seat (16), said parallel plane preferably containing the cylinder bore axis (A) and/or passing through a center of the combustion chamber (14) and extending in parallel to the axis of rotation of the associated crankshaft. Internal combustion engine as claimed in at least one of the preceding claims 1 to 7, wherein the centre intake valve seat (16) is offset by a distance (C) against a perpendicular plane (B) which contains the cylinder bore axis (A) and which extends perpendicular to said parallel plane which extends in parallel to the crankshaft. Internal combustion engine as claimed in at least one of the preceding claims 1 to 8, wherein, the remaining intake valve seat (17) served by the second intake port having a larger diameter than the side intake valve seat (18) served by the siamese intake ports. Internal combustion engine as claimed in claim 9, wherein the siamese intake passageway serves the centre intake valve seat (16) and one side intake valve seat (18), preferably that side intake valve seat (18) having a smaller diameter than the remaining side intake valve seat (17). Internal combustion engine as claimed in at least one of the preceding claims 1 to 10 wherein a control valve (38) is disposed in one of said intake ports (37), said control valve (38) is opened only at high speed/high load engine operating conditions so that the respective intake port (37) serves high speed engine operating conditions only. Internal combustion engine as claimed in claim 11, wherein the other intake port (36) not served by the control valve (38) is served by a fuel injecting means for injecting fuel into said other intake port (36). Internal combustion engine as claimed in claim 12, wherein the fuel injector is disposed with its spray axis such that it delivers substantially equal amounts of fuel to both of the intake valve seats (16,18) served by the siamesed intake port. Internal combustion engine as claimed in at least one of the preceding claims 1 to 13 wherein the control valve (38) is positioned in the substantially straight, non-siamesed intake port. Internal combustion engine as claimed in at least one of the preceding claims 1 to 14, wherein the intake port means serving the centre intake valve seat is disposed at an acute angle to a sealing surface of the cylinder head (12) so as to direct the charge flowing into the combustion chamber (14) from the centre intake valve seat (16) towards the centre of the combustion chamber to induce a tumble action to the charge entering the combustion chamber (14). Internal combustion engine as claimed in at least one of the preceding claims 1 to 15 wherein the heads of the intake valves (21,22) associated with the side intake valve seats (17,18) extend over a parallel plane containing the cylinder bore axis (A) and extending in parallel to the crankshaft. Internal combustion engine as claimed in claim 16 wherein the centres of the side intake valve seats (17,18) lie on a common plane (J) and the valve head of the intake valve (19) associated with the centre intake valve seat (16) is intersected by said plane (J). Internal combustion engine as claimed in at least one of the preceding claims 1 to 17 wherein said intake port means include a centre intake port formed in said cylinder head (12) and serving said centre intake valve seat (16), said centre intake valve port (16) having a central axis inclined at an acute angle to a lower sealing surface of said cylinder head (12) and extending generally straight up to said centre intake valve seat (16) for delivering a charge towards the combustion chamber (14) towards said power plane for generating a tumble action in said combustion chamber (14). Internal combustion engine as claimed in at least one of the preceding claims 1 to 18 wherein all of the intake port means are disposed at an acute angle to a sealing surface of the cylinder head (12) so as to direct the charge flowing into the combustion chamber (14) from the intake valve seats (16,17,18) towards the centre of the combustion chamber to induce a tumble action to the charge entering the combustion chamber (14). Internal combustion engine as claimed in claim 17, wherein a line passing through the centres of the side intake valve seats (17,18) intersects the head of the intake valve (19) for controlling the flow through said centre intake valve seat (16). Internal combustion engine as claimed in at least one of the preceding claims 1 to 20 wherein the centre intake valve seat (16) has the same diameter as one of the side intake valve seats (17,18) with the remaining intake valve seat having a different diameter, preferably said remaining intake side intake valve seat having a larger diameter than the centre intake valve seat (16). Internal combustion engine comprising an intake camshaft (27) for operating the intake valves (19,21,22) and an exhaust camshaft (56) for operating the exhaust valves (49), as claimed in at least one of the preceding claims 1 to 21 wherein the distance of a rotational axis (L1) of the intake camshaft (27) from a parallel plane is shorter than the distance of the rotational axis (L2) of the exhaust camshaft (56) from said plane, said parallel plane containing the cylinder bore axis (A) and extending in parallel to a crankshaft. Internal combustion engine as claimed in claim 22, wherein the rotational axis (L1) the intake camshaft (27) rotationally intersects a plan view projection of the cylinder bore (15) while the rotational axis (L2) of the exhaust camshaft (56) runs outside of such a cross sectional projection of the cylinder bore (15). Internal combustion engine as claimed in claims 22 or 23, having thimble tappets (29,31,32) for moving the intake and exhaust valves (19,21,22;49), wherein the diameter of the thimble tappets (29,31,32) of the intake valves (19,21,22) is in the order of the diameter of the valve heads of the associated intake valves (19,21,22). Internal combustion engine as claimed in at least one of the preceding claims 22 to 24 having intake and exhaust camshafts bearing structures comprising bearing caps (28,57) bolted to the cylinder head, wherein a distance (a) between at least one inside bolt (28a) fastening a bearing cap (28) of the intake camshaft (27) and a center of a spark plug well (62) is substantially the same as the distance (a) between an inside bolt (57a) fastening a bearing cap (57) of the exhaust camshaft (56) and said center of the spark plug well (62). Internal combustion engine as claimed in claim 25 wherein a single inside bolt (57a) is provided between two exhaust valve actuating cam lobes (55) of the exhaust camshaft (56) and two inside bolts (28a) are provided alternately between three intake valve actuating cam lobes (28) of the intake camshaft (27) so that the inside bolts (57a,28a) on the exhaust and intake sides of the engine for each cylinder are disposed on the corners of an isosceles triangle.

Inventors: AOYAMA TATEO, AOYAMA, TATEO, Aoyama, Tateo, c/o Yamaha Hatsudoki K.K.
Applicants: YAMAHA MOTOR CO LTD, YAMAHA HATSUDOKI KABUSHIKI KAISHA
Application year: 1993
Main classification: F01L1
IPC codes: F01L1, F02F1, F02B1