Exhaust control valve system for parallel multi-cylinder two-cycle engine

Abstract: An in-line, two-cycle, crankcase compression, internal combustion engine (11) having a plurality of scavenge ports (28,29,31) and an exhaust port (33) for each cylinder in which an exhaust control valve (39) is positioned. To permit a compact assembly, the ports are rotated about the cylinder bore axis (A,B,C) in a transverse plane (H,I,J) so that the exhaust ports extend at an acute angle to a common plane (D) containing the cylinder bore axes and the control shafts (42) for the exhaust control valves extends perpendicularly to this plane. A wide variety of actuators are disclosed for operating the exhaust control valves simultaneously including flexible transmitters and a linkage system.

Description: This invention relates to a multi-cylinder, two stroke cycle crankcase compression internal combustion engine comprising a cylinder block assembly defining at least a pair of adjacent cylinder bores having their axes lying in a common plane, a crankcase at one end of said cylinder block assembly, scavenge port means having at least one scavenge passage extending from said crankcase to a respective end of said cylinder bores, exhaust ports extending from said cylinder bores and discharging the exhaust gases from the cylinder bores through exhaust passages, an exhaust control valve means comprising control valves supported for rotary movement in the exhaust passages associated with the exhaust ports of each of said cylinder bores for varying the effective area and timing of opening of the individual exhaust ports. It is well known that the port timing in two-cycle, crankcase compression, internal combustion engines is very critical to the engine performance. It is also known that port timings that permit maximum power attainment normally provide poor running at low and mid-ranges. In a like manner, port timings that provide good low and mid-speed range running do not permit maximum power output. It has, therefore, been proposed to employ an exhaust control valve in the exhaust port that is effective to change the exhaust timing and permit optimum engine performance through a wider range of running conditions. With most two-cycle, crankcase compression engines, there are provided a plurality of scavenge ports formed around the cylinder bore axis for transferring the compressed intake charge to the combustion chamber. Normally, there is also provided at least one exhaust port that is somewhat in confronting relationship to the intake ports. The use of such multiple ports, therefore, gives rise to a situation wherein the cylinder bore to cylinder bore spacing must be increased to provide clearance for the individual ports and passages associated with them. One way that the engine can be made more compact is to rotate the port arrangement relative to the cylinder bore axis so as to permit the ports associated from one cylinder to nest between those of the adjacent cylinder. With inline engines, this will permit a reduction in the overall length of the engine. However, when exhaust control valves have been employed, this rotational positioning of the ports has not been done because of the difficulties in providing the control valves and operating mechanism for them. A two stroke cycle internal combustion engine according to the preamble of claim 1 is known from GB-A-2 175 643. The engine disclosed therein includes a valve in the piston-control exhaust port being controlled in response to at least engine speed and load to regulate the degree of throttling and the timing of exhaust discharge. An electronic control unit receives input from sensors of air mass flow, engine speed and temperature, throttle valve position and the position of the valve and provides output to the valve, fuel injector unit and an ignition controller. A pivot axis of this valve is inclined to the general direction of the control edge of the valve so that in the end of the control edge there is provided a greater radius with respect to the pivot axis than the other end of the control edge. Accordingly, different rates of variation can be obtained in the exhaust port area and exhaust port timing. The extent of variation between these rates is controlled by an angle of inclination between the control edge and the pivot axis of the exhaust port throttle valve. This arrangement, however, is very complicated and bulky and therefore not easy to handle. Further, document US-A-4 121 552 discloses a two stroke cycle internal combustion engine including a cylinder which is provided with one or more exhaust ports adapted to be closed by piston reciprocating in the cylinder. A valve member is provided in corporation with the upper portion or upper one of the exhaust ports. Said valve member may be interconnected with the engine throttle valve in such a manner which is closed under lower speed operation and opened under high speed operation of the engine so as to obtain optimum exhaust valve timing throughout the engine operating speed range. Accordingly, it is an objective of the present invention to provide a multi-cylinder, two stroke cycle crankcase compression internal combustion engine as indicated above having an improved port and exhaust control valve arrangement that provides a compact assembly. According to the invention, this objective is solved for a multi-cylinder, two stroke cycle crankcase compression internal combustion engine as indicated above in that said exhaust passages have their centre lines laying on vertical planes which contain the axes of the respective cylinder bores and extend, when viewed in plan view, at an acute angle to vertical planes that extend perpendicularly to said common plane and that the control valves are rotatable about non-identical axes that extend in parallel to each other. According to an embodiment of the invention, the control valves comprise flap type valves the axis of which extend perpendicularly to said vertical planes. In order to further ease the handling or operation, respectively, it is advantageous when said control valves for each of the cylinders are operated by a common actuator. Thereby, it is advantageous when flexible transmitter means are provided for transmitting motion from the common actuator to each of the control valves, whereby it is advantageous when said transmitters are separate flexible transmitters extending from the common actuator to each of the control valves. According to the invention it is possible that a port and exhaust control valve arrangement for a two stroke cycle, crankcase compression engine permits the ports to be rotated relative to the cylinder bore axis to achieve a compact construction, while at the same time ensuring ease of an operation of the control valves for the exhaust port. Therefore, according to the invention there is provided an improved exhaust port and control valve arrangement for a multiple cylinder, two stroke cycle, crankcase compression internal combustion engine. Other preferred embodiments of the present invention are laid down in further dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partial cross-sectional view taken through along a plane extending perpendicularly to the cylinder bore axes of a multi-cylinder, two-cycle, crankcase compression engine constructed in accordance with an embodiment of the engine, with the exhaust control valve control mechanism being shown schematically and generally along the line 1-1 of Figure 2. Figure 2 is a cross-sectional view taken along the line 2-2 of Figure 1. Figure 3 is a projected view of the exhaust port and shows the cooperation of the exhaust control valve therewith with the engine running at wide open throttle, full speed, full load conditions. Figure 4 is a projected view, in part similar to Figure 3, and shows the mechanism when operating at idle and low speed. Figure 5 is a partially schematic view showing another embodiment for operating the control valves. Figure 6 is a partial cross-sectional view, in part similar to Figure 1, and shows yet another embodiment of the invention. Figure 7 is a partial cross-sectional view, in part similar to Figure 1, and shows yet another embodiment of the invention. Figure 8 is a partial cross-sectional view, in part similar to Figure 2, showing this embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to the embodiment of Figures 1 through 4, a two-cycle, crankcase compression, internal combustion engine constructed in accordance with this embodiment of the invention is identified generally by the reference numeral 11. In the illustrated embodiment, the engine 11 is of the three cylinder, in line type. It may be understood that the invention may be practiced in conjunction with engines having other numbers of cylinders and also with engines having V or opposed type configurations and two or more cylinders in each bank. It should be readily apparent to those skilled in the art how this invention can be practiced with such other engine configurations. The engine 11 includes a cylinder block assembly 12 having three aligned cylinder bores 13 that are formed by pressed-in liners 14. The cylinder bores 13 have their respective axes A, B and C lying in a common plane, indicated by the reference character D in Figure 1. A crankcase member 15 is affixed, in a known manner, to the lower end of the cylinder block 12 at one end of the cylinder bores 13. Pistons 16 are slidably supported within the cylinder bores 13 and are connected by means of connecting rods 17 to a crankshaft 18 that is journaled for rotation within individually sealed crankcase chambers 19 of the engine. The crankcase chambers 19 are formed between the lower end of the cylinder block 12 and the crankcase member 15 and are each sealed relative to each other, as is conventional with two-cycle engine construction. A cylinder head, indicated generally by the reference numeral 21, is affixed to the cylinder block 12 at the end opposite the crankcase member 15 and is formed with respective recesses 22 which cooperate with the cylinder bore 13 and pistons 16 to form the combustion chambers of the engine. A charge forming system is provided for the engine and in accordance with the illustrated embodiments, this charge forming system includes an intake manifold 23 that is affixed to one side of the crankcase member 15 and which communicates with the chambers 19 through reed type check valve assemblies 24 which permits the flow of air into the crankcase chambers 19 but which prevents reverse flow when the piston 16 is compressing the air charge therein. In the embodiments of the invention, only pure air is inducted into the crankcase chambers 19. It is to be understood, however, that the invention can be utilized in conjunction with arrangements wherein a fuel/air charge is admitted to the crankcase chambers 19. The charge which is admitted to the crankcase chambers 19 and which is compressed, as aforenoted, is transferred from the crankcase chambers 22 through three angularly disposed scavenge passages 25, 26 and 27. Although different number of scavenge passages may be employed, the invention has particular utility in conjunction with engines having a plurality of scavenge passages so that the normal disposition of the scavenge passages could cause an increase in length of the engine. The scavenge passage 25 may be considered to be a center scavenge while the passages 26 and 27 may be considered to be side scavenge passages. In conventional arrangements, the scavenge passages 25 would lie on planes E, F and G which are perpendicular to the plane D and which extend at right angles thereto and which intersect the cylinder bore axes A, B and C. The side passages 26 and 27 would have their centers lying on the plane D. As should be readily apparent from an inspection of Figure 1, this orientation would cause the engine to have a greater length than with the described embodiment to provide the necessary clearance for adjacent side scavenge passages. However, in accordance with the invention, these passages are rotated about the respective cylinder bore axes A, B and C so that the centers of the side scavenge passages 25 lie on planes H, I and J that are disposed at an acute angle to the planes E, F and G. As a result, it can be clearly seen that a more compact engine is provided by this rotation of the scavenge passages without adversely affecting the flow area. Each of the scavenge passages 25, 26 and 27 extends from the crankcase chambers 19 and enters the respective combustion chamber 22 through a respective scavenge port 28, 29 and 31. The scavenge ports 28, 29 and 31 subtend an arc that is greater that 180 degrees of the cylinder bore 13. In confronting relationship to the scavenge passages 25, the cylinder block 12 is provided with exhaust passages 32 which extend from exhaust ports 33 that lie substantially within the quadrant defined by the planes D,E, D,F and D,G. The center of these passages 32 also lies along the planes H, I and J. This further adds in the compaction of the overall engine construction and affords good scavenging. A fuel/air charge is admitted to each combustion chamber 22 by an air/fuel injector indicated generally by the reference numeral 34 and which has an air injector portion 35 that receives air under pressure from a suitable air compressor (not shown). In addition, a fuel injection nozzle 36 injects fuel with the flow of fuel and air into the combustion chambers 22 being controlled by a suitable valve mechanism operated by a solenoid 37. Since the construction of the fuel/air injector 34 forms no part of the invention and since no other charge forming systems may be employed, further description of it is believed to be unnecessary. The charge which is admitted to the chamber 22 is fired by a spark plug 38 in a known manner. As has been previously discussed, it is desirable to provide a fairly substantial overlap in the operation of the scavenge ports 28, 19 and 31 and the exhaust port 33 to provide maximum power output. However, such maximum power output and high overlaps deteriorates the low speed performance. In order to obviate these problems, individual exhaust control valves, indicated generally by the reference numeral 39, are provided in each of the exhaust passages 32 for masking the exhaust ports 33 and changing the effective timing. In the illustrated embodiment, the valves 39 are of a type that are affixed to respective valve shafts 41 that extend perpendicularly to the planes H, I and J at the upper end of the passages 32 and which have valve portions that are adapted to pass into a recess 40 formed between the cylinder liner 14 and the cylinder block 12 when the control valves 39 are positioned in their fully opened position as shown in Figure 3. In this instance, the exhaust port will open as soon as the pistons 16 move downwardly so as to uncover them and there will be a substantial overlap to achieve high power. However, under low speed conditions, the control valves 39 are moved to the position shown in Figures 2 and 4 wherein they will partially obscure the exhaust ports 33 and cause a delay in their opening. This will improve significantly low speed running. Although a variety of arrangements can be employed for operating the control valves 39, it is desirable to insure that they are operated in unison and, as one possible structure for achieving this, there is affixed to the exposed end of each control valve shaft 41 a respective pulley 42. A respective wire actuator 43 is connected to each pulley 42 and is, in turn, connected at its other end to a respective pulley or groove 44 of a combined pulley that is affixed to the output shaft of a servo motor 45. The servo motor 45 is controlled by an appropriate controlled strategy so as to control the timing in relation to engine speed and/or load or other characteristics so as to achieve the aforenoted results. Figure 5 shows another arrangement for operating the exhaust control valves 39 all in unison. Because the basic construction of this embodiment is the same as the previously described embodiment, only the control valve actuating mechanism is illustrated since the basic porting arrangement is the same as that already described. In addition, this embodiment also employs as actuators, pulleys 42, that are affixed to the control valve shafts 41 and which are associated with a servo motor 45. In this embodiment, however, a series chain of remote control wire actuators is interlinked between a pulley 101 that is affixed to the output shaft of the servo motor 45 and includes a first wire actuator 102 that extends from the pulley 101 to the pulley 42 of one of the control valve shafts 41. A second wire actuator 103 extends from the other side of this first pulley 42 to the pulley 42 of the central throttle control valve shaft 41. A third wire actuator 104 extends from the other side of this pulley 42 to the remaining pulley 42 of the remaining throttle control valve shaft 41. This final pulley is then connected by means of a fourth wire actuator 105 back to the pulley 101 of the servo motor 45. As a result, operation of the pulley 101 will achieve simultaneous movement of all of the exhaust control valve shafts 41. Figure 6 shows another embodiment of the invention which is basically the same as the embodiment of Figures 1 through 4 and differs from that embodiment and that of Figure 5 only in the manner in which the control valve shafts 41 are operated. Because of these similarities, the basic construction of the engine, the exhaust control valves and the exhaust control valve shafts 41 will not be described again. The description will be limited solely to the method and structure for operating the exhaust control valves 39 and exhaust control valve shafts 41. In this embodiment, the servo motor 45 couples an actuating shaft 151 that is rotatably journaled about an axis that lies parallel to the plane D and which is angularly disposed to the axes of rotation of the control valve shafts 41. A plurality of lever arms 152 are formed either integrally with or affixed to the shaft 151 and have spherical pivotal connections 156 to links 153. The opposite end of each of the links 153 is pivoted by means of a spherical pivotal connection 158 to a lever 154 that is affixed to the respective exhaust control valve shaft 41. As a result, rotation of the shaft 151 will effect simultaneous rotation of the shafts 41 and exhaust control valves 39. It should be noted that the shaft 151 and the exhaust valve shaft 41 are both mounted on the cylinder block. Consequently, the relationship of the positions between arm 152 and lever 154 may be very accurate. The links, connecting the pivotable connections 156 to the pivotable connections 158 include adjustable screws. Therefore, the movement of each valve may be adjusted very accurately. In the embodiments of the invention as thus far described, the exhaust control valves 39 have been flap type valves. The invention can also be employed in connection with rotary type valves and Figures 7 and 8 show such an embodiment. In this embodiment, the basic construction of the engine 11 is the same as that previously described and, for that reason, components of this embodiment which are the same as the previously described embodiment have been identified by the same reference numerals and further description of components which are the same or substantially the same of the previously described embodiment are believed to be unnecessary. In this embodiment, the exhaust passages 32 are rotated from the planes E, F and G in a counterclockwise direction rather than the clockwise direction of the previously described embodiments. However, the axes of the central portions of the exhaust passages 32 lie within the quadrant defined by the planes E, F and G and the plane D. Also, there is an acute angle between the planes as with the aforenoted embodiment but on the opposite side thereof. In this embodiment, control valves, indicated generally by the reference numeral 201, are rotatably journaled within the cylinder block 12 for controlling the effective opening of the exhaust ports 33 and the timing relationship thereof. In this embodiment, each control valve 201 has a cylindrical portion 202 that is disposed at one side of the ports 33 within the passages 32. Adjacent this cylindrical portion 202, the valves 201 are provided with a semicircular portion 203 which has a flat cutout edge 204 that actually forms a valving member with the port 33. As may be seen in the solid line view of Figure 8, when the valves 201 are rotated to their fully opened positions, the flat edge 204 merely forms an extension of the passage 32 and the flow through the exhaust ports 33 will not be obstructed and will occur at a position relatively close to top dead center of the piston 16. However, when the valves 201 are rotated to their timing position as shown in phantom in Figure 8, the opening of the exhaust port 33 will be delayed with the aforenoted results. Each of the valves 201 further includes a control shaft portion 205 that is journaled within a closure plate 206 affixed to the side of the cylinder block. A control disk or pulley 207 is affixed to the exposed end of each shaft 206 and may be operated in any of the aforedescribed manners. That is, the valves 201 may be operated all by individual flexible transmitters as in the embodiment of Figures 1 through 4, by a series train of flexible transmitters as the embodiment of Figure 5 or by a linkage system as with the embodiment of Figure 6. It should be readily apparent from the foregoing description that the embodiments of the invention as described are all capable of providing good running under a wide variety of conditions through the control of the timing of the opening of the exhaust port and the area thereof. This can also be done with a very compact engine assembly due to the rotation of the exhaust ports from a plane perpendicular to the plane containing the axes of the cylinder bores. In addition, in the embodiments, the control valves are all supported for rotation about axes that extend generally perpendicularly to the exhaust passages.

Claims: A multi-cylinder, two stroke cycle crankcase compression internal combustion engine (11) comprising a cylinder block assembly (12) defining at least a pair of adjacent cylinder bores (13) having their axes (A,B,C) lying in a common plane (D), a crankcase (15) at one end of said cylinder block assembly, scavenge port means having at least one scavenge passage (25,26,27) extending from said crankcase (15) to a respective end of said cylinder bores (13), exhaust ports (33) extending from said cylinder bores (13) and discharging the exhaust gases from the cylinder bores (13) through exhaust passages (32), an exhaust control valve means comprising control valves (39, 201) supported for rotary movement in the exhaust passages (32) associated with the exhaust ports (33) of each of said cylinder bores (13) for varying the effective area and timing of opening of the individual exhaust ports (33), characterized in that said exhaust passages (32) have their centre lines laying on vertical planes (H,I,J) which contain the axes (A,B,C) of the respective cylinder bores (13) and extend, when viewed in plan view, at an acute angle to vertical planes (E,F,G) that extend perpendicularly to said common plane (D) and that the control valves (39,201) are rotatable about non-identical axes that extend in parallel to each other. An engine as claimed in claim 1, characterized in that the control valves (39) comprise flap type valves the axes of which extend perpendicularly to said vertical planes (H,I,J). An engine as claimed in claim 1 or 2, characterized in that said control valves (39,201) for each of the cylinders (13) are operated by a common actuator (45). An engine as claimed in claim 3, characterized by flexible transmitter means (43) for transmitting motion from the common actuator (45) to each of the control valves (39,201). An engine as claimed in claim 4, characterized in that said separate flexible transmitters (43) extend from the common actuator (45) to each of the control valves (39,201). An engine as claimed in claim 4 or 5, characterized in that the flexible transmitters (103,104,105) extend in series relationship from the common actuator (45) to one of the control valves (39,201), from said control valve (39,201) to another control valve (39,201) and back from said another control valve (39,201) to said common actuator (45). An engine as claimed in at least one of the preceding claims 3 to 6, characterized in that a linkage means (153) is provided for connecting the common actuator (45) through the control valves (39,201). An engine as claimed in at least one of the preceding claims 1 to 7, characterized in that the scavenge port means comprises a plurality of scavenge ports disposed circumferencially spaced around each of the cylinder bores (13). An engine as claimed in claim 8, characterized in that one of the scavenge passages is disposed in confronting relationship to the exhaust port. An engine as claimed in at least one of the preceding claims 1 to 9, characterized in that each exhaust port serves a respective exhaust passage.

Inventors: MOTOYAMA YU, OZAWA TOSHIKAZU, MOTOYAMA, YU, OZAWA, TOSHIKAZU
Applicants: YAMAHA MOTOR CO LTD, YAMAHA HATSUDOKI KABUSHIKI KAISHA
Application year: 1990
Main classification: F02D13
IPC codes: F02B75, F02B25, F02D13