Multi-cylinder two cycle internal combustion engine

Abstract: Two embodiments of two cycle crankcase compression engines wherein exhaust emissions are controlled by controlling the amount of scavenging air flow at low and mid ranges. The scavenging air flow is controlled by balance passages (49) that interconnect at least two crankcase chambers (31) of the engine and in which a control valve (52) is provided.

Description: Background of the Invention This invention relates to a multi-cylinder two cycle engine and more particularly to a two cycle engine construction that will improve the running performance of the engine. As is well known, two cycle engines operating with direct cylinder injection tend to have a very lean mixture in the combustion chamber at the time of ignition when under light and mid-range loads and this can cause high combustion temperatures which result in the formation of large amounts of NOX in the exhaust gases and also the likelihood of knocking. This problem is particularly prevalent in connection with diesel engines. In order to preclude these problems, an arrangement has been provided for throttling the intake air flow or the air flowing through the scavenge passage under light load conditions. This can be conveniently done by providing a throttle valve in the intake passage that serves the crankcase chambers and which will restrict the air flow under low load and low speed conditions. Although the aforedescribed type of construction is effective in limiting the amount of NOX emissions and also reducing the likelihood of knocking, it gives rise to another problem. In a two cycle engine during the time when the scavenge port is opened, there can be a time when the pressure in the crankcase chamber is negative when intake air throttling is employed. If this occurs, then the exhaust gases can flow back through the scavenge passage to the crankcase chamber giving rise to further problems. A multi-cylinder two cycle internal combustion engine of the crankcase compression type as described in the preamble portion of claim 1 is known from GB-A-2 022 699 wherein the exhaust port is shielded by a layer of air from the fuel/air mixture. Further improvement of the operating characteristics of such an engine in terms of NOx emissions and knocking is desirable. It is, therefore, a principal object to this invention to provide a two cycle crankcase compression engine operating in way so as to avoid NOX emissions and knocking while at the same time preclude the flow of exhaust gases back into the crankcase chambers. It is a further object to this invention to provide an arrangement for operating a two cycle crankcase compression engine so as to reduce NOX emissions, knocking and other poor running, particularly at low speed conditions. Summary of the Invention In order to perform the afore-indicated objectives, the present invention is adapted to be embodied in a multi-cylinder two cycle crankcase compression internal combustion engine having at least two combustion chambers and two crankcase chambers. In accordance with the present invention, a balance passage extends between the crankcase chambers and throttle valve means are provided in this balance passage. The throttle valve means is controlled to be opened at low and mid-range speeds so as to reduce the amount of scavenging in the engine without causing back flow of exhaust gases from the combustion chamber to the crankcase chamber through the scavenge port. Preferred embodiments of the present invention are laid down in the subclaims. In the following the present invention and the operation thereof is explained referring to specific embodiments in conjunction with the associated drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross sectional view taken through a single cylinder of a three cylinder inline two cycle crankcase compression diesel engine constructed in accordance with an embodiment of invention, with certain components shown schematically. Figure 2 is an enlarged cross sectional view taken along the line 2-2 of Figure 1. Figure 3 is a view taken in the direction of the arrow 3 in Figure 1. Figure 4 is a partially schematic cross sectional view showing how the balance passage interconnects the crankcase chambers of the various cylinders. Figure 5 is a graphical view showing the crankcase pressure in two of the crankcases in relation to crank angle. Figure 6 is a graphical view showing the torque versus engine speed curves. Figure 7 is a graphical view showing the amount of scavenging air in relation to engine load. Figures 8 through 10 are graphical views showing the amount of exhaust gas particulates in relation to engine load in accordance with a conventional engine (Figure 8) and in accordance with variations in operation of the embodiment of the invention (Figures 9 and 10). Figures 11 and 12 are graphical views showing the amount of certain exhaust gas constituents in relation to the amount of scavenging air. Figure 13 is a block diagram showing the control routine. Figure 14 is an enlarged cross sectional view, in part similar to Figure 2, and shows another embodiment of the invention. Figure 15 is another cross sectional schematic view similar to that of Figure 1 showing another embodiment of the present invention, Figure 16 is a cross sectional view along the line V-V in Figure 15. Referring first in detail to Figures 1 through 4, a three cylinder, inline, two cycle crankcase compression diesel engine constructed in accordance with an embodiment of the invention, as identified generally by the reference numeral 21. Although the invention is described in conjunction with an engine of this type, it is to be understood that the invention has applicability in engines operating on different principals and having different numbers of cylinders or, in fact, rotary engines. However, the invention is employed with engines having at least two cylinders and operating on the two stroke principal. The engine 21 has a cylinder block assembly 22 which, in the illustrated embodiment, has three aligned cylinder bores 23 formed by respective cylinder liners 24. A piston 25 is supported for reciprocation in each cylinder bore 23 and is connected by means of a piston pin 26 to a respective connecting rod 27. The connecting rod 27 has its lower end journalled on a respective throw 28 of a crankshaft 29. The crankshaft 29 is supported for rotation within a crankcase chamber 31 formed at the base of the cylinder block 22 by the skirt of the cylinder block and by a crankcase member 32 that is affixed in a known manner to the cylinder block 22. As is typical with two cycle engine practice, the crankcase chamber 31 associated with each of the cylinder bores 23 is sealed from the adjacent crankcase chambers. An air charge is delivered to each of the crankcase chambers 31 from an air induction system that includes an air cleaner and air silencer (not shown) which supplies air to an intake manifold 33 through an inlet 34. The manifold 33, in turn, delivers a charge to the individual chambers 31 through intake ports 35 in which reed type check valves 36 are interposed to preclude reverse flow when the charge in the crankcase chambers 31 is being compressed. As is well known, when the pistons 25 move upwardly from bottom dead center a reduced pressure will be experienced in the crankcase chambers 31 and the intake air charge will flow into them past the reed type check valves 36. As the pistons 25 begin their downstrokes, the charge will be compressed, the reed type check valves will be closed and eventually the compressed charge will be transferred through scavenge ports 37 to the area in the cylinder bores 23 above the heads of the pistons 25. This area, indicated by the reference numeral 38 constitutes the combustion chamber for each cylinder and is formed by the cylinder bore 24, head of the piston 25 and a cylinder head assembly, indicated generally by the reference numeral 39 which is affixed to the cylinder block 22 in an appropriate manner. In the illustrated embodiment, the cylinder head assembly 39 is of a multi part type and includes a pre-chamber or torch chamber 41 which communicates with the main combustion chamber 38 through a restricted throat 42. As the pistons 25 continue their upward stroke, the transferred charge will be further compressed both in the main combustion chamber 38 and in the pre-combustion chamber 41. A fuel charge is injected into the pre-combustion chamber 41 by a cylinder head mounted fuel injector 43, at the appropriate time. When this occurs, the highly compressed fuel air charge will burn and issue from the throat 42 into the main combustion chamber 39 to drive the piston 25 downwardly. A glow plug 44 may be provided in the pre-combustion chamber 41 so as to assist in cold starting and warm up operation. The exhaust gases from the expanding charge are discharged through a main exhaust port 45 into an exhaust system (not shown) in a known manner. If desired, the engine may also be provided with a sub or auxiliary exhaust port 46 which communicates with the main exhaust port 45 and the cylinder bore 23 at a point above the point of communication of the main exhaust port 45 with the cylinder bore. An exhaust control valve 47 is positioned in a cross bore 48 and controls the opening and closing of the auxiliary exhaust port 46 so as to control the compression ratio of the engine. Any desired control strategy may be employed for the exhaust control valve 47, as is well known in this art. In a typical diesel engine having a constructions as thus far described, there are certain problems in connection with the control of exhaust gas emissions and engine running, particularly at low and mid range conditions. By low and mid range, it is referred to the load on the engine. The reason for this is that at low and mid range performance, the amount of fuel injected into the combustion chamber 38 in relation to the air volume is relatively small. This excess air gives rise to high combustion chamber temperatures which can give rise to the emissions of nitrous oxides in the exhaust and also high temperatures can cause knocking. In addition, particulate control can become difficult in this area. It has been proposed to control the amount of nitrous oxide and particulates in the exhaust gases by throttling the amount of scavenge air flowing through the scavenge passages 37. This has been done in connection with prior art constructions by throttling the intake air flowing through the intake manifold 33. However, as may be seen in Figure 5, there is a time in the operation of a normal engine where the crankcase pressure can be less than atmospheric. Figure 5 shows the pressure curves P 1 and P 2 from two cylinders of the engine during crankshaft rotation. It can be seen that each of these curves fall into the negative area, particularly when there is throttling of the intake charge. If a negative pressure occurs, then the exhaust gases may actually be drawn back into the crankcase chambers 31 through the scavenge ports 37. Hence, the next intake air charge will be diluted and poor performance will result. Therefore, in order to throttle the scavenge air without causing the existence of negative pressures in the crankcase chambers 31, a balance passage arrangement, indicated generally by the reference numeral 49 is provided. The balance passage 49 includes individual communicating passageways 51, each of which communicates with a respective one of the crankcase chambers 31. Throttle valves 52, which are controlled in a strategy which will be described, are positioned in the passages 51 for controlling the communication of the individual crankcase chambers 31 with each other. When the crankcase chambers 31 are communicated with each other through the opening of the throttle valves 52, two things will occur. First, the amount of scavenge air flowing through the passages 37 will be decreased because the amount of air that flows into the crankcase chambers 31 will be reduced. This is because part of the intake air charge that is drawn in will flow to another chamber through the balance passage 49. Hence, the scavenging air flow will be reduced. Also, during such times as there tends to be negative pressure developed in the individual crankcase chambers 31 rather than the exhaust gases being drawn through the scavenge ports 37, air will be drawn from another crankcase chamber through the balance passage 49. Hence, the amount of scavenge air flow may be throttled while, at the same tine, precluding the flow of exhaust gases back into the crankcase chambers. The throttle control valves 52 are each supported on a respective throttle valve shafts 53 that is journalled in the balance passage 49 in an appropriate manner. Control levers 54 (Figure 3) are affixed to each of the throttle valve shafts 53 and are connected by means of a linkage system 55. This linkage system 55 is operated by means of a servo motor 56 of the stepper type which operates a control arm 57 that is connected to one of the throttle levers 54 through a link 58. Referring to Figure 1, the stepping motor 56 is operated by means of a controller 59 which receives certain input signals indicative of engine performance. In the illustrated embodiment, the engine condition signals are a temperature signal 61 which may be the temperature of the water in the cooling jacket of the engine 21, a fuel injection amount signal 62 and an engine speed signal 63. The signals 62 and 63 may be provided by any suitable sensors. The fuel injection amount signal 62 will be indicative of engine load. Particularly the operation is controlled in such a way so as to open the control valves 52 at low and mid load conditions so as to decrease the amount of scavenging air flow and to close the control valves 52 at higher load conditions so as to achieve maximum power output. Referring to Figure 6, the solid line curve in this figure identified as b is the torque curve for the engine in relation to engine speed under full load conditions. The area of the curve under the line a indicated by the shaded area A is the area in which the control valves 52 are opened either partially or fully. As may be seen, this operating range is when the engine is at idle and low speed and the operation of the control valves is decreased as the speed and load of the engine increases so that the engine will operate in a conventional manner under high load conditions. The control routine may be understood by reference to Figure 13 wherein when the program is started, it moves to the steps S 1 , S 2 and S 3 so as to instantaneously sense the engine conditions, engine speed, fuel injection amount and water temperature, respectively in the illustrated embodiment. The program then moves to the step S 4 to determine if the engine is operating within the range A where the engine load is low and medium. If the engine is not operating in this range, the program merely repeats. If, however, at the step S 4 the engine is operating in the range A then the program moves the step S 5 to determine from the controller 59 the desired opening of the control valves 52. Once the control valve opening amount is determined, the program moves to the step S 6 to output a signal to the servo motor 56 to appropriately position the control valves 52 and to limit the amount of scavenging air flow. Figure 7 is a graphical view showing how the amount of scavenging air flow is controlled in relation to engine load with two parameter lines, Y 1 and Y 2 being shown ; each line relating to a given engine speed indicated by lines X 1 resp X 2 in fig. 6. At the line Y 1 , there is greater reduction in scavenging air flow for a larger range of engine load than along the line Y 2 . The effect of this in relation to engine performance will now be described by reference to Figures 8 through 12 wherein these two control lines Y 1 and Y 2 are depicted in conjunction with various emissions parameters. Referring first to Figures 8 through 10 and initially to Figure 8, this is a curve of engine particulate emissions in relation to engine load. The engine exhaust particulates fall into two generally types, those which are insolvable in organic solvents (dry soot) and those which are solvable in organic solvents (solvable organic fraction-SOF). The main constituent of dry soot is carbon whereas the main constituent of SOF is unburn hydrocarbons. As may be seen in Figure 8, with a normal engine not having the control valves 52 or, the illustrated embodiment with the control valves 52 held in their closed positions, at low loads the amount of dry soot is relatively low and increasing as the engine reaches the mid load range and then continues to increase as the engine load continues to increase. SOF emissions, on the other hand, are high at low load ranges and then fall off toward mid range, increasing again at the high load conditions. The total soot emissions are shown also in this figure. The effect of controlling the scavenge amount by opening of the control valves 52 under low load conditions at the line Y 1 is shown in Figure 9. This shows the amount of decreasing the ratio of scavenging air amount on dry soot, SOF and total particulate emissions. As may be seen, if the scavenging air amount is reduced from standard, the SOF emissions will decrease markly while the dry soot emissions will increase only as the scavenging air amount is significantly reduced. Therefore, by picking the appropriate point on the curve, the total soot emissions can be reduced and the type of emissions controlled. On the other hand, when operating at a higher load condition at the line Y 2 , decreasing the amount of scavenging air will reduce the SOF emissions slightly but will increase the dry soot emissions. Hence, the amount of control of the control valves at this point will have no significant advantageous result and the scavenging air reduction amount rate at medium load should be relatively small to control particulate emissions. Figure 11 shows the effect of scavenging air flow at the line Y 1 on carbon monoxide, unburned hydrocarbon and NOX emissions (CO,THC and NOX) respectively. As may be seen, reducing the amount of scavenging air flow will reduce all of these emissions up to a point and beyond that point, CO and THC emissions will rise while NOX emissions will continue to fall. Therefore, it is also desirable to open the control valves 52 to a wider extent at the line Y 1 to control these emissions. On the other hand, at the line Y 2 as shown in Figure 12, the NOX emissions can still be continued to be reduced as the amount of scavenging air is reduced but CO and THC emissions will rise and a smaller amount of scavenging air reduction is desired at this condition. Therefore, is should be readily apparent that it is very effective to control both particulate and NOX emissions by decreasing the scavenging air flow at low and mid range loads. The amount of scavenging air reduction will decrease as the amount of load increases as aforedescribed. In the embodiment thus far described, the balance passage 49 has been provided by an external manifold that is mounted to the crankcase 32. Figure 14 shows another embodiment of the invention wherein the balance passageway is not provided by a separate manifold but rather is formed internally within the crankcase chamber 32. Because this is the only significant difference between these embodiments, components which are the same as the previously described embodiment have been identified by the same reference numerals and only a view corresponding to Figure 2 of the preceding embodiment is believed to be necessary to enable those skilled in the art to understand the construction and operation of this embodiment. In this embodiment, balance passages 101 are formed in adjacent walls 102 of the crankcase 32 extending between the crankcase chambers 31. Control valves 103 are positioned in these passages 101 and are operating in the manner as aforedescribed. Another preferred embodiment of the present invention wherein the balance passageway again is provided as a separate manifold attached to connect the adjacent crankcase chambers 32 is shown in Figures 15 and 16. In order to avoid any difficulties to occur with respect to the lubricating oil which occasionally may accumulate at the bottom area of each crankcase chamber 31 the embodiment of Figures 15 and 16 introduces the balance passageway to be provided by a pocket member 202 comprising the communicating manifold 201 in lengthwise direction thereof and being attached to an upper side portion of the crankcase chambers 31, respectively. As shown in Figure 15 the pocket member 202 is attached to the upper skirt portion of the crankcase 32 by means of fasteners 209 to fix a flange portion of the pocket member 202 to a seat provided at that outer face of the crankcase chambers 31. Moreover, such an assembly of the communicating manifold 201 is also advantageous from the view point of simplification of the valve operating linkage means as shown in Figure 16. As is apparent from said Figure the pocket member 202 comprises integral spacer blocks 210 defining the individual branching passageways 203 leading to each individual crankcase chamber 31. Within said branching passageways 203 the butterfly valves 204 are rotatably supported by means of a common valve shaft 205 establishing the common rotating axis for all throttle valves 204. In order to operate the control valves by means of the common valve shaft 205 a housing 208 of the pocket member 202 also comprises a side flange portion adapted to support the servo stepping motor 207 to directly drive the valve shaft 205 by means of a pair of intermeshing bevel gears 206. In this way another preferred throttling system for the scavenge air is established. The method of operation of the control valves 103, 204 may be as previously described and, for that reason, further description of this embodiment is not believed to be necessary to permit those skilled in the art to practice the invention. From the foregoing description, it should be readily apparent that the described embodiments are extremely affective in providing good control of exhaust emissions in a two cycle engine through the throttling of scavenge air flow without resulting in negative pressure conditions in the crankcase chambers that will cause exhaust gases to flow back into the crankcase chambers. Of course, the foregoing description is that of a preferred embodiment of the invention and various changes and modifications may be made without departing from the invention, as defined by the appended claims.

Claims: A multi-cylinder two cycle internal combustion engine of the crankcase compression type comprising at least two crankcase chambers (31) to which an air charge is respectively admitted and scavenge passages (37) for transferring a charge from said crankcase chambers (31) to a related combustion chamber (38), characterized by a balance passage means (49, 101, 201) interconnecting said crankcase chambers(31), and control valves means (52,103,204) for controlling the communication of said crankcase chambers (31) with each other through said balance passage (49, 101, 201), said control valves means (52,103,204) being operated in response to the load conditions of the engine (21). A multi-cylinder two cycle internal combustion engine as claimed in claim 1, characterized in that the engine (21) operates on a diesel cycle and fuel is injected into the conbustion chambers for combustion. multi-cylinder two cycle internal combustion engine as claimed in claims 1 or 2, characterized by an air induction system (33, 34, 36) independent of the balance passage means (49, 101, 201) for introducing an air charge to the crankcase chambers (31). A multi-cylinder two cycle internal combustion engine as claimed in in at least one of the preceding claims 1 to 3, characterized in that the crankcase chambers (31) are connected with each other via communicating manifold (201) with branching passageways (203) individually communicating each crankcase chamber (31) to said communicating manifold with a throttle valve (204) being disposed in each of said individual branching passageways (203). A multi-cylinder two cycle internal combustion engine as claimed in at least one of the preceding claims 1 to 3, characterized in that the balance passageway (101) comprises individual communicating passages integrally and internally provided between adjacent crankcase chambers (31) penetrating adjacent walls (102) of the crankcase (32) and accommodating control valves (103) therein commonly operated by a linkage system which, in turn, is actuated by means of a servo stepping motor in response to the detected load conditions of the engine. A multi-cylinder two cycle internal combustion engine as claimed in claim 4, characterized in that the communicating manifold (201) comprises a hollow pocket member (202) flanged to a side portion if the adjacent crankcase chambers (31) to communicate same by individual branching passageways (203) formed through the flanged attaching portion of the pocket member (202) to accommodate the throttle vavles (204) therein disposed to be rotatably around a common longitudinal axis formed by an integral valve shaft (205) extending along side flange attaching portion of the pocket member (202). A multi-cylinder two cycle internal combustion engine as claimed in at least one of the preceding claims 1 to 6, characterized in that the throttle valves (52,103,204) are of the butterfly flap valve type and a linkage means (55) is provided to operate all throttle valves (52,103,204) synchronously. A multi-cylinder two cycle internal combustion engine as claimed in claim 7, as dependent from claims 1 to 3 characterized in that the linkage means comprises control levers (54) which are affixed to each of the respective throttle valve shafts (53) supporting the throttle control valves (52) and a control arm (57) that is connected to one of the control levers (55) through a link (58) and is operated by a servo stepping motor (56). A multi-cylinder two cycle internal combustion engine as claimed in claim 6, characterized in that the throttle valves are directly affixed to said valve shaft (205) to be snychronously rotatable therewith, said individual branching passageways (203) are defined by integral spacer blocks (210) of the housing (208) of the pocket member (202) rotatably supporting the valve shaft (205) and said housing (208) of the pocket member comprises another side flange portion supporting the servo stepping motor (207) directly driving the valve shaft (205) by a bevel wheel train (206). A multi-cylinder two cycle internal combustion engine as claimed in claim 5, characterised in that said servo stepping motor (56, 207) is actuated by a control unit in response to at least one signal representing the engine load conditions in order to operate the control valve means (52, 103, 204) in response to the detected engine load in order to open the control valves (52,103,204) at low and mid-range loads and to close the control valves (52,103,204) at higher loads.

Inventors: OHKUBO AKIHIKO, OHKUBO, AKIHIKO
Applicants: YAMAHA MOTOR CO LTD, YAMAHA HATSUDOKI KABUSHIKI KAISHA
Application year: 1991
Main classification: F02B33
IPC codes: F02B39, F02D13, F02B75, F02B33, F02D9, F02B3